A method and system for recovering lithium resources in waste salt field clay by two-stage stirring coupling filtration

Abstract

The application discloses a kind of two-stage stirring coupling filter recovery lithium resources in abandoned salt field clay method and system, belong to lithium resource recovery and solid waste resource utilization technical field.The method includes: abandoned salt field clay is sent into first stirring tank (1), under the action of dispersing agent, first-stage stirring dispersion is carried out, and adsorbed lithium is released to liquid phase;After filtering by once separation device (2), first-stage filtrate is used as lithium extraction raw material, and first-stage filter cake enters second stirring tank (3) and is washed by second-stage stirring;After filtering by secondary separation device (4) again, second-stage filtrate is recycled to first stirring tank (1) and recycled, and second-stage filter cake is backfilled into salt field.The application also provides a special system for realizing the method.The application uses two-stage stirring coupling filter process, significantly strengthens clay particle dispersion and lithium elution efficiency, greatly reduces water consumption and reagent cost by filtrate recycling, process is mild, process is short, lithium recovery rate is high (can reach more than 95%), filter cake can be backfilled in situ, environment-friendly, suitable for the industrialized application of abandoned salt field clay lithium extraction in salt lake.

Description

Technical Field

[0001] This invention belongs to the field of lithium resource recovery and resource utilization of solid waste from salt lake chemical industry. Specifically, it relates to a method and a dedicated system for efficiently recovering lithium resources from abandoned salt field clay, and in particular, a lithium extraction method and system that adopts a two-stage stirring dispersion coupled with graded filtration and filtrate recycling mode. Background Technology

[0002] With the rapid development of the global new energy vehicle industry, energy storage technology, and consumer electronics, the market demand for lithium salt products has experienced explosive growth. Salt lake brine, as an important source of lithium resources, is being developed on an increasingly large scale. During the process of evaporation, concentration, and subsequent lithium extraction of salt lake brine through sun-drying in salt fields, a large amount of solid waste is generated, namely waste salt field clay and silt. This type of clay has extremely fine particle size (mostly micrometers or even nanometers), large specific surface area, strong viscosity, and high water content. More importantly, the residual lithium resources are mostly present in an ion-adsorbed state between clay mineral layers or on the surface, and some exist in an encapsulated state. Conventional single-stage water washing or mechanical stirring is insufficient to effectively break the solid-liquid interface bonding, resulting in low lithium elution rates.

[0003] To address the aforementioned issues, existing technologies have reported methods for treating similar clay minerals, such as acid leaching, alkali leaching, or high-temperature roasting activation. For example, while leaching with sulfuric acid or hydrochloric acid can improve lithium dissolution efficiency, it suffers from significant drawbacks, including high reagent consumption, severe equipment corrosion, high costs for waste acid and wastewater treatment, and the potential for secondary environmental pollution. High-temperature roasting, on the other hand, consumes enormous amounts of energy, has a lengthy process flow, and incurs high investment and operating costs, making it uneconomical. Furthermore, conventional single-stage stirring-filtration processes lack effective dispersion and deep washing of fine clay, resulting in difficult solid-liquid separation, significant lithium loss from the filter cake, low lithium concentration in the filtrate, and an overall unsatisfactory recovery rate, making it difficult to meet the requirements of continuous industrial production.

[0004] Therefore, developing a new lithium extraction method that can effectively disperse fine clay, gently and efficiently elute lithium ions, realize the recycling of water resources and reagents, and ultimately harmlessly dispose of solid waste in situ is of great practical significance and application value for improving the comprehensive utilization rate of salt lake resources, reducing environmental impact, and realizing the green and sustainable development of the salt lake chemical industry. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing lithium resource recovery technologies in abandoned salt field clay, such as poor dispersion effect, low lithium elution rate, high consumption of reagents and water, and easy generation of secondary pollution. It provides a two-stage stirring coupled filtration method and system for recovering lithium resources in abandoned salt field clay with mild process conditions, continuous and stable operation, high lithium recovery rate, environmental friendliness, and suitability for industrial application.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a method for recovering lithium resources from waste salt field clay using a two-stage stirring coupled filtration process, characterized by the following steps:

