Method for co-production of lithium, potassium and boron by step-by-step utilization of raw brine from salt lake

Abstract

The present application relates to salt lake lithium potassium boron extraction technical field, disclose a kind of salt lake original brine cascade utilization co-production lithium, potassium, boron method.The method comprises the following steps: S1, the lithium of salt lake original brine is extracted, and lithium qualified liquid and lithium tail liquid are obtained;S2, the lithium qualified liquid is used to prepare battery-grade lithium product;S3, the lithium tail liquid is obtained by salt field through salted and dried, and potassium-containing solid salt (potassium mixed salt, carnallite), liquid old brine and bischofite;S4, the potassium-containing solid salt and bischofite are used to prepare potassium chloride product;S5, the old brine is used to prepare boric acid product.The method is through "lithium extraction front", and the process technical route of salt lake brine potassium, boron, lithium is changed into lithium, potassium, boron process route, and the production cycle of lithium salt product is shortened to 2 months from original 2-3 years, and lithium yield is doubled, and the process of lithium first, potassium second and boron third solves the problem of boron extraction acidification on lithium extraction membrane and equipment corrosion, and realizes the comprehensive development and utilization of salt lake resources.

Description

Technical Field

[0001] This invention relates to the field of lithium, potassium, and boron technology in salt lakes, specifically to a method for the cascade utilization of raw brine in salt lakes to co-produce lithium, potassium, and boron. Background Technology

[0002] According to relevant data reports, China's resource dependence on foreign sources is as high as 70%, with potassium resources exceeding 50% and boron resources reaching around 70%. Salt lake resources mainly contain elements such as sodium, magnesium, potassium, lithium, and boron. However, due to limitations in the comprehensive development and utilization technology of salt lake resources, the production capacity of lithium, potassium, and boron products has not been fully released. Taking the lithium resources of the Qaidam Basin as an example, the current total lithium carbonate production capacity is nearly 200,000 tons per year, but the actual output is only about 120,000 tons per year. The traditional technical route for producing lithium, potassium, and boron products from salt lake brine is: salt lake brine → salt field evaporation → sodium chloride → potassium mixed salt (soft potassium magnesium alum, potassium halite) → carnallite (Escarne salt, carnallite) → lithium- and boron-rich old brine. The potassium mixed salt and carnallite precipitated from the salt field evaporation are sent to a flotation unit to produce potassium magnesium fertilizer and potassium chloride, or further reacted with potassium magnesium fertilizer and potassium chloride to produce potassium sulfate; the lithium- and boron-rich old brine is sent to a processing plant to produce boric acid and lithium carbonate.

[0003] Traditional production technologies for potassium, boron, and lithium products from salt lakes involve high investment costs, long production cycles, significant environmental pressures, low resource utilization, and are detrimental to the development of salt lake resources in ecologically fragile areas. Potassium extraction results in the loss of some lithium and boron resources (due to entrainment and leakage). Similarly, boron extraction also results in some lithium loss (entrainment and leakage), leading to low lithium resource yields. Furthermore, the acid used in the boron extraction process, which involves boron extraction followed by lithium extraction, can adversely affect lithium extraction equipment such as nanofiltration membranes. This acid is highly corrosive to equipment and facilities, impacting the lifespan of materials and equipment, and posing significant risks. Invention patents published under CN112390266A, CN101024502A, and CN103539142A all disclose methods for producing boric acid and lithium carbonate from salt lake brine. However, the methods of first acidifying and extracting boron, then potassium and lithium, cannot avoid the aforementioned technical problems. Furthermore, the process of extracting lithium from old brine after potassium precipitation followed by boron extraction is inefficient because the brine is diluted after potassium and lithium extraction, making direct boron extraction impossible. It requires further concentration and acidification for boron extraction, resulting in a long production cycle and high costs. In the lithium extraction process, significant lithium loss occurs during the sun-drying of salt flats, potassium extraction, and boron extraction, resulting in an actual lithium yield of only about 30%, and a production cycle of 2-3 years, which is severely inconsistent with the rapid development of the market. Traditional salt lake resource extraction methods mainly target single elements, such as lithium or potassium, which is not only inefficient but also prone to resource waste. Therefore, developing a co-production system and method capable of simultaneously and efficiently extracting lithium, potassium, and boron from salt lakes is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of high investment costs, heavy environmental pressure, long product production cycle, low yield, low production efficiency, low resource utilization rate, and single product development of salt lake resources in existing technologies. This invention provides a method for the cascade utilization of raw brine in salt lakes to co-produce lithium, potassium, and boron. This method, through "pre-lithium extraction," transforms the potassium, boron, and lithium process route in salt lake brine into a lithium-potassium-boron process route. The lithium salt production cycle is shortened from the original 2-3 years to 2 months, and the lithium yield is increased by about 100%. Simultaneously, the lithium-first, potassium-second, and boron-third process solves the problem of corrosion of the lithium extraction membrane and equipment caused by boron acidification.

[0005] To achieve the above objectives, the present invention provides a method for the 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 liquid;

[0007] S2. Prepare battery-grade lithium products using the lithium-qualified liquid;

[0008] S3. The lithium extraction tail liquid is dried in a salt field to obtain potassium-containing solid salt, liquid old brine and magnesium chloride water;

[0009] S4. Potassium chloride product is prepared using the potassium-containing solid salt and hydrated magnesium chloride.

[0010] S5. Boric acid products are prepared using the liquid brine.

[0011] Preferably, in step S1, the original brine of the salt lake 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.

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

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

[0014] Preferably, the lithium extraction tail liquid 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: lithium ion concentration of 0.1-0.3 g / L, potassium ion concentration of ≤0.94 g / L, boron ion concentration of 1-4 g / L, magnesium ion concentration of 22.8-136.8 g / L, and sulfate ion concentration of 34-42 g / L.

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

[0017] S21. The qualified lithium solution is subjected to a first-stage nanofiltration treatment to obtain first-stage nanofiltration permeate, and then the first-stage nanofiltration permeate is concentrated by a reverse osmosis device to obtain reverse osmosis concentrate.

[0018] S22. The reverse osmosis concentrate is concentrated by passing it through an electrodialysis device to obtain electrodialysis concentrate and fresh water;

[0019] S23. The electrodialysis concentrate is subjected to secondary nanofiltration treatment to obtain secondary nanofiltration permeate, and then the secondary nanofiltration permeate is subjected to a resin ion exchange calcium and magnesium removal device to remove magnesium to obtain magnesium-free solution.

[0020] S24. The magnesium-removed qualified solution is concentrated by passing it through an MVR device to obtain an MVR concentrate. Then, the MVR concentrate is passed through a resin ion exchange boron removal device to remove boron to obtain a boron-removed qualified solution.

[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 battery-grade lithium carbonate finished product. Another portion of the qualified boron removal solution is treated with a bipolar membrane to prepare battery-grade lithium hydroxide monohydrate product.

[0022] Preferably, in step S21, the primary nanofiltration permeate contains the following components: lithium ions at a content of 0.35–0.45 g / L and magnesium ions at a content of ≤2 g / L.

[0023] In step S21, the reverse osmosis concentrate contains the following components: lithium ions at a concentration of 2.5–3.8 g / L and magnesium ions at a concentration of ≤250 mg / L.

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

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

[0026] Preferably, in step S23, the secondary nanofiltration permeate contains the following components: lithium ions at a content of 11–13.5 g / L and magnesium ions at a content of 3–5 mg / L.

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

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

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

[0030] Preferably, in step S25, the lithium precipitation mother liquor 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 potassium chloride product using the potassium-containing solid salt includes:

[0032] S41. Potassium-containing solid salt is conveyed to a crusher via a belt for crushing to obtain potassium mixed salt ore;

[0033] S42. The potassium mixed salt ore is dissolved and crystallized in sequence, then floated or reversed floated, and then dewatered by pressure filtration to obtain crude potassium product and potassium extraction flotation tailings. The crude potassium product is then washed, dewatered and dried in sequence to obtain potassium chloride product.

