Distribution of Trace Elements in Fractions after Micronization and

United States. ∥ School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China. Energy Fuels , Article AS...
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Distribution of trace elements in fractions after micronization and density-gradient centrifugation of high-Ge coals from the Wulantuga and Lincang Ge ore deposits, China Qiang Wei, Susan M. Rimmer, and Shifeng Dai Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02118 • Publication Date (Web): 02 Oct 2017 Downloaded from http://pubs.acs.org on October 2, 2017

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Distribution of trace elements in fractions after micronization and

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density-gradient centrifugation of high-Ge coals from the Wulantuga and

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Lincang Ge ore deposits, China

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Qiang Weia,b, Susan M. Rimmerc, Shifeng Daia,b,d* a

State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, China b

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College of Geoscience and Survey Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

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c

Department of Geology, Southern Illinois University Carbondale, Carbondale, IL 62901, United States

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d

School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China

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Corresponding author: [email protected]

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Abbreviations: DGC, density-gradient centrifugation; WLTG, Wulantuga Ge ore deposit; LC, Lincang Ge ore deposit; REY, rare earth elements and yttrium; LREY, light rare earth elements and yttrium; MREY, medium rare earth elements and yttrium; HREY, heavy rare earth elements and yttrium; UCC, upper continental crust.

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ABSTRACT

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The Wulantuga (Inner Mongolia) and Lincang (Yunnan Province) germanium ore deposits in

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China are both considered world-class, coal-hosted Ge deposits. For this paper, two bench coals

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(WLTG C6-2 from Wulantuga and LC S3-6 from Lincang) were selected to characterize the

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associations between density fractions (maceral concentrates) and trace elements using

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micronization, density-gradient centrifugation (DGC), and inductively coupled plasma mass

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spectrometry (ICP-MS), especially for the abnormally enriched trace elements (including Ge, W,

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As, Sb, Be, U, and Nb) and rare earth elements and yttrium (REY) in the Wulantuga and/or

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Lincang high-Ge coals that are widely considered to have varying degrees of organic affinity.

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Huminite and inertinite contents of WLTG C6-2 account for 58.4% and 40.7%, respectively,

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whereas LC S3-6 is dominated by huminite (98.7%). Lower peak densities for huminite/inertinite

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and Gaussian distributions of DGC profiles after HCl-HF demineralization suggest that some

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minerals still exist in the micronized fractions. Many trace elements that are typically thought to

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have organic affinities decrease significantly after HCl-HF demineralization suggesting a mode of

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occurrence that is susceptible to acid leaching (i.e., weakly bonded to organic matter).

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In the Wulantuga high-Ge coal, Be and As are preferentially enriched in inertinite-rich

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density fractions, perhaps due to association with minerals in the heavier fractions. Higher Ge

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contents are seen in huminite fractions relative to inertinite, possibly due to differences in sites

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capable of holding Ge. Antimony is slightly more enriched in huminite-rich fractions. A positive

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Ge-W correlation and variable W concentrations across the density profile suggest a mixed

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organic-inorganic affinity for W, and Nb shows a similar distribution to W. Barium is

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predominantly associated with minerals. In the Lincang S3 seam, Ge concentration increases

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versus fraction density, probably due to the availability of more bonding sites in denser huminite

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macerals. The preferential enrichments of Be, U, and Sb in heavier fractions could be due to more

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bonding sites in denser huminites and/or their inorganic affinities. Arsenic content generally varies

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smoothly across DGC fractions, and most pyrite particles where at least part of the As occurs were

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removed in the DGC process. Tungsten, Nb, and possibly Th may occur in similar phases due to

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their comparable variation trends. In addition, REY anomalies in some fractions mainly result

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from elevated LREY, and REY (especially LREY) in WLTG C6-2 and LREY in LC S3-6 may

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occur in minerals with some trace elements, including Sc, Sr, and Ba.

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Keywords: high-Ge coal, trace elements, macerals, micronization, density-gradient centrifugation. 2

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1. INTRODUCTION

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The Wulantuga (Inner Mongolia) and Lincang (Yunnan Province) high-Ge coal deposits in China

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are both world-class coal-hosted germanium deposits that are of substantial scientific and

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economic value.1,2 Trace elements occur primarily in inorganic associations within the coal, but

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increasingly, important organic associations for certain trace elements are being recognized. Based

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on recent in-depth geochemical studies, abnormally enriched trace elements including Ge, W, As,

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and Sb in Wulantuga high-Ge coals and Ge, W, As, Sb, Be, U, Nb, and REY in Lincang high-Ge

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coals, are presumed to be associated with organic matter to varying degrees.1,2 Li et al.3 separated

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six density fractions (from 2.8 g/cm3) from two high-Ge coals from Wulantuga and

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Lincang using float-sink techniques and investigated the modes of occurrence of the enriched

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elements. Their work demonstrated that Be, B, Ge, Nb, Mo, Sb, W, and U in the Lincang coal, and

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B, Ge, Nb, W, Sb, Na, and Mg in the Wulantuga coal have strong organic affinities. Other studies

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also have suggested organic affinities for Ge, W, B, and Mo in the Wulantuga high-Ge coals4-6 and

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Ge, W, Ga, Se, Sb, Au, Hf, Ta, and K in the Lincang high-Ge coals7-9 based primarily on negative

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correlations between ash yield and trace element concentrations or other methods (e.g., density

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fractions, chemical extraction). A recent study by Etschmann et al.,10 using the cutting-edge

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technique of MSXRF (Mega-pixel Synchrotron X-ray Fluorescence) coupled with XANES and

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EXAFS to determine the occurrences of selected enriched trace elements (Ge, As, and W) in the

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Wulantuga and Lincang high-Ge coals, also suggested a major organic affinity for Ge and W. In

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addition, they found that Ge exists primarily in the tetravalent oxidation state and in a distorted

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octahedral coordination with O, and W(VI) is strongly bonded to organics, similarly to Ge(IV).

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A few preliminary studies have attempted to further clarify the relationships between trace

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elements and macerals in high-Ge coals. Zhuang et al.11 suggested that Ge in the Lincang coal is

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predominantly incorporated in huminite, especially corpohuminite. Considering the predominance

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of huminite in the Lincang high-Ge coals (over 90%),2 it is reasonable to speculate that the

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enriched trace elements with strong organic affinities are primarily associated with huminite. In

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the Wulantuga high-Ge coals that contain an average of 46.8% huminite and 52.5% inertinite,1 a

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positive correlation is observed between huminite content and Ge concentration (Figure 1).1,12 A

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similar positive correlation between huminite and Ge was reported for bench samples of the

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Wulantuga and Lincang coals by Wei and Rimmer.13 However, more research is necessary to fully

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understand the associations between the trace elements and macerals in these high-Ge coals.

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Mineral matter, including discrete crystalline mineral particles, poorly crystalline mineraloids,

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and non-mineral inorganics,14 are potential sites for trace elements. No Ge-bearing minerals were

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detected by petrographic analysis, XRD, or SEM-EDX in the Wulantuga and Lincang coal

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samples and their corresponding low-temperature ashes,1,2 and EPMA and PIXE analyses did not

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detect any Ge-bearing minerals in the Lincang high-Ge coals.11 However, in one study some minor

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fine-grained Ge-bearing oxides were reported in the Wulantuga high-Ge coal.4 Previous studies on

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the organic affinity of trace elements in the Wulantuga and Lincang high-Ge coals did not consider

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the potential for minor mineral contamination of organic-rich fractions acquired by float-sink

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techniques.3,11 The presence of minerals, which are heavier than organic matter, can influence

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density and may result in uncertainties about element affinities. Therefore, the interference of

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minerals must be taken into account in the studies on trace element affinities of high-Ge coals.

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Density-gradient centrifugation (DGC) is widely used for maceral separation15-18 and has

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been used to assess the affinity of trace elements in coal.19 This approach can produce more

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accurate and systematic density fractions than simple float-sink techniques.15 Previous studies did

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not provide direct evidence for a relationship between macerals and Ge or other trace elements in

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the high-Ge coals. In this study, DGC was used to separate micronized Wulantuga and Lincang

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high-Ge coals into different density fractions (maceral concentrates) to characterize the

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relationships between macerals and trace elements in an attempt to provide new perspectives on

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the distribution and affinity of trace elements.

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2. GEOLOGICAL SETTINGS

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The Shengli Coalfield (45 km long and 7.6 km wide) developed in the fault-controlled Shengli

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sub-basin of the Erlian Basin in northeastern Inner Mongolia, northern China. The Wulantuga Ge

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deposit is located in the southwest end of the Shengli Coalfield and covers an area of 2.2 km2

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(Figure 2A,B).20 In the study area, the lower portion of the Shengli Formation, which is deposited

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in the Lower Cretaceous sequence, is the major coal-bearing interval with an average thickness of

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368 m. Among the eight coal beds (Nos. 5, 5-lower, 6-upper, 6, 6-lower, 7, 8, and 9) in the

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Shengli Formation, the No. 6 Coal is the major coal seam that has an average thickness of 16.1 m

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and an average maximum huminite reflectance of 0.45%.1

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The Bangmai Basin (western Yunnan, southwestern China) is an asymmetric half-graben

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controlled by NW and EW-trending faults (Figure 2C),2 and is filled by the Miocene coal-bearing

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Bangmai Formation where the Lincang Ge deposits developed. The Bangmai Formation was

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deposited on a basement of middle Triassic granitic batholiths, can be divided into six zones from

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top to bottom (N1b6 to N1b1). The lignites occur in zones N1b2, N1b4-5, and N1b6, and the Ge-rich

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lignites occur in the lower zone, N1b2.2,21 At the Dazhai Mine in the Lincang deposit, the average

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random huminite reflectances of the three Ge-rich coal seams (upper S3, middle Z2 and lower X1)

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are 0.34%, 0.38%, and 0.46%, respectively.2

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3. SAMPLING AND ANALYTICAL METHODS

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Two lignite bench samples, WLTG C6-2 (huminite maximum reflectance of 0.44%)1 and LC S3-6

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(huminite random reflectance of 0.32%),2 were collected from the Early Cretaceous No. 6 Coal at

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the Wulantuga high-Ge coal deposit in the Shengli Coalfield, Inner Mongolia by Dai et al.,1 and

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the Neogene upper seam of the Dazhai Mine at the Lincang high-Ge coal deposit in the Bangmai

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Basin, Yunnan Province by Dai et al.,2 respectively. Each sample, representing a 10-cm x 10-cm

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area of the coal face, was stored immediately in plastic bags to minimize contamination and

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oxidation. The two samples were air dried and crushed to minus 20-mesh for petrographic analysis

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and minus 200-mesh for micronization. Micronization and demineralization techniques followed

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those of Wei and Rimmer.13 WC vessels, which could influence the measured W contents, were

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not used in sample preparation. These particular samples were selected for the current DGC study

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as previous work had shown that they contain elevated concentrations of trace elements and show

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a range in petrographic composition.13

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3.1. Micronization

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To liberate macerals from each other and to ensure effective exposure of mineral matter to

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acids during subsequent demineralization, a Sturtevant micronizer (fluid energy mill) was used to

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further grind the minus 200-mesh samples to ~ 3 µm. The feed speed was controlled using a FMC

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Syntron PowerPulse Electric Controller, and the feed pressure and grinding pressure were set to

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100 psi and 120 psi, respectively. Compressed nitrogen was employed as the carrier gas to avoid

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oxidation.

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3.2. Demineralization

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3 g of each micronized coal was placed in a 50 ml Nalgene test tube and allowed to react

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with 40 ml of 6N HCl (TraceMetal Grade) for 2 hrs (Brij-L23 solution was added as a surfactant

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to help wet the samples), followed by a rinse with deionized water and another treatment with 6N

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HCl. This was followed by a second series of washes with deionized water and treatment with 30

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ml of 48% HF (TraceMetal Grade) for 48 hrs before additional deionized water washes.

