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

Dihydrogenarsenate [H2AsO4−, As(V)] or dichromate [Cr2O72−, 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 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 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.