Baikov Institute of Metallurgy and Materials Science of Russian Academy of Sciences (IMET RAS):

M. S. Kuznetsov, Head of Laboratory, e-mail: gradan@mail.ru
K. S. Zaramenskykh, Lead Researcher, Candidate of Chemical Sciences, e-mail: KSZaramenskikh@rosatom.ru
O. V. Soskov, Research Intern

Laboratory for High-Purity Halide Materials for Optics, State Research and Design Institute of Rare Metals Industry Giredmet, Moscow, Russia:

A. Yu. Demina, Researcher Engineer of Laboratory of Ceramic Сomposite Мaterials (No 20), e-mail: deminaanna97@gmail.com

The focus of this paper is on analyzing different techniques and finding an optimum one to produce thallium from unused TlCl material. The recovered thallium can be used in a production laboratory for synthesis of muchin-demand optical materials – mainly, KRS-5 crystals of the TlBr – TlI composition. The authors built special units and developed processes for electrolysis of solutions, electrolysis of melts, as well as pyro-hydrochemical and metallothermic synthesis. The paper demonstrates the applicability of the above processes to produce thallium from thallium chloride. Through experiments, it was established that the application of electrolysis on the available equipment is associated with a high energy consumption, whereas the application of pyro-hydrochemical process would require that certain toxic substance requirements were met. Hence, metallothermic processprovides the quickest and most efficient and cost-saving technique. It does not require any sophisticated equipment or high energy cost in terms of the equivalent amount of product and it offers high performance. Thus, 84.1 g of thallium were produced in one cycle with the yield of 97.9%. Metal produced by metallothermic synthesis is low on impurities (According to X-ray fluorescence analysis, the concentration of the main component is 99.3%.). Moreover, most impurities are contained in the reducing metal and its salts, which can be easily removed by vacuum distillation during further refining stages. Such impurities have almost no impact on the infrared absorption spectrum of KRS-5 crystals grown from this optical material. The metallothermic process does not produce any liquid or solid waste that would contain thallium and therefore require any additional cost for their recycling or disposal.
The authors would like to thank senior researcher I. S. Lisitskiy and lead process engineer M. V. Morozov for their contribution to this paper.

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