Geochemistry of Toxic Elements and Their Removal via the Preparation of High-Uranium Coal in Southwestern China
Abstract
:1. Introduction
2. Geological Setting
3. Samples and Methods
3.1. Samples
3.2. Methods
4. Results and Discussion
4.1. Geochemistry of Toxic Elements in High-U Coal from China
4.2. Geochemistry of High-U Coal from Southwestern China
4.2.1. Coal Chemistry
4.2.2. Trace Elements
4.3. The Mode of Occurrence of Toxic Elements in High-U Coals from Southwestern China
4.3.1. Mineralogy
4.3.2. The Extraction of Toxic Elements Using Dilute HCl
4.4. The Partitioning of Toxic Elements during the Flotation of High-U Coal from Southwestern China
4.4.1. The Distribution of Toxic Elements during Flotation
- (1)
- The content of most toxic elements in the GH1 cleaned coal sample is lower than that in feed coal but, with the exception of Co and Ni, the contents of other elements are closer to those of feed coal. The contents of V, Cr, Mo, Th, and U in cleaned coal are higher than, or close to, those of feed coal.
- (2)
- Similar to the sample of GH1, the contents of most toxic elements in GH2 cleaned coal is lower than those in feed coal, while Cs and Ni have a high removal rate in cleaned coals. The contents of V, Cr, Mo, and U in cleaned coal are higher than, or near to, those of feed coal.
- (3)
- Due to flotation, the contents of most toxic elements (Co, Ni, Cu, Zn, Cs, Tl, and Th) in RY1 cleaned coal are lower than those in feed coal, while the contents of other elements (Be, V, Cr, Mo, and U) are closer to, or higher, than those in feed coal.
- (4)
- The contents of most toxic elements in RY2 cleaned coal are reduced; for example, the contents of Cr, Co, Ni, Cu, Zn, Mo, Sb, Cs, Tl, Pb, and Bi are far below those of feed coal, while the contents of V and U in cleaned coal are higher than those in feed coal.
4.4.2. The Removability of Toxic Elements by Flotation
5. Conclusions
- (1)
- High-U coals are mainly distributed in Southwestern China, and most of them are characterized by a high content of organic S and V-Cr-Mo-U element assemblage. The correlation between V, Cr, Mo, and U is good, while the elements V, Cr, Mo, and U have a negative correlation with ash yield and a positive correlation with organic S, indicating that these elements are syngenetic in origin and mainly occur in the organic matter.
- (2)
- Mineralogical characteristics indicate that U in Ganhe and Rongyang coal occurs in anatase, clay minerals, guadarramite, and pyrite, while V occurs in clay minerals, pyrite, and dolomite; Cr occurs in dolomite, and F, Pb, Se, and Hg mainly occur in pyrite. These minerals are all fine-grained.
- (3)
- Gravity separation reveals that the contents of the enriched elements V, Cr, Mo, and U in Rongyang coal are still higher than, or close to, those of feed coal because these elements are derived from hydrothermal fluids in the stage of syngenesis or early diagenesis. At the same time, other elements (F, Mn, Zn, Pb, As, Se, and Hg) can also be efficiently removed.
- (4)
- Most of the elements in Ganhe and Rongyang coals can be removed by flotation, and the content of V, Cr, Mo, and U is higher than, or close to, that of feed coal. Thus, a portion of V and Cr in the cleaned coal obtained by gravity separation are removed via a flotation test, while Mo and U still cannot be removed. The results of this study show that the use of the two industrialized coal preparation methods, gravity separation, and flotation cannot effectively remove U from high-U coal.
- (5)
- Dilute HCl was used to extract toxic elements. The extraction rate of Mo reached 74% and indicates that most Mo exists in an adsorbed state, while V, Cr, Co, Ni, and U are partially absorbed, and the remainder of these components occur in minerals or are complexed with organic matter. The results of this study show that the adsorbed elements V, Cr, Mo, and U can be removed using acid. As U cannot be fully removed from coal, we, therefore, suggest that use of high-U coal should be avoided.
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A
- Method 1: 4 g of coal is put into a centrifuge tube, then added to 30 mL of 2 M HCl for 24 h (interval ultrasonic shaking) and, finally, centrifuged;
- Method 2: 4 g of coal is put into a centrifuge tube, then added to 30 mL of 4 M HCl for 24 h (interval ultrasonic shaking) and, finally, centrifuged;
- Method 3: 0.5 g of coal is put into a centrifuge tube, then added to 20 mL of 2 M HCl for 24 h (interval ultrasonic shaking) and, finally, centrifuged;
- Method 4: 0.5 g of coal is put into a centrifuge tube, then added to 20 mL of 4 M HCl for 24 h (interval ultrasonic shaking) and, finally, centrifuged.
