CN115627535A - Method for recovering aluminum electrolyte slag - Google Patents
Method for recovering aluminum electrolyte slag Download PDFInfo
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- CN115627535A CN115627535A CN202211318004.5A CN202211318004A CN115627535A CN 115627535 A CN115627535 A CN 115627535A CN 202211318004 A CN202211318004 A CN 202211318004A CN 115627535 A CN115627535 A CN 115627535A
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Abstract
The invention discloses a method for recovering aluminum electrolyte slag, which specifically comprises the following steps: s1, mixing sodium carbonate, aluminum electrolyte slag and water and then pressing and boiling; s2, cooling the mixture obtained in the step S1 to be less than or equal to 30 ℃, and carrying out solid-liquid separation; s3, heating the liquid phase obtained in the step S2 to 75-95 ℃, and crystallizing to separate out lithium carbonate; mixing sodium hydroxide, the solid phase obtained in the step S2 and water, then performing pressure boiling, and performing solid-liquid separation to obtain calcium fluoride and a clear liquid; crystallizing sodium aluminate from the clear solution.
Description
Technical Field
The invention relates to the technical field of solid waste recovery, in particular to a method for recovering aluminum electrolyte slag.
Background
The low-grade bauxite is often used as a raw material in industry,the alumina is produced by Bayer process. Since low grade bauxite is often associated with about 0.04 to 0.1wt% lithium (present predominantly in the form of Li) 2 O), the alumina prepared by the above method usually contains a certain amount of lithium. One of the uses of alumina is to prepare elemental aluminum and elemental oxygen by electrolysis, and the nonelectrolytic components (not reacting with the electrode) remained in the process, such as lithium, are always kept in the aluminum electrolyte. Along with the prolonging of the production time, the mass fraction of lithium in the aluminum electrolyte can reach about 1 to 5 percent, and the lithium with high mass fraction can reduce the melt temperature and Al 2 O 3 Solubility in aluminium electrolyte, therefore, it is necessary to dilute or discharge the lithium-rich aluminium electrolyte, i.e. to form aluminium electrolyte slag. Practice shows that about 10-15 kg of lithium-rich aluminum electrolyte slag is discharged per 1 ton of electrolytic aluminum produced. However, with the continuous development of the electrolytic aluminum technology, the consumption of the aluminum electrolyte is reduced, the discharged aluminum electrolyte slag is difficult to return to the electrolytic aluminum process, and is often stockpiled as waste slag, and the contained alkali and fluorine pose potential risks to the environment.
The aluminum electrolyte slag can not be reused in the electrolytic aluminum industry, but is a high-quality lithium, fluorine and aluminum resource. According to the method, 10kg of aluminum electrolyte slag is discharged per 1 ton of produced electrolytic aluminum, wherein the aluminum electrolyte slag contains 1wt% of aluminum, 37wt% of fluorine and 12.8wt% of aluminum, and the production is calculated according to 3850 tons of electrolytic aluminum per year; can produce over 2 million tons of Li from the discharged aluminum electrolyte slag every year 2 CO 3 The urgent demand of the battery field on lithium resources is hopefully relieved; can also produce about 15 million tons of hydrogen fluoride, and is expected to partially replace non-metallic ore fluorite (CaF) 2 ) A resource; at the same time, al with a weight of more than 1 ten thousand tons can be produced 2 O 3 . Therefore, the development of a new technology for recycling the aluminum electrolytic slag has important economic significance and environmental protection significance on the recycling and non-toxicity of the electrolytic aluminum slag.
In the related technology, the method for extracting lithium from the aluminum electrolyte slag is to react the aluminum electrolyte slag with concentrated sulfuric acid at the temperature of 200-400 ℃, then to extract with water, to alkaline hydrolyze with sodium carbonate, to causticize with lime and to CO 2 And carrying out carbonization reaction to obtain a lithium carbonate product. The method adopts strong acid, strong base and high temperature, and has convenient productionThe safety brings inconvenience and the amount of sodium carbonate consumed is high. In order to save the application of sodium carbonate, the pH value is adjusted by adding calcium oxide before adding the sodium carbonate. In the above method, fluorine and aluminum are finally introduced into the process for preparing cryolite, but the cryolite is not expensive, so the above method also has a problem of poor economy.
