System and process for extracting lithium from salt lake

Abstract

The invention discloses a salt lake lithium extraction system and a process thereof, relates to the field of salt lake lithium extraction processes, and can solve the problems of low lithium extraction purity and low lithium extraction efficiency in salt lake lithium extraction in the prior art. The salt lake lithium extraction system comprises a pretreatment unit and a membrane treatment unit, wherein the pretreatment unit is used for discharging salt lake brine and removing impurities in the discharged salt lake brine; the membrane treatment unit is connected to the next station of the pretreatment unit and is used for intercepting divalent ions in the salt lake brine and adsorbing lithium ions in the salt lake brine; and the lithium salt production unit is connected to the next station of the membrane treatment unit and is used for preparing the lithium ions adsorbed by the membrane treatment unit into lithium salt.

Description

Technical Field

[0001] The present application relates to the field of salt lake lithium extraction technology, and specifically to a salt lake lithium extraction system and technology. Background Art

[0002] Lithium carbonate (Li2CO3) is one of the key materials for manufacturing lithium-ion batteries. With the rapid development of the global new energy industry, lithium-ion batteries are increasingly used in electric vehicles, energy storage systems and other fields, and the demand for lithium resources is also increasing rapidly. Lithium carbonate has become an important raw material for the production of lithium batteries due to its good electrochemical properties.

[0003] Lithium extraction from salt lakes is one of the important ways to obtain lithium resources. Salt lake brine contains a variety of cations and anions, mainly lithium ions (Li + ), sodium ion (Na + ), potassium ion (K + ), calcium ions (Ca 2+ ), magnesium ion (Mg 2+ ) and sulfate ions (SO4 2- ), chloride ion (Cl - ), carbonate ions (CO4 2- ) etc. Due to the complex composition of salt lake brine, these impurity ions will interfere with lithium ions during the lithium extraction process, making the extraction process more complicated. The water quality of different salt lakes varies greatly, so the lithium extraction process also needs to be optimized according to the characteristics of different salt lakes to effectively separate and purify lithium.

[0004] In the prior art, the main process steps for extracting lithium from salt lakes are usually to discharge salt lake brine into salt pans, concentrate the brine by natural evaporation, and thus extract lithium. During the evaporation process, the crystallization of impurities such as potassium salts and sodium salts contained in the salt lake brine will affect the purity of lithium extraction. Although different salts will crystallize successively at different concentrations and temperatures, when the brine concentration reaches a certain critical point, different salts may crystallize together. This eutectic phenomenon will cause the separation effect of lithium ions to deteriorate, thereby affecting the purity and extraction rate of lithium extraction. In addition, the process of salt pan evaporation requires continuous changes in the concentration and temperature of the brine to gradually precipitate various types of salts. The whole process takes a long time and is greatly affected by external conditions such as weather, and the time and efficiency of the process are difficult to control. Summary of the invention

[0005] To this end, the present application provides a salt lake lithium extraction system to solve the problems of low purity and low efficiency of lithium extraction in the prior art of salt lake lithium extraction.

[0006] In order to achieve the above objectives, this application provides the following technical solutions:

[0007] A salt lake lithium extraction system comprises a pretreatment unit for discharging salt lake brine and removing impurities in the discharged salt lake brine, a membrane treatment unit connected to the next station of the pretreatment unit and used for intercepting divalent ions in the salt lake brine and adsorbing lithium ions in the salt lake brine, and a lithium salt production unit connected to the next station of the membrane treatment unit and used for converting the lithium ions adsorbed by the membrane treatment unit into lithium salt.

[0008] Optionally, the pretreatment unit includes a raw brine tank for storing salt lake brine, a removal subunit connected to the next station of the raw brine tank and used to remove impurities in the salt lake brine, and the removal subunit is connected to the previous station of the membrane treatment unit.

[0009] Optionally, the impurity removal subunit includes an immersion ultrafiltration device connected to the next station of the raw brine tank and a magnesium removal resin device connected to the next station of the immersion ultrafiltration device, and the magnesium removal resin device is connected to the previous station of the membrane treatment unit.

[0010] Optionally, the membrane treatment unit includes a nanofiltration subunit connected to the next station of the pretreatment unit and used to intercept divalent ions in the salt lake brine, an adsorption and desorption subunit connected to the next station of the nanofiltration subunit and used to adsorb and desorb lithium ions in the salt lake brine, and a membrane concentration subunit connected to the next station of the adsorption and desorption subunit and used to concentrate the lithium solution, and the membrane concentration subunit is connected to the previous station of the lithium salt production unit.

[0011] Optionally, the nanofiltration subunit includes a first-level nanofiltration device connected to the next station of the pretreatment unit, a second-level nanofiltration device connected to the next station of the first-level nanofiltration device, a third-level nanofiltration device connected to the next station of the second-level nanofiltration device, and a fourth-level nanofiltration device connected to the next station of the third-level nanofiltration device. The fourth-level nanofiltration device is connected to the previous station of the adsorption and analysis subunit. The first-level nanofiltration device, the second-level nanofiltration device, the third-level nanofiltration device and the fourth-level nanofiltration device are all provided with nanofiltration membranes to intercept divalent ions in the salt lake brine step by step.

[0012] Optionally, the concentrated water intercepted by the secondary nanofiltration device is discharged into the water inlet of the primary nanofiltration device, and the concentrated water intercepted by the fourth-stage nanofiltration device is discharged into the water inlet of the third-stage nanofiltration device. Alkaline solution is added to the produced water of the first-stage nanofiltration device and the secondary nanofiltration device before being discharged into the next workstation, and acid solution is added to the produced water of the fourth-stage nanofiltration device before being discharged into the next workstation.