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Coalfield | Ad | So,d | V | Cr | Mo | U | Sources |
---|---|---|---|---|---|---|---|
Guiding | 23.10 | 5.19 | 892 | 391 | 364 | 211 | Dai et al. [7] |
Yanshan | 27.51 | 9.51 | 567 | 329 | 204 | 153 | Dai et al. [2] |
Heshan * | 36.69 | 7.2 | 136.13 | 69 | 44.7 | 51.13 | Dai et al. [3] |
Chenxi | 17.97 | 7.12 | 296.3 | 407.75 | 23.19 | 75.2 | Li et al. [6] |
Yishan * | 34.26 | 7.16 | 278.33 | 102.47 | 101.97 | 72.2 | Dai et al. [5] |
Guxu | 20.95 | nd | 60.7 | 22.8 | 2.48 | 15.4 | Dai et al. [41] |
Yili * | 26.88 | nd | 114 | 82.84 | 80.77 | 312 | Dai et al. [40] |
Lincang * | 25.59 | 0.72 | 18.48 | 5.56 | 3.94 | 54.6 | Dai et al. [42] |
Longquan | 35.37 | 0.89 | 98.4 | 79 | 58.8 | 34.1 | Dai et al. [43] |
Zhijin | 26.41 | 0.33 | 432.1 | 113.1 | 63.1 | 49.6 | Dai et al. [44] |
Moxinpo * | 26.83 | nd | 1507 | 1180 | 4.72 | 190.5 | Dai et al. [45] |
Rongyang | 19 | 1.06 | 283 | 62.3 | 87.5 | 70.5 | This study |
Ganhe * | 23.79 | 10.09 | 568 | 273 | 145 | 201 | This study |
World | nd | nd | 25 | 16 | 2.2 | 2.4 | Ketris and Yudovich [46] |
Sample | Mad | Ad | Vdaf | St,d | Sp, d | Ss, d | So, d |
---|---|---|---|---|---|---|---|
Ronyang | 2.6 | 19 | 8.9 | 5.44 | 4.19 | 0.19 | 1.06 |
Ganhe | 0.66 | 23.79 | 12.11 | 12.085 | 1.98 | 0.015 | 10.09 |
Nos. | Spot 1 | Spot 2 | Spot 3 | Spot 4 | Spot 5 | Spot 6 |
---|---|---|---|---|---|---|
Na2O | 0.19 | 0.46 | 0.38 | 0.29 | 0.29 | 0.35 |
MgO | 0.12 | 0.29 | 0.35 | 0.42 | 0.44 | 0.24 |
Al2O3 | 3.95 | 15.58 | 9.81 | 11.22 | 12.34 | 23.8 |
SiO2 | 12.73 | 55.63 | 35.72 | 35.79 | 42.57 | 63.9 |
P2O5 | - | - | - | 3.09 | 1.59 | - |
SO3 | 1.19 | 1.04 | 5.65 | 20.62 | 15.34 | 6.27 |
Cl | - | 0.14 | 0.62 | 0.1 | 0.11 | - |
K2O | 0.76 | 3.43 | 2.12 | 2.95 | 3.48 | 1.42 |
CaO | 0.31 | 0.54 | 1.28 | 1.57 | 2.08 | 0.67 |
TiO2 | 72.37 | 3.70 | 7.67 | 0.19 | - | - |
MnO | - | - | - | - | 0.3 | - |
V2O5 | - | - | - | - | 0.44 | 1.19 |
FeO | 4.36 | 16.12 | 30.04 | 22.29 | 19.58 | 2.19 |
I | 0.45 | - | 0.55 | 1.07 | 0.94 | - |
BaO | - | - | - | 0.16 | 0.08 | - |
La2O3 | - | - | - | - | 0.41 | - |
Nb2O5 | 0.82 | - | - | - | - | - |
UO2 | 2.76 | 3.07 | 5.79 | 0.24 | - | - |
Total | 100 | 100 | 100 | 100 | 99.99 | 100 |
Method No. | Be | V | Cr | Mn | Co | Ni | Cu | Zn | Rb | Sr | Mo | Cs | Ba | U |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 6.62 | 10.91 | 3.29 | 11.37 | 14.94 | 21.38 | 10.77 | 38.43 | 1.03 | 35.79 | 36.95 | 4.04 | 9.74 | 9.39 |
2 | 11.82 | 12.67 | 4.32 | 12.02 | 15.29 | 25.09 | 5.56 | 39.32 | 1.93 | 40.15 | 59.05 | 15.17 | 15.62 | 12.35 |
3 | 10.09 | 14.61 | 7.07 | 18.78 | 16.05 | 32.65 | 44.19 | 57.38 | 3.29 | 48.78 | 58.56 | 13.31 | 23.50 | 12.96 |
4 | 13.62 | 16.35 | 12.97 | 21.22 | 18.34 | 39.13 | 37.30 | 74.72 | 3.77 | 57.01 | 73.76 | 25.31 | 25.25 | 15.10 |
Sample No. | Flotation Products | Yield | Ad | Be | V | Cr | Co | Ni | Cu | Zn * | Mo | Sb | Cs | Tl | Pb | Bi | Th | U |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
