Process and system for heating lithium-containing materials

Abstract

A process for heat treating lithium-containing material with reduced dust generation includes: (a) feeding the lithium-containing material into a heating vessel (1); (b) heating lithium-containing dust in the heating vessel (1) using a controllable electromagnetic energy source (5) directed toward the lithium-containing material to cause a phase transformation in the lithium-containing material; and (c) extracting gas and dust from the heating vessel (1) into a gas extraction system (6). A system (10) for heating the lithium-containing material is also disclosed. The process and system enable the processing of lithium materials containing high impurities while reducing the burden of dust accumulation during calcination operations.

Description

[Technical Field]

[0001] In particular, the present invention relates to a process and system for heating lithium-containing materials by electromagnetic energy, such as microwave energy, which allows for reduced dust generation compared to prior art calcination methods. [Background technology]

[0002] The following discussion of the background art is intended solely to facilitate an understanding of the present invention and is not an acknowledgment or admission that any of the material referred to is or was part of the common general knowledge as of the priority date of this application.

[0003] The processing of lithium-bearing materials for the extraction of lithium generally involves heat treatment, usually in the form of a primary roasting or calcination step. Calcination refers to the heat treatment of minerals, including ores, or mineral concentrates to achieve structural changes (including phase changes, expansion cracking, or solid-state chemical transformations). Calcination can also include "roasting," which is the heat treatment of intentionally added reagents such as fluxes to form more leachable phases, whether for acid or alkaline leaching.

[0004] An example of a calcination process is the processing of spodumene ore, which contains lithium in the form of α-spodumene. α-Spodumene is not readily leachable in, for example, a sulfuric acid leach process. Calcination at temperatures between 1000 and 1250°C converts the α-spodumene to β-spodumene, which is more readily leachable in a sulfuric acid leach process.

[0005] Calcination is typically carried out in a rotary kiln, although flash calciners can be utilized. Rotary kilns accommodate larger or coarser particle sizes. One configuration involves a calcination system that includes a natural gas-fired rotary kiln, a rotary cooler for the calcined material, and an exhaust gas system that also extracts dust formed during calcination. In the case of α-spodumene, although this is not intended to be limiting, α-spodumene is fed into one end of a rotary kiln that is heated directly or indirectly by a fuel such as natural gas. The rotary kiln has a slight downward slope and rotates, transporting the α-spodumene as it is converted to β-spodumene. The calcined material then passes to a cooler, such as a rotary cooler, before being sent to the leaching step.

[0006] The calcination process is an identified bottleneck in lithium extraction, which has a high energy intensity associated with a resulting carbon dioxide footprint. In the case of lithium carbonate produced from spodumene, the carbon dioxide emissions can be as much as 9 tonnes of CO2 per tonne of lithium carbonate equivalent (LCE) produced.

[0007] The above process, including the operation of the rotary kiln itself, also generates a significant amount of fines or dust due to the pressure generated during the flow of the combustible gas-air mixture. The fines or dust are collected by a dust extraction system, such as a system including multiple cyclones and baghouses located in the exhaust gas system, operating with electrostatic precipitator. The dust collected by the cyclones and baghouses is recirculated to the gas-fired rotary kiln. Given the significant amount of dust that creates a recirculation load, as well as environmental and other commercial considerations, dust treatment is essential. Dust handling is also required in flash calciners, which typically operate with a feed material with a smaller particle size distribution than rotary kilns.

[0008] It is an object of the present invention to provide an alternative process for heating lithium-containing materials. Summary of the Invention

[0009] With this objective in mind, in one aspect, the present invention provides a method for producing a method for manufacturing a semiconductor device comprising: (a) delivering a lithium-containing material to a heating vessel; (b) heating the lithium-containing material in a heating vessel with a controllable electromagnetic energy source directed toward the lithium-containing material to cause a phase transformation in the lithium-containing material; (c) extracting the gas and dust from the heating vessel into a dust extraction system; The present invention provides a process for heating a lithium-containing material with reduced dust generation, comprising:

[0010] In a second aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: (a) a heating vessel for holding the lithium-containing material during heating; (b) a controllable electromagnetic energy source directed towards the lithium-containing material to heat the lithium-containing material in the heating vessel to cause a phase transformation in the lithium-containing material; Including, The heating vessel has a dust extraction system for extracting gases and dust from the vessel, thereby reducing dust generation. A system for heating a lithium-containing material is provided.

[0011] Microwave energy is the preferred electromagnetic energy. However, other forms of electromagnetic energy, such as ultrasonic energy and infrared energy, may be employed. Heating of lithium-containing materials to a wide range of temperatures, such as 200-1300°C, is possible.

[0012] Advantageously, and in one embodiment that allows for the replacement of conventional gas-fired rotary kilns, the amount of dust generated in the process and extracted using the gas extracted into the gas extraction system is very low due to the relatively low gas flow rate or draft and pressure compared to the pressurization caused by the high volume of gas and air in a gas-fired rotary kiln. When the dust is recycled to the heating vessel, the equilibrium dust recycle can advantageously be less than 2% by weight of the lithium-containing material sent to the heating vessel. This equilibrium dust recycle is significantly lower than that generated in conventional rotary kilns fired with hydrocarbon fuels such as natural gas.

