A method for extracting alkali metals from spodumene

Abstract

The invention relates to a method for obtaining lithium chlorides and optionally other alkali metal chlorides from spodumene, comprising the steps of: a) preparation of a raw material mixture by mixing spodumene, a compound containing alkaline earth metals, and a chlorinating agent, wherein the weight ratio of alkaline earth metal oxides to SiO2 in the raw material mixture is within the range of 0.8:1 to 6:1, and wherein the amount of the chlorinating agent is such that the molar ratio of chlorine in the chlorinating agent to alkali metals contained in the raw material mixture is within the range 0.8:1 to 1.5:1; b) a chlorination reaction in the raw material mixture carried out at a temperature within the range 600 to 850°C for 20 to 120 minutes in a kiln or for up to 60 seconds in a cyclone device, preferably at a minimum possible gas flow velocity in the device / kiln; or a chlorination reaction in the raw material mixture carried out by mechanochemical activation in a milling device for 30 to 180 minutes; wherein the chlorination reaction yields a reacted raw material mixture; c) a step of volatilization of alkali metal chlorides from the reacted raw material mixture at the temperature range of 900°C to 1 600°C, wherein the temperature of the reacted raw material mixture is maintained below the melting point of the reacted raw material mixture and the temperature of kiln exhaust gases is maintained above 600°C, preferably above 750°C, at gas flow velocity in the device / kiln being within the range from 2 to 40 m / s, preferably within the range of 5 to 25 m / s, for 15 to 150 minutes, preferably for 20 to 60 minutes.

Description

[0001] A method for extracting alkali metals from spodumene

[0002] Field of Art

[0003] The presented invention relates to a method of extracting alkali metals, particularly lithium, in the form of chlorides from spodumene.

[0004] Background Art

[0005] Alkali metals, especially the rare alkali metals such as Li, Rb and Cs, but also K and Na as by-product component, can be extracted by several methods from silicate, alumosilicate, phosphate, and other minerals, including but not limited to lepidolite, zinnwaldite, spodumene, petalite, pollucite and amblygonite.

[0006] The first method involves high-temperature, high-pressure autoclave leaching in either an acidic or alkali medium. However, autoclave methods are associated with significant disadvantages, including high capital investment, the requirement for decrepitation or fine milling prior to leaching, low leaching efficiency, and the generation of alumosilicate or silicate leach residue that are difficult to utilize and are typically disposed in waste landfills.

[0007] The second method, which is probably the most commonly employed, involves extracting alkali metals by sintering the alkal- metal-containing minerals with sintering additives such as CaCO,. CaO, (Ca,Mg)CC>3, MgCCL, MgO, CaSCL, CaCL. NajSCL, NaCl, NaOH, NajCCL, K2SO4, or alternatively with other substances or their mixtures thereof in varying proportions. During sintering, decomposition of silicate, alumosilicate or phosphate minerals occurs, resulting in the release of alkali metals in a soluble form: Concurrently the anionic components are either separated in an insoluble form or bound to the alkaline earth metals, thereby forming insoluble silicates, alumosilicates or phosphates. The sinters are subsequently leached in aqueous solution. Certain types of sinters disintegrate into smaller particles upon cooling in water, or spontaneously in the presence of air, whereas others require milling before the leaching step.

[0008] An industrially applied method for processing spodumene involves converting crushed a-spodumene concentrate at a temperature of 950 °C to 1 100 °C to P-spodumene, followed by roasting the P- spodumene with sulfuric acid in temperature of 175 °C to 250 °C, thereby forming LijSCfi.

