text: before a solution or slurry can be spray dryed or evaporated to yield a feed grade product , it is usually necessary to remove at least a portion of the fluorine originally present in the solution in order to establish the required solution p / f ratio of at least 30 or 35 . in the case where the solution is prepared in situ by acidulation of phosphate rock , it is always necessary to remove some of the fluorine originally present in the rock in order to establish the required solution p / f ratio of at least 30 or 35 . such partially defluorinated solutions can be prepared by heretofore known techniques . for example , one known method is to treat the solution with hydrofluoric acid in order to achieve an optimum f / al mole ratio in solution of about 14 - 16 which assures maximum precipitation of an aluminum fluorine complex whose probable formula is presented hereinbelow . precipitation of this complex not only removes the fluorine added as hydrofluoric acid but also up to 90 percent of the fluorine originally present in the rock . u . s . pat . no . 2 , 976 , 141 exemplifies the hydrofluoric acid technique . this technique by itself cannot produce solution p / f ratios of 100 or greater but will produce ratios of 30 or greater . the hydrofluoric acid technique , however , is not preferred due to the expense and highly corrosive effect of the acid . it is also possible to partially defluorinate such solutions by addition of sio 2 to the solution . the fluorine is then volatilized as sif 4 . this is not desirable , however , because of possible fouling of metal equipment and heat transfer surfaces with sio 2 at subsequent stages in the defluorination process . a preferred process which incorporates a novel partial defluorination process prior to the spray drying and crystallization steps is presented schematically in fig1 . the preparation of solution suitable for spray drying or evaporation is essentially the same . referring to fig1 phosphate rock 11 , aqueous sulfuric acid 12 , and aqueous hydrochloric acid 13 are fed to a first digestor 14 wherein the rock is digested to yield a slurry 15 comprising ( a ) a solution of water , hydrochloric acid , calcium chloride , phosphoric acid , and soluble fluorine present as a variety of soluble fluorine containing compounds , and ( b ) a solid portion made up of calcium sulfate , a variety of insolubles from the rock such as sio 2 , and an aluminum fluorine complex having the probable formula : sufficient total acidity must be provided by the sulfuric and hydrochloric acid to dissolve the phosphate rock . preferably a 20 to 30 percent excess of total acidity is used . the rock itself can be any commercial phosphate rock which is essentially fluorapatite such as florida , north carolina , or moroccan rocks , also western phosphate rocks and igneous phosphates such as quebec and kola rock . the p / f ratio in most rocks is approximately 3 . 5 . of course , nitric acid can be used in place of the hydrochloric acid but hydrochloric acid is highly preferred due to its low cost and availability . the ratio of hydrochloric to sulfuric acid employed in digestor 14 depends upon the nature of the product which is to be made . the function of the h 2 so 4 is to remove sufficient calcium from solution as calcium sulfate to establish the desired mole ratio of ca to p in solution . if monocalcium phosphate crystals are to be prepared in the crystallization process , it is desirable to use enough h 2 so 4 to establish a ca / p mole ration in solution of 0 . 4 -- 0 . 5 . if the spray drying route is to be followed to prepare a mixture of calcium phosphate and calcium chlorophosphate , sufficient h 2 so 4 should be used to establish a ca / p mole ratio in solution of & gt ; 0 . 5 - 1 . 0 . however , since the feed to the spray dryer may be either a solution or a slurry , there are several possible stages in the process where the h 2 so 4 can be conveniently added . for example , if a solution is to be spray dried , all of the required h 2 so 4 is added during the initial digestion of the rock . however , where flexibility in the phosphorus content of the product emerging from the spray drier is desired , it becomes convenient to add only a portion of the stoichiometric amount of h 2 so 4 required in the initial digestion step , adding the rest of it to the solution immediately prior to spray drying . in this case , calcium sulfate appears in the product