IL34592A - The manufacture of sodium fluoride and silica gel as solid materials by the decomposition of sodium silico-fluoride - Google Patents

Description

manufacture of sodium fluoride and silica gel as solid materials by decomposition of sodium CHEMICAL LTD The resides in the decomposition of sodium fluosilicate with ammonia or aqueous ammonium The object of this invention resides in manufacturing pure sodium fluoride and silica gel as solid materials and an aqueous ammonium fluoride solution in high The other object of this invention resides in manufacturing pure sodium fluoride in a large crystalline form and a fine powder of silica and separating them from a slurry sodium fluoride and silica gel in an aqueous ammonium fluoride in high efficiency by means of physical Another objec of this invention resides in manufacturing large crystals of pure sodium fluoride not having silica bonded to their and silica gels having good dispersability in a high yield and at the same The rther object of this inventio will be understood from the following sodium uosilicate is manufactured by the reaction of fluosilicic for as a in the manufacture of calcium superphosphate or phosphoric acid with sodium most fluosilicic aeid produced as in the phosphoric acid manufacturing industry is discarded as since economic use has not been found for fluosilicic phosphate fertilizers have been manufactured from phosphoric acid containing fluosilicic acid without recovering the fluosiliclo It is known that sodium silica gel represented is reacted with aamonia as by Equation 2 said reaction has been carried out by using a dilute aqueous ammonium hydroxide solution n to for ready separation of the silica gel from the mixed solution of fluoride and asrmonium It has been to us the aqueous solutio of sodium fluoride and luoride the manufacture of It has been found in accordance with the tha a slurr of sodium fluoride and silica ge in aqueous ammonium fluoride solution may be by reactin sodium fluosilicate with a relatively hig concentrated aqueous solution of ammonium the provides a process for the production of slurry of sodium fluoride and silica gel in an aqueous ammonium fluoride solution which comprises reacting sodium fluosilicate with an aqueous solution of ammonium whilst agitating the reaction the concentration of ammonium hydroxide in the reaction medium the course of the reaction being more than by weight and the total ammonium concentration in the reaction medium after completion of the reaction than 1 by as calculated as In accordance with a further feature o the slurry may be chemically treated by adding thereto a aqueous solution of sodium hydroxide a sodium sulfate chloride with agitation to convert the ammonium fluoride either to sodium fluoride and ammonia or to sodium fluoride and ammonium The mixed slurry thus obtained may then be treated to separate sodium silica gel and an ammonium The invention will be explained by the following examples and attached reaction of sodium fluosilicate with aqueous ammonium hydroxide may be represented as Since the solubility of sodium fluoride in the aqueous solution is relatively concentrated aqueous ammonia is sed to recover crystalline sodium fluoride from the reaction mixture in good it may to the sodium fluoride from the silica owing to formation of very fine crystals of sodium fluoride or sodium fluoride crystals having bonded to their In order to overcome the the relationship between the ammonium ion namely total ammonium ion concentration coming to ammonium fluoride and the ammonium hydroxide in the reaction mixture and the solubility of sodium fluoride in the reaction mixture has been As shown in Table when the total ammonium ion concentration in the reaction medium is namel the amount of ammonia used is greater than the stoichiometrical amount of required to react with the and the concentration of the aqueous ammonium hydroxide solution used is also relatively it has been found that solubility of sodium fluoride in the reaction sodium the total ammonium ion concentration in the reaction medium should be more than weight calculated as it is preferable to use a relatively highly concentrated aqueous ammonium hydroxide solution in an amount than the stoiehiometrical amount required to react with sodium When an ammonium hydroxide solution is as the concentration is preferably 18 by weight as In this invention it is preferable to use sodium fluosilicate having a particle size of less than 250 in order to ensure that the reaction proceeds Sable 1 Concentration Concentration Concentration Solubility of free of total of nium fluoride hydroxide ammonia sodium in the reaction in in the fluoride mixture reaction mixture reaction mixture 0 0 0 10 0 5 10 15 0 5 10 30 5 10 50 0 10 The process