Experimental determination and analysis of the solubility of corundum in 0.1 and 0.5 m NaCl solutions between 400 and 600 ℃ from 0.5 to 2.0 kbar

摘要

Corundum, α-Al_2O_3, solubility was measured in 0.1 and 0.5 m NaCl solutions from 400 to 600 ℃ between 0.5 and 0.2 kbar. The base-10 logarithm of Al molality at 2 kbar in 0.5 m NaCl increases from -2.45 at 400 ℃ to -1.52 at 600 ℃. At 1 kbar, the solubility increases from -2.33 at 400 ℃ to -1.03 at 600 ℃. These molalities are between 1 and 3 orders of magnitude greater than corundum solubility in pure H_2O (Walther, 1997). In 0.1 m NaCl, corundum solubility begins to decrease below that in pure water at 400 ℃ as pressures are decreased below ～1.2 kbar. A distribution of species calculation considering the Al species NaAl(OH)_4~0, Al(OH)_3~0 and Al(OH)_4~- and using association constants reported in the literature demonstrate that Al(OH)_4~- is a significant species in equilibrium with corundum in pure H_2O. The calculations also indicate that another Al aqueous species containing Na or Cl besides. NaAl(OH)_4~0 must be present in NaCl solutions to give the observed increase in Al with increasing NaCl concentrations to 0.5 m.