Article pubs.acs.org/EF
Diagnosis of the Surface Chemistry Effects on Fine Coal Flotation Using Saline Water Bo Wang,† Yongjun Peng,*,† and Sue Vink‡ †
School of Chemical Engineering, The University of Queensland, St Lucia, 4072, Australia Centre for Water in the Minerals Industry, Sustainable Minerals Institute, The University of Queensland, St Lucia, 4072, Australia
‡
ABSTRACT: In the present investigation, two coal samples were obtained from a typical Australian coal flotation plant using saline water and examined to identify surface chemistry effects on fine coal flotation which is an important issue confronting the coal industry. The speciation modeling indicated that hydrophilic precipitates may occur in the flotation circuits as a result of the use of high ionic strength water, negatively impacting the coal flotation. Meanwhile, Cryo-SEM (scanning electron microscopy) detected the presence of clay minerals on the coal surface which has a deleterious effect on the flotation. Surface oxidation was also found on both coal samples by XPS (X-ray photoelectron spectroscopy) analysis and well correlated with their flotation behavior. This study suggests mitigating the slime coating and addressing the oxidized coal surface simultaneously to improve the coal flotation. water.6−8 However, the perceived benefits do not seem to exist in these coal flotation plants in Australia. Although many plants process coal with combustible matter content in the feed as high as 80%, low combustible matter recovery about 75% is often achieved. Another major change in the Australian coal industry in the past few years is the processing of clayey coal as a result of a need to process low quality coal. There have been ample industrial observations that clay minerals have a deleterious effect on flotation. The flotation of high clayey coal is not possible presently. High clayey coal has to be blended with normal coal at a small proportion before flotation. A number of studies were conducted to investigate how clay minerals affect coal flotation. Arnold and Aplan found that kaolinite and illite did not significantly depress coal flotation in fresh water, while bentonite greatly depressed the flotation of all but the most hydrophobic coal.9 Therefore, they proposed that bentonite might coat the bubble and coal surfaces preventing bubble− particle attachment because of its small sizes, high specific surface area, charged sites, and ion-exchange-capacity.9 A similar conclusion was made by Oats et al. who tested a coal sample obtained from one of BHP Billiton Mitsubishi Alliance mines in Central Queensland, Australia, by using saline water.10 Based on the colloid stability theory, Oats et al. suggested that the clay coating on the coal surface was mainly governed by van der Waals attraction,10 which is different from many other researchers observation that the slime coating on the mineral surface resulted from electrostatic attraction between oppositely charged particles.11−13 Oats et al. tested a range of dispersants at different dosages to mitigate the clay slime coating, but they were not successful.10 In fact, there is a debate whether clay minerals coat the coal surface because a direct measurement is not available.
1. INTRODUCTION In Australia, coal has become a vital national resource for providing strong economic and employment growth since it was discovered in the late 18th century. In addition to providing Australian consumers with affordable electricity, coal underpins the international competitiveness of the entire Australian economy. Coal mining in Australia supplies coal to produce 85% Australia’s electricity. Fifty four percent of the coal mined in Australia is also exported, mostly to Eastern Asia. Coal in Australia is mined primarily in the Bowen Basin in the state of Queensland and the Hunter Region in the state of New South Wales. Flotation plays an important role in concentrating coal, especially fine coal, by exploiting the difference in surface wettability on coal and mineral matter. Coal is naturally hydrophobic because of its chemical composition (surface aromatic and aliphatic groups).1 In practice, poor coal flotation can be due to the decrease of coal surface hydrophobicity. This may be attributed to oxidation resulting in the formation of hydrophilic carbonyl, carboxyl, and ester groups.2−5 In Australia, high rank coal is normally processed with a conventional flotation system consisting of diesel fuel as the collector to enhance the surface hydrophobicity on coal particles and MIBC as the frother to generate smaller bubbles to capture coal particles in the pulp and form froth on the top of pulp to transport the flotation concentrate, the bubble-coal particle aggregates. In the past few years there has been a distinct change in water quality used in coal preparation plants within Australia due to stringent policy on the amount of saline water that a mine can discharge into local river systems. As a result, most coal mines have introduced water reuse as a conventional practice. One of the consequences of increased water reuse is a concomitant increase in salinity on sites and subsequently in flotation. A number of studies have been conducted to investigate coal flotation using saline water. In general, saline water increases combustible matter recovery compared to fresh © 2013 American Chemical Society
Received: May 15, 2013 Revised: June 30, 2013 Published: July 9, 2013 4869
