Lithium Extraction from Lithium-Containing Wastewater

Abstract

The present invention provides a lithium extraction process from lithium-containing wastewater, which comprises the following steps: low-temperature concentration and impurity removal: the lithium-containing wastewater stock solution is evaporated and concentrated by an evaporation crystallization device, so that the primary mixed salt in the stock solution is continuously precipitated and discharged, and the lithium-containing wastewater mother liquor is cyclically evaporated and concentrated to form a lithium concentrated solution and a primary vapor; chemical impurity removal: the lithium concentrated solution is mixed and stirred with an alkaline solution to generate a secondary mixed salt, a lithium concentrated mother liquor after impurity removal, and a secondary vapor; lithium precipitation reaction: the lithium concentrated mother liquor is mixed and stirred with a sodium carbonate solution and heated to generate a lithium carbonate precipitate, a lithium precipitation mother liquor, and a tertiary vapor; the lithium carbonate generated in the lithium precipitation reaction step is centrifugally filtered and washed to obtain a lithium carbonate product. With such an arrangement, the process is simple, no harmful by-products are generated, and the lithium recovery rate is high.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a process for extracting lithium from lithium-containing wastewater. Background Art

[0002] Oilfield brine is the oilfield water contained in underground oil wells during oil extraction. Oilfield water has the characteristics of large total amount and contains a large amount of salt minerals. In particular, oilfield brine also contains lithium, an element necessary for lithium salt products, and lithium resources are widely used in glass and ceramic manufacturing, alloy and primary aluminum production, lithium battery production, medicine and optical materials and other industries. With the development of new energy industry, the demand for lithium batteries is huge, and lithium is also called the "energy metal" of the 21st century. Therefore, the development and application of salt minerals, especially lithium elements, in oilfield brine will produce greater economic benefits.

[0003] At present, the main methods for extracting lithium from brine are: precipitation method, ion adsorption method, membrane separation, etc. or a combination of several of them. Among them, the precipitation method consumes a large amount of alkali and has a low lithium recovery rate, which is not suitable for treating low-lithium brine. The ion adsorption method is suitable for direct lithium extraction from low-lithium brine, but due to the large amount of brine to be treated, its water consumption, resin consumption, and power consumption increase accordingly, especially in areas where fresh water resources are relatively scarce. It is subject to certain restrictions. The problem with multi-stage membrane separation technology is that during the reverse osmosis concentration process, the membrane is prone to clogging or damage, and the cost of using the membrane is high.

[0004] Therefore, it is necessary to design a lithium extraction process for lithium-containing wastewater to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium extraction process for lithium-containing wastewater with a simple process, no harmful by-products and a high lithium recovery rate.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a lithium extraction process for lithium-containing wastewater, which comprises the following steps:

[0007] S1. Low-temperature concentration and impurity removal: The lithium-containing wastewater stock solution is evaporated and concentrated through an evaporation crystallization device, so that the primary mixed salt in the stock solution is continuously precipitated and discharged, and the lithium-containing wastewater mother liquor is cyclically evaporated and concentrated to form a lithium concentrate and a primary vapor. The evaporation temperature is 38°C to 60°C, the evaporation vacuum is -90kPa to -100kPa, and the lithium ion concentration in the lithium concentrate is 18g / L-22g / L;

[0008] S2, chemical impurity removal: mixing and stirring the lithium concentrate with an alkaline solution to generate a secondary mixed salt, a lithium concentrated mother liquor after impurity removal, and secondary steam;

[0009] S3, lithium precipitation reaction: the lithium concentrated mother liquor and the sodium carbonate solution are mixed, stirred and heated to generate lithium carbonate precipitate, lithium precipitation mother liquor and tertiary vapor;

[0010] S4, centrifugally filtering and washing the lithium carbonate generated in step S3 to obtain a finished lithium carbonate product;

[0011] Wherein, the lithium precipitation mother liquor is passed into the evaporation crystallization device after the pH is adjusted, and the washing water generated in the washing process in step S4 is passed into the evaporation crystallization device.