[0009] Other methods involve mixing a Li-containing mineral, optionally also containing other alkali metals, with sintering and chlorinating agents. This mixture is then preheated and subsequently subjected to high-temperature treatment, resulting in the formation of alkali metal chlorides, volatilization of the chlorides, and their condensation. In the methods according to the prior art, the formation of chloride is carried out during melting of the mixture (see, for example, WO2022167970). The above-mentioned methods require high chlorination temperatures (>1150 °C) of the raw material mixture in order to achieve higher alkali metal extraction efficiency. When spodumene is employed as the Li-containing mineral, the high-temperature conversion of a-spodumene to P-spodumene must first be carried out (as described, for example, in US 2627452).

[0010] All known methods that involve sintering with a chlorinating agent followed by leaching lithium chloride are generally highly energy-intensive and / or inefficient with respect to time and economics.

[0011] The subject of the present invention is to provide a well-defined and controlled method for efficient extraction of lithium from spodumene, which is less energy intensive.

[0012] Disclosure of the invention

[0013] The present invention relates to a process for extracting lithium chlorides and alternatively other alkali metal chlorides from spodumene, which contains the following steps: a) preparation of a raw material mixture by mixing spodumene, a compound containing alkaline earth metals, in particular Ca, and a chlorinating agent, wherein the weight ratio of alkaline earth metal oxides to SiO2in the raw material mixture is within the range of 0.8: 1 to 6: 1, and wherein the amount of the chlorinating agent is such that molar ratio of chlorine in the chlorinating agent to the alkali metals contained in the raw material mixture is within the range 0.8: 1 to 1.5: 1; b) chlorination reaction in the raw material mixture, i.e., alkali metals chlorides formation, to form a reacted raw material mixture, carried out at a temperature within the range 600 to 850 °C for 20 to 120 minutes in a kiln or for up to 60 seconds in a cyclone device, preferably at the minimum possible gas flow velocity in the device / kiln; or, chlorination reaction in the raw material mixture, i.e., alkali metals chlorides formation, carried out by mechanochemical activation in a milling device for 30 to 180 minutes; c) a step of volatilization of alkali metal chlorides from the reacted raw material mixture at a temperature within the range of 900 to 1 600 °C, wherein the temperature of the reacted raw material mixture is maintained below the melting temperature of the reacted raw material mixture and the temperature of kiln exhaust gases is maintained above 600 °C, preferably above 750 °C, at gas flow velocity in the device / kiln within the range from 2 to 40 m / s, preferably within the range of 5 to 25 m / s, for 15 to 150 minutes, preferably for 20 to 60 minutes.

[0014] In the step of alkali metals chlorides volatilization from the reacted raw material mixture, sintering of the reacted mixture takes place at the same time. The product of the sintering is a synthetic silicate material with hydraulic properties.

[0015] The above disclosed ratios of raw materials in the raw material mixture are necessary to maximize lithium extraction efficiency and obtain the hydraulic properties of the synthetic silicate material. The inventors have found, that in the process according to the invention, with a weight ratio of alkaline earth metal oxides to SiO2of 1: 1, 67 % of lithium is extracted at a temperature of 1450 °C; with a weight ratio of 3: 1, 93 % of lithium is extracted at 1350 °C, while with a weight ratio of 5: 1, 98 % of lithium is extracted at 1350 °C. The inventors have also found that it is not necessary to carry out thermal conversion of alfa-spodumene to beta spodumene before the chlorination step.

[0016] The compound containing alkaline earth metals may typically be an alkaline earth metal oxide or carbonate, or a mixture of thereof. The alkaline earth metal herein refers in particular to calcium, optionally also magnesium. A typical compound containing alkaline earth metals is limestone. For determination of raw materials ratio, the amount of the compound or compounds is recalculated to the amount of alkaline earth metal oxides (i.e., in particular CaO and / or MgO), as is common in the field of mineral processing.

[0017] For the purpose of determining the raw material ratios, spodumene is recalculated to the amount of silicon dioxide, and metal-containing materials are recalculated to the amount of the corresponding metal oxides, as is common in the given field.

[0018] Preferably, the weight ratio of alkaline earth metal oxides to SiO2is within the range 2: 1 to 5: 1, more preferably 3: 1 to 4: 1.