dx.doi.org/10.1021/ef400909r | Energy Fuels 2013, 27, 4869−4874
Energy & Fuels
Article
Process water obtained from the plant was used in this study. The compositions assayed by inductively coupled plasma (ICP) are listed in Table 2. The major ions are Na+, Mg2+, Ca+, SO42+, Cl−, and CO32−. The pH, Eh, and conductivity of the water are 8.0, 201 mV (SHE), and 9.32 mS/cm, respectively. 2.2. Methods. 2.2.1. Flotation. After screening, the pulp was transferred to a 2.5 dm3 JK Batch Flotation Cell and then conditioned with diesel fuel (160 mL/t) and MIBC (110 mL/t) for 2 min at 900 rpm of agitation. The solid percentage in the flotation cell was about 5%. This solid percentage is used in coal flotation in the plant. In flotation, four concentrates were collected after a cumulative time of 1, 2.5, 5, and 10 min. Flotation was operated at an air flow rate of 3.0 dm3/min. The flotation froth was scraped every 15 s. Process water was used throughout the flotation. The flotation products were combusted at 815 °C for 2.5 h to obtain mineral and combustible matter contents.10 2.2.2. Solution Speciation Modeling. Visual MINTEQ 3.0 was applied for solution speciation modeling calculations in this study to predict possible hydrophilic precipitates on the coal surface in the flotation system. MINTEQ is a geochemical program for modeling aqueous solutions and can be used to calculate ion speciation/ solubility and precipitation/dissolution of solid phases.14 Solution speciation analyses were carried out for both CoalA and CoalB flotation circuits. Eh and pH measured in the flotation process together with solution concentrations of the process water shown in Table 2 were used as input parameters. The equilibrium solution speciation was then calculated for each circuit. The pH and Eh were 8.3, and 317.5 mV (SHE), respectively, in the flotation of CoalA, and 8.5 and 291.9 mV (SHE), respectively, in the flotation of CoalB. CO2 was specified to be present at a fixed partial pressure equivalent to air. The mineral compositions in flotation were calculated to mole per liter based on the assay results in Table 1 and imported into the program as well. Calculations of speciation were then carried out using two different approaches: (a) No precipitation was ‘allowed’ during the calculations, as it was desired to simulate a snapshot of the species present under the prevalent nonequilibrium conditions, and (b) precipitation was allowed to occur to provide an indicator of possible previous and dynamically occurring precipitation events. 2.2.3. Cryo-SEM Analysis. Traditional scanning electron microscopy (SEM) analysis involves drying samples which may alter the surface properties. In this study, Cryo-SEM, an in situ technique, was used to detect clay slime coatings on the coal surface during flotation. The cryo-transfer method of sample preparation was used to avoid a structural change caused by surface tension during oven or freezedrying. In the cryo-vitrification SEM analysis, the sample was taken by a large-aperture (>2 mm) pipet directly from the coal slurry sample after conditioning, concentrate 1 and tailings, and washed by deionized water at pH 9.0. The sample was then mounted onto the top of a 3 mm long brass rivet with outer-diameter 2.4 mm and inner-diameter 1.7 mm. This brass rivet was fixed on a sample holder and plunged into liquid nitrogen of the cryo-vitrification unit, which reduces the temperature at >800 °C min−1 freezing the water without allowing crystallization to ice structures (i.e., vitrifying). The small volume of the sample (about 0.01 cm3) and high heat conductivity of brass minimize shrinkage and distortion of the sample during freezing. The very fast vitrification process avoids crystallization of water to ice and associated volume changes that can alter structures.15 The sample was then transferred under vacuum to the sample preparation chamber equipped with an Oxford Instrument where the frozen sample was fractured to expose a fresh surface. Then, the sample temperature was raised to 173 K (−100 °C) to sublimate vitrified water for 8 min. This sublimation process removes fine vitrified water slivers generated during fracture and allows mineral structures to stand out above the glassy background. The sample was eventually coated with gold plasma for 1.5 min to avoid charging during the imaging process by a PHILIPS XL30 field emission gun scanning electron microscopy (FESEM) instrument normally operated at 15 kV. The sample was then examined using SEM. Images were taken in backscattered electron mode (BSE), while elemental analysis was performed by energy dispersive spectrometry (EDS). The combination of BSE and
In this study, two coal samples were obtained from the feeds of two parallel circuits in an Xstrata coal plant located in the Bowen Basin, Queensland. Despite high combustible matter content about 85% in the feed, about 65% mass recovery, equivalent to 75% combustible matter recovery, is actually achieved from one of the flotation circuits in the plant. This represents the status of many flotation plants in Bowen Basin and Hunter Region in Australia. Since surface wettability is of vital importance in coal flotation, in this study, different techniques were used to diagnose the surface chemistry on coal particles of these two samples which may reduce the hydrophobicity resulting in poor flotation performance.
