DE1807312A1 - Ammonium nitrate and phosphate fertilizer - Google Patents

Abstract

Method for the prepn. of ammonium nitrate and phosphate (1) Finely ground phosphate ore is digested with HNO3, giving calcium nitrate and acid phosphate (2) Ammonia is added to pH 3-6, precipitating Ca HPO4 The pptd. phosphate is filtered off and may be dried and used as fertilizer. (3) Alt., the ppt. phosphate may be treated with more HNO3 etc. to give 'ammon-phos' (4) After filtering off the CaSO4, the soln. is concd. until almost an H2O free melt, and 'prilled', giving solid 'ammon-phos'. (5) The clear soln. from (2) is treated with NH3 and CO2, giving NH4NO3; The soln. is filtered, concd. and prilled, giving solid NH4NO3. (6) The CaSO4 isolated at (3) may be re-used to provide (NH4)2SO4 for recycling Thus all the Ca in the phosphate rock is converted to CaSO4, producing 'ammonphos' with a P2O5: N ratio 2:1, and ammonium nitrate. Fertilisers.

Description

Process for the production of ammonium nitrate and phosphate containing Material The invention relates to a pipe for the production of ammonium nitrate and phosphate-containing material, in which phosphate stone with aqueous nitric acid is open-minded.

The invention is particularly directed to a method in which the phosphate stone is digested with aqueous nitric acid and the solution for the production of ammonia nitrate and rural phosphate products. With ammonia added will. The different types of phosphate minerals are said to be called "phosphate stone" as well as the actual apatite0 The traditional method of processing of phosphate stone for the production of soluble phosphates that are used as fertilizers will see the treatment of the ground stone with sulfuric acid before. The breakdown of the stone, which takes place in pits or the like for a certain period of time, gives a normal superphosphate product in which the phosphate components are in solution brought and made available in this way for plants after addition to the soil have been. In some cases, the reaction of the phosphate stone with aqueous Sulfuric acid to a slurry of solid calcium sulfate in phosphoric acid solution higher concentrated product manufactured. The solid calcium sulfate is obtained by filtration removed, concentrated the phosphoric acid solution and used to prepare triple Superphosphate implemented with another phosphate stone.

The acidification or digestion of phosphate stone with nitric acid has already been described in US Pat. No. 2,689,175. In this procedure the ground phosphate stone is reacted with aqueous nitric acid, with the Reaction mixture through the sulfate radical required to form the calcium sulfate Addition of an ammonium sulfate solution is made available. These reactants are combined with each other in such a ratio that a sludge of filterable Calelum sulfate or gypsum in an aqueous solution of phosphoric acid and ammonium nitrate accrues. The sludge is filtered off and ammonia is added to the clear solution and gradually concentrated, mainly ammonium phosphate and ammonium nitrate will be produced. The rranz provides a similar way of working. Patent specification 705,887. Other methods known in the art are in "Chemical Engineering", Volume 74, No. 22 (1967) on pages 86 to 88, 90 and 134-136.

In contrast, the invention provides a method of production of ammonium nitrate and phosphate-containing material, in which the phosphate stone is digested with aqueous nitric acid, which is characterized by that the acidic solution obtained for neutralization and for the precipitation of the thereafter separated dicalcium phosphate is mixed with ammonia, to the remaining Solution a soluble ammonium compound, its anion in the remaining solution able to form an insoluble calcium salt, the precipitated is added Calcium salt is separated off, and that the solution remaining at the end for production concentrated by ammonium nitrate.

The ground phosphate part is thus digested with nitric acid, whereby a solution of soluble calcium salts is obtained. This solution comes with Process streams, such as ammonia, carbon dioxide and ammonium sulfate, further treated, whereby valuable fertilizer products are produced.

In the following, the invention is intended to be based on the description of the process steps and reactions are summarized.

Phosphate stone, which usually contains impurities such as calcium carbonate and calcium fluoride, is digested with aqueous nitric acid to form a solution containing calcium nitrate and an acid salt of calcium phosphate The impurities also react, as a result of which further calcium nitrate is formed in the solution: Ammonia is added to the solution obtained in the digestion of the phosphate stone according to reactions (2) and (3) in order to raise the pH of the solution to a value generally in the range from 3.0 to 6.0 and to reduce the dioalcium phosphate in to precipitate the aqueous solution: The term neutralize means setting a pH value for the precipitation of the dicalcium phosphate and not necessarily a pH value in the region of 7.

