Method for recovering lithium from lithium-containing solution with high sodium-lithium ratio

Abstract

The invention relates to the technical field of hydrometallurgy, in particular to a method for recovering lithium from a lithium-containing solution with a high sodium-lithium ratio. The method comprises the following steps: preparing an organic phase by adopting a specific extraction agent, and then extracting the organic phase and lithium-containing feed liquid to respectively obtain raffinate and a loaded organic phase; 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 precipitator, and carrying out solid-liquid separation to obtain a lithium carbonate product. According to the method disclosed by the invention, a co-extractant is not needed, so that the problems caused by using a co-extractant ferric trichloride in the prior art are avoided; moreover, the feed liquid is wide in application range (can be acidic, neutral and alkaline), the pH of the feed liquid does not need to be adjusted, extraction separation can be directly carried out, the consumption of alkali is greatly reduced, and efficient extraction separation is achieved; in addition, the pH value of the raffinate is in a near-neutral range (about 5-8), the raffinate can be directly used for preparing sodium chloride or sodium sulfate by-products, and economic benefits are increased.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrometallurgy, and in particular to a method for recovering lithium from a lithium-containing solution with a high sodium-to-lithium ratio. Background Art

[0002] In recent years, with the rapid development of electric vehicles, portable electronic devices, and the energy storage industry, lithium has become a key element in the strategic development of China's new energy and nuclear industries. Global lithium reserves are abundant, primarily occurring in salt lake brines and lithium ore. Furthermore, with the continued rise in global demand for lithium, secondary lithium resources have become a key source of lithium recovery both domestically and internationally. Currently, secondary resources with high recovery value include lithium mother liquor, spent lithium-ion batteries, and glass powder.

[0003] Against the backdrop of global carbon neutrality, industries such as new energy vehicles, communications, and 5G are developing rapidly, and the global market demand for lithium salt products continues to expand. Lithium carbonate products are important energy storage materials and are also important raw materials for lithium battery production. Existing lithium carbonate production processes mostly use sodium carbonate precipitation. The theoretical stoichiometric ratio of saturated sodium carbonate to lithium carbonate production is 1.1-1.5. The precipitation reaction is carried out at a temperature of 80-90°C. After precipitation, the mother liquor still contains 1-2g / L of lithium and a large amount of sodium or potassium impurities, with the characteristics of high sodium and low lithium.

[0004] In industry, wet processes are often used to recover lithium from solid resources (such as lithium ore and waste lithium-ion batteries). Valuable metals are transferred to the aqueous phase through acid leaching to obtain a complex leachate. Recovering lithium from the leachate involves multiple separation and purification steps. The classic process generally adopts the "separation and impurity removal-evaporation crystallization" route. First, alkali is used to adjust the pH for chemical precipitation to selectively remove impurities. Then, ion exchange or solvent extraction is used to deeply remove impurities or recover other valuable metals, and finally a purified lithium-containing solution is obtained. Due to the addition of a large amount of alkali precipitation in the early stage, the solution also has the characteristics of high sodium and low lithium. The lithium-containing solution is concentrated to more than 20g / L by evaporation and concentration process, and saturated sodium carbonate is added to precipitate to obtain a lithium carbonate product. Next, the obtained lithium precipitation mother liquor and the purified lithium-containing solution need to be mixed and concentrated again for a secondary lithium precipitation operation to ensure that the lithium yield in the entire process reaches 99% or more.

[0005] The traditional evaporation and concentration process is used to prepare lithium carbonate products from lithium-containing solutions with a high sodium-to-lithium ratio. However, there are problems such as difficulty in separating lithium from impurities such as monovalent metal ions sodium and potassium, low recovery rate, high energy consumption, high production cost, and low purity of lithium carbonate products. Therefore, it is necessary to find a suitable method to achieve efficient separation of lithium and sodium to improve the comprehensive utilization rate of lithium.

[0006] Solvent extraction is widely used for the separation and enrichment of metal ions due to its advantages of simple operation, large processing capacity, good separation effect, and ease of industrial production. Currently, the extraction systems used to extract lithium from lithium-containing solutions include tributyl phosphate (TBP) + FeCl3 and β-diketone systems. The TBP + FeCl3 system is mostly used to extract lithium from salt lake brines with high magnesium-to-lithium ratios. It has weak separation capabilities for alkali metals, suffers from high solubility losses of the extractant TBP, and uses high-concentration hydrochloric acid in the stripping stage, which can exacerbate TBP degradation and cause severe corrosion to equipment. During the extraction process, the aqueous phase must be kept acidic to ensure a high chloride ion concentration. β-Diketone extraction systems are commonly used to extract lithium from alkali metal solutions. However, the extraction ability of β-diketone extractants alone is not strong, and synergistic extraction agents such as TOPO, TRPO, and Cyanex923 are usually required. They are only suitable for extracting lithium from alkaline solutions, and the extraction equilibrium pH is relatively high (>11), requiring acid to adjust the pH to neutral for subsequent processing, increasing production costs. β-diketones dissolve severely under highly alkaline conditions, resulting in poor stability. They are not suitable for lithium extraction and separation under acidic or neutral pH conditions. The extractants are expensive, the synthesis process is complex, and their large-scale application is limited. To address the problems existing in existing lithium extraction systems, there is an urgent need to find a low-cost, energy-efficient, and easily scalable extraction system for efficient lithium recovery from high-sodium-to-lithium ratio lithium-containing solutions.