In order to improve the safety and reduce the use amount of acid and alkali, a leaching system adopted by the prior art is a sulfuric acid aqueous solution with the pH value less than 5, the sulfuric acid aqueous solution is stirred and leached at the temperature of 30-95 ℃, mixed liquor is filtered after the reaction is finished, filtrate is used for extracting lithium element, and fluoride filter cakes are washed and dried and then returned to an electrolytic aluminum plant or a leaching process. Yet another technique employs nitric acid instead of sulfuric acid for leaching.
According to the analysis, the method mostly adopts an acid leaching method to extract the lithium in the electrolyte slag, a large amount of water is needed in the process, and the energy consumption for the concentration and crystallization of the lithium carbonate is high; most importantly, the aluminum and the fluorine in the aluminum electrolyte slag cannot exert higher economic value.
In conclusion, it is necessary to provide a new method with higher safety and economy for the reuse of the aluminum electrolyte slag.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a method for recovering aluminum electrolyte slag, which improves the safety and the economical efficiency of recycling the aluminum electrolyte slag.
According to an embodiment of the first aspect of the present invention, there is provided a method for recycling aluminum electrolyte slag, the method comprising the steps of:
s1, mixing sodium carbonate, the aluminum electrolyte slag and water and then autoclaving;
s2, cooling the mixture obtained in the step S1 to be less than or equal to 30 ℃, and carrying out solid-liquid separation;
s3, heating the liquid phase obtained in the step S2 to 75-95 ℃, and crystallizing to separate out lithium carbonate;
mixing sodium hydroxide, the solid phase obtained in the step S2 and water, then performing pressure boiling, and performing solid-liquid separation to obtain filter residue and clear liquid; crystallizing sodium aluminate from said clear liquid.
The mechanism of the recovery process is explained as follows:
the recovery method fully utilizes the selective solubility of sodium carbonate and the solubility difference of generated lithium carbonate at different temperatures, and specifically comprises the following steps:
in the step S1, the carbonate ions can be fully contacted with lithium in the aluminum electrolyte slag by adopting a pressure boiling method, and the following reaction can be carried out:
2Li + (aq)+CO 3 2- (aq)→Li 2 CO 3 (s)；
after the temperature is reduced along with the step S2, the lithium carbonate is dissolved in the water, so that the lithium carbonate can exist in a liquid phase after solid-liquid separation; the following reactions occur;
Li 2 CO 3 (s)→Li 2 CO 3 (aq)；
after the temperature rise, the solubility of lithium carbonate decreases, but the solubility of sodium carbonate increases, so lithium carbonate can be crystallized and precipitated, and lithium is separated alone, and the reaction occurs as follows:
Li 2 CO 3 (aq)→Li 2 CO 3 (s)。
the sodium carbonate adopted in the step S1 has poor solubility to aluminum and fluorine, and the sodium hydroxide used in the step S3 can effectively dissolve aluminum, so that the aluminum can be separated independently; meanwhile, in step S3, calcium (or externally added) contained in the aluminum electrolyte slag reacts with fluorine to finally generate solid filter residue, and finally, separation of fluorine and other components is realized. The reactions that occur in this process are as follows:
Na 3 AlF 6 +4OH - (aq)+3Ca 2+ →AlO 2 - (aq)+2H 2 O+CaF 2 (s)+3Na + 。
the control method provided by the embodiment of the invention has at least the following beneficial effects:
(1) According to the invention, lithium, aluminum and fluorine are separated independently, so that the safety and environmental protection problems of environmental fluorine pollution are solved, and the serious waste of industrial fluorine resources is avoided; specifically, the method comprises the following steps: lithium carbonate can be used for preparing a positive electrode material, and calcium fluoride can be used for preparing an electrolyte salt. Therefore, the recovery method provided by the invention improves the economy and environmental protection of the aluminum electrolyte slag recovery.
