MEASUREMENTS OF AL(NO3)3 ACTIVITIES IN AQUEOUS NITRATE SOLUTIONS

Aluminum nitrate activity coefficients obtained by vapor pressure osmometry are compared with activity coefficients derived from nitric acid extraction measurements and Bromley's correlation. This solvent extraction approach was possible because of the poor extraction of Al3+ (distribution ratio less-than-or-equal-to 10(-3)) by the chosen solvents. The solvents compositions were 0.25M CMPO (octyl(phenyl)-N,N-diisobutylcarbamoyl methylphosphine oxide) in tetrachloroethylene (TCE) and 0.25M CMPO with 0.75M tributyl phosphate (TBP) in TCE. In both approaches, nitric acid was used to supress the hydrolysis of Al3+. At high ionic strengths, the two techniques yielded very similar activity coefficients for Al(NO3)3. However, at intermediate and very low ionic strengths, the two procedures produced considerably different activity coefficients.