FLUID SUPERSATURATION AND CRYSTALLIZATION IN POROUS-MEDIA

The relationship between the supersaturation at the point of crystalli zation and the rate at which supersaturation increases has been studie d from nucleation experiments on barite BaSO4, strontianite SrCO3, wit herite BaCO3 and gypsum CaSO4.2H(2)O. The crystallization experiments have been carried out by the counter-diffusion of cations and anions t hrough a column of porous silica gel transport medium. Nucleation is s uppressed in a finely-porous medium resulting in very high values of s upersaturation before crystallization from the solution begins. This t hreshold supersaturation for nucleation depends on the solubility of t he salt, the porosity of the medium and the supersaturation rate. Nucl eation inhibitors were used to extend the range of supersaturation att ainable. In all cases the experimental data fits the general expressio n: rate of change of supersaturation proportional to (threshold supers aturation)(m). These results are compared to previous work from the fi eld of chemical engineering on the relationship between supersaturatio n, volume and cooling rate in aqueous salt solutions. These experiment s have important implications to supersaturation in natural fluids and subsequent crystallization in relation to geological problems includi ng crystallization in low temperature sedimentary environments and flu id-rock ratios in hydrothermal mineral deposits.