KR101887412B1 - Method of preparation for Alkaline coagulant and treating method of water/wastewater using the same - Google Patents

Abstract

The present invention relates to a method for producing an alkaline coagulant which is polyaluminate sodium silicate with 3-15 wt% of Al_2O_3 content and 0.2-1.3 wt% of SiO_2 content, and a water treatment method using the same. According to the present invention, the polyaluminate sodium silicate which is an alkaline coagulant maintaining excellent fluorine removing and neutralizing abilities, and having excellent stability as precipitation of a solid precipitate is not detected during a long-term storage time.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for preparing an alkaline coagulant and a water treatment method using the same,

The present invention relates to a method for producing an alkaline flocculant, and more particularly, to a method for producing an alkaline flocculant and a water treatment method using the flocculant.

Fluorine compounds that have strong chemical activity are used in steel mills, casting mills, casting mills, mini mills, and electronic parts factories. In particular, fluorine compounds used in washing and etching operations in electronic component factories are made of sodium fluoride (NaF) AlF ₃ ) and hydrogen fluoride (HF), and it causes many difficulties in the treatment of wastewater.

The law on the conservation of water quality and aquatic ecosystem for fluorine-containing wastewater has set the emission limit below 15ppm and should be lowered to 7ppm or less in order to be designated as an environment friendly company. In order to satisfy the criteria, we are investing a lot of money in multi-stage processing, etc., and we are trying to develop various treatment agents and treatment methods in water treatment agent manufacturers and research organizations.

The wastewater treatment methods containing fluorine compounds to date include mainly a method of using an ion exchange resin and porous alumina, a coagulation precipitation method using a Ca compound and an Al compound, a precipitation method using a rare earth compound, And porous alumina are difficult to apply to industrial wastewater due to limit of exchange capacity. Coagulation and precipitation method using Ca compound and Al compound or rare earth compound is mainly used for treatment of fluorine-containing wastewater. However, In the case of removing fluorine by using Al compound, COD (Chemical Oxygen Demand) which is representative of organic substance besides fluorine can be removed. However, since the removal rate of fluorine is low and the amount of chemical input and sludge generation are large, This is a large disadvantage. In addition, the method using a rare earth compound has a problem that the removal efficiency of COD contained in the wastewater is low although the fluorine removal rate is high.

Inorganic coagulants used in flocculation facilities include aluminum sulfate (Alum), polychlorinated aluminum (PAC), polychlorinated aluminum silicate (PACS), aluminum polychlorinated calcium (PACC), low salt polychlorinated aluminum, (FeCl ₃ ), ferric sulfate, and iron salt-based inorganic flocculants such as iron polysulfate. Since these inorganic flocculants have strong acidity, the use of inorganic flocculants The use of a neutralizing agent to maintain an appropriate flocculation pH is indispensable. Neutralizing agent commonly used is sodium hydroxide (NaOH) and calcium hydroxide (Ca (OH) ₂₎ are however, calcium hydroxide (Ca (OH) ₂₎ processing costs when the sludge generation amount depending on the increase given the sludge treatment cost for And maintenance cost. In the water treatment site, caustic soda (NaOH) is the most used as a neutralizing agent.

When the content of NaOH is above 5%, it is classified as a harmful chemical substance, and many difficulties are caused due to the strengthening of regulations on the management of harmful chemical substances. This is due to a large number of accidents involving various hazardous chemical substances, ranging from the Foshan leak in Gumi in September 2012 to the sulfuric acid leak in June 2016, There are many difficulties in the countermeasures of legal regulations on the management of neutralizing agents.

