Removal mechanisms of Chromium(VI) from the soil by interaction between organic matter and Iron(III)

Abstract

Soil and water contamination by chromium (Cr) has occurred frequently in industrial areas and its vicinity, due to accidents and poor residue management. Chromium in hexavalent form (Cr(VI)) is highly toxic and carcinogenic, whereas Chromium in trivalent form (Cr(III)) and trace levels of Cr are considered beneficial for humans and animals. This study presents a review of the main mechanisms related to the interaction of Cr with soil components, when associated with an environmental contamination event. The main agents responsible for the immobilization of Cr(VI) are those capable of reducing Cr(VI) to Cr(III), such as soil organic fraction and Fe(II). However, the presence of Fe(III) minerals/compounds may also aid in the reduction of Cr(VI). In this case, Fe(III) can be reduced by organic matter to the divalent form, which, in turn, reduces chromium(VI) to the trivalent form, immobilizing it in the soil. For this to occur, in addition to the presence of organic matter, an acid medium also favors this process – such conditions are typical of tropical soils, such as Oxisol. Therefore, understanding how Cr(VI) reacts with the main components of soil is very important for the remediation of contaminated areas.