GH1 | Cleaned coal | 49.63 | 15.98 | 1.04 | 586 | 453 | 3.03 | 49.7 | 40.6 | 88.3 | 142 | 1.18 | 3.62 | 6.76 | 14.8 | 0.35 | 4.99 | 164 |
Tailings | 50.37 | 26.32 | 1.22 | 620 | 314 | 7.20 | 75.2 | 62.0 | 427.7 | 136 | 1.63 | 4.91 | 9.20 | 19.8 | 0.60 | 5.96 | 178 | |
feed coal | 100 | 24.20 | 1.11 | 603 | 344 | 5.67 | 121.5 | 40.9 | 24.6 | 138 | 1.07 | 3.87 | 7.50 | 15.7 | 0.37 | 4.90 | 173 | |
GH2 | Cleaned coal | 51.04 | 15.45 | 1.72 | 561 | 215 | 8.58 | 34.1 | 18.8 | 72.1 | 159 | 0.38 | 1.11 | 1.52 | 8.8 | 0.27 | 4.42 | 234 |
Tailings | 48.96 | 27.71 | 2.28 | 533 | 194 | 5.37 | 43.6 | 38.1 | 122.4 | 153 | 0.81 | 2.71 | 3.17 | 27.6 | 1.80 | 5.15 | 218 | |
Feed coal | 100 | 23.37 | 1.97 | 532 | 202 | 6.33 | 70.5 | 22.3 | 59.2 | 153 | 0.45 | 2.01 | 2.34 | 9.4 | 0.31 | 5.85 | 230 | |
RY1 | Cleaned coal | 65.14 | 9.19 | 0.50 | 67.4 | 16.8 | 0.74 | 3.4 | 11.4 | 41.3 | 11.6 | 0.20 | 0.57 | 0.32 | 11.1 | 0.23 | 2.40 | 16.0 |
Tailings | 34.86 | 35.59 | 0.55 | 79.9 | 15.9 | 0.92 | 3.6 | 18.0 | 64.4 | 14.1 | 0.55 | 0.92 | 0.55 | 46.6 | 0.81 | 3.25 | 14.9 | |
Feed coal | 100 | 19.00 | 0.50 | 69.0 | 16.1 | 3.32 | 20.1 | 22.5 | 58.0 | 12.0 | 0.09 | 0.86 | 0.56 | 11.7 | 0.26 | 3.07 | 19.2 | |
RY2 | Cleaned coal | 31.22 | 3.96 | 0.62 | 230 | 42.1 | 1.41 | 8.2 | 12.1 | 5.9 | 21.7 | 0.09 | 0.34 | 0.14 | 6.5 | 0.13 | 2.68 | 41.4 |
Tailings | 68.78 | 10.84 | 0.79 | 163 | 80.8 | 3.63 | 26.0 | 68.3 | 25.6 | 44.5 | 0.17 | 0.94 | 0.34 | 35.6 | 1.31 | 2.67 | 36.4 | |
Feed coal | 100 | 9.12 | 0.69 | 168 | 73.1 | 3.60 | 24.1 | 63.3 | 10.3 | 38.2 | 0.13 | 0.90 | 0.34 | 30.5 | 1.12 | 2.51 | 37.0 |
Sample No. | Ad | Be | V | Cr | Co | Ni | Cu | Zn |
GH1 | 33.97 | 6.84 | 2.93 | −31.68 | 46.54 | 59.08 | 0.70 | - |
GH2 | 33.89 | 12.58 | −5.36 | −6.28 | −35.56 | 51.54 | 15.68 | −21.79 |
RY1 | 51.63 | 1.24 | 2.28 | −4.30 | 77.56 | 83.01 | 49.24 | 28.79 |
RY2 | 56.62 | 10.17 | −36.68 | 42.43 | 60.77 | 65.90 | 80.93 | 42.72 |
Sample No. | Mo | Sb | Cs | Tl | Pb | Bi | Th | U |
GH1 | −3.17 | −10.20 | 6.62 | 9.86 | 5.69 | 3.36 | −1.84 | 5.10 |
GH2 | −4.13 | 15.53 | 44.93 | 34.90 | 6.48 | 12.08 | 24.44 | −2.02 |
RY1 | 2.96 | −120.67 | 33.20 | 42.04 | 5.55 | 10.52 | 21.82 | 16.31 |
RY2 | 43.16 | 35.15 | 62.15 | 58.44 | 78.72 | 88.62 | −6.77 | −11.88 |
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Duan, P.; Wang, W.; Sang, S.; Tang, Y.; Ma, M.; Zhang, W.; Liang, B. Geochemistry of Toxic Elements and Their Removal via the Preparation of High-Uranium Coal in Southwestern China. Minerals 2018, 8, 83. https://doi.org/10.3390/min8030083
Duan P, Wang W, Sang S, Tang Y, Ma M, Zhang W, Liang B. Geochemistry of Toxic Elements and Their Removal via the Preparation of High-Uranium Coal in Southwestern China. Minerals. 2018; 8(3):83. https://doi.org/10.3390/min8030083
Chicago/Turabian StyleDuan, Piaopiao, Wenfeng Wang, Shuxun Sang, Yuegang Tang, Mengya Ma, Wei Zhang, and Bin Liang. 2018. "Geochemistry of Toxic Elements and Their Removal via the Preparation of High-Uranium Coal in Southwestern China" Minerals 8, no. 3: 83. https://doi.org/10.3390/min8030083