(2) According to the invention, by adjusting the types and preparation methods of the reagents, the use of acid is avoided, the use of strong alkali is effectively saved, and the safety and economy of aluminum electrolyte slag recovery are improved.
(3) The raw materials adopted by the invention are industrial waste materials or cheap raw materials in the chemical field, so the recovery method has low cost. The recovery method provided by the invention is simple in process and beneficial to industrial popularization.
According to some embodiments of the invention, the recycling method further comprises refining the aluminum electrolyte slag before step S1.
According to some embodiments of the invention, the refining comprises ball milling and sieving in sequence to obtain undersize.
The ball mill has an activation effect, namely, the internal structure of the aluminum electrolyte slag is initially damaged, so that the leaching efficiency of lithium in the autoclaving process is improved. Meanwhile, the refined aluminum electrolyte slag has larger specific surface area, so that the autoclaving efficiency is improved.
According to some embodiments of the invention, the screening uses a mesh size of 150 to 200 mesh.
According to some embodiments of the invention, the mixing in step S1 comprises mixing the aluminum electrolyte slag after the sodium carbonate and water are prepared into a sodium carbonate solution. Therefore, the method is more suitable for large-scale production.
According to some embodiments of the invention, the concentration of the aqueous sodium carbonate solution is between 10 and 270g/L. For example, it may be 180 to 190g/L, 206 to 270g/L, or 30 to 200g/L.
According to some embodiments of the invention, in step S1, the mixing comprises mixing solid sodium carbonate, aluminium electrolyte slag and water; wherein the mass of the sodium carbonate accounts for 10-270 g/L of the total volume of the sodium carbonate and the water. For example, it may be 30 to 200g/L, 180 to 190g/L, or 206 to 270g/L.
According to some embodiments of the invention, in the step S1, the mass ratio of the water to the aluminum electrolyte slag is 1.1 to 80.
According to some embodiments of the invention, in step S1, the mass ratio of the water to the aluminum electrolyte slag is 4 to 45.
According to some embodiments of the invention, in step S1, the mass ratio of the water to the aluminum electrolyte slag is 20 to 25:1.
according to some embodiments of the invention, in step S1, the mass ratio of the water to the aluminum electrolyte slag is 10 to 12:1.
according to some embodiments of the invention, in step S1, the mass ratio of the water to the aluminum electrolyte slag is 5 to 6:1.
according to some embodiments of the invention, in step S1, the mass ratio of the water to the aluminum electrolyte slag is 1 to 5:1, for example, may be specifically 2 to 2.5:1, or 4 to 5:1, or 2 to 2.1:1, or 2.5 to 3:1.
according to some embodiments of the invention, in step S1, the method of mixing comprises stirring; preferably, the method of stirring comprises magnetic stirring. The stirring has the function of improving the mass transfer speed in the mixing process, and the stirring speed and the stirring duration are not limited as long as the aluminum electrolyte slag is completely wetted. For example, stirring may be about 400 rpm.
According to some embodiments of the invention, in step S1, the autoclaving is performed under stirring conditions, which may be the same or different from the mixing conditions, in order to promote mass transfer.
According to some embodiments of the invention, the temperature of the autoclaving in step S1 is between 120 and 220 ℃.
According to some embodiments of the invention, the temperature of the autoclaving in step S1 is 160 to 180 ℃.
According to some embodiments of the invention, in step S1, the duration of said autoclaving is between 0.5 and 2 hours.
According to some embodiments of the invention, in step S1, the autoclaving is performed in a reaction vessel.
The autoclaving refers to performing a high-temperature and high-pressure reaction, wherein the high temperature is generated by external heating, and the high pressure is generated by the pressure of water vapor generated by a closed reaction container at the high temperature.
According to some preferred embodiments of the present invention, in step S2, after the cooling, the temperature of the system is 0 ℃ to 30 ℃.
According to some preferred embodiments of the present invention, in step S2, after the cooling, the temperature of the system is 20 ℃ to 30 ℃.
According to some preferred embodiments of the present invention, in step S2, after the cooling, the temperature of the system is 25 ℃ to 27 ℃.
This ensures complete dissolution of the lithium carbonate in water.
