WO2018087697A1

WO2018087697A1 - Methods and systems for preparing lithium hydroxide

Info

Publication number: WO2018087697A1
Application number: PCT/IB2017/057023
Authority: WO
Inventors: David Anthony MARSH; Jia Yi GUAN; Dean J. THIBAULT; Tim R. MCKEEN; Stephanie M. GOODINE
Original assignee: Avalon Advanced Materials Inc.
Priority date: 2016-11-09
Filing date: 2017-11-09
Publication date: 2018-05-17

Abstract

A process for preparing lithium hydroxide (LiOH) includes: acid roasting a lithium-bearing source material to produce acid roast solids containing sulfates including lithium sulfate, and residue solids; leaching the sulfates from the acid roast solids into a pregnant leach solution (PLS); adjusting the PLS to a pH of about 6-7 to precipitate a first impurity and output a primary purified PLS; adjusting the primary purified PLS to a pH of about 11-13 to precipitate a second impurity and output a secondary purified PLS; removing a third impurity from the secondary purified PLS to output a tertiary purified PLS; processing the tertiary purified PLS in an electrodialysis stage to generate (i) a hydroxide stream including LiOH, (ii) an acid stream including sulfuric acid, and (iii) a spent electrolyte stream containing unconverted sulfates including lithium sulfate; and processing the hydroxide stream in a crystallization stage to extract LiOH.H2O crystals therefrom.

Description

METHODS AND SYSTEMS FOR PREPARING LITHIUM HYDROXIDE

FIELD

[0001] The specification relates generally to the processing of lithium-containing materials, and specifically to methods and systems for preparing lithium hydroxide.

BACKGROUND

[0002] Lithium is a widely employed material, for example in the production of batteries. Various processes are known for extracting lithium from lithium-containing materials. Those processes, however, may produce insufficiently pure lithium product (e.g. battery-grade lithium hydroxide crystals), or may be costly to deploy for the production of such product. Some also produce large volumes of waste products.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0003] Embodiments are described with reference to the following figures, in which FIG. 1 depicts a process flow diagram for preparing lithium hydroxide.

DETAILED DESCRIPTION

[0004] FIG. 1 depicts a process flow for preparing lithium hydroxide (LiOH). In the present embodiment, the lithium hydroxide is prepared from a lithium-bearing source material. The source material is a lithium-bearing ore, such as petalite. In a decrepitation stage 100, a feed stream 102 of ore concentrate (e.g., petalite concentrate) is fed at a controlled rate (e.g. from a feed bin, not shown) into a kiln, such as a rotary kiln operating at a temperature between 1000 °C and 1200 °C (nominally 1 ,100°C) for nominally 2 hours . The decrepitation kiln may be equipped with a dust collection system to process off-gas material 104 from the kiln, to recover ore concentrate and to minimize particulate emissions with the off-104.

[0005] The decrepitation (to convert the crystalline structure of the petalite such that the lithium becomes soluble) of the ore concentrate produces decrepitated ore concentrate 106, which is fed to an acid roasting stage 108. Prior to the acid roasting stage 108, the decrepitated ore concentrate 106 may be cooled, for example via direct and indirect water cooling in a rotary cooler. The decrepitated ore concentrate 106 is cooled, in the present embodiment, to a temperature of about 200 °C. Following cooling, the acid roasting stage 108 includes mixing the decrepitated ore concentrate 106 with input sulfuric acid (equivalent to 150-250kg/t (180kg/t nominal) of 93% sulfuric acid), for example in a paddle blender downstream of the above-mentioned rotary cooler. The sulfuric acid employed in the acid roasting stage 108 can have two sources, as shown in FIG. 1 : a fresh input stream 1 10 originating from storage, and a recycled input stream 1 12 originating from a downstream processing stage, as will be described below. In the present embodiment, about 80% of the sulfuric acid employed in the acid roasting stage 108 is provided via the recycled input stream 1 12.

