RU2496722C1 - Method of purifying waste water from phosphates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used to treat phosphate-containing waste water. The method is realised by treating waste water with calcium hydroxide to form insoluble tricalcium phosphate particles and removing the solid treatment products from the treated water. Treatment is carried out with dispersed cellulose fibres in the water, said fibres containing at least 94 wt % fibres not longer than 1.23 mm and at least 54 wt % fibres not longer than 0.63 mm, in amount of 100-300 pts.wt per 100 pts.wt cellulose fibres. The composite material is removed by pressure flotation to form a floatation sludge. In the preferred version, the fibres are dispersed in water in amount of 40-150 mg/dm³. During pressure floatation, a portion of the floatation sludge is returned to the treatment process, and the floatation sludge removed from the process is recycled.

EFFECT: high efficiency of treatment.

4 cl, 3 ex

Description

The invention relates to methods for purifying phosphate-containing wastewater and can be used for purification of effluents from phosphates in various industries.

A known method of purifying phosphate-containing wastewater, including treating water with magnesium sulfate, neutralizing water in the presence of ammonium salts, precipitating phosphates in the form of poorly soluble magnesium phosphate, followed by separation of the precipitate (AS No. 856985, C02F 1/58, publ. 23.08.81) .

The disadvantages of the method are the long duration of the process, its complexity, a significant residual concentration of phosphates in purified water.

The closest analogue of the present invention is a method of purifying wastewater from phosphates, comprising treating water with calcium hydroxide in the presence of a mineral additive with the formation of chemical precipitation of insoluble particles of calcium phosphate, removing solid treatment products from treated water. As a mineral additive, phosphate slag is used - a waste of the process of electrothermal sublimation of phosphorus (SU. No. 1339093, C02F 1/58, publ. 23.09.87).

The disadvantage of this method is the significant contamination of the refined products — tricalcium phosphate particles — with foreign impurities contained in phosphate slag.

New results when using the proposed method are to simplify the process of separating solid purification products from purified water, as well as providing the ability to obtain and utilize purification products with pure tricalcium phosphate.

These results are achieved in that in a method for purifying wastewater from phosphates, comprising treating water with calcium hydroxide to form chemical precipitation of insoluble tricalcium phosphate particles, removing solid treatment products from treated water, according to the invention, the treatment is carried out in the presence of dispersed cellulose fibers in water containing wt.%, not less than 94% of fibers with a length of not more than 1.23 mm and not less than 54% of fibers with a length of not more than 0.63 mm, with the formation of solid cleaning products in the form of a composite material yal consisting of these fibers with strongly chemically precipitated tricalcium phosphate particles sorbed firmly by them in an amount of 100-300 parts by weight per 100 parts by weight cellulose fibers, and the removal of the composite material is carried out by pressure flotation with the formation of sludge. The fibers are dispersed in water in an amount of 40-150 mg / dm ³ . Part of the sludge can be returned to the cleaning process. The sludge removed from the process is recycled.

The method is as follows. A dispersion of cellulose fibers (CV) is prepared, for example, with a concentration of 1%, as well as a suspension of calcium hydroxide with a concentration of, for example, 10%. To prepare the dispersion, fibers are used that contain, in wt.%, At least 94% of the fibers with a length of not more than 1.23 mm and at least 54% of the fibers with a length of not more than 0.63 mm. The cleaning is carried out in an installation containing a mixer, a reactor, a saturator and a flotator. In the flow mixer serves wastewater and a dispersion of CV in an amount providing a concentration of fibers in water in the range of 40-150 mg / DM ³ . The resulting dispersion from the mixer is fed into a flow reactor, to which a suspension of calcium hydroxide is also supplied in an amount stoichiometrically equal to the phosphate content in the waste water. As a result of the reaction of calcium and phosphate ions, water-insoluble tricalcium phosphate particles are formed, which are strongly sorbed by cellulose fibers under the action of tensile forces to form a composite material in the form of a fibrous dispersion.

Cellulose fibers in water without mixing for 10-20 seconds form flocculi and flakes. Fibers and these formations from them hold small air bubbles well and are therefore easy to float. The same properties are possessed by fibers with tricalcium phosphate particles sorbed by them. Therefore, to remove solid refined products, it is advisable to use the flotation method, for example, pressure flotation.

The fibrous dispersion from the reactor is sent to a saturator, it is saturated with air under pressure, for example, 2-3 atm, and fed into the water distributor in the flotator chamber. The pressure drops to normal, the air dissolved in the water is released in the form of small bubbles that trap the rapidly forming flocs and flakes and carry them to the surface of the water in the flotator chamber. The resulting sludge is taken from the surface of the water, for example, with scoops, and served for processing. Part of the sludge in some cases in the steady state cleaning is returned to the mixer.

