Preparation method of high-purity nano zinc oxide

Abstract

The invention relates to the technical field of solid waste recycling and nano material preparation, in particular to a preparation method of high-purity nano zinc oxide. Zinc is recycled through a sulfuric acid-ascorbic acid system wet leaching process, and the leaching efficiency is improved through an ultrasonic enhancement technology. On the basis of optimizing leaching conditions, a two-stage impurity removal strategy (H2O2 oxidation-alkali precipitation + ammonium persulfate fine impurity removal) is adopted to remove iron, aluminum and manganese, and a high-purity zinc sulfate solution is obtained. Then, preparing nano-zinc oxide by utilizing an ammonium bicarbonate precipitation method, and inspecting the influence of a roasting process on the product quality; and finally, nano-zinc oxide with the purity of 98.89% is prepared, the quality of the nano-zinc oxide reaches the national standard, and an effective technical scheme is provided for resource utilization of zinc-containing dust.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and nanomaterial preparation technology, and in particular to a method for preparing high-purity nano zinc oxide. Background Technology

[0002] While the steel industry has developed rapidly, the problem of hazardous solid waste generated during its production process has become increasingly serious. In key processes such as sintering, pelletizing, and rolling in steel production, 10-20 kg of dust is emitted for every ton of molten steel produced. Based on global steel production estimates, the total amount of steel dust generated annually reaches 150-230 million tons, of which the Chinese steel industry generates approximately 80-120 million tons. More concerningly, 20-30% of this dust is zinc-containing dust, meaning that the global annual production of zinc-containing dust is 30-45 million tons, with China's annual production reaching 16-24 million tons. Such a massive production of zinc-containing dust not only poses a serious threat to the environment but also represents a huge potential for resource recovery.

[0003] Therefore, developing efficient zinc-containing dust treatment technologies to achieve the recycling and utilization of zinc resources has become an important issue that urgently needs to be addressed in the current metallurgical field, with significant environmental and economic benefits. Summary of the Invention

[0004] In view of this, the present invention proposes a method for preparing high-purity nano-zinc oxide. The zinc-containing dust is wet-leached using ultrasonically enhanced mixed acid (H2SO4-C6H8O6), and a two-stage impurity removal process is developed to effectively remove iron, aluminum, and manganese. Finally, a direct precipitation method is used to prepare the high-purity nano-zinc oxide product, providing a new method for the resource utilization of zinc-containing solid waste.

[0005] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a method for preparing nano-zinc oxide, comprising the following steps: S1, zinc dust and leaching solvent are mixed and leached under ultrasonic assistance, and then the leaching slurry is filtered to obtain leaching solution and leaching residue; S2, the leachate is subjected to two-stage impurity removal to obtain a refined zinc sulfate solution; S3, NH4HCO3 solution and dispersant are added to refined zinc sulfate solution, and the reaction yields a precursor precipitate. The precursor is then washed and heat-treated to obtain nano zinc oxide.

[0006] Based on the above technical solutions, preferably, in step S1, the liquid-to-solid ratio (L / S ratio) of the leaching solvent and the zinc-containing dust is 4~7 mL / g.

[0007] Based on the above technical solution, a further preferred embodiment is that the L / S ratio of the leaching solvent to the zinc-containing dust is 7 mL / g.

[0008] Based on the above technical solutions, preferably, in step S1, the leaching solvent includes a reducing agent and sulfuric acid, and the reducing agent includes any one of ascorbic acid, formic acid and EDTA.

[0009] Based on the above technical solutions, a further preferred embodiment is that the reducing agent includes ascorbic acid.

[0010] Based on the above technical solutions, preferably, the concentration of the reducing agent is 0.02~0.08 mol / L, and the concentration of the sulfuric acid is 0.5~2 mol / L.

[0011] Based on the above technical solution, a further preferred embodiment is that the concentration of the reducing agent is 0.08 mol / L and the concentration of the sulfuric acid is 2 mol / L.

[0012] Based on the above technical solutions, preferably, in step S1, the power of the ultrasound is 300~600 W, the leaching temperature is 30~90℃, and the time is 5~30 min.

[0013] Based on the above technical solution, a further preferred embodiment is that the ultrasonic power is 600 W, the leaching temperature is 90℃, and the leaching time is 30 min.

[0014] Based on the above technical solutions, a further optimized approach was adopted. Phase analysis of the zinc-containing dust revealed a zinc content as high as 44.77%, primarily existing as zinc oxide, zinc sulfide, and zinc ferrite. Major impurities included iron, aluminum, and calcium. This complex phase composition increased the difficulty of resource recovery. Based on these phase characteristics, an ultrasonic-assisted mixed acid leaching technique was employed. Single-factor experiments yielded the optimal leaching process as follows: ultrasonic power 600W, ascorbic acid concentration 0.08 mol / L, sulfuric acid concentration 2 mol / L, liquid-to-solid ratio 7 mL / g, temperature 90℃, and time 30 min. Under these conditions, the zinc leaching rate reached 98.96%. Further kinetic studies showed that the leaching process was controlled by both diffusion and chemical reaction, and that ultrasound significantly reduced the reaction energy barrier for zinc leaching, lowering the activation energy from 35.13 kJ / mol to 27.54 kJ / mol.

[0015] The addition of ascorbic acid plays a crucial reducing role in the leaching process, reducing Fe(III) to Fe(II), thereby promoting the decomposition of ZnFe2O4 in zinc oxide dust. This reducing effect significantly improves the zinc leaching efficiency, increasing the zinc leaching rate from 88.59% when using sulfuric acid alone to 93.76%.

[0016] Secondly, ultrasound plays a significant enhancing role in the leaching system. Under conventional leaching conditions, the morphology of the encapsulated particles remains largely unchanged, limiting the reaction rate. However, under ultrasound-enhanced conditions, the cavitation effect induced by ultrasound at the liquid and solid-liquid interfaces creates numerous tiny cavitation bubbles. The instantaneous collapse of these bubbles generates intense shear stress, localized high temperature, and high pressure environments, leading to particle refinement, solid surface damage, and enhanced solution permeability to material pores and cracks. These effects collectively accelerate mass exchange and interfacial chemical reactions between the solid and liquid phases, thereby significantly improving the reaction rate and efficiency of the leaching process.