The solution of calcium and ammonium nitrates is made up of the solid dicalcium phosphate, which can represent a product per se of the process, filtered off, since the dicalcium phosphate can be used as a fertilizer or as a food supplement. In most cases However, the solid dicalcium phosphate becomes Ammophos, which is a solid mixture of Represents nonoammonium phosphate and ammonium nitrate, further processed.

The clear aqueous solution of potassium nitrate and ammonium nitrate, which is formed during the filtration of the sludge product of step (4), can be reacted with ammonia and carbon dioxide in order to convert the calcium nitrate into ammonium nitrate and to precipitate the potassium carbonate in the aqueous solution: The solution obtained in reaction (5) is filtered to remove the potassium carbonate, whereupon the clear ammonium nitrate solution obtained is concentrated, and preferably until a practically anhydrous melt is formed, which is subjected to spray drying to obtain solid ammonium nitrate granules.

The residual dioaloium phosphate precipitated and separated off in reaction (4) is preferably further processed in this way. that it is digested with aqueous nitric acid, whereby an aqueous solution is obtained which contains dissolved caluminous nitrate and phosphoric acid: The aqueous solution formed in reaction (6) is reacted with ammonium sulfate and ammonia, an aqueous solution phase g being formed which contains ammonium nitrate and monoammonium phosphate and in which solid calcium sulfate has precipitated. The reactions between the individual components involved can be illustrated by the following equations: The solution formed in reactions (7) and (8) is filtered to remove the solid calcium sulfate, whereupon the clear solution containing ammonium nitrate and monoammonium phosphate is concentrated, preferably to a practically anhydrous molten salt which is subjected to spray drying to obtain a solid fertilizer which contains available water-soluble phosphate and available nitrogen and which is generally known under the name "Ammosphos".

The solid calcium sulfate formed and separated off by reaction (7) can be used to form further ammonium sulfate in solution for reaction (7). This happens because the solid calcium sulphate is suspended in water, whereupon the blow is made to react with ammonia and carbon dioxide: In the broadest sense of the invention, the dioalcium phosphate formed by reaction (4) is a product of this process, and reaction (5) can be carried out using any suitable ammonium salt whose anion forms an insoluble salt with the calcium cation. Thus, the process result residing in the formation of ammonium nitrate from the dissolved calcium nitrate obtained in the reaction (4) can be achieved by the reaction (7). The main characteristic of the process is that the calcium contained in the phosphate stone is split into two streams by reaction (4). The first stream, which is the aqueous phase formed by reaction (4), contains a third of the calcium of the original dicalcium phosphate and the calcium of the carbonate, fluoride, silicate etc. originally present in the phosphate stone, all of which in the end are formed as calcium carbonate of ammonium nitrate of a quality suitable for fertilizer purposes. The second stream contains two thirds of the calcium of the tricalcium phosphate, which after reaction (4) forms solid Dicalotumphoqhab, which is optionally reacted with ammonium sulfate after reaction (7) which leads to the conversion of all calcium in the dicalcium phosphate into gypsum. The end product is Ammophos with a ratio of 2 parts by weight of bound phosphorus pentoxide to one part of nitrogen, which can be mixed with ammonium nitrate and potash to form a series of NPK mixtures.

The method of the invention has several important advantages. So a complete separation of the calcium of the phosphate stone is obtained and through a process that is considerably simpler from a technological perspective is as the process that calibrates us on the crystallization of calcium nitrate the partial or complete recovery of the sulfate build up. Another advantage lies in the separate production of two valuable fertilizers, namely from Ammophos, which contains all nitrate in water-soluble form, and from ammonium nitrate. This fact gives great flexibility in the construction of fertilizers from NP and NPK type. In some cases, part of the intermediate stage Dicalcium phosphate as a commercial fertilizer andXor as a feed additive be released. If all of the dicalcium phosphate according to reactions (6) and (8) Converted to ammonium phosphate, then the Ammophos contains usable phosphorus pentoxide and nitrogen in a weight ratio of the equivalent amounts of about 2 to 1. Another advantage is that the process operates under relatively normal temperature conditions can be made and that no need for deep freezing as with the odds procedure exists. Another advantage is that the entire Impurities in the phosphate stone that one in the acidic solution of the reaction (1) Insoluble slime form and which usually lead to filtration problems lead, in the dicaloium phosphate precipitate of reaction (4), then subsequently in the cake made of plaster of paris or calcium sulfate the reaction (7) and finally contained in the precipitate of calcium carbonate of reaction (9) sind0 This sequence reduces the number of those involved in eliminating this sludge Difficulties to a minimum.

