A method for preparing high-purity zinc compounds using zinc suboxide

Abstract

The application provides a method for preparing high-purity zinc compounds by using secondary zinc oxide, and belongs to the technical field of metal smelting. The method comprises the following steps: taking secondary zinc oxide as raw material, preparing a crude zinc sulfate solution through pre-washing and sulfuric acid leaching, removing fluorine ions by using an aluminum-based composite fluorine removal agent, and regenerating the fluorine removal residue containing aluminum-fluorine complexes by using ammonia water, so that the fluorine is transferred into a liquid phase and the aluminum is restored into an active phase of aluminum hydroxide; the regenerated wet filter residue is directly returned to the fluorine removal process for recycling; the regenerated liquid is added with a calcium source to generate calcium fluoride and recover ammonia; meanwhile, low-fluorine solution is subjected to calcium removal by using ammonium carbonate, and then is subjected to electrodialysis dechlorination; after purification, alkali zinc carbonate is precipitated by using ammonium bicarbonate; the mother liquor is stabilized by using ammonium phosphate to stabilize residual calcium, fluorine and heavy metals, and is then resourceized into an ammonium sulfate byproduct; and high-purity zinc oxide powder is obtained by washing, drying and thermal decomposition of the alkali zinc carbonate, and can be used in the fields of piezoresistors, external antibacterial preparations and ceramic glazes.

Description

Technical Field

[0001] This invention relates to the field of metal smelting technology, and more specifically to a method for preparing high-purity zinc compounds using zinc oxide. Background Technology

[0002] Currently, wet leaching is one of the main methods for preparing high-purity zinc compounds from zinc oxide. This method often uses sulfuric acid or sodium hydroxide leaching, combined with precipitation and impurity removal steps to obtain zinc compounds. However, it generally suffers from problems such as difficulty in removing fluoride and chloride ions, complex processes, or insufficient product purity. Therefore, how to achieve deep removal of impurities while simplifying the process remains a technical challenge that urgently needs to be solved in this field.

[0003] To address the above issues, CN114906871B discloses a method for preparing nano-zinc oxide using zinc oxide. This method involves selectively leaching zinc oxide with sodium hydroxide, allowing zinc to enter the solution as zincate ions. The solution is then pH-adjusted with sulfuric acid to precipitate impurities such as lead, aluminum, and silicon. Finally, sodium carbonate is used to precipitate zinc, followed by thermal decomposition to prepare nano-zinc oxide. However, the introduction of sodium hydroxide and sodium carbonate not only results in a large amount of sodium ions entering the process, making it difficult to completely remove sodium residues from the product and failing to meet the low-sodium requirement for electronic-grade zinc oxide, but also leaves the entire process without any measures to remove anionic impurities such as fluorine and chlorine, leading to excessive fluorine and chlorine content in the product. Furthermore, simply adjusting the pH once to precipitate impurities is insufficient to effectively remove heavy metals such as iron, copper, cadmium, and lead, thus limiting product purity. CN121344373B discloses a zinc extraction process from zinc oxide, employing rotary kiln roasting and using composite porous sheet-like reducing carbon prepared from waste paper, rice husks, and wood chips as a reducing agent. This process reduces and volatilizes the zinc-containing solid material before oxidizing and recovering the zinc oxide. This process is essentially a pyrometallurgical enrichment process, and the final product is only a coarse zinc oxide powder with a zinc oxide content of about 85%-87%, which is far from meeting the purity requirements of high-purity zinc compounds. At the same time, the pyrometallurgical process cannot effectively remove impurities such as fluorine and chlorine. These impurities will re-enter the product when they are condensed after volatilization at high temperature, resulting in uncontrollable fluorine and chlorine residues. In addition, the additives such as reducing carbon and calcium oxide introduced in the process themselves become new sources of impurities.

[0004] In summary, existing wet processes suffer from drawbacks such as the introduction of sodium ions and the inability to remove fluorine and chlorine, while pyrometallurgical processes can only yield low-purity crude zinc oxide. Neither can directly produce high-purity zinc oxide with extremely low levels of impurities such as fluorine, chlorine, sodium, and calcium from zinc oxide as a raw material. Therefore, there is an urgent need to develop a sodium-free, fully sodium-free preparation method capable of deep removal of fluorine, chlorine, and heavy metal impurities, with a closed-loop controllable process, to achieve the efficient conversion of zinc oxide into high-purity zinc compounds. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for preparing high-purity zinc compounds using zinc oxide. The method involves using zinc oxide as raw material, pre-washing and leaching with sulfuric acid to obtain a crude zinc sulfate solution, using an aluminum-based composite defluorinating agent to remove fluoride ions, and regenerating the defluorinating residue containing aluminum-fluorine complexes with ammonia water. This process transfers fluoride into the liquid phase and restores aluminum to the active phase of aluminum hydroxide. The regenerated wet filter residue is directly returned to the defluorination process for recycling. A calcium source is added to the regenerated liquid to generate calcium fluoride and recover ammonia. Simultaneously, the low-fluoride solution undergoes calcium removal via ammonium carbonate followed by electrodialysis dechlorination. After further purification, basic zinc carbonate is precipitated with ammonium bicarbonate. The mother liquor is stabilized with ammonium phosphate to remove residual calcium, fluoride, and heavy metals, and then recycled as an ammonium sulfate byproduct. The basic zinc carbonate is washed, dried, and thermally decomposed to obtain high-purity zinc oxide powder, which can be applied in fields such as varistors, topical antibacterial agents, or ceramic glazes. It solves the technical problems such as the generation of a large amount of hazardous waste from the one-time use of defluorinating agents in the traditional wet smelting of high-purity zinc compounds, the loss of zinc ions due to encapsulation during the traditional defluorination process, and the scaling of calcium ions on the membrane surface during electrodialysis dechlorination.

