Method for recovering lithium from salt lake brine with high magnesium-lithium ratio

Abstract

The invention provides a method for recovering lithium from salt lake brine with a high magnesium-lithium ratio. Lithium is extracted through the working procedures of pretreatment, adsorption, desorption, solvent extraction and precipitation, a specific extraction agent is adopted for saponification, a saponified organic phase is prepared, then the saponified organic phase and a lithium-containing desorption solution are extracted, and a raffinate and a loaded organic phase are obtained respectively; carrying out reverse extraction on the loaded organic phase to respectively obtain a lithium-containing concentrated solution and a blank organic phase; and then, mixing the lithium-containing concentrated solution with a precipitant, and carrying out solid-liquid separation to obtain lithium carbonate. According to the method disclosed by the invention, a co-extractant ferric trichloride does not need to be added, so that the problems caused by the co-extractant in the prior art are avoided, and the extraction separation of lithium in a near-neutral pH range is realized; moreover, the pH value of the raffinate is in a near-neutral range (about 7-8), so that the subsequent wastewater treatment difficulty is reduced; in the reverse extraction section, lithium in a loaded organic phase is enriched into a water phase in a phase ratio regulation and control mode, and a lithium carbonate product can be prepared through direct precipitation.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium extraction from salt lakes, and in particular to a method for recovering lithium from brine in salt lakes with a high magnesium-to-lithium ratio. Background Art

[0002] Lithium, the lightest metallic element in the periodic table, possesses unique electrochemical properties and is widely used in lithium batteries, ceramic glass, lubricants, metallurgy, medicine, and other fields, playing an irreplaceable role in national defense science and technology. With the rapid development of new energy vehicles, portable electronic devices, and energy storage components, lithium resources have become a core raw material supporting the green energy transition strategy, known as the "energy metal of the 21st century" and "white oil." Global lithium reserves total approximately 86 million tons, primarily occurring in salt lakes and lithium ore. Salt lake reserves account for 62.6% of the total reserves. Compared to extracting lithium from ore, which is subject to high energy consumption, lengthy processes, high costs, and difficult tailings disposal, extracting lithium from salt lake brines offers advantages such as low energy consumption, simple processes, low costs, and reduced pollution. Therefore, extracting lithium from salt lakes has become a major focus of lithium resource production and development.

[0003] The main characteristic of my country's salt lake brine is its high magnesium-to-lithium ratio. Due to the close ionic radius and similar chemical properties of lithium and magnesium ions, it is extremely challenging to extract and separate lithium from salt lakes. The main methods for extracting and separating lithium from salt lake brine are precipitation, adsorption, membrane, electrodialysis and solvent extraction. Based on the complex ion composition of salt lakes and the limitations of a single separation technology, the coupling of multiple separation technologies has become the current development trend of lithium extraction from salt lakes. The mainstream lithium extraction process in the domestic industry is to use adsorption-coupled membrane separation to directly extract lithium from low-concentration, high-magnesium-to-lithium ratio salt lake brine, which has been industrialized in salt lakes such as Qarhan Lake and Yiliping. The process first uses a specific adsorbent to selectively adsorb lithium ions from low-concentration, high-Mg / Li ratio salt lake brine. The lithium ions are then eluted from the adsorbent with fresh water / acid to produce a lithium-containing lysate, concentrating the lithium ions and separating them from impurity ions. The resulting lithium-containing lysate is further purified and concentrated using multiple membranes, typically nanofiltration, reverse osmosis, or electrodialysis, connected in series. The resulting lithium-enriched lysate then enters an evaporation and crystallization process to concentrate the lithium concentration to 20 g / L for direct use in the production of lithium carbonate products. However, the adsorption-coupled membrane separation process is complex, and the membranes often suffer from issues such as short membrane material life, high maintenance costs, high energy consumption, high membrane material replacement costs, and membrane clogging and contamination. Concentrating the lithium-enriched solution through evaporation and crystallization requires high equipment investment, results in significant lithium carryover losses, consumes a lot of energy, and can generate large amounts of waste gas and wastewater, causing environmental pollution. Therefore, a process with a short process, low energy consumption, low cost, high selectivity, and high recovery is urgently needed to extract lithium from high-Mg / Li salt lake brine, a challenge that currently needs to be addressed.

[0004] Solvent extraction offers the advantages of simple operation, large processing capacity, excellent separation efficiency, and ease of industrial production, offering irreplaceable advantages for the separation and enrichment of metal ions. Currently, two extraction systems used for lithium extraction from lithium-containing solutions are based on TBP + FeCl₃ and β-diketone systems. The TBP + FeCl₃ system is commonly used to extract lithium from salt lake brines with a high magnesium-to-lithium ratio. Patent CN87103431A proposes a TBP + FeCl₃ + sulfonated kerosene extraction system for direct lithium ion extraction from lithium-containing brines. However, this system suffers from significant solubility losses of the extractant TBP, and the use of high-concentration hydrochloric acid (6-8 mol / L) in the stripping stage can exacerbate TBP degradation and cause severe equipment corrosion. Furthermore, the aqueous phase must be kept acidic during the extraction process, ensuring a high chloride ion concentration (6 mol / L). Otherwise, the ferric tetrachloride complex anion in the organic phase will dissociate, compromising the extraction efficiency. Overall, this system presents a complex process flow, is challenging to control, and requires high equipment investment. It is only suitable for lithium-magnesium separations and has limited separation capabilities for alkali metals.