as diluent . it can be seen that by varying the amount of the h 2 so 4 added to the solution immediately prior to spray drying , the percentage of phosphorus in the product can be varied by the appearance of more or less calcium sulfate diluent in the product . there will be some formation of the aforementioned insoluble aluminum fluorine complex in digestor 14 causing removal of about 35 to 50 % of the fluorine originally present in the rock . as a result , the p / f ratio in the solution portion of slurry 15 is usually about 7 to 10 . the amount of fluorine removed as complex fluoride depends somewhat on the al + + + ion concentration in the solution . excessive amounts of al + + + ions in the solution tend to reduce the formation of complex fluoride crystals . however , in all cases , sufficient fluorine can be complexed to produce the required solution p / f ratio in the feed to the spray dryer or crystallizer . slurry 15 is transferred to a second digestor 16 . a water soluble sodium or potassium salt such as sodium chloride , sodium carbonate , sodium nitrate , potassium chloride , potassium nitrate , or such is added to slurry 15 in digestor 16 whereupon the salt reacts with the soluble fluorine to form the compound na 2 sif 6 or k 2 sif 6 , which then precipitates from solution removing additional fluorine . the salt is usually added in at least the stoichiometric amount required for reaction with the available fluorine . the precipitation of na 2 sif 6 or k 2 sif 6 will usually remove an additional 10 to 25 percent of the fluorine originally present in the rock resulting in a p / f ratio of about 10 to 15 in the solution portion of slurry 17 . the sodium or potassium salt can be added to digestor 15 in lieu of digestor 16 . it is preferred , however , that it be added at a point subsequent to precipitation of the aluminum fluorine complex since it appears that the more aluminum which exists in solution when the salt is added , the less na 2 sif 6 or k 2 sif 6 which is formed . therefore , by not adding salt until digestor 16 , at which point a large portion of aluminum has been removed from solution , a somewhat larger crop of na 2 sif 6 or k 2 sif 6 is obtainable , resulting in more efficient defluorination . slurry 17 is filtered 18 to remove the various insolubles 19 previously discussed . the filter cake is then advantageously washed with water to produce wash liquor 18a which is utilized at a later point in the spray - drying process . filtrate 20 is transferred to clarifier 21 where it is cooled to further precipitate insolubles . filtrate 20 is ordinarily cooled to a temperature of 10 ° to 30 ° f . solution 22 is separated from insolubles 23 . the clarification step can just as conveniently be performed prior to filtration step 18 . clarification will remove about 15 to 25 percent more of the fluorine originally present in the rock due to additional precipitation of the aluminum fluorine complex and na 2 sif 6 . consequently , the p / f ratio in solution 22 will usually be at least about 35 , a sufficiently high value to permit solution 22 to be spray dried or crystallized in accordance with the processes of this invention provided the proper ca / p mole ratio exists in solution 22 . at this point it becomes convenient to separately discuss subsequent processing of solution 22 depending on whether it is to be crystallized or spray dried . solution 22 can be fed directly to spray dryer 24 ( as shown by the dotted line in fig1 ) provided sufficient h 2 so 4 was previously added in digestor 15 to establish a ca / p mole ratio of & gt ; 0 . 5 to 1 . 0 in solution 22 . however , if solution 22 is to be spray dried , it is advantageously preconcentrated in evaporator 25 , either at ambient pressure or under vacuum to produce concentrated solution 26 which can then be fed directly to dryer 24 as shown in fig1 . on the other hand , if the election has been made to dilute the product with calcium sulfate as heretofore discussed , concentrated solution 26 will not contain the required ca / p mole ratio since not all of the h 2 so 4 required to establish this ratio was added in digestor 15 . in this event , solution 26 is transferred to mixing vessel 27 where the remainder of the h 2 so 4 required to establish a ca / p mole ratio in solution of & gt ; 0 . 5 to 1 . 0 is added to solution 26 to produce slurry 28 containing calcium sulfate solids . slurry 28 is then fed to spray dryer 24 . if the solution ca / p mole ratio exceeds 1 . 