A treatment method of lithium-containing wastewater generated in an acid leaching carbonization lithium precipitation process

Abstract

The application discloses a treatment method of lithium-containing wastewater generated in an acid leaching carbonization lithium precipitation process. Carbonization lithium precipitation mother liquor and carbonization lithium precipitation washing water generated in a carbonization lithium precipitation section are mixed, preheated and evaporated until lithium carbonate is precipitated, and after dehydration treatment of the material, solid lithium carbonate and secondary lithium mother liquor are obtained. The secondary lithium mother liquor is first added with concentrated sulfuric acid, then sodium hydroxide is added until weak alkalinity is obtained, and sodium precipitation raw water is obtained. The sodium precipitation raw water is evaporated until sodium sulfate is precipitated, and after solid-liquid separation, solid sodium sulfate and sodium precipitation mother liquor are obtained. The sodium precipitation mother liquor is subjected to freezing crystallization until sodium sulfate is crystallized and precipitated, and after separation, sodium sulfate crystals and frozen centrifugal mother liquor are obtained. The treatment method in the application can realize secondary production of industrial-grade lithium carbonate and even battery-grade product forms, and a larger proportion of sodium sulfate is produced in the form of yuanming powder products, while the consumption of sulfuric acid and sodium hydroxide is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy battery recycling, and particularly relates to a treatment method of lithium-containing wastewater generated in an acid leaching carbonization lithium precipitation process. BACKGROUND

[0002] At present, in the new energy industry, lithium carbonate is widely used as a battery material. With the development of the recycling economy mode such as reduction, reuse and resource, the production and recycling of lithium ion batteries have become an important part of the current new energy industry chain. At present, the production and recycling of lithium ion batteries mainly have two types of processes, namely, a fire method and a wet method. The fire method adopts high-temperature sintering of a rotary kiln as the core, and this process has large tail gas emission, high energy consumption and low product purity. Therefore, the production and recycling of lithium ion batteries generally adopt the wet method, especially the acid leaching technology of a sulfuric acid system, and lithium carbonate is taken as a core product. In this type of wet process, a large amount of lithium-containing wastewater is generated, and the reasonable resource recycling and classification treatment of this wastewater are particularly important for the operation efficiency and cost control of the process system. The common process of this wastewater is to first adjust the acid with sulfuric acid to convert lithium carbonate in the wastewater into lithium sulfate, and then enter an evaporation system for concentration to produce sodium sulfate for sale, and the lithium sulfate-rich liquid is returned to the front-end workshop for secondary use.

[0003] Chinese patent application document CN 109095481 A and CN 108075202 A disclose a comprehensive recovery method of lithium iron phosphate waste powder. The current common method for producing and recycling lithium ion battery materials by acid leaching carbonization and lithium precipitation is that after carbonization and lithium precipitation, the wastewater treatment process is direct acidification, pH adjustment, and then evaporation of sodium sulfate. The following disadvantages exist: (1) neither of the two methods considers the specific salt separation process of the dissolved lithium carbonate product and the byproduct sodium sulfate in the carbonization and lithium precipitation mother liquor, and the efficient recovery method of the product; (2) the total amount of the water body of the mother liquor and washing water after carbonization and lithium precipitation is large (usually, 1 ton of lithium carbonate product corresponds to 20-25 m³ of wastewater), the raw water is directly adjusted with acid and then adjusted in pH, the consumption of sulfuric acid and sodium hydroxide is large, and the concentrated sulfuric acid contains impurities, which are brought into the system in large amounts, increasing the cost of impurity removal and being not conducive to the stable operation of the process; (3) after the lithium carbonate is directly added with acid and adjusted in pH, sodium sulfate and lithium sulfate mixed salt evaporation and concentration are carried out, and when the lithium concentration in the system reaches a certain concentration, further concentration needs to be stopped to avoid the precipitation of lithium sulfate salt together with sodium sulfate salt to form mixed salt and discharge the system. The above-mentioned process inventions do not further separate and recover the lithium carbonate in the carbonization and lithium precipitation raw water, and the total amount of lithium in the wastewater system is high. Since the concentration needs to be stopped when the lithium concentration in the evaporation system reaches a certain concentration, the amount of concentrated concentrated liquid (sodium precipitation mother liquor) is larger. The sodium precipitation mother liquor needs to enter the refrigeration section for further removal of sodium sulfate (only the process of CN 109095481 A considers that the liquid after crystallization is generated, and the design is to return to the calcium and magnesium process, and the problem of the influence of the liquid after crystallization on the removal of sodium sulfate is not considered, which affects the smooth progress of the front process and the quality of the carbonization and lithium precipitation product). The amount of sodium precipitation mother liquor is large, the refrigeration section has a large burden, the energy consumption is high, the production of sodium sulfate decahydrate is high, and the amount of reverse dissolution treatment is larger. SUMMARY

[0004] In order to overcome the problems in the prior art, the present application provides a treatment method for lithium-containing wastewater generated in an acid leaching carbonization and lithium precipitation process, which realizes efficient and high-purity salt separation and recovery of lithium carbonate and sodium sulfate. The method can realize secondary production of industrial-grade and even battery-grade lithium carbonate products, and a larger proportion of sodium sulfate is produced in the form of yuanming powder, while reducing the consumption of sulfuric acid and sodium hydroxide.

[0005] To solve the above technical problems, the technical scheme provided by the present application is as follows:

[0006] The present application provides a treatment method for lithium-containing wastewater generated in an acid leaching carbonization and lithium precipitation process, which includes the following steps:

[0007] S1, mixing carbonization and lithium precipitation mother liquor produced in the carbonization and lithium precipitation section and carbonization and lithium precipitation washing water to obtain raw water.

