Targeted recovery of metals from thermoelectric generators (TEGs) using chloride brines and ultrasound

Abstract

Recovery of elemental copper, bismuth, tellurium, antimony and tin from thermoelectric generators (TEGs) is vital to recover the high content of critical metals and potential risk of environmental pollution as a result of incorrect disposal of TEGs and to enable the circular economy. In this work, aqueous choline chloride and calcium chloride hexahydrate brines were characterised and used in combination with copper(II) as an oxidising agent to leach copper and tin from TEGs. This permitted the Bi_2−xSb_xTe₃ legs to be readily separated from the ceramic substrates by filtration. It was shown that at low chloride content, surface passivation and solubility of the oxidised species were the limiting factors towards oxidation, whereas solvent viscosity (mass transport) was the limiting factor at high chloride content. The copper(II) species formed in the different brines were determined via UV-vis spectroscopy. The redox potentials of the oxidising species were found to be significantly altered by choline chloride content, but not so much by calcium chloride hexahydrate content, suggesting variation in chloride activity within the different brines. The developed approach has been shown to be a viable and scalable method to recover high value critical metals from e-waste containing TEGs.