United States Patent to in 3,708,275 Camp, Jr. (45) Jan. 2, 1973

54 MANUFACTURE OF ALKALIMETAL 2,888,321 5/1959 Baumann ...... 23/107 3,554,729 1/1971 Curless...... 71136 X PHOSPHATES 3,375,062 3/1968. Curless...... 23/102A (75. Inventor: Ernest C. Camp, Jr., Barrington, 3,010,818 11/1961 Jones et al...... 71/37 N.J. 3,574,591 4/1971 Lyons et al...... 71/36X (73) Assignee: Cities Service Company, New York, FOREIGN PATENTS OR APPLICATIONS N.Y. 1,082,963 1/1963 Japan...... 71/36 22 Filed: Oct. 28, 1970 613,794 l/1961 Canada...... 23/102 A (21) Appl. No. 84,907 1447,996 12/1964 France...... 23/102 A Related U.S. Application Data Primary Examiner-Reuben Friedman Assistant Examiner-Richard Barnes (63) Continuation-in-part of Ser. No. 725,139, April 29, Attorney-J. Richard. Geaman, Elton F. Gunn and 1968, Pat. No. 3,563,703. Joshua J. Ward (52) U.S. Cl...... 71/1, 7 1/34, 7 1/35, 57 ABSTRACT 71/36, 423/309, 423/399 (51 int. Cl...... C05b 7/00 phosphates can be prepared by adding an (58) Field of Search...... 71/35, 36, 1,34; 23/102 A, to a solution of phosphoric and 23/107,203 N; 423/309, 313,399, 386 nitric acids. The resulting gases can be recovered. After removal of halogen, as by boiling, the solution 56) References Cited can be adjusted in content and neutralized to yield a . Alternatively, the solution can be UNITED STATES PATENTS substantially denitrated, yielding an alkali metal 3,579,323 5/1971 Gauster et al...... 7 1/35 phosphate. Additionally, after denitration the resulting 3,062,617 1 1/1962 Beekhius...... 23102 A residue can be calcined to yield a water soluble fertil 3,600,152 8/1971 Drechsel et al...... 7 1/34 izer. Micronutrients incorporated in the phosphoric 3,244,500 5/1966 Stinson et al...... 7 1/34 X acid-nitric acid solution also can be rendered water 3,414,375 12/1968 Leroy et al...... 23/07 X soluble by this process. 3,347,656 10/1967 Potts et al...... 71/36 3,607,018 9/1971 Moore...... 23/107 14 Claims, No Drawings 3,708,275 1 2 MANUFACTURE OF ALKALI METAL to result in a mixture which is taught to be relatively PHOSPHATES low in total plant food and which contains, as a result of the acidulation of phosphate rock, substantial amounts CROSS-REFERENCE TO RELATED of calcium, which often is not desirable, One advantage APPLICATIONS of the present process is that it provides an integrated This application is a continuation in part of my co process for the nitric acid acidulation of phosphate pending application Ser. No. 725,139 entitled, "Im rock, subsequent treatment of the acidulate to remove proved Process for Treating Phosphate Rock' filed calcium, the treatment of the calcium-free solution Apr. 29, 1968, and assigned to the same assignee as the with an alkali metal salt to form the corresponding present application and now U.S. Pat. No. 3,563,703. O phosphate, and recovery or subsequent treatment of said phosphate. BACKGROUND OF THE INVENTION One aspect of this invention relates to the prepara This invention relates to an improvement in the tion of a tetrapotassium pyrophosphate that is totally preparation of alkali metal phosphates. There is at water-soluble. A common industrial method of forming present a great need for an economical process which 15 tetrapotassium pyrophosphate is to react phosphoric will produce alkali metal phosphates, such as acid, either furnace acid or wet process acid, with phosphates, at a cost sufficiently low to permit their use potassium hydroxide or potassium carbonate. This as . Presently, technical grade alkali metal reaction yields dipotassium hydrogen phosphate, which phosphates are made commercially from wet process is then heated and dehyrated to give the desired phosphoric acid using the alkali metal hydroxide or tetrapotassium pyrophosphate. As mentioned above, carbonate. The naturally occurring alkali metal com this method involves the reaction of the expensive pounds, however, such as those of and potassi potassium hydroxide or carbonate. Other methods of um, are most commonly mined and recovered in the adding the potassium to phosphoric acid involve form of a salt, such as the chloride. Thus, in order to 25 the addition of a material such as potassium chloride to react phosphoric acid with an alkali metal hydroxide or phosphoric acid. This mixture, when used as a fertil carbonate, the alkali metal salt must first be converted izer, suffers the disadvantage of containing appreciable to the corresponding hydroxide or