[0008] S2, evaporating the preheated raw water to precipitate lithium carbonate, maintaining the system balance after the sodium sulfate in the solution is close to saturation, and obtaining solid lithium carbonate and secondary lithium mother liquor after dehydration treatment of the material.

[0009] S3, adding concentrated sulfuric acid to the secondary lithium mother liquor to convert the carbonate in the solution into sulfate, then adding sodium hydroxide to adjust to weak alkaline to obtain sodium precipitation raw water.

[0010] S4, evaporating the sodium precipitation raw water to precipitate sodium sulfate, maintaining the system balance, and obtaining solid sodium sulfate and sodium precipitation mother liquor after dehydration treatment of the material.

[0011] S5, freezing and crystallizing the sodium precipitation mother liquor to precipitate sodium sulfate crystals, and obtaining ten-water sodium sulfate crystals and frozen centrifugal mother liquor after separation, the frozen centrifugal mother liquor is returned to the front end of the carbonization and lithium precipitation section to perform lithium precipitation operation again.

[0012] In the carbonization and lithium precipitation section, two types of lithium-containing water bodies are produced, the first is carbonization and lithium precipitation mother liquor, and the second is carbonization and lithium precipitation washing water, the volume ratio is about 1:1, and the salt components mainly include sodium sulfate, lithium carbonate and sodium carbonate. In the present application, the lithium carbonate in the mother liquor and washing water is saturated concentration, and the solubility is low, about 13 g / L. After mixing the mother liquor and washing water, the concentration of sodium sulfate is about 150-180 g / L, and the sodium carbonate is excessive (generally more than 1%-3%) added in the carbonization and lithium precipitation process and remains. Because the solubility is high, its influence can be ignored in this salt separation step.

[0013] The mother liquor is mixed with the washing water to obtain raw water, and the raw water is preheated and evaporated. Since the lithium carbonate salt in the raw water is in a saturated solution state, the lithium carbonate salt is continuously precipitated during the heating and evaporation process, and the sodium sulfate salt is continuously concentrated. During the evaporation process, when it is determined that the sodium sulfate solution is close to saturation, the material is discharged and dehydrated, and solid lithium carbonate and the solution (secondary lithium mother liquor) after centrifugation are obtained after solid-liquid separation. The secondary lithium mother liquor is added with concentrated sulfuric acid for acid adjustment treatment, and the sulfuric acid reacts with lithium carbonate and sodium carbonate in the mother liquor to convert the carbonate into lithium sulfate and sodium sulfate, so that the pH of the solution after the acid adjustment is 5-6. Then, sodium hydroxide is added to neutralize the excess sulfuric acid so as to evaporate in a weak alkaline environment, the pH is about 8-10, and the obtained solution is the sodium precipitation raw water. The sodium precipitation raw water is preheated and evaporated. Since the sodium sulfate in the sodium precipitation raw water is in a saturated solution state, the sodium sulfate salt is continuously precipitated during the evaporation process, and the lithium sulfate salt is continuously concentrated. When the solid-liquid volume ratio reaches 15-20%, the material is discharged and dehydrated, and solid sodium sulfate and sodium precipitation mother liquor are obtained after solid-liquid separation. The solid sodium sulfate salt is collected as an industrial-grade sodium sulfate product through subsequent drying and packaging equipment, and the control index is that the water content is less than 0.5% and the lithium content is less than 0.1%. The solubility of lithium sulfate is relatively high, and a large amount of lithium sulfate is not precipitated. The obtained sodium precipitation mother liquor is frozen and crystallized until sodium sulfate is precipitated. Most of the precipitated sodium sulfate is sodium sulfate decahydrate. After the freezing is completed, centrifugal dehydration is performed to obtain sodium sulfate decahydrate crystals and a frozen centrifugation mother liquor. The sodium sulfate decahydrate crystals enter the anti-dissolution system for anti-dissolution. The sodium sulfate concentration in the frozen centrifugation mother liquor is less than 30 g / L, and the lithium sulfate concentration is greater than 110 g / L. The frozen centrifugation mother liquor is returned to the front end of the carbonization and lithium precipitation for a first lithium precipitation operation. Thus, the treatment of the lithium-containing wastewater is completed.

[0014] As an optional embodiment, in the treatment method provided by the present application, the Na2SO4 in the raw water is 150-180 g / L, the Na2CO3 is 2-9 g / L, the Li2CO3 is 11-13 g / L, and the NaCl is 10-100 mg / L.

[0015] As an optional embodiment, in the treatment method provided by the present application, in step S2, when the solution density is 1.20-1.22 g / cm3, it is determined that the sodium sulfate solution is close to saturation.

[0016] In the present application, due to the presence of sodium carbonate, lithium carbonate and other components, the saturated solubility of sodium sulfate under this working condition is about 380 g / L, and the density of the mixed solution is 1.20-1.22 g / cm3. Therefore, the saturation of the sodium sulfate solution can be determined according to the density of the solution.

[0017] As an optional embodiment, in the treatment method provided by the present application, in step S2, another determination method is that when the sodium ion concentration in the solution is 120-122 g / L, the feeding and evaporation rates of the system are balanced.

[0018] The temperature rising in the present application is a continuous steady process, one side evaporates, one side feeds, reaches the concentration, one side feeds, one side evaporates, and one side discharges.

[0019] As an optional embodiment, in the treatment method provided by the present application, in step S2, the raw water is evaporated at 83-87℃; in step S4, the sodium-precipitating raw water is evaporated at 88-92℃.

[0020] Evaporating the raw water at 83-87℃ in the present application can effectively reduce the scaling phenomenon in the lithium carbonate evaporation crystallization process, and the lower temperature can also save energy. Evaporating the sodium-precipitating raw water at 88-92℃ is conducive to reducing energy consumption.