[0008] (1) The waste salt field clay is fed into the first mixing tank (1);

[0009] (2) Add liquid medium and dispersant to the first mixing tank (1), and control the solid-liquid ratio, stirring speed and stirring time to stir and disperse to obtain the first mixed slurry;

[0010] (3) The first mixed mud is fed into the primary separation device (2) for solid-liquid separation to obtain primary filtrate and primary filter cake; the primary filtrate is transported to the raw material tank as raw material for the subsequent lithium extraction process;

[0011] (4) The primary filter cake is conveyed to the second mixing tank (3), washing liquid is added, and dispersant is optionally added. The mixture is then stirred and washed a second time to obtain the second mixed slurry.

[0012] (5) The second mixed mud is sent to the secondary separation device (4) for solid-liquid separation to obtain secondary filtrate and secondary filter cake; the secondary filtrate is returned to the first mixing tank (1) as part or all of the liquid phase medium in step (2) for recycling, and the secondary filter cake is backfilled into the salt field.

[0013] Preferably, the solid-liquid ratio in steps (2) and (4) is 1:1 to 1:10 by mass; the stirring speed is 50 r / min to 500 r / min; the stirring time is 5 min to 240 min; and the stirring method is selected from one of paddle stirring, turbine stirring or spiral stirring.

[0014] Preferably, the dispersant is selected from at least one of polyacrylate, lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium citrate; the amount of dispersant added is 0.05% to 2.00% of the dry basis mass of the waste salt field clay.

[0015] Preferably, the primary separation device (2) and / or the secondary separation device (4) are independently selected from one of a plate and frame filter press, a belt filter press, a vacuum filter, or a centrifugal filter.

[0016] Preferably, the subsequent lithium extraction process includes at least one of ultrafiltration, adsorption, membrane concentration, or lithium carbonate precipitation.

[0017] The present invention also provides a system for implementing the method according to any one of claims 1-5, characterized in that it comprises:

[0018] The first mixing tank (1) is equipped with a clay inlet, a liquid medium inlet, a dispersant inlet and a stirrer;

[0019] The primary separation device (2) has its inlet connected to the outlet of the first mixing tank (1) and is used to perform solid-liquid separation on the first mixed slurry.

[0020] The second mixing tank (3) has its feed inlet connected to the filter cake outlet of the primary separation device (2), and is equipped with a washing liquid inlet and a stirrer;

[0021] The secondary separation device (4) has its inlet connected to the outlet of the second mixing tank (3) and is used to perform solid-liquid separation on the second mixed slurry.

[0022] The filtrate return line connects the filtrate outlet of the secondary separation device (4) to the liquid medium inlet of the first stirring tank (1).

[0023] Preferably, the filtrate outlet of the primary separation device (2) is connected to the raw material storage tank for collecting the primary filtrate.

[0024] Preferably, the filter cake outlet of the secondary separation device (4) is connected to the filter cake backfilling unit for transporting the secondary filter cake to the salt field for backfilling.

[0025] Preferably, the system further includes an automatic control unit for online monitoring and adjustment of the solid-liquid ratio, stirring speed and stirring time of the first stirring tank (1) and the second stirring tank (3).

[0026] The present invention achieves the following technical effects compared to the prior art:

[0027] 1. Extremely high lithium resource recovery rate: Through a two-stage stirring-coupled filtration process, the first stage achieves efficient clay dispersion and initial lithium release, while the second stage deeply and thoroughly washes the filter cake. This dual effect significantly reduces lithium entrainment loss in the filter cake. Example data shows that the total lithium leaching rate can reach over 95%, even exceeding 99%, far higher than traditional single-stage processes.

[0028] 2. Significantly reduced water consumption and reagent costs: By recycling all the lithium-containing secondary filtrate produced from the second-stage filtration to the first-stage stirred tank as the leaching medium, the process water is recycled, reducing the total water consumption by approximately 40% to 60%. Simultaneously, the residual dispersant and lithium ions in the circulating liquid help improve the leaching kinetics of the first stage, reducing the amount of fresh dispersant required and significantly lowering operating costs.

