Interactions between mineral surfaces and dissolved species: From monovalent ions to complex organic molecules

Abstract

In order to understand the interactions of inorganic and organic species from solution with mineral surfaces, and more specifically, with the growth and dissolution behavior of minerals, we start by reviewing the most basic level of interaction. This is the influence of single monovalent ions on the growth and dissolution rate of minerals consisting of divalent ions. Monovalent ions as background electrolyte can change the morphology of growth features such as growth islands and spirals. These morphology changes can be similar to the ones caused by organic molecules and are, therefore, easily mixed up. Both Na+ and Cl- promote growth and dissolution of some divalent crystals such as barite and celestite. In addition, morphology changes and the stability of polar steps on sulfates are explained using atomistic principles. Subsequently, we will increase the level of complexity by investigating the interaction between organic molecules and mineral surfaces. As an example, we describe the influence of different organic growth inhibitors on the growth velocity of barite and use molecular simulations to identify where these organic molecules attack the surface to inhibit growth. Nature provides a number of complex organic molecules, so-called siderophores that are secreted by plants to selectively extract Fe ions from the surrounding soil. The molecular simulations on siderophores are complemented by atomic force-distance measurements to mimic the interaction of these molecules with Fe and Al oxide surfaces. The combination of simulations and force-distance measurements allows us to evaluate initial complexation on metal oxide surfaces (which is different from metal complexation in solution), steric hindrances, the possibility to remove metal ions from oxide surfaces, and selectivity for removal of Fe3+ over Al3+. Finally, we describe first attempts to find polypeptide sequences that may be used as precursors for biomineralization of calcite surfaces.