CS231121B1 - Process for producing di-ammonium phosphate feed quality - Google Patents

Abstract

The described invention describes the technology of production of feed diammonium hydrogen phosphate (ΝΗψ) HPO^ with low arsenic and fluorine content by refining fertilizer ammophos, i.e. an impure salt mixture with a predominant proportion of NH^BLjPO^. Ammophos is boiled in water and reflux solution, oxidized and the resulting arsenate is coprecipitated with basic ferric phosphate by adding ferric salt. The fluorine contained in the leachate with the addition of aluminum salt is converted to hexafluoroaluminate, which is precipitated as cryolite by sodium salt or hydroxide. The sulfur filtrate is concentrated, ammoniated and brought to the crystallization of the salt (NH^jpHPO^. The mother liquor is recirculated.

Description

The present invention relates to processes for the production of crystalline diammonium phosphate which, by its quality, meets the mineral nutritional needs of animals or microorganisms in fermentation.

For feed phosphates, fluorine, arsenic and lead content are crucial. A product contaminated with not more than 0.2% F, 0.002% As and; 0.002% Pb.

Feed phosphates are prepared mainly by neutralization of thermal phosphoric acid, which is always practically free of fluorine and lead, but not arsenic. The high cost of this acid is due to the extra energy consumption of electric furnaces in reducing natural phosphates; another unfavorable trend is to be expected.

Neutralization of the more affordable extraction phosphoric acid with ammonia results in an impure mixture consisting predominantly of ammonium dihydrogen phosphate; it is used under the technical name “amofos” as fertilizers or as components of mixed and combined fertilizers. It is unsuitable for feed purposes because it contains approximately 3% F and 100 ppm As.

The above-mentioned disadvantages are eliminated by a process for the preparation of feed grade diammonium phosphate by purification of the technical raw material of the invention, which comprises treating the technical ammonium dihydrogen phosphate with water and / or mother liquor from a previous operation of the same production in an amount of 100 to 500% by weight. based on the weight of the starting raw material, at a temperature of from 60 ° C to the boiling point, the resulting suspension ^Ί or the liquid phase of the suspension is optionally oxidized with an oxidizing agent such as chlorine, alkaline hypochlorite or hydrogen peroxide

231 121 in an amount of 0.03 to 5% by weight, based on the weight of the starting raw material, and optionally treated with a ferric salt in an amount of 0.03% by weight of iron to 5% by weight of iron relative to the starting material feedstock , preferably an aqueous ferric chloride solution, then an aluminum salt in an amount of 15 to 150% by weight of aluminum relative to the weight of fluorine in the treated solution is added, a sodium compound, preferably a phosphate and / or sodium hydroxide, added, optionally concentrated, cooling precipitates crystalline hydrogen diammonium phosphate.

The principle of the invention is that the technical mixture of ammonium phosphates and other salts, prepared by the above-mentioned neutralization procedure of phosphoric acid extraction, is leached with hot water or dilute back solution after crystallization of the previously prepared product. The minimum amount of water required to leach the raw material is given by the solubility of the mixture in hot water; about 100 to 500% by weight of the dissolving liquid, based on the weight of the feedstock to be treated. The resulting suspension contains insoluble sludge, mainly fluorides or fluorosilicates of caustic soils. The amount of this sludge depends exclusively on the type of amophos being processed. It is advantageous to separate this sludge separately

filtration or sedimentation, washed with hot water and refined re-V.

a sultating solution. The refining processes, as described below, also take place in a slurry containing the primary sludge; however, the reaction of the components in the dense mixture may not be complete. It is also possible to oxidise before filtration.

The resulting hot liquor containing dissolved proportions of the feedstock and the remaining sludge is oxidized in a conventional manner, preferably with chlorine gas or sodium hypochlorite solution or hydrogen peroxide, so as to convert the iron and arsenic compounds into ferric and arsenic salts. The iron (III) salt, preferably an aqueous solution of 30% FeClg used in the water industry, is slowly added to the prooxidized solution with stirring. The amount of ferric salt required depends on the contamination of the raw material; it is desirable to apply 0.03 to 5% by weight of said solution based on the weight of the amofos charge; an excess of precipitant causes losses of the phosphorus component.

