CN113697833A - Method for preparing hydrotalcite and application thereof - Google Patents
Method for preparing hydrotalcite and application thereof Download PDFInfo
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- CN113697833A CN113697833A CN202110908132.4A CN202110908132A CN113697833A CN 113697833 A CN113697833 A CN 113697833A CN 202110908132 A CN202110908132 A CN 202110908132A CN 113697833 A CN113697833 A CN 113697833A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M12/00—Hybrid cells; Manufacture thereof
- H01M12/04—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type
- H01M12/06—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type with one metallic and one gaseous electrode
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/20—Two-dimensional structures
- C01P2002/22—Two-dimensional structures layered hydroxide-type, e.g. of the hydrotalcite-type
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
- C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
- C08J2327/04—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing chlorine atoms
- C08J2327/06—Homopolymers or copolymers of vinyl chloride
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
- C08K3/20—Oxides; Hydroxides
- C08K3/22—Oxides; Hydroxides of metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0002—Aqueous electrolytes
- H01M2300/0014—Alkaline electrolytes
Abstract
The invention discloses a method for preparing hydrotalcite and application thereof. The preparation method comprises the following steps: mixing the electrolytic waste liquid of the aluminum-air battery with a metal oxide for reaction so as to obtain a reaction liquid; carrying out filter pressing on the reaction liquid so as to obtain a filter cake precursor and a filtrate; mixing the filter cake precursor with water and sanding to obtain a precursor suspension; mixing the precursor suspension with a buffering agent, adjusting the pH value of the mixed solution to 9-13, and then carrying out hydrothermal reaction to obtain reaction slurry; and mixing the reaction slurry with a hydrophobic modifier for modification reaction, and performing solid-liquid separation on a reaction product to obtain hydrotalcite and a reacted liquid. The preparation method has the advantages of low cost, short process flow, environmental protection, no pollution and high added value of recovered products, and when the prepared hydrotalcite is used as a heat stabilizer of PVC, the thermal stability and high transparency of the PVC film can be simultaneously considered.
Description
Technical Field
The invention belongs to the field of batteries, and particularly relates to a method for preparing hydrotalcite and application thereof.
Background
The aluminum-air battery is a novel high-energy chemical power supply, has the main advantages of high energy density, high working current density, low manufacturing cost, long shelf life, greenness, environmental protection, safety, silence and the like, and has great attention in the fields of new energy automobiles, communication equipment, emergency power supplies and the like. However, the aluminum-air fuel cell generates a large amount of electrolyte after reaction, the electrolytic waste liquid has high purity and low impurity content, and the direct waste liquid treatment not only has high cost, but also wastes resources, and is not beneficial to energy conservation and environmental protection.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, it is an object of the present invention to propose a process for preparing hydrotalcites and their use. The preparation method has the advantages of low cost, short process flow, environmental protection, no pollution and high added value of recovered products, and when the prepared hydrotalcite is used as a heat stabilizer of PVC, the thermal stability and high transparency of the PVC film can be simultaneously considered.
The present application is primarily based on the following findings of the inventors:
PVC plastic has excellent properties and low price, and is widely used in various fields of industry, agriculture and life. However, PVC plastics are easily decomposed by heating, and a heat stabilizer is required to be added for inhibition in the processing process. The degradation of PVC is mainly characterized in that an active free radical Cl & lt- & gt with electrons is generated when unstable isomers in PVC molecules are degraded and is combined with H atoms in a PVC chain to generate HCl, and the generation of HCl gas can accelerate the decomposition of PVC, so that the inhibition and absorption of HCl generated by PVC degradation is the key of the performance of a heat stabilizer. Layered Double Hydroxides (LDHs) are hydrotalcite-like clay compounds consisting of lamellar cationic brucite-type metal oxides or hydroxides and interlayer anion and water sublayers, and have the general formula [ M2+ 1-xM3+ x(OH)2]x+An- x/n·mH2O, wherein M2+And M3+Are divalent and trivalent metal cations such as: mg (magnesium)2+、Zn2+、Ca2+、Al3+、Fe3+Etc., a is an interlayer anion such as: cl-、CO3 2-、SO4 2-、NO3 -And the like. Because the LDHs have high length-diameter ratio and thermal stability, the mechanical and thermal properties of the polymer can be improved, and the LDHs can be used as a thermal stabilizer of polyvinyl chloride (PVC) plastics, wherein interlayer anions of the LDHs can degrade Cl released by PVC-And (3) carrying out anion exchange reaction, and simultaneously reacting the metal hydroxide of the lamella layer with HCl, so that the content of HCl in PVC is reduced, and the effect of increasing thermal stability is achieved.
