Precipitation and Hydrolysis of Thorium in Aqueous Solution. V. Studies of the System: Thorium Nitrate-Ammonium Oxalate

The precipitation of thorium from aqueous solution of thorium nitrate (1.25 mM) and ammonium oxalate (2 .5-80 mM) was investigated at pH from 1 to 10. The following precipitates were identified with the brutto formula: Th(OH)4 and Th(C204) 2 X 6 H 20 (by means of chemical ana lyses). The soluble thorium oxalato complex is formed between these two precipitates and contains 4 oxalate bound to thorium, with the simples t formula :[Th(C20 4)4 4-] (as determined by coulometric titration). Using log Ko = 34.8 for the dissolution constant of thorium hydroxide in ammonium oxalate ~ 4 for thorium oxalate was obtained: 1.58 X 1024