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3,585,021 United States Patent Office Patented June 15, 1971 2 for the production of phosphate containing fertilizers 3,585,021 PROCESS FOR THE PRODUCTION OF AMMONUM have been developed, but none has proved to be com PHOSPHATE CONTAINING FERTLIZERS BY mericially successful. THE REACTION OF AMMONUM FLUORIDE The simplest of these processes is that wherein the WITH ALUMINUM PHOSPHATE (FE-14) aluminum phosphate ore in subjected to calcination in Paul R. Geissler, Edison, N.J., assignor to Esso a rotary kiln, resulting in a product having approximately Research and Engineering Company a 35% POs content and a 36% aluminum oxide content. No Drawing. Filed Apr. 24, 1969, Ser. No. 819,128 The main drawback of this process is that the product Int, C. C05b 7/00 formed is water insoluble, although it is soluble in am U.S. C. 71-34 16 Claims O monium citrate solution, The Tennessee Valley Authority (TVA) has done considerable work on leached zone ore and has developed ABSTRACT OF THE DISCLOSURE a nitricSulfuric acid extraction process involving calcina Reaction of aluminum phosphate with ammonium tion of the ore, extraction of the phosphatic materials fluoride, followed by removal of precipitated triammonium 5 from the ore with nitric and sulfuric acid, filtration, and aluminum hexafluoride results in the production of an ammoniation and granulation of the concentrated filtrate. ammonium phosphate fertilizer. Various N/POs ratios While producing a complete fertilizer, this process in can be obtained by adding acid to the reaction mixture. volves such serious filtration difficulties as to make com mercialization uneconomical. More importantly, the ma 20 jor part of the phosphatic component is water insoluble. PRIOR ART Several other processes have been investigated including (1) sulfuric acid treatment of aluminum phosphate to Ammonium phosphates have gained wide acceptance in produce a superphosphate type fertilizer; (2) sulfuric acid recent years as fertilizer materials. Several reasons ac leaching of the ore followed by precipitation of ammonium count for their rapid acceptance. Firstly, from an agri alum and crystallization of ammonium phosphates; and cultural standpoint, ammonium phosphates contain both (3) nitric acid acidulation followed by ammoniation to nitrogen and phosphorus in concentrated form. The com produce a mixed fertilizer. Again, filtration difficulties are bined nitrogen and POs content can approach 65% by so serious in the acid-leach processes that commercializa weight of the fertilizer in the case of diammonium phos tion is presently uneconomical in the face of competition phate. Secondly, the phosphorus is present in ammonium 30 from the high grade calcium phosphate ores. Some of phosphates in a completely water soluble form, which is thes processes also have the disadvantage of producing of great agronomic value. Thirdly, under many conditions, phosphate fertilizers that are not completely water soluble. the assimilation of fertilizer phosphate is often increased by the presence of ammoniacal nitrogen, and vice versa. FIELD OF THE INVENTION Ammonium phosphate fertilizers have generally been 35 This invention relates to a process for the production produced by ammoniating phosphoric acid. However, the of ammonium phosphate fertilizers. More particularly, overall economic efficiency of that production method this invention relates to a continuous process for the pro depends to large measure on the source of the phosphatic duction of ammonium phosphate fertilizers, wherein the material from which the phosphoric acid is made. This phosphates are produced in a completely water soluble has prompted a search for alternative methods of pro 40 form and in a wide variety of grades from the reaction duction wherein cheaper, less pure grades of phosphoric of aluminum phosphate and ammonium fluoride. acid or cheaper sources of phosphates could be utilized. This in turn has prompted a search for cheap, naturally SUMMARY OF THE INVENTION occurring phosphatic materials and for methods wherein It has been found that by reacting an aluminum phos such naturally occurring materials could be used directly phate containing source with stoichiometric or greater in producing ammonium phosphate fertilizers. 