Method for dechlorination and resource utilization of zinc suboxide powder

Abstract

The application provides a method for removing chlorine from secondary zinc oxide powder. The method comprises the following steps: (1) mixing the secondary zinc oxide powder with water, and performing first washing by introducing CO2 gas to obtain first washing slurry; (2) performing first pressure filtration treatment on the first washing slurry to obtain first washing liquid and first washing residue; (3) performing second washing on the first washing residue with water to obtain second washing liquid and second washing residue; (4) performing third washing on the second washing residue with water to obtain third washing liquid and washed secondary zinc oxide powder; wherein the chlorine content in the washed secondary zinc oxide powder is less than 0.2%. Thus, the method can realize high-quality utilization of impurities, has high washing and dechlorination efficiency, and the chlorine content in the treated secondary zinc oxide powder can be reduced to less than 0.2%, and no external impurities are introduced throughout the process.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical zinc smelting technology, specifically relating to a method for dechlorination of zinc oxide powder and chlorine resource utilization. Background Technology

[0002] Zinc oxide is a powder formed from zinc-containing materials (such as zinc concentrate and steel dust) through high-temperature reduction volatilization, oxidation, and condensation. It contains approximately 40%-70% zinc and is enriched with volatile impurities such as fluorine and chlorine. Chlorine mainly exists as chlorides (such as ZnCl2 and PbCl2), with some distributed as mechanical inclusions, reaching a content of 1%-5%, far exceeding the permissible standards for hydrometallurgical zinc smelting systems.

[0003] If conventional acid leaching process is used for zinc oxide powder, it is easy to cause Cl in the leaching solution to increase. - The concentration increases, typically reaching over 2 g / L, far exceeding the permissible range of the electrolysis system. This not only generates toxic gases such as Cl2 and HCl during the hydrometallurgical zinc smelting process, severely impacting the process operating environment; but also, during the electrolysis stage, Cl... - It will also be oxidized to ClO3 at the anode. - It reacts with lead to form soluble lead salts, some of which are deposited at the cathode, leading to a decrease in current efficiency and an increase in the lead content of the zinc sheet, resulting in reduced purity and deteriorated mechanical properties of the zinc ingot. When Cl... - When the concentration exceeds 300 mg / L, the anode lead plate may experience a "burning" phenomenon, with its consumption rate increasing by 3-5 times. In severe cases, it may even break, leading to a safety accident. Furthermore, high concentrations of Cl... - It will also shorten the service life of system pipelines, pumps and other equipment, and increase equipment maintenance costs by 30%-50%.

[0004] Currently, the existing dechlorination technologies in the industry mainly include the following three types: First, pyrometallurgical dechlorination, which uses a multi-hearth furnace or rotary kiln to roast at 800-1000℃, achieving a removal rate of 45%-60%. This technology is simple to operate, but has drawbacks such as high energy consumption, zinc loss of 5%-8%, and HCl pollution. Second, alkaline washing dechlorination, which uses Na2CO3 solution for dechlorination treatment, achieving a removal rate of 70%-85%. Its advantages are simple equipment and low cost, but its disadvantages are large wastewater treatment volume and zinc loss of 3%-5%. Third, a combination of pyrometallurgical and wet treatment processes, achieving a removal rate of 90%-95%. It has the advantages of high dechlorination efficiency and thorough impurity removal, but the process is complex and requires a large initial investment.

[0005] In summary, considering the characteristics of zinc oxide powder, developing a process that is simple, has a high chlorine removal rate, and can convert impurity chlorine into the product is of great significance for the green and efficient development of my country's hydrometallurgical zinc smelting industry. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to provide a method for removing chlorine from zinc oxide powder. This method efficiently removes impurities of chlorine from the zinc oxide powder, reducing the chlorine content in the treated powder to below 0.2%, which is superior to traditional pyrometallurgical dechlorination and alkaline washing dechlorination methods. This fully meets the requirements of hydrometallurgical zinc smelting systems for raw material chlorine content, thus solving the problem of high chlorine levels posing a threat to the electrolysis process at its source.

