GB2631909A

GB2631909A - Production of battery grade chemicals

Info

Publication number: GB2631909A
Application number: GB2215952.9A
Authority: GB
Inventors: Smith Roderick; Smith Andrew; Omelchuk Kateryna
Original assignee: Res By British Lithium Ltd
Current assignee: Res By British Lithium Ltd
Priority date: 2022-10-27
Filing date: 2022-10-27
Publication date: 2025-01-22
Also published as: GB202215952D0; WO2024089394A1

Abstract

A process for producing precipitated or crystallised anhydrous lithium hydroxide or hydrate from lithium mica may comprise blending the mica, preferably a lithium mica concentrate, with reagent(s) comprising calcium carbonate and/or sulphate salt(s), and calcining to provide a hot calcine discharge comprising lithium sulphate and/or lithium potassium sulphate. The calcine discharge may be leached aqueously, producing a lithium enriched leach liquor which may be filtered. The filtered leachate may be concentrated, and impurities removed by addition of calcium hydroxide and calcium carbonate. A carbonate source may be added to the leachate producing crude lithium carbonate slurry which may be filtered. The crude lithium carbonate may be reacted with calcium hydroxide to produce a lithium hydroxide liquor which is filtered to remove calcium carbonate. Water may be evaporated from the lithium hydroxide solution to obtain crystalised or precipitated lithium hydroxide hydrate. The hydrate may be heated to produce anhydrous lithium hydroxide.

Description

PRODUCTION OF BATTERY GRADE CHEMICALS

The present invention relates to a process for the calcination of lithium micas and extraction and purification of high purity lithium hydroxide hydrate or anhydrous lithium hydroxide, using a sustainable sulphate-based route, and to lithium mica-reagent compositions useful in said calcination process.

BACKGROUND OF INVENTION

Currently, the main sources of lithium used to make battery chemicals are salar brines enriched in lithium salts and hard rock deposits containing spodumene. Lithium from _,afar brines requires pumping and evaporation of vast quantities of water to extract and concentrate brines before impurity removal to produce a final lithium salt product.

Spodumene, a lithium-bearing pyroxene mineral, is mined from hard rock deposits and typically requires high temperature calcination at approximately 1,100 °C and hot acid leaching to produce a lithium-enriched brine or pregnant leach solution that is then purified to obtain a final lithium salt product.

Lithium micas could be an alternative hard rock source of lithium, but these have never been exploited commercially. These lithium micas occur within granites in Europe and elsewhere, and contain gangue minerals, principally quartz and feldspar. Exploiting these deposits commercially requires the formulation of economic and environmentally sustainable methods for extraction of high-grade lithium salts of saleable quality from these micas.

Lithium micas present an important potential source of lithium that is likely ko grow in significance as the demand for lithium is expected to increase considerably in light of a worldwide effort to reduce carbon emissions, Lithium micas are structurally classed as tri-octahedral micas and can exist in a solution series whose end members are polylithionite (I<Li2A1Si4020(F,OH)2; potassium lithium aluminium silicate fluorite hydroxide) and siderophyllite (I<Fe2A1(A12512)020(F,OH)2; potassium iron aluminium silicate hydroxide fluoride). Zinnwaldite (KLiFeAI(AISi3)Oio(OH,F)2; potassium lithium iron aluminium silicate hydroxide fluoride) and lepidolite K(Li, A1)3(Al, Si, Rb)40,0(F, OH)2 are examples of a mica that forms part of this solid solution series. These lithium micas contain a wider range of elements than spodumene, the conventional hard rock source of lithium, which is LiAl(Si206) (lithium aluminium inosilicate). Lithium micas are consequently less rich in lithium than spodumene, more complex to process and contain elements which may contaminate the desired end product.

The lower Li content and more complex mineralogy of lithium micas compared to spodumene gives rise to the need for an extraction process to generate brine or pregnant each solution from lithium mica minerals that affords improved recovery of lithium at a lower cost and environmental impact through reduced and more targeted use of reagents and more optimised calcining conditions, bringing fewer contaminants into solution.

One known method for the extraction of lithium salts from lithium micas relies on elevated temperature leaching of lithium micas in sulphuric acid, either at atmospheric pressure or in an autoclave or other device to increase pressure. This method does not rely on calcining in the presence of a sulphate salt, instead relying on the sulphuric acid, heated to a temperature in excess of 90 °C, to act as the lixiviant which results in a significant environmental burden in the form of acidified waste streams and a number of contaminant elements becoming solubilised.

The process disclosed herein relates to an improved sulphate base extraction route without use of acids.

SUMMARY OF INVENTION

According to a first aspect, the present invention provides a process for producing precipitated or crystallised lithium hydroxide hydrate or anhydrous lithium hydroxide from lithium mica, the process comprising: i. blending lithium mica, preferably lithium mica concentrate, with a reagent or mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s) in a functional ratio to produce a lithium mica-reagent mixture, and optionally pelletising the lithium mica-reagent mixture to provide pelletised lithium mica-reagent mixture; ii. calcining the lithium mica-reagent mixture or pelletised lithium mica-reagent mixture at a functional temperature for a functional time to provide a hot calcine discharge comprising water soluble lithium sulphate; iii. optionally further comprising heat recovery/cooling of the calcine discharge, prior to leaching to provide a calcine-product comprising lithium sulphate and/or lithium potassium sulphate; iv. leaching the calcine discharge or hot calcine discharge for a functional time and having a functional pulp density in an aqueous leach liquor to provide a lithium-enriched leach liquor; v. filtering the lithium enriched leach liquor to produce a leachate (also herein referred to as "leachate liquor" or "filtrate") and a filter leach-residue herein also referred to as "calcine filter cake"); vi. optionally adding at least one carbonate salt (preferably a Group I metal carbonate, for example sodium carbonate) to the leachate liquor in a first stage impurity removal step to provide a first impurity reduced leachate; vii. concentrating at least a portion of the leachate liquor or the first impurity reduced leachate to provide a concentrated leachate; viii. optionally removing impurities from the concentrated leachate in a second stage impurity removal step comprising addition of calcium hydroxide and calcium carbonate, and optional treatment with activated alumina, to provide a second reduced impurity containing leachate; ix. adding a carbonate source to the leachate liquor and/or concentrated leachate and/or second reduced impurity containing leachate to produce a lithium carbonate slurry comprising lithium carbonate precipitate, and subsequently filtering the lithium carbonate slurry to provide a first spent liquor and crude lithium carbonate; x. conversion of crude lithium carbonate into lithium hydroxide in water by adding calcium hydroxide (milk of lime) to the crude lithium carbonate to produce a slurry containing lithium hydroxide liquor, and subsequently filtering the slurry to provide a lithium hydroxide liquor and calcium carbonate cake, xi. optionally passing the lithium hydroxide liquor through an ion exchange column to provide a purified lithium hydroxide containing solution with a reduced concentration of, preferably substantially free of, calcium and other divalent cations; xii. Precipitating or crystallising high purity lithium hydroxide hydrate (Li0H.H20) from the purified lithium hydroxide containing solution by evaporation of the water from the liquor, and obtaining high purity precipitated or crystallised lithium hydroxide hydrate by filtration and a resultant second spent liquor; xiii. optionally heating the lithium hydroxide hydrate to a functional temperature (preferably a functional temperature of over 150 °C, preferably a functional temperature of over 180 °C) to evaporate water to produce anhydrous lithium hydroxide (LiON) under an atmosphere substantially free of carbon dioxide; and xiv. optionally precipitating or crystallising a mixed salt by-product by taking the first spent liquor obtained from the precipitation or crystallisation step (ix), and i) chilling or ii) evaporating the first spent liquor, obtaining a mixed salt byproduct by filtration of the first spent liquor and a third spent liquor, and optionally recycling the mixed salt by-product for introduction into the mixture of reagents for producing the lithium mica-reagent mixture, and/or optionally recycling the third spent liquor for introduction into the aqueous leach liquor of step iv.

The process of the present invention provides high purity lithium hydroxide hydrate or anhydrous lithium hydroxide for use, for example, in batteries. The present invention provides an efficient process for the production of high purity lithium hydroxide from lithium mica.

Each of the steps of the process and the reagents employed will be described in further detail below: i) REAGENT MIXING & PELLETISATION STEP The lithium mica, preferably lithium mica concentrate, has a Pal value (i.e. the particle size at which 80% of the lithium mica will pass when screened) of 450 pm or smaller. Preferably, at least 80% of the particles of the lithium mica have a particle size of greater than 15 p.m in diameter.