0 it becomes difficult to remove the chlorine in the spray drying step unless very high temperatures are used . if the ca / p ratio is below 0 . 5 the dried product will be undesirably contaminated with phosphoric acid and furthermore will be substantially free from calcium chlorophosphate . the spray dryer conditions are controlled by maintaining the temperature of the gaseous effluent 29 from the dryer at prescribed temperatures within a range of 200 ° f . to 380 ° f . with preferred exit gas temperature being 200 ° f . to 350 ° f . these relatively low temperatures minimize degradation of the calcium phosphates to undesirable metaphosphates and pyrophosphates and , furthermore , prevent formation of compounds such as sio 2 which can foul metallic equipment . fig2 clearly demonstrates that it is essential that the solution p / f ratio in either the solution or slurry fed to the spray dryer be at least 30 or higher if a dryed product having a p / f ratio of 100 or more is to be obtained . fig1 was prepared using a variety of data points obtained at various dryer exit gas temperatures between 200 °- 380 ° f . the thickness of the plot reflects the slight variations observed with widely varying exit gas temperatures . however it is apparent that a solution p / f ratio of 30 or higher will produce a spray dried product having a p / f ratio of 100 or more under all the process conditions of this invention . the composition of the dry product 30 produced will depend primarily on the particular value of the ca / p mole ratio in the solution dried and the temperature of dryer exit gas 29 . fig3 shows the effect of exit gas temperature upon composition of the dry product for a ca / p solution mole ratio of about 0 . 8 and solution feed rates to the dryer of 100 to 200 ml ./ min . at temperatures between 200 °- 300 ° f ., the composition of the product remained fairly constant , the product containing about 60percent monocalcium phosphate monohydrate and 40 percent calcium chlorophosphate . at temperatures between 300 °- 380 ° f ., the amount of p 2 o 5 in the product rises sharply while the amount of chlorine drops sharply . the product produced in the region between 300 °- 380 ° f . is a mixture of dicalcium phosphate , monocalcium phosphate , and calcium chlorophosphate with the product formed at 360 ° f . containing 6 . 66percent , 59 . 0percent and 32 . 15percent , respectively , of each ingredient . curves similar to fig3 can , of course , be readily constructed for ca / p mole ratios other than 0 . 8 in order to arrive at proper conditions for making a product of any desired composition . calcium chlorophosphate can be prepared in high purity using a ca / p mole ratio in solution of 1 . 0 and exit gas temperatures of 200 °- 300 ° f . monocalcium phosphate can be prepared in high purity using a ca / p mole ratio in solution approximating 0 . 5 and higher exit gas temperatures ( i . e . 350 °- 380 ° f .). dicalcium phosphate is difficult to make in high purity under any conditions and this particular phosphate will usually be made in a mixture with monocalcium phosphate and / or calcium chlorophosphate . it is preferable to leave some chloride in the product mixture to avoid the use of the high drying temperatures required to remove chloride . referring to fig1 gas stream 29 can be condensed to yield an aqueous stream of hydrochloric acid and soluble fluorine . the amount of acid in stream 29 will , of course , depend on the nature of the product to be made . obviously , products containing more calcium chlorophosphate will reduce the amount of acid in stream 29 . however , once the desired product composition is known , the acid content is readily computable . the fluorine content in stream 29 will be quite small , usually amounting to about 0 . 01 to 0 . 