[0007] In summary, the main problems in the existing technology are as follows: (1) The traditional method of preparing lithium carbonate products by evaporation and concentration is cumbersome, energy-intensive, costly, with low lithium recovery rate, high equipment investment, and prone to generating a large amount of wastewater and waste gas, which is not conducive to environmental protection. (2) For the TBP extraction system in the solvent extraction method, ferric chloride needs to be added as a co-extractant, Fe 3+ Hydrolysis can easily cause emulsification; the extractant TBP has a large solubility loss, which is not conducive to industrial application. (3) For the β-diketone extraction system in the solvent extraction method, there are common problems such as strong toxicity, large solubility loss, high cost, high extraction equilibrium pH (>11), and complex extraction synthesis process. Co-extractants such as TOPO and TRPO must be added during extraction, and lithium can only be extracted in alkaline solutions. The alkali consumption is large, resulting in high costs and difficulty in subsequent wastewater treatment. Summary of the Invention

[0008] In light of this, the present invention provides a method for recovering lithium from a lithium-containing solution with a high sodium-to-lithium ratio. This method does not require the use of a co-extractant, thus avoiding the problems associated with co-extractants in the prior art. Furthermore, the method is adaptable to a wide range of feed solutions (including acidic, neutral, and alkaline solutions), and does not require pH adjustment, allowing for direct extraction and separation, significantly reducing base consumption and achieving efficient extraction and separation. Furthermore, the raffinate has a near-neutral pH (approximately 5-8) and can be directly used to produce sodium chloride or sodium sulfate byproducts, thereby increasing economic benefits.

[0009] The present invention provides a method for recovering lithium from a lithium-containing solution with a high sodium-to-lithium ratio, comprising the following steps:

[0010] (A) mixing an extractant and a diluent to obtain an organic phase; or, mixing an extractant, a diluent, and a saponifying agent to obtain a saponified organic phase;

[0011] 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;

[0012] (B) extracting the extract phase with the lithium-containing feed solution to obtain a raffinate and a loaded organic phase, respectively;

[0013] in,

[0014] The extraction phase is the organic phase obtained in step (A) or the saponified organic phase;

[0015] The lithium-containing solution is a high sodium-to-lithium ratio lithium-containing solution; the mass ratio of Na / Li in the high sodium-to-lithium ratio lithium-containing solution is ≥3:1;

[0016] (C) mixing the loaded organic phase with a stripping agent for stripping to obtain a lithium-containing concentrate and a blank organic phase, respectively;

[0017] (D) mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain a lithium carbonate product and a lithium precipitation mother liquor, respectively.

[0018] Preferably, in step (A), the diluent is at least one of sulfonated kerosene, No. 260 solvent oil, white oil, and C6-C13 hydrocarbons;

[0019] The concentration of the organic phase obtained by mixing the extractant and the diluent is 0.3-1.5 mol / L.

[0020] Preferably, in step (A), the saponifying agent is at least one of sodium hydroxide solution, ammonia water, sodium carbonate solution, sodium bicarbonate solution, and ammonium carbonate solution;

[0021] The dosage of the saponifier is such that the saponification degree of the extractant reaches 10% to 80%.

[0022] Preferably, in step (B), the mass ratio of Na / Li in the high sodium-to-lithium ratio lithium-containing solution is (3-100):1;

[0023] The high sodium-lithium ratio lithium-containing solution + The concentration is 0.1~10g / L, Na + The concentration is 10~90g / L.

[0024] Preferably, step (B) comprises:

[0025] Extracting the organic phase with an alkaline lithium-containing feed solution to obtain a raffinate and a loaded organic phase, respectively;

[0026] or,

[0027] Extracting the saponified organic phase with a non-alkaline lithium-containing feed solution to obtain a raffinate and a loaded organic phase, respectively;

[0028] Wherein, the pH value of the alkaline lithium-containing solution is ≥10; the pH value of the non-alkaline lithium-containing solution is <10.

[0029] Preferably, in step (B):

[0030] The extraction is single-stage extraction or fractional extraction;

[0031] The fractional extraction includes two sections: countercurrent extraction and countercurrent washing;

[0032] wherein the number of extraction stages of the countercurrent extraction is 6 to 12, and the number of washing stages of the countercurrent washing is 5 to 10;

[0033] The detergent used in the countercurrent washing is at least one of water, hydrochloric acid, sulfuric acid and lithium salt solution;

[0034] In the countercurrent extraction, the flow ratio of the extraction phase, the lithium-containing liquid, and the detergent is (10-1):(10-1):1.

