Method for obtaining high-purity lithium sulfate monohydrate by leaching from lithium sulfate concentrate

Abstract

The invention relates to a method for obtaining high-purity lithium sulfate monohydrate through leaching from lithium sulfate concentrate, and aims to obtain high-grade lithium sulfate monohydrate ore with low content of impurities such as potassium, magnesium and boron. In particular, the invention relates to a method comprising leaching and washing a lithium sulfate concentrate. The process of the invention has a huge advantage that it recycles the produced industrial liquid waste, thereby reducing the water consumption of the process and using the lithium sulfate salt obtained from the salt field as feed.

Description

[0001] Overview

[0002] The present patent application relates to a method for obtaining lithium sulfate monohydrate by leaching from lithium sulfate concentrate, with the purpose of obtaining high-grade lithium sulfate monohydrate ore with low potassium, magnesium and boron impurities. In particular, the present invention relates to a method comprising leaching and washing lithium sulfate concentrate. The method of the present invention has great advantages, namely that it recycles the industrial liquid waste produced, thereby making water consumption low, and uses lithium sulfate salt obtained from a salt field as feed. Prior art

[0003] For many years, high sulfate brines were only producers of potassium, with the lithium component being returned to the salt pans via reinjection. This meant that not all brine extracted produced lithium, even if it also contained this important ionic component. Currently, nearly all brine extracted from salt pans produces potassium.

[0004] Lithium production in salt fields Consider 2 deposits, one where the main anion is chloride and the other where there is a large amount of sulfate. This difference is very important because the production and / or refining process will change depending on the raw material.

[0005] In view of the above, the methods existing in the prior art mainly focus on producing lithium carbonate (Li 2 CO 3 ) and a small amount of lithium hydroxide (LiOH·H 2 O) method; this is based on chlorine and uses very little sulfate. However, to date, there is no technically and economically feasible alternative method for treating high-sulfate brines.

[0006] In the prior art, various information on obtaining lithium salts can be found. However, all of these information are significantly different from the method of the present invention.

[0007] Chinese patent publication CN102921553 (A) describes a method for flotation of lithium potassium sulfate in a sodium chloride mixture. In this application, the flotation product is lithium sulfate, which is a mineral different from lithium potassium sulfate. In addition, in this application, the lithium sulfate is initially mixed with a variety of minerals other than sodium chloride, such as carnallite (hydrated potassium magnesium chloride), bischofite (hydrated magnesium chloride), and other contaminants present, making the method more complicated.

[0008] Chinese patent publication CN101318670 (A) describes a production method for extracting lithium chloride salt from a salt mixture containing lithium chloride salt and bischofite (hydrated magnesium chloride), the salt mixture being produced by evaporating brine in an evaporation pond. Although in both methods, the salt mixture before flotation is obtained by evaporating brine in an evaporation pond, the salt to be floated is different, because in the case of the present application, the salt is lithium sulfate, while the salt of patent CN101318670 is lithium chloride; and the salt present in the mixture is also different, because in the present application, in addition to bischofite, sodium chloride, carnallite (potassium chloride and hydrated magnesium chloride) and other contaminants are also present.

[0009] Chinese patent publication CN109174438 (A) describes a classification process for spodumene beneficiation, which belongs to the field of multi-metal beneficiation technology. Although spodumene flotation may be part of a process that produces lithium sulfate as an intermediate product, spodumene is a lithium aluminum silicate from a rock mixture rather than brine, which makes the raw material to be floated completely different from the raw material used in this application.

[0010] Publication WO2020030305202 describes a method for extracting and concentrating lithium from precipitated ore. The method consists of the following stages:

[0011] Suspending the precipitated ore in an aqueous solution;

[0012] Treating the aqueous solution with an acid to dissolve lithium and form a first precipitate; filtering the aqueous solution through a pressure filter to remove the first precipitate; neutralizing the aqueous solution to form a second precipitate, and removing the second precipitate through a pressure filter;

[0013] crystallizing the aqueous solution to form magnesium sulfate and potassium magnesium sulfate crystals, and removing the magnesium sulfate and potassium magnesium sulfate crystals; and

[0014] - Treating the aqueous solution with one or more pH adjusters and a cationic precipitant to form a third precipitate, and removing the third precipitate through a pressure filter to form a purified lithium sulfate brine.

[0015] This publication only teaches acid dissolution. However, it does not mention the leaching itself, let alone the brine / solids ratio or the step of recycling the brine to the leaching stage.

[0016] Therefore, it can be affirmed that the present invention solves a previously unsolved problem, since it seeks to concentrate lithium sulfate monohydrate having low chlorine and magnesium impurity contents from brine which is not economical for the purpose of utilizing it for lithium production. In other words, the process of the present invention has the great advantage of using salts and brines which have not been treated so far and which have been extracted for potassium production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : A schematic diagram of the method of the present invention for obtaining lithium sulfate monohydrate by leaching is described. DETAILED DESCRIPTION

[0018] The method for obtaining high-grade lithium sulfate monohydrate ore with low impurity content comprises two main stages: leaching and washing.

[0019] The process begins by feeding salt to a leaching tank, where water preheated to 80°C is fed at a water / solid w / w ratio of 1.0 to start the shaking process and dissolve impurities. Subsequently, the slurry is sent to the filtration and washing stage. Washing is performed at a water / solid w / w rate of 0.3, producing a strong filtrate stream and a weak filtrate stream, which are stored in the filter tank for later use.

[0020] In the next stage, the solids are fed again to the leaching tank, but this time with brine from a filter tank containing a mixture between strong and weak filtrates in a brine / solids w / w ratio of 1.0 from the filtration and washing stage maintained at 80°C. The resulting mixture is shaken and sent to a new filtration and washing stage, again producing a mixed strong and weak filtrate in the same filter tank.

