RU2275329C1 - Method for treatment of wet-process phosphoric acid - Google Patents

Abstract

FIELD: inorganic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for preparing phosphoric acid with low content of impurities and used in producing phosphate salts of technical and nutrition quality by using liquid extraction with tributyl phosphate and the following separation of an aqueous and organic phases and re-extraction of phosphoric acid from organic phase with water. Extraction and re-extraction are carried out in pulsation columns by mixing aqueous and organic phases to form emulsion under air effect at the extraction temperature 30-50°C and the re-extraction temperature 40-80°C followed by separation of the re-extraction process for some steps. At the first step the preliminary washed out extract is prepared and then it is fed to the step for preparing purified phosphoric acid and polluted acid recovered to the stage for extraction with tributyl phosphate. The total water flow feeding to the re-extraction step is divided for three parts in the following ratio: V₁:(V₂ + V₃) = 1:(2.5-10) and (V₂ : V₃) = 1:(1-2.5). Extract is mixed with the first part of water and after separating phases is fed successively to mixing with other part and then with the third part of water for preparing purified and highly purified phosphoric acids. Mixing the first part of water with extract is carried out in the volume ratio of phases = 1:(20-55), and mixing the second and third part of water with extract is carried out in the ratio = 1:(5-20). Proposed method provides decreasing the content of impurities in highly purified phosphoric acid preparing at the third step of re-extraction by 2-fold, i. e. to enhance quality of acid.

EFFECT: improved treatment method of phosphoric acid.

7 cl, 2 tbl, 2 ex

Description

The invention relates to a method for producing phosphoric acid with a low content of impurities, used in the production of phosphate salts of technical and food qualifications, using liquid extraction with tributyl phosphate, followed by separation of the aqueous and organic phases and re-extraction of phosphoric acid from the organic phase with water. Extraction and re-extraction is carried out in pulsating columns by mixing the aqueous and organic phases with the formation of an emulsion under the influence of air at an extraction temperature of 30-50 ° C and a temperature of reextraction of 40-80 ° C with the processes of mixing the aqueous and organic phases to form an emulsion under the influence of air in pulsation mode and dividing the re-extraction process into several stages with obtaining at the first stage a pre-washed extract, which is then supplied to the next stage - obtaining purified phosphoric acid ota, and contaminated acid returned to the extraction stage with tributyl phosphate.

The essence of the method lies in the fact that the total flow of water entering the stage of stripping is divided into three parts in accordance with V ₁ : (V ₂ + V ₃ ) = 1: (2.5-10) and V ₂ : V ₃ = 1 : (1-2.5), the extract after mixing with the first part of water and phase separation is sent to mix with the second and then with the third parts of water to obtain purified and deeply purified phosphoric acids. At the same time, it is advisable to apply extraction phosphoric acid 50-65% in accordance with P ₂ O ₅ for purification. It is advisable to mix the first part of water with the extract with a volume ratio of phases 1: (20-55), mix the second part of water with the extract with a volume ratio of 1: (5-20) and the third part of water with a ratio of 1: (5-20); extraction and re-extraction is advisable to be carried out in pulsation columns with a pulsation intensity of 50-2500 mm / min, re-extraction is carried out in three columns with a theoretical number of 0.4-2; 2-5 and 2-5.

Using re-extraction of phosphoric acid from the extract with water in three stages makes it possible to isolate the bulk of the impurities from the extract with the first water stream, utilizing the contaminated phosphoric acid formed in this process by mixing it with the extraction phosphoric acid stream supplied for purification reduces the content of Fe, Mg and SO ₄ in purified phosphoric acids. The use of small volumes of water in the first stage of reextraction compared to the second stage allows the production of contaminated acid in small quantities, thereby not causing a significant decrease in the concentration of the initial extraction phosphoric acid and thereby not significantly affect the production of purified phosphoric acid. Obtaining purified phosphoric acid from a pre-washed extract in two stages allows you to get two types of purified acid, while the acid obtained in the third stage of stripping will be the purest acid.

The invention relates to methods for producing phosphoric acid with a low content of impurities used in the production of phosphate salts of technical and food qualifications.