[0034] Preferably, the method further includes: stirring and mixing the potassium flotation tailings, the magnesium chloride, and nanofiltration concentrate to saturate the liquid phase with potassium ions, while simultaneously causing sodium chloride to precipitate from the liquid phase. After the chemical composition of the liquid phase meets the standards, it is clarified by precipitation and transported to a salt field for carnallite mineralization. The obtained solid potassium ore is returned to step S41 for crushing and potassium recovery, and the resulting solution tailings are returned to step S1 for lithium recovery. The nanofiltration concentrate is primary nanofiltration permeate and / or secondary nanofiltration permeate.

[0035] Preferably, the weight ratio of the nanofiltration concentrate, the magnesium chloride solution, and the potassium extraction flotation tailings is 1:1 to 1.5:1.5 to 1.8.

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

[0037] S51. After refining the liquid brine, adjust the pH value to 1.5±0.5 with acid, and then perform extraction and back-extraction to obtain a boron-containing back-extraction solution with a pH value of 1 to 3.

[0038] S52. Neutralize the boron-containing back-extraction solution with limestone to obtain a neutralized solution with a pH value of 3.5-4;

[0039] S53. The neutralized liquid is naturally evaporated in the evaporation tank until it reaches saturation, and then the evaporation continues to precipitate boric acid. When the thickness of the boric acid precipitated in the evaporation tank is greater than 20cm, it is harvested according to the construction procedure of dry salt field to obtain crude boron ore.

[0040] S54. The crude boron ore is mixed with pure water, an impurity removal agent is added, and then the mixture is heated and stirred. The resulting product is gradually heated to 85-90°C to obtain a hot solution.

[0041] S55. The hot solution is sequentially subjected to coarse filtration and refining to obtain refined filtrate and filter residue. The filter residue is washed with water, and the filtrate after washing is filtered by tail residue plate and frame filtration. The obtained filtrate enters the crystal slurry mother liquor tank.

[0042] S56. The refined filtrate is subjected to vacuum flash crystallization to obtain a crystal slurry at a temperature of 50-70°C. The crystal slurry is then cooled and crystallized in a cooling crystallizer to obtain a crystal slurry at a temperature of 20-25°C.

[0043] S57. The crystal slurry is separated by a centrifuge to obtain mother liquor and crystals. The mother liquor enters the crystal slurry mother liquor tank, and the crystals are dried to obtain 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 liquid is naturally evaporated to saturation in the evaporation tank, the boron concentration is 5-5.5% by weight.

[0046] In step S54, the impurity removal 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 vacuum flash crystallization include: a vacuum degree of 3000-10000 Pa and a crystallization time of 3-4 h.

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

[0050] (1) The method described in this invention realizes “pre-lithiation”, transforming the potassium, boron and lithium process route of salt lake brine into lithium, potassium and boron. The production cycle of lithium salt products is shortened from the original 2-3 years to 2 months, the lithium yield is increased by about 100%, and the potassium and boron yields remain unchanged. At the same time, the process of lithium first, then potassium and then boron solves the problems of the impact of boron acidification on the lithium extraction membrane and equipment corrosion. It also realizes the cascade utilization of salt lake brine resources and the co-production of lithium, potassium and boron products, and realizes the diversification of salt lake resource development products.

[0051] (2) The method described in this invention achieves the combined extraction of lithium, potassium and boron, which improves the comprehensive utilization rate of salt lake resources; it adopts an environmentally friendly process, which reduces pollution to the environment; the system is easy to operate and easy to scale up; it has significant economic benefits and good market application prospects. Detailed Implementation

[0052] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0053] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

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

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

[0056] S2. Prepare battery-grade lithium products using the lithium-qualified liquid;

[0057] S3. The lithium extraction tail liquid is dried in salt fields to obtain potassium-containing solid salt (the main components of potassium-containing solid salt are potassium mixed salt and carnallite), liquid old brine and hydrated magnesium chloride.

[0058] S4. Potassium chloride product is prepared using the potassium-containing solid salt and hydrated magnesium chloride.

[0059] S5. Boric acid products are prepared using the liquid brine.

[0060] The extraction sequence of the method described in this invention is lithium, potassium, and boron. By pre-extracting lithium, the lithium yield of salt lake brine can be improved, and the impact of acidification on boron extraction on the lifespan of lithium extraction membranes and corrosion of other lithium extraction equipment can be solved, which meets the requirements of green, low-carbon, and circular economic development.

[0061] In this invention, the original brine of the salt lake belongs to the high magnesium-to-lithium ratio magnesium sulfate subtype salt lake system. In some embodiments, the original brine of the salt lake 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 described in this invention, the purpose of step S1 is to extract lithium, achieving the separation of lithium from elements such as magnesium, potassium, and boron. The lithium extraction process in step S1 can be carried out using various methods well known in the art. In some embodiments, step S1 includes: filtering the original brine from the salt lake, and then extracting lithium using adsorption or membrane separation technology.

[0063] In a preferred embodiment, the lithium extraction process in step S1 includes: filtering the raw brine from the salt lake through a multi-media filter in the raw brine pool and then pumping it into a continuous adsorption lithium extraction device to adsorb lithium. Lithium is adsorbed in the continuous adsorption lithium extraction device, achieving separation from elements such as magnesium, potassium, and boron, and obtaining lithium extraction tail liquid. Then, a desorption solution is used to desorb lithium from the continuous adsorption lithium extraction device, forming a qualified lithium solution. The lithium yield of the qualified desorption solution is ≥70%, and the lithium yield of the qualified desorption solution is the lithium yield from the adsorption of lithium in the continuous adsorption lithium extraction device to the desorption of lithium by the desorption solution. In a more preferred embodiment, to improve the lithium yield during the lithium extraction process, the adsorbent in the continuous adsorption lithium extraction device can be at least one of aluminum-based adsorbents Al(OH)3, Li-Al-O-OH, and Li / Al-LDHs; the desorption solution used to desorb lithium from the continuous adsorption lithium extraction device is pure water. In the method described in this invention, in order to improve the lithium yield, when the adsorption efficiency of the continuous adsorption lithium extraction device drops below 70% after several cycles of operation, the adsorption capacity is regenerated using a regeneration reagent.

[0064] In some embodiments, the lithium extraction tail liquid 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; the low lithium ion concentration in the lithium extraction tail liquid indicates a better lithium extraction effect.

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

[0066] In this invention, step S2, which involves preparing battery-grade lithium products using the qualified lithium solution, includes passing the qualified lithium solution through gradient coupled membrane separation and purification devices such as nanofiltration membrane, ultrafiltration membrane, and electrodialysis, followed by magnesium and boron removal.

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

[0068] S21. The qualified lithium solution is pumped into a first-stage nanofiltration device for first-stage nanofiltration treatment to remove divalent calcium and magnesium ions, thereby obtaining first-stage nanofiltration permeate. The first-stage nanofiltration permeate is then concentrated by a reverse osmosis device to obtain reverse osmosis concentrate.

[0069] S22. The reverse osmosis concentrate is concentrated by passing it through an electrodialysis device to obtain electrodialysis concentrate and fresh water;

[0070] S23. The electrodialysis concentrate is subjected to secondary nanofiltration treatment through a secondary nanofiltration device to further remove divalent calcium and magnesium, thereby obtaining secondary nanofiltration permeate. Then, the secondary nanofiltration permeate is subjected to a resin ion exchange calcium and magnesium removal device to remove magnesium, thereby obtaining a qualified magnesium-removed solution.

[0071] S24. The magnesium removal qualified solution is concentrated by MVR device to obtain MVR concentrate, and then the MVR concentrate is debored by resin ion exchange boron removal device to obtain boron removal qualified solution and boron removal 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 battery-grade lithium carbonate finished product. Another portion of the qualified boron removal solution is treated with a bipolar membrane to prepare battery-grade lithium hydroxide monohydrate product.

[0073] In some embodiments, the primary nanofiltration permeate in step S21 contains the following components: lithium ions at a concentration of 0.35–0.45 g / L and magnesium ions at a concentration of ≤2 g / L.

