Abstract
The present paper is focused on the extraction of gold from high-grade e-waste, i.e., spent electronic connectors and plates, by leaching and electrowinning. These connectors are usually made up of an alloy covered by a layer of gold; sometimes, in some of them, a plastic part is also present. The applied leaching system consisted of an acid solution of diluted sulfuric acid (0.2 mol/L) with thiourea (20 g/L) as a reagent and ferric sulfate (21.8 g/L) as an oxidant. This system was applied on three different high-grade e-waste, namely: (1) Connectors with the partial gold-plated surface (Au concentration—1139 mg/kg); (2) different types of connectors with some of which with completely gold-plated surface (Au concentration—590 mg/kg); and (3) connectors and plates with the completely gold-plated surface (Au concentration—7900 mg/kg). Gold dissolution yields of 52, 94, and 49% were achieved from the first, second, and third samples, respectively. About 95% of Au recovery was achieved after 1.5 h of electrowinning at a current efficiency of only 4.06% and current consumption of 3.02 kWh/kg of Au from the leach solution of the third sample.
Highlights
The exponential growth of waste electronic and electric equipment (WEEE) has increased over the years, especially in the last twenty years
electronic equipment (EEE) contain several metals of interest, like base (Cu, Fe, Pb, Sn) and precious (Au, Ag, Pd) metals. The latter ones are abundant in motherboards, connectors, and integrated circuit pins. Many of these components are assembled in printed circuit boards (PCBs) that, contain around 70%wt of plastic-composite materials like epoxy resins, glass fibers, and brominated compounds used as flame retardants [2]
One study even tested this process on PCBs. 10 g/L sodium cyanide solution at 40 ◦C is able to dissolve 95% of gold in 15 min
Summary
The exponential growth of waste electronic and electric equipment (WEEE) has increased over the years, especially in the last twenty years. Other authors concentrated on base metals contained in PCBs, increasing the circular approach using spent solutions from PCB manufacturing processes to recover Cu, Sn, and Pb [25]. Brass is the alloy between copper and zinc and is normally plated either with gold, silver, or SUCOPLATE This alloy is used in the housings, outer conductors, and contact pins of connectors. Silver can be plated on base materials of most ferrous and non-ferrous metals and is found as a plated layer of the following connectors/cable components: conductors, contacts, and sleeves [27]. Coaxial connectors constituted by brass as the base material, gold as a plating material, and PTFE as insulating were chemically characterized and studied in order to identify a technical and economically feasible process to recover industrial interest metals, focusing on gold for his higher economic value. This study shows the preliminary results obtained in a wide experimental campaign whose aim is to design and optimize a recycling process for gold-rich materials
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