Method for producing lithium adsorbent precursor after roasting, and method for producing granulated body for lithium adsorption

Abstract

Provided is a method for producing a lithium adsorbent precursor after roasting, the precursor comprising a large amount of tetravalent manganese with low solubility in water.　The method for producing a lithium adsorbent precursor after roasting includes an oxidative roasting step for subjecting a powdery lithium adsorbent precursor containing manganese to oxidative roasting at a temperature of 300 °C to 600 °C to obtain a powdery lithium adsorbent precursor after roasting. By subjecting the powdery lithium adsorbent precursor containing manganese to oxidative roasting at a predetermined temperature, divalent manganese can be converted into tetravalent manganese. Since tetravalent manganese has low solubility in water, it is possible to suppress the lithium adsorbent from dissolving in water at the time of use of the lithium adsorbent.

Description

Method for producing precursor of roasted lithium adsorbent and method for producing granules for lithium adsorption

[0001] The present invention relates to a method for producing a precursor of a roasted lithium adsorbent and a method for producing granules for adsorbing lithium. More specifically, the present invention relates to a method for producing a precursor of a roasted lithium adsorbent by oxidatively roasting a powdery precursor of a lithium adsorbent, and a method for producing granules for adsorbing lithium, including the precursor of a roasted lithium adsorbent.

[0002] Non-Patent Document 1 discloses a system for recovering lithium from brine. In this document, lithium is adsorbed from brine using a lithium adsorbent, and the adsorbed lithium is desorbed to obtain high-purity Li. ２ CO ３ This document describes that lithium adsorption is carried out by a column method.

[0003] Furthermore, Patent Document 1 discloses a method for producing a molded body to be used in a column, which method comprises producing a molded body from a precursor of a lithium adsorbent and an inorganic binder such as alumina or silica, or from a precursor of a lithium adsorbent and an organic binder such as chitin or polyvinyl chloride.

[0004] International Publication No. 2011 / 058841

[0005] Yu, Eihei, "Development of a Lithium Recovery System from Brine," [online], June 11, 2010, Kagawa Industrial Support Foundation, [November 22, 2018], Internet (https: / / www.kagawa-isf.jp / wp-content / uploads / 2022 / 02 / 21tang.pdf)

[0006] However, in the case of a compact using an inorganic binder produced by the method described in Patent Document 1, there is a problem that the specific surface area decreases as sintering progresses, thereby reducing the adsorption capacity. Furthermore, in the case of a compact using an organic binder produced by the method described in Patent Document 1, there is a problem that the organic binder dissolves during the elution process using an acidic solution. Therefore, repeated use of the compact can lead to problems such as the compact collapsing, reducing the adsorbent, or causing the resulting powder to clog the column. In addition, for organic binders, high temperatures of around 500°C cannot be applied after molding because the organic binder carbonizes when exposed to high temperatures. When manganese is contained in a lithium adsorbent, there is a problem that divalent manganese cannot be oxidized to tetravalent manganese, which has low solubility in water, unless high temperatures can be applied.

[0007] In view of the above circumstances, an object of the present invention is to provide a method for producing a precursor of a roasted lithium adsorbent that contains a large amount of tetravalent manganese, which has low solubility in water, and a method for producing granules for adsorbing lithium, which have a high adsorption capacity, are more robust, and can easily maintain their shape.

[0008] A first aspect of the present invention relates to a method for producing a precursor of a roasted lithium adsorbent, comprising an oxidizing roasting step of oxidizing roasting a powdered precursor of a lithium adsorbent containing manganese at 300°C or higher and 600°C or lower to obtain a powdered precursor of the roasted lithium adsorbent. A second aspect of the present invention relates to a method for producing a precursor of a roasted lithium adsorbent, comprising the first aspect, wherein the oxidizing roasting step is performed at a temperature of 450°C or higher and 550°C or lower. A third aspect of the present invention relates to a method for producing granules for adsorbing lithium, comprising a kneading step of kneading the precursor of the roasted lithium adsorbent produced by the method for producing a lithium adsorbent according to the first or second aspect of the present invention with an organic binder and a curing agent for accelerating curing of the organic binder to obtain a kneaded mixture, a granulation step of granulating the kneaded mixture to obtain granules, and a baking step of baking the granules at 90°C or higher and 120°C or lower to obtain granules for adsorbing lithium. A fourth aspect of the present invention relates to a method for producing granules for adsorbing lithium according to the third aspect of the present invention, characterized in that a drying step of drying the granules at 10°C or higher and 60°C or lower is provided after the granulation step and before the baking step. A fifth aspect of the present invention relates to a method for producing granules for adsorbing lithium according to the third or fourth aspect of the present invention, characterized in that the organic binder is a copolymer polyester. A sixth aspect of the present invention relates to a method for producing granules for adsorbing lithium according to any of the third to fifth aspects of the present invention, characterized in that the curing agent is a polyisocyanate. A seventh aspect of the present invention relates to a method for producing granules for adsorbing lithium according to any of the third to sixth aspects of the present invention, characterized in that the organic binder accounts for 5% by weight or more and 20% by weight or less of the powder of the precursor of the lithium adsorbent after roasting.

