Method for extracting lithium carbonate from spodumene in pegmatite

Abstract

The invention discloses a method for extracting lithium carbonate from spodumene in pegmatite. The method comprises the following steps: (1) crushing spodumene, and carrying out crystal form conversion roasting; (2) mixing the ore sample subjected to crystal form conversion with concentrated sulfuric acid, and heating for acidification roasting; (3) adding water into the treated ore sample for leaching to obtain a leaching solution, neutralizing the leaching solution with calcium carbonate until the pH value is 5.5-6.5, and filtering to obtain a lithium sulfate solution; (4) adjusting the salt content of the lithium sulfate solution to be 10-35g / L and the aluminum-lithium ratio to be 5-35; carrying out membrane separation on the lithium sulfate solution by using a nanofiltration membrane under the conditions that the temperature is 20-35 DEG C and the pressure is 1.5-4 MPa; and (5) adding lithium carbonate into the solution separated by the nanofiltration membrane to react, and filtering and separating to obtain the lithium carbonate. According to the method disclosed by the invention, the impurities in the leachate are removed by adopting a nanofiltration membrane method, and effective separation between impurity ions and lithium ions in the leachate is realized by controlling process parameters in an impurity separation process, so that the purity of a lithium carbonate product is remarkably improved, and a battery-grade lithium carbonate product is obtained.

Description

Technical Field

[0001] The invention relates to a method for extracting lithium carbonate from spodumene in pegmatite, belonging to the technical field of lithium compound preparation. Background Art

[0002] Lithium carbonate is increasingly used in new energy fields such as medicine, electronic equipment, energy storage, and wind energy. In recent years, lithium carbonate has been widely used in new energy materials such as lithium-ion batteries. The production process of lithium carbonate can be divided into salt lake brine extraction and ore extraction according to the source of raw materials. Lithium ore extraction mainly uses lithium ores such as spodumene and lithium mica to produce lithium carbonate. Granite pegmatite-type lithium rare metal deposits are an important source of spodumene. However, in the current process of producing lithium carbonate using spodumene as raw material, there are still problems such as unstable product quality and low product purity of lithium carbonate.

[0003] The production process of extracting lithium from ore mainly includes lime sintering method and sulfuric acid method, among which sulfuric acid method is the main method currently used. There are impurities such as calcium, magnesium, and aluminum in spodumene. In the process of producing lithium carbonate by sulfuric acid method, it is difficult to obtain battery-grade lithium carbonate through roasting, acid leaching, neutralization and reaction crystallization. The impurity removal process of spodumene leachate is related to the purity of lithium carbonate products. Therefore, effective separation of impurities in lithium sulfate solution is of great significance for the production of battery-grade lithium carbonate products. Summary of the invention

[0004] The purpose of the present invention is to provide a method for extracting lithium carbonate from spodumene in pegmatite, thereby improving the purity of lithium carbonate to prepare battery-grade lithium carbonate products and ensuring the stability of product quality.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A method for extracting lithium carbonate from spodumene in pegmatite comprises the following steps: (1) crushing the spodumene and performing crystal transformation roasting; (2) mixing the ore sample after crystal transformation with concentrated sulfuric acid and heating for acidification and roasting; (3) adding water to the treated ore sample to obtain a leachate, neutralizing it with calcium carbonate to a pH of 5.5-6.5, filtering it, and obtaining a lithium sulfate solution; (4) adjusting the salt content of the lithium sulfate solution to 10-35 g / L and the aluminum-lithium ratio to 5-35; using a nanofiltration membrane to perform membrane separation on the lithium sulfate solution at a temperature of 20-35° C. and a pressure of 1.5-4 MPa; (5) Add lithium carbonate to the solution after nanofiltration membrane separation to react, and filter and separate to obtain lithium carbonate.

