Leaching behavior and organic affinity of potentially toxic elements V, Cr, Mo, and U in flotation-cleaned coal from the Ganhe Mine, China

Abstract

Abstract After flotation cleaning of high-U coal from the Ganhe Mine in China, it was found that levels of V (561\u202fμg/g), Cr (215\u202fμg/g), Mo (159\u202fμg/g), and U (234\u202fμg/g) were still significantly enriched in the clean fraction. However, it was not initially clear whether these elements were associated with organic matter or occurred in fine-grained minerals. In this study, coal samples were analyzed by acid leaching and transmission electron microscopy coupled with energy dispersive spectroscopy (TEM\u202f+\u202fEDS). Our results showed the following: (1) V and Mo were weakly bonded to organic matter, whereas Cr and U were predominantly associated with organic matter, thereby indicating that Cr and U had a strong organic affinity; (2) the results of high-resolution TEM showed that U occurred in poorly crystalline nanoscale U Ti minerals in flotation-cleaned coals where the mineral was associated with organic matter; and (3) organic-bonded V and Mo were negatively correlated with organic S, but organic-bonded Cr and U were positively related to organic S. Through acid leaching, the contents of V, Cr, Mo, and U in the residue were still much higher than those in world hard coal. Thus, the use of flotation-cleaned Ganhe coals is not recommended to avoid environmental pollution and adverse effects.