Physics and chemical properties of the volcanic ash material adsorbed with the hexavalent chromium by x-ray absorption spectroscopy

Abstract

Abstract X-ray absorption spectroscopy (XAS) was used to characterize the volcanic ash (VA) materials as a low-cost and natural environmental adsorbent for the sorption of Cr(VI). The batch adsorption method was employed to synthesize the sample of chromium(VI) sorbed by VA. The results showed that the Cr-VA material is in the chromium oxidation state(III) and can be described as a composition of Cr2O3 (47.9%), FeCr2O7 (45.2%), and Na2Cr2O7 (6.9%). The promotion of the 1s Cr core electron implies the electronic transitions 1𝑠→3𝑑(𝑡2𝑔) and 1𝑠→3𝑑(𝑒𝑔). The first and second shells in the Cr-VA material were coordinated to the oxygen and chromium atoms in a distorted geometrical arrangement. The adsorption mechanism was associated with the chemical reduction of Cr(VI) to Cr(III) via an ion-exchange process. The XAS technique significantly contributes to the characterization of environmental VA, which can be proposed as an economical and alternative adsorbent for the sorption of Cr from contaminated wastewater.