Impurity removal and leaching of lithium material

Abstract

A method of extracting lithium from lithium-mica minerals such as zinnwaldite and lepidolite by leaching a calcined product using an aqueous leach liquor to produce an enriched lithium leach liquor an

Description

The present invention relates to a process for simultaneous impurity removal and leaching of lithium material from lithium mica material. BACKGROUND OF INVENTION Lithium micas present an important source of lithium that is likely to grow in significance as the demand for lithium is expected to increase considerably in light of a worldwide effort to reduce carbon emissions. Lithium is predominantly used to make battery chemicals. It is extracted from brines and hard rock deposits containing spodumene. The former involves 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 roasting and acid leaching to produce a lithium-enriched brine or pregnant leach solution that is then purified to obtain a final lithium salt product. Alongside spodumene, lithium in mica can also present potentially economic deposits. These occur within granites in Europe and elsewhere, which also contain gangue minerals, principally quartz and feldspar. However, lithium is currently not extracted commercially from lithium-mica and so to exploit these deposits commercially there is a need to develop an environmentally sustainable and economic methods for extraction of lithium salts of acceptable quality from these micas. Lithium-mica minerals such as zinnwaldite (KLiFeAI(AISi3)Oio(OH,F)2; potassium lithium iron aluminium silicate hydroxide fluoride) and lepidolite (KLi2AISi40io(OH,F)2) are tri-octahedral mica minerals that exist in a solid solution series whose end members are siderophyllite (KFe2AI(Al2Si20io)(F,OH)2; potassium iron aluminium silicate hydroxide fluoride) and polylithionite (KLi2AI(Si40io)(F,OH)2;potassium lithium aluminium silicate hydroxide fluoride). They contain a wider range of elements than spodumene LiAI(Si20e) (lithium aluminium inosilicate) and, consequently, they are less rich in lithium. For instance, the lithium content of pure zinnwaldite is 1.59% by mass, compared to 3.73% for spodumene. Given the disadvantages of lithium-mica minerals of lower grade and higher mineral complexity compared to spodumene there is a need for a refining process for brines derived from lithium-mica minerals with improved lithium recovery efficiency and lower environmental impact. Conventional processes for obtaining enriched lithium liquor from calcined lithium containing products, as shown in Figure 1, typically involve leaching a calcine product in a first leach tank followed by filtration using a first filtration device (i.e. a leach filtration device) to obtain a calcined filter residue and an enriched lithium leach liquor. Reagents are then added to the enriched lithium leach liquor in a second tank (for example an agitation tank) which is then passed through a second filtration device (i.e. a downstream calcium impurity removal filtration device) to remove impurities and to provide purified liquor. There is a need for an improved calcination process with reduced associated energy, cost and environmental implications whilst also improving the lithium recover efficiency. SUMMARY OF INVENTION The present invention provides a process which removes the requirement for the use of a leach filtration device together with a downstream calcium impurity filtration device as required by conventional calcination processes. The present invention provide a process which is capable of simultaneously removing calcined filter residue (also referred to herein as leach residue) and calcium impurity in a single filtration step. According to a first aspect of the present invention, there is provided a process for simultaneous calcium impurity removal and leaching of lithium material from a calcined product comprising: leaching a calcined product in an aqueous leach liquor in a vessel to produce an enriched lithium leach liquor and a leach residue; introducing at least one alkaline carbonate reagent to the enriched lithium leach liquor to provide a slurry comprising precipitated calcium carbonate containing impurity, leach residue and enriched lithium leach liquor; and filtering the slurry to remove both the leach residue and the precipitated calcium carbonate containing impurity, and to provide a purified enriched lithium leach liquor. According to a second aspect of the present invention, there is provided an apparatus for simultaneous impurity removal and leaching of lithium material from lithium mica material comprising: a co-leaching and precipitation vessel in communication with a calcined product feed source and an alkaline carbonate reagent feed source to generate a product feed stream comprising a slurry comprising leach residue, precipitated calcium carbonate containing impurity, and enriched lithium leach liquor; and a filtration device in communication with the co-leaching and precipitation vessel to receive the slurry therefrom, in which the filtration device is configured to simultaneously remove both leach residue and precipitated calcium carbonate containing impurity, and to provide a purified enriched lithium leach liquor from the slurry. In one embodiment the calcium carbonate containing impurity consists of predominantly calcium carbonate. Preferably, the calcined product is formed from a lithium mica derivative. Preferably, the calcined product contains comprises lithium sulfate. In one embodiment, the calcined product is a calcinated lithium containing product, for example a calcinated lithium sulphate product. The present invention enables purified enriched lithium leach liquor to be obtained from calcined product using a simplified process and apparatus. In particular, the present invention without requiring the use of two separate filter devices. In particular, the present invention enables purified enriched lithium leach liquor to be obtained from calcined product without requiring the use of a first leach filtration device for removal of calcined filter residue, and a second downstream calcium impurity removal filtration device to remove calcium impurities in order to provide purified liquor. In contrast, the present invention enables purified enriched lithium leach liquor to be obtained as a result of a co-leaching and precipitation step followed by a single filtration step configured to remove both leach residue and precipitated calcium carbonate containing impurity to provide purified enriched lithium liquor. The present invention therefore provides for significant associated energy, carbon, time and cost savings. The carbonate salt(s) may be introduced to the aqueous leach liquor after introduction of the calcined product into the aqueous leach liquor. In one embodiment, the carbonate salt(s) is introduced after introduction of the calcined product (e.g. calcined lithium sulphate) to the aqueous leach liquor at a predetermined flow rate to minimise localised points of pH saturation which may reduce precipitate formation and increase lithium losses. The carbonate salt(s) may be a Group I metal carbonate salt. The carbonate salt is preferably one or more of: sodium carbonate and / or potassium carbonate. For example, the carbonate salt is sodium carbonate. Preferably, the alkaline carbonate reagent(s) is introduced at an amount of at least 2 g per 1 liter of calcined product. Preferably, the residence time of the calcined product and aqueous liquor with the at least one alkaline carbonate reagent is approximately 1 hour. The temperature of the aqueous leach liquor is preferably maintained as being 40 °C or less, for example at room temperature. In one embodiment, the pulp density of the enriched lithium leach liquor is between 7% and 40%, for example between 10% and 35%. In one embodiment, the enriched lithium leach liquor is filtered by the filtering device prior to the introduction of the alkaline carbonate reagent. For example, the enriched lithium leach liquor may be filtered by the filtering device and returned to the co-leaching and precipitation vessel prior to the introduction of the alkaline carbonate reagent to the vessel. It has been found that the efficiency of producing lithium carbonate is improved by the removal of the impurity calcium. The process of the present invention reduces the number of process steps and therefore reduces the risk of loss of lithium during extraction. The number of steps of the process have been reduced therefore requiring less apparatus. 