Reduction and removal of As(Ⅴ) in aqueous solution by biochar derived from nano zero-valent-iron (nZVI) and sewage sludge.

Biochar prepared by co-pyrolysis of nano-zero-valent iron and sewage sludge (nZVISB) was used to remove As(Ⅴ) from aqueous solution. When the initial pH was 2, the initial As(Ⅴ) concentration was 20 mg L, the dose of nZVISB was 10 g L, the contact time was 24 h, and the adsorption temperature was 298K, the removal efficiency of As(Ⅴ) was greater than 99%. The isothermal removal of As(Ⅴ) followed the Freundlich model better, and the maximum adsorption capacity of As(Ⅴ) was 60.61 mg g. The removal process of As(Ⅴ) could be better described by pseudo-second-order kinetic model, and the rate-controlling step should be liquid film diffusion and chemical reaction. Thermodynamic analysis indicated that the removal of As(Ⅴ) was a spontaneous and endothermic process dominated by chemical adsorption. The characterizations of nZVISB before/after adsorption and the solution after adsorption suggested that the iron-containing substances (Fe, Fe, FeOOH) and organics in the nZVISB had a great effect on the removal of As(Ⅴ), and the As was mainly immobilized on nZVISB by speciation of As-O-Fe.