Background Art [0002] Prior art related to a water treatment agent and a treatment method for removing fluorine in the treatment of fluorine-containing wastewater is disclosed in Korean Patent Registration No. 10-0984448, for example, in the treatment of wastewater containing high- Discloses a method of removing fluorine from wastewater that can stably remove fluorine using a reducing slag. In the prior art, the waste water containing fluorine is collected in a packing tower, and a reducing slug of an electric furnace is charged into the packing tower A first step of precipitating and removing fluorine in waste water in the form of fluorite (CaF ₂ ); A second step of introducing wastewater from the first step into a reactive coagulation bath and injecting calcium hydroxide (Ca (OH) ₂ ) to coagulate and precipitate residual fluorine in the wastewater; The third step is to discharge the wastewater to the settling tank after the second step and discharge only the supernatant. The fluorine is removed through the third step. A separate filling tower is required before coagulation and sedimentation. As shown in Fig. In the prior art, fluorine-containing wastewater is introduced into a primary reaction tank, and polychlorinated aluminum having a basicity of 50% or more as a fluorine removing agent is introduced into the reaction tank. A first step of injecting aluminum fluoride (AlF ₃ ) to form aluminum fluoride; A second step of transferring the product of the first reaction tank and the treated water to the second reaction tank and adding sodium aluminate to remove residual fluorine from the wastewater; Transferring the product and treated water of the secondary reaction tank to an aggregation tank and precipitating the flocculated particles using an organic flocculant; And transferring the aggregated particles to a settling tank and discharging treated water. In addition, Korean Patent Laid-Open Publication No. 1999-0046414 discloses a fluorine-containing industrial wastewater treatment agent containing 37 to 55% by weight of calcium carbonate (CaCO ₃ ), 34 to 42% by weight of hydrochloric acid and borax (Na ₂ B ₄ O ₇ · 10H ₂ O) by using a fluorine-containing industrial waste water treatment agent consisting of 0.1~12% by weight of calcium hydroxide (Ca (OH) _2), sodium hydroxide (NaOH) or 20 minutes by adjusting the aeration stirring about pH 9-10.5 by addition of a mixture thereof The reaction was carried out by adding a small amount of aluminum sulfate (Alum) and stirring for 10 minutes. The pH was adjusted to 6.5-7.5, and then a small amount of coagulant was added to precipitate for 1-3 hours. Which is capable of treating industrial wastewater containing water.

The present applicant has found that it is generally possible to replace conventional neutralizing agents used in the coagulation process during the water treatment process and to reduce the amount of coagulant used and also to improve the cohesion efficiency by using an alkaline coagulant such as polyaluminium silicate The present invention has been completed.

The present invention is directed to a method for producing sodium aluminosilicate polyaluminate, which is an alkaline flocculant, and a water treatment method using the same, and more particularly, to a method for improving sodium fluoride A method for producing sodium polyaluminate silicate which is an aggregating agent for maintaining alkalinity for fluorine removal such as improvement of flocculation efficiency, reduction of flocculant and reduction of sludge generation amount, and a water treatment method using the same.

As means for solving the process for producing sodium polyaluminate silicate which is an alkaline flocculant for the purpose of the present invention, a). (Al (OH) ₃ ) and caustic soda (NaOH) in water and reacting at a temperature of 105 to 150 ° C. to produce a sodium aluminate solution having an Al ₂ O ₃ content of 3.9 to 17.7% by weight Step reaction and b). Sodium silicate having an SiO ₂ content of 28 to 30% by weight and inorganic acid having a concentration of 20 to 50% by weight are dissolved in water and reacted at a temperature of 30 to 60 ° C to prepare a polysilicate solution having an SiO ₂ content of 1.4 to 4.2% The second stage reaction to produce and c). The polysilicic acid solution 10 of 70 to 90% by weight of the sodium aluminate solution prepared in the first step reaction and the SiO ₂ content of 1.4 to 4.2% by weight of the Al ₂ O ₃ solution prepared in the second step reaction To 30% by weight of a polyol represented by the unit of the general formula (1) below at a temperature of 30 to 60 ° C for 1 to 3 hours to obtain a polyol represented by the following general formula (1) with an Al ₂ O ₃ content of 3 to 15% by weight and a SiO ₂ content of 0.1 to 1.3% And a third-stage reaction for producing an alkaline flocculant solution which is sodium aluminate silicate.

[Formula 1]

_{(NaAlO 2 · xH 2 O)} · ySiO 2

3? X? 7, and 0.003? Y? 0.04 in the above formula

The sodium aluminate solution having a content of Al ₂ O ₃ of 3.9 to 17.7% by weight, which is the product of the first step reaction according to the present invention, specifically includes aluminum hydroxide (Al (OH) ₃ ) 10 (Al (OH) ₃ ) is dissolved in an amount of 99.0% by weight based on the weight of Al (OH) ₃ , and the reaction is carried out for 1 to 3 hours after dissolving 20 to 55 parts by weight of sodium hydroxide Or more.