Extraction phosphoric acid (EPA), obtained by the sulfuric acid decomposition of natural phosphates, contains a significant amount of impurities, for the removal of which a number of methods are used, one of which is the method of liquid extraction with organic extractants.

A known method of purification of EPA using tributyl phosphate (TBP) (RF patent No. 2149830, class C 01 B 25/46, 12/10/1999), including the stepwise extraction of phosphoric acid with tributyl phosphate at a temperature of 30-50 ° C and the extraction of phosphoric acid from the organic phase at a temperature of 40-80 ° C, which are carried out by mixing the aqueous and organic phases with the formation of an emulsion, as well as the separation of the aqueous and organic phases after the stages of extraction and aqueous reextraction, in which the extraction is carried out at a volume ratio of organic and aqueous phases equal to ohm (2.5-5.5): 1, and the number of steps 1-6, then the obtained extract is subjected to stepwise washing in a pulsation mode at a temperature of 30-60 ° С with production acid obtained at the stage of water reextraction and taken in an amount of 25- 65% of its total mass, the formed emulsion is separated, the separated wash product acid is removed, and the extract is treated at the stage of water back-extraction to obtain the product acid. In the method under consideration, purified extract phosphoric acid in the amount of 25-65% of the production is used to purify the extract entering the stripping stage, thus, the yield of acid with a low content of impurities is only 35-75%. In this case, two acid streams are formed in the technological process: washing production acid with a content of more than 600 parts of Fe and more than 6000 parts of SO ₄ per million parts of P ₂ O ₅ and a solution of purified acid with a content of 147 parts of Fe and 1579 parts of SO ₄ per million parts of P ₂ O ₅ .

In this method, the purification of one part of the production acid is due to contamination of the other part, the sale of which will be difficult.

Closest to the claimed method is a known method for the purification of EPA (RF patent No. 2219125, class C 01 B 25/46, 12.25.02), including the stepwise extraction of phosphoric acid with tributyl phosphate at 30-50 ° C, with the release of raffinate and re-extraction of phosphoric acid from the organic phase at 40-80 ° С to obtain purified phosphoric acid and subsequent circulation of the extractant, while extraction and re-extraction are carried out by mixing the aqueous and organic phases with the formation of an emulsion under the influence of air in a pulsation mode, in which the total water flow ayuschy to step stripping is divided into two parts in a ratio of V _1: V ₂ = 1: (3-9) a first portion of water and mixed with the extract after separation of the phases the aqueous phase was contaminated with impurities is mixed with phosphoric acid in a volume ratio of 1 :( 6-15) and then transferred to the extraction stage with tributyl phosphate at the beginning of the process, and the extract is sent to mixing with the second part of water to obtain purified phosphoric acid.

In the case of using the specified cleaning method as applied to EPA with a mass concentration of 52.8% P ₂ O ₅ , obtained from apatite concentrate and containing as an impurity, wt.%: Fe - 0.28; SO ₄ - 0.31, get the production purified acid composition, wt.%: P ₂ O ₅ - 39,2; Fe - 0.0049; SO ₄ - 0.11. The degree of acid purification is: from Fe - 98.25%, SO ₄ - 64.5%.

In the case of using this method in relation to 55.08% of P ₂ O ₅ acid obtained from Kovdor phosphate concentrate containing, as impurities, wt.%: Mg - 1.48; Fe - 0.218; SO ₄ - 0.38, receive production purified acid of the following composition, wt.%: P ₂ O ₅ - 41,0; Mg - 0.023; Fe - 0.014; SO ₄ - 0.011. The degree of acid purification is: from Mg - 98.4%, Fe - 93.5%, SO ₄ - 97%.

The disadvantages of the method include the relatively low degree of purification of EPA apatite concentrate from sulfates (64%) and EPA from Kovdor apatite from iron (93.5%).

We have set the task of improving the quality of purified phosphoric acid.

