TECHNICAL FIELD

[0001] This invention relates to a process and system for heating a lithium containing material, in particular by electromagnetic energy such as microwave energy, which enables reduced dust generation in comparison to prior art calcination methods.

BACKGROUND ART

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

[0003] Processing of lithium bearing materials for extraction of lithium typically involves heat treatment, typically in the form of a primary roasting or calcination step. Calcination refers to heat treatment of minerals, including ores, or mineral concentrates to effect structural changes (including phase changes, decrepitation or solid-state chemical transformations). Calcination may also include Toasting’ which is the thermal treatment of intentionally added reagents such as fluxes to form more leachable phases, whether through acid or alkaline leaching.

[0004] One example of a calcination process is processing of spodumene ore which contains lithium in the form of o-spodumene. a-spodumene is not readily leachable, for example in a sulphuric acid leaching process. Through calcination at temperatures of 1000-1250°C, the a-spodumene is converted to p-spodumene which is more readily leachable in a sulphuric acid leaching process.

[0005] Calcination is typically conducted in a rotary kiln though flash calciners are available. A rotary kiln accommodates a larger or coarse particle size. One arrangement involves a calcination system comprising a rotary kiln fired by natural gas, a rotary cooler for the calcined material and an exhaust gas system which also extracts dust formed during calcination. In the case of a-spodumene, though this is not intended to be limiting, the a-spodumene is fed to one end of the rotary kiln, directly or indirectly heated by a fuel such as natural gas. The rotary kiln has a slight downward slope and is rotated to convey the a-spodumene as it is converted to [3-spodumene. Calcined material is then passed to a cooler such as a rotary cooler prior to direction to the leach step.

[0006] The calcination process is an identified bottleneck in lithium extraction and it has high energy intensity with consequential associated carbon dioxide footprint. In the case of lithium carbonate produced from spodumene, the carbon dioxide emissions may be 9 tonne 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 quantity of fines or dust due to the pressures generated during flow of a combustible gas-air mixture. The fines or dust are collected by a dust extraction system such as one comprising a plurality of cyclones located in the exhaust gas system and a baghouse, for example operating with electrostatic precipitation. Dust recovered by the cyclones and baghouse is recycled to the gas fired rotary kiln. Given the significant quantity of dust - which generates a recirculating load - as well as environmental and other commercial considerations, dust treatment is essential. Dust handling is also required with flash calciners which typically operate with a smaller particle size distribution feed material than do rotary kilns.

[0008] It is an object of the present invention to provide an alternative process for heating a lithium containing material.

SUMMARY OF INVENTION

[0009] With this object in view, the present invention provides - in one aspect - a process for heating a lithium containing material with reduced dust generation comprising:

(a) directing a lithium containing material to a heating vessel;

(b) heating the lithium containing material in the heating vessel with a controllable source of electromagnetic energy directed toward the lithium containing material to cause a phase transformation in said lithium containing material; and

(c) extracting a gas and dust from the heating vessel into a dust extraction system. [0010] In a second aspect, the present invention provides a system for heating a lithium containing material with reduced dust generation comprising:

(a) a heating vessel for holding a lithium containing material during heating; and

(b) a controllable source of electromagnetic energy to be directed toward the lithium containing material for heating the lithium containing material in the heating vessel to cause a phase transformation in said lithium containing material. wherein said heating vessel has a dust extraction system for extracting a gas and dust from said vessel.

[001 1] Microwave energy is preferred as the electromagnetic energy. However, other forms of electromagnetic energy - for example ultrasonics and infra-red energy - may be adopted. Heating of the lithium containing material to temperatures in a wide range of, for example 200 to 1300°C, is possible.

[0012] Advantageously, and in an embodiment which allows replacement of a conventional gas fired rotary kiln, the quantity of dust generated in the process and extracted with gas extracted into the gas extraction system is very small due to the relatively small gas flow or draft and pressure in comparison to the pressurisation caused by high volumes of gas and air in a gas fired rotary kiln. Where dust is recycled to the heating vessel, the equilibrium dust recycle may advantageously be less than 2% of the weight of lithium containing material directed to the heating vessel. This equilibrium dust recycle is substantially lower than is produced in a conventional rotary kiln fired by a hydrocarbon fuel, such as natural gas.