[0007] In a first aspect, the present invention provides a method for removing chlorine from zinc oxide powder. According to an embodiment of the present invention, the method includes: (1) mixing the zinc oxide powder with water and passing CO2 gas through it for a first washing to obtain a first washed slurry; (2) subjecting the first washed slurry to a first pressure filtration treatment to obtain a first washing liquid and a first washing residue; (3) subjecting the first washing residue to a second washing with water to obtain a second washing liquid and a second washing residue; (4) subjecting the second washing residue to a third washing with water to obtain the third washing liquid and washed zinc oxide powder; wherein the chlorine content in the washed zinc oxide powder is less than 0.2%. Thus, the method of the present invention can achieve high-quality utilization of impurities, while also possessing high washing and dechlorination efficiency. The chlorine content in the treated zinc oxide powder can be reduced to below 0.2%, and no external impurities are introduced throughout the process. Meanwhile, the entire process generates no toxic gases such as Cl2 and HCl, and there is no discharge of large amounts of alkaline washing wastewater. It completely solves the problems of HCl pollution and wastewater treatment in traditional pyrometallurgical dechlorination and alkaline washing dechlorination. This not only lays a solid foundation for the stable operation of the hydrometallurgical zinc smelting system, but also significantly improves the economic benefits of enterprises. It has important practical significance for promoting the green and efficient development of my country's hydrometallurgical zinc smelting industry.

[0008] In addition, the method according to embodiments of the present invention may also have the following additional technical features: In some embodiments of the present invention, step (1) further includes, after the first washing, flash evaporation of the first washing product; and analytical treatment of the flash evaporation product to obtain the first washing slurry and CO2 gas.

[0009] In some embodiments of the present invention, step (1) satisfies at least one of the following conditions: The temperature of the first wash is 20~30℃; The first washing cycle takes 3-5 hours. The pressure of the first wash is 0.3~1.0 MPa; The CO2 injection rate is 300~600 Nm³. 3 / h; The liquid-to-solid ratio in step (1) is 3~5 L / kg; The purity of the CO2 gas is greater than 95%; The parsing process takes 0.5 to 2 hours; The analytical process was carried out under stirring conditions.

[0010] In some embodiments of the present invention, the first washing solution is returned to step (1) to perform the first washing.

[0011] In some embodiments of the present invention, the zinc ion concentration in the first washing solution is 10~50 g / L, and the method further includes: subjecting the first washing solution to sedimentation treatment and second pressure filtration treatment in sequence to obtain sedimentation filtrate and zinc carbonate; adding hydrochloric acid to the sedimentation filtrate, and sequentially evaporating, cooling crystallizing and drying to obtain zinc chloride.

[0012] In some embodiments of the present invention, the temperature of the sedimentation treatment is 25~30°C.

[0013] In some embodiments of the present invention, the settling time is 8 to 12 hours.

[0014] In some embodiments of the present invention, after the addition of hydrochloric acid, the pH value of the sediment filtrate is 3.0 to 3.5.

[0015] In some embodiments of the present invention, the evaporation time is 60-90 minutes.

[0016] In some embodiments of the present invention, the evaporation temperature is 80~110°C.

[0017] In some embodiments of the present invention, the cooling crystallization includes: subjecting the evaporation product to first cooling crystallization, redissolving the first cooled crystallized product, and subjecting the redissolved product to second cooling crystallization.

[0018] In some embodiments of the present invention, the drying temperature is 90~100°C.

[0019] In some embodiments of the present invention, the drying time is 4 to 6 hours.

[0020] In some embodiments of the present invention, step (3) satisfies at least one of the following conditions: The liquid-to-solid ratio in step (3) is 1~2 L / kg; The temperature for the second washing is 20-30℃; The second washing time is 3-5 hours; The second washing solution is returned to step (1) to perform the first washing.

[0021] In some embodiments of the present invention, step (4) satisfies at least one of the following conditions: The liquid-to-solid ratio in step (4) is 1~2 L / kg; The temperature of the third wash is 20-30℃; The third washing cycle takes 3-5 hours. The third washing solution is returned to step (3) for the second washing.

[0022] In a second aspect, the present invention provides a dechlorinated zinc oxide powder. According to an embodiment of the present invention, the dechlorinated zinc oxide powder is obtained by treating zinc oxide powder to be treated by the method described in the first aspect. Thus, the chlorine content in the zinc oxide powder of this application is as low as 0.2% or less. Those skilled in the art will understand that this zinc oxide powder possesses all the features and advantages of the methods described above, which will not be elaborated further here.

[0023] The beneficial effects of this invention are: 1. High dechlorination efficiency and good product compliance: After three-stage countercurrent washing treatment, the chlorine content of the washed zinc oxide powder can be reduced to below 0.2%, which is far superior to the effect of traditional pyrometallurgical dechlorination and alkaline washing dechlorination. It fully meets the requirements of the wet zinc smelting system for the chlorine content of raw materials and solves the problem of the harm of high chlorine to the electrolysis process from the source.

