Method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate

Abstract

The application relates to the technical field of resource recycling, and particularly discloses a method for separating low-grade brine into magnesium hydroxide and lithium carbonate. The method specifically comprises the following steps: S1, evaporating and concentrating low-lithium brine to obtain concentrated brine; S2, precipitating calcium and magnesium ions in the concentrated brine by treating the concentrated brine with a sodium hydroxide solution to obtain a colloidal solution; S3, performing solid-liquid separation on the colloidal solution after aging treatment to obtain alkaline filtrate and solid precipitate; S4, adsorbing the alkaline filtrate on a column filled with a lithium adsorbent containing titanium, then desorbing the alkaline filtrate with an acid to obtain acid desorption liquid; dissolving the solid precipitate in an acid, and then precipitating and selectively separating calcium and magnesium by using sodium sulfate; and S5, evaporating and concentrating the acid desorption liquid, precipitating lithium carbonate, and washing off impurities to obtain lithium carbonate. The method is suitable for extracting lithium from high-salt and low-grade brine, the total lithium extraction rate can be as high as 75%, and the Mg recovery rate can reach 98%.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate. Background Technology

[0002] Lithium and its compounds are core raw materials for power batteries and energy storage batteries. With the development of the new energy industry, the demand for lithium has increased dramatically. Given the large volume of low-lithium brine, the development of low-lithium salt lake resources is imperative. However, how to extract lithium from brine resources with low lithium content and high magnesium content urgently needs to be addressed.

[0003] The main methods for industrial lithium extraction from salt lake brine include evaporation precipitation, calcination, extraction, adsorption, and membrane separation. Among these, adsorption is low-cost, simple to operate, and environmentally friendly, with great application potential. Typically, it requires an industrial-grade lithium content (above 40 mg / L), and the raw brine needs to be evaporated, concentrated, and crystallized in the salt field to obtain aged brine (with a lithium content above 100 mg / L) before subsequent extraction. However, this process suffers from long drying cycles, low lithium yield, and ineffective exploitation of other elements, resulting in unsatisfactory brine resource utilization efficiency. Developing a rational and effective process route is an important direction for improving lithium extraction efficiency.

[0004] Patent CN107921328A discloses a method for extracting lithium from brine, specifically by contacting an aqueous brine solution with a titanate adsorbent, such that lithium ions are adsorbed onto the titanate adsorbent while repelling substantially all other cations. The adsorbent is provided in the form of hydrated titanium dioxide or sodium titanate. The method then produces a substantially pure lithium chloride solution. The brine contains lithium and impurities, with lithium in the range of about 500 to 1500 ppm, and impurities including: magnesium in the range of about 0.15% to 0.30%, calcium in the range of about 0.05% to 0.1%, sodium in the range of about 8% to 10%, potassium in the range of about 0.7% to 1.0%, and boric acid in the range of about 0.15% to 0.20%.

[0005] Patent CN106507816A discloses a method for extracting lithium from brine. First, brine with a high magnesium-to-lithium ratio is diluted with water or a lithium chloride solution. Then, it is passed through a lithium adsorbent packed in a column to selectively adsorb lithium. Next, it is washed with water or sodium chloride solution to remove as much magnesium as possible. Then, the lithium on the adsorbent is rinsed with lithium chloride solution or water. The rinsing solution is then further purified to remove magnesium and concentrated. The resulting solution has a lithium chloride concentration of 20-120 g / L and a magnesium concentration of less than 100 mg / L. The lithium content in the brine is 159 ppm to 252 ppm.

[0006] Currently, there are few reports on lithium extraction from low-lithium salt lake brines (lithium ion concentration of ~3 mg / L), and magnesium ions are not effectively extracted and utilized during lithium extraction and magnesium removal, resulting in a waste of magnesium resources. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate. This method involves evaporation and concentration, calcium and magnesium precipitation, lithium adsorption, acid washing and desorption, and lithium precipitation purification to finally obtain the finished product lithium carbonate. At the same time, it can also separate and extract magnesium from the brine.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate, comprising the following steps:

[0010] S1. The low-grade brine is evaporated and concentrated to obtain concentrated brine; the concentrated brine contains Li + The concentration is 10~15 ppm;

[0011] S2. The concentrated brine is treated with sodium hydroxide solution to precipitate calcium and magnesium ions, resulting in a colloidal solution;

[0012] S3. The colloidal solution is aged to separate the solid and liquid components, resulting in an alkaline filtrate and a solid precipitate.

