CS272007B1 - Method of flotation water clarification - Google Patents

Abstract

The flotation water clarification method converts the problem of water clarification with sedimenting flakes into a flotation method in which the ascending speed of the floated flakes is higher than 5 to 10 m.h-ί. Conventional coagulants are used, such as salts of iron, aluminum and magnesium, the flakes of which are floated in the presence of flotation agents, which can be ordinary soaps, i.e. sodium or potassium salts of fatty acids. Oil or fat emulsions can also be used as flotation agents. Flotation gas microbubbles are created in the liquid by dispersing air with a mechanical stirrer. Stirring is carried out at Reynolds criterion values in the range of values 1.104_1.107. In one device, a perikinetic coagulation phase is carried out simultaneously with air dispersion for 1 to 10 seconds. In the quiescent phase, coagulant flakes with entrained impurities float out without introducing additional flotation gas, such as. This is the case, for example, with electroflotation or pressure flotation. Suspended substances can be removed from water even in concentrations of several g.l-1, so the method can be used as an alternative to the filtration process.

Description

The present invention relates to flotation clarification of water and relates to operations used in water treatment, which are purification, flotation and sludge thickening.

Chemical clarification It is the dominant method of water treatment, which contains colloidal and finely suspended particles. Small volumes of these waters can be treated by coagulation filtration. Large volumes of water with a larger amount of suspended particles are treated in clarifiers. Iron and aluminum salts are used as coagulants, and magnesium salts, for example, are less commonly used. In clarifiers, the cleaning effect is achieved by means of a sludge cloud, in which metal hydroxides accumulate into larger formations and bind impurities from water to their surface and are separated from purified water by sedimentation.

Flotation is a method that is used not only in water treatment, but is also used in other fields, such as hydrometallurgy. Flotation has found great use in the treatment of wastewater containing petroleum substances in the engineering, metallurgical and petrochemical industries.

The disadvantage of coagulation filtration and treatment is the production of waste sludge, which is watery, the dry matter content in the sludge is usually less than 0.1% by weight. The clarifier function does not allow sudden changes in temperature and power. The disadvantage of flotation is relatively expensive equipment. The contact time of the flotation gas microbubbles with the purified volume of water is usually 10 to 20 minutes, so that high-performance devices are bulky.

The disadvantages of the prior art are eliminated by the method of flotation water purification, in which water purification is carried out by commonly known precipitation reactions such as precipitation of iron, aluminum, magnesium coagulants with alkalizing agents or precipitation of corrosive earth metals with phosphate, silicate, carbonate anions. that the precipitating agents are added to the clarified water at a stirring intensity characterized by Reynolds criterion values in the range of 1.10 to 1.10, with air being dispersed in the liquid, in the presence of sodium or potassium salts of fatty acids in an amount corresponding to 5 to 50 % by weight of coagulants used or in the presence of oil or fat emulsions, where the amount of oils or fats corresponds to 5 to 50% by weight of coagulants used.

In many kinetically fast precipitation reactions, the perikinetic coagulation phase can be carried out within 1 to 10 seconds and at the same time use vigorous stirring to disperse the air in the liquid into particles smaller than 0.1 mm in diameter. After this time, the vigorous stirring is stopped and the subsequent orthokinetic phase of coagulation can be carried out without further supply of mechanical energy, so that the energy of the spun column of liquid after intensive stirring is allowed to dissipate in the liquid by friction. A suitable velocity gradient for the orthokinetic phase of coagulation also occurs around rising air bubbles in the resting phase and around rapidly rising flakes.

After the addition of the coagulants and alkalizing agents, surfactants are added with vigorous stirring, which allows the air microbubbles to adhere better to the flakes. It is sufficient to use the cheapest types of sodium or potassium soaps or aqueous emulsions of fats and oils as surfactants. After stopping the vigorous stirring, it is advisable to add organic flocculants to the reaction mixture, which will make it possible to enclose further air microbubbles in the emerging flake aggregates. .....

A significant advantage of the process according to the invention is that the rising velocities of the floated flakes are generally higher than the sedimentation velocities of the flakes corresponding to the process in the clarifier. Especially in waters with low concentrations of undissolved substances, which require only small amounts of coagulants, the rising velocities of floated flakes tend to be higher than 20 mh “ ¹ . This has a positive effect on the size of the device. The method is not sensitive to changes in temperature and power. From the point of view of laboratory experiments, the method appears to be universal for the removal of suspensions and colloids, especially from wastewater.

CS 272007 Bl

Suspensions of hydroxides, oxides, sulfates, carbonates, silicates, carbonates, florides and the like can be removed from the wastewater by the process according to the invention. Biological sludge, paint paint residues from spray boxes, adhesive adhesives, greases, milk and fibers can be removed from the water. The method is useful for removing activated carbon, perlite or bentonite, which have previously been used to separate impurities from water by sorption. In an alkaline environment, it is possible to carry out deironing and demanganization, decarbonization and softening of water. The method is applicable for the treatment of sludge water that falls out of clarifiers or when washing granular filters.

