Integral method for obtaining lithium sulfate monohydrate ore with low chlorine and magnesium impurity content

Abstract

The invention relates to an integral method for obtaining lithium sulfate monohydrate ore with low chlorine and magnesium impurity content. In particular, the method includes concentrating lithium sulfate present in a potassium carnallite (KCl * MgCl2 * 6H2O) stack having a high content of lithium sulfate (Li2SO4 * H2O) and sodium chloride (NaCl) by grinding, flotation, leaching, and filtration stages. The method of the present invention has a huge advantage of using salts and brine that have not been currently treated and have been extracted for the production of potassium.

Description

[0001] Overview

[0002] The present patent application relates to an integral method for obtaining lithium sulfate monohydrate ore with low chlorine and magnesium impurities. Specifically, the method comprises: concentrating lithium sulfate present in a stockpile of potassium carnallite (KCl*MgCl2*6H2O) with high content of lithium sulfate (Li2SO4*H2O) and sodium chloride (NaCl) through grinding, flotation, leaching and filtration stages. The method of the present invention has the great advantage of using salts and brines that have not been processed so far and have been extracted for the production of potassium. 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 ionic components of this weight. Currently, nearly all brine extracted from the 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 existing methods in the prior art are mainly focused on the production of lithium carbonate (Li2CO3) and a small amount of lithium hydroxide (LiOH·H2O) from the first deposit; 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. The product of the flotation in this application 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] 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 economically viable for the purpose of utilizing it for lithium production. In other words, the process of the present invention has the great advantage of utilizing salts and brines which have not been processed to date, but which have been extracted for potassium production. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1: Schematic diagram of the overall concentration method of lithium sulfate monohydrate of the present invention.

[0012]

[0013] Figure 2: Depicts the results of laboratory-scale Li2SO4·H2O production testing.

[0014] DETAILED DESCRIPTION

[0015] The method for obtaining lithium sulfate monohydrate (Li2SO4·H2O) ore low in chlorine and magnesium impurities comprises three main stages: grinding, flotation and leaching.

[0016] The process begins by feeding potassium carnallite salts with high SO4 concentrations to a comminution stage, especially a grinding stage. This is done to reduce the size of the potassium carnallite salts and release the lithium sulfate present in the mineral. The material enters the roughing flotation stage, which aims to recover as much of the target material as possible, taking recovery into account rather than ore grade. The resulting concentrate enters the fine flotation stage, which aims to increase the grade of the concentrate to the required purity, and is then fed to the 80°C hot water leaching stage, thereby increasing the grade of the product. The leached solids enter the washing stage to replace the impregnation, achieving a Li2SO4·H2O grade of more than 90%.

[0017] The selective concentration stage favours the grade of the target mineral rather than the recovery. The tailings obtained in the concentration flotation or concentration stage are recycled to the rougher flotation to recover the material not floated in the circuit. The rougher tailings produced enter the second recovery stage, which consists of scavenger flotation, the purpose of which is to increase the total recovery of the flotation circuit, recovering the minerals not floated in the previous stage, and obtaining a discharged tailings with a grade of 0.2% Li in lithium sulphate. The concentrate obtained is characterized by its low grade, so it can be recycled to the rougher flotation.

[0018] The validated lithium sulfate feed ranges are: 4% to 30% lithium sulfate monohydrate, 50% to 70% potassium carnallite, 8% to 17% sodium chloride; in some cases, bischofite (MgCl2*6H2O) can range from 4% to 20%, with the remainder being mainly impurities related to boron (1% to 2%) and calcium (0.1% to 0.2%).

[0019] The grinding of the material is carried out in a folding crusher and a cage mill in order to release the lithium sulfate crystals present in the potassium carnallite matrix and prepare them for flotation. To avoid overstressing the mill, a pre-saturated balanced brine is added to the mill housing to remove solids that may be embedded therein.