The existing method for preparing hydrotalcite is usually to add a divalent metal salt solution and a trivalent metal salt solution into an alkali metal carbonate or alkali metal hydroxide (such as sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide) solution, and prepare hydrotalcite by a coprecipitation method, or to dissolve aluminum hydroxide by using high-concentration sodium hydroxide or potassium hydroxide, and then to add alkali metal oxide for reaction to prepare hydrotalcite. However, when hydrotalcite is used as a thermal stabilizer of PVC plastic, potassium carbonate or potassium hydroxide cannot be used as an alkali solution, because if the content of potassium carbonate is too high, a large number of black spots exist after hydrotalcite and PVC plastic film formation, which seriously affects the transparency of the plastic and also reduces the thermal stability improvement effect of hydrotalcite. In addition, most of aluminum-air fuel cells use strong base electrolyte, KOH is commonly used, in order to solve the problems of recycling of the electrolytic waste liquid of the aluminum-air fuel cells and the influence of hydrotalcite on the transparency of PVC plastics, the inventor imagines that the waste liquid treatment can be carried out by adding alkaline metal oxide into the electrolytic waste liquid of the aluminum-air fuel cells, so that the alkali liquid after reaction can be continuously used as the electrolyte of the aluminum-air cells through alkali supplementation, the use cost of the aluminum-air cells is greatly reduced, the separation of aluminum and potassium can be realized, a filter cake which can be used as an ideal precursor for producing hydrotalcite is obtained, and the problem that the transparency of PVC plastics is influenced by the prepared hydrotalcite due to the fact that the hydrotalcite contains excessive potassium in the raw materials for producing hydrotalcite is effectively solved.
To this end, according to one aspect of the present invention, a process for preparing hydrotalcite is proposed. According to an embodiment of the invention, the method comprises:
(1) mixing the electrolytic waste liquid of the aluminum-air battery with a metal oxide for reaction so as to obtain a reaction liquid;
(2) carrying out filter pressing on the reaction liquid so as to obtain a filter cake precursor and a filtrate;
(3) mixing the filter cake precursor with water and sanding to obtain a precursor suspension;
(4) mixing the precursor suspension with a buffering agent, adjusting the pH value of the mixed solution to 9-13, and then carrying out hydrothermal reaction to obtain reaction slurry;
(5) and mixing the reaction slurry with a hydrophobic modifier for modification reaction, and performing solid-liquid separation on a reaction product to obtain hydrotalcite and a reacted liquid.
The method for preparing hydrotalcite according to the above embodiment of the present invention has at least the following advantages: 1) the aluminum ions in the electrolytic waste liquid exist in the form of meta-aluminate, and the metal oxide is added into the electrolytic waste liquid for solid-liquid reaction, so that the aluminum ions in the electrolytic waste liquid can form aluminum hydroxide and are transferred into a filter cake, the separation of the aluminum ions and the potassium ions is realized, and byproducts generated during the reaction of the aluminum-air battery are removed; 2) the particle size of the finally prepared hydrotalcite can be greatly reduced by sanding the filter cake, the transparency and the thermal stability of PVC can be obviously improved when the prepared hydrotalcite is used in a PVC membrane, and the problem that the transparency and the thermal stability of the PVC membrane are reduced due to overlarge particle size of the hydrotalcite is effectively solved; 3) the hydrothermal reaction can increase the length-diameter ratio of the prepared hydrotalcite to form a large and thin structure, and the hydrotalcite with the structure is easily damaged by heating, so that the thermal stability of the hydrotalcite is influenced; 4) by adopting the hydrophobic modifier for modification treatment, the hydrophilic hydrotalcite can be changed into hydrophobic hydrotalcite, so that the compatibility of the hydrotalcite and PVC can be greatly increased, the hydrotalcite can be uniformly dispersed in PVC, and the problem that black spots are formed on a PVC film or the transparency is obviously reduced due to the hydrotalcite can be further avoided; 5) the filtrate obtained in the step (2) can be returned to an aluminum-air battery to be continuously used as electrolyte after alkali supplementation, and the service efficiency can reach more than 95 percent of that of new solution; 6) the method has the advantages of low cost, short process flow, environmental protection, no pollution and high added value of recovered products, and the prepared hydrotalcite can simultaneously consider the thermal stability and high transparency of the PVC film when being used as a heat stabilizer of PVC.
In addition, the method for preparing hydrotalcite according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the invention, step (1) satisfies at least one of the following conditions: the temperature of the mixing reaction is 75-95 ℃, and the time is 2-5 h; the metal oxide is magnesium oxide and/or calcium oxide; the aluminum ion content in the aluminum-air battery electrolytic waste liquid is 100-200g/L, and the solid-to-liquid ratio of the metal oxide to the aluminum-air battery electrolytic waste liquid is (2-4) Kg: (3-5) L.
In some embodiments of the invention, in the step (3), the solid content of the precursor suspension is 5-20 wt%; and/or in the precursor suspension, the particle size D50 of the precursor is 0.5-3 μm.
In some embodiments of the invention, in the step (3), the solid content of the precursor suspension is 5-10 wt%; and/or in the precursor suspension, the particle size D50 of the precursor is 0.5-1 μm.