carbonate. Unfortu amounts of chloride ion. Chloride ion has a deleterious nately, however, the cost of these converted materials effect on a number of crops, such as tobacco and Idaho is too expensive for fertilizer production. It is thus 30 potatoes. Also, if the phosphoric acid is wet process. readily apparent that a process for preparing alkali acid, it contains congeneric metal impurities, such as metal phosphates which employs the alkali metal salt iron and aluminum, that tend to precipitate when the directly, eliminating expensive intermediate acid is concentrated. Thus, a chloride-free and water processing, would be a highly desirable and economi soluble high analysis fertilizer is desirable. This inven cally attractive process. 35 The prior art has recognized the desirability of tion offers a process for making this type offertilizer. directly producing alkali metal phosphates from such Another aspect of this invention relates to a method inexpensive compounds as the corresponding alkali for incorporating micronutrients into the fertilizers that metal salt, such as the chloride. Exemplary of such can be prepared as described herein. prior art are U.S. Pat. No. 2,954,286 to John K. Radley 40 The importance of micronutrients (or minor ele et al. and U. S. Pat. No. 3.010,817 to Eugene D. Crit ments or trace elements) has only recently been recog tenden. Radley in Pat. No. 2,954,268 teaches a process nized in the field of fertilizers. Among the difficulties for making a fertilizer which involves reacting potassi involved in the incorporation of micronutrients into um chloride and nitric acid to produce a liquid product fertilizers are (1) uniform incorporation of the small containing free nitric acid, removing the formed 45 amount of material, (2) prevention of segregation after nitrosylchloride and chlorine and treating the product mixing, and (3) reactions that can affect agronomic ef with phosphoric acid. Crittenden in U. S. Pat. No. fectiveness and physical condition adversely. One of 3,010,817 teaches that potassium phosphate fertilizers the techniques that has been previously devised is to may be prepared by feeding potassium chloride to a charge a finely divided micronutrient material into a reactor for reaction with nitric acid and water. Follow 50 mixer, along with the principal materials, with 1 to 3 ing the reaction, chlorine and nitrosyl chloride are percent by weight of a white oil. The adherence of the separated, leaving an effluent containing mostly potas micronutrients to the oil coating during mixing disper sium , nitric acid and water. This effluent is then ses the trace elements onto the fertilizer granules. By fed to a mixing vessel to which sulfuric acid and the method described herein for adding the desired phosphoric acid are added, and this mixture is finally 55 micronutrients to the nitrate-phosphate mixture, supplied to leach phosphate rock. denitrating the solution and calcining, not only can the In each of the above cases the alkali metal salt is first micronutrients be simply and uniformly dispersed reacted with nitric acid and the reaction product is then throughout the fertilizer, but the micronutrients are ob combined with phosphate, either by treating with tained in a substantially water-soluble form, making phosphoric acid or by subsequent contact with 60 them completely useful and immediately available as phosphate rock. The disadvantages of these prior art plant food. processes are manifest when compared with the desira bility of directly obtaining the desired product. In one SUMMARY OF THE INVENTION case, the phosphoric acid must first be formed and Halide-free alkali metal phosphates can be prepared thereafter combined with the reaction product of nitric 65 by reacting a mixture of nitric and phosphoric acids acid and alkali metal salt. In the second case, potassium with an alkali metal halide. The halogen-containing off nitrate is mixed with sulfuric acid and phosphate rock, gases can be separated and recovered, with the result 3,708,275 3 4 ing solution comprising phosphate, nitrate and alkali the nitric acid content. There are several ways of in metal . In one embodiment of this invention, alkali creasing the nitric acid content of the acidulate, includ metal can be recovered from the solution by ing the addition of more concentrated nitric acid or the crystallization. In another embodiment of this inven formation of additional nitric acid in