of this invention may be carried out batchwise by adding sodium fluosilicate to a relatively highly concentrated aqueous ammonium hydroxide or by adding an aqueous ammonium hydroxide solution of relatively high concentration or ammonia gas to an aqueous slurry of sodium Said process may also be carried out on a continuous basis by simultaneously introducing an aqueous ammonium hydroxide solution of relativel high concentration ammonia gas and the aqueous slurry of sodium fluosilicate to a reaction or by simultaneously introducing an aqueous ammonium hydroxide solution relatively high concentration and powdered sodium fluosilicate to a reaction Dependin on the reaction sodium fluoride crystals having silica bonded to their very fine crystals of sodium fluoride or coagurated gel may be formed and it may be difficult to separate sodium fluoride and hydrated silica gel in good yield and high purity by physical In this the separated silica includes sodium fluoride which can be separated silica gel by washing with and the separated sodium fluoride includes silica gel which can be with sodium hydroxide but such are troublesome and It has been found that crystals sodium fluoride and silica gel fine powder can be obtained in high yield by reacting aqueous slurry of sodium fluosilicate with an aqueous ammonium hydroxide solution of relatively hig concentration or ammonia gas while strongly agitating of ammonium ions in the reaction medium reaches to more than by weight calculated as after completio of the As a result of various experiments it has been that the following conditions lead to the production of sodium fluoride and silica gel the highest The aqueous slurry of sodium fluosilicate is reacted with a relatively highly concentrated aqueous ammonium hydroxide solution or ammonia The aqueous ammonium hydroxide solution or an ammonia gas added slowly to the aqueous slurry containing the sodium agitating force used is sufficient to disperse the solid materials uniformly throughout the aqueous slurry The experimental results are explained as follows Influence of the of adding the reactants on the purity of products Experimen 1 Three kg of powdered sodium silico fluoride having an average particle size of were in predetermined portions over 90 minutes into 101 of a 25 aqueous ammonium hydroxide solution calculated on basis of in cylinderical reaction vessel having a capacity of 201 and heated to while agitating at the speed of 400 by means of a propeller type After all the sodium fluosilicate had 34592 2 a been the reaction was continued for 30 minutes while strongly total concentration of ions in the solution reached calculated on the weight basis of Experiment 2 Six o by weight aqueous ammonium hydroxide solution introduced into an aqueous slurry of kg of fluosillcate having an particle of 100 μ in 4 of water in said reactor and heated to in predetermine portions ove 90 while strongly After the aqueous ammonium hydroxide had been added the reaction was continued 0 e total concentration of ammonium ions in the reaction mixture reached 1 calculated on the weight basis of both resultant sodium fluoride and silica gel were separate from the reaction mixture by means of a apparatus under the same e sodium fluoride and silica gel obtained were analysed to determine the silica content in sodium fluoride and sodium fluoride content in silica gels The results are show as follows Table 2 in Hat in 2 It is believed the results of the experiment 1 that the concentration of ammonium hydroxide in the reaction medium influences the formation of the especially silica and that silica gel produced is not only incapable of dispersing solid material throughout reaction but is also bonded to sodium fluoride produced with a resultant decrease in the purity of the sodium since the high concentration of ammonium hydroxide in the medium at the beginning of the reaction gradually reduces to a low concentration during the course of the It is believed from the results of the experiment 2 that since the concentration of ammonium hydroxide in the reaction medium is always low during the of the reaction and silica disperses throughout the reaction silica gel the does not bond of the sodium fluoride The influence of the rate of adding ammonia on the purity of the products Seven kg of a aqueous ammonium hydroxide solutio were added continuously to an aqueous slurry containing kg of sodium fluosilicate and 3 1 of water at with strong agitation at the rates shown in Table The agitating was continued until the reaction was The reaction mixture was separated an aqueous slurry containing sodium fluoride and ammonium fluoride and an aqueous slurry containing silica gel and ammonium fluoride by means of a levigation The solid reaction namely sodium fluoride