Optimizing gold recovery from secondary resources : advanced physical separation and additively manufactured electrodes in electrochemical flow reactors

Abstract

This thesis presents optimized methods for gold recovery from electronic waste through the innovative use of additive manufacturing, commonly known as 3D printing, to enhance electrochemical reactor performance. Gold recovery from waste printed circuit boards is critical for sustainable metal recycling, given the increasing volumes of e-waste generated globally. By applying AM to fabricate high-performance electrochemical reactors, this research advances both the efficiency and environmental sustainability of precious metal recovery processes.

Central to this work is the development of a novel, noble-metal-free anode made from Ti- 6Al-4V alloy using 3D printing techniques. The anode, optimized for electrochemical applications in alkaline media (NaOH and KOH), was designed to improve surface area and performance in anodic reactions, a key requirement for efficient gold recovery. Electrochemical impedance and voltammetry analyses demonstrated that the 3D-printed scaffold structure provided a 42-fold increase in active surface area compared to traditional flat plate anodes, thereby enhancing charge transfer efficiency and minimizing passivation issues. The design allowed stable operation at potentials up to 5 V in nonflow cells. Additionally, Dynamic Electrochemical Impedance Spectroscopy was applied to model the behavior of electrode across varying conditions, revealing that a 1 M KOH solution was optimal in controlling anode corrosion and metal ion dissolution. The Ti- 6Al-4V 3D-printed anode thus offers a sustainable, cost-effective alternative to noble metals in alkaline electrochemical setups, particularly for the recovery of precious metals like gold.

Complementing the electrochemical approach, the thesis introduces an environmentally friendly, physical separation technique for concentrating precious metals (gold, palladium, and silver) from waste printed circuit boards. This method utilizes a series of steps, including crushing, grinding, and sieving, followed by hydrocyclone separation and a dilution-gravity method. Scanning electron microscopy was employed to characterize particle size and shape before and after the separation processes, with sieving effectively concentrating gold into finer fractions (<75 μm) while retaining copper in coarser fractions (70 wt.%). By optimizing hydrocyclone parameters at 3 bar pressure and an overflow-to-underflow outlet diameter ratio (Do/Du) of 6.5, the dilution-gravity method sink achieved a metal recovery efficiency of up to 87 wt.% for targeted fractions, with overall separation efficiencies of 75%, 78%, 64%, and 72% for gold, palladium, silver, and copper, respectively.

Future work will focus on further enhancing electrode performance by exploring postprocessing techniques. Additionally, potential limitations of the hydrocyclone process will be addressed to optimize its application in precious metal recovery. This research provides a comprehensive evaluation of additive manufacturing technology in producing high-efficiency electrochemical systems specifically designed for gold recovery and aims to advance scalable, sustainable solutions for precious metal recycling from e-waste.