Method for co-producing lithium, potassium and boron by gradient utilization of original brine of salt lake

Abstract

The invention relates to the technical field of extraction of lithium, potassium and boron in salt lakes, and discloses a method for co-producing lithium, potassium and boron by gradient utilization of original brine in salt lakes. The method comprises the following steps: S1, extracting lithium from original salt lake brine to obtain qualified lithium liquid and lithium extraction tail liquid; s2, preparing a battery-grade lithium product by using the qualified lithium liquid; s3, the lithium extraction tail liquid is subjected to beach drying through a salt pan, and potassium-containing solid salt (potassium mixed salt and carnallite), liquid old brine and bischofite are obtained; s4, preparing a potassium chloride product from the potassium-containing solid salt and bischofite; and S5, preparing a boric acid product by using the old brine. According to the method, a lithium extraction pre-treatment and salt lake brine potassium, boron and lithium process technical route is converted into a lithium, potassium and boron process route, the production cycle of a lithium salt product is shortened to 2 months from original 2-3 years, the lithium yield is increased by about one time, and meanwhile, the lithium-potassium-boron process is adopted, so that the problem that lithium extraction films and equipment are corroded and influenced by boron extraction acidification is solved, and the method is suitable for industrial production. Comprehensive development and utilization of salt lake resources are realized.

Description

Technical Field

[0001] The invention relates to the technical field of salt lake lithium, potassium and boron, and in particular to a method for co-producing lithium, potassium and boron by cascade utilization of original brine from a salt lake. Background Art

[0002] According to relevant data reports, the external dependence of resources is as high as about 70%, the external dependence of potassium resources is more than 50%, and the external dependence of boron resources is as high as about 70%. Salt lake resources mainly contain sodium, magnesium, potassium, lithium, boron and other elements. However, due to the limitation of comprehensive development and utilization technology of salt lake resources, the production capacity of lithium, potassium, boron and other products has not been fully released. Taking the lithium resources in the Qaidam Basin as an example, the total production capacity of lithium carbonate is nearly 200,000 t / a, and the actual output is only about 120,000 t / a. The traditional technical route for producing lithium, potassium and boron products from salt lake brine is: salt lake brine → salt pan beach drying → sodium chloride → potassium mixed salt (soft potassium magnesium alum, potassium salt) → carnallite (epsom salt, carnallite) → lithium-rich boron brine. The potassium mixed salt and carnallite precipitated from the salt pan beach drying are sent to the flotation device to produce potassium magnesium fertilizer and potassium chloride, or further react potassium magnesium fertilizer and potassium chloride to produce potassium sulfate; lithium-rich boron brine is sent to the processing plant to produce boric acid and lithium carbonate.

[0003] The traditional salt lake potassium, boron, and lithium product production technology route has high investment costs, long product production cycles, high environmental pressure, low resource utilization, and is not conducive to the development of salt lake resources in ecologically fragile areas. The potassium extraction process will result in some loss of lithium, boron and other resources (entrainment, leakage, etc.). The boron extraction process will also result in some lithium loss (entrainment, leakage, etc.), resulting in a low lithium resource yield; secondly, the process of first extracting boron and then lithium is adopted. The acid used in the acidification boron extraction process will have an adverse effect on lithium extraction devices such as nanofiltration membranes, and is highly corrosive to equipment and facilities, and affects the service life of materials and devices, posing a greater risk. The invention patents of publication number CN112390266A, CN 101024502A, and CN103539142A all disclose methods for preparing boric acid and lithium carbonate from salt lake brine. The above-mentioned technical problems cannot be avoided by first acidifying and extracting boron and then extracting potassium and lithium. At the same time, the process of extracting boron after extracting potassium and lithium from old brine is not suitable for direct boron extraction because the brine is diluted after potassium and lithium extraction. It needs to be concentrated again and then acidified for boron extraction, which has a long production cycle and high production cost. The lithium extraction process suffers from serious lithium loss during the salt pan beach drying, sodium extraction, potassium extraction, and boron extraction processes. The actual lithium yield is only about 30%, and the production cycle is as long as 2 to 3 years, which is seriously inconsistent with the rapid development of the market. The traditional method of exploiting salt lake resources mainly extracts single elements, such as extracting lithium or potassium alone. This method is not only inefficient, but also easy to cause waste of resources. Therefore, it is of great significance to develop a co-production system and method that can simultaneously and efficiently extract lithium, potassium, and boron from salt lakes. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of high investment cost, great environmental pressure, long product production cycle, low yield, low production efficiency, low comprehensive resource utilization rate, single salt lake resource development product, etc. in the prior art, and provide a method for cascade utilization of original salt lake brine to co-produce lithium, potassium and boron. The method transforms the salt lake brine potassium, boron and lithium process technology route into a lithium, potassium and boron process route through "pre-extraction of lithium". The production cycle of lithium salt products is shortened from the original 2 to 3 years to 2 months, and the lithium yield is increased by about one time. At the same time, the process of lithium first, potassium second and boron third solves the problem of the influence of boration on the corrosion of lithium extraction membrane and equipment.

[0005] In order to achieve the above object, the present invention provides a method for cascade utilization of raw brine from salt lakes to co-produce lithium, potassium and boron, the method comprising the following steps:

[0006] S1. Extract lithium from the original brine of the salt lake to obtain qualified lithium solution and lithium extraction tail solution;

[0007] S2, using the qualified lithium solution to prepare a battery-grade lithium product;

[0008] S3, drying the lithium-extracted tail liquid in salt pans to obtain potassium-containing solid salt, liquid brine and bischofite;

[0009] S4, preparing a potassium chloride product using the potassium-containing solid salt and bischofite;

[0010] S5. Using the liquid brine to prepare a boric acid product.

[0011] Preferably, in step S1, the original brine from the salt lake contains the following components: a lithium ion concentration of 0.1 to 0.4 g / L, a potassium ion concentration of 10 to 15 g / L, a boron ion concentration of 0.2 to 0.5 g / L, a magnesium ion concentration of 10 to 50 g / L, and a sulfate ion concentration of 10 to 40 g / L.

[0012] Preferably, in step S1, the lithium extraction process includes: filtering the original brine from the salt lake, and then extracting lithium using an adsorption method or a membrane separation technology.

[0013] Preferably, in step S1, the qualified lithium solution contains the following components: lithium ion concentration is 0.2-0.6 g / L, potassium ion concentration is ≤0.05 g / L, boron ion concentration is ≤0.2 g / L, magnesium ion concentration is ≤0.36 g / L, and sulfate ion concentration is ≤0.03 g / L.

[0014] Preferably, the lithium extraction tail solution contains the following components: lithium ion concentration ≤0.04 g / L, potassium ion concentration 9-14 g / L, boron ion concentration 0.2-0.5 g / L, magnesium ion concentration 10-50 g / L, and sulfate ion concentration 10-30 g / L.

[0015] Preferably, the liquid brine contains the following components: a lithium ion concentration of 0.1 to 0.3 g / L, a potassium ion concentration of ≤0.94 g / L, a boron ion concentration of 1 to 4 g / L, a magnesium ion concentration of 22.8 to 136.8 g / L, and a sulfate ion concentration of 34 to 42 g / L.

[0016] Preferably, in step S2, the process of preparing a battery-grade lithium product using the qualified lithium solution comprises:

[0017] S21, subjecting the lithium qualified solution to primary nanofiltration treatment to obtain primary nanofiltration product water, and then concentrating the primary nanofiltration product water through a reverse osmosis device to obtain a reverse osmosis concentrate;

[0018] S22, concentrating the reverse osmosis concentrate through an electrodialysis device to obtain an electrodialysis concentrate and fresh water;

[0019] S23, subjecting the electrodialysis concentrate to secondary nanofiltration treatment to obtain secondary nanofiltration product water, and then subjecting the secondary nanofiltration product water to a resin ion exchange calcium and magnesium removal device for removing magnesium to obtain a magnesium-removed qualified liquid;

[0020] S24, concentrating the magnesium-removed qualified liquid through an MVR device to obtain an MVR concentrated liquid, and then removing boron from the MVR concentrated liquid through a resin deboron removal device to obtain a boron-removed qualified liquid;

[0021] S25. A portion of the qualified boron removal solution is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor. The crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product; another portion of the qualified boron removal solution is treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product.

[0022] Preferably, in step S21, the primary nanofiltration produced water contains the following components: a lithium ion content of 0.35-0.45 g / L, and a magnesium ion content of ≤2 g / L.

[0023] In step S21, the reverse osmosis concentrated solution contains the following components: the content of lithium ions is 2.5-3.8 g / L, and the content of magnesium ions is ≤250 mg / L.

[0024] Preferably, in step S22, the electrodialysis concentrate contains the following components: a lithium ion content of 12 to 13.5 g / L, and a magnesium ion content of 500 to 1000 mg / L.

[0025] Preferably, in step S22, the fresh water contains the following components: a lithium ion content of 1000-2000 mg / L, and a magnesium ion content of 15-55 mg / L.

[0026] Preferably, in step S23, the secondary nanofiltration produced water contains the following components: a lithium ion content of 11 to 13.5 g / L, and a magnesium ion content of 3 to 5 mg / L.

[0027] Preferably, in step S23, the qualified magnesium-removal solution contains the following components: a lithium ion content of 10 to 13.5 g / L, and a magnesium ion content of 0.3 to 1 mg / L.

[0028] Preferably, in step S24, the MVR concentrate contains the following components: a lithium ion content of 19-24 g / L.

[0029] Preferably, in step S24, the qualified boron removal solution contains the following components: a lithium ion content of 18 to 22 g / L, and a boron ion content of 0 to 10 mg / L.

[0030] Preferably, in step S25, the lithium precipitation mother solution contains the following components: the content of lithium ions is 1.1-1.4 g / L, and the content of carbonate ions is 19-24 g / L.

