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 (E A = 933.536 J/mol) was more successful than precipitation by sodium chloride(E A = 7452.405 J/mol). Analyses performed on the precipitates highlighted compositions that are essential and useful constituents in the cement industry.
Highlights
IntroductionIn Senegal, fluosilicic acid (as a by-product of phosphoric acid production) is discharged into the sea
In Senegal, fluosilicic acid is discharged into the sea
We aimed to work-up an aqueous fluosilicic acid for the production of caustic soda in an 8% solution and a mixture of calcium fluoride and silica by using sodium fluosilicate. This fluosilicate is attacked by lime to produce caustic soda and a precipitated mixture which can be useful in the production of white cement
Summary
In Senegal, fluosilicic acid (as a by-product of phosphoric acid production) is discharged into the sea. We aimed to work-up an aqueous fluosilicic acid for the production of caustic soda in an 8% solution and a mixture of calcium fluoride and silica by using sodium fluosilicate. This fluosilicate is attacked by lime to produce caustic soda and a precipitated mixture which can be useful in the production of white cement. Several articles describe the manufacturing processes of sodium fluoride,[1] sodium hydroxide,[2] hydrochloric acid,[3] aluminium fluoride and mixtures of calcium fluoride and silica usable in the cement industry.[4 ] Theory
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