JP2024089040A - Boron-containing basic aluminum chloride - Google Patents

Abstract

To provide a boron-containing basic aluminum chloride which can cope with a wide range of physical property variations depending on the type of water to be treated and has excellent cohesiveness and manufacturability in basic aluminum chloride used as a coagulant for water treatment.SOLUTION: A boron-containing basic aluminum chloride contains boron and has a B/Al molar ratio of 0.01 or more and 1.00 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to basic aluminum chloride for use as a coagulant for water treatment, etc.

Aluminium-based hydrolyzed metal salts are very widely used as water treatment flocculants and play an important role in removing many impurities, such as colloidal particles and dissolved organic matter, from polluted water.

Examples of such aluminum-based hydrolyzed metal salts include aluminum sulfate, aluminum chloride, and basic aluminum chloride. Here, basic aluminum chloride is also called polyaluminum chloride (PAC), and various types are known depending on the range of basicity, the presence or absence of sulfate ions, etc. Basic aluminum chloride is generally synthesized by reacting hydrochloric acid with aluminum hydroxide, and in many cases, a basic substance is added to this to increase the basicity, resulting in highly basic aluminum chloride, or a sulfate ion-containing basic aluminum chloride is produced by adding a water-soluble sulfate.

Of the above, sulfate ions have the effect of improving the flocculation performance of basic aluminum chloride, but are known to reduce stability. Patent Document 1 describes that sulfate ions contained in basic aluminum chloride cause problems such as clouding of the liquid and even gelation during storage, and the concentration of sulfate ions contained in basic aluminum chloride is limited from the standpoint of stability.

In addition, the Japanese Industrial Standards state that the aluminum oxide content of polyaluminum chloride for water supply is restricted to 10.0% by mass or more and 11.0% by mass or less, the basicity range is restricted to 45% by mass or more and 65% by mass or less, and the sulfate ion content is restricted to 3.5% by mass or less.

Therefore, in order to obtain basic aluminum chloride with improved coagulation properties that can accommodate a wide range of physical property variations, there are limitations to controlling the basicity and sulfate ion concentration, and it is desirable to improve coagulation properties by using a substance that replaces sulfate ions.

Furthermore, Patent Document 2 discloses a highly basic aluminum chloride containing silicon in a molar ratio of Si/Al ₂ O ₃ in the range of 0.001 to 0.1. When viewed as an alternative to sulfate ions, silicon has the following problems.
(1) There are limitations on the silicon compounds that can be used. (2) There are limitations on the manufacturing method.

Silica (SiO ₂ ), the oxide of silicon used above, is hardly soluble in water, and silicic acid (Si(OH) ₄ ), the orthoacid of silicon, has the property of rapidly dehydrating and condensing, eventually turning into silica, so that industrially usable silicon compounds are limited to basic substances such as alkali silicates. Patent Document 2 also uses only alkali silicates, and because alkali silicates are basic substances, the method for producing basic aluminum chloride containing silicon is limited.

For these reasons, there is a need to improve the coagulation properties of basic aluminum chloride using a more versatile substance.

JP 2009-279512 A Patent No. 6186545

Japanese Industrial Standards (JIS) K1475-1996

The problem that this invention aims to solve is to provide basic aluminum chloride for use as a flocculant for water treatment, which can accommodate a wide range of physical property variations depending on the type of water to be treated, and has excellent flocculation properties and manufacturability.

As a result of intensive research aimed at solving the above problems, the inventors discovered that by incorporating boron into basic aluminum chloride, it became possible to treat water under conditions where it was previously difficult to remove turbidity, and thus completed the present invention.

That is, the present invention is as follows.
[1] A boron-containing basic aluminum chloride, characterized in that it contains boron and has a B/Al molar ratio of 0.01 or more and 1.00 or less.
[2] The boron-containing basic aluminum chloride according to the above [1], having an aluminum oxide concentration of 8% by mass or more and 15% by mass or less, and a basicity of 40% by mass or more and 80% or less.
[3] A water treatment flocculant containing the boron-containing basic aluminum chloride described in [1] or [2] above.
[4] A method for producing a boron-containing basic aluminum chloride, which contains boron and has a B/Al molar ratio of 0.01 or more and 1.00 or less, comprising adding a boron compound to basic aluminum chloride so that the B/Al molar ratio is 0.01 or more and 1.00 or less.
[5] A method for coagulating impurities in water to be treated, comprising mixing the water to be treated with basic aluminum chloride containing boron and having a B/Al molar ratio of 0.01 or more and 1.00 or less.