[0013] Optionally, the adsorption and analysis subunit includes an aluminum adsorption device connected to the next station of the nanofiltration subunit and used to adsorb lithium ions in the produced water of the nanofiltration subunit, the membrane concentration subunit includes a sand and gravel filter connected to the next station of the aluminum adsorption device and used to filter the desorption liquid of the aluminum adsorption device, an ultrafiltration device connected to the next station of the sand and gravel filter, and a desorption liquid reverse osmosis device connected to the next station of the ultrafiltration device, the desorption liquid reverse osmosis device is connected to the previous station of the lithium salt production unit, and the desorption liquid reverse osmosis device is connected to a pure water reverse osmosis device so that the produced water of the desorption liquid reverse osmosis device passes through the reverse osmosis of the pure water reverse osmosis device to produce pure water and concentrated water respectively.

[0014] Optionally, the lithium salt production unit includes an evaporation and concentration device connected to the next station of the membrane treatment unit and used to evaporate and concentrate the reverse osmosis concentrated water of the membrane treatment unit, and a lithium precipitation device connected to the next station of the evaporation and concentration device and used to convert the concentrated lithium liquid of the evaporation and concentration device into lithium carbonate, and a boron removal resin device is connected between the evaporation and concentration device and the lithium precipitation device.

[0015] Optionally, the three-stage nanofiltration device is connected to a five-stage nanofiltration device, so that the concentrated water intercepted by the three-stage nanofiltration device is discharged into the five-stage nanofiltration device, and the concentrated water intercepted by the three-stage nanofiltration device and the desalted water, the concentrated water of the pure water reverse osmosis device of the membrane concentration subunit and the lithium precipitation mother liquor of the lithium salt production unit are discharged into the five-stage nanofiltration device, the concentrated water intercepted by the five-stage nanofiltration device is discharged into the lithium precipitation device of the lithium salt production unit after evaporation concentration and boron removal, and the produced water of the five-stage nanofiltration device is discharged into the raw brine tank.

[0016] Optionally, the aluminum adsorption device is connected to an evaporative salt field into which the tail brine separated by the aluminum adsorption device is discharged to evaporate and precipitate sodium salt and mixed salt. The next station of the evaporative salt field is sequentially connected to a potassium chloride evaporation and crystallization device and a hot melt device to separate potassium salt from the mixed salt.

[0017] The present application also discloses a process for extracting lithium from a salt lake, comprising the following steps:

[0018] S1, pumping the salt lake brine in the salt lake into the original brine tank for storage;

[0019] S2, discharging the salt lake brine in the original brine tank into an immersion ultrafiltration device for filtration, and discharging the filtered salt lake brine into a magnesium removal resin device;

[0020] S3, discharge the salt lake brine filtered by the magnesium removal resin device into the primary nanofiltration device, the water produced by the primary nanofiltration device is discharged into the secondary nanofiltration device, the water produced by the secondary nanofiltration device is discharged into the tertiary nanofiltration device, the water produced by the tertiary nanofiltration device is discharged into the quaternary nanofiltration device, and the water produced by the quaternary nanofiltration device is discharged into the aluminum adsorption device;

[0021] Sodium hydroxide is added to the water produced by the first-stage nanofiltration device and the water produced by the second-stage nanofiltration device before entering the next station;

[0022] The concentrated water intercepted by the first-stage nanofiltration device is discharged into the salt lake;

[0023] The concentrated water intercepted by the secondary nanofiltration device flows back to the inlet water of the primary nanofiltration device;

[0024] The concentrated water from the three-stage nanofiltration device, the demineralized water, the concentrated water from the pure water reverse osmosis device of the membrane concentration subunit and the lithium precipitation mother liquor of the lithium precipitation device are discharged into the five-stage nanofiltration device together. The concentrated water intercepted by the five-stage nanofiltration device is discharged into the lithium precipitation device after evaporation concentration and boron removal, and the produced water from the five-stage nanofiltration device is discharged into the original brine tank;

[0025] The concentrated water intercepted by the fourth-stage nanofiltration device flows back to the inlet water of the third-stage nanofiltration device;

[0026] S4, the lithium ions adsorbed by the aluminum adsorption device are desorbed to form a desorption liquid, and the desorption liquid is discharged into a sand and gravel filter for filtration, the water produced by the sand and gravel filter is discharged into an ultrafiltration device, the water produced by the ultrafiltration device is discharged into a desorption liquid reverse osmosis device, and the reverse osmosis concentrated water of the desorption liquid reverse osmosis device is discharged into an evaporation concentration device, and the lithium solution concentrated by the evaporation concentration device is discharged into a lithium precipitation device after boron and magnesium removal;

[0027] The backwash water from the sand and gravel filter is discharged into the salt lake;

[0028] The water produced by the desorption liquid reverse osmosis device is treated by the pure water reverse osmosis device to produce pure water and concentrated water respectively. The concentrated water is used as the inlet water of the five-stage nanofiltration device.

[0029] After the aluminum adsorption device adsorbs lithium ions in the produced water of the four-stage nanofiltration device, the tail brine is discharged into the evaporative salt field. The tail brine is evaporated and crystallized in the evaporative salt field to first precipitate sodium chloride, and then precipitate a mixed salt of sodium chloride and potassium chloride. The mixed salt is evaporated, crystallized and hot-melted to obtain potassium chloride and miscellaneous salts.