[0021] As an optional embodiment, in the treatment method provided by the present application, in step S2, the material is further concentrated and then centrifuged to remove water, and the solid lithium carbonate obtained is washed with water and dried to a purity of ≥99.6%, and the lithium carbonate salt product can be directly recovered in this step.

[0022] As an optional embodiment, in the treatment method provided by the present application, in step S4, after evaporating to a solid-liquid volume ratio (specifically, the volume ratio after sampling and clarifying) of 15-20%, the system feeding and evaporation rate are maintained in balance, then the material is further concentrated and centrifuged to remove water, and the solid sodium sulfate obtained is dried and used as industrial sodium sulfate, and the lithium content of the industrial sodium sulfate is <0.1%.

[0023] As an optional embodiment, in the treatment method provided by the present application, in step S4, when the concentration of lithium sulfate in the sodium-precipitating mother liquor reaches 110-125g / L, part of the sodium-precipitating mother liquor is refluxed to the evaporation system, and the remaining part is subjected to freeze crystallization treatment.

[0024] In the present application, the sodium-precipitating raw water is evaporated at a temperature of 88-92℃ to a solid-liquid ratio of 15-20%, and sodium sulfate is precipitated, obtaining a sodium-precipitating mother liquor. When the concentration of lithium sulfate in the sodium-precipitating mother liquor exceeds 125g / L, the lithium content in the sodium sulfate salt obtained by evaporation crystallization may exceed the standard, so when it is detected that the concentration of lithium sulfate in the sodium-precipitating mother liquor reaches 110-125g / L, part of the sodium-precipitating mother liquor is discharged from the system to the freezing section to reduce the lithium concentration in the evaporation system.

[0025] As an optional embodiment, in the treatment method provided by the present application, in step S5, the temperature for freeze crystallization is -5℃-5℃.

[0026] As an optional embodiment, in the treatment method provided by the present application, in step S5, the freeze crystallization time is 1.5-3h.

[0027] As an optional implementation, in the treatment method provided by the application, in step S5, the refrigerated centrifugal mother liquor is returned to the front end of the carbonization lithium precipitation operation after chlorine removal by the nanofiltration membrane, and the lithium precipitation operation is performed again, and the concentrated sodium chloride water generated by the nanofiltration membrane chlorine removal is subjected to dry evaporation treatment.

[0028] In the lithium carbonate preparation and recovery process system, trace amounts of other impurity ions are inevitably brought in, for example, sodium carbonate added in the carbonization lithium precipitation process, and sodium chloride inevitably exists in the preparation process of sodium carbonate, therefore, in the refrigerated centrifugal rear end in the application, the nanofiltration membrane equipment is introduced, the chlorine ion content in the refrigerated centrifugal mother liquor is detected, the nanofiltration membrane equipment is regularly operated to remove chlorine, and the concentrated sodium chloride water generated is subjected to dry evaporation in the evaporation kettle.

[0029] As an optional implementation, in the treatment method provided by the application, in step S2, a two-stage evaporator series and forced circulation pump external circulation form evaporation system is used in the evaporation process to evaporate lithium carbonate; in the evaporation system, the evaporator, the crystallization separator, the circulation pipeline and the discharge pipeline are mirror panels or are subjected to polishing treatment; and the evaporator, the crystallization separator and the circulation pipeline are all provided with ultrasonic generators.

[0030] As an optional implementation, in the treatment method provided by the application,

[0031] Compared with the prior art, the application has the following beneficial effects:

[0032] (1) The lithium-containing wastewater after the carbonization lithium precipitation section of the lithium ion battery material is reasonably classified and recovered in the application, lithium carbonate is secondarily produced in the form of a battery-grade product, and sodium sulfate is produced in a larger proportion in the form of a yuanming powder product, so that efficient and high-purity recovery of lithium carbonate and sodium sulfate is realized, respectively.

[0033] (2) The total amount of wastewater is reduced by more than 50% after the first evaporation, and more than 70% of the lithium carbonate salt is precipitated after the first evaporation, so that the total consumption of sulfuric acid and sodium hydroxide is reduced in the acid adjusting process, the consumption of sulfuric acid and sodium hydroxide is reduced, and the material cost and the operation cost are reduced.

[0034] (3) In the application, lithium carbonate is first evaporated to directly produce lithium carbonate products, the evaporation cost is less than 4,000 yuan, the lithium carbonate products obtained can directly generate high economic benefits, and the loss of lithium carried away in sodium sulfate caused by the method of directly separating lithium sulfate and sodium sulfate in the prior art is avoided.

[0035] (4) Because the lithium carbonate is very easy to scale in the evaporation crystallization process, the lithium carbonate industry generally evaporates and crystallizes lithium sulfate or concentrates lithium carbonate solution at present. In the present application, a two-stage evaporator is used in series and an external circulation pump is used in the evaporation system, and the mirror plate or polishing treatment is used in the evaporator, crystallization separator, circulation pipeline and discharge pipeline in the evaporation system, and an ultrasonic generator is arranged to evaporate the lithium carbonate salt directly, which can effectively prevent scaling. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0037] Figure 1 The process flow diagram of the lithium-containing wastewater in the present application. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present application, the following will combine the drawings of the specification and the preferred embodiments to make a more comprehensive and detailed description of the present application, but the protection scope of the present application is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all the professional terms used in the following have the same meaning as generally understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing the specific embodiments, and are not intended to limit the protection scope of the present application.

