Method for acid leaching of lithium from spodumene by microwave and ultrasonic synergistic strengthening

Abstract

The present application belongs to the technical field of mineral processing and metallurgical engineering, and particularly relates to a method for leaching lithium from spodumene by microwave and ultrasonic synergistic strengthening. The method uses beta-spodumene as raw material, mixes the beta-spodumene with concentrated sulfuric acid and phosphoric acid after grinding, and performs rapid sulfuric acid roasting under microwave heating. The obtained roasted material is then placed in a persulfate solution, and short-time water leaching is performed under ultrasonic assistance to realize efficient leaching of lithium. The addition of phosphoric acid can selectively inhibit the dissolution of impurities such as iron and aluminum, and the combination of persulfate and ultrasonic cavitation effect can effectively destroy the mass transfer barrier of lithium ion dissolution. The method can complete water leaching within 2-5 minutes, with a lithium leaching rate of more than 97%, low impurity content, low energy consumption and acid consumption, and is suitable for continuous clean production.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing and metallurgical engineering technology, specifically relating to a method for acid leaching lithium from spodumene using a combination of microwave and ultrasonic enhancement. Background Technology

[0002] With the global energy structure shifting towards cleaner and electric power, the demand for lithium resources continues to grow rapidly. In nature, lithium resources are mainly found in salt lake brines, granite pegmatite-type lithium deposits (such as spodumene), lithium clay, and geothermal brines. Currently, global lithium supply still relies primarily on ore extraction, with spodumene being an important industrial raw material for lithium extraction due to its relatively concentrated resource distribution and stable grade.

[0003] The main mineral form of spodumene is α-spodumene, which has a dense crystal structure and stable chemical properties, making it difficult to react effectively with acids and alkalis at room temperature and pressure. Therefore, industrial lithium extraction from spodumene requires high-temperature crystal transformation roasting to convert it into the more reactive β-spodumene before subsequent leaching. The current mainstream industrial lithium extraction process is the "sulfation roasting-water leaching" method, which typically involves: mixing β-spodumene with concentrated sulfuric acid and acidifying and roasting it at 200-300°C in a rotary kiln or box furnace for about 30 minutes to break the Si-O and Al-O bonds in the mineral, converting lithium into soluble lithium sulfate; the roasted product is then leached in water for 20-30 minutes under heating conditions in a stirred reactor to allow lithium to enter the solution.

[0004] However, this traditional process has several significant drawbacks: First, the roasting process relies on fossil fuel heating, resulting in high energy consumption and low thermal efficiency. Uneven temperature distribution within the kiln can easily lead to material sintering, affecting lithium conversion and leaching. Second, sulfuric acid is easily lost due to volatilization at high temperatures, increasing acid consumption and generating harmful gases such as SO2. Third, the water leaching process is time-consuming, requires an external heating source, and has limited stirring leaching efficiency, resulting in slow mass transfer of lithium ions from the solid to the liquid phase. Fourth, the entire process is intermittent, with poor system continuity and low equipment utilization, which is not conducive to large-scale clean production.

[0005] To overcome these problems, researchers have recently attempted to introduce process intensification technologies. For example, microwave heating has been used to replace traditional roasting, leveraging its highly efficient and selective heating characteristics for polar molecules (such as sulfuric acid) to achieve rapid heating and energy savings. Other studies have employed mechanical activation or ultrasonic-assisted leaching to enhance solid-liquid mass transfer. However, existing technologies mostly focus on improving single stages, such as enhancing only roasting or only leaching, and have not yet formed a complete "roasting-leaching" synergistic intensification system. This makes it difficult to achieve efficient lithium extraction under continuous, low-energy-consumption, and low-emission conditions. Furthermore, some methods still suffer from problems such as complex equipment, inconsistent operation, and difficulties in acid recovery.

[0006] Therefore, developing a new process for efficient, clean, and continuous lithium extraction from spodumene, especially by using multi-field synergistic enhancement to shorten reaction time and reduce energy consumption and pollution, has become a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method for lithium extraction by acid leaching from spodumene using a combination of microwave and ultrasonic enhancement, in order to solve the problems of long acid roasting time, high energy consumption, low equipment efficiency, easy loss of sulfuric acid due to volatilization, and slow and poor continuity of the water leaching process in traditional processes.

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

[0009] A method for spodumene acid leaching of lithium enhanced by microwave and ultrasound synergy includes the following steps:

[0010] (1) Using β-spodumene as raw material, the raw material is ground to obtain β-spodumene powder;

[0011] (2) Mix β-spodumene powder with sulfuric acid solution and phosphoric acid solution to obtain an acidified mixture;

[0012] (3) The acidified mixture is subjected to sulfation roasting by microwave heating to obtain roasted clinker;

[0013] (4) The roasted clinker was placed in a persulfate solution and subjected to ultrasonic-assisted water immersion. After solid-liquid separation, a lithium-containing leachate was obtained.

