Method for preparing zinc-aluminum-magnesium carbonate hydrotalcite from aluminum ash

Abstract

The invention provides a method for preparing zinc-aluminum-magnesium carbonate type hydrotalcite from aluminum ash, and belongs to the field of aluminum ash resource utilization. The method comprises the following steps: desalting aluminum ash to obtain desalted aluminum ash; the method comprises the following steps: dispersing desalted aluminum ash in an alkali solution, and after reaction gas overflows, carrying out microwave activation to obtain reaction slurry; leaching the reaction slurry at high temperature to obtain a sodium aluminate leaching solution; dropwise adding the sodium carbonate solution into the zinc and magnesium salt aqueous solution, and adjusting the pH value of the reaction system to 6-8 to obtain a first mixed solution containing zinc and magnesium carbonate precipitates; dropwise adding the leaching solution into the first mixed solution, and maintaining the pH value of a reaction system to 8.5-9 at the same time, so as to obtain a second mixed solution containing a zinc-aluminum-magnesium carbonate type hydrotalcite precursor; carrying out hydrothermal reaction on the second mixed solution to obtain a third mixed solution containing zinc-aluminum-magnesium carbonate type hydrotalcite; and the leaching efficiency of aluminum in the aluminum ash is improved while the zinc-aluminum-magnesium ternary carbonate type hydrotalcite with excellent product quality is prepared.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of aluminum dross resource utilization, and particularly relates to a method for preparing zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum dross. BACKGROUND

[0002] As an inorganic material with anionic layered structure, hydrotalcite has a wide application prospect in many fields such as catalysts, catalyst carriers, pesticides, sewage treatment agents, electrorheological modifiers, medicines, medicine carriers and petroleum industry due to its unique acid-base characteristics, thermal stability, interlayer anion exchange characteristics, memory effect and catalytic performance, and therefore has attracted high attention from researchers. With the continuous deepening of research, the synthesis and preparation methods of hydrotalcite are increasingly rich, and the core goal is to realize the controllable growth of hydrotalcite crystals, crystal size and crystal morphology by controlling the process conditions. Among the many preparation methods, the direct synthesis method is one of the main methods, and the coprecipitation method and the hydrothermal method are favored due to their simple process and easy operation. The coprecipitation method is to make the mixed solution of metal ions co-precipitate under the action of alkali, for example, the low supersaturation co-precipitation method, by adding the mixed salt solution and the mixed alkali solution according to certain conditions, and then the product is obtained through subsequent treatment, which is a commonly used method in the synthesis of hydrotalcite. The hydrothermal method is to age the slurry liquid in an autoclave at a certain temperature, and to promote crystallization by increasing the aging temperature and pressure to separate the nucleation and crystallization processes.

[0003] Secondary aluminum dross is an industrial waste, and if it can be effectively utilized, not only the recycling of resources can be realized, but also the pollution to the environment can be reduced. It has important practical significance to prepare zinc-aluminum-magnesium carbonate-type hydrotalcite by using secondary aluminum dross as raw material, leaching aluminum element therein, and adding zinc salt and magnesium salt as metal components according to the molar ratio, which can realize the efficient and high-value utilization of aluminum in aluminum dross, achieve the multiple purposes of resource utilization and environmental protection. In the leaching process of aluminum element, there are two ideas of acid leaching and alkaline leaching. However, acid leaching will make the metal impurities such as iron in the aluminum dross enter the leaching solution and then precipitate into the hydrotalcite precursor, affecting the product quality, and the removal process of iron is complex, difficult to handle and has limited efficiency. In order to avoid the influence of metal iron, it is more appropriate to choose the preparation of aluminum salt by alkaline leaching, but the leaching solution obtained by alkaline leaching is strongly alkaline, and when mixing with other metal elements such as zinc salt and magnesium salt to prepare a mixed salt solution, metal precipitates are easily generated, thereby affecting the uniformity of the subsequent reaction, which is not conducive to the preparation of zinc-aluminum-magnesium carbonate-type hydrotalcite with good product quality. Therefore, in order to prepare zinc-aluminum-magnesium carbonate-type hydrotalcite with good product quality and realize the efficient and high-value utilization of aluminum element in aluminum dross, so as to achieve the dual goals of resource recycling and environmental protection. SUMMARY

[0004] The application provides a method for preparing zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash, so as to solve the technical problem of how to improve the leaching efficiency of aluminum in aluminum ash while preparing zinc-aluminum-magnesium carbonate-type hydrotalcite with excellent product quality.

[0005] The application provides a method for preparing zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash, and the method comprises the following steps:

[0006] The aluminum ash is subjected to desalination treatment to obtain desalination aluminum ash;

[0007] The desalination aluminum ash is dispersed in an alkali solution, and after reaction gas overflows, microwave activation is performed under microwave conditions of a set microwave power and a set microwave time to obtain a reaction slurry;

[0008] The reaction slurry is subjected to high-temperature leaching to obtain a sodium aluminate leaching solution;

[0009] The sodium carbonate solution is added dropwise into a zinc-magnesium salt aqueous solution, and the pH of the reaction system is adjusted to 6-8 to obtain a first mixed solution containing zinc-magnesium carbonate precipitates;

[0010] The sodium aluminate leaching solution is added dropwise into the first mixed solution, and meanwhile, the pH of the reaction system is maintained at 8.5-9 to obtain a second mixed solution containing zinc-aluminum-magnesium carbonate-type hydrotalcite precursors;

[0011] The second mixed solution is subjected to hydrothermal reaction to obtain a third mixed solution; and

[0012] The third mixed solution is subjected to solid-liquid separation, washing and drying to obtain zinc-aluminum-magnesium carbonate-type hydrotalcite.