In some embodiments of the invention, in the step (4), the precursor suspension, the aluminum-air battery electrolyte waste liquid and the buffer are mixed, and the hydrothermal reaction is performed after the pH value of the mixed liquid is adjusted to 9-13.
In some embodiments of the present invention, in the step (4), the amount of the electrolytic waste liquid of the aluminum-air battery added is adjusted so as to adjust the molar ratio of the divalent metal element to the trivalent metal element in the hydrotalcite to (1.7 to 2.3): 1, preferably to (1.9-2.1): 1.
in some embodiments of the invention, step (4) satisfies at least one of the following conditions: the addition amount of the buffering agent is 1-10 wt% of the filter cake precursor; the addition amount of the buffering agent is 3-5 wt% of the filter cake precursor; the buffer is at least one selected from urea, ammonia water, sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide; adjusting the pH value of the mixed solution to 10-11; by using CO2Adjusting the pH value of the mixed solution; the temperature of the hydrothermal reaction is 150-180 ℃, and the time is 3-8 h.
In some embodiments of the invention, step (5) satisfies at least one of the following conditions: the addition amount of the hydrophobic modifier is 3-8 wt% of the filter cake precursor; the hydrophobic modifier comprises at least one selected from stearic acid, sodium stearate, zinc stearate and calcium stearate; the temperature of the modification reaction is 80-90 ℃, and the time is 3-8 h.
In some embodiments of the present invention, the reacted liquid in step (5) is recycled to step (3) and/or step (4); and/or supplementing alkali to the filtrate obtained in the step (2) and then using the filtrate as electrolyte for the aluminum-air battery again.
According to yet another aspect of the present invention, a polyvinyl chloride film is provided. According to an embodiment of the present invention, the polyvinyl chloride film has a heat stabilizer including hydrotalcite prepared by the above-described method for preparing hydrotalcite. Compared with the prior art, the polyvinyl chloride film has good thermal stability and high transparency.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by 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 flow chart of a method for preparing hydrotalcite according to one embodiment of the present invention.
Figure 2 is a partial process flow diagram for preparing hydrotalcite according to one embodiment of the present invention.
Fig. 3 is an SEM image of hydrotalcite prepared according to example 1 of the present invention.
Fig. 4 is an SEM image of hydrotalcite prepared according to comparative example 5 of the present invention.
Fig. 5 is an SEM image of hydrotalcite prepared according to comparative example 6 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 drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
According to one aspect of the present invention, a process for preparing hydrotalcite is presented. According to the method, alkaline metal oxide is added into the electrolytic waste liquid of the aluminum-air fuel cell to carry out waste liquid treatment so as to realize the separation of aluminum and potassium, and a buffering agent and a modifying agent are introduced to improve the particle size, the morphology structure and the hydrophobicity of the hydrotalcite, so that the effect of improving the thermal stability and the transparency of the hydrotalcite on a PVC membrane is obviously improved. The preparation method has the advantages of low cost, short process flow, environmental protection, no pollution and high added value of recovered products, and the prepared hydrotalcite can simultaneously consider the thermal stability and high transparency of the PVC film when being used as a heat stabilizer of PVC. The method for preparing hydrotalcite according to the present invention will be described in detail with reference to FIGS. 1 to 2.
S100: mixing the electrolytic waste liquid of the aluminum-air battery with metal oxide for reaction to obtain reaction liquid
According to the embodiment of the invention, the aluminum ions in the electrolytic waste liquid exist in the form of meta-aluminate, and the metal oxide is added into the electrolytic waste liquid to carry out solid-liquid reaction, so that the aluminum ions in the electrolytic waste liquid can form aluminum hydroxide and be transferred to a filter cake, and therefore, byproducts generated in the reaction of an aluminum-air battery can be sufficiently removed, and the electrolytic waste liquid and aluminum can be recycled.
According to some embodiments of the present invention, the metal oxide is mainly used for removing aluminum ions from the waste electrolyte of the aluminum-air cell, and the metal oxide is alkaline, while the amphoteric metal oxide (such as ZnO) is not suitable, and preferably, the metal oxide may be magnesium oxide and/or calcium oxide.
According to some embodiments of the present invention, the addition amount of the metal oxide has a significant influence on the recovery rate of aluminum ions and the recovery and reuse of the electrolytic waste liquid, and if the addition amount of the metal oxide is too small, the aluminum ions are difficult to be sufficiently removed, which influences the recovery and reuse of the filtrate; if the addition amount of the metal oxide is too large, more impurities are introduced, which also affects the performance of the filtrate in recycling the filtrate as an electrolyte of an aluminum-air battery, and thus the electrochemical performance of the battery is reduced, the addition amount of the metal oxide is preferably just enough to completely remove aluminum ions in the electrolysis waste liquid, for example, the molar ratio of the metal oxide to the aluminum ions can be 3:1, that is, the ratio of divalent metal to trivalent metal elements in the prepared precursor can be 3: 1. Further, when the content of aluminum ions in the conventional aluminum-air battery electrolyte waste liquid is usually 100-200g/L, the solid-to-liquid ratio of the metal oxide to the aluminum-air battery electrolyte waste liquid can be (2-4) Kg: (3-5) L, for example, 2Kg/5L, 3Kg/4L, 4Kg/3L, 4Kg/5L, 2Kg/3L, etc., and the inventors have found that controlling the solid-to-liquid ratio of the metal oxide to the waste electrolyte solution based on the above-mentioned concentration range of aluminum ions can sufficiently remove aluminum ions in the waste electrolyte solution without significantly reducing the electrochemical performance when the filtrate is reused as an electrolyte solution in an aluminum-air battery.