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. Embodiments of the present invention will now be described in more detail with reference to the accompanying Figures: BRIEF DESCRIPTION OF FIGURES Figure 1 is a schematic illustration of the conventional leaching apparatus for calcined products; Figure 2 is a schematic illustration of an apparatus according one embodiment of the present invention for simultaneous impurity removal and leaching of lithium material from lithium mica material; and Figure 3 is a flow diagram of the process for simultaneous purity removal and leaching of lithium material from lithium mica material according to one embodiment of the present invention. DETAILED DESCRIPTION With reference to Figure 1, conventional processes for the purification of calcined products, such as calcined lithium sulphate containing products, comprise the use of apparatus 1 comprising a first leach tank 10 in communication with a first filtration device 11 (i.e. a leach filtration device). In use, calcined product 80 / 81 comprising lithium sulphate is leached with aqueous leach liquor in the first leach tank 10. The lithium sulphate within the calcined product, along with other impurities dissolves in the liquor. The leach liquor is then filtered by the first filtration device 11 to obtain a calcined filter residue 12 and an enriched lithium leach liquor 13. Reagents such as sodium carbonate are then added to the enriched lithium leach liquor 13 in a second tank 14 (for example an agitation tank) to produce calcium carbonate. The slurry is passed through a second filtration device 15 (i.e. a downstream calcium impurity removal filtration device) to remove calcium carbonate and to provide purified liquor 16. In a conventional purification process, as shown in Figure 1, the concentration of the leach liquor must be increased through evaporation in order to cause saturation of dissolved impurities in subsequent steps in order for the impurities to be precipitated and filtered out from the liquor leading to purification of the remaining lithium enriched liquor. The presence of calcium in the leach liquor can lead to scaling of the evaporation step and as such calcium should be removed from the leach liquor. This requires a dedicated reaction tank and filtration stage to remove the calcium impurities which increases the complexity of the process. In contrast, the present invention enables calcium impurity removal to be carried out in conjunction with the leaching of the calcined product thereby removing the need for a dedicated calcium removal step. The remaining liquor can then be purified before the production of lithium carbonate or lithium hydroxide. With reference to Figure 2, the process of the present invention uses apparatus 20 comprising a co-leaching and precipitation vessel 21, comprising an aqueous leach liquor, in communication with a calcined product feed source 80 / 81 and an alkaline carbonate reagent feed source 22. The calcined product comprising lithium sulphate 80 / 81 is received within the vessel 21 and lithium sulphate along with other impurities dissolve in the aqueous leach liquor. An alkaline carbonate reagent, for example sodium carbonate, is added so as to cause calcium carbonate to precipitate. The co-leaching and precipitation vessel 21 is configured to provide a product feed stream 23 comprising a slurry comprising leach residue, precipitated calcium carbonate containing impurity, and enriched lithium leach liquor. The product feed stream 23 is introduced into a filtration device 24 which is configured to simultaneously remove both leach residue (also herein referred to as calcined filter residue) 25 and calcium containing impurity 26, and to provide a purified enriched lithium leach liquor T1, from the slurry. The calcined product 80 may be milled or ground to produce a milled or ground calcined product 81 prior to introduction into the aqueous leach liquor. The alkaline carbonate reagent feed source is preferably introduced into the vessel after the calcined product has been leached in the aqueous leach liquor. The calcined feed source 80 / 81 may first be leached in an aqueous leach liquor within the vessel 21 and filtered through the filtration device 24 and returned 28 to the vessel 21 prior to introduction of the alkaline carbonate reagent feed source. With reference to Figure 3, the process for simultaneous impurity removal and leaching of lithium material from lithium mica material comprises obtaining calcined lithium sulphate containing product (101). Preferably this is obtained from lithium mica material. The calcining step is 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. On completion of the calcining step, the calcined lithium sulphate containing product (101) is obtained. The calcined lithium sulphate containing product (101) is introduced into an aqueous leach liquor (103) with a carbonate salt (102). In the illustrated embodiment, the carbonate salt is a sodium carbonate. It is to be understood that the carbonate salt may be any suitable carbonate salt, such as for example other Group I metal carbonate salts, or mixtures thereof. The calcined lithium sulphate containing product may be introduced to the leaching vessel, for simultaneous leaching and precipitation, directly from a calcining vessel (103). The calcined lithium sulphate containing product is leached with the aqueous leach liquor prior to introduction of the sodium carbonate salt. After introduction of the carbonate salt, the product stream is filtered by a filtration device to simultaneously recover leach residue (also herein referred to as calcined filter residue) and calcium containing impurity, and to provide a purified enriched lithium leach liquor, from the slurry. In one embodiment, the lithium enriched liquor obtained from leaching the calcined product may be filtered through the filtration device and recycled back to the co-leaching and precipitation vessel prior to introducing the sodium carbonate salt. The process of the present invention reduces the number of process steps and therefore reduces the risk of loss of lithium during extraction. The number of steps of the process have been reduced therefore requiring less apparatus. 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, carbon, 5 time and cost savings. 16 04 25

