Stabilization of iron arsenate solids by encapsulation with aluminum hydroxyl gels

Abstract

AbstractBACKGROUNDFerric arsenate solids in the form of scorodite (FeAsO4·2H2O) particles are suitable carriers for immobilization of arsenic‐rich wastes. The stability of scorodite is, however, highly pH dependent (typically at 4≤ pH ≤7) and satisfactory only under oxic disposal conditions. In this work a new stabilization technology based on the concept of encapsulation with aluminum hydroxyl gels is investigated to enhance the stability of arsenical solids over a wider range of disposal conditions.RESULTSThe encapsulation system investigated involves blending and short‐term ageing of synthetic scorodite particles with amorphous aluminum hydroxyl gels derived from partial hydrolysis of aluminum chloride or aluminum sulfate salts. Of the two gel types, the Al(SO4)1.5‐derived gel proved to be the most effective, even at the very low Al(III)/As(V) molar ratio of 0.1, apparently due to in situ development of protective aluminum hydroxide matrix and not as a simple adsorption sink for soluble arsenate species.CONCLUSIONArsenic release from the scorodite–aluminum hydroxyl gel composites was found to be drastically reduced with respect to gel‐free scorodite, making this system a very interesting candidate for further development as an effective hazardous material encapsulating material. © 2014 Society of Chemical Industry