2. EXPERIMENTAL SECTION 2.1. Raw Materials. Two coal samples (CoalA and CoalB) were obtained from the same seam but different Xstrata coal mines. CoalA is typically higher in mineral matter due to it being in a thinner section of the seam, while CoalB is slightly lower in mineral matter due to it being in a thicker section of the seam and having multiple longwalls. Both are bituminous coal, and flotation produces coking coal. In the plant, CoalA and CoalB are treated in parallel, and a higher combustible matter recovery is obtained from the flotation of CoalB. In the laboratory, both coal samples were screened to −150 μm for flotation following the procedure established in the plant where coal particles greater than 150 μm are treated by the gravity concentrator. The size distribution of the flotation feeds were measured by a Laser Diffraction Malvern Mastersizer (Model No MSX14), and the results are shown in Figure 1. The two flotation feeds have similar size
Figure 1. Size distribution of CoalA and CoalB flotation feeds. distributions. Both have more than 40% particles smaller than 30 μm. CoalA flotation feed has more fine particles. The flotation feeds were analyzed by quantitative X-ray diffraction (XRD), and the results are shown in Table 1. Both have similar mineral compositions and contain about 10−12% clay minerals such as kaolinite, smectite, and illite. The combustible matter content is about 83% in the two flotation feeds.
Table 1. CoalA and CoalB Mineral Compositions Analyzed by XRD sample
CoalA 150 μm
CoalB 150 μm
unidentified/amorphous quartz kaolinite muscovite mixed layer illite/smectite siderite pyrite albite diopside 1
82.9 5.0 3.9 2.8 3.4 1.0 0.4
83.0 4.0 5.9 3.0 2.4 1.3 0.3 0.1 0.5 4870
dx.doi.org/10.1021/ef400909r | Energy Fuels 2013, 27, 4869−4874
Energy & Fuels
Article
Table 2. Composition of Process Water Used in This Study Ca mg/L
K mg/L
Mg mg/L
Na mg/L
PO4 mg/L
SO4 mg/L
Cl mg/L
carbonate mg/L
TSS mg/L
182
21
218
1037
0.1
3948
864
260
14
EDS allows the identification of clay coating on the coal mineral surface. 2.2.4. XPS Analysis. XPS is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state, and electronic state of the elements that exist within a material. In this study, XPS was used to measure the oxidation on the coal surface. The ratio of oxidized to unoxidized surfaces may provide an insight into the development of a new reagent system by mixing conventional and nonconventional collectors to address both oxidized and unoxidized coal surfaces. XPS measurements were carried out with a KRATOS Axis Ultra (Kratos Analytical, Manchester, United Kingdom) with a monochromatic Al X-ray source operating at 15 kV and 10 mA (150 W). The analysis spot size is 300 × 700 μm. The flotation feed samples were taken and frozen in liquid nitrogen immediately. This procedure has been shown to inhibit significant surface speciation alteration.16 The frozen samples were defrosted just prior to the analysis. The solids were placed on the stainless steel bar and immediately loaded into the introduction chamber of the spectrometer. The samples were analyzed at a pressure of 9 × 10−10 Torr at room temperature. Each analysis started with a survey scan from 0 to 1200 eV using a pass energy of 160 eV at steps of 1 eV with 1 sweep. High resolution spectra of O 1s, C 1s were collected at 20 eV pass energy at steps of 100 meV with 2 sweeps. Binding energies were charge-corrected by referencing to adventitious carbon at 284.8 eV.