[0040] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0041] Example 1

[0042] A treatment method of lithium-containing wastewater generated in an acid leaching carbonization lithium precipitation process, the process flow is as shown in Figure 1 The method comprises the following steps:

[0043] (1) After the carbonization lithium precipitation reaction of a certain lithium iron phosphate battery recovery system, the Na + concentration of 60.3 g / L, Li + concentration of 2.46 g / L, SO4 2- concentration of 121.7 g / L, CO3 2- concentration of 13.2 g / L, Cl -30 ppm, i.e. Na2SO4 in raw water is about 180 g / L, residual Na2CO3 is about 4.6 g / L, Li2CO3 is about 13 g / L, and NaCl is about 60 mg / L.

[0044] (2) Take 2 portions of the raw water, each 1 L.

[0045] (3) Take one portion of the raw water, and evaporate it by negative pressure heating according to the process of the present application. After heating, a small amount of white precipitate is produced. The evaporation temperature is controlled at 84°C, and the vacuum degree is about 46 KPa. The density of the solution is detected during the evaporation process. When the density reaches 1.20 g / cm3, stop heating, and keep the temperature, filter and dry. At this time, the residual solution is about 500 ml, and about 8.9 g of lithium carbonate solid is obtained. The Li + concentration is 1.55 g / L (i.e. Li2CO3 is 8.2 g / L), and the Na + concentration is about 121 g / L (Na2SO4 is about 360 g / L, and Na2CO3 is 9.2 g / L).

[0046] (4) Pour the residual solution (i.e. secondary lithium mother liquor) into a beaker, and add H2SO4 to react with lithium carbonate and residual sodium carbonate, and fully stir to adjust the pH value to 5-6, to produce lithium sulfate and sodium sulfate, and consume 8 g of sulfuric acid. After adjusting the acid, the volume is about 505 ml. At this time, the sodium sulfate concentration is about 370 g / L.

[0047] (5) Add flake alkali to adjust the pH to 9 (trace amount, 0.02 g), to obtain 505 ml of sodium-precipitated raw water.

[0048] (6) Pour the 505 ml solution into a flask again to perform secondary negative pressure heating evaporation concentration. The evaporation temperature is 88°C, and the vacuum degree is about 36 KPa. When the Li + concentration is 14 g / L (i.e. Li2SO4 is 110 g / L), stop concentration, keep the temperature, filter and dry. At this time, the residual solution (sodium-precipitated mother liquor) is about 56 ml. The Na + concentration in the residual solution is about 129.6 g / L, and about 164 g of sodium sulfate solid is obtained. The Li + concentration in the sodium-precipitated mother liquor is about 0.02%.

[0049] (7) Put the sodium-precipitated mother liquor into a freezer, and maintain the temperature at 0°C. After 2 hours, take it out, filter to obtain 52 g of mirabilite, and 27 ml of filtrate. The Li + concentration in the filtrate is 29 g / L, and the Na + concentration is 1.6 g / L.

[0050] Example 2

[0051] A treatment method for lithium-containing wastewater produced in an acid leaching carbonization lithium precipitation process, and the process flow is as followsFigure 1 As shown, comprising the following steps:

[0052] (1) a lithium iron phosphate battery recycling system, carbonization lithium precipitation reaction, detection of the mother liquor and wash water composition of the raw water Na + concentration of 49.5g / L, Li + concentration of 2.46g / L, SO4 2- concentration of 103.3g / L, CO3 2- concentration of 11.7g / L, Cl - 6ppm, that is, the raw water Na2SO4 about 150g / L, residual Na2CO3 about 2.1g / L, Li2CO3 about 13g / L, NaCl about 10mg / L.

[0053] (2) take the original water 2, each 1L.

[0054] (3) take one of the raw water, according to the process of the present application, using negative pressure heating evaporation, after heating, there is a little white precipitate, evaporation temperature control in 84℃ (vacuum degree about 48KPa), evaporation process detection solution density, to 1.22g / cm³, stop heating, heat preservation filtration drying, at this time, the residual liquid amount is about 405ml, get lithium carbonate solid about 9.7g. Detection of residual liquid Li + concentration of 1.55g / L (i.e. Li2CO3 for 8.2g / L), Na + concentration of about 122g / L (Na2SO4 about 370g / L, Na2CO3 for 5.2g / L).

[0055] (4) take this residual liquid (i.e. secondary lithium mother liquor) pour into beaker, add H2SO4 and lithium carbonate, residual sodium carbonate reaction, and fully stirred to adjust the pH value to 5~6, lithium sulfate and sodium sulfate, the consumption of sulfuric acid is 6.5g, adjust the volume of about 409ml after acid. At this time, the concentration of sodium sulfate is about 373g / / L.

[0056] (5) add piece of alkali to adjust the pH to 10 (trace), get 409 ml of sodium precipitation raw water.

[0057] (6) the 409 ml solution is poured into the flask again for secondary negative pressure heating evaporation concentration, evaporation temperature 92 degrees Celsius, vacuum degree about 26KPa, to Li + concentration of 16g / L (i.e. Li2SO4 for 125.7g / L) stop concentration, heat preservation filtration drying, at this time, the residual liquid (sodium precipitation mother liquor) amount is about 27ml, detection of residual liquid Na + concentration of about 129.6g / L, get sodium sulfate solid about 142g, salt detection of Li + about 0.08%.

[0058] (7) The sodium precipitation mother liquor is placed in a freezer cabinet and maintained at 5°C for 3 hours, and then filtered to obtain mirabilite 23 g and filtrate 15 ml. The Li + concentration is detected as 28.8 g / L, the Na + concentration is detected as 2.3 g / L.