[0013] Optionally, the liquid-solid ratio of the mixed solution of the desalination aluminum ash and the alkali solution is (5-80):1.

[0014] Optionally, the molar concentration of the alkali solution is 1 mol / L-3.5 mol / L.

[0015] Optionally, the set microwave power is 500 W-900 W, and the set microwave time is 3 min-10 min.

[0016] Optionally, the leaching temperature of the high-temperature leaching is 60℃-90℃, and the leaching time of the high-temperature leaching is 2 h-4 h.

[0017] Optionally, the molar ratio of magnesium elements and zinc elements in the zinc-magnesium salt aqueous solution to aluminum elements in the sodium aluminate leaching solution is (2.8-3.2):1:(1.8-2.2).

[0018] Optionally, the molar ratio of the sodium carbonate to the aluminum element in the zinc and magnesium salt aqueous solution is (0.5-0.7):1.

[0019] Optionally, the temperature of the hydrothermal reaction is 110-160 DEG C, and the time of the hydrothermal reaction is 2-4 hours.

[0020] Optionally, the desalination treatment comprises the following parameters: the liquid-solid ratio of the mixture of the aluminum ash and water is (2.5-3.5):1, the reaction temperature is 35-45 DEG C, and the reaction time is 1.5-2.5 hours.

[0021] Optionally, the leaching efficiency of the aluminum in the sodium aluminate leaching solution is greater than or equal to 42%.

[0022] The zinc-aluminum-magnesium carbonate-type hydrotalcite has a layered structure, an average particle size less than 100 nm, a Pb content less than or equal to 0.0010%, and a Fe content less than or equal to 0.010%.

[0023] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages:

[0024] The embodiments of the present application provide a method for preparing a zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash, which comprises: desalination treatment of the aluminum ash to obtain desalination aluminum ash; dispersion of the desalination aluminum ash in an alkali solution, and microwave activation under a set microwave power and a set microwave time after reaction gas overflows to obtain a reaction slurry; high-temperature leaching of the reaction slurry to obtain a sodium aluminate leaching solution; dropwise addition of a sodium carbonate solution into a zinc and magnesium salt aqueous solution and adjustment of the pH of the reaction system to 6-8 to obtain a first mixture containing a zinc and magnesium carbonate precipitate; dropwise addition of the sodium aluminate leaching solution into the first mixture while maintaining the pH of the reaction system to 8.5-9 to obtain a second mixture containing a zinc-aluminum-magnesium carbonate-type hydrotalcite precursor; hydrothermal reaction of the second mixture to obtain a third mixture; and solid-liquid separation, washing and drying of the third mixture to obtain the zinc-aluminum-magnesium carbonate-type hydrotalcite.

[0025] On the one hand, through the microwave activation treatment, the "thermal effect" and "non-thermal effect" of the microwave are utilized to destroy the surface structure of the aluminum ash particles, accelerate the reaction of the aluminum and the alkali, and significantly improve the leaching activity of the aluminum; in combination with the subsequent high-temperature leaching, the dissolution of the aluminum is further promoted, the leaching efficiency of the aluminum in the aluminum ash is finally improved, and the efficient recovery of the aluminum resource in the aluminum ash is effectively realized;

[0026] On the other hand, first, the alkali leaching is adopted to make use of the chemical stability of impurities such as iron and lead under the alkaline condition, so that the impurities are left in the leaching residue to avoid entering the sodium aluminate solution; second, zinc and magnesium ions react with carbonate under pH 6-8 to preferentially form magnesium and zinc salt carbonate type seeds, and the lattice structure of these seeds matches the layer plate of hydrotalcite, providing ordered "sites" for subsequent aluminum ion intercalation; third, the sodium aluminate leaching solution is slowly added under pH 8.5-9, and AlO2 - is converted into Al 3+ , and grows into a layered structure through coordination with the remaining zinc and magnesium ions and interlayer carbonate; finally, the precursor is crystallized through hydrothermal reaction to form a regular layered structure. The step-by-step reaction avoids "disordered precipitation" caused by the simultaneous reaction of the three metal ions, ensuring the uniformity of the product structure.

[0027] Thus, while preparing zinc-aluminum-magnesium carbonate type hydrotalcite with excellent product quality, the leaching efficiency of aluminum in aluminum ash is improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor.