[0017] Finally, combining ultrasound with ascorbic acid further promoted the full contact and reaction between ascorbic acid, sulfuric acid, and zinc-containing fumes through the mechanical effect and cavitation of ultrasound. This allowed the reducing effect of ascorbic acid to be more fully utilized, significantly shortened the reaction time, and increased the leaching rate. Under this synergistic effect, the zinc leaching rate was further increased to 98.96%, fully demonstrating the significant advantages of ultrasound-enhanced leaching technology in improving the efficiency of valuable metal recovery.

[0018] Based on the above technical solutions, preferably, in step S2, the two-stage impurity removal includes primary impurity removal and secondary impurity removal. Primary impurity removal involves adding H2O2 solution to the leachate at a temperature of 30~90℃ and then adjusting the pH of the leachate to 2.5~5.0. Secondary impurity removal involves, based on primary impurity removal, controlling the temperature at 50~90℃, adding H2O2 solution to the leachate, adjusting the pH of the leachate to 3.0~5.0, and then adding ammonium persulfate.

[0019] Based on the above technical solutions, preferably, the molar ratio of ammonium persulfate to manganese ions in the solution is 2.5 to 3.75.

[0020] Based on the above technical solution, a further preferred embodiment is that the molar ratio of ammonium persulfate to manganese ions in the solution is 3.25.

[0021] Based on the above technical solutions, a further optimized method is to use H2O2 as an oxidant in the primary impurity removal stage to remove Fe. 2+ Oxidized to Fe 3+ Subsequently, the pH of the system was adjusted to 4.5 using NaOH solution, and Fe was obtained at 60℃. 3+ and A13+ Simultaneous removal; secondary impurity removal continues by using H2O2 to oxidize Fe. 2+ Ammonium persulfate was added, and under the conditions of pH 4.5, temperature 90℃, and ammonium persulfate addition coefficient 3.25, Fe... 3+ Al 3+ and Mn 2+ The removal rate reached 99.9%. This process ensures efficient impurity removal while controlling the zinc loss rate to 15.10%.

[0022] Based on the above technical solutions, preferably, in step S3, the temperature of the heat treatment is 250~650℃ and the time is 0.5~3h.

[0023] Based on the above technical solution, a further preferred embodiment is that the heat treatment temperature is 550℃ and the time is 3h.

[0024] Based on the above technical solutions, preferably, in step S3, the washing is performed by washing with water and anhydrous ethanol in sequence.

[0025] Based on the above technical solutions, preferably, in step S3, the concentration of the NH4HCO3 solution is 0.8~1.2 mol / L, and the dispersant is polyethylene glycol 400.

[0026] Based on the above technical solution, a further preferred method involves adding 1% (by mass) of polyethylene glycol 400 to the purified zinc sulfate solution while maintaining a stirring rate of 300 rpm. Subsequently, a 1.0 mol / L NH₄HCO₃ solution is added dropwise at a constant rate of 10 mL / min until the pH of the solution is adjusted to the range of 6.8 to 7.2. After the precipitation reaction is complete, the precursor is obtained by filtration. Then, the precursor is washed sequentially with deionized water and anhydrous ethanol under ultrasonic power of 600 W, with each wash lasting 15 min. After washing, the precursor is filtered again and dried at 80°C for 12 h to obtain a precursor with uniform particle distribution, no obvious agglomeration, and small particle size.

[0027] The method for preparing nano-zinc oxide of the present invention has the following advantages over the prior art: 1. This invention addresses the resource utilization of zinc-containing dust from iron and steel smelting. It employs a sulfuric acid-ascorbic acid wet leaching process to recover zinc, and utilizes ultrasonic enhancement technology to improve leaching efficiency. Based on optimized leaching conditions, a two-stage impurity removal strategy (H₂O₂ oxidation-alkali precipitation + ammonium persulfate fine impurity removal) is used to remove iron, aluminum, and manganese, obtaining a high-purity zinc sulfate solution. Subsequently, nano-zinc oxide is prepared using ammonium bicarbonate precipitation, and the impact of the roasting process on product quality is investigated. Finally, nano-zinc oxide with a purity of 98.89% is obtained, meeting national standards, providing an effective technical solution for the resource utilization of zinc-containing dust.

