A method for producing zinc oxide from a zinc-containing waste solution

Abstract

The present application relates to a kind of zinc-containing waste liquid production zinc oxide method, belong to waste liquid processing technical field.The method includes the following steps: first, the waste acid containing heavy metal is carried out deep removal treatment, arsenic and lead are removed by precipitation complexation in turn, mercury and copper are removed by reduction displacement, and chromium, cadmium and nickel are removed by adsorption;Subsequently, zinc ion is selectively adsorbed by using zinc removal resin, and then zinc chloride solution is obtained by elution;Afterwards, sodium carbonate is added to precipitate basic zinc carbonate, and finally, zinc oxide is prepared by solid-liquid separation, washing and calcination.The present application combines three-step heavy metal removal and selective zinc extraction, which can completely purify waste acid, efficiently recover zinc resources, does not affect the main components of waste acid, and can by-product industrial sodium chloride, realizes the resource utilization, harmless and high-value utilization of waste acid.

Description

Technical Field

[0001] This invention relates to the technical field of waste liquid treatment, and in particular to a method for producing zinc oxide from zinc-containing waste liquid. Background Technology

[0002] In the hot-dip galvanizing and electroplating industries of metal products, a large amount of waste acid and waste hydrochloric acid are generated during the pretreatment pickling and rust removal processes. The main components are free hydrochloric acid and ferrous chloride. Inevitably, the characteristic pollutant, the heavy metal zinc, is mixed into the waste acid during the production process. The electroplating industry and other metal surface pickling industries usually contain not only zinc (Zn) but also small amounts of other heavy metals, such as arsenic (As), lead (Pd), mercury (Hg), copper (Cu), cadmium (Cd), chromium (Cr), and nickel (Ni), which poses an obstacle to the resource-based disposal of waste acid. With increasingly stringent national environmental protection laws and regulations, especially the strengthening of the control over heavy metal pollutants, how to completely remove heavy metals from waste acid has become an urgent problem that needs to be solved.

[0003] To address the issue of heavy metals in waste acid and to better utilize it for resource recovery, there is an urgent need to develop an efficient, stable, and adaptable integrated technology for the deep removal and resource recovery of heavy metals from waste acid. This technology can effectively remove multiple heavy metals and recover zinc without affecting the main components of the waste acid. The recovered zinc can be processed into valuable zinc-based chemical products. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing zinc oxide from zinc-containing waste liquid, which aims to recover zinc from waste acid while removing other heavy metals without affecting the main components of the waste acid.

[0005] This invention provides a method for producing zinc oxide from zinc-containing waste liquid, comprising the following steps: S1. Deep removal treatment of waste acid containing heavy metals, the deep removal treatment including the following steps. S101. Arsenic and lead are removed by precipitation complexation; S102, Removal of mercury and copper by reduction and displacement; S103, removes chromium, cadmium and nickel through adsorption; S2. The waste acid after S1 is subjected to zinc removal treatment, and zinc ions in the waste liquid are removed by adsorption using zinc removal resin. S3. The resin that adsorbed zinc ions was analyzed to obtain a zinc chloride solution; S4. Add a precipitant to the zinc chloride solution to carry out a zinc precipitation reaction, generating basic zinc carbonate precipitate; S5. The mixture after the zinc precipitation reaction is subjected to solid-liquid separation. The resulting solid is washed and calcined to obtain zinc oxide.