[0029] 3. Mild process conditions and strong equipment adaptability: The entire process is carried out at room temperature, normal pressure and near neutral pH conditions, without the need for high-temperature calcination or strong acid and strong alkali leaching, avoiding equipment corrosion and safety hazards, with low material requirements, low investment and maintenance costs, and easy to achieve industrial scale-up.

[0030] 4. Compact process and continuous and stable operation: The two-stage mixing and filtration unit can be designed for continuous feeding and continuous discharging operation mode. The process is closely connected, and there is no need to buffer intermediate materials, which is conducive to automation control and production efficiency improvement.

[0031] 5. Environmentally friendly with no secondary pollution: The final secondary filter cake has extremely low lithium residue, allowing it to be directly backfilled into the salt field in situ to restore the landform without occupying land or posing a risk of leachate pollution. The entire process produces no waste gas or residue emissions, aligning with green chemical engineering and circular economy principles. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 The present invention provides a process flow diagram and structural schematic diagram of a system for recovering lithium resources from waste salt field clay through a two-stage stirring coupled filtration system.

[0034] In the diagram: 1. Primary leaching mixing tank; 2. Primary separation device; 3. Secondary leaching mixing tank; 4. Secondary separation device. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] This embodiment employs the method and system described in this invention (such as...). Figure 1(As shown) Clay extracted from a depth of 0.5 meters in an abandoned salt field of a salt lake was processed. The test results showed that the lithium content in the clay was 0.0201% (mass fraction, calculated as Li).

[0039] Process steps:

[0040] Feeding: 500 kg of excavated clay is fed into the first mixing tank (1) via a conveying device.

[0041] Primary mixing and dispersion: Add 500 L of production water to the first mixing tank (1), with a solid-liquid ratio of 1:1 (mass ratio, the same below), and add sodium hexametaphosphate at 0.3% of the dry clay mass as a dispersant. Use a paddle mixer to stir at a speed of 240 r / min for 60 minutes to obtain the first mixed slurry.

[0042] Primary filtration: The first mixed slurry is pumped into a plate and frame filter press (as a primary separation device 2) for solid-liquid separation to obtain primary filtrate A1 (volume 505 L, lithium concentration 0.167 g / L) and primary filter cake A (mass 405.8 kg).

[0043] Secondary stirring and washing: The primary filter cake A is conveyed to the second stirring tank (3), 405.8 L of production water is added, the solid-liquid ratio is 1:1, sodium citrate accounting for 0.2% of the original dry clay mass is added, and the mixture is stirred and washed for 60 minutes at a speed of 240 r / min to obtain the second mixed slurry.

[0044] Secondary filtration and circulation: The second mixed slurry is fed into another plate and frame filter press (as secondary separation device 4) for filtration to obtain secondary filtrate A2 (volume 405 L, lithium concentration 0.0390 g / L) and secondary filter cake A (mass 373.4 kg). After the secondary filter cake A passes the inspection, it is backfilled into the salt field. All of the secondary filtrate A2 is recycled back to the first mixing tank (1) as the leaching solution for the next round (fresh production water is added to make up any shortfall).

[0045] Cyclic Operation: Following the steps above, after completing round A, use the secondary filtrate A2 as the main liquid medium for the primary stirring in round B, and repeat rounds B, C, and D. See [link to specific parameters and results]. Table 1:

[0046] Results: As shown in Table 1, the calculated total lithium leaching rates for each round were 99.63%, 99.74%, 99.84%, and 97.17%, respectively, with an average total leaching rate exceeding 99%. The residual lithium content in the secondary filter cake was extremely low, meeting the standards for salt field backfilling. These results demonstrate that the method of this invention maintains extremely high lithium recovery efficiency even after multiple filtrate cycles, exhibiting good process stability.

[0047] Example 2 This embodiment treats clay at a depth of 0 meters on the surface of a salt field on the east side of a salt lake, with a lithium content of 0.043%.

[0048] Process steps: The basic process is the same as in Example 1, except that the process parameters are adjusted as follows:

[0049] Primary stirring: Solid-liquid ratio 1:2, add 0.2% (dry basis) of polyacrylate, turbine stirring at 300 r / min for 30 minutes.