The present invention can provide boron-containing basic aluminum chloride that is capable of dealing with a wide range of variations in physical properties depending on the type of water to be treated and has excellent coagulation and manufacturability.

1 is a graph showing the supernatant turbidity of Example 1 and Comparative Example 1. 1 is a graph showing the supernatant turbidity of Example 2 and Comparative Example 1. 1 is a graph showing the supernatant turbidity of Example 3 and Comparative Example 1.

The present invention is a boron-containing basic aluminum chloride that contains boron and has a molar ratio of B/Al of 0.01 or more and 1.00 or less (hereinafter, sometimes simply referred to as "the boron-containing basic aluminum chloride of the present invention").

[Content of essential constituent elements]
The molar ratio of B/Al in the boron-containing basic aluminum chloride of the present invention is 0.01 or more and 1.00 or less, more preferably 0.02 or more and 0.70 or less, and particularly preferably 0.05 or more and 0.50 or less. If the molar ratio of B/Al in the boron-containing basic aluminum chloride is less than 0.01, no improvement in coagulation properties is observed, and even if it exceeds 1, the effect becomes saturated, which is not preferable.

[Aluminum oxide concentration]
The aluminum oxide concentration of the boron-containing basic aluminum chloride of the present invention is not particularly limited, but is, for example, 8% by mass or more and 15% by mass or less. The aluminum oxide concentration is preferably 9% by mass or more and 13% by mass or less, and particularly preferably 10% by mass or more and 11% by mass or less. The aluminum oxide contained in the basic aluminum chloride is quantified in accordance with Japanese Industrial Standards (JIS) K1475.

[Basicity range]
The basicity of the boron-containing basic aluminum chloride of the present invention is not particularly limited, but is, for example, 40% or more and 80% or less, preferably 50% or more and 70% or less, and more preferably 55% or more and 65% or less. The basicity of the basic aluminum chloride is measured in accordance with Japanese Industrial Standards (JIS) K1475.

[Aluminum oxide concentration and basicity range]
The above-mentioned ranges of aluminum oxide concentration and basicity can be appropriately combined. Therefore, the boron-containing basic aluminum chloride of the present invention preferably has an aluminum oxide concentration of 8% by mass or more and 15% by mass or less, and a basicity of 40% by mass or more and 80% or less, more preferably has an aluminum oxide concentration of 9% by mass or more and 13% by mass or less, and a basicity of 50% by mass or more and 70% or less, and particularly preferably has an aluminum oxide concentration of 10% by mass or more and 11% by mass or less, and a basicity of 55% by mass or more and 65% or less.

[Definition of chloride ion content]
With regard to chloride ions, the Cl/Al molar ratio is preferably 0 or more and 3 or less. The upper limit of the Cl/Al molar ratio is more preferably 2.5, and even more preferably 2. When chloride ions are contained, for example, the Cl/Al molar ratio is preferably 0.1 or more and 2 or less.

[Other components]
The boron-containing basic aluminum chloride of the present invention contains aluminum and boron as essential components, but may contain other components as optional components as long as the components satisfy the requirements of the boron-containing basic aluminum chloride of the present invention. Examples of other components include alkali metals, alkaline earth metals, sulfate ions, etc.

[Definition of alkali metal content]
Regarding the content ratio of other components, for example, in the case of an alkali metal, when the alkali metal is M, the molar ratio of M/Al is preferably 0 or more and 1 or less. The upper limit of the molar ratio of M/Al is more preferably 0.8, and further preferably 0.7. When an alkali metal is contained, for example, the molar ratio of M/Al is preferably 0.01 or more and 0.70 or less.

[Definition of alkaline earth metal content]
With respect to the alkaline earth metal, when the alkaline earth metal is E, the molar ratio of E/Al is preferably 0 or more and 0.1 or less. The upper limit of the molar ratio of E/Al is more preferably 0.07, and even more preferably 0.05. When an alkaline earth metal is contained, for example, the molar ratio of E/Al is preferably 0.01 or more and 0.05 or less.

