JP2018149520A - Water treatment method, magnesium agen for water treatment, and method for producing magnesium agent for water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method capable of insolubilization and solid-liquid separation of a substance to be removed in a short period of time from water containing a substance to be removed, obtaining treated water of good quality, and efficiently reducing the volume of the separated solid matter.SOLUTION: In a water treatment method, at least one of a magnesium agent obtained by calcining basic magnesium carbonate at a temperature in the range of 500 to 700°C and a magnesium agent obtained by calcining magnesium hydroxide at a temperature in the range of 450 to 650°C, is added to treated water containing a substance to be removed.SELECTED DRAWING: None

Description

  The present invention relates to a method for treating water containing a removal target substance such as boron using a magnesium compound, a magnesium agent for water treatment used for the water treatment, and a method for producing the magnesium agent for water treatment.

  Wastewater containing high concentrations of substances such as boron, fluorine, selenium, silica, and heavy metals discharged in various industries needs to be treated and discharged to a level below the wastewater standard. For example, in a power generation facility that burns coal and generates power, a desulfurization facility for purifying exhaust gas is installed. For example, sulfur in the exhaust gas or dust that has not been removed by a dust collector with water in which an alkaline agent is dissolved Etc. are removed. Water that has absorbed sulfur, dust, etc. is appropriately discharged from the desulfurization facility as desulfurization effluent, treated to a level below the effluent standard, and discharged to the ocean.

This desulfurization effluent usually contains boron, fluorine, selenium, heavy metals (iron, lead, copper, chromium, cadmium, mercury, zinc, arsenic, manganese, nickel, etc.) contained in coal and the like. Among them, boron may be contained at a high concentration as boric acid (H ₃ BO ₃ ) or the like, and may be present at about 200 to 500 mg-B / L.

  In water treatment for these substances, magnesium salts that are inexpensive and hardly harmful even if they remain in water are added, the substances are insolubilized, and the insoluble matter is separated from the water to be treated by solid-liquid separation. Method may be used. It is known that a magnesium salt can insolubilize these substances at once (see Patent Document 1, Patent Document 2, and Non-Patent Document 1).

  On the other hand, when silica containing water containing silica is to be recovered and reused, the generation of scale in piping and the reverse osmosis membrane (RO) device, etc. becomes a problem. May be difficult. Therefore, it is required to reduce the amount of silica in the silica-containing water. As a method for reducing the amount of silica in the silica-containing water, a method using a magnesium salt has been studied (see Non-Patent Document 2).

  Thus, the magnesium salt can remove various substances and ions in water and is used as a water treatment agent. Magnesium salt dissolves in water and becomes magnesium ion. However, when water is adjusted to be alkaline with pH of about 10 or more, boron, fluorine, etc. and magnesium are combined to form insoluble matter, or magnesium and hydroxide ion are Boron, fluorine, and the like are adsorbed and insolubilized on the magnesium hydroxide bonded and insolubilized. By separating these insolubles into solid and liquid, various substances such as boron and fluorine can be removed from water.

  Magnesium is a resource produced in large quantities and is inexpensive, so the running cost required for processing is low. Further, when the treated water is neutralized and released into the environment, magnesium that is hardly harmful has an excellent feature that there is almost no problem even if it remains in the treated water.

Magnesium salts that can be used industrially as water treatment agents include magnesium chloride hexahydrate (MgCl ₂ · 6H ₂ O), basic magnesium carbonate (3MgCO ₃ · Mg (OH) ₂ · H ₂ O) , Magnesium hydroxide (Mg (OH) ₂ ), magnesium oxide (MgO), and the like. Any of the magnesium salts can insolubilize the substance to be removed in water with an alkaline pH of 10 or more.

  These magnesium salts have excellent characteristics as described above, but also have the following problems. First, regarding magnesium chloride hexahydrate, the magnesium content in the magnesium salt is about 12%, which is small compared to other magnesium salts, and requires a large amount of addition. Furthermore, since it does not contain a hydroxyl group, it is necessary to add an alkali agent such as caustic soda in order to make the water to be treated alkaline and insolubilize the substance to be removed.

Basic magnesium carbonate and magnesium hydroxide have a higher magnesium content than magnesium chloride hexahydrate and contain a base (hydroxyl group) in the molecule, but are hardly soluble in neutral water. It is necessary to add an acid to water to make it acidic, or add an acid to the magnesium salt itself to form an aqueous solution and then add it to the water to be treated. The water to be treated should be acidic in advance, but if it is neutral, it is necessary to add an acid, and after adding a magnesium salt, an alkali agent needs to be added to make the pH of the water to be treated alkaline. After addition of acid, most of the magnesium becomes magnesium ions, and when the pH is 9.5 or higher with an alkaline agent, most of the magnesium ions other than those bound to the substance to be removed are swollen magnesium hydroxide (Mg (OH) ₂ ) There is a problem that it becomes a slurry and the precipitate separation property and the dewatering property are poor.

