RU2230026C1 - Method for preparing ammonium phosphate - Google Patents

Abstract

FIELD: inorganic chemistry, chemical technology, fertilizers. SUBSTANCE: invention relates to methods for preparing ammonium phosphates, namely ammophos and diammonium phosphate, based on the decomposition of ammonium raw with a mixture of phosphoric and sulfuric acids to obtain phosphoric acid and its the following process for fertilizers. Such fertilizers are used in agriculture widely. Method involves decomposition of apatite concentrate with mixture of sulfuric and phosphoric acids, separation of prepared pulp by filtration and isolation of production phosphoric acid, washing out calcium sulfate precipitate with water, recovery washing out waters to decomposition stage, ammonization of acid, granulation and drying product. By this method filtrate obtained after separation of pulp is fed to clearing up to the residual content of solid substances in production phosphoric acid 0.2-0.5 % by mass and fed to ammonization stage. Condensed pulp containing 10-35% of solid substances is recovered to decomposition stage completely. The following variants in carrying out the method are possible: before feeding to ammonization a cleared acid is concentrated partially or completely up to the necessary concentration. Invention provides preparing ready product showing stability of export quality in minimal consumptions for manufacturing and also new products containing nutrient substance by 1-5% more in reducing exploitation consumptions and specific amount of metal per structure. EFFECT: improved preparing method. 3 cl, 4 ex

Description

The invention relates to methods for producing ammonium phosphates, namely ammophos and diammonium phosphate, based on the decomposition of phosphate raw materials with a mixture of phosphoric and sulfuric acids to produce phosphoric acid and its further processing into fertilizers. Such fertilizers are widely used in agriculture.

A known method of producing ammophos (MAP) from apatite concentrate by decomposing it to obtain weak phosphoric acid and ammonizing this acid to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.02-1.05, concentration of the obtained ammophos pulp in vacuum evaporators to humidity 25-35% and its subsequent drying and granulation in a drum granulator dryer.

The disadvantage of this method is: this method involves concentration, that is, evaporation of ammophosic pulp, which leads not only to increased energy costs, but also to the formation of a large amount of process wastewater containing ammonia. In addition, the fertilizer obtained does not meet the requirements of international standards (Babkin V.V., Brodsky A.A. Phosphorus fertilizers of Russia. M: Margus, 1995, p.233-235).

The closest to the described by technical essence and the achieved result is another known method for producing ammonium phosphates, including the decomposition of phosphate raw materials with a mixture of phosphoric and sulfuric acids, separation of the obtained pulp by filtration with the release of production acid, washing the precipitate of calcium sulfate with water, returning the wash water to the decomposition stage, ammonization of the acid, granulation and drying of the product.

According to this method, the pulp after decomposition enters the filtration, where it is separated into production acid and precipitate of calcium sulfate. After the first stage (filtration proper), the production acid is separated, and the wash water together with the wash water of the washing stage in the form of a dilution solution enter the apatite decomposition stage. Weak acid after the first stage of filtration is supplied in whole or in part (depending on the production technology for concentration) and only after that comes to ammonization. Depending on the need to obtain a product brand (MAF or DAP diammonium phosphate) and the used neutralizers and neutralization schemes (for example, a high-speed ammonizer - evaporator [AIS], tubular reactor) it is neutralized to the desired ratios NH ₃ : Н ₃ PO ₄ . The resulting pulp is granulated, dried and classified (Technology of phosphorus and complex fertilizers. / Under the editorship of S.D. Evenchik and A.A. Brodsky. M: Chemistry, 1987, p. 71 (Scheme), p. 191-194) .

The disadvantage of all known methods is the need for concentration (evaporation) of significant amounts of acid, which entails not only increased operating costs for the implementation of the process and increased metal consumption, but also reduces the quality of the resulting finished product (ammophos and diammonium phosphate) due to the passage of impurities into it from acid. In addition, for example, in the production of diammonium phosphate, there is a significant release of ammonia (up to 25% of the input) when the acid is neutralized.

We set the task of obtaining a finished product of stable export quality with minimal production costs, as well as new products containing 1-5% more nutrients compared to well-known brands, while reducing operating costs and reducing metal consumption. The problem is solved in the proposed method for the production of ammonium phosphates, including the decomposition of apatite concentrate with a mixture of phosphoric and sulfuric acids, the separation of the obtained pulp by filtration with the release of production acid, washing the precipitate of calcium sulfate with water, returning the wash water to the decomposition stage, acidification, granulation and drying of the product.

In this method, the filtrate (I filtrate) obtained after the first filtration step in the separation of the pulp is fed completely to the clarification step. Clarification is carried out to a residual solids content in the production extraction phosphoric acid (EPA) of 0.2-0.5% by weight and is sent to the ammonization stage.

