LITHIUM EXTRACTION APPARATUS AND PROCESS

Abstract

A method for extracting lithium from a lithium-containing material, comprising: (i) mixing the lithium-containing material, gypsum, a sulfur-containing material, and a calcium-containing material to form a feed mixture having a moisture content of at least 20% by weight; (ii) drying the feed mixture to form a dry mixture having a moisture content of less than 20% by weight; (iii) roasting the dry mixture to form a roasted mixture including a water-soluble lithium compound; and (iv) leaching lithium from the water-soluble lithium compound and forming a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound.

Description

LITHIUM EXTRACTION PROCESS AND APPARATUS FIELD OF INVENTION The invention relates to a process and apparatus for extracting lithium from a lithium-containing material. In particular, though by no means exclusively, the invention relates to a process and apparatus for extracting lithium from low-quality lithium-containing material, such as waste material from borate mining or clay formations. BACKGROUND OF THE INVENTION Lithium is used to make batteries for a variety of applications, including electric cars, cameras, and mobile phones. Lithium is obtained by extracting lithium-containing salts from underground brine deposits or by extracting lithium-containing rocks. An example of lithium-bearing rock is found in borate mine deposits, with lithium in waste rock / clay and tailings. MA / E / ZUZZ / Ul OZOO generated in the extraction and recovery process of OZOO borates. Low-value gangue material typically ends up in a tailings dam or waste rock pile. Tailings and waste rock piles contain low concentrations of lithium that cannot currently be economically extracted. The lithium in tailings and waste rock piles, although low-grade, is a potential asset that can be economically unlocked later with current or improved technology. The quantities of tailings and waste rock generated during mining can be significant, and therefore the potential value of the lithium can be substantial. Lithium is also present, typically in low concentrations, in clay formations, and to date, it has been a challenge to extract lithium from these formations in an economically viable way. There are several known processes for extracting lithium from materials that contain it. However, it has been a challenge to extract lithium in a practical and economical way from low-grade lithium-bearing material, such as tailings, waste rock, and clay formations described above. It would be desirable for a process to extract lithium from material containing low-quality lithium. The above description is not an admission of common general knowledge in Australia or elsewhere. BRIEF DESCRIPTION OF THE INVENTION The present invention provides a process for extracting lithium from lithium-containing material, particularly waste material containing low-quality lithium. The lithium-bearing material may be a sediment-hosted deposit. The sediment-hosted deposit may be tailings from an industrial processing plant, such as a primary processing plant, a boric acid processing plant, or a borate mine. The tailings may have undergone MA / E / ZUZZ / Ul OZOO to acid or water leaching. The sediment-hosted deposit may comprise clay minerals containing lithium. Clay minerals containing lithium can be processed or treated clay, for example, clay minerals found in the waste material from a processing plant that may have been processed, for example, by roasting. Clay minerals containing lithium can be virgin clays, such as natural or untreated clays, for example obtained from clay formations. Examples of clay minerals include smectites such as hectorite and / or montmorillonite, bigadic clays, and lithium-containing illite with or without lithium zeolites. Lithium-containing material can be a material in which lithium is associated with high concentrations of sodium, aluminum, silicon, and / or boron. Typically, lithium-containing material comprises 8–32% by weight of sodium, aluminum, silicon, potassium, and / or boron per kilogram of lithium-containing material. More accurately, lithium-containing material is a boron-containing mineral. The expression low grade / quality refers to a lithium concentration that ranges from 1 to 3 g / kg of lithium-containing material. The present invention provides a method for extracting lithium from a lithium-containing material comprising: (1) mixing the lithium-containing material, gypsum, a sulfur-containing material, and a calcium-containing material to form a feed mixture having a predetermined composition; (ii) roasting the mixture and forming a roasted mixture that includes a water-soluble lithium compound; and (iii) leaching lithium from the water-soluble lithium compound and forming a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound. The present invention also provides a method for extracting lithium from a lithium-containing material, which includes: (1) mixing the lithium-containing material, gypsum, a sulfur-containing material, and a calcium-containing material, and IVIA / t / ZUZZ / UI ozoo form a feed mixture that has a predetermined composition; (ii) supply the mixture to a toaster; (iii) toasting the mixture in the toaster and forming a toasted mixture that includes a water-soluble lithium compound; (iv) supply the water-soluble lithium compound to a leaching tank; (v) supplying an aqueous solution