June 5, 1934. J. H. COLEMAN 1,961,127 MAKING DISODIUM PHOSPHATE Filed Aug. 9, 1932

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UNITED STATES PATENT OFFICE

1961,127 MAKNG DSODUM PHOSPHATE John Harry Coleman, Elizabeth, N.J., assignor to The Warner Chemical Company, New York, N. Y., a corporation of New Jersey Application August 9, 1932, Serial No. 628,12 18 Claims. (C. 23-0) This invention relates to making disodium ion. The filtrate is then neutralized with SOda phosphate; and it comprises a method of making to convert the phosphoric acid into disodium disodium phosphate from calcium phosphate phosphate. A precipitate of complex constitu wherein the phosphoric acid of calcium phoS tion forms, carrying down everything insoluble in 5 phate is converted into monosodium phosphate a hot concentrated neutral or alkaline Solution in solution, the monosodium phosphate is of disodium phosphate. The precipitate con crystallized, the crystals dissolved and the Solu tans fluorin and phosphates of calcium, barium, tion neutralized to form disodium phosphate; iron, aluminum, magnesium, etc. Much, though and, more specifically, it comprises a method not all, of the impurity present in the original 10 wherein an acid liquor is made from calcium acid Solution comes out at this point, but so does 65 phosphate with the aid of Sulfuric acid, Said liquor much of the P2O5. The precipitate (“white containing. P2O5 partly as free phosphoric acid mud') is recovered as a washed press cake and is and partly as acid calcium phosphate, usually in Sold as a low grade fertilizer or fertilizer filler. about a 3:1 ratio, mother liquor from a Succeed It carries 10 to 20 per cent of the original P2O5 of * 15 ing operation is added, calcium Sulfate is pre the rock phosphate, but in an insoluble and un 70 cipitated with the aid of Sodium Sulfate, there available form. The filtrate from the press cake being often a preliminary purifying precipita is boiled to aid in removing CO2, dosed with tion to aid in obtaining merchantable calcium enough NaOH to insure completion of the forma sulfate, free phosphoric acid is neutralized to tion of disodium phosphate, cooled, and crystal 20 monosodium phosphate, in Soluble phosphates lized Na2HFO4.12H2O recovered. Residual im 75 formed thereby are removed and Set aside for re purities remain in the mother liquor. covery of contained P205, pure monosodium phOS Many improvements on this method have been phate is recovered as successive crops of crystals proposed and used, but in principle they all con from the clarified liquor resulting from removal template directly neutralizing a phosphoric acid 25 of insoluble phosphates, final mother liquor liquor obtained from a crude calcium phosphate from the crystallization being Sent back in proc to form a Solution of disodium phosphate, sepa ess, the crystallized monosodium phosphate is rating the precipitate formed by the neutraliza dissolved and neutralized to form a concen tion and crystallizing disodium phosphate from trated solution of disodium phosphate from the impure neutral or alkaline liquid resulting. 30 which crystals of the latter can be, and are, ob The actual factory processes in use are often quite 85 tained on cooling; neutralization occasionally be complex, involving many filtrations and much re ing to trisodium phosphate which is then Crystal cycling of materials, but in all, disodium phos lized in the same way; all as more fully herein phate is delivered as crystals separated from a after set forth and as claimed. more or less impure mother liquor. 35 Crystallized disodium hydrogen phosphate, In and of itself crystallization of Na2HEPO4.12H2O, known commercially as "phos 90 phate of soda', is a staple widely used mate rial made on the large scale from natural to obtain good crops of clean crystals is not al calcium phosphate or rock phosphate. It is together simple. The salt carries 60 per cent 40 made, and sold as a clean crystallized product water of crystallization and Small variations in 95 under rigid specifications as to purity and con Water content of a Saline liquor cause great dif position. Rock phosphate being an impure ma ferences in yield in making a crop of Crystals. terial, the production of pure phosphate of soda The saline liquor must be cooled below 95-115° F. by a simple and economical method giving good to produce crystals and cooling is slow, crystal ... (5 yields of the crystallized salt without waste of lization being exothermic. The specific gravity 00 material or labor is an important technical of the crystals