Studies of hexavalent chromium attenuation in redox variable soils obtained from a sandy to sub-wetland groundwater environment

Laboratory experiments were conducted to characterize and quantify the capacity and kinetics of the combined effects of natural attenuation processes, such as adsorption, reduction, and precipitation, for hexavalent chromium [Cr(VI)] in a variable geochemical (i.e. fraction of organic carbon [foc], redox) environment of glaciated soils. Equilibrium attenuation terms: linear sorption (Kd), estimated capacity, and non-linear Langmuir (KL, Q) sorption parameters; varied over several orders of magnitude. The pseudo-first-order rate of disappearance of Cr(VI) from aqueous:soil slurries ranged from 10−5 to 10−1/min. An operationally defined kinetic attenuation term, attenuation capacity (AC), describing the quantity of Cr(VI) disappearing from the slurries, ranged from 1.1 to 12 μg Cr(VI)/g soil/7 days. The linear Kdʹs and estimated attenuation capacities were indirectly and directly related to increasing soil pH and foc, respectively. The AC values decreased and increased as a function of increasing soil pH and foc, respectively. The parameters determined in this work were used to evaluate the kinetics, capacity, and stability of chromium attenuation in the sub-wetland saturated soils in Hellerich (2004. A field, laboratory, and modeling study of natural attenuation processes affecting the fate and transport of hexavalent chromium in a redox variable groundwater environment. Ph.D. Dissertation, Department of Civil and Environmental Engineering, University of Connecticut-Storrs) using a statistical simulation framework.