KR20180105533A - Bead for water treatment, method of preparing magnesium bead and method of treating water - Google Patents

Abstract

Provided is a bead for a water treatment, including a magnesium-based bead including a magnesium-based pH-increasing compound. The bead for a water treatment according to the present invention effectively and conveniently removes hardness ions in hard water. Accordingly, the present invention can simply and effectively treat water.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bead for water treatment, a method for manufacturing magnesium beads, and a method for water treatment. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a bead for water treatment, a method for producing magnesium beads, and a water treatment method, and more particularly, to a method for producing water-treating beads and magnesium-based beads for converting hard water ions into soft water.

Water used for various purposes such as household and industrial use can be divided into light water reactor when the content is high and soft water when the content is low depending on the contents of Ca ion, Mg ion, Fe ion and the like.

When raw water having a high hardness is used at home, a white foreign matter formed by precipitating the metal ions in boiling water and ice water is generated. This white foreign matter can be generated by the following reaction formula 1 while the hardness ions are concentrated.

[Reaction Scheme 1]

Ca ^{2 +} + CO ₃ ^{2 -} → CaCO ₃ (produced as a white foreign substance)

This white foreign matter is not only an aesthetically undesirable aspect, but also makes it perceived as contaminated water.

Also, for example, the hardness ions of Ca ^{2 +} in the refrigerator or water purifier chulsugu is to generate a precipitate, that is, the scale of CaCO ₃ by the following scheme 2, also generates ions residue.

[Reaction Scheme 2]

Ca ^{+ 2} (hardness ions sex) + 2HCO ₃ ^- ? CaCO ₃ + CO ₂ + H ₂ O (when heating)

On the other hand, when the hard water is used as the washing water, the washing efficiency of the washing machine and the dishwasher is lowered because the solubility of the various detergents is lowered, so that the detergent amount is excessively used. Not only that, cleaners are usually of Na ⁺ ions and soap anionic (Soap Anion) This comprises the combined compounds, react with the hardness ions of Ca ^{2 +} formed with an Na ⁺ ion Ca ^{2 +} hardness ions are substituted precipitate It also generates detergent.

Accordingly, there is a need to convert the hard water into soft water, and accordingly water treatment for converting hard water to soft water for various purposes such as domestic use or industrial use is performed.

As a water treatment method for converting hard water into soft water, there are ion exchange methods using an ion exchange resin, electrochemical ion-adsorption using electrochemical adsorption, membrane using NF (nano filtration) / RO (reverse osmosis membrane) There is a way.

First, the ion exchange method exchanges ion exchange materials (Na ⁺ or H ⁺ ions) bonded to functional groups (SO ^{3 -} , COO ^- ) of polystyrene and polyacrylic acid based resins with hard ions such as Ca ^{2 +} It is a method to remove.

However, since the ion exchange resin has a hardness of 2 to 4 eq per 1 L of the resin capable of removing hard ions, it has to be regenerated after about 100 L of water to handle the hardness of 250 mg / L CaCO ₃ have. Even if regenerated, the regeneration efficiency is continuously shortened, and it is generally required to be replaced every year.

The electrochemical ionization method (CDI) is a method of removing hard ions by adsorbing hard ions on the surface of electrodes such as carbon or titanium.

Electrochemical ion adsorption technology shows stable efficiency and high removal rate. However, when the flow rate is increased, the removal rate is lowered suddenly. If ions are accumulated on the electrode surface, periodic cleaning is required and electrode cost is about 10 times higher than other technologies have.

Methods using NF / RO membranes use polyamide-based membranes. Polyamide-based membranes have a pore size (~ a few angstroms) smaller than ions, allowing water to pass through and hardness ions to pass through. A method using NF / RO membranes is a method of removing hard ion from a polyamide-based membrane without passing through it.

However, in the method using the NF / RO membrane, the removal efficiency of the hard ion is high, but the recovery rate is as low as 50 to 20%, which is the disadvantage of the greatest water scarcity. Also, in the water treatment method using such a membrane, when a large amount of water treatment is performed, the scale due to the hard ion ions contaminates the membrane, so the scale should be periodically removed from the membrane to regenerate the membrane. In particular, on the surface of the RO membrane in contact with the RO concentrated water, the concentration of the hard ion increases by more than two times, and a scale of white foreign matter generated by the above-described reaction formula 1 is generated. Moreover, when used for high hardness raw water, the use period or the regeneration period of the film is further shortened.

