An XAS study of the binding of copper(II), zinc(II), chromium(III) and chromium(VI) to hops biomass

Abstract Due to the increasing concentrations of heavy metals in potable water and industrial wastewater governmental agencies have created stricter regulations for the treatment of metal contaminated waste. However, current technologies are both expensive and time consuming to use for water and waste treatment. As an alternative to the current technologies, phytofiltration has been proposed, but to make phytofiltration effective the process must be further studied to better understand the metal–biomass chemical interactions. This current study on the use of hops biomass to remove heavy metal ions from aqueous solutions uses X-ray absorption spectroscopy (XAS) to investigate the binding mechanism of heavy metals to hops biomass. The XAS studies showed that copper(II), zinc(II) and chromium(III) remained in the same oxidation state as when they were reacted with the hops biomass. However, the reaction of chromium(VI) with the hops biomass resulted in the reduction of chromium(VI) to chromium(III). Analysis of the XAS spectra showed that copper(II) bound to the hops biomass with a molecular geometry of copper(II) acetate; zinc(II) bound to the hops biomass with a molecular geometry of zinc(II) gluconate; and chromium(VI) bound to the biomass with the geometry of chromium(III) acetate. In addition, the XAS studies showed that the nearest neighboring atom of all the bound metal ions was an oxygen atom.