[0006] This invention proposes a method for preparing high-purity zinc compounds using zinc oxide, such as... Figure 1 As shown, the specific technical solution is as follows:

[0007] Step 1: After mixing zinc oxide with deionized water, the mixture is washed and filtered in multiple stages. The washed filter cake is then placed in a reaction vessel and deionized water and sulfuric acid are added to adjust the pH. After heating and reacting twice, the mixture is filtered to obtain a crude zinc sulfate solution. The washing waste liquid is then treated with heavy metals and crystallized salts. The condensate after treatment is recycled as washing liquid.

[0008] Step 2: Add zinc oxide powder to aluminum sulfate solution and heat. Add ammonia water dropwise to adjust the pH and let stand to obtain wet aluminum-zinc composite defluorinating agent. Then add the defluorinating agent to crude zinc sulfate solution, heat and stir, and filter to obtain low-fluoride zinc sulfate solution and defluorinating residue. Mix the defluorinating residue with ammonia water for regeneration and filter to obtain regenerated liquid and regenerated wet filter residue. Add calcium carbonate to the regenerated liquid and heat to react to obtain calcium fluoride precipitate.

[0009] Step 3: Add hydrogen peroxide to the low-fluoride zinc sulfate solution, add ammonia water to adjust the pH, filter and add zinc powder. Then pump the filtrate into an ion exchange column loaded with aminophosphonic acid macroporous resin. After cyclic adsorption, zinc sulfate solution is obtained, and electrodialysis dechlorination is performed using a monovalent selective anion exchange membrane / cation exchange membrane stack.

[0010] Step 4: After heating the dechlorinated desalinated liquid, add ammonium bicarbonate to adjust the pH and age it. Then filter to obtain filter cake and mother liquor. Wash and dry the filter cake and then thermally decompose it to obtain high-purity zinc oxide powder. Adjust the pH of the mother liquor with diammonium hydrogen phosphate and filter it. Recover the filtrate as ammonium sulfate mother liquor for preparing ammonia water.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. After adsorbing fluoride ions, the aluminum-based composite defluorinating agent undergoes a ligand exchange reaction with the aluminum-fluorine complex through ammonia treatment. The fluoride ions are transferred from the solid phase to the liquid phase, and the aluminum is converted back into aluminum hydroxide with adsorption activity. The regenerated wet filter residue can be directly returned to the defluorination process without drying, realizing the reuse of the defluorinating agent in multiple operating cycles.

[0012] 2. An ammonium carbonate calcium removal unit is set up before the electrodialysis dechlorination step. By utilizing the property of ammonium carbonate to form calcium carbonate precipitate with calcium ions, the concentration of calcium ions in the solution entering the electrodialysis unit is reduced to an extremely low level, eliminating the risk of scaling on the membrane surface during electrodialysis operation.

[0013] 3. Ammonium bicarbonate is used to precipitate zinc. The reaction mother liquor is ammonium sulfate solution. After treatment with diammonium hydrogen phosphate to remove residual calcium and fluoride, the mother liquor can be distilled with lime milk to recover ammonia and prepared into ammonia water. This ammonia water is then returned to the front end of the process for pH adjustment and defluorinating agent regeneration, forming an internal cycle of ammonium salts. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the preparation process of Example 1 of the present invention; Figure 2 The images show the XRD patterns of the samples prepared in Example 1 and Comparative Example 5 of this invention, where (a) is the XRD pattern of the sample in Example 1, (b) is the XRD pattern of the sample in Comparative Example 5, and (c) is a PDF comparison card of ZnO crystals. Detailed Implementation

[0015] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0016] This invention proposes a method for preparing high-purity zinc compounds using zinc oxide, such as... Figure 1 As shown, the specific technical solution is as follows: 1. Pre-washing and sulfuric acid leaching Zinc oxide is subjected to multi-stage water washing and then leached with sulfuric acid under heating. The resulting crude zinc sulfate solution is obtained by filtration, and the washing waste liquid is purified and recycled. The zinc oxide raw material contains soluble fluoride and chlorine compounds as well as some dust impurities. If these soluble impurities enter the leaching system directly, they will enter the subsequent purification unit with the liquid phase, increasing the burden on defluorination and dechlorination. Therefore, multi-stage water washing is required before leaching to utilize water's ability to dissolve soluble salts such as sodium fluoride and sodium chloride from the solid phase, thereby reducing the initial fluoride and chlorine concentration in the leachate.