is not much above that of the problem. mother liquor in which they are formed and Set In the original method of making disodium tling is not ready. phosphate in the factory, a method still in use, The presence of any impurity in the mother calcium phosphate is broken up with Sulfuric acid, liquor complicates the operation considerably. giving an insoluble body of calcium sulfate The presence of sodium sulfate in the mother (gypsum) gangue, etc., and an impure acid Solu liquor is considered particularly objectionable; tion containing P2O5 as free phosphoric acid. this being the reason for the removal of the Generally the solution is treated with barium sulfate ion from the acid liquor With the aid of 5 carbonate and filtered to free it of the Sulfate barium carbonate in the usual proceSS. O 2 i,961,127 In the present invention production of diso crystallizing Inonosodium phosphate and either dium phosphate is postponed until purification is lessens the solubility of calcium Sulfate. The Completed. Monosodium phosphate is made as presence of a small excess of Sodium Sulfate gives an intermediate material in pure crystallized a better precipitation of calcium Sulfate and I 5 form leaving sodium sulfate in the mother liquor. generally have this excess. 80 The monosodium phosphate crystals are then Before precipitating the calcium Sulfate, I dissolved and converted into disodium phos generally add residual mother liquor from the phate. The intermediate purification of mono crystallization of monosodium phosphate; and sodium phosphate by crystallization from the any excess of Sodium Sulfate or of acid calciun partly neutralized phosphoric acid solution per phosphate occurring in this liquor is thereby re 85 mits separation of the Sulfate ion in the form of cycled. precipitated calcium Sulfate of great purity, with The hot clear liquid resulting from the soda, obviation of the use of barium compounds for ash treatment and removal of the iron, etc, phOS removal of Sulfates, with Saving both of acid ii. phate precipitate is next cooled and deposits a 5 the rock extraction and of Soda, in neutralization crop of crystals of monosodium phosphate. 90 and with increase in both the yield aind the purity Crystals and nother liquor are separated and the of the sodium phosphate product. latter reconcentrated to obtain a second crop. In practicing my invention, fine ground native Generally, the second mother liquor is reconcen or rock phosphate is decomposed with dilute Sul trated to obtain a third crop and the final nother 20 furic acid to give an acid liquor. Advantageously liquor is sent back in process. The various crys 95 the proportion of sulfuric acid is such that a tal crops when properly washed are pure, the major fraction of the P2O5 extracted goes into mother liquor made as described containing noth solution as free acid and a minor fraction aS acid ing interfering with their purity. The final calcium phosphate. A ratio of 3:1 is desirable. nother liquor still contains in onosodium phos 25 This gives complete extraction of P2O5 and an phate and it may contain Soine acid calcium phos OC economy in sulfuric acid. The reaction mixture phate or Soime sodiuin sulfate which, in either is filter pressed and the cake of gangue and cal event, goes back for reuse. While, as Stated, cium sulfate is washed and discarded. With Sodium sulfate is objectionable in crystallizing proper operation it contains only negligible discoliu in phosphate it is not in crystallizing 30 amounts of P2O5. In the filtrate, the P2O5 is con InOn CSOdin phosphate. If chlorid occurs in the 05 verted into monosodium phosphate by Successive materials used, the chlorid concentration in Suc additions of sodium sulfate and sodium carbonate. cessive nother liquors builds up and mother liq The added sodium sulfate reacts with the acid uOr must be taken out of the systein from time to calcium phosphate, giving monosodium phos time. 35 phate and a precipitate of calcium Sulfate. To For the purposes of crystallization, monoso 110 the extent that sodium sulfate can be used in this dilun phOSphate presents na;by advantages over step it replaces sulfuric acid in treating the rock disodium phosphate from a factory point of View. and carbonate of soda, later used. Its use there It is denser and settles better and it carries only fore produces an economy. After removal of the 23 per cent Water of crystallization as against the 40 calcium sulfate the free phosphoric acid of the 60 per cent of Na2HEPO4.2H2O. Wonosodili. 