[0030] Figure 1 A flowchart of a method for preparing zinc-aluminum-magnesium carbonate type hydrotalcite from aluminum ash provided by the embodiments of the present application;

[0031] Figure 2 A flowchart of a method for preparing zinc-aluminum-magnesium carbonate type hydrotalcite from aluminum ash provided by the embodiments of the present application;

[0032] Figure 3 A physical diagram of zinc-aluminum-magnesium carbonate type hydrotalcite provided by Example 1 of the present application;

[0033] Figure 4 An XRD diagram of zinc-aluminum-magnesium carbonate type hydrotalcite provided by Example 1 of the present application;

[0034] Figure 5 An SEM diagram of zinc-aluminum-magnesium carbonate type hydrotalcite provided by Example 1 of the present application. DETAILED DESCRIPTION

[0035] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0036] The range descriptions described herein, such as numerical range, ratio range, etc., include all possible subranges and single values within the range, for example, the range description of "1 to 6" or "1-6" covers all subranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "include", "contain" and the like used herein mean "including but not limited to"; the relationship terms "first", "second" and the like are only used to distinguish different entities or operations, and do not imply actual sequence or relationship; "and / or" means that multiple cases can exist independently or simultaneously; "at least one", "multiple", "at least one" and the like refer to any combination of the corresponding objects, including single or multiple combinations of objects. The proportional relationship involved herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the proportional form according to the description order. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0037] The existing technology has a complex process for removing iron in the synthesis of zinc-aluminum-magnesium ternary carbonate-type hydrotalcite, and has limited treatment efficiency. In order to avoid the influence of metal iron, the present application uses an alkaline leaching method to prepare an aluminum salt. However, the leaching solution is strongly alkaline. In order to reduce the types and quantities of impurity ions in the leaching solution, and at the same time, avoid the reaction between the aluminum element dissolved in the strongly alkaline solution and the zinc and magnesium metal salt solution to form a precipitate, thereby affecting the uniformity and stability of the product quality. The present application uses an alkaline enhanced leaching method combined with metal directional precipitation to prepare zinc-aluminum-magnesium ternary carbonate-type hydrotalcite precursor, thereby improving the leaching efficiency of aluminum in secondary aluminum ash.

[0038] Based on this, the specific technical solutions of the present application are as follows:

[0039] Figure 1 A flowchart of a method for preparing zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash is provided for the embodiments of the present application; Figure 2 An actual flowchart of a method for preparing zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash is provided for the embodiments of the present application.

[0040] As Figure 1 and Figure 2As shown, the embodiments of the present application provide a method for preparing zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash, which comprises:

[0041] S1, desalination treatment is performed on the aluminum ash to obtain desalination aluminum ash;

[0042] The desalination treatment can remove the soluble salts (such as sodium chloride, potassium chloride, etc.) in the aluminum ash, avoid the interference of the salts with the dissolution efficiency of aluminum during subsequent alkali leaching, and reduce the impurity ion concentration in the leaching solution.

[0043] In some embodiments, the desalination treatment comprises the following parameters: the liquid-solid ratio of the mixed solution of aluminum ash and water is (2.5-3.5):1, the reaction temperature is 35-45°C, and the reaction time is 1.5-2.5h.

[0044] Limiting the liquid-solid ratio to (2.5-3.5):1 can ensure that the salts are fully dissolved, while avoiding excessive dilution of the aluminum ash. If the liquid-solid ratio is lower than 2.5:1, the water usage is insufficient, and the soluble salts cannot be completely dissolved; if it is higher than 3.5:1, the solution is excessively diluted, increasing the energy consumption and cost of subsequent treatment. Limiting the temperature to 35-45°C can accelerate the dissolution of the salts (the solubility of the salts increases slightly with the increase of temperature). If the temperature is lower than 35°C, the dissolution rate of the salts is slow, and the desalination efficiency decreases; if it is higher than 45°C, the water evaporates too quickly, causing the local salt concentration to increase, which in turn affects the dissolution effect. Limiting the time to 1.5-2.5h can ensure that the salts are fully dissolved. If the time is shorter than 1.5h, the desalination is incomplete, and the residual salts will interfere with the subsequent aluminum leaching; if it is longer than 2.5h, there is no additional desalination effect, and the energy consumption increases. Exemplarily, the liquid-solid ratio of the mixed solution of aluminum ash and water can be 2.5:1, 2.7:1, 2.9:1, 3.0:1, 3.2:1, 3.4:1, 3.5:1, etc., the reaction temperature can be 35°C, 37°C, 39°C, 40°C, 42°C, 45°C, etc., and the reaction time can be 1.5h, 1.7h, 1.9h, 2.1h, 2.3h, 2.5h, etc.

[0045] S2, dispersing the desalination aluminum ash in an alkali solution, and performing microwave activation under microwave conditions of a set microwave power and a set microwave time after the reaction gas overflows to obtain a reaction slurry;

[0046] The microwave activation can destroy the surface structure of the aluminum ash particles, accelerate the reaction of aluminum and alkali, and improve the leaching activity of aluminum.

[0047] In some embodiments, the liquid-solid ratio of the mixed solution of the desalination aluminum ash and the alkali solution is (5-80):1.

[0048] In some embodiments, the molar concentration of the alkali solution is 1-3.5mol / L.

[0049] The liquid-solid ratio of the desalted aluminum ash and the alkali solution is limited to (5-80):1, which can balance the contact efficiency of the aluminum ash and the alkali and the flowability of the solution. If the liquid-solid ratio is lower than 5:1, the concentration of the aluminum ash is too high, the alkali solution is adsorbed, and the reaction is insufficient; if the liquid-solid ratio is higher than 80:1, the concentration of the alkali is excessively diluted, and the leaching efficiency is significantly reduced. The concentration of the alkali solution is limited to 1 mol / L-3.5 mol / L, and the aluminum reacts under the alkaline condition. If the concentration is lower than 1 mol / L, the reaction rate of the aluminum and the alkali is slow, and the leaching efficiency of the aluminum is significantly reduced; if the concentration is higher than 3.5 mol / L, the excessive alkali will cause the acid consumption to increase sharply during the subsequent pH adjustment, increase the cost, and introduce impurities. Exemplarily, the liquid-solid ratio of the mixture of the desalted aluminum ash and the alkali solution is 5:1, 10:1, 20:1, 30:1, 40:1, 60:1, 80:1, etc., and the molar concentration of the alkali solution can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, etc.

