SU1641771A1 - Process for producing concentrated phosphoric acid - Google Patents

Abstract

The invention relates to a method for producing concentrated (50-55% p 0-) extraction phosphoric acid used in the production of phosphorus-containing mineral fertilizers. The purpose of the invention is to increase the yield of fluorine by reducing its losses with the precipitate of calcium sulfate hemihydrate and the gas phase at the stage of processing phosphate raw materials, reducing the downtime of absorption equipment at this stage by changing the amount and composition of released fluorine gases and reducing the degree of water flooding. Concentrated phosphoric acid is obtained by treating fluorine-containing phosphate raw material with circulating phosphoric acid, sulfuric acid and part of concentrated phosphoric acid supplied in an amount of 10-50 wt.h. P20, on 100 ma.ch. P205 raw materials, with the release and absorption of fluoride gases and the formation of calcium sulfate hemihydrate precipitate, separation of phosphoric acid from the precipitate by filtration, washing the precipitate, directing the wash water to the raw material treatment as phosphoric acid treatment, concentration of phosphoric acid in the evaporators until the content of PjjOj is 50 -55%, with the release and absorption of fluoride gases. Suitable concentrated phosphoric acid is pre-mixed with circulating phosphoric acid. These differences make it possible to reduce the yield of fluorine at the stage of decomposition of the raw material into the solid phase to 16.5-22.7%, into the gas phase to 19.1-24.2%, to increase the yield of productive fluorine to 35.5-45, 5 kg / ton of PjO, reduce the degree of hydration of calcium sulfate hemihydrate in water after 6 hours to 16–25%, increase the running time of equipment to 10–30 days. 1 hp f-ly, 2 tab. (L and J h 1

Description

The invention relates to a method for producing concentrated - (50-55% RLOC) extraction phosphoric acid | lots used in the production of phosphorus-containing mineral fertilizers.

The purpose of the invention is to increase the yield of fluorine by reducing its losses with the precipitate of calcium sulfate hemihydrate and the gas phase during the processing of phosphate raw materials, reducing downtime of the absorption equipment

this stage by changing the amount and composition of the fluorine gases in place and reducing the amount of water in the sludge.

Example 1. The implementation process with pre-mix one stripped off of phosphoric acid with circulating phosphoric acid.

In a sectioned extractor with a working volume of 740 m3, 55 t / h of apatite concentrate (39.4% of 3.15% F), a mixture of 190.3 t / h of industrial phosphoric (30.1% of P205) and 4.1 t are fed. / h (10 h. for 100 h. PjOj-phosphate raw material) one stripped off (52; 5% P205; 0.48% F; 2-4% 80E) acids, 53.6 t / h 92.5% sulfuric acid. The treatment of the apatite concentrate with acids is carried out for 4 hours at 98 ° C, the content in the liquid phase of the suspension is 38%. At the same time, 13.6 t / h of vapor-water and 0.55 t / h of fluorine compounds are removed as a mixture and RF (the F / Si atomic ratio is 5, the degree of fluoride released into gas is 24.22).

As a result of the absorption of gases withdrawn from the extractor, weak (1-2% F) solutions of hexafluorosilicic acid are obtained, which are sent for neutralization. The suspension of the semigand is separated, the precipitate is washed with washing with filtrates and water, and 190.3 t / h of recycled phosphoric acid of concentration of 30.1, 93.8 t / h of sediment (total humidity 26%) are obtained, which are sent to the dump. Phosphoric acid, containing 38% PjOj, is evaporated, while 43.3 t / h of concentrated phosphoric acid (52.5%

Pap) F; 2- “S03 and 7.0 t / h of a 14% solution of hexafluorosilicic acid (removal of production fluorine 35.8 kg / t PaO $).

4.1 t / h of concentrated phosphoric acid are returned to mixing with circulating acid and then to the extractor, and 39.2 t / h are output as product quality. The turnaround time of the absorption system of the extractor is 10-14 days.

According to a known method, phosphoric acid is obtained by treating at 90-100 ° C fluorine-containing phosphate raw material with recycled phosphoric and sulfuric acids with the release and absorption of fluorine gases and the formation of calcium sulfate hemihydrate. Phosphoric kit

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the lot is filtered, the precipitate is washed and the washings are sent for treatment. Phosphoric acid is concentrated to content. 50-55%, with the released fluoride gases absorbing. The yield of production fluorine at the stage of concentration is low (20-30 kg / t), which is due to its increased losses at the stage of processing the raw materials with acids: 23-27% of the feed with apatite remains in the solid phase, and 24-26% is released into the gas phase. phase. The atomic ratio of fluorine to silicon in the gas phase is 4-4.2, which causes precipitation of silica gel in the ducts and absorption equipment. Equipment operation time between cleanings is 5-7 days. In addition, the stability of the calcium sulfate hemihydrate is not high enough: the degree of hydration after 6 hours is 30%.

