Thomas R. Holm

A comparison of oxidation-reduction potentials calculated from the As(V)/As(III) and Fe(III)/Fe(II) couples with measured platinum-electrode potentials in groundwater

Abstract Oxidation-reduction (redox) potentials calculated from arsenic speciation showed fair correlation with measured Pt-electrode potentials (Eh) in shallow groundwaters in east-central Illinois. The observed bias in calculated potentials relative to measured Eh values could not be explained by analytical imprecision. Redox potentials calculated from Fe concentrations showed better correlation with measured potentials than the As potentials. Arsenic speciation may be a useful supplement to Eh measurements and concentrations of other solutes, but is probably not a good indicator of redox conditions when used alone.

Sorption by kaolinite of Cd2+, Pb2+ and Cu2+ from landfill leachate-contaminated groundwater

Sorption of Cd2+, Pb2+ and Cu2+ to kaolinite from landfill leachate-contaminated groundwater, artificial groundwater (same major-ion concentrations as groundwater) and NaNO3 (same ionic strenght as the groundwater) was studied. Complexation of Cu2+ and Cd2+ by dissolved organic matter (DOM) in the groundwater was also studied. There was less sorption of all three metals from groundwater than from NaNO3 for large pH ranges. Sorption of Cd2+ and Pb2+ seemed to be due to a combination of ion exchange and surface complexation. This hypothesis was suppored by agreement between an ion exchange/surface complexation model and the sorption data. There was less Cu2+ sorption from groundwater than from the NaNO3 for pH-values > 5, but Cu2+ sorption from artificial groundwater was the same as from NaNO3. Sorption of Cu2+ was apparently by surface complexation only. For fixed pH and variable total Cu, there was less Cu2+ sorption from groundwater than from NaNO3, which is consistent with the formation of nonsorbing soluble complexes with DOM. A soluble complexation/surface complexation model reproduced the trends in the data, which supports the hypothesis of nonsorbing Cu complex formation.