situ by the in tion, excess nitric acid can be evaporated and the troduction of nitrogen oxides and oxygen into the remaining solution neutralized with ammonia to acidulate. Where higher concentration nitric acid is produce a high analysis fertilizer. In still another em added, the nitric acid added is preferably more concen bodiment of this invention, substantially all nitrate can trated than the nitric acid used to acidulate the rock. be driven off and an alkali metal phosphate suitable as Thus, it is desirable that the added nitric acid be at least fertilizer can be recovered. In yet another embodiment 10 90 percent by weight HNOa, preferably greater than 95 of this invention, substantially all nitrate can be percent and, most preferably, greater than 98% HNOs removed, the residue can be calcined and a water-solu by weight. Alternatively, the nitric acid content in the ble alkali metal polyphosphate, useful as a fertilizer or a acidulate can be increased by introducing one or more detergent, can be recovered. In still another embodi nitrogen oxides and oxygen into the acidulate. In a par ment, the solution comprising phosphate, nitrate and 15 ticularly preferred embodiment, the nitric acid concen alkali metal ions can be mixed with a suitable tration is increased until the water content of the super micronutrient or mixture of micronutrients, substan natant solution is no more than about 14 percent by tially all nitrate can be removed, the residue can be cal weight. Generally, the precipitation of calcium nitrate cined, and a water-soluble polyphosphate fertilizer 20 is substantially instantaneous. Upon completion of the containing micronutrients can be recovered. precipitation, the solid and liquid phases can be The solution of nitric and phosphoric acids to which separated by conventional means, such as decantation, the alkali metal halide is added can come from any con filtration or, preferably, centrifugation. Such separa venient source and is preferably substantially free of tion is readily achieved, and, as the liquid phase is of a calcium. In one convenient embodiment, phosphate 25 low viscosity, the calcium nitrate crystals will settle rock is acidulated with concentrated nitric acid to con rapidly. Following separation, the calcium nitrate cake vert the phosphate rock to an acidulate comprising can be washed, dried and used in any convenient phosphoric acid, nitric acid and calcium nitrate in solu manner. The supernatant liquid remaining after tion, as described in my co-pending application Ser. removal of the precipitated calcium nitrate is the No. 725,139 which is hereby incorporated by 30 preferred source of the solution of nitric and phosphor reference. Subsequent to acidulation, calcium nitrate is ic acids to which the alkali metal halide is added. removed from the resulting acidulate. This step is The alkali metal cations which are useful within the preferably performed by increasing the nitric acid con scope of this invention can be selected from among tent of the acidulate. Any fluorine compound found in , sodium, potassium, and cesium, with the phosphate rock can, of course, be removed from sodium and potassium compounds being preferred the acidulate in known manner. Following separation because they are commercially available and relatively of precipitated calcium nitrate, there is added to the fil inexpensive. Potassium halides are particularly trate, comprising phosphoric acid and nitric acid, an preferred because potassium is one of the necessary amount of alkali metal salt, such as KCl, necessary to 40 macronutrients, and its incorporation into a mixture furnish the desired ratio of MO:POs, where M is the containing available nitrogen and phosphorous makes a alkali metal, in the final product. This MO:POs ratio complete fertilizer available. The halide anions useful can vary from about 0.5:1 to about 3:1, so that from 1 in this invention can be selected from among fluorine, to 6 moles of alkalimetal halide can be added per mole bromine, chlorine and iodine compounds. Since alkali of POs. ... r 45 metal chloride compounds are commercially available In the acidulation step it is desirable to use concen and relatively inexpensive, they are preferred. Thus, trated nitric acid, preferably having a concentration potassium chloride is the particularly preferred alkali from about 75 to about 85 percent by weight nitric metal halide. The alkali metal halide employed can