The lithium mica is preferably concentrated lithium mica, whereby the percentage of lithium in the material has been concentrated or beneficiated by physical or chemical means to remove all or the majority of non-lithium containing gangue or waste materials.

It has been found by the inventor's testwork that the method of the present invention can be used to extract the desired lithium salts from lithium mica without requiring the lithium mica to be finely ground prior to calcination. As a result, the method of the present invention does not require the use of a costly and high energy consuming grinding or milling process.

According to a further aspect of the present invention, there is provided a lithium mica, preferably lithium mica concentrate, as defined above.

According to further aspect of the present invention, there is provided the use of the lithium mica, preferably lithium mica concentrate, as defined above in a calcination process, and in particular in a calcination process as herein described.

According to a further aspect of the present invention, there is provided a lithium mica-reagent mixture comprising a lithium mica, preferably a lithium mica concentrate as herein defined with a reagent or mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s) in a functional ratio to produce a lithium mica-reagent mixture.

According to a further aspect of the present invention, there is provided the use of a lithium mica-reagent mixture as herein described in a calcination process, and in particular in a calcination process as herein described.

According to a further aspect of the present invention, there is provided high-purity lithium hydroxide hydrate (Li0H.H20) having a purity of at least 55 wt % lithium hydroxide (LION).

According to a further aspect of the present invention, there is provided high-purity anhydrous lithium hydroxide LiOH having a purity of at least 97 wt % lithium hydroxide (LiOH).

The reagent or mixture of reagents comprises one or more of: calcium carbonate and/or make-up sulphate salt(s), optionally further comprising mixed salt by-product (for example recycled mixed sulphate salts and/or recycled mixed calcium salts). The reagent or mixture of reagents is preferably free from hydrated lime.

The term "recycled mixed salt(s)" is used herein to refer to salts, and in particular, recycled sulphate salt(s) and/or recycled calcium salt(s), recovered during one or more stages of the process. For example, the term "recycled mixed sulphate salt(s)" may refer to the sulphate salts recovered during the mixed salt recovery stage (xiv) described herein. For example, the term "recycled mixed calcium salt(s)" may refer to the calcium salts recovered during mixed salt recovery stage (xiv) described herein. The process may therefore further comprise recovering salt(s) and/or mixed salt(s) from one or more stages of the process and recycling the recovered salt(s) into one or more other stages of the process, for example into the reagent mixing step (i). Thereby reducing the overall reagent consumption, cost and environmental burden of waste disposal.

The term sulphate salt(s) is used herein to refer to the combination of: make-up sulphate salt and mixed salt by-product.

Preferably the make-up sulphate salt(s) is calcium sulphate, for example gypsum. Calcium sulphate is cheap and readily available in the form of for example mined naturally occurring gypsum or synthetic gypsum, thereby significantly reducing processing costs.

Preferably, the sulphate salt(s) (for example calcium sulphate, such as for example present within gypsum), optionally including one or more sulphate salt(s), such as for example present within the mixed salt by-product, is present within the lithium mica-reagent mixture in an amount sufficient such that the total sulphate salt(s) (SO4) concentration is equal to or in excess of the amount required in order to fully react with the lithium present within the lithium mica to form lithium sulphate.

Preferably, the mixed salt by-product comprises (preferably predominantly comprises), for example consist of, a double salt of sodium and potassium sulphate.

Preferably, the mixed recycled calcium salts comprise one or more of (preferably each of): calcium carbonate and/or calcium sulphate.

Preferably, calcium carbonate is provided in the form of limestone CaCO3. Limestone is readily commercially available and has a reduced associated cost compared to lime CaO or hydrated lime Ca(OH)2. During calcination, at temperatures above 900°C, the lower cost limestone disassociates to lime CaO and becomes more reactive, thereby avoiding the need to purchase the more expensive lime CaO. The commonly used alternative of hydrated lime Ca(OH)2 would introduce water to the calciner, increasing energy consumption. The use of limestone within the process of the present invention therefore has reduced associated processing costs.

In one embodiment, calcium carbonate may be partly substituted with calcium oxide or calcium hydroxide such that the stoichiometric amount of calcium present is the same as had pure calcium carbonate been used. It has been found by the inventor's testwork that as the calcium carbonate (for example limestone) ratio within the lithium mica-reagent mixture increases, the lithium recovery (%) of the process also increases. This is in contrast to a process which uses a feed mixture of lithium mica, gypsum and hydrated lime, in which the lithium recovery (%) has been found by the inventor's testwork to decrease as the hydrated lime ratio within the feed mixture increases.

The use of calcium carbonate has been found by the inventor's testwork to provide a calcine discharge which does not bind to or stick to the walls of the calcination vessel thereby increasing the lithium recovery rate and efficiency of the process.

Preferably, more than 90% of the particles of calcium carbonate have a particle size greater than 10 p.m.

In one embodiment, the mixture of reagents and lithium mica are mixed together prior to being pelletised. For example, the lithium mica and reagents may be mixed together in a pug 20 mixer.

The ratio of lithium mica to calcium carbonate within the mixture is preferably within the range of 6: 1 and 6: 3, preferably between 6: 1.5 and 6: 2.5 (based on the dry mass of the components). In one embodiment, the ratio of mica to gypsum to calcium carbonate is within the range of between 6: x: 1 and 6: x: 3.

The ratio of lithium mica to sulphate salt(s) present within the mixture is within the range of 6: 1 and 6: 5 (based on the dry mass of the components). In one embodiment, the ratio of mica to sulphate salt to calcium carbonate is within the range of between 6: 1: x and 6: 5: x.

According to a further aspect of the present invention, there is provided a lithium mica-reagent mixture (for example a pelletised lithium-mica reagent mixture) comprising a ratio of lithium mica to calcium carbonate within the mixture within the range of 6: 1 and 6: 3, preferably between 6: 1.5 and 6: 2.5.

According to a further aspect of the present invention, there is provided a lithium mica-reagent mixture (for example a pelletised lithium-mica reagent mixture) comprising a ratio of mica to gypsum to calcium carbonate within the range of between 6: x: 1 and 6: x: 3.

According to a further aspect of the present invention, there is provided a lithium mica-reagent mixture (for example a pelletised lithium-mica reagent mixture) comprising a ratio of lithium mica to sulphate salt(s) within the range of 6: 1 and 6: 5.

According to a further aspect of the present invention, there is provided a lithium mica-reagent mixture (for example a pelletised lithium-mica reagent mixture) comprising a ratio of mica to gypsum to sulphate salt(s) is within the range of between 6: x: 1 and 6: x: 5.

H) CALCINATION STEP In the calcination step, the lithium mica-reagent mixture is heated to cause a series of solid-to-solid reactions to extract and convert the insoluble lithium contained in the lithium mica into water soluble lithium sulphate and/or lithium potassium sulphate.

The functional temperature of the calcining step is preferably within the range of about 750 °C to 1,100 °C, preferably within the range of 800 °C to 1,050 °C, preferably within the range of 800 °C to 1,000 °C.

The lithium mica-reagent mixture is preferably not milled prior to the calcination step. As a result, the particle size distribution of the particles of the lithium mica-reagent mixture to be calcined is unaltered from the particle size distribution of the particles of lithium mica-reagent mixture prepared in step i). In one embodiment, the process comprising calcining a lithium mica-reagent mixture comprising particles having a maximum particle size of 400 am.

Preferably, the lithium mica-reagent mixture has a Pso value (i.e. the particle size at which 80% of the mixture will pass when screened) of 300 km. Preferably, the lithium mica-reagent has a particle size distribution in which less than 25% of the particles have a particle size smaller than 20 km.

In one embodiment the lithium mica-reagent mixture is pelletised before calcination. It has been found by the inventor's testwork that pelletising the lithium mica-reagent mixture increases the recovery of lithium to solution, which the applicant believe is related to an increase in the rate of the solid-to-solid reaction and also decreasing dust loss from the calciner.

Preferably, the lithium mica-reagent mixture, for example pelletised lithium mica-reagent mixture, is heated prior to calcination. The heat may be provided by any suitable heat source. In one embodiment, the heat source is provided from excess heat or waste streams generated during the process, for example by off-gas generated from the calciner unit during the calcination step. The process may therefore further comprise recycling one or more waste streams comprising excess heat, the waste streams being generated by the process (for example recycling off-gas generated by the calciner) to heat the lithium mica-reagent mixture (for example pelletised lithium mica-reagent mixture) prior to calcination.