[0005] β-Diketone extraction systems are commonly used to extract lithium from alkali metal solutions. Patent CN107779612B discloses a process for extracting lithium from alkaline brine. Using diketone compounds as extractants and neutral phosphorus oxide compounds as co-extractants, the purpose of extracting lithium from lithium-containing alkaline brine is achieved. However, this system also has some defects: (1) The extraction ability of β-diketone extractants alone for lithium is not strong, and co-extractants TOPO, TRPO and Cyanex923 need to be added for synergistic extraction. (2) The extraction equilibrium pH of existing β-diketone extraction systems (such as Lix54+Cyanex923) is relatively high (>11), which requires the initial feed solution pH to be more alkaline and the alkali consumption is large; under high alkaline conditions, β-diketone dissolution is serious and the stability deteriorates. (3) The pH of the raffinate is high, and acid needs to be added to adjust the pH to neutral before subsequent treatment, which increases production costs. (4) This system is not suitable for the extraction and separation of lithium under acidic and neutral pH conditions. (5) The extraction agent is expensive and the synthesis process is complicated, which is not conducive to industrial production.

[0006] In summary, the existing technologies mainly have the following problems: (1) The traditional evaporation and concentration method is used to prepare lithium carbonate products, which consumes a lot of energy, has high costs, has a low lithium recovery rate, requires high equipment investment, and easily produces a large amount of wastewater and waste gas, which is not conducive to environmental protection. (2) The industry's mainstream "adsorption coupled membrane separation" process has problems such as complex process, short service life of membrane materials, high replacement costs, and high energy consumption. (3) The existing extraction system requires the addition of ferric chloride as a co-extractant, Fe 3+Hydrolysis can easily lead to emulsification and the introduction of iron impurities, which affects the purity of the lithium product. (4) The use of a β-diketone synergistic extraction system to recover lithium from an alkali metal solution generally has the following problems: the β-diketone extractant is highly toxic, has large dissolution losses, is expensive, has a high extraction equilibrium pH (>11), and has a complex extraction synthesis process. Co-extraction agents such as TOPO and TRPO must be added during extraction, and lithium can only be extracted in an alkaline solution. The alkali consumption is large, making subsequent wastewater treatment difficult. Summary of the Invention

[0007] In view of this, the present invention provides a method for recovering lithium from brine with a high magnesium-to-lithium ratio. The method not only ensures a high lithium yield, but also maintains a near-neutral pH (around 7-8) in the raffinate, effectively extracting and separating lithium under near-neutral conditions. This reduces the difficulty of subsequent wastewater treatment and allows direct precipitation of lithium carbonate products from the lithium-containing concentrate obtained through stripping. This method offers the advantages of low energy consumption, a short process, low cost, high yield, and environmental friendliness.

[0008] The present invention provides a method for recovering lithium from salt lake brine with a high magnesium-to-lithium ratio, comprising the following steps:

[0009] (A) Pretreatment:

[0010] The brine from the salt lake with a high magnesium-lithium ratio is filtered and the pH value is adjusted to obtain a pre-treated solution;

[0011] (B) Adsorption-desorption:

[0012] Adsorbing the pretreatment liquid with an adsorbent, and then eluting and analyzing it to obtain a lithium-containing analysis liquid;

[0013] (C) Solvent extraction-precipitation:

[0014] c1: mixing an extractant and a diluent to obtain an organic phase; saponifying the organic phase with a saponifying agent to obtain a saponified organic phase;

[0015] wherein the extractant is at least one of di(2-ethylhexyl)phosphoric acid, 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester, di(2,4,4-trimethylpentyl)phosphoric acid, and di(2-ethylhexyl)phosphonic acid;

[0016] c2: extracting the lithium-containing analytical solution using the saponified organic phase to obtain a raffinate and a lithium-loaded organic phase;

[0017] c3: stripping the lithium-loaded organic phase with a stripping agent to obtain a lithium-containing concentrate and a blank organic phase;

[0018] c4: mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain lithium carbonate.

[0019] Preferably, in step c1:

[0020] The diluent is at least one of sulfonated kerosene, No. 260 solvent oil, white oil, and C6-C13 hydrocarbons;

[0021] The concentration of the extractant in the diluent is 0.3-1.5 mol / L.

[0022] Preferably, in step c1:

[0023] The saponifying agent is at least one of sodium hydroxide solution, ammonia water, sodium carbonate solution, sodium bicarbonate solution, and ammonium carbonate solution;

[0024] The dosage of the saponifier is such that the saponification degree of the extractant reaches 10% to 60%.

[0025] Preferably, in step c2, the extraction is fractional extraction.

[0026] Preferably, the fractional extraction includes two sections: countercurrent extraction and countercurrent washing;

[0027] wherein the number of extraction stages of the countercurrent extraction is 4 to 10, and the number of washing stages of the countercurrent washing is 5 to 10;

[0028] The detergent used in the countercurrent washing is at least one of hydrochloric acid and lithium salt solution;

[0029] In the countercurrent extraction, the flow ratio of the saponified organic phase, the lithium-containing analytical solution, and the detergent is (20-1):(20-1):1.

[0030] Preferably, in the fractional extraction, each stage of extraction and each stage of washing include: shaking, standing and phase separation;

[0031] The oscillation rate is 200-300 rpm, and the time is 10-20 min;

[0032] The standing time is 5 to 10 minutes.

