Determination of thorium in zirconium-hafnium mixtures by aromatic polycarboxylic acids

Abstract

Results are presented for 1,3,5-benzenetricarboxylic (trimesic), 1,2,4-benzenetricarboxylic (trimellitic) and 1,2,4,5-benzenetetracarboxylic (pyromellitic) acids as precipitants for thorium. Trimesic and pyromellitic acids have been found to be better reagents than trimellitic acid. Thorium and zirconium-hafnium mixtures can be separated by precipitating zirconium-hafnium first in 0.5–0.8 N acid solution and then precipitating thorium in the filtrate at 3–4 pH. The separations are quite reproducible. The precipitates in all cases are ignited to the respective oxides. 5–10 mg samples of thorium can be estimated and separated from 10–50 mg samples of zirconium and/or hafnium. Results of investigations on interferences of cations and anions and pyrolysis curves for the decomposition of precipitates are presented.