JPH10230102A - Manufacture of iron-containing polyaluminum chloride aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare iron-containing polyaluminum chloride aqueous solution in good reproducibility at a low cost by a method wherein while as occasion demands, an alkali compound is added to polyaluminum chloride aqueous solu tion to maintain the pH of the aqueous solution within a range of a specific value, trivalent iron salt aqueous solution is added and mixed. SOLUTION: In the case where iron-containing polyaluminum chloride aqueous solution of under 0.3 in atomic ration of iron and aluminum when the iron- containing polyaluminum chloride is made by adding trivalent iron salt aqueous solution to polyaluminum chloride aqueous solution and mixing, a product which is stable for a long period of time can be prepared only by mixing both aqueous solutions. However, in the case where iron-containing polyaluminum chloride aqueous solution of 0.3 or over the above-mentioned atomic ratio is prepared by adding further trivalent iron salt aqueous solution, alkali compound, preferably caustic alkali, alkalicarbonate or aqueous solution of a mixture thereof are added, and trivalent iron salt aqueous solution is added adjusting a pH of the polyaluminum chloride aqueous solution within a range of 1.5 to 3.5.

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 a long-term stable iron-containing polyaluminum chloride aqueous solution which is made to have high performance by containing iron in a polyaluminum chloride aqueous solution (PAC) useful as a flocculant. is there.

[0002]

2. Description of the Related Art In recent years,
Under a social situation in which environmental issues are emphasized, demand for an inexpensive and high-performance flocculant is increasing. Among them, an aqueous solution of polyaluminum chloride is a flocculant widely used as a water treatment agent because of its performance and price. Attempts to increase the sedimentation rate of flocs, to remove hydrogen sulfide or phosphorus compounds, and to improve the effect of removing COD, BOD, etc. by further adding iron to this aqueous solution of polyaluminum chloride. Has been made.

Conventionally proposed methods for adding iron to an aqueous solution of polyaluminum chloride include the following methods (1) and (2). (1) The atomic ratio of aluminum to iron (aluminum / iron) is greater than about 1 by adding and reacting an alkaline substance such as calcium carbonate, sodium carbonate, and caustic soda to a strong acid salt solution of aluminum and iron, and R / X (however, R is the total amount of aluminum and iron, and X is the amount of a monovalent strong acid group). A method for producing an iron-containing basic salt having a chemical equivalent ratio of 1.5 to 4.0 (Japanese Patent Publication No. 41-41) No. 17048). (2) A soluble aluminum salt and a soluble iron salt are neutralized in an aqueous medium containing alkali carbonate so that the pH falls within a certain range according to the compounding ratio of the iron salt, so that the salt is easily soluble in hydrochloric acid. A method of obtaining an amorphous carbonate-containing aluminum iron hydroxide and dissolving the cake in hydrochloric acid (Japanese Patent Publication No. 59-1424).
No. 4).

However, in the above method (1), since a strong acidic aqueous solution of aluminum and iron salts is neutralized with an alkali, a large amount of common salts is contained. Further, it is difficult to increase the concentration of the active ingredient, that is, polyaluminum chloride containing iron. Furthermore, this flocculant has a pH
However, when used as a coagulant, not only alkali is required, but also there is a problem that the container and the like are corroded. On the other hand, in the method (2), there are various restrictions on the conditions for production, the production process is complicated, and it is difficult to produce a high-performance flocculant with good reproducibility. However, there are many technical problems in industrial production, and it is hard to say that it is a preferable method.

[0005] As described above, it is difficult to inexpensively produce a stable aqueous solution of iron-containing polyaluminum chloride having a high coagulation effect because the basic salt of iron is more susceptible to hydrolysis than a normal salt. Therefore, even if a basic salt can be produced temporarily, precipitation or colloidal formation of iron hydroxide occurs, making it difficult to use it as a flocculant or obtaining a flocculant with a large flocculant effect. This is because it is difficult to be performed. That is, a large production loss is a factor of cost increase.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned disadvantages and to provide a method of producing an iron-containing polyaluminum chloride aqueous solution which is stable for a long period of time and has a high coagulation effect with good reproducibility and at low cost. is there.

[0007]

According to the present invention, a polyvalent aluminum chloride aqueous solution is added with an alkali compound, if necessary, to maintain the pH of the aqueous solution in the range of 1.5 to 3.5 while trivalent. The above object has been attained by providing a method for producing an iron-containing aqueous solution of polyaluminum chloride, characterized by adding and mixing an aqueous solution of an iron salt.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing an aqueous solution of iron-containing polyaluminum chloride of the present invention will be described in detail. The aqueous solution of polyaluminum chloride used in the present invention has a specific gravity of 1.19 (20 ° C.) or more and an aluminum oxide concentration of 10 to 10.
It is preferably 11% by weight and a basicity of 45 to 65%, and a polyaluminum chloride aqueous solution conventionally used as a flocculant can be used.