[0013] At such low equilibrium dust recycle levels, as achieved by the process and system described herein, it is possible to remove or limit requirement for cyclone and baghouse dust extraction and recycling arrangements, which add capital and operating cost as well as taking up often limited plot area. Further, it is possible to avoid complex pre-heating cyclone arrangements which are typical for conventional rotary kilns. However, any dust generated in the vessel during steps (a) and (b) of the abovedescribed process, for example due to the rotation of a rotary kiln, may be extracted and either recycled to the heating vessel or combined with a bulk flow of calcined lithium containing material. Such material would generally have a coarse particle size relative to dust. The complex dust extraction and recycling arrangements of conventional fossil fuel fired calciners may thus conveniently and economically be replaced with a gas extraction system including a small dust collector.

[0014] Advantageously, the process and system are well adapted to minimise clinker formation, because significantly less dust is generated by the process and system, and are suitable for more impure lithium containing material feeds than typically treated. Melting point of lithium containing materials tends to fall with increasing impurity content, especially of iron (though other impurities from gangue or main lithium mineral in content may be implicated including - without limitation - impurities selected from the group consisting of beryllium, potassium, sodium, rubidium, caesium, rare earth elements, magnesium, strontium, calcium, apatites and micaceous materials) so - where significant quantities of dust are formed as in conventional gas fired calcination processes - higher temperatures are required to maintain acceptable a-spodumene to p-spodumene conversion (conversion being synonymous with phase transformation), forming clinker and causing further problems in calcination and potentially downstream too. For example, the clinker formed may be of such size as to prevent proper calciner operation and thus require additional equipment, capital cost and operating cost. Further, it may be possible to treat lithium containing materials with higher impurity levels because clinker formation is less likely due to the significantly lower quantity of dust formed during the heating process, and thus a larger buffer between the operating temperature and the melting temperature is able to be maintained. For example, it may be possible to treat materials having greater than 1% Fe2Oa, for example a-spodumene containing greater than 1% FezOs. Impurity content is acceptable in the process provided that the melting temperature of the lithium containing material (including impurities) is higher than the conversion or phase transformation of the lithium containing material. A higher impurity level, greater than 10 wt% and estimated at 20 to 25 wt% upper limit, is therefore tolerable without unacceptable clinker formation. While the energy cost may be higher for high impurity lithium containing materials, this cost would be offset at higher lithium price points.

[0015] The lithium containing material may be a lithium mineral such as a pegmatite (including spodumene), lepidolite, amblygonite, jadarite or petalite. The lithium containing mineral may be a mica or clay type material. The lithium containing material may be run of mine (ROM) from any lithium resource, a concentrate beneficiated from ROM, or a rejected stream from a beneficiation circuit, such as the fine particle size slimes obtained while classifying ROM.

[0016] In a further embodiment, the lithium containing material may be the lithium containing dust generated in calcination, in particular as generated by calcination in a gas fired rotary kiln collected in a conventional treatment facility’s baghouse. Such dust is typically enriched in lithium compared to a lithium mineral subjected to heat treatment subjected to calcination in the heating vessel. For example, calcination in a gas fired rotary kiln of a spodumene ore grading 6wt% U2O may generate dust grading 6.5 wt% U2O.

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

[0018] Alternatively, or additionally, it may be necessary to involve a susceptor material or microwave absorbing material which is heated by microwave energy, allowing direct heating of adjacent lithium containing material through transfer of heat from susceptor material to lithium containing material. The distribution of susceptor material in the lithium containing material desirably allows homogenous heating. Additionally, heating may be fully or partially from the shell of the heating vessel, where including a susceptor material. For example, a silicon carbide shell or layer may be used as a microwave absorbing material, which then transfers heat to, and indirectly heats, the lithium containing material, for example a bed of lithium containing ore.

