Mercury concentration and speciation in mine wastes in Tongren mercury mining area, southwest China and environmental effects

Abstract

Mercury mines cause mercury (Hg) contamination to local environment, because mine wastes are not properly disposed during long-term large scale Hg mining activities. This study investigated Hg concentration and speciation in mine wastes collected from Tongren Hg mining area, and evaluated the impact of Hg mines subjected to different remediation measures on the surrounding environment. Total Hg (THg) concentrations in the mine wastes varied from 4.15 to 825 mg/kg, and Hg0 was the dominant form of Hg in the mine wastes. No obvious deformation was observed in the mineral boundaries by TEM analysis, which indicated that the smelting process was incomplete. Nanometer-scale Hg compounds were observed in the mine wastes using EDS microtopography analysis, which may pose risks for the local environment. The average concentration of total soluble Hg (TSHg) in mine waste leachates was 11.27 μg/L. The THg concentrations in surrounding surface waters varied from 0.038 to 10.6 μg/L, and THg concentrations in 21.1% of samples exceeded level Ⅴ of the national standards (1 μg/L). There was a significant negative correlation between THg concentration and pH in the surface water, indicating that Hg was more mobile under acidic conditions. The total gaseous mercury (TGM) concentration above the mine waste piles varied from 13.5 to 309 ng/m3; these values are significantly lower than those recorded in previous studies. These data demonstrate that restoration and proper treatment are required for the mine waste.