The functional time for the calcining step is preferably between 15 minutes and 360 minutes.

The functional time is dependent on the temperature ramp up profile. For example, if the temperature rises slowly towards the target temperature, the time period for calcining increases.

Preferably, the calcining step occurs within either a direct fired rotary kiln/calciner, or an indirectly heated electric furnace.

It has been found by the inventor's testwork that by maintaining the temperature of the calcining step within the functional temperature ranges for a functional time that the mica breaks down or degrades to provide smaller mica particles having larger surface area which enhances reaction with gypsum and calcium carbonate. The reduced particle size of the mica provided as a result of exposure to functional temperatures for a functional time period during the calcining step eliminates the need to mill, crush or grind the mica prior to calcining.

As a result, the process of the present invention eliminates a step within the conventional lithium extraction process. Ideally, the process of the present invention is therefore free of milling, grinding or crushing of the mica prior to calcining. Furthermore, the increased surface area of the calcine discharge increases the leaching recovery rate of the product, increasing the percentage lithium recovery and decreasing cost.

Due to the fluorine content of mica, the evolution of fluorine gas (F2) and/or hydrofluoric acid (HF) during calcination is a concern which could pose a significant health risk as fluorine is highly toxic and highly reactive. The process of the present invention has also been found by the inventor's testwork to reduce fluorine gas evolution.

The fluorine content in the feed source for the calcining step, in the leach residue and in the leach liquor was assayed during the inventor's testwork. It is considered that any fluorine gas liberated from the mica during calcining, and on exposure to water, is converted to hydrofluoric acid (HF) which is subsequently neutralised by the presence of alkaline calcium carbonate, forming predominately insoluble compounds that remain in the leach residue rather than being evolved as fluorine gas or HF mist. The calcium carbonate in the feed mixture is preferably present at a level in excess of stoichiometric requirements. The presence of alkaline substances in the calcine feed such as calcium carbonate can help to neutralise the generated HF.

The present invention therefore provides a process for extracting lithium from lithium mica with reduced or no generation of fluorine gas or HF.

iii) OPTIONAL COOLING/HEAT RECOVERY STEP In one embodiment the calcine discharge is discharged straight into leach liquor without the need for cooling.

Preferably heat recovery/cooling is achieved by using methods other than indirect cooling.

Preferably, the heated, calcine discharge is deposited into the aqueous leaching liquor without the requirement for prior cooling.

For heat recovery purpose cooling may be employed to cool the calcine discharge to > 100 ° C without the use of indirect cooling.

Handling and transportation of hot materials, such as materials heated to temperatures within or over, for example 150 °C, can be time consuming, dangerous and difficult which can lead to loss of product. Conventionally, the heated, calcine discharge is cooled, by for example spraying the calcination vessel with water, to a temperature which facilitates easier handling and transportation. This cooling step can however be costly and waste energy and water.

Calcine discharge may contain sintered or fused product which are not readily amenable to leaching.

Cooled calcine discharge may be hot-milled in order to break up and reduce the particle size prior to leaching in order to increase leach recovery. Milling of heated, calcined materials can be difficult to achieve and requires the use of an additional milling circuit which introduces additional process complexity and reduced plant availability, together with associated operating, energy and capital costs.

The present invention reduces, preferably eliminates, the need for a cooling step of the calcine discharge between the calcining step and the leaching step. In one embodiment, the calcine discharge is discharged directly, without additional cooling prior to discharge, into the leach liquor. By dispensing the heated, calcine discharge directly, at a temperature, preferably of at least 150 °C, into the leaching liquor, the efficiency of transfer from a calcination kiln to the leaching liquor, within for example a leaching vessel, is rapidly improved with significantly reduced loss of product (for example as dust) during transfer leading to a higher lithium recovery from the lithium mica or lithium mica concentrate.

The present invention also provides a fluid or slurry, for ease of transportation, in the form of a slurry of calcine discharge and lithium enriched leach liquor. Transportation of a fluid or slurry is much easier to handle and results in a lower risk of loss of product during transportation between process steps.

The direct deposition of the heated, calcine discharge into significantly cooler aqueous leaching liquor causes rapid generation of steam and thermal shock which effectively breaks apart calcined material which has been sintered or fused during calcination causing the product to break at least partially into fragments. The expansion of steam bubbles created during deposition of the calcine discharge into the aqueous leaching liquor causes thermal fracture of the particles aiding processability of the quenched, leached, calcine discharge containing lithium. As a result, transportation and handling of the calcine discharge is easier with lower associated cost and time implications and reducing the risk of loss of material during handling and transportation (for example losses as dust).

By breaking down the particle size of the calcine discharge by direct deposition (without the requirement to cool the product to for example temperatures below 150 °C prior to leaching) from the calcination kiln into the leaching liquor, the surface area to volume ratio of the particles increases significantly. The increase in the surface area to volume ratio of the calcine discharge containing lithium sulphate particles and/or lithium potassium sulphate particles improves leaching efficiency as there is an increased surface area particle exposure to the leaching liquor, thereby reducing leaching time and increasing lithium recovery rates.

iv) AQUEOUS LEACHING STEP The hot calcine discharge comprising water soluble lithium sulphate and/or lithium potassium sulphate produced in the hot calcination step (ii) (or calcine product produced in step (iii)) is leached with aqueous leach-liquor (for example water leach liquor) to create aqueous lithium ions in solution. Once fully reacted (dissolved) the enriched lithium leach liquor is sent to step (v).

The aqueous leach liquor may comprise water having a neutral pH. The leach liquor, such as for example water, is preferably free of pH modifiers, in particular, free from the addition of acid. The leach liquor may comprise recycled wash water from previous batches.

The process of the present invention has been found by the inventor's testwork to achieve >80% recovery of lithium into the lithium-enriched leach liquor solution.

In one embodiment, the pulp density of the leach-liquor is between 7% and 40%, preferably between 10% and 35%, for example between 10% and 30%.

In one embodiment, the process further comprises agitation of the aqueous leach liquor during and/or after deposition of the heated, calcine discharge therein. Agitation may for example be provided by a rotary mixer. Agitation may further aid the process of fragmenting particles of the calcine discharge containing lithium sulphate and/or lithium potassium sulphate within the leaching liquor to provide a slurry.

In one embodiment, the heated, calcine discharge is deposited into the aqueous leaching liquor without hot milling of the dried calcine discharge product prior to leaching. Preferably the leaching vessel is in communication with the first outlet of the first outlet to receive heated, calcine discharge without a milling device located therebetween.

In one embodiment, the calcine discharge once added to the leach water forms a slurry which may be wet milled or attritioned to break apart residual unbroken pellets, sintered or fused lumps to improve the leaching performance. Enriched leach liquor together with calcine discharge may be passed through an attrition scrubber or milling stage to help break apart any residual unbroken pellets, sintered or fused lumps. This attritioning or milling stage is performed before the subsequent filtration.

The solubility of lithium sulphate is "retrograde" meaning it is inversely proportional to the temperature of the solvent solution. As such, any increase in the temperature of the leach liquor during leaching of lithium sulphate may result in reprecipitation of lithium sulphate thereby reducing the concentration of lithium sulphate within the liquor and reducing overall lithium recovery from the lithium mica material. An increase in the temperature of the leach liquor may also increase the solubility of other abundant aqueous salts within the calcine discharge (or hot calcine discharge), such as for example potassium sulphate and rubidium sulphate. An increase in the concentration of the other abundant aqueous salts within the liquor may therefore further reduce the solubility of lithium sulphate within the leach liquor and reduce the overall recovery of lithium from the lithium mica material.

In one embodiment, leaching of the calcine discharge (or hot calcine discharge) is at first conducted at high temperature, with subsequent stages of leaching at decreasing temperatures as the slurry returns to ambient temperature. This ensures the solubility of lithium sulphate increases as leaching proceeds, and lithium sulphate is therefore less likely to reprecipitate.

In one embodiment, the aqueous leaching liquor is maintained at a temperature below a functional temperature. The aqueous leaching liquor may be cooled during deposition of the calcine discharge or hot calcine discharge. The aqueous leaching liquor is preferably maintained at a temperature of less 90 °C, preferably less than 60 °C, preferably less than 50 °C, for example less than 40 °C.

The calcine discharge (or hot calcine discharge) is preferably deposited into the aqueous leaching liquor at a flow rate which is sufficient to ensure that the temperature of the aqueous leaching liquor does not exceed for example 60 °C, preferably 50 °C, for example 40 °C.