[0020] After the grinding stage, the salt is contacted with a brine pre-saturated with the same salt to produce a slurry with a high solids percentage (40% to 50%), to which 50% of a flotation agent (amine collector) is added to prepare the material for the flotation stage, and then the slurry is pumped into the rougher flotation cell.

[0021] The recycle stream of tailings from the cleaning flotation stage and the scavenger concentrate are fed to the rougher flotation cells; these streams have a low percentage of solids. As a result, a slurry of about 30% to 35% solids is produced as feed to the rougher flotation, with the remaining 30% being added to the tank with collectors and frothers.

[0022] The rougher flotation is run in a recycling mode to obtain a concentrate of more than 50% lithium sulfate monohydrate. The rougher flotation tailings have a low content of lithium sulfate monohydrate and are subjected to the classification and regrinding stages in a cage crusher.

[0023] The classified regrind and undersize materials are pooled together and together with the remaining percentage of collectors and frothers become the feed to the scavenger flotation stage, the aim of which is to produce an industrial tailings with the lowest level of lithium sulphate with the cells operating in a recovery mode.

[0024] On the other hand, the obtained rough concentrate is sent to the beneficiation stage (beneficiation), where it must be concentrated to a lithium sulphate level of 85%, optionally using tanks to increase the height of the cushion. Given that this is a selective flotation, the tailings of this stage are recycled to the above-mentioned rougher flotation stage to avoid losses.

[0025] The concentrate is sent to the filtering stage where a stockpile with a high lithium sulfate content of <85% is obtained, where the stockpile is washed with hot water using spray heads, the purpose of which is to dissolve the chlorine-related impurities and improve the grade of the product, thereby obtaining a grade greater than 90%.

[0026] Subsequently, the leaching stage is entered, where the filtered salts and water are added at a ratio of 0.3 water / solids. After filtration, the resulting concentrate can be washed, adding water at a ratio of 0.14 water / solids to remove remaining impurities and impregnation, thereby increasing the product's grade to more than 95% purity.

[0027] After the whole process is completed, the following results are obtained:

[0028] The proposed process for producing lithium sulfate monohydrate concentrate results in the mass balance shown in Table 1 below.

[0029]

[0030] Example

[0031] Tests were conducted at a laboratory scale using a 5-litre Denver flotation cell to use and validate a lithium sulphate concentration method by flotation, grinding and leaching.

[0032] The lithium sulfate feed range that has been verified on a laboratory scale is: 4% to 30% lithium sulfate monohydrate, 50% to 70% potassium carnallite, 8% to 17% sodium chloride, in some cases, bischofite (MgCl2*6H2O) ranges from 5% to 2%, and the rest is mainly impurities related to boron (1% to 2%) and calcium (0.1% to 0.2%). After grinding, the crushed material is evenly loaded according to the capacity of the tank.

[0033] It is emphasized that because the present application deals with salts, it is necessary to generate a brine that is saturated and in equilibrium with such salts to avoid undesirable dissolution and / or precipitation of the salts.

[0034] For rougher flotation, a 50% solids slurry was formed and treated by shaking it in a flotation cell containing flotation agents (amine collector and frother) for 10 minutes. Once the treatment time was over, the remaining brine was added to reach the solids percentage required for this stage. In this case, the process was carried out at 31% solids, releasing the air and adjusting the parameters as described above.

[0035] When the first drop of concentrate falls on the tray, the flotation time starts. For rougher flotation, this time is set to 7 minutes. The concentrate is padded every 15 seconds to reposition the brine to maintain the tank position by a peristaltic pump.

[0036] Once the flotation time is over, the air valve is closed and the oscillation is stopped, the resulting stream is kneaded and filtered to obtain a solid product and tailings, which must be kneaded to produce a new slurry to feed the concentrate flotation.

[0037] In the clean flotation, the same 5-liter tank is used and the process is repeated, adding collectors and frothers, and processing for 10 minutes at 50% solids. Once the processing is completed, the tank is filled again until 20% solids are fed and the air is released. As in the rough flotation, the flotation time starts as soon as the first drop of concentrate drips over the tank wall. The flotation time is set to 10 minutes. The concentrate material is then filtered and processed for the leaching stage.

