Investigation of hexavalent chromium sorption in serpentine sediments

摘要

In this study the removal of hexavalent chromium (Cr6+) by serpentine sediments was investigated in order to delineate Cr6+ sorption behavior in aquifers with ultrarnafic geologic background. Batch experiments were conducted in order to determine the influence of several parameters on Cr6+ removal, including the pH of the sediment solution, mineralogy, sediment's particle size and Cr6+ initial concentration. The results showed that Cr6+ removal was due to both adsorption and reduction phenomena. Reduction was attributed to the presence of a magnetic fraction in the sediment, mostly related to magnetite, which contributed almost 50% of the total removal in the pH range 3-7. Adsorption behavior was dominated by the finer sediment fraction (d < 0.075 mm). The amount of Cr6+ adsorbed was constant in the pH range 3-7, while it decreased sharply in the range 7-8.5. Cr6+ adsorption was found to increase and decrease proportionally with increasing initial Cr6+ concentration of and particle size, respectively. The linear Langmuir and Freundlich adsorption isotherms were used to describe the experimental data, with Freundlich providing a better fit to determine distribution factors for transport modeling. (C) 2017 Elsevier B.V. All rights reserved.