The effects of temperature and pressure on the stability of mineral colloids

The stability of mineral colloids is well understood through numerous theoretical, experimental, and microscopic approaches. Nearly all of these, however, are for colloids at ambient or near-ambient conditions. The lack of studies at elevated temperature and pressure presents an obstacle to understanding the role that colloids may play in high-T and/or high-P settings such as geothermal works, hot springs, epithermal ore deposits, and deep crustal fluids. This study presents a first step toward quantitatively modeling the stability of mineral colloids for pressures from liquid-vapor equilibrium to 3000 bars and for temperatures from 25 to 400 °C, using the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory as an approximation. Methods are given for recalculating each of the necessary input parameters for the pressure, temperature, and electrolyte type of interest. Example calculations for gold and silica colloids in dilute NaCl solutions show that increasing pressure stabilizes colloids, whereas increasing temperature destabilizes them, especially at lower pressures. The solutions presented are approximations, since potentially influential factors such as surface roughness, adsorbed species, and non-DLVO forces are not considered. However, the results obtained are consistent with the limited experimental data available for colloids at the relevant conditions and offer an initial step toward quantitatively modeling colloid behavior at elevated pressures and temperatures.