[0035] Preferably, in the fractional extraction, each stage of extraction and each stage of washing include: shaking, standing and phase separation;

[0036] The oscillation rate is 200-300 rpm, and the time is 10-20 min;

[0037] The standing time is 5 to 10 minutes.

[0038] Preferably, in step (C):

[0039] The stripping agent is an inorganic acid;

[0040] The ratio of the loaded organic phase to the stripping agent is (2-30):1.

[0041] Preferably, in step (C):

[0042] The stripping agent is hydrochloric acid and / or sulfuric acid;

[0043] The stripping is single-stage stripping or multi-stage stripping;

[0044] After stripping, the lithium concentration in the obtained lithium-containing concentrated solution is greater than 20 g / L.

[0045] Preferably, in step (D):

[0046] The precipitant is a saturated sodium carbonate solution;

[0047] The amount of the precipitant is 1.1 to 1.2 times the stoichiometric ratio;

[0048] The raffinate obtained in step (B) is further treated as follows: the raffinate is evaporated and crystallized to obtain sodium chloride or sodium sulfate as a by-product.

[0049] The present invention uses a single acidic phosphorus (phosphine) extractant to extract lithium from high sodium-to-lithium ratio solutions of different compositions. The extraction stage 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 present invention does not require pH adjustment of the feed solution, and the feed solution has a wide range of adaptability (acidic, neutral, and alkaline), and can directly perform extraction and separation, greatly reducing the consumption of alkali. Moreover, efficient lithium extraction and separation is achieved under near-neutral conditions. The raffinate has a pH in the near-neutral range (about 5-8) and can be directly used to prepare sodium chloride or sodium sulfate byproducts, thereby increasing economic benefits. The stripping stage enriches the lithium in the loaded organic phase into the aqueous phase by means of a phase ratio converter, and directly precipitates the lithium carbonate product from the lithium-containing concentrated solution. The present invention has the advantages of low energy consumption, short process, low cost, high yield, and environmental protection. The present invention greatly simplifies the process flow, uses a simple extractant, has good cycle stability, is inexpensive, is adaptable to different feed solutions, and is more easily applicable to industrial applications.

[0050] The test results show that the recovery process of the present invention 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 88%, and a lithium carbonate product purity of more than 99.5%, 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 Schematic diagram of the structure of the extractant used in the present invention;

[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 a lithium-containing solution with a high sodium-to-lithium ratio, comprising the following steps:

[0060] (A) mixing an extractant and a diluent to obtain an organic phase; or, mixing an extractant, a diluent, and a saponifying agent to obtain a saponified organic phase;

[0061] 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;

[0062] (B) mixing the extract phase with a lithium-containing feed solution to perform extraction, thereby obtaining a raffinate and a loaded organic phase, respectively;

[0063] in,

[0064] The extraction phase is the organic phase obtained in step (A) or the saponified organic phase;

[0065] The lithium-containing solution is a high sodium-to-lithium ratio lithium-containing solution; the mass ratio of Na / Li in the high sodium-to-lithium ratio lithium-containing solution is ≥3:1;

[0066] (C) mixing the loaded organic phase with a stripping agent for stripping to obtain a lithium-containing concentrate and a blank organic phase, respectively;

[0067] (D) mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain a lithium carbonate product and a lithium precipitation mother liquor, respectively.

[0068] Regarding step (A):

[0069] (A) mixing an extractant and a diluent to obtain an organic phase; or, mixing an extractant, a diluent and a saponifying agent to obtain a saponified organic phase.

[0070] 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). The structures of the above four extractants are as follows: Figure 1 The present invention adopts the above-mentioned specific acidic phosphorus / phosphine extractants and adjusts the saponification degree of the extractants to achieve extraction and separation of lithium under near-neutral pH conditions.

[0071] 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.

[0072] In the present invention, the concentration of the extractant after mixing with the diluent is preferably 0.3 to 1.5 mol / L. That is, the concentration of the organic phase obtained by mixing the extractant and diluent is preferably 0.3 to 1.5 mol / L, specifically 0.3 mol / L, 0.5 mol / L, 1.0 mol / L, or 1.5 mol / L. Whether preparing the organic phase or the saponified organic phase, the concentration is controlled within the above range.

[0073] 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 80%, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

[0074] In the present invention, for the preparation of the saponified organic phase, it is preferred to first mix the extractant and the diluent to obtain an organic phase, and then mix the saponifying agent with the organic phase for saponification to obtain the saponified organic phase. The mixing and saponification process is preferably accompanied by oscillation. 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 minutes.

[0075] Regarding step (B):

[0076] (B) The extraction phase is mixed with the lithium-containing feed solution for extraction to obtain a raffinate and a loaded organic phase, respectively.