[0028] 2. An ultrasonic-enhanced sulfuric acid-ascorbic acid system for efficient zinc extraction was developed, significantly improving the ability to extract zinc from zinc-containing fumes. Nano-zinc oxide products were then prepared using zinc-rich solutions, realizing the transformation of low-value-added zinc-containing fumes generated during steel production into high-value products. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the ultrasonic-enhanced leaching mechanism of the present invention; Figure 2 This is a graph showing the effect of different reducing agents and sulfuric acid leaching on the Zn leaching rate according to the present invention; Figure 3 This is a graph showing the effect of different ultrasonic powers on the Zn leaching rate according to the present invention; Figure 4 This is a graph showing the effect of different C6H8O6 concentrations on the Zn leaching rate according to the present invention. Figure 5 The XRD patterns of the leaching residues obtained during leaching with different C6H8O6 concentrations according to the present invention are shown, where (a) 0 mol / L, (b) 0.02 mol / L, and (c) 0.08 mol / L. Figure 6 This is a graph showing the effect of different sulfuric acid concentrations on the leaching rate of Zn according to the present invention; Figure 7 This is a graph showing the effect of different liquid-to-solid ratios on the leaching rate of Zn according to the present invention. Figure 8 This is a graph showing the effect of different leaching temperatures on the leaching rate of Zn according to the present invention. Figure 9 This is a graph showing the effect of different leaching times on the leaching rate of Zn according to the present invention. Figure 10 The XRD patterns of the leaching residues of different leaching systems of the present invention are shown in Figure (a), which represents conventional leaching using H2SO4, Figure (b) represents mixed acid leaching, and Figure (c) represents ultrasonic-enhanced mixed acid leaching. Figure 11 SEM-EDS images of leaching residues from different leaching systems of the present invention are shown, wherein (A) is leaching residue leached with only H2SO4, (B) is leaching residue leached with C6H8O6 and H2SO4, and (C) is leaching residue leached with ultrasonically enhanced mixed acid. Figure 12 The particle size distribution diagram of the present invention includes (A) zinc dust, (B) mixed acid leaching residue and (C) ultrasonically enhanced mixed acid leaching residue. Figure 13 For the first-stage impurity removal of Fe in this invention, pH affects 3+ Al 3+ Removal rate and Zn 2+ Impact diagram of loss rate; Figure 14 The temperature during the first-stage impurity removal of Fe in this invention 3+ Al 3+ Removal rate and Zn 2+ Impact diagram of loss rate; Figure 15 For the secondary impurity removal of Fe in this invention, pH affects 3+ Al 3+ and Mn 2+ Removal rate and Zn 2+ Impact diagram of loss rate; Figure 16 The effect of temperature on Fe during the secondary impurity removal process of this invention 3+ Al 3+ and Mn 2+ Removal rate and Zn 2+ Impact diagram of loss rate; Figure 17 The effect of sodium persulfate addition on Fe during the secondary impurity removal process of this invention. 3+ A1 3+ and Mn 2+ Effect diagram of removal rate; Figure 18 SEM images of the precursor under different washing methods of the present invention are shown, wherein (a) no water washing and no alcohol washing, (b) water washing only, and (c) water and alcohol washing in sequence. Figure 19 This is a graph showing the effect of calcination temperature on the zinc oxide content in the product according to the present invention; Figure 20 This is a graph showing the effect of calcination time on the zinc oxide content in the product according to the present invention; Figure 21The XRD pattern of the optimized nano-zinc oxide prepared according to the present invention is shown below. Figure 22 This is a microscopic morphology diagram of the optimized nano-zinc oxide prepared according to the present invention. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] The main sources of reagents used in this invention are shown in Table 1.

[0033] Table 1

[0034] Example 1: Effect of different reducing agents on zinc leaching rate.

[0035] Under an environment of 2 mol / L sulfuric acid, 7 mL / g L / S ratio, 2 mol / L reducing agent, 90℃, and 300 rpm rotation speed, zinc-containing dust was leached together with H2SO4 using seven different reducing agents: EDTA (C 10 H 16 The leaching rate of Zn is calculated using the following formula: N2O, thiourea (CH4N2S), formic acid (CH2O2), citric acid (C6H8O7), oxalic acid (H2C2O4), Na2SO3, and ascorbic acid (C6H8O6).

[0036]

[0037] In the formula, η Zn The leaching rate of zinc. C Zn The concentration of zinc in the leachate (mg / mL). V The volume of the leachate is in mL. α Zn The zinc content (%) in zinc-containing dust. m The mass (g) of zinc-containing dust.

[0038] Zinc leaching rates in different leaching systems, such as Figure 2 As shown. From Figure 2The leaching rates of Zn, from highest to lowest, are as follows: H2SO4-ascorbic acid > H2SO4-formic acid > H2SO4-EDTA > H2SO4 (without reducing agent) > H2SO4-Na2SO3 > H2SO4-thiourea > H2SO4-citric acid > H2SO4-oxalic acid. Experimental results show that the leaching rate of Zn decreased after adding some reducing agents to the system, while the leaching rate increased to 93.76% after adding ascorbic acid. Ascorbic acid is known for its excellent reducing properties and is a widely used reducing agent; adding it to the reaction solution can effectively promote the metal leaching process. In contrast, citric acid and oxalic acid exhibited lower leaching rates in the Zn leaching process, specifically 86.18% and 85.23%, respectively. This phenomenon is mainly attributed to their readily reacting with Zn. 2+ A precipitation reaction occurs, forming insoluble zinc citrate and zinc oxalate precipitates, which hinder the leaching process of Zn. Formic acid, despite possessing the dual chemical properties of both carboxylic acids and aldehydes, readily undergoes decarboxylation under high-temperature sulfuric acid conditions, limiting its potential for improving zinc leaching efficiency. EDTA is another reducing agent, its reducing power primarily stemming from the carboxyl and ethylenediamine groups in its molecular structure. However, its reducing power is slightly less than that of ascorbic acid. Experimental data further confirms that ascorbic acid exhibits stronger reducing power compared to other reducing agents, such as sodium sulfite and thiourea. Notably, under acidic conditions, ascorbic acid can effectively reduce the high-valent iron in zinc ferrite to low-valent iron. This process may disrupt the original structural stability of zinc ferrite, thereby promoting the release of zinc ions and significantly improving zinc leaching efficiency. Therefore, sulfuric acid and ascorbic acid were subsequently selected as leaching agents for further optimization of the leaching process parameters.

[0039] Example 2: Effect of process parameters on zinc leaching rate.

[0040] 1. The influence of ultrasonic power.

[0041] Under the conditions of sulfuric acid concentration of 2 mol / L, ascorbic acid concentration of 2 mol / L, liquid-to-solid ratio of 7 mL / g, temperature of 90℃, and reaction time of 30 min, the ultrasonic power was set to 300W, 400W, 500W, 600W, 700W, and 800W respectively to investigate the effect of different ultrasonic powers on zinc leaching rate. The results are as follows: Figure 3 As shown.

