JP2001162108A - Method for manufacturing iron-aluminum combined flocculant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an iron-aluminum combined flocculant strong in flocculating action and high in concentration and preservation stability at a low cost. SOLUTION: An iron-aluminum combined body, which is contained in the iron-aluminum combined flocculant and has 3 or lower iron/aluminum ratio in terms of Fe2O3/Al2O3, is manufactured by the first step to precipitate iron- aluminum multiple hydroxide or aluminum hydroxide by reacting an aqueous solution of iron salt and/or aluminum salt with an aqueous solution of aluminate of an alkali metal at 20 deg.C or lower and the second step to dissolve the iron- aluminum multiple hydroxide by acidifying the reaction system by adding an acidic material and heating the system. The aqueous solution of iron salt and/or aluminum salt is used as the acidic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an iron / aluminum composite coagulant.

[0002]

2. Description of the Related Art The necessity of purifying water, recovering useful substances or separating and removing harmful substances has been particularly important in recent years, and there is a great expectation for excellent flocculants capable of meeting such demands. . Recently, an iron / aluminum composite-based flocculant has attracted attention as a flocculant meeting such expectations. A number of studies have been made on methods for producing this type of flocculant.

Japanese Patent Publication No. 41-17048 discloses CaCO ₃ , Na ₂ CO ₃ in a strongly acidic solution of aluminum and iron.
_3. By adding and reacting an alkali substance such as NaOH, the atomic ratio of aluminum to iron (Al / Fe) is larger than about 1, R / X (R is the total amount of Al and Fe, X is a monovalent strong acid group) The present invention discloses a method for producing an iron-containing basic salt having a composition in which the chemical equivalent ratio represented by (amount) is 1.5 to 4.0. In this method, a large amount of contaminants are contained, the desired iron / aluminum complex cannot be obtained at a high concentration, and the pH is low (pH 1.2 to 1.6). Disadvantages, such as the need for addition of

Japanese Patent Publication No. Sho 59-14244 discloses that a soluble aluminum salt and a soluble iron salt are mixed in an aqueous medium containing an alkali carbonate so that the pH falls within a certain range according to the mixing ratio of the iron salt. There is disclosed a method of neutralizing to obtain an amorphous carbonate-containing aluminum iron hydroxide easily soluble in hydrochloric acid, and dissolving the cake in hydrochloric acid. This method has disadvantages that the manufacturing process is complicated, reproducibility is not good, and it is difficult to obtain a product of a constant quality.

[0005] JP-A-10-230102 discloses that P
While adding an alkaline compound to AC (polyaluminum chloride) so as to maintain the pH of the aqueous solution in the range of 1.5 to 3.5, the aqueous solution of the trivalent iron salt is added with an atomic ratio of iron to aluminum of 0.5. A production method of adding and mixing so as to have three or more is disclosed. This method is disadvantageous in terms of cost because it requires PAC processing. Also, despite adjusting the pH,
Since they are simply mixed, there is a drawback that the coagulation effect is not higher than that of a single salt of Fe or a single salt of Al.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an iron / aluminum composite which has a strong coagulation effect, has a high concentration, and has a high storage stability by using a simple production process at a low cost. An object of the present invention is to provide a method for producing a composite flocculant.

[0007]

According to the present invention, 1) an aqueous solution of an iron salt and / or an aqueous solution of an aluminum salt is reacted with an aqueous solution of an alkali metal aluminate at a temperature of 20 ° C. or lower,
A first step of precipitating the iron / aluminum hydroxide composite or aluminum hydroxide, and then 2) a second step of acidifying the system by adding an acidic substance and heating to dissolve the iron / aluminum hydroxide composite. And a method for producing an iron-aluminum composite flocculant containing an iron-aluminum composite obtained by the step of: In particular, the present invention provides that the acidic substance is an iron salt aqueous solution and
And / or a method for producing the above-mentioned iron / aluminum composite flocculant which is an aqueous solution of an aluminum salt. Further, the present invention provides the production of the above-mentioned iron / aluminum composite flocculant, wherein the precipitate in the first step is an iron / aluminum hydroxide complex, and the acidic substance in the second step is an aqueous solution of sulfuric acid, nitric acid or hydrochloric acid. About the method.