According to still other embodiments of the present invention, the temperature of the mixing reaction may be 75 to 95 ℃, for example, 80 ℃ or 85 ℃, and the time may be 2 to 5 hours, for example, 3 hours or 4 hours, and the inventors found that if the reaction temperature is too low or the reaction time is too short, the reaction of the alkali metal oxide is incomplete, and the sufficient removal of the aluminum ions cannot be achieved, and if the reaction time is too long, the preparation efficiency is affected.
S200: filter-pressing the reaction solution to obtain a filter cake precursor and a filtrate
According to the embodiment of the invention, after the alkali metal oxide reacts with the electrolytic waste liquid, aluminum ions and added alkali metal can be transferred to a filter cake in the form of hydroxide to be used as a filter cake for producing an ideal precursor of hydrotalcite, and the filtrate can be returned to an aluminum-air battery after alkali supplement to be continuously used as electrolyte, and the use efficiency can reach more than 95% of that of a new liquid.
S300: mixing the filter cake precursor with water and sanding to obtain precursor suspension
According to the embodiment of the invention, the particle size of the finally prepared hydrotalcite can be greatly reduced by sanding the filter cake, so that the transparency and the thermal stability of PVC can be obviously increased when the prepared hydrotalcite is used in a PVC membrane, and the problem that the transparency and the thermal stability of the PVC membrane are reduced due to overlarge particle size of the hydrotalcite is avoided.
According to some embodiments of the present invention, the particle size D50 of the precursor in the precursor suspension may be 0.5 to 3 μm, for example, 0.7 μm, 0.9 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, or 2.5 μm, and the like, and the inventors found that if the particle size of the precursor is too large, the transparency and thermal stability of PVC may be greatly reduced, and if the particle size of the precursor is too small, the sanding difficulty may be greatly increased, which may cause a significant increase in production cost and a reduction in production efficiency. Preferably, the particle size D50 of the precursor in the precursor suspension can be 0.5-1 μm, so that the transparency and the thermal stability of the PVC can be further improved on the premise of not significantly influencing the production cost and the production efficiency.
According to still other embodiments of the present invention, the solid content of the precursor suspension may be 5 to 20 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, etc., and the inventors found that too low or too high solid content of the precursor suspension affects the sanding effect, and it is difficult to obtain precursor particles in a desired particle size range, and further, when the solid-to-liquid ratio of the filter cake to water is too small, the sanding efficiency is also affected, and the overall productivity is reduced; when the solid content of the precursor suspension is too large, adverse effects can be generated on subsequent hydrothermal reaction, the solid content of the precursor suspension is controlled to be within the range, the sanding efficiency can be guaranteed, the sanding effect can be improved, the particle size of the precursor is finer and more uniform, and precursor particles with the particle size D50 of 0.5-3 mu m can be obtained more favorably. Preferably, the solid content of the precursor suspension can be 5-10 wt%, so that the sanding effect can be further improved, precursor particles with the particle size D50 of 0.5-1 μm can be obtained, and the subsequent hydrothermal reaction can be carried out smoothly.
S400: mixing the precursor suspension with a buffering agent, adjusting the pH value of the mixed solution to 9-13, and then carrying out hydrothermal reaction to obtain reaction slurry
According to the embodiment of the invention, compared with a coprecipitation method, hydrothermal reaction can increase the length-diameter ratio of the prepared hydrotalcite to form a large and thin structure, and the hydrotalcite with the structure is easily damaged by heating, so that the thermal stability of the hydrotalcite is affected. According to the invention, the buffer is further added before the hydrothermal reaction, so that the characteristic of relatively high electronegativity of the buffer can be utilized, sufficient anions exist between hydrotalcite layers, and a sufficient longitudinal growth space is provided, thus the length-diameter ratio of the hydrotalcite can be effectively reduced, and a small and thick structure is formed, so that the thermal stability of the hydrotalcite can be improved, and meanwhile, the transparency of the hydrotalcite and PVC after film forming can be increased.
According to the embodiment of the invention, when the solid content of the precursor in the mixed solution is more than 10 wt%, water can be further added into the mixed solution to reduce the solid content of the precursor in the mixed solution, and the solid content in the mixed solution of the hydrothermal reaction is controlled to be not more than 10 wt%.
