Extraction of Palladium(II) Using Cyanex 471 Extractant and Supported Liquid Membrane

摘要

Cyanex 471 has potential in separating Pd(II) from chloride solutions containing Pt(IV). Liquid-liquid extraction equilibria studies have demonstrated that Cyanex 471 could be used to recover palladium(II) from spent automotive catalysts. The distribution equilibria and solution chemistry of the PdCl sub 2 -HCl-H sub 2 O-Cyanex 471-xylene system is straightforward until PtCl sub 4 is added to the system, upon which the system becomes extremely complex with various complexing reactions competing at the interface. Cyanex 471 has a major problem in applications using supported liquid membranes. The extracted palladium complex becomes saturated and precipitates as a dark brown solid before diffusion of the complex across the membrane can occur. Since the loading capacity of Cyanex 471 is very high, this is not a problem in solvent extraction. In supported liquid membrane extraction, the capacity of the membrane to retain Cyanex 471 in its tortuous pores is limited, causing precipitation of the palladium complex into the feed solution. All the changes made on the system parameters in this study failed to overcome this problem. However, results of the solvent extraction study indicate that supported liquid membrane technology could be applied to the separation and concentration of palladium(II) if the proper apparatus could be designed. Such a design would need a much higher membrane surface area to feed solution volume ratio than that used in this study. It should be run at palladium concentrations that keep interfacial complexing below the Cyanex 471 loading capacity. (ERA citation 10:008877)