Reduction mechanism of hexavalent chromium by functional groups of undissolved humic acid and humin fractions of typical black soil from Northeast China

Abstract

Soil organic matters (SOM) have a great retention effect on Cr(VI) migration in subsurface environment, which act as the main electron donors for Cr(VI) reduction; however, Cr(VI) reduction mechanism by different SOM fractions is still unclear, such as undissolved humic acid (HA) and humin (HM). In this study, HA and HM fractions extracted from typical black soil from Northeast China were used to investigate the reaction mechanism between humus functional groups and Cr(VI). According to the results, phenol and hydroxyl were determined as the main electron donors for Cr(VI) reduction by HA and HM instead of carboxyl and carbonyl, which were more likely involved in Cr complexation. Furthermore, Cr(VI) reduction was more dependent on aromatic carbon, rather than aliphatic carbon, and functional groups on the particle surfaces of HA and HM were much more active for Cr(VI) reduction than their interior part. Additionally, HM was found to have a relatively low Cr(VI) reduction capability compared with HA resulting from its high content of cellulose structures that are quite resistant to Cr(VI) oxidation. These results suggest that in the soil environment, undissolved HA tends to play a much more important role than HM in Cr(VI) reduction and retention in the condition that their mass contents are comparable.

New insight into mechanism of Cr(VI) migration and transformation in typical soils of chromite ore processing residue (COPR) contaminated sites

“…On the one hand, organic matter can provide electrons for Cr(VI) reduction (Huang et al 2012). On the other hand, organic matter can also offer additional hydrogen ions to provide favorable conditions for the hydrogen consuming reduction of Cr(VI) (Zhang et al 2018b). In order to give full play to the performance of organic matter on the adsorption and reduction of Cr(VI) in soils, the reduction mechanism of Cr(VI) by soil organic matter remains to be further revealed, such as the effect of the combination of soil organic matter and soil inorganic minerals for Cr(VI) adsorption and reduction, and the influence of soil microorganisms on the reduction of Cr(VI) by soil organic matter.…”

“…Dissolved organic matter can also form water-soluble complexes with Cr(VI) and Cr(III) to enhance their mobility (Weng et al 2002). The undissolved organic matter can provide active sites for the adsorption of Cr(VI) and electrons for the reduction of Cr(VI), which plays a major role in the retention of Cr(VI) migration (Barnie et al 2018;Zhang et al 2019b;Zhang et al 2018b). In addition, pH also has an important influence on the migration of Cr(VI).…”

New Insight into Mechanism of Cr(VI) Migration and Transformation in Typical Soils of Chromite ore Processing Residue (COPR) Contaminated Sites

“…This study focused on the retardation process of the dynamic migration of Cr(VI) (Zhang et al 2018b). In order to give full play to the performance of organic matter on the adsorption and reduction of Cr(VI) in soils, the reduction mechanism of Cr(VI) by soil organic matter remains to be further revealed, such as the effect of the combination of soil organic matter and soil inorganic minerals for Cr(VI) adsorption and reduction, and the influence of soil microorganisms on the reduction of…”

Mechanism and modeling of hexavalent chromium interaction with a typical black soil: the importance of the relationship between adsorption and reduction

“…The location, landform, climate and vegetation can be found in our previous published paper. 29 The surface soil within the depth of 30 cm was sampled aer the topsoil containing substantial plant roots had been removed. The soil sample was air-dried and ground, and then was passed through a 100-mesh sieve.…”