[0006] The decrepitated ore concentrate and sulfuric acid mixture is fed into an acid roast kiln, such as an indirect-fired rotary kiln. Feeding of the material into the acid roast kiln, as well as the decrepitation kiln upstream, may be performed on a continuous or batch-wise basis. The acid roasting stage includes heating the decrepitated ore concentrate and sulfuric acid mixture to a temperature of about 250 °C to about 350 °C (300°C nominal), for a residence time selected to enable conversion of the decrepitated ore concentrate into sulfates (e.g. solid sulfates, including solid-phase lithium sulfate, Li2S0₄) and residual solids, including alumina-silicates. The residence time is up to 2 hours (1 hour nominally) in the present embodiment. The acid roast kiln may be equipped with a wet scrubber system (not shown) to remove particulate and acid mist from off-gas material 1 14. The treated off-gas 1 14 may then be released to the atmosphere.

[0007] The acid roast stage 108 produces a solids stream 1 16 containing the above- mentioned solids. The solids stream 1 16 thus includes lithium sulfate and other sulfates, such as potassium sulfate, calcium sulfate and the like, as well as metallic impurities and other residual solids (e.g. alumina-silicates, glassy solid solutions of aluminum oxide, AI2O3, and silicon dioxide, S1O2).

[0008] The acid roast solids 1 16 are fed into a leaching stage 120. Prior to the leaching stage, the acid roast solids 1 16 may be cooled, e.g. to below 100 °C, for example in a rotary cooler. In the leaching stage, the acid roast solids 1 16 are leached in recycled spent electrolyte 124 from a downstream processing stage (to be discussed below) which may be supplemented with deionized water or normal process water, provided via a water input stream 122. In the leaching stage 120, the majority of the sulfates mentioned above, including lithium sulfate, are dissolved from the acid roast solids 1 16 into the leaching solution (e.g. water 122 and spent electrolyte 124). The sulfates leached from the acid roast solids 1 16 thus include, for example, lithium sulfate and any one or more of sodium, potassium, aluminum, iron, calcium and magnesium sulfates. The dissolved sulfates are output from the leaching stage 120 as a liquid pregnant leach solution (PLS) 126. Undissolved solids, which typically include alumina- silicates, and may also include certain metallic impurities, are removed in a waste solids stream 128. Removal of the waste solids stream 128 may be facilitated by the addition of a thickener to the leaching stage 120, and the processing of the leachate by a filter, such as a vacuum belt filter. The waste solids stream 128 may also be washed; for example, the above-mentioned vacuum belt filter may be equipped with a counter- current washing function. The fluid stream employed to wash the waste solids 128 may be recycled into the leaching stage 120.

[0009] From the leaching stage 120, the PLS 126 proceeds to impurity precipitation stages. In the present embodiment, prior to the impurity precipitation stages the PLS 126 is fed to an evaporator stage 128. The PLS 126 may be stored in a buffer (e.g. a storage tank) upstream of the evaporator stage 128, to provide a consistent flow of PLS 126 to the evaporator stage (e.g., in case of fluctuations in the flow rate of the PLS 126 from the leaching stage 120).

[0010] The evaporator stage 128, in general, serves to concentrate the PLS 126. In the present example, the evaporator stage 128 is configured to concentrate the PLS 126 to reach a target lithium concentration of about 25 g/L, which may improve the efficiency of the impurity precipitation stages downstream, and may also render the PLS suitable for electrodialysis, as discussed below. The evaporation stage 128 is implemented, in the present embodiment, as a steam-driven triple effect falling film evaporator. As will now be apparent, the evaporation stage 128 may also produce residual solids (not shown), which may be removed via similar techniques to those described above in connection with the leaching stage 120.