[0019] Preferably, the molar ratio of chlorine to alkali metals is within the range of 1: 1 to 1.25: 1, more preferably 1.15: 1 to 1.2: 1.

[0020] The chlorinating agent can include, for example, metal chlorides (such as MgCT. CaCT. AICT,. FcCT. FeCh) or chlorinated hydrocarbons (for example PVC).

[0021] Preferably, for the preparation of the raw material mixture, compounds containing alkaline earth metals, in particular Ca, with a particle size below 250 micrometers, more preferably below 150 micrometers are used, and spodumene with the particle size below 500 micrometers, preferably below 300 micrometers, more preferably below 250 micrometers is used. The needed particle size of the materials can be achieved by crushing and sieving. In this dimension range, all measurement methods provide the same result for the maximum particle size in the particle set.

[0022] For the preparation of the raw material mixture, spodumene or spodumene concentrate is used. Spodumene concentrate is commercially available and is prepared by concentration of spodumene ore with the aim of increasing the lithium content. Preferably, spodumene concentrate has the content of lithium at least 0.5 weight %.

[0023] The term “spodumene” encompasses spodumene in any crystal form or their mixture. In particular, for example, alfa-spodumene, beta-spodumene, gamma-spodumene or a mixture thereof can be used.

[0024] In some preferred embodiments, the raw material mixture further contains a compound adjusting aluminum content. Such compound may be AI2O3, a mixture of AI2O3 and SiC>2, clay, feldspar, mica, lepidolite, petalite, or zinnwaldite, or AICI3 as a chlorinating agent. Preferably, the compound adjusting the aluminum content and containing aluminum is added in such an amount that the recalculated weight ratio of AI2O3 to SiC>2 in the raw material mixture is in the range of 1 : 1 to 1: 10.

[0025] In some preferred embodiments, the raw material mixture further contains a compound adjusting iron content in such an amount that the ratio of aluminum to iron, recalculated to weight ratio of AI2O3 to Fe2C>3, would be in the range of 0.8: 1 to 6: 1, preferably 1.5: 1 to 4: 1. Such compound adjusting the iron content may be iron scrap, iron oxides or mixed oxides of Fe, Al and Si.

[0026] Surprisingly, it has been found within the framework of the present invention that melting of the raw material mixture is not required for an effective chlorination reaction. Melting the raw material mixture leads to a decrease in alkali metal chlorides extraction efficiency from this mixture. During the chlorinating step, reactions between the compound containing the alkaline earth metals and spodumene lead to decomposition of spodumene structure, which allows for efficient chlorination of alkali metals. In the process according to the present invention, sufficient time is provided for efficient chlorination reaction at the appropriate temperature and under suitable conditions. Additionally, by heating only to the temperature required for the chlorination, energy savings are achieved.

[0027] Preferably, the gas flow velocity in the device in which the chlorination step takes place is minimized, thereby reducing the loss and thereby the consumption of the chlorinating agent. The minimum attainable gas flow velocity is a parameter determined by the construction of each specific device. In a preferred embodiment, the chlorination is carried out in an electric furnace or kiln.

[0028] The step of volatilization of alkali metal chlorides takes place below the melting temperature of the mixture, thereby the energy consumption is reduced. Furthermore, by ensuring that volatilization of alkali metals chlorides takes place below the melting temperature of the mixture, losses of alkali metals into the melt are prevented. The melting temperature of the mixture is different for individual possible mixtures; generally higher content of alkaline earth metals increases the melting temperature. The melting temperature of the mixture can be determined before the step c) by heating the mixture and identifying the plateau in the temperature-time dependency caused by the latent heat of fusion. These methods for determining the melting temperature are well known in the given field.

