SU977392A1 - Process for stabilizing suspension of calcium sulphate hemihydrate - Google Patents

Description

This invention relates to methods for stabilizing aqueous suspensions of calcium sulfate hemihydrate — waste from the production of phosphoric acid.

A known method of stabilizing a calcium sulfate hemihydrate suspension in the presence of a stabilizing reagent, in which alkali metal and ammonium polyphosphates 1 are used.

The disadvantage of this method is the deficiency of stabilizing agents.

Closest to the present invention is a method for stabilizing a calcium sulfate hemihydrate suspension in the presence of a stabilizing agent, which uses calcium-containing compounds (carbonate, silicate, hydroxide), the introduction of which provides the pH of the liquid phase of suspension 4-7, which increases the time of complete hydration of sulfate hemihydrate calcium to 10-12 h 2.

The disadvantage of this method is the low degree of stabilization of the suspension, which leads to its setting during transportation and storage.

The purpose of the invention is to increase the stability of the calcium sulfate hemihydrate suspension.

The goal is achieved by the fact that according to the method of stabilizing the calcium sulphate hemihydrate suspension in the presence of a calcium-containing compound stabilizer-stabilizer at pH 4-7, water-soluble fluorine-containing compounds in an amount of 0,010, 1 part by weight are introduced into the initial suspension. per 100 weight parts solid phase.

To reduce the consumption of stabilizing additives, the liquid phase is recirculated from sludge collectors for repulping fresh portions of sludge.

Fluorides and sodium silicofluorides, silicofluoric acid can be used as fluorine-containing reagents, in particular, abdominal solutions with a content of 2-8% HjSiFj and 1-3% PjOj, formed during the purification of fluorine-containing gases of phosphoric acid production or double superphosphate.

It is also possible to use the waste of fluorosilicic acid on fluoride salts.

for example, uterine production solutions of cryolite containing 0.5-0.65% F, 0.20-0.25% Ne, and 0.01-0.03% PjOg.

The minimum amount of the additive of water-soluble fluorine-containing reagents is 0.01 weight.h. (in terms of fluorine) per 100 weight.h. the solid phase is determined by the need to slow down the rate of hydration of the hemihydrate by at least 2 times (the time for the complete transition of the hemihydrate to gypsum to be / 25 h) —in this case, the setting of the precipitate almost does not occur.

With an increase in the amount of fluorine injected over 0.1 weight.h. per 100 weight parts solid phase, the duration of hydration begins to decrease, at the same time the fluorine content in the liquid phase of the suspension increases and there is a risk of environmental pollution.

Calcium sulphate hemihydrate, which is liberated in the production of extraction phosphoric acid, contains a significant amount of fluorine (0.21, 2 parts by weight per 100 parts by weight of solids). However, fluorine is predominantly in the form of water-insoluble compounds and does not stabilize the suspension. The introduction simultaneously with the calcium-containing compounds of water-soluble fluorine-containing reagents provides a significant delay in hydration due to the formation of fine calcium fluoride, blocking the faces of the hemihydrate crystals. In addition, the formation of complex type ions as well as retarding hydration is possible.

The effect of sodium fluoride additives on the hydration and setting of an industrial sample of calcium sulfate hemi-hydrate precipitate (L: T-6: 1), the pH of the liquid phase after neutralization with calcium hydroxide P1 5 is presented in the table.

12

12.5

sixteen

18

25

38

42

34

14

The composition of the sediment: .1,5%, and% voan. 0.5%.

The process of stabilizing the calcium sulphate hemihydrate suspension by the proposed method is carried out in the following manner.

