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

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

Ardau, C. / Frau, F. / Lattanzi, P.

Abstract

Abstract 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 HAsO4 ²⁻ together with other anions (Cl⁻, SO4 ²⁻, MoO4 ²⁻, HCO3 ⁻, CO3 ²⁻) to assess their competition influence on the As removing process. The competitors were added into the solution both simultaneously and afterwards with respect to HAsO4 ²⁻ 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 CO3 ²⁻, affect significantly the otherwise high efficacy of the sorption process. In fact, up to ~90% of HAsO4 ²⁻ can be removed from the solution, decreasing to ~60% in the presence of CO3 ²⁻, whilst up to ~30% of HAsO4 ²⁻ can be desorbed when CO3 ²⁻ is added afterwards into the solution. Considering the very restricted range of pH where HAsO4 ²⁻ and CO3 ²⁻ 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.

Highlights • Zn-Al sulphate LDHs as removers of arsenic from aqueous solution. • Up to 90% of initial dissolved arsenic is removed from solution by these LDHs. • Competition with other anions may influence arsenic uptake by Zn-Al sulphate LDHs. • Anion speciation in solution influences arsenic uptake by Zn-Al sulphate LDHs. • Only at pH>10 the As uptake efficiency is significantly affected by carbonate species.