The problem is solved by the proposed method, including the stepwise extraction of phosphoric acid with tributyl phosphate at 30-50 ° C with the separation of raffinate and re-extraction of phosphoric acid from the organic phase with water at 40-80 ° C with the processes of mixing aqueous and organic phases with the formation of an emulsion under the influence of air in pulsation mode and dividing the re-extraction process into several stages to obtain, at the first stage, the extract and contaminated acid that was previously washed from impurities and returned to the extraction stage tributyl phosphate at the beginning of the process, in which the total water flow entering the stripping stage is divided into three parts in the ratios V ₁ : (V ₂ + V ₃ ) = 1: (2.5-10) and V ₂ : V ₃ = 1 : (1-2.5), the extract after mixing with the first part of the water is sent sequentially to mix with the second and then with the third parts of water to obtain purified and deeply purified phosphoric acids.

The main differences of the proposed method are:

1. The separation of the flow of water supplied to the stage of stripping into three parts in the ratio V ₁ : (V ₂ + V ₃ ) = 1: (2.5-10) and V ₂ : V ₃ = 1: (1-2, 5), while the first part enters the first mixture with the extract, during which 30 to 65% of the impurities present in the extract pass into the aqueous phase, 23-54% of the impurities pass into the aqueous phase during the second stage of re-extraction and in the third stages of re-extraction into the aqueous phase passes 10-5%, respectively, while in the first stage of re-extraction into the aqueous phase goes up to 10-15% P ₂ O ₅ , in the second stage up to 35-50% P ₂ O ₅ and a third stage of stripping from 55 to 35% P ₂ O ₅ . Due to the above distribution between impurities and P ₂ O ₅ during re-extraction, the purest acid is formed in the third stage of re-extraction.

2. The use of EPA for cleaning with a concentration of 50-65% P ₂ O ₅ ensures the disposal of contaminated phosphoric acid in the process and ensures the reduction of impurities in the purified phosphoric acid. To implement the proposed method at the stage of extraction and re-extraction using pulsation columns with the optimal number of stages of phase contact in each apparatus and the optimal intensity of the pulsation.

The implementation of these measures allowed to reduce the content of metal and sulfate impurities in the purified acid obtained in the third stage of stripping compared to the prototype by 2 times, i.e. improve the quality of purified acid.

The purified acid 1 obtained in the proposed method, when mixing the extract with the second part of the water in quality, as shown in table 1, is somewhat inferior to the quality of the acid obtained in the prototype, but its quality meets the requirements of TU 2142-002-00209450-96 acid "orthophosphoric improved", the table shows information for acids stripped to 52.9% P ₂ O ₅ .

Example 1

EPK with a mass concentration of P ₂ O ₅ 53.0%, obtained from apatite concentrate, is fed into the pulsed packed column. As impurities, EPA contains, wt.%: Fe - 0.28; SO ₄ - 0.31. 3030 l / h of EPA is supplied to the upper part of the extraction column, phosphoric acid from EPA is extracted in a pulsation mode with an intensity of 300 mm / min and a temperature of 40 ° C with tributyl phosphate and a raffinate containing P ₂ O _{5 of} 23.88 wt.% Is obtained, which transferred to the production of ammophos, 14756 l / h of the extract containing 14.6% P ₂ O ₅ , transferred to the first stripping column, 615 l / h of water in a ratio of 615: 14756 = 1: 24 are fed countercurrently to the washing, whereby 712 l / h of contaminated acid, which is transferred to the head of the process at the stage of extraction with tributyl phosphate, and 14645 l / h hour Exactly washed extract. The process is conducted in one step at a pulsation intensity of 1000 mm / min and a temperature of 50 ° C.

The partially washed extract is transferred to a second stripping column, countercurrently mixed with 1076 kg / h of water in 2.5 steps in a pulsation mode at an intensity of 1300 mm / min, a temperature of 50 ° C, and production purified acid is obtained in an amount of 2100 kg / h of the following composition, wt.%: P ₂ O ₅ - 39.2%, Fe - 0.0086%; SO ₄ - 0.185%. The volumetric ratio of water to extract is 1076: 14645 = 1: 13.6.

The extract obtained in column II with a volume of 14289 l / h is sent to the third reextraction, where it is mixed countercurrently with 1394 l / h of water in three steps in a pulsation mode at an intensity of 1400 mm / min, a temperature of 55 ° C, and a deeply purified production acid is obtained in an amount 2717 kg / h of the following composition, wt.%: P ₂ O ₅ - 29.0; Fe - 0.0015; SO ₄ - 0.033. The volumetric ratio of water to extract is 1394 l / hr: 14289.2 l / hr = 1: 10.25.

