Continuous Counter-Current Foam Separation of Pd（II） in the Presence of Thiodiglycolamide Extractant

Continuous counter-current foam separation (CCFS), which features simultaneous injections of metal/surfactant solutions into the rising foam bed, was applied to the recovery of Pd(II) from hydrochloric acid solutions containing several other metals. In aqueous solutions a nonionic surfactant, poly(oxyethylene) monooleyl ether (POOPE), was added along with a series of thiodiglycolamide (TDGA) extractant as metal collector. Using tetrabutyl-TDGA, selective separation of Pd(II) was attained over the other metals, though the total amount of metal recovered in the foamate was small. This low recovery results from decreasing foam stability, which was ascertained by cavities in the foam bed, caused by the addition of organic extractant. Moreover, tetra-2-ethylhexyl-TDGA was tried and satisfactory separation could be attained; the percent recovery of Pd(II) was 95% with the enrichment 1.8 while the separation factors of Pd(II)/Pt(IV), Pd(II)/Fe(III), Pd(II)/Cu(II) and Pd(II)/Zn(II) were 518, 162, 635 and 209, respectively.