[Definition of sulfate ion content]
For sulfate ions, the molar ratio of SO ₄ /Al is preferably 0 or more and 0.18 or less. The upper limit of the molar ratio of SO ₄ /Al is more preferably 0.16, and even more preferably 0.14. When sulfate ions are contained, for example, the molar ratio of SO ₄ /Al is preferably 0.01 or more and 0.14 or less.

[Production method]
The boron-containing basic aluminum chloride of the present invention can be produced by adding a boron compound to basic aluminum chloride so that the molar ratio of B/Al is 0.01 or more and 1.00 or less.

The basic aluminum chloride used as a raw material is not particularly limited, but for example, one having an aluminum oxide concentration of 8% by mass or more and 20% by mass or less, preferably 9% by mass or more and 13% by mass or less, and particularly preferably 10% by mass or more and 11% by mass or less is used. In addition, the basic aluminum chloride used has a basicity of 40% by mass or more and 80% or less, preferably 50% by mass or more and 70% or less, and particularly preferably 55% by mass or more and 65% or less. In addition, the above-mentioned ranges of aluminum oxide concentration and basicity can be appropriately combined. Basic aluminum chloride with such aluminum oxide concentration and basicity can be produced according to a conventional method (for example, see Patent No. 3464023, etc.).

One example of a method for producing basic aluminum chloride is a method in which an aluminum compound such as aluminum hydroxide and hydrochloric acid are placed in an autoclave and subjected to hydrothermal treatment. During the hydrothermal treatment, the pressure is higher than normal pressure, for example, 0.2 MPa or more and 1.5 MPa or less, and the temperature of the water is preferably a temperature above the boiling point, for example, about 120°C or more and 200°C or less, to dissolve the aluminum hydroxide with hydrochloric acid.

In the above manufacturing method, a basicity adjuster may be used to change the basicity of the basic aluminum chloride. Examples of basicity adjusters include alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogen carbonates, alkaline earth metal hydrogen carbonates, and alkali metal aluminates.

Specific examples of hydroxides of alkali metals and alkaline earth metals include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, etc. Specific examples of carbonates and bicarbonates of alkali metals and alkaline earth metals include lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate, etc. Specific examples of aluminates of alkali metals include sodium aluminate, etc.

Sulfuric acid or aluminum sulfate may be used to change the sulfate ion concentration of basic aluminum chloride.

In addition to the basic aluminum chloride produced as described above, commercially available products sold under the names of basic aluminum chloride or polyaluminum chloride of normal basicity, high basicity, ultra-high basicity, etc., that fall within the above range may also be used.

The boron, which is a characteristic of the boron-containing basic aluminum chloride of the present invention, can be obtained by adding a boron compound to the basic aluminum chloride described above so that the molar ratio of B/Al in the final boron-containing basic aluminum chloride is 0.01 or more and 1.00 or less, preferably 0.02 or more and 0.70 or less, more preferably 0.05 or more and 0.50 or less. The boron content in the boron-containing basic aluminum chloride of the present invention can be changed by the amount of boron compound added. The method of adding the boron compound is not particularly limited, and the boron compound may be added in the above amount in any step of the steps of producing basic aluminum chloride, but is preferably added in the last step of producing basic aluminum chloride. After these steps, purification, drying, etc. may be performed according to conventional methods.

[Boron compounds]
The boron compound used in the production of the boron-containing basic aluminum chloride of the present invention is not particularly limited, but for example, a salt of an oxoacid of boron is preferred. Representative salts of an oxoacid of boron include sodium tetraborate, potassium tetraborate, sodium metaborate, and sodium perborate. Among them, sodium tetraborate is particularly preferred, since borax can be used as an industrial raw material. As the salt of an oxoacid of boron, a salt of an oxoacid of boron may be used which is produced by dissolving boric acid or diboron trioxide in water to generate borate ions, and neutralizing the hydrogen ions liberated by a basic substance to form an oxoacid of boron.

