DE1233417B - Process for the production of multi-nutrient fertilizers - Google Patents

Description

Process for the preparation of complex fertilizers The invention relates to improvements in the manufacture of compound fertilizer shakers.

Fertilizers usually consist of mixtures of salts that add the Elements necessary for the nutrition of plants, namely nitrogen, phosphorus and potassium. The nitrogen content in such mixtures is normally derived from ammonium salts such as ammonium sulfate, ammonium nitrate and the like, or other nitrogen-containing Compounds such as nitric acid and urea; the phosphorus usually comes from Rock phosphates and the potassium from potassium salts, such as potassium chloride.

However, the naturally occurring rock phosphates contain phosphates, which are difficult to absorb by the plants and are therefore used as plant nutrients are generally unsuitable, and it is therefore necessary to include the phosphates in to convert them into a form in which they are absorbed by the plants. Such Methods consist, for example, that the rock phosphates with acids or alkalis but the methods commonly used are acid digestion the rock phosphates. A large number can be used for the acid digestion of the rock phosphates of acids are used, but in technology the acids are usually the strong mineral acids, namely sulfuric acid, phosphoric acid and nitric acid. These acids can be used alone or in admixture with one another.

The present invention has a method of making complex fertilizers to the subject in which the rock phosphates with nitric acid, optionally under With the use of other acids, it can be digested. In such procedures there is one of the salts produced from calamine nitrate, which, however, because it is highly hygroscopic is generally unsuitable for the production of mixed fertilizers. It is Although known that calcium nitrate can be reacted with potassium sulfate, so that Calcium sulphate and potassium nitrate are formed.

When potassium sulfate is added to the raw phosphate digestion product obtained with nitric acid, however, the reaction does not proceed in a simple manner; instead, calcium-potassium double sulfates are frequently formed. However, these double salts are insoluble in water and their formation makes the whole process uneconomical. When carrying out this reaction, the precipitates that can be formed consist of gypsum (CaS0, -2H, 0), anhydrite (CaS04), hemihydrate (CaS04 - 1 /, H, 0), penta salt (5 CaS04 - K2S04. 1 -110) and syngenite (CaS04 - K2S04 - H20) - Due to the formation of these insoluble precipitates, a not inconsiderable part of the potassium is lost for the desired purpose, which of course greatly reduces the value of the fertilizer produced.

It is also known, digestion process of rock phosphates or phosphate rocks with nitric acid at temperatures between z. B. 80 to 95 or 80 to 100'C or at similar temperatures. However, since the formation of complex potassium-calcium double salts is only prevented if, according to the invention, a certain concentration range of soluble sulfate, namely 0.5 to 40 / ", is adhered to, these known methods also result in double salt formation and thus with the occurrence the disadvantages and potash losses already mentioned above are to be expected.

The aim of the present invention is now a continuous process for the production of phosphate fertilizers, in which the disadvantages indicated above and losses do not occur and also the formation of potassium-calcium double sulfates is avoided. For this it is necessary to have both a specific concentration to adhere to soluble sulfate as well as in a certain temperature range work.

The continuous process according to the invention for the production of complex fertilizers by digesting rock phosphates with about 40 to 80 percent strength by weight nitric acid in stirred containers, adding potassium sulfate to the digestion solution, continuous removal of the reaction solution from the digestion container and, if necessary, the following process steps: separation of the precipitated calcium sulfate from the digestion solution, neutralization the same with ammonia or the like, granulation and drying of the neutralized mass is now characterized in that the potassium sulfate is added to the nitric acid raw phosphate digestion solution in such quantities and at such a rate that a soluble sulfate concentration of 0.5 to 40% in the solution in particular 1 to 1 '5010, is maintained and this reaction temperatures of from 60 to 90'C, especially gO'C, is maintained.

If only a low-percentage fertilizer is to be produced, the gypsum can be left in the fertilizer. However, if a high-proof fertilizer is to be obtained, the precipitated calcium sulphate must be removed. The fertilizer can, under certain circumstances, also be used in the form of the acidic reaction product. In general, however, the aim is to produce a solid, practically neutral product and the product must therefore be treated with a neutralizing agent such as ammonia or potassium hydroxide. The product obtained can be dried and / or granulated.