[0031] Preferably, in step S4, the process of preparing a potassium chloride product using the potassium-containing solid salt comprises:

[0032] S41, conveying the potassium-containing solid salt to a crusher through a belt for crushing to obtain a potassium mixed salt ore;

[0033] S42, dissolving and crystallizing the potassium mixed salt ore in sequence, and then flotation or reverse flotation, and then dehydrating by filter pressing to obtain a crude potassium product and potassium flotation tailings, and then washing, dehydrating and drying the crude potassium product in sequence to obtain a potassium chloride product.

[0034] Preferably, the method further comprises: stirring and mixing the potassium extraction flotation tailings, the bischofite and the nanofiltration concentrated water to saturate the liquid phase with potassium ions and precipitate sodium chloride in the liquid phase, and after the chemical composition of the liquid phase meets the standard, the liquid phase is transported to the salt field for carnallite mineralization through precipitation clarification, and the obtained solid potassium ore is returned to step S41 for crushing and potassium recovery, and the formed solution tail liquid is returned to step S1 for lithium recovery, wherein the nanofiltration concentrated water is primary nanofiltration produced water and / or secondary nanofiltration produced water.

[0035] Preferably, the weight ratio of the nanofiltration concentrated water, the bischofite and the potassium flotation tail salt is 1:1-1.5:1.5-1.8.

[0036] Preferably, in step S5, the process of preparing the boric acid product using the liquid brine comprises:

[0037] S51, refining the liquid brine, adjusting the pH value to 1.5±0.5 with acid, and then extracting and stripping to obtain a boron-containing stripping solution with a pH value of 1 to 3;

[0038] S52, neutralizing the boron-containing stripping solution with limestone to obtain a neutralized solution with a pH value of 3.5 to 4;

[0039] S53, naturally evaporating the neutralized solution in an evaporation pond to a saturated state, and then continuing to evaporate to precipitate boric acid, and when the thickness of the precipitated boric acid in the evaporation pond is greater than 20 cm, harvesting is performed according to the construction process of dry salt field mining to obtain crude boron ore;

[0040] S54, mixing the crude boron ore with pure water, adding an impurity remover, and then heating and stirring, and gradually heating the obtained product to 85-90° C. to obtain a hot solution;

[0041] S55, subjecting the hot solution to coarse filtration and refining in sequence to obtain a refined filtrate and a filter residue, the filter residue is slurried with water, the slag liquid after slurry washing is filtered using a tailings plate and frame, and the obtained filtrate enters a crystal slurry mother liquid tank;

[0042] S56, subjecting the refined filtrate to vacuum flash crystallization to obtain a crystal slurry at a temperature of 50 to 70° C., and then subjecting the crystal slurry to cooling crystallization in a cooling crystallizer to obtain a crystal slurry at a temperature of 20 to 25° C.;

[0043] S57, separating the slurry through a centrifuge to obtain a mother liquor and crystals, wherein the mother liquor enters a slurry mother liquor tank, and the crystals are dried to obtain a refined boric acid product.

[0044] Preferably, in step S51, the acid is hydrochloric acid and / or sulfuric acid.

[0045] In step S53, when the neutralized solution evaporates naturally in the evaporation pond to a saturated state, the boron concentration is 5 to 5.5 weight %;

[0046] In step S54, the impurity removing agent is an ion exchange resin and / or a chelating resin;

[0047] In step S54, the temperature of the heating and stirring is 90-100°C;

[0048] In step S56, the conditions for the vacuum flash crystallization include: a vacuum degree of 3000 to 10000 Pa, and a crystallization time of 3 to 4 hours.

[0049] Compared with the prior art, the present invention has at least the following beneficial effects:

[0050] (1) The method described in the present invention realizes "pre-extraction of lithium", transforming the salt lake brine potassium, boron and lithium process technology route into lithium, potassium and boron, shortening the lithium salt product production cycle from the original 2 to 3 years to 2 months, and increasing the lithium yield by about one-fold, while the potassium and boron yields remain unchanged; at the same time, the process of first lithium, then potassium and then boron solves the problem of the impact of boric acid extraction on the corrosion of lithium extraction membranes and equipment, and at the same time realizes the cascade utilization of salt lake brine resources to co-produce lithium, potassium and boron products, and realizes the diversification of salt lake resource development products.

[0051] (2) The method described in the present invention realizes the combined extraction of lithium, potassium and boron, thereby improving the comprehensive utilization rate of salt lake resources; adopts environmentally friendly technology to reduce pollution to the environment; the system is easy to operate and easy to scale up production; the economic benefits are significant and have good market application prospects. DETAILED DESCRIPTION

[0052] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0053] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0054] The method for cascade utilization of original brine from salt lakes to co-produce lithium, potassium and boron provided by the present invention comprises the following steps:

[0055] S1. Extract lithium from the original brine of the salt lake to obtain qualified lithium solution and lithium extraction tail solution;

[0056] S2, using the qualified lithium solution to prepare a battery-grade lithium product;

[0057] S3, drying the lithium extraction tail liquid in salt pans to obtain potassium-containing solid salt (the main components of the potassium-containing solid salt are potassium mixed salt and carnallite), liquid brine and bischofite;

[0058] S4, preparing a potassium chloride product using the potassium-containing solid salt and bischofite;

[0059] S5. Using the liquid brine to prepare a boric acid product.

[0060] The extraction order adopted by the method of the present invention is lithium, potassium, and boron. By pre-extracting lithium, not only the yield of lithium from salt lake brine can be improved, but also the effect of acidification boron extraction on the life of lithium extraction membrane and corrosion of other lithium extraction equipment can be solved, which meets the requirements of green, low-carbon and circular economic development.

[0061] In the present invention, the salt lake original brine belongs to a high magnesium-lithium ratio magnesium sulfate subtype salt lake system. In some embodiments, the salt lake original brine in step S1 contains the following components: lithium ion concentration of 0.1-0.4 g / L, potassium ion concentration of 10-15 g / L, boron ion concentration of 0.2-0.5 g / L, magnesium ion concentration of 10-50 g / L, and sulfate ion concentration of 10-40 g / L.

[0062] In the method of the present invention, the purpose of step S1 is to extract lithium and separate lithium from elements such as magnesium, potassium, and boron. The lithium extraction process in step S1 can be carried out in various ways well known in the art. In some embodiments, in step S1, the lithium extraction process includes filtering the original brine of the salt lake and then extracting lithium using an adsorption method or a membrane separation technology.

[0063] In a preferred embodiment, the lithium extraction process described in step S1 includes: filtering the original brine of the salt lake through the original brine pool multi-media filter and then pumping it into the continuous adsorption lithium extraction device to adsorb lithium, the lithium is adsorbed in the continuous adsorption lithium extraction device to achieve separation from elements such as magnesium, potassium, and boron, and obtain lithium extraction tail liquid; then the continuous adsorption lithium extraction device is desorbed by a desorption liquid, and lithium is desorbed from the continuous adsorption lithium extraction device to form a lithium qualified liquid, wherein the yield of lithium in the desorption qualified liquid is ≥70%, and the yield of lithium in the desorption qualified liquid is the lithium yield of the process from the adsorption of lithium in the continuous adsorption lithium extraction device to the desorption of the continuous adsorption lithium extraction device by the desorption liquid. In a more preferred embodiment, in order to improve the yield of lithium in the lithium extraction process, the adsorbent in the continuous adsorption lithium extraction device can be at least one of an aluminum adsorbent Al(OH)3 adsorbent, a Li-Al-O-OH adsorbent, and a Li / Al-LDHs adsorbent; the desorption liquid for desorbing the continuous adsorption lithium extraction device is pure water. In the method described in the present invention, in order to improve the yield of lithium, when the continuous adsorption and lithium extraction device operates for several cycles and the adsorption efficiency drops below 70%, a regeneration agent is used to regenerate the adsorption capacity.

[0064] In some embodiments, the lithium extraction tail solution contains the following components: lithium ion concentration ≤0.04 g / L, potassium ion concentration of 9-14 g / L, boron ion concentration of 0.2-0.5 g / L, magnesium ion concentration of 10-50 g / L, sulfate ion concentration of 10-30 g / L; the concentration of lithium ions in the lithium extraction tail solution is relatively low, indicating that the lithium extraction effect is better.

[0065] In other embodiments, the qualified lithium solution in step S1 contains the following components: a lithium ion concentration of 0.2 to 0.6 g / L, a potassium ion concentration of ≤0.05 g / L, a boron ion concentration of ≤0.2 g / L, a magnesium ion concentration of ≤0.36 g / L, and a sulfate ion concentration of ≤0.03 g / L; the concentration of lithium ions in the qualified lithium solution is increased, and the concentrations of other ions are greatly reduced, thereby achieving the purpose of lithium extraction.

[0066] In the present invention, the process of preparing battery-grade lithium products using the qualified lithium solution in step S2 includes subjecting the qualified lithium solution to gradient coupled membrane separation and purification through nanofiltration membrane, ultrafiltration membrane, electrodialysis and other devices, and then removing magnesium and boron.

