A method for recovering lithium from a stream containing lithium

Abstract

The present invention relates to a method for recovering lithium from a stream containing lithium, the method comprising contacting the stream, or a pre-treated solution obtained from said stream, with sodium aluminate to form a slurry comprising a lithium aluminate precipitate, at an alkaline pH; and recovering the slurry containing said lithium aluminate, or a precipitate therefrom.

Description

[0001] A METHOD FOR RECOVERING LITHIUM FROM A STREAM CONTAINING LITHIUM

[0002] FIELD

[0003] The present invention relates to a method for recovering lithium from a stream containing lithium, obtained by processing ores, brines or recycled material, such as battery waste material.

[0004] In particular, the present invention relates to the method described above in connection with a soda-leaching process, wherein the stream containing lithium is a fraction obtained from soda-leaching process, lithium is recovered from such stream by the above method for recovering lithium and the recovered lithium is returned to the soda-leaching process.

[0005] BACKGROUND

[0006] Lithium (Li) is a metal used in batteries and currently the mining and processing of lithium is of great interest. The main sources of lithium include brines and ores, while recycling of various Li-containing materials, e.g. battery waste material, is also increasing.

[0007] Processes treating lithium-bearing mineral raw material, such as rocks, ores, clay or concentrates, usually involve first thermal treatment of these rocks at high temperature, followed by water leaching to release lithium values into solution. Brines are typically concentrated before further processing. The leach liquors or concentrated brines are then further treated using precipitation, ion exchange, etc., to remove residual contaminants. Carbonation using soda ash or carbon dioxide is typical to precipitate lithium carbonate as the final product, whereas lithium hydroxide (LiOH) is frequently recovered via crystallization or electrodialysis, e.g. using bipolar membranes.

[0008] However, especially in the LiOH route, there will still be significant amounts of lithium left in the solution after crystallisation and removal of the main product as a solid, the remaining solution typically still containing around 30 g / 1 lithium. One possible way to recover the remaining lithium from such solution is to use lithium carbonate and / or phosphate precipitation, which allows lowering the concentration of lithium in said solutions. When using a combination of carbonate and phosphate precipitation, a level of 250 mg / 1 can be achieved, which seems to be the lowest guaranteed level with this method. However, the current environmental concerns mean that even lower levels of lithium in the process effluent would be beneficial. Furthermore, effluents from lithium phosphate precipitation typically contain residual phosphate, which should not be released into nature.

[0009] Other existing technologies to treat effluents from lithium processing mainly consist of evaporation and crystallisation of the final waste and effluents. However, this method is known to be very expensive, and require much more space than a simple precipitation process. Furthermore, evaporation and crystallisation may take a long time, which also increases the risk of leakage into nature, due to for example heavy rains. Ion exchange may also be used but has the disadvantage that the effluent may have other harmful components, such as chloride. Ettringite might also be possible to use, but is typically not even contemplated, since it creates a mixture of impurities in a sludge, the disposal of which is a further problem.

[0010] Document EP 963950 presents a method for preparing lamellar AlLiO2 by reaction of an aqueous solution issued from industrial ion exchanges on zeolites and containing at least one lithium salt with a solution of sodium aluminate and then separating the formed lamellar lithium aluminate at a pH of 6-13. The pH can be adjusted with sulfuric acid. However, this method requires a high-purity aqueous solution in order to be able to synthesize a pristine lamellar product.

[0011] Thus, the present solutions are not generally highly efficient in recovering lithium and typically recover lithium comprising different impurities, such as chloride or sulfate, that can't be totally washed out from the obtained lithium precipitate, wherein those impurities end up to further processes in which the recovered lithium is used.

[0012] There exists thus a need to provide a suitable method for efficiently recovering lithium without undesired carryover of impurities, simultaneously lowering the amount of lithium in solutions containing lithium to a level that is below 200 mg / 1, and especially without creating new problematic effluents or waste material. A further aim is to provide such a method which at the same time uses a minimum amount of materials not yet used in current methods. Preferably, the method would be usable in existing processes with existing equipment and still further, it would preferably help in both minimizing the usage of harmful chemicals, which may be used in other known processes, and avoiding any other harmful compounds both in the recovered lithium precipitate and in the final waste material / effluents. Further, such a method would maximize lithium recovery from common raw materials.