[0008] In particular, the present invention relates to an iron-aluminum composite in which the ratio of iron to aluminum is Fe ₂ O ₃ / Al ₂ O.
_{3. The} method for producing an iron / aluminum composite flocculant according to any one of the above, which is represented by ₃ (weight ratio) and is 3 or less. Furthermore, in the present invention, the iron-aluminum composite is represented by the general formula: Fe _a Al _b (OH) _c Cl _d (SO ₄ ) _e (NO ₃ ) _f [where (a + b) × 3 = c + d + 2e + f] And the basicity represented by the following formula

(Equation 2) Is 40 to 70%, and relates to the method for producing an iron-aluminum composite flocculant according to any of the above. More specifically, the present invention relates to the present invention, wherein the iron / aluminum composite concentration in the iron / aluminum composite flocculant is 10% by weight as Fe ₂ O ₃ + Al ₂ O _3.
The present invention relates to the method for producing an iron / aluminum composite flocculant according to any of the above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing an iron / aluminum composite flocculant of the present invention, in the first step, first, an aqueous solution of an iron salt and / or an aluminum salt is reacted with an aqueous solution of an alkali metal aluminate at a temperature of 20 ° C. or lower. Then, an iron-aluminum hydroxide composite or aluminum hydroxide is precipitated. In this stage, when an aqueous solution of an iron salt and an aqueous solution of an alkali metal aluminate are reacted, an iron / aluminum hydroxide gel is formed and precipitates. Aluminum oxide gel precipitates. The present invention is characterized in that this reaction is performed at 20 ° C. or lower.
This makes the metal hydroxide gel readily acid-soluble. Preferably, the reaction temperature is between 10 and 15C. Reaction temperature 20
If the temperature is higher than ℃, it becomes a hardly acid-soluble metal hydroxide gel, and the desired product cannot be obtained. The reaction is preferably carried out while maintaining the pH of the system at 7 to 9, especially 7.5 to 8.
By adjusting the pH to this range, the iron salt and the aluminum salt are completely decomposed into a metal hydroxide, which facilitates dissolution in the second step. The concentration of the salt solution used is
The iron / aluminum composite aqueous solution, which is the final product to be produced, has a Fe ₂ O ₃ / Al ₂ O ₃ ratio (weight ratio) of 3 or less and a concentration of 10 wt% as Fe ₂ O ₃ + Al ₂ O _3. % Is not limited as long as the condition of not less than% is satisfied.

[0010] The thus obtained precipitated hydroxide system is
In the step, the system is made acidic by adding an acidic substance and heated to obtain the iron / aluminum complex in a dissolved state. By adding an acidic substance to make the system acidic, a state in which a water-soluble iron-aluminum complex is formed is obtained. However, in order to promote this reaction, it is preferable to perform heating in the present invention. As the acid to be added, any acid may be used as long as it can make the system acidic.However, water is added together with the addition of the acid, so that the iron-aluminum complex as the final product cannot be obtained at a sufficiently high concentration. . To avoid this, it is preferable to use a high-concentration aqueous acid solution, an aqueous iron salt solution and an aqueous aluminum salt solution alone or in combination.

When the precipitated hydroxide obtained in the first step is an iron / aluminum hydroxide complex, any of an aqueous solution of an iron salt and an aqueous solution of an aluminum salt may be added to the acidic substance used in the second step. However, when the precipitated hydroxide is aluminum hydroxide, it is necessary to include at least an aqueous solution of an iron salt. Otherwise, naturally, an iron-aluminum composite flocculant cannot be finally obtained.
Similarly, an aqueous acid solution as an acidic substance can be used when the precipitated hydroxide obtained in the first step is an iron / aluminum hydroxide composite. As such an acid aqueous solution, a concentrated aqueous solution of sulfuric acid, nitric acid or hydrochloric acid is preferable. The concentration of the acid aqueous solution is not particularly limited, but as the concentration is higher, the degree of dilution with water can be reduced, and the iron / aluminum composite flocculant of the present invention can be obtained at a higher concentration.