[0067] In a preferred embodiment, in order to improve the yield of lithium and obtain a battery-grade lithium product with high purity, in step S2, the process of preparing a battery-grade lithium product using the qualified lithium solution includes:

[0068] S21, pumping the lithium qualified solution into a primary nanofiltration device for primary nanofiltration treatment to remove divalent calcium and magnesium ions to obtain primary nanofiltration product water, and then concentrating the primary nanofiltration product water through a reverse osmosis device to obtain a reverse osmosis concentrate;

[0069] S22, concentrating the reverse osmosis concentrate through an electrodialysis device to obtain an electrodialysis concentrate and fresh water;

[0070] S23, subjecting the electrodialysis concentrate to secondary nanofiltration treatment through a secondary nanofiltration device to further remove divalent calcium and magnesium to obtain secondary nanofiltration product water, and then subjecting the secondary nanofiltration product water to a resin ionization and decalcification and magnesium removal device to remove magnesium to obtain a magnesium-free qualified liquid;

[0071] S24, concentrating the magnesium-removed qualified liquid through an MVR device to obtain an MVR concentrated liquid, and then removing boron from the MVR concentrated liquid through a resin deboron removal device to obtain a boron-removed qualified liquid and a boron-removed tail liquid;

[0072] S25. A portion of the qualified boron removal solution is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor. The crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product; another portion of the qualified boron removal solution is treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product.

[0073] In some embodiments, the primary nanofiltration produced water in step S21 contains the following components: a lithium ion content of 0.35 to 0.45 g / L, and a magnesium ion content of ≤2 g / L.

[0074] In some embodiments, the reverse osmosis concentrated solution in step S21 contains the following components: a lithium ion content of 2.5 to 3.8 g / L, and a magnesium ion content of ≤250 mg / L.

[0075] In some embodiments, the electrodialysis concentrate in step S22 contains the following components: a lithium ion content of 12 to 13.5 g / L, and a magnesium ion content of 500 to 1000 mg / L.

[0076] In some embodiments, the fresh water in step S22 contains the following components: a lithium ion content of 1000-2000 mg / L, and a magnesium ion content of 15-55 mg / L.

[0077] In some embodiments, the secondary nanofiltration produced water in step S23 contains the following components: a lithium ion content of 11 to 13.5 g / L, a magnesium ion content of 3 to 5 mg / L;

[0078] In some embodiments, the magnesium-removed qualified solution in step S23 contains the following components: a lithium ion content of 10 to 13.5 g / L, and a magnesium ion content of 0.3 to 1 mg / L.

[0079] In some embodiments, the MVR concentrate in step S24 contains the following components: a lithium ion content of 19-24 g / L.

[0080] In some embodiments, the boron-removed qualified solution in step S24 contains the following components: the content of lithium ions is 18-22 g / L, and the content of boron ions is 0-10 mg / L. In the present invention, the boron-removed tail liquid obtained by removing boron from the MVR concentrate by a resin ionization and deboronization device contains the following components: the content of lithium ions is 0.1-2 g / L, and the content of boron ions is 2-4 g / L.

[0081] In some embodiments, the lithium precipitation mother solution in step S25 contains the following components: a lithium ion content of 1.1-1.4 g / L, and a carbonate ion content of 19-24 g / L.

[0082] In the method of the present invention, the process of preparing a battery-grade lithium hydroxide monohydrate product after another part of the qualified boron removal solution in step S25 is treated with a bipolar membrane can be a common process in the art. In the present invention, when the continuous adsorption and lithium extraction device runs for several cycles and the adsorption efficiency drops to 70%, the regeneration reagent used for the adsorption capacity regeneration treatment is hydrochloric acid, a byproduct of the bipolar membrane production of lithium hydroxide; the regeneration process includes: using 5-10 mass% hydrochloric acid and the original brine of the salt lake in a volume ratio of 0.1-2:1000 to mix into the continuous adsorption and lithium extraction device, regenerating the continuous adsorption and lithium extraction device, and then adsorbing and extracting lithium after the adsorption efficiency is restored.

[0083] In the method described in the present invention, the battery-grade lithium carbonate product obtained in step S25 meets the brine battery grade standard, wherein Li2CO3≥99.65%, Na≤0.033%, K≤0.0016%, Mg≤0.0012%, Ca≤0.0014%, B≤0.0031%, Fe≤0.0001%, Zn≤0.0002%, Cu≤0.000017%, Pb≤0.000002%, Si≤0.0015%, Al≤0.001%, Mn≤%, Ni≤0.001%, SO4 2- ≤0.0021%, Cl≤0.01%, moisture 0.13%.

[0084] S25, a portion of the qualified solution for deboronation is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor, and the crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product; another portion of the qualified solution for deboronation is treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product

[0085] In S25 of the present invention, preferably, the preparation process of the battery-grade lithium hydroxide monohydrate product comprises:

[0086] (1) subjecting the qualified boron removal solution to bipolar membrane electrodialysis treatment, and subjecting the lithium hydroxide alkali solution produced by the bipolar membrane electrodialysis to a first flash concentration to obtain a first concentrated solution with a solid content of 15% to 40%;

[0087] (2) centrifuging the first concentrated liquid, and then washing the first solid product obtained by centrifugation with water, wherein the weight ratio of the first solid product to water is 1:0.2-0.3, to obtain a first crude salt and a first mother liquor, and then sequentially evaporating and concentrating the first mother liquor and centrifuging to obtain a second crude salt and Na + ≥50g / L of the second mother liquor, the second mother liquor is discharged, and the volume ratio of the lithium hydroxide alkali solution to the second mother liquor discharged is ≥20:1;

[0088] (3) mixing the first crude salt and the second crude salt, adding water to dissolve the mixture, and then performing a second flash concentration to obtain a second concentrated solution having a solid content of 15% to 40%;

[0089] (4) centrifuging the second concentrated liquid, and then washing the second solid product obtained by centrifugation with water, wherein the weight ratio of the second solid product to water is 1:0.2-0.3, to obtain a third crude salt and a third mother liquor, and then drying the third crude salt, and returning the third mother liquor to step (1) for reuse;

[0090] In step (2) and step (4), the flushing time is less than 40 s.

[0091] In some embodiments, step (1) further comprises: the lithium hydroxide alkali solution is preheated to a temperature ≥ 75°C before the first flash concentration, and then heated to a temperature ≥ 85°C.

[0092] In some embodiments, step (3) further comprises: preheating the heavy solution to a temperature ≥ 75°C and then heating it to a temperature ≥ 85°C before the second flash concentration.

[0093] In step S3 of the present invention, the specific process of drying the lithium extraction tail liquid through the salt pan beach to obtain potassium-containing solid salt, bischofite and liquid brine includes: transporting the lithium extraction tail liquid to the salt pan through a pipeline, drying it through the salt pan beach, evaporating the brine naturally to first precipitate sodium chloride, and then concentrating it to saturation with potassium chloride, separating the potassium-containing solid salt, and further drying it to obtain bischofite and liquid brine. Among them, the main components of the potassium-containing solid salt are potassium mixed salt and carnallite.

[0094] In some embodiments, the liquid brine contains the following components: a lithium ion concentration of 0.1 to 0.3 g / L, a potassium ion concentration of ≤0.94 g / L, a boron ion concentration of 1 to 4 g / L, a magnesium ion concentration of 22.8 to 136.8 g / L, and a sulfate ion concentration of 34 to 42 g / L.

[0095] In the present invention, the potassium-containing solid salt obtained in step S3 enters the potassium extraction unit through the conveying system, is crushed by the crushing system → dissolved, dissolved and crystallized by the crystallization system → potassium is extracted by the flotation or reverse flotation system → filtered system → washed system → dehydrated and dried system, and a potassium chloride product is obtained.

[0096] In one embodiment, in step S4, the process of preparing a potassium chloride product using the potassium-containing solid salt comprises:

[0097] S41, conveying the potassium-containing solid salt to a crusher through a belt for crushing to obtain a potassium mixed salt ore;

[0098] S42, dissolving and crystallizing the potassium mixed salt ore in sequence, and then flotation or reverse flotation, and then dehydrating by filter pressing to obtain a crude potassium product and potassium flotation tailings, and then washing, dehydrating and drying the crude potassium product in sequence to obtain a potassium chloride product.

[0099] In a more specific embodiment, the process of step S41 includes: conveying the potassium-containing solid salt to a crusher for crushing, conveying the carnallite to a high-efficiency decomposition machine for decomposition, and then mixing and ball-milling the potassium-containing solid salt and the carnallite in a ball mill to obtain a potassium mixed salt ore.

[0100] In the present invention, the method further comprises: stirring and mixing the potassium flotation tailings, the bischofite and the nanofiltration concentrated water, so that the potassium ions in the liquid phase are saturated, and sodium chloride is precipitated in the liquid phase, and the chemical composition in the liquid phase meets the standard (the standard for the chemical composition is that the potassium ion content in the liquid phase reaches 13.5g / L or more, the magnesium ion reaches 70g / L or more, and the carnallite in the liquid phase is close to the saturation precipitation node), and then transported to the salt field for carnallite mineralization through precipitation clarification, and the obtained solid potassium ore is returned to step S41 for crushing and recovery of potassium, and the formed solution tail liquid is returned to step S1 for recovery of lithium, wherein the nanofiltration concentrated water is primary nanofiltration water and / or secondary nanofiltration water. In a preferred embodiment, the weight ratio of the nanofiltration concentrated water, the bischofite and the potassium flotation tail salt is 1:1-1.5:1.5-1.8, and more preferably 1:1.2:1.6. The process is simple to operate, can be used to produce any lean potassium ore that cannot be directly used for production, and has a useful component recovery rate of more than 90%, and can be put into production on a large scale.