The calcine discharge (or hot calcine discharge) resides within the aqueous leaching liquor for a functional residence time, such as preferably for at least 30 minutes, preferably for at least minutes, for example for at least 2 hours.

v) ENRICHED LITHIUM LEACH LIQUOR FILTRATION STEP The lithium enriched leach liquor is filtered to separate the calcine residue (also referred to as the "calcine filter cake") to produce a filtered leachate liquor herein referred to as the "leachate liquor".

After filtration, the calcine filter cake may be washed and the resultant wash water may be re-used in the process. For example, the resultant wash water may be introduced into, or used in place of, the aqueous leaching liquor (iv) for treatment of a further batch of calcine discharge or hot calcine discharge. The wash water may contain residual lithium which was present on the calcine filter cake. By collecting the resultant wash water and recycling the wash water for subsequent leaching of the calcine discharge or hot calcine discharge, any lithium remaining on the filter leach residue may be recovered, thereby increasing the recovery yield of the process while also reducing water consumption.

vi) FIRST STAGE IMPURITY REMOVAL: CALCIUM IMPURITY REMOVAL STEP An optional stage is to remove some of the dissolved calcium ions from the leachate liquor ahead of the subsequent evaporation stage, by the addition of a carbonate salt to precipitate impurities from the leachate liquor, which can subsequently be filtered out, to produce a first impurity reduced leachate and a filter residue.

The carbonate salt may be a Group I metal carbonate salt. The carbonate salt is preferably one or more of: sodium carbonate and/or potassium carbonate. Preferably the carbonate salt is sodium carbonate.

In one embodiment, the Group I metal carbonate is present at a concentration of at least 0.5 g/L of leachate, preferably at least 1 g/L of leachate for example between 1 g/L of leachate and 2 g/L of leachate.

vii) LEACHATE CONCENTRATION STEP The concentration of the leachate or the first impurity reduced leachate may be achieved by any suitable method in order to produce a concentrated leachate liquor (also referred to as "concentrated leachate").

In one embodiment, concentration of the leachate or the first impurity reduced leachate is achieved by partial evaporation to increase the concentration of the dissolved lithium in solution to produce concentrated leachate.

Preferably, evaporation of the leachate or the first impurity reduced leachate is carried out to achieve a target lithium tenure within the concentrated leachate of greater > 4 g /L Li.

During evaporation, the evaporated water from the leachate or the first impurity reduced leachate may be condensed and collected. The collected, evaporated and hence purified water may be reused within the process. In one embodiment, the collected, evaporated water may be introduced into, or used in place of, the leach liquor (iv) for leaching further calcine discharge or hot calcine discharge thereby reducing contaminants introduced to the process while reducing water consumption.

In one embodiment, the concentration of leachate liquor or first impurity reduced leachate may be achieved or partially achieved by the use of Reverse Osmosis or NanoFiltration ("NF") processes. This may eliminate the need for an evaporation stage or reduce the size requirements saving cost.

viii) SECOND STAGE IMPURITY REMOVAL STEP The concentrated leachate may be further purified by precipitation or crystallisation of impurities on introduction of calcium hydroxide and sodium carbonate and further treatment with activate alumina. The resultant leachate is known as a second reduced impurity containing leachate.

Ferrous sulphate may also be introduced to the concentrated leachate.

In one embodiment, calcium hydroxide is added to the concentrated leachate followed by the addition of sodium carbonate.

The calcium hydroxide may be added to the concentrated leachate for a functional time period. In one embodiment, calcium hydroxide is added to the concentrated leachate for a functional time period, for example for a functional time period prior to the introduction of sodium carbonate. Preferably, the functional time period is at least 30 minutes.

Calcium hydroxide may be added to the concentrated leachate at any suitable addition rate.

Preferably, calcium hydroxide is added to the concentrated leachate at an addition rate of at least 0.2 g / L of concentrated leachate.

Sodium carbonate may be added to the concentrated leachate at any suitable addition rate. Preferably, sodium carbonate is added to the concentrated leachate at an addition rate of at least 0.6 g / L of concentrated leachate.

Treatment of the concentrated leachate with activated alumina provides reduced fluorine containing leachate. Activated alumina may remove fluorine present within the concentrated leachate.

The concentrated leachate may be purified by treatment with activated alumina prior to introducing calcium hydroxide. The concentrated leachate may be purified with activated alumina after the introduction of the additional reagent(s).

In one embodiment, calcium hydroxide is introduced to the concentrated leachate, and subsequently treated with activated alumina.

In one embodiment, diatomaceous earth may be used to assist with the filtration.

In one embodiment, the filter leach residue may be washed to recover leachate liquor for introduction or recycling back to one or more steps in the process to reduce lithium losses and improve recovery.

ix) CRUDE LITHIUM CARBONATE PRECIPITATION STEP A carbonate salt source is added to the leachate and/or concentrated leachate and/or second reduced impurity containing leachate to provide lithium carbonate slurry comprising lithium carbonate precipitate. Precipitation of crude carbonate occurs within the liquor.

Li2SO4 + Na2CO3 Li2COci + Na2SO4 Preferably the carbonate source is sodium carbonate.

Preferably, the carbonate salt source is added to the concentrated leachate.

Preferably, the carbonate salt source is added to the second reduced impurity containing leachate.

In one embodiment, precipitation may be aided by heating the liquor to a temperature of at least 90 °C to reduce the solubility of the crude lithium carbonate.

The precipitated or crystallised crude lithium carbonate is separated from the slurry by filtration, for example in a centrifuge. After filtration, the precipitated crystallised crude lithium carbonate may be collected, and the spent liquor may be recycled.

x) CRUDE LITHIUM CARBONATE CONVERSION STEP The crude lithium carbonate is added into an aqueous solution (for example water) to form a slurry, and calcium hydroxide (milk of lime) is added to provide a lithium hydroxide containing liquor.

In one embodiment, the crude lithium carbonate is dissolved into an aqueous solution (for example water) to provide a lithium bicarbonate containing liquor. The dissolution of the crude lithium carbonate in an aqueous solution is aided by the introduction of carbon dioxide into the solution. The solution is preferably cooled to a temperature of less than 20 °C.

Li2CO3(s)+ CO2(9)+ H20(I) +2Li HCO3(.q) Calcium hydroxide (milk of lime) may be added to the lithium bicarbonate containing liquor to provide a slurry comprising lithium hydroxide. The slurry may be filtered to provide a lithium hydroxide containing liquor.

In one embodiment, the second spent liquor may be recycled for use in this stage.

The precipitated calcium carbonate is separated from the slurry by filtration, for example in a centrifuge. After filtration, the lithium hydroxide containing liquor is collected, and the calcium carbonate may be recycled to prepare a feed mixture for the calcination process.

The temperature of the solution comprising calcium hydroxide and crude lithium carbonate or lithium bicarbonate is preferably at least 60 °C, preferably at least 70 °C, for example about 80 °C.

In one embodiment, the molar ratio of calcium hydroxide to crude lithium carbonate is preferably at least 1:1, for example 1: 1.5.

In one embodiment, the lithium concentration within the lithium hydroxide containing liquor is at least 5 g/L, preferably at least 7 g/L, for example 10 g/L. Preferably, the lithium concentration within the lithium hydroxide containing liquor is between 7 g/L and 10 g/L.

xi) ION EXCHANGE PURIFICATION STEP The lithium hydroxide containing liquor is further purified by the use of an ion-exchange column to provide a purified lithium hydroxide containing solution free or substantially free of calcium and other divalent cations. A highly selective chelating resin is used to remove calcium and other divalent cations from the lithium hydroxide containing liquor. The resin may be regenerated by treating it with diluted solutions of, for example, hydrochloric acid and sodium hydroxide.

xii) FINAL LITHIUM CRYSTALLISATION STEP Lithium hydroxide hydrate may be precipitated or crystallised by evaporation, from the high purity lithium hydroxide containing solution obtained from the ion exchange column.

The crystallised lithium hydroxide hydrate is removed from solution by a filtration device for example in a centrifuge, to produce high purity lithium hydroxide hydrate. The remaining liquor obtained from filtration, or second spent liquor, contains residual dissolved lithium, therefore the liquor may be recovered and reintroduced into the process to improve lithium recovery. For example, the second spent liquor may be reintroduced as the aqueous solution (or as part of the aqueous solution) in the conversion stage, thereby enabling the process to recover a higher yield of lithium from the lithium mica.