According to some embodiments of the invention, in step S2, the method of solid-liquid separation comprises filtration; preferably, the filtration comprises at least one of ordinary filtration, pressure filtration and suction filtration.
According to some embodiments of the invention, in step S3, the post-temperature-increase temperature is about 90 ℃.
According to some embodiments of the invention, the crystallizing out further comprises maintaining the temperature after the temperature raising for 1 to 2 hours in step S3. Thereby, a liquid phase with uniform temperature can be fully obtained, and the solubility difference of lithium carbonate and sodium carbonate in water is increased.
According to some embodiments of the present invention, in step S3, the mother solution after precipitation of the lithium carbonate crystals, the solute is mainly sodium carbonate added in step S1;
thus, the production process further comprises recycling the mother liquor to step S1, autoclaving as a substitute for the sodium carbonate and water (equivalent to an aqueous sodium carbonate solution);
furthermore, the invention skillfully uses the difference of the solubility of the sodium carbonate and the lithium carbonate in water, realizes the recycling of the sodium carbonate, avoids the discharge of sewage, and improves the economy and the environmental protection of the recovery method.
According to some embodiments of the invention, in step S3, a calcium-containing precursor is further included in the autoclave system.
In the step S3, if the calcium-containing precursor is added, the main component of the filter residue is calcium fluoride, and if the calcium-containing precursor is not added, the filter residue contains a certain amount of calcium fluoride and sodium fluoride due to the same ion effect.
According to some embodiments of the invention, the calcium-containing precursor comprises at least one of calcium oxide and calcium hydroxide.
According to some embodiments of the invention, the mass ratio of the sodium hydroxide to the calcium-containing precursor is 10g:0 to 4g.
According to some embodiments of the invention, the mass ratio of the sodium hydroxide to the calcium-containing precursor is 10g:1 to 2.5.
According to some embodiments of the invention, in step S3, the liquid-solid ratio in autoclaving is 1 to 80g. The mass of the solid was calculated as the mass of the solid obtained in step S2 after drying, and the total of sodium hydroxide, water and the liquid contained in the solid obtained in step S2 was defined as the mass of the liquid.
According to some embodiments of the invention, in step S3, the liquid-solid ratio in autoclaving is between 4 and 45g. For example, the specific ratio may be 45g:1g, 4-4.1 g:1g, 9g:1g, 2-3 g:1g, 2.5-3 g:1g.
According to some embodiments of the invention, in step S3, the mass ratio of the sodium hydroxide to the solid phase is 10. Based on the mass of the dried solid phase.
According to some embodiments of the invention, in step S3, the mass ratio of the sodium hydroxide to the solid phase is 10.
Specifically, the mass of the solid phase is a dry mass, that is, the recovery method further comprises drying the solid phase before autoclaving in step S3. The drying is performed here only for the convenience of calculating the solid-liquid ratio, and whether a drying step is included can be selected according to actual conditions in actual production.
According to some embodiments of the invention, the temperature of the autoclaving in step S3 is 140 to 220 ℃.
According to some embodiments of the invention, in step S3, the temperature of the autoclaving is between 150 and 200 ℃; for example, it may be specifically about 160 ℃ or 180 ℃.
According to some embodiments of the invention, in step S3, the length of time of said autoclaving is between 0.5 and 2 hours.
According to some embodiments of the invention, step S3 further comprises cooling the autoclave system prior to the solid-liquid separation. Preferably, the temperature after cooling is room temperature (10 to 40 ℃).
According to some embodiments of the invention, step S3 further comprises removing impurities from the supernatant prior to crystallizing the sodium aluminate.
According to some embodiments of the invention, the removing comprises testing the serum for fluorine content and adding the calcium-containing precursor for fluorine removal; and finally, carrying out solid-liquid separation to remove the generated solid calcium fluoride and the unreacted calcium-containing precursor.
According to some embodiments of the invention, the fluorine content is measured using a fluorine selective electrode.
According to some embodiments of the invention, the autoclaving in step S1 and step S3 is performed in a manner that includes an oil bath, thereby providing more uniform heating.
