Process for the CO2 treatment of tempered lithium-containing materials for the production of lithium carbonate

Abstract

Process for the production of lithium carbonate from lithium-containing minerals, comprising the steps a) Digestion of a comminuted mineral phase β-spodumene in aqueous suspension under pressure with CO2 and conversion to lithium hydrogen carbonate b) Concentration of the lithium hydrogen carbonate-containing solution and precipitation of the lithium carbonate wherein the digestion of the comminuted β-spodumene takes place in an aqueous suspension with a mass ratio of solid / water of 1:2 to 1:100 and at a pressure of 50 to 250 bar, characterized in that prior to digestion, the crushed minerals are tempered at 950 to 1200°C in an oxygen-containing gas stream to convert the lithium-containing mineral phase into β-spodumene.

Description

[0001] The present invention relates to a process for producing lithium carbonate from lithium-containing minerals by direct carbonation with CO2.

[0002] Lithium carbonate is the most important lithium derivative for the production of downstream products and is mainly obtained from salars or lithium-bearing ores such as spodumene LiAl[Si2O6], lepidolite K(Li,Al)3[(F,OH)2I(Si,Al)4O 10 ], Zinnwaldite (KLiFe 2+ Al(AlSi3)O 10 (F,OH)2), or petalite LiAl[Si4O 10 ] won.

[0003] Lithium carbonate, for example, can be extracted from saline solution, as described in US 2013 / 0 251 610 A1. The lithium-containing salt solution is first desulfurized and then concentrated for the first time by vacuum evaporation. The lithium is present in the salt solution as lithium chloride. The solution is then concentrated for a second time using electrodialysis, which primarily serves to separate divalent cations such as Ca or Mg. A monoselective cation exchange membrane is used. The concentrated lithium chloride-containing salt solution is concentrated again, and any salts that have already precipitated are removed. In the final step, the concentrated solution is carbonated using carbon dioxide. Only then does the lithium chloride convert to lithium carbonate.

[0004] Lithium carbonate is extracted on an industrial scale from ores, particularly spodumene, petalite, or lepidolite. Known processes are based on digestion with strong acids, particularly sulfuric acid (see P. Distin, C. Phillips, Hydrometallurgy 1982, 9, 1-14, or DE 36 22 105 A1) or limestone burning (addition of CaO (US 2 020 854 A) and CaSO4 or CaCl2 (US 2 627 452 A).

[0005] US 2,840,453 A describes a process for the extraction of lithium carbonate from spodumene. Crushed, concentrated α-spodumene is first converted to β-spodumene in a rotary kiln at 1000 to 1100°C. Sulfuric acid is then added to this, and the extracted lithium is converted into Li2SO4 by leaching with water. The addition of CaCO3 and subsequent filtration separates the aluminum and iron, in particular. After concentrating the solution by evaporation and adjusting the pH (pH=7-8) with sodium hydroxide solution, lithium carbonate is precipitated by adding sodium carbonate at 90-100°C.

[0006] US Patent No. 4,124,684 A - describes the extraction of lithium carbonate by digesting calcined material with sodium carbonate. The lithium carbonate is then purified with carbon dioxide.

[0007] To extract lithium carbonate from fluorine-containing minerals such as zinnwaldite or lepidolite, traditional acid-based processes (analogous to the spodumene process) are not readily transferable, as the fluorine contained in zinnwaldite or lepidolite is released upon addition of sulfuric acid. The resulting hydrofluoric acid poses a significant process-engineering problem, as it is both extremely corrosive and poses a high health risk. The disadvantage of these processes is that special, very costly safety precautions must be taken to protect the equipment and the personnel involved in the process.

[0008] Alternative processes have been published, particularly by Jandova et al. (see, for example, J. Jandovä, P. Dvoräk, HN Vu, Hydrometallurgy 2010, 103, 12-18). This involves, among other things, gypsum digestion, which is based on the sintering of zinnwaldite with CaSO4 and Ca(OH)2. The lithium, which is converted into the liquid phase, is then precipitated as carbonate in the conventional manner.

