RU2288181C1 - Method of preparing water-soluble reagent to clean natural and waste waters and to separate phases - Google Patents

Abstract

FIELD: water treatment processes.

SUBSTANCE: invention relates to method of preparing water-soluble reagents to remove suspended particles and mineral- and organic-origin contaminants. Reagent can be used both to treat moderately turbid waters for domestic and drinking demands and to clean industrial and domestic effluents. Reagent is prepared by interaction of (i) aluminum salt, in particular aluminum pentahydroxochloride with molar ratio Cl^-/Al³⁺ = 0.46-0.52, and (ii) polyacrylamide with molecular mass 3·10⁵-2·10⁶. Interaction is accomplished by mixing aqueous colloidal solution of aluminum pentahydroxochloride with 0.1-1.0% aqueous solution of polyacrylamide at molar ratio Al³⁺ to polyacrylamide unit (2-4):1 and temperature 20-30°C.

EFFECT: increased activity in separation of both moderately turbid dispersions and high-concentration suspensions.

2 cl, 1 dwg, 5 tbl, 5 ex

Description

The invention relates to methods for producing water-soluble reagents used for purification of natural and wastewater from suspensions, petroleum products, fatty, protein and other pollution of mineral and organic origin. The proposed reagent can be used both for the treatment of low-turbid waters, for example, for the preparation of household water from natural surface sources, and for the treatment of wastewater with a high content of the dispersed phase, for example, for the treatment of industrial wastewater and for the treatment of domestic wastewater. In the reagent technology of water treatment and water purification, the efficiency of the process is determined by the degree of purification of water from impurities, the duration of the process of sedimentation of impurities, the duration of the filtering cycle of purified water and other factors. One of the main ones is the reagent dose, which should be minimal in order to achieve a sufficient degree of purification, which is determined not only by economic considerations, but also by the requirements of the inspecting authorities for the quality of purified water for drinking and household purposes, as well as for waters of the reverse cycle, as well as those directed to biological treatment.

The magnitude of the required dose of the reagent depends on its activity associated with the chemical structure of the reagent and the mechanism of its interaction with colloidal impurities. The most common water-soluble reagents include inorganic salts of iron and aluminum, as well as water-soluble polymers of organic nature [Zapolsky AK, Baran A.L. Coagulants and flocculants in water purification processes. L .: Chemistry, 1987].

The former, by neutralizing the surface charge of colloidal particles, destabilize the disperse system, which is natural surface water and most wastewater, which leads to the formation of "primary" particles in the water being treated.

The second, water-soluble organic polymers combine particles into large flocs, helping to accelerate their sedimentation. However, the separate use of these two reagents in the purification process is associated with a number of technical difficulties and may be accompanied by both a synergistic and antagonistic effect during purification [V. A. Softenkov, G. V. Bulidorova. Chem. and technol. water. 1997.V.17. No. 5. S.583]. One way to solve this problem is to create composite reagents that combine the properties of an inorganic coagulant and an organic polymer flocculant.

A known method of producing a composite reagent by adding an aqueous solution of an iron or aluminum salt to an aqueous solution of an organic cationic polymer, stirring at an elevated temperature of the reaction mass for a certain time and then cooling the reaction product [Pat. 2322128 GBC 02 F 1/56 1998].

The disadvantages of the method are the process in the given technological parameters, the uncertainty of the chemical composition of the composite reagent, its unknown activity in the processes of water purification. The claimed content of cationic polymer in the composition is 0.1-10%, which suggests that this reagent can work only in low-dispersion dispersions, i.e. as a coagulant. The interaction of a positively charged metal cation from the inorganic salt with the cationic polymer chain leads to the compaction of polymer macromolecules, which will lead to a decrease in activity when using the reagent as a flocculant for concentrated dispersions.

It is known to use compositions of aluminum chloride with one of the water-soluble cationic amine-type polymers for treating water with a low suspension content (less than 0.1%) [Pat. 341357 EPO C 02 F 1/52 1989].

The disadvantage of this method is the use of aluminum chloride and an organic polymer, which by toxic properties cannot be used to prepare household water, and the marked synergistic effect during coagulation is observed only in the case of low turbidity dispersions (4.0-4.5 turbidity units).

