CS231123B1 - Process for producing ammonium dihydrogen phosphate feed quality - Google Patents

Abstract

The invention describes the technology of production of fodder ammonium dihydrogen phosphate NH^HgPO^ with a low content of fluorine and arsenic, refining of fertilizer amphos, i.e. impure mixtures of salts with a predominant proportion of NH^HgPO^. Amofos is boiled in water and the return solution, oxidized, and the resulting arsenate coprecipitates with basic iron phosphate with the addition of an iron salt. The eluor in the leachate is converted to hexafluoroaluminate with the addition of aluminum salt, which is precipitated as cryolite with sodium salt or hydroxide. The clear filtrate is adjusted to a pH of about 4.4, concentrated and led to crystallization of the NH^HgPO^ salt. The mother liquor can be recirculated.

Description

HUMILE ZDENKA, PARDUBICE

Method for producing feed grade ammonium dihydrogen phosphate

The invention describes the technology for the production of feed ammonium dihydrogen phosphate NH^HgPO^ with a low fluorine content and, arsenic, refining of fertilizer ammophos, i.e. an impure mixture of salts with a predominant proportion of NH^HgPO^. Ammophos is boiled in water and reflux solution, oxidized and the resulting arsenate is coprecipitated with basic ferric phosphate by adding ferric salt. The eluate in the leachate is converted into hexafluoroaluminate by adding aluminum salt, which is precipitated as cryolite by sodium salt or hydroxide. The clear filtrate is adjusted to pH approx. 4.4, concentrated and brought to crystallization of NH^HgPO^ salt. The mother liquor can be recirculated.

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The invention relates to a method of producing crystalline ammonium dihydrogen phosphate, the quality of which meets the needs of mineral nutrition of animals or microorganisms in fermentation production.

In feed phosphates, the content of fluorine, arsenic and lead is of decisive importance, the limit values of which are standardized; in the Czechoslovak Socialist Republic, a maximum concentration of 0.1% fluorine, 7 ppm arsenic and 18 ppm lead is assumed.

Feed phosphates are prepared mainly by neutralizing thermal phosphoric acid, which is always practically free of fluorine and lead, but not arsenic. The high price of this acid is due to the extraordinary energy consumption in electric furnaces during the reduction of natural phosphates; a further unfavorable price trend is to be expected,

Neutralization of the more affordable extractive phosphoric acid with ammonia results in an impure mixture consisting mainly of ammonium dihydrogen phosphate. It is used under the technical name arnofos as a fertilizer or as a component of mixed and combined fertilizers. In international trade, ammophos is a tariff-advantageous form for long-distance transport of phosphorus pentoxide as a component of industrial fertilizers. Ammophos is unsuitable for feed purposes because it usually contains approximately 3% fluorine and 100 ppm arsenic,

Refining methods, which consist of recrystallization and clarification of leachates, can effectively reduce the fluorine concentration in crystalline ammonium dihydrogen phosphate, but cannot significantly suppress arsenic contamination of the salt, which is apparently a consequence of the isomorphism of arsenates and phosphates.

The above disadvantages are eliminated by the method of producing dihydrogenphospho2

231 123 ammonium uretate of feed grade by purification of the starting technical raw material, which is the subject of the invention, the essence of which consists in that the technical ammonium dihydrogen phosphate of fertilizer grade is treated with water and/or mother liquor from the previous operation of the same production, in an amount of 100 to 500% by weight, based on the weight of the starting technical raw material, at a temperature of 60 °C to the boiling point, the resulting suspension or liquid phase of the suspension is optionally oxidized with an oxidizing agent, such as chlorine, alkaline hypochlorite or hydrogen peroxide in an amount of 0.03 to 5% by weight of the active substance, based on the weight of the starting technical raw material, and to the thus treated solution is optionally added a ferric salt in an amount of 0.03% by weight of iron to 5% by weight of iron relative to the starting batch of technical raw material, preferably an aqueous solution of ferric chloride, then an aluminum salt is added in an amount of 15 to 150% by weight % of aluminum relative to the weight of fluorine in the solution being processed, preferably solid aluminum sulfate or its aqueous solution, then a sodium compound is added, preferably phosphate and/or sulfate and/or sodium hydroxide, after which the pH of the suspension is adjusted with acid or alkali to a pH value of * 4.4 - 2, the sludge is separated, the filtrate is optionally concentrated and brought to crystallization.

