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The catalysts manufacturing industry is the second largest consumer of PGMs after the jewelry industry. Automotive catalysts comprise refractory oxides support on which two or more precious metals (platinum, palladium, rhodium etc.) are dispersed in very low concentration (0.1-0.3 wt.% of the monolith). The honeycomb type monolith is typically made of a cordierite (2Al2O3·2MgO·5SiO2). 2 Several researchers have dealt with the recovery of these metals as the recovery of precious metals from spent automotive catalysts is of economical importance. 3-7 Spent autocatalysts are usually smelted in the presence of larger amounts of collector metals (Cu, Fe, Pb, Ni etc.) After leaching the precious metals enriched in the collector metals with acid, the precious metals can be selectively recovered. Among PGMs, rhodium (Rh) is an exceedingly rare element, comprising only 0.0001 PPM of the earth’s crust. 8 Moreover, rhodium is especially notable for its extreme inertness to acids, even aqua regia. Because of scarcity and high price, the recovery of rhodium from scrap is an important issue. Rhodium has a special catalytic activity to reduce nitrogen oxides (NOx) to N2, and is a main element as an autocatalyst. 9 Rhodium plated electrodes are used in the soda industry for electrolysis of salt water, and for electrodes for domestic water treatment. Rhodium plating is used widely in the jewelry industry. In the electronics industry, rhodium plating is used for electric contacts, e.g., ferreed switches. 10 The purification and recovery of rhodium from the other precious metals has always been difficult because of its complex aqueous chemistry in chloride solution as well as extreme inertness to acids, even aqua regia. It should be pointed out that the key factor for success in the separation of rhodium from the other precious metals is the developing an effective dissolution process for rhodium. It is well known that the disulfate melt technique on rhodium metal is utilized for quantitative dissolution of rhodium and its separation from iridium and platinum. 11 Another method has been developed for recovering PGMs from scrap with the propose of improving Rh dissolution in acid. Reactive metal vapours such as magnesium (Mg) and calcium (Ca) were reacted with powdered Rh in a closed stainless steel reaction vessel at a constant temperature ranging from 873 to 1173 K. 9 Iron(II) oxide with NaCl structure was successfully synthesized in a quartz tube sealed under vacuum. Hematite in an evacuated silica tube progressively loses oxide ions at 1373 K depending on the heating time. Finally, α-Fe2O3 is completely transformed into the well crystallized Fe0.935O after heat treatment at 1373 K for 84 h. 12 Silica tube is very suitable one for the chemical vapour transport reactions in an inert atmosphere because of hightemperature resistance, no-contaminants including foreign metals, and the ease of sealing under vacuum. In this work, the chemical vapour transport reactions between magnesium and rhodium are attempted using silica ampules sealed under vacuum. And also, the verifications, such as the formation and dissolution of intermetallic compounds (MgxRhy), purification and recovery of rhodium, are performed.

Purification and Recovery of Rhodium Metal by the Formation of Intermetallic Compounds