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

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

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

[0077] In some embodiments, the secondary nanofiltration permeate in step S23 contains the following components: lithium ions at a content of 11-13.5 g / L and magnesium ions at a content of 3-5 mg / L;

[0078] In some embodiments, the magnesium removal solution in step S23 contains the following components: lithium ions at a content of 10–13.5 g / L and magnesium ions at a content of 0.3–1 mg / L.

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

[0080] In some embodiments, the boron-removed qualified solution in step S24 contains the following components: lithium ion content of 18-22 g / L and boron ion content of 0-10 mg / L. In this invention, the boron-removed tail liquid obtained after the MVR concentrate is debored by the resin ion exchange boron removal device contains the following components: lithium ion content of 0.1-2 g / L and boron ion content of 2-4 g / L.

[0081] In some embodiments, the lithium precipitation mother liquor in step S25 contains the following components: the content of lithium ions is 1.1 to 1.4 g / L, and the content of carbonate ions is 19 to 24 g / L.

[0082] In the method described in this invention, the process of preparing a battery-grade lithium hydroxide monohydrate product from another portion of the boron-removing qualified solution in step S25 after bipolar membrane treatment can be a common process in the art. In this invention, when the adsorption efficiency of the continuous adsorption lithium extraction device drops to 70% after several cycles of operation, the regeneration reagent used for adsorption capacity regeneration is hydrochloric acid, a byproduct of bipolar membrane lithium hydroxide production; the regeneration process includes: mixing 5-10% by mass of hydrochloric acid with the original brine of the salt lake at a volume ratio of 0.1-2:1000 and introducing it into the continuous adsorption lithium extraction device to regenerate the continuous adsorption lithium extraction device until the adsorption efficiency is restored before re-adsorption lithium extraction.

[0083] In the method described in this 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%, SO42- % 2- ≤0.0021%, Cl≤0.01%, moisture 0.13%.

[0084] S25. A portion of the boron removal qualified 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 battery-grade lithium carbonate product. Another portion of the boron removal qualified solution is treated with a bipolar film to prepare battery-grade lithium hydroxide monohydrate product.

[0085] In S25 of the present invention, in a preferred embodiment, the preparation process of the battery-grade lithium hydroxide monohydrate product includes:

[0086] (1) The qualified boron removal solution is treated by bipolar membrane electrodialysis, and the lithium hydroxide alkaline solution produced by bipolar membrane electrodialysis is concentrated by first flash evaporation to obtain a first concentrated solution with a solid content of 15%-40%.

[0087] (2) The first concentrate is centrifuged, and then the first solid product obtained by centrifugation is washed with water, wherein the weight ratio of the first solid product to water is 1:0.2-0.3, to obtain the first crude salt and the first mother liquor. Then, the first mother liquor is successively evaporated, concentrated, and centrifuged to obtain the second crude salt and Na. + The second mother liquor has a concentration of ≥50g / L, and the second mother liquor is discharged externally, with the volume ratio of the discharged lithium hydroxide alkaline solution to the discharged second mother liquor being ≥20:1;

[0088] (3) Mix the first crude salt and the second crude salt and dissolve them in water. Then, concentrate the resulting heavy solution by a second flash evaporation to obtain a second concentrated solution with a solid content of 15%-40%.

[0089] (4) Centrifuge the second concentrate, and then rinse 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 the third crude salt and the third mother liquor. Then the third crude salt is dried, and the third mother liquor is returned to step (1) for reuse.

[0090] In steps (2) and (4), the rinsing time is <40s.

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

[0093] In step S3 of this invention, the specific process of obtaining potassium-containing solid salt, magnesium chloride hydrate, and liquid brine by evaporating the lithium extraction tailings through salt pans includes: transporting the lithium extraction tailings through pipelines to salt pans; evaporating the brine naturally to first precipitate sodium chloride; then concentrating it until potassium chloride is saturated, separating the potassium-containing solid salt; and further evaporating to obtain magnesium chloride hydrate and liquid brine. 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: lithium ion concentration of 0.1–0.3 g / L, potassium ion concentration of ≤0.94 g / L, boron ion concentration of 1–4 g / L, magnesium ion concentration of 22.8–136.8 g / L, and sulfate ion concentration of 34–42 g / L.

[0095] In this invention, the potassium-containing solid salt obtained in step S3 enters the potassium extraction unit via a conveying system, and is then crushed by a crushing system, dissolved by a crystallization system, crystallized by a crystallization system, extracted by a flotation or reverse flotation system, filtered by a filtration system, washed by a washing system, and dehydrated and dried by a dehydration and drying system to obtain potassium chloride product.

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

[0097] S41. Potassium-containing solid salt is conveyed to a crusher via a belt for crushing to obtain potassium mixed salt ore;

[0098] S42. The potassium mixed salt ore is dissolved and crystallized in sequence, then floated or reversed floated, and then dewatered by pressure filtration to obtain crude potassium product and potassium extraction flotation tailings. The crude potassium product is then washed, dewatered and dried in sequence to obtain potassium chloride product.

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

[0100] In this invention, the method further includes: stirring and mixing the potassium extraction flotation tailings, the magnesium chloride, and nanofiltration concentrate to saturate the liquid phase with potassium ions and simultaneously precipitate sodium chloride. After the chemical composition of the liquid phase meets the standards (the standard for chemical composition is a potassium ion content of ≥13.5 g / L, a magnesium ion content of ≥70 g / L, and carnallite nearing the saturation precipitation point), the mixture is clarified by precipitation and transported to a salt field for carnallite mineralization. The resulting solid potassium ore is returned to step S41 for crushing and potassium recovery, and the resulting tailings solution is returned to step S1 for lithium recovery. The nanofiltration concentrate is primary nanofiltration permeate and / or secondary nanofiltration permeate. In a preferred embodiment, the weight ratio of the nanofiltration concentrate, the magnesium chloride, and the potassium extraction flotation tailings is 1:1–1.5:1.5–1.8, more preferably 1:1.2:1.6. This process is simple to operate, can utilize any low-potassium ore that cannot be directly used for production, and has a useful component recovery rate of over 90%. It can also be put into large-scale production.

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

[0102] S51. After refining the liquid brine, adjust the pH value to 1.5±0.5 with acid, and then perform extraction and back-extraction to obtain a boron-containing back-extraction solution with a pH value of 1 to 3. The raffinate is returned to the salt field after being de-oiled by an oil removal device.

[0103] S52. Neutralize the boron-containing back-extraction solution with limestone to obtain a neutralized solution with a pH value of 3.5-4;

[0104] S53. The neutralized liquid is naturally evaporated in the evaporation tank until it reaches saturation, and then the evaporation continues to precipitate boric acid. When the thickness of the boric acid precipitated in the evaporation tank is greater than 20cm, it is harvested according to the construction procedure of dry salt field to obtain crude boron ore.

[0105] S54. The crude boron ore is mixed with pure water and then an impurity removal agent (i.e., impurity adsorbent) is added. The mixture is then heated and stirred, and the resulting product is gradually heated to 85-90°C to obtain a hot solution.

[0106] S55. The hot solution is sequentially subjected to coarse filtration and refining to obtain refined filtrate and filter residue. The filter residue is washed with water. The filtrate after washing is filtered by tailings plate and frame filtration. The obtained filtrate enters the crystal slurry mother liquor tank. The obtained tailings are transported to the boiler for incineration as fuel.

[0107] S56. The refined filtrate is subjected to vacuum flash crystallization to obtain a crystal slurry at a temperature of 50-70°C. The crystal slurry is then cooled and crystallized in a cooling crystallizer to obtain a crystal slurry at a temperature of 20-25°C.

[0108] S57. The crystal slurry is separated by a centrifuge to obtain mother liquor and crystals. The mother liquor enters the crystal slurry mother liquor tank, and the crystals are dried to obtain refined boric acid product.

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

[0110] In this invention, the refining process in steps S51 and S55 is a conventional operation in the art, such as filtration.

[0111] In this invention, the acid used in step S51 can be a common inorganic acid 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 boron yield, the extractant used for extraction can be at least one of organic extractant, inorganic extractant and ion exchange resin, and the back-extraction agent used for back-extraction can be pure water with a pH value of 7±1.

