Experimental determination and analysis of the solubility of corundum in 0.1-molal CaCl 2 solutions between 400 and 600°C at 0.6 to 2.0 kbar

Abstract

Corundum (α-Al 2O 3) solubility was measured in 0.1-molal CaCl 2 solutions from 400 to 600°C between 0.6 and 2.0 kbar. The Al molality at 2 kbar increases from 3.1 × 10 −4 at 400°C to 12.7 × 10 −4 at 600°C. At 1 kbar, the solubility increases from 1.5 × 10 −4 m at 400°C to 3.4 × 10 −4 m at 600°C. These molalities are somewhat less than corundum solubility in pure H 2O (Walther, 1997) at 400°C but somewhat greater at 600°C. The distribution of species was computed considering the Al species Al(OH) 3 0 and Al(OH) 4 −, consistent with the solubility of corundum in pure H 2O of Walther (1997) and association constants reported in the literature. The calculated solubility was greater than that measured except at 600°C and 2.0 kbar, indicating that neutral-charged species interactions are probably important. A Setchénow model for neutral species resulted in poor fitting of the measured values at 1.0 kbar. This suggests that Al(OH) 3 0 has a greater stability relative to Al(OH) 4 − than given by the models of Pokrovskii and Helgeson (1995) or Diakonov et al. (1996). The significantly lower Al molalities in CaCl 2 relative to those in NaCl solutions at the same concentration confirm the suggestions of Walther (2001) and others that NaAl(OH) 4 0 rather than an Al-Cl complex must be significant in supercritical NaCl solutions to give the observed increase in corundum solubility with increasing NaCl concentrations.