[0014] The method described in this invention uses β-spodumene as raw material, which can be obtained by converting natural α-spodumene through conventional crystal transformation roasting processes in the art. This invention does not limit the specific process conditions for the crystal transformation roasting.

[0015] Furthermore, the grinding in step (1) ensures that the content of β-spodumene powder with a particle size of -0.074 mm is not less than 80%.

[0016] Further, in step (2), the mass percentage concentration of the sulfuric acid solution is 90-98%, the mass percentage concentration of the phosphoric acid solution is 85-90%, and the mass ratio of sulfuric acid to phosphoric acid is (10-20):1.

[0017] Furthermore, the total amount of sulfuric acid used in step (2) is 105-120% of the theoretical amount of sulfuric acid used.

[0018] The theoretical amount of sulfuric acid used in this invention refers to the stoichiometric mass of concentrated sulfuric acid required for the reaction of sulfuric acid with alkali metals such as lithium, sodium, and potassium in the ore powder to produce the corresponding sulfates, based on β-spodumene powder subjected to sulfation roasting. The calculation method is well known to those skilled in the art.

[0019] This invention introduces an appropriate amount of phosphoric acid into a concentrated sulfuric acid acidification roasting system. Its mechanism of action is primarily based on the selective coordination and precipitation tendency of phosphate ions with impurity metal ions. Under acidification conditions of 190–230°C, phosphoric acid can form a dense and insoluble phosphate composite layer with dissolved iron, aluminum, and other impurity ions. This layer effectively coats the surface of unreacted mineral particles or intermediate products, thereby inhibiting the continuous migration of iron, aluminum, and other impurity ions into the liquid phase. Simultaneously, the addition of phosphoric acid does not significantly alter the system's lithium extraction efficiency, as lithium sulfate exhibits higher solubility and migration ability under the same conditions. This selective inhibition effect significantly reduces the concentration of iron and aluminum in the subsequent leachate, alleviating the solution purification load and creating more favorable conditions for sulfuric acid recycling. Furthermore, as a polar molecule, phosphoric acid has dielectric loss characteristics similar to sulfuric acid, and in a microwave field, it can synergistically enhance the overall material's absorption efficiency of microwave energy, promoting uniform heat transfer.

[0020] Furthermore, the microwave heating temperature in step (3) is 190-230℃, and the sulfation roasting time is 1-3 minutes.

[0021] Microwave heating avoids the problems of large temperature gradients, high thermal inertia, and easy sintering of material surfaces caused by traditional rotary kilns or box furnaces that rely on heat conduction and radiation. At a set temperature of 190~230℃, microwaves allow sulfuric acid to fully penetrate and destroy the activated Si-O and Al-O structures in β-spodumene within minutes, promoting the release of lithium as lithium sulfate, while shortening the entire heating process time to 1~3 minutes. Due to the rapid heating speed and short holding time, the volatilization loss and decomposition of sulfuric acid are significantly reduced, which not only improves the effective utilization rate of acid but also reduces SO₂ in the exhaust gas. x The amount of material generated reduces pollution emissions and material losses at the source.

[0022] Further, the persulfate mentioned in step (4) is sodium persulfate.

[0023] Further, the concentration of the persulfate solution in step (4) is 0.05-0.2 mol / L.

[0024] Further, the mass ratio of the roasted clinker to the persulfate solution in step (4) is 1:(2.5-4).

[0025] Furthermore, the power density of the ultrasound in step (4) is 0.3-1.2 W / cm². 2.

[0026] Furthermore, the immersion time in water in step (4) is 2-5 minutes.

[0027] This invention introduces persulfate during ultrasonic-assisted water immersion, achieving a synergistic effect of physical cavitation and deep chemical oxidation. The cavitation effect of ultrasound effectively cleans and erodes the surface layer of calcined clinker particles, greatly enhancing the diffusion and mass transfer process of lithium ions from solid pores to the liquid phase. Simultaneously, the local high-temperature, high-pressure microenvironment catalyzes the generation of highly oxidizing free radicals (SO4· ... - These free radicals can effectively destroy the aluminosilicate gel or passivation film encapsulating lithium sulfate, solving the final barrier problem of lithium ion dissolution in traditional water immersion. This synergistic effect significantly reduces the water immersion time from 20-30 minutes in the traditional process to 2-5 minutes, while maintaining a stable lithium leaching rate of over 97%, while avoiding external heating and reducing energy and acid consumption.