According to some specific embodiments of the invention, when the precursor suspension and the buffer are mixed, the electrolytic waste liquid of the aluminum-air battery can be further supplemented, and the pH value of the mixed liquid is adjusted to 9-13 for hydrothermal reaction, the inventor finds that, in order to fully recover the meta-aluminate in the electrolytic waste liquid, the molar ratio of the added divalent metal element to the aluminum element is generally controlled to be about 3:1, that is, the molar ratio of the divalent metal element to the aluminum element in the precursor is also about 3:1, and the content of the trivalent metal element in the suspension can be increased by supplementing the electrolytic waste liquid in the precursor suspension, so that the number of positive charges on the surface of the hydrotalcite (LDHs) sheet layer is increased, thereby being more beneficial to the insertion of anions and greatly improving the effect of the LDHs serving as a PVC heat stabilizer on the thermal stability. Preferably, the amount of the added electrolytic waste liquid of the aluminum-air battery can be adjusted so as to adjust the molar ratio of the divalent metal element to the trivalent metal element in the hydrotalcite to (1.7-2.3): 1, such as 1.8/1, 1.9/1, 2/1, 2.1/1, 2.2/1, or 2.3/1, etc., preferably adjusted to (1.9-2.1): 1, the molar ratio can be more preferably adjusted to 2:1, and when the molar ratio of the divalent metal element to the trivalent metal element in the hydrotalcite is 2:1, the effect of improving the thermal stability of PVC is best.
According to still some embodiments of the present invention, the amount of the electrolytic waste liquid supplemented to the precursor suspension before the hydrothermal reaction is performed may be based on the filter cake precursor, and 10 to 60mL (for example, 10mL, 15mL, 20mL, 25mL, 30mL, 35mL, 40mL, 50mL, or 60mL, etc.) of the aluminum-air battery electrolytic waste liquid is added to each 100g of the filter cake precursor, and the specific amount may be adaptively adjusted according to the content of the aluminum element in the electrolytic waste liquid.
According to still other embodiments of the present invention, the inventors have found that a buffer, which may be an alkaline salt or an alkaline solution, for example, one or more of urea, ammonia, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, etc., may be added to the mixed solution before hydrothermal reaction, to ensure that sufficient anions exist between hydrotalcite layers and provide sufficient longitudinal growth space, thereby inhibiting the growth of the particle size and aspect ratio of hydrotalcite. Furthermore, the addition amount of the buffer may be 1 to 10 wt% of the filter cake precursor, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt% of the filter cake precursor, if the amount of the precursor is too small, it is difficult to obtain hydrotalcite with a relatively small length-diameter, a small length-diameter and a thick structure, the obtained hydrotalcite has a poor effect of improving the thermal stability and transparency of PVC, and if the amount of the buffer is too large, the hydrotalcite may be too thick, and the thermal stability of the hydrotalcite may be affected. Preferably, the addition amount of the buffering agent can be 3-5 wt% of the filter cake precursor, so that the problem of reduction of thermal stability of the hydrotalcite can be further avoided on the basis of obtaining the hydrotalcite with smaller particle size and aspect ratio.
According to yet another aspect of the inventionIn some specific embodiments, the inventor finds that both peracid and alkali in a mixed solution during a hydrothermal reaction affect the crystal form of the finally prepared hydrotalcite, and if the crystal form of the formed hydrotalcite is not good, the improvement effect on the thermal stability of the PVC is affected, and the hydrotalcite with a good crystal form can be obtained by controlling the pH value of the mixed solution to 9-13, so that the improvement effect on the thermal stability of the PVC is ensured; preferably, the pH value of the mixed solution can be controlled to 10-11, so that hydrotalcite with a better crystal form can be obtained, and the thermal stability of PVC can be improved. Further, CO can be introduced into the mixed solution when the pH value is adjusted2Therefore, the pH value can be adjusted, carbonate can be introduced between LDHs layers to provide interlayer anions for the preparation of hydrotalcite, and the preparation method is more favorable for preparing Cl generated in the degradation process of PVC-Anion exchange is carried out, and the thermal stability of the PVC is improved.
According to still other embodiments of the present invention, the temperature of the hydrothermal reaction may be 150 to 180 ℃, for example, 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃ or 180 ℃, and the time may be 3 to 8 hours, for example, 3.5 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, and the inventors found that the crystal structure of the hydrotalcite is affected by the excessively high or excessively low temperature of the hydrothermal reaction, and thus the thermal stability of the hydrotalcite is affected.
S500: mixing the reaction slurry with a hydrophobic modifier for modification reaction, and performing solid-liquid separation on the reaction product to obtain hydrotalcite and reacted liquid
According to the embodiment of the invention, hydrophilic hydrotalcite can be changed into hydrophobic hydrotalcite by adopting a hydrophobic modifier for modification treatment, so that the compatibility of the hydrotalcite and PVC can be greatly increased, the hydrotalcite can be uniformly dispersed in PVC, and the problem that black spots are formed on a PVC film or the transparency is obviously reduced due to the hydrotalcite can be further avoided. Specifically, the solid-liquid separation can be realized by adopting a vacuum filtration mode.