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Afterwards, a third 6N HCl treatment was followed by washes with deionized water to neutral pH

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and then the samples were dried overnight at 50°C. Nitric acid was not used in the current study as

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it could alter the organic matter.22,23

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3.3. Density-gradient centrifugation (DGC)

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DGC was performed using a BECKMAN COULTER Avanti J-26 XPI centrifuge. A gradient

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was created using CsCl and deionized water, and a few drops of 30% Brij-L23 solution was used

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as a surfactant. Each sample was centrifuged for 2 hrs at 8,000 rpm, and then the gradient was

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pumped out and collected in fractions using a PAAP-DMA 45 densitometer and a Foxy 200

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fractionator. Once separated, each fraction was filtered using 0.22 µm Millipore filters and rinsed

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repeatedly with deionized water. The procedure was modified from that of Dyrkacz and Horwitz.15

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In the present study, 18 fractions were obtained for each sample across their range of density

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(micronized WLTG C6-2, 1.3306-1.5598 g/mL; demineralized WLTG C6-2, 1.2411-1.5912 g/mL;

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micronized LC S3-6, 1.3353-1.5189 g/mL; and demineralized LC S3-6, 1.2139-1.4864 g/mL).

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3.4. Petrographic analysis

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To prepare pellets for petrographic analysis, a representative split of minus 20-mesh raw coal

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sample, micronized sample, minus 200-mesh coal sample, or DGC fraction sample was mixed

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with epoxy resin and hardener. Due to the very small amounts of material available for the DGC

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fractions, micro pellets were prepared where a small well was drilled into a blank epoxy pellet for

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the coal/epoxy mix. Pellets were processed using a Buehler Automet 250 grinder/polisher and

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polished using 320 grit, 400 grit, and 600 grit abrasive papers, and then 1.0 µm (alpha alumina)

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and, finally, 0.06 µm (colloidal silica) polishing compounds (following methods modified from

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Pontolillo and Stanton24). Macerals (huminite, inertinite, and liptinite) were determined using a

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Zeiss Universal microscope in reflected white- and blue-light illumination, under oil immersion;

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500 points for each raw coal sample pellet were counted to characterize the maceral composition.

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The maceral groups in the DGC fractions can be recognized based on their distinct reflectances,

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but it was difficult to identify individual macerals due to the small size of the micronized coal

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particles.

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3.5. Inductively coupled plasma mass spectrometry (ICP-MS)

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Trace element concentrations were determined using a Thermo Fisher, X series II ICP-MS.

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50 mg of each minus 200-mesh coal sample or DGC fraction sample was digested using an

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UltraClave Microwave High Pressure Reactor (Milestone), with 5 ml 65% HNO3 and 2 ml 40%

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HF employed as digestion reagents (GR acids further purified by sub-boiling distillation), as

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outlined by Dai et al.25 Multi-element standards (Inorganic Ventures: CCS-1, CCS-4, CCS-5, and

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CCS-6) were used for calibration of trace element concentrations. Collision/reaction cell

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technology (CCT) of ICP-MS was used to determine As and Se concentrations in order to avoid

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interference by polyatomic ions.26

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4. RESULTS AND DISCUSSION

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4.1. Maceral composition

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The huminite and inertinite contents of WLTG C6-2 are 58.4% and 40.7%, respectively,

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whereas LC S3-6 is dominated by huminite (98.7%). The liptinite maceral content of WLTG C6-2

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is minimal (0.8%) as are the inertinite (1.3%) and liptinite (0%) contents of LC S3-6 (Table 1).

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The huminite macerals of WLTG C6-2 are mostly ulminite, densinite, and attrinite, and the

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gelinite, textinite, and corpohuminite contents are low. Fusinite is the most abundant inertinite in

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WLTG C6-2, followed by inertodetrinite, semifusinite, and minor funginite and macrinite. Only

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very small amounts of resinite and cutinite can be observed in WLTG C6-2. The dominant

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huminite macerals of LC S3-6 are densinite and ulminite, and gelinite followed by textinite,

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attrinite, and corpohuminite. Funginite is the only observable inertinite in LC S3-6.

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4.2. Maceral separation

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Micronization assured subsequent reliable demineralization and maceral separation, although

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some particles > 10 µm were still present after micronization (Figure 3). Poe et al.27 suggested that

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DGC maceral separations performed on minus 100-mesh coal can also produce repeatable results.

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However, micronization is crucial in the present study because grinding samples to minus

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200-mesh did not adequately separate macerals from each other (Figure 4A,B) or isolate minerals

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from the organic matter (Figure 4C,D).

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Based on the density data (Table 2), DGC profiles are shown in Figure 5 along with

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photomicrographs of the two micronized samples and their corresponding

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micronized-demineralized samples. The densities for huminite and inertinite of

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micronized-demineralized WLTG C6-2 are around 1.36 g/mL and 1.44 g/mL, respectively.

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Without acid demineralization (micronized WLTG C6-2), these densities are somewhat higher,

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around 1.43 g/mL and 1.49 g/mL, respectively. The density of huminite in the

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micronized-demineralized LC S3-6 is around 1.35 g/mL; in the sample that was micronized but

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not demineralized, the density is higher at 1.46 g/mL. The lower peak densities after

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demineralization suggest that finely dispersed mineral matter associated with the organic matter

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can influence the DGC fraction densities, which makes sense considering that clays and quartz

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have densities of 2.6 to 2.8 g/mL and 2.65 g/mL, respectively. Thus, even small amounts of

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mineral contaminants can result in the huminite and inertinite reporting to denser fractions. Minor

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amounts of minerals (pyrite) can still be observed in some micronized-demineralized fractions,

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suggesting even lower actual maceral densities than those displayed in Figure 5B,D. Nitric acid

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was not utilized to further remove pyrite because of its potential to alter the organics.22,23

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Compared to the micronized DGC profiles (Figure 5A,C), those of micronized-demineralized

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samples are closer to Gaussian distributions (Figure 5B,D) due to the removal of mineral matter

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that can skew the density distributions. Qualitatively, it does appear that the average particle size

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in denser DGC fractions are larger than those in less-dense fractions, especially for the Lincang

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coal (Figure 5A-D), perhaps suggesting slight differences in hardness and the effectiveness of

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micronization.

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Li et al.3 obtained six density fractions (ρ < 1.43, 1.43-1.6, 1.6-2.0, 2.0-2.4, 2.4-2.8, and > 2.8

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g/cm3) for the Wulantuga and Lincang high-Ge coals using float-sink techniques. As these authors

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used minus 200-mesh, untreated coal (i.e., acid demineralization was not used), it was difficult to

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define the density ranges of the organic matter and the density boundary between organic matter

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and minerals. As a result, it was hard to determine the organic/inorganic affinities of trace

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elements, let alone their associations with macerals. The present study aims to help us better

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understand the relationships between macerals and trace elements in the high-Ge coals from China,

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especially for those enriched ones.

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4.3. Distribution of trace elements

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4.3.1. Trace element concentrations

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Compared to the average concentrations of elements in world low-rank coals,28 enrichments

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(where the concentration coefficient > 5, concentration coefficient classification used here as

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proposed by Dai et al.29) are seen for Be, Ge, As, Sb, Cs, Ba, W, and Eu in the micronized WLTG

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C6-2 coal, and Be, Zn, Ge, As, Nb, Cd, Sn, Sb, Cs, W, Tl, and U in the micronized LC S3-6 coal

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(Table 3). Most of these elements can be removed by HCl-HF leaching (reduction rate > 50%;

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Table 3), where RR (reduction rate, %) = (concentration in Micro - concentration in Demin) /

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concentration in Micro * 100%. Most of the trace elements, including Ge, W, As, and Sb in the

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Wulantuga coal and Ge, W, As, Sb, Be, U, Nb, and REY in the Lincang coal, that are widely

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considered to have organic affinities to varying degrees are significantly decreased following

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demineralization (e.g., Ge reduction rate is 95-96%; Table 3 and Figure 6). This suggests a mode

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of occurrence that is susceptible to acid dissolution. Wei and Rimmer13 proposed this may be due

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to weak bonds between these elements and organic matter (as they may occur in the form of

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chelates), thus allowing them to be removed by HCl-HF. Discussion of the distribution of these

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trace elements in the micronized-demineralized macerals is less informative as the concentrations

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have been reduced by acid demineralization and, in several cases, are below detection limits in the

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feed sample, let alone in the DGC fractions. Thus, the following discussion will focus on the trace

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element distributions in the DGC fractions obtained from the micronized coal sample that has not

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been demineralized.

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Due to the use of CsCl in the DGC process, Cs concentrations in the DGC fractions are

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extremely high (up to > 25,000 µg/g) although each fraction had been rinsed thoroughly using

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deionized water. Technically, Cs in the DGC fractions can be from both the coal and CsCl. The Cs

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values in the micronized WLTG C6-2 and LC S3-6 are low (5.04 µg/g and 17.8 µg/g, respectively;

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Table 3). Thus, Cs in the original coal is negligible compared to the extremely high Cs

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concentrations observed in the DGC fractions. To remove the influence of Cs on the concentration

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of other elements, the trace element contents of DGC fractions are recalculated to a Cs-free basis

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(Tables 4 and 5) by excluding Cs and regarding the sum of all other elements equal to 100%.

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4.3.2. Distribution of trace elements

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The trace element concentrations of each DGC fraction were determined by ICP-MS (Tables

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4 and 5). Based on the degree of "smoothness" of plots of concentration versus density, the trace

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elements from the micronized WLTG C6-2 and LC S3-6 were divided into two groups, "smooth"

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and "variable" (Figures 7-10 and Table 6). The maceral composition of DGC fractions varies with

260

density continuously and gradually; thus, in theory, trace elements associated with different

261

macerals should show concentrations that also vary gradually with density, unless they are

262

associated with mineral matter to a certain degree.

263

In the present study, the four criteria were used to interpret element associations. (a)

264

Observations from previous studies. The consensus (e.g., a primary organic affinity for Ge) as

265

derived from numerous studies, including the investigations by Dai et al.1,2 who used the same

266

samples as those analyzed in this study. (b) Comparison of element concentrations in DGC

267

fractions to those in the corresponding micronized coal. Lower concentrations of a certain element

268

in the DGC fractions relative to the micronized coal would suggest an inorganic affinity to some

269

extent, because some minerals associated with this element could have been removed in the DGC

270

process. (c) Degree of “smoothness” of plot of element content versus density. Group 1 elements,

271

or those with “smooth” plots (Figures 7 and 9), may have a predominantly organic affinity, or the

272

minerals with which they are mainly or partly associated are evenly distributed across the density

273

fractions. For Group 2 elements, or those with a more “variable” plot of concentration vs. density,

274

at least some are likely to be associated with mineral particles that are unevenly distributed in the

275

DGC fractions, resulting in abrupt changes in trace element concentrations across the density

276

profile (Figures 8 and 10). (d) Relationship between elements. The organic association of an

277

element can be inferred by the direct correlation across DGC fractions between this element and

278

another element that is widely considered to be of organic affinity (e.g., Ge).

279

4.3.2.1. Wulantuga high-Ge coal

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Based on the DGC results (Table 2), DGC profiles, and fraction photomicrographs (Figure

281

5A), the density boundary between huminite and inertinite for micronized WLTG C6-2 is around

282

1.45 g/mL. This boundary is between two adjacent fractions that are huminite-rich (fraction at

283

1.4443 g/mL) and inertinite-rich (fraction at 1.4596 g/mL), respectively. With increasing density,

284

Be concentration in the DGC fractions also increases (Figure 7). Germanium concentration in

285

huminite increases with density and then decreases in inertinite, and Ge is generally higher in

286

huminite than in inertinite (Figure 7). Arsenic basically increases with density (Figure 7).

287

Antimony content in huminite is slightly higher than that in inertinite (Figure 7). Tungsten in

288

huminite is also generally higher than in inertinite, and it shows a pronounced variation with

289

density (Figure 8). Compared to other fractions, Ba is relatively high at 1.3692 g/mL and 1.4596

290

g/mL (Figure 8).

291

Beryllium in coal can be associated with organic matter and clay minerals,30,31 and elevated

292

Be is mostly organically bound.30 Dai et al.1 suggested that Be in the Wulantuga high-Ge coals has

293

a major inorganic affinity, although Be is highly elevated. In the present study, Be is preferentially

294

enriched in inertinite (Figure 7), and it may be due to the presence of more minerals in heavier

295

fractions. Lower Be concentrations in DGC fractions (Table 4 and Figure 7) relative to the

296

micronized coal (11.3 µg/g; Table 3) also suggest its inorganic affinity because some minerals that

297

Be is associated with were removed in the DGC process.

