Method for preparing lithium carbonate from a hard rock type lithium ore

Abstract

The application discloses a method for preparing lithium carbonate from hard rock type lithium ore, and belongs to the technical field of smelting lithium carbonate from lithium-containing minerals. The method comprises the steps of transformation sintering, batching, high-pressure leaching and post-treatment, and lime milk is added in the high-pressure leaching step. In the application, lithium in the ore is transferred out of the ore in the form of lithium carbonate through high-pressure leaching, and the lime milk is added at the same time of leaching, so that sodium aluminosilicate is promoted to transform into a canasite substance; the canasite substance has small solubility and is easy to be separated, thereby reducing impurities in the product; in addition, the canasite substance can also adsorb impurities and purify the solution; finally, the canasite substance can be reused as a cement component. After high-pressure leaching, the slurry is separated from mother liquor at the leaching temperature, and is returned to batching, so that lithium carbonate returned with the mother liquor is reduced, sodium carbonate in the mother liquor is recovered, and the material flow in the post-treatment step is reduced, thereby improving the circulation efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium carbonate smelting from lithium-containing minerals, and specifically relates to a method for preparing lithium carbonate from hard rock lithium ore. Background Technology

[0002] Lithium carbonate is a raw material for manufacturing lithium-ion batteries. Most of my country's battery-grade lithium carbonate production capacity comes from hard-rock lithium mines, which mainly include minerals such as spodumene, lepidolite, and lithium clay. Currently, methods for extracting lithium from hard-rock lithium mines include lime sintering, chlorination roasting, and sulfuric acid extraction. The lithium conversion rate and yield of these methods are not high. To address this issue, patent application number 201811087941.8 discloses a process for preparing lithium carbonate using a spodumene-soda ash pressure cooking method, which can improve the lithium conversion rate. However, in this process, sodium carbonate easily reacts with silica and alumina to form slightly soluble sodium aluminosilicate, which is difficult to separate and affects the purity of lithium carbonate. Summary of the Invention

[0003] To address the above shortcomings, this invention provides a method for preparing lithium carbonate from hard rock lithium ore, which can effectively remove sodium aluminosilicate and improve the purity of lithium carbonate.

[0004] This invention protects a method for preparing lithium carbonate from hard-rock lithium ore, comprising the following steps:

[0005] The process involves: sintering and calcining hard-rock lithium ore to obtain lithium-containing silicates, wherein the hard-rock lithium ore is selected from spodumene, lepidolite, or lithium clay; batching, mixing the lithium-containing silicates, sodium carbonate, and water to obtain a first slurry, wherein the liquid-to-solid ratio of the first slurry is 1.5-2.5, and the molecular ratio of sodium carbonate to lithium oxide is 1.3-5, wherein the lithium oxide is the molecular weight of the hard-rock lithium ore; high-pressure leaching, adding lime slurry to the first slurry to obtain a second slurry, wherein the mass of the lime slurry added is 5-15% of the mass of the first slurry; reacting the second slurry at a temperature of 200-280℃ and a pressure of 1.5-6.3 MPa for 0.25-1 h to obtain a product mixture; post-treatment, filtering the product mixture under high pressure to obtain insoluble solids, and subjecting the insoluble solids to re-slurrying, hydrocarbonation, purification, lithium precipitation, washing, and drying to obtain lithium carbonate.

[0006] Further, the product mixture is filtered to obtain a filtrate, and the filtrate is cooled to 105~110℃ to obtain a first circulating mother liquor, which is added to the batching step as water.

[0007] Furthermore, the calcination temperature in the transformation sintering is 650~1250°C, and the calcination time is 30~60min; the particle size of the lithium silicate is <75μm.

[0008] Furthermore, the calcination temperature of the spodumene is 950~1150°C; the calcination temperature of the lepidolite is 650~1050°C.

[0009] Furthermore, in the re-slurrying step, liquid is added to the insoluble solids to obtain a third slurry, and the third slurry is cooled to 10~25°C to carry out the hydrocarbonation; the mass ratio of the liquid to the insoluble solids is 1~4.

[0010] Further, carbon dioxide gas is introduced into the third slurry to obtain a lithium bicarbonate solution, wherein the pressure of the carbon dioxide gas is 0.1~1MPa and the gas introduction time is 0.5~1.5h.

[0011] Further, the lithium bicarbonate solution is heated to 95-98°C to obtain lithium carbonate.

[0012] Furthermore, the lithium carbonate is washed, and the washing solution is added as the second circulating mother liquor to the re-slurrying step.

