Impurity-containing lithium fluoride mother liquor treatment method

Abstract

The invention discloses an impurity-containing lithium fluoride mother liquor treatment method which comprises the following steps: filtering the impurity-containing lithium fluoride mother liquor to remove impurities, carrying out replacement electrodialysis to remove salt, and sequentially carrying out reverse osmosis concentration, electrodialysis concentration and resin defluorination on lithium chloride feed liquid subjected to replacement electrodialysis to remove salt, so as to obtain high-quality lithium chloride mother liquor; sequentially carrying out reverse osmosis concentration and electrodialysis concentration on the potassium fluoride feed liquid subjected to replacement electrodialysis salt removal to obtain high-quality potassium fluoride mother liquor; and the diluted lithium fluoride mother liquor subjected to replacement electrodialysis salt removal is sequentially subjected to reverse osmosis concentration and resin weight removal, is softened and then flows back to replacement electrodialysis. The method is simple in treatment process, high in treatment efficiency, high in lithium ion and fluorine ion recovery rate and high in product mother liquor purity. The lithium fluoride mother liquor can be treated in a low-energy-consumption and pollution-free manner, lithium and fluorine resources of the lithium fluoride mother liquor can be effectively utilized, and secondary economic benefits can be generated.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium fluoride mother liquor resource recovery, and specifically relates to a method for treating lithium fluoride mother liquor containing impurities Background Art

[0002] Lithium fluoride is one of the key raw materials for the production of lithium hexafluorophosphate electrolyte for lithium batteries. With the rapid development of new energy vehicles, lithium batteries and other industries, the demand for lithium fluoride is also increasing, which has driven the continuous expansion of lithium fluoride production. The production capacity and output of lithium fluoride have shown a rapid growth trend in the past few years.

[0003] In the production process of lithium fluoride, considering the continuous enrichment of impurities, it is necessary to withdraw the mother liquor in a certain proportion, which makes it impossible to achieve long-term recycling of the mother liquor. The mother liquor withdrawing from the system is a saturated lithium fluoride liquid, which contains trace amounts of heavy metals and hardness and other impurity ions. Since lithium fluoride is slightly soluble, it cannot be further concentrated to increase the concentration, and trace impurity ions are difficult to remove, affecting the purity of lithium fluoride. At present, the impure lithium fluoride mother liquor is mainly removed by adding calcium salt to generate calcium fluoride precipitation, and then concentrated and evaporated into miscellaneous salts (generally recognized as solid waste) for outsourcing treatment, so as to achieve wastewater discharge that meets the standards. Considering that the lithium fluoride mother liquor contains a large amount of lithium and fluorine, it not only causes a waste of lithium resources, but also brings fluorine pollution risks to the environment. Chinese patent CN 115536044 A discloses a method for preparing industrial-grade lithium fluoride by recycling lithium fluoride mother liquor. The calcium and magnesium ions in the LiF mother liquor are first removed by an ion exchange system, and then the LiF mother liquor is converted into HF solution and LiOH solution by a bipolar membrane electrodialysis system. The HF solution and the LiOH solution are further reacted to prepare industrial-grade LiF. The low-concentration LiF solution is concentrated by reverse osmosis and returned to the bipolar membrane electrodialysis system. Although this method realizes resource utilization, since calcium fluoride is a sparingly soluble salt, the calcium ion concentration in the saturated lithium fluoride solution is extremely low (generally less than 0.5 mg / L). At this low concentration, the efficiency of removing calcium ions by resin is low, and a certain amount of lithium will be lost at the same time. In addition, since the mother liquor contains multiple heavy metals at ppb concentrations, it is also difficult to remove them simultaneously, resulting in continuous enrichment of heavy metals in the low-concentration LiF solution and accompanied by scaling of calcium fluoride, which ultimately leads to low purity of the prepared industrial-grade lithium fluoride and low lithium utilization. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of complex technology and low processing efficiency in the prior art, and to provide a method for treating lithium fluoride mother liquor containing impurities.