[0077] In the present invention, the lithium-containing solution is a high sodium-lithium ratio lithium-containing solution; the mass ratio of Na / Li in the high sodium-lithium ratio lithium-containing solution is ≥3:1, preferably (3-100):1. + The concentration is preferably 0.1 to 10 g / L, Na + The concentration is preferably 10 to 90 g / L. In the present invention, if the original lithium-containing solution contains a large number of impurities, it is preferred to first perform a pretreatment to convert the original lithium-containing solution into a solution containing only monovalent alkali metal elements and having an impurity ion concentration of 0 to 10 mg / L other than Li, Na, and K. This solution is used as the high sodium-to-lithium ratio lithium-containing solution for the recovery process of the present invention.

[0078] In the present invention, the extraction phase is the organic phase or saponified organic phase obtained in step (A). Whether to use the organic phase or the saponified organic phase depends on the acidity or alkalinity of the lithium-containing feed solution. If the lithium-containing feed solution is alkaline (pH ≥ 10), the organic phase is used; if the lithium-containing feed solution is non-alkaline (pH < 10), the saponified organic phase is used. That is, step (B) can be: mixing the organic phase with an alkaline lithium-containing feed solution for extraction to obtain a raffinate and a loaded organic phase, respectively; or, mixing the saponified organic phase with a non-alkaline lithium-containing feed solution for extraction to obtain a raffinate and a loaded organic phase, respectively. In the prior art, only alkaline lithium liquid can be extracted. If the lithium-containing liquid is acidic, it is necessary to first adjust the lithium-containing liquid to alkaline, which requires the consumption of a large amount of alkaline substances. In the present invention, regardless of whether the lithium-containing liquid is non-alkaline (that is, it can be acidic, neutral or alkaline), there is no need to adjust the pH value of the lithium-containing liquid. An organic phase or a saponified organic phase can be used for extraction, thereby achieving efficient extraction of lithium.

[0079] In the present invention, the extraction can be a single-stage extraction or a fractional extraction. In the present invention, for alkaline lithium-containing feed liquid, single-stage extraction is preferably used; for non-alkaline lithium-containing feed liquid, fractional extraction is preferably used. That is, step (B) preferably includes: single-stage extraction of the organic phase with the alkaline lithium-containing feed liquid to obtain a raffinate and a loaded organic phase, respectively; or fractional extraction of the saponified organic phase with the non-alkaline lithium-containing feed liquid to obtain a raffinate and a loaded organic phase, respectively.

[0080] About single-stage extraction:

[0081] The extraction phase is mixed with the lithium-containing feed liquid for extraction, and after shaking, the phases are allowed to stand for phase separation to obtain a raffinate and a lithium-loaded organic phase, respectively. Wherein, the ratio (O / A ratio) of the extraction phase to the lithium-containing feed liquid is preferably (10-0.1):1, that is, the extraction is carried out by mixing with the above ratio, specifically 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 0.5:1, 0.1:1. The oscillation rate is preferably 200-300rpm, specifically 200rpm, 210rpm, 220rpm, 230rpm, 240rpm, 250rpm, 260rpm, 270rpm, 280rpm, 290rpm, 300rpm. The oscillation time is preferably 10 to 20 minutes, specifically 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 minutes. The standing time is preferably 5 to 10 minutes, specifically 5, 6, 7, 8, 9, or 10 minutes. After standing, the phases are separated to obtain a raffinate and a lithium-loaded organic phase, respectively.

[0082] About fractional extraction:

[0083] In the present invention, the fractional extraction includes two sections, namely, countercurrent extraction and countercurrent washing, i.e., two processes of countercurrent extraction and countercurrent washing are performed. The fractional extraction can be performed 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, countercurrent extraction and countercurrent washing, to separate the elements in the system into an easily extractable component A (Li) and a difficultly extractable component B (Na / K), such as 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.

[0084] In the present invention, the number of extraction stages n in the fractional extraction is preferably 6 to 12, specifically 6, 7, 8, 9, 10, 11, and 12. 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 water, hydrochloric acid, sulfuric acid, and a lithium salt solution; the lithium salt solution is the lithium-containing feed solution. The concentrations of the inorganic acid and the lithium salt solution are preferably both 0.1 to 3 mol / L, specifically 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, and 3.0 mol / L. In the present invention, in the fractional extraction, the flow ratio of the extraction phase, the lithium-containing liquid and the detergent is preferably (10-1):(10-1):1, specifically 17.14:5.55:2.16 (i.e. 7.94:2.57:1), 13.7:5.68:3.39 (i.e. 4.04:1.68:1), 12.4:6.15:3.56 (i.e. 3.48:1.73:1), and 15.76:5.23:2.88 (5.47:1.82:1).

[0085] 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. After multiple cycles of oscillation-standing phase separation-phase shifting, until the whole system reaches stability, the fractional distillation extraction is terminated, and the outlet aqueous phase and the outlet organic phase are collected separately, that is, the raffinate and the loaded organic phase are obtained respectively. The whole system reaches stability means that the composition of the outlet aqueous phase and the outlet organic phase no longer changes significantly, and the system reaches extraction equilibrium. In the present invention, the pH of the obtained raffinate is in the near-neutral range (pH is 5 to 8), that is, the extraction equilibrium pH is in the near-neutral range, realizing 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 feed solution is near-neutral, but means that the extraction equilibrium pH is in the near-neutral range). The extraction system used in the present invention can achieve extraction and separation of lithium in the near-neutral range for feed solutions with different initial pH values.

