LAUSR

Abstract Adsorptive removal of arsenite from wastewater often involves pre-oxidation to the less toxic arsenate followed by adsorption. Materials capable of simultaneous oxidation and adsorption could potentially improve the treatment of arsenic contaminated water. A novel magnetic composite consisting of Fenton’s treated pine cone, an agricultural waste and magnetite nanoparticles was prepared and applied to achieve simultaneous arsenite oxidation and adsorptive removal. A mechanistic investigation of the adsorption process was conducted to provide insights into the interaction of arsenite and the composite surface. X-ray diffraction peaks of the nanoparticles matched those of synthetic magnetite and X-ray photoelectron spectroscopy (XPS) indicated that Fe2+/Fe3+ ratio was in accordance with that of magnetite at 0.5. Arsenite removal efficiency by the as-synthesised composite was approximately 90% with a maximum adsorption capacity of 17 mg g−1. Kinetic studies revealed that arsenic adsorption was a multi-step process with surface adsorption and intra-particle diffusion contributing to the rate limiting step. Ion exchange was evident from the release of pre-loaded nitrate ions during arsenite adsorption. Spectroscopic evidence confirmed ion exchange through the observance of hydroxyl peak shift, reduction in intensity of carboxylate peaks and As O Fe bond formation during adsorption. Further, XPS results confirmed that there was simultaneous reduction of Fe3+ to Fe2+, oxidation of arsenite to arsenate and adsorption of both arsenite and arsenate on the composite surface through the formation of inner sphere complexes.