In the following, the invention will be based on the accompanying drawings are explained in more detail. In the drawings: Fig. 1 is a flow diagram of a Embodiment of the method according to the invention, and FIG. 2 shows a flow diagram of a further embodiment of the invention.

In the plant according to FIG. 1, a stream 1 is made of ground phosphate stone and a stream 2 of aqueous nitric acid is transferred into the decomposition vessel 3, in which the phosphate stone is digested and made soluble after reaction (1) will. In this unit 3, the reactions (2) and (3) given above run rruoh away. The phosphate stone of stream 1 generally consists of approx. 25 to 38% or more equivalents of phosphorus pentoxide, approx. 45 to 50% equivalents of calcium oxide and about 2.5 to 4% equivalents of fluorine, all percentages being by weight are related. Stream 2 of aqueous nitric acid generally contains approx.

25 to 70 wt% nitric acid. Its flow rate is im Ratio to that of the stream 1 set sufficiently high that in the Unit 3 maintains a pH in the range of approx. 0.5 to 2.0 Uen will. Inside the digestion vessel 3, a temperature in the area Maintained from approx. 50 to 100 ° C. To mix the reactants and a stirrer 4 is provided in unit 3 to produce a uniform solution, with the solution a small amount of greasy impurities that are in the acidic Solution are insoluble, may contain. As stated earlier, happened the slimy sludge the process in different precipitations. He will then removed with the last calcium carbonate precipitate.

The stream 5 of the aqueous solution discharged from unit 3 contains as indicated by the reaction (1) above, mainly calcium nitrate and an acidic one Calcium phosphate salt, generally monocalcium phosphate. The stream 5 becomes Transferred to a neutralization vessel 6 together with an ammonia stream 7, with the latter is used to adjust the pH to a value of generally about 3.0 to 6.0 to eztöhen and in the aqueous solution after the reaction (4) the solid crystalline To precipitate dicalcium phosphate. The muddy stream 8 obtained from the unit 6 is discharged, a m solid filter 9, from which a stream 10 passes a clear solution is taken which contains dissolved calcium nitrate and ammonium nitrate.

The stream of solution 10 is passed into a conversion vessel 11, in which after the reaction (5) the calcium ions as solid calcium carbonate failed will. In the unit 11 are an ammonia stream 12 and a carbon dioxide stream 13 passed, which together in the aqueous solution essentially ammonium carbonate form, which in turn is formed after reaction (5) with the calcium nitrate of solid calcium carbonate and further ammonium nitrate. The stream of mud 14, which is discharged from the unit 11, is passed into the solids filter 15, from which a stream 16 of solid calcium carbonate is withdrawn as waste.

The stream 17 removed from unit 15 from the clear solution represents an aqueous ammonium nitrate solution, which after transfer into the concentrator 18 to a concentrated solution or a practically anhydrous melt is evaporated. The unit 18 is provided with a spiral 19 through which steam or another heating medium is conducted. The resulting water vapor is out of the unit 18 through line 20. The unit 18 can in practice on the other hand also be a thin film evaporator, t1 which case the stream 17 as Liquid film on the inner surfaces of vertical pipes through which a heated Air flow is directed, flows downwards and- the steam is heated outside the tubes will. In any case, a stream 21 is made up of practically anhydrous ammonium nitrate melt formed in the unit 18, which to achieve this result by any suitable Can be type of construction. The stream 21 is now in the head of a spray tower 22, which is conventional Is type and is usually air ventilated, sprayed or otherwise dispersed. Solid granules of ammonium nitrate are formed in unit 22. The product stream 23 obtained, which consists of granular ammonium nitrate, is the appropriate use, such as for fertilizers, supplied.