[0013] Such low equilibrium dust recycle levels achieved with the processes and systems described herein can eliminate or limit the requirement for cyclone and baghouse dust extraction and recycle configurations, which add capital and operating costs and often occupy limited plot area. Furthermore, the complex preheating cyclone configurations typical of conventional rotary kilns can be avoided. However, any dust generated within the vessel during steps (a) and (b) of the above-described process, for example due to the rotation of the rotary kiln, can be extracted and either recycled to the heating vessel or combined with the bulk stream of calcined lithium-containing material. Such material will generally have a coarse particle size compared to the dust. Therefore, the complex dust extraction and recycle configurations of conventional fossil fuel-fired calciners can be conveniently and economically replaced with a gas extraction system including a compact dust collector.

[0014] Advantageously, the process and system are well-adapted to minimize clinker formation, as they produce significantly less dust and are suitable for impure lithium-bearing material feeds than are typically processed. Because the melting point of the lithium-bearing material feed tends to decrease as the impurity content, particularly iron, increases (although other impurities from gangue minerals or primary lithium minerals in the feed may also be implied, including, without limitation, impurities selected from the group consisting of beryllium, potassium, sodium, rubidium, cesium, rare earth elements, magnesium, strontium, calcium, apatite, and micaceous materials), when significant amounts of dust are formed, as in conventional gas-fired calcination processes, higher temperatures are required to maintain acceptable α-spodumene to β-spodumene conversion (conversion being synonymous with phase transformation), forming clinker and causing further problems in the calcination and potentially downstream. For example, the clinker produced may be of a size that prevents proper calciner operation, thus requiring additional equipment, capital, and operating costs. Furthermore, because significantly less dust is formed during the heating process, clinker formation is less likely, and therefore a larger buffer can be maintained between the operating temperature and the melting temperature, making it possible to process lithium-containing materials at higher impurity levels. For example, it may be possible to process α-spodumene containing materials with greater than 1% Fe2O3, such as greater than 1% Fe2O3. The impurity content is acceptable in the process if the melting temperature of the lithium-containing material (including the impurities) is higher than the conversion or phase transformation of the lithium-containing material. Therefore, higher impurity levels, greater than 10 wt%, estimated at an upper limit of 20-25 wt%, can be tolerated without unacceptable clinker formation. While energy costs may be higher for lithium-containing materials with higher impurities, this cost will be offset by higher lithium prices.

[0015] The lithium-bearing material may be a lithium mineral such as pegmatite (including spodumene), lepidolite, amblygonite, jadalite, or petalite. The lithium-bearing mineral may be a mica- or clay-type material. The lithium-bearing material may be crude ore (ROM) from any lithium resource, a concentrate beneficiated from ROM, or a discharge stream from a mineral processing circuit, such as fine-grained slime obtained during classification of ROM.

[0016] In a further embodiment, the lithium-containing material may be lithium-containing dust produced by calcination, particularly as produced by calcination in a gas-fired rotary kiln that collects in the baghouse of a conventional processing facility. Such dust is enriched in lithium compared to lithium minerals that are typically subjected to thermal treatment by calcination in a heated vessel. For example, calcining spodumene ore rated at 6 wt% LiO in a gas-fired rotary kiln may produce dust rated at 6.5 wt% LiO.

[0017] Lithium minerals, such as those mentioned above, may not be heated by microwave energy, at least at relatively low temperatures. One reason for this is that silicate minerals, including spodumene, are transparent to microwave energy at low temperatures. Therefore, the lithium-containing material may require preheating other than by microwave energy to a predetermined temperature range where the microwave energy will have a heating effect and will remove moisture contained in the lithium material.

[0018] Alternatively or additionally, it may be necessary to include a susceptor material or microwave-absorbing material that is heated by microwave energy, allowing for direct heating of adjacent lithium-containing material by transfer of heat from the susceptor material to the lithium-containing material. Desirably, distribution of the susceptor material among the lithium-containing material allows for uniform heating. Additionally, heating may be entirely or partially from the shell of a heating vessel containing the susceptor material. For example, a silicon carbide shell or layer may be used as a microwave-absorbing material that transfers heat to the lithium-containing material, such as a bed of lithium-containing ore, and indirectly heats the lithium-containing material.

