New polymeric/inorganic hybrid sorbents based on red mud and nanosized magnetite for large scale applications in As(V) removal

Red mud (RM), a waste product generated in the industrial production of aluminium, was recovered for a second use as As(V) adsorbent. RM adsorption properties were compared to those obtained with a nanostructured in-lab synthesized iron oxide, magnetite. Operational problems associated with powdery consistency of raw materials were solved with the synthesis of new polymeric/inorganic hybrid sorbents by dispersing red mud and magnetite in chitosan. The behaviour of raw red mud and magnetite towards As(V) adsorption has been critically compared with that observed for the hybrid materials. pH dependence studies demonstrated that near neutral environments favour As(V) elimination. The sorption kinetics for the iron oxides showed that equilibrium was reached in less than 3 h for raw materials and up to 15 h for immobilized red mud and magnetite. The amount of arsenic sorbed on the four different sorbents as a function of the equilibrium arsenic concentration has been fitted to a Freundlich isotherm and a multilayer adsorption mechanism is proposed. Finally, continuous flow experiments were developed using chitosan immobilized red mud. Results allowed selecting batch conformation as the most effective for As(V) removal.Authors wish to thank Ministerio de Economía y Competitividad for the financial support through the research Project CTM2012-37272, cofounded with FEDER programme