[0030] S5, the lithium solution produces lithium carbonate through the lithium precipitation device, and the lithium precipitation mother liquor of the lithium precipitation device is discharged into the inlet water of the five-stage nanofiltration device;

[0031] S6, the lithium carbonate produced by the lithium precipitation device is centrifuged, dried, crushed and packaged.

[0032] Optionally, in step S2, the submerged ultrafiltration device and the magnesium removal resin device discharge their backwash water into the salt lake through backwashing; in step S5, the ultrafiltration device discharges its backwash water into the sand filter through backwashing.

[0033] Compared with the prior art, this application has at least the following beneficial effects:

[0034] First, the salt lake brine is discharged into the pretreatment unit, which removes impurities in the salt lake brine, including suspended matter, colloids and microorganisms, to prevent the subsequent membrane treatment unit from being contaminated. The pretreated salt lake brine enters the membrane treatment unit, which intercepts divalent ions to prevent the divalent ions from affecting the efficiency and purity of lithium extraction. The membrane treatment unit then enriches the lithium ions in the salt lake brine into the solution through a desorption process to form a lithium concentrate. The extracted lithium has higher purity and lower energy consumption. The lithium concentrate then enters the lithium salt production unit to generate lithium salt (lithium carbonate) in the lithium salt production unit.

[0035] In addition, through nanofiltration membrane separation + evaporation concentration process technology, sodium carbonate is extracted from the system as the raw material for the lithium precipitation device, saving the cost of purchasing sodium carbonate, thereby reducing operating costs and lithium extraction production costs; separating the sodium salt and potassium salt extraction process units from the main lithium extraction process can reduce the overall investment cost of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more intuitively illustrate the prior art and the present application, several exemplary drawings are given below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing the present application; for example, those skilled in the art are capable of easily making conventional adjustments or further optimizations to the addition / reduction / attribution division, specific shapes, positional relationships, connection methods, dimensional ratios, etc. of certain units (components) based on the technical concepts and exemplary drawings disclosed in the present application.

[0037] Figure 1 A schematic diagram of a salt lake lithium extraction system provided for one embodiment of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] In the description of the present application, expressions such as “including”, “comprising”, “having”, etc. also mean “not limited to” (certain units, components, materials, steps, etc.).

[0040] The present application discloses a salt lake lithium extraction system, comprising a pretreatment unit for discharging salt lake brine and removing impurities in the discharged salt lake brine, a membrane treatment unit connected to the next station of the pretreatment unit and used for intercepting divalent ions in the salt lake brine and adsorbing lithium ions in the salt lake brine, and a lithium salt production unit connected to the next station of the membrane treatment unit and used for converting the lithium ions adsorbed by the membrane treatment unit into lithium salt.

[0041] First, the salt lake brine is discharged into the pretreatment unit, which removes impurities in the salt lake brine, including suspended matter, colloids and microorganisms, to prevent the subsequent membrane treatment unit from being contaminated. The pretreated salt lake brine enters the membrane treatment unit, which intercepts divalent ions to prevent the divalent ions from affecting the efficiency and purity of lithium extraction. The membrane treatment unit then enriches the lithium ions in the salt lake brine into the solution through a desorption process to form a lithium concentrate. The extracted lithium has higher purity and lower energy consumption; the lithium concentrate then enters the lithium salt production unit, and lithium salt (lithium carbonate) is generated in the lithium salt production unit; compared with the traditional salt field evaporation method, the present application improves the purity and efficiency of lithium extraction through the synergistic effect of three main units.

[0042] It should be noted that the salt lake brine involved in this application mainly contains lithium ions (Li + ), sodium ion (Na + ), potassium ion (K + ), calcium ions (Ca 2+ ), magnesium ion (Mg 2+ ), sulfate ion (SO4 2- ), chloride ion (Cl - ), carbonate ions (CO3 2- ).

[0043] The pretreatment unit includes a raw brine tank for storing salt lake brine, a de-impurity sub-unit connected to the next station of the raw brine tank and used for removing impurities in the salt lake brine, and the de-impurity sub-unit is connected to the previous station of the membrane treatment unit.

[0044] In the treatment process of the pretreatment unit, first, the salt lake brine is stored in the raw brine tank. The raw brine tank is not only used to temporarily store the brine, but also to adjust the flow of the brine according to the process requirements to ensure the stability of the subsequent process. The impurity removal unit removes suspended matter, colloids and microorganisms;

[0045] The salt lake brine stored in the original brine tank can adjust the supply of salt lake brine discharged to the impurity removal unit according to the production progress. Since the concentration of various ions in the salt lake brine changes due to different seasons or sunny and rainy days in the salt lake, the original brine tank can also stabilize the concentration ratio of various ions in the stored salt lake brine, avoid directly discharging salt lake brine from the salt lake to the impurity removal unit, causing changes in the concentration of various ions in the salt lake brine in the system, causing additional burden on the membrane treatment unit, and affecting the final sodium carbonate production. Among them, the storage capacity of the original brine tank and the number of original brine tanks are determined according to actual conditions.

[0046] The impurity removal subunit comprises an immersion ultrafiltration device connected to the next station of the original brine tank and a magnesium removal resin device connected to the next station of the immersion ultrafiltration device, and the magnesium removal resin device is connected to the previous station of the membrane treatment unit.