[0019] Alternatively or additionally, a susceptor material, preferably in particulate form, can be included within the lithium-containing material, e.g., in the range of <1-30 wt. %. Desirably, the susceptor material is uniformly distributed within the lithium-containing material to allow for uniform heating. Oxides are generally suitable, and iron oxides (e.g., Fe2O3 or Fe3O4) can be used as the susceptor material. Iron, although an impurity in spodumene ore, does not enter solution to a substantial extent during leaching for recovery of soluble lithium salts that are further processed into lithium hydroxide or lithium carbonate. Rather, the iron remains in the leaching residue and can be separated with the leaching residue, which itself can serve as a source of susceptor material. Another suitable alternative susceptor material is carbon-based. It should be understood that other susceptor materials besides iron oxide and carbon-based susceptors can be used, such as graphite, charcoal, pulverized charcoal, activated carbon, and carbides, and mixtures thereof. Other suitable susceptor materials may include other inorganic compounds, particularly metal oxides such as aluminum oxide, magnesium oxide, copper oxide, and mixtures thereof. The susceptor material should be inert to the heating process.

[0020] Alternatively, the vessel may incorporate a susceptor material, for example, contained in a desired refractory lining or lacing of the vessel, which allows for indirect heating of the lithium-containing material.

[0021] The lithium-containing material is heated directly or indirectly by microwave energy to a temperature above 900°C, more preferably above 1000°C, and most preferably in the range of 1000°C to 1250°C.

[0022] When the lithium-containing material is spodumene, conversion of α-spodumene to β-spodumene is preferred, although γ-spodumene may be formed, which may still be acceptable as a feedstock for leaching. Furthermore, the microwave heating process may result in two phase transformations, one being the conversion of α-spodumene to γ-spodumene in a first phase transformation, and the second being the conversion of γ-spodumene to β-spodumene in a second phase transformation.

[0023] From the above description it becomes clear that the heating may be direct or indirect, or a combination of direct and indirect heating modes. Homogeneous heating is preferred. Heating also desirably includes energy recovery from a cooler, either for the gas and dust in the dust extraction system, or, preferably at least in the case of bulk lithium-containing material, for bulk material having larger particle sizes or coarser than dust. Such heat may be used for preheating and / or drying the lithium-containing material fed to the heating vessel.

[0024] The processes and systems may be applied to the calcination and / or roasting of lithium-containing materials. The roasting process may involve dissolving the lithium-containing material with an acid or alkali to extract lithium values ​​from the lithium-containing ore. The processes and systems may also be used where heat treatment forms part of the lithium extraction process.

[0025] The vessel is conveniently a rotary kiln or furnace for continuous flow, oriented at a downward angle from the feed end to facilitate gravity flow of the lithium-containing material through the rotary kiln. The rotary kiln desirably has a refractory lining or lacing to allow operation within the temperature range specified above. The refractory lining is optionally microwave-transparent, for example, composed of alumina or alumina-silica or a microwave-transparent oxide. Such a refractory lining must not interfere with the microwave heating process. The rotary kiln preferably has a single chamber and does not require any means of stirring the material, although mixing can occur through the rotation of the rotary kiln. In another embodiment, the rotary kiln can be constructed using a susceptor material, an alloy such as steel, optionally with an inner layer of silicon carbide. In another embodiment where direct heating is appropriate, the rotary kiln can be constructed using an alloy such as steel, with the choice of steel depending on the required temperature of the lithium-containing material to be fired.

[0026] In other embodiments, the vessel may comprise a fluidized bed of lithium-containing material, for example, in a flash kiln or conventional fluidized bed calciner, a vertical furnace such as a pot calciner, or a gas suspension calciner. The vessel may also be of a batch design, for example, an inclined rotary furnace, or related batch designs, as are well known to those skilled in the art of furnace design.

[0027] Conveniently, heat is recovered from one or more cooler(s), preferably a fluidized bed cooler. The cooler will generally be provided to at least cool the heat-treated material, e.g., the calcined lithium-containing material such as β-spodumene, before being sent to downstream processing. The dust extraction system may also include cooler(s) in some embodiments. Such heat may be recovered from the cooler(s), and the recovered heat may conveniently be used for purposes including preheating the lithium-containing material, including for drying the lithium-containing material. Such recovered heat may be drawn through the heating vessel or directly into preheating vessel(s) upstream of the vessel. Alternatively, the heating vessel may receive off-gas from the cooler(s).

[0028] The heating vessel may conveniently include multiple zones, including a first zone for preheating, and optionally drying, the lithium-containing material, and a second zone for heating to induce a phase transformation within the lithium-containing material. The radiation profiles of the first and second zones are preferably different. For example, the first zone has a radiation and temperature profile that is different from the radiation and temperature profile of the second zone, and the temperature of the second zone is typically higher than that of the first zone.

[0029] In a further aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: (a) delivering a lithium-containing material to a first heated vessel; (b) heating a lithium-containing material in the first heating vessel while extracting gas from the first heating vessel to cause a phase transformation in the lithium-containing material; (c) heating the lithium-containing dust from the gas extracted from the first heating vessel with a controllable electromagnetic energy source directed toward the lithium-containing dust; The present invention provides a process for heating a lithium-containing material, comprising:

[0030] Systems for implementing the above processes involving heating lithium-containing dust form a further aspect of the present invention.

[0031] In this embodiment, the first heated vessel is conveniently a rotary kiln, typically gas-fired, as such rotary kilns are currently used for calcining lithium-containing materials.

