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

Abstract

Recycling of thermoelectric materials: thermoelectric leg and copper plates removed by targeted oxidation or thermoelectric legs removed by high-intensity ultrasonication.

Concentrated Ionic Fluids: Is There a Difference Between Chloride‐Based Brines and Deep Eutectic Solvents?

“…If the etching rate follows a curved profile, then a combination of mass transport of the oxidising agent and the presence of insoluble species forming in high water environments is expected. [40] Etching rate data in Figure 4 shows that the oxidation of copper follows the predicted trend of greater etching rates in systems with lower viscosity. The two oxidising agents demonstrate similar etch rates despite their differences in redox potentials.…”

“…These metals were selected because they should proceed spontaneously in both aqueous and DES systems from their redox potentials. Additionally, the Cu(II) and Fe(III) species present in these chloride‐based DESs and brines are already well‐characterised via spectroscopy [3,13,20,39–40] . In both cases, each molar equivalent of oxidising agent will remove one electron from the target metal, so for a general process, x moles of Cu II or Fe III will be required per oxidation state number of the oxidised form of the target metal: $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr M+{xCu}^{II}\rightarrow {M}^{x+}+{xCu}^{I}\ \hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr M+{xFe}^{III}\rightarrow {M}^{x+}+{xFe}^{II}\ \hfill\cr}}$$$ …”

“…Additionally, the Cu(II) and Fe(III) species present in these chloride-based DESs and brines are already well-characterised via spectroscopy. [3,13,20,[39][40] In both cases, each molar equivalent of oxidising agent will remove one electron from the target metal, so for a general process, x moles of Cu II or Fe III will be required per oxidation state number of the oxidised form of the target metal:…”

Concentrated Ionic Fluids: Is There a Difference Between Chloride‐Based Brines and Deep Eutectic Solvents?

“…These metals were selected because they should proceed spontaneously in both aqueous and DES systems from their redox potentials. Additionally, the Cu(II) and Fe(III) species present in these chloride‐based DESs and brines are already well‐characterised via spectroscopy [3,13,20,39–40] . In both cases, each molar equivalent of oxidising agent will remove one electron from the target metal, so for a general process, x moles of Cu II or Fe III will be required per oxidation state number of the oxidised form of the target metal: $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr M+{xCu}^{II}\rightarrow {M}^{x+}+{xCu}^{I}\ \hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr M+{xFe}^{III}\rightarrow {M}^{x+}+{xFe}^{II}\ \hfill\cr}}$$$ …”

“…If the metal etching rate is related to chloride concentration, then it would be expected that etching should be fastest in the calcium chloride systems. If the etching rate follows a curved profile, then a combination of mass transport of the oxidising agent and the presence of insoluble species forming in high water environments is expected [40] …”