RU2208575C1 - Method of processing phosphate stock into phosphoric acid - Google Patents

Abstract

FIELD: inorganic materials technology. SUBSTANCE: phosphate stock containing carbon dioxide and chlorine is preliminarily treated at temperature no lower than 90 C with mixture composed of sulfuric and phosphoric acids, amount of the former corresponding to 10-20% of stoichiometry based on CaO and liquid-to-solids ratio during the preliminary treatment being (0.2-0.8): 1. Resulting mass is then treated with sulfuric and phosphoric acids, after which follows crystallization of calcium sulfate and separation of phosphoric acid product by filtration. Degree of dechlorination of phosphate is 82-90% leading to residual chlorine content 0.028-0.05%. EFFECT: enabled processing of phosphorites with high level of chlorine. 2 cl, 2 ex

Description

The invention relates to a method for processing a phosphate feed containing CO ₂ and Cl into phosphoric acid.

A known method of processing carbonate-containing phosphate feedstock to phosphoric acid by processing it with reverse phosphoric acid with a concentration of 15-18% P ₂ O ₅ for 5-20 minutes at 30-60 ^o C to a residual CO ₂ content of 2-4% in the feed, followed by processing the resulting pulp with 75-92% sulfuric acid, separation of the mixture with the separation of calcium sulfate and the withdrawal of production phosphoric acid (AS USSR 513930, class C 01 B 25/22, 1976).

The disadvantage of this method is the increased residual content of CO ₂ in the feed and increased foaming at further processing stages.

 To remove a sufficiently high price formation during the processing of carbonate-containing phosphate raw materials to phosphoric acid, a method was developed that included the preliminary processing of phosphate raw materials with sulfuric acid and pulp circulating from the extractor, which is the closest to our proposed method for processing phosphate raw materials into phosphoric acid.

According to this method, the stage of preliminary processing of phosphate raw materials is carried out at a ratio of W: T in the pulp equal to (0.5-0.8): 1, a temperature of 70-75 ^o C and a norm of sulfuric acid of 70-100% of the stoichiometry for the content of CO ₂ in phosphorite (or 4.5-6.5% of stoichiometry calculated on CaO). Reagent contact time 3-5 min. Decarbonization of phosphate feed was carried out in a small volume apparatus equipped with mixing devices. Next, the resulting pulp was fed into the extractor and processed according to the well-known scheme for the production of phosphoric acid, that is, it was treated with a mixture of reverse phosphoric and sulfuric acids, followed by crystallization of the precipitate of calcium sulfate and separation of production phosphoric acid ("Features of the processing of various types of phosphate raw materials into extraction phosphoric acid". Overview of NIITEKHIM. 1985 Series: Mineral fertilizers and sulfuric acid, pp. 20-21).

 This method allows you to fully carry out decarbonization of phosphate raw materials, practically remove the pricing during its further processing to phosphoric acid.

However, in this method it is possible to process only phosphates containing CO ₂ as impurities (for example, Karatau), and it is not possible to process phosphorites containing Cl.

The objective of the invention was to develop a method for processing phosphate raw materials containing a very large amount of chlorine (Iranian phosphorites). The composition of this raw material includes 3% CO ₂ and 0.3% Cl (whereas in the phosphate feed of Karatau it is not more than 0.03-0.05% Cl, which practically does not affect the process).

The problem is solved in the proposed method for the processing of phosphate raw materials into phosphoric acid, including its preliminary treatment with a mixture containing part of sulfuric and phosphoric acid, at elevated temperature for 3-5 minutes, followed by processing the resulting mass of reverse phosphoric and sulfuric acids, crystallization of the precipitate of calcium sulfate and separating production phosphoric acid. According to this method, sulfuric acid in an amount of 10-20% of stoichiometry per CaO is fed to the phosphate pre-treatment stage, and the process is conducted at a temperature of at least 90 ^° C. As phosphoric acid fed to the phosphate pre-treatment stage, use either reverse phosphoric acid obtained in the main stages of the process for producing phosphoric acid, or a circulating pulp containing phosphoric acid. It is advisable that the ratio W: T at the stage of preliminary processing of phosphate raw materials be maintained equal to (0.2-0.8): 1, then the process of producing phosphoric acid is carried out by known methods (treatment of reverse phosphoric and sulfuric acids, crystallization of calcium sulfate and separation of production phosphoric acid) .

