Coordination chemistry of weathering: Kinetics of the surface‐controlled dissolution of oxide minerals

Abstract

Chemical weathering processes, essentially caused by the interaction of water and the atmosphere with the Earth's crust, transform primary minerals into solutes and clays and, eventually, into sedimentary rocks; these processes participate in controlling the global hydrogeochemical cycles of many elements. Many mineral dissolution processes are controlled by a chemical mechanism at the solid‐water interface. The reaction‐controlling steps can be interpreted in terms of a surface coordination model. The tendency of a mineral to dissolve is influenced by the interaction of solutes—H+, OH−, ligands, and metal ions—with its surface. The surface reactivity is shown to depend on the surface species and their structural identity; specifically, the dependence of dissolution rates on p H and on dissolved ligand concentrations can be explained in terms of surface protonation (and deprotonation) and of ligand surface complexes. A general rate law for the dissolution of minerals is derived by considering, in addition to the surface coordination chemistry, established models of lattice statistics and activated complex theory.