[0101] In a preferred embodiment, in order to improve the yield of boron and obtain a high-purity boron product, in step S5, the process of preparing a boric acid product using the liquid brine includes:

[0102] S51, after refining the liquid brine, adjusting the pH value to 1.5±0.5 with acid, then extracting and stripping to obtain a boron-containing stripping solution with a pH value of 1 to 3, and returning the raffinate to the salt field after deoiling by a deoiling device;

[0103] S52, neutralizing the boron-containing stripping solution with limestone to obtain a neutralized solution with a pH value of 3.5 to 4;

[0104] S53, naturally evaporating the neutralized solution in an evaporation pond to a saturated state, and then continuing to evaporate to precipitate boric acid, and when the thickness of the precipitated boric acid in the evaporation pond is greater than 20 cm, harvesting is performed according to the construction process of dry salt field mining to obtain crude boron ore;

[0105] S54, mixing the crude boron ore with pure water, adding an impurity remover (i.e., an impurity adsorbent), then heating and stirring, and gradually heating the obtained product to 85-90° C. to obtain a hot solution;

[0106] S55, subjecting the hot solution to coarse filtration and refining in sequence to obtain a refined filtrate and a filter residue, the filter residue is slurried with water, the slag liquid after slurry washing is filtered using a tailings plate and frame, the obtained filtrate enters a crystal slurry mother liquid tank, and the obtained tailings are transported to a boiler for incineration as fuel;

[0107] S56, subjecting the refined filtrate to vacuum flash crystallization to obtain a crystal slurry at a temperature of 50 to 70° C., and then subjecting the crystal slurry to cooling crystallization in a cooling crystallizer to obtain a crystal slurry at a temperature of 20 to 25° C.;

[0108] S57, separating the slurry through a centrifuge to obtain a mother liquor and crystals, wherein the mother liquor enters a slurry mother liquor tank, and the crystals are dried to obtain a refined boric acid product.

[0109] In the method described in the present invention, the solution obtained by mixing the filtrate entering the slurry mother liquor tank in step S55 with the mother liquor entering the slurry mother liquor tank in step S57 is returned to step S54, mixed with the crude boron ore, and then an adsorbent is added.

[0110] In the present invention, the refining in step S51 and step S55 is a conventional operation in the art, for example, it may be filtration.

[0111] In the present invention, the acid used in step S51 can be an inorganic acid commonly used in the art. In some embodiments, the acid in step S51 is hydrochloric acid and / or sulfuric acid.

[0112] In step S51 of the present invention, in order to improve the yield of boron, the extractant used for extraction can be at least one of an organic extractant, an inorganic extractant and an ion exchange resin, and the stripping agent used for stripping can be pure water with a pH value of 7±1.

[0113] In step S53 of the present invention, when the neutralization solution evaporates naturally in the evaporation pond to a saturated state, the boron concentration may be 5 to 5.5% by weight.

[0114] In step S54 of the present invention, in order to adsorb impurities in the crude boron ore, the impurity remover is at least one of an ion exchange resin and a chelating resin.

[0115] In step S54 of the present invention, the temperature of the heating and stirring can be 90-100°C.

[0116] In step S56 of the present invention, the conditions for the vacuum flash crystallization include: a vacuum degree of 3000 to 10000 Pa, and a crystallization time of 3 to 4 hours.

[0117] In step S57 of the present invention, the drying process includes: drying the crystals by air flow or a vibrating fluidized bed or other drying processes and then drying them by cold air.

[0118] The method described in the present invention achieves the goal of simultaneously and efficiently extracting lithium, potassium, and boron from the raw brine of the salt lake through a set of integrated processes, and the technical route is changed from "first potassium, then boron, and then lithium" to "first lithium, then potassium, and then boron". The lithium yield of salt lake brine can be increased by about one-fold (the lithium yield can be increased to about 60%), and the production cycle of lithium products is shortened from the original 2 to 3 years to about 2 months. The pre-extraction of lithium can solve the effect of acidification and boron extraction on the life of lithium extraction membranes and other lithium extraction equipment corrosion, and at the same time realize the co-production of lithium, potassium, and boron from salt lake resources. The method described in the present invention meets the requirements of green, low-carbon, and circular economic development.

[0119] The following examples further illustrate the method for the co-production of lithium, potassium and boron by cascade utilization of raw brine from salt lakes of the present invention. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0120] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0121] In the following examples, the composition of the original brine from the salt lake is shown in Table 1.

[0122] Table 1

[0123]

[0124] In the following embodiments:

[0125] Lithium yield = (amount of lithium in battery-grade lithium carbonate product + amount of lithium in battery-grade lithium hydroxide monohydrate product) ÷ amount of lithium in original brine of salt lake × 100%;

[0126] Potassium yield = potassium content in potassium chloride product ÷ potassium content in original brine of salt lake × 100%;

[0127] Boron yield = amount of boron in boric acid product ÷ amount of potassium in original brine of salt lake × 100%.

[0128] In the following embodiments, in step S25, the preparation process of the battery-grade lithium hydroxide monohydrate product includes:

[0129] (1) The qualified boron removal solution is subjected to bipolar membrane electrodialysis treatment, and the lithium hydroxide alkali solution produced by the bipolar membrane electrodialysis is pumped into a condensed water fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively. After the lithium hydroxide alkali solution is preheated to 80° C., it is transported to a steam forced circulation heat exchanger by a forced circulation pump and heated to 85° C., and then the first flash concentration is performed in a crystallization separator. The liquid phase temperature of the first flash concentration is 84° C. and the pressure is 665 mbar. When the solid content of the first concentrated liquid reaches 25%, it is pumped out by a discharge pump;

[0130] (2) The discharge pump conveys the first concentrated liquid to the centrifuge for centrifugation to obtain a first solid product and a first centrifuge liquid, and then the first solid product is rinsed with water in the centrifuge to obtain a first crude salt and a first washing liquid. The first centrifuge liquid and the first washing liquid are combined into a first mother liquor, wherein the weight ratio of the first solid product to water during rinsing is 1:0.3, and the rinsing time is 30s; then the first mother liquor enters a single-effect mother liquor tank, and is conveyed to a single-effect evaporator by a high-concentration mother liquor pump for evaporation and concentration, and then centrifuged by a centrifuge to obtain a second crude salt and a second mother liquor, and the second mother liquor is discharged, and the discharge volume of the second mother liquor is 0.8m 3 ;

[0131] (3) mixing the first crude salt and the second crude salt, adding distilled water, performing a salt dissolving operation, and obtaining a heavy solution; then pumping the heavy solution into a condensed water fresh steam plate preheater, performing heat exchange with distilled water and fresh steam respectively, and preheating the heavy solution; after the heavy solution is preheated to 80° C., it is transported to the second steam forced circulation heat exchanger through a second steam forced circulation pump and heated to 85° C., and then subjected to a second flash concentration in a crystallizer to a solid content of 28%, thereby obtaining a second concentrated solution; the second flash concentration has a liquid phase temperature of 85° C. and a pressure of 425 mbar;

[0132] (4) The second concentrated liquid is conveyed to a centrifuge for centrifugation to obtain a second solid product and a second centrifugal liquid, and then the second solid product is rinsed with water in the centrifuge to obtain a third crude salt and a second washing liquid. The second centrifugal liquid and the second washing liquid are combined into a third mother liquor, wherein the weight ratio of the second solid product to water during rinsing is 1:0.3, and the rinsing time is 30 seconds; then the third mother liquor is returned to step (1) for the first flash concentration and reuse, and the third crude salt is conveyed to a rotary kiln drying system, and the dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide monohydrate product.

[0133] Example 1

[0134] S1. Extract lithium from the original brine of the salt lake to obtain qualified lithium solution and lithium extraction tail solution

[0135] The specific process includes:

[0136] The original brine from the salt lake is filtered through a multi-media filter of the original brine pool and then pumped into a continuous adsorption lithium extraction device to adsorb lithium. The lithium is adsorbed in the continuous adsorption lithium extraction device to achieve separation from elements such as magnesium, potassium, and boron, and a lithium extraction tail liquid is obtained. Then, a desorption liquid is used to desorb the continuous adsorption lithium extraction device, and lithium is desorbed from the continuous adsorption lithium extraction device to form a lithium qualified liquid. The yield of the desorbed qualified liquid lithium is ≥90%, wherein the lithium qualified liquid contains the following components: lithium ion concentration is 0.47g / L, potassium ion concentration is 0.01g / L, boron ion concentration is 0.12g / L, magnesium ion concentration is 0.16g / L, sulfate ion concentration is 0. .01g / L; the lithium extraction tail liquid contains the following components: lithium ion concentration is 0.01g / L, potassium ion concentration is 10.50g / L, boron ion concentration is 0.36g / L, magnesium ion concentration is 20.93g / L, sulfate ion concentration is 15.22g / L, the adsorbent in the continuous adsorption lithium extraction device is Li / Al-LDHs adsorbent, and the desorption liquid for desorbing the continuous adsorption lithium extraction device is pure water; when the adsorption efficiency of the continuous adsorption lithium extraction device drops to 68% after running for several cycles, the regeneration reagent is used to regenerate the adsorption capacity, and the adsorption efficiency of the adsorption device is restored to 83% after regeneration.