[0050] In some embodiments, the microwave power is set to 500W-900W, and the microwave time is set to 3min-10min.

[0051] The microwave power is limited to 500W-900W, and the time is limited to 3min-10min. The "thermal effect" and "non-thermal effect" of the microwave can destroy the surface oxide layer of the aluminum ash and promote the penetration of the alkali solution. If the power is lower than 500W or the time is shorter than 3min, the activation is insufficient, and the structure of the aluminum ash is not effectively destroyed; if the power is higher than 900W or the time is longer than 10min, local overheating is caused, and the stability of sodium metaaluminate is destroyed. Exemplarily, the microwave power can be 500W, 600W, 700W, 800W, 900W, etc., and the time can be 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, etc.

[0052] S3, high-temperature leaching is performed on the reaction slurry to obtain a sodium aluminate leaching solution;

[0053] On the basis of microwave activation, the dissolution of aluminum in the aluminum ash is further promoted by high temperature, and it is ensured that the aluminum is fully converted into sodium metaaluminate and enters the solution.

[0054] In some embodiments, the leaching temperature of the high-temperature leaching is 60°C-90°C, and the leaching time of the high-temperature leaching is 2h-4h.

[0055] The leaching temperature is limited to 60-90℃, and the increase of temperature significantly accelerates the reaction rate of aluminum and alkali. If the temperature is lower than 60℃, the reaction rate is slow, and the aluminum leaching is incomplete; if the temperature is higher than 90℃, the solution is easy to boil, leading to too fast evaporation of water, increase of alkali concentration, and inhibition of the reaction. The leaching time is limited to 2-4h, which can ensure the sufficient reaction of soluble aluminum in the aluminum ash. If the time is shorter than 2h, the leaching is incomplete; if the time is longer than 4h, there is no additional leaching gain, and the energy consumption is increased. Exemplarily, the leaching temperature of high-temperature leaching can be 60℃, 70℃, 80℃, 85℃, 90℃, etc., and the leaching time of high-temperature leaching can be 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0056] S4, drop the sodium carbonate solution into the zinc and magnesium salt aqueous solution, and adjust the pH of the reaction system to 6-8 to obtain a first mixed solution containing zinc and magnesium carbonate precipitate;

[0057] By allowing the zinc and magnesium ions to first react with carbonate ions to form stable carbonate crystal seeds, a "template" is provided for the subsequent embedding of aluminum ions, ensuring the ordered growth of the layered structure.

[0058] Adjusting the pH of the reaction system to 6-8, under weakly acidic to neutral conditions, zinc and magnesium ions preferentially react with carbonate ions to form carbonate precipitate. If the pH is lower than 6, the strong acidity will cause the decomposition of carbonate ions into CO2, and stable precipitate cannot be formed; if the pH is higher than 8, zinc and magnesium ions will form hydroxide impurities, which will destroy the purity of the crystal seeds. Exemplarily, the pH of the reaction system can be adjusted to 6, 6.5, 7, 7.5, 8, etc.

[0059] In some embodiments, the molar ratio of the sodium carbonate to the aluminum element in the zinc and magnesium salt aqueous solution is (0.5-0.7):1.

[0060] The molar ratio of sodium carbonate to aluminum is limited to 0.5-0.7:1, and carbonate ions are interlayer anions of hydrotalcite. If the ratio is lower than 0.5:1, the interlayer anions are insufficient, and the structure is incomplete; if the ratio is higher than 0.7:1, excess carbonate ions form non-layered carbonate impurities with metal ions. Exemplarily, the molar ratio of sodium carbonate to the aluminum element in the zinc and magnesium salt aqueous solution can be 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, etc.

[0061] S5, drop the sodium aluminate leaching solution into the first mixed solution, and at the same time, maintain the pH of the reaction system to 8.5-9 to obtain a second mixed solution containing zinc aluminum magnesium carbonate-type hydrotalcite precursor;

[0062] It should be noted that in the S4 and S5 steps in the present application, hydrochloric acid and / or NaOH solution is used to adjust the pH of the reaction system.

[0063] The sodium aluminate leaching solution (strong alkaline) is slowly introduced into the zinc, magnesium carbonate seed system, and under precise pH control, the aluminum ions are combined with the remaining zinc, magnesium ions and carbonate to form a zinc aluminum magnesium hydrotalcite precursor. At the same time, in step S5, the sodium aluminate and the pH regulator need to be added synchronously. The sodium aluminate is strong alkaline, and if it is added alone, it will cause a sudden increase in local pH (> 9), generating amorphous aluminum hydroxide gel, which cannot be stirred. Synchronous pH adjustment can maintain the uniformity of the system's acidity and alkalinity, ensuring uniform intercalation of aluminum ions into the seeds.