298

All previous studies have suggested that Ge in the coal-hosted Ge ore deposits at Wulantuga,

299

Lincang, and Spetzugli (Russian Far East) is associated mainly with organic matter.1,4-6,32-34

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Smooth variation (Figure 7) and comparable concentrations in DGC fractions (122-204 µg/g;

301

Table 4) to that of micronized coal (188 µg/g; Table 3) support a major organic affinity for Ge. 14

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Slightly higher Ge contents in huminite could be explained from the perspective of organic

303

structure. Huminite has more bonding sites for organically associated Ge than inertinite;

304

furthermore, compared to lighter huminite fractions, the preferential enrichment of Ge in denser

305

huminite macerals could be due to their denser structures that contain more bonding sites.

306

Antimony in coal generally occurs in sulfides,35,36 but it can also be associated with organic

307

matter.37 Arsenic in coal is generally associated with pyrite.38-44 Less commonly, it can occur also

308

in Tl-As sulfide,45,46 getchellite,36 clay minerals,35 phosphate minerals,35 and arsenic minerals;47

309

occurrences of organically-associated As have also been reported.48,49 Dai et al.1 suggested that As

310

and Sb in the Wulantuga high-Ge coals are associated with both organic matter and pyrite. Arsenic

311

tends to be more associated with heavier fractions (inertinites) because minerals (especially pyrite)

312

are more likely associated with denser fractions. A much higher As concentration in the

313

micronized coal (887 µg/g; Table 3) than in the DGC fractions (Table 4 and Figure 7) also

314

suggests an inorganic affinity because most pyrite that contains As was separated from the organic

315

matter in the DGC process. Antimony is slightly more enriched in huminite relative to inertinite,

316

and shows a 52% of reduction rate (Table 3), suggesting a mixed organic-inorganic affinity. A

317

positive Ge-Sb correlation and negative Ge-As correlation (Figure 11B,C) suggest a higher

318

organic affinity for Sb relative to As.

319

Tungsten in coal generally occurs in organic matter and oxide minerals,37,50 and the enriched

320

W in the Wulantuga, Lincang, and Spetzugli Ge ore deposits occurs primarily in organic

321

matter.1,2,32,33 The positive Ge-W correlation (Figure 11A) in the present study also supports its

322

organic affinity. However, as mentioned above, the pronounced variation in W with density and

323

higher concentration in the micronized coal (159 µg/g; Table 3) relative to those in DGC fractions 15

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(Table 4 and Figure 8) suggest an inorganic affinity to some extent. In fact, some W in the

325

Wulantuga high-Ge coals occurs in quartz and chlorite.1 In addition, a positive W-Nb correlation

326

(Figure 11D) and their similar trends (maxima at the densities of 1.4074 g/mL, 1.4596 g/mL, and

327

1.5220 g/mL; Figure 8), suggest a similar mode of occurrence, although W is enriched but Nb is

328

depleted in WLTG C6-2.

329

Barium in coal can be both organically and inorganically associated.37,51-54 Barite (BaSO4)

330

was observed in the bench sample WLTG C6-2 by Wei and Rimmer13 and considered to be the

331

major carrier of Ba. Barium concentration in the micronized WLTG C6-2 is high at 2826 µg/g, but

332

it decreases by 64% to 1011 µg/g after HCl-HF leaching (Table 3), suggesting a major inorganic

333

affinity and minor association with organic matter and/or acid-resistant minerals. Compared to the

334

average Ba concentration in world low-rank coals (150 µg/g28), the much lower Ba concentrations

335

in micronized DGC fractions (Table 4 and Figure 8) further suggest its primary association with

336

minerals, because a significant proportion of the minerals were separated from the organic matter

337

during the DGC procedure due to their higher densities (e.g., density of barite is 4.48 g/cm3). The

338

relatively high Ba concentrations at 1.3692 g/mL and 1.4596 g/mL (Figure 8) are due to the

339

presence of Ba-bearing minerals, probably barite.

340

In addition, Li, Sc, Zn, Sr, and Ba show anomalously high values in the 1.3692 g/mL fraction

341

(Figure 8); in the 1.4596 g/mL fraction, Li, Sc, Rb, Sr, Ba, Th, and U show an increase (Figure 8).

342

Similarities in variations also suggest a Li-Sc-Sr-Ba assemblage (note that Ba and Sc show a

343

positive correlation; Figure 11F), and at least a portion of these elements may occur in mineral

344

particles, hence the uneven distribution across the density profiles. Additionally, Zn, Rb, Th, and

345

U could also exist in these minerals. Chromium and Ni show significant increases at 1.4871 g/mL; 16

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similarities in their trends across the density profile (Figure 8) and the positive correlation between

347

them (Figure 11E) suggest they are associated with the same inorganic phases.

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4.3.2.2. Lincang high-Ge coal

349

The peak density for huminite in the micronized LC S3-6 sample is around 1.46 g/mL

350

(Figure 5C). Beryllium, Ge, Sb, and U generally increase with increasing density (Figure 9).

351

Arsenic is generally more enriched in less dense huminite fractions, and its concentration varies

352

gradually with density and dips at 1.4175 g/mL (Figure 9). Niobium and W display similar and

353

pronounced variations (Figure 10). Zinc concentration shows considerable fluctuation (Figure 10).

354

Tin generally shows a slightly preferential enrichment in less dense huminites (Figure 9). It seems

355

that Tl does not vary much across DGC fractions (Figure 9).

356

In the S3 seam at Lincang, Ge is considered to have primarily an organic affinity.2 Its

357

preferential enrichment in denser fractions could result from the availability of more bonding sites

358

for Ge in denser huminite macerals. Uranium in U-bearing coal deposits is generally organically

359

bound, but it also occurs in U-bearing minerals.33,55-58 Beryllium and U in the Lincang S3 coal are

360

considered to have organic affinities,2 and this is also supported by positive Ge-Be and Ge-U

361

correlations (Figure 12D,E) in the present study; however, lower concentrations of Be and U in

362

DGC fractions (Table 5 and Figure 9) relative to those in the micronized coals (Be-180 µg/g,

363

U-160 µg/g; Table 3) suggest an inorganic affinity to some extent. Antimony has a mixed

364

organic-inorganic affinity,2 and the distinct positive Ge-Sb correlation indicates the preferential

365

association of Sb with organic matter (Figure 12C). Considering the larger particle sizes seen in

366

heavier fractions (Figure 5C), denser huminite macerals are more likely to contain minerals that

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occur as inclusions in organic matter; therefore, the preferential enrichments of Be, U, and Sb in

368

heavier fractions (Figure 9) could result from more bonding sites in denser huminite macerals

369

and/or their inorganic affinities.

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370

Arsenic in the Lincang S3 coal has a mixed organic and inorganic (pyrite) affinity.2 For the

371

most part, it shows gradual variation across the density fractions (Figure 9) suggesting either an

372

organic affinity or that fine-grained pyrite remained in organic matter generally evenly distributed

373

across DGC fractions. The higher As concentration (558 µg/g; Table 3) in the micronized coal

374

relative to the DGC fractions (Table 5 and Figure 9) indicates that pyrite particles were mostly

375

separated from organic matter during the DGC process, and the negative Ge-As correlation

376

(Figure 12B) suggests that some pyrite still exists in the DGC fractions, which is consistent with

377

petrographic observations (Figure 5C,D).

378

Niobium in coal mainly occurs in oxide minerals,59 in organic association,60 or in association

379

with clay minerals.61,62 In the Lincang S3 coal, W is mostly organically associated and Nb has an

380

organic-inorganic mixed affinity,2 but neither are correlated with Ge in the DGC fractions (Figure

381

12A,F), suggesting inorganic affinities to some degree, which is also supported by their

382

pronounced variations across the density profile (Figure 10). In addition, very similar trends

383

(Figure 10) and a significant positive W-Nb correlation (Figure 12G) suggest similar controls on

384

their distribution. Thorium shows a similar density trend to W and Nb (Figure 10) and there is a

385

positive W-Th correlation (Figure 12H), suggesting similar controls on its distribution.

386 387

Tin, Tl, and Bi show very similar trends (Figure 9) and display positive correlations (Figure 12I,J), suggesting similar controls. Tl is thought to be associated with pyrite due to its high

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correlation coefficient with pyritic sulfur,2 thus, Sn and Bi could also occur in pyrite in the

389

Lincang high-Ge coal. The variation in Zn content is different from that of any other trace element

390

(Figure 10) and suggests an inorganic affinity.

391

In addition, compared to other fractions, Li, Sc, Sr, Cd, Ba, Ta, and Hf are significantly

392

elevated in the 1.5102 g/mL fraction, and Sc, Ni, Rb, Sr, and Ba spike in the 1.4846 g/mL fraction

393

(Figure 10), indicating that some of these elements could exist in mineral particles. Comparable

394

variation trends (Figure 10) and positive correlations (Figure 12K,L) suggest that Sc, Sr, and Ba in

395

the Lincang high-Ge coal share the same mode of occurrence.

396

4.3.3. Distribution of rare earth elements and yttrium (REY)

397

REY concentrations in the DGC fractions from micronized WLTG C6-2 and LC S3-6 are

398

shown in Table 7 and Table 8, respectively. The threefold geochemical classification for REY

399

(LREY – La, Ce, Pr, Nd, and Sm; MREY – Eu, Gd, Tb, Dy, and Y; HREY – Ho, Er, Tm, Yb, and

400

Lu) is used in the present study.63 Generally, HREY in coal have a higher organic affinity relative

401

to LREY.64-66 In other words, LREY are more likely to be associated with minerals, which have

402

been found in many coals, e.g., rhabdophane, florencite, carbonates, or fluorocarbonates.56

403

However, zircon in most cases is enriched in HREY.67 This observation also applies to the

404

Wulantuga and Lincang high-Ge coals. Compared to other fractions, the REY anomalies of the

405

fractions at 1.3692 g/mL, 1.4596 g/mL, 1.4266 g/mL, and maybe 1.5515 g/mL from WLTG C6-2

406

(Table 7 and Figure 13A) and the fractions at 1.4846 g/mL and 1.5102 g/mL from LC S3-6 (Table

407

8 and Figure 13B) are due to the influence of mineral matter. Specifically, REY anomalies are

408

mainly due to elevated LREY (WLTG C6-2 and LC S3-6) and, to a lesser extent, elevated MREY

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409

and HREY (WLTG C6-2) (Figure 13A,B), and REY (especially LREY) in WLTG C6-2 and LREY

410

in LC S3-6 could occur in minerals with Sc, Sr, Ba, and some other trace elements.

411

Uneven distribution of REY-bearing mineral matter could cause differentiation of REY

412

patterns among DGC fractions. Compared to Upper Continental Crust (UCC),68 three REY

413

enrichment patterns can be identified as L-type (LaN/LuN > 1), M-type (LaN/SmN < 1, GdN/LuN >

414

1), and H-type (LaN/LuN < 1).63 Most DGC fractions from WLTG C6-2 show an L/M-type

415

distribution pattern, whereas the fraction at 1.3692 g/mL is characterized by an M/H-type plot

416

(Table 7 and Figure 14A), which is most enriched in REY among all fractions due to mineral

417

inclusions. LREY in the fraction at 1.3692 g/mL have greater increases relative to HREY due to

418

the influence of minerals (Figure 13A), but HREY increase more when normalized to UCC

419

resulting in the M/H-type REY plot (Figure 14A). The REY distribution patterns do not

420

differentiate among the DGC fractions from LC S3-6, and all fractions are clearly characterized by

421

an H-type REY plot (Table 8 and Figure 14B), although some fractions are more enriched in

422

LREY (Figure 13B).

423

5. CONCLUSIONS

424

WLTG C6-2 and LC S3-6 were chosen as representative bench coals to characterize the trace

425

element distributions in DGC fractions (maceral concentrates) from the micronized Wulantuga

426

and Lincang high-Ge coals. Most of the trace elements, including Ge, W, As, and Sb in the

427

Wulantuga coal and Ge, W, As, Sb, Be, U, Nb, and REY in the Lincang coal, that are widely

428

considered to have varying degrees of organic affinity drastically decrease after HCl-HF

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demineralization suggesting their acid-susceptible modes of occurrence (weakly bonded to organic

430

matter).