[0137] S2, using the qualified lithium solution to prepare battery-grade lithium products

[0138] The specific process includes:

[0139] S21, pumping the lithium qualified solution obtained in step S1 into a primary nanofiltration device for primary nanofiltration treatment to remove divalent calcium and magnesium ions to obtain primary nanofiltration produced water, wherein the primary nanofiltration produced water contains the following components: a lithium ion content of 0.45 g / L, a magnesium ion content of 1.57 g / L, and then concentrating the primary nanofiltration produced water through a reverse osmosis device to obtain a reverse osmosis concentrated solution, wherein the reverse osmosis concentrated solution contains the following components: a lithium ion content of 3.48 g / L, a magnesium ion content of 150 mg / L;

[0140] S22, concentrating the reverse osmosis concentrated solution through an electrodialysis device to obtain an electrodialysis concentrated solution and fresh water, wherein the electrodialysis concentrated solution contains the following components: a lithium ion content of 12.81 g / L, a magnesium ion content of 0.83 g / L, and the fresh water contains the following components: a lithium ion content of 1.52 g / L, and a magnesium ion content of 30 mg / L;

[0141] S23, subjecting the electrodialysis concentrate to secondary nanofiltration treatment through a secondary nanofiltration device, further removing divalent calcium and magnesium, and obtaining secondary nanofiltration produced water, wherein the secondary nanofiltration produced water contains the following components: a lithium ion content of 12.11 g / L, a magnesium ion content of 3.54 mg / L, and then subjecting the secondary nanofiltration produced water to magnesium removal through a resin ionization and calcium and magnesium removal device to obtain a magnesium-removed qualified liquid, wherein the magnesium-removed qualified liquid contains the following components: a lithium ion content of 11.86 g / L, a magnesium ion content of 0.72 mg / L;

[0142] S24, the magnesium removal qualified liquid is concentrated by an MVR device to obtain an MVR concentrated liquid, wherein the MVR concentrated liquid contains the following components: the content of lithium ions is 21.42g / L, and then the MVR concentrated liquid is subjected to a resin ionization and deboronization device to remove boron to obtain a boron removal qualified liquid and a boron removal tail liquid, wherein the boron removal qualified liquid contains the following components: the content of lithium ions is 19.24g / L, the content of boron ions is 5.71mg / L, and the boron removal tail liquid contains the following components: the content of lithium ions is 0.73g / L, and the content of boron ions is 2.86g / L;

[0143] S25. A portion of the qualified solution for deboronation is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor, wherein the lithium precipitation mother liquor contains the following components: a lithium ion content of 1.21 g / L, a carbonate ion content of 22.17 g / L, and the crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product, wherein the battery-grade lithium carbonate product contains Li2CO3: 99.64%, Na: 200.61 ppm, K: 14.18 ppm, Mg: 13.47 ppm, Ca: 18.69 ppm, B: 32.54 ppm, Fe: 1.11 ppm, Si: 12.47 ppm, Al: 2.00 ppm, Mn≤1 ppm, Ni≤1 ppm, Zn≤1 ppm, Cu≤2 ppm, Pb≤3 ppm, SO4 2- :27.75ppm,Cl - : 58.23ppm, water 0.15%; another part of the qualified boron removal solution is prepared as a battery-grade lithium hydroxide monohydrate product after bipolar membrane treatment, wherein the composition of the battery-grade lithium hydroxide monohydrate product is LiOH: 57.46%, Ca: 1.36ppm, Mg: 1.53ppm, Na: 19.09ppm, K: 4.33ppm, B: 3.77ppm, Si: ≤1ppm, Fe: 1.07, Cl - : 18.33ppm, sulfate ion: 1.62ppm, carbonate ion: 0.63%;

[0144] Recovery process: The by-product hydrochloric acid produced by the bipolar membrane in the production of lithium hydroxide is returned to step S1 to regenerate the continuous adsorption lithium extraction device. The regeneration process includes: using 7% by mass hydrochloric acid and the original brine of the salt lake in a volume ratio of 1:1000 to mix into the continuous adsorption lithium extraction device, regenerating the continuous adsorption lithium extraction device, and performing normal adsorption lithium extraction after the adsorption efficiency reaches 83%.

[0145] S3, the lithium extraction tail liquid is dried in salt pans to obtain potassium-containing solid salt (mainly composed of potassium mixed salt and carnallite), bischofite and liquid old brine

[0146] The specific process includes:

[0147] The lithium extraction tail liquid is transported to the salt pan through a pipeline, and the brine is naturally evaporated through salt pan beach drying to first precipitate sodium chloride, and then concentrated to saturation with potassium chloride, and potassium-containing solid salt is separated. After further beach drying, bischofite and liquid brine are obtained, wherein the liquid brine contains the following components: the concentration of lithium ions is 0.23 g / L, the concentration of potassium ions is 0.71 g / L, the concentration of boron ions is 3.56 g / L, the concentration of magnesium ions is 119.26 g / L, and the concentration of sulfate ions is 38.62 g / L.

[0148] S4, using the potassium-containing solid salt and bischofite to prepare potassium chloride product

[0149] The specific process includes:

[0150] S41, conveying the potassium-containing solid salt to a crusher through a belt for crushing to obtain a potassium mixed salt ore;

[0151] S42, dissolving and crystallizing the potassium mixed salt ore in sequence, and then flotation or reverse flotation, and then dehydrating by filter pressing to obtain a crude potassium product and potassium flotation tailings, and then washing, dehydrating and drying the crude potassium product in sequence to obtain a potassium chloride product, wherein the potassium chloride product has a composition of KCl: 92.74%, K2O: 58.68%, Na: 2.43%, and H2O: 0.18%;

[0152] Recovery process: wherein the potassium flotation tailings are stirred and mixed with the bischofite and nanofiltration concentrated water to saturate the liquid phase with potassium ions and precipitate sodium chloride in the liquid phase. After the chemical composition in the liquid phase reaches the standard (the potassium ion content in the liquid phase reaches more than 13.5 g / L, the magnesium ion content reaches more than 70 g / L, and the carnallite in the liquid phase is close to the saturation precipitation node), it is transported to the salt field through precipitation clarification for carnallite mineralization, and the obtained solid potassium ore is returned to step S41 for crushing and potassium recovery, and the formed solution tail liquid is returned to step S1 for lithium recovery, wherein the nanofiltration concentrated water is primary nanofiltration produced water, and the weight ratio of the nanofiltration concentrated water, the bischofite and the potassium flotation tail salt is 1:1.2:1.6.

[0153] S5, using the liquid old brine to prepare the boric acid product

[0154] The specific process includes:

[0155] S51, after refining the liquid brine, adjusting the pH value to 1.5 with hydrochloric acid, then extracting and stripping to obtain a boron-containing stripping solution with a pH value of 2, and returning the raffinate to the salt pan after deoiling by an oil removal device, wherein the extractant used in the extraction is an alcohol composite extractant, and the stripping agent used in the stripping is pure water;

[0156] S52, neutralizing the boron-containing stripping solution with limestone to obtain a neutralized solution with a pH value of 3.8;

[0157] S53, naturally evaporating the neutralized solution in an evaporation pond to a saturated state, wherein the boron concentration is 5.25% by weight, and then continuing to evaporate to precipitate boric acid. When the thickness of the precipitated boric acid in the evaporation pond reaches 21 cm, harvesting is performed according to the construction procedure of dry salt field mining to obtain crude boron ore;

[0158] S54, mixing the crude boron ore with pure water, adding ion exchange resin to remove impurities, then heating and stirring at 90° C., and heating the obtained product step by step to 95° C. through a steam coil to obtain a hot solution;

[0159] S55, subjecting the hot solution to coarse filtration and refining in sequence to obtain a refined filtrate and a filter residue, the filter residue is slurried with water, the slag liquid after slurry washing is filtered using a tailings plate and frame, the obtained filtrate enters a crystal slurry mother liquid tank, and the obtained tailings are transported to a boiler for incineration as fuel;

[0160] S56, subjecting the refined filtrate to vacuum flash crystallization to obtain a crystal slurry at a temperature of 60° C., wherein the conditions of the vacuum flash crystallization include: a vacuum degree of 7000 Pa, a crystallization time of 3.5 h, and then subjecting the crystal slurry to cooling crystallization in a cooling crystallizer to obtain a crystal slurry at a temperature of 23° C.;

[0161] S57, separating the slurry through a centrifuge to obtain a mother liquor and crystals, the mother liquor enters a slurry mother liquor tank, the crystals are dried by air flow and then blown dry by cold wind to obtain a refined boric acid product, the purity of the refined boric acid product is 99.95%, Cl: 58.36ppm, Na: 163.53ppm, sulfate ion: 37.74ppm, Mg: 7.95ppm;

[0162] Recovery process: The solution obtained by mixing the filtrate entering the slurry mother liquid tank in step S55 with the mother liquid entering the slurry mother liquid tank in step S57 is returned to step S54, mixed with the crude boron ore, and then an adsorbent is added.

[0163] In this embodiment, the comprehensive yield of lithium in the lithium carbonate product is 60.21%, the yield of potassium is 59.82%, the yield of boron is 96.98%, and the production cycle of lithium products (battery-grade lithium carbonate finished products and battery-grade lithium hydroxide monohydrate products) is about 2 months.

[0164] Example 2

[0165] S1. Extract lithium from the original brine of the salt lake to obtain qualified lithium solution and lithium extraction tail solution

[0166] The specific process includes:

[0167] The original brine from the salt lake is filtered through the original brine pool multi-media filter and then pumped into the continuous adsorption lithium extraction device to adsorb lithium. The lithium is adsorbed in the continuous adsorption lithium extraction device to achieve separation from elements such as magnesium, potassium, and boron, and a lithium extraction tail liquid is obtained; then the continuous adsorption lithium extraction device is desorbed with a desorption liquid, and lithium is desorbed from the continuous adsorption lithium extraction device to form a lithium qualified liquid. The yield of the desorbed qualified liquid lithium is ≥90%, wherein the lithium qualified liquid contains the following components: lithium ion concentration is 0.43g / L, potassium ion concentration is ≤0.01g / L, boron ion concentration is 0.13g / L, magnesium ion concentration is 0.14g / L, sulfate ion concentration is ≤ 0.01g / L; the lithium extraction tail liquid contains the following components: lithium ion concentration is ≤0.01g / L, potassium ion concentration is 10.34g / L, boron ion concentration is 0.38g / L, magnesium ion concentration is 21.05g / L, sulfate ion concentration is 15.74g / L, the adsorbent in the continuous adsorption lithium extraction device is Al(OH)3 adsorbent, and the desorption liquid for desorbing the continuous adsorption lithium extraction device is pure water; when the continuous adsorption lithium extraction device runs for several cycles and the adsorption efficiency drops to 68%, the regeneration agent is used to regenerate the adsorption capacity, and the adsorption efficiency of the adsorption device is restored to more than 83% after regeneration.

