Ternary wastewater MVR evaporation mother liquor treatment process and system

Abstract

The invention provides a ternary wastewater MVR (Mechanical Vapor Recompression) evaporation mother liquor treatment process and system. The process comprises the following steps: (1) carrying out lithium precipitation and solid-liquid separation on ternary wastewater MVR evaporation mother liquor, and recovering solid lithium salt; (2) adjusting the water quality of the liquid obtained in the step (1) to be uniform, and recovering fluorine and phosphorus solids through first-stage phosphorus and fluorine removal, first-stage filter pressing and second-stage filter pressing; (3) carrying out advanced catalytic oxidation on the liquid obtained in the step (2), and then carrying out activated carbon adsorption to remove COD (Chemical Oxygen Demand) in the mother liquor; and (4) evaporating and crystallizing the liquid obtained in the step (3) to obtain a sodium sulfate product. According to the process, lithium is extracted from the MVR mother liquor to recover a lithium resource in the MVR mother liquor, then the wastewater is returned to MVR to be evaporated again after the procedures of phosphorus removal, fluorine removal and COD removal, and first-grade anhydrous sodium sulphate is completely formed to be sold. Through the process, the MVR mother liquor can be recycled to the maximum value, and the goal of'zero discharge 'of wastewater is really achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater recovery, and in particular relates to an MVR evaporation mother liquor treatment process and system. Background Art

[0002] In the zero-emission process of ternary wastewater treatment, MVR evaporation system is usually used to recover sodium sulfate in wastewater. After MVR evaporation, the wastewater is continuously concentrated, and lithium, fluorine, phosphorus, and COD in the wastewater are gradually enriched. This mother liquor affects the evaporation performance of MVR, which may cause corrosion and scaling, and affect the quality of sodium sulfate.

[0003] At present, most companies will regularly extract a certain amount of concentrated mother liquor from the MVR system into the drying system, and finally obtain impurity salts to maintain the impurity balance of the concentrated mother liquor, thereby ensuring the normal operation of the MVR system. After being treated by means of evaporation, drying and ozone reaction, the obtained impurity salts contain lithium, fluorine, phosphorus, COD, sodium sulfate, etc., which belong to general industrial solid waste and need to be transported out for treatment. The impurity salts cannot be separated and recovered separately. This process consumes a lot of energy and has no added value. Therefore, there is currently a lack of a graded recovery and treatment process for the ternary wastewater MVR evaporation mother liquor. Summary of the invention

[0004] The technical problem to be solved by the present invention is the treatment and recovery of MVR concentrated mother liquor, which overcomes the deficiencies and defects mentioned in the above background technology and provides a ternary wastewater MVR evaporation mother liquor treatment process and system.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A ternary wastewater MVR evaporation mother liquor treatment process comprises the following steps: (1) Evaporating the mother liquor of ternary wastewater MVR to precipitate lithium, separate the solid and liquid, and recover solid lithium salt.

[0006] (2) The liquid obtained in step (1) is homogenized, subjected to a first stage of phosphorus and fluorine removal, a first stage of filter pressing, a second stage of phosphorus and fluorine removal, and a second stage of filter pressing to recover fluorine and phosphorus solids.

[0007] (3) The liquid obtained in step (2) is subjected to advanced catalytic oxidation and then to activated carbon adsorption to remove COD in the mother liquor.

[0008] (4) Evaporating and crystallizing the liquid obtained in step (3) to obtain a sodium sulfate product and a recovered MVR evaporation mother liquor.

[0009] The advanced catalytic oxidation process can oxidize and decompose some simple macromolecular organic matter in water, and at the same time oxidize some complex organic matter into small molecular organic matter, making it easier to be adsorbed by activated carbon. Therefore, the present application adopts the advanced catalytic oxidation process followed by activated carbon adsorption, which can efficiently remove COD, and the two have a synergistic effect.

