Removal of selenate by Fe and NiFe nanosized particles

Irrigation drainage and industrial wastewaters often contain elevated levels of toxic anions such as selenate, arsenate, and chromate. Immobilizing the contaminants via reaction with zero-valent iron has been proven to be an effective remediation method. Ultrafine metallic and bimetallic particles were prepared by borohydride reduction of aqueous salt solutions and characterized. Nanosized zero-valent NiFe and iron particles rapidly reduced and immobilized selenate from aqueous solutions. Nearly 100% selenate removal was obtained in 5 h. The data show that, at identical solids concentrations, the use of NiFe particles accomplished 42 and 56% greater removals, respectively, than the use of Fe and Ni particles individually. At low selenate concentrations, the selenium removal rate followed the first-order rate kinetics that shifted to zeroth-order at higher concentrations. The maximum selenate removal (87% in 30 min at a solids concentration of 0.5 g/L) was obtained by bimetallic particles containing 70 at. % iron. High removal capacities were observed at pH lower than 8. A mechanism for the selenate removal has been developed.