Amberlite XAD-7 impregnated with Cyphos IL-101 (tetraalkylphosphonium ionic liquid) for Pd(II) recovery from HCl solutions

Abstract

Cyphos IL-101 ionic liquid (IL; tetradecyl(trihexyl)phosphonium chloride) was immobilized in Amberlite XAD-7 for the preparation of an extractant impregnated resin (EIR) that was used for Pd(II) sorption from HCl solutions. Chloro-palladate anionic species are bound to the EIR by electrostatic/anion exchange mechanism between anionic species and phosphonium cation (IL). Maximum sorption capacity increases with extractant loading and depends on HCl concentration reaching values up to 71mg Pdg−1 EIR for an EIR with 401mg ILg−1 EIR, in 0.5M HCl solutions. Uptake kinetics are controlled by the resistance to intraparticle diffusion (effective diffusivity varying in the range 1×10−11 to 20×10−11m2min−1) as confirmed by the limited impact of agitation speed (negligible resistance to film diffusion). IL loading is a key parameter since it controls the filling of resin porous network and consequently the mass transfer properties: diffusivity in the extractant phase is reduced compared to diffusivity in water. Increasing IL loading increases sorption capacity but induces supplementary limitations to intraparticle diffusion. Increasing temperature decreases IL viscosity, which, in turn, enhances diffusion in this extractant phase. Nitric acid and thiourea in hydrochloric acid solutions allows complete desorption of Pd(II) from loaded EIR. The resin can be recycled for at least five cycles maintaining high sorption and desorption efficiencies.