According to some embodiments of the invention, the composition of the aluminum electrolyte slag comprises Na 3 AlF 6 、CaF 2 、K 2 NaAlF 6 And Na 3 Li 3 (AlF 6 ) 2 。
According to some preferred embodiments of the present invention, the composition of the aluminum electrolyte slag further includes Al 2 O 3 、Na 2 O、CaO、K 2 O、MgO、BaO、SiO 2 SrO and P 2 O 5 。
According to some embodiments of the invention, the aluminum electrolyte slag contains lithium element in an amount of 1-2% by mass; preferably, between 1.1 and 1.3%.
According to some embodiments of the invention, the aluminum electrolyte has a fluorine content of between 35 and 40 wt%; preferably between 37 and 38 wt%.
According to some embodiments of the invention, the aluminum electrolyte has a mass content of aluminum element between 10 and 15 wt%; preferably between 12 and 13 wt%.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic flow diagram of an embodiment of the present invention;
FIG. 2 is an XRD test pattern and a standard XRD pattern of phases of aluminum electrolyte slag and aluminum electrolyte slag used in accordance with an embodiment of the present invention;
FIG. 3 is an XRD pattern of lithium carbonate obtained in example 2 of the present invention;
FIG. 4 is an XRD spectrum of the residue obtained in step D7 of example 1;
FIG. 5 is an XRD pattern of the residue obtained in step D7 of example 2 of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, if there are first, second, etc. described, it is only for the purpose of distinguishing technical features, and it is not understood that relative importance is indicated or implied or the number of indicated technical features is implicitly indicated or the precedence of the indicated technical features is implicitly indicated.
Unless otherwise specified, the aluminum electrolyte slag used in the embodiments mainly contains Na 3 AlF 6 、CaF 2 、K 2 NaAlF 6 And Na 3 Li 3 (AlF 6 ) 2 The specific spectrum of the test method for the composition of the physical phase of the aluminum electrolyte slag is shown in figure 2, and the result shows that the XRD spectrum of the aluminum electrolyte slag contains Na 3 AlF 6 、CaF 2 、K 2 NaAlF 6 And Na 3 Li 3 (AlF 6 ) 2 Characteristic peak of (2). In addition, the mass percentage of lithium element in the aluminum electrolyte slag is 1.2wt%, the mass percentage of fluorine element is about 37.7wt%, the mass percentage of aluminum element is 12.8wt%, the specific test method is ICP-OES, and the specific test is carried out after acid dissolution and dilution.
Example 1
The embodiment provides a method for recovering aluminum electrolyte slag, a flow schematic diagram is shown in fig. 1, and the method comprises the following specific steps:
D1. crushing and grinding the aluminum electrolyte slag by a quartering method, sieving the crushed aluminum electrolyte slag by a 150-mesh sieve, and taking undersize products;
D2. according to the weight ratio of 50g:72g:270g of the mixture is stirred and mixed under the stirring condition of 400rpm by the undersize material obtained in the step D1, sodium carbonate and water;
D3. putting the mixture obtained in the step D2 into a closed container for autoclaving, wherein the autoclaving condition is 160 ℃ for 2 hours;
D4. cooling the mixture obtained in the step D3 to about 25 ℃, and then performing suction filtration to obtain a liquid phase and a solid phase;
D5. heating the liquid phase obtained in the step D4 to 90 ℃, keeping for 2 hours, crystallizing and separating out lithium carbonate, and performing suction filtration to obtain mother liquor and lithium carbonate;
the mother liquor may be returned to the autoclaving step in step D3, which corresponds in particular to the use of a mixture of sodium carbonate and water.
D6. And D, drying the solid phase obtained in the step D4, and mixing the solid phase: naOH: water =10g:100g: mixing 450g of the raw materials, uniformly stirring at the rotating speed of 350rpm, and reacting for 2 hours (namely pressing and boiling) in a closed container at 180 ℃;
D7. filtering the mixture obtained in the step D6 to obtain clear liquid and filter residue (with same ion effect, main component of NaF, and small amount of CaF) 2 )；
Furthermore, free fluoride ions in the clear liquid can be tested, calcium oxide with 1/2 molar weight of fluoride ions is added into the clear liquid, calcium fluoride is obtained by filtration, and the filtrate is evaporated and crystallized to obtain sodium aluminate crystals with high purity.