45 amounts of ammonium fluoride, in an aqueous medium, Thus, the various phosphate rock-acidulation processes there results a fertilizer composition composed of am have been developed wherein a naturally occurring phos monium phosphate. The present process can best be sum phate source, such as phosphate rock containing calcium marized by the following equation representing the re is mixed with an inorganic acid, such as sulfuric acid, action occurring in the process: resulting in extraction from the rock of phosphatic ima terials. In the case of sulfuric acid acidulation of phosphate 6NH4F -- A1PO4 Ho, (NH); AlF6 -- (NH4)HPO4 -- NH3 rock, separation of insoluble impurities from the reaction In the practice of the present invention, an aluminum mixture and subsequent ammoniation results in the pro phosphate containing source is reacted with ammonium duction of ammonium phosphate type fertilizers. fluoride to form precipitated (NH4)3AlF6, ammonia and Large deposits of aluminum phosphate ore are known 55 diammonium phosphate. After the precipitated to exist in several places throughout the world; notably on Grand Connetable Island, in Brazil, and in Senegal, has been removed by filtration, the solution can be con Africa. Additionally, Florida phosphate deposits contain verted into a fertilizer by any of the conventional methods. a layer of material called the leached Zone, in which Due to the extreme insolubility of aluminum phosphate the principal phosphate minerals are aluminum phos 60 (Ksp=1030 at 25 C.), it had not been thought feasible phates. This zone overlies the calcium containing phosphate to utilize aluminum phosphate as a phosphate source in a rock matrix, which is presently the most popular natural fertilizer process except under acidulation conditions phosphate source, and has in practice been moved and wherein strong inorganic acids such as sulfuric or nitric discarded as waste in phosphate mining operations seeking acid are utilized to achieve digestion of the insoluble alu to reach the commercially valuable calcium containing 65 minum phosphate and wherein the exothermic heat of phosphate rock located below the leached Zone. These reaction further aids in driving the reaction to completion. deposits are a potential source of cheap naturally occurring In this regard, it was thought that, as in the case of fertil phosphate which may be utilized to produce phosphate izer processes utilizing phosphate rock Cas (PO4)3F, ex containing fertilizers. traction of the phosphate content of the starting material Various processes for utilizing the phosphate contained 70 must proceed by acidulation, and that utilization of a in aluminum phosphate ores as a cheap starting material milder coreactant, such as the ammonium fluoride utilized 3,585,021 3 4 in the present invention, would either not result in re duced by 1 mole by substitution therefor of 1 mole of HF action at all due to the extreme insolubility of aluminum for 1 mole of NHAF; while yet further, in Equation c phosphate, or at most, would result in such a low am above, 2 moles of HF can be substituted for 2 moles of monium phosphate yield as to make the process com NHF where monoammonium phosphate is the desired mercially unfeasible. The prior art process utilizing alu product. Thus when the present invention is being prac minum sulfate and ammonium fluoride to produce am ticed at a NH4F/AlPO reactant mole ratio of 6, up to /3 monium sulfate containing fertilizers did not offer any of the ammonium fluoride to be utilized in the reaction encouragement to utilizing aluminum phosphate and am can be replaced by HF or by HF in the ammonium bi monium fluoride to produce ammonium phosphate con fluoride form while maintaining the fluorine content at a taining fertilizers due to the vast divergence of solubility O mole ratio of 6. Thus, it can be seen that the present existent between aluminum sulfate (Ksp=1) and alu process provides a method of producing phosphate coin minum phosphate (Ksp=1030). Thus, while the reaction taining fertilizers wherein the prouduct can have great of aluminum phosphate and ammonium fluoride to pro variation as regards constituents and N/P2O5 ratios. Addi duce ammonium phosphate, as shown by the equation tionally, where the product contains a constituent, such as above, is theoretically possible; it was not known whether monoammonium phosphate, which can undergo further in practice, the reaction would proceed and further, neutralization by ammoniation, further variation can be whether the yield of fertilizer product would make the achieved by subjecting the filtered reaction mixture to process commercially feasible. ammoniation. However, it has been found that the reaction of alu In a preferred embodiment of the present invention, minum phosphate and ammonium fluoride will not only there is provided a process for the production of am proceed in spite of these difficulties (extreme insolubility monium phosphate containing fertilizers comprising (a) and absence of an inorganic acid digesting coreactant); reacting an aluminum phosphate containing Source with but that the process as such is commercially feasible, re ammonium fluoride in an aqueous medium, (b) filtration Sulting in a process yield of approximately 75%. It has of the (NH4)3AlF6 formed during