Development of quaternized polyethylenimine-cellulose fibers for fast recovery of Au(CN)₂^- in alkaline wastewater: Kinetics, isotherm, and thermodynamic study

The purpose of this study was to fabricate quaternized polyethylenimine-cellulose fibers (QPCFs) for the fast recovery of Au(I) from alkaline e-waste leachate. QPCFs were prepared by quaternizing PEI-modified cellulose fibers using a (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution. The maximum Au(I) adsorption capacity of QPCFs was estimated to be 109.87 ± 3.67 mg/g at pH 9.5 using the Langmuir model. The values of k₁ and k₂ calculated by the pseudo-first and pseudo-second-order models were 1.79 ± 0.15 min⁻¹ and 0.045 ± 0.003 g/mg min, respectively. Adsorption equilibrium was reached within 5 min. Thermodynamic studies revealed that the Au(I) adsorption process by the QPCFs was spontaneous (ΔG° < 0) and exothermic (ΔH° < 0). The characterization and adsorption mechanism of QPCFs were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectrometry. Quaternary amine sites were well developed in the QPCFs. Oxidation or reduction of adsorbed Au(I) was not observed. When QPCFs were applied to the solution obtained by bioleaching of e-waste, the recovery efficiencies of Au and Cu were 61.7 ± 3.1% and 11.1 ± 2.9%, respectively, indicating that QPCFs have Au selectivity. Therefore, QPCFs are suitable for actual wastewater applications because of their high adsorption performance and fast adsorption rate.