Method for extracting lithium from fly ash by ultrasonic treatment-assisted leaching before roasting

Abstract

The invention discloses a method for extracting lithium from coal ash through roasting pre-ultrasonic treatment assisted leaching. The method comprises the steps of ultrasonic pretreatment, alkali roasting activation, acid leaching or alkali leaching and the like. According to the invention, ultrasonic pretreatment is carried out before alkali roasting activation, that is, a mixture of fly ash and sodium carbonate is subjected to wet mixing and ultrasonic treatment after a small amount of water is added, so that the obvious effect of saving chemicals and energy is shown; therefore, a better activation effect and a better lithium element leaching rate can be obtained under the conditions of using fewer roasting additives and shorter roasting time, and circular economy and low-cost operation of extracting lithium from the fly ash are promoted. The research shows that the coal ash has very obvious potential as a feasible lithium source, and particularly, the ultrasonic pretreatment can play a very important role in optimization and expansion of industrial application of coal ash roasting leaching.

Description

Technical Field

[0001] The invention relates to the technical field of lithium resource recovery and utilization, and in particular to a method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting. Background Art

[0002] Lithium has attracted increasing attention due to its wide application in renewable energy and electric vehicles. Lithium batteries have the advantages of long cycle life, high energy density, low self-discharge rate and green environmental protection, and are widely used in portable electronic devices, electric vehicles, mobile phones and other fields.

[0003] Among the many potential lithium resources, fly ash produced during coal-fired power generation contains rich minerals, especially lithium, which has gradually attracted the attention of researchers. Fly ash is a byproduct of coal combustion in thermal power plants and is one of the most complex and abundant anthropogenic materials. Studies have shown that fly ash contains a relatively high Li content of about 250-1400 μg / g (Li2O content 0.06–0.30 wt%), which provides the possibility of its recycling. However, the accumulation of fly ash not only causes environmental pollution, but also causes a waste of resources.

[0004] Achieving efficient extraction of lithium from fly ash can not only reduce the impact of fly ash on the environment, but also provide new impetus for the sustainable development of the economy. In the study of the occurrence form of fly ash, the literature Sun, B., Wang, G., Zeng, F., Liu, C. and Xie, X. (2021) Discovery of spodumene in lithium rich coal and its geological significance, p. 4, Anhui Hefei, China. used TOF-SIMS to analyze the distribution of lithium, aluminum and silicon in the micro-area of ​​the No. 11 coal seam sample in Antaibao. It was found that silicon and aluminum were also enriched in the lithium-rich area, indicating that aluminosilicate minerals are the main occurrence carriers of lithium. ReferencesLi, H., Zhang, J., Wang, C., Li, S., Cao, S., Hu, P. and Zhu, Q. (2018a) Construction and research progress of clean recycling technology of high alumina coal ash associated resources. Clean Coal Technology 24(02), 1-8.Research has found that in high alumina fly ash, lithium is mainly enriched in amorphous aluminosilicate. ReferencesHu, P. (2018) Study on the occurrence state and leaching rule of lithium in high alumina coal ash during pre-desiliconization. Master, University of Chinese Academy of Sciences.The unique distribution of lithium in high alumina fly ash was highlighted by time-of-flight secondary ion mass spectrometry. The results showed that lithium was significantly enriched in the glass phase of fly ash. These studies have made important contributions to the understanding of the occurrence state of lithium in fly ash and laid the foundation for the subsequent extraction of lithium from fly ash. Summary of the invention

[0005] In order to improve the leaching rate of lithium extracted from fly ash, the present invention provides a method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting, which can significantly improve the leaching rate of lithium element while using less roasting additives and shorter roasting time, and effectively reduce the use of drugs and energy consumption.

[0006] The technical solution adopted by the present invention is as follows: The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting comprises the following steps: S1. Ultrasonic pretreatment: After the fly ash and sodium carbonate are mixed, water is added and stirred into a semi-fluid state, and then the reactor containing the semi-fluid mixture is placed in an ultrasonic generator and heated in a water bath to turn the mixture into a wet solid mixture; S2 basic calcination activation: The wet solid mixture obtained in S1 was dried and then activated by calcination, and after calcination, the mixture was crushed to obtain a calcined activated product; S3. Acid leaching: S2 obtained by adding sulfuric acid solution to the calcined activated product, leaching reaction under stirring conditions; Or alkaline leaching: add sodium hydroxide solution to the roasted activated product obtained in S2, and carry out leaching reaction under stirring conditions.