[0086] In the present invention, fractional extraction is more preferably used, which can further significantly improve the extraction rate and yield of lithium, so that the lithium extraction rate reaches more than 99%.

[0087] In the present invention, the raffinate obtained by extraction can be treated as follows: the raffinate is evaporated and crystallized (depending on whether the feed liquid is a hydrochloric acid or sulfuric acid system) to obtain sodium chloride or sodium sulfate as a byproduct.

[0088] Regarding step (C):

[0089] (C) mixing the loaded organic phase with a stripping agent for stripping to obtain a lithium-containing concentrated solution and a blank organic phase, respectively.

[0090] In the present invention, the stripping agent is preferably an inorganic acid, more preferably hydrochloric acid and / or sulfuric acid. The concentration of the inorganic acid is preferably 1 to 6 mol / L, specifically 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L. In the present invention, the ratio (O / A ratio) of the loaded organic phase to the stripping agent is preferably (1 to 30):1, specifically 1:1, 2:1, 5:1, 6:1, 10:1, 12:1, 15:1, 20:1, 25:1, or 30:1.

[0091] In the present invention, the stripping can be a single-stage stripping or a multi-stage stripping; the number of stages of the multi-stage stripping is preferably ≥3, specifically 3, 4, 5 or more stages. The stripping is a countercurrent stripping. After the loaded organic phase and the stripping agent are mixed in a certain ratio, they are shaken and phase-separated to obtain a lithium-containing concentrate (i.e., the obtained stripping solution is a lithium-containing concentrate) and a blank organic phase. Among them, 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, 300 rpm. The time of each oscillation is preferably 10-30 min, specifically 10 min, 15 min, 20 min, 25 min, 30 min. In the present invention, after stripping, the lithium concentration in the obtained lithium-containing concentrate is >20 g / L, and the lithium carbonate product can be directly precipitated from the lithium-containing concentrate.

[0092] Regarding step (D):

[0093] (D) mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain a lithium carbonate product and a lithium precipitation mother liquor, respectively.

[0094] 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.

[0095] In the present invention, a lithium-containing concentrated solution is mixed with a precipitant, and the precipitant reacts with the lithium-containing concentrated solution to precipitate lithium carbonate 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%.

[0096] In the present invention, the separated liquid (lithium precipitation mother liquor) obtained after solid-liquid separation can be treated as follows: the obtained lithium precipitation mother liquor is mixed with the lithium-containing feed liquid, and both are put into the system, and the recovery process is performed again.

[0097] The present invention uses a single acidic phosphorus (phosphine) extractant to extract lithium from high sodium-to-lithium ratio solutions of different compositions. The extraction stage 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 present invention does not require pH adjustment of the feed solution, and the feed solution has a wide range of adaptability (acidic, neutral, and alkaline), and can directly perform extraction and separation, greatly reducing the consumption of alkali. Moreover, efficient lithium extraction and separation is achieved under near-neutral conditions, and the raffinate pH is in the near-neutral range (about 5-8), which can be directly used to prepare sodium chloride or sodium sulfate byproducts, thereby increasing economic benefits. The stripping stage enriches the lithium in the loaded organic phase into the aqueous phase by means of a phase ratio, and directly precipitates the stripping solution to prepare a lithium carbonate product. The present invention has the advantages of low energy consumption, short process, low cost, high yield, and environmental protection. The present invention greatly simplifies the process flow, uses a simple extractant, has good cycle stability, is low-cost, is adaptable to different feed solutions, and is more easily applicable to industrial applications.

[0098] Compared with the prior art, the present invention has the following beneficial effects:

[0099] 1. The extraction system of the present invention does not require the additional addition of ferric chloride as a co-extractant, thereby avoiding a series of problems caused by the use of ferric chloride as a co-extractant; the extraction system does not require the use of a synergistic extraction system of β-diketone and neutral phosphine oxide, thereby avoiding the problems of the β-diketone extractant, such as strong toxicity, large dissolution loss, high cost, and high extraction equilibrium pH (>11).

[0100] 2. The existing technology requires that the treatment target be an alkaline lithium-containing solution. If the initial solution is acidic, it must be adjusted to alkaline before recovery, which consumes a large amount of alkali and increases costs. The process of the present invention is applicable to a wide range of feed solutions, including acidic, neutral, and alkaline solutions, and does not require pH adjustment, simplifying the process and reducing costs.

[0101] 3. The pH range of the raffinate aqueous phase of the extraction system used in the present invention is 5 to 8 (near neutral range), that is, the extraction system used in the present invention can achieve lithium extraction and separation in a near-neutral range for feed solutions with different initial pH values. The aqueous phase has low acidity, and the wastewater treatment is easy, so it can be directly used for the subsequent preparation of sodium chloride or sodium sulfate products.