[0064] Meanwhile, the pH of the reaction system is maintained at 8.5-9, which is the best condition for the formation of zinc aluminum magnesium hydrotalcite. If the pH is lower than 8.5, AlO2 - is not fully converted to Al 3+ , and the carbonate is easily decomposed; if the pH is higher than 9, CO3 2- competes for insertion, resulting in the formation of impurity phase ZnCO3. Exemplary, the pH of the reaction system is maintained at 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, etc.

[0065] In some embodiments, the molar ratio of magnesium elements and zinc elements in the zinc, magnesium salt aqueous solution to aluminum elements in the sodium aluminate leaching solution is (2.8-3.2):1:(1.8-2.2).

[0066] The molar ratio of magnesium: zinc: aluminum is limited to (2.8-3.2):1:(1.8-2.2), and the layered structure of hydrotalcite requires a fixed ratio of divalent metals (Zn 2+ , Mg 2+ ) and trivalent metals (Al 3+ ). If the ratio is lower than (2.8:1:1.8), the divalent metal is insufficient, and the layered structure is prone to collapse; if it is higher than (3.2:1:2.2), the proportion of trivalent metal is too low, and the structural stability decreases. Exemplary, the molar ratio of magnesium elements and zinc elements in the zinc, magnesium salt aqueous solution to aluminum elements in the sodium aluminate leaching solution can be 2.8:1:1.8, 2.9:1:1.9, 3.0:1:2.0, 3.1:1:2.1, 2.85:1:1.85, 2.95:1:1.95, 3.05:1:2.05, 3.15:1:2.15, etc.

[0067] S6, performing a hydrothermal reaction on the second mixed solution to obtain a third mixed solution; and

[0068] Under high temperature and high pressure environment, the hydrotalcite precursor undergoes crystal growth and structure optimization, improving the crystallinity and layered order. Thus, the precursor crystallization is promoted by hydrothermal reaction to form a regular layered structure.

[0069] In some embodiments, the temperature of the hydrothermal reaction is 110-160°C, and the time of the hydrothermal reaction is 2-4h.

[0070] The temperature is limited to 110-160°C, and the diffusion ability of water molecules is enhanced under the hydrothermal condition, which promotes the ion rearrangement and the crystal growth. If the temperature is lower than 110°C, the crystallization rate is slow and the structure is loose; if the temperature is higher than 160°C, the interlayer water or carbonate is removed, which destroys the layered structure. The hydrothermal time is limited to 2-4h, which can ensure the full growth of the crystal. If the time is shorter than 2h, the crystallization is incomplete and the particle size distribution is uneven; if the time is longer than 4h, the crystal is easy to agglomerate and the particle size is more than 100nm. For example, the temperature of the hydrothermal reaction can be 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 125°C, 145°C, etc. The time of the hydrothermal reaction can be 2h, 2.5h, 3h, 3.5h, 4h, 2.2h, 3.2h, 3.8h, etc.

[0071] S7, performing solid-liquid separation, washing and drying on the third mixed solution to obtain zinc-aluminum-magnesium carbonate-type hydrotalcite.

[0072] In some embodiments, the solid-liquid separation of the reaction product uses one or more of centrifugal separation, plate and frame filter pressing, belt filtration and vacuum filtration.

[0073] In some embodiments, the drying of the reaction product uses one or more of an oven, a rotary dryer, a plate dryer and a vacuum dryer.

[0074] In some embodiments, the leaching efficiency of aluminum in the sodium aluminate leaching solution is ≥42%;

[0075] The zinc-aluminum-magnesium carbonate-type hydrotalcite has a layered structure, an average particle size of less than 100nm, a Pb content of ≤0.0010% and a Fe content of ≤0.010%.

[0076] Thus, the leaching efficiency of aluminum in the aluminum ash is improved by microwave activation of the aluminum ash; a preparation method is developed in which first, magnesium and zinc salt carbonates are reacted to form magnesium and zinc carbonate seed crystals, and then aluminum ash leaching solution and acid are added to generate a layered zinc-aluminum-magnesium hydrotalcite structure, which avoids the introduction of iron impurities in the acid leaching process, and also avoids the need to repeatedly adjust the pH of the solution when zinc, aluminum, and magnesium are simultaneously reacted with carbonates, which results in waste of raw materials and increased costs, reduces the treatment of salt-containing wastewater, and the zinc-aluminum-magnesium carbonate hydrotalcite prepared by this method has the advantages of uniform and stable product quality. Exemplarily, the leaching efficiency of aluminum in the sodium aluminate leaching solution can be 42%, 45%, 50%, 55%, 60%, 43%, 48%, 52%, etc. The average particle size of the zinc-aluminum-magnesium carbonate hydrotalcite can be 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 85 nm, 75 nm, 65 nm, etc. The Pb content of the zinc-aluminum-magnesium carbonate hydrotalcite can be 0.0010%, 0.0008%, 0.0006%, 0.0005%, 0.0004%, 0.0009%, 0.0007%, 0.0003%, etc. The Fe content of the zinc-aluminum-magnesium carbonate hydrotalcite can be 0.010%, 0.008%, 0.006%, 0.005%, 0.004%, 0.009%, 0.007%, 0.003%, etc.