[0006] By adopting the above technical solution, the waste acid generally contains 3% to 5% free hydrochloric acid. Adding iron oxide to the waste acid and introducing an appropriate amount of air, or adding an appropriate amount of sodium hydroxide, can consume the hydrochloric acid while converting some of the divalent iron to trivalent iron. The trivalent iron will rapidly hydrolyze, forming amorphous iron hydroxide and iron hydroxide colloids. These colloids have a large specific surface area and strong adsorption capacity. Arsenate or arsenite in the solution will be strongly adsorbed on the surface of these iron (hydrogen) oxides, forming crystalline iron arsenate salts with extremely low solubility. Meanwhile, lead ions directly replace the hydrogen ions on the hydroxyl groups on the oxide surface, forming covalent bonds with oxygen atoms, entering the coordination layer of the oxide, and forming a stable solidified complex precipitate. S101 forms a complex precipitate of arsenic and lead, and the reaction formulas involved are as follows: Fe 3+ +HCl→FeCl3; Fe 2+ +O 2+ →Fe 3+ ; Fe 3+ +H₂O→Fe(OH) 2+ +H + ; Fe 3+ +AsO4 3- →FeAsO4↓; Fe-OH+Pb 2+ →Fe-O-Pb + ↓+H + ; After precipitating and complexing arsenic and lead, iron powder (Fe) is added to the waste acid. 0 A stronger reducing element can displace the weaker reducing elements mercury and copper from waste acid, forming a mercury-copper alloy precipitate. Simultaneously, Fe... 0 Fe in waste acid can be removed 3+ Reduced to Fe 2+ The reaction involved in S102 is as follows: Hg 2+ +Fe 0 →Hg 0 ↓; Cu 2+ +Fe 0 →Cu 0 ↓; Fe 0 +Fe 3+ →Fe 2+ ; Waste acid from processes S101 and S102 is pumped into a continuous ion exchange resin column. The column is filled with a specialized ion exchange chelating resin that selectively adsorbs chromium, cadmium, and nickel. The resin also incorporates iminodiacetic acid and thiol functional groups. After the resin adsorbs heavy metals chromium, cadmium, and nickel, the heavy metal ions are leached out using self-produced regenerated acid salt or purchased hydrochloric acid, forming a mixture of CrCl2, CdCl2, and NiCl2. This leached mixture is treated as hazardous waste and outsourced to a qualified company for disposal. After the S1 three-step process, all heavy metals arsenic, lead, mercury, copper, cadmium, chromium, and nickel are removed. The purified waste acid then enters the zinc removal process.

[0007] S2 involves pumping the waste acid treated in S1 into a zinc-removing resin column. This column consists of multiple columns connected in series, filled with zinc-selective ion-exchange chelating resin. The resin contains imino functional groups, which adsorb zinc ions from the waste acid. The waste acid, now free of heavy metals, is pumped into a tank area for further processing using existing waste acid treatment processes. S3 involves pumping hydrochloric acid and water into the resin column to precipitate the resin, producing a zinc chloride solution. This regenerates the resin for continued adsorption and recycling. S4 involves pumping the zinc chloride solution into a reaction tank, where sodium carbonate is slowly added as a precipitant. Sodium carbonate and zinc chloride undergo a double hydrolysis reaction in the aqueous solution. After adjusting the pH, basic zinc carbonate precipitate and sodium chloride are generated. The reaction equation is as follows: 3ZnCl2+3Na2CO3+3H2O=ZnCO3·2Zn(OH)2·H2O↓+6NaCl+2CO2↑ After the S5 reaction is completed, the solid-liquid mixture is pumped into a plate and frame filter press for solid-liquid separation. The solids can be washed online in the plate and frame filter press, and the resulting solid material is fed into a controlled calcining furnace for calcination to produce zinc oxide. The resulting sodium chloride liquid can be fed into a multi-effect evaporator for evaporation, concentration, and crystallization to produce industrial sodium chloride. The condensate produced by evaporation can be reused.

[0008] Preferably, step S101 includes: Waste acid is pumped into a waste acid purification and conditioning tank, iron oxide is added and air is introduced, or sodium hydroxide is added to precipitate and complex heavy metals arsenic and lead, thus obtaining waste acid 1.

[0009] Preferably, step S102 includes: Iron powder was added to waste acid 1 to reduce and replace heavy metals mercury and copper. The waste acid was then pumped into a plate and frame filter press for filtration. The filtered residue was outsourced to a qualified unit for disposal, resulting in waste acid 2.