  Magnesium oxide is obtained by calcining basic magnesium carbonate and magnesium hydroxide at a high temperature of 500 ° C. or higher, and contains a large amount of magnesium. When dissolved in water, it becomes magnesium hydroxide, and water exhibits alkalinity. Moreover, since the insoluble matter produced by alkalinity includes not only magnesium hydroxide but also some crystals of magnesium oxide and magnesium carbonate, water formed with basic magnesium carbonate and magnesium hydroxide as a water treatment agent is used. It is also characterized by better precipitation separation and dewaterability than insoluble slurry mainly composed of magnesium oxide.

  However, depending on the firing conditions, magnesium oxide is slow to dissolve in water, so it takes a long time for the insolubilization reaction of the substance to be removed, and it takes time for the treatment. There is a problem that a large amount of magnesium oxide must be added to improve the quality of the treated water.

Japanese Patent No. 3355281 Japanese Patent No. 4558633

Aya Izawa, Moyo Maeda, Chiharu Tokoro, Kyoko Togi, “Consideration of Boron Removal Mechanism in Wastewater in Magnesium Hydroxide Coprecipitation”, Journal of MMIJ, Vol.130, pp.155-161 (2014) Isabel Latour, Ruben Miranda, Angeles Blanco, `` Silica removal with sparingly soluble magnesium compounds. Part I '', Separation and Purification Technology, 138 (2014), pp. 210-218

  An object of the present invention is to insolubilize a removal target substance in a short time from water containing the substance to be removed, solid-liquid separation, obtain a treated water of good water quality, and efficiently reduce the volume of the separated solid matter. It is providing the water treatment method, the magnesium agent for water treatment used for the water treatment, and the manufacturing method of the magnesium agent for water treatment.

  The present invention is intended to remove at least one of a magnesium agent obtained by firing basic magnesium carbonate at a temperature in the range of 500 to 700 ° C and a magnesium agent obtained by firing magnesium hydroxide at a temperature in the range of 450 to 650 ° C. It is the water treatment method added to the to-be-processed water containing a substance.

In the water treatment method, the magnesium agent preferably has a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 kg or less.

  In the water treatment method, the water to be treated preferably contains at least one of boron, fluorine, selenium, heavy metal or a compound thereof, or silica as the removal target substance.

  In the water treatment method, the method further comprises a step of insolubilizing the substance to be removed after addition of the magnesium agent to the water to be treated, and a step of solid-liquid separating the insolubilized insolubilized material. It is preferable to add the magnesium agent in such an amount that the pH before solid-liquid separation is 10 or more to the water to be treated.

The present invention also includes a water treatment comprising at least one calcined product of basic magnesium carbonate and magnesium hydroxide, having a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 mm or less. Magnesium agent.

  The present invention also provides a magnesium agent obtained by calcining basic magnesium carbonate at a temperature in the range of 500 to 700 ° C. or calcining magnesium hydroxide at a temperature in the range of 450 to 650 ° C. It is a manufacturing method of the magnesium agent for a process.

In the method for producing a magnesium agent for water treatment, the magnesium agent preferably has a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 kg or less.

  According to the present invention, from the water containing the removal target substance, the removal target substance is insolubilized and solid-liquid separated in a short time to obtain treated water of good water quality, and the water treatment capable of efficiently reducing the volume of the separated solid The method, the magnesium agent for water treatment used for the water treatment, and the manufacturing method of the magnesium agent for water treatment can be provided.

It is an X-ray diffraction spectrum of each magnesium agent in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5. It is an X-ray diffraction spectrum of each magnesium agent in Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-2. It is a graph which shows the measurement result of pH of to-be-processed water in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5 1 to 120 minutes after each magnesium agent addition. It is a graph which shows the analysis result of the dissolved boron residual rate (%) in the to-be-processed water in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5 1 to 120 minutes after each magnesium agent addition. is there. It is a graph which shows the measurement result of pH of to-be-processed water in Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-2 1 to 120 minutes after each magnesium agent addition. In Example 2-1 to 2-5 and Comparative Examples 2-1 to 2-2, it is a graph which shows the analysis result of the dissolved boron residual rate (%) in the to-be-processed water for 1 to 120 minutes after each magnesium agent addition. is there.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

The water treatment method according to the embodiment of the present invention includes a magnesium agent mainly composed of magnesium oxide obtained by firing basic magnesium carbonate at a temperature in the range of 500 to 700 ° C, and 450 to 650 ° C of magnesium hydroxide. In this method, at least one of the magnesium agents mainly composed of magnesium oxide obtained by firing at a temperature in the range of 1 is added to the water to be treated containing the substance to be removed. This method makes it possible to insolubilize the removal target substance in a short time from water containing the substance to be removed using an inexpensive magnesium salt, and separate it into solid and liquid to obtain treated water with good water quality. Volume can be reduced. Moreover, since an inexpensive magnesium salt can be used efficiently, the chemical cost required for the treatment can be reduced. The magnesium agent for water treatment according to the embodiment of the present invention contains at least one calcined product of basic magnesium carbonate and magnesium hydroxide, has a BET specific surface area of 85 m ² / g or more, and a crystallite size. Is 110 mm or less. The manufacturing method of the magnesium agent for water treatment which concerns on embodiment of this invention is baking a basic magnesium carbonate at the temperature of the range of 500-700 degreeC, or magnesium hydroxide at the temperature of the range of 450-650 degreeC. In this method, the magnesium agent is obtained by firing.