The flotation sludge contains, based on solids, from 100 to 300 parts by weight. tricalcium phosphate per 100 parts by weight fibers. The capacity of the sorbent fibers is much higher than 300 wt.h. per 100 parts by weight fibers, however, with a higher value of this ratio, complications arise when dewatering the sludge due to a sharp increase in water retention of the composite material.

The following examples illustrate the possibilities of the proposed method.

Example 1. Purify water with a phosphorus content of phosphates of 8 mg / DM ³ . Prepare a suspension of calcium hydroxide with a concentration of 10%. Cellulose fibers (CV) are dispersed in a mixer in water at a flow rate of 40 mg / dm ³ . The dispersion is fed into the reactor and calcium hydroxide is added to it in an amount stoichiometrically equal to the phosphate content in water (1.94 parts by weight of Ca per 1 part by weight of P). Insoluble Ca ₃ (PO ₄ ) ₂ particles formed as a result of the reaction of calcium and phosphate ions are strongly adsorbed on the CV. The composite purification product consists, per 1 dm of water, of 40 mg of CV and 40.05 mg of Ca ₃ (PO ₄ ) ₂ , or 100.15 parts by weight of per 100 parts by weight CV The suspension is fed to the saturator, saturated with air at a pressure of 2 bar and fed to the flotator. Suspended substances float to the surface of the water in the flotator and accumulate with the formation of a layer of sludge. It is removed from the flotator, for example, using a scoop or overflow. Since the total capacity of the sorbent is significantly higher than the amount of tricalcium phosphate absorbed in this purification cycle, in the initial period of the treatment system operation, all the sludge as a sorbent is uniformly fed into the mixer. In each cycle, 40.05 mg of Ca ₃ (PO ₄ ) ₂ are adsorbed on the same portion of CV. Complete recycling of the sludge is continued until the ratio in the purification product of tricalcium phosphate: cellulose fiber, for example, equal to 100: 40, or 250: 100 (in parts by weight) is reached. From this moment, the flow of sludge is reduced, for example, to 30 mg / dm ^{3 of} water, and fresh sorbent in an amount of, for example, 10 mg / dm ^{3 is} started. In steady state, the rest of the sludge with a ratio of 280-300: 100 is removed from the process and sent for disposal.

Example 2. Purify water with a phosphorus content of phosphates of 30 mg / DM ³ . Cellulose fiber is consumed in an amount of 100 mg / DM ³ . When cleaning, ~ 250 mg of products are formed in the form of a composite material with a ratio of tricalcium phosphate: CV = 150: 100 (in parts by weight). The sludge is removed from the process and sent for disposal.

Example 3. Purify water with a phosphorus content of 60 mg / DM ³ . Cellulose fiber is consumed in an amount of 150 mg / DM ³ . During purification, 450 mg of products are formed with a ratio of tricalcium phosphate: CV = 200: 100. The sludge is completely removed from the process and sent for disposal.

Example 4. The water to be purified contains phosphorus in the phosphate composition in an amount of 300 mg / dm ³ . Water is diluted to a phosphorus content of 60 mg / dm ³ and the diluted water is purified under conditions similar to those used in example 3 to obtain similar results. Purified water is used to dilute the source water.

In all examples, phosphates are not detected in purified water.

The sludge consisting of Ca ₃ (PO ₄ ) g and cellulose fibers (fiber), dehydrated by known methods, dried and ground, can be used in feed mixtures for livestock and poultry, for cleaning sugar syrup, for preparing toothpastes and powders, “soft” "Abrasives, etc.

Claims (4)

1. The method of purification of wastewater from phosphates, including treating water with calcium hydroxide to form chemical precipitation of insoluble tricalcium phosphate particles, removing solid treatment products from treated water, characterized in that the treatment is carried out in the presence of dispersed cellulose fibers in water, containing, wt.%, not less than 94% of fibers with a length of not more than 1.23 mm and not less than 54% of fibers with a length of not more than 0.63 mm, with the formation of solid cleaning products in the form of a composite material consisting of these fibers with firmly sorbed chemically precipitated particles of tricalcium phosphate in an amount of 100-300 parts by weight per 100 parts by weight cellulose fibers, and the removal of the composite material is carried out by pressure flotation with the formation of sludge. 2. The method according to claim 1, characterized in that the fibers are dispersed in water in an amount of 40-150 mg / DM ³ . 3. The method according to claim 1, characterized in that part of the sludge is returned to the cleaning process. 4. The method according to claim 1, characterized in that the sludge removed from the process is disposed of.