Selective Separation of Pd(II), Rh(III), and Ru(III) Ions from a Mixed Chloride Solution Using Activated Carbon Pellets

Abstract

We performed batch adsorption tests with a view to separate Pd(II), Rh(III), and Ru(III) in chloride media using commercial activated carbon pellets (0.8 SUPRA, Norit) as adsorbent. The adsorption mechanism of Pd(II) [as PdCl3(H2O)− or PdCl4 2−] and Ru(III) (as RuCl5 2−) is explained by the ionization and adsorption model whereby the protonated basal plane of carbon interacts with the palladium or ruthenium species in solution. On the other hand, Rh(III) existing in solution as either hexa-aqua-rhodate Rh(H2O)6 3+ or penta-aqua-chloro-rhodate RhCl(H2O)5 2+ was adsorbed by interacting with the oxygen functional groups on the carbon surface. In general, the activated carbon pellets exhibited a strong affinity for Pd(II) in a wide range of HCl concentration (0.005–2.0 M). It was easy to remove Pd(II) selectively from a ternary solution (1.5–2.0 M HCl) containing equal metal concentrations (120 mg/L) using 0.2–0.3 g of dry carbon. We found that adsorption of Rh(III) and Ru(III) occurred simultaneously within a narrow solution pH range (2.3–2.6) but the overall adsorption rate of Rh(III) was threefold higher than that of Ru(III). The adsorption capacities of Pd(II), Rh(III), and Ru(III) in the single-component solutions were found to be 27, 15, and 4 mg/g, respectively. Finally, we found that adsorption of the metals was accompanied by an increase in solution pH up to 8.8 and was reversible at high HCl concentration. Except for Ru(III), all other metals fit the Langmuir isotherms.