[0006] Preferably, in the step (1), the calcination temperature is 1000°C to 1100°C. When the calcination temperature is above 1000°C, the conversion rate of the spodumene crystal from α-spodumene to β-spodumene is high. When the temperature is higher than 1100°C, the ore sample will undergo sintering.

[0007] Preferably, in step (2), the acidification roasting temperature is 240-260° C., and the roasting time is 20-40 min.

[0008] Preferably, in step (3), the leaching time is controlled within 15-30 minutes.

[0009] Preferably, in step (4), the salt content of the lithium sulfate solution is adjusted to 22-30 g / L, more preferably 25 g / L; the aluminum-lithium ratio is adjusted to 20-30, more preferably 25.

[0010] Preferably, in step (4), the temperature is 25° C. and the pressure is 3.5 MPa.

[0011] Preferably, the nanofiltration membrane is made of TFM or TFC, and the membrane model is DL, TS80 or NF1.

[0012] Beneficial effects of the present invention: The present invention adopts nanofiltration membrane method to remove impurities in the leachate (lithium sulfate solution), and realizes effective separation between impurity ions and lithium ions in the leachate by controlling process parameters such as temperature, pressure, salt content, aluminum-lithium ratio, etc. in the membrane separation process, thereby significantly improving the purity of lithium carbonate products and obtaining battery-grade lithium carbonate products. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention is a process flow chart of the lithium carbonate extraction method. DETAILED DESCRIPTION

[0014] The present invention is further described below by way of examples, but these examples are not intended to limit the scope of protection of the present invention.

[0015] like Figure 1 The process flow chart of the method for extracting lithium carbonate from spodumene in pegmatite of the present invention is shown in FIG. The process flow of the present invention is: crystal conversion roasting - acid roasting - leaching - neutralization - filtration - membrane separation - lithium precipitation.

[0016] In the crystal form conversion roasting step, at a temperature above 1000°C, the conversion rate of α-spodumene to β-spodumene is high, and the spodumene crystal form is effectively converted. In the experiment, it was found that when the temperature was higher than 1100°C, the ore sample showed sintering phenomenon. Therefore, the preferred roasting temperature range is 1000°C to 1100°C.

[0017] In the acidification and calcination step, when the acidification and calcination temperature is 240-260°C and the acidification and calcination time is 0-60min, the yield and purity of lithium carbonate increase with the increase of the acidification time; considering the factors such as the high economic cost caused by the large amount of materials in industrial production, the calcination time is controlled at 20-40min, preferably 30min.

[0018] In the leaching step, if the leaching and neutralization time is too long, the viscosity of the material will continue to increase, resulting in poor filtering and washing effects after leaching and neutralization, thereby causing lithium sulfate loss during leaching and washing. Therefore, the faster the leaching and neutralization process, the better, generally controlled within 15-30 minutes.

[0019] In the neutralization step, calcium carbonate (CaCO3) is selected as the neutralizing agent to avoid the introduction of impurity ions in the neutralization stage.

[0020] In the membrane separation step, nanofiltration membrane method is used to remove impurities in the lithium sulfate solution, and factors such as temperature, pressure, salt content, aluminum-lithium ratio, etc. are controlled to obtain lithium carbonate with higher purity. In this step, it is necessary to control the salt content of the leaching solution (lithium sulfate solution) to 10-35g / L and the aluminum-lithium ratio to 5-35. The so-called "aluminum-lithium ratio" refers to the ratio of the aluminum ion concentration to the lithium ion concentration in the solution. The temperature during membrane separation is controlled at 20-35°C and the pressure is controlled at 1.5-4MPa. The following formula is used to calculate and control the salt content and aluminum-lithium ratio.

[0021] Salinity refers to the salt content of spodumene leaching solution, mg / L; C Li + Indicates lithium ion concentration, mg / L; C Al 3+ Indicates aluminum ion concentration, mg / L; M Li + Indicates the molar mass of lithium ions, g / mol; M Al 3+ represents the molar mass of aluminum ion, g / mol; represents the molar mass of lithium sulfate, g / mol; represents the molar mass of aluminum sulfate, g / mol; r represents the aluminum-lithium ratio.