[0047] In the impurity removal sub-unit, first, the salt lake brine flows from the original brine tank into the submerged ultrafiltration device, which effectively removes large particle impurities such as suspended matter, colloids, and microorganisms in the brine through the ultrafiltration membrane. The working principle of the submerged ultrafiltration device is based on membrane separation technology. The pore size of the ultrafiltration membrane is small, which can block larger impurities and avoid equipment blockage or membrane pollution caused by impurity accumulation. The advantage of submerged ultrafiltration technology also lies in its low energy consumption and high filtration efficiency, which is suitable for processing large amounts of brine; the brine treated by the ultrafiltration device flows into the magnesium removal resin device. Magnesium ions (Mg 2+ ) is one of the main interfering impurities in salt lake brine. Although it is also a divalent ion, it is difficult for nanofiltration membranes to effectively separate lithium ions and magnesium ions because its atomic radius is very close to that of lithium ions. If magnesium ions enter the subsequent lithium extraction process, they may mix with lithium ions and reduce the purity of lithium carbonate products. Magnesium removal resins selectively exchange with magnesium ions through the principle of ion exchange to ensure that magnesium ions are effectively removed before entering the membrane treatment unit.

[0048] It should be noted that the boron removal resin device can be a resin tank in which the boron removal resin is arranged, and the resin tank is provided with a fat pressing layer, a resin layer (boron removal resin), etc. The resin tank and the boron removal resin are both prior arts and will not be described in detail in this application; the magnesium removal resin device is the same as the boron removal resin device, and both use the resin tank to realize the ion exchange function of the resin.

[0049] The membrane treatment unit includes a nanofiltration subunit connected to the next station of the pretreatment unit and used to intercept divalent ions in the salt lake brine, an adsorption and desorption subunit connected to the next station of the nanofiltration subunit and used to adsorb and decompose lithium ions in the salt lake brine, and a membrane concentration subunit connected to the next station of the adsorption and desorption subunit and used to concentrate the lithium solution. The membrane concentration subunit is connected to the previous station of the lithium salt production unit.

[0050] During the treatment process of the membrane treatment unit, the salt lake brine is pretreated and then enters the nanofiltration unit to selectively intercept the divalent ions in the salt lake brine, mainly carbonate ions (CO3 2- ) and sulfate ions (SO4 2- ), after being filtered by the nanofiltration subunit, the treated brine enters the adsorption and analysis subunit, which selectively adsorbs lithium ions through the adsorption material, so that the lithium ions are enriched in the adsorption material. Subsequently, through the analysis operation, the lithium ions are desorbed from the adsorption material and enter the solution. This process separates the lithium ions from the large volume of brine to form a high-concentration lithium solution. The lithium solution enters the membrane concentration subunit for further concentration. The membrane concentration subunit uses membrane technologies such as reverse osmosis to discharge water from the lithium solution, further increase the concentration of lithium ions, form a lithium concentrate, and reduce the energy consumption of subsequent evaporation and concentration.

[0051] The nanofiltration subunit includes a first-level nanofiltration device connected to the next station of the pretreatment unit, a second-level nanofiltration device connected to the next station of the first-level nanofiltration device, a third-level nanofiltration device connected to the next station of the second-level nanofiltration device, and a fourth-level nanofiltration device connected to the next station of the third-level nanofiltration device. The fourth-level nanofiltration device is connected to the previous station of the adsorption and analysis subunit. The first-level nanofiltration device, the second-level nanofiltration device, the third-level nanofiltration device and the fourth-level nanofiltration device are all provided with nanofiltration membranes to intercept divalent ions in the salt lake brine step by step. The concentrated water intercepted by the second-level nanofiltration device is discharged into the water inlet of the first-level nanofiltration device, and the concentrated water intercepted by the fourth-level nanofiltration device is discharged into the water inlet of the third-level nanofiltration device. Alkaline solution is added to the produced water of the first-level nanofiltration device and the second-level nanofiltration device before being discharged into the next station, and acid solution is added to the produced water of the fourth-level nanofiltration device before being discharged into the next station.

[0052] The pH value of the influent of the primary nanofiltration device is relatively low, and some carbonate ions will be converted into bicarbonate ions (monovalent ions) at a lower pH value. Therefore, the primary nanofiltration device intercepts most of the sulfate ions and carbonate ions. In order to intercept bicarbonate ions, an alkaline solution (sodium hydroxide) is added to the produced water of the primary nanofiltration device (the influent of the secondary nanofiltration device) to convert the bicarbonate ions into carbonate ions (divalent ions) again, so that the secondary nanofiltration device can intercept carbonate ions. The secondary nanofiltration device also intercepts some sulfate ions that are not intercepted by the primary nanofiltration device again. The tertiary nanofiltration device The device and the four-stage nanofiltration device also intercept the divalent ions remaining in the produced water of the previous nanofiltration device, and improve the ion separation efficiency through the successive interception and filtration of the first, second, third and fourth nanofiltration devices; wherein, the effect of the alkaline solution added to the produced water of the second nanofiltration device is the same as that of the alkaline solution added to the produced water of the first nanofiltration device; since the produced water of the first nanofiltration device and the second nanofiltration device are both added with alkaline solution, the pH value of the salt lake brine is relatively large, and the produced water of the fourth nanofiltration device is added with acid solution to balance the pH value of the salt lake brine, so that the pH value of the salt lake brine is neutral, so as to meet the water inlet requirement of the adsorption and analysis subunit.

[0053] It should be noted that the influent refers to the salt lake brine entering the nanofiltration device (or other devices and equipment in the system of this application), the concentrated water refers to the salt lake brine intercepted by the nanofiltration device (or other devices and equipment in the system of this application), and the produced water refers to the salt lake brine passing through the nanofiltration membrane of the nanofiltration device (or other devices and equipment in the system of this application). The produced water will enter the next-level nanofiltration device or the next process equipment.