[0013] S4. The alkaline filtrate is adsorbed onto an adsorption column containing a titanium-based lithium adsorbent, and then desorbed with acid to obtain an acid-desorbed solution; the titanium-based lithium adsorbent is lithium titanate material Li4Ti5O. 12 It is obtained by acid washing, water washing, and drying;

[0014] After dissolving the solid precipitate in acid, calcium and magnesium are selectively separated by precipitation with sodium sulfate to obtain CaSO4 and Mg(OH)2 with a purity of not less than 96%.

[0015] S5. After evaporating and concentrating the acid desorption solution, precipitating lithium carbonate, and washing away impurities, lithium carbonate with a purity of not less than 98% is obtained.

[0016] Furthermore, the evaporation and concentration temperature is 75~80℃.

[0017] Furthermore, the low-lithium brine includes low-grade salt lake brine or industrial waste liquid with low lithium content.

[0018] Furthermore, the volume ratio of the sodium hydroxide solution to the concentrated brine is 1:4 to 1:6, and the pH value of the sodium hydroxide solution is 13 to 14.

[0019] Furthermore, the aging temperature is 40~42℃, and the aging time is 110~120min.

[0020] Furthermore, the lithium titanate material Li4Ti5O 12 The preparation method is as follows:

[0021] S1. Add tetraisopropyl titanate to deionized water and stir to form a white titanate precipitate; disperse the white titanate precipitate in deionized water, then add LiOH·H2O, stir, then add 30% H2O2, and continue stirring until a pale yellow solution is formed; the volume-to-mass ratio of the tetraisopropyl titanate to the LiOH·H2O is (8~16) mL: (3-7) g;

[0022] S2. The yellow solution obtained in step S11 is heated in a water bath, and then a dry white solid product is obtained under a dry calcination mechanism. The white solid powder is then calcined in a muffle furnace to obtain Li4Ti5O. 12 ;

[0023] The dry-burning mechanism involves drying at 120℃~200℃ for 24 hours.

[0024] The calcination temperature is 450℃~650℃, and the annealing time is 3-5 hours.

[0025] Furthermore, the adsorption process in step S4 is a dynamic adsorption process performed by connecting adsorption columns in series.

[0026] Furthermore, the temperature for dynamic adsorption is 22~24℃, and the flow rate of the alkaline filtrate through the adsorption column is 4.5~5mL / min.

[0027] Furthermore, desorption was performed using 0.1M HCl.

[0028] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0029] (1) The present invention provides a method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate. Specifically, the low-lithium brine is pre-treated by initial concentration and pH adjustment, and then titanium adsorbent is directly adsorbed and desorbed. Finally, lithium is precipitated with soda ash and purified to prepare finished lithium carbonate. On the one hand, this method solves the problem of efficient lithium extraction from low-lithium brine, and on the other hand, it realizes the separation and extraction of by-products such as magnesium and boron. It is expected to realize the industrial application of lithium extraction from low-lithium brine.

[0030] (2) The technical solution provided in this aspect is for lithium extraction from high-salt, low-grade brine in Xinjiang, with a total lithium extraction rate of up to 75%.

[0031] (3) By chemical precipitation, sodium sulfate, which is relatively inexpensive, is added. Taking advantage of the different solubilities of calcium sulfate and magnesium sulfate, calcium and magnesium can be selectively separated. Further processing yields CaSO4 and high-purity Mg(OH)2, with a Mg extraction rate of 98%. Attached Figure Description

[0032] Figure 1 A schematic diagram of a process provided for this invention;

[0033] Figure 2 H4Ti5O is a titanium-based lithium adsorbent. 12 and un-acid-washed Li4Ti5O 12 XRD comparison images;

[0034] Figure 3 H4Ti5O is a titanium-based lithium adsorbent. 12 SEM image;

[0035] Figure 4 Un-acid-washed Li4Ti5O 12 SEM image;

[0036] Figure 5 H4Ti5O is a titanium-based lithium adsorbent. 12 HRTEM image;

[0037] Figure 6 H4Ti5O is a titanium-based lithium adsorbent. 12 and un-acid-washed Li4Ti5O 12 Comparison of N2 adsorption-desorption isotherms;

[0038] Figure 7 H4Ti5O is a titanium-based lithium adsorbent. 12 and un-acid-washed Li4Ti5O 12 Pore ​​distribution diagram;

[0039] Figure 8 The specific structure of a dynamic series adsorption column;

[0040] Figure 9 This is a photograph of lithium carbonate obtained by precipitation and filtration using soda ash.