and silic gel were filtered from each slurry and dried to give the final The purity of the products is shown in Table Table The time required The retaining time to adding an time after adding aqueous an aqueous ammonium in in solution solution 15 6 60 30 120 30 180 20 240 20 From the experimental has been found that if concentration of aqueous hydroxide solution is about weight and the solution is added to the aqueous slurry over a period of 60 the satisfactory results ma be In the process of this as the time required to add the aqueous ammonium hydroxide solution to the slurry depends on ammonium it is be noted that the concentratio of the aqueous ammonium hydroxide solution is than 4 by the time required to add the solution When the ammonia gas used instead of the aqueous it is necessar to maintain the concentration ee ammonia in the reaction medium in the reaction medium is preferably less than 5 The invluence of the agitating power on purity o the products of a aqueous ammonium hydroxide solution continuously added to the aqueous slurry solution of kg of sodium fluosilicate in o water in a cylindrical reactor at while agitating by means of a propelle type agitator over 120 minute periods and the reaction was continued until the reaction The reaction mixture was separated into the aqueous slurry of sodium fluoride and ammonium fluoride and an aqueous slurry of silica gel and ammonium The solid reaction namely sodium fluoride and silica gel were filtered from slurry and dried to give the final The purity of the products shown in Table Table 4 50 100 100 200 300 40 600 700 1000 150 the experimental shown in Table it has been found that if the speed of the agitato is more than 300 the purity of the sodium fluoride and silica gel may be considerably Since the agitation effect may vary depending on the size and the shape of the th type of agitation and the and the shape of the it is not possible to specify a rate of revolution which will satisfy all In any the agitating power should be more than enough to disperse the solid materials contained in the aqueous slurr uniformly through the reaction The slurry of sodium fluosilicate used in the process of this invention may be not only an aqueous slurry a slurry in aqueous ammonium The water content of the aqueous slurry will depend o the concentration of the aqueous ammonium hydroxide solution or an ammonia gas be but it is preferably 40 90 of The concentration of the aqueous ammonium hydroxide solution is suitably more tha by weight calculated as and the total concentration of ammonium ions in the reaction mixture more tha by calculated as the reaction is When dry sodium silico fluoride is directly treated with the aqueous ammonium hydroxide the concentration of the ammonium hydroxide solution is suitably more than by calculated as The mole ratio of to fluoeilicate preferably more than hut not more than in this the solubility of fluoride in the reaction medium increases as the volume of the reaction medium increases and the yield of sodium fluoride is The reaction is not but if the reaction temperature is too the solubility of sodium fluoride and the silica in the reaction medium will resulting in decrease in the purity ammonium fluoride solution and the yield of sodium fluoride and silica The reaction temperature is suitably less than The power should be more than the agitating power needed to disperse the solid materials uniformly in the aqueous When the fluoride in the aqueous slurry is reacted with sodium hydroxide or sodium salts a slurry or solution a sodium fluoride and ammonium hydroxide or an ammonium salt is sodium hydroxide or sodium salts are suitably used in a stoichiometrical amount or slightly more with respect to ammonium The sodium sodium chloride and sodium sulfate are suitably used concentration of more 10 and 20 or as reaction namely the agitation and the rate addition the same as those for According to this sodium fluoride the form of large single crystals having a particle size greater than 100 and silica gel having good dispersability and a particle siae of than 5 and the aqueous ammonium sodium fluoride not containing any bonded silica and silica gel containing reduced amount of sodium fluoride may be The products manufactured according to the process of this invention may readily be separated by means of the levigation or sedimentation When the ammonium fluoride is reacted with sodium hydroxide or sodium larger crystals of sodium fluoride may be produced due to the seed crystals of sodium fluoride already present in the said The process of this invention will be described with reference to the accompanying in Figures 2 and show flow sheets of various processes of this Referring now to Figure a sodium fluosilicate or an aqueous slurry thereof and