THE METHOD OF CONVERTING SIF4 IN THE OFF-GASES OF PHOSPHATE ROCK ACIDULATION TO UTILIZABLE PRODUCTS WHICH COMPRISES ABSORBING THE SIF4 IN WATER TO FORM H2SIF6 OF ABOUT 20-30% CONCENTRATION, FILTERING SAID SOLUTION TO REMOVE INSOLUBLE IMPURITIES, SLOWLY AND WITH VIGOROUS STIRRING ADDING TO THE FILTERED H2SIF6 A STOICHIOMETRIC QUANTITY OF KCI IN CONCENTRATED FORM, THEREBY FORMING A SLURRY OF POTASSIUM FLUOSILICATE IN HCI SOLUTION, DISTILLING AND RECOVERING THE HCI, ADDING TO THE RESIDUE A STOICHIOMETRIC AMOUNT OF NAOH, THEREBY YIELDING A THICK SLURRY OF NAF IN POTASSIUM SILICATE SOLUTION, FILTERING THE SLURRY AND WASHING THE RESIDUE TO OBTAIN SUBSTANTIALLY PURE NAF, CONCENTRATING THE FILTRATE BY EVAPORATION AT AN ELEVATED TEMPERATURE TO CYRSTALLIZE ADDITIONAL NAF, COOLING AND FILTERING THE CONCENTRATE TO REMOVE ADDITIONAL NAF, CONTINUING THE ALTERNATE CONCENTRATING AND FILTERING STEPS UNTIL POTASSIUM SILICATE OF DESIRED CONCENTRATION IS OBTAINED, WHEREBY THERE ARE OBTAINED SUBSTANTIALLY PURE POTASSIUM SILICATE, HYDROCHLORIC ACID AND SODIUM FLUORIDE. All of the fluoride chemicals used in the U.S. for water fluoridation, sodium fluoride, sodium fluorosilicate, and fluorosilicic acid, are useful byproducts of the phosphate fertilizer industry. 3,021,193 February 13, 1962 George L. Cunningham It is hereby certified that error appears in the above numbered petent requiring correction and that the said Letters Patent should read as corrected below. 1. In accordance with the present invention, the silicon tetrafiuoridecontaining gas is scrubbed in an adsorption tower with water to recover fiuosilicic acid, which is later treated with potassium chloride to yield a slurry of potassium silicofiuoride in HCl solution. The best yields of product are of the order of the loss being accounted for by product in solution in the waste water and finely divided product suspended in the waste water. Although the solubility of sodium fluoride in the present solution decreases as the concentration of potassium silicate increases, the viscosity of the solution increases considerably so that the solid removed by filtration is contaminated with adhering mother liquor. The evolved gases are condensed to yield 224.9 parts of 17.83% hydrochloric acid solution containing only a trace of fluorine and silica. At the endof this step, the recovery of sodium fluoride would amount to 88.88% and the composition of the remaining mother liquor approximately 84.6% potassium silicate and 15.3 sodium fluoride. In addition, it eliminates the necessity for washing subsequently obtained batches of sodium fluoride crystals. This acid contains a considerable amount of suspended silica, which has no utility in the present invention. The reaction mass can be heated to relatively high temperatures without appreciable increase in solubility of the solid potassium silicofluoride. The percent solids in the slurry prior to filtration would be approximately 4.0%. I have discovered a process whereby it is possible to obtain a number of utilizable products in the recovery of silicon tetrafluoride from acidulation gases and, at the same time, rid the off-gases of this noxious material. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM, Halides of sodium, potassium or alkali metals in general, Chemically treating phosphorite and obtaining separate products of fluorine and of phosphorus, Methods for prevention of surface water contamination and air pollution by fluorine compounds from phosphate plants, Process for production of potassium sulfate and hydrochloric acid, Comprehensive utilization method of acid sludge generated in acid making by smelting fume, Method of alkali fluosilicates transformation into their corresponding fluorides, and application to the preparation of sodium fluoride and sodium silioate, A method of making inorganic or organic acids, Process for the preparation of sodium fluoride from silico-fluoride sodium, Recovery of lithium compounds from brines, Process for the purification of electrolysis brine, Method for producing pure aluminium oxide, Process for the acid treatment of aluminous ores for the recovery of alumina, Method of precipitating radium to yield high purity calcium sulfate from phosphate ores, Method for producing ammonium bifluoride by recovering fluorine resource from fluorine-containing silicon slag, Removal of magnesium and aluminum impurities from wet process phosphoric acid, Method of production of high purity silica and ammonium fluoride, Process for producing clarified phosphoric