Issue 4, 2020

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

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

Supplementary files

Article information

Article type
Paper
Submitted
18 jan 2020
Accepted
06 mar 2020
First published
13 mar 2020

Environ. Sci.: Nano, 2020,7, 1082-1091

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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