[Confirmation method]
In the present invention, the production of boron-containing basic aluminum chloride having the above-mentioned properties can be confirmed by ICP-AES (inductively coupled plasma-atomic emission spectrometry), azomethine H absorptiometry, electrochemical quantitative analysis using a polyol complex, or the like.

[Water treatment]
The boron-containing basic aluminum chloride of the present invention described above can flocculate impurities in the water to be treated by mixing with the water to be treated. The amount of boron-containing basic aluminum chloride used when flocculating impurities in the water to be treated is not particularly limited, but is, for example, 1 to 1000 mg/L, preferably 3 to 300 mg/L. The boron-containing basic aluminum chloride of the present invention can be used in various water treatments similar to various water treatments using a flocculation method that flocculates impurities in the water to be treated using a conventionally known basic aluminum chloride. In addition, various conditions for the flocculation method using the boron-containing basic aluminum chloride of the present invention may be the same as those for the flocculation method that flocculates impurities in the water to be treated using a conventionally known basic aluminum chloride, except for the use of the boron-containing basic aluminum chloride.

The impurities in the water to be treated that can be flocculated by the boron-containing basic aluminum chloride of the present invention are insoluble substances suspended in the water, such as suspended solids. The "Waterworks Testing Method" defines suspended solids as substances that pass through a 2 mm sieve and remain on a filter material with a pore size of 1 μm. Examples of suspended solids include rock debris such as clay (grain size 0.004 mm or less) and silt (grain size 0.06 mm or less), inorganic substances such as metals, metal hydroxides, and metal oxides, suspended matter derived from organisms such as fungi and algae, and organic substances such as oil. The size of the impurities is, for example, 1 nm to 0.1 mm, preferably 0.01 μm to 10 μm. Examples of water to be treated that contains such impurities include raw water for waterworks (surface water from rivers, etc.), industrial water, industrial wastewater, domestic wastewater, and livestock wastewater.

The method for flocculating impurities in the water to be treated using the boron-containing basic aluminum chloride of the present invention may also be combined with other known water treatment processes. Examples of other known water treatment processes include precipitation separation, flotation separation, filtration, dehydration filtration, membrane separation, ion exchange, physical adsorption, stripping, oxidation/disinfection, electrodialysis/electrolysis, etc.

[Mechanism of coagulation]
Generally, natural turbidity has the properties of a colloid solution, and the particle surfaces have negative charges, which repel each other to create a stable state. When a normal aluminum-based flocculant is diluted with water, hydrolysis proceeds, forming aluminum polymers with larger positive charges, which neutralize the surface charges of the turbidity, creating an attractive force between the particles and forming fine clumps (flocs). Furthermore, the hydrolyzate of the aluminum-based flocculant bonds the turbidity mainly by adsorption to form flocs, which then precipitate. In contrast, when the boron-containing basic aluminum chloride of the present invention is used, the formation of flocs is promoted by boron. Boron atoms have the property of forming stable bonds with oxygen atoms, and boron compounds usually exist in the form of boric acid, which is an oxo acid, in water, and are ionized to form borate ions, which are anions. The binding caused by the adsorption of the aluminum-based flocculant is promoted by the borate ions, improving the flocculation action.

[Water treatment flocculant]
The boron-containing basic aluminum chloride of the present invention has a flocculating effect on impurities in the water to be treated, and can be used as a water treatment flocculant containing this. In this case, another flocculant may be added to the water treatment flocculant as long as it does not impair the effect of the present invention. For example, inorganic flocculants such as polyferric sulfate and organic polymer flocculants can be mentioned.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Jar Test]
In the present invention, a jar test using turbidity as an index was adopted to evaluate the coagulation property of basic aluminum chloride. There is a high correlation between the amount of suspended solids and turbidity, and turbidity is generally used as an index of the amount of impurities in water (dirt, turbidity).