[0012] As a further improved technical solution of the present invention, the primary mixed salt is continuously separated through a crystallization recovery device, which includes a crystallization recovery pipeline and a recovery circulation pump and a hydrocyclone arranged in sequence on the crystallization recovery pipeline. A crystallization recovery loop is formed between the evaporation crystallization device, the recovery circulation pump and the hydrocyclone separator. The evaporated and concentrated crystal slurry is first pumped into the hydrocyclone separator through the recovery circulation pump for solid-liquid separation, and the separated liquid is re-introduced into the evaporation crystallization device for evaporation and concentration, and the separated crystals are discharged from the hydrocyclone separator.

[0013] As a further improved technical solution of the present invention, the primary mixed salt recovered by the crystallization recovery device is filtered and dehydrated by a centrifuge.

[0014] As a further improved technical solution of the present invention, the components removed by chemical impurity removal in step S2 are Mg2+ and Ca2+.

[0015] As a further improved technical solution of the present invention, in step S1, the evaporation vacuum degree is -95kPa to -98kPa.

[0016] As a further improved technical solution of the present invention, the pH of the lithium precipitation mother solution is adjusted to 4-8.

[0017] As a further improved technical solution of the present invention, the primary steam generated in step S1 is collected and used to provide heat for one or more steps of low-temperature concentration and impurity removal, chemical impurity removal or lithium precipitation reaction.

[0018] As a further improved technical solution of the present invention, in step S2, the reaction temperature of the chemical impurity removal reaction is room temperature.

[0019] As a further improved technical solution of the present invention, in step S3, the reaction temperature of the lithium precipitation reaction is 80°C-100°C, and in step S4, the temperature of the washing process is maintained at 80°C-100°C.

[0020] As a further improved technical solution of the present invention, a pretreatment step is also included before the low-temperature concentration and impurity removal: a lime milk solution is added to the lithium-containing wastewater to remove carbonate ions, the mass concentration of the lime milk solution is 20%-40%, and the mass ratio of the lime milk solution to the lithium-containing wastewater is 0.1-0.3.

[0021] It can be seen from the above technical scheme that the present invention can not only effectively remove salts such as sodium salts and potassium salts, but also concentrate lithium ions by setting a low-temperature concentration and impurity removal step, and the low-temperature concentration step can be carried out continuously, with high impurity removal efficiency and high degree of automation; magnesium salts, calcium salts, etc. are removed through a chemical impurity removal step, so that the lithium carbonate generated in the subsequent lithium precipitation step contains less impurities, and the rinse water generated by various parts of the process continues to be circulated together with the stock solution, reducing the by-products of the process and achieving the effect of clean production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a flowchart of a lithium extraction process for lithium-containing wastewater according to an embodiment of the present invention.

[0023] Figure 2 for Figure 1 Schematic diagram of the evaporation crystallization apparatus. DETAILED DESCRIPTION

[0024] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be appreciated by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work, all belong to the scope of protection of the present invention. If the specific conditions are not indicated in the embodiments, normal conditions are followed. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0025] Please refer to Figure 1 The flowchart of a lithium extraction process from lithium-containing wastewater in one embodiment is shown. In this embodiment, the lithium extraction process from lithium-containing wastewater includes the following steps:

[0026] The stock solution pretreatment step is: adding lime milk solution to the lithium-containing wastewater to remove carbonate ions, the mass concentration of the lime milk solution is 20%-40%, and the mass ratio of the lime milk solution to the lithium-containing wastewater is 0.1-0.3.