[0011] Concentrated PLS 130 is routed from the evaporation stage 128 to a primary impurity precipitation (PIP) stage 132. In the PIP stage 132, the concentrated PLS 130 is adjusted to a pH of about 6 to about 7 (e.g. of about 6.8). As will be apparent from the discussion above, the concentrated PLS is acidic, and the pH adjustment at the PIP stage 132 includes the addition of a base. In the present embodiment, pH adjustment is achieved via the addition of mother liquor via an recycled mother liquor stream 134-A, containing lithium hydroxide as well as other hydroxides, from a downstream crystallization stage, discussed further below. That is, the introduction of an additional base material from a source external to the process (e.g. from a storage tank) may be substantially avoided in the process shown in FIG. 1. A stream of mother liquor may therefore be controlled (e.g. the flow rate may be modulated) based on the current measured pH of the concentrated PLS in the PIP stage 132, to achieve a target pH of approximately 7 (e.g. 6.8, as noted above).

[0012] The increased pH achieved in the PIP stage 132 leads to the precipitation of at least a first impurity. For example, the first impurity can include aluminum, which may be precipitated from the concentrated PLS as aluminum hydroxide (AI(OH)₃). The first impurity precipitated in the PIP stage 132 can also include any one or more of chromium, copper, iron, nickel and zinc. The precipitated impurities are removed from the concentrated PLS, for example via filtration of effluent from the PIP stage 132. In the present embodiment, PIP stage 132 effluent is filtered via a plate and frame press filter, producing a solids stream 136 containing the first impurity mentioned above, and a filtrate stream 138, also referred to as a primary purified PLS stream 138. The primary purified PLS stream 138 contains the above-mentioned dissolved sulfates.

[0013] Residence time in the PIP stage 132 is selected to adjust the pH of the concentrated PLS 130 at rate that is sufficiently low to avoid encapsulation of lithium ions in the freshly formed precipitate, and to avoid post-precipitation of residual impurities after the filtration step mentioned above. [0014] The primary purified PLS stream 138 is fed to a secondary impurity precipitation (SIP) stage 140. In the SIP stage 140, the primary purified PLS stream 138 is adjusted to a pH of about 1 1 to about 13 (nominally 12.3). As with the PIP stage 132, the pH adjustment at the SIP stage 140 includes the addition of recycled mother liquor supplemented (but only if necessary) with sodium hydroxide (not shown).

[0015] The increased pH achieved in the SIP stage 140 leads to the precipitation of at least a second impurity. The second impurity includes, for example, magnesium, manganese, remaining iron and aluminium, which may be precipitated as hydroxides The second impurity precipitated in the SIP stage 140 can also include any one or more of chromium, copper, iron, nickel and zinc. The precipitated impurities are removed from the primary purified PLS stream 138, for example via filtration of effluent from the SIP stage 140. In the present embodiment, SIP stage 140 effluent is filtered via a plate and frame press filter, producing a solids stream 142 containing the second impurity mentioned above, and a filtrate stream 144, also referred to as a secondary purified PLS stream 144. The secondary purified PLS stream 144 contains the above- mentioned dissolved sulfates. As will now be apparent, however, the secondary purified PLS stream 144 contains fewer impurities than both the primary purified PLS stream 138 and the concentrated PLS stream 130. The concentration lithium in the output stream 144 is about 25,500 mg/l Li, in some embodiments.

[0016] The solid streams 136 and 142 from the impurity precipitation stages 132 and 140, respectively, may be co-disposed with flotation plant tailings (e.g. from on-site production of ore concentrate). For example, the solids 136 and 142, as well as the solids 128, may be directed to a dry-stacked tailings management facility, not shown. Typically, the solids streams 136 and 142 account for about 0.1 percent (by weight) of the total solid residue generated from the hydrometallurgical process.

[0017] Following the SIP stage 140, the secondary purified PLS stream 144 is directed to an ion exchange stage 146. In the ion exchange stage, the secondary purified PLS stream 144 is circulated through one or more ion exchange resins to remove at least a third impurity therefrom. The ion exchange stage can include, for example, a plurality of ion exchange columns operated on a lead-lag-strip basis. No pH adjustment is performed to the stream 144 arriving at the ion exchange stage 146 (the pH of the stream 144 is therefore between about 1 1 and about 13, e.g. about 12.2).

