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Materials, Methods & Technologies, Volume 12, 2018

CRYSTALLIZATION OF THE FRAME-STRUCTURED TITANOSILICATE IN A HIGHLY ALKALINE MEDIUM
Lidia G. Gerasimova, Marina V. Maslova, Ekaterina S. Shchukina
Pages: 372-379
Published: 14 Sep 2018
Views: 623
Downloads: 167
Abstract: The conditions for the crystallization of the frame-structured titanosilicate with the use of a solution of Ti4+ sulfate with the addition of alkali in the form of liquid glass and sodium alkali to a pH of 12.5-13.5 have been studied. The optimum molar ratio of TiO2: SiO2 is 1: 4.5. To increase hydrolysis stability, partial reduction of initial solution has been fulfilled by electrochemical method with Ti4+ conversion to Ti3+ (content of Ti2O3 in the solution after reduction is 30–45 g/l). This expedient allows avoiding premature generation of a titanium amorphous phase and directing the process to creation of crystalline precipitate in a form of two structural modifications: trigonal (Na4(TiO)4(SiO4)3·6H2O) and cubic (Na3H(TiO)4(SiO4)3·4H2O); the precipitate crystallinity degree is 90–95%. Both structures are similar to the structure of the ivanyukite mineral. Crystallization proceeds under significant oversaturation system by alkaline components. Determined have been optimal conditions for titanium - siliceous precursor sol-gel obtaining and consequent hydrothermal transformation of the obtained gel to crystalline phase. It has been shown that the pore system (total volume of pores) of crystalline ivanyukite particles is approximately 1.5 times larger than that of X-ray amorphous samples and that it is mainly represented by mesopores of medium size, which are characterized by the most activity in sorption processes. Natrium and potassium ions situated in the ivanyukite frame space along with water provide high exchange velocity of cations absorption in sorption processes due to minimal diffusive obstacles. The reported preliminary data on sorption allow to describe the frame-structured crystalline alkaline titanosilicates as effective sorbents of one or two charge cations, as shown by the example of the sorption of strontium, caesium and non-ferrous metals.
Keywords: crystallization, frame-worked titanosilicates, synthesis, sol-gel process, sorbent, sorption processes
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