to the leaching tank; and (vi) leaching lithium from the water-soluble lithium compound and forming a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound in the leaching tank. MA / E / ZUZZ / Ul OZOO An advantage of the present invention is that it provides a lithium extraction process that can extract value from waste material, e.g., waste rock and tailings, generated from a variety of industrial processes including, but not limited to, borate extraction. Another advantage of the present invention is that it provides a lithium extraction process that reduces the operating cost. The roasting step in a known lithium extraction method is recognized as a key determinant of operating costs. The present invention replaces some of the gypsum used in the known roasting step with a functionally equivalent substance (i.e., sulfur-containing material including elemental sulfur or an alkali metal sulfate, such as sodium or potassium sulfate) that can be generated on-site or in situ to reduce operating costs. An additional advantage of the present invention is that it provides a process that uses an environmentally benign substance, water, in the extraction process instead of highly acidic solutions. This is achieved by a roasting step in which the lithium silicate in the clays is converted to Li₂SO₄, which is soluble in water. The sulfur-containing material may be a combination of an alkali metal sulfate and elemental sulfur. MA / E / ZUZZ / Ul OZOO Alkali metal sulfate can be a combination of sodium sulfate and potassium sulfate. Specifically, alkali metal sulfate is sodium sulfate. Alkali metal sulfate can be obtained from a waste stream effluent from a processing plant. OZOO Ideally, alkali metal sulfate is obtained from boric acid vegetable liquor or tailings pond. The calcium-containing material can be a combination of calcium carbonate, such as limestone or dolomite, and lime. The calcium-containing material can be substituted with magnesium carbonate. The mixing stage may involve blending wet lithium-containing material with gypsum, a sulfur-containing material, and a calcium-containing material to form a mixture. Conveniently, the wet lithium-containing material has a water content ranging from 30 to 60% by weight. More specifically, the wet lithium-containing material has a water content ranging from 40 to 50% by weight. The mixing stage may involve adding an aqueous solution to the lithium-containing material that has a water content of less than 30% by weight to form the wet lithium-containing material. The mixing stage can form a mixture having a composition in which the ratio of gypsum:sulfur-containing material is at least 1:1 (e.g., 1 kg of gypsum: 1 kg of sodium sulfate). Conveniently, the ratio of gypsum to sulfur-containing material is at least 2:1 (e.g., 2 kg of gypsum: 1 kg of sodium sulfate). Conveniently, the ratio of gypsum to sulfur-containing material is at least 3:1 (e.g., 3 kg of gypsum: 1 kg of sodium sulfate). Even more appropriately, the ratio of gypsum to sulfur-containing material is 7:3 (e.g., 7 kg of gypsum: 3 kg of sodium sulfate). The applicant has discovered that < 30% replacement of gypsum with a sulfur-containing material generates OZOO lithium recoveries comparable to gypsum mixtures alone, but at reduced operating costs. The applicant discovered that the complete replacement of gypsum with sodium sulfate resulted in a lithium recovery of less than 25%. OZOO The mixing step can form a mixture having a predetermined composition comprising lithium-containing material: calcium-containing material: gypsum: sulfur-containing material in a ratio of lithium-containing material (1): calcium-containing material (0.4-0.8): gypsum (0.3-0.5): sulfur-containing material (0.1-0.3). Appropriately, the mixing step focuses on a mixture comprising lithium-containing material: calcium-containing material: gypsum: sulfur-containing material in a ratio of 100:45-75:20-50:10-25. The above proportions for calcium-containing material can be applied to calcium carbonate, such as limestone or dolomite, and lime. The ratios of sulfur-containing materials listed above are particularly suitable for sodium sulfate. In this regard, someone skilled in the art would understand that adjustments to the proportions may be necessary if a different sulfur-containing material, such as potassium sulfate, is used. The method may include a granulation step to process the mixture into granules. Ideally, the granules have an average diameter of less than 15 mm. More ideally, the granules have an average diameter of less than 10 mm. Even more ideally, the granules have an average diameter of less than 5 mm. The roasting stage can be carried out at a roasting temperature ranging from 800 to 1,000°C. Appropriately, the roasting stage is carried out at a roasting temperature that ranges between 850 and 950°C. More accurately, the roasting stage is carried out at a MA / E / ZUZZ / Ul OZOO roasting temperature ranging from 857 to 925°C. Even more appropriately, the roasting stage is carried out at a roasting temperature of 900°C. The roasting stage can be carried out for a period of time ranging from 0.5 hours to 2 hours. Ideally, the roasting stage is carried out for a period of 1 hour. The roasting time is the period of time during which the mixture is exposed to the roasting temperature. This roasting time may differ from the mixture's residence time in a kiln or oven, as