[0005] The technical solution of the present invention is summarized as follows:

[0006] A method for treating lithium fluoride mother liquor containing impurities comprises the following steps:

[0007] (1) filtering and removing impurities from the impure lithium fluoride mother liquor to obtain a filtered lithium fluoride mother liquor;

[0008] (2) removing salt by displacement electrodialysis by mixing a potassium chloride aqueous solution prepared by potassium chloride and product water, or a sodium chloride aqueous solution prepared by sodium chloride and product water, with the filtered lithium fluoride mother liquor to obtain a lithium chloride feed solution, a dilute lithium fluoride feed solution, and a potassium fluoride feed solution or a sodium fluoride feed solution, respectively;

[0009] (3) the lithium chloride feed solution is sequentially subjected to a second reverse osmosis concentration, a first electrodialysis concentration and resin defluorination to obtain a lithium chloride mother solution; the fresh water produced by the first electrodialysis concentration is combined with the lithium chloride feed solution and subjected to a second reverse osmosis concentration;

[0010] (4) subjecting the potassium fluoride liquid or sodium fluoride liquid to a third reverse osmosis concentration and a second electrodialysis concentration in sequence to obtain a potassium fluoride mother liquor or a sodium fluoride mother liquor; combining the fresh water produced by the second electrodialysis concentration with the potassium fluoride liquid or the sodium fluoride liquid to a third reverse osmosis concentration; subjecting the produced water of the third reverse osmosis concentration to a second and second reverse osmosis desalination, combining the concentrated water produced by the second and second reverse osmosis desalination with the potassium fluoride liquid or the sodium fluoride liquid to a third reverse osmosis concentration;

[0011] (5) the dilute lithium fluoride feed solution is sequentially concentrated by a first reverse osmosis method and deweighted and softened by a resin, the concentrated lithium fluoride feed solution after deweighting and softening is combined with the filtered lithium fluoride mother solution, and then salt removal is performed by displacement electrodialysis;

[0012] (6) The water produced by the first reverse osmosis concentration is combined with the water produced by the second reverse osmosis concentration, and desalinated by the first and second reverse osmosis processes; the concentrated water produced by the first and second reverse osmosis desalination processes is combined with the filtered lithium fluoride mother liquor, and salt is removed by replacement electrodialysis;

[0013] The product water of the second secondary reverse osmosis desalination is combined with the product water of the first secondary reverse osmosis desalination, and part of it is refluxed for replacement electrodialysis to remove salt and dissolve potassium chloride or sodium chloride.

[0014] The salt content of the dilute lithium fluoride solution is 200-300 mg / L.

[0015] The first reverse osmosis recovery rate is between 70% and 85%.

[0016] Advantages of the present invention:

[0017] The present invention has a simple treatment process, high treatment efficiency, high recovery rate of lithium ions and fluoride ions, and high purity of product mother liquor. The present invention converts slightly soluble lithium fluoride mother liquor into lithium chloride liquid and potassium fluoride liquid (or sodium fluoride liquid) with high solubility through replacement electrodialysis salt removal. The lithium chloride liquid and potassium fluoride liquid (or sodium fluoride liquid) are further concentrated into high-concentration, high-value-added industrial raw material liquid, which not only produces significant secondary economic benefits, but also can achieve pollution-free discharge in the entire link, and belongs to a typical clean production process. The present invention utilizes the characteristics of preferential migration of fluoride ions and lithium ions in the process of replacement electrodialysis salt removal, enriches trace impurity ions such as heavy metals and hardness in dilute lithium fluoride liquid, increases the concentration of impurity ions by reverse osmosis concentration, and then removes them by resin adsorption, solving the problem that low-concentration impurity ions in lithium fluoride mother liquor are difficult to remove. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of a method for treating lithium fluoride mother liquor containing impurities according to the present invention.

[0019] Figure 2 This is the water balance diagram of Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below through specific embodiments and accompanying drawings.

[0021] Example 1

[0022] A method for treating lithium fluoride mother liquor containing impurities, see Figure 1 , Figure 2 , including the following steps:

[0023] (1) filtering and removing impurities from the impure lithium fluoride mother liquor to obtain a filtered lithium fluoride mother liquor;

[0024] The filtration is carried out in two stages. The first stage uses a self-cleaning filter with a precision of 150μm, and the second stage uses a bag filter with a precision of 50μm. The filtration flow rate is 500m 3 / d.