[0027] The stock solution pretreatment step is implemented by setting up a stock solution pretreatment device. The stock solution pretreatment device includes a lime milk stirring storage tank, a lime milk reactor and a centrifuge four. The lime milk stirring storage tank is used to prepare lime milk. The lime milk is boiled after being mixed with water, and is pumped into the lime milk reactor after cooling to room temperature. At the same time, the stock solution is passed into the lime milk reactor. After the stock solution and the lime milk react completely, it is passed into the lime milk filter. Centrifuge four is used to separate the calcium salt produced by the reaction from the stock solution. The working process of centrifuge four is liquid inlet-dehydration-rinsing-dehydration-slag discharge. After the stock solution is centrifuged and filtered, the rinsing water is pumped into the evaporation crystallization device by a pump for evaporation and crystallization.

[0028] Low-temperature concentration and impurity removal step: This step is implemented by a low-temperature concentration and impurity removal device. Specifically, the low-temperature concentration and impurity removal device includes a water inlet tank, an evaporation crystallization device and a centrifuge. The lithium-containing wastewater stock solution is evaporated and concentrated by the evaporation crystallization device, so that the primary mixed salt in the stock solution is continuously precipitated and discharged, and the lithium-containing wastewater mother liquor is cyclically evaporated and concentrated to form a lithium concentrate and a primary vapor. In this step, the evaporation temperature is 38°C to 60°C, preferably 55°C. The evaporation vacuum of the evaporation crystallization device is -90kPa to -100kPa, preferably -95kPa to -98kPa. The lithium ion concentration in the lithium concentrate after evaporation and concentration is 18g / L-22g / L. The main components excluded in the low-temperature concentration and impurity removal step are monovalent salts, such as Na + , K + Under the same temperature conditions, the solubility of Na salt and K salt is lower than that of lithium salt. Therefore, during low-temperature evaporation, Na salt and K salt precipitate before lithium salt, and lithium ions are concentrated.

[0029] For details, please refer to Figure 2 As shown, in this step, the evaporation crystallization device includes an evaporation tank 1 for evaporation crystallization, a stock solution circulation system 2, a heat pump system 3 for heating the stock solution, a crystal recovery device 5 connected to the evaporation tank 1, a condensation tank 6 connected to the evaporation tank, and a decompression device for decompressing the evaporation tank 1.

[0030] The evaporator 1 is provided with a stock solution inlet 11, a steam outlet 12, a stock solution circulation inlet 14 and a stock solution circulation outlet 13, a crystal slurry outlet 15 and a separation liquid inlet 16. The steam outlet 12 is arranged at the top of the evaporator 1 or near the top.

[0031] The primary mixed salt is continuously separated by the crystal recovery device 5, and the primary mixed salt recovered by the crystal recovery device is filtered and dehydrated by the centrifuge 1. Specifically, the crystal recovery device 5 includes a crystal recovery pipeline 51 and a valve 1 55, a recovery circulation pump 54, a hydrocyclone 53 and a valve 2 52 arranged in sequence on the crystal recovery pipeline 51, and a crystal recovery loop is formed between the evaporation tank 1, the recovery circulation pump 54 and the hydrocyclone 53. The evaporated and concentrated crystal slurry is first pumped into the hydrocyclone 53 through the recovery circulation pump 54 for solid-liquid separation, and the separated liquid is re-entered into the evaporation tank for evaporation and concentration, and the separated crystals are discharged from the hydrocyclone 53. Specifically, the crystal slurry outlet 15 is located at the bottom of the discharge part 1d, and the separation liquid inlet 16 is opened at the lower part of the evaporation tank 1. The hydrocyclone 53 is connected to the crystal discharge pipeline 56, and the crystal discharge pipeline 56 is provided with a discharge valve 57. The centrifuge 1 is connected to the crystal discharge pipeline 56, and the primary mixed salt is dehydrated by the centrifuge 1. The crystal recovery pipeline 51 is connected to the concentrated liquid discharge pipeline 58, on which a valve 59 is provided. When evaporation reaches the set time, the valve 2 52 on the crystal recovery pipeline 51 and the discharge valve 57 on the crystal discharge pipeline 56 are closed, and the valve 1 55 and valve 59 are opened to discharge the concentrated raw liquid.