The aqueous solution of a trivalent iron salt used in the present invention includes, for example, an aqueous solution of iron (III) sulfate and an aqueous solution of iron (III) nitrate.
An aqueous solution, an aqueous solution of iron (III) chloride and the like can be mentioned, and an aqueous solution of iron (III) is particularly preferred. These trivalent iron salt aqueous solutions are desirably high-concentration aqueous solutions, and usually, an aqueous solution having a saturation concentration is used.

When the aqueous solution of iron salt is added to and mixed with the aqueous solution of polyaluminum chloride to form an aqueous solution of iron-containing polyaluminum chloride, the atomic ratio of iron to aluminum (iron / aluminum) is less than 0.3. When producing an aqueous solution of aluminum chloride, a product can be produced for a long period of time by simply mixing both aqueous solutions. When it is tried to produce, it gels and it is difficult to obtain a stable liquid product. When producing an aqueous solution of iron-containing polyaluminum chloride having an atomic ratio of iron to aluminum of 0.3 or more, an aqueous solution of an alkali compound, preferably caustic, alkali carbonate or a mixture thereof, is added to form an aqueous solution of the polyaluminum chloride. pH
Is adjusted to a range of 1.5 to 3.5, preferably 1.5 to 3.0, and by adding a trivalent iron salt aqueous solution, the atomic ratio of iron to aluminum is reduced to about 2.0. A polyaluminum chloride aqueous solution containing iron in an extremely wide range can be produced. If the pH of the aqueous solution of polyaluminum chloride exceeds 3.5 during mixing, iron colloids precipitate and become jelly, and mixing becomes difficult. Also, pH
Is less than 1.5, iron precipitates as iron oxyhydroxide and becomes a reddish brown slurry, which is not preferable.

The caustic and alkali carbonate to be added are:
It can be used alone or in combination. Particularly, when the molar ratio of caustic alkali to alkali carbonate (caustic alkali / alkali carbonate) is 0.5 or less, and caustic alkali and alkali carbonate are used in combination, more preferable results are obtained. Is obtained. Although the reason for this is not clear, it is presumed that the carbonate group in the presence of a strong alkali promotes the dissolution of iron in polyaluminum chloride.

The caustic alkali and alkali carbonate used include caustic soda, caustic potash, sodium carbonate, potash carbonate, and the like. In particular, it is desirable to use caustic soda and sodium carbonate.

[0013]

EXAMPLES The details of the present invention will be described below with reference to examples, but the present invention is not limited to the following examples.
The aqueous solution of polyaluminum chloride (PAC) and the aqueous solution of iron (III) chloride used in the following Examples and Comparative Examples are as follows. PAC: Commercial product, specific gravity of 1.19 (20 ° C.) or more, aluminum oxide concentration of 10 to 11% by weight, basicity of 45 to 65% Iron (III) chloride aqueous solution: Commercial product, reagent class 1, iron (III) chloride
35% by weight concentration

Example 1 PAC stirred at room temperature
When 500 ml of iron chloride (III) aqueous solution 100 ml was gradually added to and mixed with 500 ml, 714 g of a dark brown liquid was obtained.
The pH value of the reaction system was 1.6-1.9. The composition of the obtained iron-containing PAC: Al _1.62 Fe _0.38 (O
H) _3.09 Cl _{2.91 Basicity} : 52% Aluminum oxide concentration: 12.1% by weight pH: 1.9 Specific gravity: 1.23 The iron-containing aqueous solution of polyaluminum chloride obtained in this example was stored for a long time (6 months). Even in the above case, no change was observed in the solution state, and the stability was extremely high. In addition, performance test results as a coagulant (jar test results)
Are shown in the following [Table 1].

Example 2 PAC stirred at room temperature
To 500 ml, 400 ml of an aqueous solution of iron (III) chloride was gradually added at a constant rate (130 ml / h) and mixed.
In AC, 100 ml of 5.5 M / l sodium hydroxide solution and 1.9
A mixture of 1,000 ml of an aqueous M / l sodium carbonate solution was added intermittently via a pH controller to carry out an addition reaction while maintaining the pH value at 2.5. As a result, 1521 g of a dark brown liquid was obtained. The composition of the obtained iron-containing PAC: Al _1.02 Fe _0.98 (O
H) _3.69 Cl _{2.31 Basicity} : 61% Aluminum oxide concentration: 10.2% by weight pH: 2.5 Specific gravity: 1.22 The aqueous solution of iron-containing polyaluminum chloride obtained in this example was stored for a long time (6 months). Even in the above case, no change was observed in the solution state, and the stability was extremely high. In addition, performance test results as a coagulant (jar test results)
Are shown in the following [Table 1].

