Multisolute Metal Ion Sorption at the γ-Al2O3/Water Interface

Abstract

Many environmental problems associated with raw material production and past waste management practices require reliable quantitative prediction of the fate and transport of metal ion contaminants in surface and groundwaters. Sorption reactions at the mineral/water interface typically reduce solute mobility and often control the fate and transport of metal ions. Therefore, determination of specific sorption mechanisms has been a primary focus of research aimed at understanding metal ion transport, mineral growth and the development of catalyst materials. Typically, reactions at the mineral/water interface have been studied with a combined macroscopic/microscopic approach. Sorption experiments conducted in batch reactors describe specific ion sorption to oxide and clay materials as a function of pH, background electrolyte, surface coverage and competing adions. Select samples are then studied using various spectroscopy and microscopy methods including XAS, IR, XPS, AFM, SEM and TEM to determine the structure of sorbed species relative to macroscopic observations. Spectroscopic investigations have focused primarily on single solute systems. XAS data has been used to differentiate between innersphere and outersphere complexes and reveal the formation of polymeric species at high surface coverages. The variability in structure of many transition metal ion surface complexes as a function of surface coverage indicates that competing adions may have an impact on surface complexation and speciation. The goal of this study is to determine the effect of various adions including Co 2+, Fe 2+, SeO~and SeO 2on the sorption mechanism of cobalt at different surface coverages and to evaluate the types of surface complexes formed in multisolute systems using XAS techniques. Materials and methods. Batch equilibrium studies were conducted using y-AI203 (Buehler Alumina), 82 g/m 2, and metal basis grade nitrate or chloride salts C0(NO3)2, FeC12, Na2SeO3, Na2SeO4 and NaNO3 (Johnson Matthey Co.). Metal stock solutions University of Maine, Orono, ME, USA