Concentration system

Abstract

To provide a concentration system of an alkali waste liquid which can be carried out with more energy saving.SOLUTION: A concentration system for concentrating an alkaline target liquid, comprising: a semipermeable membrane module having a semipermeable membrane and configured to concentrate the target liquid by a membrane separation method; and a pH lowering device configured to add a pH lowering agent to the target liquid to be supplied to the semipermeable membrane module.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a concentration system. [Background technology]

[0002] The separation and concentration of liquid mixtures by membrane separation is an energy-saving method because it does not involve a phase change compared to conventional separation techniques such as distillation, and because it does not involve a change in the state of the substance, it is widely used in many fields, such as the food industry, where fruit juice is concentrated and beer yeast is separated, and the recovery of organic matter from industrial wastewater.Membrane separation methods used include reverse osmosis (RO), forward osmosis (FO), and osmotically assisted reverse osmosis (OARO).

[0003] Various concentration systems using such membrane separation methods are known. For example, Patent Document 1 (JP-A-10-323664) discloses a method for concentrating acidic / alkaline wastewater that combines reverse osmosis concentration and evaporation concentration in this order. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-323664 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, the effluent discharged when recovering lithium from the electrolyte, electrode (cathode) material, etc. of used lithium-ion batteries is alkaline (strongly alkaline) and contains LiOH, Li2CO3, etc. Semipermeable membranes (organic membranes) are generally susceptible to deterioration in such alkaline effluents (e.g., changes in surface properties and a decrease in pressure resistance). For this reason, if a membrane separation method using a semipermeable membrane is directly used to concentrate the alkaline effluent, it is difficult to use the semipermeable membrane for a long period of time. Therefore, in practice, alkaline effluents are generally concentrated only by evaporation (evaporation concentration device 2) (see Figure 2). However, since concentration systems that rely solely on evaporation consume a lot of energy, there is a demand for energy-saving concentration systems that use membrane separation at least in part.

[0006] The present invention provides a system for concentrating alkaline effluent that can be implemented with less energy consumption. [Means for solving the problem]

[0007] (1) A concentration system for concentrating an alkaline target liquid, comprising: a semipermeable membrane module having a semipermeable membrane and concentrating the target liquid by a membrane separation method; A concentration system comprising: a pH-lowering device that adds a pH-lowering agent to the target liquid supplied to the semipermeable membrane module. (2) The concentration system described in (1), wherein the pH-reducing device has a control mechanism that measures the pH of the target liquid before and after adding the pH-reducing agent and adjusts the amount of the pH-reducing agent to be added based on the measured value. (3) The concentration system described in (1) or (2), wherein the pH-lowering agent is CO2. (4) The concentration system according to any one of (1) to (3), wherein the membrane separation method is at least one selected from reverse osmosis, forward osmosis, and osmotically assisted reverse osmosis. (5) Further comprising an evaporation and concentration device; The concentration system according to any one of (1) to (4), wherein the target liquid concentrated by the membrane separation method using the semipermeable membrane module is further concentrated by the evaporation concentration device. (6) The concentration system according to any one of (1) to (5), wherein the target liquid contains a lithium compound. (7) The concentration system according to any one of (1) to (6), wherein the semipermeable membrane contains cellulose triacetate. (8) The concentration system according to any one of (1) to (7), wherein the semipermeable membrane is a hollow fiber membrane. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a system for concentrating alkaline effluent that can be operated with greater energy savings. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a concentration system according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram showing an example of a conventional concentration system. DETAILED DESCRIPTION OF THE INVENTION

[0010] The concentration system of this embodiment will be described below with reference to the drawings. Note that the same reference numerals in the drawings represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

[0011] <Concentration system> Referring to FIG. 1, there is shown a concentration system for concentrating an alkaline target liquid. The concentration system of this embodiment includes a semipermeable membrane module 1 for concentrating a target liquid, and a pH-lowering device 3 for adding a pH-lowering agent to the target liquid supplied to the semipermeable membrane module 1.

[0012] (Semipermeable membrane module) The semipermeable membrane module 1 may have a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane.

[0013] The membrane separation method is not particularly limited, but is preferably at least one selected from reverse osmosis, forward osmosis, and osmotically assisted reverse osmosis.

[0014] (semi-permeable membrane) The semipermeable membrane used in the semipermeable membrane module 1 is not particularly limited, and various known semipermeable membranes that can be used in the above-mentioned membrane separation methods can be used.

[0015] The material constituting the semipermeable membrane is not particularly limited, but examples thereof include cellulose-based resins, polysulfone-based resins, polyamide-based resins, etc. The semipermeable membrane is preferably made of a material containing at least one of a cellulose-based resin and a polysulfone-based resin.