The jar test was carried out at room temperature (approximately 20°C) using a jar tester MJS-6T (Daido Kogyo Co., Ltd.) with test water containing 50 mg/L of kaolin (Hakutou soil, CAS registration number: 1332-58-7) as a simulated turbid substance and having the water quality shown in Table 1 below. The flocculation conditions for the jar test were as follows: 1 L of test water in a 1 L beaker was stirred at 100 rpm while adding basic aluminum chloride from the examples and comparative examples, followed by rapid stirring at the same 100 rpm for 1 minute, slow stirring at 60 rpm for 10 minutes, and then leaving to stand for 10 minutes. After leaving to stand, the supernatant water was collected and the turbidity, absorbance (Abs.), haze, and pH were measured. The turbidity, absorbance, and haze of the supernatant water were measured using a turbidity meter/color meter WA7700 (Nippon Denshoku Kogyo Co., Ltd.). The pH was measured using a portable pH meter D-71 (Horiba, Ltd.).

(Comparative Example 1)
Jar test of high basicity polyaluminum chloride:
A jar test was performed by injecting boron-free high basicity polyaluminum chloride (aluminum oxide concentration 10.7 mass%, basicity 61.4%) manufactured by Nankai Chemical Co., Ltd. at injection rates of 10, 15, 20, 25, and 30 mg/L into test water containing 50 mg/L of kaolin as a simulated turbidity and having the water quality shown in Table 1. Table 2 shows the turbidity, absorbance, haze, and pH of the supernatant water.

The results in Table 2 show that the test water used in the jar test, which contained kaolin as a simulated turbidity, could not reduce the turbidity of the treated water below 18 degrees simply by adding polyaluminum chloride. There was also a tendency for the amount of turbidity reduction to decrease as the amount of coagulant injected increased. This is presumably because the injected polyaluminum chloride positively charged the turbidity, creating a repulsive force between the particles, suppressing the coagulation action.

Example 1
Jar test of boron-containing basic aluminum chloride:
Sodium tetraborate (CAS registration number: 1330-43-4, molecular formula: Na ₂ B ₄ O ₇ ) was added as a boron compound to high basicity polyaluminum chloride (aluminum oxide concentration 10.7 mass%, basicity 61.4%) manufactured by Nankai Chemical Co., Ltd., so as to obtain the B/Al molar ratios shown in Table 3 (addition rates of sodium tetraborate: 1.05, 2.10, 5.26, 10.45, 20.63, 50.11, and 68.81 mg/g). After addition, the mixture was mixed and dissolved to obtain boron-containing basic aluminum chloride.

Test water containing 50 mg/L of kaolin as a simulated turbid substance and having the water quality shown in Table 1 was injected with boron-containing basic aluminum chloride as a coagulant at an injection rate of 30 mg/L, and a jar test was conducted. Table 3 shows the turbidity, absorbance, haze, and pH of the supernatant water.

Figure 1 shows the turbidity of the supernatant water in Example 1 and Comparative Example 1 at a coagulant injection rate of 30 mg/L. The horizontal axis of Figure 1 is the B/Al molar ratio, and the vertical axis is the turbidity (turbidity of the water to be treated). The smaller the turbidity value, the higher the coagulation property. As shown in Figure 1, in Comparative Example 1 (B/Al molar ratio is 0), in which only polyaluminum chloride was injected into test water containing kaolin as a simulated turbid substance, the turbidity of the water to be treated did not decrease, and the kaolin, which is a suspended substance, hardly coagulated. In contrast, as in Example 1, the turbidity of the water to be treated could be reduced by adding sodium tetraborate and adjusting the B/Al molar ratio of the coagulant to 0.01 or more and 1.00 or less. It was also found that, if the injection rate of the coagulant is constant, the turbidity of the water to be treated can be further reduced and good coagulation property can be obtained by increasing the B/Al molar ratio.

Example 2
Jar test of boron-containing basic aluminum chloride:
Sodium metaborate tetrahydrate (CAS registration number: 10555-76-7, molecular formula: _NaBO2.4H2O ) was added as a boron compound to high basicity polyaluminum chloride (aluminum oxide concentration 10.7 mass%, basicity 61.4%) manufactured by Nankai Chemical Co., Ltd., so as to obtain the B/Al molar ratios shown in Table 4 (addition rates of sodium metaborate tetrahydrate were _5.74 , 14.29, 28.12, and 54.58 mg/g). After addition, the mixture was mixed and dissolved to obtain boron-containing basic aluminum chloride.

