Recycling of Gold Using Anodic Electrochemical Deposition from Molten Salt Electrolyte

Abstract

Recycling of precious metals is becoming increasingly important as our living standards improve and electronic technologies advance. Conventional recycling processes involve multi-step hydrometallurgical treatments, in which precious metals are dissolved in aqueous solutions using a combination of strong complexing agents and oxidizing agents. However, these processes are time consuming and produce a large amount of hazardous liquid waste. Here, we present a new recycling process for Au, which is based on the direct anodic electrochemical deposition of anionic Au ions dissolved in a molten salt electrolyte. Moreover, this process is simple and does not generate harmful waste. In this process, Au is alloyed with Na to facilitate its dissolution in a molten mixture of NaCl–NaI. The existence of Au as an anionic species (Au n−) in the molten salt was proven and its anodic deposition (oxidation reaction) by application of an anodic current was demonstrated. During the anodic deposition of Au, Na is deposited on the cathode and can be recovered and reused in the process. It is expected that this electrodeposition technique to recycle Au from scrap metal could result in the development of a new environmentally friendly Au recycling process that does not generate hazardous waste.

New Process to Recycle Precious Metals Using Electrochemical Anodic Deposition

“…The metal R can be reused to form an alloy with precious metals in the scraps. This figure is adopted in an open access paper 76) .…”

“…V i e w 30) , (b) Au deposition from liquid ammonia 68) , (c) Te deposition from molten salt electrolyte 72) , (d) C deposition from molten salt electrolyte 74) , and (e) M (precious metal) deposition from molten salt electrolyte (our recent developed process 76) ).…”

“…Fig.4Previously reported anodic electrochemical deposition processes and our recently developed process. (a) Pb dissolution and deposition in liquid ammonia30) , (b) Au deposition from liquid ammonia68) , (c) Te deposition from molten salt electrolyte72) , (d) C deposition from molten salt electrolyte74) , and (e) M (precious metal) deposition from molten salt electrolyte (our recent developed process76) ).…”

“…Fig.5Schematic illustration of experimental set-up. This figure is adopted in an open access paper76) .…”

Quantitative, room‐temperature, solvent-free mechanochemical oxidation of elemental gold into organosoluble gold salts

“…[3][4][5] These methods ranges from hot aqua regia (3:1 mixture of concentrated hydrochloric or hydrobromic acid and nitric acid) at academic and small industrial scales, or on larger industrial scales, to molten alkali metal fusions, alkaline cyanidation, and high temperature chlorination. [6][7][8] All these methods produce water-soluble Au(I) or Au (III) species that are readily transformed back to elemental gold via chemical or thermal reduction or electrolysis. The recovery of these soluble gold salts in a simple, rapid, and sustainable fashion for direct use is hindered by the low volatility of water, and the water-soluble nature of excess reagents and byproducts.…”