[0013] SUMMARY

[0014] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0015] According to a first aspect, there is provided a method for recovering lithium from a stream containing lithium, the method comprising

[0016] - contacting the stream, or a pre-treated solution obtained from said stream, with sodium aluminate, to form a slurry comprising a lithium aluminate precipitate, at an alkaline pH;

[0017] - adjusting the pH of the obtained slurry using carbon dioxide to a level of 8-13, to facilitate precipitation of the lithium aluminate; and

[0018] - recovering the slurry containing said lithium aluminate, or a precipitate separated therefrom.

[0019] According to a second aspect, there is provided a process for soda-leaching a lithium- containing raw material and recovering lithium therefrom, the process comprising the steps of

[0020] - pulping the lithium-containing raw material selected from optionally calcined ore, recycled materials, or combination thereof, thus forming an aqueous slurry containing lithium;

[0021] - leaching the slurry, thus forming a partially solubilized slurry containing lithium;

[0022] - optionally carrying out further treatment steps, to adjust the lithium contents of the formed slurry containing lithium; and

[0023] - product recovery, thus precipitating the lithium, and leaving a solution containing traces of lithium, wherein at least a fraction of one or more of the slurries or solutions containing lithium is separated from the process, and subjected to a method for recovering lithium, whereafter a recovered slurry containing lithium aluminate, or a precipitate separated therefrom, is returned to the pulping or leaching step of the process. DETAILED DESCRIPTION

[0024] In the present context, the term “mineral” comprises materials obtained from the processing of metal-containing ores or rocks. The invention relates particularly to lithium-containing minerals, such as spodumene, petalite, lepidolite or zinnwaldite, or mixtures thereof. Any percentages are weight percentages (wt-%, weight / weight), unless otherwise specified. The term “stream” is used to describe any flow of material, either solid or liquid, preferably being an aqueous stream, such as a slurry, solution, filtrate or mass flow, and most suitably being an aqueous slurry or solution. The term “effluent” is used to indicate any liquid stream obtained from the process, which is typically further treated. The final liquid effluent of the method may also be called final wastewater.

[0025] The present invention relates to a method for recovering lithium from a stream containing lithium, the method comprising

[0026] - contacting the stream, or a pre-treated solution obtained from said stream, with sodium aluminate, to form a slurry comprising a lithium aluminate precipitate, at an alkaline pH;

[0027] - adjusting the pH of the obtained slurry using carbon dioxide to a level of 8-13, to facilitate precipitation of the lithium aluminate; and

[0028] - recovering the slurry containing said lithium aluminate, or a precipitate separated therefrom.

[0029] The present invention thus provides a method for recovering lithium from a stream containing lithium, in view of efficiently recovering lithium without undesired impurities, and further providing a final liquid effluent that has a lithium content that fulfils the strictest environmental specifications. The content of lithium in this liquid effluent of the method may be as low as 10 mg / 1 (i.e. 10 ppm). An optimised method also removes aluminium from the stream, to the extent required by specifications.

[0030] In particular, the present invention is based on the idea of controlling and optimizing pH in lithium recovery process by using carbon dioxide as a pH modifier during the precipitation of lithium when sodium aluminate is used as a reagent for a stream containing lithium to recover lithium as lithium aluminate (LiAlCh). In general, pH modification during the precipitation significantly enhances the precipitation of lithium aluminate, making the precipitation more efficient. It has been surprisingly found in the present invention that such combination of sodium aluminate and carbon dioxide in the context of lithium precipitation and recovery enables efficient recovery of lithium aluminate without undesired impurities, especially considering soda-leaching process.

[0031] Thus, significant advantages are achieved by the present invention. First of all, the present invention provides an efficient method for recovering lithium as lithium aluminate since it has been found that use of carbon dioxide as a pH modifier significantly facilitates the precipitation by adjusting the pH to a preferred level for precipitation, thus making the precipitation more efficient.