[0042] It can be seen that when the ultrasonic power is 300 W, the zinc leaching rate is only 94.59%. As the ultrasonic power increases from 300 W to 600 W, the zinc leaching rate gradually increases. At 600 W, the zinc leaching rate reaches its highest value of 98.87%. Beyond 600 W, the zinc leaching rate shows a decreasing trend. This is because ultrasound generates mechanical, chemical, and cavitation effects when passing through the medium. Sufficiently high ultrasonic power not only helps to stir the solution but also accelerates the rate of heterogeneous reactions. Therefore, within a certain range, the leaching rate increases with increasing ultrasonic power. When the cavitation intensity reaches a certain level, cavitation tends to saturate. Further increasing the power will produce a large number of useless bubbles, leading to scattering attenuation and reducing the cavitation intensity. Therefore, the ultrasonic method can improve the zinc leaching rate and significantly shorten the leaching time. Based on the above results, an ultrasonic power of 600 W was used in the following experiments.

[0043] 2. Effect of C6H8O6 concentration.

[0044] Under the conditions of ultrasonic power 600 W, H2SO4 concentration 2 mol / L, L / S ratio 7 mL / g, temperature 90℃, and time 30 min, C6H8O6 at concentrations of 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, and 0.10 mol / L were added respectively to investigate the effect of different C6H8O6 concentrations on the leaching rate of Zn. The results are as follows: Figure 4 and Figure 5 As shown.

[0045] according to Figure 4 It can be seen that as the C6H8O6 concentration increased from 0 mol / L to 0.02 mol / L, the Zn leaching rate increased from 94.59% to 96.41%. Figure 5 The XRD patterns show that when the C6H8O6 concentration is 0.02 mol / L, the diffraction peak intensity of zinc ferrite in the leaching residue is lower than that in the leaching residue without added C6H8O6. When the C6H8O6 concentration is 0.08 mol / L, there is almost no zinc ferrite in the leaching residue. It can be considered that the increase in zinc leaching rate is mainly due to the reduction of zinc ferrite Fe(III) in zinc-containing dust by C6H8O6.

[95] During the leaching process, C6H8O6 disrupts the structure of zinc ferrite, releasing zinc ions.

[0046] ZnFe2O4+8C6H8O6=2C6H6O6+(C6H7O6)2Zn+2(C6H7O6)2Fe+4H2O With increasing C6H8O6 concentration, the leaching efficiency reached a maximum of 98.96% at 0.08 mol / L. Further increases in acidity had little effect on the zinc leaching rate. The C6H8O6 concentration was set at 0.08 mol / L to ensure high leaching efficiency and low acid consumption.

[0047] 3. The effect of H2SO4 concentration.

[0048] Under the conditions of 600 W ultrasonic power, ascorbic acid concentration of 0.08 mol / L, L / S ratio of 7 mL / g, temperature of 90℃, and time of 30 min, leaching with H2SO4 at concentrations of 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, and 3.0 mol / L was conducted to investigate the effect of different H2SO4 concentrations on the leaching rate of Zn. The results are as follows: Figure 6 As shown.

[0049] like Figure 6 As shown, when the H₂SO₄ concentration increased from 0.5 mol / L to 2.0 mol / L, the Zn leaching rate increased from 46.94% to 98.96%. This is because the reaction between the substance and H₂SO₄ is related to the H₂SO₄ concentration. + The activity is closely related to H. + H₂SO₄ reacts with substances in dust particles through the particle boundary layer. As the concentration of H₂SO₄ increases, the concentration gradient at the solid-liquid interface also increases, allowing H₂SO₄ to pass through the boundary layer. + Increased flux facilitates the diffusion of substances and further reactions, thereby increasing the leaching rate of Zn. When the sulfuric acid concentration is further increased to 3.0 mol / L, the leaching rate of Zn remains essentially unchanged. Therefore, from an economic perspective, a sulfuric acid concentration of 2.0 mol / L is the most suitable.

[0050] 4. The effect of liquid-to-solid ratio.

[0051] Under the conditions of ultrasonic power of 600 W, C6H8O6 concentration of 0.08 mol / L, H2SO4 concentration of 2 mol / L, temperature of 90℃, and time of 30 min, the effect of different L / S ratios on the leaching rate of Zn was observed by controlling the liquid-to-solid ratios to be 4 mL / g, 5 mL / g, 6 mL / g, 7 mL / g, 8 mL / g, and 9 mL / g, respectively. The results are as follows: Figure 7 As shown.

[0052] from Figure 7As can be seen, the leaching rate of Zn increased from 86.47% to 98.96% as the L / S ratio increased from 4 mL / g to 7 mL / g. The leaching rate of zinc also increased with the increase of the L / S ratio. Increasing the L / S ratio can reduce the solid-liquid phase mass transfer resistance and the viscosity of the leaching slurry. This is because the increase in the L / S ratio dilutes the products in the leaching system, promotes the forward shift of the reaction equilibrium, and thus improves the metal leaching efficiency. When the L / S ratio is greater than 7 mL / g, increasing the L / S ratio does not bring much benefit. Therefore, based on the experimental results, an L / S ratio of 7 mL / g was selected.

[0053] 5. The effect of leaching temperature.

[0054] Under the conditions of ultrasonic power of 600 W, C6H8O6 concentration of 0.08 mol / L, H2SO4 concentration of 2 mol / L, L / S ratio of 7 mL / g, and time of 30 min, the effects of different temperature changes on the leaching rate of Zn were observed at 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, and 90°C. The results are as follows: Figure 8 As shown.

[0055] like Figure 8 As shown, the Zn leaching rate increases with increasing temperature. Specifically, when the temperature rises from 30°C to 90°C, the zinc leaching rate increases from 88.89% to 98.96%. This study indicates that the increase in leaching rate is related to temperature. This is because the solution viscosity decreases with increasing leaching temperature, which facilitates the diffusion of the leaching solvent and product at higher temperatures. Furthermore, with increasing temperature, the average kinetic energy of molecules also increases, leading to more frequent collisions, thereby accelerating the reaction and improving leaching efficiency. Therefore, a leaching temperature of 90°C was chosen.

[0056] 6. The effect of leaching time.