[0033] Preferably, in step c3:

[0034] The stripping agent is hydrochloric acid;

[0035] The stripping is a multi-stage countercurrent stripping;

[0036] The ratio of the lithium-loaded organic phase to the stripping agent is (1-30):1.

[0037] Preferably, in step c4:

[0038] The precipitant is a saturated sodium carbonate solution;

[0039] The amount of the precipitant is 1.1 to 1.2 times the stoichiometric ratio;

[0040] The mixing temperature is 80-90°C.

[0041] Preferably, in step (A):

[0042] The mass ratio of Mg / Li in the high magnesium-lithium ratio salt lake brine is ≥10:1;

[0043] The pH value is adjusted to 4 to 7;

[0044] In step (B):

[0045] The adsorbent is a specific aluminum-based adsorbent.

[0046] Preferably, in step (B):

[0047] The adsorbent is layered lithium aluminum double hydroxide;

[0048] The eluent used for the elution is water.

[0049] The present invention provides a method for recovering lithium from high-magnesium-lithium salt lake brine using an adsorption-coupled solvent extraction process. In view of the problems of long process, high energy consumption, and high cost of membrane material replacement in the mainstream "adsorption-coupled membrane separation" process in the industry, it is proposed to use solvent extraction to replace the membrane concentration and evaporation concentration sections. The extraction section uses fractional extraction to extract lithium into the organic phase, thereby achieving separation from monovalent impurity ions and ensuring a lithium yield of up to 99%; the stripping section enriches the lithium in the loaded organic phase into the aqueous phase by means of a phase shift method, and directly precipitates the lithium carbonate product from the lithium-containing concentrated solution, which has the advantages of low energy consumption, short process, low cost, high yield, and environmental protection. Solvent extraction is used to extract lithium from the adsorption and analysis solution of a high magnesium-lithium ratio salt lake. The present invention does not require the addition of ferric chloride as a co-extractant, thus avoiding a series of problems caused by the addition of ferric chloride, such as Fe 3+ Hydrolysis leads to emulsification and the introduction of iron impurities, which affects the purity of the lithium product. The present invention does not use a synergistic extraction system of β-diketone and neutral phosphine oxide, thus avoiding the problems of strong toxicity, large dissolution loss, high cost, and high extraction equilibrium pH (>11) of the β-diketone extractant. The present invention uses a single acidic phosphorus (phosphine) extractant to directly extract lithium from the adsorption and desorption liquid of a high magnesium-to-lithium ratio salt lake without adjusting the pH of the feed liquid, thereby achieving efficient extraction and separation of lithium under near-neutral conditions, greatly reducing the consumption of alkali, and keeping the pH of the raffinate in the near-neutral range (about 7-8), thereby reducing the difficulty of subsequent wastewater treatment. The extractant is easily available, the synthesis process is mature and safe, it has strong acid and alkali resistance, good stability, and a wide range of applications.

[0050] The test results show that the recovery process of the present invention can treat salt lake brine with a high magnesium-to-lithium ratio, so that the lithium extraction rate reaches more than 99%, the lithium stripping rate reaches more than 99%, the total lithium recovery rate reaches more than 85%, and the purity of the lithium carbonate product reaches more than 99%, thereby achieving efficient separation and recovery of lithium and obtaining a high-purity lithium salt product. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0052] Figure 1 The present invention is a process flow chart for recovering lithium from salt lake brine with a high magnesium-lithium ratio;

[0053] Figure 2 This is a schematic diagram of the present invention using a separatory funnel to simulate the separation and extraction process. DETAILED DESCRIPTION

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0055] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0056] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0057] As used herein, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0058] In this document, when referring to a range, if the unit is followed only by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 0.3-1.5 mol / L means that the units of the left endpoint "0.3" and the right endpoint "1.5" are both mol / L.

[0059] The present invention provides a method for recovering lithium from salt lake brine with a high magnesium-to-lithium ratio, comprising the following steps:

[0060] (A) Pretreatment:

[0061] The brine from the salt lake with a high magnesium-lithium ratio is filtered and the pH value is adjusted to obtain a pre-treated solution;

[0062] (B) Adsorption-desorption:

[0063] Adsorbing the pretreatment liquid with an adsorbent, and then eluting and analyzing it to obtain a lithium-containing analysis liquid;

[0064] (C) Solvent extraction-precipitation:

[0065] c1: mixing an extractant and a diluent to obtain an organic phase; saponifying the organic phase with a saponifying agent to obtain a saponified organic phase;

[0066] wherein the extractant is at least one of di(2-ethylhexyl)phosphoric acid, 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester, di(2,4,4-trimethylpentyl)phosphoric acid, and di(2-ethylhexyl)phosphonic acid;

[0067] c2: extracting the lithium-containing analytical solution using the saponified organic phase to obtain a raffinate and a lithium-loaded organic phase;

[0068] c3: stripping the lithium-loaded organic phase with a stripping agent to obtain a lithium-containing concentrate and a blank organic phase;

[0069] c4: mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain lithium carbonate.

[0070] The process of the present invention is as follows Figure 1 shown.