Example 3 PAC stirred at room temperature
To 500 ml, 700 ml of an aqueous solution of iron (III) chloride is gradually added at a constant rate (230 ml / h) and mixed.
In AC, 100 ml of 5.5 M / l sodium hydroxide solution and 1.9
A mixture of 1000 ml of an aqueous M / l sodium carbonate solution was intermittently added via a pH controller to carry out an addition reaction while maintaining the pH value at 2.5. As a result, 2554 g of a dark brown liquid was obtained. Composition of obtained iron-containing PAC: Al _0.75 Fe _1.25 (O
H) _3.98 Cl _{2.02 Basicity} : 66% Aluminum oxide concentration: 8.9% by weight pH: 2.7 Specific gravity: 1.18 The aqueous solution of iron-containing polyaluminum chloride obtained in this example was stored for a long time (6 months). Even in the above case, no change was observed in the solution state, and the stability was extremely high. In addition, performance test results as a coagulant (jar test results)
Are shown in the following [Table 1].

[Comparative Example 1] PAC stirred at room temperature
To 500 ml, 400 ml of an aqueous solution of iron (III) chloride was gradually added at a constant rate (130 ml / h) and mixed.
In C, 100 ml of 5.5 M / l caustic soda solution and 1.9 M
A 1000 ml / l aqueous solution of sodium carbonate was intermittently added via a pH controller to carry out the addition reaction while maintaining the pH value at 3.8. Became difficult to maintain at 3.8. The aqueous solution obtained by dissolving the reddish brown highly viscous liquid obtained in this comparative example in water was a turbid liquid, and its effect as a coagulant was extremely low.

[Comparative Example 2] PAC stirred at room temperature
400 ml of an aqueous solution of iron (III) chloride was gradually added to 500 ml with stirring at a constant rate (130 ml / h) while stirring, and the PAC was added to the PAC with 100 ml of a 5.5 M / l sodium hydroxide solution.
And a 1.9 M / l aqueous solution of sodium carbonate (1000 ml) were intermittently added via a pH controller to carry out an addition reaction while maintaining the pH at 1.3.
g of dark turbid liquid was obtained. The effect of this as a flocculant was extremely low. The reference examples shown in Table 1 below are commercially available basic aluminum chloride (PAC).
Was used as a flocculant.

[0019]

[Table 1]

The aggregating performance test method (jar test method) is as follows. [Coagulation performance test method (jar test method)] Raw water (turbidity 64
ppm, pH 7.1) to 500 ml, add 2 ml of a flocculant diluted 100 times with water, and rapidly agitate (120 rpm).
m) for 3 minutes, followed by 10 minutes of gentle stirring (60 rpm).
After performing for minutes, the size of the generated floc is visually observed. After standing still for 10 minutes, the turbidity and pH of the supernatant liquid about 2 cm below the water surface are measured. The size of the floc is determined according to the following criteria. Large: about 5mm Large: 3-5mm

[0021]

According to the production method of the present invention, an iron-containing polyaluminum chloride aqueous solution which is stable for a long period of time and has a high coagulation effect can be produced with good reproducibility and at low cost.

Claims (4)

[Claims] An iron-containing polyaluminum chloride aqueous solution having an iron / aluminum atomic ratio (iron / aluminum) of less than 0.3, wherein an aqueous solution of a trivalent iron salt is added to and mixed with an aqueous solution of polyaluminum chloride. Manufacturing method. 2. An aqueous solution of trivalent iron salt is added to an aqueous solution of polyaluminum chloride while adding an alkali compound so as to maintain the pH of the aqueous solution in the range of 1.5 to 3.5. A method for producing an aqueous solution of iron-containing polyaluminum chloride having an atomic ratio of iron to aluminum (iron / aluminum) of 0.3 or more, which is added and mixed so that (iron / aluminum) becomes 0.3 or more. 3. The method according to claim 2, wherein said alkali compound is at least one selected from the group consisting of alkali carbonates and caustic alkalis. 4. The method according to claim 3, wherein the caustic alkali and the alkali carbonate are used in combination at a molar ratio of 0.5 (caustic alkali / alkali carbonate) or less as the alkali compound.