Environmentally friendly Pd(II) recovery from spent automotive catalysts using resins impregnated with a pincer-type extractant
Manabu Yamada, Shun Kimura, Muniyappan Rajiv Gandhi, Atsushi Shibayama
Abstract
Abstract Extractant-impregnated resins have potential for recovering platinum group metals selectively and efficiently. Herein, 1,3-bis(2-(octylthio)propan-2-yl)benzene ( 1 ), a pincer-type extractant, was impregnated in Amberlite XAD-7 resin ( 1 -EIR), and the batch Pd(II) sorption conditions, including impregnated amount, shaking time, Pd(II) concentration, HCl concentration, and Pd(II) desorption reagents, were optimized. The maximum Pd(II) sorption capacity of 1 -EIR was 49 mg g −1 after 24 h in a 700 ppm Pd(II) solution. Over 20 adsorption–desorption cycles, 1 -EIR showed good reusability, with a sorption percentage ( S %) of > 92%. However, not all Pd(II) was desorbed from 1 -EIR. Complete Pd(II) collection was achieved by combining desorption with flaking of the Pd–extractant complex from Pd(II)-loaded 1 -EIR by Soxhlet extraction, as ~ 13 mg g −1 remained after the 20th adsorption–desorption cycle by absorptiometric method. The sorption mechanism was elucidated based on the Langmuir isotherm model, thermodynamic parameters, and sorption kinetics. Pd(II) sorption by 1 -EIR was spontaneous and endothermic, and the sorption kinetics followed a pseudo-second-order model. Notably, 1 -EIR also exhibited high selectivity for Pd(II) from a simulated mixed metal solution and a spent automotive catalyst leachate ( S % = 98% and > 99%, respectively). Thus, this extractant-impregnated system is promising for selective Pd(II) recovery from spent automotive catalysts and other secondary resources.