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

Minghai Wei,Honghan Chen,Samuel Barnie,Wenting Li,Jie Tang,Jia Zhang

doi:10.1007/s12665-021-09986-9

Abstract

Chromite ore processing residue (COPR) storage sites are widely distributed all over the world, causing serious soil and groundwater pollution. However, the differences in soil constituents and properties in different regions are significant, and the dynamic migration and transformation of Cr(VI) in different types of soil under alkaline condition of the COPR site is still unclear. In this study, typical black soil, red soil and loess in different regions of China were chosen to investigate the adsorption kinetics and thermodynamics of Cr(VI) under the original pH conditions of the soil, and then the alkaline Cr(VI) solution was introduced into the soil column to simulate the dynamic migration and transformation process of Cr(VI) at COPR sites. According to the results, the Cr(VI) breakthrough curve predicted by the solid–liquid distribution coefficient Kd based on the static isotherm adsorption experiments significantly underestimated and overestimated the retention effect of black soil and red soil on Cr(VI) dynamic migration, respectively. For the black soil, the retention of Cr(VI) was dominated by Cr(VI) reduction, which was a slow reaction compared with Cr(VI) adsorption. Therefore, the reduction kinetics process during the column experiment cannot be neglected. With respect to the red soil, the outlet Cr(VI) concentration turned to be higher than the inlet concentration with the soil alkalization, which indicated that the adsorbed Cr(VI) desorbed again, and this was the main reason for the overestimation of Cr(VI) retention effect by the red soil. This study shows that the environmental risks of Cr in different types of soil are quite different, mainly related to the valence and occurrence form of Cr governed by the soil constituents and properties. In addition, the stable form of Cr in the black soil column after the reaction indicates that the soil organic matter can be used as a potential environmentally friendly remediation material for Cr(VI) contaminated soils at COPR sites.

Highlights

Chromium salt is an important chemical raw material widely used in electroplating, tanning, metallurgy, ceramics, dyes and wood preservation (Dhal et al 2013)
The typical black soil, red soil and loess in different regions of China were chosen to investigate the adsorption kinetics and thermodynamics of Cr(VI) under the original pH conditions of the soil, and the alkaline Cr(VI) solution was introduced into the soil column to simulate the dynamic migration and transformation process of Cr(VI) at chromite ore processing residue (COPR) sites
This study shows that the environmental risks of Cr in different types of soil are quite different, mainly related to the valence and occurrence form of Cr that governed by the soil constituents and properties

Summary

Introduction

Chromium salt is an important chemical raw material widely used in electroplating, tanning, metallurgy, ceramics, dyes and wood preservation (Dhal et al 2013). In the past few decades, the high lime roasting technology used in the production of chromium salts has produced a large amount of chromite ore processing residue (COPR), and many COPR storage sites have been formed worldwide. About 0.04%-2.59% (w:w) of Cr(VI) remains in the COPR, and since a large amount of alkaline substances such as calcium carbonate remain, the COPR tends to exhibit a strong basic character (Chrysochoou et al 2009; Foeldi et al 2013). Cr(VI) exists in the form of CrO42- under alkaline conditions and has strong mobility (Benjamin 2002; Zhang et al 2018c). It is easy to infiltrate into the groundwater with the leaching filtrate of the precipitation, and spread to the downstream

Methods

Results

Conclusion