The principle of the invention is that the technical mixture of ammonium phosphates and other salts, prepared by the above-mentioned neutralization procedure of extractive phosphoric acid, is leached with hot or boiling water or a diluted reflux solution after crystallization of the previously prepared product. The minimum amount of water required for leaching the raw material is determined by the solubility of the salt mixture in hot water; it is about 100 to 500% by weight of the dissolving liquid, based on the weight of the processed raw material. The resulting suspension contains insoluble sludge, mainly phosphates and fluorides or fluorosilicates of caustic soils. The amount of this sludge depends exclusively on the type of ammophos being processed. It is advantageous to separate this sludge by separate filtration or sedimentation, wash it with hot water and refine the resulting solution. Refining processes, as will be described below, also take place in a suspension containing the initial sludge; however, the reaction of the components in the thick suspension may not be complete. Oxidation is also possible before filtration.

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The resulting hot leachate, containing dissolved portions of the raw material and the remaining sludge, is oxidized in a conventional manner, preferably with chlorine gas or sodium hypochlorite solution or hydrogen peroxide, so that the iron and arsenic compounds are converted into ferric and arsenic salts. A ferric salt, preferably a 30% by weight aqueous solution, is slowly added to the peroxide-boiling solution while stirring.

FeClg, used in water supply. The required amount of ferric salt depends on the contamination of the raw material; it is appropriate to apply 0.03 to 1 '% by weight of the said solution, based on the weight of the ammophos batch; excess precipitant causes losses of the phosphorus component.

The ferric salt hydrolyzes in the weakly acidic environment of the ammophos slurry, forming ferric hydroxide, which absorbs arsenic compounds, forming basic iron arsenates that are difficult to define.

Dearsenization can be performed without prior oxidation; the efficiency of this refining then varies greatly depending on the type of raw material.

At a pH value ^of 4.4 (all given pH values are understood after dilution of the liquid phase of the suspension with distilled water or after dissolution of the crystals so that the measured solution contains 1 to 2% _by weight of the sum of salts), which corresponds to a _solution of the salt _NH4H2PO4 in water, even in even less acidic solutions, the hydrolysis of fluorosilicates to form fluoride or fluorine complexes is practically complete.

The elimination of fluorine is based on the formation of a sparingly soluble salt of trisodium hexafluoroaluminate, which is known by the mineralogical name cryolite. It proceeds according to the overall reaction

Na ⁺ + Al ³ * + 6 F* = Na ₃ AlF _g (1)

The required amount of aluminum salt or its solution, preferably aluminum sulfate, used in water supply as a solution of approximately _ 8% by weight AlgO2 or as a solid with approximately 14% by weight AlgO^, is added to the hot leachate after dissolving the ammophos and possibly dearsenization.

After introducing an aluminum salt into the leachate of technical ammonium phosphates, an aluminum phosphate gel is first precipitated, which gradually dissolves with the formation of complex ions, especially hexafluoroaluminate.

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- 4 Α1Ρ0 ₄ + 6 F~ * A1f|” + P0 ₄ (2)

Fluoride precipitation occurs optimally when the aluminum salt is dosed according to the stoichiometry of equation (1) with respect to the analytically determined fluorine content in the liquid phase of the ammophos slurry.

For the actual precipitation of cryolite according to the equation

AlFg + 3 Na* » Na^AlFg (3), sodium ions are supplied as a suitable sodium salt, preferably hydrogen phosphate or sulfate or as sodium hydroxide. The dosage of sodium ions is determined by the fluorine content in the leachate and the stoichiometry of equation (3); they are precipitated in a theoretical amount up to a fivefold excess of the sodium compound.

The pH value of the suspension is adjusted to 4.4* 2,-; failure to comply with this condition would lead to a deterioration in the yield and quality of the produced salt.