[0019] Alternatively, or additionally, susceptor material, desirably in particulate form, may be included within the lithium containing material, for example in the range of from <1 to 30% by mass. Desirably, the susceptor material is uniformly distributed in the lithium containing material to allow homogenous heating. Oxides are generally suitable and iron oxides (e.g. Fe20s or Fe3O4) may be used as a susceptor material. Iron is an impurity of spodumene ore but is not taken into solution to substantial extent during the leaching for recovery of a soluble lithium salt, further processed to lithium hydroxide or lithium carbonate. Rather, the iron remains in the leach residue and may be separated with the leach residue which may itself act as a source of susceptor material. Another suitable alternative susceptor material is carbon based. It will be understood that other susceptor materials than iron oxides and carbon based susceptors, such as graphite, charcoal, crushed char, activated carbon and carbides, and mixtures thereof can be used. Other suitable susceptor materials may include other inorganic compounds, particularly metal oxides, such as aluminium, magnesium or copper oxides and mixtures thereof. The susceptor material should be inert to the heating process.

[0020] Alternatively, the vessel may incorporate the susceptor material, for example included in a desirable refractory lining or lacing of the vessel. This allows indirect heating of the lithium containing material.

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

[0022] Where the lithium containing material is spodumene, though conversion of a- spodumene to p-spodumene is preferred, y-spodumene may be formed and this may still be acceptable as a feedstock for leaching. Further, the microwave heating process could result in two phase transformations, an example being conversion of a-spodumene to y- spodumene in a first phase transformation and the second from y-spodumene to p- spodumene in a second phase transformation.

[0023] It will be apparent from the above description that 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 coolers, either for gas and dust in the dust extraction system, or preferably at least for the bulk lithium containing material, the bulk having a greater particle size or being coarser than the dust. Such heat may be used for preheating and/or drying of feed lithium containing material to the heating vessel.

[0024] The process and system may be applied to calcination and/or roasting of the lithium containing material. A roasting process may involve fluxing of the lithium containing material with an acid or alkali to extract lithium values from the lithium containing ore. The process and system may also be employed where heat treatment forms part of a lithium extraction process.

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

[0026] In other embodiments, the vessel may include a fluid bed of lithium containing material for example in a flash kiln or a traditional fluid bed calciner; a vertical kiln such as a pot calciner; or a gas suspension calciner. The vessel may also be, for example, of batch design such as a tilting rotary furnace or related batch designs as would be well known to practitioners of the art of furnace design.

[0027] Conveniently, heat is recovered from one or more cooler(s), preferably a fluid bed cooler. The cooler would generally be provided at least to cool heat treated material, such as calcined lithium containing material - for example p-spodumene, prior to direction 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 used for purposes including pre-heating of the lithium containing material, conveniently including for drying the lithium containing material. Such recovered heat may be drawn through the heating vessel or may be drawn directly to pre-heating vessel(s) upstream of the vessel. Alternatively, the heating vessel may accept off-gas from the cooler(s).

[0028] The heating vessel may comprise a plurality of zones, conveniently having a first zone to pre-heat, and conveniently dry where required, the lithium containing material and a second zone for heating to cause the phase transformation in the lithium containing material. Radiation profiles are preferably different in the first and second zones. For example, the first zone has a radiation and temperature profile different to the radiation and temperature profile of the second zone, temperature in the second zone being generally higher than in the first zone.

[0029] In a further aspect, the present invention provides a process for heating of a lithium containing material comprising:

(a) directing a lithium containing material to a first heating vessel;

(b) heating the lithium containing material in the first heating vessel to cause a phase transformation in the lithium containing material while extracting a gas from the first heating vessel;

(c) heating lithium containing dust from the gas extracted from the first heating vessel with a controllable source of electromagnetic energy directed toward the lithium containing dust.

[0030] A system for implementing the above process involving heating lithium containing dust forms a still further aspect of the present invention.

[0031] In this embodiment, the first heating vessel is conveniently a rotary kiln, typically gas fired. Such rotary kilns are currently used for the calcination of lithium containing materials.

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

[0033] The process may thus be used in a hybrid system where a traditional gas-fired rotary kiln is retained and a microwave heating system is applied to the treatment of baghouse dust, collected from the gas-fired kiln’s off-gas. Since the dust does not undergo phase transformation or conversion it still requires heat treatment and the microwave unit may be used for this duty, thus allowing the gas-fired rotary kiln to operate without an accumulating dust burden.

