Gold recovery from HCl solutions using Cyphos IL-101 (a quaternary phosphonium ionic liquid) immobilized in biopolymer capsules

Tetraalkyl phosphonium chloride (Cyphos IL-101), an ionic liquid (IL), was tested for gold recovery from HCl solutions: first in liquid/liquid extraction systems (using toluene and hexane as solvent) and in a second step, after being immobilized in a biopolymer composite matrix. SEM-EDAX analysis was used for the characterization of the resins. The sorption capacity reached up to 140mgAu(III)g(-1) in 1M HCl solutions. Base metals that do not form anionic chlorocomplexes and nitrate or chloride ions (at 5gL(-1)) did not interfere with Au(III) binding. Gold binding probably occurs through the interaction of R3R'P+ with AuCl4-. The kinetics of sorption was carried out varying agitation speed, metal concentration, IL content, and resin drying. Intraparticle diffusion played an important role on the control of sorption kinetics. Gold could be desorbed from the loaded IL-impregnated resin using thiourea (in HCl solutions). The resin could be re-used for at least 4 cycles. The resins are specially adapted for the recovery of gold from low metal concentrations.