[0022] In the lithium precipitation step, potassium carbonate is selected to react with lithium sulfate in the solution to obtain lithium carbonate.

[0023] In the present invention, the nanofiltration membrane used is made of TFM (modified polytetrafluoroethylene) or TFC (thin film composite material reverse osmosis membrane), and the membrane model is DL, TS80 or NF1.

[0024] In the present invention, the process of separation using nanofiltration membrane comprises the following steps: (1) Membrane washing: First, the membrane must be washed to reduce the conductivity of the membrane to below 10μs / cm to avoid other impurity ions that interfere with the experimental results.

[0025] (2) Rinse: Next, pour the prepared raw material liquid into the material tank of the nanofiltration system, put the cleaned nanofiltration membrane into the nanofiltration membrane storage tank, turn on the switch, and allow the raw material liquid to pass through the jacket of the material tank at a stable flow rate. Circulate for 10 minutes, then open the valve to release the raw material liquid and take out the nanofiltration membrane at the same time. After taking out the raw material liquid in the membrane layer, put the nanofiltration membrane back to its original place.

[0026] (3) Membrane separation: Pour the prepared raw liquid into the material tank of the nanofiltration system, turn on the switch, adjust the different temperatures and pressures, and make the entire system circulate under the set pressure. When the temperature reaches the set value, take samples at the outlet of the permeate.

[0027] (4) ICP determination: Since the concentration of the feed solution is too high, it needs to be diluted before determination.

[0028] The parameters used to evaluate the separation effect of impurity ions in the leachate include the retention rate, separation factor and selectivity coefficient of each ion.

[0029] [1] The retention rate refers to the ratio of the amount of solute that does not pass through the nanofiltration membrane to the amount of solute in the original solution.

[0030] R represents the interception rate, %; C F Indicates the mass concentration of ions in the raw material solution, mg / L; C P Indicates the mass concentration of ions in the permeate, mg / L.

[0031] [2] The separation factor is the ratio of the lithium ion concentration to the impurity ion concentration in the permeate to the lithium ion concentration to the impurity ion concentration in the feed solution.

[0032] SF represents aluminum-lithium separation factor; C Li + Indicates lithium ion concentration, mg / L; C Al 3+ Indicates aluminum ion concentration, mg / L.

[0033] [3] The selectivity coefficient refers to the ratio of the retention rate of impurity ions to that of lithium ions. Taking aluminum ions as an example, S represents the selectivity coefficient; R Al 3+ Indicates Al 3+The retention rate, % R Li + Represents Li + The retention rate, %.

[0034] Example 1 The blocky pegmatite spodumene was ground and crushed, and sieved with a 200-mesh (≤0.075mm) round hole fine sieve. The powdered spodumene was roasted in a muffle furnace, and the roasting temperature was set at 1050°C for 30 minutes. After the roasting, it was cooled to room temperature. After roasting, it was sieved with a 200-mesh fine sieve to obtain the stand-by ore, to which 0.07 mol / L concentrated H2SO4 was added, the temperature was set at 250°C, and roasted for 35 minutes. Then, under the condition of a liquid-to-solid volume mass ratio of 2:1, water was added for leaching, and a constant temperature timed magnetic stirrer was used for stirring, the speed was set at 150r / min, the temperature was 25°C, and stirring was performed for 25 minutes. Then calcium carbonate was added to the solution to adjust the pH to 6.5, and filtered. The ion components and contents contained in the filtrate are shown in Table 1.

[0035] Table 1 Ion components and contents in the filtrate Prepare the raw material solution, adjust its salt content to 25g / L and aluminum-lithium ratio to 25. Prepare 1L of raw material solution to rinse the membrane to avoid water residue. Prepare 2L of raw material solution, adjust the temperature to 25°C and the pressure to 3.5MPa, and perform membrane separation. The membrane of the nanofiltration membrane is DL membrane, the membrane material is TFM, the molecular weight of the organic matter retained by the nanofiltration membrane is 150-300Da, and the ability to retain magnesium sulfate is greater than 96%.