[0024] 2. Achieve resource utilization of chlorine and zinc: Breaking away from the traditional single objective of "removing impurities" in dechlorination, the process design converts the impurities of chlorine in zinc oxide powder into zinc chloride products with a purity of ≥95%, while producing zinc carbonate products with a purity of 80-90% as a byproduct. The washed zinc oxide powder can be directly returned to the hydrometallurgical zinc refining system, realizing the full utilization of zinc and chlorine elements, adding product revenue for enterprises, and significantly reducing zinc resource loss compared to the zinc loss of traditional processes.

[0025] 3. Closed-loop process and high material utilization: The process adopts a counter-current recycling washing mode. The first washing liquid is recycled to enrich chlorine, and the second / third washing liquid is reused step by step. CO2 is regenerated and recycled, and there is no waste of raw materials. The mother liquor of each process can be reused in the washing or crystallization process. The material flow forms a closed loop, which greatly improves the resource utilization rate.

[0026] 4. Environmentally friendly and free from secondary pollution: The entire process generates no toxic gases such as Cl2 and HCl, and there is no discharge of large amounts of alkaline washing wastewater, which completely solves the problems of HCl pollution and wastewater treatment in traditional pyrometallurgical dechlorination. The by-products zinc carbonate and zinc chloride are free of harmful impurities and can be sold directly. The entire production process is clean and environmentally friendly, meeting the industry development requirements of green smelting.

[0027] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart illustrating a method for removing chlorine from zinc oxide powder according to an embodiment of the present invention. Figure 2 This is a process flow diagram of a method for removing chlorine from zinc oxide powder according to an embodiment of the present invention. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0033] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0034] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] In a first aspect, the present invention provides a method for removing chlorine from zinc oxide powder. According to embodiments of the present invention, such as... Figure 1 As shown, the method includes: S100: The zinc oxide powder is mixed with water, and CO2 gas is introduced for the first washing to obtain the first washed slurry.

[0036] It should be noted that the present invention does not strictly limit the specific content of each element in the zinc oxide powder, as long as it contains zinc, chlorine, lead, fluorine, iron, and indium. As an example, by mass percentage, the zinc oxide powder may contain: 40%–70% zinc, 2.5–5% chlorine, 3%–5% lead, 0.4%–1% fluorine, 2%–10% iron, and indium content of 100–300 g / t.

[0037] According to an embodiment of the present invention, in step S100, after the first washing, the process further includes: flash evaporation of the first washing product; and analytical treatment of the flash evaporation product to obtain the aforementioned first washing slurry and CO2 gas. Thus, the method of the present invention can fully release and recover the dissolved and bound CO2 during the washing process, while obtaining a stable first washing slurry, creating conditions for subsequent pressure filtration, countercurrent washing, and chlorine enrichment processes, achieving carbon dioxide recycling, reducing raw material consumption, and improving process economy.

[0038] In the S100 process, after zinc oxide powder is mixed with water and CO2 is introduced, two types of reactions occur simultaneously in the aqueous solution: First, the selective dissolution of chlorine. The chlorine in the zinc oxide powder mainly exists in the form of zinc chloride, which dissolves and dissociates in the aqueous solution. The specific reaction formula is as follows: First, chlorine enters the liquid phase in the form of chloride ions, achieving efficient transfer of chlorine from the solid phase to the liquid phase, providing a prerequisite for subsequent chlorine enrichment and resource utilization. Second, zinc is converted and fixed. CO2 introduced into the system dissolves in water to form a weakly acidic environment, undergoing a reversible bicarbonate conversion reaction with zinc oxide. The specific reaction formula is as follows: The reaction proceeds in the forward direction under normal temperature and high pressure, converting solid ZnO into soluble zinc bicarbonate which enters the liquid phase. Subsequently, after flash evaporation and desorption, the system pressure decreases, and the reaction proceeds in the reverse direction, decomposing zinc bicarbonate into zinc carbonate precipitate and CO2. This achieves efficient recovery of zinc and creates conditions for CO2 recycling.