[0077] In summary, the method for preparing zinc-aluminum-magnesium carbonate hydrotalcite from aluminum ash disclosed in the present application has significant advantages in raw material utilization, process optimization, and product quality, as follows:

[0078] (1) Improve the leaching efficiency of aluminum in the aluminum ash and improve the utilization rate of raw materials: through microwave activation treatment (S2), the "thermal effect" and "non-thermal effect" of microwaves are used to destroy the surface structure of aluminum ash particles, accelerate the reaction of aluminum and alkali, and significantly improve the leaching activity of aluminum; combined with subsequent high-temperature leaching (S3), the dissolution of aluminum is further promoted, and the leaching efficiency of aluminum can reach 42% or more, effectively realizing the efficient recovery of aluminum resources in aluminum ash.

[0079] (2) Optimize process design, reduce costs and pollution: desalination treatment is precisely controllable, by limiting the liquid-solid ratio, temperature and time (S1), while ensuring the sufficient removal of soluble salts, the solution is prevented from being excessively diluted, the energy consumption and cost of subsequent treatment are reduced, the generation and treatment pressure of salt-containing wastewater are reduced. At the same time, the step-by-step reaction reduces waste, and the step-by-step process of "first preparing zinc and magnesium carbonate seeds (S4), and then introducing sodium aluminate leaching solution (S5)" avoids the waste of raw materials and the increase in costs caused by the need to repeatedly adjust the pH when zinc, aluminum, and magnesium are simultaneously reacted with carbonates, and reduces the complexity of process operation. In addition, the introduction of impurities is avoided, and the aluminum ash is leached by alkali method (S2-S3) instead of acid method, which avoids the introduction of iron and other impurities in the acid leaching process from the source, and reduces the difficulty of product purification.

[0080] (3) The product has excellent quality and stable performance: the structure and particle size of the prepared zinc-aluminum-magnesium carbonate-type hydrotalcite are controllable, the product has a regular layered structure, the average particle size is less than 100 nm, the crystallinity is high and the distribution is uniform; the product has high purity and low impurity content, the lead (Pb) content is less than or equal to 0.0010%, the iron (Fe) content is less than or equal to 0.010%, effectively meeting the application requirements of high purity; the quality is stable and uniform, the seed method (S4) provides a "template" for the growth of the layered structure, combined with precise pH control (S4-S5) and hydrothermal reaction (S6), to ensure that the product has an ordered structure and stable performance.

[0081] (4) The process is green and economical, and has strong feasibility: through parameter optimization (such as liquid-solid ratio, temperature, time, etc.), the efficiency is ensured while the energy consumption is reduced (such as avoiding excessive heating and shortening the invalid reaction time); and the industrial solid waste aluminum ash is used as raw material, realizing "waste to treasure", and having both environmental and economic benefits.

[0082] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods in the following examples are not specified, which are generally determined according to the industry standards. If there is no corresponding industry standard, the general international standards, conventional conditions, or the conditions suggested by the manufacturers are used.

[0083] Example 1

[0084] Desalted aluminum ash was prepared by using aluminum ash as raw material, controlling the liquid-solid ratio to be 3, the reaction temperature to be 40℃, and the reaction time to be 2h. The desalted aluminum ash was dispersed in a 1mol / L NaOH solution, and after 3min of 500W microwave activation, it was leached at 60℃ for 2h, and then sodium aluminate filtrate was obtained after filtration. A mixed solution of magnesium chloride and zinc chloride was prepared according to the molar ratio of magnesium, zinc and aluminum in the leaching solution being 3:1:2, and sodium carbonate solution was slowly added to the mixed solution, while the pH value of the reaction system was controlled by hydrochloric acid solution to be 6. After the addition was completed, sodium metaaluminate leaching solution was slowly added to the mixed system, while the pH value of the reaction system was controlled by hydrochloric acid solution to be 8.5. The reaction mixture was transferred to a reaction kettle for hydrothermal reaction at 120℃ for 2h, and then zinc-aluminum-magnesium hydrotalcite was obtained after filtration, washing and drying. Analysis showed that the aluminum leaching efficiency in the leaching solution was 42%, the Pb content in the zinc-aluminum-magnesium hydrotalcite was 0.0006%, and the Fe content was 0.004%.

[0085] Example 2

[0086] Desalted aluminum ash was prepared by using aluminum ash as raw material, controlling liquid-solid ratio as 3, reaction temperature as 40℃ and reaction time as 2h. The desalted aluminum ash was dispersed in 3mol / L NaOH solution, and after 5min microwave activation at 600W, the aluminum ash was leached at 90℃ for 4h. After filtration, sodium aluminate filtrate was obtained. Magnesium chloride and zinc chloride mixed solution was prepared according to the molar ratio of magnesium, zinc and aluminum in the leaching solution as 3:1:2, and sodium carbonate solution was slowly added into the mixed solution, while the pH value of the reaction system was controlled to 6.5 by hydrochloric acid solution. After the addition was completed, sodium metaaluminate leaching solution was slowly added into the mixed system, while the pH value of the reaction system was controlled to 9 by hydrochloric acid solution. The reaction mixture was transferred to a reaction kettle for hydrothermal reaction at 160℃ for 4h. After filtration, washing and drying, zinc-aluminum-magnesium hydrotalcite was obtained. Analysis showed that the aluminum leaching efficiency in the leaching solution was 78%, the content of Pb in the zinc-aluminum-magnesium hydrotalcite was 0.0009%, and the content of Fe was 0.01%.