The method according to the invention in the embodiment according to which removing the plaster of paris and neutralizing the product results in the recovery of one high-quality, non-hygroscopic compound fertilizer that contains the elements nitrogen, Contains phosphorus and potassium and is chloride-free.

The neutralizing agent used preferably consists of ammonia or an ammonizing solution, since these substances are the cheapest sources of nitrogen. However, other neutralizing agents such as potassium carbonate and potassium hydroxy can be used if desired. In its simplest embodiment, the method according to the invention can be represented by the following reaction equations: P, 0..3.5Ca0 + 7HNO, + 3.5K, SO4 1 2H, PO, + 7KNO, + 3.5CaS04-2H, 0 12NH, 2NH4H1P04 + 7KNO, or using less nitric acid: P, 0, - 3.5 Ca0 + 5 HNO, + 3.5 K, SO, 1 41 5 KNO, + 2 KH1P04 + 3.5 CaSO, - 2 H20 In the latter case, the product obtained is only slightly acidic, so that the ammonization may be omitted.

If it is desired to change the N: P: K ratios in the end product, for this purpose, for example, nitric acid, phosphoric acid or Potassium salts are added and then the ammonization can be carried out.

In the practical implementation of the procedure, the implementations need not exactly following the formula given above; for example, in the case of ammonization a mixture of mono- and diammonium phosphates can be produced. Can also The amount of neutralizing agent may be greater or less than specified above is.

The process can be carried out by adding the rock phosphate first digested with acid and then the sulfate is added to the product obtained. According to the preferred embodiment of the invention, however, the rock phosphate, the nitric acid and the sulfate are used simultaneously for the reaction.

An essential feature of the invention is that the method as a continuous process with continuous addition of the reactants and continuous removal of the reaction product is carried out. The present Procedure cannot be performed as a batch procedure.

If nitric acid is used alone as the disintegrating agent, it is preferably used in amounts which go beyond the niolar requirements of 5 mol per mol of P, 0 in the R-ohphosphate. The amount of acid used is expediently 5 to 15 moles per mole of P, 0, in the rock phosphate. If excess nitric acid is used, the product will also contain ammonium nitrate and, if desired, some of this excess can also be added later in the process after filtration.

If desired, the raw phosphates can also be digested with a mixture of acids consisting of nitric acid and sulfuric acid and / or phosphoric acid. With the use of acid mixtures, the amount of the nitric acid optionally also be reduced, however, that the total acidity of the acid mixtures 5 moles of nitric acid per mole of P, 0 "corresponds to rock phosphate or greater. However, the nitric acid component of the acid mixture is not less than 3 moles per Mol P, 0, in the rock phosphate.

If sulfuric acid or a sulphate is also used, this has an influence on the precipitation of the calcium sulphate and the total amount of sulphate ions present in the liquid phase and originating from any source must, according to the invention, be in the range from 0.5 to 40%. It follows from this that all components of the reaction mixture are interrelated and, apart from the specific sulfate ion concentration, can be adjusted as desired so that a fertilizer of the desired composition is obtained.

If acid mixtures are used in the acid digestion stage, nitric acid becomes Always used in the digestion stage with or without the addition of sulfuric acid. Becomes sulfuric acid is also used, it is preferably added before the filtration stage; other Acids can and can be added immediately after the filtration step mixed together or added one after the other.

If so, for example, a mixture of nitric acid and sulfuric acid and phosphoric acid is used, it may be appropriate to use the rock phosphate first to treat with sulfuric acid and nitric acid and after the filtration stage the Add phosphoric acid. On the other hand, some of the nitric acid can be combined used with the other acids to digest the rock phosphate and then the rest to be added later.