[0017] The wastewater generated from washing also contains small amounts of heavy metal ions and dissolved salts. Direct discharge would cause environmental pollution and waste of water resources. Adding sodium sulfide to the washing wastewater can convert free heavy metal ions into insoluble sulfides. After separation by pressure filtration, it can be safely disposed of as hazardous waste or used to recover valuable metals. The clear liquid after heavy metal removal mainly contains sodium chloride and sodium fluoride. Through a mechanical steam recompression evaporation crystallization system, water is forced to evaporate under high temperature and low pressure, causing salt crystallization and precipitation. The resulting mixed salts can be sold as low-grade by-products. The water vapor generated by evaporation is condensed to obtain high-purity distilled water, which can be returned to the upstream multi-stage water washing steps as washing liquid for recycling, thereby achieving zero discharge and resource utilization of washing wastewater.

[0018] In the washed filter cake, zinc mainly exists in the form of zinc oxide and zinc ferrite. Sulfuric acid leaching utilizes the acidity of sulfuric acid to convert the zinc in the solid phase into soluble zinc sulfate, which then enters the solution. Lead, silver, and other metals, as well as insoluble substances such as silicates, remain in the slag phase, achieving solid-liquid separation of zinc from some impurities. The first stage of the leaching process takes place near neutral pH, allowing the readily soluble zinc oxide to dissolve rapidly. Simultaneously, the acidity of the solution is controlled to hydrolyze and precipitate impurities such as iron and arsenic, preventing them from entering the solution in large quantities. The second stage of the leaching process is carried out at higher acidity to break down the structure of the insoluble zinc ferrite, releasing the zinc encapsulated within and thus improving the total zinc recovery rate. Both stages are completed sequentially in the same reactor. The acidity environment at different stages is controlled by adjusting the amount of acid added. Acid leaching converts the solid raw material into a zinc-containing solution, providing a liquid-phase basis for subsequent deep purification.

[0019] 2. Aluminum-zinc composite defluorinating agent for defluorination and in-situ regeneration A wet defluorinating agent prepared from aluminum sulfate and zinc oxide is added to a crude zinc sulfate solution for defluorination. The defluorinated residue is regenerated with ammonia and recycled. Calcium carbonate is added to the regenerated solution to precipitate fluoride. Fluoride ions exist in acidic zinc sulfate solutions as fluoride ions or fluoride complexes. If directly introduced into electrodialysis or electrolysis processes, they will severely corrode equipment and affect product quality. An aluminum-based composite defluorinating agent is used to remove fluoride ions. Chloride ions in aluminum sulfate hydrolyze in a weakly acidic aqueous solution to form aluminum hydroxide colloid. Utilizing the strong coordination ability of aluminum hydroxide colloid for fluoride, fluoride is adsorbed from the solution onto the solid surface. Zinc oxide in the defluorinating agent acts as a framework, providing support and dispersion for the active component of aluminum hydroxide, fully exposing the adsorption sites, and preventing the adhesion and aggregation of aluminum hydroxide colloid. The operation is carried out within a specific pH range to ensure the highest adsorption activity of aluminum and no zinc precipitation. Compared with traditional alumina or aluminum salt defluorinating agents, the aluminum-zinc composite wet defluorinating agent only needs washing to restore activity after adsorption saturation, without the need for drying. The zinc oxide framework remains intact during regeneration and can be recycled multiple times.

[0020] In the defluorination residue after adsorption saturation, aluminum forms a stable complex with fluorine, losing further adsorption capacity. To restore the activity of the defluorinating agent, the residue needs to be treated with ammonia. The hydroxide ions provided by the ammonia undergo ligand exchange with the aluminum-fluorine complex, displacing fluorine from the aluminum. The fluorine enters the liquid phase to form ammonium fluoride, while the aluminum is converted back to aluminum hydroxide, thus restoring its adsorption capacity. Since drying would damage the pore structure and surface activity of aluminum hydroxide, the regenerated wet filter residue is returned to the defluorination process directly without drying, maximizing the preservation of adsorption performance. Fluoride ions in the regenerated solution are converted to calcium fluoride precipitate by adding calcium carbonate. After separation from the system, the main component of the regenerated solution is ammonia. Ammonia gas can be generated by distillation and poured into deionized water to produce pure ammonia water for continued recycling in the process, preventing fluoride accumulation. By recycling the defluorinating agent and discharging fluoride in the stable form of calcium fluoride, the impact of fluoride impurities in the system is minimized.

[0021] 3. Multi-stage purification and electrodialysis dechlorination The low-fluoride zinc sulfate solution was subjected to oxidation, displacement, and resin adsorption for impurity removal, followed by electrodialysis to obtain a pure zinc sulfate solution. Even after defluorination, the zinc sulfate solution still contains various impurity ions, including metal ions such as iron, copper, cadmium, and lead, as well as calcium ions. Failure to remove these impurities will affect the purity of the final product and also damage the electrodialysis membrane.