[0028] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0029] This invention achieves rapid and uniform sulfation roasting through microwave heating, shortening the traditional roasting process of tens of minutes to 1-3 minutes, significantly reducing sulfuric acid volatilization and heat loss, and improving acid utilization. In the leaching stage, the synergistic effect of ultrasound and persulfate overcomes the kinetic limitations of lithium ion diffusion from the solid to the liquid phase, drastically reducing the leaching time from the traditional 20-30 minutes to 2-5 minutes, while still achieving a lithium leaching rate of over 97% without the need for an external heating source. Simultaneously, the introduction of phosphoric acid significantly reduces the leaching rate of iron and aluminum impurities without affecting lithium leaching, greatly reducing the load on subsequent solution purification. The overall process combines high efficiency, low consumption, and cleanliness, providing a promising new approach for lithium extraction from spodumene. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of a microwave and ultrasonic synergistic enhancement method for acid leaching lithium from spodumene according to the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0032] Unless otherwise specified, all raw materials used in the examples are commercially available products.

[0033] Example 1

[0034] This embodiment provides a method for acid leaching lithium from spodumene using a combination of microwave and ultrasonic enhancement. The process flow diagram is shown below. Figure 1 As shown, the method specifically includes the following steps:

[0035] (1) Take 1000g of β-spodumene roasted product obtained by crystal transformation roasting as raw material, put it into a ball mill for dry grinding, control the grinding time, so that the content of -0.074mm particle size in the powder after grinding reaches 82%, and obtain β-spodumene powder.

[0036] (2) Weigh 500g of the above β-spodumene powder, mix it with 98% sulfuric acid solution and 85% phosphoric acid solution, and stir and mix it in an acid-resistant mixer for 15 minutes until a uniform paste-like acidified mixture is obtained. The mass ratio of sulfuric acid to phosphoric acid is 16:1, and the total amount of sulfuric acid used is 110% of the theoretical amount of sulfuric acid used.

[0037] (3) Spread the above acidified mixture evenly into a quartz crucible, place it in a microwave reactor, turn on microwave heating, control the power to rapidly heat the material to 210°C within 2 minutes, and maintain the sulfation roasting at this temperature for 1.5 minutes. After the reaction is completed, roasted clinker is obtained.

[0038] (4) After crushing the roasted clinker, weigh 200g and add it to the reaction vessel. Prepare a sodium persulfate solution with a concentration of 0.1 mol / L and preheat it to 30℃. Add 640g of sodium persulfate solution to the reaction vessel at a liquid-to-solid mass ratio of 3.2:1. Start the ultrasonic generator (frequency 28kHz) and adjust the power to stabilize the ultrasonic power density in the reaction system at 0.5 W / cm³. 2 The mixture was leached for 3.5 minutes under ultrasonic treatment. After the reaction was completed, vacuum filtration was immediately performed to separate the lithium-containing leachate and leaching residue.

[0039] Example 2

[0040] This embodiment provides a method for acid leaching of lithium from spodumene using a combination of microwave and ultrasonic enhancement, comprising the following steps:

[0041] (1) Take 1000g of β-spodumene roasted product obtained by crystal transformation roasting as raw material, put it into a ball mill for dry grinding, control the grinding time, so that the content of -0.074mm particle size in the powder after grinding reaches 85%, and obtain β-spodumene powder.

[0042] (2) Weigh 500g of the above β-spodumene powder, mix it with 98% sulfuric acid solution and 85% phosphoric acid solution, and stir and mix it in an acid-resistant mixer for 15 minutes until a uniform paste-like acidified mixture is obtained. The mass ratio of sulfuric acid to phosphoric acid is 12:1, and the total amount of sulfuric acid used is 110% of the theoretical amount of sulfuric acid used.

[0043] (3) Spread the above acidified mixture evenly into a quartz crucible, place it in a microwave reactor, turn on microwave heating, control the temperature rise program, so that the material is heated to 225°C within 1 minute, and maintain the sulfation roasting at this temperature for 1 minute. After the reaction is completed, roasted clinker is obtained.

[0044] (4) After crushing the roasted clinker, weigh 200g and prepare a sodium persulfate solution with a concentration of 0.15 mol / L. Add 560g of the sodium persulfate solution to the container containing the clinker at a liquid-to-solid mass ratio of 2.8:1. Start the ultrasonic generator (frequency 20kHz) and adjust the power to achieve an ultrasonic power density of 1.0 W / cm³. 2 The mixture was leached under ultrasonic treatment for 2.5 minutes. After the reaction was completed, vacuum filtration was immediately performed to separate the lithium-containing leachate and leaching residue.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that phosphoric acid is not added in step (2).

[0047] Comparative Example 2

[0048] The difference between this comparative example and Example 1 is that in step (2), phosphoric acid is replaced with hydrochloric acid with an equimolar number of hydrogen ions.