The acids used in the process according to the invention are preferably used in the form of the commercially available concentrated acids. Thus, the nitric acid can be used in a concentration of 40 to 800 /, and expediently, for example, in a concentration of about 57% . The sulfuric acid is expediently used in a concentration of 50 to 100 / "for example a concentration of about 960 /" , and if phosphoric acid is also used, it should expediently have a concentration of 50 to 700 / " for example a concentration of about 60" /, (expressed as H2P0 ").

The raw phosphate to be processed according to the invention can consist of any of the commonly used natural phosphates, such as, for example, caleium raw phosphate, which can be obtained, for example, from Morocco, Rhodesia, Florida, various Pacific islands, Uganda, Palabora and Kola. The rock phosphate is advantageously not finely ground and has a particle size of about 1.5 mm or less.

When the potassium sulfate is added, the concentration of soluble sulfate in the liquid phase must, according to the invention, be in the range from 0.5 to 4.0 ″, and it should preferably be about 1 to 1.50 ″ sulfate, and the reaction temperature must also be are in the range of 60 to 90'C, and it should preferably be about RO'C so that the calcium sulfate as gypsum (CaSO, - 2 H.0) is precipitated.

The nature of the gypsum precipitate depends on the reaction conditions, and if working within the preferred limits of the concentration of soluble sulfate in the liquid phase of 1 to 1.50 /, and at a temperature of about 80 ° C , the gypsum precipitate is in obtained in a very easily filterable form.

The soluble sulfate content can be in the required range Appropriately maintained by a tank system with constantly circulating Agitator or a similar device is used. Such a reaction # device can consist of a tank or container or several containers. Will be expedient the method using a device made up of several reaction vessels, preferably three containers. When using a reaction device with multiple vessels, the reaction mixture flows through the vessels one after the other.

In such a device with a plurality of reaction vessels can the rock phosphate and some or all of the nitric and phosphoric acids Amount to be added to the first container. The potassium sulfate and the sulfuric acid can either only with the first container or one, depending on the type of reaction or more of the following. Container are added. A good accomplishment is however, it is essential in all parts of the reaction plant, so that there is a high local concentration soluble sulfate is avoided.

It is necessary that the supply of soluble sulphate ion is continuously regulated so that the concentration of soluble sulphate in the liquid phase is within the prescribed limit values of 0.5 to 40%. By reacting the acid with the rock phosphate, calcium ions are set free in the present process, and these react with the sulfate ions to form calcium sulfate, which is precipitated. As a result, the concentration of soluble sulfate in the liquid phase represents the available sulfate ions which are in excess of the available calcium ions. In order to maintain the concentration of soluble sulphate within the prescribed limit values of 0.5 to 40%, the rate of supply of sulphate ions must therefore not exceed the rate of the formation of calcium ions caused by the acid digestion of the rock phosphate.

In general, the acid digestion of the rock phosphate takes place quickly, and in these cases Lann the total of the required style of the first Step of the process can be added. In those cases where the acid digestion of the ore, however, is slow. takes place, the sulphate addition must be adjusted accordingly will.

The residence time of the reaction mixture in the device can vary over a wide range from, for example, 30 minutes to 2 hours, but it is preferably about 1 hour.

The total sulfate addition, whether as potassium sulfate or in the form of sulfuric acid, should expediently not be more than about 3.5 moles per mole of P.0-in the rock phosphate, and the amount of potassium sulfate should not be less than about 0.5 mole per mole P, 0, in the rock phosphate.

If desired, the method can also. with recycling of the liquid Product and / or the washing liquids. carried out from the filtration stage of the gypsum will.

The reactants used, with the exception of the specific sulfate ion concentration, can be adjusted and measured in such a way that a fertilizer of the desired composition is obtained. , K 0 15.25: For example, a fertilizer, the IRN per 100 units 58 units Pflanzepnährstoffe ratio N: P, 0, 15.25: comprises 27.5, are obtained by rock phosphate with nitric acid and sulfuric acid in the presence of reacted by potassium sulfate in the manner described above, the calcium sulfate is filtered off, further nitric acid is added and the reaction product is then ammoniated according to the following equations: P, 0, - 3.5 CaO + 5.43 HNO, + 0.785 H, SO, + 2.715 K, SO, 1 2 H, PO, + 5.43 KNO, + 3.5 CaSO, - H, 0 1,355 ENT, then 3.355 NH, 2 NH, H, PO, + 5.43 KNO, + 1.355 NHNO, The invention is illustrated in more detail by the following examples. The percentages given are percentages by weight, unless otherwise stated.