[0032] Typically, hydrochloric acid (HC1) or sulfuric acid (H2SO4) are used as possible pH modifiers and / or chloride or sulfate containing aluminium compounds are used as reagents to precipitate lithium, wherein chloride and / or sulfate, or other harmful compounds, are introduced to the lithium-containing precipitate and all of them cannot be washed out from the precipitate. Such carryover impurities are then recirculated to further processes utilizing the recovered lithium, and end up also to the obtained effluents. This results in high concentrations of such impurities in the circuits of further processes and wastewaters. When using sodium aluminate and carbon dioxide, only sodium carbonate and sodium bicarbonate are formed as impurities during the precipitation and thus end up to the lithium aluminate - containing slurry or the precipitate therefrom. This is especially beneficial in the context of soda-leaching process since there is already an excessive carbonate load in the circuit as sodium carbonate is used as a reagent in soda-leaching, wherein the recovered lithium aluminate does not introduce any new impurities to the soda-leaching process. Overall, use and formation of generally harmful compounds, such as sulfate and chloride compounds, is avoided by the present invention.

[0033] The method thus has the advantage of, in the preferred embodiment, making use of the same reagents and products already used in the process of treating lithium-containing materials. The method thus avoiding any further harmful compounds in the final wastewater and other effluents. Further, in case the streams contain aluminium, it can be removed by this same method. Further, according to one preferred embodiment, the present method is usable with minimal or no changes to existing process equipment. Moreover, as presented below, the end product of the present method is usable as such in a further process or processes.

[0034] The present method may for example be used as a replacement of lithium phosphate precipitation and reaches a much lower concentration of lithium in the final liquid effluent, as it would simply mean replacing the phosphate reagent to the aluminium reagent, i.e. sodium aluminate, and adding carbon dioxide, no other process updates would be needed. The known lithium phosphate precipitation methods can only achieve a lithium concentration of about 250 mg / 1 in the final wastewater, while residual phosphates typically also found in the final wastewater (which is in turn also undesirable). The reaction of the present invention by using sodium aluminate and carbon dioxide does also not introduce to the final effluent any compounds that would be harmful, or unnecessary.

[0035] A further advantage of the present method is that, when used to treat an effluent from a lithium recovery plant, an increased overall yield of lithium product is achieved. The combined lithium recovery can be 90%, or even higher.

[0036] A still further advantage of the present method, compared to traditional waste stream treatment (evaporation and crystallisation) is that it is significantly faster, does not require as much space, has less environmental risks and a lower investment and operation cost. Furthermore, the method does not result in the formation of any significant amounts of waste, as the ettringite process.

[0037] As stated above, the present method includes a step wherein the stream containing lithium, or a pre-treated solution obtained from said stream, is contacted with sodium aluminate to form a slurry comprising lithium aluminate precipitate, i.e. the reaction is allowed to take place. The pH during this step is alkaline, preferably 8-13.5, and the reaction time is preferably less than Ih, such as 10-30 min. The reaction can be carried out at any suitable temperature, for example at a temperature of 0-100°C, preferably 0-90°C, and more preferably 50-90°C. According to one embodiment, the alkaline pH can be provided by the stream or solution as such, or the pH can be adjusted to a suitable level as a pre-treatment step, especially by adding an acid, in particular carbon dioxide, to the stream or solution.

[0038] In one embodiment, the pH of the stream or solution is or is adjusted to a level of 8-12, preferably 8.1-12, or 8.2-12, or 8.3-12, more preferably 8.5-11, and most suitably 9-11.

[0039] Thus, according to a preferred embodiment, the step of contacting the stream or solution with sodium aluminate is carried out at an alkaline pH of 8 to 12, preferably 8.1-12, or 8.2- 12, or 8.3-12, more preferably 8.5-11, and most suitably 9-11. According to one embodiment, such pH is achieved with carbon dioxide.