[0016] The cellulose-based resin is preferably a cellulose acetate-based resin. The cellulose acetate-based resin is resistant to chlorine, a disinfectant, and can inhibit the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and from the viewpoint of durability, more preferably cellulose triacetate.

[0017] The polysulfone-based resin is preferably a polyethersulfone-based resin. The polyethersulfone-based resin is preferably a sulfonated polyethersulfone.

[0018] The shape of the semipermeable membrane is not particularly limited, but examples thereof include a flat membrane, a spiral membrane, and a hollow fiber membrane. Although the semipermeable membrane is depicted as a simplified flat membrane in the drawings, the semipermeable membrane is not limited thereto.

[0019] The semipermeable membrane is preferably a hollow fiber membrane. When the semipermeable membrane is a hollow fiber membrane, the water permeability per unit membrane area is not as large as that of a spiral membrane (flat membrane), but the membrane area per volume of the semipermeable membrane module can be increased. This allows for a larger water permeability for the entire module. In other words, this has the advantage of very high volumetric efficiency and excellent compactness.

[0020] The form of the semipermeable membrane module 1 is not particularly limited, but when hollow fiber membranes are used, examples include a module in which multiple hollow fiber membranes are arranged in a straight line, a cross-wound module in which multiple hollow fiber membranes are wound around a core tube, etc. When flat membranes are used, examples include a stacked module in which multiple flat membranes are stacked, and a spiral module in which multiple flat membranes are wrapped around a core tube in the form of an envelope.

[0021] The outer diameter of the hollow fiber membrane is not particularly limited as long as it is suitable for use in membrane separation processes, but is, for example, 150 to 250 μm. If the outer diameter is smaller than this range, the inner diameter will inevitably be small as well, which can cause problems by increasing the pressure loss of the fluid flowing through the hollow portion of the hollow fiber membrane. On the other hand, if the outer diameter is larger than this range, it will be impossible to increase the membrane area per unit volume in the module, and compactness, one of the advantages of hollow fiber membrane modules, will be lost.

[0022] (pH lowering device) The concentration system of this embodiment is equipped with a pH-reducing device 3 that adds a pH-reducing agent to the target liquid. The pH-reducing device 3 is provided, for example, midway along the piping for supplying the target liquid to the semipermeable membrane module 1 so that the pH-reducing agent can be added to the target liquid supplied to the semipermeable membrane module 1.

[0023] According to this embodiment, even when an alkaline target liquid is concentrated by a membrane separation method using the semipermeable membrane module 1, the target liquid whose pH has been lowered by the pH lowering device 3 to a range where deterioration of the semipermeable membrane is minimal, such as a neutral range (for example, pH 6.5 to 8.0), is supplied to the semipermeable membrane module 1. This suppresses deterioration of the semipermeable membrane module 1 (semipermeable membrane), making it possible to use the semipermeable membrane module 1 for a long period of time. Therefore, it is possible to provide a system for concentrating alkaline effluent that can be operated (continuously) with less energy consumption than conventional systems.

[0024] The pH-lowering agent is not particularly limited as long as it can lower the pH of an alkaline target liquid (neutralize the alkali), but it is preferable that it can lower the pH of the target liquid to a predetermined pH (e.g., 8.0) or lower, for example, within the range of pH 7.0 to 8.0, at which deterioration of the semipermeable membrane is unlikely to occur. Specific examples of pH lowering agents include carbon dioxide (CO2), sulfuric acid (H2SO4), hydrochloric acid (HCl), and citric acid. Among these, the pH-lowering agent is preferably CO2. The pH-lowering device 3 is preferably a device capable of bubbling CO2 into the target liquid. By lowering the pH of the target solution using CO2 in this way, it is possible to prevent impurities from being mixed in with the pH-lowering agent when recovering a target substance from a concentrated target liquid. When sulfuric acid, hydrochloric acid, citric acid, or the like is used as the pH-lowering agent, a dropping device can be used as the pH-lowering device 3.

[0025] (Evaporation and concentration device) As shown in FIG. 1, the concentration system may further include an evaporation concentration device 2. The evaporation concentration device 2 can further concentrate the target liquid that has been concentrated by membrane separation using the semipermeable membrane module 1. This makes it easier to recover the target substance (e.g., rare substance) present in the target liquid from the target substance. As the evaporation concentration device 2, any concentration device using various known evaporation methods can be used.

[0026] (Target liquid) The target liquid is alkaline. The pH of the target liquid may be, for example, greater than 7.5, greater than 8.0, or even 8.5 or higher. That is, the target liquid has a pH that would cause deterioration of the semipermeable membrane used in the semipermeable membrane module 1 if used as is.

