LITHIUM EXTRACTION PROCESS AND APPARATUS

Abstract

A method of extracting lithium from a lithium-bearing material including:

(i) mixing the lithium-bearing material, gypsum, a sulfur-containing material, and a calcium-containing material and forming a feed mixture having a moisture content of at least 20 wt %;

(ii) drying the feed mixture to form a dried mixture having a moisture content of less than 20 wt %;

(iii)roasting the dried mixture and forming a roasted mixture including a water-soluble lithium compound; and

(iv) leaching lithium from the water-soluble lithium compound and forming a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound.

Claims

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

2. A method of extracting lithium from a lithium-bearing material including: (i) mixing the lithium-bearing material, gypsum, a sulfur-containing material, and a calcium-containing material and forming a feed mixture having a moisture content of at least 20 wt %; (ii) drying the feed mixture to form a dried mixture having a moisture content of less than 20 wt %; (iii)supplying the dried mixture to a roaster; (iv) roasting the dried mixture in the roaster and forming a roasted mixture including a water-soluble lithium compound; (v) supplying the water-soluble lithium compound to a leach tank; (vi) supplying an aqueous solution to the leach tank; and (vii)leaching lithium from the water-soluble lithium compound and forming a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound in the leach tank.

3. The method according to claim 1, wherein the sulfur-containing material is either or a combination of an alkali metal sulfate and elemental sulfur.

4. The method according to claim 3, wherein the alkali metal sulfate is either or a combination of sodium sulfate and potassium sulfate.

5. The method according to claim 1, wherein the calcium-containing material is either or a combination of calcium carbonate and lime.

6. The method according to claim 1, wherein the mixing step involves mixing lithium-bearing material having a water content ranging from 20-60 wt % with the gypsum, the sulfur-containing material, and the calcium-containing material.

7. The method according to claim 1, wherein the mixing step involves adding an aqueous solution to a lithium-bearing material having a water content of less than 20 wt % to form the wet lithium-bearing material.

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

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

10. The method according to claim 1, wherein the drying step includes processing the mixture into granules having a mean diameter less than 30 mm.

11. The method according to claim 1, wherein the roasting step is performed at a roasting temperature ranging from 800-1,000° C. for a roasting time period ranging from 15 minutes to 2 hours.

12. The method according to claim 1, including a step of reducing the particle size of the water-soluble lithium compound to 1,000-3,000 μm (1-3 mm).

13. The method according to claim 1, wherein the leaching step includes adding an aqueous solution to the roasted mixture to form a slurry having a solids content ranging from 20-50 wt %.

14. The method according to claim 13, wherein the aqueous solution used in the leaching step has a pH ranging from 6.5-7.5.

15. The method according to claim 13, including filtering the slurry to generate a lithium-containing leachate having a lithium concentration of at least 2,000 ppm.

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

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

18. An apparatus for extracting lithium from a lithium-bearing material comprising: (i) a mixer configured to receive and mix lithium-bearing material with gypsum, a sulfur-containing material, and a calcium-containing material and form a feed mixture having a moisture content of at least 20 wt %; (ii) a dryer configured to dry the feed mixture and form a dried mixture having a moisture content of less than 20 wt %; (iii)a roaster configured to receive and roast the dried mixture and form a roasted mixture including a water-soluble lithium compound; and (iv) a leach tank configured to form a lithium-containing leachate from the water-soluble lithium compound using an aqueous solution.

19. The apparatus according to claim 18, including an evaporator to evaporate at least part of the leachate from the leach tank to form a concentrated leachate having a lithium concentration of at least 3,000 ppm.

20. The apparatus according to claim 18, wherein the roaster is connected to the mixer to recycle alkali metal sulfate in the roaster to the mixer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0134] The invention is hereinafter described by way of example only with reference to the accompanying drawings, wherein:

[0135] FIG. 1 is a process flow diagram according to one form of the invention.

[0136] FIG. 2 is a process flow diagram illustrating the process of forming the granulated mixture according to one form of the invention.

