Processes Governing Chromium Contamination of Groundwater and Soil from a Chromium Waste Source Mainak Bhattacharya, † Amritanshu Shriwastav, †,‡ Shrikant Bhole, †,§ Rahul Silori, †,∥ Tim Mansfeldt, ⊥ Ruben Kretzschmar, # and Abhas Singh* ,† † Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India ‡ Environmental Science and Engineering Department, Indian Institute of Technology Bombay, Mumbai 400076, India § Tranzact, Mumbai 400093, India ∥ Health Safety and Environmental Engineering and Civil Engineering Department, University of Petroleum and Energy Studies, Dehradun 248007, India ⊥ Faculty of Mathematics and Natural Sciences, Department of Geosciences, Institute of Geography, University of Cologne, Albertus-Magnus-Platz, D-50923 Kö ln, Germany # Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, 8092 Zurich, Switzerland * S Supporting Information ABSTRACT: Chromium (Cr) contamination of natural resources from unregulated disposal of pretanning industrial waste, chromite ore processing residue (COPR), is a serious environmental concern, especially in developing countries. Although there have been studies on COPR characterization, the fate and transport of chromium emanating from COPR remains poorly understood. In this study, processes governing Cr contamination in groundwater and soil near known COPR disposal sites were investigated. Field sampling of ground- water, irrigated soil, and COPR was conducted near Kanpur (India) to identify the extent and forms of chromium contamination. Both dissolved and suspended fractions of groundwater were analyzed to evaluate the presence of any Cr-containing colloids. At certain locations with elevated Cr levels, the saturation state of sampled groundwater was evaluated to be near equilibrium with respect to BaCrO 4(s) through speciation modeling of wet chemical data. Colloidal forms of Cr, such as BaCrO 4(s) or as Cr adsorbed on other non-Cr containing phases, were suggested through measured differences in total and dissolved Cr concentrations and SEM-EDS evidence of Ba and Cr on filtrate residues. As BaCrO 4(s) was not detected in COPR, the presence of these colloids in groundwater could be indicative of secondary precipitation of Cr upon interaction with Ba present in the subsurface. Rapid formation of colloidal BaCrO 4(s) was also supported through controlled batch experiments with Cr(VI)- and Ba-spiked ultrapure water and groundwater. These results indicate the importance of secondary precipitation of colloidal BaCrO 4(s) in determining eventual Cr(VI) solubility in aquifers impacted by Cr originating from COPR dissolution. KEYWORDS: chromium, chromite ore processing residue, speciation modeling, solubility, colloidal transport, barium chromate 1. INTRODUCTION Chromium (Cr)-based compounds are routinely utilized as tanning agents by the leather industry in the developing world. 1−4 Unregulated disposal of Cr-bearing effluents 5,6 and solid waste 7−9 from many of these tanneries, such as in the industrial city of Kanpur (India), has led to the contamination of natural resources, 10,11 including soils and sediments, 12,13 discharge water and groundwater, 14 as well as plants. 15 The carcinogenicity of hexavalent chromium (Cr(VI)) 16 and its high solubility in water under circumneutral pH conditions pose a serious threat to the environment. Although tannery-sourced Cr contamination of natural resources has been explored in detail in past studies, 17−19 contamination by upstream industries manufacturing the tanning salt, basic chromium sulfate (BCS) [Cr(OH)SO 4 ], has not received sufficient attention. Chromium ore processing residue (COPR) is a solid waste generated by these upstream BCS-producing industries. The waste is alkaline in nature with pH 9−12 20,21 and contains around 20−30% hexavalent chromium. 22,23 Uncontrolled disposal of COPR is frequently Received: August 12, 2019 Article http://pubs.acs.org/journal/aesccq Cite This: ACS Earth Space Chem. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acsearthspacechem.9b00223 ACS Earth Space Chem. XXXX, XXX, XXX−XXX Downloaded via BIU SANTE on December 14, 2019 at 14:18:24 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.