Available online at www.pelagiaresearchlibrary.com Pelagia Research Library Advances in Applied Science Research, 2014, 5(4):100-106 ISSN: 0976-8610 CODEN (USA): AASRFC 100 Pelagia Research Library Extraction of rhodium from platinum solutions in presence of aluminum chloride with tri-octylphosphine oxide in toluene M. H. H. Mahmoud 1,2* , M. A. Barakat 2,3 and Y. S. Mahrous 2 and M. F. El-Shahat 4 1 Taif University, College of Science, Chemistry Department, Taif, KSA 2 Central Metallurgical R& D Institute, Helwan, Cairo, Egypt 3 King Abdulaziz University, Faculty of Meteorology, Environment and Arid Land Agriculture, Jeddah, KSA 4 Ain Shams University, Faculty of Science, Chemistry Department, Cairo, Egypt _____________________________________________________________________________________________ ABSTRACT 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 AlCl 3 . Rh(III) extraction drastically increased with increasing AlCl 3 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 AlCl 3 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 AlCl 3 . 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. Keywords: Solvent Extraction, Platinum, Rhodium, Separation, Recovery, stripping, Tri-octyl phosphine oxide, TOPO. _____________________________________________________________________________________________ INTRODUCTION Platinum group metals (PGMs) are in extensive use for catalysis reactions, electronic devices, space materials, etc. The PGMs are increasingly employed for the manufacture of auto exhaust catalysts. The high cost and increasing demand has prompted the recovery of PGMs from spent catalysts and low grade ores. The separation and purification of these metals from their solutions is one of the difficult areas in precious metals refining, mainly due to their complex solution chemistry [1,2]. Solvent extraction is a promising separation technique based on the control of the type of metal species in aqueous phase in presence of some additives [3] Several publications are found dealing with solvent extraction of PGMs from chloride media using different organic reagents such as Tributyl phosphate (TBP), trioctyl amine (TOA) [4] and others. A series of organophosphorous compounds have been marketed under the trade name of Cyanex (272, 301, 302) as acidic extractants for metal ions, and Cyanex (921, 923, 925) as neutral extractants [5,6] which are found to be superior extractants for precious metals. Existence of several number of species makes the quantitative removal and separation of Rh salts difficult, and careful control of solution conditions is essential. To date, no industrial solvent extraction system has been published for Rh. The more classical methods used for its recovery are inefficient, because these techniques are based on several precipitation/dissolution stages to achieve the desired degree of purity. Pt(VI) and Rh(III) form varieties of chloro-complexes in acidic chloride media. Anionic, neutral and cationic chloro species can be formed depending on the chloride ion concentration. Pt(VI) and Rh(III) are known to mostly extracted into the organic solutions in the form of anionic species. These anions can be considered as Lewis bases in