In the filter unit 9, to which it was again returned, can the discharged solids stream 2X, which consists of dicalcium phosphate, via the line 25 wholly or partially its intended use as a commercial fertilizer or be transferred as feed grade material. In most cases it will however, the entire stream 24 or part of it is further processed according to the invention, what happens on the way via the stream 26, which together with a stream 28 from aqueous concentrated nitric acid, which generally has a nitric acid content from about 25 to 70% by weight, preferably from about 35 to 50% by weight, in one Digestion vessel 27 is transferred. Stream 28 makes enough nitric acid fed to the solution in the unit 27 at a pH in the range from about 0.1 to 1.0, the temperature in the unit 27 being generally in the range is kept from approx. 40 to 90 ° C. The stream 26 from the dicalcium phosphate is in the unit 27 after the reaction (6) digested and made soluble, whereby a solution is obtained which contains calcium nitrate and phosphoric acid together with a contains remaining amount of nitric acid.

The resulting stream 29 of the solution formed in the unit 27 is transferred to the reaction vessel 30, in which the solution after the reaction nen (7) and (8) with an ammonia stream @ 31 and a stream 32 from an ammonium sulfate solution is treated, whereby a sludge of precipitated solid calcium sulfate in a aqueous solution phase containing ammonium nitrate and monoammonium phosphate obtained will. The pH of the sludge in unit 30 is adjusted to a value of approx.

0.5 to 2> 0 maintained, the temperature generally in the The range from about 5000 to 1000C is, the received from the unit 30 discharged Sludge stream 33 is transferred into the solids filter 34, from which a stream 35 from a clear aqueous solution containing dissolved ammonium nitrate and monoammonium phosphate contains, is withdrawn0 The stream 35 is in an exhaust evaporator 36, the with regard to the type and function in general of the unit described above 18 is similar. A heating coil 37 is provided in the unit 36, which is used to heat the water and to evaporate from the liquid solution. The water vapor formed is removed from the unit 36 through the line 38 and the concentrated liquid solution obtained, generally in the form a practically anhydrous melt is present from the unit 36 through the conduit 39 passed into the spray tower 40, which in terms of the design and function of the Unit 22 described above is similar. The solid formed in unit 40 Granules contain both monoammonium phosphate and ammonium nitrate and are im generally intended as ammophos or nitrophosphate for use as a fertilizer.

The solid granules of Ammophos are collected from the bottom of the unit 40 removed through the line 41 and further use, for example as a fertilizer or the like. " led. Otherwise, the stream 35 can also be any suitable Granulating device are transferred.

From the solids filter unit 34, which was again referred to, the stream of solid calcium sulfate 42 is discharged and processed so that one Recyclable ammonium sulfate solution is obtained. The current 42, which is not shown, is slurried with water and placed in the decomposition vessel 43 transferred together with an ammonia stream 44 and a carbon dioxide stream 45. In this unit 43 takes place the reaction (9) with the formation of ammonium sulfate and Precipitation of the solid calcium carbonate takes place. The one discharged from unit 43 Solids stream 46 is filtered in the solids filter 47 and the separated solid Calcium carbonate stream 48 discarded. Stream 48 contains essentially all of it slimy sludge initially present in stream 5 since that in the units 6, 30 and 43 successive precipitation steps taking place the entrainment and effect containment of this sludge. As described above, the unit 47 becomes a stream 42 of clear aqueous ammonia sulfate solution is returned to unit 30.

The system according to FIG. 2 represents a further embodiment of the invention Process in which the ammonium sulfate is used to the whole Calcium originally solubilized in the course of the process, including calcium ions, those in the filtrate from the original filtration of the dicalcium phosphate are present to fail. Since the other parts of the process sequence of Fig. 2 according to the sequence.

1, they are only briefly shown in the flow sheet of FIG described.

A stream 49 of ground phosphate stone and a stream 50 of aqueous Nitric acid are poured into the stone digestion tank 51, which is equipped with stirrers inside 52 provided is convicted. The electricity produced in the tank 51 the solution 53 passes together with an ammonia stream 55, which is used in the Unit 54 to precipitate the solid dicalcium phosphate into the ammonia conversion tank 54. The sludge stream 56 obtained is discharged from the unit 54 into the solids filter 57 transferred, from which the aqueous stream of solution 58 is withdrawn, the dissolved Contains calcium nitrate and ammonium nitrate.