[0027] The target liquid may be a liquid (such as an aqueous solution) containing a target substance. The target substance may be dissolved in the target liquid, or may be contained in a suspended state without being dissolved in the target liquid. The target substance contained in the target liquid and to be concentrated is not particularly limited, but may be, for example, a lithium compound (a compound containing lithium element).

[0028] Although the target liquid is alkaline, the target substance may be a compound that exhibits alkaline properties in liquid, such as LiOH or Li2CO3, or a component other than the target substance contained in the target liquid may be a compound that exhibits alkaline properties.

[0029] The target liquid is not particularly limited, but examples thereof include effluents containing lithium compounds such as LiOH and Li2CO3 (lithium effluents). When the target liquid is a liquid containing rare substances (rare metals), such as lithium effluent, and the rare substances are to be recovered from the target liquid, in order to increase the recovery efficiency and purity of the rare substances, it is desirable that the content of substances other than the rare substances in the concentrated liquid obtained by concentrating the target liquid be as low as possible. In addition, when the pH of the target solution is lowered using carbon dioxide (CO2) bubbling as described above, it is possible to prevent impurities from being mixed in with the pH-lowering agent when recovering the target substance from the concentrated target solution. Therefore, from the viewpoint of improving the recovery efficiency and purity of rare substances, it is preferable that the pH-lowering agent is CO2 and that the pH-lowering device is a device capable of bubbling CO2 into the target solution.

[0030] (feedback control) It is preferable that the pH-lowering device 3 has a control mechanism (feedback control mechanism) that measures the pH of the target liquid before and / or after adding the pH-lowering agent and adjusts the amount of pH-lowering agent to be added based on the measured value. For example, as shown in Fig. 1, by providing a pH sensor 41 and a pH sensor 42 in the pipes upstream and downstream of the pH-reducing device, respectively, it is possible to measure the pH of the target liquid before and after adding the pH-reducing agent. The feedback control mechanism of the pH-reducing device 3 is communicatively connected to the pH sensors 41 and 42 so that data on the measurements of the pH sensors 41 and 42 can be acquired.

[0031] The feedback control is performed, for example, so that the measured pH value of the target liquid after the addition of the pH-lowering agent (measured value of the pH sensor 42) is equal to or less than a predetermined threshold value that makes it difficult for the semipermeable membrane to deteriorate. For example, if the measurement value of the pH sensor 42 exceeds a threshold value, the pH-reducing device 3 may be controlled to increase the amount of pH-reducing agent added. If the measurement value of the pH sensor 42 is too low below the threshold value, the pH-reducing device 3 may be controlled to decrease the amount of pH-reducing agent added in order to reduce consumption. When performing such control (adjusting the amount of pH-lowering agent added), in order to take into account pH fluctuations of the target liquid due to changes in the composition of the target liquid, etc., the amount of pH-lowering agent added may be adjusted according to fluctuations in the measured pH of the target liquid before the pH-lowering agent is added (measured value of pH sensor 41).

[0032] Here, the pH of the target liquid is preferably measured in-line (without sampling the target liquid, etc.) to avoid instability of the membrane separation treatment due to sampling the target liquid, etc. [Explanation of symbols]

[0033] 1 Semipermeable membrane module, 2 Evaporation concentration device, 3 pH reduction device, 41, 42 pH sensors.

Claims

1. A concentrating system for concentrating an alkaline target liquid, comprising: a semipermeable membrane module having a semipermeable membrane and concentrating the target liquid by a membrane separation method; A concentration system comprising: a pH-lowering device that adds a pH-lowering agent to the target liquid supplied to the semipermeable membrane module.

2. The concentration system of claim 1, wherein the pH-lowering device measures the pH of the target liquid before and after adding the pH-lowering agent and has a control mechanism that adjusts the amount of the pH-lowering agent to be added based on the measured value.

3. The pH-lowering agent is CO ２ 2. The concentration system of claim 1, wherein:

4. The concentration system according to claim 1 , wherein the membrane separation method is at least one selected from reverse osmosis, forward osmosis, and osmotically assisted reverse osmosis.

5. Further provided with an evaporation and concentration device, The concentration system according to claim 1 , wherein the target liquid concentrated by the membrane separation method using the semipermeable membrane module is further concentrated by the evaporation concentration device.

6. The concentration system of claim 1 , wherein the target liquid contains a lithium compound.

7. The concentration system of claim 1 , wherein the semipermeable membrane comprises cellulose triacetate.

8. The concentration system according to claim 1 , wherein the semipermeable membrane is a hollow fiber membrane.

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