State Research and Design Institute of Rare Metal Industry (JSC Giredmet), Moscow, Russia

M. S. Kuznetsov, Head of Laboratory, e-mail: gradan@mail.ru
K. S. Zaramenskikh, Leading Researcher, Candidate of Chemical Sciences, e-mail: KSZaramenskikh@rosatom.ru
S. M. Pilyushko, 1^st Category Process Engineer, e-mail: vorpat2402@bk.ru
A. A. Pakhomova, Research Project Engineer, e-mail: m1808458@edu.misis.ru

The process of reduction of metallic thallium from its halides was studied and optimized. As a result of preliminary experiments, various methods of thallium reduction were tested and improved. The metallothermic method demonstrated significant advantages and ensured high productivity, the highest percentage of the target product yield and the purity of the obtained material. The main objective of the work is to confirm the possibility of obtaining metallic thallium from its halides by the metallothermic method, which consists in the reduction of thallium halide crystals with a reducing metal at an elevated temperature, and its subsequent use for the direct synthesis of thallium nitrate by the hydrochemical method with an assessment of the quality of the resulting product for compliance with the requirements for the material for use in the electronics industry as an additive to the electrolyte, as well as for obtaining relevant thallium halides used in optics. To carry out the reaction according to the equations of metallothermic reduction of thallium from its halides, an installation equipped with a vertical electric resistance furnace was used. At the initial stage, the experiments were carried out under different conditions: in an argon atmosphere and in a vacuum, at heating temperatures of 320 and 400 oC, at heating rates of 3 and 5 ^oC/min, in a glass ampoule and a glassy carbon beaker. An experiment was also carried out by placing the material in a preheated furnace. It was experimentally established that the metallothermic reduction process is most effective in an argon atmosphere when heated to 340 ^oC at a rate of 3 ^oC/min. The next stage — a comparison of reducing metals to determine the optimal one, was carried out under the previously established conditions. Magnesium, aluminum and calcium were considered as reducing metals. A theoretical calculation of the product mass was carried out, the practically obtained mass was measured experimentally. Based on these data, the pro duct yield was calculated. The highest yield of metallic thallium (99%) was obtained when using aluminum as a reducing metal in an amount exceeding the stoichiometric amount by 5%.
The authors express their gratitude to O. V. Soskov and A. Yu. Demina for their participation in the theoretical and experimental studies.

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