Chromate adsorption from chromite ore processing residue eluates by three Indian soils

Chromite ore processing residue (COPR) is a harmful waste of the chromate (CrO42-) extraction roasting process. Nevertheless, deposition of COPR in uncontrolled surface landfills is still common practice in some countries. Leaching of carcinogenic CrO42- and contamination of groundwater is a key environmental risk arising from COPR sites. The objective of this study was to evaluate the adsorption behaviour of CrO42- from COPR eluates by soils. Prior to the adsorption experiments, batch studies at varying solid- to- liquid ratios were performed to evaluate the solubility of CrO42- from COPR. Chromate adsorption experiments were carried out in a batch system with eluates obtained from two different Indian COPRs to assess potential groundwater contamination by CrO42-. Three soils that originate from the surroundings of COPR dumping sites were chosen in order to provide realistic adsorption conditions. The data were evaluated with the Freundlich and Langmuir equation. Chromate adsorption was inhibited because of the high pH of both of the soils (pH 6.7 to 7.2) and the eluates (pH 12.3) as well as the high carbonate concentration of the eluates. The extent and behaviour of CrO42- adsorption from both eluates was similar. The main difference between the eluates was the solubility of CrO42- from COPR and thus the initial CrO42- concentration. The results presented in this study provide an improved understanding of the mobility of CrO42 in the affected area, which is important because the local population uses the groundwater not only for the needs of livestock but also as drinking water.