[0039] According to an embodiment of the present invention, the temperature of the first washing is 20~30℃. For example, it can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, etc., or any range of the above values. According to an embodiment of the present invention, the time of the first washing is 3~5 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc., or any range of the above values. Therefore, by controlling the temperature and time of the first washing within the above range, the ZnCl2 in the zinc oxide can be fully dissolved and dissociated into Zn. 2+ and Cl - The solution is entered to ensure more thorough chlorine removal, resulting in a final material chlorine content consistently below 0.2%. Simultaneously, it allows ZnO to fully react with CO2 and H2O to generate Zn(HCO3)2, achieving effective zinc conversion and subsequent recovery, and increasing the yield of zinc carbonate and zinc chloride products.

[0040] According to an embodiment of the present invention, the pressure of the first wash is 0.3~1.0 MPa. For example, it can be 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, etc., or a range of any of the above values. Therefore, high pressure can significantly increase the solubility of CO2 in the slurry, forming a sufficient bicarbonate system, promoting the full conversion of ZnO to Zn(HCO3)2, and ensuring the effective leaching and subsequent recovery of zinc.

[0041] According to an embodiment of the present invention, the CO2 gas flow rate is 300~600 Nm³. 3 / h. For example, it can be 300 Nm. 3 / h, 350 Nm 3 / h, 400 Nm 3 / h, 450 Nm 3 / h, 500 Nm 3 / h, 550 Nm 3 / h, 600 Nm 3 / h, etc., or can be any range of the above values. Therefore, providing sufficient CO2 can ensure that ZnO reacts completely to form Zn(HCO3)2, avoiding incomplete zinc oxide conversion due to insufficient CO2, which would affect zinc recovery and dechlorination efficiency.

[0042] According to embodiments of the present invention, the purity of the CO2 gas is greater than 95%. For example, it can be 95%, 96%, 97%, 98%, 99%, 99.2%, 99.5%, 99.7%, 99.9%, 100%, or any range of the above values. Therefore, high-purity CO2 can increase the effective partial pressure of the gas phase, enhance its solubility in aqueous solution, ensure the complete conversion of ZnO to Zn(HCO3)2, and guarantee the efficiency of dechlorination and zinc conversion. Simultaneously, it prevents impurities such as N2, O2, dust, and sulfides from entering the washing system with the CO2, thus avoiding the introduction of new impurities, interference with the main reaction, and impact on the resource utilization of chlorine and zinc.

[0043] According to embodiments of the present invention, the analysis and processing time is 0.5 to 2 hours. For example, it can be 0.5 hours, 0.7 hours, 1.0 hours, 1.0 hours, 1.5 hours, 1.7 hours, 2.0 hours, or any range of the above values. This allows for the full release of CO2 bound in the washing liquid, the recovery of high-purity CO2, and its return to the washing step for recycling, significantly reducing the consumption of fresh CO2 raw materials, constructing a closed-loop process, and improving resource utilization.

[0044] According to an embodiment of the present invention, the desorption process is carried out under stirring conditions. Thus, stirring can break down liquid film resistance, allowing dissolved and bound CO2 to escape rapidly from the liquid phase, thereby improving CO2 desorption efficiency and recovery rate.

[0045] According to an embodiment of the present invention, in step S100, the liquid-to-solid ratio is 3~5 L / kg. For example, it can be 3 L / kg, 3.5 L / kg, 4 L / kg, 4.5 L / kg, or 5 L / kg. This ensures that zinc chloride and water in the zinc oxide powder react sufficiently, reducing the chlorine content in the washed zinc oxide powder.

[0046] It should be noted that the "washed secondary zinc oxide powder" mentioned in this invention refers to the final solid product obtained after secondary zinc oxide powder is sequentially washed by a first washing, a second washing, and a third washing. After washing and dechlorination, the chlorine content in this product can be reduced to below 0.2%, which meets the strict requirements of the hydrometallurgical zinc smelting system for the chlorine content of raw materials.

[0047] S200: The first washing slurry is subjected to a first pressure filtration treatment to obtain a first washing liquid and a first washing residue.

[0048] According to an embodiment of the present invention, the first washing solution is returned to step S100 for the first washing to enrich chlorine. Thus, cyclic washing allows the chloride ion concentration in the first washing solution to continuously increase, reaching a high chlorine level of >30 g / L, reducing the load on subsequent evaporation and crystallization, and improving the yield and purity of zinc chloride products.