Hydroxide is converted to water-soluble iron by an acidic substance.
To accelerate the reaction to form the aluminum complex,
The system is then warmed. Heating is preferably 80 ° C. or less,
More preferably 65 ° C or less, particularly preferably 60 to 45 ° C.
C. The obtained aqueous solution containing the iron-aluminum complex may still contain insoluble components, and thus is removed by filtration. In this way, a high-concentration iron / aluminum composite flocculant which has not been easily obtained conventionally can be obtained as an aqueous solution. Since the hydroxide generated in the first step gradually shifts to a hardly soluble type,
The second step starts preferably within 15 minutes, more preferably within 10 minutes after the end of the first step.

The iron / aluminum composite, which is the final product, preferably has a ratio of iron to aluminum of 3 or less in terms of Fe ₂ O ₃ / Al ₂ O ₃ (weight ratio). Particularly preferred are those having this ratio of 0.5 to 2.0. If this ratio is larger than 3, the storage stability is undesirably reduced. Therefore, it is necessary to select the amounts of the iron salt, aluminum salt and alkali aluminate used in the first and second steps so as to have the above-mentioned ratio of Fe ₂ O ₃ / Al ₂ O ₃ .

[0014]

EXAMPLES Hereinafter, the present invention will be described more specifically and in detail with reference to examples, but the present invention is not limited to these examples. The sodium aluminate, ferric chloride, aluminum chloride and aluminum sulfate used in the examples are as follows: Sodium aluminate: Sodium aluminate # 2318 (Al ₂ O ₃ : 22.92 manufactured by Asada Chemical Industry Co., Ltd.) %, Na ₂ O: 18.
0%) Ferric chloride: Commercial product (FeCl ₃ : 36% aqueous solution) Aluminum chloride: manufactured by Asada Chemical Industry Co. (Al ₂ O ₃ : 1)
(0.7% aqueous solution) Aluminum sulfate: manufactured by Asada Chemical Industry Co., Ltd. (Al ₂ O ₃ : 8%)
Aqueous solution) Example 1 130 g of water was placed in a 1 L reactor equipped with a cooling device, and cooled to 5 ° C. While continuing cooling, sodium aluminate 130
g and ferric chloride (105 g) were gradually added while maintaining the pH at 7.5 to 8.5 and the liquid temperature at 15 ° C or lower. At the stage when the iron / aluminum hydroxide composite was precipitated, the stirring was increased to make the particles of the precipitate fine. After about 15 minutes, the particles had become sufficiently fine, and the cooling was stopped.
7 g was added in about 5 minutes and heating was started immediately. The liquid temperature was raised to 55 ° C. at a rate of temperature increase of about 1 ° C./min, aged at 55 ° C. for 30 minutes, and insoluble materials were filtered off with No. 2 filter paper.
558 g of an iron-aluminum composite flocculant was obtained as a black-brown transparent solution.

The pH of the coagulant, the compositional analysis value and specific gravity of the iron / aluminum complex in the coagulant by elemental analysis,
The concentration of the iron-aluminum complex in the flocculant was as follows: flocculant pH: 2.4 Chemical composition of iron-aluminum complex (weight fraction): Fe ₂ O ₃ (11.0 in solution) %), Al ₂ O ₃ (5.51% in solution) Basicity: 50.8% Specific gravity: 1.31 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has extremely high flocculant activity, In addition, no change was observed even after long-term storage for 6 months, indicating high stability. Table 1 shows the results of the performance evaluation as a flocculant.

Example 2 An iron / aluminum composite flocculant 7 was prepared in the same manner as in Example 1 except that 362 g of aluminum chloride was added in 10 minutes instead of 197 g of ferric chloride in the second step in 5 minutes.
10 g were obtained. The analytical values were as follows: Flocculant pH: 2.1 Chemical composition of iron / aluminum composite (weight fraction): Fe ₂ O ₃ (2.51% in solution), Al ₂ O ₃ (solution Medium 9.40%) Basicity: 48.7% Specific gravity: 1.28 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has high flocculating activity, and shows no change even after long-term storage for 6 months. No stability was observed. Table 1 shows the results of the performance evaluation as a flocculant.