An object of the present invention is to provide a bead for water treatment which is easy to use and low in cost, while having high removal efficiency of hard ion.

Another object of the present invention is to provide a beverage for water treatment, which has a high removal efficiency of hard ions and a high recovery rate, thereby minimizing water scarcity.

Another object of the present invention is to provide a beverage for water treatment which is excellent in the removal efficiency of hard ions even when applied to raw water containing a high concentration of hard ions.

When the pH of the water to be treated is increased by dissolving the magnesium-based pH-increasing compound in the water to be treated according to the present invention, the degree of supersaturation is increased so that the hardness ions contained in the water are advantageously crystallized, It becomes a state where it can be easily crystallized so that hard ions can be precipitated and removed. The bead for water treatment is manufactured in bead type and can be easily put into water to be treated. In addition, the water treatment bead has a bead-type shape so as not to be discharged together with treated water but to be easily accommodated in a container while being continuously accommodated in the container.

The water-treating beads according to the present invention include a magnesium-based pH-increasing compound that increases the degree of supersaturation of hard ions so that only precipitates that can be separated into solid phase after precipitating hard ions into direct precipitates are removed. As described above, the magnesium-based pH increasing compound increases the supersaturation of the hard ions contained in water by increasing the pH of the water to be treated. When the degree of supersaturation of the hard ion is high, the crystallization of the hard ion is favored and precipitation into the precipitate is induced.

The water-treating bead according to the present invention further comprises a coating layer which is easily detachable even if a large amount of precipitate adheres to the bead surface when water containing hard ions of high hardness is treated. If deposits are attached to the surface of the beads, they can easily be desorbed by applying ultrasonic waves or physical vibrations. The coating layer is formed of a water-soluble compound and a polymer which are dissolved in contact with water to form an opening. Since the water-soluble compound dissolves when the water-treating beads come into contact with water, the coating layer includes an opening, through which the magnesium-based pH-increasing compound can be exposed to water.

The bead for water treatment according to the present invention can be used by increasing the degree of supersaturation so that hard ions can be crystallized and effectively precipitating and removing the bead-shaped product and then putting it into the object to be treated directly, and does not use an expensive material It is possible to process easily and effectively at a low cost.

The bead for water treatment according to the present invention removes only sediments which can be separated into solid phase after precipitating hard ions directly as sediments, so that it is possible to hardly generate water to be discarded together or to remove sediments with a small amount of water.

The bead for water treatment according to the present invention can be easily regenerated when the precipitate adheres to the surface and the efficiency is lowered, so that even when applied to raw water containing high concentration of hard ions, the removal efficiency of hard ions can be maintained to be excellent.

Figure 1 shows a graph of the degree of supersaturation of CaCO ₃ .
FIG. 2 is a graph showing the degree of supersaturation according to the pH of CaCO _3. FIG.
FIG. 3 schematically shows the shape of a magnesium-based bead included in a water-treatment bead according to an embodiment of the present invention.
FIG. 4 schematically shows a cross-section of a magnesium-based bead included in a water-treatment bead according to another embodiment of the present invention.
FIG. 5 schematically shows a cross section of magnesium beads contained in beads for water treatment according to still another embodiment of the present invention, after being injected into water.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or preliminary meaning and the inventor shall properly define the concept of the term in order to describe its invention in the best possible way It should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. It should be noted that the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention, It should be understood that various equivalents and modifications are possible.

In one embodiment of the present invention, there is provided a water-treating bead comprising a magnesium-based bead containing a magnesium-based pH-increasing compound.

The water treatment beads are used for water treatment for removing hard ions from water containing hard ions such as Ca ions and Mg ions.

The bead for water treatment may be precipitated as crystals by increasing the supersaturation degree of the hard ion by increasing the pH of the water by directly injecting it into water. When hard ions are precipitated as crystals and solid precipitates are formed, only hard precipitates can be easily removed from water to remove hard ions.