[0102] 3. The present invention uses a fractional extraction method with the required number of stages and flow ratios, achieving a lithium recovery rate of 99% throughout the entire process. The outlet organic phase can be stripped to produce lithium carbonate, while the outlet aqueous phase can be directly used to produce sodium chloride or sodium sulfate byproducts.

[0103] 4. The extractant used in the present invention is cheap and readily available and can be recycled. The recovery process is easy to industrialize and has practical application value.

[0104] 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.

[0105] Example 1

[0106] The lithium-containing feed liquid to be treated is the mother liquid (feed liquid I) produced by precipitating lithium carbonate from salt lake brine, the main components of which are: lithium: 2.1 g / L, sodium: 48.9 g / L, and the pH value of the feed liquid is 10.85.

[0107] (A) The extractant P227 was mixed with the diluent sulfonated kerosene to obtain an organic phase (the organic phase concentration was 1.2 mol / L).

[0108] (B) Without adjusting the pH of the lithium-containing feed solution, the organic phase and lithium-containing feed solution I were mixed at a ratio of O / A = 1:1, shaken at 280 rpm for 30 minutes at room temperature, and allowed to stand for 5 minutes for phase separation, yielding a raffinate and a loaded organic phase, respectively. The single-stage lithium extraction efficiency was 57.83%, and the equilibrium pH of the raffinate aqueous phase was 7.12.

[0109] (C) The loaded organic phase obtained after extraction was mixed with a stripping agent (0.5 mol / L sulfuric acid) at a ratio of O / A = 1:1 for stripping. The single-stage stripping efficiency of lithium was 99.64%.

[0110] Example 2

[0111] The treatment object is lithium-containing liquid: sulfate extraction wastewater (liquid II) generated after the recovery of nickel, cobalt and manganese from waste ternary battery black powder. The main components are: lithium: 2.2g / L, sodium: 34.12g / L, and the liquid pH is 6.37.

[0112] (A) The extractant P507 was mixed with the diluent sulfonated kerosene (organic phase concentration was 1.2 mol / L), and then saponified with sodium hydroxide solution (6 mol / L). The mixture was shaken at room temperature for 30 minutes to achieve a saponification degree of 40%, thereby obtaining a saponified organic phase.

[0113] (B) Without adjusting the pH of the lithium-containing feed solution, the saponified organic phase and lithium-containing feed solution II were fractionally extracted. The process consisted of eight extraction stages and seven wash stages. The wash acid was 1.5 mol / L H₂SO₄; the flow ratio was 17.14:5.55:2.16 for saponified organic phase:feed solution:wash acid. After shaking at 270 rpm for 15 minutes and allowing the phases to separate for 5 minutes, 99.71% of the lithium was extracted into the organic phase. The equilibrium pH of the raffinate aqueous phases at each stage was between 6 and 7.

[0114] (C) The loaded organic phase obtained after extraction was mixed with a stripping agent (2 mol / L sulfuric acid) at a ratio of O / A = 30:1 for stripping. After five stages of countercurrent stripping, the lithium stripping efficiency was 99.8%, and the lithium concentration in the lithium-containing concentrate obtained by stripping was 21.3 g / L.

[0115] (D) Slowly dripping a saturated sodium carbonate solution with a stoichiometric ratio of 1.1 into the lithium-containing concentrate at 80° C., followed by filtration, yields a battery-grade lithium carbonate product with a purity of 99.51% and a lithium precipitation mother liquor. The raffinate obtained in step (B) is evaporated and crystallized to yield sodium sulfate as a byproduct.

[0116] Results: In this embodiment, the lithium extraction rate was 99.71%, the lithium stripping rate was 99.8%, the total lithium recovery rate was 90.12%, and the purity of the lithium carbonate product was 99.51%.

[0117] Example 3

[0118] Initial spodumene was leached with sulfuric acid and initially cleaned with sodium hydroxide to yield a leachate with a composition of 8.6 g / L lithium, 26.5 g / L sodium, 7.7 g / L potassium, 0.65 g / L calcium, 0.23 g / L magnesium, 0.1 g / L iron, 0.04 g / L aluminum, and 1.2 g / L manganese; the pH was 7.45. Pretreatment yielded a lithium-containing feed solution by extracting with saponified Cyanex 272 to remove impurities such as iron, aluminum, manganese, calcium, and magnesium, yielding a lithium-containing raffinate (Feed III) with a composition of 8.54 g / L lithium, 27.9 g / L sodium, and 7.65 g / L potassium, with a pH of 6.27.

[0119] (A) The extractant Cyanex 272 was mixed with the diluent sulfonated kerosene (organic phase concentration was 1.5 mol / L), and then saponified with sodium hydroxide solution (6 mol / L). The mixture was shaken at room temperature for 30 minutes to achieve a saponification degree of 50%, thereby obtaining a saponified organic phase.

