A method for extracting lithium from lepidolite

Abstract

The present invention discloses a method for extracting lithium from lepidolite, comprising: crushing the lepidolite and placing it in an aluminum salt solution for pressure leaching, filtering to obtain a first filtrate and a filter residue; removing iron from the first filtrate using an iron removal agent, filtering to obtain a second filtrate and iron-containing slag; removing fluorine and aluminum from the second filtrate, filtering to obtain a third filtrate and cryolite; precipitating lithium from the third filtrate, filtering to obtain lithium carbonate. The present invention is based on the coordination leaching of lithium from lepidolite by an aluminum salt system, achieving one-step leaching of lepidolite, the extraction method has a high yield, and the lithium carbonate finally obtained has a high purity; while extracting lithium carbonate, byproducts such as goethite and cryolite with high purity can be obtained to avoid waste. The extraction method of the present invention is simple, and the reagents used are all commercially available common reagents, with low cost and good lithium extraction effect, and is convenient for use in industrial production.

Description

Technical Field

[0001] The invention relates to the field of lithium extraction, and in particular to a method for extracting lithium from lepidolite. Background Art

[0002] Lepidolite is the most common lithium mineral and an important mineral for extracting lithium. The foreign lithium salt industry basically uses spodumene as a mineral raw material. Lepidolite is a lithium mineral resource unique to my country. Its Li2O% content is generally around 4wt.%, which is about 2% lower than spodumene. How to develop and utilize this resource is of great significance to the development of my country's lithium industry.

[0003] Extracting lithium from lepidolite is a complex chemical process. How to achieve comprehensive resource utilization, reduce pollutant emissions, and simplify the process flow are issues that need to be continuously addressed. Currently, there are several methods for extracting lithium from lepidolite: sulfate method, high-pressure alkali boiling method, sulfuric acid method, chloride method, and mechanical activation. Chinese patent document CN106755967A proposes a method for treating lithium mica by calcining with sulfuric acid and preparing lithium carbonate, and transforms the lithium in lithium mica into soluble lithium sulfate through sulfation roasting; Chinese patent document CN106745097A proposes a method for treating lithium mica by calcining with sulfate, and transforms the lithium in lithium mica into soluble lithium sulfate through high-temperature roasting with sulfate; Chinese patent document CN105907943A proposes a method for treating lithium mica by calcining with chloride salt, and transforms the lithium in lithium mica into soluble lithium chloride through high-temperature roasting with chloride salt; Chinese patent document CN108163874A proposes a method for hydrothermal treatment of lithium mica, and transforms the lithium in lithium mica into soluble lithium hydroxide through high-temperature hydrothermal treatment. Although these methods achieve the effective extraction of lithium from lithium mica, they generally have problems such as high energy consumption, large slag volume, and low leaching rate. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is that the existing method for extracting lithium from lepidolite has the defects of high energy consumption, large amount of slag and low leaching rate, so as to provide a method for extracting lithium from lepidolite.

[0005] To this end, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for extracting lithium from lepidolite, comprising the following steps:

[0007] S1: crushing the lepidolite and placing it in an aluminum salt solution for pressure leaching, and filtering to obtain a first filtrate and a filter residue;

[0008] S2: removing iron from the first filtrate using an iron removal agent, and filtering to obtain a second filtrate and iron-containing slag;

[0009] S3: removing fluorine and aluminum from the second filtrate, and filtering to obtain a third filtrate and cryolite;

[0010] S4: precipitating lithium from the third filtrate, and obtaining lithium carbonate after filtering.

[0011] Further, in step S1, the concentration of hydrogen ions in the aluminum salt solution is 3-6 mol / L, the concentration of aluminum ions is 1-3 mol / L, and the liquid-to-solid ratio of the aluminum salt solution to the lepidolite is 1-6 mL / g;

[0012] The pressure during leaching is 1-20MPa, the temperature is 80-210°C, the time is 0.5-8h, and stirring is maintained during leaching at a speed of 200-400r / min.

[0013] In step S2, before iron removal, the pH value of the first filtrate is adjusted to 0-2 with alkali, and the liquid-to-solid ratio is 1-6 g / L.

[0014] The iron removal temperature is 5-50℃, the time is 0.5-4h, and stirring is maintained during iron removal at a speed of 200-400r / min.