[0018] The third impurity removed at the ion exchange stage includes one or more of calcium, magnesium, and manganese. The resins employed in the ion exchange stage 146 are therefore selected to remove the above-mentioned impurities. The ion exchange stage 146 produces as output a tertiary purified PLS stream 150, containing significantly reduced concentrations of the above-mentioned sulfates. The concentration of lithium in the output stream 150 may be about 20,000 mg/l Li, in some embodiments.

[0019] As will now be apparent, the resin in the ion exchange stage 146 may necessitate regeneration periodically. Regeneration of the ion exchange resins is achieved, in the present embodiment, by circulating sulfuric acid (e.g. from an input stream 148) through the resin to strip and regenerate the resin, followed by circulating recycled mother liquor stream 134-C to neutralize the resin following acid regeneration. The regeneration effluent (which, due to the use of the mother liquor stream 134-C, contains a small amount of lithium) is evacuated from the ion exchange stage 146 as a waste fluid stream 152. Typically, the amount of lithium lost via the waste stream 152 is about 0.1 percent (by weight) of the total lithium contained in the ore concentrate.

[0020] As will now be apparent to those skilled in the art, the ion exchange stage 146 may include a plurality of columns that are cycled between production and regeneration in a staggered manner (in order to provide continuous processing of the secondary purified PLS stream 144).

[0021] The tertiary purified PLS stream 150 is directed from the ion exchange stage 146 to an electrodialysis stage 154. That is, the tertiary purified PLS stream 150 represents the electrolyte feed for the electrodialysis stage 154. Prior to introduction to the electrodialysis stage 154, the electrolyte feed 150 may be buffered, for example in a storage tank, to provide a consistent flow rate into the electrodialysis stage 154.

[0022] The electrodialysis stage 154 includes one or more electrodialysis stacks comprising bipolar electrodialysis membranes for converting (via the application of electrical current) the sulfates in the electrolyte feed 150 to hydroxides and acid. Specifically, the electrodialysis stage 154 produces three output streams. The first output stream is a hydroxide output stream 156, containing hydroxides derived from the sulfates (e.g. lithium sulfate and any remaining sulfates of impurities, such as sodium and potassium sulfates) in the electrolyte feed 150. Thus, the hydroxide stream contains lithium hydroxide and small values of certain contaminating hydroxides, such as sodium and potassium hydroxides. The total hydroxide concentration in the first output stream 156 is about 18,500mg/l Li.

[0023] The second output stream is a dilute sulfuric acid stream 158, with a concentration of sulfuric acid that is typically equal to or below about 10 percent (by weight). The third output stream is a spent electrolyte stream 124, mentioned earlier in connection with the leaching stage 120. The spent electrolyte stream 124 includes unreacted sulfates (e.g. lithium, sodium and potassium sulfates), which are returned to the leaching stage 120 for further processing. The acid stream 158 may be directed to an evaporation stage 160 which serves to concentrate the acid stream 158 (e.g. up to about 93 percent by weight) and return the concentrated sulfuric acid as the above- mentioned recycled acid input stream 1 12.

[0024] The electrodialysis stage 154 may be operated in a batch-wise configuration, or in a continuous-feed configuration. For example, deployments with greater production capacities may employ the continuous-feed configuration, while deployments with smaller production capacities may employ the batch-wise configuration.

