Experimental determination and interpretation of the solubility of corundum in H 2O between 350 and 600°C from 0.5 to 2.2 kbar

Abstract

Corundum solubility was measured in H2O between 350° and 600°C from 0.5 to 2.2 kbar. The base-10 logarithm of molality of Al in equilibrium with corundum along the 0.5 kbar isobar decreases with increasing temperature from −3.44 at 400°C to −5.52 at 600°C, but at 2.0 kbar the logarithm of molality of Al increases from −3.25 at 400°C to −3.09 at 600°C. Electrostatic energetics appear important in stabilizing the dominate Al species as isotherms of solubility are a linear function of the reciprocal of the dielectric constant of H 2O. These results together with values reported for corundum solubility in KOH solutions (Pascal and Anderson, 1989; Azaroual et al., 1996) are used to constrain the dominant Al species in pure H 2O solutions to Al(OH) 3 0. The base-10 logarithm of the molal equilibrium constants for the reaction: Al(OH) 4 − + H + = Al(OH) 3 0 + H 2O at 2.0 kbar and 400°, 500°, 600°, and 700°C are computed to be 6.33, 5.74, 6.39, and 6.75, respectively. It is argued that KAl(OH) 4 0 is not an important species in KOH aqueous solutions as increasing Al(OH) 4 − plus Al(OH) 3 0 with increasing pH and ionic strength can account for the increased corundum solubility within experimental uncertainty.