acid, Method of preparing caesium hydroxide solutions, Dichloroisocyanurate process and products, Recovery and treatment of hydrofluoric acid and fluorosilicic acid waste, Process for the preparation of pure silica, A kind of method of the purification co-producing white carbon black of industrial fluosilicic acid, Method of obtaining pure alumina by acid attack on aluminous minerals containing other elements, Method of producing sodium aluminum fluoride, Precipitation of lithium carbonate from lithium chloride solution, Process for recovering solid calcium fluoride containing product and colloidal silica solution from a weak aqueous fluosilicic acid solution, Process of removing cationic impurities from wet process phosphoric acid. The universal practice is to convert the SiF, to that particular product which, at the time, is in greatest demand. After removal of the HCl, the solid potassium silicofluoride is treated with concentrated sodium hydroxide. The method of recovering utilizable values from siF -containing gases comprising the steps of absorbing said SiE; in water to a concentration of 20-30% H SiF separating undissolved solids from said H SiF adding thereto suflicient KCl in concentrated form to convert the H SiF to K SiF and HCl in solution, heating said solution to distill said HCl and condensing the distillate to recover substantially pure HCl solution, adding to the residual solids a sufiicient amount of NaOH to convert the K SiF to K SiO in alkaline solution and NaF solids, filtering said solution to recover NaF as a residue, partially evaporating the filtrate to form a concentrate, cooling the concentrate to crystallize additional NaF, separating the crystallized NaF from its mother liquor, and repeating the evaporating, crystallizing and filtering step until the mother liquor has the desired concentration of K Si0 whereby there are obtained substantially pure NaF and concentrated solutions of HCl and K SiO 3. The fluoride enhances the strength of teeth by the formation of fluorapatite, a naturally occurring component of tooth enamel. It is known that sodium fluoride crystallizes from strong solutions in relatively small crystals which are very difiicult to filten. The mother liquor is evaporated to remove 1440 parts water and the slurry is cooled to 25 C. and filtered to remove 64.84 parts NaF. The HCl is driven ed and recovered. The fluosilicic acid used in the process of this invention can be of any concentration from about 3-4% by weight up to 30% by weight or even more concentrated. In another specific aspect, it relates to the utilization of low grade fluorspar in the production of fluorine-containing materials. Column 6, line 58, for "K SiF" read K 511 Signed and sealed this 23rd day of October 1962., ERNEST w. SWIDER DAVID L LADD Attesting Officer Commissioner of Patents. Accordingly the acid is filtered to remove such solids before further use. Biopharmaceutical Process Development and Manufacturing (8) Cell Biology (6) Cell Culture (1) Chemical Synthesis (15) Materials Science (5) Molecular Biology (10) Research Essentials (12) Special Grade . The manufacturing process produces two byproducts: (1) a solid, calcium sulfate (sheetrock, CaSo4); and (2) the gases, hydrofluoric acid (HF) and silicon tetrafluoride (SiF4). Current U.S. manufacturers of fluorine, hydrogen fluoride, sodium fluoride, fluorosilicic acid, and sodium silicofluoride are given in Table 5-1. 5. To obtain a recovery of this order in a single step would necessitate evaporating the original slurry to a solids content of approximately 19%. It is conceivable that the use of a salt trap, as is sometimes employed in commercial operations, to remove the sodium fluoride as it is formed would permit further evaporation than might be otherwise possible. At any temperature alkali metal ions, silicofluoride ions, chloride and hydrogen ions are present. This procedure reduces the amount of Wash water used to a level that permits adding it back to the system during the first evaporation. The composition for the above potassium silicate-sodium hydroxide-sodium fluoride system based on solubility data obtained in the present investigation is presented in the following Table 1. This slurry is evaporated to dryness by removal of 168.7 parts of water and 36.35 parts of HCl. Fluoride salts are often added to municipal drinking water (as well as to certain food products in some countries) for the purpose of maintaining dental health.

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