Silica-supported thiourea resin for efficient recovery of Pd(II): Batch, column and mechanism study

Palladium is versatile in many industrial applications due to its distinct physicochemical properties. Due to the scarcity of natural resources and the growing market demand, palladium recovery from wastes such as spent catalysts is receiving increasing attention. Here, a silica-supported thiourea resin (SiPS-TU) was prepared and applied to separate Pd(II) from spent catalysts. The SiPS-TU was fabricated through in situ polymerization and post modification method using amorphous macroporous silica as the matrix. Experimental results suggested that the optimal acidity for the adsorption process was 0.1 M under selected range, and the uptake of SiPS-TU was affected by H+ and Cl-. The adsorbent showed rapid sorption kinetics with an equilibrium attained in 30 min, while more than 3 h was required for the commercial D840 resin. Column tests showed that SiPS-TU had excellent dynamic separation property for Pd(II) in continuous process. Around 215 bed volumes (430 mL) of Pd (II) solution could be effective treated by the SiPS-TU bed before breakthrough at 4 mL/min, while D840 resin bed was less effective under equivalent conditions (20 mL). In view of its satisfactory adsorption performances, palladium was successfully separated from the catalyst leaching solution by SiPS-TU. XPS spectra and DFT calculations indicated that the adsorption mechanism of SiPS-TU for Pd(II) mainly involved anion exchange and coordination. In conclusion, this study provides a feasible material for palladium recovery from practical leachate.