[0007] Furthermore, in S1, the mass ratio of the total mass of fly ash and sodium carbonate to water is 1-4:1, preferably 2:1, to ensure that it can be stirred into a semi-fluid state.

[0008] Furthermore, in S1, the ultrasonic power is 200-400 W, preferably 200-300 W; the time of the water bath heating treatment is 40-80 min, preferably 50-70 min, and more preferably 50-60 min.

[0009] Furthermore, in S2, the drying is vacuum drying, the drying temperature is 100-120° C., and the drying time is 10-30 min.

[0010] Furthermore, in S2, the mass ratio of fly ash to sodium carbonate is 1:1-4, preferably 1:2-4, and more preferably 1:2-3.

[0011] Furthermore, in S2, the calcination temperature is 600-850°C, preferably 700-850°C; the calcination time is 30-180 min, preferably 60-180 min, and more preferably 90-150 min.

[0012] Further, in S3, the temperature of acid leaching is 40-90°C, preferably 40-80°C, more preferably 40-50°C; the leaching time is 30-180min, preferably 30-90min, more preferably 60-90min; the concentration of sulfuric acid solution is 1-6mol / L, preferably 1-4mol / L, more preferably 1-3mol / L; the liquid-to-solid ratio is 1g:10ml-1g:45ml, preferably 1g:15ml-1g:40ml, more preferably 1g:30ml-1g:35ml.

[0013] Furthermore, in S3, the alkaline leaching temperature is 40-90°C, preferably 40-60°C; the leaching time is 30-180min, preferably 60-90min; the concentration of the sodium hydroxide solution is 1-4mol / , preferably 1-3mol / L; the liquid-to-solid ratio is 1g:15ml-1g:40ml, more preferably 1g:30ml-1g:35ml.

[0014] The beneficial effects of the present invention are: (1) The present invention performs ultrasonic pretreatment before alkaline roasting activation, that is, by adding a small amount of water to the mixture of fly ash and sodium carbonate, wet mixing and ultrasonic treatment, which shows a significant effect of saving reagents and energy, thereby achieving better activation effect and lithium leaching rate under the conditions of using less roasting additives and shorter roasting time, thereby promoting the circular economy and low-cost operation of extracting lithium from fly ash.

[0015] (2) Through the exploration of the principle, it was found that the reaction between sodium carbonate and fly ash in the fly ash sample calcined after ultrasonic treatment was more complete, and no sodium carbonate residue was found in the calcined product. Sodium carbonate can cause more thorough destruction of the glass in the fly ash, providing more sufficient conditions for subsequent acid leaching or alkaline leaching, thereby ultimately significantly improving the leaching rate of lithium.

[0016] The research of the present invention shows that fly ash has very obvious potential as a feasible lithium source, especially ultrasonic pretreatment can play a very important role in the optimization and expansion of industrial application of fly ash roasting and leaching. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 These are the SEM results of fly ash before and after roasting in Example 6, where (a) is the original fly ash (50um), (b) is the original fly ash (10um), (c) is roasted with sodium carbonate (50um), and (d) is roasted with sodium carbonate (10um).

[0018] Figure 2 This is the XRD result of the fly ash before calcination (raw fly ash) in Example 6.

[0019] Figure 3 This is the XRD result of the fly ash after roasting (fly ash roasted with sodium carbonate) in Example 6.

[0020] Figure 4The SEM comparison pictures of the products of fly ash calcined with sodium carbonate and pre-ultrasound calcination, wherein (a) is the calcined product (5um) of fly ash to sodium carbonate in Example 2 with a mass ratio of 1:1.5, (b) is the calcined product (5um) of fly ash to sodium carbonate in Example 1 with a mass ratio of 1:2, (c) is the calcined product (5um) of fly ash to sodium carbonate in Example 7 with a mass ratio of 1:2 and ultrasonic pretreatment, and (d) is the calcined product (5um) of fly ash to sodium carbonate in Example 5 with a mass ratio of 1:1 and ultrasonic pretreatment.

[0021] Figure 5 This is the XRD diagram of the calcined product of Example 6 with a mass ratio of fly ash to sodium carbonate of 1:1.5 and ultrasonic pretreatment.

[0022] Figure 6 This is the SEM (10 um) image of the acid leaching residue obtained in Example 8.

[0023] Figure 7 This is the XRD pattern of the acid leaching residue obtained in Example 8. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0025] The analysis method is as follows: Scanning electron microscope (SEM, Hitachi, SU8100), X-ray diffractometer (XRD, Bruker, D8ADVANCE) and X-ray fluorescence spectrometer (XRF, PANalytical AXIOS, the Netherlands) were used to characterize the samples and analyze the micro-area morphology and mineral composition of the samples.