[0137] FIG. 3 is a process flow diagram illustrating the process of forming lithium carbonate according to one form of the invention.

DETAILED DESCRIPTION

[0138] The applicant has carried out research and development work on a known method of extracting lithium from lithium-bearing deposit. The known method includes roasting the deposit with calcium carbonate and gypsum and acid leaching the roasted mixture to extract the lithium.

[0139] Disadvantages of this process include the use of externally sourced reagents including environmentally hazardous acid. In addition, acid leaching may not be adapted to extract lithium from material containing low concentrations of lithium because of the relatively unselective nature of acid leaching compared to water leaching.

[0140] The applicant has discovered that a gypsum/sulfur-containing material mixture can reduce operating costs without losing the efficiency associated with traditional calcium carbonate: gypsum recipes in generating water-soluble lithium compounds. The applicant also discovered that a gypsum/alkali metal sulfate mixture provides a more efficient roasting process compared to a mixture that excludes gypsum.

[0141] The applicant also realised that boric acid plants produce sodium sulfate as a waste product which can be routed to the apparatus of the present invention to reduce the amount of sodium sulfate that have to be purchased or synthesised for the present invention.

[0142] The applicant further realised that the roasting step may produce in-situ sodium sulfate which can be routed to the apparatus of the present invention to further reduce the amount of sodium sulfate that have to be purchased or synthesised for the present invention.

[0143] As a result of these realisations, the applicant has developed an apparatus for extracting lithium from a lithium-bearing material in accordance with the present invention. The apparatus 10 as shown in FIG. 1 comprises a mixer in the form of an Eirich mixer 12, a roaster in the form of calciner 14, and a leach tank 16. It can be appreciated that the Eirich mixer can be replaced with any high intensity mixer.

[0144] The apparatus 10 is located near or connected to a source of lithium-bearing material and is configured to receive this material. Examples of suitable lithium-bearing material sources include a tailings pond of a borates mine or clay formations.

[0145] Suitably, the apparatus 10 is also located near or connected to a source of an alkali metal sulfate such as sodium sulfate.

[0146] The sodium sulfate and lithium-bearing material may be obtained from the same source. For example, the apparatus 10 may be connected to the tailings pond of a boric acid processing plant to receive the lithium-bearing gangue and connected to a sodium sulfate-containing effluent stream of the same plant to receive sodium sulfate.

[0147] The apparatus may include a hopper 18 to hold the lithium-bearing gangue. The gangue may be dry or wet. In this specification, wet gangue has a moisture content of at least 20 wt %.

[0148] When processing dry gangue, the hopper 18 is located over a vibrating pan (or screw) that feeds the dry gangue into an impact mill to comminute the gangue. The impact mill in turn feeds the comminuted gangue onto a vibratory screen, preferably having a 40 mesh sieve size, that is positioned over hopper 18.

[0149] The hopper 18 stores the classified gangue before it is fed into the mixer 12. In this embodiment, water may be added to increase the moisture content of the gangue to at least 20 wt %.

[0150] When handling wet gangue, the gangue from hopper 18 is transported directly to the mixer 12.

[0151] The other feed material including a calcium-containing material such as calcium carbonate and gypsum can also be stored in separate bins before being fed into the mixer 12.

[0152] The mixer 12 is configured to receive inputs of lithium-bearing material, a sulfur-containing material such as an alkali metal sulfate or elemental sulfur, gypsum and a calcium-containing material such as calcium carbonate and mix these materials in specific proportions according to a predetermined roasting recipe, for example the recipes described in Tables 1 and 2 below, to form a homogeneous mixture which is subsequently granulated. The mixer 12 may include or be connected to a dryer to reduce the moisture content of the mixed material and form the granulated mixture.

[0153] A product outlet of the mixer 12 discharges the granulated mixture into a discharge bin 42 for delivery to the calciner 14. In another embodiment, the granulated mixture is transported by some conveying system (belt conveyor, screw conveyor, pneumatic conveying, etc) from the mixer 12 to the kiln.