Example 2
The embodiment provides a method for recovering aluminum electrolyte slag, which comprises the following specific steps of:
(1) In the step D2, the dosage ratio of undersize products, sodium carbonate and water is 20g:120g:450g;
(2) In the step D3, the reaction temperature is 180 ℃;
(3) In the step D6, the material proportion of the pressure cooking system is solid phase: naOH: caO: water =50g:100g:25g:450g, correspondingly, in step D7, the main component of the obtained filter residue is CaF 2 。
Example 3
The embodiment provides a method for recovering aluminum electrolyte slag, which is different from the embodiment 1 in the following specific steps:
(1) In the step D2, the dosage ratio of undersize products, sodium carbonate and water is 100g:120g:450g;
(2) In the step D3, the reaction temperature is 180 ℃;
(3) In the step D6, the material proportion of the pressure cooking system is solid phase: naOH: caO: water =50g:100g:10g:450g, the reaction temperature is 150 ℃;
correspondingly, in the step D7, the main component of the obtained filter residue is CaF 2 。
Example 4
The embodiment provides a method for recovering aluminum electrolyte slag, which comprises the following specific steps:
A1. crushing and grinding the aluminum electrolyte slag by a quartering method, sieving the aluminum electrolyte slag by a 150-mesh sieve, and taking undersize products;
A2. according to the weight ratio of 40g:120g: stirring and mixing the undersize product obtained in the step A1, sodium carbonate and water at a ratio of 450g under the stirring condition of 400 rpm;
A3. putting the mixture obtained in the step A2 into a closed container for autoclaving, wherein the autoclaving condition is 180 ℃ for 2 hours;
A4. cooling the mixture obtained in the step A3 to about 25 ℃, and then carrying out suction filtration to obtain a liquid phase and a solid phase;
A5. heating the liquid phase obtained in the step A4 to 90 ℃, keeping for 2 hours, crystallizing and separating out lithium carbonate, and performing suction filtration to obtain mother liquor and lithium carbonate;
A6. the mother liquor obtained in the step A5 and the undersize obtained in the step A1 are mixed according to the weight ratio of 450g:40g of the mixture is mixed and placed in a closed container to react for 1 hour at 180 ℃;
A7. after the reaction in step A6 is completed, a solid phase is obtained according to the treatment method in step A4.
That is, this example corresponds to the use of a mother liquor in which lithium carbonate is precipitated by crystallization as a mixed solution of sodium carbonate and water, and the leaching rates of lithium, aluminum and calcium in step A6 are characterized.
Comparative example 1
The embodiment provides a method for recovering aluminum electrolyte slag, which comprises the following specific steps:
D1. crushing and grinding the aluminum electrolyte slag by a quartering method, sieving the crushed aluminum electrolyte slag by a 150-mesh sieve, and taking undersize products;
D2. according to the weight ratio of 20g:100g: stirring and mixing the undersize product obtained in the step D1, sodium hydroxide and water at a ratio of 450g under the stirring condition of 400 rpm;
D3. putting the mixture obtained in the step D2 into a closed container for autoclaving, wherein the autoclaving condition is that the reaction is carried out for 2 hours at 180 ℃;
D4. and D, cooling the mixture obtained in the step D3 to about 25 ℃, and then carrying out suction filtration to obtain a liquid phase and a solid phase.
Comparative example 2
The embodiment provides a method for recovering aluminum electrolyte slag, which comprises the following specific steps:
D1. crushing and grinding the aluminum electrolyte slag by a quartering method, sieving the crushed aluminum electrolyte slag by a 150-mesh sieve, and taking undersize products;
D2. according to the weight ratio of 90g:90g:18g: stirring and mixing the undersize product obtained in the step D1, sodium hydroxide, sodium carbonate and water at a ratio of 450g under the stirring condition of 400 rpm;
D3. putting the mixture obtained in the step D2 into a closed container for autoclaving, wherein the autoclaving condition is that the reaction is carried out for 2 hours at 180 ℃;
D4. and D, cooling the mixture obtained in the step D3 to about 25 ℃, and then carrying out suction filtration to obtain a liquid phase and a solid phase.
