Removal of As(III) from acidic waters using schwertmannite: Surface speciation and effect of synthesis pathway

The removal of arsenic(III) from aqueous solution by three different schwertmannite specimens that were synthesized by i) biogenic precipitation (SHM_MS), ii) slow abiotic dialysis (SHM_DS) and iii) fast abiotic oxidation of Fe(II) (SHM_FS) was studied through sorption experiments at pH 3.0. Marked differences in dissolution rates, Fe:S ratios (4.7-6.4) and structural properties were found among the specimens. The sorption mechanisms are governed by multilayer processes as indicated by highly non-linear Freundlich adsorption isotherms. The affinities increased in the sequence SHM_FS (K-F = 0.02L(0.57)/(mol(-0.43)g))