Application of siderite tailings in water-supply well for As removal: Experiments and field tests

Low-grade siderite tailings are difficult to be utilized. For further exploration on the application of siderite tailings for arsenic removal, a series of theoretic and practical studies were carried out. According to the experiment results and technical specifications, a water supply well using composite filtration materials of siderite and river sands was designed and a pilot run was conducted in Datong basin, China, where the groundwater notably contains high concentrations of arsenic. Particle size of 1-2 mm was selected as the optimum scheme considering the adsorption kinetic parameters and technical specifications. Langmuir isotherm yielded a better fit to experimental data with regard to the siderite with a grain size range of 1-2 mm (R2 = 0.983), which indicated that the process generally tends to be a monolayer adsorption reaction with a saturation adsorption capacity of 0.5233 mg g−1. Volume proportion coefficients α = 0.5 was selected as the optimal scheme in view of economic factors. The supply water well using composite filtration materials as a pilot run performed well, with average effluent concentration of 247.57 μg L−1, and arsenic removal rates of 52%-65%. The mechanism for arsenic removal is likely due to the hydroxyl group of Fe(OH)x/FeOOH which contributed from the hydrolysis of FeCO3, and subsequently substituted by aqueous arsenic. Moreover, the groundwater chemical environment contains high sulfide concentrations, which enhances the sorption of arsenic.