Method for preparing molecular sieve by taking lithium slag as raw material

Abstract

The invention discloses a method for preparing a molecular sieve by taking lithium slag as a raw material, which is characterized in that flotation tailings obtained by carrying out flotation separation on gypsum concentrate on lepidolite smelting slag are taken as a raw material, and the molecular sieve is prepared by a high-temperature alkali fusion-hydrothermal crystallization method. The method is low in cost and simple in process, the prepared molecular sieve is high in purity and crystallinity and good in adsorbability and can be widely applied to the fields of adsorbents, catalysts, drying agents and the like, gypsum in the lithium slag can be recycled, comprehensive utilization of the lithium slag is facilitated, economic and environment-friendly benefits are improved, and the application prospect is wide.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of solid waste lithium slag, and in particular to a method for preparing a molecular sieve using lithium slag as a raw material. Background Art

[0002] Lithium slag is solid waste generated during the lithium extraction process of lithium ore, and its main components are oxides of silicon, aluminum, calcium, sodium, iron, etc. In the process of producing lithium carbonate by lithium mica sulfate roasting method, nearly 40 tons of lithium slag are produced for every ton of lithium carbonate produced. The lithium slag produced by Yichun lithium carbonate production enterprises is nearly 20 million tons per year. The accumulated accumulation over the years occupies a large amount of land and pollutes the environment. Among them, lithium mica slag contains certain harmful metal substances such as Tl and Be. Open-air stacking and landfill will threaten the safety of the surrounding soil environment and surface water and groundwater resources. How to comprehensively utilize the lithium slag produced in the process of producing lithium carbonate by lithium mica sulfate roasting method, reduce the burden on enterprises, and protect the environment has become an important issue that the lithium carbonate production industry must solve.

[0003] Molecular sieve is a crystalline aluminosilicate with a uniform microporous structure. Due to its unique pore structure and surface properties, it has a wide range of applications in the fields of adsorption, separation, catalysis, etc. At present, molecular sieves have been prepared from lithium slag to achieve high value-added utilization of solid waste. For example, patent CN200910183869 discloses a method for preparing 13X molecular sieves using lithium slag as raw material, and patent 201811610136.9 discloses a low-temperature preparation method for lithium slag-based NaA molecular sieves, both of which can solve the environmental protection problem of lithium slag. However, the lithium slag used in the above methods is all treated with spodumene smelting slag, which is acidic slag. When treating it, a large amount of alkali flux needs to be added, which will increase production costs, and deacidification and iron removal processes are also required during the pretreatment process. These methods cannot be directly applied to alkaline lithium mica smelting slag. Patent CN202410132283 discloses a method for preparing a magnetic zeolite adsorbent from alkaline lithium slag, a magnetic zeolite adsorbent and its application. The raw material is alkaline lithium slag produced in the process of producing lithium carbonate from lithium mica, but the pretreatment process is relatively complicated and requires water washing, drying, ball milling and screening. The above method of preparing molecular sieves using lithium slag is relatively complicated, the cost is high, and the comprehensive utilization rate of lithium slag is low. Therefore, it is necessary to propose a new method for the comprehensive utilization of lithium slag from lithium mica smelting. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a method for preparing molecular sieves using lithium slag as raw material, which has low cost and simple process. The prepared molecular sieve has high purity and crystallinity and good adsorption property. In addition, gypsum in the lithium slag can be recovered, which is beneficial to the comprehensive utilization of lithium slag and improves economic and environmental benefits.

[0005] The present invention provides a method for preparing a molecular sieve using lithium slag as a raw material, comprising the following steps:

[0006] S1. After crushing and screening the lithium mica smelting slag, gypsum is separated by flotation to obtain gypsum concentrate and flotation tailings; the components of the lithium mica smelting slag are as follows: CaSO4 25-40%, SiO2 25-50%, Al2O3 15-25%, Na2SO4 5-25%, Fe2O3 1.5-4.5%, and other impurities 0-5%, and the sum of the weight percentages of the above components is 100%;

[0007] S2, mixing the flotation tailings with an alkali flux, and subjecting the mixture to high-temperature alkali melting to obtain aluminosilicate clinker;

[0008] S3, adding water to the aluminosilicate clinker, subjecting it to aging and hydrothermal crystallization in sequence to obtain a molecular sieve.