[0015] Step S3 specifically comprises first adding alkali to adjust the pH value of the second filtrate to 2-5, and then adding fluoride, wherein the excess coefficient of fluoride is 1-1.2;

[0016] The reaction temperature is 25-90°C, the reaction time is 0.5-4h, stirring is maintained during the reaction, and the stirring speed is 200-400r / min.

[0017] In step S4, the lithium precipitation conditions are: sodium carbonate excess coefficient is 1-1.3, temperature is 50-100° C., time is 0.5-4 h, stirring is maintained during lithium precipitation, and the stirring speed is 200-400 r / min.

[0018] In step S4, the third filtrate is concentrated to 1 / 5-1 / 3 of the original volume before lithium precipitation.

[0019] The base is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the aluminum salt is at least one of aluminum sulfate, sodium aluminate, and aluminum chloride; the acid is at least one of sulfuric acid and hydrochloric acid;

[0020] The iron removal agent is at least one of sodium ferrocyanide, potassium ferrocyanide and ammonium ferrocyanide;

[0021] The fluoride is at least one of sodium fluoride, potassium fluoride and hydrofluoric acid.

[0022] Preferably, the method further comprises the step of regenerating the iron-containing slag, wherein the iron-containing slag is added into an alkaline solution having a pH of 9-14 for treatment to obtain a solution containing an iron removal agent and goethite;

[0023] The liquid-to-solid ratio of the alkali solution and the iron-containing slag is 1-3 mL / g, the reaction temperature is 25-90° C., the reaction time is 0.5-4 h, and stirring is maintained during the reaction at a stirring speed of 200-400 r / min.

[0024] In step S1, the lithium mica is crushed to a particle size of 150 mesh to 300 mesh.

[0025] The technical solution of the present invention has the following advantages:

[0026] (1) The extraction method of the present invention has a high yield, and the lithium carbonate finally obtained has a high purity; while extracting the lithium carbonate, by-products such as goethite and cryolite with high purity can be obtained, thus avoiding waste.

[0027] (2) The present invention uses an aluminum salt system to coordinately leach lithium from lithium mica, thereby achieving one-step leaching of lithium mica. Under pressurized conditions, lithium ions are easily combined with acid radical ions to form soluble lithium. The aluminum ions are located at the center of the tetrahedral lattice formed by the original three lithium ion lattices, which is close in size to the lattice vacancies in the mineral, forming a stable and irreversible coordination reaction. The present invention uses aluminum salts for coordination leaching, and cryolite can be formed during the lithium extraction process to help remove fluorine from the mica ore. At the same time, since aluminum itself is one of the elements contained in lithium mica, it will not introduce new elements, nor will it affect the remaining elements in the lithium mica to cause instability in lithium extraction.

[0028] (3) Ferrocyanide is used for iron removal. Ferrocyanide is suitable for acidic systems. The residual iron rate in the liquid after iron removal is low, the iron removal efficiency is high, and the precipitate generated after iron removal can be recycled, reducing the cost of iron removal.

[0029] (4) The extraction method of the present invention is simple, and the reagents used are all common commercially available reagents, which are low in cost, have good lithium extraction effects, and are easy to use in industrial production. DETAILED DESCRIPTION

[0030] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0031] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0032] The lepidolite used in the specific implementation of the present application comes from Yichun, Jiangxi Province, wherein the content of the main compounds is shown in Table 1:

[0033] Table 1 Content of main compounds of lithium mica (wt%)

[0034] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Li2O]]> MnO F 67.65 17.53 4.19 5.21 0.61 0.05 1.01 2.37 0.22 0.15

[0035] Example 1

[0036] This embodiment provides a method for extracting lithium from lepidolite, and the specific steps are as follows:

[0037] (1) 100 g of lithium mica was crushed to 150-300 mesh, placed in 500 mL of aluminum salt solution, pressurized to 2 MPa at 160° C. and 300 rpm, and leached for 2 h, and filtered to obtain a first filtrate and a filter residue;

[0038] The aluminum salt solution contains 3M HCl, 2M AlCl3,

[0039] In the first filtrate, the leaching rate of fluorine is 96.0%, the leaching rate of lithium is 99.0%, the leaching rate of iron is 61.0%, and the leaching rate of aluminum is 52.0%;

[0040] (2) adjusting the pH of the first filtrate to 0 with lithium hydroxide, adding sodium ferrocyanide with an excess coefficient of 1.1, reacting at 25° C. and 300 rpm for 1 hour, and filtering to obtain a second filtrate and iron-containing slag;

[0041] The iron removal rate in the second filtrate was 99.0%, and the concentrations of other ions did not change significantly;