[0041] Figure 10 This is a photograph of the finished lithium carbonate product after purification and drying.

[0042] Figure 11 The image shows the XRD pattern of the prepared lithium carbonate. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific test methods, instruments, or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0044] refer to Figure 1 A schematic flowchart of a method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate is provided by the present invention. The specific process is as follows:

[0045] S1. Evaporate and concentrate the low-lithium brine to obtain concentrated brine;

[0046] S2. The above concentrated brine is treated with sodium hydroxide solution to precipitate calcium and magnesium ions, resulting in a colloidal solution.

[0047] S3. The above colloidal solution is aged to separate the solid and liquid components, resulting in an alkaline filtrate and a solid precipitate.

[0048] S4. The above alkaline filtrate is adsorbed onto an adsorption column containing a titanium-based lithium adsorbent, and then desorbed with acid to obtain an acid-desorbed solution; the above titanium-based lithium adsorbent is lithium titanate material Li4Ti5O 12 It is obtained by acid washing, water washing, and drying;

[0049] After dissolving the solid precipitate obtained in step S3 in acid, calcium and magnesium are selectively separated by precipitation using sodium sulfate to obtain CaSO4 and Mg(OH)2 with a purity of not less than 96%.

[0050] S5. After evaporating and concentrating the above acid desorption solution, precipitating lithium carbonate, and washing away impurities, lithium carbonate with a purity of not less than 98% is obtained.

[0051] The following describes a specific implementation method.

[0052] This embodiment describes the separation of magnesium and lithium from brine in the Tarim Basin of Xinjiang and the preparation of magnesium hydroxide and lithium carbonate.

[0053] The composition information of brine in the Tarim Basin of Xinjiang is shown in Table 1 below.

[0054] Table 1.

[0055]

[0056] Example 1

[0057] This embodiment provides a method for separating magnesium and lithium from low-grade brine and producing magnesium hydroxide and lithium carbonate, specifically including the following steps:

[0058] Step S1: 75 L of raw brine is rapidly evaporated and concentrated to 15 L at 80 °C; Li in the concentrated brine... + The concentration was 14.77 ppm;

[0059] Step S2: The concentrated brine is treated with sodium hydroxide solution to precipitate calcium and magnesium ions, resulting in a colloidal solution; the concentration of the sodium hydroxide solution is 40%, and the pH value is adjusted to 13.

[0060] Step S3: The above colloidal solution is aged to achieve solid-liquid separation, obtaining an alkaline filtrate and a solid precipitate; the aging temperature is 40℃, and the aging time is 120 min; Li + The transfer rate can reach 91%;

[0061] Step S4: The above alkaline filtrate is adsorbed through an adsorption column containing titanium-based lithium adsorbent, and then desorbed with acid to obtain acid desorbed solution.

[0062] After dissolving the solid precipitate in acid, calcium and magnesium were selectively separated by precipitation with sodium sulfate to obtain CaSO4 and Mg(OH)2 with a purity of not less than 96%, and the Mg extraction rate reached 98%.

[0063] The specific structure of the tandem adsorption column is as follows: Figure 8 As shown, the brine solution flows through two adsorption columns connected in series under the action of a peristaltic pump. The adsorption conditions are 24℃ and a flow rate of 5 mL / min, with two dynamic adsorption processes. After adsorption, the adsorption columns are desorbed with 0.1 M HCl at 24℃ and a flow rate of 6 mL / min for 10 min, achieving Li+ adsorption. + Rapid desorption, with a desorption rate of up to 90%.

[0064] In step S5, the above acid-electrolysed solution is evaporated and concentrated in a water bath at 80°C. The pH is then adjusted to neutral with sodium hydroxide, followed by the introduction of a sodium carbonate solution to form a precipitate. After washing away impurities with water, the precipitate is dried to obtain lithium carbonate with a purity of 98%. The total lithium extraction rate reaches 75%.

