Recovery of Au(III) from electronic waste using solid phase extraction based on a magnetic nanobiocomposite, OCBs@Fe3O4@UiO-66-SH.

A zirconium-based MOF (UiO-66-NH₂) with thiol groups attached to its magnetic corn surface was used for the adsorption and extraction of Au(III) from electronic waste. The composite was characterized using FTIR, XRD, FESEM, TGA, and BET techniques. The effects of the temperature, adsorption period, and pH on Au(III) adsorption were investigated. The optimal conditions to achieve the maximum adsorption of Au(III) on the adsorbent surface were pH 6.0, 50◦C, 40 min, and 10 mg of adsorbent. Moreover, oxidized magnetic corncobs functionalized with thiol (OCBs@Fe₃O₄@UiO-66-SH) showed a notable ability to adsorb Au(III), with a capacity of 1587 mg/g. With the mass ratios of Au(III) to competing ions (Mg, Mn, Cu, Zn, Co, Cd, and Ni) fixed at 1:1 or extended to 1:5, this adsorbent prefers Au(III) ions while showing negligible adsorption to other ions. This study validated a technique to extract Au (III) from various electronic waste samples, achieving high recoveries  (95.30% to 104.75%), demonstrating its effectiveness and lack of matrix interference. Examining various isotherm and kinetic models demonstrated that the Langmuir and pseudo-first-order models could effectively interpret the experimental and kinetic data. Thermodynamic calculations showed that the adsorption process is endothermic and occurs spontaneously. The optimal utilization of renewable waste as an adsorbent base, high adsorption capacity, recoverability, and reusability owing to its magnetic properties, high recovery rate of Au(III) from electronic matrices, and highly selective adsorption in the presence of competing ions are among the advantages of this adsorbent. Together, these features highlight the novelty of the present study.