The prepared suspension is filtered, the filtrate is concentrated in a known manner and the crystalline ammonium dihydrogen phosphate is separated by cooling. The product is usually separated by centrifugation and washed. It is shipped wet or dried. The mother liquor and the water after washing the crystal are preferably recirculated and, after being supplemented with water, used for further leaching of the raw material.

Depending on the concentration ratios in the processed solution, a certain proportion of relatively poorly soluble ammonium cryolite (NH^gAlFg) may be precipitated during refining in addition to cryolite. A particularly pure product is prepared if subsequent clarification filtration with the addition of an adsorption agent, preferably carborafine, is included.

The production process is shown as discontinuous for illustrative purposes. The production line can be modified as partially or completely continuous. The dearensing and defluorination operations are chemically independent; the first or second refining step can be omitted if a completely purified product is not commercially required.

For a further explanation of the nature of the invention, examples of embodiments are given (where the percentages given are understood as being by weight), but the subject matter of the invention is not exhausted or limited by them.

Examples of implementation.

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1) In the production plant of diammonium hydrogen phosphate, a filtered, otherwise untreated aqueous ammophos leachate was taken, in which 24.5 g F 1~^ and 26 ppm As were found.

Towards 1,300 ml of this solution was constant stirring released 210 ml solution with a concentration of Al ₂ ,(S0 ₄ ) ₃ = 0.65 mol . Γ She was excreting yellowish white precipitate, from quickly dissolves letting go. After 15 minutes, slowly pour in 165 ml of rožtok at the end NaOH concentration * 5 mol. I ¹ . The resulting white suspension was filtered and washed with cold water. By drying, a white microcrystal- lic powder, which was analyzed. Ion Found Na^AlFg calculated % by weight % by weight F 56.0 54.30 AI 9.9 12.85 On 17.9 32.85 nh ₄ 12.1 - Total 95.9 100,-

3—

The reaction to P0 ₄ was weakly positive.

2) Samples of 650 ml of operational filtered araofos extract, the composition of which is described in example 1, were boiled with the addition of ml of a 30% HgOg solution and then, with constant stirring, a solution with a concentration of Fe(S0 ₄ ) ₃ =1 mol · l” ¹ was added. After sedimentation of the precipitate, the clear solution was analyzed. Found

34»

Addition of Fe salt solution /ml/: 0 5 10 20 60

Determined As /ppm/ : 26 12 5 6 4

3) Simultaneously with the filtered leachate according to example 1, the unfiltered slurry after boiling the ammophos was taken in the production plant. 500 ml of this suspension was slightly acidified with phosphoric acid to pH » 4.6 and cryolite precipitation was carried out by introducing solutions in volume ratios as described in the example. Ammophos and cryolite sludge were separated by common filtration. The filtrate was evaporated to approximately half the volume. After cooling, ammonium dihydrogen phosphate crystallized. The crystals were sucked off, successively soaked twice with cold water and sucked off again. An approximately two percent solution of crystals in distilled water showed pH = 4.4 and the crystals contained

Claims (1)

SUBJECT OF THE INVENTION Process for preparing feed grade ammonium dihydrogen phosphate by purification of a feedstock, characterized in that the feedstock of fertilizer grade ammonium phosphate is treated with water and / or a mother liquor from a previous operation of the same production, in an amount of 100 to 500 wt. ° C to the boiling point, the resulting suspension or liquid phase of the suspension is optionally oxidized with an oxidizing agent such as chlorine, alkaline hypochlorite or hydrogen peroxide in an amount of 0.03 to 5% by weight of the active substance based on the weight of the starting technical feedstock optionally from 0.03% by weight of iron to 5% by weight of iron relative to the feedstock of the feedstock, preferably an aqueous solution of iron (III) chloride, is added thereto, followed by the addition of aluminum salt in an amount of 15 to 150% by weight The sodium compound, preferably phosphate and / or sodium sulphate and / or sodium hydroxide is then added, after which the pH of the suspension is adjusted to pH by acid or base. The slurry is separated, the filtrate is optionally concentrated and crystallized.