[0022] Because ferrous ions in the solution are unstable in air and easily oxidize and hydrolyze to form a colloidal precipitate, although the oxidation rate is slow, adding hydrogen peroxide can quickly oxidize ferrous ions to ferric ions. By adjusting the pH of the system, ferric ions can form ferric hydroxide precipitate, which can then be removed by filtration. This process also causes some impurities such as arsenic and antimony to co-precipitate. The potentials of heavy metal ions such as copper, cadmium, and lead in the solution are higher than those of zinc. When zinc powder is added, it displaces these heavy metals, causing them to precipitate in a metallic state. Filtration then separates these metals to obtain a pure zinc solution. Calcium ions in the solution are removed by pumping the filtrate into an ion exchange column loaded with aminophosphonic acid-type macroporous resin. The selective chelation and adsorption of calcium ions by the aminophosphonic acid groups on the resin reduces the calcium ion concentration in the solution to extremely low levels.

[0023] After removing these metal ions, electrodialysis is performed using a monovalent selective anion exchange membrane. Under the action of an electric field, chloride ions preferentially permeate through the membrane into the concentration chamber, thereby achieving deep removal of chloride ions.

[0024] 4. Preparation of high-purity zinc oxide and recovery of mother liquor High-purity zinc oxide is obtained by precipitating pure zinc sulfate solution with ammonium bicarbonate and then thermally decomposing it. The mother liquor is purified with diammonium hydrogen phosphate, and the ammonium sulfate is recovered for the preparation of ammonia water. The main component of the purified system is zinc sulfate. When ammonium bicarbonate is added, it undergoes a metathesis reaction with zinc sulfate to generate basic zinc carbonate precipitate and ammonium sulfate solution. The crystals of basic zinc carbonate are made more complete by adjusting the temperature and pH. The basic zinc carbonate crystals are washed and dried multiple times and then thermally decomposed at high temperature to decompose them into zinc oxide, carbon dioxide, and water vapor. During the thermal decomposition process, residual trace impurities such as fluorine and chlorine volatilize and escape in the form of hydrogen fluoride and hydrogen chloride, thereby further improving the chemical purity of the product. This high-purity zinc oxide can be used in the preparation of the defluorinating agent in the aforementioned steps to achieve raw material recycling. Meanwhile, the escaped hydrogen fluoride and hydrogen chloride gases can be sent into a series of packed absorption towers by an induced draft fan. The towers are used for high-pressure countercurrent spraying and washing with a weak alkaline solution. In the towers, through the intense mass transfer and acid-base neutralization reaction between the gas and liquid phases, the hydrogen fluoride and hydrogen chloride molecules in the gas phase are completely absorbed and converted into stable soluble inorganic salts. After being deodorized by activated carbon adsorption, they can finally be discharged through a high-altitude chimney to meet emission standards.

[0025] The mother liquor after precipitation is mainly composed of ammonium sulfate, and also contains trace amounts of impurities such as calcium and fluorine. After adding diammonium hydrogen phosphate, it reacts with calcium ions to form calcium hydrogen phosphate precipitate, and with fluoride ions to form fluorapatite precipitate. After filtering the precipitate, a pure ammonium sulfate solution is obtained. When mixed with lime milk and heated, it undergoes a double decomposition reaction to generate ammonia gas. The ammonia gas is then absorbed by condensation to obtain ammonia water, which can be reused in the aforementioned steps, thereby realizing the recycling of ammonium salts.

[0026] The following are some embodiments of the present invention to illustrate the actual effects of the present invention, wherein Table 1 contains information on the raw materials used in the embodiments.