[0013] Beneficial effects:

[0014] (1) In this invention, lime milk is added during the high-pressure leaching step. Lime milk promotes the transformation of sodium aluminosilicate into calcium nepheline, which has low solubility and is easily separated, reducing impurities in the product. Furthermore, calcium nepheline can adsorb impurities and purify the solution. Finally, calcium nepheline can be reused as a cement component. The solution from which sodium aluminosilicate is removed can be reused, saving resources.

[0015] (2) By setting up the first circulating mother liquor, the amount of liquid is reduced, thereby reducing the amount of carbon dioxide used in the hydrocarbonation step and reducing the waste of resources. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0017] in: Figure 1 This is a schematic flowchart of a method for preparing lithium carbonate from hard rock lithium ore according to one embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In this invention, the auxiliary materials are screened according to their particle size. The process to which the materials enter is selected based on the particle size, which will not be described in detail below.

[0020] refer to Figure 1 This invention protects a method for preparing lithium carbonate from hard-rock lithium ore, comprising the following steps:

[0021] S1. Transformation sintering. Calcination of hard rock lithium ore yields lithium silicates. The hard rock lithium ore is selected from spodumene, lepidolite, or lithium clay.

[0022] Natural lithium-containing minerals, due to their dense structure, react weakly or not at all with alkalis. Therefore, they require calcination at specific temperatures, ranging from approximately 650 to 1000°C, depending on the specific lithium-containing silicate mineral, to alter their crystal lattice or cause dissociation. For example, natural spodumene is α-spodumene, which hardly reacts with various acids or bases, only with hydrofluoric acid. Only after transformation calcination to convert it into β-spodumene can it react. Calcination of α-spodumene transforms it into easily processed β-spodumene.

[0023] S2. Ingredients. Lithium silicate, sodium carbonate and water are mixed to obtain the first slurry. The liquid-to-solid ratio of the first slurry is 1.5~2.5, and the molecular ratio of sodium carbonate to lithium oxide is 1.3~5.

[0024] In order to ensure the lithium leaching rate, sodium carbonate is used in excess.

[0025] S3. High-pressure leaching. Lime slurry is added to the first slurry to obtain a second slurry, the mass of which is 5-15% of the mass of the first slurry; the second slurry is reacted at a temperature of 200-280℃ and a pressure of 1.5-6.3MPa for 0.25-1h to obtain a product mixture.

[0026] A sodium-lithium substitution reaction is achieved by reacting an aqueous solution of sodium carbonate with lithium-containing silicates, resulting in the formation of lithium carbonate from lithium, while aluminum and silicon react with sodium to form zeolite-like substances. The reaction equations are as follows:

[0027] Li2O·l2O3·4SiO2+Na2CO3=Na2O·Al2O3·4SiO2+Li2CO3

[0028] To ensure lithium leaching efficiency, the sodium carbonate aqueous solution is typically supersaturated in the process formulation, and sodium carbonate must be in excess. However, because the sodium carbonate aqueous solution can undergo displacement reactions with lithium, as well as reactions with silica and alumina to form highly dispersed fine suspensions—sodium aluminosilicate—it poses difficulties for subsequent sludge separation. Furthermore, sodium aluminosilicate is only slightly soluble. To overcome these difficulties, lime milk is added at the leaching temperature to promote the transformation of sodium aluminosilicate (Na₂O·Al₂O₃·2SiO₂) into nepheline-like substances, forming precipitates with lower solubility. This helps reduce the amount of sodium aluminosilicate in the product mixture, improves the recycling efficiency of the product mixture, and also facilitates solid separation and washing. Nepheline-like substances can be used as a major component of building materials such as cement and can also adsorb some impurities, allowing the solution to be purified with only simple purification treatment.

[0029] S4. Post-processing. The product mixture is filtered to obtain insoluble solids, which are then subjected to re-slurrying, hydrocarbonation, and lithium precipitation to obtain lithium carbonate.

[0030] Before lithium precipitation, the lithium bicarbonate solution is separated into liquid and solid to obtain a separation liquid, which is then purified by resin.

[0031] This invention introduces lime slurry into the high-pressure leaching step. The lime slurry promotes the conversion of sodium aluminosilicate into nepheline compounds, which have low solubility and are easily separated, reducing impurities in the product. Furthermore, the nepheline compounds adsorb impurities, purifying the solution. Finally, the nepheline compounds can be reused as a cement component. The solution from which sodium aluminosilicate is removed can be reused, saving resources. By incorporating a first-cycle mother liquor, the amount of liquid is reduced, thereby reducing the amount of carbon dioxide used in the hydrocarbonation step and minimizing resource waste.

