[A-HW23] Hydrology & Water Environment

[AHW23-P02] Molybdenum Contamination in Rivers near the Erdenet Mining Area, Mongolia: Field Evidence and laboratory confirmation of High Mobility of Mo at pH >8

*Keisuke Fukushi¹, Solongo Tsetsgee^3,2,4, Akihiro Okuyama², Altansukh Ochir³, Ariuntungalag Yunden³, Enkhjin Odgerel³, Taivanbat Batbold³, Enkhuur Munkhsuld^3,6, Yoshio Takahashi⁴, Takashi Munemoto⁵, Masato Honda¹ (1.Institute of Nature & Environmental Technology, Kanazawa University, 2.Graduate School of Natural Science and Technology, Kanazawa University, 3.National University of Mongolia, 4.Department of Earth and Planetary Sciences, The University of Tokyo, 5.Ishikawa Industrial Research Institute, 6.Department of Trans-Disciplinary Science and Engineering, Tokyo Institute of Technology)

Keywords:Molybdenum, Erdenet mine, adsorption

Although recent research points to molybdenum (Mo) as a candidate for anthropogenically induced contamination of natural waters, there has been little research on Mo contamination in river water. 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 from March to November 2018 showed that in the Khangal River, which is downstream of the Erdenet mining area, Mo concentrations exceeded 70 ppm (the World Health Organization health-based guideline) during summer. The sources of the Mo in river water are groundwater used for cooling in 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 distribution coefficients of Mo adsorbed on iron oxides in water at pH >8.