The polysilicate solution having a SiO ₂ content of 1.4 to 4.2 wt%, which is the product of the second-step reaction according to the present invention, specifically comprises 100 parts by weight of water (water), and SiO ₂ content of 28 to 30 wt% Wherein the inorganic acid is prepared by dissolving 5.5 to 20 parts by weight of an inorganic acid and 3.5 to 14 parts by weight of an inorganic acid at a concentration of 20 to 50% by weight and reacting the mixture for 1 to 3 hours, wherein the inorganic acid is any one of sulfuric acid, hydrochloric acid and nitric acid Is selected.

The Al ₂ O ₃ content of the sodium polyaluminate silicate prepared according to the third step reaction of the present invention is a resultant value obtained by the test analysis, and the sodium polyaluminate silicate is obtained as a liquid phase as an alkaline flocculant.

In addition, sodium polyaluminate silicate, which is an alkaline flocculant represented by the unit represented by the general formula (1) prepared in the present invention, has excellent fluorine-removing ability and neutralizing ability, and does not precipitate solid precipitates during a long- And the like.

The sodium polyaluminate silicate, which is an alkaline coagulant adjusted to an Al ₂ O ₃ content of 3 to 15% by weight and a SiO ₂ content of 0.2 to 1.3% by weight, produced according to the production method of the present invention maintains excellent fluorine removal ability, And exhibits excellent stability such as precipitation of solid phase precipitates during long-term storage period.

1 is a graph showing FT-IR analysis results of the polysilicic acid produced in Examples 1 and 2
2 is a graph showing FT-IR analysis results of sodium polyaluminate silicate, which is an alkaline coagulant prepared in Example 1

Hereinafter, the present invention will be described in more detail with reference to examples and test examples, but the following examples do not limit the present invention.

≪ Example 1 >

- First step reaction

40 kg of aluminum hydroxide [Al (OH) ₃ , Al (OH) ₃ 99.0% or more], 55 kg of caustic soda (NaOH, 98.0%) and 105 kg of water (H ₂ O) To prepare a sodium aluminate solution having an Al ₂ O ₃ content of 12 wt%.

- Second stage reaction

Sodium silicate _{(Na 2 O · SiO 2 ·} H 2 O; SiO 2 content is 28-30 wt.%) 30kg, water (H ₂ O) 270kg, sulfuric acid _{(H 2 SO 4, 30%} ) temperature of the 17kg 45 ℃ It was reacted for 2 hours to prepare a poly-silicate solution (SiO ₂ content of 2.6% by weight).

- The third stage reaction

180 kg of a sodium aluminate solution (Na ₂ O.Al ₂ O ₃ ; Al ₂ O ₃ content: 12 wt%, Na ₂ O content: 25 wt%), which is the first step reaction product, and 180 kg of a polysilicic acid solution (SiO ₂ content: 2.6 wt%) were reacted at a temperature of 60 ° C for 2 hours to obtain an alkali flocculant sodium polyaluminate solution having an SiO ₂ content of 0.26 wt% and an Al ₂ O ₃ content of 10.8 wt% 200 kg.

≪ Example 2 >

- First step reaction

20 kg of aluminum hydroxide [Al (OH) ₃ , Al (OH) ₃ , 99.0 wt% or more], 55 kg of caustic soda (NaOH, 98.0 wt%) and 210 kg of water (H ₂ O) To prepare a sodium aluminate solution having an Al ₂ O ₃ content of 4.2 wt%.

- Second stage reaction

Sodium silicate _{(Na 2 O · SiO 2 ·} H 2 O, SiO 2 content of 28 to 30% by weight) 30kg, water (H ₂ O) 270kg, sulfuric acid (H ₂ SO _4, 30% by weight) of a 17kg 45 ℃ It was reacted for 2 hours at a temperature to prepare a poly-silicate solution (SiO ₂ content of 2.6% by weight).