[0071] The present invention provides a method for recovering lithium from brine with a high magnesium-to-lithium ratio. It proposes an integrated process of "adsorption-coupled solvent extraction" and uses solvent extraction to replace the membrane section and evaporation concentration section in the "adsorption-coupled membrane separation" process. A single acidic phosphorus (phosphine) extractant is used to directly extract lithium from the salt lake adsorption solution without adjusting the pH value of the feed solution. By simulating fractional extraction through a separatory funnel method, efficient separation of lithium and monovalent impurity ions under near-neutral pH conditions is achieved, ensuring a lithium yield of up to 99%. The lithium-containing loaded organic phase can be efficiently enriched with lithium to a concentration of more than 20g / L by adjusting the ratio of the stripping section. Lithium carbonate products are directly precipitated from the lithium-containing concentrated solution. The method provided by the invention has a wide range of applications, high lithium yield, simple and easily available extractants, low energy consumption, low production costs, a simple process flow, small equipment investment, and is easy to implement industrial applications.

[0072] About step (A) :

[0073] Pretreatment: Filter the brine from the salt lake with a high magnesium-lithium ratio, adjust the pH value, and obtain a pretreatment solution.

[0074] In the present invention, the mass ratio of Mg / Li in the high magnesium-lithium ratio salt lake brine is ≥10:1, more specifically (10-1500):1.

[0075] In the present invention, the high-Mg-Li ratio salt lake brine is first filtered to remove suspended matter such as silt and clay, as well as colloids, to prevent them from clogging the adsorbent pores or covering the membrane surface, hindering mass transfer. After filtration, the pH is adjusted to facilitate subsequent adsorption operations. In the present invention, the pH is preferably adjusted to 4 to 7, specifically 4, 4.5, 5, 5.5, 6, 6.5, or 7. The adjusting agent used is preferably at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, aqueous ammonia, and ammonium carbonate.

[0076] About step (B) :

[0077] Adsorption-desorption: The pretreatment liquid is subjected to adsorption treatment by an adsorbent, and then eluted and desorbed to obtain a lithium-containing desorption liquid.

[0078] In the present invention, the adsorbent is a specific aluminum-based adsorbent, preferably layered lithium aluminum double hydroxide (Li / Al-LDHs).

[0079] In the present invention, the adsorption treatment is preferably a cascade adsorption treatment, that is, the adsorption treatment is performed through multiple stages of adsorption columns connected in series (the adsorption columns contain adsorbents); specifically, the pretreatment liquid is passed into a first-stage adsorption column, and after a certain amount of lithium is adsorbed by the adsorbent, the liquid is passed into the next-stage adsorption column to continue the adsorption treatment, and so on.

[0080] In the present invention, after the adsorption treatment is completed, the lithium adsorbed on the adsorbent is eluted and analyzed. Water is preferably used for elution and analysis; the water is preferably deionized water. After elution and analysis, a lithium-containing analysis solution is obtained.

[0081] In the present invention, the indicators of the lithium-containing analytical solution are preferably: lithium ion concentration ≥ 1 g / L, and pH 6 to 8.5.

[0082] About step (C) :

[0083] Solvent extraction-precipitation: includes steps c1 to c3.

[0084] [About step c1]:

[0085] c1: mixing an extractant and a diluent to obtain an organic phase; saponifying the organic phase with a saponifying agent to obtain a saponified organic phase.

[0086] In the present invention, the extractant is an acidic phosphorus / phosphine extractant, specifically, the extractant is at least one of di(2-ethylhexyl)phosphoric acid (P204), 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester (P507), di(2,4,4-trimethylpentyl)phosphoric acid (Cyanex272), and di(2-ethylhexyl)phosphonic acid (P227).

[0087] In the present invention, the diluent is preferably at least one of sulfonated kerosene, No. 260 solvent oil, white oil, and C6-C13 hydrocarbons; wherein the C6-C13 hydrocarbons preferably include at least one of n-heptane and cyclohexane.

[0088] In the present invention, the concentration of the organic phase is preferably 0.3 to 1.5 mol / L, specifically 0.3 mol / L, 0.5 mol / L, 0.75 mol / L, 1.0 mol / L, or 1.5 mol / L.

[0089] In the present invention, the saponifying agent is preferably at least one of sodium hydroxide solution, ammonia water, sodium carbonate solution, sodium bicarbonate solution, and ammonium carbonate solution. In the present invention, the amount of the saponifying agent is preferably such that the saponification degree of the extractant reaches 10% to 60%, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

[0090] In the present invention, the process of saponifying the organic phase with a saponifying agent preferably includes: mixing and oscillating the organic phase and the saponifying agent to obtain a saponified organic phase. The oscillation rate is preferably 200-300 rpm, specifically 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, or 300 rpm. The oscillation time is preferably 30-60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0091] [About step c2]:

[0092] c2: extracting the lithium-containing analytical solution using the saponified organic phase to obtain a raffinate and a lithium-containing loaded organic phase.

[0093] In the present invention, the extraction is fractional extraction.

[0094] About fractional extraction:

[0095] In the present invention, the fractional extraction includes two sections, namely, countercurrent extraction and countercurrent washing. The fractional extraction can be carried out in a separatory funnel, a mixing and settling tank or a centrifugal extraction device. In the laboratory, a separatory funnel can be used to simulate the separation and extraction process, which is decomposed into two processes, namely, countercurrent extraction and countercurrent washing. Figure 2 As shown, the fractional extraction process consists of n-stage extraction and m-stage washing. The first stage feeds the organic phase, the nth stage feeds the liquid, and the n+mth stage feeds the washing acid. Each separatory funnel simulates a single-stage extraction or single-stage washing. The specific laboratory operation is as follows: All separatory funnels are divided into two rows of odd and even numbers. One row is oscillated at a time. After the first oscillation of the odd-numbered rows, the phases are allowed to stand and separate. The aqueous phase and organic phase in each separatory funnel are transferred to the adjacent even-numbered rows of separatory funnels, with the organic phase moving in the direction of the larger number and the aqueous phase moving in the direction of the smaller number. The even-numbered rows are then oscillated again and the phases are allowed to stand and separate. The outlet aqueous phase and outlet organic phase are collected for testing and analysis. The operation is repeated multiple times until the entire system reaches stability.

