SU1452787A1 - Method of producing phosphoric acid - Google Patents

Abstract

The invention relates to a method for producing phosphoric acid from phosphate raw materials and can be used in the production of mineral fertilizers. The aim of the invention is to reduce the gypsum casting of the foil cloth and increase the overhaul time of the equipment while maintaining high filtration performance. Phosphoric acid is obtained by treating phosphate C1F with circulating phosphoric and sulfuric acids to form calcium sulfate dihydrate pulp, filtering 5-20% of this pulp through a filter cloth with a residual pressure of 40-30 kPa, mixing the remaining part of the pulp with calcium sulfate hemihydrate, administered in the amount 15-80% by weight of calcium sulphate digramte, by keeping the resulting pulp and filtering through this same filter through a layer of calcium sulphate dihydrate. Receive phosphoric acid concentration of 30-34%. The time of complete filtering of the gypsum is 9-88 days, the driving time of filtration equipment (or between-repairs) is 45-115 days. Filtration performance 1100-1770. 1 tab. i W Slo 00

Description

The invention relates to a method for producing phosphoric acid I from phosphate raw materials and can be used in the production of mineral fertilizers. The aim of the invention is to reduce the gypsum of the filter cloth and increase the overhaul of the equipment while maintaining high filtration performance.

Example 1. 100 kg of apatite concentrate containing 39.4% are treated with 100.1 kg of 92% sulfuric acid and 290 kg of circulating phosphoric acid containing 19.6% of P-jOj. Taking into account the evaporated water, 480 kg of the reaction pulp is formed. From this amount, J24 kg of pulp or 5% is taken and fed to the first filtration stage, at which the residual pressure is maintained at 60 kPa. As a result of filtration a precipitate is formed with a thickness of 6 mm | with a density of 1.88. I The remaining 456 kg of pulp are mixed, with 24 kg of calcium sulfate hemihydrate 15% by weight of the dihydrate, the mixture is distilled for 0.1 h at 72 ° C and filtered through a layer of giis precipitate at a residual pressure of 40 kPa. Formed: a sediment with a thickness of 42 mm is countercurrently washed with 193 kg of hot water and 280 kg of precipitate is obtained with a humidity of 44, 8%

In the first and second stages of filtration, 127 kg of production phosphoric acid containing 30% are separated, and in the washing stage, 290 kg of a first turn of filtrate is recovered, which is returned to the decomposition stage.

The productivity of F1 is equal to 1100 in terms of dry washed precipitate. The service life of the fabric is 68 days, the overhaul mileage of the equipment is 95 days.

According to a known method, the phosphate raw material is treated with a mixture of sulfuric and circulating phosphoric acid with crystal 1zatz and its calcium sulfate dihydrate (gypsum). Calcium sulfate hemihydrate in the amount of 15--80% by weight of gypsum is added to the gypsum reaction slurry, the mixture is aged at 72- for 0.1-6 h and filtered on a continuous vacuum filter. Filtration capacity reaches 1100-1700 kg / m2.h dry washed sludge. The filtering cloth’s total casting time is 5–8 days,

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and the driving time of filtration equipment (or between-repairs) is 30-40 days.

Intense plastering of the fabric is caused by the recrystallization of the metastable calcium sulfate hemihydrate into a stable dihydrate, especially when the concentration in the liquid phase of the sludge decreases during washing. The clogging of the apparatus is caused by the slipping of small crystals of the hemihydrate through the pores of the fabric, their deposition on the walls of pipes and tanks and further recrystallization into stable gypsum with the formation of dense inlays.

Example 2. 100 kg of apatite concentrate containing 39.4% process 100.1 kg of 92% sulfuric acid and 290 kg of recycled filtrate (19.6%) for 5 hours at 78 ° C. 10 kg of water is evaporated and 480 kg of gypsum slurry in phosphoric acid is formed. 20% of this mass - 96 kg is filtered on stage I of the filling vacuum filter with a residual pressure of 80 kPa and a precipitate is obtained with a thickness of 15 mm with a density of 1.91 g / cm. To the remaining 384 kg of bullet. 40 kg calcium sulphate hemihydrate (25% of the weight of hpc) is added to the dust, holding the mass for 1 hour at 75 ° C (3 kg-water evaporates) and 421 kg of the reaction slurry are fed to the second filtration stage, where a residual pressure of 45 kPa is maintained . In total, in the first and second stages, 127 kg of production phosphoric acid with a concentration of 30.2% is filtered off. The wet acidic precipitate is counter-washed with 193 kg of hot water. At the same time, 290 kg of recycled filtrate is formed, which returns to the decomposition of phosphate and 296 kg of washed sludge with moisture.

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bone 32%. Filtration capacity reaches 1770: kg / m2 h of dry washed sludge. The fabric has a lifespan of 87 days, and equipment overhaul time is 108 days.

The table presents data on the effect of filtering on process indicators.

When carrying out the process, the pulp containing the metastable hemihydrate does not directly touch the tissue, 4 1ltrarts it through a layer of stable gypsum, which allows to increase the time of complete bleeding of the filter fabric up to 87 days.

In addition, when filtering pulp containing both hydrated forms of calcium sulphate through the gypsum layer, leakage of the hemihydrate into the filter apparatus is practically eliminated, and overshoot is also removed in the gypsum layer. Therefore, the overhaul distance of the equipment, i.e. the period during which it is necessary to clean the pipes and tanks increases from 30-40 days in the known method to 115 days in the proposed.

The resulting precipitate has a loose, sufficiently permeable structure and has little resistance to subsequent filtration, but reliably protects the filter cloth from calcium sulfate hemihydrate.

The bulk of the hemihydrate-dihyd-. -Natural pulp is filtered at a residual pressure of 60-80 kPa, which ensures high filtration performance and at the same time does not result in the hemihydrate slipping into the pores of the filter cloth.

Claims (1)

Invention Formula A method for producing phosphoric acid, which includes processing phosphate raw materials with circulating phosphoric and sulfuric acids to form a dihydrate pulp. calcium sulfate, mixing pulp with calcium sulfate hemihydrate, taken in an amount of 15-80Z by weight of calcium sulfate dihydrate, holding the resulting pulp, separating the product from calcium sulfate by filtering through filter cloth, 5, its washing and the direction of flushing water for processing as circulating phosphoric acid, characterized in that, in order to reduce the filter fabric's gypsum and increase equipment overhaul time while maintaining high filtration performance, 80-% are mixed with calcium sulfate hemihydrate. 95% pulp and filtration 5, the remaining part of the pulp is carried out successively at a residual pressure of 60-80 kPa, then the pulp after mixing through a layer of calcium sulfate dihydrate formed on 0 filter cloth. 50 50 50 50 60 70 15 60 68 1100 With a small thickness of the first layer 1200 (less than 5 mm) due to irregularities 1200 fabrics residual uncake areas that quickly become swellable 95 1100 According to example 1 15-80 40 5-8 30-40 1100-V700  Depending on the ratio of gypsum and hemihydrate in the mixture. Editor G. Volkova Compiled by G. Tselishchev Tehred-L. Serdyukova Order 7131/15 Circulation A35 VYIITSH of the State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab. D. 4/5 Printing and printing company, Uzhgorod, st. Project, 4 neither due to the mixture of gypsum and hemihydrate in the I filtration zone Proofreader N. King Subscription