A method for preparing battery-grade lithium carbonate from low-grade lithium phosphate

Abstract

The present invention provides a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate, belonging to the field of chemical engineering. The method prepares lithium carbonate from low-grade lithium phosphate solid raw material using the following process steps: mixing ingredients, microwave roasting, leaching treatment, filtration and impurity removal, and centrifugal washing. The method removes a large amount of impurities from the low-grade lithium phosphate solid raw material through pretreatment roasting. The process is short and easy to operate, and the resulting lithium carbonate is battery-grade, with high resource utilization.

Description

Technical field:

[0001] The present invention relates to the field of chemical industry, and in particular to a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate. Background technology:

[0002] Lithium carbonate is an indispensable raw material in current high-tech fields such as lithium-ion batteries, aerospace, and military technology. A large amount of low-grade lithium phosphate exists on the market, most of which are by-products formed during the production of lithium carbonate. This low-grade lithium phosphate has high impurity content, coarse particle size, and low content of effective ingredients. With the demand for environmental protection and resource recycling, there is an urgent need for a method to effectively recover low-grade lithium phosphate. Current low-grade lithium phosphate recovery methods are overly dependent on acid-base reactions and are still at the stage of high-efficiency lithium recovery in the laboratory theory, but there is still a certain gap in high-efficiency recovery in practice. The present invention provides a method for efficiently and cost-effectively recovering lithium and preparing battery-grade lithium carbonate.

[0003] For example, patent CN108675323A, entitled "A method for preparing lithium carbonate for batteries by acidic conversion of low-grade lithium phosphate," uses soluble salts of iron, ferrous iron, aluminum, and calcium as conversion agents. Under low-acid conditions, the conversion agent fully reacts with lithium phosphate to initially separate the lithium ions and phosphate groups in the lithium phosphate. The pH value of the double decomposition reaction product is then adjusted to allow the phosphate ions to react with the metal ions and precipitate to remove the phosphate ions. The metal ions are then removed by adding a large amount of alkaline substances. This not only has a long production process, high production costs, and a low lithium conversion rate, but also generates a large amount of waste.

[0004] Patent CN111740102A, entitled "Method for preparing lithium phosphate for use in new energy batteries based on low-grade lithium phosphate," uses slurry preparation and complexation reaction of low-grade lithium phosphate, followed by ultrasonic crystallization and purification and drying steps to convert the impurities of calcium compounds, magnesium compounds, and iron compounds in the low-grade lithium phosphate into water-soluble compounds, thereby converting low-grade lithium phosphate into lithium phosphate that can be used in new energy batteries on a large scale. However, this process has relatively high requirements for lithium phosphate raw materials and requires ultrasonic crystallization in specific equipment, which is not easy to industrialize. Based on the above problems, the present invention can efficiently process lithium phosphate of different grades and convert it into battery-grade lithium carbonate, which is currently in short supply, broaden the preparation channels for battery-grade lithium carbonate, and solve the problem of efficient recycling of low-grade lithium phosphate. Summary of the invention:

[0005] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0006] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments, and that the embodiments described herein are merely some, not all, embodiments of the present invention.

[0007] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0008] The present invention provides a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate. The low-grade lithium phosphate is a solid raw material, and the main elements are as follows: Li ≥ 14.18%, Na ≥ 2.04%, Ma ≥ 0.53%, Ca ≥ 0.32%, Al ≥ 0.26%, Fe ≥ 0.18%, O and P ≥ 82.49%. The following process steps are used:

[0009] 1) Mixing ingredients: mixing low-grade lithium phosphate solid raw material with reagent a and reagent b to obtain raw material;

[0010] 2) Microwave roasting: roasting the raw material obtained in step 1) in air at a certain temperature for a certain time to obtain a roasted clinker;

[0011] 3) Leaching treatment: mixing the roasted clinker obtained in step 2) with water in a certain mass ratio, and leaching the mixture at room temperature for a certain period of time to obtain a mixed slurry;

[0012] 4) Filtration and impurity removal: Filter the mixed slurry obtained in step 3) to obtain a lithium filtrate, then add an impurity remover to precipitate lithium to obtain a refined lithium solution;

[0013] 5) Centrifugal washing: The refined lithium solution obtained in step 4) is sequentially washed, purified, and centrifuged to obtain a battery-grade lithium carbonate product; the purity of the battery-grade lithium carbonate product is greater than or equal to 99.5%.

