Study on Reduction of Chromium Using Humic Substances and Clay Minerals

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  • KANO Naoki
    Department of Chemistry and Chemical Engineering, Faculty of Engineering, Niigata University
  • OTSUKI Yusuke
    Graduate School of Science and Technology, Niigata University
  • LU He
    Graduate School of Science and Technology, Niigata University
  • IMAIZUMI Hiroshi
    Department of Chemistry and Chemical Engineering, Faculty of Engineering, Niigata University

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Abstract

In this study, laboratory model experiments on the interactions of Cr with natural ecological restoration substances were carried out to estimate optimum conditions for the reduction of Cr in soils and/or waters. For natural ecological restoration substances, humic substances (humic acid and fulvic acid) and clay minerals (bentonite and imogolite) were used. The experiments, performed at pH 4-8, yielded the following results: (1) Cr(VI) was reduced to Cr(III) by the humic substances; moreover, the reduction ability of the humic substances decreased with increasing pH. (2) The complexation of Cr(III) proceeded faster than the reduction of Cr(VI) and reached a maximum at pH 5. (3) Cr(III) was best removed at pH 4 and 5 by bentonite, but the removal ratio decreased with increasing pH. Furthermore, the removal effect of bentonite decreased with the addition of a humic substance. (4) While Cr(VI) was never removed by bentonite, the removal was slightly improved by the addition of a humic substance and an increase in pH. (5) An effect of imogolite on the removal of Cr(VI) was observed at pH 4 and 5. Reaching a maximum at pH 4, the effect was not indicated at pH 6-8.

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