Solubility of cerium in melts (NaCl–KCl)–CeCl₃ at a temperature of 850°С

Abstract

Molten mixtures of chlorides of alkali and polyvalent metals have found wide application in the electrolytic refining of a number of metals, such as plutonium. The current efficiency in such processes depends on many factors, among which the most significant are the corrosion resistance of products made of ceramic materials in contact with melts, as well as the solubility of the metal to be purified in melts containing its chloride. Thus, when carrying out refining electrolysis to purify liquid cerium in a molten equimolar mixture of sodium and potassium chlorides with an initial concentration of cerium trichloride of 3 mol. %, it was possible to obtain a maximum current efficiency of 63%. It was shown that a significant part of the losses is due to the release of alkali metal and the dissolution of metallic cerium. There are no data on the solubility of a (polyvalent) metal in molten salt compositions containing its chloride in the literature. Therefore, the purpose of this work was to determine the solubility of metallic cerium in the (NaCl–KCl)–CeCl₃ melt at an electrolysis temperature of 850°C. An installation was created to determine the solubility of cerium with sampling of the salt melt without access to oxidizers. This was achieved by pouring the salt melt from the beaker, where the melt was saturated with cerium, into an external beaker without opening the device. It is shown that the solubility of cerium drops sharply with a decrease in the concentration of cerium trichloride and can be approximated by the equation: NCe = 1.67∙10–5∙x3–9.62∙10–4∙x2 + 4.50∙10–2∙x, NCe in mol. %, and x is the concentration of cerium trichloride in the melt in mol. %.