[0049] Comparative Example 3

[0050] The difference between this comparative example and Example 1 is that microwave heating is replaced with oil bath heating in step (3). The specific steps are as follows: place the acidified mixture in an acid-resistant reaction container, put it into an oil bath that has been preheated to 210°C, start timing and maintain the oil bath temperature, so that the material is heated in the oil bath for sulfation roasting, with a total duration of 30 minutes.

[0051] Comparative Example 4

[0052] The difference between this comparative example and Example 1 is that persulfate is not used in step (4). The specific steps are as follows: after the roasted clinker is put into the reaction vessel, deionized water preheated to 30°C is added, the liquid-solid mass ratio is kept at 3.2:1, and it is leached for 3.5 minutes under the same ultrasonic conditions as in Example 1.

[0053] Comparative Example 5

[0054] The difference between this comparative example and Example 1 is that in step (4), sodium persulfate is replaced with an equal mass of hydrogen peroxide (calculated as pure H2O2).

[0055] Performance testing

[0056] The leachates from Examples 1-2 and Comparative Examples 1-5 were diluted, and the concentrations of Li, Fe, and Al were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The leaching rate of each element was calculated based on the initial composition of the materials.

[0057] The results are shown in Table 1.

[0058] Table 1 Performance Test Results

[0059]

[0060] The above results demonstrate that the process of this invention achieves a lithium leaching rate exceeding 97% within an extremely short microwave acidification and ultrasonic water immersion time. Simultaneously, the leaching rates of iron and aluminum impurities are successfully suppressed to extremely low levels, proving the synergistic effect of the process in both efficient lithium extraction and selective impurity suppression.

[0061] In Comparative Example 1, the lack of phosphoric acid resulted in the loss of selective inhibition of iron and aluminum impurities. The leaching rates of iron and aluminum increased significantly, which will substantially increase the cost and difficulty of subsequent impurity removal. In Comparative Example 2, while hydrochloric acid provided an acidic environment, chloride ions could not form a stable passivation film under the reaction conditions to inhibit impurity dissolution, unlike phosphate ions. This resulted in not only a high impurity leaching rate but also potential instability due to the volatility of hydrochloric acid, leading to a decrease in lithium leaching rate. In Comparative Example 3, replacing microwave heating with traditional oil bath heating required up to 30 minutes to complete the sulfation reaction. Prolonged heating caused significant decomposition and volatilization of sulfuric acid, resulting in poor reaction uniformity and a significant decrease in lithium leaching rate, along with a substantial increase in energy consumption and time costs. In Comparative Example 4, no persulfate was added to the aqueous leaching solution; only the physical action of ultrasound was used. Although the impurity inhibition effect was maintained, the lack of synergistic chemical oxidation made it difficult to break down the dense layer encapsulating lithium, resulting in slower lithium leaching kinetics and a leaching rate of less than 93% within the same leaching time. Comparative Example 5 used hydrogen peroxide instead of sodium persulfate, and its oxidation mechanism and stability were different. Under ultrasonic conditions, hydrogen peroxide decomposed too quickly, and the hydroxyl radicals produced were less efficient at unblocking specific aluminosilicate structures than sulfate radicals. Therefore, its enhanced leaching effect was weaker than that of the persulfate system.

[0062] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for acid leaching of lithium from spodumene with microwave and ultrasonic synergistic reinforcement, characterized in that, The method comprises the following steps: (1) taking β-spodumene as raw material, grinding the raw material to obtain β-spodumene powder; (2) mixing the β-spodumene powder with a sulfuric acid solution and a phosphoric acid solution to obtain an acidified mixture; the mass percentage concentration of the sulfuric acid solution is 90-98%, the mass percentage concentration of the phosphoric acid solution is 85-90%, and the mass ratio of sulfuric acid to phosphoric acid is (10-20):1; (3) adopting microwave heating to perform sulfuric acid roasting on the acidified mixture to obtain a roasted material; the temperature of microwave heating is 190-230°C, and the time of sulfuric acid roasting is 1-3 minutes; (4) placing the roasted material in a persulfate solution with a concentration of 0.05-0.2 mol / L to perform ultrasonic-assisted water leaching, the time of water leaching is 2-5 minutes, and a lithium-containing leaching solution is obtained after solid-liquid separation; the persulfate is sodium persulfate, and the mass ratio of the roasted material to the persulfate solution is 1:(2.5-4).

2. The method of claim 1, wherein, The grinding in step (1) makes the particle size of the β-spodumene powder meet the requirement that the content of the-0.074 mm particle size fraction is not less than 80%.

3. The method of claim 1, wherein, The total amount of sulfuric acid in step (2) is 105-120% of the theoretical amount of sulfuric acid.

4. The method of claim 1, wherein, The power density of the ultrasound in step (4) is 0.3-1.2 W / cm 2 .

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