Mineral Precipitation Kinetics

Abstract

Precipitation of solid phases in aqueous solutions which deviate from thermodynamic equilibrium is an ubiquitous kinetic phenomena. It may occur in soft chemistry experiments where the concentration of a solute in the aqueous solution, is prepared in excess with respect to the solubility of a desired compound (Adamson 1960; Markov 1995). As first recognized by Gibbs, the solid phase first appears as small nuclei which subsequently grow. The understanding and control of these nucleation and growth processes is of prime importance in modern technology which aims at producing artificial nano-size objects, such as ultra-thin films, nano-dots, nano-clusters, whether by molecular beam epitaxy methods (Pimpinelli and Villain 1998), chemistry in aqueous solution (Jolivet et al. 2004), electro-deposition (Schmickler 1996), etc. For example, it has recently been possible (Jolivet et al. 2006) to synthesize oxide nano-particles with a high surface to volume ratio displaying interesting properties: catalytic activity, optical, electronic and magnetic properties, liquid crystal properties, etc. The control of many of their size and shape dependent characteristics can be obtained by playing with external parameters, such as the acidity of the solution, the presence of specific anions, the temperature, etc. In the geochemical context, nucleation and growth processes are also particularly relevant for complex oxides, such as alumino-silicates or clays, which are ubiquitous in our environment, being often produced as secondary nano- to micro-phases in all alteration processes of rock forming minerals: weathering processes near the Earth’s surface, diagenetic or hydrothermal processes in the Earth’s crust, etc. The geochemical modeling of water-rock interactions has been intensively developed since the pioneering work of Helgeson and co-workers (1970). The aim of geochemists was to be able to better understand the evolution of the aqueous solution (AS) composition in the different water cycles as summarized by Drever (1997): in weathering systems …