The dissolution of oxides and aluminum silicates; examples of surface-coordination-controlled kinetics

Abstract

The weathering of rocks and the formation of soils as well as the processes in the formation, alteration, and dissolution of sediments are ruled by surface reactions at the interface between minerals and water. Most of the dissolution reactions are critically dependent on the coordinative interactions taking place on these surfaces, above all on the interaction of hydrous oxide surfaces with H<sup>+</sup>, OH<sup>-</sup> (surface protonation), and suitable ligands (anions and weak acids).<br />Surface processes rather than transport processes are typically the rate-controlling steps in the dissolution of most hydrous oxides and aluminum silicates; thus, the reaction rates simply depend on the concentration of surface species. Linear dissolution kinetics are observed if the surface protonation and surface ligand concentration remain constant. This indicates that the detachment of the surface metal species is rate-determining. Surface chelates, especially those present as five- and six-membered rings, for example, with oxalate or salicylate, are most efficient in enhancing the dissolution reaction.