Arsenic Releasing from Poly-Metallic Sulfide Deposits at Hetao Plain, China

Abstract

Arsenic (As)-bearing ores of poly-metallic sulfide deposits provide water-bearing medium containing As for high-As aquifer and release As in leaching process. Two ores samples M1 and M4 were collected from two big-scale poly-metallic sulfide deposits, Dongshengmiao and Tanyaokou, with As contents of 78 and 69 μg/g, respectively. Pyrite as the major mineral in ores accounts for over 70 and 20% of all minerals in M1 and M4, respectively. The carbonate contents including dolomite (CaMg(CO₃)₂), smithsonite (ZnCO₃), and siderite (FeCO₃) in M4 are higher than in M1. As the major As speciation in M1 and M4, residual As accounts for 97.55 and 95.17% of the total detected As, respectively. Results of leaching experiment indicate that under the reducing condition in column filled with M1, As (V) can be produced by pyrite dissolution and oxidation and then reduced as As(III) which is difficult to be adsorbed onto the mineral surface but easy to migrate in aquatic solution. HFO prevents ore surface from contacting with the oxygen in leaching solution, and adsorbs As onto its surface, leading to the relatively lower concentrations of Fe and As in leachate of M4. The leaching rates of As would be are 0.46 for M1 and 0.13% for M4. According to geological survey information, the demonstrated reserves of pyrite at Tanyaokou and Dongshengmiao reach up to 86 288 000 000 and 216 915 000 000 kg, respectively. Assuming that the releasing capability of the ores in natural environment is nearly equal to that in our experiments, 6 730 000 and 15 000 000 kg of As from Tanyaokou and Dongshengmiao mine is expected to be in the risk of release. This study will provide a better understanding of the genesis of high-As groundwater in the Hetao Plain.