A jar test was conducted by injecting boron-containing basic aluminum chloride at an injection rate of 30 mg/L into 1 L of test water containing 50 mg/L of kaolin as a simulated turbid substance and having the water quality shown in Table 1. Table 4 shows the turbidity, absorbance, haze, and pH of the supernatant water.

Figure 2 shows the turbidity of the supernatant water in Example 2 and Comparative Example 1 at a coagulant injection rate of 30 mg/L. By adding sodium metaborate tetrahydrate and adjusting the B/Al molar ratio of the coagulant to 0.01 or more and 1.00 or less, the turbidity of the treated water could be reduced.

Example 3
Jar test of boron-containing basic aluminum chloride:
Sodium perborate tetrahydrate (CAS registration number: 10486-00-7, molecular formula: NaBO3.4H2O) was added as a boron compound to high basicity polyaluminum chloride (aluminum oxide concentration 10.7 mass%, basicity _61.4 %) manufactured by Nankai Chemical Co., Ltd., so as to obtain the B/Al molar ratios shown in Table 5 (addition rates of sodium perborate tetrahydrate were _6.40 , 15.93, 31.28, and 60.53 mg/g). After addition, the mixture was mixed and dissolved to obtain boron-containing basic aluminum chloride.

A jar test was conducted by injecting boron-containing basic aluminum chloride at an injection rate of 30 mg/L into 1 L of test water containing 50 mg/L of kaolin as a simulated turbid substance and having the water quality shown in Table 1. Table 5 shows the turbidity, absorbance, haze, and pH of the supernatant water.

Figure 3 shows the turbidity of the supernatant water in Example 3 and Comparative Example 1 at a coagulant injection rate of 30 mg/L. By adding sodium perborate tetrahydrate and adjusting the B/Al molar ratio of the coagulant to 0.01 or more and 1.00 or less, the turbidity of the treated water could be reduced.

(Comparative Example 2)
Jar test of high-basic aluminum chloride with silicon and magnesium:
According to the method described in Patent Document 2 (JP Patent No. 6186545), highly basic aluminum chloride containing silicon and magnesium (aluminum _{oxide concentration 10.3 mass%, basicity 70.5%) was obtained. The composition of the obtained highly basic aluminum chloride was Si/Al2O3 ( molar} ratio) ₌ 0.008, Mg/ _Al2O3 (molar ratio) = _0.06 , Na/ _Al2O3 (molar ratio) = 0.6, Cl/ _Al2O3 (molar ratio) = 2.6, _{SO4 / Al2O3} (molar ratio) = 0.072. The analysis of each element was performed according to the JIS analysis method.

Test water containing 50 mg/L of kaolin as simulated turbidity and with the water quality shown in Table 1 was injected with high-basic aluminum chloride containing silicon and magnesium as a coagulant at injection rates of 10, 15, 20, 25, and 30 mg/L, and a jar test was conducted. Table 6 shows the turbidity, absorbance, haze, and pH of the supernatant water.

The results in Table 6 show that the test water used in the jar test this time contained kaolin as a simulated turbidity, and the turbidity of the treated water could not be reduced to 23 degrees or less simply by adding high-basic aluminum chloride containing silicon and magnesium. Also, as in Comparative Example 1, there was a tendency for the amount of turbidity reduction to decrease when the amount of coagulant injected was increased.

The boron-containing basic aluminum chloride of the present invention can be used for water treatment because it can coagulate impurities in the water being treated.

Claims (5)

A boron-containing basic aluminum chloride characterized by containing boron and having a molar ratio of B/Al of 0.01 or more and 1.00 or less. The boron-containing basic aluminum chloride according to claim 1, wherein the aluminum oxide concentration is 8% by mass or more and 15% by mass or less, and the basicity is 40% by mass or more and 80% by mass or less. A water treatment flocculant containing the boron-containing basic aluminum chloride according to claim 1 or 2. A method for producing boron-containing basic aluminum chloride, which contains boron and has a molar ratio of B/Al of 0.01 or more and 1.00 or less, characterized by adding a boron compound to basic aluminum chloride so that the molar ratio of B/Al is 0.01 or more and 1.00 or less. A method for coagulating impurities in water to be treated, comprising mixing the water to be treated with basic aluminum chloride which contains boron and has a B/Al molar ratio of 0.01 or more and 1.00 or less.