Mercury speciation and mercury isotope fractionation during ore roasting process and their implication to source identification of downstream sediment in the Wanshan mercury mining area, SW China

Abstract

The environment of Guizhou province of SW China is in part significantly impacted by mercury (Hg) mining activities. The exploitation and processing of Hg-bearing ore in the past have led to multiple sources of Hg contamination, including unprocessed ores and Hg waste calcines and liquid elemental Hg, making source control strategies difficult and expensive to implement. In this study, initially extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the Hg species and to estimate the relative proportions of these species present in Hg-bearing wastes from the Wanshan Hg mine (WSMM) of the eastern Guizhou province. The results showed that cinnabar is the dominant Hg species in the unroasted ore samples, while the most prevalent Hg compounds in mine waste calcine is in the following order: meta-cinnabar, cinnabar and mercuric chloride. Our study demonstrated that mass dependent fractionation of Hg isotopes may occur during transformation of cinnabar to by-products (such as meta-cinnabar and mercuric chloride) by the roasting process. Hg stable isotope analysis of unroasted Hg ores and Hg waste calcines showed that Hg waste calcines (0.08±0.20‰, 2ó, n=11) were enriched by ~0.80‰ in δ202Hg values compared to the unroasted Hg ores (−0.74±0.11‰, 2ó, n=14). Finally, using a combined triple mixing model, the source attribution of the downstream sediment in WSMM was estimated. Our study suggested that the Hg isotope could be a useful tool to trace and quantify the source of Hg in the environment.