[0025] The main impurities and ion contents are shown in Table 1:

[0026] Table 1

[0027]

[0028] (2) removing salt from the filtered lithium fluoride mother solution by displacement electrodialysis using a potassium chloride aqueous solution prepared from potassium chloride and product water to obtain a lithium chloride feed solution, a dilute lithium fluoride feed solution (the salt content of the dilute lithium fluoride feed solution is adjusted to 240 mg / L, and can also be any number between 200-300 mg / L, such as 200 mg / L, 220 mg / L, 260 mg / L, 280 mg / L, 300 mg / L) and a potassium fluoride feed solution;

[0029] The displacement electrodialysis adopts a four-compartment structure, and the polar water is a 2% sodium sulfate aqueous solution;

[0030] The potassium chloride aqueous solution is intermittently prepared. When the potassium ion concentration is less than 3812 mg / L or the chloride ion concentration is less than 3470 mg / L, the preparation is started. The potassium ion and chloride ion concentrations after preparation are shown in Table 2. The product water flow rate required for preparing the potassium chloride aqueous solution is 6.6 m 3 / d, the mass of potassium chloride is 1950kg / d;

[0031] The flow rates of lithium chloride solution, potassium fluoride solution and dilute lithium fluoride solution are 126.4m 3 / d, 116.9m 3 / d, 698.7m 3 / d.

[0032] The main ion content is shown in Table 2:

[0033] Table 2

[0034]

[0035] (3) the lithium chloride feed solution is sequentially subjected to a second reverse osmosis concentration, a first electrodialysis concentration and resin defluorination to obtain a lithium chloride mother solution; the fresh water produced by the first electrodialysis concentration is combined with the lithium chloride feed solution and subjected to a second reverse osmosis concentration;

[0036] The second reverse osmosis concentration operation pressure is 35 bar, the recovery rate is 70%, and the water production flow rate is 114.4m 3 / d, the concentrated water flow rate is 49.1m 3 / d;

[0037] First electrodialysis concentration, fresh water flow rate 37.1m 3 / d, concentrated water flow rate is 12.0m 3 / d; the resin defluorination flow rate is 12.0m 3 / d.

[0038] The main ion contents are shown in Table 3.

[0039] Table 3:

[0040]

[0041] (4) The potassium fluoride material is sequentially subjected to a third reverse osmosis concentration and a second electrodialysis concentration to obtain a potassium fluoride mother liquor (which can be used as a high-quality industrial raw material); the fresh water produced by the second electrodialysis concentration is combined with the potassium fluoride liquid to undergo a third reverse osmosis concentration; the produced water of the third reverse osmosis concentration is subjected to a second and second reverse osmosis desalination, and the concentrated water produced by the second and second reverse osmosis desalination is combined with the potassium fluoride liquid to undergo a third reverse osmosis concentration;

[0042] The third reverse osmosis concentration operation pressure is 35 bar, the recovery rate is 70%, and the water production flow rate is 116.6m 3 / d, concentrated water flow rate is 50.0m 3 / d;

[0043] The second electrodialysis concentrated fresh water flow rate is 38.0m 3 / d, concentrated water flow rate is 12.0m 3 / d;

[0044] The second stage reverse osmosis operating pressure is 13 bar, the recovery rate is 90%, and the product water flow rate is 104.9m 3 / d, the concentrated water flow rate is

[0045] 11.7m 3 / d. The main ion contents are shown in Table 4.

[0046] Table 4:

[0047]

[0048] (5) the dilute lithium fluoride feed solution is sequentially concentrated by a first reverse osmosis method and deweighted and softened by a resin, the concentrated lithium fluoride feed solution after deweighting and softening is combined with the filtered lithium fluoride mother solution; and salt removal is performed by replacement electrodialysis;

[0049] The first reverse osmosis operating pressure is 15 bar, the recovery rate is 80%, and the water production flow rate is 558.9m 3 / d, the concentrated water flow rate is 139.8m 3 / d; resin softening and weight removal flow rate is 139.8m 3 / d.