Figure 1 shows a graph of the degree of supersaturation of CaCO ₃ . In FIG. 1, the points indicated by the dots indicate a pH of about room temperature and neutral, and CaCO ₃ exists in an ionic state. In this state, in order to change CaCO ₃ to a crystalline state, it is necessary to increase the temperature or to increase the pH. The arrowed direction of the dotted line in FIG. 1 means that when the temperature is increased or the pH is increased, the solution is crystallized through the supersaturation curve.

When the pH is 9.5 or more, the hard ion spontaneously crystallizes rapidly in the hard water, and when the pH is 9 to 9.5, the metastable and the crystallized state are mixed.

Further, the degree of supersaturation of CaCO ₃ can be calculated by the following equation.

Where [Ca ^{2 +} ] is the concentration of Ca ^{2 +} , [CO ₃ ^- ] is the concentration of CO ₃ ^- , and K _sp is the solubility product constant.

Also in this equation, the pH is proportional to [CO ₃ ^- ] and the temperature is inversely proportional to the solubility product constant. That is, pH and temperature are the main factors increasing the degree of supersaturation.

In the present invention, the magnesium-based beads are added to water to increase the pH of the water, thereby allowing the hard ions in the water to become supersaturated.

FIG. 2 is a diagram showing the degree of supersaturation according to the pH of CaCO ₃ . FIG. 2 also shows the removal rate of Ca ions which can be removed by applying the water treatment beads according to the degree of supersaturation. As pH increases, the degree of supersaturation of CaCO ₃ increases. In addition, the degree of supersaturation of CaCO ₃ increases proportionally with the increase of Ca.

Fig. 3 schematically shows the shape of the magnesium-based beads 10. Fig.

The magnesium-based beads are bead-shaped particles. The bead shape may be not only a perfect spherical shape but also a distorted shape, a crushed shape in which the cross section becomes an elliptical shape, and the like, and is used macroscopically or usually as a term encompassing a shape commonly referred to as a bead.

For example, the magnesium-based beads may have a particle diameter of 0.1 mm to 3 mm, and may be specifically 0.2 mm to 1 mm.

The magnesium-based pH-increasing compound includes one selected from the group consisting of Mg, MgO, Mg (OH) _2, and combinations thereof.

When the magnesium-based beads are added to water, the magnesium-based pH-increasing compound reacts with water to increase the pH of the water.

For example, when the exemplified magnesium-based pH-increasing compounds, Mg, MgO, and Mg (OH) ₂ , respectively, react with water, the following reaction proceeds to increase the pH of the water.

When the Mg metal reacts with water, the reaction proceeds as shown below, and the pH can be increased up to 10.

Mg + H ₂ O → Mg (OH) ₂ + H ₂ ↑

Mg (OH) ₂ → Mg ^{2 +} + 2OH ^- (increased up to pH 10)

When MgO reacts with water, the reaction proceeds as shown below, and the pH can increase to a maximum of 10.

_{MgO + H 2 O → Mg (} OH) 2

Mg (OH) ₂ → Mg ^{2 +} + 2OH ^- (increased up to pH 10)

When Mg (OH) ₂ reacts with water, the reaction proceeds as shown below, and the pH can also increase to a maximum of 10.

Mg (OH) ₂ → Mg ^{2 +} + 2OH ^- (increased up to pH 10)

The magnesium-based beads may further include a binder material selected from the group consisting of polymers, metal oxides, and combinations thereof.

That is, the magnesium-based beads can be mixed with the binder material to assemble the magnesium-based pH-increasing compound into a bead shape.

For example, the binder material may be a polymer material such as polyethylene or polypropylene, or a metal oxide of Al ₂ O ₃ may be used.

The content of the binder material may be used only to the extent that the magnesium-based pH-increasing compound can be produced in the form of a bead. Specifically, the magnesium-based beads may include 100 parts by weight of the magnesium-based pH increasing compound and 0 to 10 parts by weight of the binder material.

The magnesium-based beads may further include a coating layer.

The thickness of the coating layer may be 0.01 탆 to 1 탆.

Fig. 4 schematically shows a cross section of the magnesium-based bead 20. Fig. The magnesium-based beads 20 further include a coating layer 2 together with the inside of the coating layer 1.

The coating layer (2) comprises a polymer; And water soluble compounds. The water-soluble compound may include one selected from the group consisting of water-soluble inorganic compounds, water-soluble polymer compounds, and combinations thereof.

