RU2498942C1 - Method of purifying waste water from phosphates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used to purify wastes from phosphates in chemical, metallurgical or petrochemical industry. The method is realised by treating water with aluminium sulphate to form insoluble aluminium phosphate particles and removing the solid treatment products from the treated water. Treatment is carried out in the presence of dispersed cellulose fibres in the water, said fibres containing at least 94 wt % fibres with length of not more than 1.23 mm and at least 54 wt % fibres with length of not more than 0.63 mm. The obtained solid treatment products in form of a composite material consist of said fibres with strongly sorbed chemically deposited aluminium phosphate particles. The composite material is removed by pressure floatation. In the preferred version, the fibres are dispersed in water in amount of 40-150 mg/dm³, wherein the composite material is removed from the treated water with aluminium phosphate content therein of 50-300 pts.wt per 100 pts.wt cellulose fibres, and a portion of the floatation sludge is returned to the treatment process.

EFFECT: method simplifies treatment by enabling treatment of water at a high volume rate equal to the rate of sludge formation, which cuts the duration of the treatment process.

4 cl, 4 ex

Description

The invention relates to methods for purifying phosphate-containing wastewater and can be used in many 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 aluminum sulfate and titanium tetrachloride in a mass ratio of (2-5): 1 with the formation of insoluble particles of aluminum phosphate and titanium phosphate by chemical precipitation, removal of treated solid solids from treated water sedimentation, as well as filtration of clarified water (SU, No. 1699948, C02F 1/58, publ. 12/23/91).

The disadvantages of the method are the long duration of the process, the complexity of the processing of sludge, the need to use an expensive chemical - titanium tetrachloride.

New results from the use of the invention are to simplify the process, reduce its duration, provide the ability to purify water with a space velocity equal to, for example, the rate of runoff formation.

These results are achieved in that in a method for treating wastewater from phosphorus compounds, comprising treating water with aluminum sulfate to form insoluble particles of aluminum phosphate by chemical precipitation, 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, in 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 refined products in the form of composition material consisting of these fibers with chemically precipitated particles of aluminum phosphate firmly sorbed by them, and the removal of the composite material is carried out by pressure flotation with the formation of a sludge, while the fibers are dispersed in water in an amount of 40-150 mg / dm ³ . The composite material is removed from the treated water with an aluminum phosphate content of 50-300 parts by weight thereof. per 100 parts by weight cellulose fibers. Part of the sludge can be returned to the cleaning process, and the resulting sludge from the process can be disposed of.

The method is as follows. A dispersion of cellulose fibers (CV) is prepared, for example, with a concentration of 1%, as well as a solution of aluminum sulfate 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. Continuous 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, which also contains a solution of aluminum sulfate in an amount stoichiometrically equal to the content of phosphates in the waste water. As a result of the reaction of aluminum and phosphate ions, water-insoluble aluminum 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 aluminum phosphate particles placed by them. Therefore, to remove solid refined products, it is advisable to use the flotation method, for example, pressure flotation.

The dispersion of the composite material from the reactor is sent to the saturator, 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.

Flotoshlama contains, in the calculation of solids, from 50 to 300 parts by weight aluminum phosphate per 100 parts by weight fibers. The capacity of the sorbent fibers is much higher than 300 parts by weight, 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 phosphate 6 mg / DM ³ . Prepare a solution of aluminum sulfate with a concentration of 10%. In the mixer in the wastewater dispersed cellulose fibers (CV) containing, in 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, at their expense 40 mg / dm ³ . The dispersion is fed into the reactor and aluminum sulfate is added to it in an amount stoichiometrically equal to the phosphate content in water (0.87 parts by weight of Al per 1 part by weight of P). Insoluble AlPO ₄ particles formed as a result of the reaction of aluminum ions and phosphate are strongly adsorbed on the CV. The composite purification product consists, per 1 dm ^{3 of} water, of 40 mg of CV and 23.62 mg of AlPO ₄ , or 59 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 phosphate bound in this purification cycle, in the initial period of the treatment system operation, the entire sludge is uniformly fed into the mixer as a sorbent. In each cycle, 23.62 mg of AlPO ₄ are adsorbed on the same portion of CV. Complete recycling of the sludge is continued until the ratio in the purification product of aluminum phosphate (FA): cellulose fiber, equal, for example, in parts by weight, 100: 40, or 250: 100, 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. In contrast to example 1, purify water with a phosphorus content of phosphates of 75 mg / DM ³ . Cellulose fiber is consumed in an amount of 100 mg / DM ³ . During purification, ~ 395 mg of products are formed in the form of a composite material with a ratio of FA: CV = 295: 100 in it. The sludge is removed from the process and sent for disposal.

Example 3. In contrast to example 1, 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, 236 mg of products are formed with a ratio of FA: CV = 157: 100 (in parts by weight). Flotam is completely removed from the process and sent for disposal.

Example 4. In contrast to example 1, 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. In steady state, purified water is used to dilute the source water.

In all examples, phosphates are not detected in purified water. The sludge removed from the process is washed and used as a filler in paper production.

Claims (4)

1. The method of purification of wastewater from phosphates, including treating water with aluminum sulfate to form chemical precipitation of insoluble particles of aluminum phosphate, 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, in 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 strongly sorbed Rowan of chemically precipitated particles of aluminum phosphate, and removing the composite material are pressurized flotation. 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 the composite material is removed from the treated water with an aluminum phosphate content of 50-300 parts by weight thereof. per 100 parts by weight cellulose fibers. 4. The method according to claim 1, characterized in that part of the sludge is returned to the cleaning process.