Extraction of Hf(IV) from strongly acidic solutions with N-benzoyl-N-phenylhydroxylamine

Abstract

The extraction of Hf(IV) by N-benzoyl-N-phenylhydroxylamine (HBPHA) from strongly acidic solutions of perchloric and hydrochloric acids has been investigated. The distribution constant of HBPHA between acid solutions and chloroform decreases with increasing acid concentration. The combined effects of higher acidity and lower distribution constant at first lead to a decrease in concentration of the N-benzoyl-N-phenylhydroxamate ion [A −] in the aqueous phase; at higher acidities, however, [A −] increases with increasing acid concentration. It is suggested that the variation of [A −] with acid concentration, rather than a change in the extraction mechanism, causes the previously observed variation of hafnium extraction with HBPHA from strongly acidic solutions. It appears that for perchloric acid concentrations up to 7·5 M, Hf(BPHA) 4 can be regarded as the only extracted complex. At higher hydrochloric acid concentrations, however, chloride ions are probably also coordinated to hafnium.