the mixture may not be exposed to the roasting temperature for its entire residence time. For example, the mixture may be exposed to a variable temperature profile while being transported through a kiln. In this example, the roasting time refers to the period when the mixture is transported to a location within the kiln where it is exposed to the roasting temperature. The roasting stage can be carried out at a roasting temperature ranging from 800 to 1,000°C for a roasting time period ranging from 0.5 hours to 2 hours. OZOO MA / E / ZUZZ / Ul OZOO When the mixture is toasted in an oven, the toasting stage is carried out at a toasting temperature of 850°C for a toasting time period of 1 hour. When the mixture is roasted in a crucible placed in an oven, the roasting stage is carried out at a roasting temperature of 900°C for a roasting time period of 1 hour. Sulfur-containing material, including sodium, potassium, and calcium sulfates, can be generated during the roasting stage. Unreacted sulfur-containing material may also be present in the roasted material. Since this material is an ingredient in the roasting recipe, recycling it back into the mixing tank reduces feed costs. As such, the method may include a stage of adding sulfur-containing material from the roasting stage to the mixing stage. The method may include a step of separating the sulfur-containing material from the roasted material. Conveniently, the step of separating the sulfur-containing material from the roasted material involves crystallization. The method may include a step of adding sulfur-containing material from the crystallization stage to the mixing stage. The water-soluble lithium compound may be lithium sulfate. The method may include a crushing stage of the water-soluble lithium compound prior to the leaching stage. Ideally, the crushing stage involves reducing the particle size of the water-soluble lithium compound to 1000–3000 µm (1–3 mm). The leaching step may include adding an aqueous solution to the roasted mixture to form a suspension having a solids content ranging from 20 to 50% by weight96, or, more appropriately, a solids content ranging from 25 to 45%. MA / E / ZUZZ / Ul OZOO by weight, more appropriately, a solids content ranging from 30 to 40% by weight. The method may include countercurrent leaching of the lithium from the water-soluble lithium compound. Conveniently, the method may include two or more stages of countercurrent leaching. In this specification, the aqueous solution used in the leaching step can have a pH ranging from 6.5 to 7.5. Conveniently, the pH of the aqueous solution is 7. It can be seen that although it is preferred that the aqueous solution used in the process have a pH of 7, the process can also use water from a variety of sources that may contain minerals or substances that cause the pH to deviate from 7 by +0.5. The leaching stage can be carried out at a temperature below 60°C. Ideally, the leaching stage is carried out at a temperature below 50°C. More ideally, the leaching stage is carried out at a temperature between 20 and 40°C. MA / E / ZUZZ / Ul OZOO The method may include filtering the slurry to remove undissolved solids, such as calcium carbonate and clay. Properly carried out, the filtration stage generates a lithium-containing leachate with a lithium concentration of at least 2,000 ppm. The method may include concentrating the leachate. The concentration step may involve evaporating part of the leachate to obtain a concentrated leachate that has a lithium concentration of at least 3000 ppm. Conveniently, the concentration step involves evaporating part of the leachate to form a concentrated leachate that has a lithium concentration of at least 4000 ppm. More accurately, the concentration stage involves evaporating part of the leachate to form a concentrated leachate that has a lithium concentration of at least 4500 ppm. The concentration step can result in the formation of impurities including calcium and sodium salts and / or particulate matter including tenardite, glaserite, glauberite or anhydrite. The method may include filtering the leachate containing concentrated lithium to remove impurities. The filtered, concentrated lithium-containing leachate can be processed through a series of steps to form lithium carbonate. The applicant has developed a process for forming lithium carbonate from the filtered, concentrated lithium-containing leachate, which is the subject of a U.S. patent application filed on the same day as this application by the same applicant, the description of which is incorporated herein by reference. The method may include recycling alkali metal sulfate (e.g., sodium sulfate) formed during the roasting step to supplement the sulfur-containing material in the feed material. The invention also provides an apparatus for performing the MA / E / ZUZZ / Ul OZOO method described above. In one form, the invention provides an apparatus for extracting lithium from a lithium-containing material comprising: (i) a mixing tank configured to receive and mix lithium-containing material with gypsum, sulfur-containing material, and calcium-containing material to form a feed mixture having a predetermined composition; (ii) a roaster configured to receive and roast the mixture and form a roasted mixture that includes a water-soluble lithium compound; and (iii) a leaching tank configured to form a lithium-containing leachate from the