Solution concentration method

Abstract

To provide a solution concentration method capable of highly concentrating a solution while suppressing precipitation of a solute.SOLUTION: A solution concentration method includes a step of adding a scale dispersant to raw water, and a concentration step of concentrating the raw water added to the scale dispersant by concentration means by OARO or heating concentration. The concentration step subjects the concentration water from the concentration step to deactivation treatment of the scale dispersant, after concentrated to a supersaturated region. Then, a solid content is precipitated, and then solid-liquid separation is performed. The liquid obtained by the solid-liquid separation is returned to the raw water or the raw water to which the scale dispersant is added.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for concentrating a solution, and particularly to a method for concentrating a solution to a high concentration, for example, to a supersaturated region.

Background Art

[0002] As a method for highly concentrating an aqueous solution, an osmotic pressure-assisted reverse osmosis (OARO) method or an evaporative concentration method using an evaporator or the like is performed.

[0003] For example, Patent Document 1 describes concentrating an aqueous solution of a lithium salt by the OARO method. According to the OARO method, a solution can be concentrated with lower energy consumption than the RO method. The OARO method is a membrane separation method in which salt water of the same concentration is supplied to both sides of a semipermeable membrane, and pressure is applied to only one side. Since no osmotic pressure acts between the salt waters separated by the semipermeable membrane and water permeation occurs even with a slight applied pressure, high concentration or high dilution of the salt water can be achieved by multi-staging this.

[0004] Patent Document 2 describes a method for evaporatively concentrating an acid-containing aqueous solution.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When a solution is highly concentrated, even if the solute is a sodium salt, a lithium salt, etc. with high solubility, the solute precipitates, and the continuous operation of the concentration device is inhibited.

[0007] An object of the present invention is to provide a method for concentrating a solution that can highly concentrate the solution while suppressing precipitation of a solute. **Means for Solving the Problems**

[0008] The method for concentrating a solution of the present invention includes a step of adding a scale dispersant to raw water, and a concentration step of concentrating the raw water to which the scale dispersant has been added using an OARO device or an evaporation concentrator.

[0009] In one aspect of the present invention, a preliminary concentration step of concentrating the raw water or the raw water to which the scale dispersant has been added using RO is included before the concentration step.

[0010] In one aspect of the present invention, the scale dispersant includes at least one of a phosphonic acid-based scale dispersant and a polymer-based scale dispersant.

[0011] In one aspect of the present invention, the polymer-based scale dispersant is an acrylic acid / AMPS copolymer or an acrylic acid homopolymer.

[0012] In one aspect of the present invention, the weight average molecular weight of the polymer-based scale dispersant is 1000 or more and 10000 or less.

[0013] In one aspect of the present invention, in the concentration step, after concentrating to the supersaturated region, the concentrated water from the concentration step is subjected to a deactivation treatment of the scale dispersant, then solids are precipitated, and then solid-liquid separation is performed.

[0014] In one aspect of the present invention, the liquid obtained by solid-liquid separation is returned to the raw water or the raw water to which the scale dispersant has been added. **Advantages of the Invention**

[0015] According to the present invention, since a dispersant is added to the raw water for concentration treatment, precipitation of the solute in the concentrator is suppressed, and it becomes possible to stably and highly concentrate the solute.

[0016] In one aspect of the present invention, when subjecting the concentrated water from the concentration device to crystallization treatment for solid-liquid separation, by adding a deactivator to the concentrated water, the crystallization inhibition effect of the dispersant in the crystallization treatment is suppressed, and crystallization is efficiently performed. Further, the water quality of the treated water can be improved thereby.

Brief Description of the Drawings

[0017]

Figure 1

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments will be described.

[0019] The method for concentrating a solution of the present invention includes a step of adding a scale dispersant to raw water, and a concentration step of concentrating the raw water to which the scale dispersant has been added by an OARO device or an evaporation concentration device. Examples of the solute of the raw water (water to be concentrated) to be concentrated by the present invention include, but are not limited to, metal ions, soluble organic substances, soluble silica, and mixtures thereof. The solute may be, for example, chlorides, sulfates, nitrates, carbonates, bicarbonates of alkali metals such as lithium, sodium, and potassium, water-soluble magnesium salts such as magnesium chloride, boric acid, potassium iodide, palladium, ammonia, cobalt, lithium, platinum group metal ions, aluminum hydroxide, gallium, nickel, phosphorus, calcium fluoride, silver, ammonium cerium nitrate, and mixtures of two or more of these.