The stream 58 is now according to a further embodiment of the invention Process processed so that a solid calcium sulfate salt is precipitated and further ammonium nitrate is formed in solution. The stream 58 becomes together passed with the stream 60 of ammonium sulfate solution into a reaction vessel 59. In of the unit 59 takes place between the streams 58 and 60, the reaction indicated above (7) instead, resulting in the precipitation of solid calelum sulfate and the formation of more Ammonium nitrate happens in solution.

The obtained sludge flow 61 is from the unit 59 into the solids filter 62 transferred, from which the stream 63 is taken from separated solid calcium sulfate and used for the production of further ammonium sulphate solution for the recycling will. The clear liquid solution discharged from unit 62 by stream 64 now consists essentially of an aqueous ammonium nitrate solution contained in the Unit 65 is heated and concentrated, heating by means of a steam spiral 66 takes place. From the unity 65 is the water vapor through the pipe 67 discharged and the stream 68, which consists of essentially anhydrous ammonium nitrate melt, which is formed in the unit 65 consists, transferred into a spray tower 69, in which solid ammonium nitrate granulate is formed, which is discharged through line 70 will.

The solid filter unit 57, which was referred to, becomes discharged a stream 71 of solid dicalcium phosphate, which is partly through the leltung 96 can be recycled. Part or all of the stream 71 Current reaches the digestion tank 73 by way of the line 72 in order to react to enter with stream 74 of aqueous nitric acid. The received Solution stream 75, which now contains dissolved phosphate and nitrate, comes from the Unit 73 into the gypsum precipitation vessel 76, in which the stream 75 with the ammonia stream 77 and the ammonium sulfate solution stream 78 to precipitate the calcium sulfate and to Formation of ammonium nitrate and monoammonium phosphate is implemented in solution The sludge flow 79 received passes from the unit 76 into the solids filter 80, from which the stream 81 from the clear solution, the ammonium nitrate and monoammonium phosphate contains, is passed into the concentrator 82.

The concentrator vessel 82 is provided with a steam spiral 83. Of the resulting water vapor is discharged through line 84. The one in unit 82 stream 85 formed from concentrated and essentially anhydrous melt reaches the spray tower 86, in which a solid ammophos granulate is formed.

The solid granulate is discharged from the unit 86 by the stream 87, the consists of granules, the ammonium nitrate and nonoammonium phosphate, which are used as fertilizers are suitable, contains, discharged.

The unit 80, which was referred to, becomes through the line 88 Removed calcium sulfate which is combined with stream 83 to stream 89. The combined calcium sulfate stream 89 is now processed further in such a way that Streams 78 and 60 are formed from ammonium sulfate solution for recycle Stream 89 is fed into digestion and reaction vessel 90 along with the ammonia stream 91 and the carbon dioxide stream 92 transferred. In this unit 90 takes place the above given reaction (9) instead. The resulting sludge stream 93, which consists of solid Calcium carbonate in ammonium sulphate solution passes from the unit 90 into the Solid filter 94. This unit 94 becomes stream 95 of solid calcium carbonate discarded and streams 60 and 78 of clear ammonium sulfate into the process, such as described above, returned again.

Numerous are within the scope of the invention presented herein further refinements. The ones for the process variables, such as the concentration of the solution conditions, pH values and temperature, the ranges given are preferred Embodiments for the optimal use of the concept of the invention Procedure, but this can also be outside these limits in suitable cases It can be seen that the various vessels used for reaction, to the Digestion and precipitation of solids in practice with suitable mixing and stirring means such as elements 4 or 52 may be provided. The under Formation of further ammonium nitrate in solution, solid precipitation taking place Calcium salt from process streams 10 or 58 can thereby be achieved in practice that the dissolved calcium nitrate with any suitable ammonium salt, its Anion with which calcium cation forms an insoluble salt, is reacted. A part of the plurality of solution concentrators 18, 36, 65 and 82 or all of them can be thin-film evaporators represent in which the dilute solution on the inner surface of a multitude vertical tubes through which heated air to entrain the water vapor is directed above, as a liquid film is directed downwards, with the vertical Pipes are heated externally by steam or another suitable heating medium. In some cases, one or more of the concentrated liquid streams 21, 39, 68 and 85 as concentrated aqueous liquid solutions for use as liquid fertilizers are formed. In some cases it may be desirable to design the fertilizer products as granulated or crystalline products, in which cases the streams 17, 35, 64 or 81 in a suitable granulator, a vacuum crystallization device or the like. be convicted.