[0059] Example 3

[0060] A treatment method of lithium-containing wastewater generated in an acid leaching carbonization lithium precipitation process, a process flow as shown in the figure, comprising the following steps: Figure 1

[0061] (1) A certain lithium iron phosphate battery recycling system, after the carbonization lithium precipitation reaction, the Na + concentration in the original water composed of the mother liquor and washing water is 54.4 g / L, the Li + concentration is 2.08 g / L, the SO4 2- concentration is 105.5 g / L, the CO3 2- concentration is 14 g / L, and the Cl - concentration is 12 ppm, that is, the Na2SO4 in the original water is about 156 g / L, the residual Na2CO3 is about 9 g / L, the Li2CO3 is about 11 g / L, and the NaCl is about 20 mg / L.

[0062] (2) Take 2 portions of the original water, each 1 L.

[0063] (3) Take one portion of the original water, and use negative pressure heating evaporation according to the process of the present application. After heating, a small amount of white precipitate is generated, the evaporation temperature is controlled at 87°C (vacuum degree is about 39 KPa), the solution density is detected during the evaporation process, and when the density is 1.22 g / cm3, heating is stopped, and the solution is filtered and dried after heat preservation. At this time, the residual solution is about 422 ml, and lithium carbonate solid is about 7.6 g. The Li + concentration in the residual solution is 1.51 g / L (that is, the Li2CO3 is 8 g / L), and the Na + concentration is about 129 g / L (Na2SO4 is about 370 g / L, and Na2CO3 is 21.3 g / L).

[0064] (4) Pour the residual solution (i.e. the second lithium mother liquor) into a beaker, add H2SO4 to react with lithium carbonate and residual sodium carbonate, and fully stir to adjust the pH value to 5-6 to generate lithium sulfate and sodium sulfate. The sulfuric acid consumption is 13 g, and the volume after acid adjustment is about 429 ml. At this time, the sodium sulfate concentration is about 398 g / L.

[0065] (5) Add flake alkali to adjust the pH to 9 (trace), and obtain sodium precipitation original water 429 ml.

[0066] ​(6) The 429 ml solution was poured into the flask again for secondary negative pressure heating evaporation concentration, the evaporation temperature was 90 degrees Celsius, the vacuum degree was about 31 KPa, and the Li + concentration was 15 g / L (i.e. Li2SO4 was 117.9 g / L) to stop concentration, and the residual liquid (sodium precipitation mother liquor) was about 43 ml, and the Na + concentration was about 129.6 g / L, and about 153.5 g of sodium sulfate solid was obtained, and the salt detection contained Li + about 0.06%.

[0067] (7) The sodium precipitation mother liquor was placed in a freezer and frozen, the temperature was maintained at -5°C, and after 1.5 hours, 39 g of mirabilite was obtained by filtration, the filtrate was 21 ml, the Li + concentration detection was 30.7 g / L, and the Na + concentration detection was 1.6 g / L.

[0068] In summary, the lithium carbonate concentration / saturation concentration in the raw water is greater than the sodium sulfate concentration / saturation concentration, that is, it has the feasibility of evaporating and collecting lithium carbonate salt in advance, and the following will further introduce the equipment used in the process of treating lithium-containing wastewater according to a production example and a comparative example:

[0069] (1) A certain lithium iron phosphate battery recycling production line adopts acid leaching carbonization to precipitate lithium, and a carbonization lithium precipitation section adopts 4 lithium precipitation kettles, and each kettle produces about 10 cubic meters of raw water and 10 cubic meters of washing water. The lithium precipitation of each device is 3 times, and the water body is 60 m³, that is, the mother liquor and raw water after carbonization lithium precipitation of the production line form its wastewater of 240 h / day. The Na + concentration in the wastewater was 60.5 g / L, the Li + concentration was 2.46 g / L, the SO4 2- concentration was 121.7 g / L, the CO3 2- concentration was 13.2 g / L, and the Cl - was 350 ppm, that is, the Na2SO4 in the raw water was about 180 g / L, the residual Na2CO3 was about 4.6 g / L, the Li2CO3 was about 13 g / L, and the NaCl was about 0.6 g / L.

[0070] (2) Preheat 1: The mixed wastewater (hereinafter referred to as raw water) is sent to the condensate (i.e. evaporated condensate) preheating plate heat exchanger for primary preheating through the feed pump (flow rate 10 m³ / h), and then enters the steam preheating tubular heat exchanger. After preheating, the temperature and live steam regulating valve are interlocked to control the wastewater heat exchange temperature, i.e. the feed temperature is 85°C, which meets the bubble point feed requirement.

[0071] (3) MVR evaporation 1: The system is designed as an evaporation system with double-stage evaporators in series and an external circulation pump. After preheating 1, the wastewater enters the upper part of the crystallization separator, and the raw water flows out from the middle pipe of the crystallization separator and enters the top of the first-stage tube evaporator. The first-stage heater has an area of 200 m2, and the inside of the tube is the wastewater solution, and the outside of the tube is the secondary steam (live steam during the start-up period). After passing through the first-stage heater, it flows out from the bottom and enters the bottom pipe of the forced circulation pump. After being pressurized by the forced circulation pump, it enters the bottom of the second-stage tube evaporator. The second-stage heater has an area of 300 m2, and the inside of the tube is the wastewater solution, and the outside of the tube is the secondary steam (live steam during the start-up period). After passing through the second-stage heater, it flows out from the top and returns to the upper part of the crystallization separator. The steam generated after entering the crystallization separator rises, and the liquid sinks. The rising steam is extracted from the top of the crystallization separator, enters the centrifugal steam compressor after passing through the steam washing tower, and is compressed to a temperature of 101°C, which is called secondary steam. The secondary steam is discharged from the outlet of the compressor, enters the shell side of the first-stage and second-stage tube evaporators for evaporation and heating, and is condensed and discharged from the bottom of the shell side of the first-stage and second-stage tube evaporators, which is called steam condensate. The amount of condensate is related to the evaporation capacity of the MVR evaporation 1 system, and the design evaporation speed is 5 m3 / h. The condensate is transported by the condensate discharge pump, exchanges heat with the raw water, and is discharged from the system to be reused before carbonization and lithium precipitation.