[0010] The content of macromolecular organic matter in the ternary wastewater MVR evaporation mother liquor wastewater is high. When activated carbon is used alone for adsorption, the macromolecular organic matter will adhere to the surface of the activated carbon layer after being adsorbed by the activated carbon, thereby preventing other organic matter from migrating to the inside of the activated carbon bed, reducing the adsorption capacity and pollution holding capacity of the activated carbon bed, and increasing the consumption of activated carbon and operating costs. On the contrary, the use of advanced catalytic oxidation technology and activated carbon synergistic treatment can convert macromolecular organic matter into small molecular organic matter, increase the migration depth of organic matter in the activated carbon bed, thereby improving the pollution holding capacity of activated carbon, reducing the consumption of activated carbon, and reducing operating costs.

[0011] Preferably, the ternary wastewater MVR evaporation mother liquor is the concentrated mother liquor in the MVR system after the ternary wastewater is evaporated and recovered by the MVR system; in the ternary wastewater MVR evaporation mother liquor, the lithium ion concentration is not less than 700 mg / L, the fluoride ion concentration is not less than 800 mg / L, the phosphorus ion concentration is not less than 800 mg / L, and the COD concentration is not less than 1000 mg / L.

[0012] Preferably, after the liquid water quality in step (2) is uniform, the liquid is naturally cooled to below 60°C before the first stage of phosphorus and fluorine removal is performed. The feed temperature of an ordinary plate and frame filter press should be controlled below 60°C. When the temperature is over 60°C, a high-temperature plate and frame filter press should be selected, thereby increasing the equipment investment cost.

[0013] Preferably, the lithium precipitation in step (1) adopts a lithium precipitation agent, and the lithium precipitation agent includes sodium carbonate and / or sodium phosphate. The first and second stage phosphorus and fluorine removal in step (2) adopt a phosphorus and fluorine removal agent, and the phosphorus and fluorine removal agent includes a calcium salt phosphorus and fluorine removal agent or a composite cationic inorganic polymer flocculant with aluminum ions as the core.

[0014] The dephosphorus and defluoridation agent of the present invention can be a calcium salt dephosphorus and defluoridation agent, which can remove phosphate and fluoride ions in water by chemical reaction to generate calcium phosphate and calcium fluoride precipitation. It can also be a composite cationic inorganic polymer flocculant with aluminum ions as the core, which mainly forms precipitates through coordination exchange, adsorption, ion exchange, complex precipitation and other action mechanisms to achieve the purpose of removing fluoride ions and phosphate ions in wastewater. Preferably, the advanced catalytic oxidation comprises one or more of ozone oxidation, Fenton reaction, electrocatalytic oxidation or UV photolysis.

[0015] Under the same technical concept, the present invention also provides a ternary wastewater MVR evaporation mother liquor treatment system, which includes a lithium precipitation system, a first-stage and second-stage phosphorus and fluorine removal systems, a catalytic oxidation system, an activated carbon adsorption system and an evaporation crystallization system connected in sequence.

[0016] Preferably, the lithium precipitation system includes a lithium precipitation tank, a lithium precipitation centrifuge and a lithium precipitation liquid regulating tank, and the lithium precipitation centrifuge is connected to the lithium precipitation tank and the lithium precipitation liquid regulating tank; the lithium precipitation liquid regulating tank adopts physical means to retain and stir to adjust the water volume and water quality; the stirring adopts air stirring and / or mechanical stirring, and the material of the mechanical stirring equipment includes one or more of steel-lined PPH, steel-lined rubber or steel-lined fiberglass.

[0017] Preferably, the first-stage and second-stage phosphorus and fluorine removal systems include a first-stage phosphorus and fluorine removal reaction tank, a first-stage filter press, a second-stage phosphorus and fluorine removal reaction tank and a second-stage filter press connected in sequence, and the first-stage filter press and the second-stage filter press are plate and frame filter presses.

[0018] Preferably, the evaporation crystallization system comprises a filter, a pre-evaporation liquid tank and an MVR system connected in sequence, and the filter is connected to an activated carbon adsorption system; the filter comprises a microfiltration-grade filter with automatic backwashing and / or without a backwashing device.