[0032] The stock liquid circulation system 2 includes a stock liquid circulation pipeline 21 and an evaporation circulation pump 22 connecting the evaporation tank 1 and the heat pump system 3. The evaporation tank 1, the evaporation circulation pump 22, the heat pump system 3 and the stock liquid circulation pipeline 21 connected therebetween constitute a stock liquid heating evaporation circuit. The two ends of the stock liquid circulation pipeline 21 are respectively connected to the stock liquid circulation inlet 14 and the stock liquid circulation outlet 13 to circulate and evaporate the stock liquid in the evaporation tank 1. Preferably, the stock liquid circulation outlet 13 is located above the stock liquid circulation inlet 14. During operation, the stock liquid is passed into the evaporation tank 1 through the stock liquid inlet 11. After reaching the set liquid level, the stock liquid is circulated, heated and evaporated through the stock liquid heating evaporation circuit.

[0033] In this embodiment, the heat pump system 3 includes a compressor 32, a first heat exchanger 33 for heating the raw liquid, a throttling device 35, an air condenser 34, and a second heat exchanger (not shown) for condensing the steam. Preferably, the throttling device 35 is an expansion valve. In other embodiments, the throttling device can also be other throttling structures, such as a capillary tube. The compressor 32, the first heat exchanger 33, the air condenser 34, the throttling device 35 and the second heat exchanger are connected to form a loop through a heat exchange medium pipeline 31, and a heat exchange medium flows in the loop.

[0034] The first heat exchanger 33 of this embodiment is an external heat exchanger arranged outside the evaporation tank 1, preferably a plate heat exchanger, and can also be set as other types of heat exchangers as long as they are suitable for heating the raw liquid.

[0035] The air condenser 34 cools down the heat exchange medium after heat exchange with the raw liquid. After the evaporation stage, the heat exchange medium flows out of the first heat exchanger 33, absorbs a large amount of heat through the air cooling of the air condenser 34 and the throttling effect of the expansion valve 35, and then enters the second heat exchanger to cool the steam. After absorbing the heat of the steam, the heat exchange medium is re-formed into a gaseous state and enters the compressor 32 for recirculation.

[0036] The condenser 6 is connected to the steam outlet 12 through a steam pipe, so that the steam generated in the evaporator 1 enters the condenser 6 through the steam pipe for cooling. The second heat exchanger is arranged inside the condenser 6, preferably a tube-in-tube heat exchange tube; in other embodiments, the second heat exchanger can also be other heat exchangers, such as a coil heat exchanger.

[0037] The decompression device is used to evacuate the evaporation tank 1. The decompression device of this embodiment includes a centrifugal water pump 42 and a water ejector 41, wherein the centrifugal water pump 42, the water ejector 41 and the condensation tank 6 are connected to form a loop through a pipeline, and the water ejector 41 is connected to the second heat exchanger, and further connected to the evaporation tank 1. In other embodiments, the decompression device also selects other methods according to actual needs, which are not limited here.

[0038] Chemical impurity removal step: In this step, the lithium concentrate generated in the low-temperature concentration and impurity removal step is mixed and stirred with an alkaline solution to generate secondary mixed salt, lithium concentrated mother liquor after impurity removal, and secondary steam. Specifically, the alkaline solution is a sodium hydroxide solution, and the component removed in the chemical impurity removal step is Mg 2+ , Ca 2+ Under alkaline conditions, Mg 2+ , Ca 2+ The precipitate is formed through chemical reaction, and further, the lithium ions in the stock solution are further enriched. At the same time, the impurity salt is prevented from being precipitated simultaneously with the lithium carbonate in the lithium precipitation reaction step, so that the purity of the generated lithium carbonate is improved.

[0039] The chemical impurity removal step is implemented by setting up a chemical impurity removal device. The chemical impurity removal device includes a sodium hydroxide storage tank, an impurity removal reactor and a centrifuge 2, and the impurity removal reactor is connected to the centrifuge 1. The sodium hydroxide storage tank is used to prepare a sodium hydroxide solution, and the impurity removal reactor is used to react the lithium concentrated mother liquor with the sodium hydroxide solution. The reaction temperature of this step is room temperature.