[0009] According to the first invention, divalent manganese can be converted to tetravalent manganese by oxidizing roasting a powdered lithium adsorbent precursor containing manganese at a predetermined temperature. Tetravalent manganese has low solubility in water, which prevents the lithium adsorbent from dissolving in water during use. According to the second invention, the oxidizing roasting temperature is 450°C or higher and 550°C or lower, thereby converting divalent manganese to tetravalent manganese and maintaining high lithium adsorption capacity. According to the third invention, the method includes a kneading step in which an organic binder and a curing agent are mixed together, and a baking step in which first granules are baked to obtain second granules. This method produces granules for lithium adsorption that have high adsorption capacity, are robust, and easily maintain their shape. According to the fourth invention, a drying step in which the granules are dried at a predetermined temperature is provided before the baking step. This allows the granules to be subjected to the baking step with low moisture content, resulting in more robust granules. According to the fifth aspect of the present invention, the organic binder is a copolymer polyester, which can further suppress elution in an acidic solution, making the granules even more robust. According to the sixth aspect of the present invention, the curing agent is a polyisocyanate, which can further increase the bonding strength of the organic binder, making the granules even more robust. According to the seventh aspect of the present invention, the organic binder to be kneaded is 5% by weight or more and 20% by weight or less of the powder of the precursor of the lithium adsorbent, so that the adsorption capacity of the lithium adsorbent can be maintained at a high level.

[0010] 1 is a graph showing the relationship between the oxidizing roasting temperature and the amount of manganese eluted from a precursor of a lithium adsorbent; FIG. 2 is a graph showing the relationship between the oxidizing roasting temperature and the amount of lithium adsorption from a precursor of a lithium adsorbent; FIG. 3 is a flow diagram of a method for producing granules for adsorbing lithium according to a first embodiment of the present invention; FIG. 4 is a flow diagram of a method for producing granules for adsorbing lithium according to a second embodiment of the present invention; FIG. 5 is a graph showing the difference in the amount of lithium adsorption depending on the binder; and FIG. 6 is a graph showing the progress of reduction in granules.

[0011] Next, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below exemplify a method for producing a precursor of a roasted lithium adsorbent and a method for producing granules for lithium adsorption to embody the technical concept of the present invention, and the present invention does not limit the methods for producing a precursor of a roasted lithium adsorbent and a method for producing granules for lithium adsorption to those described below.

[0012] The method for producing a precursor of a roasted lithium adsorbent according to the present invention includes an oxidizing roasting step of oxidizing roasting a powdered precursor of a lithium adsorbent containing manganese at 300°C or more and 600°C or less to obtain a powdered precursor of a roasted lithium adsorbent.

[0013] Divalent manganese can be converted to tetravalent manganese by oxidizing and roasting a powdered precursor of a lithium adsorbent containing manganese at a predetermined temperature. Tetravalent manganese has low solubility in water, so dissolution of the lithium adsorbent in water can be suppressed when the lithium adsorbent is used.

[0014] In addition, in the method for producing a precursor of a roasted lithium adsorbent according to the present invention, the oxidizing roasting temperature in the oxidizing roasting step is 450° C. or more and 550° C. or less. By setting the oxidizing roasting temperature to 450° C. or more and 550° C. or less, divalent manganese can be converted to tetravalent manganese, and the lithium adsorption capacity can be maintained at a high level.

[0015] Furthermore, the method for producing granules for adsorbing lithium according to the present invention includes a kneading step of kneading a precursor of the roasted lithium adsorbent, an organic binder, and a curing agent for accelerating curing of the organic binder to obtain a kneaded mixture; a granulation step of granulating the kneaded mixture to obtain granules; and a baking step of baking the granules at a temperature of 90°C or higher and 120°C or lower to obtain granules for adsorbing lithium.