surface chemistry on CoalA and CoalB which may have a deleterious effect on coal flotation. 3.2. Solution Speciation Modeling. The solution species and their activities calculated by MINTEQ for CoalA and CoalB flotation circuits are provided in Figure 3. The
Figure 3. Solution species and their activities in CoalA and CoalB flotation circuits calculated by MINTEQ.
3. RESULTS AND DISCUSSION 3.1. Flotation. Figure 2 shows the combustible or mineral matter recovery as a function of flotation time in the flotation of
predominant species in solutions (log (activity (mol dm−3)) > −5) are similar between the two flotation circuits (i.e., Ca2+, CaCO3 (aq), CaSO4 (aq), Cl−, HCO3−, K+, Mg2+, MgCO3 (aq), MgSO4 (aq), Na+, NaCl, and SO42−). The activity of the Na+ is the largest followed by Cl− and SO42−. The carbonate containing species have the largest numbers of log (activity), which are higher than 5, with the sulfate containing species as the second largest. The calculated saturation indices of possible precipitates are shown in Table 3. Both CoalA and CoalB flotation circuits are Table 3. Saturation Indices of Possible Secondary Minerals in Sample Solutions
Figure 2. Combustible or mineral matter recovery as a function of flotation time.
CoalA and CoalB. Mineral matter shows a similar behavior in the flotation of both CoalA and CoalB, reaching about 15% recovery at the completion of flotation. However, combustible matter recovery is always higher in the flotation of CoalB. At the completion of flotation, combustible matter recovery reaches 84% in the flotation of CoalB but 74% in the flotation of CoalA. The combustible matter content in the final flotation concentrate is about 95% with 5% mineral matter content for both CoalA and CoalB. The results in the laboratory match those in the plant. Obviously, CoalB is a higher rank coal than CoalA, exhibiting better floatability. Higher combustible matter recovery is expected from both CoalA and CoalB flotation circuits given such high combustible matter contents in flotation feeds. Tests were then performed to detect the
minerals
CoalA
CoalB
aragonite calcite chrysotile diaspore dolomite (disordered) dolomite (ordered) greenalite hercynite huntite hydroxyapatite magnesite sepiolite vaterite
0.184 0.328 0 0.845 0.574 1.124 4.126 3.523 0 4.728 0 0 0
0.661 0.805 2.495 0.845 1.528 2.078 4.126 0.103 3.523 5.644 0.123 0.701 0.238
super saturated with respect to a range of carbonates, silicates, and aluminates, as their saturation indices are greater than zero. In particular, hydroxyapatite, hercynite, and greenalite have high saturation indices. In addition, a significant difference in saturation indices of the possible secondary minerals was observed between CoalA and CoalB flotation circuits. In the 4871
dx.doi.org/10.1021/ef400909r | Energy Fuels 2013, 27, 4869−4874
Energy & Fuels
Article
CoalB flotation circuit, there are more species being observed than in the CoalA flotation circuit (i.e., huntite, magnesite, sepiolite, and vaterite). For most minerals, the saturation indices of the CoalB flotation circuit are larger than that of the CoalA flotation circuit. However, for CoalA, the saturation of hercynite is higher. The calculations for CoalA and CoalB flotation circuits were repeated allowing precipitation to occur. For both CoalA and CoalB flotation circuits, the predicted precipitates are chrysotile, calcite, dolomite, and aragonite as shown in Table 4. Chrysotile and dolomite are the major precipitates in the