[0009] The principle use of sc-CO2 for the carbonation of minerals, as a process for carbon dioxide binding (see e.g. KS Lackner, CH Wendt, DP Butt, EL Joyce, DH Sharp, Energy 1995, 20, 1153-1170; EH Oetkers, SR Gislason, J. Matter, Elements 2008, 4, 333-337.) is known and has been extensively investigated on ores such as wollastonite (D. Daval, I. Martinez, J.-M. Guigner, R. Hellmann, J. Corvisier, N. Findling, C. Dominici, B. Goffe, F. Guyot, American Mineralogist 2009, 94, 1707-1726.).

[0010] Chen et al. (Y. Chen, Q. Tian, ​​B. Chen, X. Shi, T. Liao, Hydrometallurgy 2011, 109, 43-46) describe the conversion of a fluorine-free α-spodumene concentrate from Jiangsu Province (China) into β-spodumene, which is digested with a sodium carbonate solution according to the following reaction: β-[Li2O·Al2O3-SiO2] + Na2CO3 + H2O → Li2CO3 + [Na2O·Al2O3·SiO2-H2O]

[0011] The resulting lithium carbonate then exists as a suspended, contaminated solid. For purification, it is converted to lithium bicarbonate in an aqueous solution using CO2 under pressure in an autoclave. It is then reprecipitated as lithium carbonate. However, the recovery rate for lithium carbonate is only 70%. Another disadvantage of this process is that digestion solutions from minerals with lower lithium content would have to be concentrated prior to carbonation.

[0012] The use of CO2 to purify technical-grade lithium carbonate via lithium bicarbonate is also known from DE 198 09 420 A1 and US Pat. No. 6,048,507 A. For example, DE 198 09 420 A1 describes a process for producing high-purity Li2CO3, in which technical-grade Li2CO3 is converted into LiHCO3 in an aqueous mixture by introducing CO2. Impurities are removed using an ion exchange process, and the high-purity lithium carbonate is subsequently precipitated from the aqueous mixture.

[0013] Experiments on the digestion of unannealed crushed minerals (spodumene, lepidolite, petalite, and zinnwaldite) with CO2 or sub-CO2 in an aqueous medium at various temperatures (100-215 °C), pressures (1-150 bar), and digestion times (0.5-24 h) show only Li digestion rates below 5%. The process is therefore extremely inefficient and economically hardly viable. (M. Fuhrland, M. Bertau, Hybrid Lithium Extraction, Final Report, TU Bergakademie Freiberg, 2013.)

[0014] US 2013 / 0 302 237 A1 also describes a process that does not require annealing. It is used to produce lithium carbonate from minerals containing silicon, aluminum, and lithium using CO2 digestion. The minerals are first crushed to grain sizes <50 µm and then suspended in water. The suspension is heated to 200 to 600 °C and treated with CO2 at a pressure of 30 to 100 bar. The solid residue of aluminosilicates is filtered off, and the solution is evaporated to yield solid lithium carbonate. The lithium yield is said to be 70%, based on the lithium content of the starting material.

[0015] The object of the invention is to provide an economically efficient process with high recovery rates for the extraction of lithium carbonate from lithium-containing minerals.

[0016] The task is solved by a process for the production of lithium carbonate from lithium-containing minerals, with the steps a) Digestion of a crushed β-spodumene mineral phase in aqueous suspension under pressure with CO2 and conversion to lithium bicarbonate b) Concentration of the lithium bicarbonate-containing solution and precipitation of the lithium carbonate, wherein the digestion of the crushed β-spodumene takes place in an aqueous suspension with a solid / water mass ratio of 1: 2 to 1:100 and at a pressure of 50 to 250 bar, characterized in that, before digestion, the crushed minerals are tempered at 950 to 1,200°C in an oxygen-containing gas stream to convert the lithium-containing mineral phase into β-spodumene.