[0016] The method for producing lithium-adsorbing granules includes a kneading step of kneading an organic binder and a curing agent together, and a baking step of baking the granules to obtain lithium-adsorbing granules. This makes it possible to obtain lithium-adsorbing granules that have high adsorption capacity and that easily maintain their shape.

[0017] Furthermore, in the method for producing granules for lithium adsorption according to the present invention, a drying step of drying the granules at a temperature of 10° C. to 60° C. is preferably performed after the granulation step and before the baking step. This allows the granules to be subjected to the baking step with a low moisture content, making the granules more robust.

[0018] In the method for producing granules for adsorbing lithium according to the present invention, the organic binder is preferably a copolymer polyester, which can further suppress elution in an acidic solution and make the granules even more robust.

[0019] In the method for producing granules for adsorbing lithium according to the present invention, the curing agent is preferably polyisocyanate, which can further increase the bonding strength of the organic binder and make the granules even more robust.

[0020] In the method for producing lithium adsorbing granules according to the present invention, the organic binder is preferably contained in an amount of 5% by weight to 20% by weight of the precursor powder of the lithium adsorbent, thereby enabling the adsorption capacity of the lithium adsorbent to be maintained at a high level.

[0021] <Embodiment of Method for Producing Precursor of Roasted Lithium Adsorbent> (Precursor of Lithium Adsorbent) The lithium adsorbent is not particularly limited as long as it contains manganese and selectively adsorbs lithium from a solution containing lithium. Examples of the lithium adsorbent include H obtained from lithium manganate. １．６ Mn １．６ O ４ , H １．３３ Mn １．６７ O ４ These lithium adsorbents are preferably manufactured by a wet manufacturing method, because they can be easily obtained in powder form at the manufacturing stage. However, there is no limitation to this, and those manufactured by a dry manufacturing method are also acceptable. The lithium adsorbent is prepared by using Li, which is a precursor of the lithium adsorbent. １．６ Mn １．６ O ４ , Li １．３３ Mn １．６７ O ４can be obtained by substituting Li for hydrogen as shown in Equations 1 and 2.

[0022] [Math 1] Li １．６ Mn １．６ O ４ +1.6HCl → H １．６ Mn １．６ O ４ +1.6LiCl

[0023] [Math 2] Li １．３３ Mn １．６７ O ４ +1.33HCl → H １．３３ Mn １．６７ O ４ +1.33LiCl

[0024] (Oxidizing Roasting Step) A lithium adsorbent precursor may contain a composition that is not sufficiently oxidized. Therefore, the method for producing a roasted lithium adsorbent precursor according to this embodiment includes an oxidizing roasting step. In the oxidizing roasting step, a powdered lithium adsorbent precursor containing manganese is oxidizing roasted at 300°C or higher and 600°C or lower to obtain a roasted lithium adsorbent precursor. For example, an electric furnace or the like is used for the oxidizing roasting step. The oxidizing roasting time is preferably, for example, 2 hours or higher and 24 hours or lower. The atmosphere inside the electric furnace does not pose a problem as long as oxygen is present. For example, a preferable atmosphere can be achieved by supplying air into the furnace. In order to promote oxidizing roasting, the temperature inside the furnace is preferably 300°C or higher and 600°C or lower, as described above. Furthermore, considering the lithium adsorption capacity after oxidizing roasting, a temperature of 450°C or higher and 550°C or lower is more preferable.

[0025] By oxidizing and roasting a powdered precursor of a lithium adsorbent containing manganese at a predetermined temperature, divalent or trivalent manganese can be converted to tetravalent manganese. ０．８ Mn １．８ O ３．５ For example, the reaction is expressed as in Equation 3. Tetravalent manganese has low solubility in water, so when a lithium adsorbent is used, it can prevent the lithium adsorbent from dissolving in water.

[0026] [Equation 3] 4Li ０．８ Mn １．８ O ３．５ +O ２ → 2Li １．６ Mn １．６ O ４ + 4MnO ２

[0027] In addition, in the method for producing a precursor of a roasted lithium adsorbent according to the present invention, the oxidizing roasting temperature in the oxidizing roasting step is 450° C. or more and 550° C. or less. By setting the oxidizing roasting temperature to 450° C. or more and 550° C. or less, divalent manganese can be converted to tetravalent manganese, and the lithium adsorption capacity can be maintained at a high level.