[0020] When the scale dispersant is used in combination, the concentration of the solute in the raw water is preferably about 10 to 80%, particularly about 33 to 66%, with the concentration at which the solute starts to precipitate being 100%. However, higher or lower concentrations may also be used.

[0021] Examples of such raw water include, but are not limited to, high-concentration wastewater discharged by wastewater recovery treatment, such as concentrated water in reverse osmosis membrane treatment. The raw water may be, for example, water generated in a wastewater recovery process in a semiconductor factory, a seawater desalination process, a lithium recovery process, or a valuable substance recovery process.

[0022] As the concentration device, in addition to the OARO device, an evaporative concentration device such as an evaporator is used.

[0023] In the present invention, when concentrating relatively low-concentration raw water, it may first be pre-concentrated by an RO device (reverse osmosis membrane device) and then supplied to the above concentration device.

[0024] In the present invention, a scale dispersant is added to the raw water or the raw water pre-concentrated by the RO device, and then it is supplied to the concentration device for concentration treatment.

[0025] The scale dispersant preferably contains at least one of a phosphonic acid-based scale dispersant and a polymer-based scale dispersant. As the phosphonic acid-based scale dispersant, generally, hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylene phosphonic acid (ATMP), phosphonobutane tricarboxylic acid (PBTC), etc. can be used.

[0026] The polymer-based scale dispersant may have only a carboxyl group and no sulfonic acid group, but a polymer having a sulfonic acid group and a carboxyl group is preferred.

[0027] Examples of polymers having a sulfonic acid group and a carboxyl group, which are suitable as polymer scale dispersants, include copolymers of a monomer having a sulfonic acid group and a monomer having a carboxyl group, or alternatively, terpolymers of these monomers and other monomers copolymerizable therewith. Among these, examples of monomers having a sulfonic acid group include conjugated diene sulfonic acids such as 2-methyl-1,3-butadiene-1-sulfonic acid, unsaturated (meth)allyl ether-based monomers having a sulfonic acid group such as 3-(meth)allyloxy-2-hydroxypropanesulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, styrenesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylenesulfonic acid, or salts thereof. Preferably, 3-allyloxy-2-hydroxy-1-propanesulfonic acid (HAPS) and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) are mentioned. These may be used alone or in combination of two or more.

[0028] On the other hand, examples of monomers having a carboxyl group include acrylic acid (AA), methacrylic acid, crotonic acid, isocrotonic acid, vinylacetic acid, atropic acid, maleic acid, fumaric acid, itaconic acid, hydroxyethylacrylic acid, or salts thereof. Preferably, acrylic acid and methacrylic acid are mentioned. These may be used alone or in combination of two or more.

[0029] Examples of monomers copolymerizable with these monomers include alkenes such as isobutylene, and amides such as N-tert-butylacrylamide (N-tBAA) and N-vinylformamide.

[0030] As the polymer scale dispersant, an acrylic acid·AMPS copolymer or an acrylic acid homopolymer is particularly preferred.

[0031] The weight average molecular weight of the polymer scale dispersant is preferably about 1000 to 10000, particularly 5000 to 10000, especially about 6000 to 8000.

[0032] The addition amount of the scale dispersant varies depending on the solute to be dispersed and is not particularly limited, but is usually 1 to 2000 mg / L, and particularly preferably about 10 to 1000 mg / L.

[0033] In one aspect of the present invention, the concentrated water concentrated to the supersaturated region by the concentration device is subjected to crystallization treatment (treatment for precipitating solid components). As the crystallization treatment, a treatment for lowering the temperature of the concentrated water is preferable.

[0034] In the present invention, in order to efficiently perform crystallization, it is preferable to perform a deactivation treatment such as adding a deactivator to the concentrated water before the crystallization treatment.

[0035] As the deactivator added to the concentrated water, it is preferable to use an iron salt and a cationic polymer. As the iron salt, ferric salts such as ferric chloride and ferric sulfate are suitable.

[0036] The addition amount of the iron salt is preferably 0.1 to 5 times, particularly about 0.5 to 2 times, the concentration of the scale dispersant in the concentrated water. The addition amount of the iron salt may be adjusted in consideration of conditions such as the salt concentration of the raw water.

[0037] As the cationic polymer, for example, at least one of DMA-epi (dimethylamine-epichlorohydrin polycondensate) and pDADMAC (polydiallyldimethylammonium chloride) is preferable.

[0038] The weight average molecular weight of the cationic polymer may be, for example, 1000 to 1000000, preferably 50000 to 800000, and more preferably 100000 to 700000.