[Magnesium agent]
As raw materials for producing a magnesium agent used in the water treatment method according to this embodiment, basic magnesium carbonate (mMgCO ₃ .Mg (OH) ₂ .nH ₂ O) and magnesium hydroxide (Mg (OH) ₂ ) are used. At least one of them. The basic magnesium carbonate is such that m is 3 to 5 and n is 3 to 7 with respect to Mg (OH) ₂ .

As temperature at the time of baking a raw material, when basic magnesium carbonate is a raw material, it is the range of 500-700 degreeC, the range of 500-650 degreeC is preferable, and the range of 550-650 degreeC is more preferable. When magnesium hydroxide is the raw material, it is in the range of 450 to 650 ° C, more preferably in the range of 450 to 550 ° C. By firing the raw material at a temperature within this range, hydrated water and hydroxyl groups in the raw material are eliminated by a dehydration reaction. When basic magnesium carbonate is the raw material, carbonic acid is also eliminated by a decarboxylation reaction, and magnesium oxide is removed. Substances as main components are produced. This substance is considered to have a large specific surface area (for example, a BET specific surface area of 80 m ² / g or more) due to elimination of hydrated water, hydroxyl group, carbonic acid and the like by firing. On the other hand, the crystallite size of the obtained magnesium agent containing magnesium oxide as a main component is smaller than that when calcined at a temperature exceeding 700 ° C., and the crystallinity is low. Thus, it is thought that it can melt | dissolve in water faster than the conventional magnesium oxide for reasons, such as a large specific surface area and low crystallinity. If the calcination temperature is less than 500 ° C., it is considered that the specific surface area is small and the dissolution rate in water does not increase due to the reason that hydration water, hydroxyl group, carbonic acid and the like cannot be sufficiently removed. On the other hand, when the firing temperature exceeds 700 ° C., it is considered that the substance containing magnesium oxide as a main component has high crystallinity and is difficult to dissolve in water.

When the basic magnesium carbonate is the raw material, the firing time is a time during which the weight loss due to the firing is 50% or more of the weight of the raw material, preferably 50% or more and 65% or less. When the magnesium hydroxide is the raw material , A time when the weight loss by firing is 25% or more of the weight of the raw material, preferably 25% or more and less than 30%, a BET specific surface area of 85 m ² / g or more, and a crystallite size of 110 mm or less. It is preferable that it is time to become.

  The basic magnesium carbonate and magnesium hydroxide used for firing are powdered (for example, 0.5 μm to 30 μm in volume average particle size), granular to sufficiently remove hydrated water, hydroxyl group, carbonic acid and the like. It is preferable to use those having a volume average particle diameter of 0.5 μm to 2 μm.

The BET specific surface area of the magnesium agent thus obtained is, for example, 80 m ² / g or more, preferably 85 m ² / g or more, and more preferably 100 m ² / g or more. The upper limit of the BET specific surface area is not particularly limited, and the larger the better. If the BET specific surface area of the magnesium agent is less than 80 m ² / g, it may be difficult to dissolve in water. The BET specific surface area of the magnesium agent can be measured by a method based on JIS8830: 2013.

  As an index representing the crystallinity of the magnesium agent, the crystallite size obtained by the Halder-Wagner method based on the measurement result of the X-ray diffraction spectrum can be used. From the viewpoint of solubility in water, the crystallite size is preferably 110 mm or less, and more preferably 100 mm or less. When the crystallite size exceeds 110 mm, the crystallinity is high and it may be difficult to dissolve in water. The smaller the crystallite size, the better.

  As the particle size of the magnesium agent, the volume average particle size is preferably 1,000 μm or less, and more preferably in the range of 0.5 μm to 30 μm. When the volume average particle diameter of the magnesium agent exceeds 1,000 μm, the inside of the particles cannot be sufficiently brought into contact with water even in water, and the proportion of the agent that is not used for insolubilizing the substance to be removed increases. In solid-liquid separation after insolubilization of the removal target substance, this unused part has the effect of increasing the solid-liquid separation speed, but if there is too much unused part, the removal target substance cannot be sufficiently insolubilized and the quality of the treated water deteriorates. Or in order to sufficiently insolubilize the substance to be removed, the amount of magnesium agent added may be large. When the volume average particle size is less than 0.5 μm, handling may be difficult, for example, it may be easily scattered by wind during use.

  When the volume average particle size of the magnesium agent after firing exceeds 1,000 μm, use a raw material with a particle size such that the volume average particle size after firing is within this range, or crush or sieve after firing, etc. It is preferable to adjust the particle diameter by the above method.