[0057] Under the conditions of ultrasonic power of 600 W, C6H8O6 concentration of 0.08 mol / L, H2SO4 concentration of 2 mol / L, L / S ratio of 7 mL / g, and temperature of 90℃, leaching time was investigated for 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min to determine the effect of leaching time on the leaching rate of Zn in zinc-containing dust. Figure 9 As shown.

[0058] from Figure 9As can be seen, the zinc leaching rate increased from 91.37% to 98.96% within 5 to 30 minutes, and then decreased slightly after 30 minutes. This is because, over time, most metals, including zinc, will transform into sulfate-containing compounds. On the other hand, due to consumption in other reactions and slight volatilization at high temperatures, prolonged time in a closed reaction vessel would reduce the concentration of H2SO4. Therefore, after comprehensive consideration, a leaching time of 30 minutes was chosen to obtain a high leaching rate in a short time.

[0059] This embodiment determined the optimal leaching conditions for zinc-containing dust through research on leaching conditions: ultrasonic power of 600 W, C6H8O6 concentration of 0.08 mol / L, H2SO4 concentration of 2 mol / L, temperature of 90℃, and leaching time of 30 min. Under these conditions, the ultrasonic-enhanced mixed acid leaching system showed significant leaching effect on zinc, achieving the highest leaching efficiency of 98.96%.

[0060] Example 3: Characterization and leaching mechanism of leaching residue.

[0061] 1. Elemental analysis.

[0062] Quantitative analysis was performed on the elements in the leaching residue and leachate obtained under the optimal leaching conditions in Example 2, and the results are shown in Tables 2 and 3, respectively. Table 2 shows that the main components of the mixed leaching residue include Fe, S, Pb, Si, Zn, and Ca. Table 3 shows that under optimal conditions, the leachate mainly contains high concentrations of Zn, Fe, K, and Na. This indicates that ultrasonic-enhanced mixed acid leaching can effectively achieve efficient zinc leaching, providing a good foundation for the subsequent preparation of nano-zinc oxide.

[0063] Table 2 Chemical composition of leaching residue (wt.%)

[0064] Table 3. Concentrations of major chemical components in the leachate (mg / L)

[0065] Figure 10 The leaching residue from conventional leaching using H2SO4 was demonstrated. Figure 10 (a) Figure in the middle), leaching residue from mixed acid leaching ( Figure 10 (b) and the leaching residue from ultrasonic-enhanced mixed acid leaching ( Figure 10 The XRD pattern of Figure (c) in the diagram. From Figure 10 As can be seen, the three types of leaching residues have similar compositions. The diffraction peak of ZnO disappears, and the leaching residues are mainly composed of CaSO4, Fe2O3, PbSO4, and SiO2. Furthermore, in comparison... Figure 10 Figures (a) and (b) show that after the addition of ascorbic acid, the diffraction peaks of ZnFe2O4 in the leaching residue decreased significantly, while the zinc leaching efficiency increased. The XRD pattern after further ultrasonic treatment is shown in Figure (c). The diffraction peaks of zinc ferrite almost disappeared. This is because the high temperature and pressure generated by ultrasound dispersed the particles covering zinc ferrite and zinc oxide, allowing the internal substances to fully react with the mixed acid, further improving the zinc leaching rate.

[0066] 2. SEM analysis.

[0067] To investigate the effect of ultrasound-enhanced C6H8O6-H2SO4 reaction on metal leaching rate, the micro-surface morphology and elemental composition of H2SO4 leaching residue, mixed acid leaching residue, and ultrasound-enhanced mixed acid leaching residue were analyzed using SEM-EDS. The results are as follows: Figure 11 As shown. By observing the morphology of the material in each process, the main forms of material distribution were determined. SEM images show the differences in the microstructure of C6H8O6 and the leaching residue after ultrasonic treatment. Figure 11 Figure (A) shows a SEM image of the leaching residue produced when leaching was performed using only H2SO4. The residue is primarily columnar and amorphous, with uneven particle size distribution and large gaps. Observation of its energy dispersive spectroscopy (EDS) reveals that zinc is mainly concentrated in irregular shapes, and in some areas, zinc, iron, and oxygen highly overlap, indicating the presence of a large amount of unleached zinc ferrite, resulting in low zinc leaching efficiency.

[0068] Figure 11 Figure (B) is a SEM image of the leaching residue obtained from mixed acid leaching. The particles are mainly columnar with a small amount of randomly shaped fragments. Based on the distribution of Ca, Pb, S, and O elements in the energy dispersive spectroscopy (EDS) image, it can be seen that the main leaching residue consists of calcium sulfate and lead sulfate, primarily distributed in the columnar portion, which is consistent with the XRD analysis results. Furthermore, almost no overlapping areas of Zn, Fe, and O are found, suggesting the absence of zinc ferrite. Through comparison... Figure 11 Figures (A) and (B) show that adding C6H8O6 can effectively reduce the presence of zinc ferrite.

[0069] Figure 11 Figure (C) is a SEM-EDS image of the leaching residue obtained by ultrasonically enhanced (600 w) mixed acid leaching. The particles are uniformly dispersed in size and there is no mineral particle adhesion. Figure 11Figures (B) and (C) show that the addition of ultrasound can reduce particle size. This phenomenon is due to the formation of dense cavitation bubbles when ultrasound passes through the liquid medium. The collapse of these bubbles generates instantaneous local high temperature and high pressure, which in turn breaks the zinc-containing dust particles into finer fragments. This is beneficial for the renewal of active surfaces and solid-liquid reactions, thereby enhancing the opening of the encapsulated particles and coatings and promoting the reaction. In addition, elemental distribution analysis showed no significant enrichment of zinc, indicating that the vast majority of zinc was dissolved in the solution.

[0070] 3. Particle size analysis.