particles in the SEM image. Clay minerals are small, and their shapes are difficult to identify by SEM images. The SEM image shows that the coal surface is very clean in the concentrate (Figure 4a), but in the tailings, it is extensively covered by small bumps suggesting that slime coatings occurred on coal particles that entered flotation tailings (Figure 4b). The SEM image is consistent with the EDS analysis. On the coal particle in the flotation concentrate, a very strong signal from C element was detected and other clear signals detected are from O and Au (Figure 5a). In contrast, on the particle in flotation tailings, the signal from C is very weak, but clear signals from Si, O, Al, and Mg were detected (Figure 5b) further confirming that slime coatings occurred on coal particles in flotation tailings. The same observations were found when the concentrate and tailings from the CoalB flotation circuit were measured by the Cryo-SEM analysis. The clay minerals indicated in Table 1 are mainly composed of Si, Al, Mg, and O, and signals from all of them were detected on particles in the tailings. It is therefore deduced that clay minerals did coat some coal particles and depress their flotation. However, it is not clear whether the precipitated products predicted in Table 4 coated the coal particles or not. The major precipitated product is chrysotile composed of Mg, Si, and O elements. Signals from these elements were detected from coal particles in the tailings, but they are also part of the elements from clay minerals. Other precipitated products are aragonite, calcite, and dolomite, all consisting of Ca element. However, a signal from Ca was not detected. According to Kursula the theoretical detection limits in SEM−EDS measurements are about 0.1 wt % depending on individual elements.17 Assuming all Ca species precipitated adsorb on the mineral surface, the Ca concentration is about 0.1 wt % based on the predicted concentration in Table 4. As a result, SEM-EDS may not be able to detect the actually precipitated species predicted by MINTEQ on the mineral surface in this study. This study is in line with other studies proposing clay slime coatings on the coal surface.9,10 The nature of this study is the natural pH (about 8.5) and high ionic strength of water used. Previous studies indicated that edges and faces of clay minerals were negatively charged at alkaline pH values normally18,19 and coal particles were negatively charged as well.10 It is therefore expected that clay minerals may be electrostatically repulsive from coal particles at alkaline pH. However, calcium and
Table 4. Predicted Concentrations of Precipitated Species in CoalA and CoalB Circuits (mmol/L) mineral
CoalA
CoalB
aragonite calcite dolomite chrysotile hydroxyapatite
0.25 0.25 1.61 2.42
0.28 0.28 0.67 1.01 1.40
CoalA flotation circuit, while hydroxyapatite and chrysotile are the major precipitates in the CoalB flotation circuit. The concentration of the total precipitates is about 4.5 and 3.6 mmol/L in CoalA and CoalB flotation circuits, respectively. The calculations were also conducted by replacing process water with deionized water, and no precipitate occurred in both flotation circuits. Apparently, electrolytes in the process water promote these precipitates. The results from the speciation modeling indicate that some precipitation of these species may have already occurred and been widespread on the surfaces of the coal samples within the slurries. They are hydrophilic precipitates and likely to have a negative effect on the flotation. 3.3. Cryo-SEM Analysis. Cryo-SEM was used to detect the slime coating on the coal surface. For comparison, flotation concentrate and tailings samples were measured. Figure 4 and 5 show SEM images and EDS elemental analysis on the randomly chosen particle indicated by the arrow from the flotation concentrate and tailings obtained from the CoalA circuit, respectively. The black background in the SEM images is the vitrified water. Coal composed of C is present as the larger
Figure 4. BSE images of the flotation (a) concentrate and (b) tailings taken from the CoalA flotation circuit. 4872
dx.doi.org/10.1021/ef400909r | Energy Fuels 2013, 27, 4869−4874
Energy & Fuels
Article
Figure 5. EDX analysis on the randomly chosen particle from the flotation (a) concentrate and (b) tailings taken from the CoalA flotation circuit.
Figure 6. XPS C 1s spectra of CoalA (a) and CoalB (b) flotation feeds.