According to some embodiments of the present invention, the kind of the hydrophobic modifier in the present invention is not particularly limited, and may be selected by those skilled in the art according to actual needs, for example, the hydrophobic modifier may be an oily modifier or a surfactant commonly used for PVC, and further, for example, one or more selected from stearic acid, sodium stearate, calcium stearate, or zinc stearate. In addition, the addition amount of the hydrophobic modifier may be 3 to 8 wt% of the filter cake precursor, for example, may be 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, or 8 wt%, and the inventors found that if the addition amount of the hydrophobic modifier is too small, the modification effect on hydrotalcite is not good, and if the addition amount of the hydrophobic modifier is too large, not only is raw material wasted, but also the modifier remains a lot in the reaction solution, which affects recycling thereof; according to the invention, by controlling the hydrophobic modifier to be in the range, the modification effect can be ensured, and the raw material cost can be reduced.
According to some embodiments of the present invention, the temperature of the modification reaction may be 80 to 90 ℃, for example, 82 ℃, 85 ℃ or 88 ℃, and the time may be 3 to 8 hours, for example, 3.5 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, and the inventors found that if the modification temperature is too low or the modification time is too short, the hydrophobic modification effect on the hydrotalcite is not significant, and if the modification time is too long, the production efficiency is affected. By controlling the reaction conditions, the invention can not only ensure the production efficiency and the modification effect, but also avoid excessive energy consumption waste.
According to the embodiment of the invention, the liquid after the reaction obtained after the solid-liquid separation can be reused in the sanding treatment and/or the hydrothermal reaction, so that a required liquid environment can be provided for the sanding treatment and/or the hydrothermal reaction, and raw materials or additives such as a buffering agent, a hydrophobic modifier and the like remained in the liquid after the reaction can be further effectively utilized, so that the resource utilization of the raw materials can be realized, the raw material cost can be reduced, and the cyclic utilization of water can be realized.
According to some embodiments of the present invention, after the alkali metal oxide reacts with the waste electrolyte solution and is filtered to obtain a filtrate, the filtrate may be washed in advance, and then the washed filtrate may be made up with alkali and reused as the electrolyte. Wherein the washing water for washing the filtrate can be reused in the sand grinding treatment and/or the hydrothermal reaction.
According to some specific embodiments of the invention, 3-5L (the aluminum ion content is 100-200g/L, the alkali metal ion content is 200-300 g/L) of naturally precipitated aluminum-air battery waste electrolyte can be taken, 2-4 kg of alkali metal oxide is added, the mixture is reacted in a 30L reaction kettle, the reaction time is 2-5 h, the temperature is 75-95 ℃, and a precursor is obtained after washing and filter pressing; sanding the particle size of the precursor until the D50 is 0.5-1 mu m; using 100-200g of precursor for size mixing, supplementing 20-30 mL of electrolysis waste liquid with trivalent metal elements, and introducing appropriate amount of CO2When the pH value of the slurry is 10-11, adding a buffering agent accounting for 3-5 wt% of the mass of the precursor, and then finishing size mixing, wherein the hydrothermal reaction temperature is 150-180 ℃, and the reaction time is 3-8 h; after the hydrothermal reaction is finished, reducing the temperature to 80-90 ℃, transferring the temperature to a 5L glass reaction kettle, adding a hydrophobic modifier accounting for 4-8 wt% of the mass of the precursor, and reacting for 3-8 h at 80-100 ℃; and carrying out vacuum filtration and washing on the reactant, and drying at 80-100 ℃ to obtain the LDHs.
In summary, the method for preparing hydrotalcite according to the above embodiment of the present invention has at least the following advantages: 1) the aluminum ions in the electrolytic waste liquid exist in the form of meta-aluminate, and the metal oxide is added into the electrolytic waste liquid for solid-liquid reaction, so that the aluminum ions in the electrolytic waste liquid can form aluminum hydroxide and are transferred into a filter cake, the separation of the aluminum ions and the potassium ions is realized, and byproducts generated during the reaction of the aluminum-air battery are removed; 2) the particle size of the finally prepared hydrotalcite can be greatly reduced by sanding the filter cake, the transparency and the thermal stability of PVC can be obviously improved when the prepared hydrotalcite is used in a PVC membrane, and the problem that the transparency and the thermal stability of the PVC membrane are reduced due to overlarge particle size of the hydrotalcite is effectively solved; 3) the hydrothermal reaction can increase the length-diameter ratio of the prepared hydrotalcite to form a large and thin structure, and the hydrotalcite with the structure is easily damaged by heating, so that the thermal stability of the hydrotalcite is influenced; 4) by adopting the hydrophobic modifier for modification treatment, the hydrophilic hydrotalcite can be changed into hydrophobic hydrotalcite, so that the compatibility of the hydrotalcite and PVC can be greatly increased, the hydrotalcite can be uniformly dispersed in PVC, and the problem that black spots are formed on a PVC film or the transparency is obviously reduced due to the hydrotalcite can be further avoided; 5) the filtrate obtained in the step (2) can be returned to an aluminum-air battery to be continuously used as electrolyte after alkali supplementation, and the service efficiency can reach more than 95 percent of that of new solution; 6) the method has the advantages of low cost, short process flow, environmental protection, no pollution and high added value of recovered products, and the prepared hydrotalcite can simultaneously consider the thermal stability and high transparency of the PVC film when being used as a heat stabilizer of PVC.
