Synthesis of an ethylene diamine modified tannin polymer and recovery of gold(iii) ions from electronic wastes

Abstract

Electrical and electronic wastes are one of the biggest solid waste problems today and contain many recyclable materials such as gold. In this study, an adsorbent was synthesized by modifying the valonia tannin polymer with ethylenediamine to increase the electrostatic interaction. The obtained ethylenediamine-modified tannin polymer (ATAR) was characterized by Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) and thermogravimetric analysis (TGA), and it was confirmed that the amine group was successfully attached to the main structure within the scope of the synthesis. Under optimum conditions for gold(III) ion adsorption at varying pH, adsorbent mass, initial concentration, time, and temperature values, the adsorption performance of gold ion-containing solutions was investigated. Adsorption isotherm, kinetic and thermodynamic calculations were made from the data obtained from these experiments, and it was seen that the kinetic equation that best fits the experimental data is intraparticle diffusion and the best-fit isotherm equation is Langmuir's equation. According to the Langmuir isotherm, the monolayer saturation capacity of Au(III) ions on the ethylenediamine-modified tannin polymer was determined to be 1488.4 mg g⁻¹ at a temperature of 328 K. In the FTIR analysis performed after adsorption, it was determined that the ethylenediamine functional groups actively participated in the adsorption of Au(III) species and had an effect increasing the adsorption performance besides the polyphenolic groups. In X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, it was determined that almost all of the Au(III) ions were reduced to metallic gold after adsorption. It was observed that the adsorbent showed high performance for the adsorption of Au(III) from the real leaching solution obtained from electronic wastes.