RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Adsorption of divalent metal ions (M²⁺) onto oxide and hydroxide surfaces from solutions of strong electrolytes has typically been inferred to take place without the involvement of the electrolyte anion. Only in situations where M²⁺} forms a strong enough aqueous complex with the electrolyte anion (for example, CdCl⁺ or PbCl⁺) has it been frequently suggested that the metal and the electrolyte anion adsorb simultaneously. A review of experimental data for the adsorption of Cd²⁺, Pb²⁺, Co²⁺, UO₂²⁺, Zn²⁺, Cu²⁺, Ba²⁺, Sr²⁺, and Ca²⁺ onto quartz, silica, goethite, hydrous ferric oxide, corundum, {gamma}-alumina, anatase, birnessite, and magnetite, from NaNO₃, KNO₃, NaCl, and NaClO₄ solutions over a wide range of ionic strengths (0.0001 M-1.0 M), reveals that transition and heavy metal adsorption behavior with ionic strength is a function of the type of electrolyte. In NaNO₃ solutions, metal adsorption exhibits little or no dependence on the ionic strength of the solution. However, in NaCl solutions, transition and heavy metal adsorption decreases strongly with increasing ionic strength. In NaClO₄ solutions, metal adsorption decreases strongly with increasing ionic strength. In NaClO₄ solutions, metal adsorption exhibits little dependence on ionic strength but is often suggestive of an increase in metal adsorption with increasing ionic strength. Analysis of selected adsorption edges was carried out using the extended triple-layer model and aqueous speciation models that included metal-nitrate, metal-chloride, and metal-hydroxide complexes.