According to yet another aspect of the present invention, a polyvinyl chloride film is provided. According to an embodiment of the present invention, the polyvinyl chloride film has a heat stabilizer including hydrotalcite prepared by the above-described method for preparing hydrotalcite. Compared with the prior art, the polyvinyl chloride film has good thermal stability and high transparency. It should be noted that the features and effects described for the above-mentioned method for preparing hydrotalcite are also applicable to the polyvinyl chloride film, and are not described in detail here.
The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Example 1
Taking 5L (the content of aluminum ions is 136g/L and the content of alkali metal ions is 284g/L) of aluminum-air battery waste electrolyte after natural precipitation, adding 3kg of magnesium oxide, reacting in a 30L reaction kettle for 3h at the temperature of 85 ℃, washing and filter-pressing to obtain a precursor; sanding the particle size of the precursor until the particle size of D50 is 0.5-1 mu m; using 100g of precursor for size mixing, and supplementing 34mL of electrolysis waste liquid with trivalent metalElement, introducing appropriate amount of CO2When the pH value of the slurry is 10.21, adding ammonia water accounting for 3 wt% of the mass of the precursor, and then finishing size mixing, wherein the hydrothermal reaction temperature is 160 ℃, and the reaction time is 5 h; after the hydrothermal reaction is finished, reducing the temperature to 90 ℃, transferring the temperature to a 5L glass reaction kettle, adding stearic acid accounting for 4 wt% of the mass of the precursor, and reacting for 3 hours at 8 ℃; and carrying out vacuum filtration and washing on the reactant, and drying at 80 ℃ to obtain the LDHs.
Comparative example 1
The difference from example 1 is that: the precursor is not sanded, and D50 is 10-15 mu m.
Comparative example 2
The difference from example 1 is that: introducing excessive CO in the pulp mixing process2And the pH of the slurry is less than 8.
Comparative example 3
The difference from example 1 is that: the hydrothermal reaction temperature was 140 ℃.
Comparative example 4
The difference from example 1 is that: no buffer was added.
Comparative example 5
Preparing LDHs by a coprecipitation method: 4.69g of aluminum nitrate and 9.01g of magnesium nitrate were dissolved in 200mL of deionized water; dissolving 3.84g of sodium hydroxide and 2.97g of sodium carbonate in another 200mL of deionized water, slowly dripping the sodium hydroxide and the sodium carbonate into 250mL of deionized water, controlling the pH of the solution to be 10 during dripping, reacting at 80 ℃ for 12h to prepare an LDHs precursor after finishing dripping, adding the LDHs precursor into a hydrothermal reaction kettle, reacting at 180 ℃ for 5h, filtering, washing and drying to obtain the LDHs.
Comparative example 6
Preparing LDHs by a coprecipitation method: 23.45g of aluminum nitrate and 48.05g of magnesium nitrate are dissolved in 250ml of deionized water, 21.39g of potassium hydroxide and 15.46g of potassium carbonate are dissolved in 200ml of another part of deionized water, the two parts are simultaneously and slowly dripped into 250ml of deionized water, the pH value of the solution is controlled to be 10 during dripping, after the dripping is finished, the solution reacts for 12 hours at 80 ℃ to prepare LDHs precursors, the LDHs precursors are added into a hydrothermal reaction kettle for reacting for 5 hours at 180 ℃, and the LDHs precursors are obtained after filtration, washing and drying.
The thermal stability of the LDHs prepared in example 1 and comparative examples 1 to 6 was evaluated:
the testing process comprises the following steps:
(1) LDHs and soft transparent PVC are formed into a film, a double-roller mixing roll is used for mixing for 4min at 180 ℃ according to a fixed formula of the soft transparent PVC film, and then an electric vulcanizing forming machine is used for pressing the film. And (3) placing the formed film on an aluminum sheet, placing the formed film into a thermal ageing oven for heating at 180 ℃, taking out a sample at an interval of 10min, and recording the change condition of the color of the sample along with time.
(2) The transmittance of the sample was measured using an ultraviolet-visible spectrophotometer.