15 solution is converted into monosodium phosphate phosphate crystals are readily Settled, Washed by an addition of sodium carbonate. This addi and drained in a centrifugal, giving a pure prod tion of sodium carbonate causes a precipitation uct. of insoluble phosphates of iron, aluminum, etc. There is no particular difference in purity be 45 but the precipitate is of different character from tween the three crops of crystals of monosodium. 2 0. that obtained in the usual process and is much phosphate obtained as described and they are more amenable to treatinent for the recovery of united and dissolved with addition of hot water. P2O5. It is removed, washed and set aside for The Solution is treated with sodiural carbonate subsequent treatment. The liquid after the addi as long as free effervescence occurs and caustic tion of the right amount of Soda ash is neutral Soda is then added to complete the formation of to methyl orange but acid to most other indicators. disodium phosphate. If the annount of Water is The addition of sodium sulfate gives me a pre properly chosen, the hot solution on cooling gives cipitate of CaSO4 which is clean and white, hav a good Crop Of pure disodiurn phosphate crystals. ing been formed in an acid solution. It often, My primary purpose is that of an ul however, contains sodium fluosilicate as an in facturing commercial “phosphate of soda' purity. Where fiuorin is present in the rock (Na2HPO4.12H2O) as loose crystals of the usual phosphate and it is desirable to market the CaSO4 size, weight and character; that being a staple as a pigment, paper filler, etc., it is advisable to and standard article of commerce. To this end remove hydrofluosilicic acid from the acid liquor I Ordinarily make hot solutions of such concen 60 before making the CaSO4. This can be done by tration, say about 70 per cent water, that on cool a small addition to the original acid liquor of ing a good crop of crystals of marketable size Sodium carbonate which precipitates the diffi and a mother liquor are produced. In so doing cultly soluble Sodium fluosilicate by an addition I have the incidental advantage that the mother of barium phosphate dissolved in phosphoric acid, liquor is, or may be, of such purity that washing 65 which gives barium fluosilicate; or by a Small the crystals is not necessary; the wet crystals preliminary addition of Sodium sulfate, which may be directly dried. Because of this purity gives a mixed precipitate containing sodiuin fluo of liquid however I an enabled moreover to silicate and a little calcium sulfate. After precip make certain articles of Solid or massive phos itation of the fluosilicate, pure calcium sulfate phate which are commercially novel. A hot pure 70 may be recovered in a marketable condition by Solution containing about 60 per cent of water 145 the described addition of sodium sulfate. In this has the same composition as the crystallized salt; latter precipitation, no great nicety in the use of it may be regarded as disodium phosphate in a reagentS is necessary since neither acid calcium molten condition. And it may be cast in molds phosphate nor Sodium Sulfate in excess in Small and solidified as a whole to give blocks, balls or amounts injures the subsequent operation of Sticks of definite weight and composition. Pound 15) 1961,127 3 and half-pound balls and sticks are convenient enough to make the liquid neutral to methyl for storage, shipment and use and because of the Orange. A phosphate precipitate formed co less Surface area are less affected by exposure to taining iron oxid, alumina, and a minor quantity air than the usual loose crystal article. . of fluorin etc. This was filtered off and washed. The liquid also lends itself readily to the pro The press cake weighed 87 pounds on a dry 80 duction of flakes containing 12 or less molecules basis and contained 35 pounds of P205; an Of Water. amount corresponding to 10 per cent of the If there is a demand for the heptahydrated P2O5 entering the System. The cake Was digest phosphate Na2HPO4.7H2O or the dihydrated, ed. With 50 per cent NaOH solution at about 10 Na2HPO4.2H2O either can be produced by nod 80° C. This Solution after digestion contained 85 ifying the crystallization operation. But, as trisodium phosphate, etc. The digested and stated, the dodecahydrated Na2HPO4.12H2O in Washed cake contained 3.5 pounds of residual loose crystals is a standard article in the market. P2O5; say 1 per cent of the P2O5 entering the As stated, I contemplate producing Solid phoS System. 