[0049] In some embodiments of the present invention, after multiple cycles, the first washing solution has a chlorine content >30 g / L, a pH value of 6-7, and a zinc content of 25-30 g / L. This first washing solution is mainly used for the efficient enrichment of chlorine and zinc ions, providing a raw material solution for the preparation of zinc carbonate and zinc chloride products. It can ensure that the zinc chloride concentration reaches a certain level in the subsequent evaporation and crystallization process, improve the purity of the zinc chloride product, and reduce the production cost of the evaporation and crystallization process.

[0050] According to an embodiment of the present invention, when the zinc ion concentration in the first washing solution is 10~50 g / L, exemplarily, it can be 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, etc., or can be any range of the above values, the first washing solution is not returned to the first step S100 for the first washing, but instead undergoes sedimentation treatment and second pressure filtration treatment sequentially. During this process, the zinc bicarbonate in the first washing solution undergoes a decomposition reaction, the specific reaction formula of which is as follows: Zinc precipitates as zinc carbonate. After pressure filtration, zinc carbonate product and sediment filtrate are obtained, with the zinc carbonate purity reaching 80-90 wt%. Hydrochloric acid is added to the sediment filtrate to adjust the pH, stabilizing the zinc and chlorine in the filtrate as zinc chloride. Subsequently, evaporation concentration, cooling crystallization, and drying are performed sequentially. The relevant reactions are as follows: The reaction formula for the evaporation and crystallization process is... The reaction formula for the drying process is: The final product obtained is high-purity zinc chloride with a purity greater than 95 wt%. This demonstrates that this method can achieve efficient open-circuiting and resource utilization of chlorine impurities in zinc oxide powder, while simultaneously producing high-value-added byproducts such as zinc carbonate and zinc chloride.

[0051] According to an embodiment of the present invention, the sedimentation treatment temperature is 25~30℃. For example, it can be 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, etc., or any range of the above values. According to an embodiment of the present invention, the sedimentation treatment time is 8~12 h, for example, 8 h, 9 h, 10 h, 11 h, 12 h, etc., or any range of the above values. Therefore, by controlling the sedimentation treatment temperature and time within the above range, Zn(HCO3)2 in the solution can be completely decomposed into ZnCO3 precipitate, avoiding zinc loss due to incomplete decomposition and improving the zinc carbonate yield.

[0052] According to an embodiment of the present invention, after adding hydrochloric acid, the pH value of the sediment filtrate is 3.0 to 3.5. For example, it can be 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, or any range of the above values. Therefore, the weakly acidic environment can effectively inhibit Zn... 2+Hydrolysis produces byproducts such as zinc hydroxide and basic zinc chloride, ensuring that all zinc exists in the stable ZnCl2 form, thus improving the yield and purity of zinc chloride.

[0053] According to an embodiment of the present invention, the evaporation time is 60-90 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, etc., or any range of the above values. According to an embodiment of the present invention, the evaporation temperature is 80-110°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, etc., or any range of the above values. Therefore, by controlling the evaporation time and temperature within the above range, the water in the solution can be fully evaporated, allowing the zinc chloride concentration to reach a supersaturated state for crystallization, providing a qualified feed solution for subsequent cooling and crystallization.

[0054] According to an embodiment of the present invention, cooling crystallization includes: subjecting the evaporation product to first cooling crystallization, redissolving the first cooled crystallized product, and subjecting the redissolved product to second cooling crystallization. This ensures the purity of the evaporation crystallization product, zinc chloride.

[0055] According to an embodiment of the present invention, the temperature of the first cooling crystallization is cooled from 80~110℃ to 20~30℃ (cooling rate 5~8℃ / h). For example, it can be cooled from 80℃, 90℃, 100℃, 110℃ to 20℃, 22℃, 25℃, 27℃, 30℃, etc., and the cooling rate can be 5℃ / h, 6℃ / h, 7℃ / h, 8℃ / h, etc. According to an embodiment of the present invention, the time for the first cooling crystallization is 10~15 h, for example, it can be 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, etc., or it can be any range of the above values. Therefore, the purity of the evaporated crystallized product, zinc chloride, can be guaranteed.

[0056] According to an embodiment of the present invention, the redissolution temperature is 80~85℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, etc., or it can be any range of the above values. According to an embodiment of the present invention, the solvent for redissolution is selected from a dilute hydrochloric acid solution with a pH of 3.0. This ensures the purity of the evaporated crystallized product, zinc chloride.