[0096] In the present invention, the number of extraction stages n in the fractional extraction is preferably 4 to 10, specifically 4, 5, 6, 7, 8, 9, and 10. The number of washing stages m in the fractional extraction is preferably 5 to 10, specifically 5, 6, 7, 8, 9, and 10. In the present invention, the detergent used in the fractional extraction (i.e., the detergent used in the washing section) is preferably at least one of hydrochloric acid and a lithium salt solution; the lithium salt solution is a lithium chloride solution. The concentrations of the inorganic acid and the lithium salt solution are preferably both 0.1 to 2 mol / L, specifically 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, and 2.0 mol / L. In the present invention, in the fractional extraction, the flow ratio of the saponified organic phase, the lithium-containing analytical solution, and the detergent is preferably (20-1):(20-1):1, specifically 7.78:3.33:0.8638, 13.13:9.99:3.455, 14.95:13.33:3.18 (i.e., 4.7:4.19:1), and 15.3:9.99:4.26 (i.e., 3.59:2.35:1).

[0097] In the present invention, as described above, in the process of fractional extraction, each stage of extraction and each stage of washing includes: oscillation and standing for phase separation. The speed of each oscillation is preferably 200-300 rpm, specifically 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, and 300 rpm. The time of each oscillation is preferably 10-20 minutes, specifically 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, and 20 minutes. The time of standing after each oscillation is preferably 5-10 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes. The entire system is subjected to multiple cycles of oscillation, standing, phase separation, and phase transfer until the entire system reaches stability. Fractional extraction is terminated, and the outlet aqueous phase and outlet organic phase are collected separately to obtain the raffinate and the loaded organic phase, respectively. The entire system reaching stability means that the compositions of the outlet aqueous phase and outlet organic phase no longer change significantly, and the system has reached extraction equilibrium.

[0098] In the present invention, fractional extraction is adopted to significantly improve the extraction rate and yield of lithium, so that the lithium extraction rate reaches more than 99%.

[0099] In the present invention, the pH of the obtained raffinate is in the near-neutral range (pH 7-8), that is, the extraction equilibrium pH is in the near-neutral range, thereby achieving efficient extraction and separation of lithium under near-neutral conditions (extraction and separation under near-neutral conditions does not mean that the pH of the initial lithium-containing analytical solution used is near-neutral, but means that the extraction equilibrium pH is in the near-neutral range).

[0100] [About step c3]:

[0101] c3: stripping the lithium-loaded organic phase with a stripping agent to obtain a lithium-containing concentrated solution and a blank organic phase, respectively.

[0102] In the present invention, the stripping agent is preferably hydrochloric acid. The concentration of the hydrochloric acid is preferably 1 to 6 mol / L, specifically 1 mol / L, 2 mol / L, 3 mol / L, 3.8 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L.

[0103] In the present invention, the ratio of the lithium-loaded organic phase to the stripping agent (O / A ratio) is preferably (1-30):1, specifically 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1.

[0104] In the present invention, the stripping process comprises: mixing the lithium-loaded organic phase with a stripping agent for stripping, shaking, and allowing the phases to separate, thereby obtaining a stripping solution (i.e., a lithium-containing concentrated solution) and a blank organic phase. In the present invention, the stripping is preferably a multi-stage countercurrent stripping. In the present invention, after stripping, the lithium concentration in the obtained lithium-containing concentrated solution is greater than 20 g / L, and the lithium carbonate product can be directly precipitated from the stripping solution.

[0105] In the present invention, the blank organic phase after stripping can be recycled. Specifically, the blank organic phase is mixed with water and washed until neutral to obtain a regenerated organic phase. The water is preferably deionized water. Thus, the extractant used in the present invention is recyclable, has good extraction performance, and is simple to operate.

[0106] [About step c4]:

[0107] c4: mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain lithium carbonate.

[0108] In the present invention, the precipitant is preferably a saturated sodium carbonate solution. The amount of the precipitant is preferably 1.1 to 1.2 times the stoichiometric ratio. In the present invention, the mixing method is preferably to dropwise add the precipitant to the lithium-containing concentrated solution. The mixing temperature is preferably 80 to 90°C, specifically 80°C, 85°C, or 90°C.

[0109] In the present invention, after mixing the lithium-containing concentrate with a precipitant, carbonate ions react chemically with lithium ions to form a lithium carbonate precipitate in the system. Solid-liquid separation is then performed to obtain lithium carbonate and a separated liquid (i.e., a lithium precipitation mother liquor). The solid-liquid separation method is not particularly limited and can be any conventional separation method in the art, such as filtration. The resulting lithium carbonate is battery-grade lithium carbonate with a purity of 99.5%.

