DETERMINATION OF FORMATION-CONSTANTS OF HYDROXO AND CARBONATE COMPLEXES OF PR3-K( IN 2 M NACL AT 303)

The hydrolysis of praseodymium III in 2 M sodium chloride at 303 K was studied. Two methods were used: pH titration followed by a computatio nal refinement and solvent extraction in the presence of a competitive ligand. The hydrolysis constants obtained by pH titration were: log b eta(1,H) = -7.68 +/- 0.07, log beta(1,2H) = -15.10 +/- 0.03, and beta( 1,3H) = -23.80 +/- 0.04. The stability constants of praseodymium carbo nate complexes were determined by pH titration as well and were: log b eta(1,CO23-) = 5.94 +/- 0.08 and log beta(1,2CO23-) = 11.15 +/- 0.15. Praseodymium carbonate species were taken into consideration for calcu lating the first hydrolysis constants by the solvent extraction method and the value obtained was: log beta(1,H) = -7.69 =/- 0.27. The value s for log beta(1,H) attained by both methods are the same. The species -distribution diagram was obtained from the stability constants of pra seodymium carbonate complexes and hydrolysis products in the condition s of the present work. (C) 1997 Elsevier Science B.V.