Comparative example 3
The embodiment provides a method for recovering aluminum electrolyte slag, which comprises the following specific steps:
D1. crushing and grinding the aluminum electrolyte slag by a quartering method, sieving the crushed aluminum electrolyte slag by a 150-mesh sieve, and taking undersize products;
D2. according to the weight ratio of 90g:90g:90g: stirring and mixing the undersize product obtained in the step D1, sodium hydroxide, sodium carbonate and water at a ratio of 450g under the stirring condition of 400 rpm;
D3. putting the mixture obtained in the step D2 into a closed container for autoclaving, wherein the autoclaving condition is that the reaction is carried out for 2 hours at 180 ℃;
D4. and D, cooling the mixture obtained in the step D3 to about 25 ℃, and then carrying out suction filtration to obtain a liquid phase and a solid phase.
Test example
The test example tests the leaching rates of lithium, aluminum and calcium after autoclaving sodium carbonate and aluminum electrolyte slag, and the leaching rates of aluminum and calcium after autoclaving sodium hydroxide and a solid phase;
the specific test method is that the mass of the corresponding element in the residual solid is tested, and the mass percentage of the corresponding element in the solid before autoclaving is calculated as 1; the quality test method of the corresponding elements in the solid is ICP-OES.
The test results are shown in tables 1 and 2.
Table 1 results of leaching rate (%)
| Lithium ion source | Aluminium | Calcium (ll) containing calcium (II) | ||
| Example 1 | Step D3 | 79.81 | 0.75 | 0.20 |
| Step D6 | 81.39 | 0.12 | ||
| Example 2 | Step D3 | 93.70 | 1.93 | 0.72 |
| Step D6 | 72.72 | 0.55 | ||
| Example 3 | Step D3 | 81.80 | 0.25 | 0.22 |
| Step D6 | 60.12 | 0.06 | ||
| Example 4 | Step A3 | 87.07 | 1.24 | 0.23 |
| Step A6 | 66.91 | ～0 | 0.32 |
TABLE 2 results of extraction ratio (%)
| Lithium ion source | Aluminium | Calcium carbonate | ||
| Comparative example 1 | Step D3 | 82.67 | 69.51 | ～0 |
| Comparative example 2 | Step D3 | 35.30 | 0.58 | ～0 |
| Comparative example 3 | Step D3 | 15.22 | 0.61 | ～0 |
The results in table 1 show that the recovery method provided by the invention can respectively recover lithium element, fluorine element, aluminum element and calcium element in the aluminum electrolyte slag, the recovery rate is high, and the impurities in the obtained product are few. Wherein:
comparison of the results of step D3 in examples 1 and 2 or examples 2 and 3 shows that the higher the ratio of sodium carbonate to undersize, the higher the liquid-solid ratio, and the higher the autoclaving temperature in the first autoclaving (step D3), the higher the leaching rate of aluminum and calcium, but the higher the leaching rate of lithium.
As is clear from the results obtained in steps D6 of comparative examples 1 to 3, the higher the ratio of the amounts of sodium hydroxide and solid phase, the higher the leaching rate of aluminum; as is clear from the results obtained in steps D6 of comparative examples 2 to 3, calcium oxide also acts as a partial alkaline substance, and if the amount of sodium hydroxide added is insufficient, the leaching rate of the leaching rate is increased by adding calcium oxide, but the leaching rate of calcium is slightly increased by increasing the amount of calcium oxide added.
As is clear from the results of the two-stage leaching in comparative example 4, the mother liquor after crystallization of lithium carbonate was found to be slightly inferior in effect, though it was confirmed that the mother liquor was a leaching solution for leaching the fresh aluminum electrolyte slag. This is probably because the concentration of sodium carbonate in the solution is lower than that used in the first leaching, and therefore it can be expected that if the sodium carbonate concentration in the mother liquor is adjusted in production and then used as a leaching solution, the leaching effect of the mother liquor on lithium in the aluminum electrolyte slag can be effectively improved.