[Water treatment method]
When the magnesium agent used in the water treatment method according to the present embodiment is added to water, part of the magnesium agent is dissolved to become magnesium ions and hydroxide ions, and the pH of the water to be treated is increased. At this time, if it is a substance that forms an insoluble matter with magnesium ions and coprecipitates, it becomes a substance to be removed by the magnesium agent. In addition, the pH of the water to be treated is increased, and magnesium ions and hydroxide ions form an insoluble substance of magnesium hydroxide. A substance adsorbed on the insoluble substance is also a removal target substance. That is, the removal target substance contained in the water to be treated is not particularly limited as long as it forms an insoluble matter with the magnesium agent or is insolubilized by being adsorbed by insolubilized magnesium hydroxide or the like. Boron (for example, borate ion), fluorine (for example, fluoride ion), selenium (for example, selenate ion (SeO ₄ ²⁻ : hexavalent selenium), selenite ion (SeO ₃ ²⁻ : tetravalent selenium) ), Heavy metals (eg, iron, lead, copper, chromium, cadmium, mercury, zinc, arsenic, manganese, nickel, etc.) or their compounds (eg, arsenic acid), or silica preferable.

  The water to be treated is not particularly limited as long as it contains at least one of the substances to be removed. When the water to be treated is water containing two or more of the substances to be removed, the water treatment method according to the present embodiment is suitably applied. The treated water is premised on drainage premised to be discharged into public waters after treatment, or the use of purified substances such as reverse osmosis membranes after use to remove soluble substances and reuse them. Water may be used. Examples of the former include desulfurization effluent, plating effluent, and glass manufacturing effluent from a coal-fired power plant. In the latter case, water in the water recovery system in factories of various industries is targeted, and the water treatment method according to the present embodiment is performed before the reverse osmosis membrane treatment step, which causes blockage of the reverse osmosis membrane and the like. The main purpose is to reduce silica and the like. In addition, since the magnesium agent used with the water treatment method according to the present embodiment can aggregate suspended substances in water, the water to be treated may contain suspended substances other than the substance to be removed.

  The content of the substance to be removed in the water to be treated is, for example, in the range of 0.01 to 50 mmol / L, and the content of the suspended substance is, for example, in the range of 50 to 1,000 mg / L.

  Moreover, content of the boron in to-be-processed water is the range of 10 mg / L-550 mg / L, for example, Preferably it is the range of 20 mg / L-500 mg / L. The fluorine content in the water to be treated is, for example, in the range of 15 mg / L to 950 mg / L, and preferably in the range of 20 mg / L to 100 mg / L. The content of selenium in the water to be treated is, for example, in the range of 0.1 mg / L to 10 mg / L, and preferably in the range of 0.2 mg / L to 2 mg / L. The content of heavy metal in the water to be treated is, for example, in the range of 0.1 mg / L to 100 mg / L, and preferably in the range of 0.1 mg / L to 20 mg / L. The content of silica in the water to be treated is, for example, in the range of 10 mg / L to 120 mg / L, and preferably in the range of 40 mg / L to 120 mg / L. The water treatment method according to the present embodiment can be suitably applied particularly to water to be treated containing high-concentration boron of 100 mg / L or more.

  The water treatment method according to the present embodiment includes at least a magnesium agent obtained by baking basic magnesium carbonate at a temperature in the range of 500 to 700 ° C, and a magnesium agent obtained by baking magnesium hydroxide at a temperature in the range of 450 to 650 ° C. One includes a step of adding to the water to be treated containing the substance to be removed (addition step). The water treatment method according to the present embodiment includes a step of performing an insolubilization reaction of a substance to be removed after addition of a magnesium agent to water to be treated (insolubilization step), and a step of solid-liquid separation of the insolubilized material insolubilized in the insolubilization step (solid solution). A liquid separation step).

  In the addition process, the magnesium agent may be added to the water to be treated in the form of powder, or the magnesium agent is once purified water (for example, industrial water or the present implementation) with a low content of substances to be removed and suspended substances. Treated water treated by the water treatment method according to the embodiment may be mentioned, and they may be added to neutral (for example, water adjusted to a pH of about pH 6 to 8) and the water may be added to the water to be treated. However, it is preferable to add the magnesium agent to the water to be treated in the form of powder from the viewpoint that the operation is simple.

  Since the added magnesium agent is more effective when it is immediately dispersed in the water to be treated, the addition of the magnesium agent to the water to be treated was well agitated by a stirrer or the like. It is good to do in the state.

  The amount of magnesium agent added in the addition process varies depending on the type and concentration of the substance to be removed in the water to be treated, the required quality of the treated water (target substance removal rate), coexisting substances, etc. It is preferable to add such an amount that the pH of the treated water is 10 or more, preferably 10.5 or more.

  For example, when 500 mg-B / L of a boron compound (boric acid) is contained in the water to be treated as a substance to be removed and is reduced to a seawater drainage standard of 230 mg-B / L or less, the magnesium agent is added to the water to be treated by 7.5. What is necessary is just to add -10g / L.