The thickened portion of the filtrate containing 10-35% solids is completely returned to the decomposition stage of apatite directly or pre-mixed with the filtrate obtained after washing the precipitate (II filtrate) and returned to the decomposition stage. In the latter case, the clarification of weak EPC is carried out in a closed cycle of the filtration unit.

There are also possible versions of the method, when the clarified acid is partially or completely concentrated to the required concentration before being fed for ammonization, which is caused by the type of marketable products (MAF or DAF), the method of production of EPA (dihydrate or hemihydrate), the need to utilize fluoride compounds in the target AlF products ₃ , Na ₂ SiF ₆ , NaF, etc.).

Depending on the technological conditions and the equipment available, the clarification process is carried out in different devices, for example, in radial sumps. It is most advisable to carry out this process in thin-layer sumps that work more intensively with an overall high efficiency of cleaning from solids. In this regard, the clarification time ranges from 0.5 to 6 hours.

The essence of the method is as follows. The stage of clarification of weak EPA can significantly reduce the ingress of ballast impurities (solids) into the product, thereby creating conditions for improving the quality of the finished product while reducing the energy component of the production of ammonium phosphates and metal consumption by eliminating the stage of concentration or concentration reduction. The clarification process is carried out at a regulated solids content in the clarified weak EPC at the level of 0.2-0.5% by weight. A decrease in the solids content in production weak EPA of less than 0.2% is associated with a significant decrease in the intensity of the operation of sedimentation tanks (an increase in the settling time), which leads to a complication and cost of the process. At the same time, the physical and mechanical properties of the finished product are deteriorating (granule strength, product dustiness, etc.) due to a decrease in the content of calcium ions in the solution, which leads to disruption of the construction of salt bridges during granulation. An increase in solids content of more than 0.5% leads to a destabilization of the quality of the manufactured product by chemical composition, especially in the production of ammonium phosphates directly from weak EPA.

The limits of the solids content in the thickened pulp 10-35% are due to the following. With a decrease in the solids content of less than 10%, the efficiency of the sump decreases (the yield of clarified acid decreases), which leads to an increase in the cost of the process. An increase in solids content of more than 35% is not advisable due to the deterioration of the rheological properties of the thickened pulp and clogging with sediments of communications, sedimentation tanks, etc.

The process of clarification of EPA in a closed loop filtration unit will significantly simplify the process, reduce the cost of manufacturing equipment and its maintenance. The technological scheme of the clarification process in this case is completely waste-free.

Using the proposed method for producing ammonium phosphates from apatite concentrate allows you to:

- to obtain export-grade MAF in chemical composition (12.0: 52.0) from weak dihydrate EPA without using the acid concentration stage (reduction in capital and operating costs);

- to obtain MAF of 13.0% N and 56.0% P ₂ O ₅ from one-off hemihydrate EPA, which reduces the cost of transportation and fertilizing by about 7-8%;

- to obtain MAF from mixtures of weak and one stripped off dihydrate and hemihydrate acids with a minimum consumption of one stripped off EPA (reduced operating costs);

- in the production of DAP from one stripped off of dihydrate and hemihydrate acids, to obtain a high-quality product with lower molar ratios of NH ₃ : Н ₃ РО ₄ , which helps to reduce the content of НН ₃ in the gases leaving the apparatus (stage of ammonization, granulation and drying) to the absorption cleaning system reduction of capital and operating costs for the purification of exhaust gases);

- to increase the overhaul mileage of plants for the concentration of weak EPC due to the reduction of incrustations by precipitation of the vapar plant.

The method is illustrated by the following examples.

EXAMPLE 1. The decomposition of the Khibiny apatite concentrate (39.0% P ₂ O ₅ , the content of the fraction +0.16 mm - 13%) is carried out with a mixture of sulfuric (93% H ₂ SO ₄ ) and phosphoric acid in the dihydrate process mode (temperature in the reaction zone 80 ° C, the ratio of T: W = 1: 2.5; the content of P ₂ O ₅ and H ₂ SO ₄ in the liquid phase of the pulp 29.0 and 2%, respectively) to obtain the 1st filtrate, which contains 28, 5% P ₂ O ₅ and 2% solids.

The 1st filtrate is clarified in a thin-layer sump for 1.0 hour, resulting in a production clarified EPA with a content of 28.6% P ₂ O ₅ and 0.3% solids and a thickened pulp with a content of 20% solids. The thickened portion of the 1st filtrate is completely fed into the collection of the 2nd filtrate, from which the dilution solution containing the solid phase is sent to the decomposition stage of apatite.