1 percent . since gas stream 29 contains non - condensables as well , it is advantageous to convert the water soluble condensable fraction of stream 29 to an aqueous hcl solution 31 for recycle by contacting stream 29 with a mixture of the condensed gaseous effluent 32 of evaporator 25 and wash liquor 18a from filtration step 18 . stream 31 can then be recycled to digestor 15 for use in acidulating rock or to reservoir 13 . since some hydrochloric acid will usually be consumed as product 30 , it will be necessary in a continuous process to add make - up hydrochloric acid 33 from time to time to the system . the mixtures of calcium phosphate and calcium chlorophosphate prepared by the spray - drying process of this invention have a level of phosphorus availability to animals which is comparable to commercially available feed grade calcium phosphates . this property , coupled with the acceptable p / f ratio , makes these mixtures suitable for use in supplementing the phosphorus requirements of a variety of animals including commercial livestock such as cattle , pigs , and poultry . the mixture is typically admixed with the diet fed to the animals in biologically acceptable amounts , said amounts being well established in the art . it must be understood that for purposes of clarity a particular processing sequence was presented in fig1 . it is not intended that the processes of fig1 represent inflexible process routes since it is readily apparent to those skilled in the art that a number of different arrangements and permutations of process steps could be used with acceptable results . such varied arrangements and permutations , of course , fall within the scope of the claims appended hereto . referring again to fig1 solution 22 is fed directly to crystallizer 34 , the crystallizer containing therein phosphoric acid . the ca / p solution mole ratio in solution 22 must not be greater than 0 . 5 , otherwise there will be a buildup of calcium in crystallizer 34 with an attendant loss of acid available for recycle . a ca / p mole ratio somewhat lower than 0 . 5 , i . e . 0 . 4 - 0 . 5 , will cause build - up of phosphoric acid in crystallizer 34 . however , such a lower ca / p ratio would be acceptable provided crystallizer 34 is purged from time to time to prevent phosphoric acid build - up . the proper ca / p mole ratio in solution 22 is preferably established by addition of the required amount of h 2 so 4 to digestor 15 . it is most undesirable for solution 22 to contain solids such as , for example , calcium sulfate since it will make the product difficult to filter and will , additionally , defeat the objective of a pure high grade crystalline monocalcium phosphate . the solution p / f ratio in solution 22 must be at least about 35 or greater . this is somewhat higher than the lower range of p / f ratio which is permissible in the spray dryer feed . however , the defluorination steps described above are suitable for partially defluorinating solution 22 to provide solution p / f ratios of 35 or greater . fig4 presents equilibrium data which indicates the conditions of pressure and temperature within the crystallizer which are required to establish a given percentage of p 2 o 5 in the crystallizer slurry . fig5 presents equilibrium data which indicates the amount of hcl in both the crystallizer slurry and in the condensed effluent gas stream 35 from crystallizer 34 as a function of the amount of p 2 o 5 in the crystallizer slurry . of particular interest , especially when a continuous process is to be used , is the acid strength of stream 35 . this acid strength can be fixed at any of a variety of concentrations , by simply maintaining the required amount of p 2 o 5 in the crystallizer slurry ( as obtained from fig5 ). this required amount of p 2 o 5 is obtained by merely selecting the required pressure and temperature within the crystallizer ( as obtained from fig4 ). the strength of the recovered hydrochloric acid stream 35 depends primarily upon the concentration of hydrochloric acid in feed solution 22 . for example , if solution 22 contained 10 percent hcl and 40 percent water , the strength of recovered acid stream 35 would under equilibrium conditions be about 18 - 20 percent if minor loss of water as water of crystallization in monocalcium phosphate is taken into consideration . to obtain an acid strength of 18 - 20 percent in stream 35 , the p 2 o 5 content in the slurry of crystallizer 34 must be , according to fig5 somewhere between 40 and 45 percent . when the process is operated continuously under equilibrium conditions , the amount of p 2 o 5 in the crystallizer slurry is preferably maintained at 35 to 60 percent , corresponding to an evaporator condensate 35 containing from about 5 to 25 percent hcl . if the hcl content of stream 35 is less than about 5 percent , the acid is too weak for use in the further acidulation of phosphate rock . if the hcl content of stream 35 exceeds about 25 percent , it is too concentrated to adequately solubilize the phosphate rock . plots similar to fig4 and 5 can , of course , be readily prepared for a nitric acid system . the gaseous effluent 36 from crystallizer 34 contains water , hydrochloric acid , and soluble compounds of fluorine in small amounts . stream 36 typically contains 0 . 