[0025] In the batch-wise configuration (e.g. in deployments employing fewer than ten electrodialysis stacks), a stock tank of electrolyte feed 150 is circulated through the electrodialysis stacks (for the salt loop), while low concentration acid and base (e.g. residual sulfuric acid output and hydroxide output from a previous batch) and water are circulated for the acid and base loops. During a batch, the salt concentration decreases in the salt loop, as the sulfates are converted to acid and hydroxide. Meanwhile, the concentrations of sulfuric acid and hydroxides increases in the acid and base loops of the electrodialysis stacks. When a minimum set point (e.g. monitored based on conductivity) is reached in the salt loop (that is, a minimum concentration of sulfates) and maximum set points are reached in the acid and base loops, the batch tanks (one per loop, containing the three output streams discussed above) are emptied out and a new batch may be initiated. A batch-wise system as described above thus has a continuously decreasing feed solution concentration (i.e. sulfate concentration), and typically has a lower resistance and higher voltage requirements than a continuous process.

[0026] For larger installations with, for example, more than ten electrodialysis stacks, it may be preferable to implement the electrodialysis stage as multiple units running continuously in a feed and bleed mode and maintaining substantially constant sulfate, acid and base concentrations. Such a system typically has a high resistance and lower voltage requirements. In a variation of the above system, a continuously fed multisystem/stage process may be implemented, in which a first stage operates at a lower product (i.e. hydroxide) concentration. The product of the first stage proceeds to a second stage operating with a greater product concentration, in turn feeding a final stage operating with a still greater product concentration.

[0027] Following the electrodialysis stage 154, the hydroxide output stream 156 is directed to a crystallization stage. In particular, in the present embodiment the hydroxide output stream 156 is directed to a primary crystallization stage 162, which may also be referred to as a crude crystallization stage. The primary crystallization stage 162 includes an evaporative crystallization circuit, configured to evaporate water from the hydroxide output stream 156 and thereby crystallize a substantial portion (e.g. about 90%) of the lithium hydroxide from the hydroxide output stream 156 into lithium hydroxide monohydrate (LiOH.h O). Sodium and potassium hydroxide have higher solubility than lithium hydroxide, and the primary crystallization stage 162 can therefore be configured to selectively crystallize lithium hydroxide to a greater degree than the sodium and potassium hydroxides.

[0028] The primary crystallization stage 162 generates a solid output stream of lithium hydroxide crystals 164, which may also contain trace amounts of crystallized sodium and/or potassium hydroxide. The primary crystallization stage 162 also generates a liquid mother liquor output stream 134, mentioned earlier as a recycled input into the PIP and SIP stages 132 and 140, as well as into the ion exchange stage 146 for resin regeneration. [0029] Prior to a dissolution stage 166, the crystals 164 can be dewatered (e.g. in a centrifuge) and washed with a secondary mother liquor stream 168 from a secondary crystallization stage 170, to remove sodium and potassium hydroxide remaining in the aqueous phase after the dewatering. At the dissolution stage 166, the crystals 164 are re-dissolved in a minimal amount of water (e.g. distilled water, to a concentration of about 29g/l Li) and the dissolved hydroxide is processed in a secondary crystallization stage 168 (which may also be referred to as a product crystallization stage). The secondary crystallization stage 168, like the primary crystallization stage 162, is configured to selectively crystallize lithium hydroxide preferentially to sodium and potassium hydroxide. Due to the limited carryover of sodium and potassium impurities from the crude to the product crystallization stage, the resulting lithium hydroxide monohydrate crystals 172 contain low levels of impurities (e.g. the crystals 172 are typically at least 99.5% lithium hydroxide monohydrate by weight).

[0030] The product crystals 172 are fed to a drying stage 174, where they are dewatered (e.g., in a centrifuge) and washed with an amount of distilled water selected to minimize re-dissolution, before being dried under a nitrogen atmosphere. Drying under nitrogen atmosphere reduces or eliminates adsorption of carbon dioxide by the lithium hydroxide crystals during the drying process. The final lithium hydroxide monohydrate product 176 may then be packaged, for example in bags for shipment to an end user.