[0065] Total lithium extraction rate = Mass of finished lithium carbonate × Purity × 28 / (Concentration of original lithium halide × Volume of original halide × 74)

[0066] The specific preparation method of the titanium-based lithium adsorbent for the adsorption column packing provided in step S4 of this embodiment is as follows:

[0067] First, 10 mL of tetraisopropyl titanate was added to 100 mL of deionized water while stirring to form a white titanate precipitate. The product was dispersed in 170 mL of deionized water, and 5.5 g of LiOH·H2O was added while stirring the solution for 30 min. Then, 30 mL of 30% H2O2 was added, and stirring continued until a pale yellow solution was formed. The solution was heated in an 85°C water bath for about 3 h. The product was collected by centrifugation and then dried in an oven at 80°C for 24 h. The white solid product was then dried in the oven by the following steps: drying at 120°C for 6 h, drying at 150°C for 6 h, and drying at 200°C for 12 h. Excess lithium salt in the white product was washed away with deionized water, and the white solid powder was annealed in a muffle furnace at 550°C for 4 h to obtain Li4Ti5O. 12 Li4Ti5O 12 The sample was acid-washed in 0.1 M HCl for 24 h, and then centrifuged to separate the acid from the powder. Finally, it was washed several times with deionized water until the solution was neutral, and then dried in an oven at 60 °C for 8 h to obtain the titanium-based adsorbent H4Ti5O. 12 .

[0068] Example 2

[0069] The process is basically the same as in Example 1, except that the aging temperature in step S3 is 50°C and the aging time is 100 min. + The transfer rate was 75%. The total lithium extraction rate reached 61%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0070] Example 3

[0071] Basically the same as Example 2, except that the aging temperature in step S3 is 60°C. + The transfer rate was 69%. The total lithium extraction rate reached 57%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0072] Example 4

[0073] Basically the same as Example 2, except that the aging temperature in step S3 is 70°C. + The transfer rate was 80%. The total lithium extraction rate reached 66%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0074] Example 5

[0075] Basically the same as Example 2, except that the aging temperature in step S3 is 80°C. +The transfer rate was 72%. The total lithium extraction rate reached 59%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0076] Example 6

[0077] The process is basically the same as in Example 1, except that the aging time in step S3 is 60 minutes. + The transfer rate was 70%. The total lithium extraction rate reached 57%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0078] Example 7

[0079] The process is basically the same as in Example 1, except that the aging time in step S3 is 80 minutes. + The transfer rate was 72%. The total lithium extraction rate reached 59%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0080] Example 8

[0081] The process is basically the same as in Example 1, except that the aging time in step S3 is 100 minutes. + The transfer rate was 83%. The total lithium extraction rate reached 68%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0082] Example 9

[0083] The process is basically the same as in Example 1, except that the aging time in step S3 is 140 minutes. + The transfer rate was 90%. The total lithium extraction rate reached 74%. The purity of the prepared lithium carbonate was not less than 98%, and the purity of Mg(OH)2 was not less than 96%.

[0084] Example 10

[0085] The process is basically the same as in Example 1, except that the preparation method of the titanium-based lithium adsorbent used in step S4 is different. 10 mL of tetraisopropyl titanate is added to 100 mL of deionized water while stirring to form a white titanate precipitate. 70 mL of deionized water is added to the precipitate, followed by 4.1248 g of LiOH·H2O, and the solution is stirred for 30 min. Then, 30 mL of 30% H2O2 is added dropwise while stirring continuously until a pale yellow solution is formed. The solution is then heated in an 85°C water bath for about 3 h to form a milky white liquid. The product is collected by centrifugation and then dried in an oven at 80°C for 24 h. The white solid product is then dried in the oven using the following steps: drying at 130°C for 12 h and then at 180°C for 12 h. Excess lithium salts in the product are washed away with deionized water, and the white solid powder is annealed in a muffle furnace at 450°C for 3 h to obtain Li4Ti5O. 12 Li4Ti5O 12 The sample was acid-washed in 0.1M HCl for 24 h, and then centrifuged to separate the acid from the powder. Finally, it was washed several times with deionized water until the solution was neutral, and then dried in an oven at 60℃ for 8 h to obtain the titanium-based adsorbent H4Ti5O. 12 Li + The desorption rate reached 80%. The total lithium extraction rate reached 66%.

[0086] Example 11

[0087] The process is basically the same as in Example 1, except that the preparation method of the titanium-based lithium adsorbent used in step S4 is different. First, 10 mL of tetraisopropyl titanate is added to 100 mL of deionized water while stirring to form a white titanate precipitate. Then, 70 mL of deionized water is added, followed by 6.8747 g of LiOH·H2O. After stirring continuously for 30 min, 30 mL of 30% H2O2 is added dropwise while stirring continuously until a clear, pale yellow solution is formed. The solution is heated in an 85°C water bath for about 3 h. The product is collected by centrifugation and then dried in an oven at 80°C for 24 h. The white solid product is then dried in the oven by the following steps: drying at 150°C for 12 h and then at 200°C for 12 h. Excess lithium salt in the white product is washed away with deionized water, and the white solid powder is annealed in a muffle furnace at 650°C for 5 h to obtain Li4Ti5O. 12 Li4Ti5O 12 The sample was acid-washed in 0.1 M HCl for 24 h, and then centrifuged to separate the acid from the powder. Finally, it was washed several times with deionized water until the solution was neutral, and then dried in an oven at 60 °C for 8 h to obtain the titanium-based adsorbent H4Ti5O. 12 Li + The desorption rate reached 85%. The total lithium extraction rate reached 70%.