[0168] S2, using the qualified lithium solution to prepare battery-grade lithium products

[0169] The specific process includes:

[0170] S21, pumping the lithium qualified solution obtained in step S1 into a primary nanofiltration device for primary nanofiltration treatment to remove divalent calcium and magnesium ions to obtain primary nanofiltration produced water, wherein the primary nanofiltration produced water contains the following components: a lithium ion content of 0.42 g / L, a magnesium ion content of 1.63 g / L, and then concentrating the primary nanofiltration produced water through a reverse osmosis device to obtain a reverse osmosis concentrated solution, wherein the reverse osmosis concentrated solution contains the following components: a lithium ion content of 3.30 g / L, a magnesium ion content of 143 mg / L;

[0171] S22, concentrating the reverse osmosis concentrate through an electrodialysis device to obtain an electrodialysis concentrate and fresh water, wherein the electrodialysis concentrate contains the following components: a lithium ion content of 12.13 g / L, a magnesium ion content of 0.91 g / L, and the fresh water contains the following components: a lithium ion content of 1.43 g / L, a magnesium ion content of 28.36 mg / L;

[0172] S23, subjecting the electrodialysis concentrate to secondary nanofiltration treatment through a secondary nanofiltration device, further removing divalent calcium and magnesium, and obtaining secondary nanofiltration produced water, wherein the secondary nanofiltration produced water contains the following components: a lithium ion content of 11.92 g / L, a magnesium ion content of 3.21 mg / L, and then subjecting the secondary nanofiltration produced water to magnesium removal through a resin ionization and calcium and magnesium removal device to obtain a magnesium-removed qualified liquid, wherein the magnesium-removed qualified liquid contains the following components: a lithium ion content of 11.53 g / L, a magnesium ion content of 0.54 mg / L;

[0173] S24, the magnesium removal qualified liquid is concentrated by an MVR device to obtain an MVR concentrated liquid, wherein the MVR concentrated liquid contains the following components: the content of lithium ions is 21.03g / L, and then the MVR concentrated liquid is subjected to a resin ionization and deboronization device to remove boron, to obtain a boron removal qualified liquid and a boron removal tail liquid, wherein the boron removal qualified liquid contains the following components: the content of lithium ions is 19.05g / L, the content of boron ions is 5.31mg / L, and the boron removal tail liquid contains the following components: the content of lithium ions is 0.80g / L, and the content of boron ions is 2.47g / L;

[0174] S25. A portion of the qualified solution for deboronation is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor, wherein the lithium precipitation mother liquor contains the following components: a lithium ion content of 1.18 g / L, a carbonate ion content of 20.42 g / L, and the crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product, wherein the battery-grade lithium carbonate product contains Li2CO3: 99.61%, Na: 195.18 ppm, K: 13.68 ppm, Mg: 12.47 ppm, Ca: 17.16 ppm, B: 30.76 ppm, Fe: 0.71 ppm, Si: 10.83 ppm, Al: ≤2 ppm, Mn≤1 ppm, Ni≤1 ppm, Zn≤1 ppm, Cu≤1 ppm, Pb≤1 ppm, SO4 2- :26.94ppm,Cl -: 52.46ppm, water 0.14%; another part of the qualified boron removal solution is treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product, wherein the battery-grade lithium hydroxide monohydrate product has a composition of LiOH: 56.89%, Ca: 1.41ppm, Mg: 1.57ppm, Na: 15.41ppm, K: 3.11ppm, B: 3.74ppm, Si: ≤1ppm, Fe: 0.63ppm, Cl - : 15.34ppm, sulfate ion: 1.46ppm, carbonate ion: 0.72%;

[0175] The hydrochloric acid produced as a byproduct of the bipolar membrane production of lithium hydroxide is returned to step S1 to regenerate the continuous adsorption lithium extraction device. The regeneration process includes: using 7% by mass hydrochloric acid and the original brine of the salt lake in a volume ratio of 1:1000 to mix into the continuous adsorption lithium extraction device, regenerating the continuous adsorption lithium extraction device, and performing normal adsorption lithium extraction after the adsorption efficiency reaches 83%.

[0176] S3, the lithium extraction tail liquid is dried in salt pans to obtain potassium-containing solid salt, bischofite and liquid old brine

[0177] The specific process includes:

[0178] The lithium extraction tail liquid is transported to the salt pan through a pipeline, and the brine is naturally evaporated through salt pan beach drying to first precipitate sodium chloride, and then concentrated to saturation with potassium chloride, and potassium-containing solid salt is separated. After further beach drying, bischofite and liquid brine are obtained, wherein the liquid brine contains the following components: the concentration of lithium ions is 0.21 g / L, the concentration of potassium ions is 0.73 g / L, the concentration of boron ions is 3.52 g / L, the concentration of magnesium ions is 120.17 g / L, and the concentration of sulfate ions is 38.59 g / L.

[0179] S4, using the potassium-containing solid salt and bischofite to prepare potassium chloride product

[0180] The specific process includes:

[0181] S41, conveying the potassium-containing solid salt to a crusher through a belt for crushing to obtain a potassium mixed salt ore;

[0182] S42, dissolving and crystallizing the potassium mixed salt ore in sequence, and then flotation or reverse flotation, and then dehydrating by filter pressing to obtain a crude potassium product and potassium flotation tailings, and then washing, dehydrating and drying the crude potassium product in sequence to obtain a potassium chloride product, wherein the potassium chloride product has a composition of KCl: 91.18%, K2O: 57.95%, Na: 2.46%, and H2O: 0.21%;

[0183] The potassium flotation tailings are stirred and mixed with the bischofite and nanofiltration concentrated water to saturate the potassium ions in the liquid phase and precipitate sodium chloride in the liquid phase. After the chemical composition in the liquid phase reaches the standard (the potassium ion content in the liquid phase reaches more than 13.5 g / L, the magnesium ion content reaches more than 70 g / L, and the carnallite in the liquid phase is close to the saturation precipitation node), it is transported to the salt field through precipitation clarification for carnallite mineralization, and the obtained solid potassium ore is returned to step S41 again for crushing and potassium recovery, and the formed solution tail liquid is returned to step S1 to recover lithium, wherein the nanofiltration concentrated water is primary nanofiltration produced water, and the weight ratio of the nanofiltration concentrated water, the bischofite and the potassium flotation tail salt is 1:1.2:1.6.

[0184] S5, using the liquid old brine to prepare the boric acid product

[0185] The specific process includes:

[0186] S51, after refining the liquid brine, adjusting the pH value to 1.5 with hydrochloric acid, then extracting and stripping to obtain a boron-containing stripping solution with a pH value of 2, and returning the raffinate to the salt pan after deoiling by an oil removal device, wherein the extractant used in the extraction is an alcohol composite extractant, and the stripping agent used in the stripping is pure water;

[0187] S52, neutralizing the boron-containing stripping solution with limestone to obtain a neutralized solution with a pH value of 3.8;

[0188] S53, naturally evaporating the neutralized solution in an evaporation pond to a saturated state, wherein the boron concentration is 5.23% by weight, and then continuing to evaporate to precipitate boric acid. When the thickness of the precipitated boric acid in the evaporation pond reaches 21 cm, harvesting is performed according to the construction procedure of dry salt field mining to obtain crude boron ore;

[0189] S54, mixing the crude boron ore with pure water, adding ion exchange resin as an impurity remover, and then heating and stirring at 90° C., and heating the obtained product step by step to 95° C. through a steam coil to obtain a hot solution;

[0190] S55, subjecting the hot solution to coarse filtration and refining in sequence to obtain a refined filtrate and a filter residue, the filter residue is slurried with water, the slag liquid after slurry washing is filtered using a tailings plate and frame, the obtained filtrate enters a crystal slurry mother liquid tank, and the obtained tailings are transported to a boiler for incineration as fuel;

[0191] S56, subjecting the refined filtrate to vacuum flash crystallization to obtain a crystal slurry at a temperature of 60° C., wherein the conditions of the vacuum flash crystallization include: a vacuum degree of 7000 Pa, a crystallization time of 3.5 h, and then subjecting the crystal slurry to cooling crystallization in a cooling crystallizer to obtain a crystal slurry at a temperature of 23° C.;

[0192] S57, separating the slurry through a centrifuge to obtain a mother liquor and crystals, the mother liquor entering a slurry mother liquor tank, the crystals being dried by air flow and then blown dry by cold wind to obtain a refined boric acid product, the purity of the refined boric acid product being 99.91%, Cl: 65.39 ppm, Na: 172.24 ppm, sulfate ion: 41.03 ppm, Mg: 8.04 ppm;

[0193] The solution obtained by mixing the filtrate entering the slurry mother liquid tank in step S55 with the mother liquid entering the slurry mother liquid tank in step S57 is returned to step S54, mixed with the crude boron ore, and then an adsorbent is added.

[0194] In this embodiment, the yield of lithium is 59.47%, the yield of potassium is 58.67%, the yield of boron is 96.32%, and the production cycle of lithium products (battery-grade lithium carbonate products and battery-grade lithium hydroxide monohydrate products) is about 2 months.