Since the flakes of the coagulants are floated to the surface by the method according to the invention, there is no need to use conventional weights to load the flakes during sedimentation. By creating a foam with a higher dry matter content, it is possible to bridge the need for thickeners. The method makes it possible to build small continuously and discontinuously operating devices which, for example in galvanic plating processes, would make it possible to segregate individual metal precipitates and then reuse them.

In the field of alkaline clarification, the process according to the invention can be used even at high doses of cheap and readily available ferrous sulphate as coagulant, since the oxidation of ferrous iron is very fast in alkaline media and the amount of oxygen solubility in water at a given temperature.

When clarifying waste waters containing bio-sludge or waste from food production or other waters containing usable organic substances which are useful as fertilizers or compost bases, it is appropriate to use magnesium salts as coagulant. Although flotation clarification can then be carried out in the pH range 11, the flotation foams then contain, in addition to organic substances, magnesium hydroxide, which is usable as a source of a biogenic element and optionally as a neutralizing agent for acidic soils.

Organic flocculants improve the coagulation of precipitates. The polyacrylate amide, which was dosed in an amount of 1 to 10 mg.l * ^1, was tested with good results. Good results have been obtained using a domestic starch-based flocculant.

The dispersion of air in water is aided by the addition of non-coagulating surfactants. With their increasing concentration ae increases the volume of foams formed. Flotation clarification was in most cases performed at pH values higher than 8, because the activity of soaps decreases with increasing acidity of the environment. A suitable concentration of surfactant in the alkaline range is about 1 to 10 mg.! ^'1. At high surfactant concentrations, disproportionately large foam volumes can occur, so that, for example, at surfactant concentrations higher than 1,000 mg.I · ^1, it is advisable to operate in the pH range around 5.

In addition to the precipitating products of iron, aluminum and magnesium, other substances which form bulky precipitates, such as hydroxides of copper, zinc, manganese and nickel, float very well. Phosphate, silicate and sulphate float very well from calcium precipitates.

Soaps precipitated with calcium salts themselves can also be used as coagulants. Soap doses are then hundreds of mg.1 ^. The advantage of soap foams is the high dry matter content, which can reach values of over 20% by weight. When soaps are used as coagulants, an even larger amount of undissolved substances remains to be removed after flotation in water, which must be removed in a further step, for example iron or aluminum coagulants. The soaps themselves are then a suitable coagulant for removing gypsum, calcium hydroxide, activated carbon, perlite, etc.

Foams obtained from conventional coagulants, with the exception of calcium salt precipitated soaps used as coagulant, contain 2 to 10% of dry matter. Foams disintegrate over time and reduce their volume, the disintegration of foams can be greatly accelerated by vacuuming. It is also possible to break up foams with mineral acid. This is useful when suspensions are removed from water in selinách of acids ^of insoluble and acidic solutions to remove. Iron coagulants, hli

EN 272007 The magnesium, magnesium and phosphate can then be recovered and reused.

The following examples of the process according to the invention were made using a laboratory mixer at a stem speed n «6000 min stirrer that was mounted on the motor shaft to be made of a circular metal sheet strength of 0.5 mm and 40 mm diameter (criterion R * ⁵ 1.10 ). 8 radial slots 10 mm long were made into the blanket and the resulting wings were deflected against the plane of the board by 30 degrees.

The experiments were performed in a vessel with a diameter of 100 mm, the stirrer was situated 50 mm below the surface and its direction of rotation was chosen so that the stirred liquid was driven by the stirrer towards the bottom. The work was performed with a 1,000 ml sample of water at a temperature of about 20 ° C. After stirring, the contents of the reaction vessel were immediately poured into a 1000 ml graduated cylinder. The inner diameter of the cylinder was 60 mm. After pouring the reaction mixture, the column of liquid in the cylinder was spun by 10 revolutions of a 10 mm diameter wooden log, which reached to the bottom of the cylinder and was slid along the cylinder wall at a speed of>> 400 to 400 rpm. Flocculants with a concentration of 0.1% were metered into an empty cylinder, so that they were mixed after pouring the reaction mixture into the cylinder. Undissolved substances in solution after flotation were determined by filtration through Synpor-size 4 membrane filters. The flotated foams from the measuring cylinders were transferred to a watch glass with a spoon. The glasses were set first obliquely, later vertically. Water separated from the foams even further spontaneously. Once the water stopped separating from the foams, the glasses were weighed and dried at 105 ° C. After further weighing, the dry matter was calculated from the difference.

Example 1

Deironing: 2,000 mg of technical grade FeSO 4 .THgO was dissolved and made up to 1,000 ml with tap water.

