An experimental and computational study of sodium-aluminum complexing in crustal fluids

The stoichiometry and stability constants of Na-aluminate (NaAl(OH)40) ion pair were determined from both boehmite solubility and potentiometric measurements. Boehmite solubility was measured at temperatures from 125 to 350 °C at pressures corresponding to equilibrium between liquid and vapor (PSAT) in the system Na-NH4-Cl-OH. Potentiometric measurements were performed at temperatures from 75 to 200 °C in Na-Al-Cl-OH solutions, using a Na-selective glass electrode. NaAl(OH)40 stability constants derived independently from these two methods are in excellent agreement and increase markedly with increasing temperature from 0.8 at 25 °C to 209 at 350 °C.