CoalA (Figure 6a) and CoalB (Figure 6b) flotation feeds. The XPS C 1s spectra of coal are composed of four components.24,25 The first component near 284.6 eV is attributed to C−C and C−H species, or the aliphatic species of unoxidized coal. The other three components near 285.6, 286.6, and 289.1 eV are due to oxidation and attributed to C− O (alcohol, phenol, or ether), CO (carbonyl), and OC O (carboxyl) groups, respectively. Figure 6 shows that CoalA and CoalB flotation feeds did not expose OCO groups indicating that the surface oxidation was not very strong. On the CoalA and CoalB flotation feeds, about 19 at. % C and 11 at. % C were associated with the oxidation species. Apparently, the CoalA surface was more oxidized than the CoalB surface, which is consistent with the lower flotation of CoalA. It has been established that diesel fuel is a collector suitable for high rank of coal without oxidation and for oxidized coal polar collectors are more effective.26,27 Apparently, to effectively float CoalA and CoalB, a polar collector may have to be mixed with diesel fuel to attack the oxidized surface on coal particles. In addition to increasing the surface hydrophilicity, coal oxidation products alter the electrical properties on the surface through acidic oxygen groups.28 In this study, electrostatic interactions may be minimized in the process water. However, it is likely that hydrogen bonding between clay minerals and hydrophilic carbon oxidation products enhances the adsorption of clay minerals.
magnesium ions present could change or reverse the negative surface charges and therefore the electrostatic interaction between clay minerals and coal particles. Previous studies also indicated that with the increase in the ionic strength, the electrostatic interaction was decreased due to the compression of electrical double layers.20 In this study, high ionic strength of water is used. It is unlikely that electrostatic attraction promotes the coating. It is very likely that the van der Waals attraction, which is independent of the ionic strength, contributes to the clay slime coating on the coal surface, as proposed by Oats et al.10 Oats et al. tested a number of dispersants to mitigate clay slime coatings without success.10 All these dispersants are ionic and may not be effective in saline water. Peng and Seaman tested CMC (carboxymethyl cellulose) with different charge density in dispersing serpentine slime coatings from pentlandite surfaces in saline water and found that the lower the charge density of the CMC, the better the dispersion.21 They also demonstrated that a nonionic triblock copolymer dispersant successfully mitigated the negative effect of serpentine particles in pentlandite flotation using saline water.22 In fact, the flotation of CoalA and CoalB was improved significantly in the presence of the triblock copolymer dispersant, as demonstrated by Liu et al.23 3.4. XPS Analysis. Besides the slime coating, hydrophilic oxidation products such as hydrophilic carbonyl, carboxyl, and ester groups on coal surfaces depress the flotation.2−5 In this study, the feeds to CoalA and CoalB flotation circuits were taken and measured by XPS. Of particular interest to this study is the XPS C spectrum showing the oxidized and unoxidized carbon chemical state. Figure 6 shows XPS C 1s spectra of
4. CONCLUSIONS The flotation behavior of CoalA and CoalB in saline water was closely related to the surface chemistry. Hydrophilic calcium and magnesium species may precipitate in the flotation circuit 4873
dx.doi.org/10.1021/ef400909r | Energy Fuels 2013, 27, 4869−4874
Energy & Fuels
Article
(18) Gupta, V.; Miller, J. D. J. Colloid Interface Sci. 2010, 344, 362− 371. (19) Liu, J.; Xu, Z.; Masliyah, J. J. Colloid Interface Sci. 2005, 287, 507−520. (20) Rattanakawin, C.; Hogg, H. Colloids Surf., A 2001, 177, 87−98. (21) Peng, Y.; Seaman, D. Miner. Eng. 2011, 24 (5), 479−481. (22) Peng, Y.; Liu, D.; Chen, X. XXVI Int. Miner. Process. Congress 2012, 4179−4190. (23) Liu, D.; Wang, B.; Peng, Y.; Vink, S. Proc. 11th AusIMM Mill Operators’ Conf. 2012, 151−158. (24) Briggs, D.; Seah, M. P. Practical Surface Analysis by Augler and XPS; Wiley & Sons: New York, 1983. (25) Pietrzak, R.; Grzybek, T.; Wachowska, H. Fuel 2007, 86, 2616− 2624. (26) Fuerstenau, D. W.; Harris, G. H.; Jia, R. ACS Symp. Ser. 1999, 230−246. (27) Jia, H.; Harris, G. H.; Fuerstenau, D. W. Int. J. Miner. Process. 2000, 58, 99−118. (28) Paulik, M. Handb. Surf. Colloid Chem. 2008, 655−680.