[0036] The experimental results show that Al 3+ , Ca 2+ , Fe 3+ The interception rates of Li + The interception rate of Al 3+ / Li + , Ca 2+ / Li + , Fe 3+ / Li + The separation factors are: 294.3561, 20.7291, 266.7089, Al 3+ , Ca 2+ , Fe 3+ The selectivity coefficients are 25.0905, 24.0065, and 25.0820.

[0037] Potassium carbonate is added to the solution after separation and impurity removal by nanofiltration membrane to precipitate lithium to obtain lithium carbonate. According to the test, the purity of the obtained lithium carbonate is ≥99.8%; the sodium content is ≤0.019%; the water content in the product is ≤0.25%; and the particle size distribution of the lithium carbonate meets 3μm≤D50≤8μm.

[0038] Comparative Example 1 The process flow of this comparative example is: crystal conversion roasting - acidification roasting - leaching - neutralization - filtration - lithium precipitation. Except that the membrane separation step is not included, the other process parameters are the same as those of the embodiment.

[0039] After testing, the purity of the obtained lithium carbonate is ≤98.8%; the sodium content is ≥0.0969%; the moisture content in the product is ≤0.25%; and the particle size distribution D50 of the lithium carbonate is 12μm≤D50≤78μm.

[0040] Comparative Example 2 The process of this comparative example is basically the same as that of Example 1, except that the salt content of the raw liquid used for membrane separation is 10 g / L, the aluminum-lithium ratio is 5, the temperature is adjusted to 25° C., and the pressure is 3.5 MPa.

[0041] After testing, the purity of the obtained lithium carbonate is ≤99.2%; the sodium content is ≥0.053%; the moisture content in the product is ≤0.25%; and the particle size distribution D50 of the lithium carbonate is 3μm≤D50≤17μm.

Claims

1. A method for extracting lithium carbonate from spodumene in pegmatite, characterized in that: The following steps are involved: (1) crushing the spodumene and performing crystal transformation roasting; (2) mixing the ore sample after crystal transformation with concentrated sulfuric acid and heating for acidification and roasting; (3) adding water to the treated ore sample to obtain a leachate, neutralizing it with calcium carbonate to a pH of 5.5-6.5, filtering it, and obtaining a lithium sulfate solution; (4) adjusting the salt content of the lithium sulfate solution to 10-35 g / L and the aluminum-lithium ratio to 5-35; using a nanofiltration membrane to perform membrane separation on the lithium sulfate solution at a temperature of 20-35° C. and a pressure of 1.5-4 MPa; (5) Add lithium carbonate to the solution after nanofiltration membrane separation, and filter and separate to obtain lithium carbonate.

2. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 1, wherein: In the step (1), the calcination temperature is 1000°C to 1100°C.

3. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 1, wherein: In the step (2), the acidification roasting temperature is 240-260° C., and the roasting time is 20-40 min.

4. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 1, wherein: In the step (3), the leaching time is controlled within 15-30 minutes.

5. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 1, wherein: In step (4), the salt content of the lithium sulfate solution is adjusted to 22-30 g / L and the aluminum-lithium ratio is adjusted to 20-30.

6. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 5, characterized in that: In step (4), the salt content of the lithium sulfate solution is adjusted to 25 g / L; the aluminum-lithium ratio is adjusted to 25.

7. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 1, characterized in that: In step (4), the temperature is 25° C. and the pressure is 3.5 MPa.

8. The method for extracting lithium carbonate from spodumene in pegmatite according to claim 1, characterized in that: The nanofiltration membrane is made of TFM or TFC, and the membrane model is DL, TS80 or NF1.

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