The test results are shown in table 1:
TABLE 1 LDHs used as heat stabilizer for soft transparent PVC Performance test results
Results and conclusions:
the results in Table 1 show that:
(1) comparative example 1 the crystal grain size is too large, which seriously affects the thermal stability of PVC and reduces the transparency of the film;
(2) in comparative example 2, CO was introduced during the preparation of LDHs2The purpose is to introduce carbonate between LDHs layers, which is beneficial to generating Cl in the degradation process of PVC-Anion exchange is carried out, but the introduction amount is too large, which destroys the optimum pH for producing LDHs crystal grains and thus affects the thermal stability thereof.
(3) As can be seen from comparative example 3, sufficient temperature and pressure conditions were required for LDHs formation.
(4) Fig. 3 to 5 are SEM images of the LDHs prepared in example 1, comparative example 5 and comparative example 6 in sequence, wherein, as can be seen from fig. 5, the LDHs prepared by the reaction system of potassium hydroxide and potassium carbonate in example 6 have a thin lamellar thickness and a large and irregular lamellar size, and as can be seen from fig. 3, after the buffer is introduced in example 1, the lamellar thickness is increased while the size is increased, and the structure is similar to that of the hydrotalcite prepared by the co-precipitation method in comparative example 5, but the LDHs have better thermal stability than that of comparative examples 5 and 6, and not only the problem that a large number of black spots exist after the LDHs and the soft transparent PVC in comparative example 6 are formed into a film is solved.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A process for preparing hydrotalcite comprising:
(1) mixing the electrolytic waste liquid of the aluminum-air battery with a metal oxide for reaction so as to obtain a reaction liquid;
(2) carrying out filter pressing on the reaction liquid so as to obtain a filter cake precursor and a filtrate;
(3) mixing the filter cake precursor with water and sanding to obtain a precursor suspension;
(4) mixing the precursor suspension with a buffering agent, adjusting the pH value of the mixed solution to 9-13, and then carrying out hydrothermal reaction to obtain reaction slurry;
(5) and mixing the reaction slurry with a hydrophobic modifier for modification reaction, and performing solid-liquid separation on a reaction product to obtain hydrotalcite and a reacted liquid.
2. The method of claim 1, wherein step (1) satisfies at least one of the following conditions:
the temperature of the mixing reaction is 75-95 ℃, and the time is 2-5 h;
the metal oxide is magnesium oxide and/or calcium oxide;
the aluminum ion content in the aluminum-air battery electrolytic waste liquid is 100-200g/L, and the solid-to-liquid ratio of the metal oxide to the aluminum-air battery electrolytic waste liquid is (2-4) Kg: (3-5) L.
3. The method according to claim 1, wherein in the step (3), the solid content of the precursor suspension is 5-20 wt%; and/or in the precursor suspension, the particle size D50 of the precursor is 0.5-3 μm.
4. The method according to claim 1, wherein in the step (3), the solid content of the precursor suspension is 5-10 wt%; and/or in the precursor suspension, the particle size D50 of the precursor is 0.5-1 μm.
5. The method according to claim 1, wherein in the step (4), the precursor suspension, the aluminum-air battery electrolyte waste liquid and the buffer are mixed, and the hydrothermal reaction is performed after the pH value of the mixed liquid is adjusted to 9-13.
6. The method according to claim 5, wherein in the step (4), the amount of the electrolytic waste liquid of the aluminum-air battery added is adjusted so as to adjust the molar ratio of the divalent metal element to the trivalent metal element in the hydrotalcite to (1.7 to 2.3): 1, preferably to (1.9-2.1): 1.
7. the method according to claim 1 or 5, wherein step (4) satisfies at least one of the following conditions:
the addition amount of the buffering agent is 1-10 wt% of the filter cake precursor;
the addition amount of the buffering agent is 3-5 wt% of the filter cake precursor;
the buffer is at least one selected from urea, ammonia water, sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide;
adjusting the pH value of the mixed solution to 10-11;
by using CO2Adjusting the pH value of the mixed solution;
the temperature of the hydrothermal reaction is 150-180 ℃, and the time is 3-8 h.
8. The method of claim 1, wherein step (5) satisfies at least one of the following conditions:
the addition amount of the hydrophobic modifier is 3-8 wt% of the filter cake precursor;
the hydrophobic modifier comprises at least one selected from stearic acid, sodium stearate, zinc stearate and calcium stearate;
the temperature of the modification reaction is 80-90 ℃, and the time is 3-8 h.
9. The method according to claim 1, wherein the reacted liquid in the step (5) is recycled to the step (3) and/or the step (4); and/or the presence of a gas in the gas,
and (3) supplementing alkali to the filtrate obtained in the step (2), and using the filtrate as electrolyte for the aluminum-air battery again.
10. A polyvinyl chloride film characterized by having a heat stabilizer comprising hydrotalcite obtained by the method according to any one of claims 1 to 9.
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| CN113526532A (en) * | 2021-06-30 | 2021-10-22 | 云南创能斐源金属燃料电池有限公司 | Method for treating waste electrolyte of aluminum-air battery |
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