[0054] It should be noted that nanofiltration membranes and nanofiltration devices are existing technologies. The main function of nanofiltration membranes is to utilize their unique pore size and charge characteristics to selectively retain divalent ions (such as sulfate and carbonate) in salt lake brine while allowing monovalent ions to pass through.

[0055] The adsorption and analysis subunit includes an aluminum adsorption device connected to the next station of the nanofiltration subunit and used to adsorb lithium ions in the produced water of the nanofiltration subunit. The membrane concentration subunit includes a gravel filter connected to the next station of the aluminum adsorption device and used to filter the desorption liquid of the aluminum adsorption device, an ultrafiltration device connected to the next station of the gravel filter, and a desorption liquid reverse osmosis device connected to the next station of the ultrafiltration device. The desorption liquid reverse osmosis device is connected to the previous station of the lithium salt production unit. The desorption liquid reverse osmosis device is also connected to a pure water reverse osmosis device so that the produced water of the desorption liquid reverse osmosis device is subjected to reverse osmosis by the pure water reverse osmosis device to produce pure water and concentrated water respectively.

[0056] In the adsorption and analysis subunit, the produced water after being treated by the nanofiltration subunit enters the aluminum adsorption device. The aluminum adsorption device is filled with aluminum-based adsorbents. The aluminum-based adsorbents selectively adsorb lithium ions through the principle of ion exchange to separate lithium from brine. As the adsorbent gradually reaches saturation, desorption operation is performed to separate lithium ions from the adsorbent to form a desorption liquid rich in lithium ions. The desorption liquid then enters the membrane concentration subunit. The unit first performs a preliminary filtration on the desorption liquid through a sand and gravel filter to remove suspended particles and other large particle impurities in the desorption liquid. The filtered desorption liquid enters the ultrafiltration device. The ultrafiltration device further removes smaller particles and colloidal substances in the desorption liquid through the ultrafiltration membrane. The pore size of the ultrafiltration membrane is small, which can effectively filter out suspended matter and tiny particle impurities, further improving the purity of the desorption liquid. After the ultrafiltration treatment, the desorption liquid enters the desorption liquid reverse osmosis device. The desorption liquid reverse osmosis device uses high pressure to push water molecules through the reverse osmosis membrane, while retaining the ions (lithium ions) in the solution on the other side of the membrane, forming the reverse osmosis concentrated water of the desorption liquid reverse osmosis device, that is, lithium concentrated solution, and the water produced by the desorption liquid reverse osmosis device enters the pure water reverse osmosis device. The pure water reverse osmosis device uses the same reverse osmosis principle to produce pure water (for self-use) and concentrated water (used to add to the concentrated water retained by the three-stage nanofiltration device to form the inlet water of the five-stage nanofiltration device). The adsorption and analysis subunit not only improves the processing efficiency of the system and reduces energy consumption, but also ensures the high efficiency of the lithium extraction process and the high purity of the lithium salt product.

[0057] The lithium salt production unit comprises an evaporation and concentration device connected to the next station of the membrane treatment unit and used for evaporating and concentrating the reverse osmosis concentrated water of the membrane treatment unit, and a lithium precipitation device connected to the next station of the evaporation and concentration device and used for converting the concentrated lithium liquid of the evaporation and concentration device into lithium carbonate, and a boron removal resin device is connected between the evaporation and concentration device and the lithium precipitation device.

[0058] In the lithium salt production unit, the concentration of lithium concentrate and the production of lithium carbonate are achieved through evaporation concentration and lithium precipitation processes. First, the reverse osmosis concentrated water (lithium concentrate) from the membrane treatment unit (desorption liquid reverse osmosis device) enters the evaporation concentration device, which evaporates the water in the concentrated water by heating and evaporation to further concentrate the lithium concentrate; before the lithium concentrate enters the lithium precipitation device, the boron ions in the concentrated lithium solution are removed by the boron removal resin device, and the boron ions in the lithium solution are selectively adsorbed and removed by the ion exchange effect of the boron removal resin; after boron removal, the concentrated lithium solution enters the lithium precipitation device, in which sodium carbonate (Na2CO3) solution is added, lithium ions react with carbonate ions to generate lithium carbonate precipitate (Li2CO3), and the precipitated lithium carbonate is processed through solid-liquid separation, centrifugation, drying, crushing and other steps to finally form a high-purity lithium carbonate product.

[0059] Among them, the boron removal resin is arranged at the tail of this system. In this way, the liquid volume of the salt lake brine gradually decreases after the steps of filtration, interception and concentration of the impurity removal subunit, nanofiltration subunit, adsorption and analysis subunit and lithium precipitation device, which can reduce the use of the boron removal resin.

[0060] It should be noted that the lithium precipitation device is an existing technology, which usually includes a precipitation reactor, a stirring device, a solid-liquid separation device and a drying device, etc. The lithium precipitation device generates lithium carbonate precipitation by the reaction of sodium carbonate and lithium ions. The reaction process is controlled by many factors such as temperature and alkali concentration to ensure that a high-purity lithium carbonate product is finally obtained; the sand and gravel filter, ultrafiltration device and reverse osmosis device (including desorption liquid reverse osmosis device and pure water reverse osmosis device) are all existing technologies; the evaporation concentration process can be achieved by existing technologies such as multiple-effect evaporation technology or MVR (mechanical vapor recompression), and can also be evaporated and concentrated by ordinary evaporators.