When the magnesium-based beads come into contact with water, the water-soluble compounds are dissolved in water, thereby forming openings in which the inside of the coating layer 1 is exposed. The magnesium-based pH-increasing compound can be exposed to water through the opening.

Therefore, the magnesium-based beads form a coating layer including the openings at the time of water treatment, that is, after being put into water.

FIG. 5 schematically shows a cross section of magnesium beads contained in beads for water treatment according to still another embodiment of the present invention, after being injected into water.

5, the magnesium-based beads 30 after being charged into water include a coating layer 2 including an opening portion 3, and the inside of the coating layer 1 is exposed through the opening portion 3.

Specific examples of the water-soluble inorganic compound include CaO, Ca (OH) ₂ , and the like, and combinations thereof.

A specific example of the water-soluble polymer compound may be polyvinyl alcohol.

In the case where the hardness is high (for example, 100 mg / L as CaCO ₃ or more), the CaCO ₃ crystal adheres to the surface of the magnesium-based bead, so that the pH increase efficiency can be drastically reduced.

When the magnesium-based beads further include a coating layer, the rate at which CaCO ₃ crystals adhere to the upper portion of the coating layer becomes lower than in the case where the coating layer does not exist, and CaCO ₃ crystals adhered to the upper portion of the coating layer can be easily detached.

For example, when a coating layer of magnesium-based beads is present, CaCO ₃ crystals adhered to the upper part of the coating layer are subjected to physical vibration using ultrasonic waves outside the container containing the magnesium-based beads, or the magnesium- A stirrer may be inserted into a receiving container to be stirred and removed. For example, when CaCO ₃ crystals adhere to the surface of a coating layer of magnesium-based beads into which water to be treated is charged in a container containing magnesium-based beads having a coating layer, and the water treatment efficiency is lowered, The CaCO ₃ crystal attached to the surface of the coating layer of the magnesium-based bead can be more easily desorbed.

In the magnesium-based beads 20 of FIG. 2, the content ratio of the polymer and the water-soluble compound in the coating layer 2 is designed according to the area occupied by the openings on the surface of the magnesium-based beads 30 after being charged into the water of FIG. 3 .

Specifically, the coating layer may include 100 parts by weight of the polymer and 1 to 10 parts by weight of the water-soluble compound.

The diameter of the opening may be specifically 0.1 mu m to 3 mu m. By forming the opening having the diameter within the above range, the magnesium-based pH-increasing compound in the coating layer can be in contact with water well, and the CaCO ₃ crystal can be easily desorbed by the coating layer.

The diameter of the opening may be formed to a certain extent when the size of the powder of the water-soluble inorganic compound, which is easily dissolved in water, or the molecular weight of the water-soluble polymer compound or the size of the powder is adjusted.

Specific examples of the polymer include, but are not limited to, materials capable of easily desorbing CaCO ₃ crystals while being well adhered to the interior of the coating layer. For example, the polymer may be polyacrylamide, polyacrylic acid, polypropylene, And at least one selected from the group consisting of

The water treatment bead may further include a seed bead together with the magnesium bead.

The seed beads are bead-shaped particles comprising a seed material and a binder material. The seed material in the seed beads can cause the hardness ions to crystallize more quickly because hardness ions can act to provide the energy needed for crystal formation.

And a seed material is mixed with a binder material to prepare seed beads in the form of bead particles.

The seed material may comprise CaCO ₃ . Specifically, CaCO ₃ powder may be used as the seed material, or a material such as calcite and CaCO ₃ arnonite may be used.

The binder material for forming the seed beads may include one selected from the group consisting of polymers, metal oxides, and combinations thereof. For example, as the binder material for forming the seed beads, a polymer material such as polyethylene or polypropylene may be used, or a metal oxide of Al ₂ O ₃ may be used.

The seed beads may include the seed material and the binder material in a weight ratio of 5: 5 to 9: 1. The seed beads formed at the mixing ratio within the above range are easily produced in a bead shape while effectively precipitating the hard ions in the water to be treated.

The particle diameter of the seed beads may be 0.2 mm to 1 mm. By using the seed beads having the above-mentioned range, the hard ions in the water to be treated are effectively precipitated, and the water is easily accommodated and handled in the vessel used in the water treatment.