EXAMPLE 1 425 parts per hour of rock phosphate from Morocco (33.40 %, P, 05, 50.3'1, Ca0) with 600 parts of 570% nitric acid per hour and 80 parts 960% sulfuric acid per hour and 473 parts of potassium sulfate per hour and 500 parts of water per hour at 80.degree . The reaction was carried out in a reaction vessel with a rotating stirrer, from which the product was drawn off by overflow. The residence time was 30 minutes and the SO, concentration was 0.80 / ,. The product withdrawn from the container was filtered on a belt filter in order to remove the precipitated gypsum, whereupon 150 parts of 570% nitric acid per hour were added to the filtrate. 57 parts of anhydrous ammonia were also added to the filtrate per hour, whereby, after granulating and drying the ammoniated mass, a fertilizer was obtained which contained monoammonium phosphate, ammonium nitrate and potassium nitrate.

This fertilizer, which has 501 impurities, contained 58 plant nutrient units per 100 parts, and the ratio of N -. P, 0, K, 0 was according to analysis 15,25: 15,25: 27,5. The precipitated calcium sulfate was essentially in the form of gypsum.

EXAMPLE 2 425 parts per hour with 334 parts 5711/0i-er nitric acid per hour, 203 parts 960% sulfuric acid per hour, 263 % per hour of a morocco phosphate (33.4 %, P, 0 " 50.3 Ca0) Parts of potassium sulfate and 650 parts of water reacted per hour at 80 ° C. The reaction was carried out in a reaction vessel equipped with a stirrer, from which the product was drawn off by overflow. The residence time was 11 /. Hours and the SO, concentration was 1.40 / The continuously withdrawn liquid product was filtered using a belt filter to separate the precipitated gypsum, and 508 parts of 571% nitric acid were added to the filtrate per hour . 129 parts of ammonia were also added to the filtrate per hour Granulating and drying the ammoniated product, a fertilizer was obtained which contained mono- and diammonium phosphate, ammonium nitrate and potassium nitrate.

The end product, which has 501, impurities, contained 51 units of plant nutrients in an N: P20.5: K.0 ratio of 3: 2 : 2; the analysis showed a nutrient ratio of 22: 14.5 : 14.5. The precipitated calcium sulfate consisted essentially of gypsum.

Example 3 In the first vessel of a reaction apparatus which consisted of three containers equipped with stirrers and was maintained at 80'C, were with a residence time of 20 minutes in each tank per hour 425 parts unground Florida phosphate (33.40 /, PA, 480 /, Ca0) are used. 278 parts of 700% sulfuric acid, 334 parts 570% of nitric acid, 176 parts of potassium sulfate and 540 parts of water were also added to the first container per hour. 87 parts of potassium sulfate were added per hour to the second container. The concentration of soluble sulfate in the aqueous phase was kept at 1.10 / 1.

After draining through the overflow from the third container, the slurry was filtered to remove the gypsum, and 283 parts of 571% nitric acid were added to the filtrate per hour. Ammonia was then added in an amount of 77 parts per hour. After granulating and drying the mass, a fertilizer with an N: P, 05: K, 0 ratio of 1: 1: 1 was obtained that contained about 55 plant nutrient units in the ratio of 18.25: 18.25: 18.25 . The precipitated calcium sulfate consisted essentially of gypsum.

Example 4 Morocophosphate # 33, 40 /, P, 0,) corresponding to an amount of 100 parts of P, 0, was continuously mixed with 277.5 parts of potassium sulfate, 86.3 parts of 980% sulfuric acid, 304 parts of 660 per hour /, iger nitric acid and 1000 parts of recycled filter washing water (or returned material) implemented at 78'C. During this ongoing acid digestion reaction, the sulfate concentration of the liquid phase was adjusted to 0.6 percent by weight SO 2.