[0113] In step S53 of this invention, when the neutralizing liquid is naturally evaporated to saturation in the evaporation tank, the boron concentration can be 5-5.5% by weight.

[0114] In step S54 of the present invention, in order to adsorb impurities in crude boron ore, the impurity removal agent is at least one of ion exchange resin and 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 vacuum flash crystallization include: a vacuum degree of 3000-10000 Pa and a crystallization time of 3-4 h.

[0117] In step S57 of the present invention, the drying process includes: drying the crystal by airflow or vibrating fluidized bed and then drying it with cold air.

[0118] The method described in this invention achieves the simultaneous and efficient extraction of lithium, potassium, and boron from raw brine in salt lakes through an integrated process, shifting the technical route from "potassium first, then boron, then lithium" to "lithium first, then potassium, then boron." The lithium yield from salt lake brine can be increased by approximately 100% (to approximately 60%), and the lithium production cycle is shortened from 2-3 years to about 2 months. Pre-processing for lithium extraction solves the impact of acidification during boron extraction on the lifespan of lithium extraction membranes and the corrosion of other lithium extraction equipment, while simultaneously achieving the co-production of lithium, potassium, and boron from salt lake resources. The method described in this invention aligns with the requirements of green, low-carbon, and circular economy development.

[0119] The following examples further illustrate the method for the cascade utilization of raw brine from salt lakes to co-produce lithium, potassium, and boron according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0120] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0121] In the following examples, the composition of the original brine of 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 the original brine of the salt lake × 100%.

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

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

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

[0129] (1) The qualified boron removal solution is treated by bipolar membrane electrodialysis. The lithium hydroxide alkaline solution produced by bipolar membrane electrodialysis is pumped into the condensate steam plate preheater and exchanged with distilled water and fresh steam respectively. After the lithium hydroxide alkaline solution is preheated to 80°C, it is transported to the first steam forced circulation heat exchanger by a forced circulation pump and heated to 85°C. Then, it is concentrated in the crystallizer by the first flash evaporation. The liquid phase temperature of the first flash evaporation is 84°C and the pressure is 665 mbar. When the solid content of the first concentrated solution reaches 25%, it is discharged by the discharge pump.

[0130] (2) The discharge pump delivers the first concentrated liquid to a centrifuge for centrifugation to obtain a first solid product and a first centrifuged liquid. The first solid product is then rinsed with water in the centrifuge to obtain a first crude salt and a first washing liquid. The first centrifuged liquid and the first washing liquid are combined to form a first mother liquor. During rinsing, the weight ratio of the first solid product to water is 1:0.3, and the rinsing time is 30 seconds. The first mother liquor is then transferred to a single-effect mother liquor tank and pumped into a single-effect evaporator for evaporation and concentration. After centrifugation, a second crude salt and a second mother liquor are obtained. The second mother liquor is discharged, with a discharge volume of 0.8 m³. 3 ;

[0131] (3) After mixing the first and second crude salts, distilled water is added to dissolve the salt to obtain a heavy solution. Then, the heavy solution is pumped into the condensate steam plate preheater to exchange heat with distilled water and fresh steam respectively to preheat the heavy solution. After the heavy solution is preheated to 80°C, it is transported to the second steam forced circulation heat exchanger through the second steam forced circulation pump and heated to 85°C. Then, it is concentrated in the crystallizer to the solid content of 28% to obtain the second concentrate. The liquid phase temperature of the second flash concentration is 85°C and the pressure is 425 mbar.

[0132] (4) The second concentrate is sent to a centrifuge to centrifuge to obtain the second solid product and the second centrifuged liquid. Then, the second solid product is rinsed with water in the centrifuge to obtain the third crude salt and the second washing liquid. The second centrifuged liquid and the second washing liquid are combined into the third mother liquor. The weight ratio of the second solid product to water during rinsing is 1:0.3, and the rinsing time is 30s. Then, the third mother liquor is returned to step (1) for the first flash evaporation concentration and reuse. The third crude salt is sent to the rotary kiln drying system. The dried salt is separated by a vibrating screen, and the screened material is 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 liquid.

[0135] The specific process includes:

[0136] The raw brine from the salt lake is filtered through a multi-media filter in the original brine pool and then pumped into a continuous adsorption lithium extraction unit to adsorb lithium. Lithium is adsorbed in the continuous adsorption lithium extraction unit, achieving separation from elements such as magnesium, potassium, and boron, and yielding lithium extraction tailings. Then, a desorption solution is used to desorb lithium from the continuous adsorption lithium extraction unit, forming a qualified lithium solution. The lithium yield of the qualified desorption solution is ≥90%, and the qualified lithium solution contains the following components: lithium ion concentration of 0.47 g / L, potassium ion concentration of 0.01 g / L, boron ion concentration of 0.12 g / L, magnesium ion concentration of 0.16 g / L, and sulfate ion concentration of 0. The lithium extraction tail liquid contains the following components: lithium ion concentration of 0.01 g / L, potassium ion concentration of 10.50 g / L, boron ion concentration of 0.36 g / L, magnesium ion concentration of 20.93 g / L, and sulfate ion concentration of 15.22 g / L. The adsorbent in the continuous adsorption lithium extraction device is a Li / Al-LDHs adsorbent, and the desorption solution for desorption in the continuous adsorption lithium extraction device is pure water. When the adsorption efficiency of the continuous adsorption lithium extraction device drops to 68% after several cycles of operation, the adsorption capacity is regenerated using a regeneration reagent. After regeneration, the adsorption efficiency of the adsorption device is restored to 83%.

[0137] S2. Using the lithium-grade liquid solution, prepare battery-grade lithium products.

[0138] The specific process includes:

[0139] S21. The qualified lithium solution obtained in step S1 is pumped into a primary nanofiltration unit for primary nanofiltration treatment to remove divalent calcium and magnesium ions, thereby obtaining primary nanofiltration permeate containing the following components: lithium ion content of 0.45 g / L and magnesium ion content of 1.57 g / L. Then, the primary nanofiltration permeate is concentrated by passing it through a reverse osmosis unit to obtain reverse osmosis concentrate containing the following components: lithium ion content of 3.48 g / L and magnesium ion content of 150 mg / L.

[0140] S22. The reverse osmosis concentrate is concentrated by passing it through an electrodialysis device to obtain electrodialysis concentrate and fresh water. The electrodialysis concentrate contains the following components: lithium ion content is 12.81 g / L, magnesium ion content is 0.83 g / L, and the fresh water contains the following components: lithium ion content is 1.52 g / L, magnesium ion content is 30 mg / L.

[0141] S23. The electrodialysis concentrate is subjected to secondary nanofiltration treatment through a secondary nanofiltration device to further remove divalent calcium and magnesium, resulting in secondary nanofiltration permeate containing the following components: lithium ion content of 12.11 g / L and magnesium ion content of 3.54 mg / L. The secondary nanofiltration permeate is then subjected to a resin ion exchange calcium and magnesium removal device to remove magnesium, resulting in a qualified magnesium-removed solution containing the following components: lithium ion content of 11.86 g / L and magnesium ion content of 0.72 mg / L.

[0142] S24. The magnesium-removed qualified solution is concentrated using an MVR device to obtain an MVR concentrate, wherein the MVR concentrate contains the following components: lithium ion content is 21.42 g / L. Then, the MVR concentrate is passed through a resin ion exchange boron removal device to remove boron, to obtain a boron-removed qualified solution and a boron-removed tail liquid, wherein the boron-removed qualified solution contains the following components: lithium ion content is 19.24 g / L, boron ion content is 5.71 mg / L, and the boron-removed tail liquid contains the following components: lithium ion content is 0.73 g / L, boron ion content is 2.86 g / L.