[0057] According to an embodiment of the present invention, the temperature for the second cooling crystallization is cooled from 80-85°C to 20-30°C (cooling rate 3-5°C / h). For example, it can be cooled from 80°C, 81°C, 82°C, 83°C, 84°C, 85°C to 20°C, 22°C, 25°C, 27°C, 30°C, etc., and the cooling rate can be 3°C / h, 4°C / h, 5°C / h, etc. According to an embodiment of the present invention, the time for the second cooling crystallization is 15-20 hours, for example, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, etc., or any range of the above values. This ensures the purity of the evaporated crystallized product, zinc chloride.

[0058] According to an embodiment of the present invention, the drying temperature is 90~100℃, for example, 90℃, 92℃, 95℃, 97℃, 100℃, etc., or any range of the above values. According to an embodiment of the present invention, the drying time is 4~6 hours, for example, 4 hours, 5 hours, 6 hours, etc., or any range of the above values. Thus, zinc chloride hydrate crystals can be completely dehydrated to obtain anhydrous zinc chloride product, ensuring that the product moisture content meets the standard and the purity is >95%.

[0059] S300: The first washing residue is washed with water to obtain a second washing solution and a second washing residue.

[0060] According to an embodiment of the present invention, during the second washing process, the zinc chloride remaining in the first washing residue further dissolves and dissociates in the aqueous solution, as shown in the following reaction formula: The second washing process allows for deep dechlorination of the washing residue, further reducing the chlorine content in the solid materials and ensuring that the chlorine content of the final product meets the required standards. Simultaneously, the resulting second washing liquid is returned to step S100 for use in the first washing process. Through multi-stage countercurrent washing circulation, chlorine is enriched in stages, improving the resource utilization rate of chlorine and zinc, and achieving closed-loop circulation of the washing liquid while conserving water and reducing emissions.

[0061] According to an embodiment of the present invention, in step S300, the liquid-to-solid ratio is 1~2 L / kg. For example, it can be 1 L / kg, 1.2 L / kg, 1.5 L / kg, 1.7 L / kg, or 2 L / kg. This ensures efficient removal of chlorine from the zinc oxide powder and enriches and increases the chlorine content in the first washing solution.

[0062] According to an embodiment of the present invention, the temperature of the second washing is 20-30℃, for example, it can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, etc., or it can be any range of the above values. According to an embodiment of the present invention, the time of the second washing is 3-5 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc., or it can be any range of the above values. Therefore, efficient removal of chlorine from the zinc oxide powder can be ensured, and the chlorine content in the first washing solution can be increased.

[0063] S400: The second washing residue is washed with water for a third time to obtain the third washing solution and washed zinc oxide powder.

[0064] According to an embodiment of the present invention, during the third washing process, the zinc chloride remaining in the second washing residue further dissolves and dissociates in the aqueous solution, as shown in the following reaction formula: The third washing process allows for deep dechlorination of the washing residue, further reducing the chlorine content in the solid materials and ensuring that the chlorine content of the final product meets the required standards. Simultaneously, the resulting third washing liquid is returned to step S300 for the second washing process. Through multi-stage countercurrent washing circulation, chlorine is enriched in stages, improving the resource utilization rate of chlorine and zinc, and achieving closed-loop circulation of the washing liquid while conserving water and reducing emissions.

[0065] According to an embodiment of the present invention, in step S400, the liquid-to-solid ratio is 1~2 L / kg. For example, it can be 1 L / kg, 1.2 L / kg, 1.5 L / kg, 1.7 L / kg, or 2 L / kg. This ensures efficient removal of chlorine from the zinc oxide powder and enriches and increases the chlorine content in the first washing solution.

[0066] According to an embodiment of the present invention, the temperature of the third washing is 20-30℃, for example, it can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, etc., or it can be any range of the above values. According to an embodiment of the present invention, the time of the third washing is 3-5 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc., or it can be any range of the above values. Therefore, efficient removal of chlorine from the zinc oxide powder can be ensured, and the chlorine content in the first washing solution can be increased.