[0010] Preferably, step S103 includes: Waste acid 2 is pumped into a continuous ion exchange resin column to adsorb heavy metals chromium, cadmium, and nickel in the waste liquid. Hydrochloric acid is then added to leach out the chromium, cadmium, and nickel, forming a chloride mixture. This mixture is then outsourced to a qualified unit for disposal, yielding waste acid 3.

[0011] Preferably, the ion exchange resin is a special resin for ion exchange chelation, wherein the resin contains functional groups iminodiacetic acid and / or mercapto groups.

[0012] Preferably, the zinc-removing resin is in multiple sets connected in series, and the column is filled with zinc-selective ion-exchange chelating resin, with imino functional groups bonded to the resin.

[0013] Preferably, in step S3, the analysis is performed by pumping in regenerated hydrochloric acid / hydrochloric acid and water to generate zinc chloride analysis solution, and the resin is regenerated.

[0014] Preferably, in step S4, the precipitant is sodium carbonate, and the pH of the reaction system is adjusted to 8-9 to carry out the zinc precipitation reaction.

[0015] Preferably, in step S5, the calcination is carried out in a hydrogen or carbon monoxide atmosphere at a temperature of 300–400°C for 2–4 hours.

[0016] Preferably, in step S5, the sodium chloride produced after washing can enter a multi-effect evaporator for evaporation, concentration, and crystallization to prepare industrial sodium chloride.

[0017] The beneficial effects of this invention are: This invention achieves efficient and clean resource recovery from complex zinc-containing waste acid through a three-step integrated process: deep purification, selective zinc extraction, and resource conversion. First, iron-based chemical precipitation and displacement methods are used to efficiently remove heavy metals such as arsenic, lead, mercury, and copper, which are prone to chemical transformation. Then, residual chromium, cadmium, and nickel are removed by adsorption using specific chelating resins. Finally, zinc is specifically recovered using highly selective resins. This process avoids interference between different heavy metals, ensuring thorough deep purification and the purity of the final zinc oxide product. While effectively removing all target heavy metals, this method retains the main components of free hydrochloric acid and ferrous chloride in the waste acid to the greatest extent possible, without affecting the subsequent planned disposal and reuse pathways of the waste acid, achieving synergy between hazardous waste reduction and resource recovery. By analyzing the recovered zinc in the form of zinc chloride solution and then converting it into a high-value-added zinc oxide product through sodium carbonate precipitation and calcination, not only is the heavy metal pollution problem solved, but the pollutants are also transformed into marketable chemical raw materials, aligning with the concept of a circular economy. In addition, the sodium chloride solution produced as a byproduct of the precipitation process is evaporated and crystallized to obtain industrial salt, and the condensate is reused, which further improves the resource utilization rate and environmental benefits of the entire process, forming an efficient, stable, widely adaptable, and environmentally and economically beneficial integrated solution for the resource utilization of waste acid. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0019] A method for producing zinc oxide from zinc-containing waste liquid includes the following steps: S1. Deep removal treatment of waste acid containing heavy metals, the deep removal treatment including the following steps. S101. Arsenic and lead are removed by precipitation complexation; S102, Removal of mercury and copper by reduction and displacement; S103, removes chromium, cadmium and nickel through adsorption; S2. The waste acid after S1 is subjected to zinc removal treatment, and zinc ions in the waste liquid are removed by adsorption using zinc removal resin. S3. The resin that adsorbed zinc ions was analyzed to obtain a zinc chloride solution; S4. Add a precipitant to the zinc chloride solution to carry out a zinc precipitation reaction, generating basic zinc carbonate precipitate; S5. The mixture after the zinc precipitation reaction is subjected to solid-liquid separation. The resulting solid is washed and calcined to obtain zinc oxide.