[0143] S25. A portion of the qualified boron-removing solution undergoes lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor. The lithium precipitation mother liquor contains the following components: lithium ion content is 1.21 g / L, carbonate ion content is 22.17 g / L. The crude lithium carbonate is washed and dried to obtain battery-grade lithium carbonate product. 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, SO₄²⁻. 2- 27.75 ppm, Cl - The concentration of Mg2+ is 58.23 ppm, and the water content is 0.15%. Another portion of the qualified boron-removing solution is treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product. The battery-grade lithium hydroxide monohydrate product has the following composition: LiOH: 57.46%, Ca: 1.36 ppm, Mg: 1.53 ppm, Na: 19.09 ppm, K: 4.33 ppm, B: 3.77 ppm, Si: ≤1 ppm, Fe: 1.07 ppm, Cl... - : 18.33ppm, sulfate ions: 1.62ppm, carbonate ions: 0.63%;

[0144] Recycling process: Hydrochloric acid, a byproduct of bipolar membrane lithium hydroxide production, is returned to step S1 to regenerate the continuous adsorption lithium extraction device. The regeneration process includes: mixing 7% by mass hydrochloric acid with the original brine of the salt lake at a volume ratio of 1:1000 and feeding it into the continuous adsorption lithium extraction device to regenerate the device. Once the adsorption efficiency reaches 83%, normal adsorption lithium extraction is carried out.

[0145] S3. The lithium extraction tail liquid is dried over a salt flat to obtain potassium-containing solid salt (mainly composed of potassium mixed salt and carnallite), magnesium chloride hydrate, and liquid old brine.

[0146] The specific process includes:

[0147] The lithium extraction tailings are transported to salt fields via pipeline. Through sun-drying in the salt fields, the brine is naturally evaporated to first precipitate sodium chloride. Then, it is concentrated until potassium chloride saturation, separating potassium-containing solid salts. Further sun-drying yields a liquid brine containing magnesium chloride and other minerals. This liquid brine contains the following components: lithium ions at a concentration of 0.23 g / L, potassium ions at a concentration of 0.71 g / L, boron ions at a concentration of 3.56 g / L, magnesium ions at a concentration of 119.26 g / L, and sulfate ions at a concentration of 38.62 g / L.

[0148] S4. Prepare potassium chloride product using the potassium-containing solid salt and hydrated magnesium chloride.

[0149] The specific process includes:

[0150] S41. Potassium-containing solid salt is conveyed to a crusher via a belt for crushing to obtain potassium mixed salt ore;

[0151] S42. The potassium mixed salt ore is dissolved and crystallized sequentially, then floated or reversed floated, and then dewatered by pressure filtration to obtain crude potassium product and potassium extraction flotation tailings. The crude potassium product is then washed, dewatered and dried sequentially to obtain potassium chloride product, wherein the composition of the potassium chloride product is KCl: 92.74%, K2O: 58.68%, Na: 2.43%, H2O: 0.18%.

[0152] Recovery process: The potassium extraction flotation tailings are stirred and mixed with the magnesium chloride and nanofiltration concentrate to saturate the liquid phase with potassium ions and precipitate sodium chloride. After the chemical composition of the liquid phase meets the standards (potassium ion content of ≥13.5g / L, magnesium ion content of ≥70g / L, and carnallite near saturation precipitation point), the precipitate is clarified and transported to the salt field for carnallite mineralization. The resulting solid potassium ore is returned to step S41 for crushing and potassium recovery. The resulting solution tailings are returned to step S1 for lithium recovery. The nanofiltration concentrate is primary nanofiltration permeate, and the weight ratio of the nanofiltration concentrate, magnesium chloride, and potassium extraction flotation tailings is 1:1.2:1.6.

[0153] S5. Prepare boric acid products using the liquid aged brine.

[0154] The specific process includes:

[0155] S51. After refining the liquid brine, the pH value is adjusted to 1.5 with hydrochloric acid, and then extraction and back-extraction are performed to obtain a boron-containing back-extraction solution with a pH value of 2. The raffinate is returned to the salt field after being de-oiled by an oil removal device. The extractant used in the extraction is an alcohol-based composite extractant, and the back-extraction agent used in the back-extraction is pure water.

[0156] S52. Neutralize the boron-containing back-extraction solution with limestone to obtain a neutralized solution with a pH of 3.8;

[0157] S53. The neutralized liquid is naturally evaporated in an evaporation tank until it reaches saturation, with a boron concentration of 5.25% by weight. Then, evaporation continues to precipitate boric acid. When the thickness of the boric acid precipitated in the evaporation tank reaches 21 cm, it is harvested according to the construction procedures of dry salt fields to obtain crude boron ore.

[0158] S54. The crude boron ore is mixed with pure water and then ion exchange resin is added to remove impurities. The mixture is then heated and stirred at 90°C, and the resulting product is heated to 95°C step by step through a steam coil to obtain a hot solution.

[0159] S55. The hot solution is sequentially subjected to coarse filtration and refining to obtain refined filtrate and filter residue. The filter residue is washed with water. The filtrate after washing is filtered by tailings plate and frame filtration. The obtained filtrate enters the crystal slurry mother liquor tank. The obtained tailings are transported to the boiler for incineration as fuel.

[0160] S56. The refined filtrate is subjected to vacuum flash crystallization to obtain a crystal slurry at a temperature of 60°C. The conditions for vacuum flash crystallization include: a vacuum degree of 7000 Pa and a crystallization time of 3.5 h. The crystal slurry is then cooled and crystallized in a cooling crystallizer to obtain a crystal slurry at 23°C.

[0161] S57. The crystal slurry is separated by a centrifuge to obtain mother liquor and crystals. The mother liquor enters the crystal slurry mother liquor tank, and the crystals are dried by airflow and then dried by cold air to obtain a refined boric acid product. The refined boric acid product has a purity of 99.95%, Cl: 58.36ppm, Na: 163.53ppm, sulfate ion: 37.74ppm, and Mg: 7.95ppm.

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

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

[0166] The specific process includes:

[0167] The raw brine from the salt lake is filtered through a multi-media filter in the original brine pool and then pumped into a continuous adsorption lithium extraction unit to adsorb lithium. Lithium is adsorbed in the continuous adsorption lithium extraction unit, achieving separation from elements such as magnesium, potassium, and boron, and yielding lithium extraction tailings. Then, a desorption solution is used to desorb lithium from the continuous adsorption lithium extraction unit, forming a qualified lithium solution. The lithium yield of the qualified desorption solution is ≥90%, and the qualified lithium solution contains the following components: lithium ion concentration of 0.43 g / L, potassium ion concentration of ≤0.01 g / L, boron ion concentration of 0.13 g / L, magnesium ion concentration of 0.14 g / L, and sulfate ion concentration of ≤ The lithium extraction tail liquid contains the following components: lithium ion concentration ≤0.01g / L, potassium ion concentration 10.34g / L, boron ion concentration 0.38g / L, magnesium ion concentration 21.05g / L, and sulfate ion concentration 15.74g / L. The adsorbent in the continuous adsorption lithium extraction device is Al(OH)3 adsorbent, and the desorption solution for desorption in the continuous adsorption lithium extraction device is pure water. When the adsorption efficiency of the continuous adsorption lithium extraction device drops to 68% after several cycles of operation, the adsorption capacity is regenerated using a regeneration reagent. After regeneration, the adsorption efficiency of the adsorption device recovers to over 83%.

[0168] S2. Using the lithium-grade liquid solution, prepare battery-grade lithium products.

[0169] The specific process includes:

[0170] S21. The qualified lithium solution obtained in step S1 is pumped into a primary nanofiltration device for primary nanofiltration treatment to remove divalent calcium and magnesium ions, thereby obtaining primary nanofiltration permeate, wherein the primary nanofiltration permeate contains the following components: lithium ion content of 0.42 g / L and magnesium ion content of 1.63 g / L. Then, the primary nanofiltration permeate is concentrated by passing it through a reverse osmosis device to obtain reverse osmosis concentrate, wherein the reverse osmosis concentrate contains the following components: lithium ion content of 3.30 g / L and magnesium ion content of 143 mg / L.