as a result of high ionic strength of water used and negatively impact coal flotation. Due to the low concentration, these precipitates were not detected by Cryo-SEM on the coal surface. However, Cryo-SEM detected the presence of clay minerals on the coal surface, which played an important role in depressing coal flotation. XPS analysis revealed that both CoalA and CoalB were oxidized with a higher degree of oxidation on the CoalA surface corresponding to the lower flotation of CoalA. This study suggests that mitigating slime coating and addressing the oxidized coal surface have to be considered to improve the flotation of CoalA and CoalB representing the current coal resource in Australia.
■
AUTHOR INFORMATION
Corresponding Author
*Phone: 61-7-3365 7156. Fax: 61-7-3365 4799. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This paper has been published with the permission of ACARP (The Australian Coal Industry’s Research Program), and the authors greatly appreciate financial support from ACARP, as well as discussions and suggestion from Frank Mercuri and John Gartlan at Xstrata Coal and Ian Brake, Ben Cronin, and Susan Watkins from BHP Billiton Mitsubishi Alliance (BMA). Thanks also to the scientific and technical assistance of the Australian Microscopy and Microanalysis Research Facility at the University of Queensland on the coal surface analysis.
■
REFERENCES
(1) Brady, G. A.; Gauger, A. W. Ind. Eng. Chem. 1940, 32 (12), 1599−1604. (2) Xiao, L.; Somasundaran, P.; Vasudevan, T. V. Colloids Surf. 1990, 50 (0), 231−240. (3) Buckley, A. N.; Lamb, R. N. Int. J. Coal Geol. 1996, 32 (1−4), 87−106. (4) Somasundaran, P.; Zhang, L.; Fuerstenau, D. W. Int. J. Miner. Process. 2000, 58 (1−4), 85−97. (5) Ding, L. P. Energy Fuels 2009, 23 (11), 5536−5543. (6) Kurniawan, A. U.; Ozdemir, O.; Nguyen, A. V.; Ofori, P.; Firth, B. Int. J. Miner. Process. 2011, 98, 137−144. (7) Harvey, P. A.; Nguyen, A. V.; Evans, G. M. J. Colloid Interface Sci. 2002, 250, 337−43. (8) Yoon, R. Min. Congr. J. 1982, 68, 76−80. (9) Arnold, B. J.; Aplan, F. F. Int. J. Miner. Process. 1986, 17 (3−4), 225−242. (10) Oats, W. J.; Ozdemir, O.; Nguyen, A. V. Miner. Eng. 2010, 23 (5), 413−419. (11) Xu, Z.; Liu, J.; Choung, J. W.; Zhou, Z. Int. J. Miner. Process. 2003, 68 (1−4), 183−196. (12) Quast, K.; Ding, L.; Fornasiero, D.; Ralston, J. Proc. Chemeca 2008, 130−139. (13) Celik, M. S.; Elma, I.; Hancer, M.; Miller, J. D. Proc. Int. Miner. Process. 7th Symp. 1998, 153−157. (14) Gerson, A. R.; Smart, R. S. C.; Li, J.; Kawashima, N.; Weedon, D.; Triffett, B.; Bradshaw, D. Int. J. Miner. Process. 2012, 106−109, 16− 30. (15) Battersby, B. J.; Sharp, J. C. W.; Webb, R. I.; Barnes, G. T. J. Microsc. 1994, 176, 110−120. (16) Smart, R.; St, C. Surface layers in base metal sulphide flotation. Miner. Eng. 1991, 4, 891−909. (17) Kursula, P. K. X-Ray Spectrom. 2000, 29, 111−118. 4874
dx.doi.org/10.1021/ef400909r | Energy Fuels 2013, 27, 4869−4874
