Acid solubility and affinities of trace elements in the high-Ge coals from Wulantuga (Inner Mongolia) and Lincang (Yunnan Province), China

The most likely explanation for the observations made in this study is that the abnormally enriched trace elements (especially Ge) in the Wulantuga and Lincang high-Ge coals are weakly bonded to organic matter, possibly occurring in the form of chelates, thus allowing them to be removed by HCl-HF. Alternatively, these elements may be associated with fine-grained minerals (or poorly crystalline mineraloids or non-mineral inorganics) that are closely associated with organic matter but are difficult to detect.