water-soluble lithium compound using an aqueous solution. OZOO The device may be located near or connected to a source of lithium-containing material and be configured to receive this material. The mixing tank can be connected to a tailings pond to receive the lithium-containing material. The mixing tank can be connected to a boric acid plant to receive at least some of the sulfur-containing material, such as an alkali metal sulfate. Conveniently, the mixing tank is configured to receive an alkali metal sulfate from the boric acid plant liquor or the tailings pond. More appropriately, the mixing tank is connected to a crystallizer to separate sodium sulfate from the waste material generated by the boric acid plant. The apparatus may include a granulator to process the mixture from the mixing tank into granules. Ideally, the granules have an average diameter of less than 15 mm. More ideally, the granules have an average diameter of less than 10 mm. Even more ideally, the granules have an average diameter of less than 5 mm. OZOO The apparatus may include a granulator to process the mixture from the mixing tank into granules. Ideally, the granules have an average diameter of less than 15 mm. More ideally, the granules have an average diameter of less than 10 mm. Even more ideally, the granules have an average diameter of less than 5 mm. MA / E / ZUZZ / Ul OZOO The mixing tank can be configured to receive alkali metal sulfate generated during the roasting step. The device may include a crystallizer to separate the sulfur-containing material from the roasted mixture. This allows the sulfur-containing material to be recycled back into the mixing tank. The crystallizer can be configured for flash crystallization. Flash crystallization is a process that allows the solution to quickly reach its crystallization temperature. The mixing tank can be connected to the crystallizer to receive the separated sulfur-containing material. The toaster can be an oven. The apparatus may include a crusher to reduce the particle size of the roasted mixture from the roaster to 1,000-3,000 pm (hull 1-3). The leaching tank can be part of a countercurrent leaching circuit. The apparatus may comprise three leaching tanks arranged in series. The leaching tank may include a filter to generate a lithium-containing leachate with a lithium concentration of at least 2000 ppm. The apparatus may include an evaporator to evaporate at least part of the leachate from the leaching tank to form a concentrated leachate having a lithium concentration of at least 3,000 ppm. The evaporator may include a filter to remove impurities from the leachate that contains concentrated lithium. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below by way of example only with reference to the accompanying Figure 1, which is a process flow diagram according to one form of the invention. DETAILED DESCRIPTION OF THE INVENTION The applicant has conducted research and development work on a known method for extracting lithium from a lithium-bearing deposit. The known method involves roasting the deposit with calcium carbonate and gypsum and then acid-leaching the roasted material to extract the lithium. The disadvantages of this process include the use of externally sourced reagents, including environmentally hazardous acid. Furthermore, acid leaching may not be suitable for extracting lithium from material containing low concentrations of lithium due to its relatively non-selective nature compared to water leaching. OZOO The applicant has discovered that a mixture of materials containing gypsum / sulfur can reduce operating costs without sacrificing the efficiency associated with traditional calcium carbonate-gypsum recipes for generating water-soluble lithium compounds. The applicant also discovered that a gypsum / alkali metal sulfate mixture provides a more efficient roasting process compared to a mixture that excludes gypsum. MA / E / ZUZZ / Ul OZOO The applicant also realized that boric acid plants produce sodium sulfate as a waste product that can be sent to the apparatus of the present invention to reduce the amount of sodium sulfate that needs to be purchased or synthesized for the present invention. The applicant also realized that the roasting stage can produce sodium sulfate in situ that can be routed to the apparatus of the present invention to further reduce the amount of sodium sulfate that needs to be purchased or synthesized for the present invention. As a result of these methods, the applicant has developed an apparatus for extracting lithium from a lithium-containing material according to the present invention. The apparatus 10, as shown in Figure 1, comprises a mixing tank 12, a calciner-shaped roaster 14, and a leaching tank 16. Apparatus 10 is located near or connected to a source of lithium-containing material and is configured to receive this material. Examples of suitable sources of lithium-containing material include a tailings pond from a borate mine or clay formations. Conveniently, apparatus 10 is also located near or connected to a source of alkali metal sulfate, such as sodium sulfate. Sodium sulfate and lithium-containing material can be obtained from the same source. For example, apparatus 10 can be connected to the tailings pond of a boric acid processing plant to receive lithium-containing gangue and connected to an effluent stream containing sodium sulfate from the same plant to receive sodium