[0040] The present invention further includes a step of adjusting the pH of the obtained slurry using carbon dioxide. Carbon dioxide is used to adjust the pH of the slurry to a level of 8-13 to facilitate precipitation of the lithium aluminate. In particular, the pH of the obtained slurry is adjusted to a level of 8-12, preferably 8.1-12, or 8.2-12, or 8.3-12, more preferably 8.5- 11 , and most suitably 9-11.

[0041] In one embodiment, the carbon dioxide for the pH adjustment is added after contacting the stream or solution with sodium aluminate, wherein the precipitation reaction is continued after decreasing the pH to a suitable level by the addition of carbon dioxide. In another embodiment, the carbon dioxide for the pH adjustment is added at least partly, for example 20 wt.%, 40 wt.%, 60 wt.%, 80 wt.% or 100 wt.% of the carbon dioxide, simultaneously with the sodium aluminate, wherein the carbon dioxide is present already from the start of the precipitation. Thus, in one embodiment, carbon dioxide can be added simultaneously with and / or after the addition of sodium aluminate. In both cases, the carbon dioxide facilitates the precipitation of lithium aluminate.

[0042] In a preferred embodiment, the carbon dioxide is used to adjust the pH in the range of 9-11, either after the lithium-containing stream or solution and sodium aluminate have been contacted or simultaneously with the addition of sodium aluminate.

[0043] According to a preferred embodiment, the carbon dioxide for the pH adjustment is added in gaseous form, typically using a pressure of 0 to 15 bar(g), more typically 0 to 10 bar(g). According to one embodiment, carbon dioxide is added gradually to the obtained slurry, such as during the time period of 10 to 60 minutes, such as 20 to 40 minutes, for example during the time period of 30 minutes.

[0044] As being said, according to one embodiment, the initial pH of the stream-containing lithium can also be adjusted with an acid, in particular with carbon dioxide, to obtain the preferred alkaline pH for the step of contacting the stream with sodium aluminate. Thus, in one embodiment, carbon dioxide can be added before as well as after / simultaneously with the addition of the sodium aluminate.

[0045] In a preferred embodiment, only carbon dioxide is used as a pH control agent in the present invention.

[0046] At the end of the process, the lithium aluminate which has formed by precipitation in the reaction between the lithium-containing stream or solution and the sodium aluminate is recovered, typically as a slurry. The lithium aluminate may also be recovered as a precipitate separated from the slurry containing said lithium aluminate.

[0047] Thus, the method comprises the step of recovering the slurry containing said lithium aluminate, or a precipitate separated therefrom.

[0048] Indeed, lithium aluminate is insoluble in water. In one embodiment, the slurry containing the lithium aluminate may be recovered for example by solid / liquid separation, such as filtration, settling or flotation. One exemplary recovery method is dissolved air flotation (DAF).

[0049] In one embodiment, the method can comprise also a solid / liquid separation step following the recovery of the slurry, thus recovering the lithium product as a precipitate. Alternatively, the product can be reacted further to another lithium product, or treated further, e.g. by washing and drying.

[0050] According to an embodiment, the stream containing lithium is an industrial stream, especially an effluent originating from a lithium recovery plant. The lithium recovery plant may comprise high temperature conversion of lithium-containing ore and leaching with water, or treatment of brine or recycled materials, such as battery waste materials. When lithium is recovered from ore, the lithium recovery plant can for example comprise high temperature conversion of lithium-containing ore and leaching with water. Such conversion typically comprises

[0051] - calcining the mineral in one or more calcination steps, resulting in a calcined material containing lithium;

[0052] - pulping the calcined material into a slurry, preferably together with a leaching reagent in an aqueous solution;

[0053] - water-leaching the formed slurry; and

[0054] - separating lithium-containing solids in a solid-liquid separation step from a solution containing the leaching reagent.