[0050] Primary filtration: Vacuum filter is used.

[0051] Secondary stirring: Solid-liquid ratio 1:2, add 0.25% sodium lignosulfonate, stir for 30 minutes.

[0052] Secondary filtration: vacuum filtration.

[0053] Perform two rounds of cyclical operations, A and B. See Table 2 for specific data.

[0054] Results: As shown in Table 2, the total leaching rate was 96.65% in round A and 96.57% in round B, with the lithium recovery rate remaining stable above 96%. The secondary filtrate was successfully recycled, significantly reducing the amount of fresh water used.

[0055] Example 3

[0056] This embodiment treats a B11 salt field clay with a lithium content of 0.19% (relatively high grade).

[0057] Process steps:

[0058] The basic process is the same as in Example 1, but the process parameters are adjusted as follows:

[0059] Primary stirring: Solid-liquid ratio 1:4, add 0.15% sodium pyrophosphate, spiral stir at 150 r / min for 90 minutes.

[0060] Primary filtration: Centrifugal filter is used.

[0061] Secondary stirring: Solid-liquid ratio 1:4, add 0.20% sodium citrate, stir for 90 minutes.

[0062] Secondary filtration: centrifugal filtration.

[0063] Perform two rounds of cyclical operations, A and B. See Table 3 for specific data.

[0064] Results: As shown in Table 3, the method of the present invention is still effective for high-grade clay. The total leaching rate in the A round was 98.60%, and in the B round it was 97.74%, with stable leaching rates.

[0065] To verify the technical effectiveness of the method of the present invention, the leaching solutions obtained in Examples 1-3 were tested and analyzed, and the lithium leaching rate was calculated. Specific data are shown in Tables 1-3 above. The formula for calculating the leaching rate of the first round (A round) is as follows:

[0066] η A1 =α A1 *V A1 / W A ×100% (1)

[0067] Where, η A1 The leaching rate (%) is the single leaching rate; α A1 Lithium concentration (g / L) in the primary leaching solution; V A1 The volume of the leachate in one extraction (L); W A The total lithium content (g) in the clay added to the first mixing tank for A-round leaching.

[0068] The formula for calculating the secondary leaching rate in Round A is as follows:

[0069] η A2 =α A2 *V A2 / (W) A -α A1 *V A1 (2) × 100%

[0070] Where, η A2 Secondary leaching rate (%); α A2 Lithium concentration (g / L) in the secondary leaching solution; V A2 Let α be the volume of the secondary leachate (L); A1 *V A1 The total lithium content (g) in a single leaching solution; W A The total lithium content (g) in the clay added to the first mixing tank for A-round leaching.

[0071] The formula for calculating the total leaching rate of Round A is as follows:

[0072] η A =α A1 *V A1 +α A2 *V A2 / W A ×100% (3)

[0073] α A1 *V A1 The total lithium content (g) in a single leaching solution; αA2 *V A2 The total lithium content (g) in the secondary leaching solution of Round A; W A The total lithium content (g) in the clay added to the first mixing tank for A-round leaching.

[0074] The formula for calculating the leaching rate in the B round is as follows:

[0075] η B1 =(α B1 *V B1 -α A2 *V A2 ) / W B ×100% (4)

[0076] Where, η B1 Leaching rate per cycle (%); α B1 Lithium concentration (g / L) in the leaching solution after one cycle; V B1 The volume of the leachate in one cycle (L); α A2 *V A2 The total lithium content (g) in the secondary leaching solution (recycled) of Round A; W B The total lithium content (g) in the clay added to the first mixing tank for the B-cycle.

[0077] The formula for calculating the secondary leaching rate in the B-cycle is as follows:

[0078] η B2 =α B2 *V B2 / (W) B -α B1 *V B1 ) × 100% (5)

[0079] Where, η B2 The leaching rate for the second cycle is (%); α B2 Lithium concentration (g / L) in the secondary leaching solution; V B2 The volume of the secondary leaching solution (L); α B1 *V B1 The total lithium content (g) in the leaching solution after one cycle; V A1 Volume of the initial leachate (L); W B The total lithium content (g) in the clay added to the first mixing tank in the B round.

