Abstract
Chromium occurs in nature mainly in its trivalent or hexavalent form. Hexavalent chromium Cr(VI) is particularly toxic to humans, animals, and plants. The extensive pollution of groundwaters with Cr(VI) necessitates the complete understanding of natural chromium oxidation and reduction mechanisms, both for assessing the risk of hexavalent chromium formation and for the development of techniques for the reduction and removal of Cr(VI) from contaminated water bodies. In this work, the possibility of hexavalent chromium reduction by discarded or low-cost materials, which contain reducing compounds, is investigated regarding the creation of a compact, pump-and-treat filter for Cr(VI) removal from groundwater.
Highlights
Chromium (Cr) occurs in nature mainly in its trivalent (Cr(III)) or hexavalent (Cr(VI)) form
Five different metallic iron materials were used for the experimental setups, iron wool, iron wires, iron screens, and scrap iron fillings and chips, as well as granulated activated carbon (Table S1, Supplementary Material)
A plethora of experimental setups was conducted in order to confirm the mechanisms of geogenic chromium oxidation and reduction by manganese oxide and divalent iron, respectively
Summary
Chromium (Cr) occurs in nature mainly in its trivalent (Cr(III)) or hexavalent (Cr(VI)) form. The form of Cr(III) is predominant and is favored by reducing and acidic conditions. Cr(VI) can be found in groundwater either as the result of the natural oxidation of the Cr(III), mainly contained in ultramafic rocks and serpentinites of ophiolitic complexes, or as the result of a wide range of anthropogenic activities [1]. Mn oxides are the only naturally occurring minerals capable of oxidizing Cr(III) to Cr(VI), while V2+, Fe2+, S2−, HNO2, HSO3− and some organic species can reduce Cr(VI) [3,4,5,6,7].
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