[0072] (4) Centrifugation: After the wastewater is concentrated by evaporation, white crystals are precipitated and enriched in the bottom of the crystallization separator. The crystals flow out from the bottom pipe of the crystallization separator, enter the circulating discharge pump, and are transported. A pipe density meter is installed on the discharge pipe. After passing through the density meter, the pipe is divided into two paths, one of which returns to the bottom of the crystallization separator, and the other of which goes to the double-stage thickener. When the pipe density meter displays 1.20-1.22 g / cm3, the sodium sulfate concentration is about 355-380 g / L, the circulating valve is closed to 30%, the discharge valve is opened to 50%, and the discharge continues to the double-stage thickener. After being concentrated by the thickener, the supernatant (secondary lithium mother liquor) is discharged from the side top of the thickener, and the flow rate is 5 m3 / h. The crystallized solid is enriched in the bottom of the thickener, and the small opening of the thickener bottom valve is continuously opened to discharge to the vertical scraper centrifuge (PZ1250 type). After centrifugation, the lithium carbonate wet salt is obtained, which is mixed with the first carbonization and lithium precipitation wet salt, dried by a disc dryer, and the lithium carbonate content is ≥99.6%. In this evaporation and centrifugation section, the parts in contact with the liquid, such as the evaporator, crystallization separator, circulating pipe, and discharge pipe, are treated with mirror surface or polishing, with a minimum requirement of Ra0.4. Ultrasonic generators are installed in the evaporator, crystallization separator, and circulating pipe.

[0073] (5) Acid adjustment: The secondary lithium mother liquor flow rate is 5 m3 / h, and the mother liquor tank with stirring and heat preservation is used for collection and storage. The acid adjustment feed pump is used to transfer the solution into the acid adjustment tank A / B, the single tank acid adjustment treatment capacity is 20 m3, 98% concentrated sulfuric acid 560 kg is uniformly injected into the acid adjustment tank to react with lithium carbonate and sodium carbonate, and the acid adjustment treatment is carried out. The acid adjustment tank is provided with a stirring driving device, a mixed defoaming integrated stirrer is designed to make the reaction stable and efficient, the single batch reaction time is short, and the control is about 45 min, and after the reaction is completed, the solution pH is 5-6.

[0074] (6) pH adjustment: After the acid adjustment, the solution is stored in the intermediate tank, the pH adjustment feed pump is used to transport the solution into the pH adjustment tank A / B, the single tank treatment capacity is 20 m3, 10 kg of sodium hydroxide is added into the single tank, the pH value is observed, and after stabilization, the value is not less than 9. The pH adjustment tank is provided with a stirring driving device, a high-efficiency multi-layer stirrer is designed to ensure that the single batch adjustment time is less than 30 min.

[0075] (7) Preheating 2: The solution after pH adjustment (hereinafter referred to as sodium precipitation raw water) is transported into the condensate water (i.e. evaporated condensate water) preheating plate heat exchanger for primary preheating, and then into the steam preheating tube heat exchanger. The temperature after preheating and the live steam regulating valve are connected in a chain, the waste water heat exchange temperature, i.e. the feed temperature is controlled to be 90°C, and the bubble point feed requirement is reached.

[0076] (8) MVR evaporation 2: The system is designed as a two-stage evaporator series and a forced circulation pump external circulation type evaporation system. After the preheating 2, the waste water enters the upper part of the crystallization separator, the raw water flows out from the middle part of the crystallization separator into the top of the first-stage tube heat exchanger. The first-stage heater has an area of 220 m2, the inside of the tube is the waste water solution, and the outside of the tube is the secondary steam (live steam during the start period). After passing through the first-stage heater, the solution flows out from the bottom into the forced circulation pump on the bottom pipe. After being pressurized by the forced circulation pump, the solution enters the bottom of the second-stage tube heat exchanger. The second-stage heater has an area of 330 m2, the inside of the tube is the waste water solution, and the outside of the tube is the secondary steam (live steam during the start period). After passing through the second-stage heater, the solution flows out from the top back to the upper part of the crystallization separator. The generated steam rises in the crystallization separator, the liquid sinks, the rising steam is extracted from the top of the crystallization separator, enters the centrifugal steam compressor after passing through the steam washing tower, and is compressed. The temperature of the steam rises by 16°C to reach 106°C, which is called secondary steam. The secondary steam is discharged from the outlet of the compressor, enters the shell side of the first-stage and second-stage tube heat exchangers for evaporation heating, and is discharged from the bottom of the shell side of the first-stage and second-stage tube heat exchangers after condensation, which is called steam condensate water. The amount of condensate water is related to the evaporation capacity of the MVR evaporation 2 system. In this embodiment, the maximum evaporation speed is designed to be 5.5 m3 / h. The condensate water is transported by the condensate water discharge pump, is discharged from the system after heat exchange with the raw water, and is used for recycling before carbonization and lithium precipitation or for cleaning.