Example 3 130 g of water was placed in a 1 L reactor equipped with a cooling device, and cooled to 5 ° C. While continuing cooling, sodium aluminate 130
g and 120 g of aluminum chloride were gradually added while maintaining the pH at 7.5 to 8.5 and the liquid temperature at 15 ° C or lower. At the stage when the aluminum hydroxide gel was precipitated, the stirring was increased to make the particles of the precipitate fine. After about 15 minutes, the particles had become sufficiently fine. The cooling was stopped, 70 g of aluminum sulfate and then 169 g of ferric chloride were added, and heating was started immediately. The liquid temperature was raised to 55 ° C. at a rate of temperature increase of about 1 ° C./min, aged at 55 ° C. for 30 minutes, and insoluble materials were filtered off with No. 2 filter paper. Iron / aluminum composite flocculant 605
g was obtained as a dark brown clear solution.

The product analysis results were as follows: Flocculant pH: 2.7 Chemical composition of iron-aluminum complex (weight fraction): Fe ₂ O ₃ (4.80% in solution); Al ₂ O ₃ (7.78% in solution) Basicity: 54.0% Specific gravity: 1.27 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has a very high flocculant activity and 6 months No change was observed even after storage for a long time, and the product was highly stable. Table 1 shows the results of the performance evaluation as a flocculant.

Example 4 Instead of adding 105 g of ferric chloride in the first step, 70 g of aluminum sulfate and 60 g of ferric chloride were added, and instead of adding 197 g of ferric chloride in the second step, 120 g of aluminum chloride and 120 g of chloride were added. 596 g of an iron / aluminum composite flocculant was obtained in the same manner as in Example 1 except that 109 g of ferric iron was added and heating was performed at 60 ° C. for 20 minutes. The analytical values were as follows: pH: 2.6 Chemical composition of iron-aluminum complex (weight fraction): Fe ₂ O ₃ (4.78% in solution), Al ₂ O ₃ (7 in solution) (76%) Basicity: 53.2% Specific gravity: 1.29 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has extremely high flocculating activity and shows no change even after long-term storage for 6 months. The stability was high. Table 1 shows the results of the performance evaluation as a flocculant.

Example 5 575 g of an iron / aluminum composite coagulant was obtained in the same manner as in Example 2 except that the amount of aluminum chloride added in the second step was 230 g. The analytical values were as follows: Flocculant pH: 2.5 Chemical composition of iron / aluminum composite (weight fraction): Fe ₂ O ₃ (3.10% in solution), Al ₂ O ₃ (solution Mediumity: 9.13%) Basicity: 58.0% Specific gravity: 1.26 / 20 ° C The iron / aluminum composite flocculant obtained in this example has extremely high flocculating activity, and does not change at all even after long-term storage for 6 months. Was not recognized and the stability was high. Table 1 shows the results of the performance evaluation as a flocculant.

Example 6 Iron / aluminum composite coagulation was carried out in the same manner as in Example 3 except that 214 g of ferric chloride was used alone instead of aluminum sulfate and ferric chloride as salts added in the second step. 577 g of the agent were obtained. The analytical values were as follows: Flocculant pH: 2.5 Chemical composition of iron / aluminum composite (weight fraction): Fe ₂ O ₃ (7.40% in solution), Al ₂ O ₃ (solution Medium: 7.49%) Basicity: 52.8% Specific gravity: 1.29 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has extremely high flocculating activity, and does not change at all even after long-term storage for 6 months. Was not recognized and the stability was high. Table 1 shows the results of the performance evaluation as a flocculant.