[0014] Preferably, in step 1), the reagent a comprises Ca(OH)2, CaCO3, CaO or CaSO4; and the reagent b comprises sulfuric acid, hydrochloric acid or phosphoric acid.

[0015] Preferably, in step 1), the molar ratio of phosphate ions in the low-grade lithium phosphate solid raw material to calcium ions in reagent a is 1:1.65-1.75, and the molar ratio of lithium ions in the low-grade lithium phosphate solid raw material to hydrogen ions in reagent b is 1:1.1-1.2.

[0016] Preferably, the raw material obtained in step 1) is microwave-roasted in air at a certain temperature for a certain time, specifically roasting the raw material in three stages; the certain temperature is 300-500° C., and the certain time is 60-240 minutes.

[0017] The three-stage roasting is sequentially and continuously carried out at low, medium and high temperatures; the low-temperature roasting is carried out at 300-350°C for 10-20 minutes to obtain a low-temperature roasted material; the medium-temperature roasting is carried out by stirring the low-temperature roasted material and then roasting it at 280-400°C for 40-100 minutes to obtain a medium-temperature roasted material; the high-temperature roasting is carried out by stirring the medium-temperature roasted material and then roasting it at 380-500°C for 10-120 minutes to obtain a roasted clinker.

[0018] The low-temperature calcined material is stirred from the center to the surrounding at a stirring rate of 5-10s / r for 1-2min; the medium-temperature calcined material is stirred from the center to the surrounding at a stirring rate of 8-12s / r for 1-2min.

[0019] Preferably, the certain mass ratio in step 3) is a mass ratio of the roasted clinker to water of 1:(2.5-3.5); and the certain time of the leaching treatment is 30-60 minutes.

[0020] Preferably, the impurity remover in step 4) is a mixed solution of sodium hydroxide and sodium carbonate.

[0021] The present invention has the following beneficial effects:

[0022] 1. Microwave roasting is used for pre-reaction. The reaction is from the inside out, converting lithium phosphate into lithium salt that is easily soluble in water. The phosphate group remains solid when combined with calcium, and other metal compounds are not easily soluble in water. Impurities are greatly reduced, and no other concentration and impurity removal processes are required.

[0023] 2. There is no need to carry out a large amount of acid-base neutralization reaction to remove impurities, which reduces the reaction steps and greatly reduces the intermediate reaction waste.

[0024] 3. It can be applied to various low-grade lithium phosphate raw materials, with easy operation and strong practicality.

[0025] 4. The recovery rate of industrial lithium is greatly improved, and the recovery rate can reach more than 97%. Description of the drawings:

[0026] In order to more clearly illustrate the solutions in this application, a brief introduction will be given below to the drawings required for use in the description of the embodiments of this application. Obviously, the drawings described below are some embodiments of this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0027] Figure 1 This is a process flow chart of a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate described in an embodiment of the present invention. Specific implementation method:

[0028] The present invention is further described below with reference to specific examples. Unless otherwise specified, all raw materials used in the present invention can be obtained commercially. The following unspecified parts are all based on mass ratio, mass or weight.