[0032] The dust may be collected in a dust extraction or separation system, conveniently a baghouse in communication with the first heating vessel (conveniently a rotary kiln), before heating the dust with a controllable electromagnetic energy source in the second heating vessel. The dust may be enriched in lithium compared to the lithium content of the lithium-containing material sent to the first heating vessel. The heat-treated dust from the second heating vessel is preferably not recycled to the rotary kiln, but is instead directed to a cooler for further processing steps, including leaching for recovery of the heat-treated material and lithium. Heat may be recovered from the cooler for either preheating, drying, or other process purposes.

[0033] Thus, the process can be used in a hybrid system where a conventional gas-fired rotary kiln is retained and a microwave heating system is applied to treat baghouse dust recovered from the gas-fired furnace off-gas. Because the dust does not undergo a phase transformation or conversion, the dust still requires heat treatment and a microwave unit can be used for this dust, thus allowing the gas-fired rotary kiln to operate without accumulating a dust load.

[0034] The process and system may be operated on a batch or continuous basis. Those skilled in the art will recognize that mass flows of solids, liquids, and gases may be directed in various iterations to obtain the desired morphological changes in the lithium-containing material, particularly the lithium-containing ore. The process and system may be adapted to allow for the use of electromagnetic energy to heat a conventional calciner.

[0035] By using the processes and systems for heating lithium-containing materials as described above, dust formation and the requirement for extensive and / or complex dust handling equipment are significantly reduced. At the same time, lithium materials with higher impurity levels may be handled. Also, the conversion of materials from one microstructure to another, such as the conversion of α-spodumene to β-spodumene, can be accomplished to the same extent as conventional calcination processes. The roasting process may also be performed with the same efficiency as conventional roasting processes.

[0036] Further features of the process and system for heating lithium-containing materials of the present invention are more fully described in the following description of non-limiting embodiments of the invention. This description is included for purposes of illustrating the invention only and should not be understood as limiting the broad summary, disclosure, or description of the invention as set forth above. The description is made with reference to the accompanying drawings. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a schematic diagram of a system for heating a lithium-containing material, according to one embodiment of the present invention. [Figure 2] 2 is a schematic diagram of a system for heating a lithium-containing material similar to that shown in FIG. 1, showing the relationship between an electromagnetic energy source and a container for holding the lithium-containing material. [Figure 3] FIG. 1 is a schematic diagram of an inclined rotary furnace suitable for batch heating of lithium-containing materials according to another embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram showing the process flow of a hybrid system suitable for reducing the fines load on a conventional gas-fired furnace by microwave heating of dust from a baghouse. [Figure 5]1A and 1B are schematic diagrams of a system for utilizing off-gas heat from a process material cooler to dry and preheat feed ore. Embodiment (a) sends the off-gas directly to a preheating facility. Embodiment (b) directs the off-gas to a microwave calciner, which then sends the off-gas to a drying and preheating facility. [Figure 6] FIG. 1 is a schematic diagram of a system for a single microwave kiln including zones dedicated to different functions, such as a drying and preheating zone with an adjacent kiln high temperature zone. DETAILED DESCRIPTION OF THE INVENTION

[0038] 1 and 2, a system 10 is shown for heating a lithium-containing material, here α-spodumene concentrate feed (a lithium aluminosilicate mineral), for purposes of heat treatment, commonly referred to as calcination. Calcination converts the α-spodumene to β-spodumene, which is then leached for extraction of lithium in the form of lithium hydroxide or lithium carbonate for use in lithium-ion batteries. It should be understood that the present invention is not limited to the calcination of α-spodumene ore, and that other lithium ores, minerals, and lithium-containing materials may be calcined in system 10.

[0039] Heating system 10 includes a heating vessel 1 for holding a bed of α-spodumene ore for calcination, a controllable electromagnetic energy source 5 directed by waveguide(s) 8 towards the α-spodumene bed, and a dust extraction or dust recycling system 6 for extracting dust and gases and recycling any dust generated within vessel 1. In some embodiments described below, dust recycling is omitted.

[0040] In this embodiment, the vessel 1 is a rotary kiln in the form of a tube having a riding ring 4, although it will be appreciated that other forms of heated vessels may be used. An advantage of the rotary kiln configuration is that the rotary kiln is a design well known to those skilled in the art of lithium extraction.

[0041] The rotary kiln 1 has a metal shell with an insulating or refractory lining or lacing to retain heat and also to protect the metal shell from hot α-spodumene. The discharge port(s) and ducts, or duct sections, for delivering gas to the dust extraction or dust recycling system 6, if metallic, may also be insulated to allow the passage of hot gas from the rotary kiln 1. The refractory lining is preferably transparent to microwaves and is made of, for example, alumina or alumina-silica or a microwave-transparent oxide. Such a refractory lining must not interfere with the microwave heating process.

[0042] The rotary kiln 1 may, in a further embodiment, be constructed solely from a steel alloy, or from a metal or metal alloy with an inner lining of a microwave absorbing material such as silicon carbide.