05 to 0 . 3 percent fluorine . stream 36 is condensed to give an aqueous acid solution 35 which is then recycled for use in acidulating additional phosphate rock in digestor 15 . when the crystallization process is operated continuously at equilibrium , a stream 37 of mother liquor mixed with monocalcium phosphate crystals is continuously withdrawn from crystallizer 34 . stream 37 is filtered 38 or centrifuged to separate mother liquor 39 from the crystalline monocalcium phosphate product 40 whereupon mother liquor 39 is advantageously recycled to crystallizer 34 . the mother liquor comprises water , phosphoric acid , calcium chloride ( or calcium nitrate ), monocalcium phosphate , hydrochloric acid ( or nitric acid ), and impurities derived from phosphate rock . the concentration of these ingredients depends , of course , on the crystallizer operating conditions such as temperature , pressure , feed solution composition , the rate of feed introduction into the crystallizer , recycle rate , and such . the absolute pressure in the crystallizer can range from 1 cm . of hg . to atmospheric pressure or higher . however , low pressures are preferred since this permits the use of lower operating temperatures . the type of monocalcium phosphate crystallized , i . e . either anhydrous or the monohydrate , depends upon the temperature and p 2 o 5 concentration of the mother liquor and is readily obtainable from a cao - p 2 o 5 - hcl - h 2 o phase diagram . preparation of partially defluorinated solutions for use as a feedstock to the spray - dryer or crystallizer 50 parts of phosphate rock were digested with 62 . 4 parts of 21 . 5 percent aqueous hcl and 29 . 7 parts of 96 percent aqueous h 2 so 4 . after a 2 hour digestion period , 2 parts of nacl were added to the digestion mixture and digestion continued for an additional 2 hours . the slurry produced was filtered with the filtrate analysis being as follows : the ca / p mole ratio of the filtrate was about 0 . 65 and the p / f ratio about 26 , corresponding to removal of 86 percent of the fluorine initially present in the rock . the filtrate was then cooled to a temperature of 10 ° c . whereupon some insolubles precipitated from solution . the resulting mixture was filtered to yield a filtrate containing 0 . 12 percent fluorine and having a p / f ratio of about 60 and a ca / p mole ratio of 0 . 65 . the p / f ratio of 60 indicated that 93 percent of the fluorine initially present in the rock was removed . 230 parts of primary phosphate rock was digested with 458 parts of 24 . 4 percent aqueous hcl , 65 . 6 parts of 96 percent aqueous h 2 so 4 , and 16 . 2 parts of 48 . 9 percent aqueous hf . the f / al mole ratio in the digestion mixture was 14 . after a 16 hour digestion period , the slurry was filtered . the filtrate analyzed as follows : the ca / p mole ratio in the filtrate was 1 . 08 and the p / f ratio was 61 , corresponding to removal of 93 percent of the fluorine initially present in the rock . preparation of feed grade calcium phosphate by spray - drying of a partially defluorinated solution the solution prepared in example 1 ( a ) was dried in a conventional spray dryer at various feed rates and dryer exit gas temperatures . results are tabulated below and indicate that products having p / f ratios of 100 or greater were produced under all conditions studied . __________________________________________________________________________exampledryer temp . ( f .) feed rate product productno . inlet gas exit gas ( ml ./ min .) % p . sub . 2 o . sub . 5 % cl % f p / f composition__________________________________________________________________________2 850 360 100 50 . 03 5 . 99 0 . 22 100 ca ( h . sub . 2 po . sub . 4 ). sub . 2 caclh . sub . 2 po . sub . 4 . h . sub . 2 o cahpo . sub . 43 600 305 50 45 . 91 10 . 35 0 . 17 118 caclh . sub . 2 po . sub . 4 . h . sub . 2 o ca ( h . sub . 2 po . sub . 4 ). sub . 24 455 245 45 44 . 80 10 . 88 0 . 164 119 caclh . sub . 2 po . sub . 4 . h . sub . 2 o ca ( h . sub . 2 po . sub . 4 ). sub . 25 350 200 40 44 . 62 10 . 14 0 . 168 116 caclh . sub . 2 po . sub . 4 . h . sub . 2 o ca ( h . sub . 2 po . sub . 4 ). sub . 