- The third stage reaction

180 kg of a sodium aluminate solution (Na ₂ O.Al ₂ O ₃ ; Al ₂ O ₃ content: 4.2 wt%, Na ₂ O content: 18.5 wt%), which is the first step reaction product, and 180 kg of a polysilicic acid solution a (SiO ₂ content of 2.6% by weight) 20kg at a temperature of 60 ℃ by reacting for 2 hours, 200 kg of an alkali flocculant polyaluminic acid sodium silicate solution having an SiO ₂ content of 0.26% by weight and an Al ₂ O ₃ content of 3.8% by weight was prepared.

The FT-IR analysis results of the polysilicate prepared in Example 1 and Example 2 are shown in FIG. 1, and the results are shown in FIG. 1. In FIG. 1, 972, 1085, 1200, 1500, 2340 and An absorption band was formed at around 3300 cm ^-1 . The absorption band near 1500 and 3300 cm ^-1 indicates an absorption band indicating the presence of water molecules as in the case of 2.6% (as SiO ₂ ) sodium silicate diluent. And the weakly absorptive band near 2340 cm ^-1 is a Si-H form due to hydrogen bonding with silicon (Si) atoms. The absorption band near 972, 1085 and 1200 cm ^-1 indicates the absorption band region due to the water molecules coordinated to the silicon (Si) atoms. It is produced by adding sulfuric acid to a sodium silicate dilution diluted with 2.6% (as SiO ₂ ) It is judged to be an absorption band formed by attack of hydrogen by sulfuric acid in a region which is weakly crosslinked with Si-O-Si in one polysilicic acid. (aquatic chemistry, p781-783)

And were expressed as the <Example 1> of the alkaline coagulant according to the invention prepared in poly aluminate, sodium silicate (Al ₂ O ₃ content of 10.8 wt%) of the FT-IR analysis of the [2] [2] Turning to the, 870, 980, 1630, 2350, and the absorption band was formed in the vicinity 3200㎝ ^-1, 870, the absorption band in the vicinity 980㎝ ^-1 is aluminum contained by a poly silicic acid to be added to the sodium aluminate (OH ^- ) coordinating to the silicon (Si) atom, and the absorption band near 1630 and 2350 cm ^-1 is considered to be an absorption band due to aluminum (Al). And an absorption band near 3200 cm ^-1 indicates an absorption band indicating the presence of water molecules.

&Lt; Test Example 1 >

In order to secure the stability of the sodium polyaluminate silicate prepared in the above <Examples 1 and 2>, freezing and precipitation occurred during long-term storage at -20 ° C, room temperature 20 ° C and high temperature 50 ° C for 4 months, And the freezing condition were measured. The results of the test (stability of the product) are shown in Table 1 below.

Item Example 1 Example 2 Temperature Minus 20 ° C 20 ℃ 50 ℃ Minus 20 ° C 20 ℃ 50 ℃ Freezing none - - none - - Sediment generation none none none none none none condition stability stability stability stability stability stability Whether to freeze none - - none - -

As shown in Table 1, it was confirmed that the sodium polyaluminate silicate as an alkaline coagulant according to the present invention exhibits excellent stability such as not precipitating a solid phase precipitate during a long-term storage period.

&Lt; Test Example 2 &

For the comparative test of the fluorine removal efficiency of the sodium polyaluminate sodium silicate coagulant prepared in Example 1 according to the present invention, the fluorine removal efficiency was measured by using poly (aluminum chloride) (PAC) widely used in the water treatment field And the results are shown in Table 2 below. However, the raw water used in the test was wastewater generated from the electronic component factory, and the wastewater contained 48.5 mg / L of fluorine concentration, pH 7.5 and turbidity of 300 NTU.

division
Input (ppm) Fluorine concentration (mg / L) and removal efficiency (%) Turbidity (NTU) and Removal Efficiency (%) mg / L % NTU % Invention Example 1 400 7.5 84.5 4.5 98.5 Aluminum polychloride (PAC) 400 13.5 72.2 12.8 95.7

&Lt; Test Example 3 >

For the comparative test of the fluorine removal efficiency of the sodium polyaluminate silicate, which is an alkaline coagulant prepared in Example 2 according to the present invention, the fluorine removal efficiency was measured by using poly (aluminum chloride) (PAC) widely used in the water treatment field And the results are shown in Table 3 below. However, the used raw water is always equal to the raw water of <Test Example 2>.

division
Input (ppm) Fluorine concentration (mg / L) and removal efficiency (%) Turbidity (NTU) and Removal Efficiency (%) mg / L % NTU % Invention 700 11.5 76.3 9.8 96.7 Aluminum polychloride (PAC) 700 14.5 70.1 13.2 95.6

As shown in [Table 2] and [Table 3], it was confirmed that the sodium silicate polyaluminate, which is an alkaline coagulant according to the present invention, has improved fluorine removal efficiency as compared with the conventional polyaluminum chloride (PAC).