[0039] When the cationic polymer is DMA-epi, the weight average molecular weight of DMA-epi may be, for example, 50000 to 200000. When the cationic polymer is pDADMAC, the weight average molecular weight of pDADMAC may be, for example, 100000 to 800000, and more preferably 300000 to 600000.

[0040] The weight-average molecular weight is the weight-average molecular weight in terms of standard polystyrene determined by gel permeation chromatography (GPC).

[0041] The iron salt and the cationic polymer may be added after being mixed in one agent, or may be added separately.

[0042] The addition amount of the cationic polymer is preferably 0.05 to 5 times, particularly about 0.5 to 2.5 times, the addition amount of the scale dispersant.

[0043] The ratio of the iron salt addition amount to the cationic polymer addition amount (iron salt addition amount: cationic polymer addition amount) is preferably 1:0.1 to 10, particularly about 1:0.5 to 2.

[0044] By adding this deactivator, the precipitation amounts of calcium sulfate, calcium carbonate, calcium hydroxide, calcium phosphate, sodium hydrogen carbonate, calcium fluoride, barium sulfate, silica, etc. increase.

[0045] Regarding the mechanism by which the addition of the deactivator suppresses crystal growth inhibition, it is not fully clear, but it is presumed that the iron salt and the cationic polymer act as follows. That is, the binding between the scale component and the dispersant is inhibited by the iron salt binding to the dispersant. The iron salt also acts as an active site for crystal growth, and the scale component binds to the iron salt, promoting the aggregation of the scale component. The cationic polymer neutralizes the charge of the dispersant and suppresses the crystal growth inhibition effect of the dispersant. The cationic polymer also forms a gel with the dispersant when the dispersant is a polymer, suppressing the crystal growth inhibition effect of the dispersant.

[0046] In the present invention, instead of adding a deactivator to the concentrated water, decomposition treatment of the scale dispersant by UV irradiation or ozone addition may be performed. Further, the addition of the deactivator and the decomposition treatment of the scale dispersant by UV irradiation or ozone addition may be used in combination.

[0047] In the present invention, after the concentrated water is subjected to crystallization treatment, solid-liquid separation is performed to separately recover the solid content and the liquid content, and this liquid content may be returned to the raw water or the preliminary concentrated water and concentrated again. At this time, a scale dispersant may be added to the liquid content before returning it. Note that the liquid content after solid-liquid separation may be subjected to a drying treatment such as evaporation without returning it to the raw water or the like in this manner.

Example

[0048] [Test Example 1] (Test on the scale dispersion effect of simulated raw water by adding a scale dispersant) In a flask, the following scale dispersant in Table 1 was added to the following simulated raw water (simulated coal seam gas drainage) in the addition amounts shown in Table 1, and it was allowed to stand at 25°C, and the change over time in M-alkalinity was measured. Note that the acrylate-based cationic polymers in Test Examples 1-4 are acrylamide·2(acryloyloxy)ethyltrimethylammonium chloride copolymers.

[0049] <Simulated raw water (prepared using reagent grade)> NaHCO3: 150 g / L SiO2: 300 mg / L pH: 9

[0050]

Table 1

[0051] [Discussion (1)] As shown in Table 1, by adding a scale dispersant, the precipitation of NaHCO3 is suppressed. In particular, Test Examples 1-1 and 1-2 using the AA / AMPS polymer have an excellent precipitation suppression effect compared to Test Examples 1-3 to 1-5.

[0052] Note that 150 g / L of the NaHCO3 solution corresponds to 87,000 mg / L as M-alkalinity. Also, the saturation concentration of the NaHCO3 solution is 9.6% at 25°C, and 9.6 g / L corresponds to 55,770 mg / L as M-alkalinity.

[0053] [Test Examples 2-1 to 2-3] In Test Example 1-1, the following AA / AMPS polymers A and B were used as the AA / AMPS polymer, the addition amounts of the respective polymers A and B were as shown in Table 2, and the same test was conducted except that the turbidity was measured as the scale dispersion effect of the simulated raw water. The results are shown in Table 2. AA / AMPS polymer A: AA:AMPS = 89:11, Mw = 6000 AA / AMPS polymer B: AA:AMPS = 97:3, Mw = 7000

[0054]

Table 2

[0055] [Discussion (2)] As shown in Table 2, when the AA / AMPS polymer B was added, the turbidity was lower, indicating a high precipitation inhibition ability and an effect on the dispersion of NaHCO3.

[0056] [Example 1] A concentration test of the simulated raw water was conducted using the OARO concentration device shown in FIG. 1.