[0071] Figure 12 The particle size distributions of zinc-containing dust (A), mixed acid leaching residue (B), and ultrasonically enhanced mixed acid leaching residue (C) are shown in detail. Figure 12 It is evident that the zinc-containing dust mainly consists of particles ranging from 5 to 30 μm in size. After acid leaching, compared to the initial zinc-containing dust, the D of the mixed acid leaching residue... 10 The parameter value increases, while D 50 D 90 The values ​​of Dav and specific surface area all decreased. These changes may be related to the disappearance of the ZnO phase, which is mainly present in fine particles. A small number of encapsulated particles were present in the mixed acid leaching residue, while ultrasonic-assisted leaching significantly reduced the particle size of the mineral powder to below 10 μm. With increasing specific surface area, Dav... 10 D 50 D 90 Both the Dav parameter and the ZnO phase decreased, consistent with the SEM analysis results. The observed changes can be attributed to the numerous bubbles generated by ultrasonic cavitation. As these bubbles grow and collapse, they release a significant amount of energy, promoting the detachment of inclusions from the ZnO phase surface, leading to the dissociation of encapsulated particles and the generation of numerous tiny particles.

[0072] Example 4: Primary impurity removal.

[0073] To remove Fe from the solution 3+ Al 3+ For primary impurity removal, a constant-temperature water bath is preheated to maintain a constant leaching system temperature (30℃-90℃) with an accuracy of ±1℃. An excess of H2O2 solution is added to the leachate, and Fe... 2+ Oxidized to Fe 3+ Add sodium hydroxide solution dropwise to change the pH of the leachate and keep the pH within a certain range (2.5~5.0).

[0074] 1. pH effect on Fe 3+ Al 3+ The impact of removal rate.

[0075] Under the conditions of reaction temperature 60℃, stirring speed 400 rpm, and reaction time 30 min, and pH values ​​of 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 respectively, Fe was measured. 3+ Al 3+ Removal rate and Zn 2+ Loss rate, and the relationship between the results of each ion and the solution pH are as follows: Figure 13 As shown.

[0076] Depend on Figure 13 It can be seen that as the pH increases from 2.5 to 4.5, Fe... 3+ The removal rate of iron increased significantly, rising from 20.30% to 96.76%. Further increasing the pH to 5.0 resulted in a slight decrease in the removal rate of iron and Al. 3+ The removal rate of Zn gradually increased with increasing solution pH, reaching 90.72% at pH 5. However, the bar chart shows that Zn... 2+ The loss rate of Zn also increases with increasing pH, reaching a maximum at pH 5. 2+ The loss rate reached 12.93%. Therefore, to ensure the Zn content in the leachate... 2+ While removing most of the Fe with a relatively small loss rate. 3+ And Al 3+ The optimal pH was selected as 4.5. Under these conditions, the removal rates of iron and aluminum in the leachate were 96.76% and 80.62%, respectively, and Zn... 2+ The loss rate was 7.27%.

[0077] 2. Temperature effect on Fe 3+ Al 3+ The impact of removal rate.

[0078] Under conditions of pH 4.5, stirring speed 400 rpm, and reaction time 30 min, the Fe was measured at temperatures of 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃. 3+ Al 3+ Removal rate and Zn 2+ Loss rate, and the relationship between the results of each ion and the solution pH are as follows: Figure 14 As shown.

[0079] Depend on Figure 14It can be seen that temperature has little effect on the iron removal rate, reaching its maximum at 60℃. Further increases in temperature actually decrease the removal rate. The aluminum removal rate, however, is only 38.58% at 30℃, but increases significantly with rising temperature, reaching 96.37% at 80℃. Meanwhile, the zinc loss rate also increases slowly with increasing temperature, indicating that higher temperatures intensify molecular motion, causing more metal ions to combine with hydroxide ions to form precipitates. However, considering that the iron removal rate decreases above 60℃, and that Zn... 2+ The loss increased, so the reaction temperature was determined to be 60℃.

[0080] Example 5: Two-stage impurity removal.

[0081] Preheat the water bath to maintain a constant temperature in the impurity removal system. Add excess H2O2 solution to the leachate and wait for Fe... 2+ Oxidized to Fe 3+ Adding sodium hydroxide solution to change the pH of the leachate, and then adding a certain amount of (NH4)2S2O8 to remove Mn 2+ .

[0082] 1. pH effect on Fe 3+ A1 3+ and Mn 2+ The impact of removal rate.

[0083] Under the conditions of an ammonium persulfate addition coefficient (i.e., the molar ratio of ammonium persulfate to manganese ions in the solution) of 3.5, a stirring speed of 400 rpm, a reaction temperature of 90℃, and a reaction time of 30 min, the pH was adjusted to 3.0, 3.5, 4.0, 4.5, and 5.0, respectively, to study the effect of pH on Fe. 3+ Al 3+ and Mn 2+ Removal rate and Zn 2+ The relationship between the loss rate and the results are shown in [link to relevant documentation]. Figure 15 As the pH of the system increases, Fe 3+ Al 3+ and Mn 2+ The removal rates all increased significantly, especially when the pH rose to 4.5, for Fe... 3+ Al 3+ and Mn 2+ The removal rates reached 99.97%, 99.90%, and 99.99%, respectively, indicating that the precipitation efficiency of impurity metal ions was nearly complete under these pH conditions. Further increasing the pH value did not significantly change the removal rate; instead, Zn... 2+The loss rate gradually increases with increasing pH. Based on the above analysis, and considering both the efficient removal of impurity metal ions and the effective retention of zinc, this study ultimately determined the optimal pH value to be 4.5 to achieve the best separation effect.

[0084] 2. Temperature effect on Fe 3+ A1 3+ and Mn 2+ The impact of removal rate.