  An insolubilization process is a process of making a removal target substance insoluble by making magnesium and a removal target substance react after addition of a magnesium agent. In this step, the pH of the water to be treated is monitored so that the pH before shifting to the solid-liquid separation step is 10 or more, preferably 10.5 or more.

  The reaction temperature in the insolubilization step may be, for example, if the water to be treated is not frozen at 0 ° C. or higher, but the higher the temperature, the better the removal performance of the substance to be removed, preferably 15 ° C. or higher, more preferably 20 ° C. It is in the range of ˜40 ° C.

  The reaction time in the insolubilization step is not particularly limited as long as the removal target substance is sufficiently insolubilized. For example, the reaction time is in the range of 1 minute to 720 minutes, and preferably in the range of 10 to 120 minutes. If the reaction time in the insolubilization step is less than 1 minute, the removal target substance may not be sufficiently insolubilized, and even if it exceeds 720 minutes, a further large reduction effect of the removal target substance may not be obtained. is there.

  The solid-liquid separation method in the solid-liquid separation step is not particularly limited as long as it is a method capable of separating the insolubilized material and the treated water. As a solid-liquid separation method, precipitation separation is the simplest operation and is preferable. However, fine bubbles may be supplied to cause floating separation, or membrane filtration using a microfiltration membrane or the like may be performed. Moreover, you may perform vacuum suction filtration and pressure filtration operation with a filter cloth. The slurry containing the separated solid content may be further filtered by vacuum suction or pressure filtration using a filter cloth or the like to perform solid-liquid separation.

  In addition, in order to increase the solid-liquid separation rate of the insolubilized product in the solid-liquid separation step after the insolubilization step and before the solid-liquid separation step, a flocculant such as a polymer flocculant is added to the water to be treated, A step of agglomerating and growing into a granular material having a large diameter and strong strength (aggregation step) may be provided.

  Examples of the flocculant used in the aggregation step include inorganic flocculants and polymer flocculants, and examples of the polymer flocculant include cationic polyacrylamide. The addition amount of a flocculant such as a polymer flocculant is, for example, in the range of 1 to 10 mg / L, and the reaction time is, for example, in the range of 3 to 15 minutes.

  The treated water obtained by the water treatment method according to the present embodiment may be discharged into a public water area such as the ocean or may be reused.

  The content of the substance to be removed in the treated water obtained by the water treatment method according to this embodiment is, for example, 30 mmol / L or less, and the content of the suspended substance is, for example, 20 mg / L or less.

  Moreover, content of the boron in treated water is 250 mg / L or less, for example, Preferably it is 200 mg / L or less. The fluorine content in the treated water is, for example, 15 mg / L or less, preferably 8 mg / L or less. The content of selenium in the treated water is, for example, 0.1 mg / L or less, preferably 0.05 mg / L or less. The content of heavy metals in the treated water is, for example, 2 mg / L or less, preferably 1 mg / L or less. The content of silica in the treated water is, for example, 20 mg / L or less, preferably 10 mg / L or less. By the water treatment method according to the present embodiment, in particular, treated water having a boron content of 250 mg / L or less can be obtained from water to be treated containing high-concentration boron of 500 mg / L or more.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

<Examples 1-1 to 1-5, 2-1 to 2-5, Comparative Examples 1-1 to 1-5, 2-1 to 2-2>
[Preparation of magnesium agent]
10 g of 5 g of basic magnesium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., heavy) was taken and measured at 400 ° C. (Comparative Example 1-1), 450 ° C. (Comparative Example 1-2), and 500 ° C. (Example 1). 1) 550 ° C. (Example 1-2), 600 ° C. (Example 1-3), 650 ° C. (Example 1-4), 700 ° C. (Example 1-5), 800 ° C. (Comparative Example 1-) 3) At 900 ° C. (Comparative Example 1-4) and 1000 ° C. (Comparative Example 1-5), each temperature was baked in an electric furnace for 1 hour. In addition, 7 g of magnesium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) was measured, and 400 g (Comparative Example 2-1), 450 ° C. (Example 2-1), and 500 ° C. (Example 2-2), respectively. ) At 550 ° C. (Example 2-3), 600 ° C. (Example 2-4), 650 ° C. (Example 2-5), and 700 ° C. (Comparative Example 2-2). Firing for an hour in an electric furnace.

  After firing, the mixture was allowed to cool, and the BET specific surface area of each obtained magnesium agent was measured with a specific surface area measuring device (ASAP2010) manufactured by Shimadzu Corporation according to a method based on JIS8830: 2013.