[0029] Preferably the temperature in the step of the volatilization of alkali metal chlorides from the reacted raw material mixture is within the range of 1100 to 1550 °C, more preferably within the range of 1200 to 1450 °C, whereby the temperature is held below the melting temperature of the reacted raw material mixture.

[0030] Increased gas flow velocity in the kiln and maintaining the temperature of kiln exhaust gasses in the step c) facilitates the volatilization of alkali metal chlorides below their boiling point (which is around 1 400 °C).

[0031] By dividing the process into two steps, namely the chlorination step and the alkali metal chlorides volatilization step, a higher kiln exhaust gas temperature is ensured compared to a single-step process (e.g., according to US 2627452). This minimizes condensation of alkali metal chlorides in the kiln, while also minimizing the loss of chlorination agent and thus its consumption. Furthermore, the control over the process is increased.

[0032] The chlorination step and the alkali metal chlorides volatilization step are typically carried out in separate devices.

[0033] Preferably, as the fuel or fuel additive, solid alternative fuel with the content of chlorine up to 60 weight %, more preferably with the chlorine content from 5 to 30 weight. %, is used in the alkali metal chlorides volatilization step. This reduces the energy consumption of the process and improves the efficiency of alkali metals chlorides extraction.

[0034] After the volatilization, the alkali metal chlorides contained in the kiln exhaust gas are directed to a condensation unit, where they are condensed for further processing as needed. In a preferred embodiment, the hot kiln exhaust gas, after condensation of alkali metals chlorides and their removal from the gas, is directed to the chlorination step and used to heat the raw material mixture. This further improves the overall energy balance of the process.

[0035] Preferably, chemically active substances are added to the cooling medium in the condensation unit, which allow the capture of gaseous fluorinated compounds (in particular HF, SiF.4) and / or chlorinated compounds (in particular HC1, Ch) and / or SO3 present in the kiln off-gases, while also increasing the efficiency of alkali metals chlorides condensation. These chemically active substances include raw materials containing oxides and / or hydroxides and / or carbonates of alkaline earth metals, in particular Ca.

[0036] The solid residue of the raw material mixture after the volatilization of alkali metal chlorides can be processed according to the requirements for the further use, for example to a clinker or a granulated slag analog or other synthetic silicate materials with hydraulic properties, which may require remelting and / or milling of the mixture.

[0037] For the clinker formation, the weight ratio of alkaline earth metal oxides to SiO2in the raw material mixture is preferably in the range of 1.5: 1 to 5: 1, more preferably 2.5: 1 to 3.5: 1, and weight ratio of SiO? to AI2O3 is preferably in the range of 1 : 1 to 10: 1, more preferably 3 : 1 to 7 : 1.

[0038] For the slag formation, the weight ratio of alkaline earth oxides to SiCE in the raw material mixture is preferably in the range of 0,8: 1 to 2: 1, preferably 1: 1 to 1,5: 1.

[0039] In this disclosure, “alkali metals” refer in particular to lithium, potassium, and rubidium, with lithium being the main component obtained in this process.

[0040] Examples of carrying out the invention

[0041] Example 1.

[0042] Chlorination in a electrical tunnel kiln with minimal gas exhaustion, sintering in a rotary kiln

[0043] The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in weight ratio of 3.5: 1:0.24. This corresponds to a molar ratio of Cl to alkali metals of about 1.2: 1 and weight ration of CaO to SiCE of about 3.2: 1. The prepared mixture is chlorinated in an electrical tunnel kiln in a temperature of approximately 800 °C for about 15 minutes, with a gas flow velocity of 0.2 m / s. The resulting chlorination product is subsequently subjected to the alkali metal chloride extraction in a rotary kiln, which operates at a temperature of 850 °C at the kiln feeding point and at about 1 450 °C in the sintering zone (the melting temperature of this mixture is >1500 °C). The material residence time in the kiln is maintained at 45 minutes. In the alkali metal chlorides extraction step, an extraction efficiency of 96 % of alkali metal chlorides, primarily LiCl, is achieved, while venting the furnace gas at a flow rate of 10 m / s and maintaining the kiln gas temperature at the exit point of the kiln at 800 °C. The solid residue discharged from the kiln is rapidly cooled with air to a temperature of about 250 °C. The extracted furnace gas, containing volatile chlorides and other solid particles, is processed in a condensation unit operated at a temperature below 500 °C, whereby alkali metal chlorides are recovered. The extracted percentage of alkali metal chloride is expressed on a molar-basis and refers to the total amount of alkali metals present in the initial raw material mixture in all examples.