[0088] refer to Figure 2 Li4Ti5O prepared according to the technical solution of Example 1 12 and H4Ti5O after pickling 12 X-ray diffraction (XRD) pattern of L4Ti5O; results show L4Ti5O 12 No other impurity peaks appeared, indicating that a pure phase was obtained. After acid washing, H4Ti5O 12 The leftward shift of the peak indicates a change in cell size, resulting in Li... + and H + exchange.

[0089] refer to Figure 3 and Figure 4 , Figure 3 The image shows a scanning electron microscope (SEM) image of the sample prepared according to the technical solution of Example 1. Figure 4 Un-acid-washed Li4Ti5O 12 The SEM images show that the sample exhibits a nanorod morphology with relatively uniform size. The width of the rods ranges from 0.2 to 2 μm, mainly concentrated around 1 μm. The sample maintains a one-dimensional nanorod morphology both before and after acid washing, indicating that H4Ti5O... 12 The sample exhibits a certain degree of stability.

[0090] refer to Figure 5 Figure 1 shows a high-resolution transmission electron microscope (HRTEM) image of the sample prepared according to the technical solution of Example 1. Figure a) shows that the random absence of octahedral blocks forms a mesoporous structure inside the microrod, and the aggregation of some mesoporous regions forms an interconnected pore structure, which is beneficial for Li… + Entering the adsorption sites inside the crystal reduces mass transfer resistance; in figure b), Li4Ti5O 12 The electron diffraction (SAED) patterns of the two regions selected for the microrod are both single-crystal diffraction patterns, and they are almost identical to each other (a region SAED pattern is shown). These patterns indicate that Li4Ti5O 12 The microrods have a single-crystal structure; as shown in Figure c), the sample exhibits a directionally grown single-crystal structure, and there are obvious channels within the rods, as indicated by the arrows.

[0091] refer to Figure 6 and Figure 7 The figures show the N2 adsorption-desorption isotherms and pore size distribution (BET) curves of the sample prepared in Example 1; the curves can be classified as typical N-type isotherms. Based on the BJH method, Li4Ti5O 12 and H4Ti5O 12 The surface area of ​​BET is 35.51 m². 2 / g and 46.10 m 2 / g. Li4Ti5O 12and H4Ti5O 12 The pore size distribution is mainly concentrated at 11.10 nm and 10.47 nm, which can be attributed to the size of the crystal pores. A large surface area can promote the contact area between the adsorbent and the LiCl solution, and the porosity of the adsorbent may be more favorable for LiCl. + Diffusion from solution to adsorbent.

[0092] refer to Figure 8 The dynamic series adsorption device constructed for this invention;

[0093] refer to Figure 9 This is a photograph of lithium carbonate obtained by precipitation and filtration using soda ash.

[0094] refer to Figure 10 This is a photograph of the finished lithium carbonate product after purification and drying.

[0095] refer to Figure 11 The obtained lithium carbonate XRD pattern was matched with the lithium carbonate standard card.

[0096] The alkaline filtrate obtained from the method for extracting lithium from low-lithium brine provided by this invention not only has extremely low calcium and magnesium content, but its alkaline environment is also highly conducive to the subsequent adsorption process of the titanium-based adsorbent developed by our team, eliminating the need for further treatment and ensuring the continuity of the process flow. The resulting solid precipitate has a high magnesium content. To effectively utilize the magnesium element in the brine resources, this invention acid-dissolves the obtained solid precipitate and then uses a chemical precipitation method, adding relatively inexpensive sodium sulfate. The difference in solubility between calcium sulfate and magnesium sulfate is used to remove calcium. Further precipitation is then performed based on the pH range of calcium hydroxide and magnesium hydroxide precipitation to obtain Mg(OH)2 product, achieving a Mg recovery rate of 98%.