[0027] Table 1 Raw Material Information Table

[0028] Example 1 S1: Take 1000g of zinc oxide and add it to 40℃ deionized water for two-stage countercurrent washing at a liquid-to-solid ratio of 2:1. After stirring and washing for 30 minutes, filter to obtain a primary filter cake and washing liquid. Mix the primary filter cake with 40℃ deionized water at a liquid-to-solid ratio of 2:1 and stir and wash for 30 minutes. Filter to obtain a secondary filter cake and washing liquid. Combine the two washing liquids and add the secondary filter cake to a reactor containing 5L of deionized water. Slowly add sulfuric acid to the reactor while stirring at 200rpm to adjust the pH of the system to 5.1. Then raise the temperature of the reactor to 55℃ and continue... The reaction was stirred for 1.5 hours for the first leaching. After filtering and separating the filtrate, 270 mL of sulfuric acid was added to the system. The reactor was heated to 85°C and stirred for 2 hours for the second leaching. After the reaction was completed, the mixture was filtered under pressure, and the filtrate was collected to obtain a crude zinc sulfate solution. 5 g of sodium sulfide was added to the combined washing solution, and after stirring for 30 minutes, the mixture was filtered under pressure. The filtrate was pumped into a mechanical steam recompression evaporation crystallization system and forced to evaporate at 80°C and -0.08 MPa. The precipitated crystals were collected, and the evaporated condensate was returned to the two-stage washing steps at the front end as washing solution for recycling. S2: Dissolve 170g of aluminum sulfate hexahydrate in 1L of deionized water, add 60g of ZnO powder, heat to 35℃, and add ammonia water dropwise to adjust the pH to 7.2 while stirring at 200rpm. Then age for 45min and filter to obtain a wet aluminum-zinc composite defluorinating agent filter cake. Adjust the pH of the crude zinc sulfate solution obtained in S1 to 5.8 with ammonia water, then add 80g of defluorinating agent. Heat the system to 55℃ and stir at 300rpm for 50min. After filtration, obtain a low-fluoride zinc sulfate solution and defluorinating residue. Transfer the defluorinating residue to a regeneration tank, add 2wt% ammonia water, with a liquid-to-solid ratio of 4:1, heat to 40℃ and stir for 40min. After filtration, obtain a regenerated wet defluorinating agent and regeneration liquid. The regenerated wet defluorinating agent can be directly recycled. Add 3g of lime milk to the regeneration liquid, heat to 55℃, stir for 30min and filter to obtain calcium fluoride precipitate. S3: Add 5 mL of hydrogen peroxide to the low-fluoride zinc sulfate solution, stir for 30 min, adjust the pH of the system to 4.5 with ammonia, filter to remove iron and aluminum slag, then add 8 g of zinc powder to the filtrate, stir for another 30 min, filter to remove copper, cadmium, and lead, pump the filtrate into an ion exchange column loaded with aminophosphonic acid macroporous resin at a flow rate of 5 mL / min, circulate the filtrate in the adsorption column for 30 min to obtain a low-calcium zinc sulfate solution, filter the low-calcium zinc sulfate solution through a 0.1 μm ceramic membrane, and then pump it into the electrodialysis desalination chamber. The electrodialysis membrane stack uses a poly(alkyl-biphenylpyridine) anion exchange membrane / (pyrrole / chitosan) cation exchange membrane stack with an effective membrane area of ​​0.1 m². 2 There are 10 pairs of membranes in total, with a current density of 90 A / m. 2The operating temperature is 25℃. Electrodialysis is stopped when the chloride ion concentration at the desalination chamber outlet is lower than 30mg / L, thus obtaining a pure zinc sulfate solution. S4: Heat the pure zinc sulfate solution to 60℃, and slowly add 20wt% ammonium bicarbonate solution to adjust the pH of the system to 6.5 while stirring at 150rpm. Then continue stirring and aging for 60min. Filter to obtain basic zinc carbonate filter cake and ammonium sulfate mother liquor. Wash the filter cake three times with deionized water, 1L of water each time. Then dry the washed filter cake at 110℃ for 4h. Then put it into a corundum crucible and thermally decompose it at 430℃ for 90min in a box-type resistance furnace. Naturally cool to room temperature to obtain high-purity zinc oxide powder. Add 18g of diammonium hydrogen phosphate to the ammonium sulfate mother liquor to adjust the pH to 7.3, stir for 30min and filter. Remove the precipitate and recover the filtrate as pure ammonium sulfate solution.

[0029] Example 2 The difference from the preparation method in Example 1 is as follows: S3: Replace the poly(alkyl-biphenylpyridine) anion exchange membrane with a polyaromatic quinine anion exchange membrane, and replace the (pyrrole / chitosan) cation exchange membrane with a UV-initiated co-deposition modified cation exchange membrane. All other steps are the same.

[0030] Example 3 The difference from the preparation method in Example 1 is as follows: S3: Replace the poly(alkyl-biphenylpyridine) anion exchange membrane with a piperidinyl functionalized anion exchange membrane, and the remaining steps are the same.

[0031] Example 4 The difference from the preparation method in Example 1 is as follows: S1: Adjust the pH to 4.9, the temperature for the first leaching is 50℃, and the temperature for the second leaching is 80℃; S2: After adding the defluorinating agent, the reaction temperature is 50℃. Add 1.5wt% ammonia water to the regeneration tank, the regeneration temperature is 35℃, and the regeneration time is 30min. S3: Adjust pH to 4.3, circulate adsorption for 25 min, and use a current density of 80 A / m. 2 ; S4: Heat the pure zinc sulfate solution to 55°C, age for 50 minutes, and set the thermal decomposition temperature at 400°C. All other steps are the same.

[0032] Example 5 The difference from the preparation method in Example 1 is as follows: S1: Adjust the pH to 5.3, the temperature for the first leaching is 60℃, and the temperature for the second leaching is 90℃; S2: After adding the defluorinating agent, the reaction temperature is 60℃. Add 2.5wt% ammonia water to the regeneration tank, the regeneration temperature is 45℃, and the regeneration time is 60min. S3: Adjust pH to 4.7, circulate adsorption for 50 min, current density is 100 A / m 2 ; S4: Heat the pure zinc sulfate solution to 65°C, age for 80 minutes, and set the thermal decomposition temperature at 450°C. All other steps are the same.