[0028] <First embodiment of method for producing granules for adsorbing lithium> Fig. 3 shows a flow diagram of a method for producing granules for adsorbing lithium according to a first embodiment of the present invention. The precursor powder of the lithium adsorbent is used in the oxidation roasting step of the method for producing a precursor of the roasted lithium adsorbent, and the obtained precursor of the roasted lithium adsorbent is used in the kneading step described below.

[0029] (Organic Binder) The organic binder is used in the kneading process. Examples of the organic binder include copolymer polyester, which is a type of polyester, chitin, PVC, etc., but copolymer polyester is preferred. When the organic binder is copolymer polyester, elution in an acidic solution can be further suppressed, and the granules become even more robust.

[0030] (Hardening Agent) A hardener is used in the kneading process. The hardener is used to accelerate the hardening of the organic binder. "Accelerating hardening" means, for example, making the finished product harder or accelerating the hardening process, thereby increasing the effect of the organic binder as a binder. There are various hardening agents, but polyisocyanate is preferred. Hexamethylene diisocyanate-based polyisocyanate is even more preferred. By using polyisocyanate as the hardener, the bonding strength of the organic binder can be further increased, making the granules even more robust.

[0031] (Kneading step) When a production method for obtaining a lithium-containing solution containing lithium from a lithium adsorbent is realized on a commercial basis, the most appropriate method is to granulate the lithium adsorbent, place it in a predetermined container, and pass an acid solution such as hydrochloric acid through the container. In this case, it is necessary to granulate the precursor of the lithium adsorbent after roasting.

[0032] The method for producing lithium adsorbent granules according to this embodiment includes a kneading step. In this kneading step, a powder of a precursor of the roasted lithium adsorbent, an organic binder, and a curing agent are kneaded together to obtain a kneaded product. In the kneading step, the powder of the precursor of the roasted lithium adsorbent, the organic binder, and the curing agent are kneaded together, and it is preferable that a liquid such as water is added during the kneading step.

[0033] The amount of organic binder used in the kneading step is preferably 5% by weight or more and 20% by weight or less of the powder of the precursor of the roasted lithium adsorbent. If it is less than 5% by weight, the amount of organic binder is too small to bond the powder. If it is more than 20% by weight, the proportion of the precursor of the roasted lithium adsorbent contained in the final granules becomes small, making it impossible to obtain the desired adsorption capacity. By keeping the amount of organic binder within the above range, the adsorption capacity of the lithium adsorbent can be maintained at a high level. In addition, it is preferable to determine the amount of curing agent to be a preferred amount relative to the organic binder.

[0034] (Granulation Process) As shown in FIG. 3 , in the granulation process, the kneaded material obtained in the kneading process is granulated to obtain granules. The size of the granules is not particularly limited, but it is preferable that the particle size of the granules be 0.5 mm or more and 1.5 mm or less so that the particle size of the final lithium adsorption granules is 0.5 mm or more and 1.5 mm or less. Specifically, whether the particle size of the granules according to this embodiment is within a specific range can be confirmed using a sieve with openings corresponding to each particle size according to the JIS Z8801 standard. It is not necessary for all of the granules to have this particle size; a predetermined proportion is acceptable. For example, the predetermined proportion is preferably 90% or more. When the granules of the present invention have a particle size of 0.5 mm or more, when the granules are filled in a container and water is passed through it, the granules are less likely to clog the container, preventing an increase in pressure loss within the container. Furthermore, if the particle size is larger than 1.5 mm, the lithium adsorption rate will be slow and the adsorption efficiency will be poor, but by setting the particle size to 1.5 mm or less, it is possible to improve the adsorption performance.

[0035] In the granulation process, granulation processing, i.e., extrusion processing, is first performed, and the extruded material is then converted into granules by, for example, stirring and mixing granulation, rolling granulation, extrusion granulation, crushing granulation, fluidized bed granulation, spray drying granulation (spray drying), compression granulation, etc. Since the as-extruded material has angular corners, removing the corners by granulation can prevent the generation of fragments due to damage when packed into a column for use. The granules are preferably spherical. By making the granules spherical, there are no edges, so crushing due to contact between granules is suppressed. When considering the three mutually orthogonal coordinates X, Y, and Z from the center of the particle, it is preferable that the lengths of the granules in the X, Y, and Z directions are approximately the same (for example, the maximum length is three times or less than the minimum length).