[0017] Preferably, the minerals are crushed before tempering to grain sizes of 0.1 to 20,000 µm, preferably 2 to 1,000 µm, particularly preferably 5 to 100 µm.

[0018] Crushers (primary gyratory crushers, jaw crushers, horizontal impact crushers, etc.) and grinding mills (impact and impact mills) are preferably used to crush the minerals.

[0019] The conversion of α-spodumene to β-spodumene above 950 °C is known to the person skilled in the art.

[0020] Therefore, the crushed minerals are first thermally pretreated, whereby the lithium-containing mineral phases are converted to β-spodumene (LiAlSi2O6).

[0021] The crushed minerals are tempered at temperatures of 950 to 1,200 °C, preferably 950 to 1,100 °C, in an oxygen-containing gas stream, preferably in an air or oxygen stream. The applicable furnace types, such as tube furnaces, rotary kilns, induction furnaces, muffle furnaces, or continuous furnaces, are known to those skilled in the art. A rotary kiln or tube furnace is preferably used.

[0022] The residence time of the mineral in the furnace depends on the type of furnace used, the temperature and the grain size of the material used and is generally less than 24 h, preferably < 5 h, particularly preferably < 2 h.

[0023] For the subsequent reaction with CO2, starting material with a high surface area and thus a small grain size is required. Crushing is also necessary because the tempered material tends to sinter or glaze.

[0024] Preferably, the β-spodumene formed by tempering is comminuted to grain sizes <1,000 µm, preferably <100 µm, particularly preferably <20 µm.

[0025] Crusher (primary gyratory crusher, jaw crusher, horizontal impact crusher, etc.) and grinding mills (impact and impact mills) are preferably used to crush the tempered material

[0026] According to the invention, in the next step the crushed material is suspended in water in order to be reacted with CO2 under pressure and thereby broken down.

[0027] The mass ratio of solid to water is preferably 1:5 to 1:30.

[0028] The suspension is filled into a pressure vessel equipped with a stirrer. The pressure vessel and stirrer are made of industrially available materials, preferably high-quality stainless steel.

[0029] While stirring, the suspension is mixed with approximately 20 to 50 bar of CO2 at room temperature and then heated. The pressure in the pressure vessel increases with increasing temperature, with gaseous CO2 entering the supercritical state at temperatures >30.98 °C and a pressure >73.75 bar, which serves to decompose the β-spodumene. According to the invention, the pressure in the autoclave is 50 to 250 bar, preferably 100 to 150 bar. This results in the conversion of the lithium bound in the β-spodumene to lithium carbonate, which is dissolved in the liquid phase.

[0030] The digestion temperature in the pressure vessel is regulated by a heat supply and is preferably 100 to 400 °C, particularly preferably 200 to 300 °C.

[0031] The CO2 conversion is usually completed in less than 24 hours, preferably in less than 4 hours. After the reaction is complete, the heat supply is first turned off and the internal temperature is adjusted to 10 to 40°C, preferably 20 to 30°C. At these temperatures, the lithium is present in the form of lithium bicarbonate, LiHCO3, in an aqueous solution. Unconverted CO2 is then vented and can advantageously be recycled for further carbonation. This also advantageously allows the process to be used in batch operation.

[0032] In an advantageous embodiment of the invention, in addition to spodumene (LiAl[Si2O6]) and petalite (LiAl[Si4O 10 ]) fluorine-containing lithium-containing minerals can also be used. Well-known fluorine-containing lithium ores are lepidolite (K(Li,Al)3[(F,OH)2I(Si,Al)4O 10 ]) or zinnwaldite (KLiFe 2+ Al(AlSi3)O 10(F,OH)2). The extraction of fluorine-containing minerals has so far proven to be extremely problematic due to the potential release of HF, especially in wet chemical processes, and has posed a major process engineering challenge.