sulfate. The apparatus may include a hopper to hold the lithium-bearing gangue. In this configuration, the hopper is located above a vibrating tray (or screw conveyor) that feeds an impact mill to crush the gangue. The impact mill, in turn, feeds the combined gangue to a 40-mesh vibrating screen positioned above a buffer tank. The apparatus may include a compensation container for storing the sorted gangue before feeding it into mixing tank 12. The other feed material, which includes a calcium-containing material such as calcium carbonate and gypsum, can also be stored in separate containers before being introduced into mixing tank 12. Mixing tank 12 is configured to receive inputs of lithium-containing material, a sulfur-containing material such as an alkali metal sulfate or elemental sulfur, gypsum, and a calcium-containing material such as calcium carbonate, and mix these materials in specific proportions according to a predetermined roasting recipe, e.g., the recipes described in Tables 1 and 2 below. A product outlet from mixing tank 12 can be connected to a granulator to granulate the mixture. The granulator can in turn be connected to a dryer to dry the granulated mixture. IVIA / t / ZUZZ / UI ozoo MA / E / ZUZZ / Ul OZOO A calciner 14 is configured to receive and roast the granulated mixture to convert the lithium-containing material into a water-soluble lithium compound such as lithium sulfate. A product outlet from calciner 14 is connected to a feed inlet of a leaching tank 16. In some embodiments, the calciner 14 can be connected to a cooler to cool the roasted material before it is directed to the leaching tank 16. In these embodiments, the cooler can be connected to a crusher to reduce the particle size of the roasted mixture to 1000-3000 µm (1-3 mm). The crushed compound can be stored in an offset container to contain the roasted material before it is directed to leaching tank 16. The leaching tank 16 also includes a fluid inlet 18 to receive water. Leaching tank 16 is configured to allow countercurrent flow of lithium-containing feed material and water during the leaching of the water-soluble lithium compound to form a lithium-containing leachate. OZOO The applicant discovered that the countercurrent flow of lithium-containing material and water during the leaching process, along with a number of operating parameters, optimized the extraction of lithium from the lithium-containing material. The temperature of leaching tank 16 can be controlled to allow the leaching process to be carried out at a predetermined temperature. The leaching tank 16 may include a filter 22 to remove any undissolved solids formed during the leaching process. Other suitable solid-liquid separation techniques, including centrifugation, may be used to remove undissolved solids formed during the leaching process. The leaching tank 16 includes a product outlet that is connected to an evaporator inlet 24. A compensation tank can be connected to the leaching tank 16 to contain the filtered leachate before it is directed to the evaporator 24. Evaporator 24 receives and concentrates the leachate from the surge tank or directly from the leaching tank. Impurities such as thenardite, glaserite, glauberite, and anhydrite may precipitate during the evaporation process. The leaching tank 16 may include another filter 22 to remove precipitates from the leachate, forming a concentrated leachate 26 that can be directed downstream for further processing or stored for later use. In operation, the apparatus according to the invention is connected to a berates processing plant 26. The feed material comprising lithium-containing waste material, for example from a tailings pond or plant heap, is directed to a flotation circuit 30 to remove some of the non-lithium-containing material. MA / E / ZUZZ / Ul OZOO lithium from waste material. The lithium-containing concentrate exiting the flotation circuit is then directed to a dryer 32 to reduce the concentrate's water content, preferably to 40–50% by weight, before being stored in a vessel. Suitable examples of lithium-containing material include residual lithium-bearing clay minerals, including smectites such as hectorite and / or montmorillonite. Bigadic clays and illite containing lithium, with or without lithium zeolites, that have undergone a variety of treatment steps, such as roasting at the processing plant, are also suitable. Feeding lithium-containing material with a water content ranging from 40 to 50% by weight has been found to improve the roasting stage because the increased water content enhances the granulation of the feed material prior to roasting. MA / E / ZUZZ / Ul OZOO Separate containers can be used to store sulfur-containing material, such as elemental sulfur or an alkali metal sulfate, gypsum, and calcium-containing material, such as calcium carbonate. The alkali metal sulfate can be obtained from an effluent stream that normally contains sodium sulfate, from the same plant. These containers are connected to mixing tank 12, which receives these materials in specific proportions to form a mixture that will eventually be processed through a series of intermediate steps to form a concentrated lithium solution of at least 4000 ppm. The gypsum and calcium-containing material are generally sourced externally. The calcium-containing material can be substituted with magnesium carbonate, dolomite, or lime. The sulfur-containing