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Two-Step Ammoniation of By-Product Fluosilicic Acid to Produce High Quality Amorphous Silica
Minerals and Materials Processing Div., Korea Institute of Geology, Mining and Materials (KIGAM), 30 Kajung-dong, Yusung-ku, Taejon 305-350, Korea
Korean Journal of Chemical Engineering, July 2000, 17(4), 401-408(8), 10.1007/BF02706850
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Abstract
A two-step ammoniation was applied to neutralize the fluosilicic acid generated in the production of super-phosphate fertilizer, and to recover high-quality amorphous silica in the second step. A fluosilicic acid solution at 12.6% or 25.3 wt% H2SiF6 was reacted with aqueous ammonia, precipitating silica and subsequently leaving NH4F behind in the filtrate. Based on a fixed total of 7.2 moles of ammonia per mole of H2SiF6 (120% stoichiometry) ammonia at a molar ration of ammonia to H2SiF6 of 2 to 6 was charged in the first step and the balance of 5.2-1.2 in the second step in four combination sets of ammonia addition. At a combination of 3 and 4.2 molar ratios in the respective first and second steps, amorphous silica of 99.7% purity was readily produced in the second step while a majority of the impurities were precipitated in the first step. The two-step ammoniation was near completion despite a non-equilibrium reaction. However, rapid ammoniation favored the crystallization of ammonium fluosilicate. A sharp pH change occurred between 1.5 and 2.5 NH3/H2SiF6 molar ratios, indicating the rapid disappearance of SiF62- ion from the solution.
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Butler JN, "Ionic Equilibrium-A Mathematical Approach," Addison Wesley, Reading, Massachusetts (1964)
Chemical Society, Stability Constants of Metal-ion Complexes, London (1964)
Chieng PC, "Method of Production of High Purity Silica and Ammonium Fluoride," U.S. Patent 4,981,664 (1991)
Dragicevic T, Hraste M, Chem. Biochem. Eng. Q., 7(2), 89 (1993)
Dragicevic T, Hraste M, Chem. Biochem. Eng. Q., 8(3), 141 (1994)
Iler RK, "The Chemistry of Silica," John Wiley and Sons, New York (1979)
Kirk F, Othmer DF, "Silica in Encyclopedia of Chemical Technology," third ed., John Wiley & Sons, New York, 30 (1982)
Min BH, "Introducing a New Product of Fluosilicic Acid for Use in Preventing Teeth from Decay," a News Report of Joongang Ilbo, Seoul, Feb. 18 (1997)
Nickerson JD, Burkert GM, "Silica Pigments from Fluosilicic Acid," U.S. Pat. 3,271,107 (1966)
Private Conversation with G.P. Panasyuk of N.S. Kurnakov Inst. of General and Inorg. Chem., Moscow, March 29 (1998)
Scholten JJF, van Montfoort A, "Process for Preparing Pure Silicon Dioxide Having High Mechanical Strength, as well as Silicon Dioxide Obtained by Applying This Process," European Patent 94,138 (1983)
Spijker R, "Process for the Preparation of Pure Silicon Dioxide," European Patent 94,139 (1983)
Thiessen PA, Koerner O, Z. Anorg. Allg. Chem., 189, 171 (1930)
Tsugeno M, Takako Y, Kubo M, Yuri Y, "Silica Particles and Process for Producing the Same," European Patent 435,513 (1991)
Weast RC, Astle MJ, "CRC Handbook of Chem. and Physics," 62nd ed., CRC Press, Inc., Boca Raton, Florida (1981)
Yoon YR, Ju WH, Chem. Ind. Technol., 16(2), 98 (1998)