[0020] By adopting the above technical solution, the waste acid generally contains 3% to 5% free hydrochloric acid. Adding iron oxide to the waste acid and introducing an appropriate amount of air, or adding an appropriate amount of sodium hydroxide, can consume the hydrochloric acid while converting some of the divalent iron to trivalent iron. The trivalent iron will rapidly hydrolyze, forming amorphous iron hydroxide and iron hydroxide colloids. These colloids have a large specific surface area and strong adsorption capacity. Arsenate or arsenite in the solution will be strongly adsorbed on the surface of these iron (hydrogen) oxides, forming crystalline iron arsenate salts with extremely low solubility. Meanwhile, lead ions directly replace the hydrogen ions on the hydroxyl groups on the oxide surface, forming covalent bonds with oxygen atoms, entering the coordination layer of the oxide, and forming a stable solidified complex precipitate. S101 forms a complex precipitate of arsenic and lead, and the reaction formulas involved are as follows: Fe 3+ +HCl→FeCl3; Fe 2+ +O 2+ →Fe 3+ ; Fe 3+ +H₂O→Fe(OH) 2+ +H + ; Fe 3+ +AsO4 3- →FeAsO4↓; Fe-OH+Pb 2+ →Fe-O-Pb+ ↓+H + ; After precipitating and complexing arsenic and lead, iron powder (Fe) is added to the waste acid. 0 A stronger reducing element can displace the weaker reducing elements mercury and copper from waste acid, forming a mercury-copper alloy precipitate. Simultaneously, Fe... 0 Fe in waste acid can be removed 3+ Reduced to Fe 2+ This will not affect the established disposal and reuse pathway of the subsequent waste acid. The reaction formulas involved in S102 are as follows: Hg 2+ +Fe 0 →Hg 0 ↓; Cu 2+ +Fe 0 →Cu 0 ↓; Fe 0 +Fe 3+ →Fe 2+ ; Waste acid from processes S101 and S102 is pumped into a continuous ion exchange resin column. The column is filled with a specialized ion exchange chelating resin that selectively adsorbs chromium, cadmium, and nickel. The resin also incorporates iminodiacetic acid and thiol functional groups. After the resin adsorbs heavy metals chromium, cadmium, and nickel, the heavy metal ions are leached out using self-produced regenerated acid salt or purchased hydrochloric acid, forming a mixture of CrCl2, CdCl2, and NiCl2. This leached mixture is treated as hazardous waste and outsourced to a qualified company for disposal. After the S1 three-step process, all heavy metals arsenic, lead, mercury, copper, cadmium, chromium, and nickel are removed. The purified waste acid then enters the zinc removal process.

[0021] S2 involves pumping the waste acid treated in S1 into a zinc-removing resin column. This column consists of multiple columns connected in series, filled with zinc-selective ion-exchange chelating resin. The resin contains imino functional groups, which adsorb zinc ions from the waste acid. The waste acid, now free of heavy metals, is pumped into a tank area for further processing using existing waste acid treatment processes. S3 involves pumping hydrochloric acid and water into the resin column to precipitate the resin, producing a zinc chloride solution. This regenerates the resin for continued adsorption and recycling. S4 involves pumping the zinc chloride solution into a reaction tank, where sodium carbonate is slowly added as a precipitant. Sodium carbonate and zinc chloride undergo a double hydrolysis reaction in the aqueous solution. After adjusting the pH, basic zinc carbonate precipitate and sodium chloride are generated. The reaction equation is as follows: 3ZnCl2+3Na2CO3+3H2O=ZnCO3·2Zn(OH)2·H2O↓+6NaCl+2CO2↑ After the S5 reaction is completed, the solid-liquid mixture is pumped into a plate and frame filter press for solid-liquid separation. The solids can be washed online in the plate and frame filter press, and the resulting solid material is fed into a controlled calcining furnace for calcination to produce zinc oxide. The resulting sodium chloride liquid can be fed into a multi-effect evaporator for evaporation, concentration, and crystallization to produce industrial sodium chloride. The condensate produced by evaporation can be reused.