[0034] The process and system may be operated on a batch or continuous basis. Skilled practitioners will appreciate that solid, liquid, and gas mass flows may be directed in various iterations to obtain the desired morphological change, in the lithium containing material, in particular a lithium containing ore. The process and system may be retrofitted allowing conventional calcination kilns to be heated using electromagnetic energy.

[0035] Use of the process and system for heating lithium containing materials as described above significantly reduces dust formation and requirements for extensive and/or complicated dust handling equipment. At the same time, lithium materials with higher impurity levels may potentially be handled. Conversion of materials from one microstructure to another, such as the conversion of a-spodumene to [3-spodumene, is also achievable to the same extent as with conventional calcination processes. Roasting processes may also be conducted with the same efficiency as conventional roasting processes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further features of the process and system for heating a lithium containing material of the present invention are more fully described in the following description of non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0037] Figure 1 is a: schematic of a system for heating a lithium containing material according to one embodiment of the present invention.

[0038] Figure 2 is a: schematic of a system for heating a lithium containing material similar to that shown in Figure 1 and showing the relationship between source of electromagnetic energy and vessel for holding the lithium containing material. [0039] Figure 3 is a schematic of a tilting rotary furnace suitable for batch heating of lithium containing material according to another embodiment of the present invention.

[0040] Figure 4 is a schematic showing the process flow for a hybrid system suitable for reducing the fines burden on a traditional gas-fired kiln by the microwave heating of dust from a baghouse.

[0041 ] Figure 5 is a schematic of a system for utilising the off-gas heat from a process material cooler to dry and pre-heat the feed ore. Embodiment (a) directs the off-gas directly to the pre-heating equipment. Embodiment (b) directs the off-gas to the microwave calciner, which in turn directs the off-gas to the drying and pre-heating equipment.

[0042] Figure 6 is a schematic of a system for a single microwave calcination kiln containing zones dedicated to different duties such as a drying and pre-heating zone with an adjacent calcining hot zone.

[0043] DESCRIPTION OF PREFERRED EMBODIMENTS

[0044] Referring to Figs. 1 and 2, there is shown a system 10 for heating of a lithium containing material, here a concentrate feed of a-spodumene - a lithium aluminosilicate mineral - for the purposes of a heat treatment, typically called calcination. Calcination causes the a-spodumene to be converted to p-spodumene to be leached for extraction of lithium in the form of lithium hydroxide or lithium carbonate for use in lithium ion batteries. It will be understood that the present invention is not limited to calcination of a- spodumene ore and other lithium ores, minerals and lithium containing materials may be calcined in system 10.

[0045] Heating system 10 comprises a heating vessel 1 for holding a bed of the a- spodumene ore for calcination; a controllable source of electromagnetic energy 5 to be directed by waveguide(s) 8 toward the a-spodumene bed; and a dust extraction or dust recycling system 6 for extracting dust and gas and recycling any dust generated in the vessel 1 . In some embodiments, as described below, dust recycling is omitted.

[0046] In this embodiment, vessel 1 is a rotary kiln in the form of a tube with riding rings 4 though it will be appreciated that other forms of heating vessel may be used. The advantage of a rotary kiln arrangement is that it is a familiar design to those skilled in the art of lithium extraction.

[0047] Rotary kiln 1 has a metal shell with an insulation or refractory lining or lacing to retain heat and also to protect the metal shell from the hot a-spodumene. Outlet port(s) and ducts, or duct portions, for delivering gas to the dust extraction or dust recycling system 6, if metallic, may also be insulated to allow passage of hot gas from rotary kiln 1 . The refractory lining is preferably transparent to microwaves, for example being of alumina or alumina silica or a microwave transparent oxide. Such a refractory lining should not interfere with the microwave heating process.

[0048] Rotary kiln 1 may, in a further embodiment, be constructed of a steel alloy only, or be constructed of a metal or metal alloy with an inner lining of a microwave absorbing material such as silicon carbide.

[0049] Rotary kiln 1 may, in a further embodiment, also be constructed entirely of a microwave absorbing material such as silicon carbide, with adequate thermal protection surrounding the kiln. The kiln 1 may also be provided with a radiation shield, such as the wide range of available conductive metals and alloys used for this purpose in the microwave metallurgical processing art.