[0085] Under the conditions of ammonium persulfate addition coefficient of 3.5, stirring speed of 400 rpm, pH of 4.5, and reaction time of 30 min, impurity removal was carried out at temperatures of 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃, respectively, to investigate the effect of temperature on Fe. 3+ Al 3+ and Mn 2+ Removal rate and Zn 2+ The tube with the loss rate, the results are shown in [link to tube]. Figure 16 When the temperature rises from 50℃ to 90℃, Fe 3+ And Al 3+ The removal rate remained consistently above 99%, indicating that temperature changes had little impact on the precipitation efficiency of these two metal ions. In contrast, Mn 2+ The removal rate of Mn increased significantly with increasing temperature, rising sharply from an initial 11.40% to 99.99%, indicating that temperature is the controlling factor for Mn removal. 2+ Key factors in precipitation. Meanwhile, Zn 2+ Although the loss rate increases slowly with increasing temperature, it is only 5.45% at 90℃, which is still at a low level. Based on the above results, 90℃ was chosen as the reaction temperature.

[0086] 3. The effect of sodium persulfate addition on Fe 3+ A1 3+ and Mn 2+ The impact of removal rate.

[0087] Impurity removal was carried out under the conditions of stirring speed of 400 rpm, pH of 4.5, reaction temperature of 60℃, and reaction time of 30 min, with sodium sulfate addition coefficients of 2.5, 2.75, 3.0, 3.25, 3.5, and 3.75, respectively. The effect of sodium persulfate addition on Fe... 3+ Al 3+ and Mn 2+ Removal rate and Zn 2+ The relationship of loss rate is as follows Figure 17 As shown. When the addition coefficient increases from 2.5 to 3.75, Fe 3+ And Al 3+The removal rate remained consistently above 99%, indicating that the dosage of ammonium persulfate had virtually no impact on the removal efficiency of these two metal ions. Meanwhile, Mn... 2+ The removal rate initially increased rapidly with increasing addition coefficient, then tended to stabilize, reaching a peak of 99.94% at an addition coefficient of 3.25. Afterward, further increases in dosage had no significant effect on improving the removal rate. Meanwhile, Zn... 2+ The loss rate remained stable throughout the experimental range and was not significantly affected. Based on experimental data and economic evaluation, the optimal ammonium persulfate addition coefficient was determined to be 3.25.

[0088] Through the above single-factor experimental analysis, the optimal process parameters for staged precipitation purification were determined: in the first-stage purification stage (removing Fe... 3+ Al 3+ The reaction was carried out under the following conditions: pH=4.5, reaction temperature 60℃, stirring speed 400 rpm, and reaction time 30 min; in the secondary impurity removal stage (removal of Fe)... 3+ Al 3+ and Mn 2+ The reaction was carried out under the following conditions: ammonium persulfate addition coefficient of 3.25, stirring speed of 400 rpm, pH of 4.5, reaction temperature of 90℃, and reaction time of 30 min. The purified solution obtained under these conditions was subjected to ICP analysis, as shown in Table 4.

[0089] Table 4. Elemental concentrations (mg / L) of the solution after purification

[0090] As can be observed from Table 4, after the above process, the residual concentrations of impurity elements (Fe, Al, Mn, etc.) in the purified solution are all below 0.1 mg / L, with the main components being Zn, Na, K ions, etc. The resulting high-concentration Zn solution provides an excellent raw material for the preparation of nano-zinc oxide.

[0091] Example 6 In this experiment, under a stirring speed of 300 rpm, 1% (w / w) of polyethylene glycol 400 from the reaction solution was added to a purified zinc sulfate solution, followed by the addition of 1.0 mol / L NH4HCO3 solution at a rate of 10 mL / min until the solution pH reached 6.8–7.2. The precursor was obtained by precipitation and filtration.

[0092] 1. The effect of washing conditions on precursors.

[0093] The precursors obtained by different washing methods—no washing, water washing only, and washing with water and alcohol sequentially—were observed using scanning electron microscopy (SEM). The SEM images of the precursors are shown below. Figure 18As shown, (a) is washed without water or alcohol, (b) is washed with water only, and (c) is washed with water and alcohol in sequence.

[0094] like Figure 18 As shown in Figure (a), if the precursor is filtered and dried directly without washing, a large amount of precursor agglomeration will be observed. This is mainly due to the residual Cl in the precursor. - Na + The agglomeration of precursor particles is caused by impurity ions, particularly chloride ions, which, due to their chlorine bridging effect, readily promote particle aggregation during drying, leading to the formation of hard, difficult-to-disperse agglomerates after calcination. Figure (b) shows the results obtained after washing the precursor twice with deionized water at an ultrasonic power of 600 W, each time for 15 min, followed by filtration and drying at 80°C for 12 h. It can be observed that the agglomeration of the precursor was significantly alleviated after water washing, but the particle size remained relatively large. This may be because the residual moisture in the precursor, through oxygen bonding, still maintains a certain tendency for agglomeration between precursor particles.

[0095] To further optimize the dispersibility and particle size of the precursor, this study employed a method of sequential washing with water and anhydrous ethanol, with ultrasonic oscillation at 600 W applied during each wash for 15 min. The precursor was then filtered and dried at 80℃ for 12 h. As shown in Figure (c), after the double washing treatment, the precursor particles exhibited a uniform distribution, significantly reduced particle size, and no obvious agglomeration was observed. This is mainly because anhydrous ethanol effectively replaced the residual water in the precursor, thereby reducing the influence of oxygen bonding during drying. Simultaneously, the ultrasonic oscillation further refined the particles, reducing particle accumulation during washing. Furthermore, OH... - Cl - Na + After washing, various ions are almost completely removed, which reduces the agglomeration phenomenon during the drying process to a certain extent.

[0096] Based on the direct precipitation method for preparing the precursor, this invention further involves washing with water and anhydrous ethanol under an ultrasonic power of 600 W for 15 min each time, followed by filtration and drying at 80°C for 12 h, ultimately obtaining a precursor with uniform particle distribution, small particle size and no agglomeration.

[0097] 2. The effect of different roasting temperatures on product purity.

[0098] The precursors obtained in the above experiments were calcined in a muffle furnace. Under a calcination time of 3 hours, the effects of different calcination temperatures on product purity were investigated at 150℃, 250℃, 350℃, 450℃, and 550℃. The results are shown in [Figure number missing]. Figure 19 As shown.