The results in table 2 show that the sodium hydroxide autoclaving recovery method adopted in comparative example 1 leaches lithium and aluminum simultaneously, and has no selectivity for leaching lithium; the recovery method of sodium carbonate and sodium hydroxide system adopted in the comparative examples 2-3 by one-time pressure cooking has low leaching rate of lithium element and poor effect.
In this test example, the XRD pattern of the lithium carbonate recovered in example 2 is also tested, and the result shows that the obtained lithium carbonate has a good crystalline state, and no peak corresponding to an impurity appears, that is, the recovery method provided by the present invention can obtain lithium carbonate with a good crystalline state and a high purity. The corresponding XRD pattern is shown in figure 3.
In the test example, the specific test method of the phase components in the filter residue obtained in the step D7 in the step D1 and the step D2 is XRD, and the test result shows that the filter residue obtained in the step D1 mainly contains NaF doped with a small amount of CaF 2 The filter residue obtained in example 2 contains CaF as the main component 2 From this, it is expected that CaF having a high purity can be obtained by adding a certain amount of calcium oxide to the autoclaving system in the step D6 2 Otherwise, the filter residue is mainly sodium fluoride due to the same ion effect. The corresponding XRD results are shown in fig. 4 to 5.
In conclusion, the recovery method provided by the invention has high selectivity for extracting each element and high purity of the obtained product, so the recovery method has high industrial practicability; meanwhile, the preparation raw material is low in price, the raw material sodium carbonate can be recycled, the produced product is high in price, and the economy of the recovery method is correspondingly improved; in addition, the use of acid is avoided, the use amount of alkali is saved, and the operation safety is improved; most importantly, through the design of the flow, the recovery method provided by the invention has no wastewater discharge, and the environmental protection property is improved.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (10)
1. The method for recovering the aluminum electrolyte slag is characterized by comprising the following steps of:
s1, mixing sodium carbonate, the aluminum electrolyte slag and water, and then pressing and boiling;
s2, cooling the mixture obtained in the step S1 to be less than or equal to 30 ℃, and carrying out solid-liquid separation;
s3, heating the liquid phase obtained in the step S2 to 75-95 ℃, and crystallizing to separate out lithium carbonate;
mixing sodium hydroxide, the solid phase obtained in the step S2 and water, then performing autoclaving, and performing solid-liquid separation to obtain filter residue and clear liquid; crystallizing sodium aluminate from said clear liquid.
2. The recycling method according to claim 1, wherein in step S1, the mixing comprises mixing the aluminum electrolyte slag after preparing the sodium carbonate solution from the sodium carbonate and water; preferably, the concentration of the sodium carbonate aqueous solution is 10-270 g/L.
3. The recycling method according to claim 1, wherein in step S1, the mass ratio of the water to the aluminum electrolyte slag is 1.1 to 80.
4. The recycling method according to claim 1, wherein the temperature of the autoclaving in step S1 is 120 to 220 ℃.
5. The recycling method according to claim 1, wherein the autoclaving in step S1 is carried out for a period of 0.5 to 2 hours.
6. The recovery method according to claim 1, wherein in step S3, the liquid-solid ratio in the autoclave system is 1.1 to 80g.
7. The recycling method according to claim 1, wherein the temperature of the autoclaving in step S3 is 140 to 220 ℃.
8. The recycling method according to claim 1, wherein the autoclaving in step S3 is carried out for a period of 0.5 to 2 hours.
9. The recycling method according to any one of claims 1 to 8, wherein in step S3, the autoclaving system further comprises a calcium-containing precursor.
10. A recovery method according to claim 9, characterized in that the calcium-containing precursor comprises at least one of calcium oxide and calcium hydroxide.
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| CN116334411A (en) * | 2023-04-11 | 2023-06-27 | 珠海市瑞斐门特科技有限公司 | Recovery method for extracting lithium element from aluminum electrolyte slag at low temperature in multiple stages |
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