[0040] Lithium precipitation reaction step: In this step, the lithium concentrated mother liquor is mixed with the sodium carbonate solution, stirred and heated to generate lithium carbonate precipitate, lithium precipitation mother liquor and tertiary vapor. In other embodiments, sodium carbonate can be replaced by other carbonates such as potassium carbonate, ammonium carbonate, ammonium bicarbonate, etc., which are not limited here.

[0041] The lithium precipitation reaction step is implemented by setting up a lithium precipitation device. The lithium precipitation device includes a sodium carbonate stirring storage tank, a lithium precipitation reactor, a heater, a centrifuge three and a washing machine. The lithium precipitation reactor is connected to the centrifuge two. The sodium carbonate stirring storage tank is used to prepare a sodium carbonate solution. The sodium carbonate solution and the lithium concentrated mother liquor after impurities are passed into the lithium precipitation reactor for lithium precipitation reaction. The reaction temperature of the lithium precipitation reaction is preferably 80°C-100°C. The generated lithium carbonate precipitate and the lithium precipitation mother liquor are passed into the centrifuge three for centrifugal dehydration to generate crude lithium carbonate. Further, the crude lithium carbonate is repeatedly rinsed and dehydrated by the washing machine and the centrifuge three to obtain a lithium carbonate product. Preferably, the temperature of the washing process is maintained at 80°C-100°C.

[0042] The lithium precipitation mother liquor generated in the lithium precipitation reaction step and the flushing water generated in the flushing process are introduced into the lime milk reactor after adjusting the pH, and the above steps are repeated together with the original solution. The pH adjustment process is implemented by setting a neutralization tank and a hydrochloric acid storage tank. The hydrochloric acid storage tank is used to prepare a hydrochloric acid solution, and the hydrochloric acid solution, the lithium precipitation mother liquor and the flushing water are introduced into the neutralization tank for pH adjustment. Preferably, the pH is adjusted to 4-8.

[0043] In this embodiment, the primary steam, secondary steam and tertiary steam generated in the low-temperature concentration and impurity removal step, the chemical impurity removal step and the lithium precipitation reaction step are directly condensed and recovered. In other embodiments, the above steam can be used to provide heat for one or more steps in the process.

[0044] The present invention also provides a mobile wastewater lithium extraction equipment for implementing the above-mentioned lithium extraction process of lithium-containing wastewater, which includes a container, a low-temperature concentration and impurity removal device, a chemical impurity removal device, and a lithium sinking device arranged in the container body. The structure and connection relationship of the low-temperature concentration and impurity removal device, the chemical impurity removal device, and the lithium sinking device are detailed in the above-mentioned lithium extraction process of lithium-containing wastewater, and will not be repeated here. The stock solution pretreatment device described in the above process can be arranged outside the container. In particular, the input end of the mobile wastewater lithium extraction equipment connected to the outside is only the stock solution water inlet pipe and the tap water water inlet pipe (for configuring hydrochloric acid solution, sodium carbonate solution, and sodium hydroxide solution) connected to the water inlet tank, and the output end is the sodium carbonate product and steam condensate outputted by the centrifuge three times. The cleaning water generated in the process and the mother liquor generated by each device can be recycled, and the products can be recovered. The equipment as a whole does not produce other harmful by-products, and the process is simple and clean.

[0045] In the present invention, a low-temperature concentration and impurity removal device, a chemical impurity removal device, and a lithium precipitation device are integrated in a container to form an overall movable device, which has good maneuverability, high internal equipment integration, is not restricted by the environment, and works stably and reliably. In addition, the boxes of various parts of the equipment are small in size and are arranged separately, which is convenient for disassembly and lifting transportation.