an aqueous ammonium hydroxide solution or ammonia at least one of the reactants being in the form of a slurry or are continuously fed to the reaction an aqueous ammonium hydroxide solution may be fed to a reaction vessel containing an aqueous slurry of sodium In either the reaction mixture is agitated and an aqueous slurry of ammonium fluoride containing solid silica gel and solid sodium fluoride is This slurry is led to the middle portion of the levigation Near the bottom of said an aqueous ammonium fluoride solution as described is introduced to form the upstream flow within said apparatus so that silica gel contained in the aqueous slurry transfers upwardly and sodium fluoride crystals descend so that silica gel is discharged the top of the levigation apparatus in the of a slurry in aqueous ammonium fluoride solution and The silica gel is washed with water and dried to give the final A part of the filtrate obtained is recycled to the levigation apparatus and the residual part thereof is for various Referring now to a sodium fluosilicate or its aqueous slurr is reacted with an aqueous hydroxide solution as described in connection h The aqueous slurry of ammonium fluoride containing silica gel and sodium fluoride is led to the middle portion of levigation and silica gel is discharged from the top of the levigation apparatus in the form o the aqueous washed with water and dried to give the final product as in The fluoride crystals precipitated in the bottom said apparatus are removed in the form of an aqueous and separated from the aqueous ammonium fluoride solution by washed with water and dried to give the final The filtrates from the slurries removed from the top and the bottom are gathered a part of the filtrate is recycled to levigation apparatus and the residual part of the filtrate is used for various purposes Referring now to a sodium fluosilicate is reacted with ammonium hydrate as shown in The aqueous slurry of ammonium fluoride containing solid silica gel and sodium fluoride is filtered and the mixture of silica gel and sodium fluoride is after washing with water and said mixture is separated to sodium fluoride and Since sodium fluoride according to the process of this invention of high sodium fluoride may be used for preservations for or as a fungicide or The silica obtained are of high purity and of fine particle and ma be used as a filler for gums and synthetic plastics and as drying The aqueous ammonium fluoride solution may be used as a starting material for the production of or cryolite ammonium or may be crystallized the solution for further In sodium silica gels ammonium fluoride having wide utilization are produced by means of a simple process in high yield and high purity according to the process of this The process this invention has important values in the industrial point of Example 1 Pour kghour o a aqueous ammonium oxide solution on the weight basis of were continuously fed to a reaction vessel together with of a aqueous slurry of sodium The reaction was carried out at while agitating at a speed of about 60 by means of propeller type The mean retention time in the reactor was about 5 The aqueous slurry solution discharged from the reaction vessel was introduced into the middle portion of a levigation Aqueous ammonium fluoride solution as described was introduced into the levigation apparatus from the bottom thereof form the upstream flow of about 20 cm per An aqueous slurry of ammonium fluoride containing silica gel slurry containing sodium fluoride was drawn out from the bottom of said The sodium fluoride and silica in each slurry filtered washed with water and dried to recover sodium fluoride having a purity of greater at a rate of and silica gel having a purity of at a rate of 320 of the total aqueous solution of ammonium fluoride were recovered in the form of The filtrate recovered contained wt of ammonium fluoride and wt of sodium Example Pour of a aqueous ammonium hydroxide solution as were continuously fed to a reaction vessel with of sodium reaction was carried out at while agitating at a speed of about 120 by of the propeller type The mean retention time in the reactor was about an The aqueous slurry discharged from the reactor was allowed to settle for 12 hours while cooling to and then separated to an aqueous slurry of fluoride containing silica gel and an aqueous slurry of ammonium fluoride containing sodium as described in the Example The upstream flow rate in the levigation apparatus was 15 cm per Sodium fluoride and silica gel were filtered from the slurries and washed with water and dried to give silica having a purity of greater than at a rate of 640 and sodium fluoride having a purity of at a rate of 890 total filtrate of amounted to and contained wt of ammonium fluoride