Sorption of arsenate and dichromate on polymerin, Fe(OH)x–polymerin complex and ferrihydrite

Abstract Dihydrogenarsenate [H 2 AsO 4 − , As(V)] or dichromate [Cr 2 O 7 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 ( x m ) of arsenate sorbed on Fe(OH) x –polymerin complex was similar to that on ferrihydrite (880.26 and 743.02 mmol kg −1 , respectively), and was much greater than that sorbed on polymerin (384.25 mmol kg −1 ). The sorption of dichromate was to a comparable extent on Fe(OH) x –polymerin complex and ferrihydrite (205.90 and 254.88 mmol kg −1 , respectively). Cr(III), a less toxic chromium form, mainly, and Cr(V) were indeed the effective forms sorbed on polymerin (200 mmol kg −1 ), as a consequence of the redox reaction of the strongly toxic Cr(VI) with the CH 2 OH 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.