[0029] Example 1:

[0030] In this embodiment, the calcination temperature is adjusted to 400° C. The present invention provides a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate. The low-grade lithium phosphate is a solid raw material, and the main elements are as follows: Li ≥ 14.18%, Na ≥ 2.04%, Ma ≥ 0.53%, Ca ≥ 0.32%, Al ≥ 0.26%, Fe ≥ 0.18%, O and P ≥ 82.49%. The following process steps are used:

[0031] 1) Mixing ingredients: 100 g of a low-grade lithium phosphate solid raw material (lithium content of 12.3 wt%) is mixed with 80 g of reagent a and 20 g of reagent b to obtain a raw material; the reagent a is a mixture of CaCO3 and CaSO4 in a ratio of 1:1; the reagent b is a mixture of sulfuric acid and hydrochloric acid in a ratio of 1:1; the molar ratio of phosphate ions in the low-grade lithium phosphate solid raw material to calcium ions in reagent a is 1:1.65-1.75, and the molar ratio of lithium ions in the low-grade lithium phosphate solid raw material to hydrogen ions in reagent b is 1:1.1-1.2.

[0032] 2) Microwave roasting: the raw material obtained in step 1) is microwave roasted in air at a certain temperature for a certain time to obtain roasted clinker. Specifically, the raw material is roasted in three stages.

[0033] The three-stage roasting is continuous low-, medium- and high-temperature roasting in sequence; the low-temperature roasting is roasting at 300°C for 10 minutes to obtain a low-temperature roasted material; the medium-temperature roasting is stirring the low-temperature roasted material and then roasting at 350°C for 40 minutes to obtain a medium-temperature roasted material; the high-temperature roasting is stirring the medium-temperature roasted material and then roasting at 400°C for 70 minutes to obtain a roasted clinker.

[0034] The low-temperature calcined material is stirred from the center of the low-temperature calcined material to the surrounding area at a stirring rate of 5s / r for 1 minute; the medium-temperature calcined material is stirred from the center of the low-temperature calcined material to the surrounding area at a stirring rate of 8s / r for 2 minutes.

[0035] 3) Leaching treatment: the roasted clinker obtained in step 2) is mixed with water in a certain mass ratio, and then leached at 50°C for a certain time to obtain a mixed slurry; the certain mass ratio is a mass ratio of roasted clinker to water of 1:2.5; the leaching treatment time is 30 minutes

[0036] 4) Filtration and impurity removal: The mixed slurry obtained in step 3) is filtered to obtain a lithium filtrate, and then an impurity remover is added to precipitate lithium to obtain a refined lithium solution; the impurity remover is a mixed solution of sodium hydroxide and sodium carbonate.

[0037] The lithium content in the refined lithium solution in step 4) is 25.3 g / L, the calcium content is 0.09 g / L, and the lithium content in the slag is 0.13%.

[0038] 5) Centrifugal washing: The refined lithium solution obtained in step 4) is sequentially washed, purified, and centrifuged to obtain a battery-grade lithium carbonate product; the purity of the battery-grade lithium carbonate product is greater than or equal to 99.5%, and the total lithium recovery rate reaches 97.56%.

[0039] According to this embodiment, the chemical composition content of the prepared lithium carbonate is

[0040]

[0041] Example 2:

[0042] In this embodiment, the roasting temperature is adjusted to 600° C. to provide a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate. The low-grade lithium phosphate is a solid raw material, and the main elements are as follows: Li ≥ 14.18%, Na ≥ 2.04%, Ma ≥ 0.53%, Ca ≥ 0.32%, Al ≥ 0.26%, Fe ≥ 0.18%, O and P ≥ 82.49%. The following process steps are used:

[0043] 1) Mixing ingredients: 100 g of a low-grade lithium phosphate solid raw material (lithium content of 12.3 wt%) is mixed with 80 g of reagent a and 20 g of reagent b to obtain a raw material; the reagent a is a mixture of CaCO3 and CaSO4 in a ratio of 1:1; the reagent b is a mixture of sulfuric acid and hydrochloric acid in a ratio of 1:1; the molar ratio of phosphate ions in the low-grade lithium phosphate solid raw material to calcium ions in reagent a is 1:1.65-1.75, and the molar ratio of lithium ions in the low-grade lithium phosphate solid raw material to hydrogen ions in reagent b is 1:1.1-1.2.