[0032] In one specific embodiment, the product mixture is filtered to obtain a filtrate, which is then cooled to 105-110°C to obtain a first circulating mother liquor. This first circulating mother liquor is added as water to the batching step. The amount of sodium carbonate added in the batching step S2 can be reduced based on the amount of sodium carbonate in the first circulating mother liquor.

[0033] In one specific embodiment, the calcination temperature during the transformation sintering is 650~1250°C, and the calcination time is 30~60min; the particle size of the lithium silicate is <75μm.

[0034] In one specific embodiment, the calcination temperature of spodumene is 950~1150°C; the calcination temperature of lepidolite is 650~1050°C.

[0035] In one specific embodiment, during the re-pulping step, liquid is added to the insoluble solids to obtain a third slurry, and the third slurry is cooled to 10~25°C for hydrocarbonation; the mass ratio of liquid to insoluble solids is 1~4.

[0036] In one specific embodiment, carbon dioxide gas is introduced into the third slurry to obtain a lithium bicarbonate solution. The pressure of the carbon dioxide gas is 0.1~1MPa, and the gas introduction time is 0.5~1.5h.

[0037] In one specific embodiment, lithium bicarbonate solution is heated to 95-98°C to obtain lithium carbonate.

[0038] In one specific embodiment, lithium carbonate is washed, and the washing solution is added as a second circulating mother liquor to the re-slurrying step.

[0039] The following are specific examples.

[0040] Example 1:

[0041] Using spodumene containing 5.2% lithium oxide as raw material, it is calcined at high temperature in a rotary kiln. The spodumene is preheated before entering the rotary kiln by using 550°C high-temperature flue gas from the kiln tail to preheat the raw material to 280°C. It then enters the rotary kiln and is calcined at 1050°C to transform it from α-type spodumene to β-type spodumene. The calcined spodumene is cooled to <100°C before being discharged.

[0042] After roasting, spodumene is crushed and ground to a particle size D90 < 75 μm before entering the batching system. The qualified spodumene is then mixed with soda ash, water, first-cycle mother liquor, and a portion of the second-cycle mother liquor. The batching ratio uses a sodium-to-lithium molecular ratio of 1.5 and a liquid-to-solid ratio of 2.4 (solid content approximately 30%).

[0043] The prepared slurry is fed into a high-pressure leaching system at a leaching temperature of 280℃ and held in the leachator for 10 minutes. During the leaching process, to precisely control the phases in which impurities are formed in the ore, 5-15% lime slurry is added to the high-temperature leachator to promote the transformation of zeolite tailings into calcium nepheline. Because calcium nepheline has lower solubility than zeolite, more impurities are introduced into the tailings, reducing the amount of impurities in the solution. Simultaneously, as zeolite is converted into calcium nepheline, the separation of the solution from impurities becomes easier.

[0044] The leached slurry undergoes liquid-solid separation under high temperature and high pressure. The advantage of high-temperature, high-pressure separation is that lithium carbonate has minimal solubility in high-temperature solutions, resulting in a smaller amount of lithium carbonate returning to the upstream feed with the first-cycle mother liquor. Therefore, the lithium carbonate recovery rate is increased, the recycling efficiency is improved, and the overall plant economy is significantly enhanced. The separated insoluble solids are then re-slurryed using the second-cycle mother liquor from product separation and water, with a slurrying ratio of L / S = 4.

[0045] The pulped slurry is fed into the hydrocarbonation process, where countercurrent hydrocarbonation is performed using excess carbon dioxide. Hydrocarbonation is carried out for 1 hour at 25°C and 0.4 MPa. To ensure reaction time, a multi-stage series connection is used to achieve high conversion and high carbon dioxide utilization. In this process, lithium carbonate is converted from the solid phase to lithium bicarbonate, which then enters the liquid phase, achieving separation of lithium carbonate from the tailings.

[0046] The slurry from the hydrocarbonation process enters a centrifuge for liquid-solid separation and residue washing. The washing water addition rate is 4 L / S, and the washing water temperature is 95℃. The separated lithium bicarbonate solution then proceeds to a purification process. The washed solid tailings are discharged externally.

[0047] The lithium bicarbonate solution enters the impurity removal process, which uses chelating resin to remove calcium and magnesium ions from the solution, ultimately yielding a pure solution.

[0048] After purification, the solution is fed into a continuous pyrolysis system. An external heater is used in the pyrolysis system to reduce scaling, while ensuring a certain crystallization time to guarantee the particle size of the lithium carbonate crystals.

[0049] The pyrolysis slurry is separated and washed to obtain battery-grade lithium carbonate.

[0050] The impurity content of the lithium carbonate product is shown in Table 1.

[0051] Table 1. Lithium carbonate impurity content:

[0052] .

