A PROCESS AND SYSTEM FOR HEATING A LITHIUM CONTAINING MATERIAL

Abstract

A process for heat treating 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 gas and dust from the heating vessel into a gas extraction system. A system for the heating the lithium containing material is also disclosed. The process and system allow higher impurity lithium materials to be treated while reducing the burden of an accumulating dust load during calcination operations.

Claims

1-43. (canceled)

44. A process for heating a lithium containing material with reduced dust generation comprising: (a) directing a lithium containing material to form a bed of the lithium containing material in a heating vessel; (b) heating the bed of lithium containing material in the heating vessel with a controllable source of microwave energy directed toward the lithium containing material to cause a solid phase transformation in said lithium containing material; (c) discharging said lithium containing material from the heating vessel; and (d) extracting gas and dust from the heating vessel into a dust extraction system, wherein the dust extraction system enables recycling of dust to the heating vessel, an equilibrium dust recycle being less than 2% of the weight of lithium containing material feed directed to the heating vessel; and wherein gas and dust extracted from the heating vessel is cooled in a cooler, heat being recovered from the cooler for heating the lithium containing material feed directed to the heating vessel.

45. The process of claim 44, wherein said lithium containing material contains greater than 10 wt % impurities, said impurities including components from the group consisting of beryllium, potassium, sodium, rubidium, caesium, rare earth elements, magnesium, strontium, calcium, apatites and micaceous materials.

46. The process of claim 45, wherein said lithium containing material contains up to 20 to 25 wt % impurities.

47. The process of claim 44, wherein said lithium containing material is a lithium mineral selected from the group consisting of a pegmatite (including spodumene), lepidolite, amblygonite, jadarite or petalite.

48. The process of claim 47, wherein the lithium containing material is selected from the group consisting of run of mine (ROM), a concentrate beneficiated from ROM, or a rejected stream from a beneficiation circuit.

49. The process of claim 44, wherein the lithium containing material feed includes the lithium containing dust generated by calcination in a gas fired rotary kiln.

50. The process of claim 49, wherein said dust is enriched in lithium compared to a lithium mineral subjected to calcination in said heating vessel.

51. The process of claim 44, wherein the lithium containing material is pre-heated to a first predetermined temperature range for removal of moisture contained in the lithium material.

52. The process of claim 51, wherein said lithium containing material is heated by heat recovered from gas extracted from the heating vessel in a preheating vessel.

53. The process of claim 51, wherein said heating vessel includes a susceptor material which is heated by microwave energy, allowing direct heating of adjacent lithium containing material through transfer of heat from susceptor to lithium containing material.

54. The process of claim 53, wherein said susceptor material is distributed in the lithium containing material in the vessel.

55. The process of claim 54, wherein a distribution of said susceptor material in said lithium containing material allows homogenous heating thereof.

56. The process of claim 53, wherein said vessel has a shell, said shell including a susceptor material to enable full or partial heating from the shell of the vessel.

57. The process of claim 55, wherein said susceptor material is in particulate form and included within the lithium containing material in the range of from <1 to 30% by mass.

58. The process of claim 44, wherein said calcined lithium containing material is leached and a leach residue is used as the susceptor material.

59. The process of claim 57, wherein said susceptor material is selected from the group consisting of graphite, charcoal, crushed char, iron oxides, activated carbon, carbides and mixtures thereof.

60. The process of claim 59, wherein said lithium containing material is directly or indirectly heated by microwave energy to temperature higher than 900 C.

61. The process of claim 60, wherein said lithium containing material is heated by microwave energy to a temperature in the range 1000 C. to 1250C.

62. The process of claim 61, wherein said lithium containing material is -spodumene and heating of said -spodumene in calcination results in two phase transformations, a first phase transformation being from -spodumene to -spodumene and a second phase transformation being from -spodumene to -spodumene.

63. The process of claim 58, wherein said heating comprises calcination and further comprises a roasting process involving fluxing of -spodumene with an acid or alkali to extract lithium values from the -spodumene.

64. The process of claim 60, wherein said recovered heat is used for pre-heating the lithium containing material upstream of the heating vessel.

65. The process of claim 60, wherein said recovered heat is used for drying the lithium containing material; and wherein said recovered heat is drawn through the heating vessel to at least one pre-heating vessel upstream of the heating vessel.

66. The process of claim 60, wherein the heating vessel accepts off-gas from the cooler.

67. The process of claim 60, wherein said lithium containing mineral is directed through a plurality of zones in the heating vessel, said lithium containing material being preheated in a first zone and said lithium containing material being heated in a second zone of the heating vessel to cause the phase transformation in the lithium containing material; and wherein said controllable source of microwave energy is controlled so that the first zone has a temperature profile different to the temperature profile of said second zone, temperature in the second zone being generally higher than in said first zone.