[0009] The present invention uses the flotation tailings obtained after flotation separation of gypsum concentrate from lithium mica smelting slag as raw materials, and prepares the molecular sieve through a high-temperature alkali melting-hydrothermal crystallization method. After the lithium mica smelting slag is subjected to flotation separation of gypsum, the gypsum in the raw material can be effectively removed, and the gypsum content in the obtained flotation tailings is very low, which greatly reduces the interference of gypsum impurities in the subsequent high-temperature alkali melting and hydrothermal crystallization processes, thereby obtaining a molecular sieve with significantly improved purity and crystallinity, and effectively improving the adsorption of the molecular sieve, thereby improving the performance and quality of the molecular sieve product.

[0010] In the present invention, the lepidolite smelting slag is preferably leached slag produced in the process of producing lithium carbonate by lepidolite sulfate roasting method.

[0011] Preferably, in S1, the lithium mica smelting slag is crushed and sieved to a size below 40 mesh. The present invention crushes and sieves the lithium mica smelting slag to a certain particle size before flotation, which is beneficial to the flotation of gypsum in lithium slag, thereby more efficiently separating gypsum and further improving the purity of the molecular sieve.

[0012] In the present invention, the method of crushing and screening the lithium mica smelting slag to less than 40 mesh can be: using a crushing device to crush the lithium mica smelting slag to less than 40 mesh, and then passing through a 40-mesh sieve to remove particles larger than 40 mesh; the crushing device is preferably a wet ball mill.

[0013] Preferably, in the flotation tailings, the content of SiO2 is ≥60%, the content of CaSO4 is ≤5%, and the content of Al2O3 is ≥25%. In the present invention, by limiting the components and contents in the flotation tailings, the impurities contained in the prepared molecular sieve can be further reduced, the purity and crystallinity of the molecular sieve can be improved, and the adsorption performance of the molecular sieve can be better improved.

[0014] In the present invention, the method and reagent for separating gypsum by flotation can adopt conventional gypsum flotation methods and reagents, as long as the purpose of flotation separation of gypsum can be achieved, and there is no need to specifically limit it. Preferably, the step of separating gypsum by flotation can include: crushing and screening the lepidolite smelting slag and mixing the material with water to obtain a slurry, then adjusting the pH of the slurry to 8-10.5 by a pH adjuster, adding a gypsum collector and an inhibitor, and obtaining gypsum concentrate and flotation tailings through selection and scavenging; the concentration of the slurry is preferably 20-40wt%; the number of selection and scavenging can be one or more times, preferably 1-3 times; the amount of the gypsum collector is preferably 200-800g / t per ton of lepidolite smelting slag, and the amount of the inhibitor is preferably 1000-5000g / t per ton of lepidolite smelting slag; the inhibitor is water glass; the pH adjuster is preferably sodium carbonate, sodium hydroxide or a combination thereof.

[0015] Preferably, in S2, the temperature of the high-temperature alkali melting is 400-800° C., and the time is 2-12 hours.

[0016] Preferably, in S2, the alkali flux is at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate; the amount of the alkali flux is such that the alkali / silicon molar ratio Na2O / SiO2=1-5.

[0017] In the present invention, by optimizing the process parameters of high-temperature alkali melting and the amount of alkali flux, the conversion rate of the shaped quartz crystals in the tailings into amorphous SiO2 that can be used to synthesize molecular sieves can be improved, thereby improving the purity of the molecular sieve.

[0018] In the present invention, the container used for high-temperature alkali melting is preferably a graphite container.

[0019] Preferably, in S3, the amount of water added is water / alkali molar ratio H2O / Na2O=5-50.

[0020] In the present invention, by controlling the ratio of water to alkali in the aluminosilicate clinker during aging and hydrothermal crystallization, it is beneficial to quickly destroy the silicate structure in the original clinker during the aging process, and quickly catalyze the crystallization to generate a new crystal structure during the crystallization process, thereby improving the crystal purity and porosity of the molecular sieve and improving its adsorption performance.