The volume ratio between the first, second and third parts of water was V ₁ : (V ₂ + V ₃ ) = 615: (1076 + 1394) = 1: 4.02 and V ₂ : V ₃ = 1076: 1394 = 1: 1, 29.

After evaporation of the purified acid obtained in the second stage of stripping to 52.9% P ₂ O ₅ , the Fe content in it will be 0.012%, SO ₄ 0.25%, which corresponds to the quality of Improved Acid according to TU 2142-002-00209450 -96 ".

When evaporating a deeply purified acid obtained in the third stage of stripping to 52.9% P ₂ O ₅ , the Fe content in the acid is 0.0027%, the SO ₄ content is 0.06%, which is 2.4-2.5 times less than the acid obtained by the prototype (table 1).

Example 2

EPK with a mass concentration of P ₂ O _{5 of} 55.08% from Kovdor phosphate concentrate is fed to the pulsed packed column. As impurities, EPA contains, wt.%: Mg - 1.48; Fe - 0.218; SO ₄ - 0.38.

At the top of the extraction column, 3500 l / h EPC is supplied. Phosphoric acid from EPA is extracted in a pulsation mode with an intensity of 500 mm / min and a temperature of 45 ° C with tributyl phosphate to obtain a raffinate containing P ₂ O ₅ - 46.6% by weight, which is transferred to the production of ammophos, and 9844 l / h of the extract, containing 16.25% P ₂ O ₅ . The extract is fed into the first stripping column, and 250 l / h of water are supplied countercurrently to the washing. The process is conducted in a pulsation mode with an intensity of 800 mm / min in one step at a temperature of 50 ° C. In this case, an acid contaminated with impurities is formed, containing, wt.%: P ₂ O ₅ - 43.13; Mg 0.88; Fe - 0.19; SO ₄ - 0.165, which is sent to mixing with extraction phosphoric acid and then to the beginning of the process to the extraction stage with tributyl phosphate. A mixture of I part of water with the extract is carried out at a ratio of 250 l / h: 9844 = 1: 40.

The partially washed extract with a volume of 9767 l / h is transferred to a second stripping column and countercurrently mixed with 500 l / h of water in 1.3 steps in a pulsation mode at an intensity of 1300 mm / min and a temperature of 55 ° C to obtain purified acid in an amount of 1146 kg / hour of the following composition, wt.%: P ₂ O ₅ - 41; Mg - 0.05; SO ₄ is 0.024 and Fe is 0.03.

The volume ratio of water and extract is 500 l / h: 9767 l / h = 1: 19.5.

The resulting extract with a volume of 9537 l / h is sent for the third reextraction, mixed countercurrently with 1237 l / h of water in a pulsation mode in 3.5 steps at an intensity of 1400 mm / min and a temperature of 55 ° C, while receiving deeply purified production acid in an amount of 2534 kg / h of the following composition, wt.%: P ₂ O ₅ - 37.1; Fe - 0.0059; Mg - 0.009; SO ₄ - 0.0045. The volume ratio of water and extract is 1237 l / h: 9537 l / h - 1: 7.71.

The volume ratio between the first, second and third parts of water was: V ₁ : (V ₂ + V ₃ ) = 250: (500 + 1237) = 1: 6.95; V ₂ : V ₃ = 500: 1237 = 1: 2.47.

When evaporating the purified acid obtained in the second stage of reextraction to 52.9% P ₂ O ₅ , the Fe content in it will be 0.039%, Mg - 0.065%, SO ₄ - 0.031%, which corresponds to the quality of the Improved acid according to TU 2142 -002-00209450-96.

When evaporating the purified acid obtained in the third stage of re-extraction to 52.9% P ₂ O ₅ , the Fe content in the acid will be 0.008%, Mg 0.013%, SO ₄ 0.006%, which is 1.8-2.3 less than in the acid of the prototype (table 1). A comparison of process parameters with the claims is presented in table 2.