[0043] The rotary kiln 1 may also in further embodiments be constructed entirely from microwave absorbing materials such as silicon carbide, with appropriate thermal protection surrounding the furnace. The furnace 1 may also be equipped with radiation shielding, such as the wide range of available conductive metals and alloys used for this purpose in microwave metallurgical processing techniques.

[0044] Rotary kiln 1, rotated by a suitable drive motor arrangement (not shown), is positioned at an angle to the horizontal to support gravity flow of α-spodumene therethrough from a feed 2 at one end to a discharge 3 at the other. Rotary kiln 1 has a single undivided chamber, which would prevent the desired downward flow of material from feed 2 to discharge 3.

[0045] Other than its heat source, rotary kiln 1 is operated in a manner known in the art of lithium mineral calcination. The α-spodumene concentrate feed may have a relatively high level of impurities, for example, in the form of iron oxides and silicates, grading between 2 and 4%. Other impurities may also be present. By way of example, the impurity content of the α-spodumene concentrate feed may be about 10% by weight.

[0046] The more leachable β-spodumene form of the emitted material 3 is sent to a cooler to cool from the calcination temperature to a temperature approaching that suitable for the acid roasting step.

[0047] Rotary kiln 1 allows for heating of α-spodumene feed 2 by microwave energy delivered from microwave generating device 5 via waveguide(s) 8, which transmit power from microwave generating device 5 to α-spodumene feed 2. Because heating to 1000-1250°C is required to achieve the conversion of α-spodumene to β-spodumene, microwave generating device 5 and rotary kiln 1 are configured with a radiation profile and power output to allow for heating to this temperature. Additionally, the inclusion of a refractory lining within rotary kiln 1 allows for this elevated temperature range. Microwave heating is at ambient pressure with little airflow, rather than the high pressures typical of prior art calciners pressurized by substantial gas and air flows.

[0048] Microwave energy may be transmitted through waveguide 8 from an industrial-scale microwave generating device 5 at frequencies provided under International Industrial, Scientific and Medical (ISM) standards, such as 896 MHz, 915 MHz, and 2450±50 MHz. However, other embodiments may use microwave energy throughout that frequency range, 0.3 to 300 GHz. The microwave energy may be pulsed, delivering energy at, for example, 20 kW or more, or 50 kW or more. The use of pulsed microwave energy is expected to be more energy efficient.

[0049] α-Spodumene alone may not be heated by microwave energy, at least at relatively low temperatures. One potential reason is that α-spodumene, as a silicate rather than an oxide, and possibly also containing some permeable gangue minerals, is transparent to microwave energy at low temperatures below about 570-660°C, depending on the microwave power input. This problem can be addressed by using a susceptor material, such as an oxide, that absorbs and is heated by microwave energy.

[0050] In one embodiment, particulate susceptor material, such as iron oxide (e.g., Fe2O3 or Fe3O4), may be included in the α-spodumene concentrate feed 2 in the range of <1-30 wt. %. The distribution of the susceptor material in the lithium-containing material is desirably uniform to enable homogeneous heating. The iron oxide susceptor is heated by microwave energy, and heat from the heated iron oxide particles is transferred directly to the α-spodumene, enabling its conversion to β-spodumene in a direct heating process.

[0051] With respect to whether iron introduced as a susceptor can affect downstream processing steps, this is unlikely to be an issue. Lithium extraction processes typically involve a leaching step, such as the acid roasting process described below. In such leaching steps, where neutralization is carried out with agents such as limestone or lime, iron is not incorporated into solution to a substantial extent during leaching. Rather, iron remains in the leaching residue and may be separated therewith. Indeed, it may be possible to recycle a portion of such leaching residue for use as a susceptor during microwave heating of α-spodumene. The same applies to carbon-based susceptors, which may be separated by methods such as filtration or decantation, or may be even more beneficial if present within the leaching residue utilized as a building material.

[0052] Alternatively, the rotary kiln 1 may incorporate susceptor material, for example, as described above, in a working layer of refractory lining or lacing on the walls of the rotary kiln 1. As a result, the refractory-lined or lacing-equipped rotary kiln 1 is suitable for direct heating by microwave energy. This allows, for example, for heating of α-spodumene, which may be used in combination with the indirect microwave heating described above.

[0053] While some dust is generated during firing in the rotary kiln 1 due to the tumbling motion of α-spodumene and β-spodumene as the rotary kiln 1 rotates, the amount of dust is very small, providing an equilibrium dust recycle of, for example, less than 2% of the weight of the lithium-containing material fed to the rotary kiln 1. This equilibrium dust recycle is significantly less than that generated in conventional rotary kilns fired with hydrocarbon fuels such as natural gas. Such low equilibrium dust recycle levels eliminate the requirement for cyclone and baghouse dust extraction and recycle configurations, which not only add capital and operating costs but often occupy limited plot area. Such dust extraction and recycle configurations can be replaced by a compact dust collector 6 that extracts dust from the feed end of the rotary kiln 1 through line 61. The collected dust is recycled through line 7 and reintroduced into the rotary kiln 1 with the α-spodumene feed 2. Furthermore, using the heating system 1 it is possible to avoid the complex preheat cyclone configurations that are typical for conventional rotary kilns.