[0021] In S3, before adding water to the aluminosilicate clinker, a step of grinding the aluminosilicate clinker into powder may be included, the purpose of which is to allow the aluminosilicate clinker to fully contact and react with water, which is beneficial to the aging process and the crystallization process.

[0022] Preferably, in S3, the aging temperature is 45 to 90° C., and the aging time is 2 to 48 hours.

[0023] Preferably, in S3, the hydrothermal crystallization temperature is 50-120° C., and the time is 6-48 hours.

[0024] In the present invention, the porosity, purity and crystallinity of the molecular sieve can be improved by optimizing the aging and hydrothermal crystallization process parameters, thereby improving the adsorption performance of the molecular sieve.

[0025] In the present invention, the container used for hydrothermal crystallization is preferably a stainless steel reactor or a polytetrafluoroethylene reactor.

[0026] In the present invention, conventional post-treatment steps may be included after hydrothermal crystallization, for example, washing and drying the product after hydrothermal crystallization to obtain a molecular sieve; preferably, washing is performed with water until the product has a pH value of 8 to 11; preferably, drying is performed by drying at a temperature of 80 to 120° C. for 2 to 12 hours.

[0027] In the present invention, the gypsum concentrate recovered by flotation can be reused for calcining lepidolite, thereby improving the comprehensive utilization rate of lithium slag and improving economic and environmental benefits.

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention proposes a method for preparing a molecular sieve using lithium slag as a raw material, wherein the flotation tailings after flotation separation of gypsum concentrate from lithium mica smelting slag are used as raw materials, and the molecular sieve is prepared by a high-temperature alkali melting-hydrothermal crystallization method. The method has low cost and simple process, and the prepared molecular sieve has high purity and crystallinity, good adsorption, and can be widely used in the fields of adsorbent, catalyst, desiccant, etc., and the gypsum in the lithium slag can be recovered, which is conducive to the comprehensive utilization of the lithium slag, improves the economic and environmental benefits, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 to Figure 4 The SEM images of the molecular sieves prepared in Examples 1 to 4 of the present invention are shown.

[0031] Figure 5 The adsorption isotherm test results of water on the molecular sieves synthesized from lithium slag in the examples of the present invention and the comparative examples are shown. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described in detail below through specific embodiments.

[0033] Example 1

[0034] Preparation of molecular sieves:

[0035] S1. 400 g of lithium mica smelting slag (by weight percentage, the components of lithium mica smelting slag are: CaSO4 30.6%, SiO2 40.7%, Al2O3 17.4%, Na2SO4 5.3%, Fe2O3 2.5%, other impurities 3.5%, the main crystal phase is quartz and gypsum) is crushed to 40 mesh by a wet ball mill, and then sieved through a 40-mesh vibrating screen to remove particles larger than 40 mesh, and the sieved materials below 40 mesh are mixed with water to obtain a slurry with a concentration of 30wt%, and then slurried with sodium hydroxide and sodium carbonate. The pH value of the slurry is adjusted to 10 by the mixed solution, and a gypsum collector and water glass are added. After 2 times of concentration and 2 times of scavenging, each time of concentration and scavenging is 4 minutes, a gypsum concentrate and 210g of flotation tailings are obtained. In the flotation tailings, the content of SiO2 is 63.6wt%, the content of Al2O3 is 26.4wt%, the content of CaSO4 is 2.3wt%, and the content of Na2O is 3.4wt%; wherein the amount of the gypsum collector is 300g / ton of lithium mica smelting slag, and the amount of the water glass is 3000g / ton of lithium mica smelting slag;

[0036] S2, the flotation tailings obtained in S1 are mixed with 384g of sodium hydroxide solid to make the alkali / silicon molar ratio Na2O / SiO2=2; then subjected to high temperature alkali melting at 800°C for 6h to obtain aluminosilicate clinker;

[0037] S3. After grinding the aluminosilicate clinker into powder, add 2074g of water to make the water / alkali molar ratio H2O / Na2O=24, then age at 45°C for 4h, transfer to a stainless steel reactor, and then hydrothermally crystallize at 95°C for 12h, filter, wash the hydrothermally crystallized product with water to pH=8, and then dry at 105°C for 8h to obtain a molecular sieve, which is detected by SEM scanning electron microscopy to be MCM-22 molecular sieve.

