Weir building: A potential cost-effective method for reducing mercury leaching from abandoned mining tailings

Abstract

To mitigate mercury (Hg) pollution and reduce Hg transportation downstream, a weir was designed across a river system impacted by leachate from the slagheap of the Yanwuping Hg mine in Wanshan Hg mining area. A whole year monitoring of Hg species was conducted, and the efficiency of Hg reduction by the weir application was evaluated. The Hg concentrations in river water were significantly higher during the wet season than during the dry season. Waterflow was confirmed to be the main driving factor for Hg mobilization and transportation, and an episode study revealed that most Hg was released during storms. Increased monitoring and preventive maintenance work should be performed on barriers in advance of storms. A large fraction of total Hg (THg) and methylmercury (MeHg) is associated to particles. During the study period, approximately 412 g THg and 4.04 g total MeHg (TMeHg) were released from the YMM slagheap, of which 167 g THg and 1.15 g TMeHg were retained by the weir. Annually, 40.4% THg and 38.4% TMeHg was retained by the weir. Weir construction is considered as a potential cost-effective measure to mitigate Hg in river water and should be promoted and extended in the future after optimization.