A waste precipitate of calcium sulfate hemihydrate washed from phosphoric acid is repulped in water or its mixtures with a circulating solution, while simultaneously adding calcium and fluorinated reagents to the suspension. The suspension is stirred for 15 minutes and pumped to the slurry field. Clarified as a result

18

20

thirty

50

88

100

100

95

22

Claims (2)

In order to preserve the suspension, it is advisable to return the solution for repulping of fresh portions of sediment. This allows even with a minimum consumption of stabilizing reagents to ensure a sharp slowdown of hydration, to simplify storage in the organization of further processing of the sludge. Example 1. 1.33 tons of calcium sulfate hemihydrate precipitate washed out from phosphoric acid, containing,%: P, j.05Bp, lj F- 0,8; H OGIGR-. 25, mixed with 4.6 tons of fresh water, 7.6 kg of carbonate and 7.6 kg of calcium hydroxide, 1.1 kg of fluoride or 0.83 kg of sodium silicofluoride (0.05 parts by weight of fluorine per 100 weight. h. solid phase). The suspension, the pH of the liquid phase which is 4.8, is stirred for 10-15 minutes and pumped to the sludge field. The total hydration time of the hemihydrate in such a suspension is about 40 hours as compared with 11 hours in the absence of addition of fluoride or sodium silicofluoride. Example 2. 1.33 tons of phosphoric acid-washed osashka calcium sulfate hemihydrate containing,%: PyjOjep. 0.5: F 0.8: HsOp.rp. 2 is mixed with 4.5 tons of fresh water, 35.5 kg of waste liquor of hydrofluoric acid containing 2.8% 0.3% (0.1 weight fluorine per 100 weight parts of the solid phase), 7.5 kg hydroxide calcium. The suspension, the pH of the liquid phase of which is 4.5, is stirred for 15-20 minutes and pumped to the slurry field. The total hydration time of the hemihydrate in such a suspension is about 35 hours compared to 12 hours when removed. fluorosilicic acid additives. Example 3. 1.33 tons of calcium sulphate hemihydrate precipitate washed out from phosphoric acid, containing,%: Р205ВР. 0.5; F- 0.3; HjOrnrp. 25 is mixed with 4 tons of working solution obtained by separating the suspension of the hemihydrate in the slurry field, 0.6 tons of fresh water, 2 kg of the mother liquor obtained during the processing of H.jSiFg and containing 0.5% p- (0.01 weight of fluorine per 100 parts by weight of solids), 9.5 kg of calcium carbonate. The suspension of the pH of the liquid phase of which is 5.2, is stirred for 10-15 minutes and pumped to the slurry field where it is separated and returned to repulping fresh portions of sediment 4 tons of liquid phase. The time of complete hydration of the hemihydrate in suspension is about 48 hours compared to 26 hours with repulping the same sediment only in fresh water and 12 hours in the absence of addition of mother liquors. Example 4. A mixture of calcium sulfate dihydrate and hemihydrate washed from phosphoric acid containing, in%, is: 1.4% (120 73 CaS04-0.5 25; P2O5bg. 0.2; P0.15; HgOgigr. 29, mixed with 4 tons working solution with alcohol, 1 ton of fresh water, 2 kg of hydrofluorosilicic acid solution containing 6.5% F and 3% P2O5 (0.013 parts by weight of fluorine per 100 parts by weight of solid phase), 2.5 kg of calcium hydroxide The suspension, the pH of the liquid phase of which is 4.7, is stirred for 5 minutes and pumped to the sludge field. The total hydration time of the hydrate is at least 20 hours compared to absence of fluorosilicic acid supplement. Thus, the proposed method for stabilizing a hemihydrate slurry makes it possible to increase the stability of the precipitate to hydration 2.5-4 times and to prevent its setting during transportation and storage. / or calcium oxide hydrate at pH 4-7, characterized in that, in order to improve the stability of the target product, water-soluble fluorine-containing compounds are introduced into the initial suspension and in the amount of 0.01-0.1 weight.h. per 100 weight parts solid phase. Sources of information taken into account in the examination 1. USSR author's certificate number 548566, cl. From 01 F 11/46, 1974. 2. Authors certificate of the USSR 570551, cl. C 01 F 11/46, 1973 (prototype).