[0033] Surprisingly, during the tempering of the lithium-containing minerals according to the invention, even fluorine-containing lithium-containing minerals such as lepidolite and zinnwaldite show the transformation of the lithium-containing mineral phases to β-spodumene.

[0034] In addition, at temperatures above 860 °C (lepidolite) or at temperatures above 870 °C (zinnwaldite), the fluorine contained is completely removed via the gas phase.

[0035] Advantageously, the fluorine contained in the minerals is completely removed during annealing in the inventive digestion process. It therefore no longer represents a disruptive factor in the subsequent digestion process.

[0036] In one embodiment of the invention, the lithium-containing minerals are therefore fluorine-containing minerals. Fluorine-containing minerals are preferably selected from lepidolite (K(Li,Al)3[(F,OH)2I(Si,Al)4O 10 ]) or zinnwaldite (KLiFe 2+ Al(AlSi3)O 10 (F,OH)2).

[0037] Since the originally contained fluorine is completely removed via the gas phase during the previous annealing of the minerals, originally fluorine-containing and non-fluorine-containing lithium-containing minerals now behave virtually identically under a CO2 atmosphere, since the remaining iron and aluminum oxide compounds cannot be carbonated. This advantageously allows a single process step to be used to anneal various lithium-containing minerals. This fact is surprising even to those skilled in the art, since no hydro- or pyrometallurgical process is known to date in which these minerals can be treated in an identical manner.

[0038] Following CO2 digestion, a solid-liquid separation is carried out to separate the leaching residue (8) by means of filtration, sedimentation in a decanter or centrifugation.

[0039] The leaching residue is preferably separated by filtration. In principle, any type of filter can be used. A belt filter is preferred, preferably one with a filter belt with a pore size between 1 and 100 µm. A clear filtrate is always required for the subsequent electrodialysis process.

[0040] This process advantageously achieves high lithium extraction rates. The lithium extraction rate is 70 to 95%, preferably 80 to 95%, depending on pressure, temperature, stirring speed, grain size, and the mass ratio of solids to water.

[0041] The lithium content of the lithium bicarbonate-containing solution obtained after filtration is in the range of 100 to 1,500 mg / L, typically 500 to 900 mg / L. Therefore, according to the invention, the separation of the lithium bicarbonate-containing solution from the solid leaching residue is followed by concentration of this solution.

[0042] The concentration of the lithium bicarbonate-containing solution is preferably carried out by electrodialysis with an ion exchange membrane.

[0043] Electrodialysis is a method known to those skilled in the art for removing ionic components from aqueous solutions by transporting them through ion exchange membranes. These ion exchange membranes are located in an electrodialysis cell, also called a membrane stack. The ions are transported under the driving force of an electric field.

[0044] The Li contents after completion of electrodialysis are < 100 mgLi / L, preferably < 20 mgLi / L in the diluate circuit and > 4.0 g Li / L, preferably > 6.0 g Li / L in the concentrate circuit.

[0045] However, the Li content after completion of electrodialysis is below the saturation limit of lithium hydrogen carbonate (e.g. at 20 °C 87 g / L (~8.9 gLi / L)) in order to avoid precipitation in the concentrate circuit, so-called membrane scaling.

[0046] Materials used for electrodes and electrolyte, pumps and containers are those known from the state of the art and in particular to those skilled in the art.

[0047] Preferably, the ion exchange membrane is a cation exchange membrane for the migration of preferably monovalent cations (including Neosepta ® CMS Tokuyama Corporation). This allows for the advantageous separation of soluble carbonates and bicarbonates of multivalent ions during the concentration process.

[0048] Thus, alkaline earth metal bicarbonates, such as strontium as bicarbonate Sr(HCO3)2, remain in the diluate cycle.

[0049] After concentration of the lithium bicarbonate solution, precipitation of lithium carbonate occurs in a known manner.