With vigorous stirring, 760 mg of NaOH was added to the sample as a solution. After one minute of stirring, 100 mg of greasy soap was added and after another 5 seconds the stirring was stopped and the contents were quickly poured into a graduated cylinder containing 5 mg of polyacrylamide and the column of liquid was spun with a wooden log. After only 30 seconds, 880 ml of liquid were clear (upward velocity of the flakes around 40 mh). After 5 minutes, the volume of the clarified liquid was 950 ml, pH 9.0. ^{8 mg.I 1 of} undissolved substances was found in the liquid. The volume of the foam after 5 minutes was 180 ml and its dry matter was 4.2%.

Example 2

Magnesium precipitation: 1000 mg of MgSO 4 .THgO was dissolved and made up to 1000 ml with tap water.

With vigorous stirring, 360 mg of NaOH was added to the solution, and after 10 seconds, 100 mg of greasy soap was added to the solution. After a further 5 seconds, stirring was stopped and the contents of the reaction vessel were poured into a graduated cylinder in which 1 mg of polyacrylamide was introduced and the column of liquid was spun with a wooden log. After 5 minutes, 960 ml of clarified water and 40 ml of foam were in the cylinder. 1 mg of undissolved substances was determined in water, KNK 8.5 1.0 mmol.l ^ ·. The dry matter of the foam was 3.6%. . . . ...

Under the same repeated conditions, the experiment was repeated with the addition of only 10 mg of greasy soap. After 5 minutes, the layer of clarified water was β containing 5 mg.I ^{1 of} undissolved substances with a volume of 930 ml and the foam layer had a volume of 60 ml.

Example 3

Demanganation: 1 g of MnSO 4 .1HgO was dissolved in 1000 ml of water.

CS 272007 Bl ₄

480 mg NaOH was added to the solution with vigorous stirring. After stirring for 60 seconds, 100 mg of greasy soap was added and after stirring for 5 seconds, the stirring was stopped and the contents of the reaction vessel were poured into a graduated cylinder with 5 mg of starch flocculant and mixed with wood logs.

After 5 minutes was obtained 940 ml of clarified water KNK · 8.5 * 0.5 mmol.I ^'1 with 6 mg.1 -1 solids and 40 ml of foam with a proportion of 6.3% solids.

Example 4

Zinc precipitation 1 g of ZnSO 4 .7HgO was dissolved in 1000 ml of water.

With vigorous stirring, 300 mg of NaOH and 10 mg of greasy soap were added in the solution after 5 seconds, and after another 5 seconds, the stirring was stopped and the vessel was poured into a cylinder with 5 mg of starch flocculant and the column of liquid was spun.

After 5 minutes, 910 ml of clarified KNK 8.5 water contained 0.1 mmol.I ^-1 containing 10 mg.I ^{-1 of} undissolved substances and 110 ml of foam containing 2.8% of dry matter in a cylinder.

Example 5

Coagulation of the medium: 2 g of CuSO ^ .5H ₂ O dissolved in 1000 ml of water.

With vigorous stirring, 670 mg of NaOH were added to the solution and after 30 seconds of stirring 100 mg of greasy soap and after 5 seconds the stirring was turned off and the contents of the vessel were poured into a 1 mg polyacrylamide measuring cylinder and spun.

After 10 minutes, 930 ml of a clear liquid containing 5 mg / l of insolubles and 100 ml of a foam with 4.5% dry matter were obtained.

Example 6

Removal of limestone suspension: To 1,000 ml of water was added 5,000 mg of finely ground limestone for agricultural purposes.

With vigorous stirring, 2,000 mg of technical grade FeSO 4 .THgO were added and, after dissolving it, 760 mg of Na OH in the form of a solution. After stirring for 60 seconds, 200 mg of greasy soap was added and after another 5 seconds, stirring was stopped and the reaction mixture was poured into a graduated cylinder with the present 10 mg of polyacrylamide and mixed.

After 5 minutes, there was 860 ml of clarified water under 180 ml of foam.

After 30 minutes the aqueous layer was about 8.5 0.2 KNK imnol.1 "^ a volume of 920 ml and the concentration of suspended solids was 15 mg.I ^'1. The foam at this time had a volume of 120 ml and the dry matter of the upper half of the foam taken from the cylinder was 4.3%.

Example 7

Purification of water containing chromium suspension: 5 hours old sludge of chromium hydroxide, formed by settling the suspension obtained by neutralization of the chromium salt after reduction of dichromate in an acidic medium using sodium metabisulphite. The sediment obtained contained 0.77% of dry matter, the pH of the solution was 8.0.