[0038] The SEM spectrum of the molecular sieve prepared in Example 1 is shown in Figure 1 .

[0039] Example 2

[0040] The only difference between Example 2 and Example 1 is that in S2, the temperature of high-temperature alkali melting is 600° C., the aging time is 2 h, and the hydrothermal crystallization time is 6 h.

[0041] The molecular sieve prepared in Example 2 was detected by SEM scanning electron microscopy to be MCM-22 molecular sieve. The SEM spectrum is shown in Figure 2 .

[0042] Example 3

[0043] Preparation of molecular sieves:

[0044] S1. 400 g of lithium mica smelting slag (by weight percentage, the components of lithium mica smelting slag are: CaSO4 30.6%, SiO2 40.7%, Al2O3 17.4%, Na2SO4 5.3%, Fe2O3 2.5%, other impurities 3.5%, the main crystal phase is quartz and gypsum) is crushed to 40 mesh by a wet ball mill, and then sieved through a 40-mesh vibrating screen to remove particles larger than 40 mesh, and the sieved materials below 40 mesh are mixed with water to obtain a slurry with a concentration of 30wt%, and then slurried with sodium hydroxide and sodium carbonate. The pH value of the slurry is adjusted to 9 by the mixed solution, and a gypsum collector and water glass are added. After 2 times of concentration and 2 times of scavenging, each time of concentration and scavenging is 4 minutes, a gypsum concentrate and 231g of flotation tailings are obtained. In the flotation tailings, the content of SiO2 is 65.8wt%, the content of Al2O3 is 27.6wt%, the content of CaSO4 is 1.1wt%, and the content of Na2O is 3.6wt%; wherein the amount of the gypsum collector is 400g / ton of lithium mica smelting slag, and the amount of the water glass is 5000g / ton of lithium mica smelting slag;

[0045] S2, the flotation tailings obtained in S1 are mixed with 618g of sodium hydroxide solid to make the alkali / silicon molar ratio Na2O / SiO2=3; then subjected to high temperature alkali melting at 800°C for 12h to obtain aluminosilicate clinker;

[0046] S3. After grinding the aluminosilicate clinker into powder, add 4867g of water to make the water / alkali molar ratio H2O / Na2O=35, then age at 65°C for 4h, transfer to a stainless steel reactor, and then hydrothermally crystallize at 95°C for 12h, filter, wash the hydrothermally crystallized product with water to pH=9, and then dry at 110°C for 12h to obtain a molecular sieve, which is detected by SEM scanning electron microscopy to be ZSM-5 molecular sieve.

[0047] The SEM spectrum of the molecular sieve prepared in Example 3 is shown in Figure 3 .

[0048] Example 4

[0049] The only difference between Example 4 and Example 1 is that in S2, the temperature of high-temperature alkali melting is 600° C., the aging time is 6 h, and the hydrothermal crystallization time is 18 h.

[0050] The molecular sieve prepared in Example 4 was detected by SEM scanning electron microscopy to be ZSM-5 molecular sieve. The SEM spectrum is shown in Figure 4 .

[0051] Depend on Figures 1 to 4 It can be seen that the present invention successfully prepared a molecular sieve with uniform and fine morphology and good crystallinity.

