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The sorption of Sr&sup2+; and Pb&sup2+; on zeolitized tuffs from the Nevada Test Site (NTS) was investigated using macroscopic batch sorption experiments and X-ray absorption spectroscopy (XAS) asaction of geochemical parameters, including pH, ionic strength, and type of background electrolyte. The sorption of Sr&sup2+; is dependent on the ionic strength of the medium and independent of pH, suggesting that Sr&sup2+; sorption is controlled by ion exchange at permanent charge sites. At higher ionic strengths, background electrolyte cations compete effectively with Sr&sup2+; for cation-exchange sites and Sr&sup2+; sorption is suppressed. At the two lower ionic strengths (0.01 and 0.1 M), Pb&sup2+; sorption is also consistent with adsorption by cation exchange. At the highest ionic strength (1.0 M), however, exclusion of Pb&sup2+; from cation-exchange sites resulted in pH dependent adsorption, consistent with sorption on amphoteric surface hydroxyl sites or formation of surface precipitates. XAS was used to test these hypotheses. Based on XAS data, Sr&sup2+; formed hydrated surface complexes coordinated with approximately eight O atoms at an average distance of 2.60 (± 0.02) Å, regardless of conditions, consistent with the formation of mononuclear, outer-sphere surface complexes at the Ca2 site in the B channel of clinoptilolite. The coordination environment of sorbed Pb&sup2+; was more complex and a function of pH and ionic strength. The first shell consisted of two to three O atoms at an average distance of 2.20 (±0.02) Å. At low pH and ionic strength, XAS data were consistent with Pb&sup2+; adsorption at the Na1 and Ca2 cation exchange sites in channels A and B of clinoptilolite, respectively. At the highest ionic strength (1.0 M) and low pH, XAS provide evidence for formation of Pb&sup2+; monodentate, corner-sharing inner-sphere complexes, whereas at higher pH, XAS analysis is consistent with formation of edge-sharing bidentate... [ABSTRACT FROM AUTHOR]

Studies the sorption of cadmium II and selenite on two, porous high surface area aluminum oxide using X-ray photoelectron spectroscopy. Measurement of binding energies of aluminum and oxygen for the aluminum oxides; Estimation of surface coverages of the adsorbents; Measurement of cadmium and selenite adsorbed.

Reports that the rate of cadmium and selenite uptake is controlled by intraparticle mass transfer based on batch sorption experiments. Modeling of fate and transport of hazardous chemicals in subsurface environment; Conduct of time-dependent sorption experiments with porous alumina particles; Comparison of cadmium and selenite.

The societal impacts of As in water resources in the arid western USA are potentially acute as a consequence of the combined effects of limited water supplies and the pervasive occurrence of naturally occurring As in subsurface geologic formations, including the carbonate-hosted, disseminated gold-bearing formations of the Carlin Trend. The prevalence of As in secondary minerals in gold-bearing carbonate-hosted ores is of interest because of the potential for As release as a result of ore development. A key component to gold mining is the engineering and construction of large-scale heap-leach and waste-rock containment structures that are characterized by variably saturated hydrology. Estimating As release behavior from these structures with a variably saturated reactive flow and transport numerical model requires the quantification of the significant differences in the sorption behavior for the stable redox states for As. Therefore, the objective of this study was to quantify this sorption behavior and to represent the observed behavior with an isotherm formulation. The pH-dependent sorption behavior of arsenite, As(III), and arsenate, As(V), onto two carbonate-hosted gold ores is presented. The experimentally determined pH-dependent sorption behavior for both As(III) and As(V) is consistent with sorption on metal oxides as reported in studies on rock and soils with similar bulk mineralogical properties. The experimental sorption data are represented with two modified isotherm formulations. Modified formulations of the Langmuir isotherm and of the Sips isotherm are presented that include the pH of the sorbate solution as an additional model parameter. These formulations are applied to both As(III) and As(V) sorption data to generate an isotherm surface. The pH-dependent isotherm methodology can be incorporated readily into numerical models for the purposes of estimating As transport behavior in field-scale, variably saturated environments. [ABSTRACT FROM AUTHOR]