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UNITED STATES PATENT Office SVEND S Patented May 24, 1932 1,859,998 UNITED STATES PATENT oFFICE SVEND S. SVENDSEN, OF CHICAGO, ILLINOIS, ASSIGNOR TO CLAY REDUCTION comi PANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIs . HYDRATED SILICA No Drawing. Application filed December 23, 1927. Serial No. 242,291. This invention relates to the production of silicofluoride is also volatilized and collected hydrated silica from a silicious material such in aqueous animonia. The volatilization oc as silica and silicates generally. - - - - curs about 300 C. The following reactions According to the invention the silicious take place in the aqueous ammonia at tem 5 material is treated with ammonium fluoride peratures below 34 C.: 5 5 or bifluoride and silicon ammonia fluorine compounds are produced. These compounds 2SiF(NH) +2H.O= are volatilized and converted into hydrated (NH4)2SiFs--SiO, (hydrated) + silica by the action of water and ammonia. 2NH.F. (IV) O Metallic silicates or substances containing (NH)SiF+4NH,+2HO = them can be subjected to this treatment di SiO, (hydrated) + 6NH.F. (V) rectly. In treating silica in the form of quartz it is found to be necessary to subject It is thus apparent that O heating the it to a preliminary treatment in order to fa silicious material with the ammonium-flu cilitate the action of the ammonium fluoride oride, ammonia-silicon-fluorine compounds a or bifluoride thereon. A suitable preliminary are formed, and by employing suitable tem treatment is to heat the quartz to a bright red peratures are volatilized from the reaction heat and suddenly cool it by immersion in mixture. These compounds may be silicon water. It is then pulverized and is ready for fluoride-ammonia, ammonium-silicofluoride or mixtures thereof, according to the relative 70. 20 U.S. proportion of the silica to the ammonium The silicious materialis mixed with a solu fluoride in the reaction mixture. tion of ammonium fluoride and the mixture The hydrated silica thus produced from is heated to between 34 and 100.C., prefer the silicon diammino tetrafluoride (Equation ably between 60° and 100°C., while stirring, IV) by the action of water is , white and 25 until the ammonium fluoride is converted into opaque, while the hydrated silica precipi ammonium silico-fluorideas follows: tated by ammonia from ammonium silico SiO, + 6NHF = . , , fluoride (Equation V) is transparent and has (NHL) SiF.+2H.O+4NH. (I) a tendency to form silica sol. 30 The ammonia liberated is collected and may The hydrated silica is washed free fro 80 be used later in the process. ammonium fluoride which is recovered and On further evaporation and heating ammo reused in the initial part of a subsequent nium silicofluoride reacts with silica as foll process. The silica may be used for any suit lows: able purposes, for example, as an adsorbent t 35 or the like. It may be formed and pressed 85. into any desired shape and after drying and 2SiF, (NH), +SiF, +2H.O. (II) ignition acquires considerable strength. It By continuous heating the silicon diammino is thought that the transparent hydrated tetrafluoride is volatilized together with the silica acts as a binder for the opaque variety. 40 silicon fluoride and passed into a precipitat The opaque variety of hydrated silica may ing chamber containing aqueous ammonia. be obtained separately by passing silicon On coming into contact with ammonia, the diamino tetrafluoride into water in the ab silicon fluoride is converted into silicon diam sence of ammonia and filtering from the pre mino-tetrafluoride. cipitate. The hydrated silica thus produced 45 is white and clay-like to the touch. The fil 95. SiF,+2NH,-SiF.(NH.). (III) trate contains ammonium silicofluoride. Hy An excess of ammonium fluoride may be drated silica may be precipitated therefrom employed so that a part of the ammonium by adding ammonia. This transparent hy silicofluoride is not converted into silicon drated silica is more highly “soluble’ than 50 diammino tetrafluoride. This ammonium hydrated silicas produced by methods hereto f 2 1859,998 fore known, that is, it is more readily trans and 444 lbs. of ammonium fluoride, 90 lbs. formed into a solby dilution. of the opaque variety and 90 lbs. of the trans The residue from which the silicon com parent variety (as SiO2) are obtained. pounds have been volatilized contains metallic Eacample II.