and wt of sodium Example 3 hundred kg of sodium fluosilicate having a purity of and 1001 of water were fed in the cylindrical reactor having the capacit of 6001 to form an aqueous The aqueous slurry was heated to while agitating the of 400 by means of an agitator of the propeller and 2001 of a 45 wt aqueous ammonium solution calculated as were to the slurry in the predetermined portions over a period of 90 After the reaction was the mixed slurry obtained was cooled to Sodium fluoride and silica gels contained in the slurry were separated by The sodium fluoride crystals were washed with and dried to give 41 kg of fluoride having a purity of greater than 99 and a particle size of 100 μ and 31 kg of silica gel having a purity of and a particle size of less than The volume of aqueous ammonium fluoride solution obtained was 8201 and concentration was 22 Example 4 One hundred kg of sodium fluosilicate having a purity of were fed to a cylindrical After 3001 of water had been added to said the slurry was heated to while strongly agitating at a speed of 500 by means of an agitator of the propeller and 45 of ammonia gas were introduced into the slurry in predetermined portions ove a perio of 90 After the reaction was 175 a sodium hydroxide solution were added to said slurry in the predetermined portions to react with the ammonium aqueous ammonium hydroxide slurry containing sodium fluoride crystals and an aqueous ammonium hydroxide slurry containing silica Each of said slurries was and sodium fluoride cyrstals and silic gel obtained were washed with water and dried to give 120 kg of fluoride crystals having a particle size of 500 and a purity greater than and 33 of silica gel having a purity of and the particle size of less than The volume of the aqueous ammonium hydroxide solution obtained was 4501 and its concentration was 16 wt as An aqueous slurry of ammonium fluoride containing sodium fluoride and silica gel produced as in Example 1 was filtered to give a mixture of sodium fluoride and silica gel which was with water and The mixture was then separated in cyclon type separator to give sodium having a purity greater than at a rate of 430 and silica gel having a purity of a rate o 320 of aqueous ammonium fluoride solution was Example 6 One hundred kg of fluosilicate having a purity were fed to a cylindrical 200 1 of added to the reactor the slurry was heated to while strongly agitating at a speed of 500 by means the agitator of the propeller 45 of ammonia gas were introduced into said solution in portions over a period of 90 After the reaction was slurry in predetermined portions to reac with the ammonium After the reaction was the aqueous slurry was cooled and introduced into the apparatus to separate an aqueous slurry containing sodium fluoride crystals and an aqueous ammonium chloride solution containing silica Each of the slurries was filtered and the sodium fluoride crystals and silica gel obtained were washed with water and dried to give 115 of sodium fluoride crystals having a particle sise of 100 150 μ and a purity greater than and 33 of silica gels having a purity of and a particle size of less than volume of the aqueous ammonium chloride solution was 610 1 and its concentration was 16 wt insufficientOCRQuality

Claims (1)

1. CLAIMS A process for the production of a slurry of sodium fluoride and silica gel in an aqueous ammonium fluoride solution which comprises reacting sodium fluosilicate with an aqueous solution of ammonium hydroxide which has a calculated as free of at least about by whilst agitating the reaction the concentration of free ammonia in the reaction medium during the course of the reaction being more tha by weight and the total ammonium ion concentration in the reaction after completion of the being more than by A process as claimed in Claim 1 in whic the aqueous ammonium hydroxide has a calculated as free of 15 by A process as claimed in an one of the preceding claims in which the resultant slurry is subsequently reacted with an aqueous solution of sodium sodium sulphate or sodium chloride to produce a slurry of fluoride and silica in aqueous ammonium ammonium sulphate or ammonium A process as claimed in Claim in which the sodium hydroxide solution has a concentration of greater than 10 by A process claimed in Claim 3 in which the sodium chloride solution has a concentration of greater than 10 by A process as claimed in Claim which the sodium sulphate solution has a concentration of greater than by aa la any of in a separated slurry containing fluoride and a slurry containing Claim 7 in which the solid filtered off from both of the process any 1 in which slurry produced is filtered to give a Mixture of silica which subsequently separated into oonGtituents by a physical insufficientOCRQuality