[0026] The content of trace element lithium in fly ash, roasting products and leached products was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). The brief procedure was as follows: the analyte was digested with hydrofluoric acid (HF, 40% by weight), hydrogen peroxide (H2O2, 30 wt%) and nitric acid (HNO3, 65 wt%) at 210 °C for 20 minutes. After the digestion was completed, the digestion solution was diluted with dilute nitric acid (1wt%). Finally, the concentration of lithium in the liquid phase was determined by ICP-OES. Example 1

[0027] The method for extracting lithium from fly ash comprises the following steps: (1) Alkali calcination activation: fly ash and sodium carbonate are mixed in a mass ratio of 1:2, and the resulting mixture is placed in a tube furnace for activation calcination. The temperature of the tube furnace is programmed to 850°C at a heating rate of 15°C / min and maintained for 120 min. After calcination, the mixture is crushed to obtain a calcined activation product. (2) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (1) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0028] The product after the reaction was separated into solid and liquid, and the lithium content of the remaining residue was analyzed by ICP-OES method.

[0029] The experimental results show that the leaching rate of lithium is 84.72%. Example 2

[0030] The method for extracting lithium from fly ash comprises the following steps: (1) Alkali calcination activation: fly ash and sodium carbonate were mixed in a mass ratio of 1:1.5, and the resulting mixture was placed in a tube furnace for activation calcination. The temperature of the tube furnace was programmed to 850°C at a heating rate of 15°C / min and maintained for 120 min. After calcination, the mixture was crushed to obtain a calcined activated product. (2) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (1) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0031] The product after the reaction was separated into solid and liquid, and the lithium content of the remaining residue was analyzed by ICP-OES method.

[0032] The experimental results show that the leaching rate of lithium is 78.60%. Example 3

[0033] The method for extracting lithium from fly ash comprises the following steps: (1) Alkali calcination activation: fly ash and sodium carbonate were mixed in a mass ratio of 1:4, and the resulting mixture was placed in a tube furnace for activation calcination. The temperature of the tube furnace was programmed to 850°C at a heating rate of 15°C / min and maintained for 120 min. After calcination, the mixture was crushed to obtain a calcined activated product. (2) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (1) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0034] The product after the reaction was separated into solid and liquid, and the lithium content of the remaining residue was analyzed by ICP-OES method.

[0035] The experimental results show that the leaching rate of lithium is 89.32%. Example 4

[0036] The method for extracting lithium from fly ash comprises the following steps: (1) Alkali calcination activation: fly ash and sodium carbonate were mixed in a mass ratio of 1:2, and the resulting mixture was placed in a tube furnace for activation calcination. The temperature of the tube furnace was programmed to 850°C at a heating rate of 15°C / min and maintained for 180 min. After calcination, the mixture was crushed to obtain a calcined activated product. (2) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (1) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0037] The product after the reaction was separated into solid and liquid, and the lithium content of the remaining residue was analyzed by ICP-OES method.

[0038] The experimental results show that the leaching rate of lithium is 87.44%. Example 5

[0039] The method for extracting lithium from fly ash comprises the following steps: (1) Ultrasonic pretreatment: Add 10 ml of pure water to a corundum boat containing a mixture of fly ash and sodium carbonate (the mass ratio of fly ash to sodium carbonate is 1:1, and the total mass is 20 g), stir evenly to make it semi-fluid, then place the corundum boat in an ultrasonic generator with an ultrasonic power of 200 W and heat it in a water bath for 60 min until the mixture is in a wet solid state; (2) Alkali calcination activation: The wet solid mixture obtained in step (2) is dried at 120°C for 20 min, and then placed in a tube furnace for activation calcination. The tube furnace is heated to 850°C at a heating rate of 15°C / min and maintained for 180 min. After calcination, the mixture is crushed to obtain a calcined activated product. (3) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (2) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0040] The product after the reaction was separated into solid and liquid, and the remaining residue was analyzed for lithium content using ICP-OES. The experimental results showed that the leaching rate of lithium was 89.04%. Example 6