[0077] (9) Centrifugation: After the wastewater is concentrated by evaporation, white crystals are precipitated and enriched at the bottom of the crystallization separator, and flow out from the bottom pipe of the crystallization separator into the circulating discharge pump for transportation. A sampling port is arranged on the discharge pipe, which is divided into two pipelines, one of which returns to the bottom of the crystallization separator, and the other of which goes to the double-stage thickening thickener. When the solid-liquid ratio of the sample reaches 15% to 20% at a certain time, the circulating valve is closed to 30%, and the discharge valve is opened to 50%. The discharge is continued until the thickener, and after being concentrated by the thickener, the supernatant (sodium precipitation mother liquor) is overflowed from the side top of the thickener to the mother liquor tank, and the crystallized solid is enriched at the bottom of the thickener. The discharge is continued by opening the thick kettle bottom valve at a small opening to the centrifuge (HR500 double-stage piston push centrifuge is designed). After centrifugation, sodium sulfate wet salt is obtained. It is transported to the vibrating fluidized bed for drying and ton bag packaging. A water curtain dust removal system is arranged, and the output of sodium sulfate salt is 1680 kg / h. The quality control index is that the water content is less than 0.5%, and the lithium content is less than 0.1%. After centrifugation, the mother liquor is discharged into the mother liquor tank and transported by the sodium precipitation mother liquor circulating discharge pump. It is divided into two pipelines, one of which returns to the system, and the other of which is discharged to the rear end of the refrigeration system. A flow meter is arranged on the discharge pipeline for metering, and the average discharge speed is 0.45 m³ / h. The actual discharge is intermittent according to the discharge condition, and the average discharge amount is controlled to be 10.8 m³ / day.

[0078] (10) Refrigeration crystallization: The sodium precipitation mother liquor is heat exchanged with the MVR evaporation 2 sodium precipitation raw water preheating heat exchanger by the sodium precipitation mother liquor circulating discharge pump, and the temperature of the sodium precipitation mother liquor is reduced to 50°C. Then it is sent to the mother liquor transfer tank, and is cooled to 35-38°C (not too low, to avoid sodium sulfate precipitation) by the refrigeration water heat exchanger cooler, and then is sent to the refrigeration crystallization kettle A / B. The single-kettle treatment capacity is 5 m³, and the refrigeration crystallization is carried out. The cold source is a 50 kW frequency conversion refrigerator unit, and the refrigeration temperature is adjustable from -5°C to 5°C. The inner wall of the refrigeration crystallization kettle is polished, and it is designed as a jacketed crystallization kettle with stirring. The single-kettle refrigeration crystallization time is controlled to be 3h. When the refrigeration time reaches the requirement, no crystals are precipitated in the kettle, and the refrigeration crystallization is completed.

[0079] (11) Centrifugation: After the refrigeration crystallization is completed, the mixed slurry in the refrigeration crystallization kettle is transported to the high double-stage piston push centrifuge (HR400 double push) by the discharge pump for centrifugal dewatering operation, and sodium sulfate decahydrate is obtained. The average output of sodium sulfate decahydrate is 380 kg / h, and the single-kettle output of sodium sulfate decahydrate is 4200 kg. The average amount of mother liquor after refrigeration is 0.235 m³ / h, and the single-kettle output of mother liquor is about 2.6 m³. The Li + concentration in the mother liquor is 26 g / L, and the Na + concentration is 14.6 g / L. The sodium sulfate decahydrate is re-dissolved and enters the MVR evaporation 2 system again, and the mother liquor is transported to the carbonization lithium precipitation front end for recycling, or can be selected to enter the rear-end nanofiltration membrane system.

[0080] (12) Nanofiltration membrane: The main process lithium carbonate deposition section uses sodium carbonate for lithium deposition. Due to the unavoidable presence of sodium chloride residues during sodium carbonate preparation, chloride ion impurities are introduced. Since this recovery is a zero-emission process, chloride ions will accumulate. In this embodiment, the chloride ion concentration in the mother liquor after freezing reaches 1280 ppm, with a flow rate of 5.64 m³ / day. This embodiment is equipped with a single-stage nanofiltration membrane, which can be selected for high-pressure filtration. The interception rate is set to a low value of 90%, and the generated sodium chloride concentrate is 30% of the influent. That is, when all the frozen mother liquor passes through the membrane system, approximately 1.7 m³ / day of sodium chloride concentrate is generated. The dilute water and wash water are transported to the front-end lithium carbonate deposition section.

[0081] (13) Evaporation of mixed salts: The sodium chloride concentrate produced by the nanofiltration membrane is stored in the intermediate concentrate tank. It is transported by a transfer pump and preheated by exchanging heat with the non-condensable gas of the MVR system through a plate heat exchanger. Then it is sent to a jacketed mixed salt evaporator with stirring for drying and evaporation. In this embodiment, the heat source in the jacket of the mixed salt evaporator is live steam. The inlet of the compressor in the front-end MVR process is connected to the evaporator. The generated steam is drawn into the compressor for reuse. At the same time, the compressor can draw a certain vacuum to keep the evaporation temperature at about 90°C, thereby improving the evaporation efficiency. After continuous concentration and drying, crystal slurry is produced. The solid-liquid ratio is measured by sampling. After reaching 20%, it is discharged from the bottom of the evaporator and sent to a centrifuge for centrifugation and dehydration. The mixed salts are packaged and collected, and the mother liquor is returned to the mixed salt evaporator for further evaporation.

[0082] Comparative Example 1

[0083] In a lithium iron phosphate battery recycling system, after the lithium carbonization precipitation reaction, the Na+ content in the raw water, composed of the mother liquor and wash water, is measured. + The concentration was 60.3 g / L, Li + The concentration was 2.46 g / L, SO4 2- The concentration was 121.7 g / L, CO3 2- The concentration was 13.2 g / L, Cl - The concentration is 30 ppm, which means that the raw water contains approximately 180 g / L of Na2SO4, approximately 4.6 g / L of residual Na2CO3, approximately 13 g / L of Li2CO3, and approximately 60 mg / L of NaCl.

