Abstract
The fate of the arsenic (As) under neutral hydrogeochemical conditions in the mining ecosystem has attracted increasing concern, as the ecological restoration of As provides a possibility for safe use of mine water. However, successful cases are still inadequately reported worldwide. Therefore, to investigate the As-behavior in the mine tailings ecosystem, a study of the Wanniangou tailings pond (regional largest V-Ti-Fe mine tailings pond, Sichuan province, China) and the downstream (Rehe River) was conducted. It involves hydro-geochemistry, mineralogy, biogeochemistry, and the Geographically Weighted Regression model (GWR). The results reveal that: (1) the pH range of the mine water is 6.32 to 7.21. The chemical weathering of tailings resulted in an abnormal As concentration in water (e.g., transport pipe wastewater 76.5 μg L−1, the outlet of tailings pond 28.4 μg L−1), and it declines to the national water quality guideline (<10 μg L−1) after 2.59 km from the pond outlet. (2) Although sulfide oxidation boosts As migration in the tailings, As ecological refixation is promoted by tailings particle percolation, river sediment absorption, and aquatic plant uptake. The As refixation behaviors vary spatially, corresponding with the diversity of precipitation and absorption. Besides, Manganese (oxides or/and hydroxides) is conducive to As coprecipitation in the neutral hydrogeochemical environment. (3) The site selection of the V-Ti-Fe mine tailings pond with a downstream longer than 3 km creates a toxic metals self-restoration buffer zone, which could relieve the contamination probability and make the mining wastewater re-utilization feasible.
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