Competitive Adsorption at Surface Aluminum Sites: An Approach to Determining Feldspar Dissolution Rates in Mixed Proton/Ligand Systems

Abstract

Bacteria can affect the dissolution rates of aluminumsilicate minerals by a number of mechanisms. Principal among these are the production of protons and complexing ligands resulting in proton-promoted and ligand-promoted dissolution. However, dissolution inhibition has also been noted as a result of exopolysaccharide production and adsorption on mineral surfaces (Welch and Vandevivere, 1994). In a natural setting, all of these mechanisms may take place simultaneously and the net impact of bacteria and microbial processes on mineral stability may be difficult to predict. A series of laboratory dissolution experiments with bytownite feldspar (An75) in solutions containing both protons and ligands and ligands and polysaccharide suggest that a competitive adsorption model based on the Langmuir isotherm may be useful in making such predictions. This model supposes that the mechanism limiting dissolution rate is the adsorption of the attacking proton or ligand to mineral surface sites and that dissolution is then directly related to the number of sites that have been attacked.