Optionally, the high-purity lithium hydroxide hydrate may be heated under an atmosphere free or substantially free of carbon dioxide to a temperature above 150°C, preferably above 180°C to form high-purity anhydrous lithium hydroxide.

Preferably, the high-purity lithium hydroxide hydrate (LiOH.H2O) has a purity of at least 55 wt % LiOH.

Preferably, the high-purity lithium hydroxide anhydrous (LiOH) has a purity of at least 97 wt % LiOH.

In one embodiment, the high purity lithium hydroxide hydrate may be washed to remove any entrained liquor which further removes impurities.

In another embodiment filtration may be replaced or complemented by a centrifuge or gravity dewatering stage.

xiv) MIXED SALT RECYCLING STEP The first spent liquor from the crude lithium carbonate precipitation (ix) preferably comprises an aqueous solution of sodium, potassium, lithium and sulphate ions amongst others.

In one embodiment, the recovery of the dissolved sulphate ions to a solid is achieved by cooling the spent liquor obtained from the crude carbonate precipitation (ix) step to cause the precipitation and/or crystallisation of a mixed salt. When filtered, the salt mixture residue is referred to as the mixed-salt-by-product; the remaining filtrate is called the third-spentliquor.

In one embodiment, the recovery of the dissolved sulphate ion to a solid is achieved by partial evaporation of the spent liquor, causing a mixed-salt precipitation.

The recycled mixed salt by-product preferably predominately comprises, for example consists of, a double salt of sodium and potassium sulphate, and may contain entrained lithium.

The recovery of mixed salts, for example sulphate salts, from the spent liquor preferably enables the mixture of sulphate salts to be recycled for use, optionally together with one or more additional sulphate salt(s), in the reagent mixing (i), thereby reducing costs associated with the supply of feed material whilst also reducing costs and environmental burdens associated with removal and disposal of waste products. By recovering the spent liquor and recycling this for further use within the lithium extraction process, the process has lower associated material, operational and processing costs and less environmental impacts compared to conventional lithium extraction processes. The process may also be more efficient than known conventional processes due to the ready supply and recovery of mixed sulphate salts as a feed material.

In one embodiment, part of the mixture of sulphate salts may bleed out (for example be rejected from the circuit) to control the balance of sodium and other impurities in the recycle liquor stream.

The third spent liquor may be recycled to the leaching stage, and as a such any remaining aqueous lithium ions present within the third spent liquor, remaining within the circuit of the process have another chance of being recovered to the lithium carbonate product. The present invention preferably reduces the amount of lithium lost during the recovery process by ensuring that the spent liquor is recycled as a leaching water, thereby remaining within the system.

BRIEF DESCRIPTION OF FIGURES

Figure 1 is a schematic illustration of a flow chart of one embodiment of the process of the present invention; Figure 2 is a schematic illustration of the reagent mixing and optional pelletising stage (i) according to one embodiment of the process of the present invention; Figure 3 is a schematic illustration of the calcination stage (ii) according to one embodiment of the present invention; Figure 4 is a schematic illustration of the leaching and filtration stage (iv) and (v) according to one embodiment of the present invention.

Figures 5A and SB are graphs illustrating the relationship between lithium recovery and ground or unground lithium mica -reagent mixture; Figure 6 is a graph illustrating the relationship between lithium recovery and pulp density; Figure 7 is a graph illustrating the relationship between lithium recovery and leaching time; Figure 8 is a graph illustrating the relationship between lithium recovery and residence time using different ratios of lithium mica and reagent mixtures; Figure 9 is a graph illustrating the relationship between lithium recovery and quench time.

DETAILED DESCRIPTION

With reference to Figures 1 and 2, the process for extracting lithium from lithium mica comprises mixing lithium mica (86) with a mixture of reagents comprising a sulphate salt (for example gypsum) (89) and calcium (for example calcium carbonate (CaCO3)) (88) in water, and optionally mixed recycled salts (230) recovered during the process, to provide a lithium mica-reagent mixture. The lithium mica-reagent mixture may optionally be pelletised to produce pelletised lithium mica-reagent mixture (74).

The amount of sulphate salt(s) and optionally mixed salt by-product may be present within the lithium mica-reagent mixture such that the total amount of Sulphate (504) contained is in stoichiometric excess in order to fully react with the lithium present within the lithium mica to form lithium sulphate.

Calcium carbonate may be provided in the form of limestone.

Two mixtures were prepared: Mixture 1: the ratio of lithium mica to sulphate salt (within gypsum) to carbonate salt (within limestone) is 6: 3: 2; and Mixture 2: the ratio of lithium mica to sulphate salt (within gypsum) to carbonate salt (within limestone) is 3: 3: 1.

It is however to be understood that the ratio of lithium mica to carbonate salt(s) within the lithium mica -reagent mixture or pelletised lithium mica -reagent mixture is preferably within the range of 6: 1 and 3: 1, preferably within the range of 6:1.5 and 6:2.5.

The ratio of lithium mica to sulphate salt(s) within the lithium mica-reagent mixture is preferably within the range of 6: 1 and 6: 5. The ratio of lithium mica to sulphate salt(s) to carbonate salt(s) within the lithium mica-reagent mixture is preferably within the range of between 6: 1: x and 6: 5: x. The ratio of lithium mica to sulphate salt(s) to carbonate salt(s) within the lithium mica-reagent mixture is preferably within the range of between 6: 1: x and 6: 3: x. The lithium mica and reagents are first mixed ahead of the pelletising stage The lithium mica-reagent mixture or pelletised lithium mica -reagent mixture (74) is optionally preheated using the recovered heat or off gas (71) from the calciner. The lithium mica-reagent mixture or pelletised lithium mica-reagent mixture (74) may be heated to a functional temperature prior to being introduced into a calciner. The lithium mica-reagent mixture or pelletised lithium mica-reagent mixture (74) is calcined within the calciner at a functional temperature for a functional time to provide a calcine discharge.

As shown in Figure 3, the pre-heated lithium mica-reagent mixture or preheated lithium mica-reagent mixture pellets (x) are calcined within a rotary calciner. It is however to be understood that the mixture may be calcined in any suitable calcining vessel as is not to be limited to a rotary calciner.

The rotation speed of the calciner tube, and rotation speed of the screw feeder of the rotary calciner can each be varied. The dynamics of the mixture within the calcining vessel, for example within the rotary calciner, is of importance to ensure sufficient mixing and blending of the material (for example the lithium mica-reagent mixture) to increase energy efficiency, to improve the desired chemical reactions and to reduce sintering of the mixture by preventing material from contacting inner walls of the vessel for prolonged periods of time.

The rotary parameters of the rotary calciner (such as for example rotation speed of the calciner tube and rotation speed of the screw feeder) are each selected to provide a cascading mixing motion of the mixture within the vessel.

The rotary parameters of the calcining vessel 204 are optimised to maximise residence time inside the tube. Preferably, the speed of rotation is approximately 1 rpm, for example between 0.5 rpm and 2 rpm.

The lithium mica-reagent mixture, optionally the lithium mica-reagent pellets, are heated to any suitable temperature within the calcining vessel within the range of about 750 °C to 1,100 °C. It is to be understood that the lithium mica-reagent mixture, optionally the lithium mica-reagent pellets may be heated to any suitable temperature within the calcining vessel, for example within the range of 800 °C to 1,100 °C, preferably within the range of 800 °C to 1,000 °C, preferably within the range 840 °C to 1,000 °C.

The calcining step is carried out such that the time maintained at temperature to complete the desired reactions is a period of between 30 and 50 minutes, however it is to be understood that the calcining step may be performed for any suitable duration, such as for example between 15 minutes and 120 minutes.

On completion of the calcining step, the calcine discharge comprising lithium sulphate and/or lithium potassium sulphate is obtained.

It is to be understood that the lithium recovery percentage is dependent on a combination of residence time and calcining temperature.

The calcine discharge can be added to the leach liquor at any temperature without the need for deliberate cooling.

The hot calcine discharge may however be cooled using heat recovery equipment, for example a rotary cooler or grate cooler, to an extent on completion of the calcining process and prior to deposition into the aqueous liquor for the purpose of heat recovery.

The ability to discharge the calciner discharge straight into an aqueous solution at any temperature removes the need for indirect cooling. Thus, any cooling can be for the sole purpose of energy recovery.

Any required breakup of the particles can be in a wet state, by a combination thermal fragmentation (shock quenching), agitation of the leach vessel, or attrition scrubbing.

It can therefore be seen that the process of the present invention may eliminate the need to further hot mill or grind the heated calcine discharge on completion of the calcining stage and prior to leaching.