[0036] When the particle size of the lithium adsorbing granules is 0.5 mm or more and 1.5 mm or less, the contact area between the lithium adsorbing granules and the lithium contained in the lithium-containing solution can be further increased, and clogging of the column can be prevented.

[0037] 3, in this embodiment, the granules obtained in the granulation step are dried for a predetermined time at a temperature of 10° C. to 60° C. By drying in this manner, the granules can be subjected to the baking step with less moisture in the granules, and the granules become more robust.

[0038] The temperature in the drying step is preferably room temperature, and more preferably, for example, from 20° C. to 30° C. The predetermined time is preferably, for example, from 20 hours to 30 hours.

[0039] (Baking Step) As shown in Fig. 3, in the baking step, the granules obtained in the granulation step and that have been through the drying step are baked to obtain granules for adsorbing lithium. The granules are baked by, for example, maintaining them in an electric furnace at a predetermined temperature for a predetermined time, thereby becoming granules for adsorbing lithium. The optimum values ​​for this temperature and time are determined depending on the organic binder and curing agent used.

[0040] The temperature is preferably 90° C. or higher and 120° C. or lower, more preferably 100° C. or higher and 110° C. or lower. The holding time is preferably 0.5 hours or higher and 2 hours or lower.

[0041] (Treatment after the baking step and before the desorption step) The lithium adsorption granules produced by the method for producing lithium adsorption granules described above are preferably subjected to an acid wash to remove readily soluble divalent manganese and an alkali wash to remove hexavalent and heptavalent manganese before the subsequent desorption step in which a precursor of the lithium adsorbent is used as the lithium adsorbent. For example, the acid wash is preferably carried out using 1 mol / L hydrochloric acid in an amount approximately 15 times the amount of the lithium adsorbent precursor. The alkali wash is preferably carried out by immersing the granules in a 1 mol / L lithium hydroxide solution for one hour. In this case, the amount of the lithium hydroxide solution is preferably 6 times the amount of the lithium adsorbent precursor. After the alkali wash is completed, the granules are preferably washed with pure water and then dried.

[0042] <Second embodiment of method for producing lithium adsorbent granules> Fig. 4 shows a flow diagram of a method for producing lithium adsorbent granules according to a second embodiment of the present invention. The difference from the first embodiment is that the drying step provided between the granulation step and the baking step is omitted. Since the other points are the same as those in the first embodiment, detailed explanations will be omitted.

[0043] In this embodiment, the granules obtained in the granulation step are subjected to the baking step without undergoing the drying step. In this case, the materials in the kneading step are adjusted, or the temperature or time in the baking step is adjusted, so as to reduce the moisture content in the granules.

[0044] <Examples of Method for Producing Precursor of Roasted Lithium Adsorbent> Specific examples of the method for producing a precursor of a roasted lithium adsorbent according to the present invention will be described below, but the present invention is not limited to these examples.

[0045] Example 1: Manganese-containing powdered lithium adsorbent precursor L produced by a wet method １．６ Mn １．６ O ４ 20 g of the lithium adsorbent precursor was prepared. An oxidizing roasting process was performed on this lithium adsorbent precursor. That is, the lithium adsorbent precursor was oxidizing roasted at 300°C for 5 hours using an electric furnace. A roasted lithium adsorbent precursor was obtained by this oxidizing roasting. The obtained roasted lithium adsorbent precursor was added to 300 ml of pure water and stirred for 10 minutes. After stirring, the supernatant was separated, and the manganese content of this supernatant was measured using an ICP atomic emission spectrometer. The results are shown in Table 1 and FIG. 1.

[0046] After separating the supernatant, the roasted lithium adsorbent precursor was contacted with hydrochloric acid in powder form as an adsorption pretreatment to produce a lithium adsorbent. This lithium adsorbent weighed 10 g. Using this lithium adsorbent, an adsorption step was carried out on a lithium solution containing 0.5% lithium, and an elution step was carried out using 2% hydrochloric acid, and the lithium adsorption amount per unit weight of the lithium adsorbent was measured. The results are shown in Table 1 and Figure 2.

