Mineralogy, distribution, occurrence and removability of trace elements during the coal preparation of No. 6 coal from Heidaigou mine

Optical microscopy and scanning electron microscopy in conjunction with energy dispersed X-ray spectrometry (SEM–EDX) were used to study the minerals and the concentrations of 33 trace elements in No. 6 coal from Heidaigou mine. The distributions, organic affinity and removability of 18 trace elements were studied by float-sink experiments. A determination of the maceral groups was also undertaken. A high mineral content, dominated by kaolinite, was found in No. 6 coal from Heidaigou mine. The bauxite content was relatively high and it was mainly present as individual particles in fusinite lumens or was intimately intergrown with carbonate minerals. The pyrite and quartz contents were low. Some marcasite with a parallel twin structure was observed by cross-polar reflected light. A small amount of bean-like goyazite was present in the calcite. The weighted trace element content in Heidaigou formations is relatively low, which is beneficial for coal processing and utilization. The concentrations of Ga, Hg, Pb, Se, Th, Ta are relatively high compared with the average values of Chinese coals. As, Hg, Mo, Ge, Ga, Ta, Ti, W, Mn are mainly present in minerals while B, Be, Th, P, Sc, Sr, V, Y, Yb are mainly found in organic matter. As, Ge, Hg, Mo are mainly present in sulfides and Be, Th, P, Sc, Sr, Y, Yb are mainly present in inertinite. B and V are mainly present in vitrinite. The high organic affinity and the low theoretical removability of most trace elements cause difficulties in removing them during coal preparation.