[0042] (3) adding the iron-containing slag to a lithium hydroxide solution with a pH of 12, with a liquid-to-solid ratio of 2 mL / g, and reacting at 70° C. and 300 rpm for 1 h to obtain a solution containing an iron remover and goethite;

[0043] (4) adjusting the pH value of the second filtrate to 3 with lithium hydroxide, adding sodium fluoride with an excess coefficient of 1.1, reacting at 80° C. and 300 rpm for 90 min, and filtering to obtain a third filtrate and cryolite;

[0044] The removal rates of aluminum and fluorine in the third filtrate were 99.0% and 98%, respectively, and the concentrations of other ions did not change significantly;

[0045] (5) The third filtrate was evaporated and concentrated to 1 / 4 of the original volume, and then sodium carbonate with an excess coefficient of 1.2 was added, and the reaction was carried out at 95° C. and 300 rpm for 60 minutes to obtain lithium carbonate with a purity of 99.12 wt.%, and the lithium yield was 91.53%.

[0046] Example 2

[0047] This embodiment provides a method for extracting lithium from lepidolite, and the specific steps are as follows:

[0048] (1) 100 g of lithium mica was crushed to 150-300 mesh, placed in 500 mL of aluminum salt solution, pressurized to 10 MPa at 100° C. and 300 rpm, and leached for 2 h, and filtered to obtain a first filtrate and a filter residue;

[0049] The aluminum salt solution contains 2M H2SO4, 2M Al2(SO4)3,

[0050] In the first filtrate, the leaching rate of fluorine is 97.32%, the leaching rate of lithium is 98.36%, the leaching rate of iron is 67.66%, and the leaching rate of aluminum is 62.8%;

[0051] (2) adjusting the pH of the first filtrate to 0 with lithium hydroxide, adding sodium ferrocyanide with an excess coefficient of 1.1, reacting at 25° C. and 300 rpm for 1 hour, and filtering to obtain a second filtrate and iron-containing slag;

[0052] The iron removal rate in the second filtrate was 99.06%, and the concentrations of other ions did not change significantly;

[0053] (3) adding the iron-containing slag to a lithium hydroxide solution with a pH of 12, with a liquid-to-solid ratio of 2 mL / g, and reacting at 70° C. and 300 rpm for 1 h to obtain a solution containing an iron remover and goethite;

[0054] (4) adjusting the pH value of the second filtrate to 3 with lithium hydroxide, adding sodium fluoride with an excess coefficient of 1.1, reacting at 80° C. and 300 rpm for 90 min, and filtering to obtain a third filtrate and cryolite;

[0055] The removal rates of aluminum and fluorine in the third filtrate were 99.0% and 98%, respectively, and the concentrations of other ions did not change significantly;

[0056] (5) The third filtrate was evaporated and concentrated to 1 / 3 of the original volume, and sodium carbonate with an excess coefficient of 1.2 was added, and the reaction was carried out at 95° C. and 300 rpm for 60 min to obtain lithium carbonate with a purity of 99.08 wt.%, and the lithium yield was 93.67%.

[0057] Example 3

[0058] This embodiment provides a method for extracting lithium from lepidolite, and the specific steps are as follows:

[0059] (1) 100 g of lithium mica was crushed to 150-300 mesh, placed in 500 mL of aluminum salt solution, pressurized to 18 MPa at 100° C. and 300 rpm, and leached for 2 h, and filtered to obtain a first filtrate and a filter residue;

[0060] The aluminum salt solution contains 3M HCl, 2M AlCl3,

[0061] In the first filtrate, the leaching rate of fluorine is 99.63%, the leaching rate of lithium is 99.07%, the leaching rate of iron is 69.96%, and the leaching rate of aluminum is 72.45%;

[0062] (2) adjusting the pH of the first filtrate to 1 with lithium hydroxide, adding sodium ferrocyanide with an excess coefficient of 1.1, reacting at 20° C. and 300 rpm for 1 hour, and filtering to obtain a second filtrate and iron-containing slag;

[0063] The iron removal rate in the second filtrate was 98.0%, and the concentrations of other ions did not change significantly;

[0064] (3) adding the iron-containing slag to a lithium hydroxide solution with a pH of 12, with a liquid-to-solid ratio of 2 mL / g, and reacting at 70° C. and 300 rpm for 1 h to obtain a solution containing an iron remover and goethite;