[0021] The validated lithium sulfate feed range is about 90% to 85% lithium sulfate monohydrate, 1% to 4% potassium carnallite, 0.1% to 2.6% sodium chloride, 0.2% to 0.3% boron, 0.3% to 0.8% insoluble elements; the remainder is mainly sulfate-related impurities, among which are found: 0.2% to 2.5% potassium sulfate, 0.2% to 0.3% calcium sulfate dihydrate, 0.7% to 1.5% magnesium sulfate.

[0022] After the washing stage, the product obtained has a lithium sulfate monohydrate level of more than 97%. Figure 1 Included is a schematic diagram of the method of the invention.

[0023] The following chemical analysis was conducted on the production method of leaching lithium sulfate monohydrate of the present invention, and the details are shown in Table 1.

[0024]

[0025] Table 2: Chemical analysis of lithium sulfate feed and leached product

[0026] Example

[0027] First, laboratory-scale tests were conducted to test the method of obtaining high-purity lithium sulfate by leaching using beakers, shakers and a filtration system.

[0028] The range of lithium sulfate feed that has been demonstrated at pilot scale is about 89% lithium sulfate monohydrate.

[0029] Settling beakers are used for the leaching stage where salt and water are added at a solids / water w / w ratio of 1.0. Mechanical agitation is applied and the slurry is then fed into a filtration system to increase the grade to 92% lithium sulfate.

[0030] The table below shows the results obtained from tests performed in the laboratory.

[0031] stage K[％] Na[%] Mg[%] Ca[%] <![CDATA[SO 4 [%]]]> Li[%] Cl[％] <![CDATA[H 3 BO 3 [%]]> Feed 0.81％ 0.18％ 1.06％ 0.05％ 68.55％ 9.78％ 3.54％ 1.39％ #1 Batch 0.35％ 0.01％ 0.11％ 0.01％ 72.91％ 10.45％ 0.21％ 0.59％ #2 batch 0.37％ 0.01％ 0.17％ 0.02％ 70.98％ 10.15％ 0.36％ 0.87％ #3 batch 0.42％ 0.02％ 0.17％ 0.04％ 72.73％ 10.39％ 0.37％ 0.91％ #4 batch 1.22％ 0.02％ 0.30％ 0.07％ 74.56％ 10.50％ 0.75％ 1.17％ Batch #5 0.50％ 0.02％ 0.18％ 0.04％ 71.62％ 10.22％ 0.42％ 1.13％

[0032] Table 2: Chemical analysis, leaching test, laboratory scale

[0033] In view of these results, a pilot scale test was conducted to use and validate the lithium sulfate concentration method by leaching using an oscillating reactor and a filtration device.

[0034] The lithium sulfate feed that has been demonstrated at pilot scale ranges from about 89% lithium sulfate monohydrate, with the remainder being primarily impurities related to potassium (0.4% to 1.6%), sodium (0.05% to 1.0%), magnesium (0.1% to 0.6%), boron (0.2% to 0.3%), and chloride (0.5% to 3.1%).

[0035] For the leaching stage, an oscillating reactor is used, in which the feed salt and brine are added at a brine / solid w / w ratio of 1.0 and oscillated by a mechanical oscillator. The resulting slurry is then passed through a filtration system to increase the grade of lithium sulfate monohydrate to more than 97% purity.

Claims

1. A method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate in order to obtain high-grade lithium sulfate monohydrate ore with low impurity contents of potassium, magnesium and boron. It is characterized in that The first phase consists of: Lithium sulphate monohydrate salt was fed into a tank where leaching was carried out using water preheated to 80°C and fed at a water / solids w / w ratio of 1.0 to start the shaking process in order to dissolve the impurities; The shaking process then produces a slurry which is sent to a filtering and washing stage, thereby producing a strong filtrate stream and a weak filtrate stream which are stored in a filter tank for later use.

2. A method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 1, It is characterized in that The slurry was washed at a water / solids w / w ratio of 0.

3.

3. A method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 1, It is characterized in that After the leaching stage, the strong and weak filtrate streams are recycled and mixed with the feed salt in a leaching tank at a solids / brine w / w ratio of 1.0 for leaching again.

4. A method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 3, It is characterized in that The newly produced filtered pulp from leaching was washed at a water / solid w / w ratio of 0.3 to displace the remaining impurities and impregnated materials again, thereby increasing the grade of the lithium sulfate monohydrate concentrate to more than 97% purity.

5. The method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 3, It is characterized in that Brine is produced in both the first filtration and washing stages and is then recycled to the leaching to reduce yield losses and lower water consumption.

6. A method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 3, It is characterized in that Filtration takes place in a filtration device which separates the brine and allows it to be subsequently recirculated into the system.

7. A method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 1, It is characterized in that The lithium sulfate range of the feed consists of about 90% to 85% lithium sulfate monohydrate, 1% to 4% potassium carnallite, 0.1% to 2.6% sodium chloride, 0.2% to 0.3% boron and 0.3% to 0.8% insoluble elements; The remainder consists primarily of sulfate-related impurities, including: 0.2% to 2.5% potassium sulfate, 0.2% to 0.3% calcium sulfate dihydrate, and 0.7% to 1.5% magnesium sulfate.

8. The method for obtaining lithium sulfate monohydrate from lithium sulfate concentrate for obtaining high-grade lithium sulfate monohydrate ore according to claim 1, It is characterized in that The lithium sulfate range of the feed consisted of approximately 89% lithium sulfate monohydrate.

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