Moscow Technological University, Institute of Fine Chemical Technologies, Moscow, Russia:

M. M. Sadykova, Post-Graduate Student, e-mail: sadykova.mm@mail.ru
M. V. Tsygankova, Senior Researcher
G. V. Zimina, Leading Researсher

Lomonosov Moscow State University, Moscow, Russia:
F. M. Spiridonov, Assistant Professor

We investigated the range of chemical reactions, allowing the decomposition of anion [SiF₆]^2– with obtaining of single fluoric salts and silicates. Na₂CO₃, K₂CO₃, NH₄OH and H₂SO₄ were used as decomposition agents. We also investigated the interaction of Na₂SiF₆ with Na₂CO₃ in solution: NaF, SiO₂·nH₂O and CO₂ are its products. Usage of K₂CO₃ in similar conditions leads to formation of NaF and K₂SiF₆ as intermediate products. Re-processing of the obtained sediment with K₂CO₃ solution leads to formation of KF and SiO₂·nH₂O, removed by alkali washing. Usage of K₂CO₃ as an agent for Na₂SiF₆ decomposition requires its excess. Mixture of NaF and KF is the product of this interaction. Interaction of NH₄OH with Na₂SiF₆ leads to sedimentation of sodium fluoride and SiO₂·nH₂O. Only sodium fluoride reflexes stay on radiogram after washing the reaction product with alkali. Water phase contains the products of silicon fluoride interaction with water solution of ammonia: ammonium fluoride and silicon acid. Evaporation of water phase and processing of obtained sediment by sodium hydroxide solution leads to release of NH4F and its purification from SiO₂·nH₂O. Usage of concentrated sulfuric acid as decomposition agent leads to sedimentation of Na₃H(SO₄)₂ and release of HF and SiF₄ mixture in gaseous phase. We offered the possibility of the synthesis of fluorides of rare-earth metals and yttrium using ammonia fluoride (product of sodium hexafluorsilicate processing). Fluoride synthesis used the method, concluded in the interaction of solutions of neodymium and yttrium nitrates with ammonium fluoride solution. NdF₃ and NH₄F are formed as a result of vacuum thermal treatment (200 ^oC) of sediment, obtained from neodymium nitrate solution. The complex of NH₄Y₂F₇ was obtained using the yttrium nitrate as a result of vacuum thermal treatment of sediment (200 ^oC). We offered the principal flowsheet of sodium hexafluorsilicate processing with obtaining of marketable products NaF and LnF₃ (Ln — La – Sm) and intermediate products Na₂SiO₃ and NH₄NO₃, which may be used in chemical industry and fertilizer production.

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