<Test Example 4>

Neutralization experiments were carried out with polyaluminic acid sodium silicate, which is an alkaline coagulant prepared in Examples 1 and 2 according to the present invention, and neutralization tests were carried out using caustic soda (NaOH, 50%), The results are shown in Table 4 below.

The raw water used in the neutralization capacity test was wastewater generated from a food factory, and the wastewater contained 520 mg / L of COD (Chemical Oxygen Demand), 1,300 mg / L of SS and pH of 4.93.

division Coagulant
input
(ppm) Coagulant
After input
pH corrector
input
(ppm) corrector
After input
pH COD
(mg / L) SS
(mg / L) Sludge amount
(ml / L) Invention
(Example 1)
200
4.63
450
6.51
68.3
27.6
80 Invention
(Example 2)
200
4.63
560
6.54
72.7
46
90 Comparative Example 1
PAC
200
4.62
520
6.56
107.6
63
100 Comparative Example 2
PAC
400
4.49
570
6.55
98.3
60
100 Comparative Example 3
PAC
600
4,33
610
6.60
82.9
59
90 Comparative Example 4
PAC
1,000
3.78
720
6.45
78.1
55
80

As shown in the above Table 4, it can be confirmed that the amount of the coagulant and the amount of the neutralizing agent are reduced compared to the conventional polyaluminum chloride (PAC), which is the alkaline flocculant of the present invention, sodium aluminosilicate polyaluminate, It was found that the neutralization ability of sodium polyaluminate silicate as a flocculant was excellent, and that the amount of sludge also decreased.

Claims (6)

a). 10 to 45 parts by weight of aluminum hydroxide (Al (OH) ₃ ) and 20 to 55 parts by weight of caustic soda (NaOH) are dissolved in 100 parts by weight of water and reacted at 105 to 150 ° C for 1 to 3 hours to obtain Al ₂ O ₃ content of 3.9% to 17.7% by weight of sodium aluminate solution,
b). A second stage reaction in which SiO ₂ content is 28 to 30% by weight of sodium silicate and 20 to 50% by weight of inorganic acid is dissolved in water and then reacted to prepare a polysilicic acid solution having a SiO ₂ content of 1.4 to 4.2%
c). The polysilicic acid solution 10 of 70 to 90% by weight of the sodium aluminate solution prepared in the first step reaction and the SiO ₂ content of 1.4 to 4.2% by weight of the Al ₂ O ₃ solution prepared in the second step reaction To 30 wt% is reacted at a temperature of 30 to 60 ° C for 1 to 3 hours to obtain a polymer having an Al ₂ O ₃ content of 3 to 15 wt% and an SiO ₂ content of 0.1 to 1.3 wt% And a third stage reaction for producing an alkali flocculant solution of sodium polyaluminate silicate.
[Formula 1]
_{(NaAlO 2 · xH 2 O)} · ySiO 2
3? X? 7, and 0.003? Y? 0.04 in the above formula delete delete The method according to claim 1, wherein the inorganic acid is selected from the group consisting of sulfuric acid, hydrochloric acid and nitric acid. An alkaline flocculant solution, which is sodium polyaluminate silicate expressed by the unit of the general formula (1) below, having an Al ₂ O ₃ content of 3 to 15% by weight and an SiO ₂ content of 0.1 to 1.3% by weight prepared according to the production method of claim 1 Is added to the wastewater to coagulate and neutralize the wastewater.
[Formula 1]
_{(NaAlO 2 · xH 2 O)} · ySiO 2
3? X? 7, and 0.003? Y? 0.04 in the above formula The method according to claim 5, wherein the fluorine ion concentration in the wastewater is reduced.

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