[0031] Table 1 , below, illustrates a set of configuration parameters for the process illustrated in FIG. 1

Table 1 - Process Configuration Parameters

Parameter Units Value

Maximum [OH ] in LiOH solution M OH^" 3

Lithium hydroxide solution composition mg/L Li 18,310 mg/L Na 7,098 mg/L K 2,055

Regenerated sulphuric acid solution

M H2S04 0.75 concentration

Recycle sulphuric acid strength after

wt% H2S04 93.00% evaporation

Crude mother liquor solution composition wt% LiOH 5.00%

wt% NaOH 15.40% wt% KOH 3.68%

Pure lithium hydroxide monohydrate product

wt% LiOH-H₂0 99.90% composition

wt% moisture 0.10% ppm Na 0.97 ppm K 0.28

Hydromet solid residue percent moisture wt% 10%

Lithium recovery in hydrometallurgical facility wt% of hydromet feed 90%

[0032] The scope of the claims should not be limited by the embodiments set forth in the above examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

1. A process for preparing lithium hydroxide, comprising:

acid roasting a lithium-bearing source material to produce acid roast solids containing (i) sulfates including lithium sulfate, and (ii) residue solids;

in a leaching stage, leaching the sulfates from the acid roast solids into a pregnant leach solution (PLS) containing the sulfates;

in a primary impurity purification (PIP) stage, adjusting the PLS to a pH of about 6 to about 7 to precipitate a first impurity and output a primary purified PLS;

in a secondary impurity purification (SIP) stage, adjusting the primary purified PLS to a pH of about 1 1 to about 13 to precipitate a second impurity and output a secondary purified PLS;

in an ion exchange stage, removing a third impurity from the secondary purified PLS to output a tertiary purified PLS;

processing the tertiary purified PLS in an electrodialysis stage to generate (i) a hydroxide stream including lithium hydroxide, (ii) an acid stream including sulfuric acid, and (iii) a spent electrolyte stream containing unconverted sulfates including lithium sulfate; and

processing the hydroxide stream in a crystallization stage to extract lithium hydroxide crystals from the hydroxide stream.

2. The process of claim 1 , wherein the source material includes petalite concentrate.

3. The process of claim 1 , further comprising:

prior to the acid roasting, decrepitating the source material.

4. The process of claim 1 , wherein the acid roasting comprises introducing sulfuric acid recycled from the acid stream of the electrodialysis stage.

5. The process of claim 4, further comprising:

prior to introducing sulfuric acid recycled from the acid stream of the

electrodialysis stage into the acid roasting, concentrating the acid stream.

6. The process of claim 1 , further comprising:

downstream of the leaching stage, extracting the residue solids for disposal.

7. The process of claim 1 , further comprising:

prior to adjusting the PLS to a pH of about 6 to about 7, concentrating the PLS via an evaporation stage.

8. The process of claim 1 , comprising adjusting the PLS to a pH of about 6.5 to about 7.

9. The process of claim 1 , wherein adjusting the PLS to a pH of about 6 to about 7 comprises introducing a mother liquor from the crystallization stage to the PIP stage.

10. The process of claim 1 , wherein the first impurity includes aluminum hydroxide.

1 1. The process of claim 1 , comprising adjusting the primary purified PLS to a pH greater than 1 1.

12. The process of claim, adjusting the primary purified PLS to a pH of about 1 1 to about 13 comprises introducing a mother liquor from the crystallization stage to the SIP stage.

13. The process of claim 1 , wherein the second impurity includes magnesium

hydroxide.

14. The process of claim 1 , further comprising:

regenerating the ion exchange stage via the introduction of sulfuric acid and a mother liquor from the crystallization stage.

15. The process of claim 1 , wherein the third impurity includes at least one of calcium and magnesium.

16. The process of claim 1 , further comprising:

returning the spent electrolyte stream to the leaching stage.

17. The process of claim 1 , wherein the crystallization stage includes primary and secondary crystallization stages.

18. The process of claim 1 , wherein the crystallization stage is an evaporative crystallization stage.

19. The process of claim 18, further comprising dissolving the output of the primary crystallization stage prior to the second crystallization stage.