431

In the Wulantuga coal, Be and As are preferentially enriched in inertinite probably due to the

432

presence of more minerals in the heavier fractions. More bonding sites result in higher Ge contents

433

in huminite relative to inertinite. Antimony is slightly more enriched in huminite. A positive Ge-W

434

correlation and highly variable W concentrations vs. density suggest a mixed organic-inorganic

435

affinity for W, and Nb shares a similar mode of occurrence with W. Barium is mainly associated

436

with minerals. In the Lincang S3 coal, Ge content increases with density resulting from more

437

bonding sites in denser huminites. Beryllium, U, and Sb show preferential enrichments in the

438

heavier fractions due to the presence of more bonding sites in denser huminites and/or their

439

inorganic affinities. Arsenic concentration generally varies smoothly with density. Tungsten, Nb,

440

and possibly Th co-exist due to their comparable variation trends. For both of the Wulantuga and

441

Lincang coals, REY anomalies in some fractions result from elevated LREY. REY (especially

442

LREY) in WLTG C6-2 and LREY in LC S3-6 could occur in minerals with some trace elements,

443

including Sc, Sr, and Ba.

444

ACKNOWLEDGEMENTS

445

This research was supported by the National Natural Science Foundation of China (No.

446

41420104001), the National Key Basic Research Program of China (No. 2014CB238902), the

447

“111” Project (No. B17042), and the GSA Energy Geology Division A.L. Medlin Scholarship

448

(2016). William Huggett of the Department of Geology at Southern Illinois University Carbondale

449

is thanked for his help in preparing the micronized samples and for guidance in the DGC

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procedures. Siyu Zhang, Xiaoyun Yan, Zhen Wang, and Lei Wang of China University of Mining

451

and Technology (Beijing) are thanked for performing the ICP-MS analyses.

452

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516 517 518 519 520 521

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(27) Poe, S. H.; Taulbee, D. N.; Keogh, R. A. Density gradient centrifugation of -100 mesh coal: An alternative to using micronized samples for maceral separation. Org. Geochem. 1989, 14, 307-313. (28) Ketris, M. P.; Yudovich, Ya. E. Estimations of Clarkes for Carbonaceous biolithes: World average for trace element contents in black shales and coals. Int. J. Coal Geol. 2009, 78, 135-148. (29) Dai, S.; Graham, I. T.; Ward, C. R. A review of anomalous rare earth elements and yttrium in coal. Int. J. Coal Geol. 2016, 159, 82-95.

522

(30) Eskenazy, G. M. Geochemistry of beryllium in Bulgarian coals. Int. J. Coal Geol. 2006, 66, 305-315.

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(31) Kolker, A.; Finkelman, R. B. Potentially hazardous elements in coal: modes of occurrence and summary of

524 525 526 527 528 529

concentration data for coal components. Coal Prep. 1998, 19, 133-157. (32) Seredin, V. V.; Danilcheva, Yu. A.; Magazina, L. O.; Sharova, I. G. Ge-bearing coals of the Luzanovka Graben, Pavlovka brown coal deposit, Southern Primorye. Lithol. Miner. Resour. 2006, 41, 280-301. (33) Seredin, V. V.; Finkelman, R. B. Metalliferous coals: a review of the main genetic and geochemical types. Int. J. Coal Geol. 2008, 76, 253-289. (34) Hu, R.; Qi, H.; Zhou, M.; Su, W.; Bi, X.; Peng, J.; Zhong, H. Geological and geochemical constraints on the

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origin of the giant Lincang coal seam-hosted germanium deposit, Yunnan, SW China: a review. Ore Geol. Rev.

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2009, 36, 221-234.

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(35) Swaine, D. J. Trace Elements in Coal; Butterworths: London, 1990; pp 278.

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(36) Dai, S.; Zeng, R.; Sun, Y. Enrichment of arsenic, antimony, mercury, and thallium in a late Permian

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anthracite from Xingren, Guizhou, southwest China. Int. J. Coal Geol. 2006, 66, 217-226. (37) Finkelman, R. B. Modes of occurrence of environmentally sensitive trace elements in coal. In Environmental

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Aspects of Trace Elements in Coal; Swaine, D. J., Goodarzi, F., Eds.; Kluwer Academic Publishing: Dordrecht,

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1995; pp 24-50.

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Microcharacterization of arsenic- and selenium-bearing pyrite in Upper Freeport coal, Indiana County,

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Pennsylvania. Scan. Electron Microsc. 1984, 4, 1515-1524.

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Coal Geochemistry; Chyi, L. L., Chou, C.-L., Eds.; Special Paper of the Geological Society of America, 1990; vol

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248, pp 13-26.

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(40) Ruppert, L. F.; Minkin, J. A.; McGee, J. J.; Cecil, C. B. An unusual occurrence of arsenic-bearing pyrite in the Upper Freeport coal bed, west-central Pennsylvania. Energy Fuels 1992, 6, 120-125.

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(41) Eskenazy, G. M. Geochemistry of arsenic and antimony in Bulgarian coals. Chem. Geol. 1995, 119, 239-254. (42) Hower, J. C.; Robertson, J. D.; Wong, A. S.; Eble, C. F.; Ruppert, L. F. Arsenic and lead concentrations in the Pond Creek and Fire Clay coal beds, Eastern Kentucky coal field. Appl. Geochem. 1997, 12, 281-289.

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(43) Ward, C. R. Mineralogical analysis in hazard assessment. In Geological Hazards-The Impact to Mining;

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81-88.

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(44) Yudovich, Ya. E.; Ketris, M. P. Arsenic in coal: a review. Int. J. Coal Geol. 2005, 61, 141-196.

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(45) Hower, J. C.; Eble, C. F.; Quick, J. C. Mercury in Eastern Kentucky coals: geologic aspects and possible

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reduction strategies. Int. J. Coal Geol. 2005, 62, 223-236. (46) Hower, J. C.; Ruppert, L. F.; Eble, C. F.; Clark, W. L. Geochemistry, petrology, and palynology of the Pond Creek coal bed, northern Pike and southern Martin counties, Kentucky. Int. J. Coal Geol. 2005, 62, 167-181. (47) Ding, Z.; Zheng, B.; Zhang, J.; Long, J.; Belkin, H. E.; Finkelman, R. B.; Zhao, F.; Chen, C.; Zhou, D.; Zhou,

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Y. Geological and geochemical characteristics of high arsenic coals from endemic arsenosis areas in southwestern

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Guizhou Province, China. Appl. Geochem. 2001, 16, 1353-1360.

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(48) Belkin, H. E.; Zheng, B. S.; Zhou, D. X. Preliminary results on the geochemistry and mineralogy of arsenic

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in mineralized coals from endemic arsenosis area in Guizhou Province. 14th Annual International Pittsburgh Coal

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Conference and Workshop Proceedings; Taiyuan, Shanxi, China, Spet, 23-27, 1997; pp 1-20 (CD-ROM).

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(49) Zhao, F.; Ren, D.; Zheng, B.; Hu, T.; Liu, T. Modes of occurrence of arsenic in higharsenic coal by extended X-ray absorption fine structure spectroscopy. Chin. Sci. Bull. 1998, 43, 1660-1663.

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(50) Eskenazy, G. M. The geochemistry of tungsten in Bulgarian coals. Int. J. Coal Geol. 1982, 2, 99-111.

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(51) Dai, S.; Ren, D.; Tang, Y.; Yue, M.; Hao, L. Concentration and distribution of elements in Late Permian

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coals from western Guizhou Province, China. Int. J. Coal Geol. 2005, 61, 119-137. (52) Spears, D. A.; Borrego, A.; Cox, A.; Martinez-Tarazona, R. Use of laser ablation ICP-MS to determine trace element distributions in coals, with special reference to V, Ge and Al. Int. J. Coal Geol. 2007, 72, 165-176. (53) Gürdal, G. Geochemistry of trace elements in Çan coal (Miocene), Çanakkale, Turkey. Int. J. Coal Geol. 2008, 74, 28-40. (54) Sia, S. G.; Abdullah, W. H. Concentration and association of minor and trace elements in Mukah coal from

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Sarawak, Malaysia, with emphasis on the potentially hazardous trace elements. Int. J. Coal Geol. 2011, 88,

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179-193.

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(55) Dai, S.; Song, W.; Zhao, L.; Li, X.; Hower, J. C.; Ward, C. R.; Wang, P.; Li, T.; Zheng, X.; Seredin, V. V.;

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Xie, P.; Li, Q. Determination of boron in coal using closed vessel microwave digestion and inductively coupled

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plasma mass spectrometry (ICP-MS). Energy Fuels 2014, 28, 4517-4522.

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rare earth elements in the Late Permian coals of the Moxinpo Coalfield, Chongqing, China: Genetic implications

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from geochemical and mineralogical data. Ore Geol. Rev. 2017, 80, 1-17.

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(57) Hower, J. C.; Eble, C. F.; O’Keefe, J. M. K.; Dai, S.; Wang, P.; Xie, P.; Liu, J.; Ward, C. R.; French, D.

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Petrology, Palynology, and Geochemistry of Gray Hawk Coal (Early Pennsylvanian, Langsettian) in Eastern

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Kentucky, USA. Minerals 2015, 5, 592-622.

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(58) Liu, J.; Yang, Z.; Yan, X.; Ji, D.; Yang, Y.; Hu, L. Modes of occurrence of highly-elevated trace elements in superhigh-organic-sulfur coals. Fuel 2015, 156, 190-197. (59) Finkelman, R. B. Trace and minor elements in coal. In Organic Geochemistry; Engel, M. H., Masko, S. A., Eds.; Plenum Press: New York, 1993; pp 593-607. (60) Seredin, V. V. The first data on abnormal niobium content in Russian coals. Dokl. Russ. Akad. Nauk 1994, 335, 634-636. (61) Dai, S.; Luo, Y.; Seredin, V. V.; Ward, C. R.; Hower, J. C.; Zhao, L.; Liu, S.; Tian, H.; Zou, J. Revisiting the

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late Permian coal from the Huayingshan, Sichuan, southwestern China: Enrichment and occurrence modes of

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minerals and trace elements. Int. J. Coal Geol. 2014, 122, 110-128.

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(62) Zhao, L.; Dai, S.; Graham, I. T.; Li, X.; Liu, H.; Song, X.; Hower, J. C.; Zhou, Y. Cryptic sediment-hosted

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critical element mineralization from eastern Yunnan Province, southwestern China: Mineralogy, geochemistry,

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relationship to Emeishan alkaline magmatism and possible origin. Ore Geol. Rev. 2017, 80, 116-140.

597 598 599 600 601 602 603

(63) Seredin, V. V.; Dai, S. Coal deposits as potential alternative sources for lanthanides and yttrium. Int. J. Coal Geol. 2012, 94, 67-93. (64) Eskenazy, G. M. Rare earth elements and yttrium in lithotypes of Bulgarian coals. Org. Geochem. 1987, 11, 83-89. (65) Eskenazy, G. M. Rare earth elements in a sampled coal from the Pirin Deposit, Bulgaria. Int. J. Coal Geol. 1987, 7, 301-314. (66) Dai, S.; Zhang, W.; Ward, C. R.; Seredin, V. V.; Hower, J. C.; Li, X.; Song, W.; Wang, X.; Kang, H.; Zheng,

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L.; Wang, P.; Zhou, D. Mineralogical and geochemical anomalies of late Permian coals from the Fusui Coalfield,

605

Guangxi Province, southern China: Influences of terrigenous materials and hydrothermal fluids. Int. J. Coal Geol.

606

2013, 105, 60-84.

607 608 609 610

(67) Dai, S.; Finkelman, R. B. Coal as a promising source of critical elements: Progress and future prospects. Int. J. Coal Geol. 2017, https://doi.org/10.1016/j.coal.2017.06.005. (68) Taylor, S. R.; McLennan, S. M. The continental crust: its composition and evolution; Blackwell: Oxford, 1985; pp 312.

611

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612

Figure Captions

613

Figure 1. Relationship between maceral content (A. Huminite; B. Inertinite) and Ge concentrations from 13 bench

614

samples of the No. 6 coal seam, Wulantuga. Original data from Dai et al..1 Note that the two outliers could be

615

influencing the correlation coefficient.

616 617

Figure 2. Location (A) and geological settings of the Wulantuga (B; modified after Du et al.6) and Lincang (C;

618

modified after Hu et al.34) Ge ore deposits.

