Selective Recovery of Gold from Aqueous Media Using Magnetic PEG-Crosslinked Polystyrene

PEG-cross-linked and triethylenetetramine (TETA)-terminated polystyrene chains were formed on the surface of magnetic nanoparticles through atom transfer radical polymerization (ATRP). The prepared organic-inorganic hybrid material (denoted as MNP-PEGPS-L) was used to adsorb Au(III) ions from aqueous solutions. The MNP-PEGPS-L adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and vibrating-sample magnetometry (VSM). BET measurements showed that the particles have a porous structure, and their specific surface area was found to be 29.13 m²·g^-1. Dynamic light scattering (DLS) analysis revealed that the hydrodynamic diameter distribution of the adsorbent particles follows a bimodal pattern, with two peaks appearing at 705 nm and 4087 nm. The particles in an aqueous solution with pH = 3 exhibited the highest zeta potential value (+22 mV) and, therefore, showed greater resistance to agglomeration. In adsorption studies, the equilibrium concentrations of ions (C_e values) were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The equilibrium adsorption capacity (Q_e) was optimized in Au(III)-containing solutions at a pH of 3, an adsorbent dose of 0.2 mg·mL^-1, a contact time of 60 min, and a temperature of 25 °C. Examination of the adsorption kinetics indicated that the adsorption of Au(III) ions occurs via chemisorption. The maximum adsorption capacity (Q_max) obtained from the Langmuir isotherm model (monolayer adsorption), was measured to be approximately 280 mg·g^-1. Additionally, the study of the thermodynamics of adsorption demonstrated that the adsorption phenomenon is endothermic and occurs spontaneously. Overall, the prepared magnetic polymer adsorbent showed promising results in the recovery of gold ions from aqueous solutions due to its high hydrophilicity, high porosity, and excellent recyclability.