[0171] S22. The reverse osmosis concentrate is concentrated using an electrodialysis device to obtain electrodialysis concentrate and fresh water. The electrodialysis concentrate contains the following components: lithium ion content of 12.13 g / L and magnesium ion content of 0.91 g / L. The fresh water contains the following components: lithium ion content of 1.43 g / L and magnesium ion content of 28.36 mg / L.

[0172] S23. The electrodialysis concentrate is subjected to secondary nanofiltration treatment through a secondary nanofiltration device to further remove divalent calcium and magnesium, resulting in secondary nanofiltration permeate containing the following components: lithium ion content of 11.92 g / L and magnesium ion content of 3.21 mg / L. The secondary nanofiltration permeate is then subjected to a resin ion exchange calcium and magnesium removal device to remove magnesium, resulting in a qualified magnesium-removed solution containing the following components: lithium ion content of 11.53 g / L and magnesium ion content of 0.54 mg / L.

[0173] S24. The magnesium-removed qualified solution is concentrated using an MVR device to obtain an MVR concentrate, wherein the MVR concentrate contains the following components: lithium ion content is 21.03 g / L. Then, the MVR concentrate is passed through a resin ion exchange boron removal device to remove boron, to obtain a boron-removed qualified solution and a boron-removed tail liquid, wherein the boron-removed qualified solution contains the following components: lithium ion content is 19.05 g / L, boron ion content is 5.31 mg / L, and the boron-removed tail liquid contains the following components: lithium ion content is 0.80 g / L, boron ion content is 2.47 g / L.

[0174] S25. A portion of the qualified boron-removing solution undergoes lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor. The lithium precipitation mother liquor contains the following components: lithium ion content is 1.18 g / L, carbonate ion content is 20.42 g / L. The crude lithium carbonate is washed and dried to obtain battery-grade lithium carbonate product. 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, SO₄²⁻. 2- 26.94 ppm, Cl -The concentration of the boron-removing solution was 52.46 ppm, and the water content was 0.14%. Another portion of the qualified boron-removing solution was treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product. The battery-grade lithium hydroxide monohydrate product had the following composition: LiOH: 56.89%, Ca: 1.41 ppm, Mg: 1.57 ppm, Na: 15.41 ppm, K: 3.11 ppm, B: 3.74 ppm, Si: ≤1 ppm, Fe: 0.63 ppm, Cl... - : 15.34 ppm, sulfate ions: 1.46 ppm, carbonate ions: 0.72%;

[0175] Hydrochloric acid, a byproduct of bipolar membrane lithium hydroxide production, is returned to step S1 to regenerate the continuous adsorption lithium extraction device. The regeneration process includes: mixing 7% hydrochloric acid by mass with the original brine of the salt lake at a volume ratio of 1:1000 and feeding it into the continuous adsorption lithium extraction device to regenerate the device. Once the adsorption efficiency reaches 83%, normal adsorption lithium extraction is carried out.

[0176] S3. The lithium extraction tail liquid is dried over a salt flat to obtain potassium-containing solid salt, magnesium chloride hydrate, and liquid brine.

[0177] The specific process includes:

[0178] The lithium extraction tailings are transported to salt fields via pipeline. Through sun-drying in the salt fields, the brine is naturally evaporated to first precipitate sodium chloride. Then, it is concentrated until potassium chloride saturation, separating potassium-containing solid salts. Further sun-drying yields a liquid brine containing magnesium chloride and other minerals. This liquid brine contains the following components: lithium ions at a concentration of 0.21 g / L, potassium ions at a concentration of 0.73 g / L, boron ions at a concentration of 3.52 g / L, magnesium ions at a concentration of 120.17 g / L, and sulfate ions at a concentration of 38.59 g / L.

[0179] S4. Prepare potassium chloride product using the potassium-containing solid salt and hydrated magnesium chloride.

[0180] The specific process includes:

[0181] S41. Potassium-containing solid salt is conveyed to a crusher via a belt for crushing to obtain potassium mixed salt ore;

[0182] S42. The potassium mixed salt ore is dissolved and crystallized sequentially, then floated or reversed floated, and then dewatered by pressure filtration to obtain crude potassium product and potassium extraction flotation tailings. The crude potassium product is then washed, dewatered and dried sequentially to obtain potassium chloride product, wherein the composition of the potassium chloride product is KCl: 91.18%, K2O: 57.95%, Na: 2.46%, H2O: 0.21%.

[0183] The potassium extraction flotation tailings are stirred and mixed with the magnesium chloride and nanofiltration concentrate to saturate the liquid phase with potassium ions and simultaneously precipitate sodium chloride. After the chemical composition of the liquid phase meets the standards (potassium ion content of ≥13.5g / L, magnesium ion content of ≥70g / L, and carnallite near saturation precipitation point), the precipitate is clarified and transported to the salt field for carnallite mineralization. The resulting solid potassium ore is returned to step S41 for crushing and potassium recovery, and the resulting solution tailings are returned to step S1 for lithium recovery. The nanofiltration concentrate is primary nanofiltration permeate, and the weight ratio of the nanofiltration concentrate, magnesium chloride, and potassium extraction flotation tailings is 1:1.2:1.6.

[0184] S5. Prepare boric acid products using the liquid aged brine.

[0185] The specific process includes:

[0186] S51. After refining the liquid brine, the pH value is adjusted to 1.5 with hydrochloric acid, and then extraction and back-extraction are performed to obtain a boron-containing back-extraction solution with a pH value of 2. The raffinate is returned to the salt field after being de-oiled by an oil removal device. The extractant used in the extraction is an alcohol-based composite extractant, and the back-extraction agent used in the back-extraction is pure water.

[0187] S52. Neutralize the boron-containing back-extraction solution with limestone to obtain a neutralized solution with a pH of 3.8;

[0188] S53. The neutralized liquid is naturally evaporated in an evaporation tank until it reaches saturation, with a boron concentration of 5.23% by weight. Then, evaporation continues to precipitate boric acid. When the thickness of the boric acid precipitated in the evaporation tank reaches 21 cm, it is harvested according to the construction procedures of dry salt fields to obtain crude boron ore.

[0189] S54. The crude boron ore is mixed with pure water and then ion exchange resin is added as an impurity removal agent. The mixture is then heated and stirred at 90°C, and the resulting product is heated to 95°C step by step through a steam coil to obtain a hot solution.

[0190] S55. The hot solution is sequentially subjected to coarse filtration and refining to obtain refined filtrate and filter residue. The filter residue is washed with water. The filtrate after washing is filtered by tailings plate and frame filtration. The obtained filtrate enters the crystal slurry mother liquor tank. The obtained tailings are transported to the boiler for incineration as fuel.

[0191] S56. The refined filtrate is subjected to vacuum flash crystallization to obtain a crystal slurry at a temperature of 60°C. The conditions for vacuum flash crystallization include: a vacuum degree of 7000 Pa and a crystallization time of 3.5 h. The crystal slurry is then cooled and crystallized in a cooling crystallizer to obtain a crystal slurry at 23°C.

[0192] S57. The crystal slurry is separated by a centrifuge to obtain mother liquor and crystals. The mother liquor enters the crystal slurry mother liquor tank, and the crystals are dried by airflow and then dried by cold air to obtain a refined boric acid product. The refined boric acid product has a purity of 99.91%, Cl: 65.39ppm, Na: 172.24ppm, sulfate ion: 41.03ppm, and Mg: 8.04ppm.

[0193] The solution obtained by mixing the filtrate entering the crystal slurry mother liquor tank in step S55 with the mother liquor entering the crystal slurry mother liquor tank in step S57 is returned to step S54 and mixed with the crude boron ore before adding the adsorbent.

