Chemical separation of p- and n-type thermoelectric chips from waste thermoelectric module and valorization through synthesis of Bi2Te3nanopowder: a sustainable process for synthesis of thermoelectric materials

What is it about?

A laboratory scale sustainable process for chemical separation of p-and-n-type thermoelectric chips from thermoelectric module and valorization through the synthesis of Bi2Te3 thermoelectric nanopowder is developed. Both the p-and-n-type chips of the thermoelectric modules are separated from the substrate through thermal treatment followed by chemical dissolution. Residual solder from separated chips is selectively dissolved by HCl. From the separated chips, n-type chips are selectively separated from p-type chips through HNO3 dissolution. The p-type chips are passive for dissolution are recovered without degradation, which can be reused for the thermoelectric modules. From the dissolved substance of n-type chips, semiconductor grade, 20 nm, and 99.999% pure thermoelectric Bi2Te3 nanopowder is synthesized through wet chemical reduction using hydrazine, which can be used for manufacturing of the n-type of chips. The dissolved solders are precipitated as Sn(OH)4 and Pb(OH)2 using NaOH, which can be disposed of without harming the environment. As the process uses the hydrazine, a green solvent as reductant, and mineral acids, the selective separation followed by recovery of the p-and-n-type chips can be a sustainable green process. The developed process is a close-loop, cost effective, and environmentally friendly valorization technology for synthesis of energy harvesting thermoelectric material synthesis.

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Why is it important?

Separation of p-and n-type thermoelectric chips from the waste thermoelectric module of the semiconductor industry has been achieved through a combination of a series of processes, like; thermal treatment, dissolution of soldering material, selective dissolution of n-type semiconductor material followed by synthesis of n-type of semiconductor material by the wet chemical reduction process. The selective dissolution characteristics of Pb and Sn in the HCl, Bi and Te in the HNO3, and passivity of Bi0.5Sb1.5Te3 material have played important roles for complete separation of p-type, n-type and soldering materials from the waste. The dissolved soldering materials can be precipitated as Sn(OH)4 and Pb(OH)2 using NaOH. The metal hydroxide precipitate successfully can be disposed of without harming the environment. As in the process only cheaper nonhazardous chemicals and hydrazine a green solvent has been used, the separation followed by synthesis process can be a sustainable green process. As the separated p-type of chips has not been degraded from original quality, shape, and structure, it can be used directly for manufacturing of the thermoelectric module. The synthesized Bi2Te3 nanopowder by the wet chemical reduction reaction was 20 nm, can be directly used for manufacturing of the n-type thermoelectric chips in the semiconductor industry.

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