[0057] This OARO concentration device has two OARO modules 10 and 20 connected in series. Each OARO module 10 and 20 includes semipermeable membranes 13 and 23, and a first chamber 11 and 21 and a second chamber 12 and 22 partitioned by the semipermeable membranes 13 and 23.

[0058] The raw water in the raw water tank 1 is passed through the pump 2 into the first chamber 11 of the OARO module 10. The concentrated water flowing out of the first chamber 11 is passed through the pipe 3 into the first chamber 21 of the OARO module 20. The concentrated water flowing out of the second chamber 21 flows out through the pipe 4, and a part of it is returned to the raw water tank 1 through the pipe 4a.

[0059] The remainder of the concentrated water flowing out into the pipe 4 is diverted into the pipe 4b, depressurized by the pressure reducing device 5, then passes through the second chamber 22 of the OARO module 20, and flows into the second chamber 12 of the OARO module 10 via the pipe 6. As a result, a part of the water contained in the raw water flowing in the first chambers 11, 21 permeates through the semi-permeable membranes 13, 23 and transfers to the aqueous solution in the second chambers 12, 22, and the diluted aqueous solution diluted from the second chamber 12 is discharged to the diluted water tank 8 via the pipe 7.

[0060] Here, in the OARO modules 10, 20, since the concentration of the aqueous solution flowing out from the first chambers 11, 21 is almost the same as the concentration of the aqueous solution flowing into the second chambers 12, 22, the osmotic pressures are almost equal. Therefore, the raw water is concentrated by applying a relatively low pressure.

[0061] <OARO module used> In this Example 1, a Holosep Mini (registered trademark) manufactured by Toyobo Co., Ltd. was used as the OARO module. This Holosep Mini has a hollow fiber membrane arranged as a semi-permeable membrane inside a tubular pressure-resistant container (shell).

[0062] The inside of the hollow fiber membrane (Bore side) is the first chambers 11, 21, and the space between the hollow fiber membrane and the tubular shell is the second chambers 12, 22.

[0063] The volume of the first chambers 11, 21 is 71.3 mL (9.5 mm φ × 1000 mm L), and the volume of the second chambers 12, 22 is 71.3 mL.

[0064] <Raw water> As the raw water, a 100 g / L NaHCO3 aqueous solution added with 150 mg / L of Polymer B was used.

[0065] <Water flow conditions> The above raw water was supplied to the first chamber 11 at normal temperature under a pressure of 5.6 MPa and a flow rate of 0.12 L / min. The concentrated water from the pipe 4b was depressurized to a pressure of 1.9 MPa and passed through the second chamber 22 at a flow rate of 0.05 L / min. The amount of raw water in the raw water tank at the start of operation was 20 L.

[0066] Table 3 shows the change over time in the NaHCO3 concentration in the raw water tank 1 and the dilute water tank 8.

[0067]

Table 3

[0068] [Consideration (3)] As shown in Table 3, from the point where the concentrated water is returned through the pipe 4a, the concentration of the aqueous solution in the raw water tank 1 increased over time. On the other hand, the concentration of the aqueous solution in the dilute water tank 8 was almost constant. Note that no precipitation of NaHCO3 occurred in the system.

Explanation of symbols

[0069] 1 Raw water tank 2 Pump 8 Dilute water tank 10 OARO module 11, 21 First chamber 12, 22 Second chamber 13, 23 Semipermeable membrane

Claims

1. A step of adding a scale dispersant to raw water, and a concentration step of concentrating the raw water to which the scale dispersant has been added by an OARO device or an evaporation concentration device A method for concentrating a solution having the above steps.

2. The method for concentrating a solution according to claim 1, further comprising a preliminary concentration step of concentrating the raw water or the raw water to which the scale dispersant has been added by RO before the concentration step.

3. The method for concentrating a solution according to claim 1, wherein the scale dispersant contains at least one of a phosphonic acid-based scale dispersant and a polymer-based scale dispersant.

4. The method for concentrating a solution according to claim 3, wherein the polymer-based scale dispersant is an acrylic acid / AMPS copolymer or an acrylic acid homopolymer.

5. The method for concentrating a solution according to claim 4, wherein the weight average molecular weight of the polymer-based scale dispersant is 1000 or more and 10000 or less.

6. In the concentration step, after concentrating to the supersaturated region, deactivating the scale dispersant in the concentrated water from the concentration step, then precipitating solids, and then performing solid-liquid separation. The method for concentrating a solution according to any one of claims 1 to 5.

7. The method for concentrating a solution according to claim 6, wherein the liquid obtained by solid-liquid separation is returned to the raw water or the raw water to which the scale dispersant has been added.

Images