619 620

Figure 3. Photomicrographs of the Wulantuga and Lincang high-Ge coals before and after micronization. (A)

621

WLTG C6-2, minus 20-mesh coal; (B) WLTG C6-2, micronized coal; (C) LC S3-6, minus 20-mesh coal; (D) LC

622

S3-6, micronized coal.

623 624

Figure 4. Minus 200-mesh coals showing coal fragments containing a mix of macerals and minerals. (A, B)

625

WLTG C6-2; (C, D) LC S3-6.

626 627

Figure 5. DGC profiles of micronized and micronized-demineralized coal samples (WLTG C6-2 and LC S3-6).

628

Photomicrographs show petrographic composition of selected fractions. (A) micronized WLTG C6-2; (B)

629

micronized-demineralized WLTG C6-2; (C) micronized LC S3-6; (D) micronized-demineralized LC S3-6. Scale

630

bar on photomicrographs is 20 microns, and fraction density (g/mL) is at the bottom-left of each photomicrograph.

631

Some fine-grained pyrite can still be observed in the DGC fractions.

632 633

Figure 6. Comparison of the concentrations of selected trace elements and REY before and after demineralization

634

in WLTG C6-2 and LC S3-6. Micro, micronized coal; Demin, micronized-demineralized coal.

635 636

Figure 7. Distribution of trace elements (Group 1) in DGC fractions of micronized WLTG C6-2 (µg/g). The

637

vertical red line represents the boundary between huminite-rich (H) and inertinite-rich (I) density fractions.

638 639

Figure 8. Distribution of trace elements (Group 2) in DGC fractions of micronized WLTG C6-2 (µg/g). The

640

vertical red line represents the boundary between huminite-rich (H) and inertinite-rich (I) density fractions; orange

641

dots indicate concentrations below detection limits that are regarded as 0.

642 643

Figure 9. Distribution of trace elements (Group 1) in DGC fractions of micronized LC S3-6 (µg/g). The vertical

644

pink line represents the peak density of huminite.

645 646

Figure 10. Distribution of trace elements (Group 2) in DGC fractions of micronized LC S3-6 (µg/g). The vertical

647

pink line represents the peak density of huminite; orange dots indicate concentrations below detection limits that

648

are regarded as 0.

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Page 28 of 51

649 650

Figure 11. Relationships between selected trace elements in DGC fractions from micronized WLTG C6-2.

651 652

Figure 12. Relations between selected trace elements in DGC fractions from micronized LC S3-6.

653 654

Figure 13. REY distribution by density in the DGC fractions from micronized WLTG C6-2 (A) and LC S3-6 (B).

655

The vertical red lines represent the density boundary between huminite and inertinite from WLTG C6-2 (A), and

656

the vertical pink line represents the peak density of huminite in LC S3-6 (B).

657 658

Figure 14. REY distribution patterns for DGC fractions from micronized WLTG C6-2 (A) and LC S3-6 (B). REY

659

plots are normalized to Upper Continental Crust (UCC).68

660

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661

Table 1. Maceral Compositions of WLTG C6-2 and LC S3-6 (vol. %; Mineral-free Basis) Sample

Tex

Ulm

Att

Den

Corp

Gel

Fus

Sf

Ma

Fun

Inert

Res

Cut

Total

T-Hum

T-Inert

T-Lip

WLTG C6-2

2.0

25.1

11.0

16.9

1.2

2.2

23.1

6.6

0.6

1.0

9.4

0.6

0.2

99.9

58.4

40.7

0.8

LC S3-6

4.6

30.7

3.0

46.0

0.8

13.6

0

0

0

1.3

0

0

0

100

98.7

1.3

0

662 663 664

Tex, textinite; Ulm, ulminite; Att, attrinite; Den, densinite; Corp, corpohuminite; Gel, gelinite; T-Hum, total huminite; Fus, fusinite, Sf, semifusinite; Mac,

665 666

Table 2. Average Density (g/mL) and Normalized Weight (g) for DGC Fractions from Micronized and

macrinite; Fun, funginite; Inert, inertodetrinite; T-Inert, total inertinite; Res, resinite; Cut, cutinite; T-Lip, total liptinite.

Micronized-demineralized Coal Samples (WLTG C6-2 and LC S3-6) Micro WLTG C6-2

Demin WLTG C6-2

Micro LC S3-6

Demin LC S3-6

Density

Norm. Wt.

Density

Norm. Wt.

Density

Norm. Wt.

Density

Norm. Wt.

1.5598

0.0917

1.5912

0.0186

1.5189

0.1113

1.4864

0.0029

1.5572

0.1081

1.5817

0.0183

1.5143

0.1568

1.4768

0.0056

1.5515

0.1499

1.5732

0.0265

1.5102

0.2128

1.4661

0.0084

1.5426

0.2035

1.5649

0.0352

1.5069

0.2746

1.4554

0.0225

1.5333

0.2820

1.5533

0.0450

1.5009

0.4167

1.4448

0.0770

1.5220

0.3808

1.5382

0.0847

1.4932

0.5812

1.4319

0.1761

1.5106

0.4883

1.5174

0.1655

1.4846

0.7851

1.4172

0.3224

1.4985

0.5765

1.4952

0.2698

1.4742

0.9663

1.4021

0.4839

1.4871

0.6375

1.4699

0.4728

1.4638

1.0000

1.3844

0.7134

1.4742

0.7289

1.4453

0.7299

1.4523

0.9602

1.3660

0.9531

1.4596

0.8190

1.4187

0.8046

1.4412

0.8916

1.3471

1.0000

1.4443

0.8512

1.3912

0.9686

1.4305

0.8822

1.3284

0.6417

1.4266

1.0000

1.3642

1.0000

1.4175

0.8534

1.3096

0.2631

1.4074

0.4560

1.3382

0.3389

1.4026

0.7587

1.2907

0.0979

1.3879

0.2349

1.3132

0.0910

1.3864

0.5841

1.2717

0.0469

1.3692

0.1390

1.2887

0.0380

1.3693

0.3574

1.2527

0.0271

1.3513

0.0847

1.2647

0.0248

1.3529

0.1998

1.2338

0.0190

1.3306

0.0545

1.2411

0.0204

1.3353

0.1028

1.2139

0.0132

667 668 669

Micro, micronized coal; Demin, micronized-demineralized coal; Norm. Wt., normalized fraction weight. The weight of each

670 671

Table 3. Trace Element Concentrations (µg/g) for Micronized and Micronized-demineralized Coal Samples (WLTG C6-2

fraction was normalized to the fraction containing the most material.

and LC S3-6), Along with Concentration Coefficients (CC) and Reduction Rates (RR) WLTG C6-2

LC S3-6

Elements Li

a

b

Micro

Demin

CC

RR

Micro

Demin

CCa

RRb

4.01

bdl

0.40

100e

10.2

bdl

1.02

100e

Worldc 10

Be

11.3

1.50

9.42

87

180

1.73

150

99

1.2

Sc

0.82

0.21

0.20

74

5.00

0.20

1.22

96

4.1

V

3.94

bdl

0.18

100e

4.50

bdl

0.20

100e

22

Cr

10.9

5.58

0.73

49

11.7

5.25

0.78

55

15

Co

0.72

0.24

0.17

67

2.95

0.19

0.70

94

4.2

Ni

7.67

3.48

0.85

55

14.9

2.86

1.66

81

9

Cu

5.92

1.94

0.39

67

13.6

4.41

0.91

68

15

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3.95

0.04

ndf

119

Page 30 of 51

Zn

0.77

20.7

6.61

83

18

Ga

1.24

0.56

0.23

55

8.42

0.47

1.53

94

5.5

Ge

188

9.76

94.0

95

1490

64.7

745

96

2

As

887

36.2

117

96

558

187

73.4

66

d

f

7.6 e

Se

bdl

bdl

nd

nd

0.17

bdl

0.17

100

Rb

4.52

bdl

0.45

100e

32.4

6.67

3.24

79

10

1

Sr

149

8.84

1.24

94

27.4

1.95

0.23

93

120

Zr

7.28

3.80

0.21

48

7.96

1.84

0.23

77

35

Nb

0.58

0.23

0.18

60

25.2

4.63

7.64

82

3.3

Mo

1.48

0.46

0.67

69

7.33

4.22

3.33

42

2.2

0.101

0.012

1.12

88

0.09

1.615

0.178

6.73

89

Ag

0.071

bdl

0.79

100

Cd

0.021

0.004

0.09

81

In

bdl

d

bdl

nd

e

f

nd

0.01

bdl

0.48

100 f

0.24 e

0.021

Sn

2.72

0.05

3.44

98

4.80

6.00

6.08

nd

0.79

Sb

46.0

22.0

54.8

52

34.5

22.8

41.1

34

0.84

Cs

5.04

2.00

5.14

60

17.8

6.36

18.2

64

0.98

Ba

2826

1011

18.8

64

56.3

10.2

0.38

82

150

Hf

0.32

0.11

0.27

66

0.21

0.11

0.18

48

1.2

Ta

0.07

0.01

0.27

86

0.81

0.74

3.12

9

0.26

W

159

14.2

133

91

403

102

336

75

1.2

Tl

2.14

0.08

3.15

96

9.17

2.95

13.5

68

0.68

Pb

4.04

bdl

0.61 d

e

25.9

0.55

3.92

98

6.6

f

100

Bi

bdl

bdl

nd

nd

1.70

0.26

2.02

85

0.84

Th

0.74

0.07

0.22

91

4.78

0.36

1.45

92

3.3

U

0.29

0.20

0.10

31

160

1.92

55.2

99

2.9

La

3.62

1.00

0.36

72

2.54

0.41

0.25

84

10

Ce

6.13

1.69

0.28

72

6.50

0.87

0.30

87

22

Pr

0.74

0.24

0.21

68

0.89

0.10

0.25

89

3.5

Nd

3.03

0.94

0.28

69

3.76

0.39

0.34

90

11

Sm

0.62

0.20

0.33

68

1.27

0.16

0.67

87

1.9

Eu

2.50

0.91

5.00

64

0.21

0.03

0.42

86

0.5

Gd

1.01

0.32

0.39

68

1.42

0.20

0.55

86

2.6

Tb

0.13

0.05

0.41

62

0.55

0.07

1.72

87

0.32

Dy

0.51

0.21

0.26

59

3.80

0.50

1.90

87

2

Y

2.51

1.00

0.29

60

17.96

2.84

2.09

84

8.6

Ho

0.10

0.04

0.20

60

0.78

0.10

1.56

87

0.5

Er

0.24

0.11

0.28

54

2.62

0.28

3.08

89

0.85

Tm

0.04

0.01

0.13

75

0.46

0.06

1.48

87

0.31

Yb

0.20

0.09

0.20

55

3.50

0.42

3.50

88

1

Lu

0.03

0.01

0.16

67

0.54

0.05

2.84

91

0.19

REY

21.40

6.83

0.33

68

46.80

6.46

0.72

86

65.27

LREYg

14.14

4.07

0.29

71

14.96

1.94

0.31

87

48.4

MREYg

6.66

2.49

0.48

63

23.94

3.63

1.71

85

14.02

g

0.60

0.27

0.21

55

7.90

0.90

2.77

89

2.85

HREY

30

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

672 673 674 675 676 677 678 679 680 681

Micro, micronized coal; Demin, micronized-demineralized coal; bdl, below detection limit. REY=REE+Y. a

CC, concentration coefficient, ratio of concentrations of elements in Micro to world low-rank coals; bRR, reduction rate (%),

(concentration in Micro - concentration in Demin) / concentration in Micro * 100%; caverage concentrations of elements in world low-rank coals shown for comparison;28 dnd, no data due to bdl concentration in Micro; eRR is regarded as 100% due to the bdl concentration in Demin; fnd, no data due to bdl concentration in Micro or higher concentration in Demin than that in Micro; gas described by Seredin and Dai,63 the threefold geochemical classification for REY (LREY– La, Ce, Pr, Nd, and Sm; MREY – Eu, Gd, Tb, Dy, and Y; HREY – Ho, Er, Tm, Yb, and Lu) is used in the present study.