[0084] (1) As a comparison with Example 1, another portion of the raw water was taken and reacted with lithium carbonate and residual sodium carbonate using a common process, namely, acid-adjusted evaporation process. The pH value was adjusted to 5 by stirring thoroughly, resulting in the production of lithium sulfate and sodium sulfate. The sulfuric acid consumed was 22g. The solution volume was 1022ml.

[0085] (2) Add caustic soda to adjust the pH to 9 (trace amount, 0.04g).

[0086] (3) Pour this solution into a flask and evaporate and concentrate it at room temperature until Li+ Concentration of 14 g / L (i.e. Li2SO4 110 g / L) stop concentrating, incubation filter drying, at this time, the residual liquid amount is about 175 ml, detection of residual liquid Na + Concentration of about 129.6 g / L, get about 110 g of sodium sulfate solid, detection of Li + About 0.02%.

[0087] (4) Put this solution into the freezer, the temperature is maintained at 0℃, after 1.5 hours, take out and filter to get sodium sulfate decahydrate (mirabilite) 148 g, Li + Concentration detection is 26 g / L.

[0088] According to the above, take 1L of the lithium iron phosphate battery wastewater after carbonization and lithium precipitation, ignoring the influence of trace impurities, experimental error, etc., the results are as follows:

[0089] The conventional process recycles 110 g of sodium sulfate, produces 175 ml of residual liquid into the refrigeration crystallization section, consumes 22 g of sulfuric acid, consumes 0.04 g of sodium hydroxide flake, and produces 133 g of mirabilite.

[0090] The process of the present application recycles 8.9 g of lithium carbonate and 164 g of sodium sulfate, produces 56 ml of residual liquid into the refrigeration crystallization section, consumes 8 g of sulfuric acid, consumes 0.02 g of sodium hydroxide flake, and produces 52 g of mirabilite.

[0091] Therefore, it can be seen that the present application has high recovery value, can directly recycle 68% of lithium carbonate in wastewater, the by-product sodium sulfate is 1.5 times that of the conventional process, the raw material consumption is low, the sulfuric acid consumption is about 36% of the conventional process, the alkali consumption is about 50% of the conventional process, and the mirabilite that needs to be returned to solution is only 39% of the conventional process.

[0092] The above content is a further detailed description of the present application in combination with a specific preferred embodiment, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be considered as belonging to the protection scope of the present application.

Claims

1. A method for treating lithium-containing wastewater produced in an acid leach carbonation lithium precipitation process, characterized by, The method comprises the following steps: S1, mixing carbonization and lithium precipitation mother liquor produced in the carbonization and lithium precipitation section and carbonization and lithium precipitation washing water to obtain raw water; Na2SO4 in the raw water is 150-180 g / L, Na2CO3 is 2-9 g / L, Li2CO3 is 11-13 g / L, and NaCl is 10-100 mg / L; S2, the raw water is preheated and evaporated at 83-87℃ until lithium carbonate is precipitated, the solution is close to saturation of sodium sulfate, and the system is balanced, the solution density is 1.20-1.22g / cm 3 The material is dewatered to obtain solid lithium carbonate and secondary lithium mother liquor; a double-stage evaporator is used in series and an external circulation pump is used in the evaporation system; the evaporator, the crystallization separator, the circulation pipeline and the discharge pipeline are mirror-faced or polished; an ultrasonic generator is arranged in the evaporator, the crystallization separator and the circulation pipeline. S3, adding concentrated sulfuric acid to the secondary lithium mother liquor to convert carbonates in the solution into sulfates, and then adding sodium hydroxide to adjust the pH to 8-10 to obtain sodium precipitation raw water; S4, evaporating the sodium precipitation raw water at a temperature of 88-92 ℃ until sodium sulfate is precipitated, maintaining system balance, and then dehydrating the material to obtain solid sodium sulfate and sodium precipitation mother liquor; specifically, after evaporation to a solid-liquid volume ratio of 15-20%, the system is kept in balance by adjusting the feeding and evaporation rate, and then the material is further concentrated and centrifuged to obtain solid sodium sulfate; when the concentration of lithium sulfate in the sodium precipitation mother liquor reaches 110-125 g / L, part of the sodium precipitation mother liquor is returned to the evaporation system, and the remaining part is subjected to freezing crystallization treatment; S5, freezing and crystallizing the sodium precipitation mother liquor until sodium sulfate is precipitated, and then centrifuging to obtain sodium sulfate crystals and frozen centrifugation mother liquor, which is returned to the front end of the carbonization and lithium precipitation section for lithium precipitation operation.

2. The method of claim 1, wherein the lithium-containing wastewater is treated by a method comprising: In step S2, the concentration of sodium sulfate is 360-370 g / L when the material is discharged and separated. ​ 3. The method of claim 1, wherein the lithium-containing wastewater is treated by a method comprising: In step S4, the solid sodium sulfate is dried and used as industrial sodium sulfate, and the lithium content of the industrial sodium sulfate is <0.1%. ​ 4. The method of claim 1, wherein the lithium-containing wastewater is treated by adding a coagulant to the wastewater. In step S5, the freezing crystallization temperature is -5 ℃ to 5 ℃.

5. The method of claim 1, wherein the lithium-containing wastewater is treated by a method comprising: adding a coagulant to the wastewater to form a coagulated wastewater; and separating the coagulated wastewater into a solid and a liquid. In step S5, the freezing crystallization time is 1.5-3 h.

6. The method of treating lithium-containing wastewater produced in an acid leach-carbonate precipitation-lithium precipitation process according to claim 1, wherein In step S5, the frozen centrifugation mother liquor is returned to the front end of the carbonization and lithium precipitation section for lithium precipitation operation after removing chlorine through a nanofiltration membrane, and the sodium chloride concentrated water produced by the nanofiltration membrane is subjected to drying and evaporation treatment.

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