[0154] Alternatively, the mixer may be connected to a granulator for receiving and granulating the mixed material from the mixer 12.

[0155] The granulator may include a dryer to dry the granulated mixture.

[0156] FIG. 2 provides a process flow diagram illustrating an apparatus for forming the granulated mixture. The apparatus comprises a mixer, in the form of an Eirich mixer 12, hopper 18 for storing lithium bearing material, bin 20 for storing limestone (calcium carbonate), and bin 38 for storing gypsum.

[0157] Reagents including sulfur containing material such as elemental sulfur or an alkali metal sulfate are stored in additional bins or silos before being introduced into the mixer.

[0158] When mixing wet feed material including lithium-bearing gangue having a moisture content of at least 20 wt %, glauber salts and glaserite formed during the crystallization step may be pumped from the process into the mixer.

[0159] Dust collector 39 controls dust levels during the mixing process and discharge bin 42 receives the granulated mixture.

[0160] The Eirich mixer 12 is configured via a conveyor system to receive lithium-bearing material in the form of gangue from a tailings pond of a borates mine or clay formations from hopper 18, limestone from bin 20 and gypsum from bin 38. Typically, feed material comprises wet gangue having a moisture content ranging from 40-60 wt %, −200 mesh dry limestone and −200 mesh gypsum. Elemental sulfur or an alkali metal sulfate is delivered into the mixer 12 via a separate bin/silo.

[0161] The gangue, limestone, gypsum and the sulfur containing material are mixed under high shear intensity in the Eirich mixer for a minimum of 10 minutes, typically 15-45 minutes to form a homogeneous mixture.

[0162] The apparatus further includes a heater/dryer 44 to reduce the moisture content of the mixed material to about 10 wt % or less.

[0163] Under the appropriate conditions, a granulated mixture comprising homogenous pellets ranging from 5-20 mm and having a moisture content between 5-10% is formed. In some embodiments, the mixer may be connected to a granulator to granulate the mixed material.

[0164] The granulated mixture is discharged into discharge bin 42 and delivered to a calciner 14. In a continuous process, the granulated mixture is discharged onto a conveyor and delivered to the calciner 14.

[0165] The calciner 14 converts the lithium-bearing material into a water-soluble lithium compound such as lithium sulfate.

[0166] A product outlet of the calciner 14 is connected to a feed inlet of a leach tank 16 to discharge the calcined material into the leach tank. In some embodiments, the calciner 14 may be connected to a cooler to cool the roasted mixture before it is delivered to the leach tank 16. In these embodiments, the cooler may be connected to a crusher to reduce the particle size of the roasted mixture to 1,000-5,000 μm (1-5 mm).

[0167] The crushed compound may be stored in a surge bin to hold the roasted mixture before it is directed to the leach tank 16.

[0168] The leach tank 16 is further connected to a water supply to receive water for the leaching step.

[0169] The leach tank 16 is configured to enable countercurrent flow of the lithium-bearing feed material and water during leaching of the water-soluble lithium compound to form a lithium-containing leachate.

[0170] The applicant discovered that countercurrent flow of the lithium bearing material and water during the leaching process, along with a number of operating parameters, optimised the extraction of lithium from the lithium bearing material. However, co-current leaching may also be performed.

[0171] The leach tank 16 may be temperature controlled to enable the leaching process to be performed at a predetermined temperature.

[0172] The leach tank 16 may include a filter 22 to remove any undissolved solids 23 formed during the leaching process. Other suitable solid-liquid separation techniques may be used to remove undissolved solids formed during the leaching process, including centrifugation.

[0173] The leach tank 16 includes a product outlet which is connected to an inlet of evaporator 24.

[0174] A surge tank may be connected to the leach tank 16 to hold the filtered leachate before it is directed to the evaporator 24.

[0175] The evaporator 24 receives and concentrates the leachate from the surge tank or directly from the leach tank. Impurities such as calcite, thenardite, glaserite, glauberite, and anhydrite may precipitate during the evaporation process. The leach tank 16 may include another filter 22 to remove the precipitates from the leachate to form a concentrated leachate 28 which can be directed downstream for further processing or stored for later use.