[0061] The three-stage nanofiltration device is connected to the five-stage nanofiltration device, so that the concentrated water intercepted by the three-stage nanofiltration device is discharged into the five-stage nanofiltration device, and the concentrated water intercepted by the three-stage nanofiltration device, the desalted water, the concentrated water of the pure water reverse osmosis device of the membrane concentration subunit and the lithium precipitation mother liquor of the lithium salt production unit are discharged into the five-stage nanofiltration device, the concentrated water intercepted by the five-stage nanofiltration device is discharged into the lithium precipitation device of the lithium salt production unit after evaporation concentration and boron removal, and the produced water of the five-stage nanofiltration device is discharged into the original brine tank.

[0062] The concentrated water intercepted by the tertiary nanofiltration device contains carbonate ions. The concentrated water intercepted by the tertiary nanofiltration device is added with desalted water, concentrated water from a pure water reverse osmosis device and a lithium precipitation mother liquor. The lithium precipitation mother liquor is rich in sodium carbonate. The desalted water and concentrated water from the pure water reverse osmosis device are used to dilute the concentrated water intercepted by the tertiary nanofiltration device to make the ion concentration in the concentrated water more uniform. The concentrated water intercepted by the fifth nanofiltration device contains carbonate ions (divalent ions). The carbonate ions combine with the sodium ions in the concentrated water intercepted by the tertiary nanofiltration device to form a sodium carbonate solution. The sodium carbonate solution is then discharged into the lithium precipitation device after evaporation, concentration and boron removal, for lithium precipitation reaction to generate lithium carbonate precipitate; the produced water of the fifth nanofiltration device is used to be discharged into the original brine tank and reused in the cycle of lithium extraction from the salt lake, thereby improving the recycling of water resources.

[0063] The aluminum adsorption device is connected to an evaporative salt field into which the tail brine separated by the aluminum adsorption device is discharged to evaporate and precipitate sodium salt and mixed salt. The next station of the evaporative salt field is sequentially connected to a potassium chloride evaporation crystallization device and a hot dissolution device to separate potassium salt from the mixed salt.

[0064] After the aluminum adsorption device adsorbs lithium ions, the remaining liquid is called tail brine, which is rich in sodium ions, potassium ions and chloride ions, which cannot be directly separated during the lithium extraction process. In order to make full use of these resources, the system discharges the tail brine of the aluminum adsorption device into the evaporative salt field, and gradually concentrates the solution through natural solar evaporation or evaporation process to precipitate sodium salt and mixed salt; first, in the evaporative salt field, as the water evaporates, the concentration of the solution continues to increase. Sodium salt (sodium chloride, NaCl) is crystallized first due to its low solubility. By regularly collecting the precipitated sodium salt from the salt field, the sodium salt can be recycled; with further evaporation, the concentration of the remaining solution in the salt field continues to increase, gradually forming a mixed salt containing potassium salt (potassium chloride) and a small amount of sodium chloride. Next, the system sends the mixed salt to the potassium chloride evaporation crystallization device and the hot melt device. The potassium chloride evaporation and crystallization device evaporates the water in the mixed salt to precipitate potassium salt. The hot melt device heats the mixed salt to dissolve potassium chloride and sodium chloride again, and then uses the solubility difference of different salts at a specific temperature to separate potassium salt from the mixed salt. Among them, the construction and installation of the evaporation salt field, the potassium chloride evaporation and crystallization device and the hot melt device do not affect the construction and implementation of the main process route in this application. That is to say, the extraction of lithium salt (lithium carbonate) can be independent of the extraction of sodium salt and potassium salt. Compared with the traditional process in which lithium salt, sodium salt and potassium salt are crystallized and precipitated in sequence, the process system involved in this application significantly improves the output efficiency of lithium salt and also speeds up the construction cycle of the overall system.

[0065] It should be noted that the hot dissolving device for the mixed salt can be realized by a series of equipment such as a hot dissolving kettle in the prior art. The hot dissolving kettle dissolves the mixed salt by heating, and promotes the precipitation of potassium chloride by regulating the cooling rate of the solution; the potassium chloride evaporation and crystallization device can be a common evaporator.

[0066] The present application also discloses a process for extracting lithium from a salt lake, comprising the following steps:

[0067] S1, pumping the salt lake brine in the salt lake into the original brine tank for storage;

[0068] S2, discharging the salt lake brine in the original brine tank into an immersion ultrafiltration device for filtration, and discharging the filtered salt lake brine into a magnesium removal resin device;

[0069] S3, discharge the salt lake brine filtered by the magnesium removal resin device into the primary nanofiltration device, the water produced by the primary nanofiltration device is discharged into the secondary nanofiltration device, the water produced by the secondary nanofiltration device is discharged into the tertiary nanofiltration device, the water produced by the tertiary nanofiltration device is discharged into the quaternary nanofiltration device, and the water produced by the quaternary nanofiltration device is discharged into the aluminum adsorption device;

[0070] Sodium hydroxide is added to the water produced by the first-stage nanofiltration device and the water produced by the second-stage nanofiltration device before entering the next station;

[0071] The concentrated water intercepted by the first-stage nanofiltration device is discharged into the salt lake;

[0072] The concentrated water intercepted by the secondary nanofiltration device flows back to the inlet water of the primary nanofiltration device;

[0073] The concentrated water from the three-stage nanofiltration device, the demineralized water, the concentrated water from the pure water reverse osmosis device of the membrane concentration subunit and the lithium precipitation mother liquor of the lithium precipitation device are discharged into the five-stage nanofiltration device together. The concentrated water intercepted by the five-stage nanofiltration device is discharged into the lithium precipitation device after evaporation concentration and boron removal, and the produced water from the five-stage nanofiltration device is discharged into the original brine tank;

[0074] The concentrated water intercepted by the fourth-stage nanofiltration device flows back to the inlet water of the third-stage nanofiltration device;