[0110] Compared with the prior art, the present invention has the following beneficial effects:

[0111] 1. This invention proposes an adsorption-coupled solvent extraction process for the efficient recovery of lithium from high-Mg / Li ratio salt lake brine. To address the shortcomings of the industry's mainstream adsorption-coupled membrane separation process, solvent extraction replaces the membrane and evaporation concentration stages. The extraction stage utilizes fractional distillation to extract lithium into the organic phase, thereby separating it from monovalent impurity ions and ensuring a lithium yield of up to 99%. The stripping stage efficiently enriches lithium from the loaded organic phase into the aqueous phase by regulating the phase ratio. Lithium carbonate can be directly precipitated from the lithium-containing concentrate. This process offers the advantages of low energy consumption, a short process, low cost, high yield, and environmental friendliness.

[0112] 2. The extraction system does not require the additional addition of ferric chloride as a co-extractant, thus avoiding a series of problems caused by the use of ferric chloride as a co-extractant; the extraction system does not use a synergistic extraction system of β-diketone and neutral phosphine oxide, thus avoiding the problems of strong toxicity, large dissolution loss, high cost, and high extraction equilibrium pH (>11) of the β-diketone extractant. A single acidic phosphorus (phosphine) extraction system is used, eliminating the need to adjust the pH of the feed solution, achieving the extraction and separation of lithium under near-neutral conditions and reducing the consumption of alkali solution; the extractant has strong acid and alkali resistance, good stability, safety and convenience, the pH of the raffinate is within the near-neutral range, wastewater treatment is easy, the price is low, it is easily available, and the synthesis process is safe, reliable, and mature.

[0113] 3. The present invention uses a separatory funnel method to simulate fractional extraction, which has a wide range of applications, a lithium yield of up to 99%, a simple process flow, low production cost, low equipment investment, and high operational reliability. The extractants used in the present invention can be recycled and applied, which facilitates industrial production and has practical application value.

[0114] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0115] Example 1

[0116] (A) Pretreatment:

[0117] The brine from the high magnesium-lithium ratio salt lake is filtered to remove suspended matter such as silt, clay, and colloids contained in the brine, and then the pH value is adjusted to 7.

[0118] (B) Adsorption-desorption:

[0119] A specific aluminum-based adsorbent, layered lithium aluminum double hydroxide (Li / Al-LDHs), is used for cascade adsorption treatment, which is then eluted with deionized water to obtain a lithium-containing analytical solution, which serves as the raw material solution for the subsequent extraction process without adjusting the pH value of the raw material solution.

[0120] The main composition of the obtained lithium-containing analytical solution is shown in Table 1:

[0121] Table 1: Main components of lithium-containing analytical solution

[0122]

[0123] (C) Solvent extraction-precipitation:

[0124] c1: The extractant P204 was mixed with the diluent sulfonated kerosene to prepare an organic phase (the organic phase concentration was 0.75 mol / L); the organic phase was saponified by mixing with sodium hydroxide solution (7 mol / L) and shaking at room temperature for 30 minutes to achieve a saponification degree of 30%, thereby obtaining a saponified organic phase.

[0125] c2: The saponified organic phase was fractionally extracted with a lithium-containing analytical solution, using 1 mol / L HCl as the wash acid. A cascade simulation was conducted with a flow ratio of saponified organic phase: lithium-containing analytical solution: wash acid = 7.78:3.33:0.8638. The process consisted of nine extraction stages and seven wash stages. After oscillation at 270 rpm for 15 minutes and 5 minutes of quiescence for phase separation, 99.61% of the lithium was extracted into the loaded organic phase, with a sodium content of 0.20 g / L. The equilibrium pH of the raffinate aqueous phases at each stage was between 5 and 7.

[0126] c3: The lithium-loaded organic phase was stripped by mixing it with a stripping agent (3 mol / L hydrochloric acid) at a ratio of O / A = 25:1. After three stages of countercurrent stripping, a lithium-containing concentrate and a blank organic phase were obtained. The lithium stripping efficiency was 99.28%, and the lithium concentration in the lithium-containing concentrate was 20.75 g / L.

[0127] The blank organic phase was mixed with deionized water and washed to neutrality to obtain a regenerated organic phase.

[0128] c4: Saturated sodium carbonate solution with a stoichiometric ratio of 1.1 is slowly added dropwise to the lithium-containing concentrate at 80°C, and then filtered to obtain battery-grade lithium carbonate with a purity of 99.55%.

[0129] Results: In this embodiment, the lithium extraction rate was 99.61%, the lithium stripping rate was 99.28%, the total lithium recovery rate was 90.25%, and the purity of the lithium carbonate product was 99.55%.

[0130] Example 2

[0131] (A)~(B): Same as Example 1.

[0132] (C) Solvent extraction-precipitation:

[0133] c1: The extractant Cyanex 272 was mixed with the diluent sulfonated kerosene to prepare an organic phase (the organic phase concentration was 0.8 mol / L); the organic phase was saponified by mixing with sodium hydroxide solution (7 mol / L) and shaking at room temperature for 30 minutes to achieve a saponification degree of 50%, thereby obtaining a saponified organic phase.

[0134] c2: The saponified organic phase was fractionally extracted with a lithium-containing analytical solution, using 0.75 mol / L HCl as the wash acid. A cascade simulation was conducted with a flow ratio of saponified organic phase: lithium-containing analytical solution: wash acid = 13.13:9.99:3.455. The process consisted of eight extraction stages and seven wash stages. After oscillation at 270 rpm for 15 minutes and 5 minutes of quiescence for phase separation, 99.29% of the lithium was extracted into the loaded organic phase, with a sodium content of 0.20 g / L. The equilibrium pH of the raffinate aqueous phases at each stage was between 7 and 8.

