M. H. H. Mahmoud, M. A. Barakat, and Y. S. Mahrous and M. F. El-Shahat
Solvent extraction of rhodium(III) and platinum(IV) in 2 M hydrochloric acid with tri-octyl phosphine oxide (TOPO) was found to be substantially changed after addition of aluminium chloride to the aqueous solution. The extraction of the two metal ions was as low as 45 and 22 %, respectively, in absence of AlCl3. Rh(III) extraction drastically increased with increasing AlCl3 concentration to reach > 95% in 2M, while that of Pt(IV) sharply decreased to reach almost 0.0 in 0.5 M. This behavior may be related with steric effect created by interaction between AlCl3 as Lewis acid and chloro species of metal ions as Lewis bases. These findings have been utilized to separate Rh from Pt in a real leach liquor originally contains AlCl3. The extraction of Rh reached about 57% after 3 hours, while that of Pt was neglected along with time. Nearly quantitative extraction of Rh(III) was obtained by increasing HCl concentration to 3 M for only 2 min mixing time. Rh(III) was stripped from TOPO and precipitated in 2 M KOH
