Experimental studies of aluminum solubility and speciation in brines

摘要

The solubility of gibbsite -- Al(OH)(sub 3) -- has been measured in (a) Na(sup +)-H(sup +)-Al(sup 3+)-Cl(sup (minus)) brines to 70(degrees)C and 5 molal ionic strength; (b) Na(sup +)K(sup +-)OH(sup (minus))-Cl(sup (minus))-Al(OH)(sub 4)(sup (minus)) brines to 80(degrees)C and 5 molal; and (c) at 50(degrees)C in 0.1 molal NaCl with the H(sup +) concentration controlled by acetate, bis-tris and tris buffers at -log(H(sup +)) -- 3 to 9. The activity coefficient ratios, ((gamma)Al(sup 3+))/((gamma)H(sup +))(sup 3) and ((gamma)Al(OH)(sub 4)(sup (minus)))/((gamma)OH(sup (minus))), have been modeled in the 0--100(degrees)C range using the Pitzer ion interaction treatment. Complexes of Al(sup 3+) with acetate and Al(OH)(sub 4)(sup (minus)) with bis-tris have been identified. Our results indicate that complexation of Al(sup 3+) by chloride is insignificant in this temperature range. The formation constants of Al(OH)(sup 2+) have been quantitatively determined by potentiometric titrations in the range 25--125(degrees)C and 0--5 molal ionic strength in NaCl media. After correcting for complexation of aluminum ions with the buffers, our solubility data at near neutral pH's are shown to be in quantitative agreement with the potentiometric results.