[0041] The method for extracting lithium from fly ash comprises the following steps: (1) Ultrasonic pretreatment: Add 10 ml of pure water to a corundum boat containing a mixture of fly ash and sodium carbonate (the mass ratio of fly ash to sodium carbonate is 1:1.5, and the total mass is 20 g), stir evenly to make it semi-fluid, then place the corundum boat in an ultrasonic generator with an ultrasonic power of 200 W and heat it in a water bath for 60 min until the mixture is in a wet solid state. (2) Alkali calcination activation: The wet solid mixture obtained in step (2) is dried at 120°C for 20 min, and then placed in a tube furnace for activation calcination. The tube furnace is heated to 850°C at a heating rate of 15°C / min and maintained for 120 min. After calcination, the mixture is crushed to obtain a calcined activated product. (3) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (2) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0042] The product after the reaction was separated into solid and liquid, and the remaining residue was analyzed for lithium content using ICP-OES. The experimental results showed that the leaching rate of lithium was 90.74%. Example 7

[0043] The method for extracting lithium from fly ash comprises the following steps: (1) Ultrasonic pretreatment: Add 10 ml of pure water to a corundum boat containing a mixture of fly ash and sodium carbonate (the mass ratio of fly ash to sodium carbonate is 1:2, and the total mass is 20 g), stir evenly to make it semi-fluid, then place the corundum boat in an ultrasonic generator with an ultrasonic power of 200 W and heat it in a water bath for 60 min until the mixture is in a wet solid state. (2) Alkali calcination activation: The wet solid mixture obtained in step (2) is dried at 120°C for 20 min, and then placed in a tube furnace for activation calcination. The tube furnace is heated to 850°C at a heating rate of 15°C / min and maintained for 90 min. After calcination, the mixture is crushed to obtain a calcined activated product. (3) Alkaline leaching: add 4 mol / L sodium hydroxide solution to the calcined activated product obtained in step (2) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 120 min under stirring.

[0044] The product after the reaction was separated into solid and liquid, and the remaining residue was analyzed for lithium content using ICP-OES. The experimental results showed that the leaching rate of lithium was 90.13%. Example 8

[0045] The method for extracting lithium from fly ash comprises the following steps: (1) Ultrasonic pretreatment: Add 10 ml of pure water to a corundum boat containing a mixture of fly ash and sodium carbonate (the mass ratio of fly ash to sodium carbonate is 1:2, and the total mass is 20 g), stir evenly to make it semi-fluid, then place the corundum boat in an ultrasonic generator with an ultrasonic power of 200 W and heat it in a water bath for 60 min until the mixture is in a wet solid state. (2) Alkali calcination activation: The wet solid mixture obtained in step (2) is dried at 120°C for 20 min, and then placed in a tube furnace for activation calcination. The tube furnace is heated to 850°C at a heating rate of 15°C / min and maintained for 180 min. After calcination, the mixture is crushed to obtain a calcined activated product. (3) Acid leaching: Add 2 mol / L sulfuric acid solution to the calcined activated product obtained in step (2) at a solid-liquid ratio of 1 g:30 ml, and carry out leaching reaction at 80 °C for 90 min under stirring.

[0046] The product after the reaction was separated into solid and liquid. Since there was less residue after the acid leaching reaction, the leachate was retained. The volume of the leachate was recorded and the lithium content in the leachate was analyzed by ICP-OES to obtain the leaching rate.

[0047] The experimental results show that the leaching rate of lithium is 98.68%.

[0048] By analyzing the above embodiments, by comparing the experimental data of Example 2 and Example 6, it can be seen that when alkaline leaching is also used, under the condition that the mass ratio of fly ash to sodium carbonate is 1:1.5, the ultrasonic pretreated sample obtains a lithium element leaching rate of 90.74% (Example 6), which is significantly higher than the lithium element leaching rate of 78.60% (Example 2) obtained by the product without pre-ultrasonic pretreatment. It can be seen that the reasonable use of ultrasonic pretreatment of the present invention can significantly improve the lithium element leaching rate. By comparing the experimental data of Example 1 and Example 6, it can be seen that ultrasonic pretreatment before roasting activation can obtain a higher lithium element leaching rate under the condition of using a lower mass ratio of fly ash to sodium carbonate. By comparing the experimental data of Example 4 and Example 7, it can be seen that ultrasonic pretreatment before roasting activation can obtain a higher lithium element leaching rate under the condition of significantly shorter roasting time. Under the joint action of ultrasonic pretreatment, alkaline roasting activation and acid leaching, the lithium element leaching rate is further improved, up to 98.68%.

[0049] The SEM results of fly ash before and after calcination in Example 1 are as follows: Figure 1 As shown. Figure 1It can be seen that before roasting, the fly ash is seen as round and complete fly ash particles, but after roasting, the edges of the particles are unclear and the particles are wrapped by sodium carbonate and adhere to each other. Sodium carbonate destroys the glass in the fly ash and its particle integrity, which increases the activity of the next leaching step.