[0022] In some embodiments, step S101 includes: Waste acid is pumped into a waste acid purification and conditioning tank, 0.3-0.5g of iron oxide per liter is added and air is introduced, or sodium hydroxide is added to precipitate and complex heavy metals arsenic and lead, thus obtaining waste acid 1.

[0023] By adopting the above technical solutions, arsenic and lead can be efficiently converted into stable iron salt precipitates or complexes, thereby achieving deep removal of arsenic and lead. Moreover, the precipitates are easily removed by subsequent solid-liquid separation without affecting the main components in the waste acid.

[0024] In some embodiments, step S102 includes: Add 0.2-0.6g of iron powder per liter to waste acid 1 to reduce and replace heavy metals mercury and copper. Pump the waste acid into a plate and frame filter press for filtration. The filtered residue is handed over to a qualified unit for outsourced disposal to obtain waste acid 2.

[0025] By adopting the above technical solutions and utilizing the reducing and displacement effect of iron powder, mercury and copper can be effectively removed. At the same time, the ferric iron in the waste acid is reduced to ferrous iron, maintaining the main component of ferrous chloride in the waste acid and creating conditions for subsequent resource-based disposal.

[0026] In some embodiments, step S103 includes: Waste acid 2 is pumped into a continuous ion exchange resin column to adsorb heavy metals chromium, cadmium, and nickel from the waste liquid. Hydrochloric acid is then added to leach the chromium, cadmium, and nickel, forming a chloride mixture. This mixture is then outsourced to a qualified unit for disposal, yielding waste acid 3. The ion exchange resin used is a specialized ion exchange chelation resin, in which functional groups iminodiacetic acid and / or mercapto groups are bonded.

[0027] By adopting the above technical solutions and using ion exchange chelating resins bonded with specific functional groups, residual heavy metals such as chromium, cadmium, and nickel can be selectively adsorbed, achieving precise removal of these heavy metals and ensuring thorough purification of waste acid.

[0028] In some embodiments, the zinc-dezinc resin consists of 2 to 4 groups connected in series, and the column is filled with zinc-selective ion-exchange chelating resin, the resin being bonded with imino functional groups.

[0029] By adopting the above technical solutions, multiple sets of zinc removal resin columns connected in series can ensure efficient and selective adsorption of zinc ions, reducing the zinc ion concentration in the effluent to an extremely low level, while avoiding interference from other ions and ensuring the zinc recovery rate.

[0030] In some embodiments, in step S3, the degradation is achieved by pumping in regenerated hydrochloric acid / hydrochloric acid and water to generate a zinc chloride degradation solution, and the resin is regenerated.

[0031] By adopting the above technical solutions, the zinc removal resin is designed with 2 to 4 sets in series, realizing continuous and streamlined treatment of waste acid 3. This effectively extends the contact time between waste acid and zinc removal resin. Combined with zinc selective ion exchange chelating resin with bonded imino functional groups, which have specific adsorption properties for zinc ions, it can fully and efficiently adsorb zinc ions in waste acid, avoiding the problem of zinc ion leakage caused by single column adsorption saturation.

[0032] In some embodiments, in step S4, the precipitant is sodium carbonate, and the amount of sodium carbonate added is 400 mL of saturated sodium carbonate solution per liter of eluent, and the pH of the reaction system is adjusted to 8-9 to carry out the zinc precipitation reaction.

[0033] By adopting the above technical solution, and by adding sodium carbonate and controlling the pH, zinc chloride can be converted into easily filterable basic zinc carbonate precipitate, while sodium chloride is produced as a byproduct, laying the foundation for subsequent zinc oxide preparation and salt recovery.

[0034] In some embodiments, in step S5, calcination is carried out in a hydrogen or carbon monoxide atmosphere at a temperature of 300–400°C for 2–4 hours.