[0054] Additionally, the calcination system 10 is well-adapted to minimize clinker formation, allowing for the processing of impure lithium-containing materials than are typically processed. Because the melting point of the lithium-containing material feed tends to decrease as the impurity content, particularly iron, increases, when significant amounts of dust are formed, as in conventional gas-fired calcination processes, the higher temperatures required to achieve acceptable α-spodumene to β-spodumene conversion tend to indirectly cause clinker formation, causing further problems in the calcination and potentially downstream.

[0055] The process and system may be applied to the calcination and / or roasting of lithium-containing materials. The roasting process may involve, for example, roasting the cooled β-spodumene product 3 from the calciner 1 with concentrated sulfuric acid to extract lithium values. The roaster for this process may also conveniently include a microwave generating device and waveguide to deliver microwave energy to the β-spodumene under the same or different conditions used in the calciner 1. For example, the heating rate may differ between the roaster and the calciner 1.

[0056] The process and system may be operated on a batch or continuous basis. FIG. 3 shows a batch heating system 100 for α-spodumene concentrate feed according to another embodiment of the present invention, in which an inclined rotary furnace 101 is used for batch heating of the α-spodumene. The inclined rotary furnace 101 may be substantially shorter than the rotary tube kiln 1 or a rotary tube kiln as used in conventional calcination practices. Microwave energy is delivered to the α-spodumene from the microwave generating device 5 through the waveguide(s) 8, as described above. A rotation mechanism 107 enables rotation of the inclined rotary furnace 101, which may be tilted forward to discharge the β-spodumene into a cooler at the end of a predetermined calcination time.

[0057] FIG. 4 is a schematic diagram of a process 200 that utilizes microwave heating to treat only dust from a conventional gas-fired calciner 3 used to calcinate bulk α-spodumene concentrate feed 6 that is preheated in a preheater 17. Dust 31 is collected in a dust extraction system in the form of a baghouse and diverted (31a) to a microwave calciner 2 of the same design as shown in FIG. 1 and described above. Baghouse 1 may be of conventional design known in the art of lithium mineral calcination. This diversion 31a of dust 31 to microwave calcination in microwave calciner 2 replaces the conventional recycling of dust to the gas-fired calciner 3. After the conversion or phase transformation of the dust in the microwave calciner 2, the heat-treated dust 16 is sent to cooler(s) 4, where the solids stream (crude calcined lithium-containing material 14 and dust 16) is consolidated into stream 24 for downstream processing, for example, by roasting or other leaching schemes known in the art for lithium extraction. In this embodiment, preheating or drying of the feed to the microwave calciner 2 is not required. However, in one embodiment of the illustrated process 200, off-gas 5 from cooler(s) 4 is sent to the microwave calciner 2 to preheat the dust 31a, either within the calciner in some embodiments or in a small preheater located before the microwave calciner 2. In another embodiment, preheating is performed by an alternative heating method without using off-gas 5 within the microwave calciner 2. Advantageously, this use of heat recovered from cooler(s) 4, via the intermediation of off-gas 5, increases the energy efficiency of the process 200. The heat recovered from the cooler(s) 4 will also be used in the preheater 17 depending on the energy analysis and the heat available.

[0058] 5 is a schematic diagram of process 300 demonstrating two embodiments of a scheme in which off-gas from fluidized bed cooler 4 (which cools β- or γ-spodumene calcine 26 from microwave calciner 2) is used to dry and preheat lithium-bearing material in the form of α-spodumene concentrate feed 6. Pre-heating can raise the temperature of α-spodumene concentrate feed 6 from ambient to over 200° C., depending on the energy recovery capacity of pre-heating facility 17. In this embodiment (a) of process 300, off-gas 15, including dust and gases, is sent directly to drying and pre-heating facility 17, bypassing microwave calciner 2. This embodiment (a) may be selected if energy recovery from fluidized bed cooler 4 is highly efficient. Another embodiment (b) involves directing the off-gas 15A from the fluidized bed cooler 4 (which cools the β- or γ-spodumene calcine 26 from the microwave calcine 2) to the microwave calcine 2 and then in stream 15B to the drying and preheating facility 17. This embodiment (b) may be selected if more preheating is required in the drying and preheating facility 17 compared to embodiment (a). The calcine 24 is then sent to downstream processing, for example, by acid roasting or other leaching schemes known in the art for lithium extraction.

[0059] FIG. 6 is a schematic diagram of a process 400 suitable for microwave calcination in which a single microwave calciner 1 is utilized for drying, preheating, and calcination. The calciner 1 is divided into temperature zones 1a and 1b by utilizing different microwave radiation profiles in the two zones, which in turn provides different temperature profiles for the two zones 1a and 1b. The first zone 1a of the calciner 1 is a cooler zone associated with preheating and drying, and the second zone 1b of the calciner 1 is a high-temperature zone (having a higher temperature than that associated with preheating and drying) for converting lithium-containing materials, such as, for example, α-spodumene to β-spodumene. The calciner 1 divided into temperature zones can be constructed of various materials to achieve different purposes. For example, the drying and preheating zone 1a can have an inner shell layer of silicon carbide, while the high-temperature zone can be constructed solely of an alloy, such as steel.

