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

Abstract

Environmental context Chromate (CrO42–)-containing waste is illegally dumped in some places in the state of Uttar Pradesh, north India, although CrO42– is known to be toxic and carcinogenic. Because CrO42– is leached from the landfills, this study investigated the adsorption of CrO42– by soils. The results indicated that CrO42– is highly leachable and adsorption is inhibited, which leads to contamination of the groundwater and drinking water in this area. Abstract 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.