68. A process for heating of a lithium containing material comprising: (a) directing a lithium containing material to form a bed in a rotary gas fired kiln; (b) heating the bed of lithium containing material in the rotary gas fired kiln to cause a solid phase transformation in the lithium containing material while extracting a gas from the heating vessel in a dust separation system coupled to the first heating vessel; (c) heating lithium containing dust recovered in the dust separation system from the gas extracted from the rotary gas fired kiln with a controllable source of microwave energy directed toward the lithium containing dust in a second heating vessel, wherein heat treated dust from the second heating vessel is directed to a cooler and downward processing steps including leaching for recovery of lithium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] 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:

[0045] FIG. 1 is a: schematic of a system for heating a lithium containing material according to one embodiment of the present invention.

[0046] FIG. 2 is a: schematic of a system for heating a lithium containing material similar to that shown in FIG. 1 and showing the relationship between source of electromagnetic energy and vessel for holding the lithium containing material.

[0047] FIG. 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.

[0048] FIG. 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.

[0049] FIG. 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.

[0050] FIG. 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.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0051] Referring to FIGS. 1 and 2, there is shown a system 10 for heating of a lithium containing material, here a concentrate feed of -spodumenea lithium aluminosilicate mineralfor the purposes of a heat treatment, typically called calcination. Calcination causes the -spodumene to be converted to -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 -spodumene ore and other lithium ores, minerals and lithium containing materials may be calcined in system 10.

[0052] Heating system 10 comprises a heating vessel 1 for holding a bed of the -spodumene ore for calcination; a controllable source of electromagnetic energy 5 to be directed by waveguide(s) 8 toward the -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.

[0053] 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.

[0054] 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 -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.

[0055] 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.

[0056] 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.

[0057] 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 -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.

[0058] 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 -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 -spodumene concentrate feed would be about 10wt %.

[0059] The discharge material 3, in the form of more leachable -spodumene, is directed to a cooler for cooling from calcination temperature to a temperature approaching that suitable for an acid roasting stage.

[0060] Rotary kiln 1 allows heating of the -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 -spodumene feed 2. As heating to 1000 to 1250 C. is necessary to achieve conversion of -spodumene to -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.

[0061] 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 245050 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.

[0062] -spodumene alone may not be heated by microwave energy, at least at relatively low temperature. One potential reason is thatas a silicate rather than an oxide and likely including some transparent gangue minerals as well-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.

[0063] In one embodiment, particulate susceptor material, for example an iron oxide (e.g. Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4) may be included within the -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 -spodumene to allow conversion to -spodumene in a direct heating process.

[0064] 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 -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.

[0065] 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 -spodumene which may be employed in combination with direct microwave heating as described above.

[0066] Whilst some quantity of dust is generated during calcination in rotary kiln 1, due to tumbling motion of -spodumene and -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 -spodumene feed 2. Further, with heating system 1, it is possible to avoid complex pre-heating cyclone arrangements which are typical for conventional rotary kilns.

[0067] 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 sowhere significant quantities of dust are formed as in conventional calcination processesdust particles tend to indirectly cause clinker formation because of a higher temperature requirement to achieve acceptable -spodumene to -spodumene conversion causing further problems in calcination and potentially downstream too.

[0068] 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 -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 -spodumene under the same or different conditions than used for calciner 1. For example, heating rates may be different between roaster and calciner 1.

[0069] The process and system may be operated on a batch or continuous basis. FIG. 3 shows a batch heating system 100 for an -spodumene concentrate feed according to another embodiment of the invention in which a tilting rotary furnace 101 is used for batch heating of -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 -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 -spodumene into a cooler at the end of a predetermined calcination time.

[0070] FIG. 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 -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 31a to microwave calciner 2, of the same design as shown in FIG. 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, 31a 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 31a 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.

[0071] FIG. 5 is a schematic of process 300 demonstrating two embodiments of a scheme wherein off-gas from a fluidised-bed cooler 4 (cooling the - or -spodumene calcine 26 from microwave calciner 2) is used to dry and pre-heat the lithium containing material in the form of an -spodumene concentrate feed 6. Pre-heating may increase the temperature of the -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 - or -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.

[0072] FIG. 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 1a and 1b by the utilisation of different microwave radiation profiles in the two zones, this in turn providing different temperature profiles for the two zones 1a and 1b. A first zone 1a of calciner 1 is a cooler zone associated with preheating and drying and a second zone 1b of calciner 1 is a hot zonewith higher temperature than associated with preheating and dryingfor conversion of lithium containing material, for example from -spodumene to -spodumene. The temperature zoned-calciner 1 may be constructed with various materials that fulfil different purposes. For example, the drying and pre-heating zone 1a may have an inner shell layer of silicon carbide while the hot zone may be constructed with an alloy such as steel only.

[0073] The first drying and pre-heating zone 1a in microwave calciner 1 receives lithium containing material in the form of -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 -spodumene concentrate feed 6 is subjected to calcination in the second hot zone 1b, which is at a temperature required for a phase transformation or conversion from -spodumene to -spodumene, which occurs after an ore-specific residence period. Cooler 4 for the calcine (-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 1a, 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.

[0074] 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.

[0075] 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 -spodumene to -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.

[0076] 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.

[0077] 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.