[0053] Example 2:

[0054] Using lepidolite containing 2% lithium oxide as raw material, it is calcined at high temperature in a rotary kiln. The lepidolite is preheated before entering the rotary kiln by using 450°C high-temperature flue gas from the kiln tail to preheat the raw material to 230°C. It then enters the rotary kiln and is calcined at 1050°C to volatilize its volatile elements (F and OH), defluorinate it, and decompose it into a mixture of β-spodumene and leucite. The calcined clinker is then cooled to <100°C before being discharged.

[0055] The clinker, after being crushed and ground to a particle size of D90 < 75 μm, enters the batching system. The clinker with the appropriate particle size is then mixed with soda ash, water, circulating mother liquor 1, and circulating mother liquor 2. The batching ratio uses a sodium-lithium molecular ratio of 1.3 and a liquid-to-solid ratio of 2.4.

[0056] The prepared slurry is fed into a high-pressure leaching system at a leaching temperature of 280℃ and held in the leachator for 10 minutes. During the leaching process, to precisely control the phases in which impurities are formed in the ore, 5-25% lime slurry is added to the high-temperature leachator to promote the transformation of zeolite tailings into calcium nepheline. Because calcium nepheline has lower solubility than zeolite, more impurities are introduced into the tailings, reducing the amount of impurities in the solution. Simultaneously, as zeolite is converted into calcium nepheline, the separation of the solution from impurities becomes easier.

[0057] The leached slurry undergoes liquid-solid separation under high temperature and high pressure. The advantage of high-temperature, high-pressure separation is that lithium carbonate has minimal solubility in high-temperature solutions, resulting in a smaller amount of lithium carbonate returned to the upstream feed with the recycled mother liquor 1. Therefore, the lithium carbonate recovery rate is increased, the recycling efficiency is improved, and the overall plant economy is significantly enhanced. The separated insoluble solids are then re-slurryed using the recycled mother liquor 2 from the product separation and water, with a slurrying ratio of L / S = 5.

[0058] The pulping process is the same as in Example 1, ultimately yielding battery-grade lithium carbonate.

[0059] The impurity content of the lithium carbonate product is shown in Table 2.

[0060] Table 2. Impurity content of lithium carbonate:

[0061] ;

[0062] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing lithium carbonate from hard-rock lithium ore, characterized in that, Includes the following steps: The process involves: sintering and calcining hard-rock lithium ore to obtain lithium-containing silicates, wherein the hard-rock lithium ore is selected from spodumene, lepidolite, or lithium clay; batching, mixing the lithium-containing silicates, sodium carbonate, and water to obtain a first slurry, wherein the liquid-to-solid ratio of the first slurry is 1.5-2.5, and the molecular ratio of sodium carbonate to lithium oxide is 1.3-5; high-pressure leaching, adding lime slurry to the first slurry to obtain a second slurry, wherein the mass of lime slurry added is 5-15% of the mass of the first slurry; reacting the second slurry at a temperature of 200-280℃ and a pressure of 1.5-6.3 MPa for 0.25-1 h to obtain a product mixture; post-treatment, filtering the product mixture under high pressure to obtain insoluble solids, and then subjecting the insoluble solids to re-slurrying, hydrocarbonation, purification, lithium precipitation, washing, and drying to obtain lithium carbonate.

2. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 1, characterized in that, The product mixture is filtered to obtain a filtrate, and the filtrate is cooled to 105~110℃ to obtain a first circulating mother liquor. The first circulating mother liquor is added to the batching step as water.

3. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 1, characterized in that, The calcination temperature in the transformation sintering is 650~1250°C, and the calcination time is 30~60min; the particle size of the lithium silicate is <75μm.

4. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 3, characterized in that, The calcination temperature of the spodumene is 950~1150°C; the calcination temperature of the lepidolite is 650~1050°C.

5. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 1, characterized in that, In the re-slurrying step, liquid is added to the insoluble solids to obtain a third slurry, and the third slurry is cooled to 10~25℃ to carry out the hydrocarbonation; the mass ratio of the liquid to the insoluble solids is 1~4.

6. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 5, characterized in that, Carbon dioxide gas is introduced into the third slurry to obtain a lithium bicarbonate solution. The pressure of the carbon dioxide gas is 0.1~1 MPa, and the aeration time is 0.5~1.5 h.

7. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 6, characterized in that, Lithium carbonate is obtained by heating the lithium bicarbonate solution to 95-98°C.

8. The method for preparing lithium carbonate from hard-rock lithium ore according to claim 7, characterized in that, The lithium carbonate is washed, and the washing solution is added as the second circulating mother liquor to the re-slurrying step.

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