[0075] S4, the lithium ions adsorbed by the aluminum adsorption device are desorbed to form a desorption liquid, and the desorption liquid is discharged into a sand and gravel filter for filtration, the water produced by the sand and gravel filter is discharged into an ultrafiltration device, the water produced by the ultrafiltration device is discharged into a desorption liquid reverse osmosis device, and the reverse osmosis concentrated water of the desorption liquid reverse osmosis device is discharged into an evaporation concentration device, and the lithium solution concentrated by the evaporation concentration device is discharged into a lithium precipitation device after boron and magnesium removal;

[0076] The backwash water from the sand and gravel filter is discharged into the salt lake;

[0077] The water produced by the desorption liquid reverse osmosis device is treated by the pure water reverse osmosis device to produce pure water and concentrated water respectively. The concentrated water is used as the inlet water of the five-stage nanofiltration device.

[0078] After the aluminum adsorption device adsorbs lithium ions in the produced water of the four-stage nanofiltration device, the tail brine is discharged into the evaporative salt field. The tail brine is evaporated and crystallized in the evaporative salt field to first precipitate sodium chloride, and then precipitate a mixed salt of sodium chloride and potassium chloride. The mixed salt is evaporated, crystallized and hot-melted to obtain potassium chloride and miscellaneous salts.

[0079] S5, the lithium solution produces lithium carbonate through the lithium precipitation device, and the lithium precipitation mother liquor of the lithium precipitation device is discharged into the inlet water of the five-stage nanofiltration device;

[0080] S6, the lithium carbonate produced by the lithium precipitation device is centrifuged, dried, crushed and packaged.

[0081] In step S2, the submerged ultrafiltration device and the magnesium removal resin device discharge their backwash water into the salt lake through backwashing; in step S5, the ultrafiltration device discharges its backwash water into the sand filter through backwashing.

[0082] The technical features of the above embodiments may be arbitrarily combined (as long as there is no contradiction in the combination of these technical features). To make the description concise, not all possible combinations of the technical features in the above embodiments are described; these embodiments that are not explicitly written should also be considered to be within the scope of this specification.

[0083] The above is a relatively specific and detailed description of the present application through general description and specific embodiments. It should be understood that, based on the technical concept of the present application, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not deviate from the technical concept of the present application, the technical solutions obtained by these conventional adjustments or further innovations also fall within the scope of protection of the claims of the present application.

Claims

1. A salt lake lithium extraction system, characterized in that: The invention comprises a pretreatment unit for discharging salt lake brine and removing impurities in the discharged salt lake brine, a membrane treatment unit connected to the next station of the pretreatment unit and used for intercepting divalent ions in the salt lake brine and adsorbing lithium ions in the salt lake brine, and a lithium salt production unit connected to the next station of the membrane treatment unit and used for converting the lithium ions adsorbed by the membrane treatment unit into lithium salt.

2. The salt lake lithium extraction system according to claim 1, characterized in that: The pretreatment unit comprises a raw brine tank for storing salt lake brine, a de-impurity sub-unit connected to the next station of the raw brine tank and used for removing impurities in the salt lake brine, and the de-impurity sub-unit is connected to the previous station of the membrane treatment unit.

3. The salt lake lithium extraction system according to claim 2, characterized in that: The impurity removal subunit includes an immersion ultrafiltration device connected to the next station of the raw brine tank and a magnesium removal resin device connected to the next station of the immersion ultrafiltration device, and the magnesium removal resin device is connected to the previous station of the membrane treatment unit.

4. The salt lake lithium extraction system according to claim 1, characterized in that: The membrane treatment unit includes a nanofiltration subunit connected to the next station of the pretreatment unit and used to intercept divalent ions in the salt lake brine, an adsorption and desorption subunit connected to the next station of the nanofiltration subunit and used to adsorb and desorb lithium ions in the salt lake brine, and a membrane concentration subunit connected to the next station of the adsorption and desorption subunit and used to concentrate the lithium solution. The membrane concentration subunit is connected to the previous station of the lithium salt production unit.

5. The salt lake lithium extraction system according to claim 4, characterized in that: The nanofiltration subunit includes a primary nanofiltration device connected to the next station of the pretreatment unit, a secondary nanofiltration device connected to the next station of the primary nanofiltration device, a tertiary nanofiltration device connected to the next station of the secondary nanofiltration device, and a quaternary nanofiltration device connected to the next station of the tertiary nanofiltration device. The quaternary nanofiltration device is connected to the previous station of the adsorption and analysis subunit. The primary nanofiltration device, the secondary nanofiltration device, the tertiary nanofiltration device and the quaternary nanofiltration device are all provided with nanofiltration membranes to intercept divalent ions in the salt lake brine step by step.

6. The salt lake lithium extraction system according to claim 5, characterized in that: The concentrated water intercepted by the secondary nanofiltration device is discharged into the water inlet of the primary nanofiltration device, and the concentrated water intercepted by the fourth-stage nanofiltration device is discharged into the water inlet of the third-stage nanofiltration device. Alkaline solution is added to the produced water of the first-stage nanofiltration device and the secondary nanofiltration device before being discharged into the next workstation, and acid solution is added to the produced water of the fourth-stage nanofiltration device before being discharged into the next workstation.