Table 4. Trace Element Concentrations (µg/g, Cs-free Basis) of DGC Fractions Obtained from Micronized WLTG C6-2 Coal Sample Densitya

1.5515

1.5426

1.5333

1.522

1.5106

1.4985

1.4871

1.4742

1.4596

1.4443

1.4266

1.4074

1.3879

1.3692

Li

0.71

0.63

0.50

0.45

0.27

0.28

0.22

0.20

0.58

0.19

0.18

0.29

0.41

3.21

Be

9.49

9.58

9.18

8.82

8.13

7.77

6.99

6.13

5.35

4.26

3.24

2.94

2.79

3.22

Sc

0.98

0.59

0.60

0.52

0.52

0.45

0.41

0.33

1.76

0.34

0.80

0.34

0.33

2.51

V

2.63

2.48

2.36

2.23

1.94

1.94

1.97

2.02

1.95

1.94

1.89

2.10

2.31

2.60

Cr

4.54

4.29

3.78

4.18

3.31

3.56

6.95

4.24

3.81

4.40

4.54

5.57

5.85

6.84

Co

0.34

0.32

0.31

0.28

0.24

0.23

0.26

0.24

0.28

0.27

0.30

0.36

0.41

0.73

Ni

3.10

2.98

2.75

2.52

2.09

2.22

4.78

2.40

2.43

2.49

2.60

2.99

3.10

3.58

Cu

8.39

7.45

6.91

6.13

5.67

5.51

5.81

5.97

6.09

6.81

7.46

8.93

10.2

10.2

Zn

3.19

2.64

2.80

2.24

1.41

1.24

1.28

1.47

1.06

1.23

2.39

1.83

95.4

125

Ga

1.03

0.94

0.86

0.80

0.71

0.71

0.71

0.69

0.84

0.79

0.85

0.98

1.10

1.47

Ge

123

122

122

130

129

140

153

169

189

204

196

195

169

139

As

nd

428

410

384

337

333

326

330

337

374

262

249

217

nd

Se

nd

0.28

0.16

0.20

0.03

0.12

bdl

0.04

bdl

bdl

bdl

0.05

bdl

nd

Rb

2.71

1.72

1.56

1.47

1.25

1.14

1.22

1.05

1.84

1.31

1.34

1.27

1.37

1.58

Sr

8.52

7.90

8.21

8.96

9.72

10.0

10.2

9.74

17.9

8.04

7.36

4.19

3.34

12.9

Zr

4.12

3.73

3.86

3.78

3.59

3.50

3.77

4.05

4.84

5.10

5.64

6.81

6.88

7.10

Nb

0.02

bdl

0.003

0.05

0.03

0.05

0.06

0.10

0.18

0.16

0.26

0.38

0.30

0.22

Mo

0.31

0.18

0.11

0.11

bdl

bdl

0.31

bdl

bdl

bdl

bdl

0.13

0.09

bdl

Ag

bdl

bdl

bdl

0.20

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

Cd

0.012

0.014

0.012

0.010

0.008

0.004

0.008

0.006

0.008

0.004

0.012

0.028

0.022

0.038

In

bdl

0.001

bdl

0.001

bdl

bdl

bdl

bdl

bdl

bdl

bdl

0.001

0.001

0.001

Sn

0.01

bdl

bdl

bdl

bdl

bdl

0.02

bdl

bdl

0.05

0.05

0.15

0.15

0.11

Sb

43.7

40.7

39.2

38.5

36.4

37.3

38.9

41.4

44.4

46.2

45.7

47.8

44.8

39.6

Ba

12.9

10.3

11.4

9.57

8.41

8.21

8.61

8.23

16.7

9.59

10.1

8.01

7.69

20.6

Hf

0.13

0.10

0.11

0.09

0.10

0.10

0.10

0.11

0.14

0.15

0.16

0.19

0.19

0.19

Ta

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

W

24.7

18.3

16.3

85.0

80.3

77.5

79.1

93.0

115

107

105

124

93.4

83.4

Tl

0.51

0.45

0.48

0.43

0.32

0.34

0.37

0.33

0.34

0.37

0.41

0.51

0.61

0.55

Pb

1.11

0.95

0.95

0.80

0.69

0.56

0.66

0.58

0.64

0.51

0.52

0.59

0.72

0.88

Bi

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

Th

0.51

0.51

0.39

0.42

0.41

0.32

0.31

0.32

1.01

0.34

0.59

0.55

0.50

0.57

U

0.19

0.19

0.16

0.15

0.14

0.13

0.12

0.13

0.18

0.14

0.17

0.18

0.19

0.21

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Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

682 683 684 685 686 687

Note: Compared to Cs value in the micronized WLTG C6-2 coal sample (5.04 µg/g; Table 3), Cs contents in DGC fractions are extremely high (up to > 25,000 µg/g) and cannot be used due to use of CsCl in DGC processing, thus trace element concentrations are given on a Cs-free basis. adensity reported as g/mL. bdl, below detection limit; nd, no data.

Table 5. Trace Element Concentrations (µg/g, Cs-free Basis) of DGC Fractions Obtained from Micronized LC S3-6 Coal Sample Densitya

688 689 690 691 692

Page 32 of 51

1.5102

1.5069

1.5009

1.4932

1.4846

1.4742

1.4638

1.4523

1.4412

1.4305

1.4175

1.4026

1.3864

1.3693

1.3529

Li

4.92

3.78

3.33

3.33

3.53

3.19

3.39

3.38

3.25

3.18

2.94

2.74

2.64

2.70

2.76

Be

76.5

78.6

82.0

83.5

78.1

75.7

77.6

73.4

71.9

69.5

66.7

61.4

56.8

51.8

50.8

Sc

4.27

3.27

3.32

3.38

4.34

2.97

2.85

2.73

2.57

2.53

2.18

2.05

1.87

1.85

1.98

V

3.18

3.17

2.96

3.11

3.04

2.95

3.01

3.02

2.98

2.94

2.82

2.74

2.68

2.61

2.56

Cr

4.24

3.77

3.57

3.74

4.56

3.78

3.55

4.56

4.12

4.35

3.54

4.75

4.32

3.98

3.64

Co

0.51

0.50

0.48

0.48

0.51

0.43

0.42

0.39

0.39

0.38

0.35

0.36

0.34

0.34

0.36

Ni

3.15

3.10

2.95

2.97

3.62

2.89

2.90

3.03

3.12

3.01

2.79

2.83

2.48

2.35

2.34

Cu

8.29

7.92

7.82

7.93

8.60

8.57

9.23

9.66

10.0

10.7

10.3

10.4

10.5

10.9

11.1

Zn

52.9

56.9

26.8

38.8

41.2

36.8

40.9

6.68

36.9

34.0

33.2

51.0

52.8

48.7

67.7

Ga

6.65

6.55

6.20

6.14

5.93

5.33

5.01

4.66

4.37

4.05

3.70

3.42

3.25

3.20

3.22

Ge

1761

1712

1693

1666

1587

1564

1519

1550

1524

1483

1421

1378

1289

1206

1037

As

nd

240

251

256

271

284

292

302

321

328

287

333

314

260

nd

Se

nd

bdl

0.30

0.42

0.46

0.44

0.43

0.41

0.41

0.36

0.44

0.44

0.75

bdl

nd

Rb

13.3

11.8

10.8

10.8

13.3

10.7

11.3

11.4

11.4

11.0

10.0

9.49

9.36

9.70

10.0

Sr

11.4

3.87

3.79

3.60

16.3

3.20

3.13

3.31

3.03

3.39

2.64

2.32

2.00

1.87

3.45

Zr

5.41

5.95

5.37

6.08

6.30

6.44

6.69

7.41

7.70

8.46

7.94

7.75

7.42

7.99

7.65

Nb

26.1

26.9

8.81

12.0

27.7

20.1

8.59

27.4

26.0

27.9

26.8

21.2

26.2

25.5

23.9

Mo

5.02

5.07

4.57

4.81

5.24

5.38

5.22

5.81

6.03

6.43

6.45

6.59

6.58

6.64

5.81

Ag

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

bdl

Cd

0.315

0.083

0.072

0.077

0.091

0.075

0.069

0.069

0.070

0.065

0.067

0.059

0.052

0.064

0.085

In

0.015

0.013

0.013

0.013

0.013

0.013

0.011

0.013

0.013

0.013

0.011

0.013

0.013

0.015

0.013

Sn

2.75

2.76

2.23

2.30

2.56

2.61

2.47

2.96

3.03

3.05

2.90

2.82

2.92

3.02

3.00

Sb

47.0

45.9

42.8

42.2

43.5

41.5

38.1

39.7

38.5

38.0

37.2

36.9

36.6

36.1

33.4

Ba

23.7

16.8

15.7

14.9

29.5

13.6

14.1

14.9

12.3

13.5

10.6

10.2

8.3

7.79

10.8

Hf

0.39

0.12

0.08

0.10

0.11

0.09

0.09

0.11

0.11

0.13

0.10

0.09

0.09

0.10

0.10

Ta

3.33

1.06

bdl

bdl

0.69

0.07

bdl

0.52

0.42

0.61

0.36

0.06

0.49

0.34

0.38

W

279

365

141

99.7

380

266

73.4

304

332

352

338

232

244

283

236

Tl

2.17

2.09

1.72

1.79

2.04

1.98

1.94

2.28

2.29

2.27

2.15

2.05

2.13

1.97

1.84

Pb

11.5

11.0

10.4

10.4

10.6

10.3

10.9

11.2

11.4

11.3

10.7

10.5

10.2

9.96

10.0

Bi

1.00

1.07

0.87

0.81

0.93

1.02

0.89

1.09

1.16

1.21

1.16

1.08

1.13

1.22

1.26

Th

1.77

1.47

1.17

1.01

2.62

1.71

1.09

1.83

1.95

1.93

1.84

1.73

1.78

1.99

2.07

U

65.9

66.0

70.6

73.4

71.1

70.7

70.2

68.5

66.3

56.2

55.0

59.6

56.7

54.1

51.8

Note: Compared to Cs value in the micronized LC S3-6 coal sample (17.8 µg/g; Table 3), Cs contents in DGC fractions are extremely high (up to > 7,000 µg/g) and cannot be used due to use of CsCl in DGC processing, thus trace element concentrations are given on a Cs-free basis. adensity reported as g/mL. bdl, below detection limit; nd, no data.

Table 6. Trace Elements Roughly Classified by the Smoothness Degree of Variation with Density

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Energy & Fuels

Group No.

Smoothness degree of variation

1

Smooth

2

693 694 695 696 697

Variable

Micro LC S3-6

Be, V, Co, Cu, Ga, Ge, As, Zr, Sb, Hf,

Be, V, Co, Cu, Ga, Ge, As, Zr, Mo,

Tl, Pb

Sn, Sb, Tl, Pb, Bi, U

Li, Sc, Cr, Ni, Zn, Se, Rb, Sr, Nb, Mo,

Li, Sc, Cr, Ni, Zn, Se, Rb, Sr, Nb, Cd,

Cd, Sn, Ba, W, Th, U

In, Ba, Ta, Hf, Th, W

Note: Cs is not included because CsCl was employed during the DGC procedure. Micro, micronized coal. Some trace elements are excluded here and their variations cannot be plotted properly in Figures 7-10, due to concentrations that are below detection limits in most DGC fractions, including Ag, In, Ta, and Bi in micronized WLTG C6-2 and Ag in micronized LC S3-6.