[0097] Subsequently, using a self-made high-performance titanium-based adsorbent as the core, adsorption columns were filled and connected in series for dynamic adsorption. The lithium-containing alkaline filtrate produced in the previous stage was then passed into a dynamic adsorption lithium extraction device (such as...). Figure 8 (As shown). Under conditions of 24℃ and a flow rate of 5 mL / min, two dynamic adsorption processes were performed using a series adsorption column. The results showed that the device exhibited high selectivity for low-grade lithium brine, with the distribution coefficient (Kd) of different ions being Li... + Na + >Ca 2+ >K + The lithium adsorption rate reached 92.6%. Under conditions of 24℃ and a flow rate of 6 mL / min, desorption with 0.1 M HCl resulted in the desorption of Li within 10 min. + The highest content indicates that the adsorbent can be rapidly desorbed in the dynamic adsorption column; and Na + K + Mg 2+ Ca 2+Ti 4+ The concentration of Li desorbed from the brine was low, much lower than the concentration in the brine itself, indicating that the adsorbent could effectively enrich Li. + And reduce K + Na + Mg 2+ Ca 2+ , for Li + The desorption rate reached 90%.

[0098] Finally, the hydrochloric acid desorption solution was collected, evaporated and concentrated, lithium carbonate was precipitated, and impurities were washed away, resulting in a total lithium extraction rate of 75%.

[0099] In summary, this invention has developed an effective and reasonable process route to achieve efficient preparation of lithium carbonate and other by-products from low-grade brine. This method can be applied to high-salinity, low-lithium brine.

[0100] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low-grade brine magnesium-lithium separation and production of magnesium hydroxide and lithium carbonate, characterized in that, The method comprises the following steps: S1, evaporating and concentrating low-grade brine to obtain concentrated brine; the concentration of Li + in the concentrated brine is 10-15 ppm; S2, the concentrated brine is treated by a sodium hydroxide solution with a concentration of 40% to precipitate calcium and magnesium ions, to obtain a colloidal solution; the volume ratio of the sodium hydroxide solution to the concentrated brine is 1:4-1:6, and the pH value of the sodium hydroxide solution is 13; S3, the colloidal solution is subjected to aging treatment for solid-liquid separation, to obtain an alkaline filtrate and a solid precipitate; the aging temperature is 40°C, and the aging time is 120-140 min; S4, adsorbing the alkaline filtrate through an adsorption column containing a titanium-based lithium adsorbent, then desorbing with acid to obtain an acid desorption solution; the titanium-based lithium adsorbent is a lithium titanate material Li4Ti5O 12 After pickling and washing with water, drying is obtained; After the solid precipitate is dissolved in acid, sodium sulfate is used for selective separation of calcium and magnesium, to obtain CaSO4 and Mg(OH)2 with a purity of not less than 96%; The lithium titanate material Li4Ti5O 12 is prepared as follows: S11, 10 mL of tetraisopropyl titanate is added to 100 mL of deionized water, and stirred to form a white titanate precipitate; the white titanate precipitate is dispersed in 170 mL of deionized water, and then 5.5 g of LiOH·H2O is added, followed by stirring, and then 30 mL of 30% H2O2 is added, and stirring is continued until a light yellow solution is formed; S12, the yellow solution prepared in step Sll is heated in a water bath at 85 °C for about 3 h, dried, and then a dry white solid product is obtained under dry heating, and the white solid powder is calcined in a muffle furnace to obtain Li4Ti5O 12 ; The dry burning mechanism is 120°C drying for 6 h, 150°C drying for 6 h, and 200°C drying for 12 h; The calcination temperature is 550°C annealing for 4 h; S5, after the acid desorption solution is evaporated and concentrated, and lithium carbonate is precipitated and impurities are removed, lithium carbonate with a purity of not less than 98% is obtained.

2. The method of claim 1, wherein, The temperature for evaporation and concentration is 75-80°C.

3. The method of claim 1, wherein, The low-grade brine includes low-grade salt lake brine or industrial waste liquid with low lithium content.

4. The method of claim 1, wherein, The adsorption process in step S4 is multiple dynamic adsorption by a series of adsorption columns.

5. The method of claim 4, wherein, The temperature for dynamic adsorption is 22-24°C, and the flow rate of the alkaline filtrate through the adsorption column is 4.5-5 mL / min.

6. The method of claim 5, wherein, 0.1M HCl is used for desorption.

7. The method according to any one of claims 1-6 is applied to comprehensive utilization of brine in the Tarim Basin of Xinjiang.

Images