In one embodiment, the heated, calcine discharge is deposited into the aqueous leaching liquor whilst the temperature difference between the calcine discharge and the aqueous leaching liquor is sufficient to cause thermal fracturing (shock quenching) of the calcine discharge.

The heated, calcine discharge may exit the calcining vessel directly, without any cooling, into the leaching vessel containing the leaching liquor. For example, the heated, calcine discharge may exit the calcining vessel at the temperature maintained during the calcining process.

The heated, calcine discharge preferably exits the cooler at a temperature in excess of 150 °C, preferably in excess of 200 °C, into an aqueous liquor at ambient temperature (or at least less than 60 °C).

The heated, calcine discharge may be discharged into an open-top pump and into the leaching vessel directly.

The temperature difference between the heated, calcine discharge and the aqueous liquor may be at least 125 °C. It is to be understood that the greater the temperature difference, the potentially greater thermal fracturing of the product. It is therefore to be understood that the temperature difference may for example be at least 150 °C, preferably at least 200 °C.

By dispensing the heated, calcine discharge directly, at a temperature of at least 150 °C, into the leaching liquor, the efficiency of transfer from a calcination kiln to the leaching liquor, within for example a leaching vessel, is rapidly improved with significantly reduced loss of product during transfer (such as in the form of dust) leading to a higher lithium recovery from the lithium mica, and improved environmental performance.

The direct deposition of the heated, calcine discharge into significantly cooler aqueous leaching liquor causes rapid generation of steam which causes thermal fragmentation effectively breaking apart the calcine discharge material which has been sintered or fused during calcination causing the product to break at least partially into fragments. The expansion of steam bubbles created during deposition of the calcine discharge into the aqueous leaching liquor causes thermal fracture of the particles aiding the processability of the quenched, leached, lithium containing calcine discharge.

Preferably the heated, calcine discharge firstly breaks into fragments on deposition into the aqueous leaching liquor by thermal fragmentation, and the agitation further breaks these fragments apart to form a slurry providing an increased surface area thereby improving the efficiency of leaching of the material, for example by reducing leach time and increasing lithium recovery.

It is however to be understood that dependent on a number of factors including: temperature of calcination, residence time during calcination, the temperature difference (on deposition) between the heated, calcine discharge and the aqueous leaching liquor, and residence time within the aqueous leaching liquor that the presence of additional agitation means in order to provide a slurry may not be required and may be achieved by thermal fragmentation alone.

The addition of attrition scrubbing, or wet milling may be required to break up sintered or fused lumps of calcine discharge.

The direct deposition of the heated, calcine discharge eliminates the need for an extra dry-milling step of the calcine discharge and therefore reduces the complexity, energy consumption and associated costs of the process.

By breaking down the particle size of the calcine discharge by direct deposition (without the requirement to cool the product to for example temperatures below 150 °C prior to leaching) from the calcination kiln into the leaching liquor, the surface area to volume ratio of the particles increases significantly. The increase in surface area to volume ratio of the calcine discharge containing lithium sulphate particles improves leaching efficiency of the product as there is an increased surface area particle exposure to the leaching liquor, thereby reducing leaching time and increasing lithium recovery rates.

The calcium is present to aid the conversion process by raising the sintering temperature of the mixture as well as capturing gases that may evolve during the calcining process such as fluorine gas and hydrogen fluoride mist. The calcium carbonate also binds with free silica preventing the back reaction of silica with lithium sulphate., thereby increasing lithium recovery.

The calcium is present to neutralise hydrofluoric acid which may be released from the lithium mica, so producing calcium fluoride, and preventing or reducing the emission to atmosphere of hydrofluoric acid.

The calcining process (i.e. the addition of the sulphate salt(s) and calcium carbonate) may be carried out in any directly or indirectly heated furnace or calciner in an oxidising atmosphere. The furnace or calciner may provide a controlled residence time of between 15 minutes and 120 minutes in the hot zone at the desired reaction temperature.

As shown in Figure 4, the calcine discharge 81 is subsequently exposed to leaching by introducing the calcine discharge 81 to a leaching vessel 82 comprising an aqueous leach liquor. The leach process preferably uses water with a natural pH (for example a pH of approximately between 9 and 10), with no requirement for any pH adjustment.

The aqueous leach liquor leaches the calcine discharge 81 to produce a lithium enriched leach liquor 83.

The leaching step may be carried out at a temperature between 15°C and 65°C to produce a lithium-enriched leach liquor.

The leach vessel may be agitated, and the reaction may be left running for between 0.1 hrs and 24 hrs to reach the desired recovery of lithium sulphate into the leach solution. The leach reaction may be carried out continuously or batch-wise.

The leaching step is preferably done over a period of time between 1 hrs and 4 hrs, at ambient temperature, or temperatures of up to 90°C and at less than 25% solids m/m (preferably greater than 10%). It is however to be understood that the leaching step may be carried out over any suitable time period, such as for example over a time period as short as 10 minutes, or over a time period as long as 24 hours.

The resultant lithium enriched leach liquor 83 may contain between 0.1 and 45 g/L, preferably between 5 g/L and 45 g/L of Li.

Once leaching has been completed, the lithium enriched leach liquor 83 is filtered using a filtration device 90. Filtration may occur using any suitable physical means, including for example pressure filtration or vacuum filtration.

As shown in Figure 1, the filter leach residue or calcine filter cake 79 can be disposed of or used for further processing. The solid filter leach residue or calcine filter cake 79 may be washed and the wash water 91 may be collected and recycled for use as (or as part of) the aqueous leach liquor in the leach vessel 82 of the leaching step.

The leachate 77 (or leachate liquor) may be optionally purified using a first stage impurity removal step 92. Sodium carbonate, soda ash, is added to the leachate 77 resulting in the precipitation of impurities, in the form of for example calcium carbonate. The precipitated impurities are removed by filtration 93. The first impurity reduced leachate 84 is then evaporated 87 to provide a concentrated leachate 224. In this step, the concentrate of lithium in solution is increased.

Impurities are then removed from the concentrated leachate 224 in a second stage impurity removal step 94 using a two-stage process comprising the addition of calcium hydroxide followed by treatment with activated alumina to produce a second impurity reduced leachate 99.

A carbonate source is then added to the second impurity reduced leachate (99) to provide a precipitated crude lithium carbonate slurry 121. The slurry is then filtered to provide crude lithium carbonate 138 and a first-spent-liquor 102. This first spent liquor 102 is then chilled to cause a mixed salt precipitation within the now chilled slurry 104. The chilled slurry is then filtered to separate the mixed salts (Glauber Salt Dewatering) leaving behind the filtrate as the third spent liquor. The mixed salts can be recycled 230 as a calcination reagent into the reagent mixing stage. The third-spent-liquor can be recycled 106 to the leach water.

The crude lithium carbonate 138 is then added to distilled water and calcium hydroxide (milk of lime) is added to provide a slurry of calcium carbonate in a lithium hydroxide liquor 140. The slurry is then filtered to provide a lithium hydroxide containing liquor 141 and calcium carbonate cake. The lithium hydroxide containing liquor 140 is passed through an ion exchange column as a polishing stage to remove additional impurities to produce a polished lithium hydroxide solution 185.

The polished lithium hydroxide solution 185 is then evaporated to cause a crystallisation of a high purity lithium hydroxide 189 which is then dewatered and washed to provide high grade lithium hydroxide hydrate 196 which can then be optionally dried under inert atmosphere before packing.

As shown in Figure 9, by directly depositing heated, calcine discharge into aqueous leaching liquor (with a temperature difference of at least 125 °C; and with a residence time of 50 minutes) it can be seen that the recovery rate of lithium (84.8 %) is comparable to the recovery rate of lithium (86.5%) achieved using a more complex process which requires milling of hot, calcine discharge (after calcination) prior to deposition of the product in aqueous leaching liquor. As a result, it can be seen that the process of the present invention can be used successfully to provide good recovery rates of lithium from lithium mica without requiring complex processing, such as hot milling or grinding of calcine material. The process of the present invention is therefore more energy efficient, with lower associated time requirements, processing costs and operating costs, lower risk of material losses during extraction, and lower associated carbon footprint with higher plant availability whilst achieving the same or improved recovery rates of lithium as conventional leaching of calcined lithium mica.