Table 7. REY Concentrations in DGC Fractions from Micronized WLTG C6-2 (µg/g, Cs-free Basis) Densitya

698 699 700 701

Micro WLTG C6-2

1.5515

1.5426

1.5333

1.522

1.5106

1.4985

1.4871

1.4742

1.4596

1.4443

1.4266

1.4074

1.3879

1.3692

La

2.11

1.62

1.58

1.56

1.67

1.51

1.48

1.27

3.37

1.14

1.97

1.00

1.11

3.04

Ce

3.60

2.98

2.91

2.94

2.87

2.80

2.69

2.38

5.64

2.07

3.01

1.83

2.05

8.15

Pr

0.50

0.36

0.38

0.36

0.36

0.33

0.32

0.27

0.82

0.23

0.44

0.22

0.23

0.89

Nd

2.06

1.55

1.60

1.54

1.56

1.39

1.38

1.11

3.31

0.99

1.74

0.88

0.94

3.84

Sm

0.44

0.32

0.33

0.32

0.34

0.27

0.27

0.22

0.67

0.18

0.35

0.16

0.18

0.90

Eu

0.09

0.05

0.07

0.05

0.06

0.05

0.04

0.03

0.14

0.03

0.07

0.02

0.02

0.20

Gd

0.47

0.33

0.38

0.35

0.34

0.31

0.28

0.25

0.68

0.18

0.35

0.16

0.17

0.98

Tb

0.06

0.04

0.04

0.04

0.04

0.03

0.03

0.02

0.08

0.01

0.04

0.01

0.01

0.15

Dy

0.36

0.26

0.33

0.28

0.25

0.22

0.20

0.17

0.55

0.13

0.27

0.11

0.13

1.02

Y

1.94

1.63

1.81

1.54

1.62

1.37

1.30

1.03

2.61

0.75

1.38

0.69

0.80

5.08

Ho

0.07

0.04

0.05

0.04

0.04

0.04

0.04

0.03

0.10

0.02

0.05

0.02

0.02

0.19

Er

0.18

0.14

0.16

0.13

0.15

0.12

0.12

0.09

0.30

0.07

0.17

0.08

0.08

0.63

Tm

0.02

0.01

0.01

0.01

0.01

0.01

0.01

0.003

0.03

0.001

0.02

0.003

0.001

0.07

Yb

0.16

0.14

0.14

0.12

0.12

0.11

0.10

0.08

0.28

0.07

0.15

0.08

0.09

0.57

Lu

0.02

0.01

0.01

0.01

0.01

0.01

0.01

0.004

0.03

0.004

0.02

0.004

0.01

0.07

LREY

8.72

6.83

6.81

6.71

6.80

6.29

6.14

5.25

13.80

4.61

7.52

4.08

4.51

16.83

MREY

2.92

2.32

2.63

2.25

2.31

1.97

1.85

1.51

4.06

1.10

2.11

0.98

1.13

7.44

HREY

0.46

0.34

0.39

0.31

0.33

0.29

0.27

0.20

0.74

0.16

0.40

0.18

0.20

1.54

REY

12.10

9.49

9.83

9.27

9.44

8.55

8.25

6.96

18.61

5.87

10.03

5.24

5.83

25.81

LaN/Lu N

1.04

1.58

1.11

1.51

1.64

2.48

1.79

3.10

1.09

2.79

1.21

2.47

1.82

0.45

LaN/Sm N

0.72

0.76

0.72

0.74

0.75

0.85

0.82

0.86

0.75

0.97

0.85

0.96

0.95

0.51

GdN/LuN

1.84

2.55

2.09

2.68

2.64

3.96

2.67

4.88

1.73

3.45

1.68

3.10

2.22

1.14

a

density reported as g/mL. LREY = La + Ce + Pr + Nd + Sm. MREY = Eu + Gd + Tb + Dy + Y. HREY = Ho + Er + Tm + Yb +

Lu. REY = REE + Y.

Table 8. REY Concentrations in DGC Fractions from Micronized LC S3-6 (µg/g, Cs-free Basis) Densitya

1.5102

1.5069

1.5009

1.4932

1.4846

1.4742

1.4638

1.4523

1.4412

1.4305

1.4175

1.4026

1.3864

1.3693

1.3529

La

2.91

0.92

0.95

0.99

3.08

0.87

0.87

1.02

0.92

1.13

0.86

0.88

0.80

0.81

1.10

Ce

6.30

2.43

2.51

2.54

8.47

2.31

2.31

2.54

2.35

2.55

2.20

2.20

2.15

2.22

2.68

Pr

0.72

0.30

0.31

0.32

0.76

0.28

0.26

0.31

0.28

0.32

0.25

0.27

0.25

0.25

0.33

Nd

2.80

1.30

1.44

1.41

3.05

1.22

1.23

1.41

1.27

1.48

1.13

1.25

1.14

1.20

1.46

Sm

0.79

0.52

0.56

0.51

0.83

0.49

0.47

0.47

0.48

0.50

0.43

0.45

0.40

0.43

0.50

Eu

0.14

0.06

0.06

0.06

0.11

0.06

0.05

0.05

0.05

0.06

0.05

0.04

0.04

0.04

0.05

33

ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Gd

702 703

1.02

0.89

0.97

0.92

1.25

0.84

0.87

0.84

Page 34 of 51

0.80

0.81

0.71

0.77

0.72

0.73

0.89

Tb

0.24

0.22

0.22

0.23

0.25

0.20

0.20

0.19

0.19

0.18

0.16

0.17

0.16

0.17

0.18

Dy

1.69

1.77

1.84

1.82

1.99

1.61

1.58

1.61

1.50

1.45

1.34

1.37

1.34

1.33

1.49

Y

7.17

9.44

9.56

9.65

10.02

8.93

8.80

8.65

8.33

8.15

7.59

7.50

7.23

7.53

8.08

Ho

0.34

0.35

0.35

0.36

0.40

0.32

0.32

0.32

0.30

0.28

0.27

0.27

0.25

0.27

0.28

Er

1.07

1.19

1.21

1.21

1.29

1.10

1.09

1.07

1.00

0.96

0.88

0.89

0.85

0.90

0.93

Tm

0.19

0.19

0.21

0.20

0.21

0.19

0.18

0.18

0.17

0.15

0.14

0.14

0.14

0.14

0.14

Yb

1.56

1.77

1.81

1.85

1.88

1.65

1.61

1.59

1.50

1.44

1.32

1.26

1.23

1.28

1.30

Lu

0.22

0.25

0.26

0.26

0.26

0.24

0.23

0.23

0.21

0.20

0.19

0.18

0.18

0.18

0.18

LREY

13.51

5.46

5.77

5.77

16.19

5.16

5.15

5.75

5.29

5.97

4.87

5.06

4.74

4.91

6.07

MREY

10.26

12.38

12.64

12.68

13.62

11.64

11.50

11.35

10.87

10.65

9.85

9.84

9.49

9.80

10.68

HREY

3.39

3.77

3.84

3.90

4.04

3.50

3.43

3.39

3.17

3.04

2.81

2.75

2.66

2.77

2.83

REY

27.16

21.60

22.25

22.34

33.85

20.30

20.08

20.48

19.33

19.66

17.52

17.64

16.88

17.48

19.59

LaN/Lu N

0.13

0.04

0.04

0.04

0.12

0.04

0.04

0.04

0.04

0.06

0.05

0.05

0.04

0.05

0.06

LaN/Sm N

0.55

0.26

0.26

0.29

0.55

0.27

0.28

0.32

0.29

0.34

0.30

0.29

0.30

0.28

0.33

GdN/LuN

0.37

0.28

0.29

0.28

0.38

0.28

0.30

0.29

0.30

0.31

0.30

0.33

0.32

0.32

0.40

a

density reported as g/mL. LREY = La + Ce + Pr + Nd + Sm. MREY = Eu + Gd + Tb + Dy + Y. HREY = Ho + Er + Tm + Yb +

Lu. REY = REE + Y.

34

ACS Paragon Plus Environment

Figure 1

Page 35 of 51

(A)

100 90

(B)

70 60

80 70

Inertinite (vol. %)

Huminite (vol. %)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

60

y = 0.04 x + 35.36 R² = 0.59

50 40 30 20

y = -0.04 x + 64.10 R² = 0.59

50 40 30 20 10

10 0

0 0

200

400

600

800

1000

1200

1400

0

Ge concentration (μg/g)

200

400

600

800

1000

Ge concentration (μg/g)

ACS Paragon Plus Environment

1200

1400

Figure 2 (A)

Page 36 of 51

(C)

Wulantuga Inner Mongolia

c

Yunnan Province Lincang

0

Bangmai c

Zhongzhai

1km

Legend K1b

P1zs K2c

Q1

P1

gn

K1b

J3mn

by 1

Pt

Bangmai Formation

Unconformable Contact

P1zs

Legend 1

10 J3mn

P1zs

Faults

2

3

Q1

4

N2b

5

K2c

6

K1b

7 J3mn

8

J3by

9

P1gn

Xilinhaote Pt1by

K1b

Biotite Granite

gn

J3by

N2b

n

Pt1by

Area of Ge-rich lignites

P1 al fie ld Co

Sh en gli

gn P1 K1b

Two-mica granite

J3by

bn C2

gn P1 bn C2

(B)

0

Dazhai

1000km

J3m

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Energy & Fuels

P1zs

11 C2bn

12 Pt1by

13

14

15

16

17

18

1 unconformity, 2 Ge-coal deposit, 3 Quaternary, 4 Bogedawula Fm. of Tertiary, 5 Erlian Fm of upper Cretaceous, 6 Beiyanhua Fm. of lower Cretaceous, 7 Manitu Fm. of upper Jurassic, 8 Beiyingaolao Fm. of upper Jurassic,

9 Gegenaobao Fm. of lower Permian, 10 Zesi Fm. of lower Permian, 11 Benbatu Fm. of upper Carboniferous, 12 Baoyintu Fm. of Proterozoic, 13 Quaternary basalt, 14 Hercynian diorite, 15 Hercynian granodiorite, Plusgranite, Environment 15km ACS Paragon 16 Mesozoic 17 Fault, 18 City

Figure 3

Page 37 of 51

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(A)

20 μm

(B)

20 μm 20 μm

Densinite

Fusinite

Semifusinite

Fusinite

Textinite

Huminite

(C)

20 μm 20 μm

(D)

20 μm 20 μm

Corpohuminite Pyrite

Pyrite

Densinite

Densinite Funginite

Densinite

ACS Paragon Plus Environment

Figure 4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(A)

20 μm

Page 38 of 51

(B)

20 μm

Densinite Huminite Funginite Semifusinite

Pyrite

Ulminite

Fusinite

Fusinite

20 μm

(C)

(D)

20 μm

Densinite Pyrite

Pyrite

Densinite

Ulminite

ACS Paragon Plus Environment

Page 39 of 51

Energy & Fuels

Figure 5(A) 20 μm

1.4266

20 μm

1.4074

20 μm

20 μm

1.4596

1.4871

20 μm

20 μm

20 μm

1.4443

1.4742

1.4985

100

Normalized Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(A)

80

Micro WLTG C6-2 60

40 20 0 1.20

1.25

1.30

1.35

1.40

Density (g/mL)

ACS Paragon Plus Environment

1.45

1.50

1.55

1.60

Energy & Fuels

Figure 5(B) 20 μm

20 μm

20 μm

20 μm

1.3642

1.4187

1.4699

20 μm

20 μm

20 μm

1.3382

1.3912

1.4453

1.4952

100

Normalized Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 51

(B)

80

Demin WLTG C6-2 60 40 20 0 1.20

1.25

1.30

1.35

1.40

Density (g/mL)

ACS Paragon Plus Environment

1.45

1.50

1.55

1.60

Page 41 of 51

Energy & Fuels

Figure 5(C)

20 μm

20 μm

20 μm

1.4305

1.4523

1.4742

20 μm

20 μm

1.4175

20 μm

20 μm

1.4412

1.4638

1.4846

100

Normalized Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(C)

80

Micro LC S3-6 60 40 20 0 1.20

1.25

1.30

1.35

1.40

Density (g/mL)

ACS Paragon Plus Environment

1.45

1.50

1.55

1.60

Energy & Fuels

Figure 5(D) 20 μm

20 μm

1.3284

20 μm

1.3660

1.4021

20 μm

20 μm

1.3096

20 μm

1.3471

20 μm

1.3844

1.4172

100

Normalized Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 51

(D)

80

Demin LC S3-6 60 40 20 0 1.20

1.25

1.30

1.35

1.40

Density (g/mL)

ACS Paragon Plus Environment

1.45

1.50

1.55

1.60

Figure 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Element concentration (μg/g)

Page 43 of 51

1000 900 800 700 600 500 400 300 200 100 0

(A)

25

(B)

20 15 Micro WLTG C6-2 Demin WLTG C6-2

Micro WLTG C6-2 10

Demin WLTG C6-2

5 0 Ge

As

Sb

W

LREY

1600

(C)

1400 1200 1000 800

Micro LC S3-6

600

Demin LC S3-6

400 200 0 Be

Ge

As

Nb

Sb

W

U

MREY

HREY

REY

50 45 40 35 30 25 20 15 10 5 0

(D)