acid. The use of lower concentrations of nitric acid come from any of the usually available salts and can be frequently causes the formation of excess gangue, while 50 of high or low purity. The alkali metal halide can be digesting with concentrations of nitric acid greater than used in a solid form, preferably finely divided, or as a about 85 percent proceeds rather slowly and results in solution, as desired. losses of phosphoric acid, on the order of as much as 9 The reacting components can be combined and percent. Most preferably, nitric acid of from 80 to 85 mixed in any convenient manner. It is often preferred percent by weight is employed. The temperature of the 55 to add the alkali metal halide to the mixed acids at a acidulation is not critical and can range from about temperature below about 60°C., since there is practi 160 to about 240°F. In the acidulation step, it is desira cally no reaction at or below this temperature level. ble to use at least sufficient nitric acid to convert the Thus, the slurry can be introduced into a closed system phosphate rock to calcium nitrate and phosphoric acid. without giving off fumes that would be evolved at a Preferably, an excess of up to about 15 percent by 60 higher temperature. The gases evolved as a result of the weight of nitric acid is used, based on the calcium reaction with the preferred alkali metal chloride com present, calculated as calcium oxide. When employing prise chlorine, nitrogen dioxide and nitrosyl chloride. a 10 to 15 percent excess of nitric acid, there is attained The gases can be recycled back through the solution an acidulation ratio of from about 2.5 to 2.6 parts by and, where the concentration of nitric acid is suffi weight of nitric acid per part of calcium calculated as 65 ciently high, nitrosyl chloride can be oxidized to form calcium oxide. As previously indicated, calcium nitrate nitrogen dioxide and chlorine. Alternatively, the gases is removed from the acidulate, preferably by increasing can be passed through concentrated nitric acid to ac 3,708,275 5 6 complish said oxidation. The resultant gases, compris That the micronutrient content must be carefully con ing nitrogen dioxide and chlorine, can be recovered trolled can be seen from the fact that the range and readily separated by well-known fractionation between inadequate and toxic amounts of many techniques. The solution remaining can be treated in micronutrients is fairly small. The principal several ways. micronutrients are usually added in the form of borax In one embodiment alkali metal nitrate can be and the sulfates of the other metals, although other prepared by removing excess nitric acid from the above compounds can be used. In accordance with the en solution, as by boiling, and thereafter crystallizing the alkali metal nitrate from the solution. bodiment described above, the micronutrients, for ex In still another embodiment, the solution comprising O ample, in the form of powdered borax and sulfates of alkali metal ions, nitric acid and phosphoric acid can be the metals, can be added to the acid solution in suffi substantially denitrated, as by boiling. The remaining cient amount to satisfy the proposed minimum require phosphoric acid solution can be appropriately neutral ments of the locale in which they are to be used, thereafter substantially denitrating the resulting solu ized, such as by the addition of ammonia, to yield a sub 15 stantially chloride-free, high analysis mixed fertilizer. tion, as by boiling, and thereafter calcining the residue By adjusting the amounts of nitric acid, phosphoric at a temperature and for a period of time sufficient to acid, potassium chloride and ammonia, fertilizers hav form an alkali metal polyphosphate matrix containing ing varying ratios of N-P-K can be obtained. the micronutrients. The calcined product is substan In still another embodiment, a metaphosphate-type tially completely water soluble. fertilizer can be prepared. To the solution comprising In still another embodiment, the fertilizer comprising nitric acid and phosphoric acid is added sufficient al a mixture of micronutrients dispersed in the alkali kali metal halide to obtain an MO:POs ratio (where M metal phosphate fertilizer base, prepared as described is the alkali metal) of approximately 1:1 which is above, can be combined or mixed with the complete characteristic of alkali metal metaphosphate. Excess 25 fertilizer formed by the ammoniation of the alkali metal nitrate can be driven off, as by boiling, and the residue, phosphate base. By proper adjustment and manipula comprising alkali metal dihydrogen phosphate, is cal tion of the various components, a commercially valua cined to give a product comprising alkali metal ble complete fertilizer containing micronutrients can metaphosphate. 