SORPTION OF ARSENATE AND DICHROMATE ON POLYMERIN, FE(OH) X-POLYMERIN COMPLEX AND FERRIHYDRITE

Dihydrogenarsenate [H2AsO4 −, As(V)] or dichromate [Cr2O7 2−, Cr(VI)] at pH= 4.0 showed to be sorbed on a Fe(OH)x–polymerin complex and ferrihydrite to a greater extent than on polymerin, the organic polymeric fraction of olive oil mill wastewater (OMW). In particular, the maximum amount (xm) of arsenate sorbed on Fe(OH)x–polymerin complexwas similar to that on ferrihydrite (880.26 and 743.02mmolkg−1, respectively), and was much greater than that sorbed on polymerin (384.25mmolkg−1). The sorption of dichromate was to a comparable extent on Fe(OH)x–polymerin complex and ferrihydrite (205.90 and 254.88mmolkg−1, respectively). Cr(III), a less toxic chromium form, mainly, and Cr(V) were indeed the effective forms sorbed on polymerin (200mmolkg−1), as a consequence of the redox reaction of the strongly toxic Cr(VI) with the CH2OH groups of the polysaccharide moiety of this bio-sorbent, according to the data deriving from XPS and DRIFT analyses. The potential exploitation of the selected sorbents for the removal of As(V) or Cr(VI) from aqueous effluents is briefly discussed.