Table 1 Comparison of the quality of the purified acids of the presented method and the prototype. The name of the method Purified Acid Characterization Content,% wt. P ₂ O ₅ SO ₄ Fe Mg The standard according to TU 2142-002-00209-450-96 purified orthophosphoric acid 52.9 0.35 0.04 - Prototype Apatite concentrate Khibiny deposit 52.9 0.15 0.0066 - The degree of purification,% 64.9 98.28 - Kovdor apatite,
The degree of purification,% 52.9 0.014
97 0.018
93.5 0,03
98.4 The proposed method of cleaning Apatite concentrate Khibiny deposit Purified Acid No. 1 52.9 0.25 0.012 The degree of purification,% 1.40 96.9 Purified Acid No. 2 52.9 0.06 0.0027 The degree of purification,% 85.5 99,2 Kovdor apatite, Purified Acid No. 1 52.9 0,031 0,039 0,065 The degree of purification,% 93.6 86.2 96.6 Purified Acid No. 2
The degree of purification,% 52.9 0.006
98.7 0.008
97 0.013
99.3

table 2 Process parameters. Process name Indicator value Example 1 Example 2 Formula Volume I part of water (V ₁ ), l / h 615 250 Volume II of the water (V ₂ ), l / h 1076 500 The volume of the III part of water (V ₁ ), l / h 2300 1237 The ratio of V ₁ : (V ₂ + V ₃ ) 1: 4.02 1: 6.95 1: (2.5-10) The ratio of V ₂ : V ₃ 1: 1.29 1: 2.47 1: (1-2.5) The volume of extract supplied to the first column of stripping, l / h 14756 9844 The volume of extract supplied to the second column of stripping, l / h 14645 9757 The volume of extract supplied to the third column of stripping, l / h 14289 9537 The volume ratio of I part of water (V ₁ ) with the volume of extract supplied to the first stripping column 1:24 1:40 1: (20-55) The volume ratio of the second part of water (V ₂ ) with the volume of extract supplied to the second column of stripping 1: 13.6 1: 19.5 1: (5-20) The volumetric ratio of the III part of water (V ₃ ) with the volume of extract supplied to the III column of stripping 1: 10.25 1: 7.71 1: (5-20) The intensity of the ripple, mm / min 300-1400 800-1400 50-2500 The number of theoretical stages in the columns I column one one 0.4-2 II column 2,5 1.3 2-5 III column 3 3,5 2,5

Information sources

1. RF patent 2149830, cl. S 01 B 25/46, 10/12/1999

2. RF patent 2214125, cl. From 01 to 25/46, 12/25/2002

Claims (7)

1. The method of purification of extraction phosphoric acid, including the stepwise extraction of phosphoric acid with tributyl phosphate at 30-50 ° C with the separation of raffinate and re-extraction of phosphoric acid from the organic phase with water at 40-80 ° C with the mixing processes of the aqueous and organic phases with the formation of an emulsion under the influence air in the pulsation mode and dividing the re-extraction process into several stages with obtaining at the first stage a pre-washed extract supplied further to the next stage - obtaining purified phosphoric acid Ota contaminated acid to be recycled to the extraction stage with tributyl phosphate in the beginning of the process, characterized in that the total flow of water supplied to the stripping step, is divided into three parts in the ratios V ₁ (V ₂ + V ₃₎ = 1: (2.5 -10) and V ₂ : V ₃ = 1: (1-2.5), the extract after mixing with the first part of the water and phase separation is directed sequentially to mix with the second and then with the third parts of water to obtain purified and deeply purified phosphoric acids. 2. The method according to claim 1, characterized in that 50-65% of P ₂ O ₅ extraction phosphoric acid is fed for cleaning. 3. The method according to claims 1 and / or 2, characterized in that the mixing of the first part of the water with the extract is carried out with a volume ratio of phases 1: (20-55). 4. The method according to PP.1 and / or 2, characterized in that the mixing of the second parts of the water with the extract are carried out at a volume ratio of phases 1: (5-20). 5. The method according to claims 1 and / or 2, characterized in that the mixing of the third part of the water with the extract is carried out with a volume ratio of phases 1: (5-20). 6. The method according to claims 1 and / or 2, characterized in that the extraction and stripping are carried out in pulsation columns with a pulsation intensity of 50-2500 mm / min. 7. The method according to claims 1 and 6, characterized in that the extraction is carried out in three pulsation columns with a number of theoretical stages of 0.4-2; 2-5 and 2-5.