[0065] (4) adjusting the pH value of the second filtrate to 4 with lithium hydroxide, adding sodium fluoride with an excess coefficient of 1.1, reacting at 80° C. and 300 rpm for 90 min, and filtering to obtain a third filtrate and cryolite;

[0066] The removal rates of aluminum and fluorine in the third filtrate were 98.0% and 98%, respectively, and the concentrations of other ions did not change significantly;

[0067] (5) The third filtrate was evaporated and concentrated to 1 / 5 of the original volume, and sodium carbonate with an excess coefficient of 1.2 was added, and the reaction was carried out at 95° C. and 300 rpm for 45 minutes to obtain lithium carbonate with a purity of 99.15 wt.%, and the lithium yield was 96.79%.

[0068] Comparative Example 1

[0069] 100 g of lithium mica was crushed to 150-300 mesh, placed in 500 mL of hydrochloric acid solution, pressurized to 2 MPa at 160° C. and 300 rpm, and leached for 2 h, and filtered to obtain a filtrate and a filter residue;

[0070] The aluminum salt solution contained 5M HCl.

[0071] In the filtrate, the leaching rate of fluorine is 36.13%, the leaching rate of lithium is 37.0%, the leaching rate of iron is 57.56%, and the leaching rate of aluminum is 46.53.0%. This is because the lithium in lithium mica is in the form of KLiFeAl[AlSi3O 10 ](F,OH)2 exists in the form of complex minerals. Single acid leaching cannot achieve effective leaching of lithium, but when aluminum ions are coordinated with fluoride ions, effective leaching of lithium can be achieved.

[0072] Comparative Example 2

[0073] 100 g of lithium mica was crushed to 150-300 mesh, and then placed in 500 mL of aluminum salt solution for leaching at 100° C. and 300 rpm for 2 h, and filtered to obtain a filtrate and a filter residue;

[0074] The aluminum salt solution contains 3M HCl, 2M AlCl3,

[0075] In the filtrate, the leaching rate of fluorine is 33.65%, the leaching rate of lithium is 35.54%, the leaching rate of iron is 54.12%, and the leaching rate of aluminum is 41.33%. This is because the structure of lepidolite is stable, and the leaching efficiency of each element is relatively low under relatively low temperature and low pressure conditions.

[0076] Comparative Example 3

[0077] The difference between this comparative example and Example 1 is that no iron removal operation is performed, and the specific method is as follows:

[0078] (1) 100 g of lithium mica was crushed to 150-300 mesh, placed in 500 mL of aluminum salt solution, pressurized to 2 MPa at 160° C. and 300 rpm, and leached for 2 h, and filtered to obtain a first filtrate and a filter residue;

[0079] The aluminum salt solution contains 3M HCl, 2M AlCl3;

[0080] (2) adjusting the pH value of the first filtrate to 3 with lithium hydroxide, adding sodium fluoride with an excess coefficient of 1.1, reacting at 80° C. and 300 rpm for 90 min, and filtering to obtain a second filtrate and cryolite;

[0081] The removal rates of aluminum and fluorine in the second filtrate were 85.53% and 78.77%;

[0082] (3) The third filtrate was evaporated and concentrated to 1 / 4 of the original volume, and sodium carbonate with an excess coefficient of 1.2 was added, and the reaction was carried out at 95° C. and 300 rpm for 60 minutes to obtain lithium carbonate with a purity of 98.65 wt.%, and the lithium yield was 87.87%.

[0083] It can be seen from Comparative Example 3 that iron removal was not performed before aluminum and fluorine removal, and the aluminum and fluorine removal rates were significantly lower than those in Example 1, and the final lithium yield was low, indicating that failure to perform iron removal would affect the effects of subsequent steps.

[0084] Comparative Example 4

[0085] The difference between this comparative example and Example 1 is that an alkali pH adjustment method is used to remove iron, and the specific method is as follows:

[0086] (1) 100 g of lithium mica was crushed to 150-300 mesh, placed in 500 mL of aluminum salt solution, pressurized to 2 MPa at 160° C. and 300 rpm, and leached for 2 h, and filtered to obtain a first filtrate and a filter residue;

[0087] The aluminum salt solution contains 3M HCl, 2M AlCl3;

[0088] (2) adjusting the pH value of the first filtrate to 2 with lithium hydroxide, adding sodium fluoride with an excess coefficient of 1.1, reacting at 80° C. and 300 rpm for 90 min, and filtering to obtain a second filtrate and cryolite;