[0060] The first drying and preheating zone 1a of the microwave calciner 1 receives lithium-containing material in the form of α-spodumene concentrate feed 6, which resides in this zone for a period of time required to dry the material (remove substantially all of the moisture), depending on the moisture level and nature of the lithium-containing material, with dust 34 being collected in the dust extraction system 3. For example, lithium-containing material with poor thermal conductivity will require a longer residence time than lithium-containing material with a relatively high thermal conductivity. Dust 33 from the dust extraction system 3 is also returned to the microwave calciner 1. Once dried and preheated, the α-spodumene concentrate feed 6 is subjected to calcination in the second high-temperature zone 1b at the temperature required for the phase transformation or conversion of α-spodumene to β-spodumene, which occurs after a residence time specific to the ore. A cooler 4 for calcine (β-spodumene) 26 and any associated gases 150 can then be incorporated into the continuous flow system, with the off-gas from cooler 4 being utilized for energy recovery. Such energy is conveniently recovered heat that can be used for drying and preheating in zone 1a or other uses within the process and system. This reduces the carbon footprint of the calcination, which was an issue in previous configurations. The calcine 24 is then sent for downstream processing, for example, by acid roasting or other leaching schemes known in the art for lithium extraction.

[0061] By using the processes and systems for heating lithium-containing materials as described above, dust formation and the requirement for complex dust handling equipment, which may occupy extensive and / or significant plot areas, are significantly reduced. This potentially allows the calcination process to be carried out at or closer to the mining site rather than at a remote processing plant, potentially further saving processing plant space and transportation costs. Additionally, heat recovery in the cooler(s) increases energy efficiency and reduces the carbon footprint.

[0062] At the same time, lithium materials with higher impurity levels (up to 20-25 wt% impurities) can potentially be handled. Also, the conversion of materials from one microstructure to another, such as α-spodumene to β-spodumene, can be achieved to the same extent as conventional calcination processes. The roasting process can also be performed with the same efficiency as conventional roasting processes.

[0063] Modifications and variations of the processes and systems for heating lithium-containing materials described herein may be apparent to the skilled reader, and such modifications and variations are considered to be within the scope of the present invention.

[0064] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising" will be understood to mean the inclusion of a specified integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. 1. A process for heating a lithium-containing material with reduced dust generation, comprising: (a) delivering a lithium-containing material to a heating vessel; (b) heating the lithium-containing material in the heating vessel with a controllable electromagnetic energy source directed toward the lithium-containing material to cause a phase transformation in the lithium-containing material; (c) extracting gas and dust from the heating vessel into a dust extraction system; The process comprising:

2. 1. A system for heating a lithium-containing material with reduced dust generation, comprising: (a) a heated vessel for holding a lithium-containing material; (b) a controllable electromagnetic energy source directed towards the lithium-containing material in the heating vessel to heat the lithium-containing material and cause a phase transformation in the lithium-containing material; Equipped with the heating vessel having a dust extraction system for extracting gases and dust from the heating vessel; The system.

3. 3. The process of claim 1 or the system of claim 2, wherein the microwave energy is the electromagnetic energy.

4. 4. The process of claim 1 or 3, or the system of claim 2 or 3, wherein dust is recycled to the heating vessel, and the equilibrium dust recycle is less than 2% by weight of the lithium-containing material fed to the heating vessel.

5. 5. The process of claim 1, 3, or 4, or the system of claim 2, 3, or 4, wherein the lithium-containing material contains greater than 10 wt. % impurities, the impurities including components from the group consisting of beryllium, potassium, sodium, rubidium, cesium, rare earth elements, magnesium, strontium, calcium, apatite, and micaceous materials.

6. 6. The process or system of claim 5, wherein the lithium-containing material contains a maximum of 20-25 wt% impurities.

7. 10. The process or system of any one of the preceding claims, wherein the lithium-containing material is a lithium mineral selected from the group consisting of pegmatite (including spodumene), lepidolite, amblygonite, jadalite, or petalite.

8. 8. The process or system of claim 7, wherein the lithium-containing material is crude ore (ROM), a concentrate beneficiated from ROM, or a stream discharged from a beneficiation circuit.

9. 10. The process or system of any one of the preceding claims, wherein the lithium-containing material is the lithium-containing dust produced by calcination in a combustion rotary kiln.

10. 10. A process or system according to any one of the preceding claims, wherein the dust is rich in lithium compared to the lithium minerals that are subjected to calcination in the heating vessel.

11. 10. A process or system according to any one of the preceding claims, wherein the lithium-containing material is preheated to a predetermined temperature range for removal of moisture contained in the lithium material.