The closest is a method of obtaining a water-soluble reagent by polymerization of acrylamide under the action of a radical initiator in an aqueous solution of aluminum hydroxochloride. The process is carried out at temperatures of 60-90 ° C in a certain range of hydroxyalkyl-tert-butylperoxide-iron ratios and with an acrylamide content of aluminum oxychloride from 3.2% wt. up to 34.9% wt. [Pat. 2174105 RF C 02 F 1/52 2001]. The disadvantages of this method include the following:

firstly, the reaction of obtaining the reagent is carried out at elevated temperature, which requires the use of heat exchange equipment, the use of heat carrier, and the process itself is energy-intensive;

secondly, the polymerization reaction of acrylamide is sensitive to the content of iron, which determines the decay rate of the initiator, and thus depends on the quality of aluminum hydrochloride, the composition of which may vary depending on the starting material to obtain aluminum hydrochloride;

thirdly, the polymerization reaction of vinyl monomers and acrylamide, in particular, is very sensitive to the presence of impurities, which can be in the composition of an aqueous solution of aluminum hydroxychloride, which can lead to the formation of low molecular weight polymerization products;

fourthly, the resulting polymer product has a low molecular weight, as evidenced by the value of the characteristic viscosity [η] ≤2.85;

fifthly, insufficiently high molecular weight of the product may be the reason for the low efficiency of the reagent in the process of flocculation of suspensions.

The present invention solves the important task of obtaining a water-soluble reagent in a technically simple way, without energy consumption, without the use of auxiliary reagents, which is highly active in the purification of low-turbid aqueous dispersions, such as natural water, as well as in the separation of concentrated suspensions in the form of wastewater of various origins.

When implementing the proposed method for producing a water-soluble reagent, the following result is obtained:

firstly, the reaction of the formation of a water-soluble reagent - polymer-colloidal complex (PAC) occurs during mechanical mixing of a solution of highly basic aluminum pentahydroxochloride (PHCA) with an aqueous solution of polyacrylamide (PAA) due to cooperative interactions of the polymer functional groups with hydrated aluminum ions in the polynuclear complex ( colloidal particles) PGA;

secondly, the reaction between the water-soluble polymer and PHCA proceeds under normal conditions in a homogeneous medium without the formation of a new phase and practically without a thermal effect, i.e. does not require supply or removal of heat;

thirdly, in the reaction of formation of a water-soluble reagent, high molecular weight polyacrylamide can be used, which contributes to the production of a reagent with increased flocculating ability;

fourthly, the polymer-colloidal complex of PHA and polyacrylamide, obtained at a specific molar ratio, is a hybrid reagent combining the properties of an inorganic coagulant and a high molecular weight flocculant and, therefore, is highly effective in the separation of both low-concentration dispersions and highly concentrated suspensions;

The technical result achieved is achieved in a method for producing a water-soluble reagent for purifying natural and waste waters and phase separation using an aluminum salt, moreover, aluminum pentahydroxochloride is taken as an aluminum salt in the form of an aqueous colloidal solution and it is reacted with polyacrylamide with a molecular weight of 3 · 10 ⁵ - 2 · 10 ⁶ , taken in the form of an aqueous 0.1-1.0% solution, by mixing them with a molar ratio of Al ³⁺ : polyacrylamide unit equal to (2 ÷ 4): 1 at a temperature of 20-30 ° C. In this case, aluminum pentahydroxochloride of the composition in which the molar ratio Cl ^- / Al ³⁺ is equal to 0.46-0.52 is taken.

The reason for the formation of the polymer-colloidal complex (PAC) is the donor-acceptor cooperative bonds arising between the AI ³⁺ atoms in the composition of PGA and the nitrogen atoms in the PAA macromolecule. The strength of such complexes is explained by the cooperative (summarized) nature of such an interaction, which is associated with the polymer nature of PHCA particles. Other aluminum salts or low-basic aluminum chlorides are not capable of forming strong independently existing polycomplexes.