In tab. Figure 1 presents data on the effect of additives of concentrated phosphoric acid on the performance of the extraction process (introduction to the processing stage of phosphate raw materials). Extraction conditions: temperature 98 ° C, PjjOj-content in the liquid phase of suspensions 37.5-38.5%, sulfuric acid concentration 75-92s5%. Composition of one stripped off acid,%: P20U 52.5; 50 $ 3.0; F 0.48. Composition of apatite,%: PrGo 39.0-39.4; F 3.0-3.15.

As can be seen from the data table. 1, when working without supplying one of the evaporated phosphoric acid to the treatment zone of the phosphate raw material (carrying out the process by a known method) under the studied conditions with a solid phase (precipitate hemihydrate), 26.8% of fluorine introduced with apatite is lost, 25 % The absorption solutions formed during the purification of the latter contain a large amount of silica gel (atomic ratio F / Si is 4.2), its release contributes to the rapid overgrowth of the gas path (5-7 days). Introduction of a small amount of evaporated acid (5 h. PgOu per 100 hours of phosphate raw material) is ineffective; a noticeable decrease in the degree of fluorine transfer to a half-centered sediment (by 4%) and to the gas phase (by 0.8%) with an increase in the specific removal of fluorine from 31.2 to 35.5 kg per ton takes place at a flow of 10 hours.

one stripped off acid (in terms of PjO-) per 100 h. RloD. phosphate raw materials. At the same time, a significant increase (from 4.2 to 5) of the F / Si atomic ratio in the gas phase is observed, which causes a decrease in the silica fugitive tract of the fluorine gas removal path and an increase in equipment overhaul time. Increasing the amount of the additive of evaporated phosphoric acid over 50 hours. P-0 s-100 hours. PfcPs phosphate raw materials do not contribute to a further significant decrease in fluorine losses and are irrational due to the need to increase the load on the evaporation unit.

PRI mme R 2. The implementation of the process with separate submission to the extractor one stripped off of phosphoric acid and circulating phosphoric acid.

55 t / h of apatite concentrate (39.4% P20 $ -; 3.15% F), 173.1 t / h of recycled phosphorus (28.7%) and 20.7 t are fed into the sectioned extractor with a working volume of 740 m3. / h (50 parts per 100 parts of J-phosphate raw material one stripped off (52.5% of 0.48% F; 2-4% SOj acids, 54 t / h of 92.5% sulfuric acid. Processing of apatite concentrate acidified for 4 hours at 98 ° C, the content in the liquid phase of the suspension is 38.5%. At the same time, 13.8 tons / h of water vapor and 0.43 tons / h of fluoride compounds in the form of a SiF mixture are removed in the gas phase and HF (the F / Si atomic ratio is 5.5, the degree of emission of fluorine into gas is 19.4%).

As a result of the absorption of gases withdrawn from the extractor, weak (1-2% F) solutions of hexafluorosilicic acid are obtained, which are sent for neutralization. The hemihydrate suspension is separated, the precipitate is washed with washing filtrates, water and 173.1 t / h of circulating phosphoric acid concentration (28.7%) is obtained, which is returned to the extractor, 93.8 t / h of precipitate (total humidity 26%), which is are dumped. Phosphoric acid containing 38.5% is evaporated to give 59.9% F; 2-4% S03) and 8.8 t / h of a 14% aqueous solution of hexafluorosilicic acid (eat

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production fluorine 45% kg / t P20).,

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20.7 t / h concentrated

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the acids are returned to the extractor, and 39.2 t / h are output as product. The overhaul time of the extractor's absorption system is 20-28 s, ut.

Claims (2)

1. A method of producing concentrated phosphoric acid, which includes treating fluorine-containing phosphate raw materials with circulating phosphoric and sulfuric acids with the release and absorption of fluorine gases and the formation of calcium sulfate hemihydrate precipitate, separation of phosphoric acid from the precipitate by filtration, washing the precipitate, the direction of wash water for processing the raw material the quality of circulating phosphoric acid, the concentration of phosphoric acid in the evaporators to a content of 50-55% with the release and absorption of fluoride gases, characterized by about the purpose increasing the yield of fluorine, reducing the degree of hydration of the precipitate and the downtime of the absorption equipment, part of the concentrated phosphoric acid in the amount of 10-50 wt.h. P20g- per 100 mah. raw materials return to the processing of phosphate raw materials. 2. Method as claimed in claim 1, characterized in that the concentrated phosphoric acid is premixed with circulating phosphoric acid. Table 1 table 2