Selective sorption-based separation of palladium from process solutions using chemically modified silica

This study focuses on investigating the possibility of selective separation of palladium (II) from solutions containing non-ferrous metals and iron by sorption onto chemically modified silica. The study used both individual (single-metal) and model multicomponent solutions. The sorbents included silicas functionalized with iminodiacetic acid (IDA-D), phosphonic acid (PA-D), and aminomethylphosphonic acid (AMPA-D) groups, as well as a well-known chemically modified silica bearing grafted γ-aminopropyltriethoxysilane (APTES) groups at a grafting density of 1.63 mmol/g. Under static conditions at room temperature, the time required to reach equilibrium sorption values for Cu(II), Ni(II), and Fe(III) ions – typically present in process solutions – was determined for the IDA-D, PA-D, and AMPA-D sorbents. Sorption dependencies on hydrochloric acid concentration were established for these metal ions. For IDA-D, the effect of halide ion concentration on sorption was also studied. It was shown that these ions are sorbed in weakly acidic media but not in 1–2 M HCl, and that sorption capacity decreases in the order: IDA-D > AMPA-D > PA-D. However, the conclusion that quantitative separation of Pd(II) from base metal ions could be achieved using these complexing sorbents (exemplified by IDA-D) under dynamic conditions was not confirmed. The sorption behavior of Pd(II), Cu(II), and Al(III) ions was also examined under static and dynamic conditions using the APTES-functionalized silica and chloride and chloride-bromide solutions, including model solutions simulating leach liquors generated from the treatment of spent catalysts for low-temperature carbon monoxide oxidation. These solutions contained 0.004–0.015 mol/L Pd, 0.014–0.049 mol/L Cu, and 0.015–0.060 mol/L Al. The results demonstrated the feasibility of selectively separating Pd(II) from leach solutions of spent catalysts using this sorbent. A processing scheme was proposed, comprising sorption from 0.1 M HCl, water rinsing of the loaded sorbent, and elution of Pd(II) with a 5 % thiourea solution in 0.1 M HCl. It was shown that separation of palladium from non-ferrous metals occurs already at the sorption and washing stages.