Furthermore, in order to confirm the crystal state of the magnesium agent baked at each temperature, an X-ray diffraction (XRD) spectrum was measured with an X-ray diffraction device (RINT Ultimate III, manufactured by Rigaku Corporation). In the measurement of the X-ray diffraction spectrum, magnesium oxide (manufactured by Wako Pure Chemical Industries, Wako first grade, heavy) was used to confirm the peak appearance position of magnesium oxide (horizontal axis 2θ (θ: black angle)). The X-ray diffraction spectrum of was measured as a comparative reference. From the 2θ = 42.9 ° and 62.2 ° peaks of this spectrum, the crystallite size was calculated by the Halder-Wagner method using the spectrum of silicon (powder, 4N, manufactured by Kanto Chemical Co., Inc., high purity) as an external standard. did. The Halder-Wagner method plots a graph represented by (β / tan θ) ² = (Kλ / L) × [β / (tan θ × sin θ)] + 16 × e ² based on the integral width of the peak. The crystallite size is calculated from the slope (Kλ / L). Here, β is the peak integration width, θ is the Bragg angle, K is the Scherrer constant, L is the crystallite size, λ is the X-ray wavelength, and e is the lattice strain.

Weight of magnesium agent before and after firing and weight reduction ratio (weight reduction ratio (%) = (weight before firing−weight after firing) ÷ weight before firing × 100), BET specific surface area (m ² / g), crystallite size (Å ) Are shown in Tables 1 and 2, and X-ray diffraction spectra are shown in FIGS.

  As shown in Table 1, when basic magnesium carbonate was used as a raw material, the weight loss rate was 26.8% at a firing temperature of 400 ° C. in Comparative Example 1-1, which was smaller than the weight loss rate of other firing temperatures, and the firing temperature was 450. At ℃ (Comparative Example 1-2), the weight loss rate is abruptly increased to 51.2%. Therefore, it is considered that carbonic acid and the like remain in the magnesium agent at 400 ℃ in Comparative Example 1-1. . Since the increase in the weight loss rate accompanying the firing temperature increase is small at a firing temperature of 500 ° C. or higher after Example 1-1, it is presumed that moisture, carbonic acid, etc. are sufficiently vaporized at a firing temperature of 500 ° C. or higher.

  As shown in FIG. 1, in the XRD spectrum at a firing temperature of 500 ° C. or higher, peaks appeared at 2θ = 42 ° and 62 °, as in the known magnesium oxide spectrum measured as a comparative reference. From this, it was confirmed that magnesium oxide is the main component at a firing temperature of 500 ° C. or higher (Examples 1-1 to 1-5 and Comparative Examples 1-3 to 1-5).

As shown in Table 1, regarding the specific surface area of the magnesium agent, the BET specific surface area was as small as 36.0 m ² / g or less at the firing temperature of 450 ° C. or less in Comparative Examples 1-1 to 1-2, whereas the firing temperature was However, in Examples 1-1 to 1-5 at 500 ° C. to 700 ° C., the BET specific surface area was large, and was 85.4 to 148 m ² / g. In addition, when a calcination temperature exceeded 700 degreeC, it exists in the tendency for a BET specific surface area to become small, and the BET specific surface area of Comparative Examples 1-3 to 1-5 with a calcination temperature of 800 degreeC or more was 119 m < ² > / g or less.

  On the other hand, regarding the crystal size of the magnesium agent, the crystallite size calculated by the Halder-Wagner method based on the XRD spectrum tends to increase as the firing temperature increases, and the firing temperature is 450 ° C. or less (Comparative Example). In 1-1 to 1-2), it is 36.1 で or less, whereas in the firing temperature of 500 to 700 ° C (Examples 1-1 to 1-5), it is 54.0 to 97.4 、 and the firing temperature is 800. The temperature was 201 ° C. or higher at a temperature of ° C. or higher (Comparative Examples 1-3 to 1-5).

  As shown in Table 2, when magnesium hydroxide is used as the raw material, the weight loss rate is 12.6% at the firing temperature of 400 ° C. in Comparative Example 2-1, which is smaller than the weight loss rate of other firing temperatures, and the firing temperature is 450 ° C. In (Example 2-1), since the weight loss rate is rapidly increased to 27.0%, undehydrated magnesium hydroxide remains in the magnesium agent at 400 ° C. in Comparative Example 2-1. it is conceivable that. Since the increase in the weight loss rate accompanying the increase in the firing temperature is small at the firing temperature of 450 ° C. or higher after Example 2-1, it is estimated that the dehydration was sufficiently performed at the firing temperature of 450 ° C. or higher.

  As shown in FIG. 2, in the XRD spectrum having a firing temperature of 450 ° C. or higher, peaks appeared at 2θ = 42 ° and 62 ° as in the known magnesium oxide spectrum measured as a comparative reference. From this, it was confirmed that magnesium oxide is the main component in all of the firing temperatures of 450 ° C. or higher (Examples 2-1 to 2-5 and Comparative Example 2-2).

As shown in Table 2, regarding the specific surface area of the magnesium agent, the BET specific surface area is as small as 81.9 m ² / g or less at the firing temperature of 400 ° C. of Comparative Example 2-1, whereas the firing temperature is 450 ° C. to 650 ° C. In Examples 2-1 to 2-5, the BET specific surface area was large, 111 to 229 m ² / g. In addition, when a calcination temperature exceeded 550 degreeC, it exists in the tendency for a BET specific surface area to become small, and the BET specific surface area of the comparative example 2-2 with a calcination temperature of 700 degreeC or more was 76.4 m < ² > / g.