It can be seen from Figures 5A and SB that heated calcine discharge produced at a calcining temperature of between 900 °C and 1,000 °C, with a residence time of between 30 and 50 minutes, produces similar lithium recovery (%) as reground calcine discharge at the same temperature, for example having a lithium recovery of between 35% and 90%. Heated calcine discharge produced at a calcining temperature of 1,000 °C, with a residence time of between 30 and 50 minutes, has been found to produce a similar lithium recovery (%) as reground calcine discharge at the same temperature, for example having a lithium recovery of roughly 90%.

Pulp density can be an important consideration in hydrometallurgical separation as water evaporation to increase the concentration of liquors has a high associated operational and energy cost.

With reference to Figure 6, various pulp densities at different calcination conditions (calcination temperature and residence time) were evaluated. Figure 6 shows that at 1,000 °C, with a residence time of 30 minutes, there is a small reduction in lithium recovery from 10% to 20% pulp density. The lithium recovery then plateaus to 30% pulp density. Maintaining this lithium recovery is considered beneficial as i) a reduced residence time of 30 minutes is favourable from a calcination perspective as having a reduced residence time increases throughput; and ii) maintaining a high pulp density is favourable for process economics.

Leaching time can also influence the lithium recovery rate. The results of leaching time on lithium recovery are shown in Figure 7. It can be seen that in general, the longer the leaching time, the higher the lithium recovery. With an increased leaching time, the conglomerates of calcined material have longer to break apart, increasing the surface area and improving dissolution of lithium sulphate and/or lithium potassium hydroxide.

The use of calcium sulphate (gypsum) in the calcining step was found in the inventor's testwork to significantly reduce binding of the mica material/calcined mica material to the sides of the equipment. Furthermore, when using calcium sulphate, it was found in the inventor's testwork that the feed mixture had greater mobility within the apparatus.

The use of calcium sulphate has also been found in the inventor's testwork to promote conglomeration and pellitisation of the lithium mica-reagent mixture. Conglomeration and pellitisation of the feed material helps to reduce loss of lithium during extraction. For example, without conglomeration and pellitisation lithium containing material and/or reagents may be lost as dust. The conglomeration and pellitisation is thought to occur as a result of calcium sulphate absorbing moisture.

Increasing the temperature has been found by the inventor's testwork to improve lithium recovery, even with reduced residence time.

The process of the present may be carried out without requiring additional milling circuits whilst achieving high lithium recovery rates.

As shown in Figure 8, the lithium mica-reagent mixture was heated to temperatures within the calcining vessel of: 800 °C, 850 °C, 900 °C and 1,000 °C.

From Figure 8, the feed source (Mixture A) comprises a ratio of lithium mica to sulphate salt (preferably gypsum) to carbonate salt (preferably limestone) of 6: 3: 2 and heated during the calcining step to a temperature within the range of 800 °C to 1,100 °C. By using a feed source comprising a ratio of lithium mica to sulphate salt (preferably gypsum) to carbonate salt (preferably limestone) of 6: 3: 2 and heating the mixture during the calcining step to a temperature within the range of 850 °C to 1,100 °C, preferably within the range of 900 °C to 1,000 °C, with a residence time of between 30 and 50 minutes, the lithium recovery has been found in the inventor's testwork to be in the range of from 35% to 90%. By using a feed source comprising a ratio of lithium mica to sulphate salt (preferably gypsum) to carbonate salt (preferably limestone) of 6: 3: 2 and heating the mixture during the calcining step to a temperature within the range of 850 °C to 1,100 °C, preferably within the range of 900 °C to 1,000 °C, with a residence time of between 40 and 50 minutes, the lithium recovery has been found by the inventor's testwork to be in the range of from 50% to 90%.

The feed source (Mixture B) comprises a ratio of lithium mica to sulphate salt (preferably gypsum) to carbonate salt (preferably limestone) of 3: 3: 1 and heated during the calcining step to a temperature within the range of 850 °C to 1,100 °C. By using a feed source comprising a ratio of lithium mica to sulphate salt (preferably gypsum) to carbonate salt (preferably limestone) of 3: 3: 1 and heating the feed source during the calcining step to a temperature within the range of 900 °C to 1,000 °C, with a residence time of between 30 and 50 minutes, the lithium recovery has been found by the inventor's testwork to be in the range of from 55% to 90%. By using a feed source comprising a ratio of lithium mica to sulphate salt (preferably gypsum) to carbonate salt (preferably limestone) of 3: 3: 1 and heating the mixture during the calcining step to a temperature within the range of 900 °C to 1,000 °C, with a residence time of between 40 and 50 minutes, the lithium recovery has been found by the inventor's testwork to be in the range of from 70% to 90%.

The calcining step was carried out for a period of between 30 and 50 minutes, however, it is to be understood that the calcining step may be performed for any suitable duration, such as for example between 15 minutes and 120 minutes.

The process of the present invention reduces the risk of loss of lithium during extraction. The number of steps of the process have been reduced therefore requiring less apparatus and increasing overall process availability. The associated process and operating costs, labour and energy consumption of the apparatus and the process of the present invention are therefore reduced whilst the lithium recovery has been improved compared to conventional lithium mica extraction processes.

The process and apparatus of the present invention provide for improved lithium recovery from lithium mica material, whilst also providing for significant associated energy use, carbon emissions, time and cost savings.

