New data on arsenic sorption properties of Zn-Al sulphate layered double hydroxides: Influence of competition with other anions

The adequacy of synthetic Zn-Al-sulphate LDHs to remove arsenic from aqueous systems was tested through sorption experiments, using a series of aqueous solutions with dissolved HAsO42 − together with other anions (Cl−, SO42 −, MoO42 −, HCO3−, CO32 −) to assess their competition influence on the As removing process. The competitors were added into the solution both simultaneously and afterwards with respect to HAsO42 − in order to verify the effectiveness and the possible reversibility of the As sorption process. The results showed that only carbonates species, in particular in the fully deprotonated form CO32 −, affect significantly the otherwise high efficacy of the sorption process. In fact, up to ~ 90% of HAsO42 − can be removed from the solution, decreasing to ~ 60% in the presence of CO32 −, whilst up to ~ 30% of HAsO42 − can be desorbed when CO32 − is added afterwards into the solution. Considering the very restricted range of pH where HAsO42 − and CO32 − are simultaneously the predominant species in the solution (~ 10 < pH < ~ 11.5), Zn-Al-sulphate LDHs could be successfully used for the treatment of As contaminated waters with pH ranging from circum-neutral to moderately alkaline.