[0176] In operation, the apparatus according to the invention is connected to a borates processing plant 26. Feed material comprising lithium-containing waste material, for example from a tailings pond or a stacked heap from the plant, is directed to a flotation circuit 30 to remove some of the non-lithium bearing material from the waste material. The lithium-bearing concentrate exiting the flotation circuit is then directed towards a dryer 32 to reduce the water content of the concentrate, preferably to 20-50 wt % before it is stored in a hopper 18. Suitable examples of lithium-bearing material include waste lithium-bearing clay minerals include smectites such as hectorite and/or montmorillonite, Bigadic clays, and lithium bearing illite with or without lithium zeolites that have been subjected to a variety of treatment steps such as roasting in the processing plant. It was discovered that feeding lithium-bearing material having a water content ranging from 20-50 wt % enhanced the roasting step because the water content improves the granulation of the feed material prior to roasting.

[0177] Separate bins may be used to store a sulfur-containing material such as elemental sulfur or an alkali metal sulfate, gypsum and calcium-containing material such as calcium carbonate. The alkali metal sulfate may be sourced from an effluent stream typically containing sodium sulfate, from the same plant. In FIG. 2, bin 20 is used to store limestone, bin 38 is used to store gypsum. Elemental sulfur or an alkali metal sulfate is stored in another bin (not shown).

[0178] Each of the feed material may be comminuted or screened prior to delivery to their respective bins to limit their maximum particle sizes. For example, the calcium-containing material may be limited to a maximum particle size of 88 microns (−170 mesh), the gypsum may be limited to a maximum particle size of 88 microns (−170 mesh) and the calcium-containing material having maximum particle size of 88 microns (—170 mesh).

[0179] These bins are connected to the mixer in the form of a high shear intensity Eirich mixer 12 which receives these materials in specific proportions to form a mixture that will eventually be processed via a series of intermediate steps to form a concentrated lithium-containing solution of at least 4,000 ppm. The gypsum and calcium-containing material are typically sourced externally. The calcium-containing material can be substituted with magnesium carbonate, dolomite or lime.

[0180] The sulfur-containing material is used to replace part of the gypsum in the roasting recipe. This reduces the need to commercially source gypsum and may repurpose the waste output from the borates processing plant. Importantly, this arrangement allows commercial value to be extracted from waste products from a boric acid processing plant which would otherwise have been discarded and reduces the reliance on externally sourced reagents. It also improves tailings pond management.

[0181] The gangue material may be directed to an impact mill and passed through a classification screen to obtain −40 mesh particles before being fed to the Eirich mixer 12, particularly if the gangue material is dry.

[0182] The various components are fed into the Eirich mixer 12 based on a preselected recipe to form a mixture having a lithium-bearing material: calcium carbonate: gypsum: sodium sulfate ratio of 100:30-40:20:20. Another suitable recipe has a gypsum: sodium sulfate ratio of 7:3.

[0183] The feed mixture is mixed for 15-45 minutes at a speed ranging from 15-70 rpm to form a homogeneous mixture. A heater is used to reduce the moisture content of the mixed material to about 10 wt % or less to form a granulated mixture comprising homogenous pellets ranging from 5-20 mm and having a moisture content between 5-10%.

[0184] In one embodiment, the dried mixture is processed in a granulator to form granules having a mean diameter ranging from 5-20 mm.

[0185] The granulated mixture is then directed to a calciner 14 for roasting at a temperature ranging from 857-925° C. for about one hour.

[0186] In one embodiment, the mixture may be mixed with water to facilitate the granulation process. This step is typically used on dry feed material having a water content of less than 20 wt %. Alternatively, a wet mixture having a water content of greater than 20 wt % may be fed directly into the granulator.

[0187] Examples of suitable roasting recipes wherein the lithium-bearing material is waste lithium-bearing clay material are reproduced in Tables 1 and 2 below.