[0035] By adopting the above technical solutions, the process parameters of calcination at 300–400℃ for 2–4 hours in a hydrogen or carbon monoxide atmosphere are highly compatible with the decomposition characteristics of basic zinc carbonate. This temperature range ensures that basic zinc carbonate decomposes slowly and completely into zinc oxide. The calcination time of 2–4 hours avoids incomplete decomposition due to insufficient calcination and also prevents problems such as zinc oxide grain growth and decrease in specific surface area due to over-calcination. The reducing atmosphere of hydrogen or carbon monoxide effectively prevents zinc oxide from being oxidized during calcination and avoids the residue of impurities generated by the decomposition of basic zinc carbonate, ensuring the high purity of the final zinc oxide product.

[0036] In some embodiments, in step S5, the sodium chloride produced after washing can enter a multi-effect evaporator for evaporation, concentration, and crystallization to prepare industrial sodium chloride.

[0037] By adopting the above technical solutions, the sodium chloride solution generated during washing can be evaporated and crystallized to produce industrial sodium chloride, realizing the resource utilization of by-products. At the same time, the condensate can be reused to improve resource utilization and reduce wastewater discharge.

[0038] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0039] Waste acid generated during the rust removal and pickling process in an electroplating industry was used as raw material. The concentrations of the main heavy metals in the waste acid were determined as follows: Zn 2+ 10.67 g / L, Fe 2+ 69g / L, Cr 6+ 86 mg / L, Cu 2+ 43 mg / L, Hg 2+ 47 mg / L, Ni 2+ 30mg / L, As 3+ 22 mg / L, Cd 2+ : 52mg / L; the pH of the electroplating wastewater is 3.1.

[0040] Example

[0041] Example 1: A method for producing zinc oxide from zinc-containing waste liquid, comprising the following steps: S101. Pump the waste acid into the waste acid purification and conditioning tank, add iron oxide at a dosage of 0.3 g / L, and introduce air at a flow rate of 0.1 L / min. Stir and react for 30 min to precipitate and complex heavy metals arsenic and lead, and obtain waste acid 1. S102. Add iron powder to waste acid 1 at a dosage of 0.4 g / L, stir for 30 min to reduce and replace heavy metals mercury and copper, and after the reaction, perform plate and frame filter press. The filtered residue is handed over to a qualified unit for outsourced disposal to obtain waste acid 2. S103. Waste acid 2 is pumped into a continuous ion exchange column filled with ion exchange chelating resin bonded with iminodiacetic acid groups (CR11 resin) to adsorb heavy metals chromium, cadmium, and nickel in the waste liquid. Chromium, cadmium, and nickel are leached out using 5% hydrochloric acid at a volume of 2.5 times the resin column volume to form a chloride mixture. The mixture is then outsourced to a qualified unit for disposal to obtain waste acid 3. S2. Pump waste acid 3 into four sets of selective dezincification chelating resin columns (resin brand HH-65S) connected in series and filled with bonded imino functional groups to adsorb zinc ions in waste acid 3 into the resin until the zinc ion concentration in the effluent is lower than 1 mg / L. S3. After adsorption saturation, the resin is desorbed using a 10% hydrochloric acid aqueous solution at a volume of 3 times the resin volume to produce zinc chloride desorption solution, thus regenerating the resin. S4. Pump the zinc chloride eluent into the reaction tank, and slowly add 400 mL of saturated sodium carbonate solution per liter of eluent. Adjust the pH value to 8 to generate basic zinc carbonate precipitate and sodium chloride. S5. The product after reaction S4 is pumped into a plate filter press for solid-liquid separation. The solid is washed online in the plate and frame filter press. The obtained solid material is calcined at 350°C for 3 hours in a controlled calcination furnace to produce zinc oxide.

[0042] S6. Sodium chloride solution enters a multi-effect evaporator, where it is evaporated, concentrated, and crystallized to produce industrial salt sodium chloride.