To 100 mL of this suspension was added 100 mg of CaCl ₂ and 300 mg of MgSO ₄ .7H ₂ O, and 40 mg of NaOH was added with vigorous stirring in a 300 mL flask. After stirring for 30 seconds, 100 mg of greasy soap was added, and after a further 10 seconds, stirring was stopped and the contents of the vessel were poured into a 100 ml graduated cylinder with 1 mg of polyacrylamide present.

After 10 minutes, the volume of the clarified aqueous phase was 77 ml, the volume of the foam was 53 ml (7 ml of water were added as solutions).

CS 272007 Bl

After 40 minutes, the volume of the aqueous phase was 67 ml and the volume of the foam 40 ml. The flotation foam contained 6.5% dry matter.

The foam of Example 6t was treated in a similar manner

To 80 ml of the collected foam was added 300 mg of MgSO ₄ .7H ₂ O, 100 mg of CaCl ₂ , 40 mg of NaOH, 100 mg of greasy soap and 4 mg of polyacrylamide according to the above procedure. After 2 hours, 58 ml of clear water were obtained (12 ml of water were added in the form of solutions) and 73 ml of foam, the upper half of which contained 10.1% of dry matter.

Example 8

Coagulation with soap alone: The water ee of the slurry of lime slurry after neutralization with sulfuric acid contains a suspension of calcium sulphate.

To 1000 ml of a gypsum suspension with a pH of 8.5 was added 500 mg of greasy soap with vigorous stirring and after 10 seconds stirring was stopped, the reaction mixture was poured into a graduated cylinder with 5 mg of polyacrylamide and mixed.

After 5 minutes, 810 ml of an aqueous phase with 120 mg.l of ¹ insoluble matter were obtained. The foam contained 8.5% dry matter and its total weight after drying was 9.5 g.

By using higher doses of soap than 1000 mg.I ^1, it is possible to reduce the content of undissolved substances in the aqueous phase and to increase the dry matter content of the foam above 20% by weight.

Example 9

Removal of activated carbon from the solution: 1000 mg of activated carbon (Carbosorb) was stirred in 1000 ml of water, which was adjusted to pH 9.0 by the addition of NaOH.

To 1000 ml of the suspension were added 500 mg of greasy soap and 500 mg of CaCl ₂ with vigorous stirring. After 5 seconds, stirring was stopped and the reaction mixture was poured into a graduated cylinder with 5 mg of polyacrylamide and stirred.

After 1 minute, the volume of the aqueous phase was 980 ml and the volume of the foam was 30 ml. The aqueous phase contained 95 mg / l of insoluble matter. The foam contained 16.6% dry matter.

Similarly, an experiment was performed with 1000 mg of finely ground titanium white for painting purposes. The aqueous phase after one minute indentation had a volume of 1000 ml and the solids content of 130 mg l ^'1. The volume of the foam was 30 ml and its dry matter content was 20.5% »

In both cases, the residual content of undissolved substances can be reduced, for example, by precipitation with PeClp NaOH, a greasy soap, but the dry matter content of the resulting foams will already be less than 5% ·

Example 10

Removal of milk from water: 20 ml of drinking whole milk was made up to 1000 ml with water and basified to pH * 8.5 by the addition of lye.

With vigorous stirring, solutions of 500 mg CaCl 2 and 500 mg Na 2 PO 4 were added in one portion. .10H ₂ 0. Stirring was stopped after 5 seconds and the contents of the vessel were poured into a graduated cylinder in which 10 mg of starch flocculant was introduced and the contents of the cylinder were mixed with wood logs.

After 5 minutes, 940 ml of a clear, slightly opalescent aqueous phase and 80 ml of a white foam were obtained.

The separated foam was acidified with 3 mL of 1N HCl with very slow stirring and poured into a 100 L graduated cylinder. After 10 minutes, 22 ml of a white fat emulsion and 61 ml of milky turbid water remained in the top of the cylinder. The bottom layer, which contains dissolved phosphates, can be used in the next cycle in combination with lime milk for further precipitation.

OS 272007 Bl

The process according to the invention can find application in industries where the problems of clarification, flotation and sludge thickening occur. In principle, the process according to the invention can be used as an alternative to the filtration process as regards the separation of suspensions in which the concentration of insolubles is several g.1. possibly further used as fertilizer or feed.

Claims (1)

OBJECT OF THE INVENTION A method of flotation water purification, in which water purification is carried out by reactions in which water technology involves in particular the precipitation of iron, aluminum and magnesium coagulant salts with alkalizing agents or the precipitation of corrosive earth metals with phosphate, silicate, carbonate and sulphate anions, characterized in that the precipitating agents are added to the clarified water at a stirring intensity characterized by Reynolds criterion values in the range of 1.10% to 1.10 ° C, while air is simultaneously dispersed in the liquid, in the presence of sodium or potassium salts coagulants or in the presence of oil or fat emulsions, where the amount of oils or fats corresponds to 5 to 50% by weight of the coagulants used.