The reason for the high efficiency and hybrid nature of the polymer-colloidal complex in the separation of dispersions is that in the resulting polycomplex positively charged PHCA particles are located on the periphery of the PAA macromolecular coil. An increase in the molar ratio Al ³⁺ : PAA unit leads to an increase in the number of PHA particles bound to the PAA macromolecule and increase in the Coulomb repulsion forces between the PHA particles, which leads to an increase in the size of macromolecular tangles of the polymer-colloidal complex.

The invention is illustrated by the following examples:

Example 1. In this example, due to the influence of the nature of the salt on the possibility of the formation of a polymer-colloidal complex with PAA.

In a 500 ml flask was placed 100 ml of a 1% aqueous solution of PAA ([η] = 5.07 dl / g) and a portion of an aluminum salt in the form of a 3% aqueous solution was added with stirring. Salts used were: aluminum nitrate, aluminum sulfate, 1/3-aluminum oxychloride, 2/3-aluminum oxychloride and 5/6-aluminum oxychloride (PHCA).

The values of the salt weights corresponded to a molar ratio of Al ³⁺ : PAA unit equal to 2: 1, and are presented in table 1.

Table 1.
The values of the weights of aluminum salts taken in the complexation reaction with PAA. №№ pp Salt Formula Mass g one. Aluminum sulphate Al ₂ (SO ₄ ) ₃ 4.81 2. Aluminum nitrate Al (NO ₃ ) ₃ 5.99 3. 1/3 aluminum oxychloride (OXA) Al (OH) Cl ₂ 8.94 four. 2/3 aluminum oxychloride (OXA) Al (OH) ₂ Cl 7.24 5. 5/6 aluminum oxychloride (PHCA) Al ₂ (OH) ₅ Cl 6.33

The resulting mixtures were planted in a 2-fold excess of methanol and dried to constant weight. Methanol was chosen as a precipitant because all of the above salts are soluble in its aqueous solutions. Redeposited samples were analyzed for aluminum and chlorine (Table 2).

Table 2.
Elemental analysis of the products of the interaction of PAA solutions with aluminum salts №№ pp Salt Elemental composition Attitude Al Cl Cl / Al ³⁺ mol. one. Al ₂ (SO ₄ ) ₃ 0 0 - 2. Al (NO ₃ ) ₃ 0 0 - 3. Al (OH) Cl ₂ 0 0 - four. Al (OH) ₂ Cl 0 0 - 5. Al ₂ (OH) ₅ Cl 14,4 8.71 0.46-0.52

From the data in Table 2 it follows that the polymer-colloidal complex is formed only with PHCA, and the Cl ^- / Al ³⁺ molar ratio ^is close to this ratio in the PHCA itself, which indicates the interaction of PAA with the polymer particles of PHCA - [Al ₂ (OH) ₅ Cl] n.

Example 2. In this example, the influence of the ratio of reagents on the composition of the resulting polymer-colloidal complex of PHA with PAA is determined. The reaction of the formation of the polymer-colloidal complex was carried out analogously to example 1, changing the molar ratio of Al ³⁺ : unit PAA in the initial mixture of reagents.

The obtained polycomplexes were planted in methanol, dried, and analyzed for the content of aluminum, chlorine, and nitrogen (Table 3).

Table 3.
The effect of the ratio of reagents on the composition of the resulting PAC. №№ pp Al ³⁺ Ratio: PAA Link The elemental composition of the polycomplex,% the initial mixture, moln. Al Cl N one. 0.5 9.1 5.5 12.1 2. one 14,4 8.7 8.5 3. 2 19.1 11.5 5.5 four. four 23,2 13.8 5,6 5. 6 23.1 14.0 5,6 6. 8 23.3 13.9 5,4

From the data in Table 3 it follows that an increase in the content of PHA in the initial mixture during the formation of PAC is accompanied by an increase in the content of Al and Cl in the polycomplex up to the ratio Al ³⁺ : PAA unit = 4.

Example 3. In this example, the use of polymer-colloidal complexes as flocculants in the separation of concentrated dispersions is caused. To assess the effectiveness of the reagents, the spectrophotometric method was used, in which the absorbance of the supernatant was measured after a certain dispersion settling time with and without flocculant added. After that, the dimensionless parameter was calculated — the clarification effect — Eosv. [Novakov I.A., Radchenko S.S., Radchenko F.S. Journal of Applied Chemistry. 2004. V.77. No. 10. S.1699].