[0050] The rotary kiln 1 , which is rotated by a suitable driving motor arrangement (not shown) is disposed at an angle to the horizontal to assist gravity flow of a-spodumene through it from feeding 2 at one end to discharge 3 at the other end. Rotary kiln 1 has a single chamber, not being partitioned, which would obstruct the desired downward flow of material from feeding 2 to discharge 3.

[0051] The rotary kiln 1 , other than its source of heating, is operated in a manner as known in the art of lithium mineral calcination. The a-spodumene concentrate feed may have a relatively high level of impurities, for example grading between 2 and 4% iron in the form of iron oxides and silicates. Other impurities are also likely to be present. For purposes of example, the impurity content of the a-spodumene concentrate feed would be about 10wt%.

[0052] The discharge material 3, in the form of more leachable p-spodumene, is directed to a cooler for cooling from calcination temperature to a temperature approaching that suitable for an acid roasting stage. [0053] Rotary kiln 1 allows heating of the a-spodumene feed by microwave energy which is delivered from microwave generation device 5 via waveguide(s) 8 which transfer power from the microwave generation device 5 to the a-spodumene feed 2. As heating to 1000 to 1250°C is necessary to achieve conversion of a-spodumene to [3-spodumene, microwave generation device 5 and rotary kiln 1 are configured with radiation profile and power output to enable heating to this temperature. The inclusion of a refractory lining within the rotary kiln 1 also takes account of this elevated temperature range. Microwave heating is at ambient pressure, with only a low air draft, and not an elevated pressure typical of prior art calciners which are pressurised by substantial flows of gas and air.

[0054] Microwave energy may be directed from an industrial scale microwave generation device 5 through waveguides 8 at frequencies as provided under Industrial, Scientific and Medical (ISM) standards under International treaties, for example 896 MHz, 915 MHz and 2450±50 MHz. However, other embodiments may employ microwave energy throughout its frequency range, 0.3 to 300 GHz. The microwave energy may be pulsed and may, for example, deliver energy at 20 kW or more, or 50 kW or more. Use of pulsed microwave energy is expected to be more energy efficient.

[0055] a-spodumene alone may not be heated by microwave energy, at least at relatively low temperature. One potential reason is that - as a silicate rather than an oxide and likely including some transparent gangue minerals as well - a-spodumene is transparent to microwave energy at lower temperatures, below about 570-660°C dependent on microwave power input. This problem may be addressed by use of a susceptor material, such as an oxide, which absorbs and is heated by microwave energy.

[0056] In one embodiment, particulate susceptor material, for example an iron oxide (e.g. Fe20s or Fe3O4) may be included within the a-spodumene concentrate feed 2 in the range of from <1 to 30% by mass. The distribution of susceptor material in lithium containing material is desirably uniform to allow homogenous heating. The iron oxide susceptor is heated by microwave energy and the heat from heated iron oxide particles is directly transferred to the a-spodumene to allow conversion to [3-spodumene in a direct heating process.

[0057] As to whether iron introduced, as a susceptor, may influence downstream processing steps, this is unlikely to be problematic. Lithium extraction processes typically involve a leaching step, such as the acid roasting process described below. In such leaching steps where neutralisation is carried out with agents such as limestone or lime, iron is not taken into solution to substantial extent during the leaching. Rather, the iron remains in the leach residue and may be separated with the leach residue. Indeed, it may be possible for a portion of such leach residue to be recycled for use as a susceptor during microwave heating of a-spodumene. The same is true of carbon based susceptors which may be separated by methods such as filtration or decantation or, if present in a leach residue to be directed as a construction material, may even be beneficial.

[0058] Alternatively, the rotary kiln 1 may incorporate the susceptor material, for example in the working layer of the refractory lining or lacing of the walls of rotary kiln 1 as described above. The refractory lined or laced rotary kiln 1 is then amenable to direct heating by microwave energy. This allows indirect heating of for example a-spodumene which may be employed in combination with direct microwave heating as described above.