[0033] Example 6 The difference from the preparation method in Example 1 is as follows: S1: Adjust the pH to 5.0, the temperature for the first leaching is 58℃, and the temperature for the second leaching is 88℃; S2: After adding the defluorinating agent, the reaction temperature is 58℃. Add 2.3wt% ammonia water to the regeneration tank, the regeneration temperature is 42℃, and the regeneration time is 50min. S3: Adjust pH to 4.6, circulate adsorption for 45 min, current density is 95 A / m 2 ; S4: Heat the pure zinc sulfate solution to 62℃, age for 70 minutes, and set the thermal decomposition temperature at 420℃. All other steps are the same.

[0034] Comparative Example 1 The difference from the preparation method in Example 1 is as follows: S3: Without adding ammonium carbonate solution, add zinc powder, stir, filter, and then filter directly through a ceramic membrane. All other steps are the same.

[0035] Comparative Example 2 The difference from the preparation method in Example 1 is as follows: S2: Change the pH adjustment from ammonia water to NaOH water by adding 2wt% NaOH to the regeneration tank; S3: Replace the 20wt% ammonium carbonate solution with a 20wt% sodium carbonate solution; S4: Replace the 20wt% ammonium bicarbonate solution with a 20wt% sodium bicarbonate solution, and the remaining steps are the same.

[0036] Comparative Example 3 The difference from the preparation method in Example 1 is as follows: S3: Replace the electrodialysis membrane module with a conventional anion exchange membrane and cation exchange membrane module; the remaining steps are the same.

[0037] Comparative Example 4 The difference from the preparation method in Example 1 is as follows: S2: No defluorinating agent is added, and no defluorinating step is performed; all other steps are the same.

[0038] Comparative Example 5: Zinc oxide is prepared from zinc oxide using conventional wet acid methods, without pre-washing, only one acid leaching, and no impurity removal steps.

[0039] Experimental Example 1 Take 0.5 g of zinc oxide powder prepared in Examples 1-6 and Comparative Examples 1-5 and place it in a beaker. Wet it with a small amount of deionized water, and then slowly add 10 mL of nitric acid to dissolve the sample. Transfer the solution to a 50 mL volumetric flask, dilute to the mark with deionized water and shake well. Filter the solution through a 0.22 μm microporous membrane and inject it into an ion chromatograph for analysis. The ion chromatograph uses an anion separation column and KOH solution as the eluent for gradient elution at a flow rate of 1.0 mL / min. Detect the fluorine and chlorine content in the sample using a conductivity detector and record the results.

[0040] 0.5 g of zinc oxide powder prepared in Examples 1-6 and Comparative Examples 1-5 was placed in a polytetrafluoroethylene digestion vessel, 10 mL of hydrochloric acid and 2 mL of nitric acid were added, and the vessel was sealed and placed in a microwave digestion apparatus. The temperature was raised from room temperature to 180 °C and kept at that temperature for 20 min for digestion. The solution was then cooled to room temperature, and the digestion solution was transferred to a 100 mL volumetric flask. The solution was diluted to the mark with deionized water and shaken well. The solution was then introduced into an ICP-OES apparatus. The plasma power was set to 1.2 kW, the nebulizing gas flow rate to 0.8 L / min, the auxiliary gas flow rate to 0.5 L / min, and the cooling gas flow rate to 12 L / min. The emission intensities of sodium, calcium, and zinc were measured at 589.592 nm, 317.933 nm, and 213.857 nm, respectively, and the concentrations of sodium, calcium, and zinc in the solution were recorded. The purity of zinc oxide was calculated using the formula: zinc oxide content = zinc content × 1.2448, where 1.2448 is the molar mass ratio of ZnO to Zn. The test results are shown in Table 2.

[0041] Table 2 Purity data of the prepared samples

[0042] As shown in Table 2, the samples in the examples all exhibited high zinc oxide purity and low residual levels of impurity elements. This indicates that the aluminum-zinc composite defluorinating agent recycling system, the calcium removal and protection electrodialysis membrane system, the monovalent selective electrodialysis dechlorination system, and the sodium-free zinc precipitation system constructed in the examples are beneficial for the samples to exhibit excellent impurity removal and high purification performance. Comparative Example 1 eliminated the ammonium carbonate calcium removal process, resulting in calcium ions forming scale on the electrodialysis membrane surface, significantly reducing dechlorination efficiency. Therefore, the chlorine and calcium contents were high, and the zinc oxide purity was low. Comparative Example 2 replaced ammonia and ammonium carbonate / bicarbonate with sodium hydroxide and sodium carbonate / bicarbonate, leading to the introduction of a large amount of sodium ions into the system and disruption of the ammonium salt cycle. Therefore, the sodium content was extremely high, and the residual levels of fluoride, chloride, and calcium were all high, resulting in low zinc oxide purity. Comparative Example 3 replaced the monovalent selective anion exchange membrane with a conventional membrane, causing sulfate and chloride ions to compete for migration, preventing deep removal of chloride ions. Therefore, the chlorine content was high, leading to lattice distortion and stress defects in the zinc oxide crystals and reducing thermal stability. Comparative Example 4, by eliminating the aluminum-zinc composite defluorinating agent, resulted in the failure to remove fluoride ions, leading to extremely high fluoride content, which damages the grain boundary structure and surface activity of zinc oxide. Comparative Example 5, employing a conventional wet acid process, resulted in impurity accumulation, leading to extremely high levels of sodium, fluoride, chloride, and calcium, with very low purity. This caused numerous lattice defects and dislocations in the zinc oxide crystals, significantly reducing thermal stability. During high-temperature thermal decomposition, it easily generates low-melting-point eutectic phases, causing particle melting, adhesion, or abnormal growth. Simultaneously, the impurities are highly hygroscopic, causing the product to rapidly deliquesce and clump.

