Selective adsorption and recovery of precious metal ions from water and metallurgical slag by polymer brush graphene–polyurethane composite

Abstract

Achieving flexible composite materials with high selectivity and adsorption capacity for gold and platinum group elements remains a challenging endeavor. In this study, a series of polyurethane foam (PUF) composites was synthesized using PUF as matrix. Scanning electron microscopy, Raman spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy survey spectra, contact angle, and Brunauer–Emmett–Teller specific surface area were used for characterization. Solid-phase extraction of precious metal ions from acidic chloride solutions was performed via batch experiments. Results showed that cysteine polymer brush-grafted PDA@GPUF (poly-Cys-g-PDA@GPUF) contained a high concentration of hydroxyl, imine, and thiol groups on the surface, which endowed the composite with high separation performance for Au(III), Pd(II), Pt(IV), and Ru(III). Batch adsorption studies for poly-Cys-g-PDA@GPUF were performed with various parameters, such as solution pH, contact time, initial metal ion concentration, and temperature. The maximum adsorption capacity was found at pH 0 for Au(III), Pd(II), and Pt(IV) and at pH 3.0 for Ru(III). Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models were applied to analyze the experimental data. The best interpretation for the experimental data was given by the Langmuir isotherm. The effects of solution acidity, contact time, initial concentration of metal ions, temperature, coexisting ions, and recovery behavior were reported. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to determine the kinetic data. The pseudo-second-order kinetic model fitted the experimental data. Thermodynamic parameters, such as enthalpy (ΔH0), Gibbs' free energy (ΔG0), and entropy (ΔS0), were calculated for poly-Cys-g-PDA@GPUF. Poly-Cys-g-PDA@GPUF as solid-phase extractant was successfully applied for the preconcentration of Au(III), Pd(II), Pt(IV), and Ru(III) in aqueous samples, metallurgical slag, and certified sample with satisfactory results.