The Erdenet mine in Mongolia is the one of the largest Mo mines in the world. Our systematic temporal and spatial monitoring of Mo concentrations in river waters around the Erdenet mine showed that in the Khangal River, which is downstream of the Erdenet mining area, Mo concentrations exceeded the World Health Organization health-based guideline during summer. The sources of the Mo in river water are groundwater used for the Erdenet power plant and seepage from mine tailing ponds. Mo concentrations had a positive correlation with the pH of the river water. Laboratory adsorption experiments confirmed that the pH dependency of Mo concentrations originates from the adsorption/desorption reactions of iron oxide in the river sediments. Mo concentrations in river water were still higher 10 km downstream of the contamination sources. Our observations provided field evidence of high solubility and mobility of Mo in river water that were caused by the lower adsorption affinity of Mo in water at pH >8.

ACS ES&T water, doi.org/10.1021/acsestwater.1c00046

Mo Contamination in Rivers near the Erdenet Mining Area, Mongolia: Field Evidence of High Mobility of Mo at pH >8

Solongo Tsetsgee, Akihiro Okuyama, Altansukh Ochir, Ariuntungalag Yunden, Enkhjin Odgerel, Taivanbat Batbold, Enkh-Uur Munkhsukd, Yoshio Takahashi, Takashi Munemoto, Masato Honda, and Keisuke Fukushi