[0019] Preferably, the lithium precipitation tank, the post-lithium precipitation liquid regulating tank, the first-stage phosphorus and fluorine removal reaction tank, the first-stage post-filter press liquid tank, the second-stage phosphorus and fluorine removal reaction tank and the second-stage post-filter press liquid tank are made of one or more of PPH, fiberglass, steel-lined rubber, steel-lined fiberglass or concrete-lined anti-corrosion coating.

[0020] Compared with the prior art, the present invention has the following beneficial effects: In this process, the MVR mother liquor is first subjected to lithium extraction to recover the lithium resources therein, and then after the phosphorus removal, fluorine removal, and COD removal processes, the wastewater is returned to the MVR for re-evaporation, and all of them form the first-grade alum for sale. Through this process, the MVR mother liquor can be resourced with the greatest value, and the goal of "zero discharge" of wastewater can be truly achieved; the treatment process of the present invention has the advantages of great engineering significance, strong water quality pertinence, high treatment efficiency, stable operation, low investment and operating costs, and convenient operation and maintenance. The present invention removes phosphorus and fluorine from the MVR mother liquor to prevent the corrosion and scaling of the MVR system caused by the concentration of fluorine and phosphorus in the mother liquor, and can ensure the continuous and stable operation of the MVR system; the COD in the MVR mother liquor is removed, which can greatly reduce the foaming problem generated during the operation of the MVR system, reduce the addition of defoaming agents, reduce the operating costs, and reduce the impact of external agents on the quality of alum. After the implementation of the present invention, it is not necessary to regularly extract the MVR mother liquor for salt evaporation to maintain the balance of impurities, which not only reduces the investment in one-time equipment, but also reduces the steam consumption, and reduces the amount of salt treatment. Using the first and second stage phosphorus and fluorine removal processes, the effect of primary phosphorus and fluorine removal is generally not good, and it is difficult to achieve the removal rate described in the present invention. Secondary phosphorus and fluorine removal can meet the needs of actual production. After the advanced catalytic oxidation process, activated carbon adsorption is performed again. The removal rate of organic matter directly using activated carbon adsorption is up to about 70%, and solid waste will be generated after the activated carbon adsorption is saturated. The cost of activated carbon itself is also relatively high. In summary, first using an advanced catalytic oxidation process to remove a portion of organic matter and then performing activated carbon adsorption can improve the organic matter removal rate, reduce the generation of solid waste, and reduce operating costs. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 This is a schematic diagram of the mother liquor treatment system of a ternary wastewater MVR evaporation system.

[0022] In the figure: 1. evaporation mother liquor storage tank; 2. lithium precipitation tank; 3. lithium precipitation centrifuge; 4. lithium precipitation post-liquid regulating tank; 5. first-stage dephosphorization and defluorination reaction tank; 6. first-stage filter press; 7. first-stage post-filter pressure liquid tank; 8. second-stage dephosphorization and defluorination reaction tank; 9. second-stage filter press; 10. second-stage post-filter pressure liquid tank; 11. advanced catalytic oxidation device; 12. activated carbon adsorption device; 13. filter; 14. pre-evaporation liquid tank. DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] Embodiment 1: This embodiment adopts a ternary wastewater MVR evaporation mother liquor treatment system, as shown in the schematic diagram Figure 1 As shown, the system is connected to the MVR system and receives the lithium precipitation mother liquor derived from the MVR system 1; the system includes a lithium precipitation system, a first-stage and second-stage phosphorus and fluorine removal system, a catalytic oxidation system, an activated carbon adsorption system and an evaporation crystallization system connected in sequence. Specifically, the lithium precipitation system includes an evaporation mother liquor storage tank 1, a lithium precipitation tank 2, a lithium precipitation centrifuge 3, and a lithium precipitation post-liquid regulating tank 4; the first-stage and second-stage phosphorus and fluorine removal systems include a first-stage phosphorus removal and fluorine removal reaction tank 5, a first-stage filter press 6, a first-stage post-filtering liquid tank 7, a second-stage phosphorus removal and fluorine removal reaction tank 8, a second-stage filter press 9, and a second-stage post-filtering liquid tank 10; the catalytic oxidation system includes an advanced catalytic oxidation device 11, and the first-stage filter press 6 and the second-stage filter press 9 are plate and frame filter presses; the activated carbon adsorption system includes an activated carbon adsorption device 12; the evaporation crystallization system includes a filter 13 and a pre-evaporation liquid tank 14 connected in sequence, and the filter includes a microfiltration grade filter with automatic backwashing and / or without backwashing device. The materials of the lithium precipitation tank 2, the post-lithium precipitation liquid regulating tank 4, the first-stage phosphorus and fluorine removal reaction tank 5, the first-stage post-filter pressure liquid tank 7, the second-stage phosphorus and fluorine removal reaction tank 8 and the second-stage post-filter pressure liquid tank 10 are one or more of PPH, fiberglass, steel-lined rubber, steel-lined fiberglass or concrete-lined anti-corrosion coating.

