The distribution and occurrence of mercury in Chinese coals

Abstract Mercury is one of the most concerned hazardous elements in coals. 1018 coal samples of different coal-forming periods, coal-accumulating areas and coal ranks all over the country were collected to study the distributions of mercury in Chinese coals. The modes of occurrence of mercury were studied with float-sink experiments of 10 coals from different basins in China and correlation analyses were conducted between concentrations of mercury and maceral and sulfur contents, as well as the ash yield. The theoretic concentrations and affinities of mercury in vitrinite, inertinite, clay and pyrite were then calculated following the methods proposed by Solari. The weighted average concentration of mercury in Chinese coals is 0.154 µg/g, which is similar to that in the word coals in general. The mercury concentrations vary largely in the coals of different coal-forming period and coal-accumulating areas as geological settings play key roles in determining the geochemistry of mercury. The concentrations of mercury in coals from south and southwest China and those from North China of C3–P1 are relatively higher while those from North China of J1–2 and Northeast of J3–K1 relatively lower. The general distribution trends of mercury are very similar to that of ash yield, sulfur contents in coals. Pyrite is the dominant carrier of mercury in most coals, especially in some high-sulfur coals with abundant epigenetic pyrite formed during diagenesis and metamorphism. Mercury has higher affinity to vitrinite than to inertinite in most coals, which accords with the geological origin of macerals and geochemistry of mercury