[0120] (B) Without adjusting the pH of the lithium-containing feed solution, the saponified organic phase and lithium-containing feed solution III were fractionally extracted. The process consisted of eight extraction stages and eight wash stages. The wash acid was 2 mol / L H₂SO₄; the flow ratio was 13.7:5.68:3.39 for saponified organic phase:feed solution:wash acid. After shaking at 270 rpm for 15 minutes and allowing the phases to separate for 5 minutes, 99.27% ​​of the lithium was extracted into the organic phase. The equilibrium pH of each raffinate aqueous phase was between 6 and 7.

[0121] (C) The loaded organic phase obtained after extraction was mixed with a stripping agent (2 mol / L sulfuric acid) at a ratio of O / A = 6:1 for stripping. After three-stage countercurrent stripping, the lithium stripping efficiency was 99.63%, and the lithium concentration in the lithium-containing concentrate obtained by stripping was 21.24 g / L.

[0122] (D) Slowly dripping a saturated sodium carbonate solution with a stoichiometric ratio of 1.15 into the lithium-containing concentrate at 80° C., followed by filtration, yields a battery-grade lithium carbonate product with a purity of 99.52% and a lithium precipitation mother liquor. The raffinate obtained in step (B) is evaporated and crystallized to yield sodium sulfate as a byproduct.

[0123] Results: In this embodiment, the lithium extraction rate was 99.27%, the lithium stripping rate was 99.63%, the total lithium recovery rate was 90.78%, and the purity of the lithium carbonate product was 99.52%.

[0124] Example 4

[0125] Original object: Spent lithium iron phosphate batteries were leached with sulfuric acid and hydrogen peroxide, resulting in a lithium-containing leachate with a primary composition of 4.6 g / L lithium, 0.78 g / L aluminum, and 0.43 g / L copper, with a pH of 1.87. Pretreatment yielded a lithium-containing feed solution by adjusting the pH with sodium hydroxide and extracting with saponified P204 to remove aluminum and copper impurities. This yielded a lithium-containing raffinate (Feed IV) with a composition of 4.36 g / L lithium and 22.17 g / L sodium, with a pH of 5.42.

[0126] (A) The extractant P204 was mixed with the diluent sulfonated kerosene (organic phase concentration was 1.5 mol / L), and then saponified with sodium hydroxide solution (6 mol / L). The mixture was shaken at room temperature for 30 minutes to achieve a saponification degree of 60%, thereby obtaining a saponified organic phase.

[0127] (B) Without adjusting the pH of the lithium-containing feed solution, the saponified organic phase and lithium-containing feed solution IV were fractionally extracted. The process consisted of eight extraction stages and seven wash stages. The wash acid was 1 mol / L H₂SO₄; the flow ratio was 12.4:6.15:3.56 for saponified organic phase:feed solution:wash acid. After shaking at 270 rpm for 15 minutes and allowing the phases to separate for 5 minutes, 99.19% of the lithium was extracted into the organic phase, with a sodium content of 0.35 g / L. The equilibrium pH of the raffinate aqueous phases at each stage was between 5 and 7.

[0128] (C) The loaded organic phase obtained after extraction was mixed with a stripping agent (2 mol / L sulfuric acid) at a ratio of O / A = 10:1 for stripping. After three-stage countercurrent stripping, the lithium stripping efficiency was 99.54%, and the lithium concentration in the lithium-containing concentrate obtained by stripping was 21.62 g / L.

[0129] (D) Slowly dripping a saturated sodium carbonate solution with a stoichiometric ratio of 1.2 into the lithium-containing concentrate at 80° C., followed by filtration, to obtain a battery-grade lithium carbonate product with a purity of 99.57% and a lithium precipitation mother liquor. The raffinate obtained in step (B) is evaporated and crystallized to obtain sodium sulfate as a byproduct.

[0130] Results: In this embodiment, the lithium extraction rate was 99.19%, the lithium stripping rate was 99.54%, the total lithium recovery rate was 89.54%, and the purity of the lithium carbonate product was 99.57%.

[0131] Example 5

[0132] The sulfate lithium precipitation mother liquor produced by lithium carbonate precipitation in Example 4 was mixed uniformly with feed solution IV at a certain volume ratio (the volume of the lithium precipitation mother liquor accounted for 10% of the total volume) to obtain lithium-containing feed solution V. The main composition was: lithium: 5.48 g / L, sodium: 25.83 g / L, and the feed solution pH was 8.36.

[0133] (A) The extractant P227 was mixed with the diluent sulfonated kerosene (organic phase concentration was 1.35 mol / L), and then saponified with sodium hydroxide solution (6 mol / L). The mixture was shaken at room temperature for 30 minutes to achieve a saponification degree of 60%, thereby obtaining a saponified organic phase.