12. 12. The process or system of claim 11, wherein the lithium-containing material is heated by gas extracted from the heating vessel or heat recovered from the calcined lithium-containing material.

13. 13. The process or system of claim 11 or 12, wherein the heating vessel comprises a susceptor material that is heated by microwave energy, allowing direct heating of adjacent lithium-containing material by transfer of heat from the susceptor to the lithium-containing material.

14. 14. The process or system of claim 13, wherein the susceptor material is distributed throughout the lithium-containing material within the container.

15. 15. The process or system of claim 14, wherein the distribution of the susceptor material in the lithium-containing material allows for homogeneous heating thereof.

16. 15. The process or system of claim 13 or 14, wherein the vessel has a shell, the shell including a susceptor material to allow for complete or partial heating of the vessel from the shell.

17. 17. The process or system of claim 16, wherein the shell includes a silicon carbide layer for absorbing microwave energy, which layer in turn transfers heat to the lithium-containing material.

18. 16. The process or system of claim 14 or 15, wherein the susceptor material is in particulate form, for example in the range of <1-30% by weight of the lithium-containing material.

19. Iron oxide (optionally Fe ２ O ３ or Fe ３ O ４ 20. The process or system of claim 18, wherein:

20. 20. The process or system of claim 19, wherein the calcined lithium-containing material is leached and a leached residue is used as the susceptor material.

21. 20. The process or system of any one of claims 14, 15, or 18, wherein the susceptor material is a carbon-based susceptor selected from the group consisting of graphite, charcoal, pulverized charcoal, activated charcoal, carbides, and mixtures thereof.

22. 19. The process or system of any one of claims 14, 15, or 18, wherein the susceptor material is a metal oxide, and the metal oxide is selected from aluminum oxide, magnesium oxide, and copper oxide.

23. 23. The process or system of any one of claims 3 to 22 when dependent on claim 2, wherein the lithium-containing material is heated directly or indirectly by microwave energy to a temperature above 900°C, more preferably above 1000°C.

24. 24. The process or system of claim 23, wherein the lithium-containing material is heated directly or indirectly by microwave energy to a temperature in the range of 1000°C to 1250°C.

25. 25. The process or system of claim 23 or 24, wherein said heating of said lithium-containing material causes two phase transformations.

26. 26. The process or system of claim 25, wherein the lithium-containing material is α-spodumene, a first phase transformation is from α-spodumene to γ-spodumene, and a second phase transformation is from γ-spodumene to β-spodumene.

27. 10. The process or system of any one of the preceding claims, wherein the heating comprises a roasting process which involves dissolving the lithium-containing material with an acid or alkali to extract lithium values ​​from the lithium-containing material.

28. 10. A process or system according to any one of the preceding claims, wherein the heating vessel is a rotary kiln or furnace having a refractory lining.

29. 30. The process or system of claim 28, wherein the heating vessel is a single-chamber rotary kiln.

30. 30. The process or system of claim 29, wherein the rotary kiln mixes the bed of lithium-containing material by rotation of the kiln.

31. 10. A process or system according to any one of the preceding claims, wherein the heating vessel is a fluidised bed.

32. 13. The process or system of claim 12, wherein the gas extraction system comprises a cooler, preferably a fluidized bed cooler, and heat is recovered from the cooler.

33. 33. The process or system of claim 32, wherein the recovered heat is used to preheat the lithium-containing material.

34. 34. The process or system of claim 32 or 33, wherein the recovered heat is used to dry the lithium-containing material.

35. 35. The process or system of any one of claims 32 to 34, wherein the recovered heat is extracted through the heating vessel.

36. 36. The process or system of any one of claims 32 to 35, wherein the recovered heat is extracted to a preheater(s) upstream of the heating vessel.

37. 37. The process or system of any one of claims 32 to 36, wherein the heating vessel receives off-gas from the cooler.

38. 10. The process or system of any one of the preceding claims, wherein the vessel comprises a plurality of zones, a first zone for preheating the lithium-containing material and a second zone for heating to cause the phase transformation within the lithium-containing material.

39. 39. The process or system of claim 38, wherein the first zone has a temperature profile that is different from the temperature profile of the second zone, the temperature of the second zone being typically higher than in the first zone.

40. 1. A process for heating a lithium-containing material, comprising: (d) delivering the lithium-containing material to a first heated vessel; (e) heating the lithium-containing material in the first heating vessel while extracting gas from the heating vessel to cause a phase transformation in the lithium-containing material; (f) heating the lithium-containing dust from the gas extracted from the heating vessel with a controllable electromagnetic energy source directed toward the lithium-containing dust; The process comprising:

41. 41. The process of claim 40, wherein the first heating vessel is a rotary gas-fired furnace.

42. 42. The process of claim 40 or 41, wherein the dust is collected in a dust separation system prior to heating the dust with the controllable electromagnetic energy source in a second heating vessel.

43. 43. The process of any one of claims 40 to 42, wherein the heat-treated dust from the second heated vessel is passed to a cooler and further processing steps including leaching for recovery of lithium.

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