Example 7 Instead of 197 g of ferric chloride added in the second step, 35
448 g of an iron / aluminum composite flocculant was obtained in the same manner as in Example 1 except that 110 g of% hydrochloric acid was used. Analytical values were as follows: pH of flocculant: 2.8 Chemical composition of iron-aluminum composite (weight fraction): Fe ₂ O ₃ (3.94% in solution), Al ₂ O ₃ (solution Medium 6.62%) Basicity: 54.0% Specific gravity: 1.26 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has extremely high flocculating activity, and does not change during long-term storage for 6 months. Was not recognized and the stability was high. Table 1 shows the results of the performance evaluation as a flocculant.

Example 8 130 g of water was placed in a 1 L reactor equipped with a cooling device, and cooled to 5 ° C. While continuing cooling, sodium aluminate 106
g and 123 g of polyiron were gradually added while maintaining the pH at 7.5 to 8.5 and the liquid temperature at 15 ° C or lower. At the stage when the iron / aluminum hydroxide composite was precipitated, the stirring was increased to make the particles of the precipitate fine. After about 15 minutes, the particles had become sufficiently fine.
51 g was added in about 5 minutes, and heating was started immediately. The temperature of the solution was raised to 55 ° C at a rate of about 1 ° C / min,
After aging for minutes, insolubles were filtered off with No. 2 filter paper. 596 g of an iron / aluminum composite flocculant was obtained.

The results of analysis of the products were as follows: flocculant pH: 2.7 Chemical composition of iron-aluminum complex (weight fraction): Fe ₂ O ₃ (3.07% in solution); Al ₂ O ₃ (8.74% in solution) Basicity: 51.5% Specific gravity: 1.29 / 20 ° C. The iron / aluminum composite flocculant obtained in this example has a very high flocculant activity and 6 months No change was observed even after storage for a long time, and the product was highly stable. Table 1 shows the results of the performance evaluation as a flocculant.

COMPARATIVE EXAMPLE 1 In the first step, 106 g of sodium aluminate was used in 81 g, in 123 g of polyiron was used in 94 g, and in the second step, aluminum chloride 2 was used.
633 g of an iron / aluminum composite coagulant was obtained in the same manner as in Example 8 except that 338 g was used instead of 51 g. The analytical values were as follows: pH: 2.0 Chemical composition of iron-aluminum composite (weight fraction): Fe ₂ O ₃ (2.19% in solution), Al ₂ O ₃ (10 in solution) .31%) Basicity: 30.2% Specific Gravity: 1.28 / 20 ° C. Table 1 shows the performance evaluation results of the obtained flocculant.

Comparative Example 2 Sodium aluminate 1 was prepared by adding 130 g of water in the first step to 91 g.
An iron / aluminum composite was prepared in the same manner as in Example 1 except that 30 g was replaced with 91 g, ferric chloride 105 g was replaced with 74 g, and 197 g of ferric chloride in the second step was replaced with 481 g of aluminum chloride and added in 10 minutes. 726 g of coagulant was obtained. The analytical values were as follows: pH: 1.8 Chemical composition of iron-aluminum complex (weight fraction): Fe ₂ O ₃ (1.79% in solution), Al ₂ O ₃ (9 in solution) (.86%) Basicity: 35.3% Specific gravity: 1.29 / 20 ° C. Table 1 shows the results of performance evaluation as a flocculant.

Evaluation of Performance as Coagulant The coagulability of the coagulants obtained in Examples 1 to 6 and Comparative Examples 1 and 2 was evaluated by the following method. [Coagulation Performance Evaluation Method (Jar Test Method)] In a 500 mm glass beaker, raw water (kaolin was added to tap water with a turbidity of 1)
A substance added in an amount of 00 ppm. pH 7.45) 50
To 20 ml of a flocculant was added 20 ppm (weight) as a stock solution using a microsyringe using a microsyringe.
The mixture was rapidly stirred for 120 minutes (120 ppm) and then slowly stirred for 8 minutes (50 ppm), and then allowed to stand. The size of the floc immediately before standing and the sedimentation of the floc due to standing were observed. In addition, supernatant water (3 cm below the water surface) after 5 minutes of standing was collected, and turbidity and pH were measured. The results are shown in Table 1.
In addition, PAC [polyaluminum chloride for commercial water supply (Al ₂ O ₃ : 10.2%)] (Comparative Example 3) and polyiron [commercial product (Fe ₂ O ₃ : 16% or more)] (comparative examples) Example 4) was used.