[0050] For the precipitation of lithium carbonate, the solubility behavior of alkali carbonate compounds and the lithium carbonate-hydrogen carbonate equilibrium, which are known to those skilled in the art, are utilized. While the solubility of Li2CO3 in water decreases with increasing temperature, the solubilities of Na2CO3, K2CO3, Rb2CO3, Cs2CO S to.

[0051] At temperatures above 50 °C, the conversion of LiHCO3 to Li2CO3 occurs with the release of CO2. For this reason, the concentrated LiHCO3-containing solution is heated to temperatures of 60 to 100 °C, preferably 80 to 90 °C at atmospheric pressure, for precipitation, whereby pure lithium carbonate precipitates, while the carbonates of other monovalent ions remain in the solution.

[0052] The precipitated lithium carbonate is separated from the filtrate by solid-liquid separation through filtration, sedimentation in a decanter, or centrifugation. The saturated Li2CO3-containing filtrate is advantageously used as a leaching medium for recarbonation of the tempered rocks. The separated Li2CO3 typically has a purity of >98% and can be used directly or further processed into high-purity lithium carbonate using a state-of-the-art purification process. Examples of implementation

[0053] The invention will now be explained in more detail with reference to the following figures and exemplary embodiments, without, however, being limited thereto.

[0054] Showing: Fig. 1: Process for the CO2 treatment of tempered lithium-containing materials to produce lithium carbonate, comprising the steps: 1) Addition of spodumene or 2) Addition of lepidolite or 3) Addition of Zinnwaldite 4) Addition of Petalite 5) Tempering of the crushed minerals at 700 to 1500°C in an oxygen-containing gas stream to convert the minerals into β-spodumene 6) Crushing of the β-spodumene to a grain size of 10 to 150 µm 7) Crushing the tempered minerals and suspending the β-spodumene in water with a solid / water mass ratio of 1:1 to 1:100 8) Digestion of the aqueous suspension of the crushed tempered minerals under pressure with CO2 and conversion to lithium bicarbonate 9) Separation of the leaching residue from the lithium bicarbonate-containing solution, 10) Leaching residue 11) Concentration of the lithium bicarbonate-containing solution by electrodialysis 12) Precipitation of lithium carbonate by heating the concentrated solution containing lithium bicarbonate 13) Separation of lithium carbonate by filtration Fig. 2: Schematic structure of the membrane stack for electrodialysis 14) Concentrate circuit 15) Diluate circuit 16) Cation exchange membrane, 17) Anion exchange membrane

[0055] The low-concentration lithium bicarbonate-containing solution is fed into the diluate circuit (15), and water into the concentrate circuit (14). During the process, the lithium cations migrate through the cation exchange membrane (16) from the diluate to the concentrate circuit. The bicarbonate anions (HCO3 - ) also migrate through the anion exchange membrane (17) into the concentrate circuit.

[0056] Due to the volume ratios (V Diluat >> V konzentrat) a more concentrated lithium hydrogen carbonate solution is obtained in the concentrate circuit, from which the lithium carbonate can then be precipitated. Example 1: Production of lithium carbonate from spodumene

[0057] In the tube furnace, 150 g of crushed spodumene-containing rock (d 50 =50 µm, Li content=1.5 wt.%) at 1,000 °C for 3 h in an air stream. After cooling, the sintered material is crushed in the planetary ball mill (d 50=10 µm). 100 g of the crushed, tempered material are suspended with 2,000 mL of water in a pressure vessel using a stirrer. The reactor atmosphere is replaced with CO2 by injecting CO2 (40 bar) three times and releasing the pressure. The operating pressure of 40 bar is reached by injecting CO2 again. The reaction mixture is heated to 270 °C, causing the pressure in the autoclave to rise to 100 bar, and the temperature is kept constant for 4 hours while stirring.

[0058] The pressure vessel is then cooled to 25 °C and depressurized after another hour, ensuring that no CO2 enters the laboratory atmosphere. The Li decomposition rate is 79 to 82%, and the LiHCO3-containing solution has a Li content of 600 mg / L.