  On the other hand, regarding the crystal size of the magnesium agent, the crystal size calculated by the Halder-Wagner method based on the XRD spectrum tends to increase as the firing temperature increases, and the firing temperature is 400 ° C. (Comparative Example 2- In 1), it is 54.8 ° C. or less, whereas in the baking temperature 450 to 650 ° C. (Examples 2-1 to 2-5), it is 64.1 to 107 ° C. and the baking temperature 700 ° C. (Comparative Example 2-2). Then it was 158cm.

[Water treatment method]
Here, water treatment was performed with a magnesium agent obtained by firing basic magnesium carbonate or magnesium hydroxide at each temperature for boron-containing water.

(Operating procedure)
Boron-containing water was prepared by adding boric acid to distilled water so that the boron concentration was about 500 mg / L, and further adding potassium hydroxide so that the pH was 7.0. Each 300 mL of boron-containing water was prepared in 10 beakers, which were treated water (water temperature about 20 ° C.).

  While stirring each water to be treated, production methods of Examples 1-1 to 1-5, 2-1 to 2-5 and Comparative Examples 1-1 to 1-5, 2-1 to 2-2, respectively. 7.46 g of the magnesium agent powder prepared in the above was added, and the reaction was continued while stirring for 720 minutes after the addition. During this time, while continuously measuring the pH of the water to be treated with a pH sensor, 0.5 ml of the water to be treated was appropriately sampled 1 minute to 720 minutes after the addition (just before the stirring was stopped). The collected water was immediately filtered through a filter having a diameter of 0.1 μm to remove insoluble matters, and used as an analytical sample of the concentration of residual boron in water during each reaction time.

  Furthermore, after stirring for 720 minutes, 300 mL of water to be treated was immediately suction filtered with a filter paper having a diameter of 0.45 μm. The time (second) required for this filtration was measured.

  In addition, the density | concentration of the residual boron in to-be-processed water was analyzed by the ICP emission method using the ICP emission analysis apparatus (The product made by Seiko Instruments, SPS7800 type) based on the method prescribed | regulated to JIS0102.

(result)
[When using magnesium agent calcined from basic magnesium carbonate]
The results of measuring the pH of the water to be treated up to 120 minutes after the reaction after adding each magnesium agent calcined from basic magnesium carbonate are analyzed in FIG. 3, and the dissolved boron remains in the water to be treated. The result of calculating the rate (ratio to boron in the water to be treated) is shown in FIG. Table 3 shows the time required for filtration with filter paper after the reaction for 720 minutes.

  As shown in FIG. 3, the pH after adding the magnesium agent calcined at each temperature is 10.6 or more in 10 minutes of reaction in each of Examples 1-1 to 1-5, and thereafter 10.6 to 10. It moved in the range of 8. In Comparative Examples 1-1 to 1-2 where the firing temperature is low, the reaction was 10 minutes or more after 10 minutes and changed from 10.5 to 10.7, but in Comparative Examples 1-3 to 1-5 where the firing temperature was high It was 10.2 to 10.4 after 30 minutes and 10.3 to 10.4 after 120 minutes.

  At this time, as shown in FIG. 4, the dissolved boron residual rate in the water to be treated is 64 to 72% in 30 minutes and 50 to 60 in 60 minutes in Examples 1-1 to 1-5 having a baking temperature of 500 to 700 ° C. 62% and 28-50% in 120 minutes. On the other hand, in Comparative Examples 1-1 to 1-5, the reaction was 88 to 100% in 30 minutes, 77 to 100% in 60 minutes, and 59 to 97% in 120 minutes. From 120 minutes, the dissolved boron residual ratio in the same reaction time is significantly lower in Examples 1-1 to 1-5 than in the comparative example, and thus the insolubilization rate of boron is the firing temperature of 500 to 700 ° C. It can be said that Examples 1-1 to 1-5 to which the magnesium agent was added are clearly higher.

  In addition, the residual rate of the dissolved boron after making it react for a long time of 720 minutes was 21-35% in Examples 1-1 to 1-5. The comparative examples were 19 to 40% except for Comparative Example 1-5 having a firing temperature of 1000 ° C., and there was no significant difference from the examples (the dissolved boron residual ratio of Comparative Example 1-5 was 60%).

  However, as shown in Table 3, the filtration time when the water to be treated after the reaction for 720 minutes was sucked with a filter paper (the time required for filtration) was Comparative Examples 1-1 to 1-1 at a baking temperature of 400 to 450 ° C. -2 took 120 to 180 seconds, whereas Examples 1-1 to 1-5 and Comparative Examples 1-3 to 1-5 took 32 to 50 seconds. That is, it was confirmed that the solid-liquid separation rate of the insoluble matter was remarkably increased by using a magnesium agent having a firing temperature of 500 to 700 ° C.

