Chemical controls of the aqueous environment on mineral growth and dissolution

Interfacial processes of mineral growth and dissolution are dictated by the local chemical environment. Even the distance from equilibrium, called the solution saturation, is dependent on the aqueous environment. If we look at organic molecules that do not interact directly with dissolved ions we can see that solubility changes with ionic strength [1]. This is known as salting out and is caused by the change in the structure and hydration properties of water molecules, altering enthalpy and entropy contributions within the solution. When dissolved ions can interact with each other, as is common for mineral constituents, the story becomes more complicated. In this case, ion-pair formation can alter the saturation of the aqueous solution with respect to the mineral [2]. Furthermore, ions in solution may also interact directly with the mineral surface [3], enhancing or inhibiting the addition or removal of ions and molecules to/from the surface. In this presentation I will review our knowledge of how aqueous solutions affect the growth and dissolution of carbonate minerals, which have been studied in detail at the interfacial level. Through this I will show that one of our major challenges to predict and understand fluid-rock interaction is modelling and characterizing the aqueous environment and its transitory nature.

[1] Whitehouse, B. G. The effects of temperature and salinity on the aqueous solubility of polynuclear aromatic hydrocarbons. Mar. Chem. 1984, 14, 319−332.
[2] King, H. E.; Satoh, H.; Tsukamoto, K.; Putnis, A. Nanoscale observations of magnesite growth in chloride-and sulfate-richsolutions. Environ. Sci. Technol. 2013, 47, 8684−8691.
[3] King, H. E.; Putnis, C. V. Direct observations of the influence of solution composition on magnesite dissolution. Geochim. Cosmochim. Acta 2013, 109, 113−126.