[0059] Following solid-liquid separation by pressure filtration, the LiHCO3-containing filtrate is electrodialytically concentrated. For this purpose, the lithium-containing solution is introduced into the diluate circuit (14) of the electrodialysis, and 0.15 L of distilled water is added to the concentrate circuit (13). A 2.5 wt.% Li2SO4 solution is used as the electrolyte to flush the electrode materials. To prevent a sharp drop in current efficiency, the process is stopped at 98% Li conversion. Due to ion and hydration shell migration, the water volume added to the concentrate circuit increases from 0.15 L to 0.2 L. The remaining Li content in the diluate is ~10 mg / L. In the concentrate circuit, the Li content after electrodialytic concentration is 5.8 g / L.

[0060] When the concentrated solution is heated to 80 °C, crystalline Li2CO3 (dry substance: -4.6 g Li2CO3) precipitates, which after filtration and drying at 80 °C has a purity of 99.4% (main impurities K, Na). Example 2: Production of lithium carbonate from zinnwaldite

[0061] In the tube furnace, 150 g of crushed Zinnwaldite rock (d 50 =20 µm, Li content=1.4 wt. %) at 1,000 °C for 3 h in an air stream. After cooling, the sintered material is crushed in the planetary ball mill (d 50=10 µm). 100 g of the crushed, tempered material are suspended in 2.0 L of water in a pressure vessel using a stirrer and mixed with 40 bar of CO2. Digestion is carried out by heating to 270 °C at a resulting CO2 pressure of 100 bar for 4 h. The pressure vessel is then cooled to 25 °C, and after another hour, any unreacted CO2 is vented. The Li digestion rate is 75%, and the LiHCO3-containing solution has a Li content of 530 mg Li / L.

[0062] Following solid-liquid separation by pressure filtration, the LiHCO3-containing filtrate is electrodialytically concentrated. For this purpose, the lithium-containing solution is introduced into the diluate circuit (15) of the electrodialysis system, and 0.15 L of distilled water is added to the concentrate circuit (14). A 2.5 wt. % Li2SO4 solution is used as the electrolyte for flushing the electrode materials. To prevent a sharp drop in current efficiency, the process is stopped at 98% Li conversion. Due to ion and hydrate shell migration, the water volume added to the concentrate circuit increases from 0.15 L to 0.2 L. The remaining Li content in the diluate is ~10 mg / L. In the concentrate circuit, the Li content after electrodialytic concentration is 5.1 g / L.When the concentrated solution is heated to 80 °C, crystalline Li2CO3 (dry substance: ~3.7 g Li2CO3) precipitates, which after filtration and drying at 80 °C has a purity of 99.2% (main impurities K, Na).

Claims

[1] A process for producing lithium carbonate from lithium-containing minerals, comprising the steps of a) Digestion of a crushed mineral phase β-spodumene in aqueous suspension under pressure with CO2 and conversion to lithium bicarbonate b) Concentration of the lithium bicarbonate-containing solution and precipitation of the lithium carbonate wherein the digestion of the crushed β-spodumene takes place in an aqueous suspension with a solid / water mass ratio of 1:2 to 1:100 and at a pressure of 50 to 250 bar, characterized by that before digestion, the crushed minerals are tempered at 950 to 1200°C in an oxygen-containing gas stream to convert the lithium-containing mineral phase into β-spodumene. [2] Process according to claim 1, characterized in that the digestion temperature is 100 to 400°C. [3] Process according to one of claims 1 or 2, characterized in that fluorine-containing lithium-containing minerals are used. [4] Process according to one of claims 1 to 3, characterized in that the concentration of the lithium hydrogen carbonate-containing solution is carried out by means of electrodialysis with an ion exchange membrane. [5] Method according to claim 4, characterized by that the ion exchange membrane is a cation exchange membrane for the migration of preferentially monovalent cations.

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