Micro LC S3-6 Demin LC S3-6

LREY

ACS Paragon Plus Environment

MREY

HREY

REY

Figure 7

Page 44 of 51

WLTG C6-2 Be 12

H

V 3.0

I

10

H

Co 0.8

I

H

Cu 12

I

2.5

H

I

10

0.6

Trace element concentration (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

8

2.0

6

1.5

4

1.0

8 0.4

6 4

0.2 2

0.5

0 1.35

0.0 1.40

1.45

1.50

1.55

1.60

2 1.35

1.40

1.45

Ga 1.6

H

1.50

1.55

0 1.35

1.60

1.40

1.45

250

1.2

H

1.55

1.60

1.40

1.45

As

Ge I

1.50

0 1.35

500

I

200

400

150

300

H

1.50

1.55

1.60

1.50

1.55

1.60

1.55

1.60

Zr 8

I

H

I

6

0.8

4

0.4 0.0 1.35

1.40

1.45

1.50

1.55

1.60

100

200

50

100

0 1.35

1.40

1.45

Sb 60

H

1.50

1.55

1.60

1.40

1.45

Hf 0.25

I

50

H

1.50

1.55

1.60

0.8

I

H

1.2

I

0.6 0.4

0.2

0.05

0.2

0.00 1.50

1.55

1.60

I

0.8

0.10

1.45

H

1.0

0.4

1.40

1.45

0.6

30

10

1.40

Pb

0.15

20

0 1.35

Tl

0.20

40

0 1.35

0 1.35

2

1.35

1.40

1.45

1.50

1.55

1.60

0 1.35

Density (g/mL) ACS Paragon Plus Environment

0.0 1.40

1.45

1.50

1.55

1.60

1.35

1.40

1.45

1.50

Page 45 of 51

Energy & Fuels

Figure 8

WLTG C6-2 Li 3.5

H

3.0

Sc 3.0

I

H

Cr 8

I

H

7

2.5

Ni 6

I

H

I

5

6

2.5

2.0

2.0

4

3

3

1.0

1.0

4

5

1.5

1.5

2

2

0.5

0.5

0.0

0.0 1.35

Trace element concentration (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1.40

1.45

1.50

1.55

1.60

1.35

1.40

1.45

1.50

H

120

0.30

I

80 60 40 20 1.40

1.45

H

0.25

100

0 1.35

1.50

H

1.60

1.40

1.45

1.55

3.0

H

0.15

1.5

0.10

1.0

0.05

0.5

1.50

1.55

1.60

20

H

1.50

1.55

1.60

1.50

1.55

1.60

1.50

1.55

1.60

I

0.00

0.0

10 5

1.35

1.40

1.45

1.50

1.55

1.60

1.35

1.40

1.45

H

1.50

1.55

1.60

0 1.35

1.40

1.45

Cd 0.04

I

0.3

H

Sn 0.20

I

H

I

0.16

0.03

0.12 0.2

0.02

0.2

0.08 0.1

0.1

1.40

1.45

1.50

1.55

1.60

0 1.35

0.01

25

H

1.40

1.45

1.50

1.55

1.60

140

I

1.35

1.40

1.45

H

120

15

1.2

I

1.60

0 1.35

1.40

1.45

H

U 0.25

I

H

I

0.20 0.15 0.10

0.4

0.05

0.2

20 1.55

1.35

0.6

40

1.50

1.60

0.8

60

5

1.55

1.0

80

10

1.50

Th

100

1.45

0.00

W

20

1.40

0.04

0.00

Ba

0 1.35

1.45

Sr

0.3

0 1.35

1.40

15 2.0

0.4

0.4

1.60

I

Mo I

1.55

2.5

0.20

1.60

1.50

0 1.35

Rb I

Nb 0.5

1.55

0 1.35

Se

Zn 140

1

1

0.0 1.40

1.45

1.50

1.55

1.60

0.00 1.35

Density (g/mL)

ACS Paragon Plus Environment

1.40

1.45

1.50

1.55

1.60

1.35

1.40

1.45

Energy & Fuels

Figure 9

LC S3-6 Be

V

100

Co

4

80

2 40

0.6

12

0.5

10

0.4

8

0.3

6

0.2

4

1

20 0 1.30

Cu

3

60

Trace element concentration (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 51

Peak 1.35

1.40

1.45

1.50

1.55

0 1.30

0.1

Peak 1.35

1.40

Ga

1.45

1.50

1.55

0 1.30

1.35

1.40

6

1.45

1.50

1.55

0 1.30

Peak 1.35

1.40

As

Ge

8

2

Peak

1.45

1.50

1.55

1.50

1.55

1.50

1.55

Zr

2000

400

10

1600

300

8

1200

6 200

4 800 2

4 100

400

0 1.30

Peak 1.35

1.40

1.45

1.50

0 1.30

1.55

Peak 1.35

1.40

Mo

1.45

1.50

1.55

0 1.30

2

Peak 1.35

1.40

Sn

8

4

6

3

4

1.45

1.50

1.55

0 1.30

Peak 1.35

1.40

Sb

1.45

Tl

50

2.5

40

2.0

30

1.5

20

1.0

10

0.5

2

2

1

0 1.30

Peak 1.35

1.40

1.45

1.50

1.55

0 1.30

Peak 1.35

1.40

Pb

1.45

1.50

1.55

0 1.30

80

12

1.2

60

8

0.8

40

4

0.4

20

Peak 1.40

1.40

1.45

1.50

1.55

0 1.30

Peak 1.35

1.40

1.45

1.45

1.50

1.55

0 1.30

1.50

1.55

1.50

1.55

Density (g/mL)

ACS Paragon Plus Environment

Peak 1.35

1.40

1.45

Peak

0.0

U

1.6

1.35

1.35

Bi

16

0 1.30

Peak

1.30

1.35

1.40

1.45

Page 47 of 51

Energy & Fuels

Figure 10

LC S3-6 Li

Sc

Cr

6

5

5

5

4

4

3

3

2

2

1

1

4

Ni 4 3

3

2

2 1 0 1.30

Trace element concentration (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Peak 1.35

1.40

1.45

1.50

1.55

0 1.30

Peak 1.35

1.40

Zn

1.45

1.50

1.55

1

Peak

0 1.30

1.35

1.40

Peak 60

1.50

1.55

Peak 1.35

1.40

Rb

Se

80

1.45

0 1.30

0.8

16

0.6

12

1.45

1.50

1.55

1.50

1.55

1.50

1.55

1.50

1.55

Sr 20

Peak 16 12

40

8

0.4

8 20 0 1.30

4

0.2

1.35

1.40

1.45

1.50

0 1.30

1.55

Peak 1.35

1.40

Nb

1.45

1.50

1.55

0 1.30

Peak 1.35

1.40

Cd

30

1.45

1.50

1.55

0.020

0.3

25

10

0.012

20

0.008

15 10

0.1

1.35

1.40

1.45

0.004

0.0 1.50

1.55

1.30

1.35

1.40

1.45

1.50

1.55

1.30

1.35

1.40

Ta

1.45

1.50

1.55

1.35

1.40

1.45

3.0

Peak

2.5

3

300 2.0

0.3 2

200

1

100

1.5

0.2

1.0

0.1 0 1.30

Peak

Th

400

Peak

0 1.30

W

4

0.4

5

Peak

0.000

Hf 0.5

1.45

30

0.2

Peak

1.40

35

0.016

20

5

1.35

Ba

Peak

15

0 1.30

In

0.4

25

0 1.30

4

1.35

1.40

1.45

1.50

1.55

0 1.30

1.35

1.40

1.45

1.50

1.55

0 1.30

Density (g/mL) ACS Paragon Plus Environment

0.5

Peak 1.35

1.40

1.45

Peak

0.0 1.50

1.55

1.30

1.35

1.40

1.45

Figure 11 R² = 0.68

140

48

(B)

60 40

Sb (μg/g)

80

350 300 250

20 0 120

140

160

180

200

220

120

140

160

180

200

60 40 20

120

140

0

3.5 3.0 2.5

0.5

180

200

220

23

R² = 0.96

(F)

21 17 15 13 11 9 7

1.5 0.4

160

19

4.0

2.0

Nb (μg/g)

100

Ba (μg/g)

80

0.3

38

220

(E)

4.5

Ni (μg/g)

100

0.2

40

Ge (μg/g)

R² = 0.76

5.0

(D)

120

0.1

42

Ge (μg/g)

R² = 0.54

0

44

34 100

Ge (μg/g)

140

(C)

36

200 100

R² = 0.61

46

400

100

As (μg/g)

W (μg/g)

Page 48 of 51

R² = 0.34

450

(A)

120

W (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Energy & Fuels

5 3

4

5

6

Cr (μg/g) ACS Paragon Plus Environment

7

8

0.0

0.5

1.0

1.5

Sc (μg/g)

2.0

2.5

3.0

Figure 12

Page 49 of 51

R² = 0.001

400

340

(A)

350

R² = 0.22

320

200 150

44

300 280 260

100

0 1000

1200

1400

1600

1200

1400

Ge (μg/g)

75

U (μg/g)

Be (μg/g)

70 60 50

1800

1400

1600

25

65

20

60 55

3.0

350

1200

1400

1600

200 150 100

10

1200

1400

1600

1800

Ge (μg/g)

R² = 0.61

2.4

(H)

(I)

R² = 0.50

2.3 2.2

2.0 1.5

2.1 2.0 1.9 1.8 1.7

1.0

50

1.6

0

0.5 0

5

10

15

20

25

30

35

1.5 50

150

Nb (μg/g)

250

350

450

2.1

R² = 0.90

30

(J)

1.2

Ba (μg/g)

1.1 1.0 0.9 0.8 0.7 2.3

2.5

2.7

Sn (μg/g)

2.5

2.9

3.1

2.7

2.9

3.1

Sn (μg/g)

R² = 0.89

R² = 0.89

30

(K)

25

2.1

2.3

W (μg/g)

(L)

25

Ba (μg/g)

1.3

15

0 1000

1800

Tl (μg/g)

Th (μg/g)

250

1800

5

2.5

300

1600

(F)

Ge (μg/g)

(G)

1400

R² = 0.06

30

(E)

70

45 1000

1800

R² = 0.85

400

1200

Ge (μg/g)

R² = 0.66

Ge (μg/g)

W (μg/g)

1600

50

1200

36

30 1000

Nb (μg/g)

(D)

80

40 1000

38

Ge (μg/g)

R² = 0.89

90

40

32

220 1000

1800

42

34

240

50

(C)

46

Sb (μg/g)

As (μg/g)

W (μg/g)

250

R² = 0.83

48

(B)

300

Bi (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

20 15

20 15

10

10

5

5 1.5

2.0

2.5

3.0

3.5

4.0

Sc (μg/g) ACS Paragon Plus Environment

4.5

5.0

0

5

10

Sr (μg/g)

15

20

Figure 13

Energy & Fuels 30

H

LC S3-6

40

(A)

I

(B)

Peak

35

25 20 15 REY 10

LREY

5 MREY HREY

0 1.36

1.41

1.46

Density (g/mL)

1.51

1.56

REY (μg/g)

30

REY (μg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

WLTG C6-2

Page 50 of 51

REY

25 20 15

LREY

10

MREY

5

HREY

0 1.34

ACS Paragon Plus Environment

1.39

1.44

Density (g/mL)

1.49

Figure 14

Page 51 of 51

0.35

(A) WLTG C6-2

0.30

Density (g/mL) 1.5515 1.5426 1.5333 1.5220 1.5106 1.4985 1.4871 1.4742 1.4596 1.4443 1.4266 1.4074 1.3879 1.3692

Samples/UCC

0.25 0.20 0.15 0.10 0.05 0.00 La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Y

Ho

Er

Tm

Yb

Lu

1.00

(B)

0.90

Density (g/mL)

LC S3-6

0.80

1.5102 1.5069 1.5009 1.4932 1.4846 1.4742 1.4638 1.4523 1.4412 1.4305 1.4175 1.4026 1.3864 1.3693 1.3529

0.70

Samples/UCC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.60 0.50 0.40 0.30 0.20 0.10 0.00 La

Ce

Pr

Nd

Sm

Eu

Gd

Tb ACS Paragon Plus Environment

Dy

Y

Ho

Er

Tm

Yb

Lu