Characterization of the chromium retention potential of non polluted aquifer solids in an industrial site

Abstract
A hydrogeochemical study of an industrial site where sulfuric acid and copper sulfate ("bouillie bordelaise") are manufacture showed that the phreatic aquifer is contaminated by copper, sulfate, chromium, arsenic and has an acid pH. Field observations and laboratory experiments, both necessary if we are to understand the processes controlling tranfers at the solid-liquid interface, were used to investigate the behaviour of chromium. In the field, monitoring the mixing of polluted and unpolluted water with a conservative tracer, we shows that chromium disappears from solution. In the laboratory, the potential for retendon of dissolved chromium by an unpolluted aquifer solid was studied as a function of pH, with and without a complexing agent. Adding high concentrations of a complexing agent, EDTA, mobilizes the previously fixed chromium at basic pH (90%). Addition of Cr(III) with EDTA gathered, sorption is greatest (50%) for neutral and basic pH values. Unpolluted aquifer solids have a high sorption capacity for Cr(III). However, adding a complexing agent significantly mobilizes the chromium. Sorption of the complexed chromium is also considerably decreased. There should, therefore, be little risk of immediate chromium pollution in the absence of dissolved complexing agents, as long as the pH of the system is neutral.