From these results, the high boron removal rate and the high solid-liquid separation rate are obtained by adding the magnesium agent obtained by baking at 500 to 700 ° C. using basic magnesium carbonate as a raw material. It was shown to be 1 to 1-5. It was also shown that a magnesium agent having a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 Å or less is preferable.

[When using magnesium agent baked from magnesium hydroxide]
FIG. 5 shows the measurement results of the pH of water to be treated up to 120 minutes after the addition of each magnesium agent calcined from magnesium hydroxide, and the dissolved boron in the water to be treated is analyzed. The results of calculating the ratio of boron to the water to be treated are shown in FIG. Table 4 shows the time required for filtration with filter paper after 120 minutes of reaction.

  As shown in FIG. 5, the pH after addition of the magnesium agent calcined at each temperature was 10.3 or more after 10 minutes of reaction in each of Examples 2-1 to 2-5, and thereafter 10.3 to 10. It changed in the range of 7. In Comparative Example 2-1 having a low calcination temperature and Comparative Example 2-2 having a high calcination temperature, the reaction became 10.2 to 10.3 in 10 minutes and changed from 10.3 to 10.4. It changed.

  At this time, as shown in FIG. 6, the dissolved boron residual rate in the water to be treated was 67 to 80% in 30 minutes and 48 to 60 in 60 minutes in Examples 2-1 to 2-5 having a firing temperature of 450 to 600 ° C. 66%, 27-48% in 120 minutes. On the other hand, in Comparative Examples 2-1 and 2-2, the reaction was 87% for 30 minutes, 75 to 77% for 60 minutes, and 59 to 64% for 120 minutes. Since the residual boron is remarkably lower in Examples 2-1 to 2-5 in 120 minutes, the insolubilization rate of boron was determined in Example 2-1 in which a magnesium agent having a firing temperature of 450 to 650 ° C. was added. It can be said that ˜2-5 is clearly higher.

  In addition, the residual rate of the dissolved boron after making it react for 720 minutes for a long time was 16 to 24% in Examples 2-1 to 2-5. Comparative Example 2-2 was 17%, which was the same as the example, but Comparative Example 2-1 was 56%, which was significantly different from the example.

  As shown in Table 4, the filtration time when the water to be treated after the reaction for 720 minutes was sucked with filter paper (time required for filtration) was as shown in Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-1 Although 2-2 was 28 to 50 seconds, the filtration time was significantly shorter than the filtration times of Examples 1-1 to 1-5. That is, it was confirmed that a high solid-liquid separation rate can be obtained by using a magnesium agent having a firing temperature of 450 to 650 ° C.

From these results, Example 2-1 having a high boron removal rate and a high solid-liquid separation rate was obtained by adding magnesium agent obtained by firing magnesium hydroxide as a raw material at 450 to 650 ° C. It was shown to be ˜2-5. It was also shown that a magnesium agent having a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 Å or less is preferable.

  Thus, implementation using at least one of a magnesium agent calcined with basic magnesium carbonate at a temperature in the range of 500 to 700 ° C. and a magnesium agent calcined with magnesium hydroxide at a temperature in the range of 450 to 650 ° C. The example shows that the removal target substance can be insolubilized and solid-liquid separated in a short time from the water containing the removal target substance to obtain treated water of good water quality, and the volume of the separated solid can be efficiently reduced. It was.

Claims (7)

  At least one of a magnesium agent obtained by calcining basic magnesium carbonate at a temperature in the range of 500 to 700 ° C. and a magnesium agent obtained by calcining magnesium hydroxide at a temperature in the range of 450 to 650 ° C. is coated with the substance to be removed. A water treatment method comprising adding to treated water. The water treatment method according to claim 1,
The magnesium agent has a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 Å or less. The water treatment method according to claim 1 or 2,
The water to be treated contains at least one of boron, fluorine, selenium, heavy metal or a compound thereof, or silica as the substance to be removed. The water treatment method according to any one of claims 1 to 3,
Performing an insolubilization reaction of the substance to be removed after addition of the magnesium agent to the treated water;
Solid-liquid separation of the insolubilized insolubilized material,
Further including
A water treatment method, comprising adding the magnesium agent in an amount such that a pH before solid-liquid separation of the insolubilized product is 10 or more to the water to be treated. Magnesium for water treatment comprising at least one calcined product of basic magnesium carbonate and magnesium hydroxide, having a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 mm or less Agent.   For water treatment, characterized in that a magnesium agent is obtained by calcining basic magnesium carbonate at a temperature in the range of 500 to 700 ° C. or calcining magnesium hydroxide at a temperature in the range of 450 to 650 ° C. A method for producing a magnesium agent. It is a manufacturing method of the magnesium agent for water treatment according to claim 6,
The method for producing a magnesium agent for water treatment, wherein the magnesium agent has a BET specific surface area of 85 m ² / g or more and a crystallite size of 110 kg or less.