Research Articles

Processes for working-up an aqueous fluosilicic acid solution

Alpha O. Toure, Falilou M. Sambe, Démo Koita, Codou M.G. Diop, Oumar Sock
South African Journal of Science | Vol 108, No 11/12 | a919 | DOI: https://doi.org/10.4102/sajs.v108i11/12.919 | © 2012 Alpha O. Toure, Falilou M. Sambe, Démo Koita, Codou M.G. Diop, Oumar Sock | This work is licensed under CC Attribution 4.0
Submitted: 07 September 2011 | Published: 02 November 2012

About the author(s)

Alpha O. Toure, Cheikh Anta Diop University of Dakar, Polytechnic Upper School, Laboratory of Electrochemistry and Membrane Process, Dakar, Senegal
Falilou M. Sambe, Cheikh Anta Diop University of Dakar, Polytechnic Upper School, Laboratory of Electrochemistry and Membrane Process, Dakar, Senegal
Démo Koita, Cheikh Anta Diop University of Dakar, Polytechnic Upper School, Laboratory of Electrochemistry and Membrane Process, Dakar, Senegal
Codou M.G. Diop, Cheikh Anta Diop University of Dakar, Polytechnic Upper School, Laboratory of Electrochemistry and Membrane Process, Dakar, Senegal
Oumar Sock, Cheikh Anta Diop University of Dakar, Polytechnic Upper School, Laboratory of Electrochemistry and Membrane Process, Dakar, Senegal


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Abstract

Aqueous fluosilicic acid solutions were once considered to be only adverse by-products of phosphoric acid production, which required treatment to prevent ecosystem destruction when discharged into the sea. However, a range of chemicals can be generated by the transformation of this industrial waste product. Through experiments undertaken in the laboratory, we have shown the possibility of caustic soda production. Volumetric analysis showed caustic soda to be present as a 6% – 7% solution with yields of about 70% – 80% by weight. Two processes were investigated for the caustification of sodium fluoride, using different precipitates: sodium chloride and ethanol and are described by modelling caustification curves. The activation energies of precipitation determined by semi-empirical correlations showed that precipitation by ethanol (EA = 933.536 J/mol) was more successful than precipitation by sodium chloride(EA = 7452.405 J/mol). Analyses performed on the precipitates highlighted compositions that are essential and useful constituents in the cement industry.


Keywords

caustic soda; caustification; ethanol; precipitation; sodium chloride

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