[0099] The calcination temperature significantly affects the final zinc oxide content. Specifically, when the calcination temperature is below 550℃, the zinc oxide content in the product increases with increasing temperature. The purity of the product reaches its peak at 550℃, at 98.89%. This result can be attributed to the incomplete decomposition reaction of the precursor, basic zinc carbonate, at lower calcination temperatures, resulting in insufficient conversion of the precursor into zinc carbonate. However, with further increases in temperature, the purity of the product did not change significantly. Therefore, to obtain nano-zinc oxide products with higher purity, this study selected 550℃ as the optimal calcination temperature.

[0100] 3. The effect of roasting time on product purity.

[0101] Under a calcination temperature of 550℃, calcination times of 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, and 3.5 h were controlled to investigate the effect of different calcination times on product purity. The results are shown in [Figure number missing]. Figure 20 As shown.

[0102] The purity of nano-zinc oxide changed with increasing calcination time, increasing from 95.45% at 0.5 h to 98.89% at 3 h. This increase is attributed to insufficient calcination time leading to incomplete precursor decomposition and consequently, a relatively low zinc oxide content. However, it is worth noting that excessively long calcination times may result in increased product particle size. Therefore, after weighing the relationship between purity and particle size, 3 h was selected as the appropriate calcination time.

[0103] Example 7: Product characterization.

[0104] 1. Representation of objects.

[0105] Elemental analysis was performed on the nano-zinc oxide obtained under the optimal reaction conditions, and the results are shown in Table 5.

[0106] Table 5 Chemical composition of nano zinc oxide (wt.%)

[0107] As can be seen from Table 5, the mass percentage of Zn in nano zinc oxide is as high as 79.43%, while the content of Fe, Pb, Al, and Mn elemental impurities is extremely low.

[0108] Figure 21 The image shows the XRD pattern of nano-zinc oxide. Below the image is the corresponding pattern for zinc oxide (ZnO) (standard card PDF#36-1451). Figure 21 It can be seen that the characteristic peaks of nano zinc oxide match the characteristic peaks of the ZnO standard card.

[0109] 2. SEM analysis.

[0110] Nano-sized zinc oxide was successfully prepared by calcining the precursor at 550℃ for 3 h. The product was then characterized using scanning electron microscopy, and the results are as follows: Figure 22 As shown. Specifically, Figure 22 Figures (a) and (b) show SEM images of nano-zinc oxide at different magnifications. Observation of the images reveals that the product obtained in this study exhibits a uniform spherical and near-spherical morphology. Particle size analysis shows that the average particle size of the product is approximately 87 nm.

[0111] 3. Measurement of product technical indicators.

[0112] The nano zinc oxide products prepared under optimal conditions were determined according to the method in GB / T 19589-2004 Nano Zinc Oxide, and the results are shown in Table 6.

[0113] Table 6 Comparison of technical indicators of the products studied with national standards

[0114] As can be seen from Table 6, the product of this study meets the Class 2 standard for nano zinc oxide in terms of zinc oxide purity, average electronic particle size, and agglomeration index, while all other indicators meet or even exceed the Class 3 standard for nano zinc oxide.

[0115] 4. Zinc recovery rate.

[0116] Based on the principle of mass balance, the zinc recovery rate was calculated by quantitatively analyzing the zinc content in the raw materials, leachate, impurity removal solution and final product, as shown in Table 7.

[0117] Table 7 Direct recovery rate of zinc at each process stage

[0118] The total recovery rate of zinc was calculated to be 82.68%. This result indicates that the ultrasonic-enhanced mixed acid leaching-two-stage impurity removal-direct precipitation method for preparing nano-zinc oxide established in this study can efficiently realize the recovery and utilization of zinc resources from zinc-containing dust.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing nano-zinc oxide, characterized in that, Includes the following steps: S1, zinc dust and leaching solvent are mixed and leached under ultrasonic assistance, and then the leaching slurry is filtered to obtain leaching solution and leaching residue; S2, the leachate is subjected to two-stage impurity removal to obtain a refined zinc sulfate solution; S3, NH4HCO3 solution and dispersant are added to refined zinc sulfate solution, and the reaction yields a precursor precipitate. The precursor is then washed and heat-treated to obtain nano zinc oxide.

2. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S1, the liquid-to-solid ratio of the leaching solvent and the zinc-containing dust is 4~7 mL / g.

3. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S1, the leaching solvent includes a reducing agent and sulfuric acid, wherein the reducing agent includes any one of ascorbic acid, formic acid and EDTA.

4. The method for preparing nano-zinc oxide as described in claim 3, characterized in that: The concentration of the reducing agent is 0.02~0.08 mol / L, and the concentration of the sulfuric acid is 0.5~2 mol / L.

5. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S1, the ultrasonic power is 300~600 W, the leaching temperature is 30~90℃, and the leaching time is 5~30 min.

6. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S2, the two-stage purification includes primary purification and secondary purification. Primary purification involves adding H2O2 solution to the leachate at 30-90°C and adjusting the pH of the leachate to 2.5-5.

0. Secondary purification involves adding H2O2 solution to the leachate at 50-90°C, adjusting the pH of the leachate to 3.0-5.0, and then adding ammonium persulfate, based on the primary purification.

7. The method for preparing nano-zinc oxide as described in claim 6, characterized in that: The molar ratio of ammonium persulfate to manganese ions in the solution is 2.5 to 3.

75.

8. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S3, the heat treatment temperature is 250~650℃ and the time is 0.5~3h.

9. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S3, the washing process involves washing with water and anhydrous ethanol sequentially.

10. The method for preparing nano-zinc oxide as described in claim 1, characterized in that: In step S3, the concentration of the NH4HCO3 solution is 0.8~1.2 mol / L, and the dispersant is polyethylene glycol 400.

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