[0028]

[Table 1] The turbidity in the above measured values is represented by the kaolin concentration in kaolin dispersion water having the same light transmittance (concentration of standard kaolin contained in 1 L of purified water).

The features of the present invention are summarized as follows: 1) To neutralize an iron salt or aluminum hydrochloric acid solution, instead of simply using an alkali agent, a high concentration of sodium aluminate is used. Iron / aluminum composite flocculant can be produced, and contaminating salts can be reduced. 2) By neutralizing at a low temperature, it is not necessary to use alkali carbonate, which is a source of carbon dioxide, which is one of the factors of global warming, as a neutralizing agent. 3) The iron salt is neutralized with an aluminum salt to obtain an iron-aluminum composite hydroxide, which is dissolved in an iron salt or an aluminum salt or a mixture thereof, so that an iron-aluminum composite flocculant is obtained. 4) Since it can be manufactured from a simple chemical without using PAC (polyaluminum chloride), the manufacturing cost can be reduced.

[0030]

According to the method for producing an iron-aluminum composite flocculant of the present invention, a high-concentration flocculant having a strong flocculating ability and excellent storage stability can be easily prepared as compared with the conventional method. There is an advantage that it can be obtained at low cost by using a cheap raw material in a manufacturing process.

Claims (10)

[Claims] 1. An aqueous solution of an iron salt and / or an aqueous solution of an aluminum salt and an aqueous solution of an alkali metal aluminate are reacted at a temperature of not more than 20 ° C. to precipitate an iron / aluminum hydroxide complex or aluminum hydroxide. One step, and then 2) a step of acidifying the system by adding an acidic substance and heating to dissolve the iron-aluminum hydroxide complex, and a second step of dissolving the iron-aluminum complex. A method for producing an iron / aluminum composite flocculant. 2. The method according to claim 1, wherein the acidic substance is an aqueous solution of an iron salt and / or an aqueous solution of an aluminum salt. 3. The iron / aluminum composite coagulation according to claim 1, wherein the precipitate in the first step is an iron / aluminum hydroxide complex, and the acidic substance in the second step is an aqueous solution of sulfuric acid, nitric acid or hydrochloric acid. Method of manufacturing the agent. 4. The heating temperature is not higher than 80 ° C.
4. The method for producing an iron-aluminum composite flocculant according to any one of the above items 3. 5. The iron / aluminum composite has an iron / aluminum ratio of 3 as expressed by Fe ₂ O ₃ / Al ₂ O ₃ (weight ratio).
The method for producing an iron-aluminum composite flocculant according to any one of claims 1 to 4, which is as follows. 6. The iron-aluminum composite is represented by a general formula: Fe _a Al _b (OH) _c Cl _d (SO ₄ ) _e (NO ₃ ) _f [(a + b) × 3 = c + d + 2e + f] The basicity represented by the following equation The method for producing an iron-aluminum composite flocculant according to any one of claims 1 to 5, wherein the iron content is 40 to 70%. 7. An iron / aluminum composite coagulant having an iron / aluminum composite concentration of 10% as Fe ₂ O ₃ + Al ₂ O _3.
7% by weight or more of iron or iron according to any one of claims 1 to 6.
A method for producing an aluminum composite flocculant. 8. The iron / aluminum composite coagulation according to claim 1, wherein the iron salt aqueous solution is an aqueous solution of ferric chloride, ferric sulfate or polyferrous sulfate (basic ferric sulfate). Method of manufacturing the agent. 9. The iron according to claim 1, wherein the aluminum salt aqueous solution is an aqueous solution of one or more salts selected from the group consisting of aluminum sulfate, aluminum chloride, aluminum nitrate and basic salts thereof. -A method for producing an aluminum composite flocculant. 10. The method for producing an iron / aluminum composite flocculant according to claim 1, wherein the aqueous alkali metal aluminate solution is an aqueous solution of sodium aluminate or potassium aluminate.