30 readily be obtained, with the kind and concentration of In another embodiment the solution can be substan micronutrients, as well as the N-P-K ratio, being varia tially denitrated, as by boiling, and the residue can be ble upon demand. calcined at a temperature of from about 650°C. to about 800°C., for a period of from about 1 hour to DESCRIPTION OF THE PREFERRED about 2 hours, to form an alkali metal polyphosphate. 35 EMBODIMENTS In this embodiment, a ratio of MO:POs of about 2:1 (where M is the alkali metal) is needed to yield a EXAMPLE I polyphosphate such as MPO. The conditions for cal Phosphate rock, containing approximately 30 per cining are well-known. The polyphosphates formed are cent by weight POs and approximately 47 percent by substantially completely water-soluble, even in the 40 weight calcium (measured as calcium oxide) was presence of iron and aluminum congeneric metal impu crushed to a particle size that substantially passed rities found in the phosphoric acid derived from the through a 30 Tyler Mesh screen. Nitric acid was then phosphate rock. Thus, this process has the advantages added to stoichiometric crushed rock, with the acid of making substantially chloride-free, substantially concentration being about 80 percent by weight and completely water-soluble high analysis P-K fertilizer. 45 The product is quite desirable and is less expensive the amount of acid being about 10 percent in excess of than polyphosphates from other processes. the stiochiometric amount needed to produce calcium In still another embodiment, micronutrients can be nitrate and phosphoric acid. After the phosphate rock incorporated into the solution of phosphate, nitrate and was digested for about 2 hours at a temperature of alkali metal ions that remains after the removal of 50 about 160°F., concentrated nitric acid (approximately, nitrogen dioxide and chlorine gases. The 95 percent by weight HNO3) was added in an amount micronutrients most usually incorporated in fertilizers such that the water content of the supernatant solution are boron, zinc, iron and manganese. Copper and was less than about 14 percent by weight. The calcium molybdenum are less frequently used because deficien 55 nitrate which precipitated was removed by filtration. cies of these metals are usually less widespread than The filtrate analyzed 62.33% NO, 8.55% POs and one those of the micronutrients described above. The 0.53% CaO. Potassium chloride was added to this fil following minimum percentages by weight of the more trate so as to furnish a 1:1 ratio of K2O:POs in the final frequently employed micronutrients have been product. The potassium chloride-nitric acid-phosphor adopted as standard by some states and may be con 60 ic acid mixture was then heated to boiling, evolving sidered as typical of the amounts which can be incor halogen-containing off-gases. The solution resulting porated in a fertilizer: from this treatment comprised phosphate, nitrate, potassium and hydrogen ions. Excess nitric acid was B 0.02 Fe 0.10 65. evaporated from the solution until the residue was sub M 0.05 stantially a solution of in phosphoric Zn 0.05 acid. Cooling of this solution resulted in the precipita tion of crystalline potassium nitrate. 3,708,275 7 8 EXAMPLE I c. recovering a solution containing phosphate, A solution of potassium, hydrogen, nitrate and nitrate and alkali metal ions. phosphate ions prepared as described in Example I was 2. A method according to claim 1 in which the nitric denitrated by evaporation to dryness, resulting in a acid concentration is sufficient to oxidize at least part residue comprising KHPO. Calcining of this residue at 5 of the halide reaction products to free halogen. 425C. for a period of about 1 hour gave a product 3. A method according to claim 2 in which at least comprising KPOa and analyzing 37.78% K2O, 50.2% part of the halogen-containing off-gases are recycled POs and 1.15% N, or about 89% total plant food. through4. A method the solution. according to claim 1a in which the alkali 10 metal halide is added in an amount such that the EXAMPLE III resultant MO:PO mole ratio, where M is alkali metal, Water-soluble fertilizers were prepared as follows: lies in the range of from about 0.5:1 to about 3:1. To a portion of the filtrate solution obtained as 5. A method according to claim 1 in which the alkali described in Example I was added KCl to provide about metalhalide is potassium chloride. 