[0055] In one embodiment, lithium-containing ore is selected from ores comprising lithium- containing minerals. The lithium-containing mineral is preferably selected from spodumene, petalite, lepidolite, or zinnwaldite, or mixtures thereof, more preferably being spodumene. When carrying out the calcination on the spodumene of the preferred option, it turns into the more soluble beta-spodumene (P-spodumene). In particular embodiment, the lithium- containing mineral is selected from lithium bearing clay minerals, such as lepidolite, zinnwaldite, masutomilite, swine fordite, hectorite, cookeite or jadarite, or mixtures thereof.

[0056] The liquid stream obtained from the solid-liquid separation step of the above described conversion process is preferably an alkaline solution, more preferably a solution having a pH of 8-11.5. As stated above, this solution contains one or more carbonates, preferably one or more alkali metal carbonates, such as sodium carbonate (Na2COs).

[0057] In one embodiment, the stream containing lithium is obtained from a plant for soda-leaching a lithium containing raw material and recovering lithium therefrom.

[0058] However, the stream containing lithium, that is treated according to the present invention, can be obtained from any other industrial process, even if the stream to be treated contains high concentrations of impurities. Common impurities in such industrial lithium-containing streams include, but are not limited to, the ions and solutes of sodium (Na), calcium (Ca) or other alkaline earth metals, potassium (K), borates and carbonates. Other possible alternatives include soluble silica and silicate species, phosphates (also hydrogen phosphates) and fluoride (F-). Typically, silica / silicates, carbonate ions (CO32-), sodium ions (Na+) and potassium ions (K+) are present in the highest amounts. Minor metals that may be present include Arsenic (As), Vanadium (V), molybdenum (Mo), manganese (Mn) and iron (Fe). None of these prevent achieving the advantage, mentioned above, of the present invention, i.e. achieving a sufficiently low content of lithium in the resulting final effluent.

[0059] In an embodiment, the step of contacting the lithium-containing stream or solution with the sodium aluminate can be carried out by electrochemical water treatment (EWT), preferably by electrocoagulation, to obtain a solution deprived of undesired solutes.

[0060] In an alternative embodiment, the EWT is used as a pre-treatment step or post-treatment step to the contacting step. Thus, according to one embodiment, a pre-treatment or a posttreatment is carried out on the stream containing lithium or on the slurry comprising the lithium aluminate, respectively, the pre-treatment or post-treatment involving electrochemical water treatment (EWT), preferably being electrocoagulation, intended to provide a pre-treated or post-treated solution deprived of undesired solutes.

[0061] As a pre-treatment step, EWT can be used either to reduce the content of undesired solutes of the Li-containing stream before Li precipitation, or to precipitate an initial fraction of Li. As a post-treatment step, EWT can be used either to reduce the content of undesired solutes of the lithium aluminate -containing slurry, or to precipitate a further fraction of Li.

[0062] The EWT is a technology used to treat aqueous streams to reduce the contents of undesired components therein, without the need for further chemical addition, by utilizing processes, such as electrodesinfection, electrochemical reduction, electrocoagulation, electroflotation, and electrodialysis. As mentioned above, electrocoagulation is a preferred alternative for use in the present invention.

[0063] The electrocoagulation that may be used in the contacting step in the present method, or as a pre-treatment or post-treatment step, is known per se and is carried out using a metal electrode containing Al. Power is supplied to the metal electrode serving as anode-cathode. Material selection is based individually on water quality. The principle of operation is to destabilize dissolved pollutants charge and to produce flocs suitable for mechanical removal. Chemical handling is eliminated, though electrode material is still counted as a consumable. The settings of the electrocoagulation can be easily determined by a person skilled in the art, while an exemplary charge loading would be 73 MC / mf

[0064] The present method may be used in the process as a main step for recovering lithium from process streams, or it may be used after another step used for removing lithium from process effluents, as a polishing step. The decision typically depends on the amount of lithium in the process streams, the existing process equipment as well as the possibilities for further use of the lithium aluminate with reasonable costs. As stated above, the present method can be used even for streams and effluents containing high concentrations of impurities.