- The procedure with talc is 5 fluorides. The fluorine may be recovered in similar to that described in Example I with 70 the form of ammonium fluoride by passing reference to silica. No preliminary heat ammonium chloride or a mixture of ammonia treatment is necessary and the amount of am and hydrochloric acid gas therethrough at monium fluoride must be sufficient to convert high temperature. In this operation certain the metals into fluorides and the silica into O schlorides such as ferric and aluminum, if the desired proportions of ammonium silico 75 these metals are present, may be volatilized fluoride and silicon diammino tetrafluoride. and recovered. No claim is made in the pres Thus assume that 100 lbs. of talc contain ent application for such production of alu ing 63.5% silica and 31.7% of magnesia are minum chloride since that method is de treated with 215.4 lbs. ammonium fluoride. 5 scribed and claimed in my co-pending appli The ammonium fluoride combines with 58.2 80 cation Serial No. 191,267, filed May 13, 1927, lbs. of the silica giving 172.7 lbs. of ammo of which this is in part a continuation. nium silicofluoride and 66 lbs. of ammonia The invention will be readily understood in accordance with Equation I. On further from the following examples: heating 141 lbs. of the ammonium silicoflu 20 Eacample I-210 lbs. of quartz are heated oride react with the 31.7 lbs. of magnesia ac 85 to a bright red heat, suddenly cooled by im cording to the equation mersionin water and pulverized. The quartz is now mixed with 555 lbs. of ammonium flu oride dissolved in water and the mixture heat MgF, --SiF(NH,) +H.O. (VI) 25 ed above 34° C. and preferably between 60 to form 109.4 lbs. of silicon diammino tetra 90 and 100° C. In accordance with Equation I fluoride and 49.1 lbs. of magnesium fluoride. the ammonium fluoride combines with 150 The remaining silica (5.3 lbs.) reacts with lbs. of the quartz forming about 445 lbs. the remaining ammonium fluosilicate (31.7 of ammonium silicofluoride and liberating lbs.) to give 24.6 lbs. silicon diammino tetra 30 about 170 lbs. of ammonia. On evaporation fluoride and 9.2 lbs. of silicon fluoride in ac 95 to dryness and further heating the remaining cordance with Equation II. If a slightly 60 lbs. of quartz react with 356 lbs. of am less quantity of ammonium fluoride or a talc monium fluosilicate giving 276 lbs. of silicon containing slightly more magnesia is used, diammino tetrafluoride and 104 lbs. of sili substantially no silicon fluoride is formed. 35 confluoride. The silicon fluoride forms with the am 00 The remaining 89 lbs. of ammonium silico monia 12.3 lbs. of silicon diammino tetraflu fluoride, the 276 lbs. of silicon diamino tetra oride. On reaction with water and ammonia fluoride and 104 lbs. of silicon fluoride are according to Equations IV and V 31.75 lbs. volatilized at about 300° C. into a precipita (as SiO) of each modification of hydrated 40 tion chamber containing an aqueous solution silica are formed. r - 05 of at least 170 lbs. of ammonia. By reaction The fluorine is recovered from the magne of the silicon fluoride with 34 lbs. of the am sium fluoride by passing an equimolecular monia gas a further 138 lbs. of silicon diam mixture of hydrochloric acid gas and ammo mino tetrafluoride are produced in accord nia vapor therethrough at a temperature of 45 ance with Equation III. The 414 lbs. of sili about 400° C. to 500° C. The ammonium 0 con diammino tetrafluoride react with 54 lbs. fluoride is volatilized and is precipitated by of water giving 267 lbs. of ammonium silico cooling the fume to between 200 and 300° C. fluoride, 90 lbs. of hydrated silica (as SiO,) Eacample III-Dried clay containingfeld and 111 lbs. of ammonium fluoride. This hy sparis mixed, on hollanders, with ammonium 50 drated silica is white and opaque. fluoride solution containing sufficient fluoride 15 The 356 lbs. of ammonium silicofluoride to convert the silica into silicon-diammino react with 136 lbs. of ammonia and 72 lbs. tetrafluoride and the metallic oxides into of water to yield 120 lbs. of transparent hy fluorides. The mixture is heated to between drated silica (as SiO) and 444 lbs. of am 34° and 100° C. preferably between 60° and 55 monium fluoride. Thus the amount of am 100° C. The ammonium fluoride is thereby 20 monia necessary in the final stage of the proc dissociated into ammonia and ammonium bi ess is theoretically the same as that lib fluoride; the latter attacks the clay, reform erated in the first stage of the process and ing normal ammonium fluoride which is the recovery of ammonium fluoride is theo again decomposed. Ammonia gas is evolved 60 retically equal to that used in the first stage. and recovered. The final result of this reac 25 The relative amounts of the two kinds of tion is principally ammonium silicofluoride hydrated silica can be controlled within wide ((NH4)2SiF6), metallic fluorides and metal limits by adjusting the elative proportions lic oxides. - . of silica and ammonium fluoride in the initial The mixture is evaporated to dryness and 65 mixture. Thus starting with 180 lbs.
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