[0050] Combined with Figure 2 and Figure 3 XRD analysis shows that the main phases of fly ash before roasting are mullite phase, quartz phase and a small amount of iron microbeads. After roasting with sodium carbonate, nepheline and magnetite phases are generated, and it can be seen that some sodium carbonate has not reacted completely.

[0051] The SEM comparison of fly ash roasted with sodium carbonate and pre-ultrasonic roasting products is shown in the figure Figure 4 shown. Figure 4 In (b), it can be seen that there are a large number of incompletely reacted sodium carbonate crystals (fine and dense long granular attachments) in the calcined product without ultrasonic pretreatment, which melted first and then crystallized when cooled down. Figure 4 (c) Even when the mass ratio of fly ash to sodium carbonate is 1:2, the reaction degree is almost the same as that of the product with a mass ratio of fly ash to sodium carbonate of 1:1.5 in the roasting without ultrasonic pretreatment ( Figure 4 (a)), while under the condition of a mass ratio of fly ash to sodium carbonate of 1:1 ( Figure 4 (d)), almost no excess sodium carbonate residue was observed after ultrasonic treatment. Figure 3 and Figure 5 It can be seen that the characteristic peak of sodium carbonate disappears significantly under ultrasonic treatment. Therefore, it can be proved that ultrasonic treatment before roasting with sodium carbonate has a significant effect on saving additives and improving roasting activation efficiency.

[0052] The SEM image of the acid leaching residue obtained in Example 8 is as follows Figure 6 As shown. Figure 6 It can be seen that the particles of the acid leaching residue are more thoroughly destroyed. There are almost no spherical residues in the large particles, and the residues in the background are also very fine and smooth, with less large particle leaching residues. At the same time, it can be seen that fine residues appear in the acid leaching residues to wrap the destroyed fly ash roasting particles. The XRD spectrum of the acid leaching residue (such as Figure 7 The XRF results (Table 1) show that the fine residue is a mixture of silica and sulfite (the H element cannot be detected by XRF detection). It can be inferred that a large amount of silicic acid is produced in the solution after the acid leaching reaction.

[0053] Table 1 XRF composition of acid leaching residue

[0054] The above research of the present invention shows that fly ash has very obvious potential as a feasible lithium source, especially ultrasonic pretreatment can play a very important role in the optimization and expansion of industrial application of fly ash roasting and leaching.

Claims

1. A method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting, characterized in that: The steps include: S1. Ultrasonic pretreatment: After the fly ash and sodium carbonate are mixed, water is added and stirred into a semi-fluid state, and then the reactor containing the semi-fluid mixture is placed in an ultrasonic generator and heated in a water bath to turn the mixture into a wet solid mixture; S2 basic calcination activation: The wet solid mixture obtained in S1 was dried and then activated by calcination, and after calcination, the mixture was crushed to obtain a calcined activated product; S3. Acid leaching: S2 obtained by adding sulfuric acid solution to the calcined activated product, leaching reaction under stirring conditions; Or alkaline leaching: add sodium hydroxide solution to the roasted activated product obtained in S2, and carry out leaching reaction under stirring conditions.

2. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S1, the mass ratio of the total mass of fly ash and sodium carbonate to water is 1~4:

1.

3. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S1, the ultrasonic power is 200-400 W, preferably 200-300 W; the time of water bath heating treatment is 40-80 min, preferably 50-70 min, more preferably 50-60 min.

4. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S2, the drying is vacuum drying, the drying temperature is 100-120° C., and the drying time is 10-30 min.

5. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S2, the mass ratio of fly ash to sodium carbonate is 1:1~4.

6. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S2, the mass ratio of fly ash to sodium carbonate is 1:2~3.

7. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S2, the calcination temperature is 600~850℃; the calcination time is 30~180min.

8. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S3, the acid leaching temperature is 40~90℃; the leaching time is 30~180min; the concentration of the sulfuric acid solution is 1~6mol / L; and the liquid-to-solid ratio is 1g:10ml~1g:45ml.

9. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 1, characterized in that: In S3, the alkaline leaching temperature is 40~90℃; the leaching time is 30~180min; the concentration of the sodium hydroxide solution is 1~4mol / L; and the liquid-to-solid ratio is 1g:15ml~1g:40ml.

10. The method for extracting lithium from fly ash by leaching assisted by ultrasonic treatment before roasting according to claim 8 or 9, characterized in that: The liquid-to-solid ratio is 1g:30ml~1g:35ml.

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