5 phate in various forms but hot concentrated pure Returning to the monosodium phosphate solu 90 solutions of disodium phosphate produced as de tion filtered from the iron phosphate press cake, scribed are useful for other purposes. In the in this was substantially pure, as stated, a little vention of another, such a hot liquid containing monosodium Sulfate being about the only foreign about 60 per cent water and capable of Setting matter. I concentrated the liquid by heat until 20 to a solid mass on cooling, is placed in a thermal a Sample on cooling gave a copious crystalliza 95 ly insulated receiver or stock tank and Stored, tion of monosodium phosphate. Evaporation was shipped and used as “liquid phosphate of Soda'. in an ordinary vacuum evaporator, the finishing My invention, as described above and also as temperature being about 150 F. and the density illustrated in the following Specific example, can about 52 B. This liquid contained about 46 25 be visualized with greater clarity by reference per cent NaH2PO4. he inot liquor was cooled 100 to the accompanying drawing which shows, in and a crop of crystals removed. The mother the form of a flow sheet, an advantageous em liquor was again concentrated and the hot liq bodiment thereof, wherein phosphate rock is luid cooled to give a second crop of crystals. An treated by a series of successive operations with other concentration gave a third crop of crys 30. the ultimate production of Na2HPO4.12H2O. The tals and a final mother liquor enriched in so 105 several Successive operations are indicated in dium Sulfate. This final mother liquor went back the flow sheet by appropriate legends. as described. The crystals of the three crops In a particular operation embodying the pres Were washed a little; the Washings being united ent invention, in which native phosphate rock With the final mother liquor. A hot solution was 35 was converted into marketable crystals of diso then prepared from the monosodium phosphate 110 dium phosphate, a batch of fine-ground Florida, Crystals. Wet monosodium phosphate crystals phosphate rock carrying 35 per cent P2O5 and Were melted in their water of crystallization by Weighing 1000 pounds was treated With 900 heating to temperatures between 125° and 200 pounds of 77 per cent H2SO4. This amount of F. giving a liquid of approximately 60° Bé., com 40 acid was sufficient to neutralize the carbonates posed of approximately 93 per cent NaH2PO4 115 present and part but not all of the calcium of 2H2O and about 7 per cent, H2O as free water. the calcium phosphate, giving an acid liquor Con A saturated solution of soda, ash (Na2CO3) di taining free phosphoric acid with some acid cal luted with a little water, was added to the hot cium phosphate. The ratio of the P2O5 in the Solution as long as vigorous evolution of CO oc 45 two forms in this instance was 3:1. The in Solu Curred. At this point the Solution contained 120 ble residue of gangue and CaSO4 was filtered about 5 per cent of unreacted Na2CO3. The solu off, washed and sent out of the system. It con tion was then agitated and heated until free tained only 1.5 per cent of P2O5; a negligible CO2 was driven off. The Solution was then about amount. The distribution of the P205 between 42 B. and contained approximately 90 to 95 50 free phosphoric acid and acid calcium phosphate, per cent of Na2HPO4.12H2O and 5 to 10 per cent 125 of course, can be varied. But with the usual residual NaH2PO4. Sufficient NaOH was added grades of phosphate rock, I find it desirable to to the hot solution to finish the conversion of extract P2O5 as phosphoric acid and as acid cal NaH2PO4 into Na2HPO4. I Sometimes use tri cium phosphate in ratios between 80:20 and Sodium phosphate in finishing, replacing all Or 55 75:25. part of the NaOH. The hot solution of disodium 30 The united filtrate and washings carried as hy phosphate thus prepared was diluted with a small drofluosilicic acid 2 per cent fluorin figured on amount of water and then filtered and decolor the phosphoric acid and acid phosphate extract ized. Commercial decolorizing carbon was used. ed. In this particular operation just enough Soda. The hot solution contained approximately 70 per 60 ash was added to convert the acid into Sodium cent of water. It was cooled with stirring to pro- 135 fluosilicate or silicofluorid. The precipitate Was duce a crystal crop and the Crystals separated filtered out. With the filtered acid liquor WaS from the mother liquor. This mother liquor was mixed the final mother liquor recovered in Crys used to dilute the next batch of disodium phos tallizing monosodium phosphate in a previous phate