[0044] 2) Microwave roasting: the raw material obtained in step 1) is microwave roasted in air at a certain temperature for a certain time to obtain roasted clinker. Specifically, the raw material is roasted in three stages.

[0045] The three-stage roasting is continuous low-, medium- and high-temperature roasting in sequence; the low-temperature roasting is roasting at 350°C for 10 minutes to obtain a low-temperature roasted material; the medium-temperature roasting is stirring the low-temperature roasted material and then roasting at 400°C for 40 minutes to obtain a medium-temperature roasted material; the high-temperature roasting is stirring the medium-temperature roasted material and then roasting at 600°C for 70 minutes to obtain a roasted clinker.

[0046] The low-temperature calcined material is stirred from the center of the low-temperature calcined material to the surrounding area at a stirring rate of 5s / r for 1 minute; the medium-temperature calcined material is stirred from the center of the low-temperature calcined material to the surrounding area at a stirring rate of 8s / r for 2 minutes.

[0047] 3) Leaching treatment: the roasted clinker obtained in step 2) is mixed with water in a certain mass ratio, and then leached at 50° C. for a certain time to obtain a mixed slurry; the certain mass ratio is a mass ratio of roasted clinker to water of 1:2.5; and the leaching treatment time is 30 minutes.

[0048] 4) Filtration and impurity removal: The mixed slurry obtained in step 3) is filtered to obtain a lithium filtrate, and then an impurity remover is added to precipitate lithium to obtain a refined lithium solution; the impurity remover is a mixed solution of sodium hydroxide and sodium carbonate.

[0049] The lithium content in the refined lithium solution in step 4) is 25.3 g / L, the calcium content is 0.09 g / L, and the lithium content in the slag is 0.13%.

[0050] 5) Centrifugal washing: The refined lithium solution obtained in step 4) is sequentially washed, purified, and centrifuged to obtain a battery-grade lithium carbonate product; the purity of the battery-grade lithium carbonate product is greater than or equal to 99.5%, and the total lithium recovery rate reaches 88.12%.

[0051] According to this embodiment, the chemical composition content of the prepared lithium carbonate is

[0052]

[0053] Comparative Example:

[0054] In this embodiment, the roasting temperature is adjusted to 200° C. to provide a method for preparing battery-grade lithium carbonate from low-grade lithium phosphate. The low-grade lithium phosphate is a solid raw material, and the main elements are as follows: Li ≥ 14.18%, Na ≥ 2.04%, Ma ≥ 0.53%, Ca ≥ 0.32%, Al ≥ 0.26%, Fe ≥ 0.18%, O and P ≥ 82.49%. The following process steps are used:

[0055] 1) Mixing ingredients: 100 g of a low-grade lithium phosphate solid raw material (lithium content of 12.3 wt%) is mixed with 80 g of reagent a and 20 g of reagent b to obtain a raw material; the reagent a is a mixture of CaCO3 and CaSO4 in a ratio of 1:1; the reagent b is a mixture of sulfuric acid and hydrochloric acid in a ratio of 1:1; the molar ratio of phosphate ions in the low-grade lithium phosphate solid raw material to calcium ions in reagent a is 1:1.65-1.75, and the molar ratio of lithium ions in the low-grade lithium phosphate solid raw material to hydrogen ions in reagent b is 1:1.1-1.2.

[0056] 2) Microwave roasting: the raw material obtained in step 1) is microwave roasted in air at 200° C. for 120 min to obtain roasted clinker.

[0057] 3) Leaching treatment: the roasted clinker obtained in step 2) is mixed with water in a certain mass ratio, and then leached at 50° C. for a certain time to obtain a mixed slurry; the certain mass ratio is a mass ratio of roasted clinker to water of 1:2.5; and the leaching treatment time is 30 minutes.

[0058] 4) Filtration and impurity removal: The mixed slurry obtained in step 3) is filtered to obtain a lithium filtrate, and then an impurity remover is added to precipitate lithium to obtain a refined lithium solution; the impurity remover is a mixed solution of sodium hydroxide and sodium carbonate.

