Moscow State University of Fine Chemical Technologies named after M.V. Lomonosov, Moscow, Russia:

A. G. Smirnova, Researcher
M. V. Tsygankova, Senior Researcher, e-mail: tender-mitht@mail.ru
G. V. Zimina, Leading Researcher

JSC “Akron”, Veliky Novgorod, Russia:

I. I. Nikolaeva, Deputy Head of Central Chemical Laboratory

Nowadays, apatite concentrate is processed by two (HNO₃ and H₂SO₄) acid technological schemes. Phosphate concentrate of rare-earth elements (REE) with apatite-accompanying impurities is obtained as a result of apatite concentrate processing by HNO₃ technological scheme. The solubility values of REE phosphates and some impurities in nitric acid should be known for the purpose of development of the method of REE concentrate purifying from impurities and for its preparation to extraction process. Experimental data of dissolubility of rare-earth element (cerium, neodymium, dysprosium) phosphates and yttrium, calcium and titanium phosphates in nitric acid are given in this article. Dissolubility of both individual phosphates and phosphate mixture in 20 and 30% nitric acid solutions is investigated. It is noted that CeO₂ is oxidized and is obtained during the dissolution of cerium phosphate in nitric acid Ce (III). It is found that rare-earth element phosphate dissolubility value correlates with solubility of neodymium phosphate, which is the least soluble phosphate in mixture. Only hydrated phosphates are supersoluble, and salting-out process is observed during their mixture dissolution. Solubility of synthesized phosphates slightly depends on temperature (25–60 ^oС), which is determined by retention of hydrated phosphate structure. Light rare-earth element phosphates, as well as dysprosium and yttrium, are slightly dissolved in nitric acid after full evaporation.

Corresponding results were obtained within the State task of the Ministry of Education and Science of Russian Federation.

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