[0135] c3: The lithium-loaded organic phase was stripped with a stripping agent (3 mol / L hydrochloric acid) at a ratio of O / A = 15:1. Four stages of countercurrent stripping were performed to obtain a lithium-containing concentrate and a blank organic phase, respectively. The lithium stripping efficiency was 99.62%, and the lithium concentration in the lithium-containing concentrate was 21.1 g / L.

[0136] The blank organic phase was mixed with deionized water and washed to neutrality to obtain a regenerated organic phase.

[0137] c4: Saturated sodium carbonate solution with a stoichiometric ratio of 1.1 is slowly added dropwise to the lithium-containing concentrate at 80°C, and then filtered to obtain battery-grade lithium carbonate with a purity of 99.52%.

[0138] Results: In this embodiment, the lithium extraction rate was 99.29%, the lithium stripping rate was 99.62%, the total lithium recovery rate was 89.13%, and the purity of the lithium carbonate product was 99.52%.

[0139] Example 3

[0140] (A)~(B): Same as Example 1.

[0141] (C) Solvent extraction-precipitation:

[0142] c1: The extractant P507 was mixed with the diluent sulfonated kerosene to prepare an organic phase (the organic phase concentration was 0.75 mol / L); the organic phase was mixed with sodium hydroxide solution (7 mol / L) for saponification, and shaken at room temperature for 30 minutes to achieve a saponification degree of 60%, thereby obtaining an extracted organic phase.

[0143] c2: The saponified organic phase was fractionally extracted with a lithium-containing analytical solution, using 1 mol / L HCl as the wash acid. A cascade simulation was conducted with a flow ratio of saponified organic phase: lithium-containing analytical solution: wash acid = 14.95:13.33:3.18. The process consisted of eight extraction stages and six wash stages. After oscillation at 270 rpm for 15 minutes and 5 minutes of quiescence for phase separation, 99.18% of the lithium was extracted into the loaded organic phase, with a sodium content of 0.20 g / L. The equilibrium pH of the raffinate aqueous phases at each stage was between 6 and 8.

[0144] c3: The lithium-loaded organic phase was stripped by mixing it with a stripping agent (3 mol / L hydrochloric acid) at a ratio of O / A = 20:1. After three stages of countercurrent stripping, a lithium-containing concentrate and a blank organic phase were obtained. The lithium stripping efficiency was 99.5%, and the lithium concentration in the lithium-containing concentrate was 24.18 g / L.

[0145] The blank organic phase was mixed with deionized water and washed to neutrality to obtain a regenerated organic phase.

[0146] c4: Saturated sodium carbonate solution with a stoichiometric ratio of 1.1 is slowly added dropwise to the lithium-containing concentrate at 80°C, and then filtered to obtain battery-grade lithium carbonate with a purity of 99.54%.

[0147] Results: In this embodiment, the lithium extraction rate was 99.18%, the lithium stripping rate was 99.5%, the total lithium recovery rate was 90.45%, and the purity of the lithium carbonate product was 99.54%.

[0148] Example 4

[0149] (A)~(B): Same as Example 1.

[0150] (C) Solvent extraction-precipitation:

[0151] c1: The extractant P227 was mixed with the diluent sulfonated kerosene to prepare an organic phase (the organic phase concentration was 0.9 mol / L); the organic phase was mixed with sodium hydroxide solution (7 mol / L) for saponification, and shaken at room temperature for 30 minutes to achieve a saponification degree of 40%, thereby obtaining a saponified organic phase.

[0152] c2: The saponified organic phase was fractionally extracted with a lithium-containing analytical solution using 0.5 mol / L HCl as the wash acid. A cascade simulation was conducted with a flow ratio of saponified organic phase: lithium-containing analytical solution: wash acid = 15.3:9.99:4.26. The process consisted of eight extraction stages and five wash stages. After shaking at 270 rpm for 15 minutes and allowing the phases to stand for 5 minutes, 99.73% of the lithium was extracted into the loaded organic phase, with a sodium content of 0.14 g / L.

[0153] c3: The lithium-loaded organic phase was stripped with a stripping agent (3.8 mol / L hydrochloric acid) at a ratio of O / A = 20:1. Four stages of countercurrent stripping were performed to obtain a lithium-containing concentrate and a blank organic phase, respectively. The lithium stripping efficiency was 99.76%, and the lithium concentration in the lithium-containing concentrate was 23.1 g / L.

[0154] The blank organic phase was mixed with deionized water and washed to neutrality to obtain a regenerated organic phase.

[0155] c4: Saturated sodium carbonate solution with a stoichiometric ratio of 1.2 is slowly added dropwise to the lithium-containing concentrate at 80°C, and then filtered to obtain battery-grade lithium carbonate with a purity of 99.56%.

[0156] The main compositions of the obtained extract and stripping solution are shown in Table 2:

[0157] Table 2: Main components of extract and stripping solution

[0158]

[0159] The purity of the obtained battery-grade lithium carbonate product is shown in Table 3:

[0160] Table 3: Purity of battery-grade lithium carbonate products

[0161]

[0162] Results: In this embodiment, the lithium extraction rate was 99.73%, the lithium stripping rate was 99.76%, the total lithium recovery rate was 89.32%, and the purity of the lithium carbonate product was 99.56%.

