PNNL

Abstract

When negatively charged sediments come into contact with groundwater, the solution cations are attracted to and the solution unions are repelled from the sediment. This repulsion process, referred to as anion exclusion, may result in enhanced transport of anions through porous aquifer sediments. Laboratory batch experiments and theoretical calculations based on the Gouy theory of the diffuse double layer were conducted to evaluate anion exclusion by technetium (as TcO4-) in two smectite-containing sediments. All distribution coefficients (Kd: the ratio of the concentration of sorbed solute to the concentration of dissolved solute) were very low for both sediments, ranging from -0.18 to +0.11 mL/g. The standard deviations associated with these means were generally quite low, typically