Claims

CLAIMS1. A process for producing crystallised or precipitated lithium hydroxide hydrate or anhydrous lithium hydroxide from lithium mica, the process comprising: i. blending lithium mica, preferably lithium mica concentrate, with a reagent or mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s) in a functional ratio to produce a lithium mica-reagent mixture, and optionally pelletising the lithium mica-reagent mixture to provide pelletised lithium mica-reagent mixture; ii. calcining the lithium mica-reagent mixture or pelletised lithium mica-reagent mixture at a functional temperature for a functional time to provide a hot calcine discharge comprising water soluble lithium sulphate; iii. optionally further comprising heat recovery/cooling of the calcine discharge, prior to leaching to provide a calcine-product comprising lithium sulphate and/or lithium potassium sulphate; iv. leaching the calcine discharge or calcine product for a functional time and having a functional pulp density in an aqueous leach liquor to provide a lithium-enriched leach liquor; v. filtering the lithium enriched leach liquor to produce a leachate (also herein referred to as leachate liquor or filtrate) and a filter leach-residue herein also referred to as "calcine filter cake"); vi. optionally adding at least one carbonate salt (preferably a Group I metal carbonate, for example sodium carbonate) to the leachate liquor in a first stage impurity removal step to provide a first impurity reduced leachate; vii. concentrating at least a portion of the leachate liquor or the first impurity reduced leachate to provide a concentrated leachate; viii. optionally removing impurities from the concentrated leachate in a second stage impurity removal step comprising addition of calcium hydroxide and calcium carbonate, and optional treatment with activated alumina, to provide a second reduced impurity containing leachate; ix. adding a carbonate source to the leachate liquor and/or concentrated leachate and/or second reduced impurity containing leachate to produce a lithium carbonate slurry comprising lithium carbonate precipitate, and subsequently filtering the lithium carbonate slurry to provide a first spent liquor and crude lithium carbonate; x. conversion of crude lithium carbonate into lithium hydroxide in water by adding calcium hydroxide (milk of lime) to the crude lithium carbonate to produce a slurry containing lithium hydroxide liquor, and subsequently filtering the slurry to provide a lithium hydroxide liquor and calcium carbonate cake; xi. optionally passing the lithium hydroxide liquor through an ion exchange column to provide a purified lithium hydroxide containing solution with a reduced concentration of, preferably substantially free of, calcium and other divalent cations; xii. Precipitating or crystallising high purity lithium hydroxide hydrate (Li0H.H20) from the purified lithium hydroxide containing solution by evaporation of water from the solution, and obtaining high purity crystallised or precipitated lithium hydroxide hydrate by filtration and a resultant second spent liquor; xiii. optionally heating the lithium hydroxide hydrate to a functional temperature (preferably a functional temperature of over 150 °C, preferably a functional temperature of over 180 °C) to evaporate water to produce anhydrous lithium hydroxide NOW; and xiv. optionally precipitating or crystallising a mixed salt by-product by taking the first spent liquor obtained from the crystallisation step (ix), and i) chilling and/or ii) evaporating the first spent liquor, obtaining a mixed salt by-product by filtration of the crystallised first spent liquor and a third spent liquor, and optionally recycling the mixed salt by-product for introduction into the mixture of reagents for producing the lithium mica-reagent mixture, and/or optionally recycling the third spent liquor for introduction into the aqueous leach liquor of step iv.
2. A process as claimed in claim 1, in which the lithium mica-reagent mixture or pelletised lithium mica-reagent mixture comprises particles, each particle having a maximum particle size of no more than 30 mm.
3. A process as claimed in either of claims 1 and 2, in which the crystallisation and/or precipitation of the mixed salt by-product occurs by either i) chilling the first spent liquor, and/or ii) evaporating off first spent liquor to cause crystallisation and/or precipitation.
4. A process as claimed in claim 3, in which the crystallisation or precipitation of the mixed salt by-product is achieved by chilling the first spent liquor to a temperature of less than 10 °C, preferably less than 7 °C.
5. A process as claimed in any preceding claim, in which the second spent liquor is recycled and introduced into step ix and/or step (x) in whole or partial replacement of water.
6. A process as claimed in any preceding claim, in which the first stage impurity removal step (vi) is omitted.
7. A process as claimed in any preceding claim, in which the lithium mica comprises of particles whose accumulated particle size distribution as measured by P80 value (i.e. the particle size at which 80% of the concentrate will pass when screened) is of 450 km or smaller.
8. A process as claimed in any preceding claim, in which the lithium mica comprises of particles, in which at least 80% of the particles have a particle size of greater than 15 km in size.
9. A process as claimed in any preceding claim, in which the reagent or mixture of reagents comprises less than 5 wt %, preferably is substantially free of, hydrated lime.
10. A process as claimed in any preceding claim, in which the make-up sulphate salt(s) is predominantly calcium sulphate.
11. A process as claimed in any preceding claim, in which the sulphate salt(s) is present within the lithium mica-reagent mixture such that the total sulphate salt(s) concentration, optionally including one or more sulphate salt(s) present within the mixed salt by-product, is present within the mixture in an amount sufficient such that the total amount of sulphate (SO4) present is equal to or in excess of the amount required in order to fully react with the lithium present within the lithium mica to form lithium sulphate.
12. A process as claimed in any preceding claim, in which calcium carbonate is provided in the form of limestone.
13. A process as claimed in any preceding claim, in which a residue obtained from the first stage impurity removal step is recycled into one or more steps of the process.
14. A process as claimed in any preceding claim, in which the one or more of: the ratio of lithium mica to calcium carbonate within the mixture is within the range of 6: 1 and 6:3; and/or the ratio of lithium mica to sulphate salts within the mixture is preferably within the range of 6: 2 and 6:5.
15. A process as claimed in any preceding claim, in which the lithium mica-reagent mixture is heated prior to calcination.
16. A process as claimed in any preceding claim, in which the functional temperature of the calcining step is within the range of about 800 °C to 1,050 °C.
17. A process as claimed in any preceding claim, in which the functional time held at the functional temperature for the calcining step is between 30 minutes and 380 minutes.
18. A process as claimed in any preceding claim, in which the calcining step occurs within a rotary kiln.
19. A process as claimed in any preceding claim, in which the aqueous leach liquor comprises water having a neutral pH without the need for acid addition.
20. A process as claimed in any preceding claim, in which the aqueous leach liquor comprises wash water recovered from previous batches of the process.
21. A process as claimed in any preceding claim, in which the pulp density of the lithium enriched leach liquor is between 7% and 40%.
22. A process as claimed in any preceding claim, in which the aqueous leaching liquor is maintained at a temperature of less 90 °C, optionally in which initially the aqueous leaching liquor is heated to the boiling point of the liquor.
23. A process as claimed in any preceding claim, in which the calcine discharge resides within the aqueous leaching liquor for between 10 minutes and 120 minutes or longer.
24. A process as claimed in any preceding claim, further comprising washing the calcine filter cake to recover residual lithium.
25. A process as claimed in any preceding claim, in which the recovered mixed salt byproduct comprises one or more of: sodium salt(s), potassium salt(s), calcium salt(s) and lithium salt(s), or any combination thereof.
26. A process as claimed in claim 25, in which the recovered mixed salt by-product comprises one or more of: sodium sulphate, potassium sulphate, calcium sulphate and/or lithium sulphate, or any combination thereof.
27. A process as claimed in any preceding claim, further comprising precipitating or crystallising mixed sulphate salt from the first spent liquor.
28. A process as claimed in any preceding claim, further comprising one or more of: a further dissolution/bicarbonate step is provided prior to conversion of purified lithium carbonate into lithium hydroxide (step x); and/or removal of a mixed sulphate salt between leaching of the calcine discharge or calcine product (step iv) and production of the lithium carbonate slurry (step ix); and/or Passing crude lithium sulphate liquor through activated alumina to remove fluoride and/or rubidium prior to the production of the lithium carbonate slurry (step ix).
29. A process as claimed in any preceding claim, in which step x comprises dissolving the crude lithium carbonate produced in step ix in water with a stream of carbon dioxide gas bubbling therethrough to produce lithium bicarbonate containing liquor, adding calcium hydroxide to the lithium bicarbonate containing liquor to provide a slurry comprising lithium hydroxide, and subsequently filtering the slurry to provide a lithium hydroxide liquor and calcium carbonate cake.
30. A process as claimed in any preceding claim, further comprising purification of the high purity precipitated or crystallised lithium hydroxide hydrate or anhydrous lithium hydroxide by precipitation or crystallisation.
31. A lithium mica-reagent mixture comprising a lithium mica concentrate with a reagent or mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s), optionally further comprising mixed salt and/or recycled mixed calcium salts, in which the lithium mica-reagent mixture is substantially free from hydrated lime.
32. A lithium mica-reagent mixture as claimed in claim 31, in which the particle size of the lithium mica concentrate has a Pgo value (i.e. the particle size at which 80% of the particles will pass when screened) of 450 p.m or smaller.
33. A lithium mica-reagent mixture as claimed in claim 31, in which the lithium mica concentrate contained within the mixture has a particle size distribution such that >80% of the particles of the lithium mica concentrate are greater than 15km.
34. A pelletised lithium mica-reagent mixture comprising a lithium mica, preferably a lithium mica concentrate, with a reagent or mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s) and/or recycled mixed sulphate salts and/or recycled mixed calcium salts.
35. A pelletised lithium mica-reagent mixture as claimed in claim 34, in which pellet particles have a maximum particle size of no more than 30 mm.
36. A pelletised lithium mica-reagent mixture as claimed in either of claims 34 and 35, in which the mixture is substantially free from hydrated lime.
37. A lithium mica-reagent mixture as claimed in any one of claims 31 to 33 or a pelletised lithium mica-reagent mixture as claimed in any one of claims 34 to 36, in which the sulphate salt(s) is calcium sulphate.
38. A lithium mica-reagent mixture as claimed in any one of claims 31 to 33 or a pelletised lithium mica-reagent mixture as claimed in any one of claims 34 to 36, in which the sulphate salt(s) is present within the mixture such that the total sulphate salt(s) concentration, optionally including one or more sulphate salt(s) present within the mixed salt by-product, is present within the mixture in an amount sufficient such that the total amount of sulphate salt(s) present is equal to or in excess of the amount required in order to fully react with the lithium present within the lithium mica concentrate to form lithium sulphate.
39. A lithium mica-reagent mixture as claimed in anyone of claims 31 to 33 or a pelletised lithium mica-reagent mixture as claimed in any one of claims 34 to 3, in which calcium carbonate is provided in the form of limestone.
40. A lithium mica-reagent mixture as claimed in claim 31 to 33 or a pelletised lithium mica-reagent mixture as claimed in any one of claims 34 to 36 in which the ratio of lithium mica to calcium carbonate within the mixture is within the range of 6: 1 and 6: 3.
41. Use of at least one carbonate salt(s) in the calcination of a lithium mica-reagent mixture or pelletised lithium mica-reagent mixture comprising a mixture of lithium-mica concentrate with a mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s), optionally further comprising mixed salt by-product and/or recycled mixed calcium, in which the ratio of lithium mica to carbonate salt(s) within the lithium mica-reagent mixture or pelletised lithium mica-reagent mixture is within the range of 6: 1 and 6: 3.
42. Use of at least one sulphate salt(s) in the calcination of a lithium mica-reagent mixture or pelletised lithium mica-reagent mixture comprising a mixture of lithium-mica concentrate with a mixture of reagents comprising one or more of: calcium carbonate and/or sulphate salt(s), optionally further comprising mixed salt by-product and/or recycled mixed calcium salts, in which the ratio of lithium mica to sulphate salt(s) (including mixed salt by-product) within the lithium mica-reagent mixture or pelletised lithium mica-reagent mixture is within the range of 6: 2 and 6:5.