Gravimetric Determination of Zirconium and Hafnium by Aromatic Carboxylic Acids

1,3,5-Benzenetricarboxylic (trimesic) acid, 1,2,4benzenetricarboxylic (trimellitic) acid, and 1,2,4,5benzenetetracarboxylic (pyromellitic) acid are proposed as new reagents for the gravimetric determination of zirconium and hafnium. Bismuth(III) and cerium(IV) are the only interferences and their prior removal presents no difficulty. For 10 determinations of zirconium at a 95% confidence interval, the confidence limit ranges from 0.30 to 0.33 mg for 19.7-mg samples for the three reagents; for hafnium the confidence limit ranges from 0.28 to 0.30 mg for 17.1-mg samples. Five- to 8-mg quantities of zirconium and hafnium can be determined. The precipitates contain the reagent molecule and zirconyl and hafnyl ions in a 1 to 1 ratio. Data on thermal decomposition of the precipitates are presented. (auth)