Solubility behavior of quartz and corundum in supercritical water: A quantitative thermodynamic interpretation

摘要

Dissolution reaction equilibria for (alpha)-quartz (SiO(sub 2)) and corundum ((alpha)-Al(sub 2)0(sub 3)) in pure, supercritical water are quantified using a density-dependent thermodynamic model. The database of existing solubility literature for (alpha)-quartz (0.2-10 kb, 200--575(degrees)C) is shown to be consistent with the presence of two hydrolyzed SI(IV) ion forms: Si(OH)(sub 4)(aq) and Si(sub 2)O(OH)(sub 6)(aq); the corundum database (1-20 kb, 400--700(degrees)C) is consistent with Al(OH)(sub 3)(aq) and Al(OH)(sub 4)(sup (minus)). A third Si(IV) ion hydroxocomplex, Si(sub 2)O(sub 2)(OH)(sub 5)(sup (minus)), is indicated at lower pressures (0.03-0.10 kb). The characteristic sigmoidal nature of the solubility isobars is explained by dimerization of Si(OH)(sub 4)(aq) (at high densities) or the formation of anionic hydrolysis products, Si(sub 2)0(sub 2)(OH)(sub 5)(sup (minus)) and Al(OH)(sub 4)(sup (minus)), in the low density region (p < 0.01 gm/cc). By means of the evaluated equilibria, thermochemical properties of Si(sub 2)O(OH)(sub 6)(aq) and Si(sub 2)O(sub 2)(OH)(sub 5)(sup (minus)) are made available for the first time.