TABLE-US-00001 TABLE 1 Examples of predetermined roasting recipes for lithium-bearing clay including sodium sulfate Recipe No Clay Limestone Gypsum Sodium Sulfate 1 100 45 40 10 2 100 45 45 15

[0188] In Table 1, the mixture is roasted at a roasting temperature of 900° C. for a roasting time period of 60 minutes.

TABLE-US-00002 TABLE 2 Examples of predetermined roasting recipes for lithium- bearing clay including sodium sulfate and/or elemental sulfur. System Recipe Limestone/ Sodium Elemental % Li recovery No Clay Lime Gypsum Sulfate S Recovery STD. DEV % 1 100 45 50 0 85.2 2.1 76.7 2 100 60 30 0 10 84.4 1.3 75.9 3 100 70 0 0 15 70.0 5.4 63.0 4 100 65 20 10 10 78.7 1.2 70.8 5 100 75 0 25 10 73.5 2.8 66.1 6 100 45 40 10 78.0 2.3 70.2

[0189] This roasting step converts the lithium bearing material into a water-soluble form for a subsequent water leaching step.

[0190] Representative chemical equations of the roasting process are set out below (Crocker.L Lithium and its recovery from low-grade nevada clays [Report].-[s.l.]: Bureau of Mines, 1988).

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[0191] Reaction (B) above produces sodium sulfate and/or potassium sulfate which can be recovered and returned to the Eirich mixer 12 to supplement the source of alkali metal sulfate.

[0192] The roasted material is fed into the leach tank 16 in countercurrent flow to a leaching solution of water to leach lithium from the formed water-soluble lithium compounds. The solids content of the roasted mixture in the leach tank ranges from 10-40 wt %, suitably about 20 wt %. The roasted mixture may be directed into a cooler before being fed to the leach tank.

[0193] The water used in the leaching step is ideally at a pH of 7. However, it can vary between 6.5-7.5 depending on the water source.

[0194] In some embodiments, the method may include a step of crushing the roasted material, including the water-soluble lithium compound, before the leaching step. This step may enhance the leaching process. Suitably, the crushed material has a particle size ranging from 1,000-5,000 μm.

[0195] The leaching step is performed at a temperature of less than 50° C. The applicant determined that a leaching temperature of about 50° C. optimised the leaching efficiency in view of the inverse relationship of solubility with temperature of lithium sulfate.

[0196] During the leaching step, any undissolved solids such as calcium carbonate and clay are removed by filter 22. At this stage, the leachate typically has a lithium concentration of at least 2,000 ppm.

[0197] The filtered leachate is then directed to an evaporator 24 to be concentrated.

[0198] During the evaporating step, impurities in the form of calcium and sodium salts and particulate matter including any one or more of thenardite, glaserite, glauberite, and anhydrite may be formed. These impurities 25 are removed by filter 22 to form a lithium-containing leachate 28 having a concentration of at least 4,500 ppm. This leachate may be further processed downstream via a series of steps to form lithium carbonate or stored for other uses.

[0199] One of these steps involves crystallisation of the lithium-containing leachate to remove further impurities from the solution. In one embodiment, the waste material obtained from the crystallisation step is returned to the flotation circuit 30 via stream 34 to recover lithium from the crystallisation step impurities.

[0200] Another step during the production of lithium carbonate is a lithium carbonate precipitation step which generates a filtrate which can be recycled back to the evaporator via stream 36.

[0201] FIG. 3 provides a second process flow diagram including unit operations for processing the lithium-containing leachate 28 into lithium carbonate. In this embodiment, the leachate 28 is directed into a crystalliser 40. The filtrate from the crystalliser is transferred into a chamber 43 to precipitate lithium carbonate which is sent into centrifuge 45. The stream 36 obtained from the centrifuge 45 is returned to the evaporator 24 while the raw lithium carbonate is processed in refinery 46 into refined lithium carbonate which is subsequently dried and forms the final product 48.

[0202] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.