[0065] Moreover, the present invention relates to a process for soda-leaching a lithium-containing raw material and recovering lithium therefrom. In one embodiment, the process comprises the steps of

[0066] - pulping a lithium-containing raw material selected from optionally calcined ore, recycled materials, or combination thereof, thus forming an aqueous slurry containing lithium;

[0067] - leaching the slurry, thus forming a partially solubilized slurry containing lithium;

[0068] - optionally carrying out further treatment steps, to adjust the lithium contents of the formed slurry containing lithium; and

[0069] - product recovery, thus precipitating the lithium, and leaving a solution containing traces of lithium, wherein at least a fraction of one or more of the slurries or solutions containing lithium is separated from the process, and subjected to the method for recovering lithium according to the present invention, whereafter a recovered slurry containing lithium aluminate, or a precipitate separated therefrom, is returned to the pulping or leaching step of the process.

[0070] Thus, the present invention also concerns the combination of a soda-leaching process of a lithium-containing raw material and the lithium recovery method as described above. Thus, all the above described embodiments concerning the lithium recovery method also applies to the soda-leaching process. In such process, the lithium recovery method of the present invention is thus used to recover lithium from the fractions obtained from soda-leaching, wherein the recovered lithium can be recycled back to the soda-leaching.

[0071] The embodiments and variants described above in connection with the method, use and / or apparatus apply mutatis mutandis to the system. The present system thus allows the production of commercial lithium products, such as lithium carbonate and lithium hydroxide, even as battery grade products, while reducing the amount of lithium in the industrial effluents of e.g. these production processes, or other processes, to a level that fulfils the strictest requirements. All the products from the system are usable for a purpose, and only water is either released or re-circulated into the system.

[0072] Both the apparatus and system described above can be automated as is known in the art, including any control and follow up of the efficiency of the process as well as the quality and quantity of products resulting from the various steps.

[0073] It is to be understood that the embodiments disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0074] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0075] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another but are to be considered as separate and autonomous representations of the present invention.

[0076] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In this description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognise, however, that the invention can be practiced without one or more of the specific details.

[0077] While the forgoing examples are illustrative of the principles in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0078] The following non-limiting examples are intended merely to illustrate the advantages obtained with the embodiments of the present invention.

[0079] EXPERIMENTAL SECTION

[0080] Example 1

[0081] The present method for recovering lithium was tested in a laboratory unit. The compositions of the original feed solutions, i.e. the effluent solutions, to lithium recovery tests (1-4) are given in Table 1. Plasma Optical Emission Spectrometry (ICP-OES; ISO 11885) was used to analyse a set of 9 different elements, namely Li, B, Al, Si, P, S, K and Ca.

[0082] Table 1. Feed solution analysis.

[0083] The feed solutions had very similar compositions with relatively high Li concentrations.

[0084] Initial sulfate concentration levels varied between 223 to 339 mg / 1. The tests were conducted at 40 °C temperature in an agitated reactor. The used lithium precipitation reagent was prepared with solid sodium aluminate (NaAlCh) dissolved to water to come up with a 120 grams per liter solution. Concentrated sulfuric acid as 96% liquid (H2SO4) was used as a reference pH control reagent, whereas carbon dioxide gas (CO2) was used in the test performed according to the method of the present invention (test 4).

[0085] As a pre-treatment step, the effluent solution was heated to 40 °C and pH adjusted to initial target of 9.5 with the pH control reagent; either H2SO4 (in tests 1 -3) or the pH control reagent of the present invention, i.e. CO2 gas (in test 4). The lithium precipitation reagent NaAlCh was then added to the effluent solution. The amount of reagent NaAlCh was equal to 3 times the stoichiometric amount of lithium in the solution. Immediately after the addition of NaAlCh reagent, the pH of the mixture was further adjusted to a target pH 10.0 by addition of the pH control reagent H2SO4 or CO2 during 30 minutes reaction time. Finally, the solids and solution were separated on a filter, and the obtained precipitate was washed with water using on average 3 m3 / ton (dry solids) wash ratio to provide a washed solid cake. The composition analyses from the filtrate and from the washed solid cake is presented in Tables 2 and 3.

[0086] Table 2. Solution analyses from lithium precipitation tests. Table 3. Solid analyses from lithium precipitation tests.

