Distribution characteristics of trace elements in different density fractions of high-germanium coal from Wulantuga, Inner Mongolia, China

The exploitation and utilization of critical metals in coal measures is of great significance to alleviate the shortage of strategic mineral resources in China. In addition to the critical metal germanium (Ge), the low-rank coal from Wulantuga Coal Mine of Shengli Coalfield in Inner Mongolia, China is enriched with the toxic elements Be, F, As, Hg, Sb and W. Considering the extraction and utilization of key metals and environmental protection, the coal in the study area must be washed. As shown in the previous study, flotation is relatively good for the removal of As, Sb and W inWulantuga coal, but relatively poor for the removal of F and Hg. Hence, the distribution characteristics of the critical metal Ge and the toxic elements, such as Be, F, As and Hg, in different density fractions of coal were studied with the experiment and test methods, including floating-sinking experiment (the gravity separation), XRD, XRF, SEM-EDS and EMPA. The results show the following: (1) The minerals in Wulantuga coal mainly include gypsum, quartz, pyrite and kaolinite, the mineral content increases with the increasing of coal density fraction, and the Co, As, Sb and Hg occurs in pyrite according to the results of electron probe analysis. (2) After gravity separation, Ge is enriched in the low-density cleaned coal, indicating that Ge mainly exists in organic state, and Be, F, and As may be associated with the organic matter or occur in the fine grained minerals embedded in organic matter. Hg and most lithophile elements have higher concentrations in coals at higher density fractions, which indicates they occur in minerals. (3) Gravity separation is good for the removal of Hg, and flotation has a better effect for the removal of Be, F, As and some sulfurophilic or siderophile elements than gravity separation. Therefore, the gravity separation and flotation combined process is recommended for the removal of toxic elements in Wulantuga low-rank coal.