[0134] (B) Without adjusting the pH of the lithium-containing feed solution, the saponified organic phase and lithium-containing feed solution V were fractionally extracted. The process consisted of eight extraction stages and seven wash stages. The wash acid was 1.5 mol / L H₂SO₄; the flow ratio was 15.76:5.23:2.88 for saponified organic phase:feed solution:wash acid. After shaking at 270 rpm for 15 minutes and allowing the phases to separate for 5 minutes, 99.35% of the lithium was extracted into the organic phase, with a sodium content of 0.7 g / L. The equilibrium pH of the raffinate aqueous phases was between 7 and 8.

[0135] (C) The loaded organic phase obtained after extraction was mixed with a stripping agent (2 mol / L sulfuric acid) at a ratio of O / A = 12:1 for stripping. After four stages of countercurrent stripping, the lithium stripping efficiency was 99.69%, and the lithium concentration in the lithium-containing concentrate obtained by stripping was 21.89 g / L.

[0136] (D) Slowly dripping a saturated sodium carbonate solution with a stoichiometric ratio of 1.15 into the lithium-containing concentrate at 80° C., followed by filtration, to obtain a battery-grade lithium carbonate product with a purity of 99.53% and a lithium precipitation mother liquor. The raffinate obtained in step (B) is evaporated and crystallized to obtain sodium sulfate as a byproduct.

[0137] Results: In this embodiment, the lithium extraction rate was 99.35%, the lithium stripping rate was 99.69%, the total lithium recovery rate was 90.05%, and the purity of the lithium carbonate product was 99.53%.

[0138] Comparative Example 1

[0139] The process was carried out in accordance with Example 2, except that the composition of the organic phase for extraction was changed to the following: 1.2 mol / L P507, tributyl phosphate (TBP, 10% of the total volume) and sulfonated kerosene; the saponification process and saponification degree were the same as those in Example 2.

[0140] Results: The lithium-sodium separation coefficient was significantly reduced, and the phase separation time at the two-phase interface was significantly prolonged (over 50 minutes), which was not conducive to industrial application.

[0141] In summary, the recovery process of the present invention 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 88%, and a lithium carbonate product purity of more than 99.5%, thereby achieving efficient separation and recovery of lithium and obtaining a high-purity lithium salt product.

[0142] 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 a lithium-containing solution with a high sodium-to-lithium ratio, characterized in that: The following steps are involved: (A) mixing an extractant and a diluent to obtain an organic phase; or, mixing an extractant, a diluent, and 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; (B) extracting the extract phase with the lithium-containing feed solution to obtain a raffinate and a loaded organic phase, respectively; in, The extraction phase is the organic phase obtained in step (A) or the saponified organic phase; The lithium-containing solution is a high sodium-to-lithium ratio lithium-containing solution; the mass ratio of Na / Li in the high sodium-to-lithium ratio lithium-containing solution is ≥3:1; (C) mixing the loaded organic phase with a stripping agent for stripping to obtain a lithium-containing concentrate and a blank organic phase, respectively; (D) mixing the lithium-containing concentrated solution with a precipitant, and performing solid-liquid separation to obtain a lithium carbonate product and a lithium precipitation mother liquor, respectively.

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

3. The method according to claim 1, characterized in that In step (A), 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 80%.

4. The method according to claim 1, wherein In step (B), the mass ratio of Na / Li in the high sodium-to-lithium ratio lithium-containing solution is (3-100):1; The high sodium-lithium ratio lithium-containing solution + The concentration is 0.1~10g / L, Na + The concentration is 10~90g / L.

5. The method according to claim 1, wherein Step (B) comprises: Extracting the organic phase with an alkaline lithium-containing feed solution to obtain a raffinate and a loaded organic phase, respectively; or, Extracting the saponified organic phase with a non-alkaline lithium-containing feed solution to obtain a raffinate and a loaded organic phase, respectively; Wherein, the pH value of the alkaline lithium-containing solution is ≥10; the pH value of the non-alkaline lithium-containing solution is <10.

6. The method according to claim 1, characterized in that In step (B): The extraction is single-stage extraction or fractional extraction; The fractional extraction includes two sections: countercurrent extraction and countercurrent washing; wherein the number of extraction stages of the countercurrent extraction is 6 to 12, 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 water, hydrochloric acid, sulfuric acid and lithium salt solution; In the countercurrent extraction, the flow ratio of the extraction phase, the lithium-containing liquid, and the detergent is (10-1):(10-1):

1.

7. The method according to claim 6, 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.

8. The method according to claim 1, characterized in that In step (C): The stripping agent is an inorganic acid; The ratio of the loaded organic phase to the stripping agent is (2-30):

1.

9. The method according to claim 1, characterized in that In step (C): The stripping agent is hydrochloric acid and / or sulfuric acid; The stripping is single-stage stripping or multi-stage stripping; After stripping, the lithium concentration in the obtained lithium-containing concentrated solution is greater than 20 g / L.

10. The method according to claim 1, characterized in that In step (D): The precipitant is a saturated sodium carbonate solution; The amount of the precipitant is 1.1 to 1.2 times the stoichiometric ratio; The raffinate obtained in step (B) is further treated as follows: the raffinate is evaporated and crystallized to obtain sodium chloride or sodium sulfate as a by-product.

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