[0027] The MVR evaporation mother liquor exported by the MVR system is 50.0m 3 / d, temperature about 90℃, Li + About 600mg / L, F + About 600mg / L, P 3+ About 500mg / L, COD about 1000mg / L, pH9-11, salt (sodium sulfate) about 20%.

[0028] The processing technology of this embodiment is: +The lithium ion concentration in the MVR evaporation mother liquor is about 700 mg / L, which can be reduced to below 70 mg / L after the treatment of the above invention, and the lithium recovery rate is greater than 90%.

[0029] The fluoride ion concentration in the MVR mother liquor is about 800 mg / L, which can be reduced to below 40 mg / L after the treatment of the above invention, and the fluoride removal rate is greater than 95%.

[0030] The phosphorus concentration in the MVR mother liquor is about 800 mg / L, which can be reduced to below 10 mg / L after the treatment of the above invention, and the phosphorus removal rate is greater than 98%.

[0031] The COD concentration in the MVR mother liquor is about 1000 mg / L, which can be reduced to below 150 mg / L after being treated by the above invention, and the phosphorus removal rate is greater than 85%.

[0032] After the evaporation mother liquor treated by the above invention, all of it is returned to the MVR system for evaporation and crystallization to obtain the glauber salt product, without the need to regularly discharge a certain amount of concentrated mother liquor and waste a large amount of steam energy for evaporation and crystallization, and what is obtained is worthless miscellaneous salts containing lithium, fluorine, phosphorus, COD, and sodium sulfate.

[0033] Comparative Example 1: The same treatment system as in Example 1 is used, and the remaining steps are consistent with Example 1, except that only the first-stage phosphorus and fluorine removal is used, and the second-stage phosphorus and fluorine removal is not used; the effluent is measured to contain about 80 mg / L of fluorine and about 20 mg / L of phosphorus.

[0034] Comparative Example 2: The same treatment system as in Example 1 was used, and the remaining steps were consistent with those in Example 1, except that the advanced catalytic oxidation step was not used; the COD measured in the effluent was almost not removed without advanced catalytic oxidation and activated carbon adsorption, the inlet COD was about 1000 mg / L, and the effluent COD was about 950 mg / L.

Claims

1. A ternary wastewater MVR evaporation mother liquor treatment process, characterized in that: The following steps are involved: (1) Evaporating the mother liquor of ternary wastewater MVR to precipitate lithium, separate the solid and liquid, and recover solid lithium salt; (2) homogenizing the liquid obtained in step (1), performing a first-stage dephosphorization and defluorination, a first-stage filter press, a second-stage dephosphorization and defluorination, and a second-stage filter press to recover fluorine and phosphorus solids; (3) subjecting the liquid obtained in step (2) to advanced catalytic oxidation and then to activated carbon adsorption to remove COD in the mother liquor; (4) Evaporating and crystallizing the liquid obtained in step (3) to obtain a sodium sulfate product and a recovered MVR evaporation mother liquor.