[0043] Example 2, a method for producing zinc oxide from zinc-containing waste liquid, differs from Example 1 only in that the calcination temperature in step S5 is 300°C.

[0044] Comparative Example

[0045] Comparative Example 1, a method for producing zinc oxide from zinc-containing waste liquid, differs from Example 1 only in that the calcination temperature in the step is 270°C.

[0046] Performance testing: 1.Zn 2+ and Fe 2+ The detection was performed in accordance with the "HJ 700-2014 Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" standard. 2. The detection of the main content of zinc oxide and key impurity elements (lead, copper, cadmium, iron) shall refer to "GB / T 3185-2016 Zinc Oxide".

[0047] Table 1 Performance test results

[0048] Experimental results show that the method of this invention can efficiently remove multiple heavy metals and successfully prepare high-purity zinc oxide. The entire process is carried out under mild conditions, without damaging the main composition of the waste acid, and simultaneously achieves the reduction of heavy metal hazardous waste and the recovery of zinc resources, demonstrating the systematic and innovative nature of the process design.

[0049] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for producing zinc oxide from zinc-containing waste liquid, characterized in that, Includes the following steps: S1. Deep removal treatment of waste acid containing heavy metals, the deep removal treatment including the following steps. S101. Arsenic and lead are removed by precipitation complexation; S102, Removal of mercury and copper by reduction and displacement; S103, removes chromium, cadmium and nickel through adsorption; S2. The waste acid after S1 is subjected to zinc removal treatment, and zinc ions in the waste liquid are removed by adsorption using zinc removal resin. S3. The resin that adsorbed zinc ions was analyzed to obtain a zinc chloride solution; S4. Add a precipitant to the zinc chloride solution to carry out a zinc precipitation reaction, generating basic zinc carbonate precipitate; S5. The mixture after the zinc precipitation reaction is subjected to solid-liquid separation. The resulting solid is washed and calcined to obtain zinc oxide.

2. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, The steps in S101 include: Waste acid is pumped into a waste acid purification and conditioning tank, iron oxide is added and air is introduced, or sodium hydroxide is added to precipitate and complex heavy metals arsenic and lead, thus obtaining waste acid 1.

3. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, The steps in S102 include: Iron powder was added to waste acid 1 to reduce and replace heavy metals mercury and copper. The waste acid was then pumped into a plate and frame filter press for filtration. The filtered residue was outsourced to a qualified unit for disposal, resulting in waste acid 2.

4. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, The steps in S103 include: Waste acid 2 is pumped into a continuous ion exchange resin column to adsorb heavy metals chromium, cadmium, and nickel in the waste liquid. Hydrochloric acid is then added to leach out the chromium, cadmium, and nickel, forming a chloride mixture. This mixture is then outsourced to a qualified unit for disposal, yielding waste acid 3.

5. The method for producing zinc oxide from zinc-containing wastewater according to claim 4, characterized in that, The ion exchange resin is a special resin for ion exchange chelation, and the resin contains functional groups iminodiacetic acid and / or mercapto groups.

6. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, The zinc-removing resin consists of multiple sets connected in series, and the column is filled with zinc-selective ion-exchange chelating resin, which is bonded with imino functional groups.

7. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, In step S3, the analysis is performed by pumping in regenerated hydrochloric acid or hydrochloric acid and water to generate zinc chloride analysis solution, and the resin is regenerated.

8. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, In step S4, the precipitant is sodium carbonate, and the pH of the reaction system is adjusted to 8-9 to carry out the zinc precipitation reaction.

9. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, In step S5, the calcination is carried out in a hydrogen or carbon monoxide atmosphere at a temperature of 300–400°C for 2–4 hours.

10. The method for producing zinc oxide from zinc-containing wastewater according to claim 1, characterized in that, In step S5, the sodium chloride produced after washing can enter a multi-effect evaporator for evaporation, concentration, and crystallization to prepare industrial sodium chloride.

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