The essence of the method is as follows. As you know, the technological equipment for the large-scale production of phosphoric acid is very voluminous and, with a large amount of chlorine in the raw material, is subject to severe corrosion, which makes it practically impossible to process such raw materials in conventional technological equipment. In this regard, it is necessary to remove chlorine from phosphate raw materials before the main processing. The stage of pretreatment of phosphate raw materials is aimed not only to remove foaming (i.e. to decarbonize it), but also to remove chlorine in the form of HCl in the gas phase at this stage. This effect can only be achieved by combining factors such as temperature, the rate of sulfuric acid supplied to the pretreatment stage, and also W: T in the mixture. The temperature should be at least 90 ^o C, since at a lower temperature, water vapor, and not HCl, are released into the gas phase. The effect of the release of Hcl into the gas phase is no less dependent on the amount of sulfuric acid supplied to this stage. At a sulfuric acid consumption of less than 10% of the stoichiometry calculated on CaO, phosphate feed will be decarbonized, but not dechlorinated, with an increase in the norm of sulfuric acid, dechlorination at this temperature will increase, but if the norm is exceeded above 20%, the recovery coefficient of P ₂ O _{5 will} decrease at the main stages of the process. The specified ratio W: T at this stage is due to the need for almost complete decarbonization of phosphate raw materials. However, the temperature and the increased amount of sulfuric acid allow you to work in a wider range, namely W: T, equal to (0.2-0.8): 1. It should be noted that only compliance with all conditions, namely temperature, the norm of sulfuric acid and compliance with the ratio W: T, allows to achieve almost complete dechlorination and decarbonization of phosphate raw materials. Since this stage is conducted in a relatively small volume apparatus and in a short period of time - 3-5 minutes, its execution from corrosion-resistant materials will not cause a significant increase in the cost of technological equipment.

 The method is illustrated by the following examples.

 Example 1

50 t / h of Iranian phosphorite containing 37% P ₂ O ₅ , 51.5% CaO and 0.28% Cl, 20 t / h of circulating pulp at W: T = 2: 1 are fed into a mixer with a volume of 3.0 m ³ and 4.9 t / h of sulfuric acid at a concentration of 92%. Sulfuric acid consumption is 10% of stoichiometry on CaO in phosphate. A temperature of 100 ^° C is maintained in the mixer ^{. A} pulp is obtained with a ratio of W: T = 0.2: 1 and a degree of phosphate dechlorination of 82% (residual content of Cl in phosphate is 0.05%). The residence time of the reagents in the mixer is 4.6 minutes The pulp is fed to the extractor, where 44.1 t / h of sulfuric acid and 157 t / h of reverse phosphoric acid with a concentration of 17% P ₂ O ₅ are added. The process is carried out at a temperature of 80 ^o C, the ratio of W: T in the pulp 2: 1, the concentration of P ₂ O ₅ in the liquid phase of the pulp 28% to achieve a recovery rate of P ₂ O ₅ in solution of 98.5%. From the extractor, 20 t / h of pulp is fed to a mixer, and 240 t / h of pulp is fed to a vacuum filter, where calcium sulphate is filtered and washed, the washing coefficient is 99%.

 Example 2

50 t / h of Iranian phosphorite containing 37% P ₂ O ₅ , 51.5% CaO and 0.28% Cl, 40 t / h of reverse phosphoric acid with a concentration of 17% P ₂ O ₅ are fed into a mixer with a volume of 3.0 m ³ and 9.8 g / h of sulfuric acid at a concentration of 92%. Sulfuric acid consumption is 20% of stoichiometry on CaO in phosphate. In the mixer maintain a temperature of 95 ^o C. Get a pulp with a ratio of W: T = 0.8: 1 and the degree of dechlorination of phosphate 90% (residual content of phosphate in 0.028%). The residence time of the reagents in the mixer is 3 minutes The pulp is fed to the extractor, where 39.2 t / h of sulfuric acid and 117 t / h of reverse phosphoric acid with a concentration of 17% P ₂ O ₅ are added. The process is carried out at a temperature of 80 ^o C, the ratio of W: T in the pulp (2.0-2.5): 1, the concentration of P ₂ O ₅ in the liquid phase of the pulp 28% with reaching the recovery coefficient of P ₂ O ₅ in the solution of 98.3 % From the extractor, the pulp is fed to a vacuum filter, where the filtering and washing of the precipitate of calcium sulfate is carried out, the washing coefficient is 98.6%.

Claims (2)

1. A method of processing phosphate feedstock into phosphoric acid, comprising pretreating it with a mixture containing part of sulfuric acid and phosphoric acid at an elevated temperature for 3-5 minutes, followed by treatment of the resulting mass with sulfuric and phosphoric acids, crystallization of calcium sulfate and separation of production phosphoric acid filtration, characterized in that for the preliminary processing of raw materials sulfuric acid is introduced in an amount of 10-20% of stoichiometry per CaO and the process is carried out at a temperature of at least 90 ^o FROM.  2. The method according to p. 1 characterized in that G: T at the stage of preliminary processing of raw materials is maintained equal to (0.2-0.8): 1.