material is used to replace some of the gypsum in the roasting recipe. This reduces the need to source gypsum commercially and allows for the reuse of waste products from the borate processing plant. Importantly, this arrangement enables the extraction of commercial value from waste products of a boric acid processing plant that would otherwise have been discarded, and reduces reliance on reagents from external sources. It also improves the management of tailings ponds. The gangue material can be directed to an impact mill and passed through a classification screen to obtain -40 mesh particles before being fed into mixing tank 12. Mixing tank 12 feeds the various components based on a preselected recipe to form a mixture that has a lithium-containing material: calcium carbonate: gypsum: sodium sulfate ratio of 100:30-40:20:20. Another suitable recipe has a gypsum:sodium sulfate ratio of 7:3. The mixture can be processed in a granulator to form granules before being directed to a calciner 14 to be roasted at a temperature ranging from 857 to 925°C for approximately one hour. In one configuration, the mixture can be blended with water to facilitate the granulation process. Alternatively, a moist mixture with a water content of 40–50% by weight can be fed directly into the granulator. If necessary, the granulated mixture can be dried in a dryer. OZOO before sending it to the calciner 14. Examples of suitable roasting recipes where the lithium-containing material is clay material containing residual lithium are reproduced in Tables 1 and 2 below. Table 1: Examples of pre-set roasting recipes for clay containing lithium, including sodium sulfate Recipe No. Clay Lime Gypsum Sodium sulfate 1 100 45 40 10 2 100 45 45 15 In Table 1, the mixture is roasted at a roasting temperature of 900°C for a roasting time period of minutes. Table 2: Examples of predetermined roasting recipes for clay containing lithium, including sodium sulfate and / or elemental sulfur. IVIA / t / ZUZZ / UI ozoo Recipe No. Clay Limestone / Lime Gypsum Sodium Sulfate Elemental Sulfur % Lithium Recovery STD. DEV. % System Recovery • • «·* '* * ” ; - ♦ * t ♦ ♦ • .. * i - - • • ' - . • - • • i _ * * 4 • - ; - - - - This roasting step converts the lithium-containing material into a water-soluble form for a subsequent water leaching step. The representative chemical equations for the roasting process are set out below (Crocker.l, Lithium and its recovery from low-grade nevada clays [Report]. - [sl] : Bureau of Mines, 1988). CaSO4-2H2O + SiO2- CaSiO, + SO-, - V? O2(A) + 2H2O and Li2Si2O5 + SO2+ 'Λ O2* Li2SO4+ 2SiO2. (b) The above reaction (B) produces sodium sulfate and / or potassium sulfate that can be recovered and returned to mixing tank 12 to supplement the source of alkali metal sulfate. MA / E / ZUZZ / Ul OZOO The roasted material is fed into leaching tank 16 in countercurrent flow to a water leaching solution to leach lithium from the water-soluble lithium compounds formed. The solids content of the calcined material in the leaching tank ranges from 20 to 40% by weight, conveniently around 38% by weight. The roasted material can be directed to a cooler before being fed into the leaching tank. The water used in the leaching step ideally has a pH of 7. However, it can vary between 6.5 and 7.5 depending on the water source. In some formulations, the method may include a crushing stage of the roasted material, including the water-soluble lithium compound, before the leaching stage to improve the leaching process. Ideally, the crushed material has a particle size ranging from 1000 to 3000 µm. The leaching stage is carried out at a temperature below 500°C. The applicant determined that a leaching temperature of approximately 50°C optimized leaching efficiency in view of the inverse relationship between the solubility and temperature of lithium sulfate. During the leaching stage, filter 23 removes undissolved solids, such as calcium carbonate and clay. At this stage, the leachate typically has a lithium concentration of at least 2000 ppm. Next, the filtered leachate is directed to an evaporator 24 for concentration. During the evaporation stage, impurities may form in the form of calcium and sodium salts and particulate matter, including any or more of thenardite, glaserite, glauberite, and anhydrite. These impurities are removed by filter 22 to form a lithium-containing leachate with a concentration of at least 4,500 ppm. This leachate can be processed downstream through a series of steps to form lithium carbonate or stored for other uses. MA / E / ZUZZ / Ul OZOO One of these steps involves crystallizing the lithium-containing leachate to remove further impurities from the solution. In one embodiment, the waste material obtained from the crystallization step is returned to the flotation circuit 30 via stream 34 to recover lithium from the impurities in the crystallization step. Another step during the production of lithium carbonate is a lithium carbonate precipitation step that generates a filtrate that can be recycled back to the evaporator through stream 36. MA / E / ZUZZ / Ul OZOO In the claims that follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word comprises or variations such as comprises or comprising is used in an inclusive sense, i.e., to specify the presence of the stated features but not to exclude the presence or addition of additional features in various embodiments of the invention.

