EXPERIMENTAL STUDY OF CHROMIUM ADSORPTION IN UNCONSOLIDATED SEDIMENTS

Heavy metals contamination such as those by chromium (Cr) are serious threats to groundwater resources due to their non-biodegradable nature and bioaccumulation processes. Adsorption is mainly responsible for heavy metal accumulation on sediment surfaces. Two most common valence states of Cr are Cr (III) and Cr (VI) with Cr (VI) having a higher solubility and mobility in groundwater. Redox reaction can change the valence state of Cr. In this work, we study a Cr contaminated site in Qiqihar city in Heilongjiang province, China in order to understand adsorption mechanisms. We combined laboratory experiments and numerical simulations. Specifically, we studied effects of different factors including temperature, pH, and sand grain size on the Cr sorption coefficient through series of batch experiments. We found Freundlich isotherm to be an appropriate representation of adsorption behavior. We performed column experiments on Cr(VI) transport and applied a deterministic equilibrium model as well as a chemical non-equilibrium model to fit the breakthrough curves. We estimated parameters such as conductivity, dispersion coefficient, retardation factor from our experiments. Our results provide better understanding of adsorption and desorption processes of Cr(VI) in unconsolidated sediments.