[0059] Whilst some quantity of dust is generated during calcination in rotary kiln 1 , due to tumbling motion of a-spodumene and p-spodumene as rotary kiln 1 is rotated, the quantity of dust is very small, for example providing an equilibrium dust recycle of less than 2% of the weight of lithium containing material directed to the rotary kiln 1 . This equilibrium dust recycle is substantially lower than is produced in a conventional rotary kiln fired by a hydrocarbon fuel, such as natural gas. At such low equilibrium dust recycle levels, requirement for cyclone and baghouse dust extraction and recycling arrangements, which add capital and operating cost as well as taking up often limited plot area, is removed. Such dust extraction and recycling arrangements may be replaced with a small dust collector 6 extracting dust from the feed end of rotary kiln 1 through line 61 . Collected dust is recycled through line 7 to be reintroduced to rotary kiln 1 with the a- spodumene feed 2. Further, with heating system 1 , it is possible to avoid complex preheating cyclone arrangements which are typical for conventional rotary kilns.

[0060] Further, the calcination system 10 is well adapted to minimise clinker formation allowing processing of more impure lithium containing materials than typically treated. Melting point of lithium containing materials tends to fall with increasing impurity content, especially of iron so - where significant quantities of dust are formed as in conventional calcination processes - dust particles tend to indirectly cause clinker formation because of a higher temperature requirement to achieve acceptable a-spodumene to - spodumene conversion causing further problems in calcination and potentially downstream too.

[0061] The process and system may be applied to calcination and/or roasting of the lithium containing material. A roasting process may for example involve roasting of cooled P-spodumene product 3 from the calciner 1 with concentrated sulphuric acid to extract lithium values. The roaster, for the process, is conveniently also provided with a microwave generation device and waveguides to direct microwave energy to the p- spodumene under the same or different conditions than used for calciner 1 . For example, heating rates may be different between roaster and calciner 1 .

[0062] The process and system may be operated on a batch or continuous basis. Figure 3 shows a batch heating system 100 for an a-spodumene concentrate feed according to another embodiment of the invention in which a tilting rotary furnace 101 is used for batch heating of a-spodumene. Tilting rotary furnace 101 would be substantially shorter than a rotary tube kiln 1 or a rotary tube kiln as used in conventional calcination practice. Microwave energy is directed at a-spodumene from microwave generation device 5 through waveguide(s) 8 as described above. Rotation mechanism 107 allows rotation of the tilting rotary furnace 101 which can be tilted forward to discharge p- spodumene into a cooler at the end of a predetermined calcination time.

[0063] Figure 4 is a schematic of a process 200 that utilises microwave heating to treat dust only from a conventional gas-fired calciner 3 used to calcine a bulk a- spodumene concentrate feed 6 preheated in preheater 17. Dust 31 is collected in a dust extraction system in the form of baghouse 1 and diverted 31 a to microwave calciner 2, of the same design as shown in Figure 1 and described above. The baghouse 1 may be of conventional design as known in the art of lithium mineral calcination. This diversion of dust 31 , 31 a to microwave calcining in microwave calciner 2 replaces a conventional recycle of the dust to the gas-fired calciner 3. After any conversion or phase transformation of the dust in microwave calciner 2, the heat treated dust 16 is directed to the cooler(s) 4, where the solid streams (coarse calcined lithium containing material 14 and dust 16) are consolidated into stream 24 for downstream processing, for example by acid roasting or other leaching schemes as known in the art of lithium extraction. In this embodiment, no pre-heating or drying of the feed to the microwave calciner 2 is required. However, in one embodiment of process 200 as shown, off-gas 5 from the cooler(s) 4 is directed to microwave calciner 2 for pre-heating the dust 31 a either within the calciner, in some embodiments, or to a small pre-heater located before the microwave calciner 2. In another embodiment, pre-heating is carried out by an alternative heating method without use of off-gas 5 in microwave calciner 2. This use of recovered heat from cooler(s) 4, conveniently through the agency of off-gas 5, improves the energy efficiency of process 200. Recovered heat from cooler(s) 4 could also be used in preheater 17 dependent on exergy analysis and available heat.