[0163] Example 5

[0164] (A)~(B): Same as Example 1.

[0165] (C) Solvent extraction-precipitation:

[0166] c1: Same as Example 4.

[0167] c2: Same as Example 4.

[0168] c3: The difference from Example 4 is that the stripping agent is changed to 4 mol / L hydrochloric acid. As a result, the lithium stripping rate is 99.85%, and the lithium concentration in the lithium-containing concentrate is 23.27 g / L.

[0169] The blank organic phase was mixed with deionized water and washed to neutrality to obtain a regenerated organic phase.

[0170] c4: Saturated sodium carbonate solution with a stoichiometric ratio of 1.1 is slowly added dropwise to the lithium-containing concentrate at 80°C, and then filtered to obtain battery-grade lithium carbonate with a purity of 99.53%.

[0171] The main composition of the obtained lithium-containing concentrated solution is shown in Table 4:

[0172] Table 4: Main components of lithium-containing concentrate

[0173]

[0174] Results: In this embodiment, the lithium extraction rate was 99.66%, the lithium stripping rate was 99.85%, the total lithium recovery rate was 90.17%, and the purity of the lithium carbonate product was 99.53%.

[0175] Example 6

[0176] The process was carried out in accordance with Example 4, except that the extractant was replaced with P204+P507 (the volume ratio of the two was 1:1).

[0177] Results: In this embodiment, the lithium extraction rate was 99.37%, the lithium stripping rate was 99.65%, the total lithium recovery rate was 87.42%, and the purity of the lithium carbonate product was 99.56%.

[0178] In summary, the recovery process of the present invention treats salt lake brine with a high magnesium-to-lithium ratio, which can achieve a lithium extraction rate of more than 99%, a lithium stripping rate of more than 99%, a total lithium recovery rate of more than 85%, and a lithium carbonate product purity of more than 99%, thereby achieving efficient separation and recovery of lithium and obtaining a high-purity lithium salt product.

[0179] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that are not substantially different from the literal description of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for recovering lithium from brine with a high magnesium-to-lithium ratio, characterized in that: The following steps are involved: (A) Pretreatment: The brine from the salt lake with a high magnesium-lithium ratio is filtered and the pH value is adjusted to obtain a pre-treated solution; (B) Adsorption-desorption: Adsorbing the pretreatment liquid with an adsorbent, and then eluting and analyzing it to obtain a lithium-containing analysis liquid; (C) Solvent extraction-precipitation: c1: mixing an extractant and a diluent to obtain an organic phase; saponifying the organic phase with a saponifying agent to obtain a saponified organic phase; wherein the extractant is at least one of di(2-ethylhexyl)phosphoric acid, 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester, di(2,4,4-trimethylpentyl)phosphoric acid, and di(2-ethylhexyl)phosphonic acid; c2: extracting the lithium-containing analytical solution using the saponified organic phase to obtain a raffinate and a lithium-loaded organic phase; c3: stripping the lithium-loaded organic phase with a stripping agent to obtain a lithium-containing concentrate and a blank organic phase; c4: mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain lithium carbonate.

2. The method according to claim 1, characterized in that In step c1: The diluent is at least one of sulfonated kerosene, No. 260 solvent oil, white oil, and C6-C13 hydrocarbons; The concentration of the extractant in the diluent is 0.3-1.5 mol / L.

3. The method according to claim 1, characterized in that In step c1: The saponifying agent is at least one of sodium hydroxide solution, ammonia water, sodium carbonate solution, sodium bicarbonate solution, and ammonium carbonate solution; The dosage of the saponifier is such that the saponification degree of the extractant reaches 10% to 60%.

4. The method according to claim 1, wherein In step c2, the extraction is fractional extraction.

5. The method according to claim 4, characterized in that The fractional extraction includes two sections: countercurrent extraction and countercurrent washing; wherein the number of extraction stages of the countercurrent extraction is 4 to 10, and the number of washing stages of the countercurrent washing is 5 to 10; The detergent used in the countercurrent washing is at least one of hydrochloric acid and lithium salt solution; In the countercurrent extraction, the flow ratio of the saponified organic phase, the lithium-containing analytical solution, and the detergent is (20-1):(20-1):

1.

6. The method according to claim 4 or 5, characterized in that In the fractional extraction, each stage of extraction and each stage of washing includes: shaking, standing and phase separation; The oscillation rate is 200-300 rpm, and the time is 10-20 min; The standing time is 5 to 10 minutes.

7. The method according to claim 1, characterized in that In step c3: The stripping agent is hydrochloric acid; The stripping is a multi-stage countercurrent stripping; The ratio of the lithium-loaded organic phase to the stripping agent is (1-30):

1.

8. The method according to claim 1, characterized in that In step c4: The precipitant is a saturated sodium carbonate solution; The amount of the precipitant is 1.1 to 1.2 times the stoichiometric ratio; The mixing temperature is 80-90°C.

9. The method according to claim 1, characterized in that In step (A): The mass ratio of Mg / Li in the high magnesium-lithium ratio salt lake brine is ≥10:1; The pH value is adjusted to 4 to 7; In step (B): The adsorbent is a specific aluminum-based adsorbent.

10. The method according to claim 1 or 9, characterized in that In step (B): The adsorbent is layered lithium aluminum double hydroxide; The eluent used for the elution is water.

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