[0089] The removal rates of aluminum and fluorine in the second filtrate were 85.54% and 88.91%;

[0090] (3) adding 20 ml of hydrogen peroxide to the second filtrate and reacting for 30 min, adjusting the pH to 4.5-5.0 with lithium hydroxide to form Fe(OH)3 precipitate, and filtering to obtain the iron hydroxide precipitate and the third filtrate;

[0091] The Fe removal rate in the third filtrate was 91.06%;

[0092] (4) The third filtrate was evaporated and concentrated to 1 / 4 of the original volume, and sodium carbonate with an excess coefficient of 1.2 was added, and the reaction was carried out at 95° C. and 300 rpm for 60 minutes to obtain lithium carbonate with a purity of 97.51 wt.%, and the lithium yield was 83.32%.

[0093] Comparative Example 4 uses an alkali pH adjustment method to remove iron, which is to remove iron after removing aluminum and fluorine. Therefore, like Comparative Example 3, the removal rate of aluminum and fluorine is obviously not as good as that in Example 1. The iron removal effect of the alkali pH adjustment method is obviously not as good as the iron removal using ferrocyanide in Example 1, and it will also affect the subsequent lithium yield.

[0094] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for extracting lithium from lepidolite, characterized in that: The steps include: S1: crushing the lepidolite and placing it in an aluminum salt solution for pressure leaching, and filtering to obtain a first filtrate and a filter residue; The concentration of hydrogen ions in the aluminum salt solution is 3-6 mol / L, the concentration of aluminum ions is 1-3 mol / L, and the liquid-to-solid ratio of the aluminum salt solution to lithium mica is 1-6 mL / g; During leaching, the pressure is 1-20MPa, the temperature is 80-210℃, the time is 0.5-8h, and stirring is maintained during leaching at a stirring speed of 200-400 r / min; S2: removing iron from the first filtrate using an iron removal agent, and filtering to obtain a second filtrate and iron-containing slag; S3: taking the second filtrate, first adding alkali to adjust the pH value of the second filtrate to 2-5, then adding fluoride, the fluoride excess coefficient is 1-1.2, reacting, filtering to obtain the third filtrate and cryolite; S4: precipitating lithium from the third filtrate, and obtaining lithium carbonate after filtering.

2. The extraction method according to claim 1, characterized in that In step S2, before iron removal, the pH value of the first filtrate is adjusted to 0-2 with alkali, and the liquid-to-solid ratio is 1-6 mL / g. The iron removal temperature is 5-50℃, the time is 0.5-4 h, and stirring is maintained during iron removal at a speed of 200-400 r / min.

3. The extraction method according to claim 1, characterized in that In step S3, the reaction temperature is 25-90° C., the reaction time is 0.5-4 h, and stirring is maintained during the reaction at a stirring speed of 200-400 r / min.

4. The extraction method according to claim 1, characterized in that In step S4, the lithium precipitation conditions are: sodium carbonate excess coefficient is 1-1.3, temperature is 50-100° C., time is 0.5-4 h, stirring is maintained during lithium precipitation, and the stirring speed is 200-400 r / min.

5. The extraction method according to claim 1, characterized in that In step S4, the third filtrate is concentrated to 1 / 5-1 / 3 of the original volume before lithium precipitation.

6. The extraction method according to any one of claims 1 to 5, characterized in that The alkali is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the aluminum salt is at least one of aluminum sulfate, sodium aluminate, and aluminum chloride; the hydrogen ions in the aluminum salt solution are provided by an acid, and the acid is at least one of sulfuric acid and hydrochloric acid; The iron removal agent is at least one of sodium ferrocyanide, potassium ferrocyanide and ammonium ferrocyanide; The fluoride is at least one of sodium fluoride, potassium fluoride and hydrofluoric acid.

7. The extraction method according to any one of claims 1 to 5, characterized in that The method further comprises the step of regenerating the iron-containing slag, wherein the iron-containing slag is added into an alkaline solution having a pH value of 9-14 for treatment to obtain a solution containing an iron removal agent and goethite; The liquid-to-solid ratio of the alkali solution to the iron-containing slag is 1-3 mL / g, the reaction temperature is 25-90° C., the reaction time is 0.5-4 h, and stirring is maintained during the reaction at a stirring speed of 200-400 r / min.

8. The extraction method according to any one of claims 1 to 5, characterized in that In step S1, the lithium mica is crushed to a particle size of 150 mesh to 300 mesh.