[0195] Example 3

[0196] S1. Extract lithium from the original brine of the salt lake to obtain qualified lithium solution and lithium extraction tail solution

[0197] The specific process includes:

[0198] The original brine of the salt lake is filtered through the original brine pool multi-media filter and then pumped into the continuous adsorption lithium extraction device to adsorb lithium. The lithium is adsorbed in the continuous adsorption lithium extraction device to achieve separation from elements such as magnesium, potassium, and boron, and a lithium extraction tail liquid is obtained; then the continuous adsorption lithium extraction device is desorbed with a desorption liquid, and lithium is desorbed from the continuous adsorption lithium extraction device to form a lithium qualified liquid. The yield of the desorbed qualified liquid is 90%, wherein the lithium qualified liquid contains the following components: lithium ion concentration is 0.45g / L, potassium ion concentration ≤0.01g / L, boron ion concentration is 0.13g / L, magnesium ion concentration is 0.15g / L, sulfate ion concentration is ≤0. 01g / L; the lithium extraction tail liquid contains the following components: lithium ion concentration is ≤0.01g / L, potassium ion concentration is 10.47g / L, boron ion concentration is 0.35g / L, magnesium ion concentration is 20.92g / L, sulfate ion concentration is 15.34g / L, the adsorbent in the continuous adsorption lithium extraction device is Li-Al-O-OH adsorbent, and the desorption liquid for desorbing the continuous adsorption lithium extraction device is pure water; when the adsorption efficiency of the continuous adsorption lithium extraction device drops to 68% after running for several cycles, the regeneration reagent is used to regenerate the adsorption capacity, and the adsorption efficiency of the adsorption device is restored to 83% after regeneration.

[0199] S2, using the qualified lithium solution to prepare battery-grade lithium products

[0200] The specific process includes:

[0201] S21, pumping the lithium qualified solution obtained in step S1 into a primary nanofiltration device for primary nanofiltration treatment to remove divalent calcium and magnesium ions to obtain primary nanofiltration produced water, wherein the primary nanofiltration produced water contains the following components: a lithium ion content of 0.44 g / L, a magnesium ion content of 1.61 g / L, and then concentrating the primary nanofiltration produced water through a reverse osmosis device to obtain a reverse osmosis concentrated solution, wherein the reverse osmosis concentrated solution contains the following components: a lithium ion content of 3.21 g / L, a magnesium ion content of 143 mg / L;

[0202] S22, concentrating the reverse osmosis concentrate through an electrodialysis device to obtain an electrodialysis concentrate and fresh water, wherein the electrodialysis concentrate contains the following components: a lithium ion content of 12.69 g / L, a magnesium ion content of 0.78 g / L, and the fresh water contains the following components: a lithium ion content of 1.42 g / L, a magnesium ion content of 29.97 mg / L;

[0203] S23, subjecting the electrodialysis concentrate to secondary nanofiltration treatment through a secondary nanofiltration device, further removing divalent calcium and magnesium, and obtaining secondary nanofiltration produced water, wherein the secondary nanofiltration produced water contains the following components: a lithium ion content of 11.98 g / L, a magnesium ion content of 3.39 mg / L, and then subjecting the secondary nanofiltration produced water to magnesium removal through a resin ionization and calcium and magnesium removal device to obtain a magnesium-removed qualified liquid, wherein the magnesium-removed qualified liquid contains the following components: a lithium ion content of 11.69 g / L, a magnesium ion content of 0.66 mg / L;

[0204] S24, the magnesium removal qualified liquid is concentrated by an MVR device to obtain an MVR concentrated liquid, wherein the MVR concentrated liquid contains the following components: the content of lithium ions is 21.39g / L, and then the MVR concentrated liquid is subjected to a resin ionization and deboronization device to remove boron, to obtain a boron removal qualified liquid and a boron removal tail liquid, wherein the boron removal qualified liquid contains the following components: the content of lithium ions is 19.46g / L, the content of boron ions is 5.53mg / L, and the boron removal tail liquid contains the following components: the content of lithium ions is 0.68g / L, and the content of boron ions is 2.57g / L;

[0205] S25. A portion of the qualified solution for deboronation is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor, wherein the lithium precipitation mother liquor contains the following components: the content of lithium ions is 1.24 g / L, the content of carbonate ions is 22.32 g / L, and the crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product, wherein the battery-grade lithium carbonate product contains Li2CO3: 99.62%, Na: 210.90 ppm, K: 13.85 ppm, Mg: 11.38 ppm, Ca: 16.97 ppm, B: 30.68 ppm, Fe: 0.73 ppm, Si: 9.46 ppm, Al: ≤2 ppm, Mn≤1 ppm, Ni≤1 ppm, Zn≤1 ppm, Cu≤1 ppm, Pb≤1 ppm, SO4 2- :25.40ppm,Cl - : 61.10ppm, water 0.12%; another part of the qualified boron removal solution is prepared as a battery-grade lithium hydroxide monohydrate product after bipolar membrane treatment, wherein the battery-grade lithium hydroxide monohydrate product has a composition of LiOH: 57.33%, Ca: 1.04ppm, Mg: 1.47ppm, Na: 15.1ppm, K: 1.23ppm, B: 1.01ppm, Si: 4.13ppm, Fe: 0.80, Cl - : 18.96ppm, sulfate ion: 1.24ppm, carbonate ion: 0.58%;

[0206] The hydrochloric acid produced as a byproduct of the bipolar membrane production of lithium hydroxide is returned to step S1 to regenerate the continuous adsorption lithium extraction device. The regeneration process includes: using 7% by mass hydrochloric acid and the original brine of the salt lake in a volume ratio of 1:1000 to mix into the continuous adsorption lithium extraction device, regenerating the continuous adsorption lithium extraction device, and performing normal adsorption lithium extraction after the adsorption efficiency reaches 83%.

[0207] S3, the lithium extraction tail liquid is dried in salt pans to obtain potassium-containing solid salt, bischofite and liquid old brine

[0208] The specific process includes:

[0209] The lithium extraction tail liquid is transported to the salt pan through a pipeline, and the brine is naturally evaporated through salt pan beach drying to first precipitate sodium chloride, and then concentrated to saturation with potassium chloride, and potassium-containing solid salt is separated. After further beach drying, bischofite and liquid brine are obtained, wherein the liquid brine contains the following components: the concentration of lithium ions is 0.22 g / L, the concentration of potassium ions is 0.69 g / L, the concentration of boron ions is 3.54 g / L, the concentration of magnesium ions is 119.86 g / L, and the concentration of sulfate ions is 38.65 g / L.

[0210] S4, using the potassium-containing solid salt and bischofite to prepare potassium chloride product

[0211] The specific process includes:

[0212] S41, conveying the potassium-containing solid salt to a crusher through a belt for crushing to obtain a potassium mixed salt ore;

[0213] S42, dissolving and crystallizing the potassium mixed salt ore in sequence, and then flotation or reverse flotation, and then dehydrating by filter pressing to obtain a crude potassium product and potassium flotation tailings, and then washing, dehydrating and drying the crude potassium product in sequence to obtain a potassium chloride product, wherein the potassium chloride product has a composition of KCl: 91.69%, K2O: 57.48%, Na: 2.83%, and H2O: 0.19%;

[0214] The potassium flotation tailings are stirred and mixed with the bischofite and nanofiltration concentrated water to saturate the potassium ions in the liquid phase and precipitate sodium chloride in the liquid phase. After the chemical composition in the liquid phase reaches the standard (the potassium ion content in the liquid phase reaches more than 13.5 g / L, the magnesium ion content reaches more than 70 g / L, and the carnallite in the liquid phase is close to the saturation precipitation node), it is transported to the salt field through precipitation clarification for carnallite mineralization, and the obtained solid potassium ore is returned to step S41 again for crushing and potassium recovery, and the formed solution tail liquid is returned to step S1 to recover lithium, wherein the nanofiltration concentrated water is primary nanofiltration produced water, and the weight ratio of the nanofiltration concentrated water, the bischofite and the potassium flotation tail salt is 1:1.2:1.6.

[0215] S5, using the liquid old brine to prepare the boric acid product

[0216] The specific process includes:

[0217] S51, after refining the liquid brine, adjusting the pH value to 1.5 with hydrochloric acid, then extracting and stripping to obtain a boron-containing stripping solution with a pH value of 2, and returning the raffinate to the salt pan after deoiling by an oil removal device, wherein the extractant used in the extraction is an alcohol composite extractant, and the stripping agent used in the stripping is pure water;

[0218] S52, neutralizing the boron-containing stripping solution with limestone to obtain a neutralized solution with a pH value of 3.8;

[0219] S53, evaporating the neutralized solution naturally in an evaporation pond to a saturated state, wherein the boron concentration is 5.27% by weight, and then continuing to evaporate to precipitate boric acid. When the thickness of the precipitated boric acid in the evaporation pond reaches 21 cm, the boric acid is harvested according to the construction procedure of dry salt field mining to obtain a crude boron ore;

[0220] S54, mixing the crude boron ore with pure water, adding ion exchange resin as an impurity remover, and then heating and stirring at 90° C., and heating the obtained product step by step to 95° C. through a steam coil to obtain a hot solution;

[0221] S55, subjecting the hot solution to coarse filtration and refining in sequence to obtain a refined filtrate and a filter residue, the filter residue is slurried with water, the slag liquid after slurry washing is filtered using a tailings plate and frame, the obtained filtrate enters a crystal slurry mother liquid tank, and the obtained tailings are transported to a boiler for incineration as fuel;

[0222] S56, subjecting the refined filtrate to vacuum flash crystallization to obtain a crystal slurry at a temperature of 60° C., wherein the conditions of the vacuum flash crystallization include: a vacuum degree of 7000 Pa, a crystallization time of 3.5 h, and then subjecting the crystal slurry to cooling crystallization in a cooling crystallizer to obtain a crystal slurry at a temperature of 23° C.;

[0223] S57, separating the slurry through a centrifuge to obtain a mother liquor and crystals, the mother liquor entering a slurry mother liquor tank, the crystals being dried by air flow and then blown dry by cold wind to obtain a refined boric acid product, the purity of the refined boric acid product being 99.93%, Cl: 55.76ppm, Na: 156.38ppm, sulfate ion: 35.53ppm, Mg: 7.24ppm;

[0224] The solution obtained by mixing the filtrate entering the slurry mother liquid tank in step S55 with the mother liquid entering the slurry mother liquid tank in step S57 is returned to step S54, mixed with the crude boron ore, and then an adsorbent is added.