[0050] The main ion contents are shown in Table 5.

[0051] Table 5

[0052]

[0053] (6) The water produced by the first reverse osmosis concentration is combined with the water produced by the second reverse osmosis concentration to perform the first and second reverse osmosis desalination, and the concentrated water produced by the first and second reverse osmosis desalination is combined with the filtered lithium fluoride mother liquor to perform replacement electrodialysis desalination;

[0054] The product water of the second secondary reverse osmosis desalination is combined with the product water of the first secondary reverse osmosis desalination, and part of it is refluxed for replacement electrodialysis to remove salt and dissolve potassium chloride.

[0055] The first and second stage reverse osmosis desalination operating pressure is 15 bar, the recovery rate is 90%, and the product water flow rate is 606.0m 3 / d, concentrated water flow rate is 67.3m 3 / d;

[0056] The product water flow rate of the reflux replacement electrodialysis salt removal is 228.3m3 / d

[0057] The main ion contents are shown in Table 6.

[0058] Table 6:

[0059]

[0060] By replacing the potassium chloride of this embodiment with sodium chloride and remaining the same as this embodiment, the mother liquor containing lithium fluoride impurities can be treated, and the effect is similar to that of this embodiment.

Claims

1. A method for treating lithium fluoride mother liquor containing impurities, characterized in that The following steps are involved: (1) filtering and removing impurities from the impure lithium fluoride mother liquor to obtain a filtered lithium fluoride mother liquor; (2) removing salt by displacement electrodialysis by mixing a potassium chloride aqueous solution prepared by potassium chloride and product water, or a sodium chloride aqueous solution prepared by sodium chloride and product water, with the filtered lithium fluoride mother liquor to obtain a lithium chloride feed solution, a dilute lithium fluoride feed solution, and a potassium fluoride feed solution or a sodium fluoride feed solution, respectively; (3) the lithium chloride feed solution is sequentially subjected to a second reverse osmosis concentration, a first electrodialysis concentration and resin defluorination to obtain a lithium chloride mother solution; the fresh water produced by the first electrodialysis concentration is combined with the lithium chloride feed solution and subjected to a second reverse osmosis concentration; (4) subjecting the potassium fluoride liquid or sodium fluoride liquid to a third reverse osmosis concentration and a second electrodialysis concentration in sequence to obtain a potassium fluoride mother liquor or a sodium fluoride mother liquor; combining the fresh water produced by the second electrodialysis concentration with the potassium fluoride liquid or the sodium fluoride liquid to a third reverse osmosis concentration; subjecting the produced water of the third reverse osmosis concentration to a second and second reverse osmosis desalination, combining the concentrated water produced by the second and second reverse osmosis desalination with the potassium fluoride liquid or the sodium fluoride liquid to a third reverse osmosis concentration; (5) the dilute lithium fluoride feed solution is sequentially concentrated by a first reverse osmosis method and deweighted and softened by a resin, the concentrated lithium fluoride feed solution after deweighting and softening is combined with the filtered lithium fluoride mother solution, and then salt removal is performed by displacement electrodialysis; (6) The water produced by the first reverse osmosis concentration is combined with the water produced by the second reverse osmosis concentration to perform the first and second reverse osmosis desalination; the concentrated water produced by the first and second reverse osmosis desalination is combined with the filtered lithium fluoride mother liquor to perform replacement electrodialysis desalination; The product water of the second secondary reverse osmosis desalination is combined with the product water of the first secondary reverse osmosis desalination, and part of it is refluxed for replacement electrodialysis to remove salt and dissolve potassium chloride or sodium chloride.

2. The method for treating a lithium fluoride mother liquor containing impurities according to claim 1, characterized in that: The dilute lithium fluoride solution has a salt content of 200-300 mg / L.

3. The method for treating a lithium fluoride mother liquor containing impurities according to claim 1, characterized in that: The first reverse osmosis recovery rate is between 70% and 85%.

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