2. The treatment process according to claim 1, characterized in that: The ternary wastewater MVR evaporation mother liquor is the concentrated mother liquor in the MVR system after the ternary wastewater is evaporated and recovered by the MVR system; in the ternary wastewater MVR evaporation mother liquor, the lithium ion concentration is not less than 700 mg / L, the fluoride ion concentration is not less than 800 mg / L, the phosphorus ion concentration is not less than 800 mg / L, and the COD concentration is not less than 1000 mg / L.

3. The treatment process according to claim 2, characterized in that: After the liquid water quality in step (2) is uniform, the liquid is naturally cooled to below 60° C. before the first stage of phosphorus and fluorine removal is performed.

4. The treatment process according to claim 1, characterized in that: The lithium precipitation in step (1) adopts a lithium precipitation agent, and the lithium precipitation agent includes sodium carbonate and / or sodium phosphate. The first and second stage phosphorus and fluorine removal in step (2) adopt a phosphorus and fluorine removal agent, and the phosphorus and fluorine removal agent includes a calcium salt phosphorus and fluorine removal agent or a composite cationic inorganic polymer flocculant with aluminum ions as the core.

5. The treatment process according to claim 1, characterized in that: The advanced catalytic oxidation includes one or more of ozone oxidation, Fenton reaction, electrocatalytic oxidation or UV photolysis.

6. A ternary wastewater MVR evaporation mother liquor treatment system, characterized in that: The treatment system comprises a lithium precipitation system, a first-stage and a second-stage phosphorus and fluorine removal system, a catalytic oxidation system, an activated carbon adsorption system and an evaporation crystallization system which are connected in sequence.

7. The processing system according to claim 6, characterized in that The lithium precipitation system comprises an evaporation mother liquor storage tank (1), a lithium precipitation tank (2), a lithium precipitation centrifuge (3) and a lithium precipitation liquid regulating tank (4), wherein the lithium precipitation centrifuge (3) is connected to the lithium precipitation tank (2) and the lithium precipitation liquid regulating tank (4); the lithium precipitation liquid regulating tank (4) uses physical means to stop and stir to adjust the water volume and water quality; the stirring uses air stirring and / or mechanical stirring, and the material of the mechanical stirring equipment includes one or more of steel-lined PPH, steel-lined rubber or steel-lined fiberglass.

8. The processing system according to claim 6, characterized in that The first-stage and second-stage phosphorus and fluorine removal systems comprise a first-stage phosphorus and fluorine removal reaction tank (5), a first-stage filter press (6), a first-stage post-filter press liquid tank (7), a second-stage phosphorus and fluorine removal reaction tank (8), a second-stage filter press (9) and a second-stage post-filter press liquid tank (10) which are connected in sequence, wherein the first-stage filter press (6) and the second-stage filter press (9) are plate and frame filter presses.

9. The processing system according to claim 6, characterized in that The catalytic oxidation system comprises an advanced catalytic oxidation device (11), the activated carbon adsorption system comprises an activated carbon adsorption device (12), the evaporation crystallization system comprises a filter (13) and a pre-evaporation liquid tank (14) connected in sequence, the filter being connected to the activated carbon adsorption system; the filter comprises a microfiltration grade filter with an automatic backwashing device and / or without a backwashing device.

10. The processing system according to claims 7-9, characterized in that The lithium precipitation tank (2), the post-lithium precipitation liquid regulating tank (4), the first-stage phosphorus and fluorine removal reaction tank (5), the first-stage post-filter pressure liquid tank (7), the second-stage phosphorus and fluorine removal reaction tank (8) and the second-stage post-filter pressure liquid tank (10) are made of one or more materials selected from the group consisting of PPH, glass fiber reinforced plastics, steel-lined rubber, steel-lined glass fiber reinforced plastics or concrete-lined anti-corrosion coating.

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