[0038] For the leaching stage, a container is used, into which the filtered salt and water are added at a water / salt ratio of 0.3, then shaken for 15 minutes with a mechanical shaker and subsequently filtered. After filtration, the concentrate formed in the funnel can be washed, adding water at a water / salt ratio of 0.14 to displace the remaining impurities and impregnations, thereby increasing the taste of the product to a purity of more than 95%.

Claims

1. A method for obtaining lithium sulfate monohydrate ore with low chlorine and magnesium impurity contents from uneconomical brine to utilize said brine for lithium production, characterized in that: The method comprises the following three main stages: grinding, flotation and leaching; Therein, to carry out the first stage, potassium carnallite salt having a high concentration of SO4 is fed to a comminution stage, in particular a grinding stage, in order to reduce the size of the potassium carnallite salt and release the lithium sulfate present in the ore; The ground material is subjected to a roughing flotation stage, the purpose of which is to recover as much of the target material as possible, which is more favorable to the recovery rate than the grade of the mineral; The concentrate produced in the roughing flotation stage enters the cleaning flotation stage or cleaning stage, where a concentrate of the desired purity is obtained to be fed to the leaching stage; The concentrate obtained from the concentration flotation stage or the concentration stage is subjected to a leaching stage, wherein the concentrate obtained from the concentration flotation stage or the concentration stage and water are added together at a water / solid ratio of 0.

3.

2. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: The method comprises: After the filtration stage, the concentrate obtained is washed; Water was added at a water / solid ratio of 0.14 to displace the remaining impurities and impregnation was performed to increase the grade of the lithium sulfate monohydrate concentrate to more than 95% purity.

3. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: recycling tailings produced by the clean flotation stage to the rougher flotation to recover material not floated in the route; The tailings produced by the roughing flotation are introduced into the second recovery stage, which consists of scavenging flotation, the purpose of which is to increase the total recovery rate of the flotation route, recover materials that were not floated in the previous stage, and obtain discharged tailings with a lithium sulfate grade of 0.2% Li.

4. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: Grinding of the material is carried out in a folding crusher and a cage mill with the aim of releasing the lithium sulfate crystals present in the potassium carnallite matrix and preparing the potassium carnallite matrix for the rougher flotation.

5. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 4, characterized in that: The pre-saturated, balanced brine is added to the mill housing of the cage mill to remove solids that may be embedded in the pre-saturated, balanced brine.

6. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: After the grinding stage, the salt is contacted with a brine pre-saturated with the same salt to produce a slurry with a high solids percentage (40% to 50%) to which 50% of a flotation agent (amine collector) is added to condition the resulting material.

7. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: The recycle stream of tailings obtained from the cleaning flotation stage and the scavenging flotation concentrate are added to the roughing flotation to produce a slurry of about 30% to 35% solids fed to the roughing flotation; in addition, the remaining 30% of collectors and frothers are added to the tank for the roughing flotation.

8. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: The rougher flotation is operated in a recovery mode to obtain more than 50% lithium sulfate monohydrate; The rougher flotation tailings with low sulfate monohydrate content are subjected to classification and regrinding stages in a cage mill.

9. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 8, characterized in that: The regrind and undersize materials extracted from the fractionation are pooled together and together with the remaining percentage of collectors and frothers become the feed to the scavenger flotation stage where the industrial tailings produced have the lowest levels of lithium sulphate.

10. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 1, characterized in that: The rough concentrate obtained from the clean flotation stage is concentrated to a lithium sulphate level of 85%.

11. The method for obtaining lithium sulfate monohydrate ore with low impurity content according to claim 8, characterized in that: The material obtained from the concentration flotation stage is subjected to a filtration stage to obtain a stockpile with a high lithium sulfate content of less than 85%.

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