solution. The Na2HPO4.12H2O was bagged operation and sodium sulfate added; the amount for the market. The size of the Crystals or grains 140 being sufficient to precipitate most of the calci was commercially Satisfactory. um as calcium sulfate. The mother liquor used The washed White nud press cake of insciuble contained some sodium sulfate for which allow matters formed in converting acid calcium phos ance was made. The precipitated calcium Sul phate and free phosphoric acid into monosodium fate was filtered off. It was of pure, clean, phosphate was digested With caustic Soda solu 45 white, iron-free character and marketable. tion. This brought most of the P2O5 and the The filtrate from the calcium Sulfate carrying alumina in Solution, leaving a residue Which was both monosodium phosphate and free phosphoric mostly iron oxid carrying a Small and negligible acid was treated. With just Sufficient SOda ash amount of P2O5. The hot solution formed in 5 to convert H3PO4 into monosodium phosphate; digestion was diluted with enough water to fur- 50 4. 1,961,127 nish Water of crystallization for Na3PO4.12H2O process which comprises treating such a calcium and cooled. This gave a crop of crystallized phosphate material with enough sulfuric acid to trisodium phosphate. This trisodium phosphate produce Some free phosphoric acid and some acid was directly marketed. The mother liquor from calcium phosphate in solution, precipitating con the trisodium phosphate was used to furnish an tained fluosilicic acid as an insoluble salt, sep 80 other crop of crystals. The final mother liquor arating calcium sulfate as a precipitate by an Contained a negligible amount of P2O5 and a addition of Sodium sulfate, converting free phos form of sodium aluminate which for some rea phoric acid into monosodium phosphate by neu Sons has particular properties making it market tralizing with soda, separating the precipitate, 0 able as a water purifying preparation. It was concentrating the solution and crystallizing out 85 utilized as such. mOnOSOdium phosphate, separating mother liq What I claim is: llor, redissolving the crystals, neutralizing the 1. In the manufacture of sodium phosphates Solution and crystallizing out a pure non-acid from native calcium phosphates, the process phosphate as pure crystals of a hydrated salt. Which comprises producing an acid liquor con 9. In the process of claim 8, removing fluosilicic .90 taining free phosphoric acid from Such native acid as a barium salt. phosphate, neutralizing the acid with enough 10. In the process of claim. 8, removing fluo Soda to form a monosodium phosphate solution, Silicic acid as a sodium salt. Separating insoluble phosphates of iron and 11. In the process of claim 8, removing fluo 20 aluminum thereby produced, crystallizing out Silicic acid as an insoluble sodium salt admixed 95 mOn OSOdiu in phosphate with separation of a With Some calcium sulfate by a small addition of mother liquor, returning the mother liquor to a Sodium sulfate prior to the main addition of Succeeding acid liquor, purifying, redissolving Sodium sulfate. and neutralizing the separated monosodium 12. In the manufacture of pure commercial 25 phosphate to form a non-acid sodium phosphate Crystallized disodium and trisodium phosphates 00 in Solution and crystallizing the non-acid phos from acid liquors produced by treating calcium phate to obtain a solid marketable product. phosphate with Sulfuric acid the process which 2. The process of claim 1 in which the non-acid comprises converting the P205 of Such a liquor Sodiun phosphate is disodium hydrogen phos into monosodium phosphate, separating precip 30 phate. itates formed in conversion, crystallizing mono 105 3. The process of claim 1 in which the non-acid Sodium phosphate and removing mother liquor Sodium phosphate is trisodium phosphate. With contained sulfates, returning the mother 4. The process of claim I wherein the acid liquor to a Succeeding acid liquor, redissolving liquor contains acid calcium phosphate as well the monosodium phosphate, alkalizing to form a 35 as free phosphoric acid and the calcium is sep pure Solution of a non-acid sodium phosphate, 110 arated as calcium sulfate by an addition of sodi and Crystallizing Out Such non-acid phosphate. um sulfate prior to neutralizing to monosodium 13. In the manufacture of commercial “phos phosphate, phate of Soda containing disodium phosphate 5. In the manufacture of disodium phosphate Crystallized With about 60 per cent Water of 40. the process which comprises preparing a liquor Crystallization, the