[0087] As can be seen, all tests were equally successful in lithium recovery. Almost 100% of lithium can be recovered by aluminate precipitation. The present results show that carbon dioxide performance as a pH control reagent was at least equally efficient as with sulfuric acid. The solids from test 4 contains naturally the lowest sulfate level compared to test 1-3, with >75% reduction achieved.

[0088] Further, it can be seen that the method according to the present invention also provides a final solution (final effluent) having lithium concentration of significantly less than 10 mg / 1, i.e. 10 ppm, thus providing an efficient method for recovering lithium.

Claims

CLAIMS1. A method for recovering lithium from a stream containing lithium, the method comprising- contacting the stream, or a pre-treated solution obtained from said stream, with sodium aluminate, to form a slurry comprising a lithium aluminate precipitate, at an alkaline pH;- adjusting the pH of the obtained slurry using carbon dioxide to a level of 8-13, to facilitate precipitation of the lithium aluminate; and- recovering the slurry containing said lithium aluminate, or a precipitate separated therefrom.

2. The method according to claim 1, wherein the pH of the stream or solution is adjusted to a level of 8-12, preferably 8.1-12, or 8.2-12, or 8.3-12, more preferably 8.5-11, and most suitably 9-11.

3. The method according to claim 1 or 2, wherein the step of contacting the stream or solution with sodium aluminate is carried out at a temperature of 0-100°C, preferably 0-90°C, and more preferably 50-90°C.

4. The method according to any preceding claim, wherein at least part of the carbon dioxide for the pH adjustment is added simultaneously with the sodium aluminate.

5. The method according to any preceding claim, wherein the carbon dioxide for the pH adjustment is added in gaseous form, typically using a pressure of 0 to 15 bar(g), more typically 0 to 10 bar(g).

6. The method according to any of the preceding claims, wherein the stream containing lithium is a stream containing one or more of the ions of sodium (Na+), calcium (Ca2+) or potassium (K+), borates, carbonates, soluble silica and silicate species, phosphates (also hydrogen phosphates) and fluoride (F ) as impurities.

7. The method according to any of the preceding claims, wherein the stream containing lithium is an industrial stream, preferably being a stream originating from a lithium recovery plant.

8. The method according to any preceding claim, wherein the stream containing lithium is obtained from a plant for soda-leaching a lithium-containing raw material and recovering lithium therefrom.

9. The method according to claim 7 or 8, wherein the lithium recovery plant comprises high temperature conversion of lithium-containing ore and leaching with water, treatment of brine, or recovery of lithium from recycled materials, such as battery waste materials.

10. The method according to claim 9, wherein the lithium-containing ore is selected from ores comprising lithium-containing minerals, such as spodumene, petalite, lepidolite or zinnwaldite, or mixtures thereof.

11. The method according to any of the preceding claims, wherein the slurry containing the lithium aluminate is recovered by solid / liquid separation.

12. The method according to any of the preceding claims, wherein a pre-treatment or a posttreatment is carried out on the stream containing lithium or on the slurry comprising the lithium aluminate, respectively, the pre-treatment or post-treatment involving electrochemical water treatment, preferably being electrocoagulation, intended to provide a pre-treated or post-treated solution deprived of undesired solutes.

13. A process for soda-leaching a lithium-containing raw material and recovering lithium therefrom, the process comprising the steps of- pulping the lithium-containing raw material selected from optionally calcined ore, recycled materials, or combination thereof, thus forming an aqueous slurry containing lithium;- leaching the slurry, thus forming a partially solubilized slurry containing lithium;- optionally carrying out further treatment steps, to adjust the lithium contents of the formed slurry containing lithium; and- product recovery, thus precipitating the lithium, and leaving a solution containing traces of lithium, wherein at least a fraction of one or more of the slurries or solutions containing lithium is separated from the process, and subjected to the method for recovering lithium of any preceding claim, whereafter a recovered slurry containing lithium aluminate, or a precipitate separated therefrom, is returned to the pulping or leaching step of the process.

Images