[0067] According to an embodiment of the present invention, the process flow diagram of the method for removing chlorine from zinc oxide powder is as follows: Figure 2 As shown, it includes the following steps: (1) Mix zinc oxide powder and water, pass CO2 gas through for the first wash (or primary wash), flash evaporate the product of the first wash, and desorb the product of the flash evaporated treatment to obtain the first wash slurry (or primary wash slurry) and CO2 gas. (2) The first washing slurry is subjected to a first pressure filtration treatment to obtain a first washing liquid (or primary washing liquid) and a first washing residue (or primary washing residue); the first washing liquid is returned to step (1) for the first washing. (3) The first washing residue is washed with water for a second time (or secondary washing) to obtain a second washing solution (or secondary washing solution) and a second washing residue (or secondary washing residue); the second washing solution is returned to step (1) for the first washing. (4) The second washing residue is washed with water for a third washing (or three washings) to obtain a third washing solution (or three washing solutions) and washed zinc oxide powder; the third washing solution is returned to step (3) for the second washing; (5) When the zinc ion concentration in the first washing solution is 10~50 g / L, the first washing solution is subjected to sedimentation treatment and second pressure filtration treatment in sequence to obtain sedimentation filtrate and zinc carbonate. (6) Add hydrochloric acid to the sediment filtrate, and then evaporate, cool and crystallize, and dry in sequence to obtain zinc chloride.

[0068] Therefore, by adopting the technical solution of this invention, efficient and deep dechlorination of zinc oxide powder can be achieved under mild conditions, ensuring that the chlorine content of the washed material is consistently below 0.2%, meeting the requirements of hydrometallurgical zinc smelting systems. This process uses CO2 as the reaction medium and achieves the reuse of gas and washing liquid through a closed-loop circulation, significantly reducing water and energy consumption, with no wastewater or waste gas emissions, making it environmentally friendly. Simultaneously, this invention can efficiently utilize chlorine and zinc elements, which are originally impurities, to simultaneously produce high-purity zinc carbonate and zinc chloride, among other high-value-added products, truly achieving integrated deep dechlorination, zinc resource recovery, chlorine resource utilization, low-cost operation, and clean production. This process has a short flow chart, stable operation, and outstanding economic efficiency, possessing strong prospects for industrial application.

[0069] In a second aspect, the present invention provides a dechlorinated zinc oxide powder. According to an embodiment of the present invention, the dechlorinated zinc oxide powder is obtained by treating zinc oxide powder to be treated by the method described in the first aspect. Thus, the chlorine content in the zinc oxide powder of this application is as low as 0.2% or less. Those skilled in the art will understand that this zinc oxide powder possesses all the features and advantages of the methods described above, which will not be elaborated further here.

[0070] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0071] Example 1 Raw materials: The zinc oxide powder contains elements such as zinc, chlorine, fluorine, lead, iron, and indium. After testing, its main components and contents are as follows: by mass percentage, the zinc oxide powder contains Zn 58.48%, Cl 4.62%, Pb 4.16%, F 0.47%, Fe 6.24%, and indium 150g / t.

[0072] The zinc oxide powder undergoes dechlorination treatment; the specific process flow is as follows: Figure 2 As shown: 1. Add zinc oxide powder and water to a high-pressure reactor (liquid-to-solid ratio of 5 L / kg). At 20°C and 400 rpm, add CO2 with a purity greater than 95% at a speed of 400 Nm³ / min. 3 A flow rate of / h is fed into the high-pressure reactor, and the reactor pressure is controlled at 0.3MPa for a single washing at room temperature and high pressure for 3 hours. After flash evaporation, the slurry is washed, stirred in a closed system, and desorbed at room temperature and pressure for 0.5 hours to obtain CO2 and the first-washed slurry. The CO2 content of the tail gas at the outlet of the absorption tower is 0.5%. 2. The primary washing slurry from step 1 is filtered through a filter press to obtain primary washing liquid and primary washing residue. The primary washing liquid is returned to step 1 for a second washing to enrich chlorine. The pH of the first washing solution (after enrichment) was 6.41, and it contained Zn 26.1 g / L, Cl 31.5 g / L, F 0.16 g / L, and Fe 0.098 g / L. 3. Add the primary washing residue from step 2 to water for secondary washing (liquid-solid ratio of 2 L / kg), wash at 20℃ for 3 hours, filter by pressure to obtain secondary washing liquid and secondary washing residue, and return the secondary washing liquid to step 1 for primary washing. The secondary washing solution had a pH of 6.87 and contained Zn 3.11 g / L, Cl 3.5 g / L, F 0.043 g / L, and Fe 0.015 g / L. 4. Add the secondary washing residue from step 3 to water for three washings (liquid-solid ratio of 2 L / kg), wash at 20℃ for 3 hours, filter by pressure to obtain the three washing solutions and the washed zinc oxide powder, and return the three washing solutions to step 3 for a second washing. The pH of the three washing solutions was 7.08, containing 1.99 g / L Zn, 2.2 g / L Cl, 0.021 g / L F, and 0.005 g / L Fe. By mass percentage, the secondary zinc oxide powder after washing contained 54.61% Zn, 0.18% Cl, 4.14% Pb, 0.44% F, 6.09% Fe, and 148 g / t indium. 5. Let the washing solution from step 2 stand at 25°C for 8 hours to settle, then filter to obtain the sediment filtrate and zinc carbonate. The sedimentation filtrate had a pH of 6.27 and contained 20.4 g / L Zn, 31.1 g / L Cl, 0.15 g / L F, and 0.096 g / L Fe. By mass percentage, the zinc carbonate contained 42.23% Zn, 0.001% Cl, 0.001% F, and 0.0001% Fe, with a purity of 81.2%. 6. Place the sediment filtrate from step 5 into a reaction tank, add hydrochloric acid to lower the pH to 3.0, and evaporate at 80℃ for 90 min. For the first cooling crystallization process, cool the temperature from 80℃ to 20℃ (cooling rate 5℃ / h) and crystallize for 12 h. Filter to obtain mother liquor and zinc chloride crystals. Add the zinc chloride crystals to a dilute hydrochloric acid solution with pH 3.0 and dissolve at 80℃. For the second cooling crystallization process, cool the temperature to 20℃ again (cooling rate 3℃ / h) and crystallize for 20 h. Filter to obtain mother liquor and zinc chloride crystals. Dry the zinc chloride crystals at 90℃ for 6 h to obtain the zinc chloride product. The mother liquor contained 5.2 g / L Zn and 36.7 g / L Cl, and the purity of zinc chloride was 96.5% by mass percentage.

