Electrochemically Mediated Recovery and Purification of Gold for Sustainable Mining and Electronic Waste Recycling

Abstract

Rapid growth of the industrial and electronics sectors has led to an ever-mounting demand for gold. Gold mining can be highly resource-intensive, due to the need for selective gold separations from dilute streams, in the presence of multicomponent metallic species. The development of efficient gold separation technologies is critical to mitigate the declining gold purity in mined ores and to meet the need for electronic waste recycling. We propose a modular electrochemical separation platform via metallopolymer-functionalized electrodes to selectively recover and concentrate gold from electronic waste and simulated mining streams. Polyvinylferrocene (PVF) redox-electrodes captured cyano-gold with 10-fold higher uptake (>200 mg/g) than conventional activated carbon and, importantly, demonstrated an exceptional separation factor >20 for gold vs competing metals in mining and electronic waste, including silver, copper, nickel, and iron. Rapid gold uptake was observed within 5 min, and electrochemically mediated release and concentration achieved a remarkable up-concentration ratio of 20:1. Electrochemical recycling of gold from real-world electronic waste (e.g., RAM boards) highlighted our system as a drop-in replacement for activated carbon sorbent, with a recovery efficiency 99% and superior technoeconomics, leading to a 94% cost reduction and over 90% final gold purity. Redox-mediated electrochemical separations can be a promising avenue for the energy-efficient, sustainable, and process-intensified gold recovery and recycling.

Molecularly Selective Polymer Interfaces for Electrochemical Separations

“…Redox-responsive homopolymers have gained attention in electrochemical separation owing to their simple yet robust polymer structures consisting of repetitive single redox-responsive monomer units. Free radical polymerization and electropolymerization have been widely used for the synthesis of redox-active polymers for electrochemical separation due to their facile synthesis. ,, In addition, the reversible addition–fragmentation chain transfer (RAFT) method is frequently employed as a polymerization technique to precisely control the molecular weight distribution of polymers. ,, Redox-active homopolymers can be classified into two categories based on the arrangement of the redox-active units within their chemical structures, as depicted in Figure : (i) incorporation of the redox-active center into the polymer backbone ,− and (ii) attachment of the redox-active unit as a pendant group. ,,,,,,− …”

“…While incorporating the redox-active unit into the main chain of metallopolymers allows for robust electrochemical responsive electrosorption and release, it can present challenges in modulating the strength of electrostatic interactions and maintaining polymer stability. − Besides, the modification of main-chain polymers can often increases the complexity of the synthesis. On the other hand, when a redox-active unit such as ferrocene, ,,,,− cobaltocene, , or TEMPO , is attached as a pendant group of polymers, the electrochemical activity or selectivity of redox-active metallopolymers can be effectively modulated based on the electrochemical and physicochemical properties of the non-redox-active pendant group while enhancing the polymer stability. , This approach also allows for more facile and modular synthesis routes for the creation of the polymer itself.…”

“…The systematic design and investigation of redox-active polymers have enabled unprecedented anion selectivity in electrosorption platforms, going beyond the capabilities of conventional intercalating and reactive materials. Prior work on crystalline electroactive materials (e.g., LiMnO 2 and Prussian blue analogues) as well as reactive electrode materials (e.g., Ag/AgCl and Bi/BiOCl) has been predominantly centered around cation-selective separations, − and in the few instances when anions were targeted, they were mostly limited to chloride. , Switchable redox-active polymers have dramatically expanded the target species scope, enabling the selective removal of toxic anionic species such as per- and polyfluoroalkyl substances (PFAS), − the recovery of valuable anionic species such as gold from electronic waste, and also the recycling of homogeneous catalysts from chemical processes . Upon the oxidation of redox-active polymers, anions can be selectively captured via specific intermolecular interactions and subsequently released upon the reduction of the redox moieties.…”

Kinetic and Thermodynamic Studies of Precious Metals Sorption on Impregnated Lewatit VP OC 1026 from Chloride Solutions

“…Electrochemical processes can be also employed for their recovery. A modular electrochemical separation platform via metallopolymer‐functionalized electrodes was applied to recover gold from electronic waste and simulated mining streams [8] . Moreover, various types of adsorbents are also common.…”

“…A modular electrochemical separation platform via metallopolymer-functionalized electrodes was applied to recover gold from electronic waste and simulated mining streams. [8] Moreover, various types of adsorbents are also common. An adsorbent obtained by crosslinking polyethylenimine with 5,5-dithiodisalicylic acid was used for recovery of gold and palladium ions.…”