[0047] Example 2 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 350° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0048] Example 3 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 400° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0049] Example 4 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 450° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0050] Example 5 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 500° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0051] Example 6 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 550° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0052] Example 7 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 600° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0053] Comparative Example 1 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 250° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0054] Comparative Example 2 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 650° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0055] Comparative Example 3 The oxidizing roasting step was carried out under the same conditions as in Example 1, except that the temperature in the oxidizing roasting step was set to 700° C. The manganese amount is shown in Table 1 and FIG. 1. The lithium adsorption amount is shown in Table 1 and FIG. 2.

[0056]

[0057] The reference value for the amount of eluted manganese was 40 mg. From Fig. 1 and Table 1, it can be seen that the amount of eluted manganese was suppressed in Examples 1 to 7, i.e., when the oxidizing roasting temperature was 300°C or higher and 600°C or lower.

[0058] Regarding the amount of adsorbed Li, the vertical axis of FIG. 2 represents the amount of Li, which is the precursor of the lithium adsorbent after roasting. １．６ Mn １．６ O ４ The amount of Li obtained is expressed in mmol per gram of the adsorbed material. The reference value at this time is 3.7 mmol / g. From FIG. 2 and Table 1, it can be seen that the adsorption capacity of Li was maintained in Examples 4 to 6, i.e., when the oxidizing roasting temperature was 450°C or higher and 550°C or lower.

[0059] <Example of the method for producing a granule for lithium adsorption> <Example 1a> (Kneading step) In Example 6 of the method for producing a precursor of the roasted lithium adsorbent, that is, lithium manganate Li, which is a precursor of the roasted lithium adsorbent that has been oxidatively roasted at an oxidative roasting temperature of 550°C, １．６ Mn １．６ O ４ 900 g of the powder was placed in a kneader and the kneader was left rotating. Next, 451 g of the organic binder, a water-dispersible polyester resin (Vylonal MD1500 manufactured by Toyobo Co., Ltd.: copolymer polyester content 30%), and 29 g of the curing agent, a hexamethylene diisocyanate-based polyisocyanate (Duranate WM44-L70G manufactured by Asahi Kasei Co., Ltd.: block polyisocyanate content 60-70%), were weighed and placed in the kneader. In this case, the organic binder was 30% of 451 g, or 135.3 g, which is 15.03 wt % of 900 g of lithium manganate powder. The mixed powder was rotated in the kneader for approximately 15 to 20 minutes, until the organic binder was thoroughly distributed and small lumps formed, resulting in a kneaded mixture.

[0060] (Granulation step) The kneaded material obtained in the kneading step was fed into a granulator to obtain cylindrical compacts with a diameter of about 1 mm and a length of 1 mm. This compact was then fed into a rotating tumbling granulator and subjected to tumbling granulation (size regulation) for about 3 to 10 seconds to obtain granules with a diameter of about 1 mm.

[0061] (Drying Step) The granules obtained in the granulation step were spread in a tray and allowed to dry naturally at room temperature for about one day.

[0062] (Baking Step) The granules that had been subjected to the drying step were subjected to a heat treatment in an electric furnace at a temperature of 90° C. for 0.5 hours to harden the organic binder and the like, thereby obtaining granules for adsorbing lithium.

[0063] (Desorption step) The lithium adsorbing granules that had been subjected to the baking step were packed into a column and desorbed with 0.5 mol / L hydrochloric acid. After desorption, the column was washed with pure water to remove the remaining hydrochloric acid.

[0064] (Adsorption step) After the desorption step, salt lake brine having a predetermined lithium concentration was passed through a column packed with lithium adsorbing granules, so that Li contained in the salt lake brine was adsorbed by the lithium adsorbent contained in the lithium adsorbing granules. After the salt lake brine was passed through the column, pure water was passed through the column to remove the remaining salt lake brine.

[0065] (Elution Step) After the adsorption step, 0.5 mol / L hydrochloric acid was passed through the column packed with the lithium adsorbent granules to elute the lithium adsorbed on the lithium adsorbent. Figure 5 shows a graph of the amount of lithium eluted in the elution step. The horizontal axis of Figure 5 represents time, and the vertical axis represents the molar amount of lithium obtained relative to the weight of the lithium adsorbent. The results of Example 1 are indicated by squares.

[0066] (Repetition) After the elution step, the column packed with the lithium adsorption granules was used as is to repeatedly perform the adsorption step and the elution step, and the proportion of the lithium adsorption granules that could no longer maintain their shape is shown in Figure 6. The horizontal axis of Figure 6 represents the number of cycles, and the vertical axis represents the proportion of the lithium adsorption granules that could no longer maintain their shape, i.e., the granule reduction rate. The results of Example 1, which used a copolymer polyester, are represented by squares.