[0087] Example 3

[0088] Desalted aluminum ash was prepared by using aluminum ash as raw material, controlling liquid-solid ratio as 3, reaction temperature as 40℃ and reaction time as 2h. The desalted aluminum ash was dispersed in 2mol / L NaOH solution, and after 5min microwave activation at 700W, the aluminum ash was leached at 70℃ for 2h. After filtration, sodium aluminate filtrate was obtained. Magnesium chloride and zinc chloride mixed solution was prepared according to the molar ratio of magnesium, zinc and aluminum in the leaching solution as 3:1:2, and sodium carbonate solution was slowly added into the mixed solution, while the pH value of the reaction system was controlled to 7 by hydrochloric acid solution. After the addition was completed, sodium metaaluminate leaching solution was slowly added into the mixed system, while the pH value of the reaction system was controlled to 8.5 by hydrochloric acid solution. The reaction mixture was transferred to a reaction kettle for hydrothermal reaction at 150℃ for 4h. After filtration, washing and drying, zinc-aluminum-magnesium hydrotalcite was obtained. Analysis showed that the aluminum leaching efficiency in the leaching solution was 62%, the content of Pb in the zinc-aluminum-magnesium hydrotalcite was 0.0008%, and the content of Fe was 0.006%.

[0089] Example 4

[0090] Desalted aluminum ash was prepared by using aluminum ash as raw material, controlling liquid-solid ratio of 3, reaction temperature of 40℃ and reaction time of 2h. The desalted aluminum ash was dispersed in 3mol / L NaOH solution, and after microwave activation for 10min at 900W, leaching was carried out at 70℃ for 4h. After filtration, sodium aluminate filtrate was obtained. Magnesium chloride and zinc chloride mixed solution was prepared according to the molar ratio of magnesium, zinc and aluminum in the leaching solution of 3:1:2, and sodium carbonate solution was slowly added into the mixed solution, while the pH value of the reaction system was controlled to 6 by hydrochloric acid solution. After the addition was completed, sodium metaaluminate leaching solution was slowly added into the mixed system, while the pH value of the reaction system was controlled to 9 by hydrochloric acid solution. The reaction mixture was transferred to a reaction kettle for hydrothermal reaction at 140℃ for 4h. After filtration, washing and drying, zinc-aluminum-magnesium hydrotalcite was obtained. Analysis showed that the aluminum leaching efficiency in the leaching solution was 68%, the content of Pb in the zinc-aluminum-magnesium hydrotalcite was lower than the detection limit, and the content of Fe was 0.007%.

[0091] Example 5

[0092] Desalted aluminum ash was prepared by using aluminum ash as raw material, controlling liquid-solid ratio of 3, reaction temperature of 40℃ and reaction time of 2h. The desalted aluminum ash was dispersed in 3mol / L NaOH solution, and after microwave activation for 10min at 700W, leaching was carried out at 90℃ for 3h. After filtration, sodium aluminate filtrate was obtained. Magnesium chloride and zinc chloride mixed solution was prepared according to the molar ratio of magnesium, zinc and aluminum in the leaching solution of 3:1:2, and sodium carbonate solution was slowly added into the mixed solution, while the pH value of the reaction system was controlled to 7 by hydrochloric acid solution. After the addition was completed, sodium metaaluminate leaching solution was slowly added into the mixed system, while the pH value of the reaction system was controlled to 8.5 by hydrochloric acid solution. The reaction mixture was transferred to a reaction kettle for hydrothermal reaction at 160℃ for 3h. After filtration, washing and drying, zinc-aluminum-magnesium hydrotalcite was obtained. Analysis showed that the aluminum leaching efficiency in the leaching solution was 67%, the content of Pb in the zinc-aluminum-magnesium hydrotalcite was lower than the detection limit, and the content of Fe was 0.008%.

[0093] Comparative Example 1

[0094] Desalinated aluminum ash was prepared using aluminum ash as raw material, with a liquid-to-solid ratio of 3, a reaction temperature of 40℃, and a reaction time of 2 hours. The desalinated aluminum ash was dispersed in a 3 mol / L NaOH solution and leached at 70℃ for 4 hours. After filtration, sodium aluminate filtrate was obtained. A mixed solution of magnesium chloride and zinc chloride was prepared according to a molar ratio of magnesium, zinc, and aluminum in the leaching solution of 3:1:2. Sodium carbonate solution was slowly added dropwise to the mixed solution, while the pH of the reaction system was controlled at 6 using hydrochloric acid solution. After the addition was completed, sodium aluminate leaching solution was slowly added dropwise to the mixed system, while the pH of the reaction system was controlled at 9 using hydrochloric acid solution. The reaction mixture was transferred to a reactor and hydrothermally reacted at 140℃ for 4 hours. After filtration, washing, and drying, zinc-aluminum-magnesium hydrotalcite was obtained. Analysis showed that the aluminum leaching efficiency in the leaching solution was 38%, the Pb content in the zinc-aluminum-magnesium hydrotalcite was below the detection limit, and the Fe content was 0.007%.

[0095] The aluminum leaching efficiency, Pb content, and Fe content in zinc-aluminum-magnesium hydrotalcite of Examples 1-5 and Comparative Example 1 are summarized, and the results are shown in Table 1.

[0096] Table 1. Aluminum leaching efficiency, Pb content, and Fe content in zinc-aluminum-magnesium hydrotalcite of Examples 1-5 and Comparative Example 1.