[0052] Comparative Example 1

[0053] Preparation of molecular sieves:

[0054] S1. 400 g of lithium mica smelting slag (by weight percentage, the components of lithium mica smelting slag are: CaSO4 30.6%, SiO2 40.7%, Al2O3 17.4%, Na2SO4 5.3%, Fe2O3 2.5%, other impurities 3.5%, and the main crystal phases are quartz and gypsum) is crushed to 40 meshes by a wet ball mill, and then sieved through a 40-mesh vibrating screen to remove particles larger than 40 meshes to obtain a sieved material below 40 meshes;

[0055] S2, mixing the material below 40 mesh obtained in S1 with solid sodium hydroxide to make the alkali / silicon molar ratio Na2O / SiO2=2; then subjecting it to high temperature alkali melting at 800°C for 6h to obtain aluminosilicate clinker;

[0056] S3. After grinding the aluminosilicate clinker into powder, add water to make the water / alkali molar ratio H2O / Na2O=24, then age at 45°C for 4h, transfer to a stainless steel reactor, and then hydrothermally crystallize at 95°C for 12h, filter, wash the hydrothermally crystallized product with water to pH=8, and then dry at 105°C for 8h to obtain a molecular sieve.

[0057] Comparative Example 2

[0058] Preparation of molecular sieves:

[0059] S1. 400 g of lithium mica smelting slag (by weight percentage, the components of lithium mica smelting slag are: CaSO4 30.6%, SiO2 40.7%, Al2O3 17.4%, Na2SO4 5.3%, Fe2O3 2.5%, other impurities 3.5%, and the main crystal phases are quartz and gypsum) is crushed to 40 meshes by a wet ball mill, and then sieved through a 40-mesh vibrating screen to remove particles larger than 40 meshes to obtain a sieved material below 40 meshes;

[0060] S2, mixing the material below 40 mesh obtained in S1 with solid sodium hydroxide to make the alkali / silicon molar ratio Na2O / SiO2=3; then subjecting it to high temperature alkali melting at 800°C for 12h to obtain aluminosilicate clinker;

[0061] S3. After grinding the aluminosilicate clinker into powder, add water to make the water / alkali molar ratio H2O / Na2O=35, then age at 65°C for 4h, transfer to a stainless steel reactor, and then hydrothermally crystallize at 95°C for 12h, filter, wash the hydrothermally crystallized product with water to pH=9, and then dry at 110°C for 12h to obtain a molecular sieve.

[0062] At 25°C, the adsorption isotherms of water on the molecular sieves synthesized from lithium slag in the embodiment and the comparative example were measured respectively. The test results are as follows: Figure 5 shown.

[0063] Depend on Figure 5 It can be seen that the molecular sieve prepared by alkali fusion and hydrothermal synthesis method using the tailings of lithium slag after gypsum flotation as raw material has better adsorption performance.

[0064] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing molecular sieves using lithium slag as raw material, characterized in that: The following steps are involved: S1. After crushing and screening the lithium mica smelting slag, gypsum is separated by flotation to obtain gypsum concentrate and flotation tailings; the components of the lithium mica smelting slag are as follows: CaSO4 25-40%, SiO2 25-50%, Al2O3 15-25%, Na2SO4 5-25%, Fe2O3 1.5-4.5%, and other impurities 0-5%, and the sum of the weight percentages of the above components is 100%; S2, mixing the flotation tailings with an alkali flux, and subjecting the mixture to high-temperature alkali melting to obtain aluminosilicate clinker; S3, adding water to the aluminosilicate clinker, subjecting it to aging and hydrothermal crystallization in sequence to obtain a molecular sieve.

2. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In S1, the lepidolite smelting slag is crushed and sieved to below 40 mesh.

3. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In the flotation tailings, the content of SiO2 is ≥60%, the content of CaSO4 is ≤5%, and the content of Al2O3 is ≥25%.

4. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In S2, the high temperature alkali melting is carried out at a temperature of 400 to 800°C and for a time of 2 to 12 hours.

5. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In S2, the alkali flux is at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate; the amount of the alkali flux is such that the alkali / silicon molar ratio Na2O / SiO2 is 1 to 5.

6. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In S3, the amount of water added is water / alkali molar ratio H2O / Na2O=5~50.

7. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In S3, the aging temperature is 45 to 90° C., and the aging time is 2 to 48 hours.

8. The method for preparing molecular sieve using lithium slag as raw material according to claim 1, characterized in that: In S3, the hydrothermal crystallization temperature is 50-120° C. and the time is 6-48 hours.

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