The bead for water treatment according to the present invention improves the removal effect of the hard ion by using the magnesium bead and the seed bead together.

The water-treating beads may contain the magnesium-based beads and the seed beads in a weight ratio of 1: 1 to 1:10. By using the magnesium-based beads and the seed beads at the above-mentioned content ratios, the hard ions can be effectively removed.

In another embodiment of the present invention,

Adding heat to a powder of a magnesium-based pH-increasing compound and extruding it to produce pellets; And

Preparing magnesium beads as bead-shaped particles from the pellets;

Based beads. The present invention also provides a method for producing the magnesium-based beads.

The magnesium-based beads may be prepared by the method for producing the water-treatment beads and used as bead for water treatment.

In the step of applying the heat, the powder may be heat-treated at 250 ° C to 500 ° C. When the temperature exceeds 500 ° C, the calcium carbonate is converted into CaCO ₃ → CaO and can be dissolved in water. If the temperature falls below 250 ° C, the bead can not be formed and can easily break.

And forming a coating layer containing a water-soluble compound and a polymer on the surface of the bead-shaped particles.

Details of the coating layer and the water-soluble compounds and polymers contained therein are as described above.

In another embodiment of the present invention,

Introducing the water treatment bead into water to be treated; And

Removing the precipitate when a solid precipitate is generated after the pH of the water to be treated is increased;

And a water treatment method.

The water treatment method is a method for water treatment using the above water treatment bead, wherein the water treatment bead is charged into the water to be treated, and the pH of the water to be treated is adjusted to 9.5 to 10, and then the hard ions are crystallized, It is possible to obtain water from which hard ions are removed by treating water after removing it.

The method for removing the precipitate may be a known method and is not limited to a specific method. For example, solid phase precipitate can be simply removed by filtration.

The bead for water treatment according to the present invention can be used by increasing the degree of supersaturation so that hard ions can be crystallized and effectively precipitating and removing the bead-shaped product and then putting it into the object to be treated directly, and does not use an expensive material It is possible to process easily and effectively at a low cost.

The bead for water treatment according to the present invention removes only sediments which can be separated into solid phase after precipitating hard ions directly as sediments, so that it is possible to hardly generate water to be discarded together or to remove sediments with a small amount of water.

The bead for water treatment according to the present invention can be easily regenerated when the precipitate adheres to the surface and the efficiency is lowered, so that even when applied to raw water containing high concentration of hard ions, the removal efficiency of hard ions can be maintained to be excellent.

The bead for water treatment according to the present invention is manufactured in a bead shape that is easy to use and is easy to use by being filled in a filter and can be applied to various types of reactors for industrial use such as a batch type, a continuous type and a semi batch type have.

The water treatment method using the bead for water treatment according to the present invention can control the hardness ion removal efficiency according to the pH range and can remove Ca hard ion from 50% to 90% at pH 9.5 to 10.

( Example )

Example  One

(Magnesium-based bead production)

Magnesium metal was polished into a ball shape. Activated carbon powder and Ca (OH) ₂ powder were mixed at a weight ratio of 1: 9, and 1 wt% of Al ₂ O ₃ binder was mixed with magnesium metal while stirring with magnesium metal, . Thereafter, the mixture was heated at 250 DEG C for 8 hours and sintered to produce magnesium beads having a diameter of 2 mm as bead-shaped particles.

(Seed bead production)

Calcium carbonate and Al ₂ O ₃ binder were mixed in a weight ratio of 9: 1, kneaded in a predetermined mold, mixed, extruded by an extruder heated to 200 ° C, and cut at regular intervals to prepare a pellet shape. And then sintered by heating at 500 ° C.

A seed bead having a diameter of 1 mm was produced from the pellet as bead-shaped particles.

(Making bead for water treatment)

The thus prepared magnesium-based beads and seed beads were mixed at a weight ratio of 1: 2.

evaluation

Experimental Example  One

10 g of the water treatment beads prepared in Example 1 was put into tap water containing 0.5 L of hard ions contained in the container and left.

Four water samples were taken and the precipitate was removed by filtration and the pH and Ca removal rate of the treated water were measured.

The pH of the treated water was measured using a pH meter (Handheld pH / ORP meter, DDK-TOA, hm-31P).

