Molecular structure-reactivity correlations of humic acid and humin fractions from a typical black soil for hexavalent chromium reduction

Jia Zhang; Huilin Yin; Hui Wang; Lin Xu; Barnie Samuel; Jingjie Chang; Fei Liu; Honghan Chen

doi:10.1016/j.scitotenv.2018.10.165

Molecular structure-reactivity correlations of humic acid and humin fractions from a typical black soil for hexavalent chromium reduction

Sci Total Environ. 2019 Feb 15;651(Pt 2):2975-2984. doi: 10.1016/j.scitotenv.2018.10.165. Epub 2018 Oct 12.

Authors

Jia Zhang¹, Huilin Yin¹, Hui Wang¹, Lin Xu¹, Barnie Samuel¹, Jingjie Chang¹, Fei Liu², Honghan Chen¹

Affiliations

¹ Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China.
² Beijing Key Laboratory of Water Resources & Environmental Engineering, China University of Geosciences, Beijing 100083, China. Electronic address: feiliu@cugb.edu.cn.

PMID: 30463148
DOI: 10.1016/j.scitotenv.2018.10.165

Abstract

Different soil humus fractions are structurally distinct from each other molecularly, however, the relationship between their microscopic molecular structures and the macroscopic reduction of Cr(VI) is still unknown, especially for the humin fraction. In this study, different humus fractions (HA, humic acid; HMi, humin linked to iron oxides; HMc, humin linked to clay; and HMr, humin residue) were sequentially extracted from a typical black soil and well characterized. It was found that HA, HMi and HMc were the same type of humus with similar molecular structures, while HMr was structurally different from the other fractions with a high cellulose content. The removal rate of Cr(VI) in solution decreased with progressive humus fractionation, namely, HA > HMi > HMc > HMr. Based on the two-dimensional correlation spectroscopic analysis (2DCOS) of the FTIR data, the changing functional groups of all humus fractions during reacting with Cr(VI) followed a similar order: carboxyl > phenol > hydroxyl > methyl > methylene. According to the correlation analysis, Cr(VI) reduction rates by different humus fractions were mainly determined by the content of phenol (R² = 0.99) instead of carboxyl (R² = 0.28). Except for HMr, the Cr(VI) reduction rates of different humus fractions were also positively correlated with surface and bulk polarity (R² = 0.98 and 0.99) but not with aromaticity or aliphaticity (R² = 0.21).

Keywords: Correlation analysis; Hexavalent chromium; Humic acid; Humin; Two-dimensional correlation spectroscopy.