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

[0197] The specific process includes:

[0198] The raw brine from the salt lake is filtered through a multi-media filter in the original brine pool and then pumped into a continuous adsorption lithium extraction unit to adsorb lithium. Lithium is adsorbed in the continuous adsorption lithium extraction unit, achieving separation from elements such as magnesium, potassium, and boron, and yielding lithium extraction tailings. Then, a desorption solution is used to desorb lithium from the continuous adsorption lithium extraction unit, forming a qualified lithium solution. The lithium recovery rate of the qualified lithium solution is 90%, and the qualified lithium solution contains the following components: lithium ion concentration of 0.45 g / L, potassium ion concentration ≤0.01 g / L, boron ion concentration of 0.13 g / L, magnesium ion concentration of 0.15 g / L, and sulfate ion concentration ≤0. The lithium extraction tail liquid contains the following components: lithium ion concentration ≤0.01g / L, potassium ion concentration 10.47g / L, boron ion concentration 0.35g / L, magnesium ion concentration 20.92g / L, and sulfate ion concentration 15.34g / L. The adsorbent in the continuous adsorption lithium extraction device is Li-Al-O-OH adsorbent, and the desorption solution for desorption in the continuous adsorption lithium extraction device is pure water. When the adsorption efficiency of the continuous adsorption lithium extraction device drops to 68% after several cycles of operation, the adsorption capacity is regenerated using a regeneration reagent. After regeneration, the adsorption efficiency of the adsorption device recovers to 83%.

[0199] S2. Using the lithium-grade liquid solution, prepare battery-grade lithium products.

[0200] The specific process includes:

[0201] S21. The qualified lithium solution obtained in step S1 is pumped into a primary nanofiltration unit for primary nanofiltration treatment to remove divalent calcium and magnesium ions, thereby obtaining primary nanofiltration permeate containing the following components: lithium ion content of 0.44 g / L and magnesium ion content of 1.61 g / L. Then, the primary nanofiltration permeate is concentrated by passing it through a reverse osmosis unit to obtain reverse osmosis concentrate containing the following components: lithium ion content of 3.21 g / L and magnesium ion content of 143 mg / L.

[0202] S22. The reverse osmosis concentrate is concentrated using an electrodialysis device to obtain electrodialysis concentrate and fresh water. The electrodialysis concentrate contains the following components: lithium ion content of 12.69 g / L and magnesium ion content of 0.78 g / L. The fresh water contains the following components: lithium ion content of 1.42 g / L and magnesium ion content of 29.97 mg / L.

[0203] S23. The electrodialysis concentrate is subjected to secondary nanofiltration treatment through a secondary nanofiltration device to further remove divalent calcium and magnesium, resulting in secondary nanofiltration permeate containing the following components: lithium ion content of 11.98 g / L and magnesium ion content of 3.39 mg / L. The secondary nanofiltration permeate is then subjected to a resin ion exchange calcium and magnesium removal device to remove magnesium, resulting in a qualified magnesium-removed solution containing the following components: lithium ion content of 11.69 g / L and magnesium ion content of 0.66 mg / L.

[0204] S24. The magnesium-removed qualified solution is concentrated using an MVR device to obtain an MVR concentrate, wherein the MVR concentrate contains the following components: lithium ion content is 21.39 g / L. Then, the MVR concentrate is passed through a resin ion exchange boron removal device to remove boron, to obtain a boron-removed qualified solution and a boron-removed tail liquid, wherein the boron-removed qualified solution contains the following components: lithium ion content is 19.46 g / L, boron ion content is 5.53 mg / L, and the boron-removed tail liquid contains the following components: lithium ion content is 0.68 g / L, boron ion content is 2.57 g / L.

[0205] S25. A portion of the qualified boron-removing solution undergoes lithium precipitation to obtain crude lithium carbonate and lithium precipitation mother liquor. The lithium precipitation mother liquor contains the following components: lithium ion content is 1.24 g / L, carbonate ion content is 22.32 g / L. The crude lithium carbonate is washed and dried to obtain battery-grade lithium carbonate product. 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, SO₄²⁻. 2- 25.40 ppm, Cl - The concentration of the boron-removing solution was 61.10 ppm, and the water content was 0.12%. Another portion of the qualified boron-removing solution was treated with a bipolar membrane to prepare a battery-grade lithium hydroxide monohydrate product. The battery-grade lithium hydroxide monohydrate product had the following composition: LiOH: 57.33%, Ca: 1.04 ppm, Mg: 1.47 ppm, Na: 15.1 ppm, K: 1.23 ppm, B: 1.01 ppm, Si: 4.13 ppm, Fe: 0.80 ppm, Cl: 61.10 ppm, water: 0.12%. - : 18.96ppm, sulfate ions: 1.24ppm, carbonate ions: 0.58%;

[0206] Hydrochloric acid, a byproduct of bipolar membrane lithium hydroxide production, is returned to step S1 to regenerate the continuous adsorption lithium extraction device. The regeneration process includes: mixing 7% hydrochloric acid by mass with the original brine of the salt lake at a volume ratio of 1:1000 and feeding it into the continuous adsorption lithium extraction device to regenerate the device. Once the adsorption efficiency reaches 83%, normal adsorption lithium extraction is carried out.

[0207] S3. The lithium extraction tail liquid is dried over a salt flat to obtain potassium-containing solid salt, magnesium chloride hydrate, and liquid brine.

[0208] The specific process includes:

[0209] The lithium extraction tailings are transported to salt fields via pipeline. Through sun-drying in the salt fields, the brine is naturally evaporated to first precipitate sodium chloride. Then, it is concentrated until potassium chloride saturation, separating potassium-containing solid salts. Further sun-drying yields a liquid brine containing magnesium chloride and other minerals. This liquid brine contains the following components: lithium ions at a concentration of 0.22 g / L, potassium ions at a concentration of 0.69 g / L, boron ions at a concentration of 3.54 g / L, magnesium ions at a concentration of 119.86 g / L, and sulfate ions at a concentration of 38.65 g / L.

[0210] S4. Prepare potassium chloride product using the potassium-containing solid salt and hydrated magnesium chloride.

[0211] The specific process includes:

[0212] S41. Potassium-containing solid salt is conveyed to a crusher via a belt for crushing to obtain potassium mixed salt ore;

[0213] S42. The potassium mixed salt ore is dissolved and crystallized sequentially, then floated or reversed floated, and then dewatered by pressure filtration to obtain crude potassium product and potassium extraction flotation tailings. The crude potassium product is then washed, dewatered and dried sequentially to obtain potassium chloride product, wherein the composition of the potassium chloride product is KCl: 91.69%, K2O: 57.48%, Na: 2.83%, H2O: 0.19%.

[0214] The potassium extraction flotation tailings are stirred and mixed with the magnesium chloride and nanofiltration concentrate to saturate the liquid phase with potassium ions and simultaneously precipitate sodium chloride. After the chemical composition of the liquid phase meets the standards (potassium ion content of ≥13.5g / L, magnesium ion content of ≥70g / L, and carnallite near saturation precipitation point), the precipitate is clarified and transported to the salt field for carnallite mineralization. The resulting solid potassium ore is returned to step S41 for crushing and potassium recovery, and the resulting solution tailings are returned to step S1 for lithium recovery. The nanofiltration concentrate is primary nanofiltration permeate, and the weight ratio of the nanofiltration concentrate, magnesium chloride, and potassium extraction flotation tailings is 1:1.2:1.6.

[0215] S5. Prepare boric acid products using the liquid aged brine.

[0216] The specific process includes:

[0217] S51. After refining the liquid brine, the pH value is adjusted to 1.5 with hydrochloric acid, and then extraction and back-extraction are performed to obtain a boron-containing back-extraction solution with a pH value of 2. The raffinate is returned to the salt field after being de-oiled by an oil removal device. The extractant used in the extraction is an alcohol-based composite extractant, and the back-extraction agent used in the back-extraction is pure water.

[0218] S52. Neutralize the boron-containing back-extraction solution with limestone to obtain a neutralized solution with a pH of 3.8;

[0219] S53. The neutralized liquid is naturally evaporated in an evaporation tank until it reaches saturation, with a boron concentration of 5.27% by weight. Then, evaporation continues to precipitate boric acid. When the thickness of the boric acid precipitated in the evaporation tank reaches 21 cm, it is harvested according to the construction procedures of dry salt fields to obtain crude boron ore.

[0220] S54. The crude boron ore is mixed with pure water and then ion exchange resin is added as an impurity removal agent. The mixture is then heated and stirred at 90°C, and the resulting product is heated to 95°C step by step through a steam coil to obtain a hot solution.