The precipitated gypsum was filtered off on a circulating belt filter, and 121.5 parts of 6611% nitric acid and 45.7 parts of anhydrous ammonia were then added continuously per hour to the filtrate, so that a fertilizer was obtained after the ammoniated mass had been granulated and dried , which contained 56 units of plant nutrients, in a ratio of N: P, 0 ,: K, 0 of 16:16:24. The filter cake was washed with water and the wash waters were returned to the process. The precipitated calcium sulfate was essentially in the form of gypsum.

Example 5 Florida phosphate (33.5 "/, P20,) corresponding to an amount of 100 parts of P, 0, per hour was continuously added per hour with 277.5 parts of potassium sulfate, 87.3 parts of 980% sulfuric acid, 304 parts of 660 / ,) nitric acid and 1000 parts of recycled filter washing water are reacted at 85 ° C. During this continuous acid digestion reaction, the sulfate ion concentration of the liquid phase was regulated to 1.2 percent by weight SO.

The precipitated gypsum was filtered off on a circulating filter, whereupon 121.5 parts of 660/0 strength nitric acid and 45.7 parts of anhydrous ammonia were added per hour to the filtrate, whereby, after granulating and drying the ammonium product, a fertilizer was obtained which contained 56 plant nutrient units in a ratio of N: P2O5: K, 0 of 16:16:24. The filter cake was washed with water and the wash waters were returned to the process. The precipitated calcium sulfate was essentially in the form of gypsum.

For comparison, Florida phosphate (33.40%, P, 0,) corresponding to an amount of 100 parts of P, 0 per hour, continuously per hour with 277.5 parts of potassium sulfate, 87.3 parts of 98% sulfuric acid, 304 parts 66 "/, iger nitric acid and 1000 parts of the filter wash water recycled from the above process reacted at 550C. The sulfate concentration of the liquid phase was kept at 1.9 percent by weight SO4. The slurry overflowing to the filter contained calcium sulfate in the form of pentasalt and syngenite, so that substantial losses of potassium occur in this procedure. Example 6 Unmilled moroccan phosphate (33.40 /, P, 0,) of a particle size such that it passed through a 16 mesh sieve (British Standard), equivalent to an amount of 100 parts of P, Q, per hour, was the first of three tanks or vessels equipped with agitators were added to an overflow reaction plant maintained at 70 ° C. with a residence time of 20 minutes in each vessel. 190 parts of potassium sulfate, 88.4 parts of 980% strength sulfuric acid and 304 parts 660% strength nitric acid and 1000 parts of filter wash water and reflux were also added to the first container per hour. 87.5 parts of potassium sulfate were added per hour to the second container. The sulfate concentration of the liquid phase of the slurry emerging from the third vessel was regulated to 2 percent by weight SO.

After draining from the third container, the precipitated gypsum was filtered off on a rotating filter, and 121 parts of 660 pounds per hour nitric acid and 45.7 parts of anhydrous ammonia were then added to the filter, so that the ammoniated mass was granulated and dried a fertilizer was obtained containing 56 units of plant nutrient in an N: P.05: K2O ratio of 16:16:24 The precipitated calcium sulfate consisted essentially of gypsum.

For comparison, unmilled moroccan phosphate (33.40 ″) of the particle size mentioned corresponding to an amount of 100 parts of P20.5 per hour was added continuously per hour with 277.5 parts of potassium sulfate, 101.3 parts of 98 ″ sulfuric acid, 304 Parts of 660 /, i, -, e nitric acid and 1000 parts of recycled filter washing water at 80'C in a reaction system consisting of stirred tanks as described above with a residence time of 20 minutes in each tank. The sulphate concentration of the liquid phase of the slurry exiting the third vessel was maintained at 6% SO 1 by weight. The calcium sulphate in the slurry running off from the third container consisted of penta salt (5 CaS04 - K2S04 - H, 0), so this procedure leads to substantial losses of potassium.