[0044] Example 2.

[0045] Chlorination in a cyclone apparatus, sintering in a rotary kiln, kiln gas without solid chlorides reused in the cyclone apparatus

[0046] The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in a weight ratio of 3.5 : 1 : 0.24. This corresponds to a molar ratio of Cl to alkali metals of about 1.2: 1 and weight ration of CaO to Si CL of about 3.2: 1. The prepared mixture is chlorinated in a cyclone apparatus at a temperature of 700 °C for approximately for 15 s. The resulting chlorination product is subsequently subjected to the alkali metal chloride extraction in a rotary kiln, which operates at a temperature of 800 °C at the kiln feeding point and at about 1 400 °C in the sintering zone (the melting temperature of this mixture is >1500 °C). The material residence time in the kiln is maintained at 45 minutes. In the alkali metal chlorides extraction step, an extraction efficiency of 94 % of alkali metal chlorides, primarily Li Cl, is achieved, while venting the furnace gas at a flow rate of 12 m / s and maintaining the kiln gas temperature at the exit point of the kiln at around 800 °C. The solid residue discharged from the kiln is rapidly cooled with air to a temperature of about 250 °C. The extracted furnace gas, containing volatile chlorides and other solid particles carried, is processed in a condensation unit, operated at a temperature below 500 °C, whereby alkali metal chlorides are obtained. Hot gas, after the removal of solid chlorides is recycled to the cyclone apparatus in the chlorination step.

[0047] Example 3.

[0048] Raw material pelletizing, chlorination in a rotary kiln, sintering in a rotary kiln, gas without solid chlorides reused in chlorination kiln

[0049] The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in a weight ratio of 3.5 : 1 : 0.24. This corresponds to a molar ratio of Cl to alkali metals of about 1.2: 1 and a weight ratio of CaO to SiOz of about 3.2: 1. FezOs, in a weight ratio of 0.06: 1 relative to spodumene concentrate, is added to the raw material mixture. This corresponds to a weight ratio of AI2O3 to FezOs of 3.13: 1. The raw material mixture is then subjected to a pelletizing step, producing pellets with an average size of about5 mm and a moisture content of approximately 10 %. The prepared pellets are chlorinated in a rotary kiln at the temperature of approximately 800 °C for about 30 minutes, with the gas flow velocity of 3 m / s. The resulting chlorination product is subsequently subjected to the alkali metal chloride extraction in a rotary kiln, which operates at a temperature of 850 °C at the kiln feeding point and at a temperature of 1 450 °C in the sintering zone (the melting temperature of this mixture is >1500 °C). The material residence time in the kiln is maintained at 45 minutes.

[0050] In the alkali metals chlorides extraction step, an extraction efficiency of 97% of alkali metal chlorides, primarily Li Cl, is achieved, while venting the furnace gas at flow rate of 7 m / s and maintaining the kiln gas temperature at the exit point of the kiln of 800 °C. The solid residue discharged from the kiln is rapidly cooled with air to a temperature of about 250 °C. The extracted furnace gas, containing volatile chlorides and other solid particles, is processed in a condensation unit at a temperature below 500 °C, whereby yielding alkali metal chlorides. Hot gas, after the removal of solid chlorides, is reused in rotary kiln in the chlorination step.

[0051] Example 4.