[0080] The formula for calculating the total leaching rate in Series B is as follows:

[0081] η B =(α B1 *V B1 -α A2 *V A2 )+αB2 *V B2 / W B ×100% (6)

[0082] Where, α B1 *V B1 The total lithium content (g) in the primary leaching solution of Round B; α A2 *V A2 The total lithium content (g) in the secondary leaching solution (recycled) of Round A; α B2 *V B2 The total lithium content (g) in the secondary leaching solution of Round B; W B The total lithium content (g) in the clay added to the first mixing tank in the B round.

[0083] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for recovering lithium resources from abandoned salt field clay using a two-stage stirring coupled filtration process, characterized in that, Includes the following steps: (1) The waste salt field clay is fed into the first mixing tank (1); (2) Add liquid medium and dispersant to the first mixing tank (1), and control the solid-liquid ratio, stirring speed and stirring time to stir and disperse to obtain the first mixed slurry; (3) The first mixed mud is fed into the primary separation device (2) for solid-liquid separation to obtain primary filtrate and primary filter cake; the primary filtrate is transported to the raw material tank as raw material for the subsequent lithium extraction process; (4) The primary filter cake is conveyed to the second mixing tank (3), washing liquid is added, and dispersant is optionally added. The mixture is then stirred and washed a second time to obtain the second mixed slurry. (5) The second mixed mud is sent to the secondary separation device (4) for solid-liquid separation to obtain secondary filtrate and secondary filter cake; the secondary filtrate is returned to the first mixing tank (1) as part or all of the liquid phase medium in step (2) for recycling, and the secondary filter cake is backfilled into the salt field.

2. The method according to claim 1, characterized in that, The solid-liquid ratios in steps (2) and (4) are each independently expressed as a mass ratio of 1:1 to 1:10; the stirring speeds are each independently expressed as 50 r / min to 500 r / min; the stirring durations are each independently expressed as 5 min to 240 min; and the stirring method is selected from one of paddle stirring, turbine stirring, or spiral stirring.

3. The method according to claim 1, characterized in that, The dispersant is selected from at least one of polyacrylate, lignin sulfonate, sodium hexametaphosphate, sodium pyrophosphate, and sodium citrate; the amount of dispersant added is 0.05% to 2.00% of the dry mass of the waste salt field clay.

4. The method according to claim 1, characterized in that, The primary separation device (2) and / or secondary separation device (4) are independently selected from one of a plate and frame filter press, a belt filter press, a vacuum filter or a centrifugal filter.

5. The method according to claim 1, characterized in that, The subsequent lithium extraction process includes at least one of ultrafiltration, adsorption, membrane concentration, or lithium carbonate precipitation.

6. A system for implementing the method according to any one of claims 1-5, characterized in that, include: The first mixing tank (1) is equipped with a clay inlet, a liquid medium inlet, a dispersant inlet and a stirrer; The primary separation device (2) has its inlet connected to the outlet of the first mixing tank (1) and is used to perform solid-liquid separation on the first mixed slurry. The second mixing tank (3) has its feed inlet connected to the filter cake outlet of the primary separation device (2), and is equipped with a washing liquid inlet and a stirrer; The secondary separation device (4) has its inlet connected to the outlet of the second mixing tank (3) and is used to perform solid-liquid separation on the second mixed slurry. The filtrate return line connects the filtrate outlet of the secondary separation device (4) to the liquid medium inlet of the first stirring tank (1).

7. The system according to claim 6, characterized in that, The filtrate outlet of the primary separation device (2) is connected to the raw material storage tank for collecting primary filtrate.

8. The system according to claim 6, characterized in that, The filter cake outlet of the secondary separation device (4) is connected to the filter cake backfilling unit, which is used to transport the secondary filter cake to the salt field for backfilling.

9. The system according to claim 6, characterized in that, The system also includes an automatic control unit for online monitoring and adjustment of the solid-liquid ratio, stirring speed and stirring time of the first stirring tank (1) and the second stirring tank (3).

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