[0225] In this embodiment, the yield of lithium is 59.98%, the yield of potassium is 58.93%, the yield of boron is 96.75%, and the production cycle of lithium products (battery-grade lithium carbonate finished product and battery-grade lithium hydroxide monohydrate product) is about 2 months.

[0226] Comparative Example 1

[0227] S1. The original brine from the salt lake is dried in the salt pan to obtain potassium-containing solid salt (potassium mixed salt, carnallite), liquid old brine and bischofite;

[0228] S2, preparing a potassium chloride product using the potassium-containing solid salt and bischofite;

[0229] S3, using the liquid old brine to prepare boric acid to obtain a boron extraction tail liquid;

[0230] S4. Utilizing the boron extraction tail liquid to extract lithium by adsorption to prepare a lithium carbonate product.

[0231] The steps for preparing potassium chloride, boric acid and lithium carbonate products are the same as those in Example 1 except that step S2, step S4 and step S5 recycling processes are omitted.

[0232] In this comparative example, the yield of lithium was 30.45%, the yield of potassium was 47.64%, and the yield of boron was 97.05%.

[0233] The purity of the products obtained in the examples and comparative examples and the yields of lithium, potassium and boron are shown in Tables 1 and 2.

[0234] Table 1

[0235]

[0236] Table 2

[0237]

[0238] It can be seen from the results in Table 1 and Table 2 that by adopting the technical solution of the embodiment of the present invention, the yields of lithium and potassium are significantly improved, and the yield of boron remains basically unchanged.

[0239] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for the co-production of lithium, potassium and boron by cascade utilization of raw brine from salt lakes, characterized in that: The method comprises the following steps: S1. Extract lithium from the original brine of the salt lake to obtain lithium qualified liquid and lithium extraction tail liquid; S2, using the qualified lithium solution to prepare a battery-grade lithium product; S3, drying the lithium-extracted tail liquid in salt pans to obtain potassium-containing solid salt, liquid brine and bischofite; S4, preparing a potassium chloride product using the potassium-containing solid salt and bischofite; S5. Using the liquid brine to prepare a boric acid product.

2. The method according to claim 1, characterized in that In step S1, the original brine of the salt lake contains the following components: lithium ion concentration is 0.1-0.4 g / L, potassium ion concentration is 10-15 g / L, boron ion concentration is 0.2-0.5 g / L, magnesium ion concentration is 10-50 g / L, and sulfate ion concentration is 10-40 g / L.

3. The method according to claim 1 or 2, characterized in that: In step S1, the lithium extraction process includes: filtering the original brine of the salt lake, and then extracting lithium using an adsorption method or a membrane separation technology.

4. The method according to any one of claims 1 to 3, characterized in that: In step S1, the lithium qualified solution contains the following components: lithium ion concentration is 0.2-0.6 g / L, potassium ion concentration is ≤0.05 g / L, boron ion concentration is ≤0.2 g / L, magnesium ion concentration is ≤0.36 g / L, and sulfate ion concentration is ≤0.03 g / L; Preferably, the lithium extraction tail solution contains the following components: lithium ion concentration ≤ 0.04 g / L, potassium ion concentration 9-14 g / L, boron ion concentration 0.2-0.5 g / L, magnesium ion concentration 10-50 g / L, sulfate ion concentration 10-30 g / L; Preferably, the liquid brine contains the following components: a lithium ion concentration of 0.1 to 0.3 g / L, a potassium ion concentration of ≤0.94 g / L, a boron ion concentration of 1 to 4 g / L, a magnesium ion concentration of 22.8 to 136.8 g / L, and a sulfate ion concentration of 34 to 42 g / L.

5. The method according to any one of claims 1 to 4, characterized in that: In step S2, the process of preparing a battery-grade lithium product using the qualified lithium solution includes: S21, subjecting the lithium qualified solution to primary nanofiltration treatment to obtain primary nanofiltration product water, and then concentrating the primary nanofiltration product water through a reverse osmosis device to obtain a reverse osmosis concentrate; S22, concentrating the reverse osmosis concentrate through an electrodialysis device to obtain an electrodialysis concentrate and fresh water; S23, subjecting the electrodialysis concentrate to secondary nanofiltration treatment to obtain secondary nanofiltration product water, and then subjecting the secondary nanofiltration product water to a resin ion exchange calcium and magnesium removal device for removing magnesium to obtain a magnesium-removed qualified liquid; S24, concentrating the magnesium-removed qualified liquid through an MVR device to obtain an MVR concentrated liquid, and then removing boron from the MVR concentrated liquid through a resin deboron removal device to obtain a boron-removed qualified liquid; S25. A portion of the qualified boron removal solution is subjected to lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor. The crude lithium carbonate is washed and dried to obtain a battery-grade lithium carbonate product; another portion of the qualified boron removal solution is treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product.

6. The method according to claim 5, characterized in that In step S21, the primary nanofiltration produced water contains the following components: the content of lithium ions is 0.35-0.45 g / L, and the content of magnesium ions is ≤2 g / L; In step S21, the reverse osmosis concentrate contains the following components: a lithium ion content of 2.5 to 3.8 g / L, and a magnesium ion content of ≤250 mg / L; Preferably, in step S22, the electrodialysis concentrate contains the following components: a lithium ion content of 12 to 13.5 g / L, and a magnesium ion content of 500 to 1000 mg / L; Preferably, in step S22, the fresh water contains the following components: a lithium ion content of 1000-2000 mg / L, a magnesium ion content of 15-55 mg / L; Preferably, in step S23, the secondary nanofiltration produced water contains the following components: a lithium ion content of 11 to 13.5 g / L, a magnesium ion content of 3 to 5 mg / L; Preferably, in step S23, the qualified magnesium removal solution contains the following components: the content of lithium ions is 10-13.5 g / L, and the content of magnesium ions is 0.3-1 mg / L; Preferably, in step S24, the MVR concentrate contains the following components: a lithium ion content of 19 to 24 g / L; Preferably, in step S24, the qualified boron removal solution contains the following components: a lithium ion content of 18 to 22 g / L and a boron ion content of 0 to 10 mg / L; Preferably, in step S25, the lithium precipitation mother solution contains the following components: the content of lithium ions is 1.1-1.4 g / L, and the content of carbonate ions is 19-24 g / L.

7. The method according to any one of claims 1 to 6, characterized in that: In step S4, the process of preparing a potassium chloride product using the potassium-containing solid salt comprises: S41, conveying the potassium-containing solid salt to a crusher through a belt for crushing to obtain a potassium mixed salt ore; S42, dissolving and crystallizing the potassium mixed salt ore in sequence, and then flotation or reverse flotation, and then dehydrating by filter pressing to obtain a crude potassium product and potassium flotation tailings, and then washing, dehydrating and drying the crude potassium product in sequence to obtain a potassium chloride product.

8. The method according to claim 7, characterized in that The method further comprises: stirring and mixing the potassium extraction flotation tailings, the bischofite and the nanofiltration concentrated water to saturate the liquid phase with potassium ions and precipitate sodium chloride in the liquid phase, and after the chemical composition of the liquid phase meets the standard, the liquid phase is transported to the salt field for carnallite mineralization through precipitation clarification, and the obtained solid potassium ore is returned to step S41 for crushing and potassium recovery, and the formed solution tail liquid is returned to step S1 for lithium recovery, wherein the nanofiltration concentrated water is primary nanofiltration produced water and / or secondary nanofiltration produced water; Preferably, the weight ratio of the nanofiltration concentrated water, the bischofite, and the potassium flotation tail salt is 1:1-1.5:1.5-1.

8.

9. The method according to any one of claims 1 to 8, characterized in that: In step S5, the process of preparing a boric acid product using the liquid brine includes: S51, refining the liquid brine, adjusting the pH value to 1.5±0.5 with acid, and then extracting and stripping to obtain a boron-containing stripping solution with a pH value of 1 to 3; S52, neutralizing the boron-containing stripping solution with limestone to obtain a neutralized solution with a pH value of 3.5 to 4; S53, naturally evaporating the neutralized solution in an evaporation pond to a saturated state, and then continuing to evaporate to precipitate boric acid, and when the thickness of the precipitated boric acid in the evaporation pond is greater than 20 cm, harvesting is performed according to the construction process of dry salt field mining to obtain crude boron ore; S54, mixing the crude boron ore with pure water, adding an impurity remover, and then heating and stirring, and gradually heating the obtained product to 85-90° C. to obtain a hot solution; S55, subjecting the hot solution to coarse filtration and refining in sequence to obtain a refined filtrate and a filter residue, the filter residue is slurried with water, the slag liquid after slurry washing is filtered using a tailings plate and frame, and the obtained filtrate enters a crystal slurry mother liquid tank; S56, subjecting the refined filtrate to vacuum flash crystallization to obtain a crystal slurry at a temperature of 50 to 70° C., and then subjecting the crystal slurry to cooling crystallization in a cooling crystallizer to obtain a crystal slurry at a temperature of 20 to 25° C.; S57, separating the slurry through a centrifuge to obtain a mother liquor and crystals, wherein the mother liquor enters a slurry mother liquor tank, and the crystals are dried to obtain a refined boric acid product.

10. The method according to claim 9, characterized in that In step S51, the acid is hydrochloric acid and / or sulfuric acid; In step S53, when the neutralized solution evaporates naturally in the evaporation pond to a saturated state, the boron concentration is 5 to 5.5 weight %; In step S54, the impurity removing agent is an ion exchange resin and / or a chelating resin; In step S54, the temperature of the heating and stirring is 90-100°C; In step S56, the conditions for the vacuum flash crystallization include: a vacuum degree of 3000 to 10000 Pa, and a crystallization time of 3 to 4 hours.

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