2__________________________________________________________________________ preparation of feed grade calcium phosphate by spray - drying of a partially defluorinated slurry 94 . 5 parts of the solution prepared in example 1 ( b ) was reacted with 4 . 6 parts of 96 percent aqueous h 2 so 4 . the caso 4 . 2h 2 o thus formed was not removed from the solution . the mole ratio of ca / p in the solution portion of the slurry was about 0 . 825 . the slurry was then preconcentrated in a vacuum evaporator before spray drying . the gaseous effluent from this evaporator was condensed to produce a weak aqueous hcl solution which was subsequently used along with filter cake washings to absorb the hc1 and other water soluble components of the gaseous effluent of the spray dryer so that the hc1 might be recycled for use in acidulating more rock . the concentrated slurry was then spray dried in conventional equipment with the temperature of the dryer exit gases being maintained at 360 ° f . the slurry feed rate to the dryer was about 150 ml ./ min . the gaseous effluent from the dryer gas circulated through the evaporator condensate to recover the hc1 as an aqueous solution . the product from the dryer analyzed as follows : corresponding to a p / f ratio of 121 . the product was a mixture of cahpo 4 , ca ( h 2 po 4 ) 2 , caclh . sub . 2 po 4 , and caso 4 . recovery of hc1 was 95 %. the f / hc1 weight ratio in the recovered hcl stream was 0 . 0023 . preparation of feed grade monocalcium phosphate crystals by crystallization from a partially defluorinated solution a partially defluorinated calcium nitrate - phosphoric acid solution was prepared by digesting phosphate rock with mixed nitric and sulfuric acids by a method similar to that of example 1 ( a ). the filtered solution analyzed : the p / f ratio of the solution was about 36 indicating that 89 percent of the fluorine initially present in the rock was removed by the formation of the insoluble aluminum fluourine complex and na 2 sif 6 . the solution was fed to a crystallizer containing a mother - liquor saturated with respect to ca ( h 2 po 4 ) 2 and having the following analysis : the crystallizer was operated at 125 ° c . and 6 cm . hg . absolute pressure . the solution fed to the crystallizer had a ca / p mole ratio of about 0 . 5 . in the crystallizer the feed solution was converted into two phases : ( 1 ) a solid phase containing ca ( h 2 po 4 ) 2 and ( 2 ) a vapor phase containing hno 3 , h 2 o and small amount of fluorine as sif 4 and / or hf . the vapor phase was condensed for recycle to the rock digestion system . crystalline monocalcium phosphate was separated by filtration of the mother - liquor . the product analyzed as follows before washing : preparation of feed grade calcium phosphate by spray drying an acid free - partially defluorinated solution an aqueous solution of calcium dichloride was mixed with phosphoric acid of high fluorine content to produce a solution having a ca / p mole ratio of 0 . 8 and a solution p / f ratio of about 20 . the solution was treated with nacl and chilled to produce a precipitate in accordance with the procedure of example 1 ( a ). the slurry was filtered yielding a filtrate having a ca / p mole ratio of 0 . 8 and a p / f ratio of about 60 . the solution was then fed to a conventional spray dryer at a rate of about 125 ml ./ min ., with the exit gas temperature of the dryer being maintained at about 320 ° f . the dried product had a p / f ratio in excess of 100 and comprised a mixture of cahpo 4 , caclh 2 po 4 . h 2 o , and ca ( h 2 po 4 ) 2 . preparation of feed grade monocalcium phosphate crystals by crystallization from an acid free - partially defluorinated solution phosphoric acid of high fluorine content was treated with nac1 in accordance with the procedure of example 1 ( a ) to yield a defluorinated phosphoric acid having a p / f ratio of about 65 . the phosphoric acid and an aqueous solution of calcium dichloride were separately fed to a crystallizer containing therein phosphoric acid . the ca / p mole ratio in the feed to the crystallizer was about 0 . 5 and the p / f ratio about 65 ( based on the ca , p , and f in the two feed streams only ). the crystallizer was operated at 125 ° c . and 6 cm . hg . absolute pressure . crystalline monocalcium phosphate was recovered from the crystallizer having a p / f ratio in excess of 100 . in any of the prior examples , hydrochloric and nitric acid can , of course , be used interchangeably .