[0221] S55. The hot solution is sequentially subjected to coarse filtration and refining to obtain refined filtrate and filter residue. The filter residue is washed with water. The filtrate after washing is filtered by tailings plate and frame filtration. The obtained filtrate enters the crystal slurry mother liquor tank. The obtained tailings are transported to the boiler for incineration as fuel.

[0222] S56. The refined filtrate is subjected to vacuum flash crystallization to obtain a crystal slurry at a temperature of 60°C. The conditions for vacuum flash crystallization include: a vacuum degree of 7000 Pa and a crystallization time of 3.5 h. The crystal slurry is then cooled and crystallized in a cooling crystallizer to obtain a crystal slurry at 23°C.

[0223] S57. The crystal slurry is separated by a centrifuge to obtain mother liquor and crystals. The mother liquor enters the crystal slurry mother liquor tank, and the crystals are dried by airflow and then dried by cold air to obtain a refined boric acid product. The refined boric acid product has a purity of 99.93%, Cl: 55.76ppm, Na: 156.38ppm, sulfate ion: 35.53ppm, and Mg: 7.24ppm.

[0224] The solution obtained by mixing the filtrate entering the crystal slurry mother liquor tank in step S55 with the mother liquor entering the crystal slurry mother liquor tank in step S57 is returned to step S54 and mixed with the crude boron ore before adding the adsorbent.

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

[0226] Comparative Example 1

[0227] S1. The original brine of the salt lake is dried in the salt fields to obtain potassium-containing solid salt (potassium mixed salt, carnallite), liquid old brine and water magnesium chloride;

[0228] S2. Potassium chloride product is prepared using the potassium-containing solid salt and hydrated magnesium chloride.

[0229] S3. Boric acid is prepared using the liquid old brine to obtain boron extraction tail liquid;

[0230] S4. Use the boron extraction tail liquid for adsorption and lithium extraction to prepare lithium carbonate product.

[0231] The preparation steps for potassium chloride, boric acid, and lithium carbonate products are the same as in Example 1, except that steps S2, S4, and S5 (recovery process) 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 from the examples and comparative examples, as well as the yields of lithium, potassium, and boron, are shown in Tables 1 and 2.

[0234] Table 1

[0235]

[0236] Table 2

[0237]

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

[0239] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for the cascade utilization of raw brine from salt lakes to co-produce lithium, potassium, and boron, characterized in that, This method consists of the following steps: S1. Lithium is extracted from the original brine of the salt lake to obtain a qualified lithium solution and a lithium extraction tailings. The qualified lithium solution contains the following components: lithium ion concentration of 0.2-0.6 g / L, potassium ion concentration of ≤0.05 g / L, boron ion concentration of ≤0.2 g / L, magnesium ion concentration of ≤0.36 g / L, and sulfate ion concentration of ≤0.03 g / L. The lithium extraction tailings contain the following components: lithium ion concentration of ≤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, and sulfate ion concentration of 10-30 g / L. S2. Prepare battery-grade lithium products using the lithium-qualified liquid; S3. The lithium extraction tail liquid is dried in a salt field to obtain potassium-containing solid salt, liquid old brine and magnesium chloride water; S4. Potassium chloride product is prepared using the potassium-containing solid salt and hydrated magnesium chloride. S5. Prepare boric acid products using the liquid brine; In step S4, the preparation of potassium chloride product using the potassium-containing solid salt is carried out according to the following steps: S41. Potassium-containing solid salt is conveyed to a crusher via a belt for crushing to obtain potassium mixed salt ore; S42. Dissolve and crystallize the potassium mixed salt ore in sequence, then perform flotation or reverse flotation, and then dewater it by pressure filtration to obtain crude potassium product and potassium extraction flotation tailings. Then wash, dewater and dry the crude potassium product in sequence to obtain potassium chloride product. The potassium flotation tailings, the magnesium chloride, and the nanofiltration concentrate are stirred and mixed to saturate the liquid phase with potassium ions and simultaneously precipitate sodium chloride. After the chemical composition of the liquid phase meets the standards, it is clarified by precipitation and transported to the salt field for carnallite mineralization. The obtained solid potassium ore is returned to step S41 for crushing and potassium recovery, and the resulting solution tailings are returned to step S1 for lithium recovery. The nanofiltration concentrate is primary nanofiltration permeate and / or secondary nanofiltration permeate. In step S5, the process of preparing boric acid products using the liquid brine includes: S51. After refining the liquid brine, adjust the pH value to 1.5±0.5 with acid, and then perform extraction and back-extraction to obtain a boron-containing back-extraction solution with a pH value of 1~3. S52. Neutralize the boron-containing back-extraction solution with limestone to obtain a neutralized solution with a pH value of 3.5-4; S53. The neutralized liquid is naturally evaporated in the evaporation tank until it reaches saturation, and then the evaporation continues to precipitate boric acid. When the thickness of the boric acid precipitated in the evaporation tank is greater than 20cm, it is harvested according to the construction procedure of dry salt field to obtain crude boron ore. S54. The crude boron ore is mixed with pure water, an impurity removal agent is added, and then the mixture is heated and stirred. The resulting product is gradually heated to 85-90°C to obtain a hot solution. S55. The hot solution is sequentially subjected to coarse filtration and refining to obtain refined filtrate and filter residue. The filter residue is washed with water, and the filtrate after washing is filtered by tail residue plate and frame filtration. The obtained filtrate enters the crystal slurry mother liquor tank. S56. The refined filtrate is subjected to vacuum flash crystallization to obtain a crystal slurry at a temperature of 50~70℃. The crystal slurry is then cooled and crystallized in a cooling crystallizer to obtain a crystal slurry at a temperature of 20~25℃. S57. The crystal slurry is separated by a centrifuge to obtain mother liquor and crystals. The mother liquor enters the crystal slurry mother liquor tank, and the crystals are dried to obtain refined 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 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.

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

4. The method according to claim 1, characterized in that, In step S3, the liquid brine contains the following components: lithium ion concentration of 0.1-0.3 g / L, potassium ion concentration of ≤0.94 g / L, boron ion concentration of 1-4 g / L, magnesium ion concentration of 22.8-136.8 g / L, and sulfate ion concentration of 34-42 g / L.

5. The method according to claim 1, characterized in that, In step S2, the process of preparing battery-grade lithium products using the qualified lithium solution includes: S21. The qualified lithium solution is subjected to a first-stage nanofiltration treatment to obtain first-stage nanofiltration permeate, and then the first-stage nanofiltration permeate is concentrated by a reverse osmosis device to obtain reverse osmosis concentrate. S22. The reverse osmosis concentrate is concentrated by passing it through an electrodialysis device to obtain electrodialysis concentrate and fresh water; S23. The electrodialysis concentrate is subjected to secondary nanofiltration treatment to obtain secondary nanofiltration permeate, and then the secondary nanofiltration permeate is subjected to a resin ion exchange calcium and magnesium removal device to remove magnesium to obtain magnesium-free solution. S24. The magnesium-removed qualified solution is concentrated by passing it through an MVR device to obtain an MVR concentrate. Then, the MVR concentrate is passed through a resin ion exchange boron removal device to remove boron to obtain a boron-removed qualified solution. 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 battery-grade lithium carbonate finished product. Another portion of the qualified boron removal solution is treated with a bipolar membrane to prepare battery-grade lithium hydroxide monohydrate product.

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

7. The method according to claim 1, characterized in that, The weight ratio of the nanofiltration concentrate, the magnesium chloride solution, and the potassium extraction flotation tailings is 1:1~1.5:1.5~1.

8.

8. The method according to claim 7, characterized in that, In step S51, the acid is hydrochloric acid and / or sulfuric acid; In step S53, when the neutralized liquid is naturally evaporated to saturation in the evaporation tank, the boron concentration is 5-5.5% by weight. In step S54, the impurity removal agent is an ion exchange resin and / or a chelating resin; In step S56, the conditions for vacuum flash crystallization include: a vacuum degree of 3000-10000 Pa and a crystallization time of 3-4 h.

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