7. The salt lake lithium extraction system according to claim 4, characterized in that: The adsorption and analysis subunit includes an aluminum adsorption device connected to the next station of the nanofiltration subunit and used to adsorb lithium ions in the produced water of the nanofiltration subunit. The membrane concentration subunit includes a gravel filter connected to the next station of the aluminum adsorption device and used to filter the desorption liquid of the aluminum adsorption device, an ultrafiltration device connected to the next station of the gravel filter and a desorption liquid reverse osmosis device connected to the next station of the ultrafiltration device. The desorption liquid reverse osmosis device is connected to the previous station of the lithium salt production unit. The desorption liquid reverse osmosis device is connected to a pure water reverse osmosis device so that the produced water of the desorption liquid reverse osmosis device passes through the reverse osmosis of the pure water reverse osmosis device to produce pure water and concentrated water respectively.

8. The salt lake lithium extraction system according to claim 1 or 7, characterized in that: The lithium salt production unit comprises an evaporation and concentration device connected to the next station of the membrane treatment unit and used for evaporating and concentrating the reverse osmosis concentrated water of the membrane treatment unit, and a lithium precipitation device connected to the next station of the evaporation and concentration device and used for converting the concentrated lithium liquid of the evaporation and concentration device into lithium carbonate, and a boron removal resin device is connected between the evaporation and concentration device and the lithium precipitation device.

9. The salt lake lithium extraction system according to claim 6, characterized in that: The three-stage nanofiltration device is connected to a five-stage nanofiltration device, so that the concentrated water intercepted by the three-stage nanofiltration device is discharged into the five-stage nanofiltration device, and the concentrated water intercepted by the three-stage nanofiltration device and the desalted water, the concentrated water of the pure water reverse osmosis device of the membrane concentration subunit and the lithium precipitation mother liquor of the lithium salt production unit are discharged into the five-stage nanofiltration device, the concentrated water intercepted by the five-stage nanofiltration device is discharged into the lithium precipitation device of the lithium salt production unit after evaporation concentration and boron removal, and the produced water of the five-stage nanofiltration device is discharged into the raw brine tank.

10. The salt lake lithium extraction system according to claim 7, characterized in that: The aluminum adsorption device is connected to an evaporative salt field into which the tail brine separated by the aluminum adsorption device is discharged to evaporate and precipitate sodium salt and mixed salt. The next station of the evaporative salt field is sequentially connected to a potassium chloride evaporation crystallization device and a hot dissolution device to separate potassium salt from the mixed salt.

11. A process for extracting lithium from a salt lake, characterized in that: The following steps are involved: S1, pumping the salt lake brine in the salt lake into the original brine tank for storage; S2, discharging the salt lake brine in the original brine tank into an immersion ultrafiltration device for filtration, and discharging the filtered salt lake brine into a magnesium removal resin device; S3, discharge the salt lake brine filtered by the magnesium removal resin device into the primary nanofiltration device, the water produced by the primary nanofiltration device is discharged into the secondary nanofiltration device, the water produced by the secondary nanofiltration device is discharged into the tertiary nanofiltration device, the water produced by the tertiary nanofiltration device is discharged into the quaternary nanofiltration device, and the water produced by the quaternary nanofiltration device is discharged into the aluminum adsorption device; Sodium hydroxide is added to the water produced by the first-stage nanofiltration device and the water produced by the second-stage nanofiltration device before entering the next station; The concentrated water intercepted by the first-stage nanofiltration device is discharged into the salt lake; The concentrated water intercepted by the secondary nanofiltration device flows back to the inlet water of the primary nanofiltration device; The concentrated water from the three-stage nanofiltration device, the demineralized water, the concentrated water from the pure water reverse osmosis device of the membrane concentration subunit and the lithium precipitation mother liquor of the lithium precipitation device are discharged into the five-stage nanofiltration device together. The concentrated water intercepted by the five-stage nanofiltration device is discharged into the lithium precipitation device after evaporation concentration and boron removal, and the produced water from the five-stage nanofiltration device is discharged into the original brine tank; The concentrated water intercepted by the fourth-stage nanofiltration device flows back to the inlet water of the third-stage nanofiltration device; S4, the lithium ions adsorbed by the aluminum adsorption device are desorbed to form a desorption liquid, and the desorption liquid is discharged into a sand and gravel filter for filtration, the water produced by the sand and gravel filter is discharged into an ultrafiltration device, the water produced by the ultrafiltration device is discharged into a desorption liquid reverse osmosis device, and the reverse osmosis concentrated water of the desorption liquid reverse osmosis device is discharged into an evaporation concentration device, and the lithium solution concentrated by the evaporation concentration device is discharged into a lithium precipitation device after boron and magnesium removal; The backwash water from the sand and gravel filter is discharged into the salt lake; The water produced by the desorption liquid reverse osmosis device is treated by the pure water reverse osmosis device to produce pure water and concentrated water respectively. The concentrated water is used as the inlet water of the five-stage nanofiltration device. After the aluminum adsorption device adsorbs lithium ions in the produced water of the four-stage nanofiltration device, the tail brine is discharged into the evaporative salt field. The tail brine is evaporated and crystallized in the evaporative salt field to first precipitate sodium chloride, and then precipitate a mixed salt of sodium chloride and potassium chloride. The mixed salt is evaporated, crystallized and hot-melted to obtain potassium chloride and miscellaneous salts. S5, the lithium solution produces lithium carbonate through the lithium precipitation device, and the lithium precipitation mother liquor of the lithium precipitation device is discharged into the inlet water of the five-stage nanofiltration device; S6, the lithium carbonate produced by the lithium precipitation device is centrifuged, dried, crushed and packaged.

12. The process for extracting lithium from salt lake according to claim 11, characterized in that: In step S2, the submerged ultrafiltration device and the magnesium removal resin device discharge their backwash water into the salt lake through backwashing; in step S5, the ultrafiltration device discharges its backwash water into the sand filter through backwashing.

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