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Issue 4, 2020
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Efficient extraction of slowly-released Cr(vi) from nano-sized ion channels in Cr(vi)–ettringite from reduced chromite ore processing residue

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Abstract

Residual unreacted Cr(VI) incorporated in ferrous-sulfate-reduced chromite ore processing residue (rCOPR) can be slowly released during deposition, posing a significant threat to the environment. Recent studies indicate that such Cr(VI) mainly exists within the nano-sized ion channels of ettringite, forming Cr(VI)–ettringite. Therefore, efficient extraction and recovery of the incorporated Cr(VI) from rCOPR, especially from Cr(VI)–ettringite, are urgently needed in order to eliminate the long-term hazardous effects of rCOPR. In this work, NaHCO3 was used to extract Cr(VI) from rCOPR with or without hydrothermal treatment, and the process under hydrothermal conditions (up to 120 °C) was able to nearly completely (>98%) extract Cr(VI). The results of X-ray diffraction, aberration-corrected scanning transmission electron microscopy, and X-ray absorption fine structure spectroscopy analyses were combined to elucidate the underlying extraction mechanisms. First, CO32− exchanged with CrO42− in the ion channels of Cr(VI)–ettringite, transforming ettringite into nano-CaCO3. This transformation effectively destroyed the ion-channel structure of Cr(VI)–ettringite, causing the release of incorporated CrO42−. However, in this stage, some CrO42− ions were still strongly adsorbed onto the nano-CaCO3, leading to the incomplete extraction of Cr(VI). Furthermore, the hydrothermal treatment was demonstrated to be essential to the acceleration of the nano-CaCO3 crystal growth to achieve the full Cr(VI) extraction. This novel strategy provides a viable approach to eliminate the pollution associated with the slow release of Cr(VI) from rCOPR in a fast and cost-effective manner.

Graphical abstract: Efficient extraction of slowly-released Cr(vi) from nano-sized ion channels in Cr(vi)–ettringite from reduced chromite ore processing residue

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Supplementary files

Article information


Submitted
18 Jan 2020
Accepted
06 Mar 2020
First published
13 Mar 2020

Environ. Sci.: Nano, 2020,7, 1082-1091
Article type
Paper

Efficient extraction of slowly-released Cr(VI) from nano-sized ion channels in Cr(VI)–ettringite from reduced chromite ore processing residue

W. Liu, Y. Song, J. Li, L. Ling, C. Tian, X. Liu and Z. Lin, Environ. Sci.: Nano, 2020, 7, 1082
DOI: 10.1039/D0EN00074D

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