[0046] The above embodiments are only used to illustrate the present invention but not to limit the technical solutions described in the present invention. The understanding of this specification should be based on the technical personnel in the relevant technical field. Although this specification has described the present invention in detail with reference to the above embodiments, the technical personnel in the relevant technical field should understand that the technical personnel in the relevant technical field can still modify or replace the present invention with equivalents, and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A process for extracting lithium from lithium-containing wastewater, characterized in that: It includes the following steps: S1. Low-temperature concentration and impurity removal: The lithium-containing wastewater stock solution is evaporated and concentrated through an evaporation crystallization device, so that the primary mixed salt in the stock solution is continuously precipitated and discharged, and the lithium-containing wastewater mother liquor is cyclically evaporated and concentrated to form a lithium concentrate and a primary vapor. The evaporation temperature is 38°C to 60°C, the evaporation vacuum is -90kPa to -100kPa, and the lithium ion concentration in the lithium concentrate is 18g / L-22g / L; S2, chemical impurity removal: mixing and stirring the lithium concentrate with an alkaline solution to generate a secondary mixed salt, a lithium concentrated mother liquor after impurity removal, and secondary steam; S3, lithium precipitation reaction: the lithium concentrated mother liquor and the sodium carbonate solution are mixed, stirred and heated to generate lithium carbonate precipitate, lithium precipitation mother liquor and tertiary vapor; S4, centrifugally filtering and washing the lithium carbonate generated in step S3 to obtain a finished lithium carbonate product; Wherein, the lithium precipitation mother solution is passed into the evaporation crystallization device after the pH is adjusted, and the washing water generated in the washing process in step S4 is passed into the evaporation crystallization device; The evaporation crystallization device comprises an evaporation tank for evaporation crystallization, a stock solution circulation system, a heat pump system for heating the stock solution, a crystal recovery device connected to the evaporation tank, a condensation tank connected to the evaporation tank, and a decompression device for decompressing the evaporation tank; The crystal recovery device comprises a crystal recovery pipeline and a valve 1, a recovery circulation pump, a hydrocyclone and a valve 2 which are sequentially arranged on the crystal recovery pipeline, a crystal recovery loop is formed between the evaporator, the recovery circulation pump and the hydrocyclone, the crystal slurry outlet is located at the bottom of the discharge part, the separation liquid inlet is opened at the lower part of the evaporator, the hydrocyclone is connected to the crystal discharge pipeline, and a discharge valve is arranged on the crystal discharge pipeline; The heat pump system includes a compressor, a first heat exchanger for heating the raw liquid, a throttling device, an air condenser and a second heat exchanger for condensing the steam; The stock liquid circulation system comprises a stock liquid circulation pipeline and an evaporation circulation pump connecting the evaporation tank and the heat pump system. The evaporation tank, the evaporation circulation pump, the heat pump system and the stock liquid circulation pipeline connected therebetween constitute a stock liquid heating evaporation loop.

2. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: The crystallization recovery device recovers the obtained primary mixed salt, and the primary mixed salt is filtered and dehydrated by a centrifuge.

3. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: The component removed by chemical impurity removal in step S2 is Mg 2+ and Ca 2+ .

4. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: In step S1, the evaporation vacuum degree is -95 kPa to -98 kPa.

5. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: The pH of the lithium precipitation mother liquor is adjusted to 4-8.

6. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: The primary steam generated in step S1 is collected and used to provide heat for one or more steps of low-temperature concentration and impurity removal, chemical impurity removal or lithium precipitation reaction.

7. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: In step S2, the reaction temperature of the chemical impurity removal reaction is room temperature.

8. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: In step S3, the reaction temperature of the lithium precipitation reaction is 80°C-100°C, and in step S4, the temperature of the washing process is maintained at 80°C-100°C.

9. The lithium extraction process from lithium-containing wastewater according to claim 1, characterized in that: Before low-temperature concentration and impurity removal, a pretreatment step is also included: adding lime milk solution to the lithium-containing wastewater to remove carbonate ions, the mass concentration of the lime milk solution is 20%-40%, and the mass ratio of the lime milk solution to the lithium-containing wastewater is 0.1-0.3.

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