[0059] The lithium content in the refined lithium solution in step 4) is 10.6 g / L, the calcium content is 0.18 g / L, and the lithium content in the slag is 1.56%.

[0060] 5) Centrifugal washing: The refined lithium solution obtained in step 4) is sequentially washed, purified, and centrifuged to obtain a battery-grade lithium carbonate product; the purity of the battery-grade lithium carbonate product is greater than or equal to 99.5%, and the total lithium recovery rate reaches 68.57%.

[0061] According to this embodiment, the chemical composition content of the prepared lithium carbonate is

[0062]

[0063] The above embodiments are some preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the scope of protection of the present invention.

Claims

1. A method for preparing battery-grade lithium carbonate from low-grade lithium phosphate, wherein the low-grade lithium phosphate is a solid raw material, and the main elements are as follows: Li ≥ 14.18%, Na ≥ 2.04%, Ma ≥ 0.53%, Ca ≥ 0.32%, Al ≥ 0.26%, Fe ≥ 0.18%, O and P ≥ 82.49%; characterized in that: The following process steps are used: 1) Mixing ingredients: mixing low-grade lithium phosphate solid raw material with reagent a and reagent b to obtain raw material; 2) Microwave roasting: roasting the raw material obtained in step 1) in air at a certain temperature for a certain time to obtain a roasted clinker; 3) Leaching treatment: mixing the roasted clinker obtained in step 2) with water in a certain mass ratio, and leaching the mixture at room temperature for a certain period of time to obtain a mixed slurry; 4) Filtration and impurity removal: The mixed slurry obtained in step 3) is filtered to obtain a lithium filtrate, and then an impurity remover is added to precipitate lithium to obtain a refined lithium solution; 5) Centrifugal washing: washing, purifying, and centrifuging the refined lithium solution obtained in step 4) to obtain a battery-grade lithium carbonate product; the purity of the battery-grade lithium carbonate product is greater than or equal to 97%; Step 1) The reagent a includes Ca(OH)2, CaCO3, and CaO; the reagent b includes sulfuric acid, hydrochloric acid, or phosphoric acid; Step 1) The molar ratio of the phosphate ions in the low-grade lithium phosphate solid raw material to the calcium ions in reagent a is 1:1.65-1.75, and the molar ratio of the lithium ions in the low-grade lithium phosphate solid raw material to the hydrogen ions in reagent b is 1:1.1-1.2; The raw material obtained in step 1) is microwave-roasted in air at a certain temperature for a certain time, specifically, the raw material is roasted in three stages; the certain temperature is 300-500° C., and the certain time is 60-240 minutes; The three-stage calcination is sequentially carried out at low, medium and high temperatures; the low-temperature calcination is carried out at 300-350°C for 10-20 minutes to obtain a low-temperature calcined material; The intermediate temperature roasting is to stir the low temperature roasting material, and then roast it at 280-400°C for 40-100 minutes to obtain the intermediate temperature roasting material; The high-temperature roasting is to stir the medium-temperature roasting material, and then roast it at 380-500° C. for 10-120 minutes to obtain roasted clinker.

2. The method for preparing battery-grade lithium carbonate from low-grade lithium phosphate according to claim 1, wherein: The low-temperature calcined material is stirred from the center to the surrounding at a stirring rate of 5-10s / r for 1-2min; the medium-temperature calcined material is stirred from the center to the surrounding at a stirring rate of 8-12s / r for 1-2min.

3. The method for preparing battery-grade lithium carbonate from low-grade lithium phosphate according to claim 1, characterized in that The certain mass ratio in step 3) is a mass ratio of the roasted clinker to water of 1:(2.5-3.5); and the certain time for the leaching treatment is 30-60 minutes.

4. The method for preparing battery-grade lithium carbonate from low-grade lithium phosphate according to claim 1, characterized in that The impurity remover in step 4) is a mixed solution of sodium hydroxide and sodium carbonate.

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