[0067] <Comparative Example 1a> (Kneading step) As in Example 1a, after roasting, lithium manganate Li, which is a precursor of the lithium adsorbent, １．６ Mn １．６ O ４ 800 g of the powder and 200 g of alumina, an inorganic binder, were weighed and placed in a vinyl bag and pre-mixed. 1000 g of this mixed powder was placed in a kneader, and the kneader was rotated while adding water. The kneader was rotated for several minutes to ensure that the water was distributed throughout the mixture, yielding a kneaded product.

[0068] (Granulation step) The kneaded material obtained in the kneading step was fed into an extrusion granulator, and cylindrical pellets with a diameter of about 1 mm to 3 mm were obtained from the holes. The pellets thus formed were then cut into pellets with lengths of 3 mm to 6 mm.

[0069] (Drying Step) The compacts obtained in the granulation step were spread in a tray and dried in a dryer at 80° C. or higher for about one day.

[0070] (Sintering Step) The compact that had been subjected to the drying step was sintered in an electric furnace at 500° C. for 1.5 hours to obtain sintered granules.

[0071] (Desorption step) The sintered granules were packed into a column and desorbed with 1 mol / L hydrochloric acid. After desorption, the column was washed with pure water to remove the remaining hydrochloric acid.

[0072] (Adsorption step) After the desorption step, salt lake brine having a predetermined lithium concentration was passed through the column packed with the sintered granules, and the Li contained in the salt lake brine was adsorbed by the lithium adsorbent contained in the lithium adsorption granules. After the salt lake brine was passed through the column, pure water was passed through the column to remove the remaining salt lake brine.

[0073] (Elution Step) After the adsorption step, 1 mol / L hydrochloric acid was passed through the column packed with the sintered granules to elute the lithium adsorbed to the lithium adsorbent. The amount of lithium eluted in this elution step is shown in Figure 5. The results of Comparative Example 1 are indicated by circles. In addition, for reference, the case where lithium was adsorbed in the form of a lithium adsorbent powder is indicated by triangles.

[0074] From FIG. 5 , it can be seen that the adsorption capacity of the lithium adsorption granules using the copolymer polyester, which is an organic binder, is an adsorption amount of approximately 2 mmol per 1 g of the precursor of the lithium adsorbent, which is worse than that of the powder state, whereas the adsorption amount of the sintered granules using alumina, which is an inorganic binder, is approximately 1.3 mmol / g, and that the lithium adsorption granules using an organic binder have a higher adsorption power than inorganic binders.

[0075] (Repetition) After the elution step, the column packed with the sintered granules was used as it was to repeatedly perform the adsorption step and the elution step, and the percentage of the sintered granules that could no longer maintain their shape is shown in Figure 6. The results of Comparative Example 1, which used alumina, are represented by circles.

[0076] As shown in Figure 6, the sintered granules formed using an inorganic alumina binder gradually began to disintegrate after about 50 cycles, and the disintegration progressed rapidly after 60 cycles. On the other hand, the lithium adsorption granules using the copolymer polyester showed a reduction rate of only 10% even after 300 cycles, demonstrating that the progress of disintegration was hardly observed.

Claims

1. an oxidizing roasting step of oxidizing and roasting a powdered precursor of a lithium adsorbent containing manganese at 300° C. or more and 600° C. or less to obtain a powdered precursor of a roasted lithium adsorbent containing lithium manganate; a kneading step of kneading the precursor of the roasted lithium adsorbent, an organic binder, and a curing agent for promoting curing of the organic binder to obtain a kneaded mixture; a granulation step of granulating the kneaded mixture to obtain granules; and a baking step of baking the granules at 90° C. or more and 120° C. or less to obtain a granule for adsorbing lithium, the organic binder is a copolymer polyester, The curing agent is a polyisocyanate.

2. The method for producing a granule for adsorbing lithium, comprising:

2. (delete)

3. (delete)

4. A drying step of drying the granules at 10° C. or more and 60° C. or less, The baking step is performed after the granulation step and before the baking step.

2. The method for producing a lithium adsorbing granule according to claim 1 .

5. (delete)

6. (delete)

7. The organic binder is 5% by weight or more and 20% by weight or less of the powder of the precursor of the roasted lithium adsorbent; The method for producing a granule for adsorbing lithium according to claim 1 or 4.