[0052] Chlorination by mechanochemical activation in milling apparatus, sintering in rotary kiln, kiln gas without solid chlorides reused in milling step

[0053] The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in a weight ratio of 3.5 : 1 :0.24. This corresponds to a molar ratio of Cl to alkali metals of about 1.2: 1 and weight ration of CaO to SiCL of about 3.2: 1. The prepared mixture is subjected to mechanochemical activation in a ball mill for 45 minutes. The reacted mixture is subsequently subjected to the alkali metal chloride extraction in a rotary kiln, which operates at a temperature of 850 °C at the kiln feeding point and at 1 300 °C in the sintering zone (the melting temperature of this mixture is >1500 °C). The residence time of the material in the kiln is maintained at 45 minutes.

[0054] In the alkali metals chlorides extraction step, an extraction efficiency of 93% of alkali metal chlorides, primarily LiCl, is achieved, while venting the furnace gas at flow rate of 9 m / s and maintaining the kiln gas temperature at the exit point of the kiln of 800 °C. The solid residue discharged from the kiln is rapidly cooled with air to a temperature of about 200 °C. The extracted furnace gas, containing volatile chlorides and other solid particles, is processed in a condensation unit at a temperature below 500 °C, whereby yielding alkali metal chlorides. The hot gas, after removal of solid chlorides and other solid phases is fed into the ball mill for drying of the raw material mixture and its mechanochemical activation.

[0055] Example 5.

[0056] Raw material pelletizing, chlorination in a rotary kiln, sintering in a rotary kiln, use of solid alternative fuel for maintaining the chlorinated atmosphere, kiln gas without solid chlorides reused in chlorination kiln

[0057] The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in a weight ratio of 3.5: 1:0.24. This corresponds to a molar ratio of Cl to alkali metals of about 1.2: 1 and weight ration of CaO to SiCL of about 3.2: 1

[0058] The raw material mixture is then subjected to a pelletizing step, producing pellets with an average size of about 5 mm and a moisture content of approximately 10 %. The prepared pellets are chlorinated in a rotary kiln at the temperature of approximately 800 °C for about 30 minutes, with the gas flow velocity of 3 m / s.

[0059] The resulting chlorination product is subsequently subjected to the alkali metal chloride extraction in a rotary kiln, which operates at a temperature of 850 °C at the kiln feeding point and at a temperature of 1 450 °C in the sintering zone (the melting temperature of this mixture is >1500 °C). The residence time of in the kiln is maintained at 30 minutes. As a part of the fuel for the rotary kiln in extraction step, a solid alternative fuel containing about 5% of chlorine is used, ensuring that the concentration of gaseous compounds (HC1, CI2) in the kiln gas remains above 0,05 % by volume. In the alkali metals chlorides extraction, an extraction efficiency of 98% of alkali metal chlorides, primarily LiCl, is achieved, while venting the furnace gas at flow rate of 15 m / s and maintaining the kiln gas temperature at the exit point of the kiln of 800 °C. The solid residue discharged from the kiln is rapidly cooled with air to a temperature of about 200 °C. The extracted furnace gas, containing volatile chlorides and other solid particles, is processed in a condensation unit at a temperature below 500 °C, whereby alkali metal chlorides are recovered. The hot gas, after removal of the solid chlorides and other solid phases is recycled and fed into the rotary kiln in chlorination step for drying of the raw material mixture and for its chlorination.

[0060] Example 6.

[0061] Raw material pelletizing, chlorination in a rotary kiln, sintering in a rotary kiln, melting in melting kiln and cooling for granulated slag analog, kiln gas without solid chlorides reused in chlorination kiln The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in a weight ratio of 1.5 : 1 : 0.22. This corresponds to a molar ratio of Cl to alkali metals of about 1.1: 1 and weight ration of CaO to SiOz of about 1.4: 1.