Flocculation of kaolin dispersion was carried out in the free deposition mode (concentration of the dispersed phase — 0.6 wt.%). Flocculation was carried out at a dose of flocculant - 6 mg / L.

Table 4.
The dependence of the clarification effect on the composition of the PAC №№ p p The ratio of Al ³⁺ : link PAA (mol.) In the PAC Eosv one. 0.5: 1 61 2. 1: 1 120 3. 2: 1 205 four. 4: 1 145

From the data of table 4 it follows that the greatest effect are polycomplexes with a composition of 2: 1 and 4: 1.

Example 4. In this example, the effect of the molecular weight of polyacrylamide on the efficiency of the obtained PAC based on flocculation of concentrated dispersion is determined. To obtain the PAC composition Al ³⁺ : unit PAA = 2: 1, PAA of various molecular weights was used. PAC was obtained analogously to example 1. Flocculation was carried out analogously to example 3 (table 5).

Table 5.
Dependence of the clarification effect of kaolin dispersion (С _D = 0.6 wt.%) On the molecular weight of PAA used to obtain PAC (composition Al ³⁺ : PAA-2: 1 unit). Like mass of PAA in the composition of the PAC Eosv 3 · 10 ⁵ 88 5 · 10 ⁵ 105 1 · 10 ⁶ 120 2 · 10 ⁶ 132

The reagent dose is 4 mg / l.

From the data of table 5 it follows that the use of higher molecular weight PAA to obtain PAC leads to an increase in the effectiveness of the latter during flocculation.

Example 5. In this example, the use of PAC in the process of coagulation of a low-concentration dispersion that simulates natural water is caused. The dispersion was prepared on the basis of 0.8% kaolin dispersion, which was defended for 24 hours. The upper layer was decanted and sedimentation analysis was performed, according to which the content of the dispersed phase in the dispersion was 30-40 mg / dm ³ , the particle size of the dispersed phase was in the range of 1.6-2.5 μm. The effectiveness of coagulants was evaluated by changing the turbidity of the water after treatment with reagents. For comparison, the most famous reagents in water purification processes were used: PGA, PAA, Praestol-650 and Zetag-92. The graph shows the curves of the turbidity of kaolin dispersion depending on the type and dose of coagulant.

From the graph it follows that typical flocculants: PAA- (1), Praestol-650- (2) and Zetag-92- (3) are inactive under these conditions. PHCA- (4) is an effective coagulant at doses of 10 mg / l or more. With a low content of Al ^{3+, the} polymer-colloidal complex is not effective (PAC-0.5) - (5), however, with the composition of Al ³⁺ : PAA unit = 2: 1 (PAC-2) - (6) PAC is an effective coagulant superior to the results of purification known from the practice of preparing water pentahydroxochloride aluminum.

Thus, the method for producing the polymer-colloidal complex, which consists in the interaction of colloidal particles of polynuclear aluminum complexes with macromolecules of polyacrylamide at their molar ratio (2: 4): 1, which occurs when a water solution of aluminum pentahydroxochloride is mixed with a molar ratio Cl ^- / Al ³⁺ = 0.46-0.52 with a 0.1-1.0% aqueous solution of polyacrylamide at a temperature of 20-30 ° C, allows you to get a water-soluble reagent with both high coagulating and flocculating properties.

Claims (2)

1. The method of obtaining a water-soluble reagent for the purification of natural and waste water and phase separation using an aluminum salt, characterized in that the aluminum salt is taken as aluminum pentahydroxochloride in the form of an aqueous colloidal solution and interact with a molecular weight polyacrylamide of 3 · 10 ⁵ -2 · 10 ⁶ , taken in the form of an aqueous 0.1-1.0% solution, by mixing them at a molar ratio of Al ⁺³ : polyacrylamide unit equal to (2-4): 1, at a temperature of 20-30 ° C. 2. The method according to claim 1, characterized in that they take aluminum pentahydroxochloride composition, in which the molar ratio Cl ^- / Al ³⁺ = 0.46-0.52.