[0043] Experiment Example 2 0.5 g of zinc oxide powder prepared in Examples 1-6 and Comparative Examples 1-5 was placed in a polytetrafluoroethylene digestion vessel, 10 mL of hydrochloric acid and 2 mL of nitric acid were added, and the vessel was sealed and placed in a microwave digestion apparatus. The temperature was raised from room temperature to 180 °C and kept at that temperature for 20 min for digestion. The solution was then cooled to room temperature, and the digestion solution was transferred to a 100 mL volumetric flask. The solution was diluted to the mark with deionized water and shaken well. The solution was then introduced into an ICP-OES apparatus. The plasma power was set to 1.2 kW, the nebulizer gas flow rate to 0.8 L / min, the auxiliary gas flow rate to 0.5 L / min, and the cooling gas flow rate to 12 L / min. The emission intensities of Cu, Pb, Cd, and Fe were measured at 324.754 nm, 220.353 nm, 228.802 nm, and 259.940 nm, respectively, and the total content of heavy metal elements was recorded based on the test results.

[0044] 0.5 g of zinc oxide powder prepared in Examples 1-6 and Comparative Examples 1-5 was placed in the sample tube of a surface area analyzer and dried under vacuum at 105 °C for 2 h to remove surface adsorbed water and impurities. The dried samples were then loaded into a surface area and porosity analyzer, and nitrogen adsorption / desorption was measured at different relative pressures using nitrogen as the adsorbate at a liquid nitrogen temperature of -196 °C. The specific surface area of ​​the samples was recorded. The test results are shown in Table 3.

[0045] Table 3 Total Heavy Metal Content and Specific Surface Area of ​​Samples

[0046] As shown in Table 3, the sample examples all exhibited low total heavy metal content and moderate specific surface area, indicating that the oxidation-displacement-zinc precipitation-thermal decomposition process chain can effectively remove heavy metals such as iron, copper, cadmium, and lead, and regulate grain growth during the thermal decomposition process. Therefore, it demonstrates excellent heavy metal removal and specific surface area control performance. Comparative Example 1, by eliminating ammonium carbonate for calcium removal, resulted in scaling on the electrodialysis membrane surface. Trace amounts of heavy metals penetrated into the product with fine particles, causing heavy metal agglomerates to be mixed into the product. Furthermore, the crystal integrity was destroyed, and the powder uniformity decreased, thus reducing the specific surface area. Comparative Example 2 showed low zinc powder displacement efficiency. Simultaneously, the precursor generated by the reaction of sodium carbonate and zinc sulfate during zinc precipitation did not selectively adsorb heavy metal ions, causing undisplaced heavy metal ions in the solution to co-precipitate into the product. After thermal decomposition, the heavy metals remained in the zinc oxide as oxides, severely degrading the chemical purity of the powder. Moreover, the particles severely sintered after thermal decomposition, leading to abnormal grain growth and particle melting, resulting in an extremely low specific surface area. Comparative Example 3: Replacing the monovalent selective anion exchange membrane with a conventional membrane resulted in some heavy metal complexes permeating through the membrane or adsorbing and remaining, causing heavy metal oxides to adhere to the grain surface and form a surface contamination layer. Comparative Example 4: Removing the aluminum-zinc composite defluorinating agent resulted in a large amount of fluoride ions remaining. Fluorine forms soluble complexes with heavy metals, hindering the displacement reaction, leading to co-residue of heavy metals and fluorine. Furthermore, the fluorine residue promotes grain coarsening in the sample, resulting in a decrease in specific surface area. Comparative Example 5: The conventional wet acid method resulted in the retention of a large amount of heavy metal impurities. The heavy metals coexisted as independent phases, resulting in a multiphase crude mixture. The impurities formed a low-melting-point eutectic phase, inducing particle agglomeration and leading to an extremely low specific surface area.

[0047] Experimental Example 3 The zinc oxide powders prepared in Example 1 and Comparative Example 5 were ground to a fine powder of 10 μm, dried in a vacuum drying oven at 80°C for 6 hours, and then tested using an X-ray powder diffractometer. The scanning range was 20°~80°, and the scanning rate was 0.05° / s. The scanning results are as follows: Figure 2 As shown.

