Modes of occurrence and removal of toxic elements from high-uranium coals of Rongyang Mine by stepped release flotation

The Rongyang coals from Guizhou, southwestern China, are significantly enriched with uranium (U) and other toxic elements, such as vanadium (V), chromium (Cr), molybdenum (Mo), cobalt (Co), copper (Cu), and selenium (Se). Therefore, it is necessary to remove these toxic elements from high-U coals before combustion. Previous studies have shown that U cannot be effectively removed by flotation and gravity separation. In this study, the stepped release flotation and acid leaching tests were conducted for coals of the Longtan Formation from the Rongyang Mine. The results from these analyses are as follows: (a) Stepped release analyses revealed that a multistage cleaning process can help to separate toxic elements from cleaned coals; (b) The removal of toxic elements by stepped release and acid leaching is closely related to their mode of occurrence. Vanadium, Cr, Mo, and U were difficult to be removed by stepped release flotation, which due to a significant proportion of them occur in organic matter and fine-grained minerals; (c) Compared to flotation, most elements were better to be removed by stepped release flotation. In comparison with gravity separation, U had a higher removability by stepped release flotation, while the removal effect of thiophilic element by gravity separation was greater than by flotation; (d) After stepped release flotation, toxic elements Sc, V, Cu, Se, Mo, Hg, and U are still enriched in cleaned coals, suggesting that these elements cannot be fully removed through stepped release flotation.