2 moles KO per mole POs. The off-gases were 15 6. A method according to claim 1 in which the solu removed and the solution was concentrated by boiling. tion recovered is heated to evaporate excess nitric acid This solution was evaporated to dryness and the residue and then neutralized with ammonia to produce a sub heated to 740°C. for one-half hour. The product stantially halide-free fertilizer. analyzed 40.1% POs, 55.54% KO and 0.01% nitrogen 7. A method according to claim 1 in which the solu 20 tion recovered is treated to drive off substantially all and was substantially completely water soluble, in spite nitrates, and an alkali metal phosphate residue is of the presence of such congeneric metals as iron and recovered. aluminum. X-ray diffraction confirmed its structure as 8. A method according to claim 7 in which the substantially K.P.O. phosphate residue recovered comprises about 89 per EXAMPLE IV 25 cent total plant food. 9. A method according to claim 1 in which the solu A water-soluble fertilizer containing soluble tion recovered in step (c) is treated to remove halogen micronutrients can be prepared as follows: values and nitrates and then calcined to convert at least To a portion of the filtrate solution of nitric and part of the phosphate present to the polyphosphate phosphoric acids prepared as described in Example I is form. added sufficient KCl to provide a KO:POs ratio of 10. A method according to claim 9 in which the al 2: 1. To this solution, after removal of volatile gases, are kali metal halide is potassium chloride, added in an added the micronutrient compounds. Thus, to suffi amount of from about 2 to about 6 moles of KCl per cient filtrate solution to provide one hundred lbs., dry mole of PO, the solution is boiled to remove chloride basis, of potassium phosphate, are added a powdered 35 and water and the residue obtained thereby is calcined mixture of 0.178 lb. borax, 0.203 lb. manganous sulfate at a temperature of about 740C. for from 1 to 2 hours. tetrahydrate and 0.22 lb. zinc sulfate heptahydrate. 11. A method according to claim 10 in which the cal After boiling until dry and calcining at 740°C. for one cined product is characterized by substantial freedom hour, a water-soluble product is obtained. from chloride, nitrate and calcium and by being sub When wet process phosphoric acid is used, as is the 40 stantially water soluble. , , case in the above examples, the addition of iron, in the 12. A method according to claim 1 in which plant form of ferrous sulfate, is generally unnecessary insofar micronutrients are added to the solution recovered in as the wet process acid often contains 1 percent or step (c), the solution is heated to remove halogen more iron, calculated as FeCa. . values, excess water and nitrates, and the residue ob A fertilizer containing micronutrients prepared as 45 tained thereby is calcined to convert at least part of the described above can be applied directly or can be phosphate therein to polyphosphate. mixed with a fertilizer not containing such 13. A method according to claim 12 in which the al micronutrients and blended so as to obtain a fertilizer kali metal halide is potassium chloride, added in an whose properties can be tailored for a specific use. amount of from about two to about six moles of KCl claim: 50 per mole of POs, the solution is boiled to remove 1. A method for making substantially halide-free water, chlorine values and nitrates, and the residue is metal phosphates which comprises; m calcined at a temperature of from about 650°C. to a. reacting an alkali metal halide with a mixture of about 800°C. for a period of from about one-half to nitric and phosphoric acids in which the concen about 2 hours. tration of said mixture is from about 55 percent wt. 55 14. A method according to claim 13 in which the to about 70 percent wt. nitric acid and less than product obtained is characterized by substantially about 14 percent water, complete water solubility. 1. •. b. separating the halogen-containing off-gases, and - it is

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