Claims

1. A method for extracting lithium from a lithium-containing material, comprising: (i) mixing the lithium-containing material, gypsum, a sulfur-containing material, and a calcium-containing material to form a feed mixture having a predetermined composition; (ii) roasting the mixture to form a roasted mixture including a water-soluble lithium compound; and (iii) leaching lithium from the water-soluble lithium compound to form a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound.

2. The method of claim 1, wherein the sulfur-containing material is a combination of an alkali metal sulfate and elemental sulfur. OZOO 3. The method of claim 2, wherein the alkali metal sulfate is a combination of sodium sulfate and potassium sulfate.

4. The method of claim 1, wherein the calcium-containing material is a combination of calcium carbonate and lime. 5 5. The method according to claim 1, wherein the mixing step involves mixing lithium-containing material having a water content ranging from 30 to 60% by weight with gypsum, sulfur-containing material, and calcium-containing material.

6. The method according to claim 1, wherein the mixing step involves adding an aqueous solution to a lithium-containing material having a water content of less than 30% by weight to form the wet lithium-containing material.

7. The method according to claim 1, wherein the mixing step forms a mixture in which the ratio of gypsum:sulfur-containing material is at least 1:

1.

8. The method according to claim 1, wherein the mixing step forms a mixture having a predetermined composition comprising lithium-containing material: calcium-containing material: gypsum: sulfur-containing material in a ratio of lithium-containing material (1): calcium-containing material (0.4-0.8): gypsum (0.3-0.5): sulfur-containing material (0.1-0.3).

9. The method according to claim 1, comprising a granulation step for processing the mixture into granules having an average diameter of less than 15 mm.

10. The method of claim 1, wherein the roasting step is carried out at a roasting temperature ranging from 800 to 1,000°C for a roasting time period ranging from 0.5 hours to 2 hours.

11. The method according to claim 1, comprising a step of separating the sulfur-containing material from the roasted material using crystallization. OZOO 12. The method according to claim 11, comprising a step of adding the sulfur-containing material obtained from the crystallization step to the mixing step.

13. The method of claim 1, comprising a step of reducing the particle size of the water-soluble lithium compound to 1000-3000 pm (1-3 mm).

14. The method according to claim 1, wherein the leaching step includes adding an aqueous solution to the roasted mixture to form a suspension having a solids content ranging from 20 to 50% by weight.

15. The method of claim 14, wherein the aqueous solution used in the leaching stage has a pH ranging from 6.5 to 7.

5.

16. The method of claim 14, comprising filtering the suspension to generate a lithium-containing leachate having a lithium concentration of at least 2,000 ppm.

17. The method according to claim 1, comprising evaporating part of the leachate to form a concentrated leachate having a lithium concentration of at least 3,000 ppm.

18. The method of claim 17, comprising filtering the concentrated lithium-containing leachate to remove impurities.

19. The method according to claim 1, comprising recycling the alkali metal sulfate formed during the roasting step to supplement the sulfur-containing material in the feed mixture.

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