The Ca removal rate was calculated by calculating the removal rate of Ca ²⁺ by measuring the ion concentration of Ca ²⁺ after filtering with a 0.45um filter by taking 10mL of samples before and after treatment using Ion chromatography (Thermodionex, ICS-2100IC) Respectively.

Ca removal rate = (1- [Ca ^{2 +} (after treatment)] / [Ca ^{2 +} (before treatment)]) X 100

2 is a view showing the measurement result. In FIG. 2, it can be seen that the degree of supersaturation of CaCO ₃ increases proportionally with the increase of Ca. In addition, at pH 9.5 ~ 10, Ca hardness ions could be removed by 50 ~ 90%.

It is to be understood that the above-described embodiments are to be considered in all respects as illustrative and not restrictive, and the scope of the present invention will be indicated by the appended claims rather than by the foregoing detailed description. It is intended that all changes and modifications that come within the meaning and range of equivalency of the claims, as well as any equivalents thereof, be within the scope of the present invention.

1: Inside coating layer
2: Coating layer
3: opening
10, 20: Magnesium-based beads
30: Magnesium-based beads after being put into water

Claims (20)

A beverage for water treatment comprising a magnesium-based bead containing a magnesium-based pH-increasing compound.
The method according to claim 1,
Wherein the magnesium-based pH increasing compound comprises one selected from the group consisting of Mg, MgO, Mg (OH) _2, and combinations thereof
Water treatment beads.
The method according to claim 1,
The magnesium-based beads further include a binder material selected from the group consisting of polymers, metal oxides, and combinations thereof.
Water treatment beads.
The method according to claim 1,
Wherein the magnesium-based beads include 100 parts by weight of the magnesium-based pH increasing compound and 0 to 10 parts by weight of a binder material
Water treatment beads.
The method according to claim 1,
The magnesium-based beads have a particle diameter of 0.1 mm to 3 mm
Water treatment beads.
The method according to claim 1,
Wherein the magnesium-based bead further comprises a coating layer
Water treatment beads.
The method according to claim 6,
Wherein the coating layer comprises a polymer and a water-soluble compound
Water treatment beads.
8. The method of claim 7,
Wherein the polymer comprises at least one member selected from the group consisting of polyacrylamide, polyacrylic acid, polypropylene, and combinations thereof
Water treatment beads.
The method according to claim 6,
When the thickness of the coating layer is 0.01 탆 to 1 탆
Water treatment beads.
8. The method of claim 7,
The water-soluble compound is dissolved in contact with water to form an opening
Water treatment beads.
8. The method of claim 7,
The water-soluble compound includes one selected from the group consisting of a water-soluble inorganic compound, a water-soluble polymer compound and a combination thereof
Water treatment beads.
8. The method of claim 7,
Wherein the coating layer contains 100 parts by weight of the polymer and 1 to 10 parts by weight of the water-
Water treatment beads.
The method according to claim 1,
Further comprising a seed bead comprising a seed material and a binder material,
The seed material comprises CaCO ₃
Water treatment beads.
14. The method of claim 13,
Wherein the seed bead comprises the seed material and the binder material in a weight ratio of 5: 5 to 9: 1
Water treatment beads.
14. The method of claim 13,
The particle diameter of the seed beads is preferably from 0.2 mm to 1 mm
Water treatment beads.
14. The method of claim 13,
Wherein the magnesium-based beads and the seed beads are contained in a weight ratio of 1: 1 to 1:10
Water treatment beads.
Adding heat to a powder of a magnesium-based pH-increasing compound and extruding it to produce pellets; And
Preparing magnesium beads as bead-shaped particles from the pellets;
≪ / RTI >
18. The method of claim 17,
In the step of applying the heat, the powder is heat-treated at 250 ° C to 500 ° C
A method for producing a magnesium-based bead.
18. The method of claim 17,
And forming a coating layer containing a water-soluble compound and a polymer on the surface of the bead-shaped particles
A method for producing a magnesium-based bead.
16. A method for producing a water-treating bead, comprising the steps of: injecting a water-treating bead according to any one of claims 1 to 16 into water to be treated; And
Removing the precipitate when a solid precipitate is generated after the pH of the water to be treated is increased;
≪ / RTI >

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