process which comprises pre 115 containing phosphoric acid and acid calcium paring a purified Solution of monosodium phos phosphate with the aid of sulfuric acid, purifying phate from raw calcium phosphate, crystalliz said liquor and converting both the phosphoric ing the monosodium phosphate with separation acid and the acid calcium phosphate into mono of impurities in a mother liquor to give a pure 45. Sodium phosphate, filtering the liquid, crystal Crystallized product, redissolving the crystals to 120 lizing monosodium phosphate from the liquid in form a hot pure Solution, neutralizing the hot so purified form, redissolving the crystals and neu lution. With Sodium carbonate and with sodium tralizing a hot Solution thereof to form disodium hydrate to produce a pure hot solution of di phosphate. Sodium phosphate and recovering from said so 6. In the manufacture of disodium phosphate lution Crystallized solid dodecahydrated disodi 125 the process which comprises preparing a liquor un phosphate carrying about 60 per cent water containing phosphoric acid from calcium phos of Crystallization as a commercial product. phate with the aid of Sulfuric acid, purifying said 14. In the method of claim 13, producing a liquor and converting the phosphoric acid into loose crystalline mass of Na2HPO4.12H2O by 5 5 monosodium phosphate, filtering the liquid, forming a hot Solution of disodium phosphate 130 crystallizing monosodium phosphate from the carrying more than 60 per cent by weight of wa liquid in purified form with separation of a ter in the Solution, cooling said solution with mother liquor, redissolving the crystals, neu deposition of Crystals and formation of a mother tralizing a hot solution thereof to for disodium liquor, Separating the crystals from the mother 60 phosphate and cooling the Solution to form crys liquor and drying the crystals. 135 tals of a hydrated disodium phosphate. 15. In the method of claim 13, forming a hot 7. In the manufacture of disodium phosphate Solution of disodium phosphate containing about the process which comprises preparing a liquor 60 per cent Water and cooling said solution to containing phosphoric acid from calcium phos Solidify it as a whole to a solid mass having a phate With the aid of Sulfuric acid, purifying said Composition approximating Na2HPO4.12H2O. 40 liquor and converting the phosphoric acid into 16. In the method of claim 5, forming from monosodium phosphate, filtering the liquid, crys nonOSodium phosphate a hot disodiuin phosphate tallizing monosodium phosphate from the liquid Solution containing about 60 per cent by weight of in pure form With separation of a nother liquor, Water and thereby producing as a commercial redissolving the Crystals, neutralizing a hot solu product a liquid having a composition approxi 145 tion thereof to form disodium phosphate nating Na2HPO4.2H2O. and cooling the Solution to form crystals of 17. In manufacturing commercial sodium Na2HPO4.12H2O. phosphate from native calcium phosphate, a 8. In the manufacture of commercial sodium proceSS which comprises extracting the native 5 phosphates from calcium phosphate material the phosphate With Sulfuric acid so as to produce a 50

1,961,127 5 liquid extract containing a major part of the 18. In the manufacture of sodium phosphates P2O5 of the native phosphate as free phosphoric from natural calcium phosphates, a process acid and a minor part as monocalcium phosphate, which comprises preparing a phosphoric acid adding sodium Sulfate to Said liquor to precipi liquor by extracting the natural phosphate With tate calcium Sulfate and to form monosodium Sulfuric acid, precipitating residual calcium from 80 phosphate in Solution, Separating iron and al the liquor as Sulfate, precipitating iron and al lumina, as insoluble phosphates from the liquor unina, as insoluble phosphates from said acid by neutralizing the free phosphoric acid therein liquor by neutralizing the phosphoric acid there to monosodium phosphate, Crystalizing out in to monosodium phosphate, Separating the 10 monoSOdium phosphate With Separation of moth liquor from said precipitated phosphates, crystal 85 er liquor, returning the mother liquor to a Subse lizing out monoSOdium phosphate from the quent Sulfuric acid phosphate extract, redissolv liquor and recycling the mother liquor from said ing the crystallized monosodium phosphate and crystallization to the calcium removing operation. neutralizing it with SOda, to obtain a marketable JOHN HARRY COLEMAN. 5 phosphate of Soda. 90

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