An Efficient Leaching of Palladium from Spent Catalysts through Oxidation with Fe(III)

Abstract

Reclamation of spent catalysts for the efficient recovery of palladium (Pd) is gaining growing attention due to its scarcity and high supply risk. Currently Pd extraction from spent catalysts through an efficient, economical, and green method has remained a challenge. In this study, Fe3+ is utilized for leaching through oxidation of Pd in a mild condition. Before leaching, distillation was proposed to remove and recover the organics from spent catalysts. The effects of HCl concentration, Fe3+ concentration, NaCl concentration, leaching time, and temperature on the leaching efficiency of Pd were investigated to determine the optimum leaching conditions. The results show that Pd extraction and dissolution of Al2O3 increase with higher HCl concentration. The effect of NaCl on Pd leaching efficiency is significant at low acid concentration (2.0 mol/L HCl). The leaching efficiency was 99.5% for Pd under the following conditions: 2.0 mol/L HCl, 4.0 mol/L NaCl, and 0.67 mol/L Fe3+ at 80 °C for 90 min. The leaching kinetics fits best to the shrinking-core model of surface chemical reaction. The activation energy for the leaching of Pd was 47.6 kJ/mol. PdCl42− was selectively adsorbed by anion exchange resin. The filtrate containing adequate H+, Cl-, and Fe3+ was reused as leaching agent. Pd leaching efficiency was over 96% after five cycle times. This study provides an efficient process for recovery of Pd from spent catalysts.

Promising polymer-assisted extraction of palladium from supported catalysts in supercritical carbon dioxide

“…This weight ratio of polymer/catalyst of 1.2 is quite low compared to the amount of solvent used in hydrometallurgy where the liquid/solid ratio for leaching is typically in the range of 10 [48]. The extraction methods such as pyrometallurgical processes and various hydrometallurgical and leaching methods [49] have been reviewed for the recovery of precious metals from supported catalysts [50,51]. Among them, alternative methods such as supercritical fluids extraction (scCO2 and supercritical water), ionic liquid-assisted extraction [52], ultrasound-assisted pre-treatments for bioleaching [53] and microwave-assisted leaching [44] are considered to also have good potential to leach precious metals such as Pd.…”

Platinum nanoparticle decorated vertically aligned graphene screen-printed electrodes: electrochemical characterisation and exploration towards the hydrogen evolution reaction

“…In order to investigate whether the Pt/VG-SPEs exhibited poor stability due to the discharging of Pt 0 nanoparticles from the surface of the Pt/VG-SPEs, ICP-OES was utilised. 72,73 ICP-OES coupled with electrochemical stability measurements (chronoamperometry for 36 000 seconds at −0.1 V (vs. RHE) whilst the electrolyte (0.5 M H 2 SO 4 ) was flowed over the electrodes surface at 4 mL h −1 ), in order to assess whether the Pt 0 nanoparticles were detaching from the Pt/VG-SPEs surface, and thus causing the observed decrease in HER activity. Fig.…”

Tandem Synthesis of ϵ‐Caprolactam from Cyclohexanone by an Acidified Metal‐organic Framework

“…Such a problem had also been encountered by Shin et al ., where Pd/Sc(OTf) 3 /ionic liquid system was employed as the catalyst for the tandem synthesis of CPL from phenol [16] . To account for such “quenched” activity, we perform ICP‐MS (Table S3) analysis of the used catalyst and find that 40 % of Pd leaches from the MOF support after the first round of tandem catalysis, which could be induced by the strong acidic condition and chloride ions which facilitate the dissolving of Pd by coordination [27] . Currently, more endeavors are ongoing to resolve the Pd leaching issue.…”