[0048] from Figure 2As can be seen from the comparison card of the ZnO crystal in (c), (a) shows that the sample of Example 1 has sharp diffraction peaks at 2θ = 31.7°, 34.4°, 36.2°, 47.5°, and 56.6°, which correspond to the standard diffraction peaks of ZnO. These strong diffraction peaks indicate that the ZnO crystal structure prepared in Example 1 is very complete and has almost no impurity phases. The high intensity and narrow half-width of the diffraction peaks show good crystallinity, indicating that the sample is a high-purity wurtzite structure. In addition, there are almost no impurity peaks or stray signals in the sample background, indicating that there are almost no common impurities such as calcium fluoride and sodium chloride in the sample. (b) The ZnO sample prepared in Comparative Example 5 shows that the diffraction peaks at positions 31.7°, 34.4°, and 36.2° are broadened and asymmetrical, with decreased intensity. Furthermore, obvious impurity diffraction peaks are visible next to these peaks, indicating that impurities such as fluorine, chlorine, and heavy metals have entered the lattice of the ZnO sample prepared in Comparative Example 5 or have undergone interstitial doping, leading to lattice distortion and affecting the crystal structure of ZnO. Therefore, it can be seen that Example 1 effectively improved the purity of zinc oxide through a multi-stage purification and impurity removal process, which is more conducive to preparing high-purity zinc compounds with higher precision requirements.

Claims

1. A method for preparing high-purity zinc compounds using zinc oxide, characterized in that, Includes the following steps: S1: After mixing zinc oxide with deionized water, the mixture is washed and filtered in multiple stages. The washed filter cake is then placed in a reaction vessel and deionized water and sulfuric acid are added to adjust the pH. After heating and reacting twice, the mixture is filtered to obtain a crude zinc sulfate solution. The washing waste liquid is then treated with heavy metals and crystallized salts. The condensate after treatment is recycled as washing liquid. S2: Add zinc oxide powder to aluminum sulfate solution and heat. Add ammonia water dropwise to adjust the pH and let stand to obtain wet aluminum-zinc composite defluorinating agent. Then add the defluorinating agent to crude zinc sulfate solution, heat and stir, and filter to obtain low-fluoride zinc sulfate solution and defluorinating residue. Mix the defluorinating residue with ammonia water to regenerate and filter to obtain regenerated liquid and regenerated wet filter residue. Add calcium carbonate to the regenerated liquid and heat to react to obtain calcium fluoride precipitate. S3: Add hydrogen peroxide to the low-fluoride zinc sulfate solution, add ammonia water dropwise to adjust the pH, filter, add zinc powder to the filtrate, and then pump the filtrate into an ion exchange column loaded with aminophosphonic acid macroporous resin. After cyclic adsorption, zinc sulfate solution is obtained, and electrodialysis dechlorination is performed using a monovalent selective anion exchange membrane / cation exchange membrane stack. S4: After heating the dechlorinated desalinated liquid, add ammonium bicarbonate to adjust the pH and age it. Then filter to obtain filter cake and mother liquor. Wash and dry the filter cake and then thermally decompose it to obtain high-purity zinc oxide powder. Adjust the pH of the mother liquor with diammonium hydrogen phosphate and filter it. Recover the filtrate as ammonium sulfate mother liquor for preparing ammonia water.

2. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: S1 describes adjusting the pH to 4.9~5.3; the temperature of the first heating reaction is 50~60℃, and the temperature of the second heating reaction is 80~90℃.

3. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: The heating and stirring temperature in S2 is 50~60℃; the ammonia concentration is 1.5wt%~2.5wt%; the temperature during mixing and regeneration is 35~45℃, and the regeneration time is 30~60min.

4. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: The anion exchange membrane described in S3 is one or more of the following: poly(alkyl-biphenylpyridine) anion exchange membrane, polyaromatic quinine-based anion exchange membrane, and piperidinyl functionalized anion exchange membrane; and the cation exchange membrane is one or more of the following: pyrrole / chitosan modified cation exchange membrane and UV-initiated co-deposition modified cation exchange membrane.

5. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: S3 describes adjusting the pH to 4.3-4.7; the cyclic adsorption time to 25-50 min; and the electrodialysis current density to 80-100 A / m. 2 .

6. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: The heating temperature in S4 is 55~65℃; the aging time is 50~80min; and the thermal decomposition temperature is 400~450℃.

7. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: The wet aluminum-zinc composite defluorinating agent described in S2 is a recyclable defluorinating agent; the recycling is achieved by using the regenerated wet filter residue as a wet defluorinating agent; the ammonia water is recyclable ammonia water; the recovery is achieved by removing calcium fluoride precipitate from the regenerated liquid, distilling out ammonia gas and absorbing it with deionized water to recover the ammonia water.

8. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: The ammonium sulfate mother liquor mentioned in S4 is another raw material for preparing recyclable ammonia water. It can generate ammonia gas by mixing it with lime milk and heating it, and then recover the ammonia water by condensation and absorption.

9. The method for preparing high-purity zinc compounds using zinc oxide according to claim 1, characterized in that: The zinc oxide powder described in S4 can be used to prepare the wet aluminum-zinc composite defluorinating agent.

10. The high-purity zinc compound prepared by the method for preparing high-purity zinc compounds using zinc oxide as described in any one of claims 1 to 9, characterized in that: The high-purity zinc compound is ZnO powder with a purity of ≥99.85%.

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