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Response to “Comments on ‘Geochemical Characteristics of RareMetal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China’ by Dai et al.” Shenjun Qin, Kang Gao, Yuzhuang Sun, Jinxi Wang, Cunliang Zhao, Shenyong Li, and Qingfeng Lu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01668 • Publication Date (Web): 06 Jul 2018 Downloaded from http://pubs.acs.org on July 8, 2018
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Energy & Fuels
Response to “Comments on ‘Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China’ by Dai et al.”
Shenjun Qin,† Kang Gao,∗,†,‡ Yuzhuang Sun,† Jinxi Wang,† Cunliang Zhao,† Shenyong Li,† and Qingfeng Lu† †
Key Laboratory for Resource Exploration Research of Hebei Province, Hebei University of Engineering,
‡
Department of Chemical Engineering, Université Laval, Québec G1V 0A6, Canada
Handan 056038, China
We thank Dai et al. for their valuable opinions about our research. Our reply to the comments are as follows: (1) Firstly, we would like to emphasize that the main objective of the study was to investigate the geochemical characteristics (e.g., vertical distribution, enrichment, and modes of occurrence) of the elements in the Moxinpo Coals using the classification of Rare-Metal, Rare-Scattered, and Rare-Earth Elements (TREs). Although the coal seam analyzed by Dai et al. 1 was the same as the seam we studied (K2 coal), the difference in sampling sections, and hence the variations in local coal-forming environments, may have given rise to the inconformity in the experimental results. For instance, the discrepancy of REEs appears between different researchers Dai et al. 1 and Zou et al. 2 (Table 1). As we could not discuss all aspects in detail (e.g., elaborate identification of each mineral), some arguments in the paper may be insufficient (as mentioned in the comments). Table 1. The average concentration of rare earth elements in Moxinpo Mine from different researchers (µg/g) La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Y
1
52.1
95.1
10.7
40.90
6.96
0.87
9.01
1.34
8.26
46.10
1.68
5.13
0.72
4.83
0.69
Zou et al. 2
98.2
193
18.3
64.30
10.8
0.59
9.11
1.31
6.17
50.80
1.25
3.22
0.58
3.48
0.42
Qin et al. 3
49.12
72.45
9.93
32.48
5.67
0.60
5.75
1.03
4.30
33.83
1.18
2.54
0.49
2.27
0.48
Dai et al.
Ho
Er
Tm
Yb
Lu
(2) Coal rank and calorific value The vitrinite reflectance (Ro%) of the coal samples was determined using a polarizing microscope (Axioskop 40 Pol, ZEISS, Germany). The inconsistency of coal rank determined from these values compared with that indicated from the percentage of volatile matter (Vdaf) will be investigated further. The units of calorific value were written incorrectly. We confirmed that they should instead be MJ/kg. If necessary, we can prepare a corrigendum. (3) Mineralogy The characteristic illite peaks were not observed in the 2θ (5–10°) range when processing the data (as shown in the Figure 1). Therefore, the XRD patterns of our coal samples were only plotted over the interval of 10–70°. It is also possible that the presence of illite might not have been detected because it is below the detection limit of XRD. ACS Paragon Plus Environment
Energy & Fuels
d=1.4492
d=1.6338 d=2.4240
d=1.9158
d=1.5023
20
d=2.2126
30
d=3.2695 d=3.2095 d=3.1307 d=3.0350
d=4.4763 d=4.3680 d=4.2646 d=4.1828
40
d=2.3395
50
d=2.7114
d=7.1865
60
d=2.5657 d=2.4951
d=3.5789 d=3.3488
[K-MXP-1-1529-1.raw] K-MXP-1 - 20180427 70
Intensity(Counts)
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10 0 24-0076> Pyrite - FeS2 85-1108> CaCO3 - Calcium Carbonate 14-0164> Kaolinite-1A - Al2Si2O5(OH)4 05-0490> Quartz - SiO2
10
20
30
40
50
60
70
80
2-T heta(°
Figure 1. X-ray powder diffraction patterns of LTA ash of the K2 coal (MXP-1 sample)
In the study, a qualitative approach was used when examining the mineral assemblage in the coal. This was done to provide relevant information for the elemental analysis. The main conclusion remains valid without quantitative evaluation of the minerals. The idea we intended to convey in the paper may be consistent with that mentioned in the comments of Dai et al., that is, anatase and other fine-grained minerals are admixed with kaolinite, resulting in the peaks of elements such as Ti, S, and Ca. Figure 10H illustrates that the pyrite did not exist by itself. It was difficult to distinguish TiO2 in the samples precisely because of its fine grain size and because it was mixed with pyrite. However, we were able to capture an EDX image of TiO2, as shown in Figure 11B. Likewise, fine-grained xenotime was admixed with kaolinite. Because the peak time of Y is close to that of P in the EDS image of xenotime, the two peaks overlapped and were difficult to differentiate. The same has been reported in previous studies. 1 The morphology of clay minerals suggested that they predominantly originated from terrigenous detrital sources. Nonetheless, we did not rule out other potential origins. As was pointed out in the comments, there are several possible reasons for an association of pyrite with vitrinite. In this study, we determined that pyrite was more closely (has a strong selectivity) to maceral components (gelovitrinite group) in comparison to other components and with reference to the coal-forming environment. The conclusion of the paper intended to state that terrigenous detrital input was the primary source for the minerals in the coals, but it did not intend to eliminate other possible origins. (4) Geochemistry The geochemical indicator (Fe2O3+CaO+MgO)/(SiO2+Al2O3) has already been published. 4 In this study, it was used as supplementary evidence for the coal-forming environment of the K2 coal seam, not as the only proof of our argument. Moreover, the depositional environment and the sources of the coals were inferred using Ce and Eu anomalies. ACS Paragon Plus Environment
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We thank Dai et al. for strengthening our understanding of some minerals (calcite, dolomite, and gypsum). Regarding their formation, it is noteworthy that we only stated the most probable formation mechanism, without eliminating other possibilities. The ICP-MS data were also determinated with parallel determination. The accuracy of data can thus be assured. The discrepancy in the enrichment of elements may have been caused by the differences in sampling locations of the coals (local variations in the coal seam). The related discussion could have been conveyed more precisely. However, the argument we sought to deliver was consistent with the interpretation of Dai et al. ■ AUTHOR INFORMATION Corresponding Author ∗ Telephone: +001-4182710683. E-mail:
[email protected] Notes The authors declare no competing financial interest.
■ REFERENCES (1) Dai, S. F.; Xie, P. P.; Jia, S. H.; Ward, C. R.; Hower, J. C.; Yan, X. Y.; French, D. Ore Geol. Rev. 2017, 80: 1-17. (2) Zou, J. H.; Liu, D., Tian, H. M.; Li, T.; Liu, F.; Tan, L. Int. J. Coal Sci. Technol. 2014, 1(1), 23-30.
(3) Qin, S. J.; Gao, K.; Sun, Y. Z.; Wang, J. X.; Zhao, C. L.; Li, S. Y.; Lu, Q. F. Energy & Fuels, 2018, 32(3): 3138-3151. (4) Ye, D. M.; Luo, J. W.; Xiao, W. Z. Geological Publishing House: Beijing, 1997, pp 20-23.
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