The clarified weak EPA is subjected to single-stage ammonization in a high-speed ammonizer-evaporator (AIS) at a molar ratio of NH ₃ : H ₃ PO ₄ = 1.05-1.10. The resulting pulp is granulated, dried in BHS (drum granulator-dryer) to obtain a product containing N - 12.0-12.2%; P ₂ O ₅ - 52.0-52.1% at a moisture content of 1.0-1.2%.

EXAMPLE 2. The decomposition of the Khibiny apatite concentrate (for the composition, see Example 1) is carried out with a mixture of sulfuric (95% H ₂ SO ₄ ) and phosphoric acid in the mode of hemihydrate process (pulp temperature in the reactor 92 ° C, ratio T: W = 1: 2 ; the content of P ₂ O ₅ and H ₂ SO ₄ in the liquid phase of the pulp is 37.5 and 1.3%, respectively) to obtain the 1st filtrate, which contains 37.0% P ₂ O ₅ and 1.2% solids .

The 1st filtrate is subjected to clarification in a thin-layer sump for 0.5 hours, resulting in a production clarified EPA with a content of 37.2% P ₂ O ₅ and 0.2% solids. The condensed portion of the 1st filtrate (with a content of 10% solids) is sent to the decomposition stage of apatite.

The clarified EPA is concentrated in an evaporator to a content of 54% P ₂ O _{5 in it} . One stripped off EPA is subjected to two-stage ammonization (1st stage in a tubular reactor; 2nd stage - in an ammonizer granulator (AG)) to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.15, granulation in an AG apparatus and drying in a drying oven drum to a residual moisture content of 1.2%. Commodity MAF contains N - 13.0%; P ₂ O ₅ - 56.0%. Transportation costs for transportation of the resulting concentrated product are reduced by 7-8%.

EXAMPLE 3. The process of obtaining EPA is carried out in hemihydrate mode (see Example 2).

The 1st filtrate is clarified in a radial settler for 6.0 hours to obtain a production clarified EPA containing 37.1% P ₂ O ₅ and 0.5% solids. The thickened portion of the 1st filtrate, containing 35% solids, is directly fed to the decomposition stage of apatite.

The clarified EPA is concentrated in an evaporator to a content of 52-54% P ₂ O ₅ .

One stripped off phosphoric acid diluted with absorption effluents from gas purification is subjected to two-stage ammonization in a tubular reactor to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.6. The resulting pulp is simultaneously granulated and dried in a BGS apparatus. Ready DAF contains N - 18%; P ₂ O ₅ - 46% at a moisture content of 1.5%. The ammonia content in the gases leaving the GHS when neutralizing with ammonia to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.6 (compared with the accepted molar ratio of NH ₃ : H ₃ PO ₄ = 1.80-1.85) decreases 20-25%.

EXAMPLE 4. The process of obtaining EPA is carried out in the dihydrate mode (see Example 1).

The first filtrate is subjected to clarification in a thin-layer sump for 0.75 hours, resulting in a production clarified EPA with a content of 28.6% P ₂ O ₅ and 0.5% solids and thickened pulp with a content of 15% solids. The thickened portion of the first filtrate is completely fed to the collection of the 2nd filtrate, from which the dilution solution containing the solid phase is sent to the decomposition stage of apatite.

A portion of the clarified weak EPA, equivalent to 40% of the mass of P ₂ O ₅ in it, is concentrated to 52% and mixed with another portion of the clarified EPA. The resulting mixture is subjected to single-stage ammonization in AIS at a molar ratio of NH ₃ : H ₃ PO ₄ = 1.05-1.10. The resulting pulp is granulated and dried in BHS. Get a product containing N - 12.2; P ₂ O ₅ - 52.2% at a moisture content of 1.5%.

Claims (3)

1. A method of producing ammonium phosphates, including the decomposition of apatite concentrate with a mixture of sulfuric and phosphoric acids, the separation of the resulting pulp by filtration with the release of production phosphoric acid, washing the precipitate of calcium sulfate with water, returning the washing water to the decomposition stage, ammonization of the acid, granulating and drying the product, characterized in that the production acid obtained after separation of the pulp is fed to clarification, the process is conducted until the residual solids content in it is 0.2-0.5% by weight, and sent to adiyu ammoniation and after clarification thickened pulp containing 10-35% solids, is completely recycled to the decomposition step. 2. The method according to claim 1, characterized in that before serving for ammonization, the clarified acid is partially or completely concentrated to the desired concentration. 3. The method according to claim 1 or 2, characterized in that the clarification of the production acid is carried out in a closed cycle of the filtration unit by mixing the condensed pulp with the filtrate obtained after washing.