[0062] The raw material mixture is then subjected to a pelletizing step, producing pellets with an average size of about 5 mm and a moisture content of approximately 10 %. The prepared pellets are chlorinated in a rotary kiln at a temperature of approximately 800 °C for 30 minutes with the gas flow velocity of 2 m / s. The resulting chlorination product is subsequently subjected to the alkali metal chloride extraction in a rotary kiln, which operates at a temperature of 850 °C at the kiln feeding point and at a temperature of 1 250 °C in the sintering zone. The residence time of the material in the kiln is maintained at 25 minutes. As a part of the fuel for the rotary kiln in extraction step, a solid alternative containing about 5% of chlorine is used, ensuring that the concentration of gaseous compounds (HC1, CI2) in the kiln gas remains above 0.05 % by volume. In the alkali metals chlorides extraction step, an extraction efficiency of 92% of alkali metal chlorides, primarily LiCl, is achieved, while venting the furnace gas at flow rate of 15 m / s and maintaining the kiln gas temperature at the exit point of the kiln of 800 °C.

[0063] The solid residue discharged from the kiln is subjected to melting in electrical melting furnace at temperature of 1 500 °C. The resulting melt, after rapid cooling with water to a temperature below 200 °C, is obtained as a granulated blast furnace slag analog. The extracted furnace gas, containing volatile chlorides and other solid particles, is processed in a condensation unit at a temperature below 500 °C, whereby alkali metal chlorides are recovered. The hot gas, after removal of solid chlorides and other solid phases is recycled and fed into the rotary kiln in chlorination step for drying of the raw material mixture and for its chlorination.

[0064] Example 7.

[0065] Raw material pelletizing, surface coating of the pellet with a layer of CaO, chlorination in a rotary kiln, sintering in a rotary kiln, kiln gas without solid chlorides reused in chlorination kiln

[0066] The raw material mixture is prepared by mixing the limestone having a particle size below 150 pm, a spodumene concentrate containing 2.44 wt. % Li and having a particle size below 250 pm, and calcium chloride in a weight ratio of 3.5: 1:0.24. This corresponds to a molar ratio of Cl to alkali metals of about 1.2: 1 and a weight ratio of CaO to SiOz of about 3.2: 1

[0067] The raw material mixture is then subjected to a pelletizing step, producing pellets with an average size of about 5 mm and a moisture content of approximately 10 %. At the end of the pelletizing step, powder CaO is added, forming a surface layer of CaO or Ca(OH)2 on the pellets. The prepared pellets are chlorinated in a rotary kiln at a temperature of approximately 800 °C for 30 minutes with the gas flow velocity of 2,5 m / s.

[0068] The resulting chlorination product is subsequently subjected to the alkali metal chloride extraction step in a rotary kiln, which operates at a temperature of 850 °C at the kiln feeding point and at a temperature of 1 450 °C in the sintering zone (the melting temperature of this mixture is >1500 °C). The residence time of the material in the kiln is maintained at 30 minutes. In the alkali metals chlorides extraction step, an extraction efficiency of 96% of alkali metal chlorides, primarily LiCl, is achieved, while venting the furnace gas at flow rate of 8 m / s and maintaining the kiln gas temperature at the exit point of the kilnof 800 °C.

[0069] The solid residue discharged from the kiln is rapidly cooled with air to a temperature of about 250 °C. The extracted furnace gas, containing volatile chlorides and other solid particles from the kiln, is cooled in a condensation unit by a mixture of air and CaO at a temperature below 500 °C, whereby alkali metal chlorides are recovered. The hot gas, after removal of solid chlorides and other solid phases is recycled and fed into the rotary kiln in chlorination step.