[0097] Group Aluminium leaching efficiency, % Pb content in zinc aluminium magnesium hydrotalcite, wt.% Fe content in zinc aluminium magnesium hydrotalcite, wt.% Example 1 42 0.0006 0.004 Example 2 78 0.0009 0.010 Example 3 62 0.0008 0.006 Example 4 68 Below detection limit 0.007 Example 5 67 Below detection limit 0.008 Comparative Example 1 38 Below detection limit 0.007

[0098] As shown in Table 1, the leaching efficiency of aluminum in the sodium aluminate leaching solution in Examples 1 to 5 is ≥42%, and the Pb content and Fe content of the zinc aluminum magnesium carbonate root-type hydrotalcite are ≤0.0010% and ≤0.010%, respectively.

[0099] The difference between Comparative Example 1 and the Example is that the microwave activation step was missing, the aluminum ash structure was not effectively destroyed, and the reaction between aluminum and alkali was insufficient, so the aluminum leaching efficiency was only 38%.

[0100] Figure 3 This is a physical image of the zinc-aluminum-magnesium carbonate root-type hydrotalcite provided in Example 1 of this application.

[0101] Depend on Figure 3 It can be seen that zinc aluminum magnesium carbonate root-type hydrotalcite is in the form of a white powder and has good dispersibility.

[0102] Figure 4 The image shows the XRD pattern of the zinc-aluminum-magnesium carbonate root-type hydrotalcite provided in Example 1 of this application.

[0103] Depend on Figure 4 It can be seen that the zinc-aluminum-magnesium carbonate root-type hydrotalcite has a complete crystal structure, and its XRD pattern shows small-angle diffraction, exhibiting characteristics of nanomaterials.

[0104] Figure 5 This is a SEM image of the zinc-aluminum-magnesium carbonate root-type hydrotalcite provided in Example 1 of this application.

[0105] Depend on Figure 5 It can be seen that zinc-aluminum-magnesium carbonate root-type hydrotalcite has uniform particle size, a layered structure, good dispersibility, and an average particle size of less than 100 nm.

[0106] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0107] In this embodiment, the leaching rate of aluminum in aluminum ash is improved, avoiding the problems of high iron content in the leachate, complex removal process, high treatment difficulty, and limited treatment efficiency. At the same time, it avoids the waste of raw materials and increased costs caused by repeated pH adjustment when using alkaline sodium aluminate leachate as raw material. The hydrotalcite product prepared by this invention has uniform quality, simple process, low cost, and high hydrotalcite preparation efficiency, which has great advantages.

[0108] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a zinc-aluminum-magnesium carbonate-type hydrotalcite from aluminum ash, the method comprising: subjecting the aluminum ash to a desalting treatment to obtain desalted aluminum ash; dispersing the desalted aluminum ash in an alkali solution, and, after the overflow of reaction gas, subjecting the mixture to microwave activation under microwave conditions of a set microwave power and a set microwave time to obtain a reaction slurry; subjecting the reaction slurry to high-temperature leaching to obtain a sodium aluminate leaching solution; adding a sodium carbonate solution to a zinc-magnesium salt aqueous solution and adjusting the pH of the reaction system to 6-8 to obtain a first mixture containing a zinc-magnesium carbonate precipitate; adding the sodium aluminate leaching solution to the first mixture while maintaining the pH of the reaction system to 8.5-9 to obtain a second mixture containing a zinc-aluminum-magnesium carbonate-type hydrotalcite precursor; subjecting the second mixture to a hydrothermal reaction to obtain a third mixture; and subjecting the third mixture to solid-liquid separation, washing, and drying to obtain a zinc-aluminum-magnesium carbonate-type hydrotalcite. The liquid-solid ratio of the mixture of the desalted aluminum ash and the alkali solution is (5-80):

1.

2. The method of claim 1, wherein, The molar concentration of the alkali solution is 1 mol / L-3.5 mol / L.

3. The method of claim 2, wherein, The set microwave power is 500 W-900 W, and the set microwave time is 3 min-10 min.

4. The method of claim 1, wherein, The leaching temperature of the high-temperature leaching is 60℃-90℃, and the leaching time of the high-temperature leaching is 2 h-4 h.

5. The method of claim 1, wherein, The molar ratio of magnesium and zinc in the zinc-magnesium salt aqueous solution to aluminum in the sodium aluminate leaching solution is (2.8-3.2):1:(1.8-2.2).

6. The method of claim 1, wherein, The molar ratio of sodium carbonate to aluminum in the zinc-magnesium salt aqueous solution is (0.5-0.7):

1.

7. The method of claim 1, wherein, The temperature of the hydrothermal reaction is 110℃-160℃, and the time of the hydrothermal reaction is 2 h-4 h.

8. The method of claim 1, wherein, The desalting treatment comprises the following parameters: the liquid-solid ratio of the mixture of aluminum ash and water is (2.5-3.5):1, the reaction temperature is 35℃-45℃, and the reaction time is 1.5 h-2.5 h.

9. The method of claim 1, wherein, The leaching efficiency of aluminum in the sodium aluminate leaching solution is ≥42%; 10. The method of claim 1, wherein, The zinc-aluminum-magnesium carbonate-type hydrotalcite has a layered structure, an average particle size of less than 100 nm, a Pb content of ≤0.0010%, and a Fe content of ≤0.010%. ​

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