[0064] Figure 5 is a schematic of process 300 demonstrating two embodiments of a scheme wherein off-gas from a fluidised-bed cooler 4 (cooling the [3- or y-spodumene calcine 26 from microwave calciner 2) is used to dry and pre-heat the lithium containing material in the form of an a-spodumene concentrate feed 6. Pre-heating may increase the temperature of the a-spodumene concentrate feed 6 from ambient to 200°C or higher depending on the ability of the pre-heating equipment 17 to recover energy. In this embodiment (a) of process 300, off-gas 15 including dust and gas is directed to drying and pre-heating equipment 17 directly, bypassing the microwave calciner 2. This embodiment (a) may be selected if the energy recovery from the fluidised-bed cooler 4 is exceptionally efficient. Another embodiment (b) involves directing off-gas 15A from fluidised bed cooler 4 (cooling the p- or y-spodumene calcine 26 from microwave calciner 2) to microwave calciner 2 and then in stream 15B to drying and pre-heating equipment 17. This embodiment (b) may be selected if more pre-heating is required in drying and pre-heating equipment 17 compared to embodiment (a). Calcine 24 is then directed to downstream processing, for example by acid roasting or other leaching schemes as known in the art of lithium extraction.

[0065] Figure 6 is a schematic of a process 400 suitable for microwave calcination wherein a single microwave calciner 1 is utilised for drying, pre-heating and calcination. Calciner 1 is divided into temperature zones 1 a and 1 b by the utilisation of different microwave radiation profiles in the two zones, this in turn providing different temperature profiles for the two zones 1 a and 1 b. A first zone 1a of calciner 1 is a cooler zone associated with preheating and drying and a second zone 1 b of calciner 1 is a hot zone - with higher temperature than associated with preheating and drying - for conversion of lithium containing material, for example from a-spodumene to [3-spodumene. The temperature zoned-calciner 1 may be constructed with various materials that fulfil different purposes. For example, the drying and pre-heating zone 1 a may have an inner shell layer of silicon carbide while the hot zone may be constructed with an alloy such as steel only. [0066] The first drying and pre-heating zone 1 a in microwave calciner 1 receives lithium containing material in the form of a-spodumene concentrate feed 6, which is resident in this zone for the prerequisite period of time to dry the material (remove substantially all moisture), dependent on the moisture level and the nature of the lithium containing material with dust 34 being collected in dust extraction system 3. For example, a lithium containing material having poor heat conduction would require longer residence time than a lithium containing material having relatively higher heat conductivity. Dust 33 from dust extraction system 3 is also returned to the microwave calciner 1 . Once dry and pre-heated the a-spodumene concentrate feed 6 is subjected to calcination in the second hot zone 1 b, which is at a temperature required for a phase transformation or conversion from a- spodumene to p-spodumene, which occurs after an ore-specific residence period. Cooler 4 for the calcine ([3-spodumene) 26 and any associated gas 150 may then be incorporated in a continuous flow system wherein off-gas from the cooler 4 is utilised for energy recovery. Such energy is conveniently recovered heat which may be used for drying and preheating, conveniently in zone 1 a, or other uses within the process and system. This reduces the carbon footprint of calcination which has been a problem with prior arrangements. Calcine 24 is then directed to downstream processing, for example by acid roasting or other leaching schemes as known in the art of lithium extraction.

[0067] Use of the process and system for heating lithium containing materials as described above significantly reduces dust formation and requirements for extensive and/or complicated dust handling equipment which may take up significant plot area. This potentially allows calcination processes to be conducted at or close to a minesite rather than at a distant processing plant, allowing potential for further savings in processing plant area and transportation costs. Heat recovery at the cooler(s) also improves energy efficiency and reduces carbon footprint.

[0068] At the same time, lithium materials with higher impurity levels (up to 20-25wt% impurities) may potentially be handled. Conversion of materials from one microstructure to another, such as the conversion of a-spodumene to p-spodumene, is also achievable to the same extent as with conventional calcination processes. Roasting processes may also be conducted with the same efficiency as with conventional roasting processes. [0069] Modifications and variations to the process and system for heating a lithium containing material described in this specification may be apparent to skilled readers. Such modifications and variations are deemed within the scope of the present invention.

[0070] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.