Claims

CLAIMS1. A method for obtaining chlorides of lithium and optionally other alkali metals from spodumene, said method comprising the steps of: a) preparation of a raw material mixture by mixing spodumene, a compound containing alkaline earth metals, and a chlorinating agent, wherein the weight ratio of alkaline earth metal oxides to SiCh in the raw material mixture is within the range of 0.8: 1 to 6: 1, and wherein the amount of the chlorinating agent is such that the molar ratio of chlorine in the chlorinating agent to alkali metals contained in the raw material mixture is within the range 0.8: 1 to 1.5: 1; b) a chlorination reaction in the raw material mixture carried out at a temperature within the range 600 to 850 °C for 20 to 120 minutes in a kiln or for up to 60 seconds in a cyclone device, preferably at a minimum possible gas flow velocity in the device / kiln; or a chlorination reaction in the raw material mixture carried out by mechanochemical activation in a milling device for 30 to 180 minutes; wherein the chlorination reaction yields a reacted raw material mixture; c) a step of volatilization of alkali metal chlorides from the reacted raw material mixture at the temperature range of 900 °C to 1 600 °C, wherein the temperature of the reacted raw material mixture is maintained below the melting point of the reacted raw material mixture and the temperature of kiln exhaust gases is maintained above 600 °C, preferably above 750 °C, at gas flow velocity in the device / kiln being within the range from 2 to 40 m / s, preferably within the range of 5 to 25 m / s, for 15 to 150 minutes, preferably for 20 to 60 minutes.

2. The method according to claim 1, wherein the raw material mixture has a weight ratio of alkaline earth metal oxides to S i O2 within the range of 2 : 1 to 5 : 1 , preferably 3 : 1 to 4 : 1.

3. The method according to claim 1 or 2, wherein the raw material mixture has a molar ratio of chlorine to alkali metals within the range of 1: 1 to 1.2: 1, preferably 1.15: 1 to 1.2: 1.

4. The method according to any one of the preceding claims, wherein the chlorinating agent is selected from metal chlorides, chlorinated hydrocarbons and mixtures thereof.

5. The method according to any one of the preceding claims, wherein the raw material mixture further comprises a compound containing aluminum, in an amount such that the ratio of aluminum to silicon, expressed as the weight ratio of AI2O3 to SiCh, is within the range of 1: 1 to 1: 10, preferably the compound containing aluminum is selected from the group consisting of AI2O3, mixtures of AI2O3 and SiCh, clay, feldspar, mica, lepidolite, petalite and zinnwaldite.

6. The method according to any one of the preceding claims, wherein the raw material mixture further comprises a substance containing iron, in an amount such that the ratio of aluminum to iron, expressed as the weight ratio of AI2O3 to FezCh, is within the range of 0.8: 1 to 6: 1, preferably 1.5: 1 to 4: 1; preferably the compound containing iron is selected from the group consisting of iron scrap, iron oxides, mixed Fe, Al and Si oxides.

7. The method according to any one of the preceding claims, wherein the gas flow velocity in the apparatus / kiln during the alkali metal chloride volatilization step is from 5 to 25 m / s.

8. The method according to any one of the preceding claims, wherein the chlorination and chloride volatilization steps are caried out in separate apparatuses.

9. The method according to any one of the preceding claims, wherein in the chloride volatilization step, a solid alternative fuel with the content of chlorine up to 60 weight %, preferably with the chlorine content from 5 to 30 weight %, is used as a fuel or fuel additive.

10. The method according to any one of the preceding claims, wherein the extracted furnace gas, containing volatilized chlorides, is transferred to a condensation unit, where alkali metals chlorides condense and hot gas after condensing of the alkali metals chlorides and their removal is transferred into the chlorination step.

11. The method according to any one of the preceding claims, wherein the extracted furnace gas, containing volatilized chlorides, is transferred to a condensation unit, where alkali metals chlorides condense, wherein chemically active compounds are added to the cooling medium for capturing the gaseous fluorinated compounds and / or chlorinated compounds and / or SO, in kiln exhaust gasses, wherein the chemically active compounds are preferably oxide and / or hydroxide and / or carbonate of alkali earth metals, in particular Ca.