The conditional acidity constants, pK a , of methyl red and phenol red were determined in (10, 30, and 50) wt % binary aqueous mixtures of methanol and ethanol at 298.15 K and at constant low ionic strength (2.5 • 10 -3 mol • dm -3 ) by a spectrophotometric method. For methyl red and phenol red and in the studied cosolvent + water systems, pK a ranged from 3.78 ( 0.06 to 5.50 ( 0.04 and 8.50 ( 0.1 to 6.71 ( 0.03, respectively. Variations in the pK a of methyl red and phenol red as functions of wt % cosolvents are discussed in terms of solvent properties.

Equivalent conductivities of dilute solutions of calcium nitrate, cadmium nitrate, zinc nitrate, and calcium chloride (c < 0.0021 eq·dm−3) were measured in binary aqueous mixtures containing up to 70 wt % cosolvent (methanol, ethanol, and acetone) at 298.15 K ± 0.1. Data were treated by the Fuoss−Edelson equation, and its parameters, the limiting equivalent conductivity, Λ0, and the primary association constants, K 1 A, were evaluated. Variations in Walden products and K 1 A were interpreted in terms of ionic properties as well as solvent structure and dielectric constant.

The effect of mixed aqueous-organic solvents on exchange and adsorption reactions onto clay minerals is examined in this study while accounting for the effect of cosolvents on metal solution properties, ionic activity and complexation. In the absence of published values, a determination of the primary association constant of selected ions in solution was conducted using conductometric methods. These stability constant values were used to correct for ion-pairing in the exchange and the adsorption experiments. A spectrophotometric determination of pH was accomplished through the quantification of the conditional dissociation constants, s K I , of two indicators (methyl red and phenol red) at constant ionic strength and at 25 o C±2.0 in ethanol and methanol-water mixtures. In these mixtures and under these conditions, solution pH was determined from measurements of the indicator absorbance ratios at two wavelength λ HIn and λ In-within the range 4.5≤pH≤8.5. Calcium-sodium exchange on Wyoming bentonite in methanol, ethanol and acetone-water systems were investigated at constant total chloride concentration and at room temperature. In all treatments, Ca-Na exchange in cosolvents was a surface-controlled phenomenon involving electrostatic and specific solvent-surface interactions. The effect of cosolvents on Cd and Zn sorption to Ca-saturated bentonite and illite in mixed alcohol-water systems at low ionic strength and low initial metal concentration in the presence of nitrate varied between metals. Cd 2+ sorption to bentonite and illite was independent of the solvent dielectric constant suggesting a specific mechanism for Cd 2+ sorption involving inner-sphere complexes with the surface edge sites. Zn 2+ sorption to both clay minerals was strongly dependent on ε r with both increases (illite) and decreases (bentonite) in retention observed with decreased ε r. Although it is not yet possible to predict the effects of cosolvents on metal-surface reactions, it is clear that cosolvents can affect metal concentrations in solution, and therefore contaminant transport (increased hydraulic conductivity resulting from flocculation as Ca 2+ replaces Na + , and hence greater risk of clay liners failure). Additional study is needed on the effects of cosolvents on surface charge density, changes in the interlayer spacing, surface acidity and pH changes before and after sorption. I would like to express my gratitude to Mr. Nicholas Salazar, Ms. Monica Lecaros and Mr. Sunny Baidwan for their encouragement and support. I don't know how to thank Ms. Lina Gomez for being my friend and my family in all the good and the bad times.