Turning waste into wealth: efficient and rapid capture of gold from electronic waste with a thiourea functionalised magnetic core stirring rod adsorbent and its application for heterogeneous catalysis

Abstract

A method to selectively capture and separate gold from secondary resources is urgently needed to offset the increasing depletion of gold resources, and to meet the sustainable supply of precious metal resources and to reduce the environmental impact from toxic metals. Unfortunately, the lack of viable recycling techniques in developing countries results in extremely low precious metal recovery rates. In this work, highly selective and redox active adsorbent-thiourea functionalised magnetic core stirring rods (MCSR-ATU) were prepared for use in the recycling of gold in actual e-waste. Benefiting from the stirring motion of the rotating magnetic field, the MCSR-ATU exhibits an enhanced adsorption capacity and kinetics, reaching the maximum adsorption capacity (224.97 mg g⁻¹) for Au(III) at 30 min at a pH of 3.0 at 313 K. The adsorption process follows the pseudo-second order model and the Langmuir model. The distribution coefficient (K_d = 405 500 mL g⁻¹), the selection coefficient (αAu³⁺/Mⁿ⁺ = >8730) and the concentration coefficient (CF = 997.54 mL g⁻¹) reveal the remarkable selectivity of the MCSR-ATU for Au(III), which is mainly attributed to the strong Lewis soft-soft interaction and the redox reaction between Au(III) and the S-containing groups. Furthermore, the MCSR-ATU demonstrated excellent selectivity with a 94.66% gold capture rate even in actual samples, showing great potential for recycling gold from complex e-waste leaching solution with a low concentration of gold and a high level of interfering cations. It should be mentioned that the redox-active thiourea groups can convert, in situ, the captured Au(III) directly into Au(0), which can then be used for hydrogenation of 4-nitrophenol with excellent catalytic activity (the rate constant k = 2.394 min⁻¹) and reusability. This work provides a sustainable and circular strategy for the disposal of e-waste.