Only for a further comparison was unground morocco phosphate (33.40 /, P.0,) corresponding to 100 parts of P, 05 per hour continuously per hour with 277.5 parts of potassium sulfate, 105 parts of 980 /, sulfuric acid and 304 parts of 66 "/ , nitric acid and 1000 parts of filter wash waters and return material at 85'C in a three stirred vessels reaction system and a residence time of 20 minutes, reacted in each container, as has been described above. the sulfate concentration in the liquid phase was 8 0 / ,. The slurry overflowing from the third container contained large amounts of unreacted rock phosphate and syngenite (CaSO, - K, SO, - H, 0), so that the conversion of the phosphate was not only incomplete but also associated with substantial losses of potassium 7 Unmilled moroccan phosphate (33, 40 /, P, 0,) of a particle size such that it passed through a 16-mesh sieve (British Standard), -, an amount per hour was equivalent to d 142 parts P, 0 " fed to the first stirred tank of a system consisting of three such tanks and working with overflow, which was kept at 80 ° C , with a dwell time of 30 minutes in each tank. The first container were also per hour 459 parts of potassium sulfate, 1105 parts of 57 "/, nitric acid and 1500 parts of recirculated filter washings or return material is added. The second container were per hour added to 150 parts of potassium sulfate. The sulfate concentration of the liquid phase of the slurry was adjusted to 1, 2 percent by weight sulphate included.

After draining from the third container, the precipitated gypsum was filtered off on a non-running filter, and 85 parts of anhydrous ammonia were then added to the filtrate per hour. After granulating and drying the ammoniated product, a fertilizer with an N: P, 0,: K, 0 ratio of 1.5-1: 2.32 was obtained. The precipitated calcium sulfate consisted essentially of gypsum.

Claims (2)

Patent claims: 1. Continuous process for the production of complex fertilizers by digesting raw phosphates with about 40 to 80 weight percent nitric acid in stirred tanks, adding potassium sulfate to the digestion solution, continuous removal of the reaction solution from the digestion tank and, if necessary, the following process steps: Separation of the precipitated calcium sulfate from the digestion solution , Neutralization of the same with ammonia or the like, granulation and drying of the neutralized mass, characterized in that the potassium sulfate of the nitric acid raw phosphate digestion solution is added in such amounts and at such a rate that a soluble sulfate concentration of 0.5 to 40 / "in particular 1 to 1.5010, is maintained and reaction temperatures of 60 to 90'C, in particular 80'C, are maintained. 2. The method according to claim 1, characterized in that nitric acid is used in an amount of 5 to 15 moles per mole of P, 0 in the rock phosphate. 3. The method according to claim 1, characterized in that the reaction mixture sulfuric acid is added to a concentration of 50 to 100% , the total acidity of the mixed acids is not measured less than it corresponds to 5 moles of nitric acid per mole of P, 0, in the rock phosphate, but the amount of nitric acid present is at least 3 moles per mole of P, 0, in the rock phosphate. 4. The method according to claims 1 to 3, characterized in that the rate of addition of the sulfate ions is such that it does not go significantly beyond the rate of formation of the calcium ions and the total sulfate addition comprising potassium sulfate and sulfuric acid is preferably not more than about 3 5 moles per mole of P is 0, dimensioned in rock phosphate, and preferably the addition of potassium sulphate is not less than 0.5 mole per mole of P, 0, is in the rock phosphate. 5. Process according to Claims 1 to 4, characterized in that part of the liquid reaction product and / or the washing liquids from the stage of filtering off the gypsum is fed back to the first stage of the process. 6. Process according to Claims 1 to 5, characterized in that phosphoric acid is added to the liquid reaction product. Considered publications: German Patent Nos. 405 832, 418 874, 440 001, 542 957, 569 733, 571 496, 851807; Austrian Patent No. 165 866; French patents nos. 631233, 663 215, 690 013, 710 932, 925 332, 977 112, 999 066, 1007276; British Patent No. 615,476. U.S. Patent No. 1788,828.