- 3,231,121 £ The ferrous salt in the slightly acidic amphosic slurry hydrolyzes to form ferric hydroxide, which absorbs arsenic compounds to form ferric hydroxide, which absorbs arsenic compounds to form hardly definable basic iron arsenates ·

Dearsenisation can also be carried out without prior oxidation; the efficiency of this refining then varies greatly depending on the type of raw material.

- At pH = 4,4 (the pH-value being indicated after dilution of the liquid phase or the dissolution of the crystals with distilled water so that the resulting solution contains 1 to 2% by weight of the sum of salts) corresponding to a solution of ammonium dihydrogen phosphate in water in even less acidic solutions, the fluorosilicate hydrolysis is virtually complete.

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

Na ⁺ + Al ³⁺ + 6 F ~ -Na "AlF",

6 to which other stoichiometric data also apply.

The required amount of aluminum salt or a solution thereof, preferably commercial aluminum sulphate formulations used in the water industry, is added to the hot solution after dissolution of the amophos and possibly dearsenisation. In the first phase, an aluminum phosphate gel is precipitated, which gradually dissolves to form complex ions, in particular AlFg.

Sodium ions are introduced as sodium hydroxide or as a suitable sodium salt, preferably dibasic phosphate or sulphate. Precipitated by a theoretical amount of up to five times the excess sodium compound.

The treated suspension is filtered and the filtrate is concentrated in a known manner, and then diammonium hydrogen phosphate is crystallized with ammonia gas or liquid ammonia while cooling and cooling. A much cleaner product is obtained by hot ammoniacalization of the concentrated filtrate in a pressurized vessel and control filtration of this solution before entering the closed crystallizer; this technological adjustment is more demanding in terms of apparatus.

231 121

Crystalline diammonium phosphate is separated conventionally by centrifugation, washed with cold water and shipped dried or moist.

For illustrative purposes, the manufacturing process is described as discontinuous. The production line can be modified as partially or completely continuous. The production can advantageously be combined with the preparation of crystalline ammonium phosphate dihydrate or liquid phosphorus and nitrogenous mineral feed additives for animal production.

The described refining process comprises two independent operations, dearsenization, which is achieved by oxidation of the leachate and the introduction of ferric salt, and defluorination, which is achieved by the action of aluminum and sodium salt. If, for commercial or technological reasons, it is not appropriate to carry out a complete refining of the leachate of the raw material, it is possible to carry out purification only from one or the other of the impurities.

For purposes of illustration, an exemplary embodiment is provided, but is not limited to the scope of the invention.

Exemplary embodiment

At the diammonium hydrogen phosphate manufacturing plant, a filtered, otherwise untreated aqueous amophosic liquor was collected, in which 24.5 g F / l and 26 ppm As were found.

To 1300 ml of this solution was added 210 ml of an aqueous solution of aluminum sulfate concentration with stirring while stirring. 0.65 mol.l -1 A yellowish-white precipitate precipitated, initially rapidly dissolving. After 15 minutes, 165 ml of an aqueous solution of sodium hydroxide (R) 5 mol. The sludge was filtered off and the filtrate was ammonia-adjusted to pH = 8.38, evaporated to approximately half volume and allowed to crystallize. Diammonium hydrogen phosphate containing 0.186% F and 6 ppm As was precipitated.

231 121

Claims (1)

SUBJECT OF THE INVENTION A process for the production of feed grade diammonium phosphate by purification of an industrial feedstock, characterized in that the industrial ammonium dihydrogen phosphate is treated with water and / or a mother liquor from a previous operation of the same production in an amount of 100-500% by weight. 60 ^e C to the boiling point, the resulting suspension or liquid phase of the suspension is optionally oxidized with an oxidizing agent such as chlorine, hypochlorite or hydrogen peroxide in an amount of 0.03 to 5% by weight, based on the weight of the starting technical feedstock, and to the treated solution optionally, ferric salt is added in an amount of 0.03% iron by weight to 5% iron by weight relative to the feedstock of the feedstock, preferably aqueous ferric chloride solution, then aluminum salt in an amount of 15 to 150% by weight aluminum relative to the fluorine weight in the treated m solution, further adding a sodium compound, preferably a phosphate and / or sodium hydroxide, the filtrate is optionally thickened, mono-crystallized and, upon cooling, crystalline diammonium phosphate is precipitated »