Claims

1. A process for calcium impurity removal and leaching of lithium material from a calcined lithium sulphate product derived from a lithium-mica mineral comprising:5 leaching a calcined product in an aqueous leach liquor in a vessel to produce an enrichedlithium leach liquor and a leach residue;introducing at least one alkaline carbonate reagent to the enriched lithium leach liquor to provide a slurry comprising precipitated calcium carbonate containing impurity, leach residue and enriched lithium leach liquor; and10 filtering the slurry to simultaneously remove both the leach residue and theprecipitated calcium carbonate containing impurity, and a purified enriched lithium leach liquor.

2. A process as claimed in claim 1, in which the alkaline carbonate reagent is a Group I metal carbonate salt.

3. A process as claimed in claim 2, in which the carbonate salt is one or more of: sodium15 carbonate and / or potassium carbonate.

4. A process as claimed in claim 3, in which the carbonate salt is sodium carbonate.

5. A process as claimed in any preceding claim, in which the temperature of the leachliquor is maintained as being 40 °C or less.

6. A process as claimed in any preceding claim, in which the enriched lithium leach liquor 20 is filtered and reintroduced prior to introduction of the alkaline carbonate reagent.

7. An apparatus for impurity removal and leaching of lithium material from a calcined lithium sulphate product derived from a lithium mica material comprising:a co-leaching and precipitation vessel in communication with a calcined lithium sulphate product feed source and an alkaline carbonate reagent feed source to generate a product feed stream comprising a slurry comprising leach residue, precipitated calcium carbonate containing impurity, and enriched lithium leach liquor; anda filtration device in communication with the co-leaching and precipitation vessel to receive the slurry therefrom, in which the filtration device is configured to simultaneously remove both leach residue and precipitated calcium carbonate containing impurity, and to provide a purified enriched lithium leach liquor, from the slurry.16 04 25

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