The following is an example of the method according to the invention in Laboratory scale.

Example For testing the method according to the invention on a laboratory scale was ground Florida phosphate stone with a content of 33.6% phosphorus pentoxide, 48.00 ffi calcium oxide and 3.56% fluorine used. 500 g of phosphate stone were with 1450 g of a 24.85% nitric acid solution were digested for one hour at 750C. The pH of the sludge was 0.6. The sludge was then mixed with 275 ml of 28% strength aqueous ammonia added to a pH of 4.1. The mixture became one hour stirred and filtered. The resulting cake was dried at 8000 and weighed at a content of 32.33% phosphorus pentoxide and 35.01% calcium oxide 513 g. It found This means 99% of the phosphorus pentoxide from the stone in the filter cake.

The dry cake was then further digested with nitric acid, including 454 g of the cake, which was digested with 750 g of 42% nitric acid, was used. The dry cake was digested for one hour at 6500, the pH of the sludge being 0.3. After the exposure period, 975 g of a 40% strength ammonium sulfate solution were added and the reaction mixture for three hours heated to 800C. The pH of the sludge was 0.9, with 2 moles of nitric acid per mole of calcium in the dicalcium phosphate was required.

The sludge was then filtered at a high rate of filtration. The total volume of the filtrate was 2630 ml, the filtrate being 5.22 g of phosphorus pentoxide contained per 100 ml of solution. The filtrate contained 92 ff of the phosphorus pentoxide the phosphate stone.

On the basis of the double digestion technique according to the present Invention, 97.9% of the phosphorus pentoxide was made soluble from the phosphate stone, whereby the nitric acid consumption is about 80% of the consumption from the US patent 2,689,175 known processes

Claims (9)

P a t e n t a n s p r ü c h e 1. Process for the production of ammonium nitrate and phosphate-containing material, in which phosphate stone with aqueous nitric acid is digested, thereby g e -k e n n z e 1 c h n e t that the acid obtained Solution for neutralization and for the precipitation of the dicalcium phosphate which is then separated off ammonia is added, a soluble ammonium compound is added to the remaining solution, their anion to form an insoluble calcium salt in the remaining solution capable, is added, the precipitated calcium salt is separated, and that Concentrate the remaining solution for the production of ammonium nitrate will. 2. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t, that the soluble ammonium compound is ammonium sulfate or ammonium carbonate. 3. The method according to claim 2, daduroh g e k e n n -z e 1 e h n e t, that the ammonium carbonate by adding ammonia and carbon dioxide to the remaining Solution is formed. 4. The method according to any one of the preceding claims, characterized g e it is not noted that the dioalotum phosphate is aqueous with a second stream Nitric acid is digested, to the separated precipitated calcium sulfate Ammonia and ammonium sulphate are added and that the remainder in the end Solution is concentrated to a nitrogen-containing phosphate product. 5. The method according to any one of claims 1 to 4, characterized g e k e n n it is noted that the aqueous nitric acid contains 25 to 70% by weight of nitric acid. 6. The method according to any one of claims 1 to 5, characterized g e k e n n shows that the remaining solution by evaporation to a melt, which is spray dried is concentrated. 7. The method according to any one of claims 4 to 6, characterized g e k e n n notifies that the phosphate product containing nitrogen is available phosphate contains, its equivalent amounts of phosphorus pentoxide and usable nitrogen are in a weight ratio of approx. 2: 1. 8. The method according to any one of claims 4 to 7, characterized g e k e n n notices that the precipitated calcium sulfate is suspended in water and with Ammonia and carbon dioxide are reacted to precipitate calcium carbonate, which from the aqueous ammonium sulfate solution, which is returned to the precipitation of the calelum sulfate is separated. 9. The method according to claim 8, characterized in that g e k e n n -z e i o h n e t, that the solution remaining in the separation of the dicalcium phosphate is ammonium sulfate is added, the separated calcium sulfate with that from the stream after the digestion calcium sulfate precipitated from the calcium phosphate is combined, and that the combined Calcium sulfate then slurried in water to convert into ammonia and carbon dioxide will. L e r s e i t e