[0073] Example 2 Raw materials: The zinc oxide powder contains elements such as zinc, chlorine, fluorine, lead, iron, and indium. After testing, its main components and contents are as follows: by mass percentage, the zinc oxide powder contains Zn 58.48%, Cl 4.62%, Pb 4.16%, F 0.47%, Fe 6.24%, and indium 150g / t.

[0074] The zinc oxide powder undergoes dechlorination treatment; the specific process flow is as follows: Figure 2 As shown: 1. Add zinc oxide powder and water to a high-pressure reactor (liquid-to-solid ratio of 4 L / kg). At 25°C and 350 rpm, add CO2 with a purity greater than 95% at a speed of 500 Nm³ / min. 3 A flow rate of / h is fed into the high-pressure reactor, and the reactor pressure is controlled at 0.6MPa for a single washing at room temperature and high pressure for 4 hours. After flash evaporation, the slurry is washed, stirred in a closed system, and desorbed at room temperature and pressure for 1 hour to obtain CO2 and the first-washed slurry. The CO2 content of the tail gas at the outlet of the absorption tower is 0.4%. 2. The primary washing slurry is filtered through a filter press to obtain primary washing liquid and primary washing residue. The primary washing liquid is returned to step 1 for a second washing to enrich chlorine. The pH of the first washing solution (after enrichment) was 6.53, and it contained 28.3 g / L Zn, 35.7 g / L Cl, 0.17 g / L F, and 0.01 g / L Fe. 3. Add the primary washing residue from step 2 to water for secondary washing (liquid-solid ratio of 1.5 L / kg), wash at 25℃ for 4 hours, filter by pressure to obtain secondary washing liquid and secondary washing residue, and return the secondary washing liquid to step 1 for primary washing. The secondary washing solution had a pH of 6.87 and contained Zn 3.25 g / L, Cl 4.1 g / L, F 0.049 g / L, and Fe 0.016 g / L. 4. Add the secondary washing residue from step 3 to water for three washings (liquid-solid ratio of 1.5 L / kg), wash at 25℃ for 4 hours, filter by pressure to obtain the three washing solutions and the washed zinc oxide powder, and return the three washing solutions to step 3 for a second washing. The pH of the three washing solutions was 6.82, and it contained 2.28 g / L Zn, 2.24 g / L Cl, 0.024 g / L F, and 0.007 g / L Fe. By mass percentage, the zinc oxide powder after washing contained 52.93% Zn, 0.15% Cl, 4.11% Pb, 0.39% F, 6.14% Fe, and 149 g / t indium. 5. Let the washing solution from step 2 stand at 27°C for 10 hours to settle, then filter to obtain the sediment filtrate and zinc carbonate. The sedimentation filtrate had a pH of 6.33 and contained 21.7 g / L Zn, 33.4 g / L Cl, 0.14 g / L F, and 0.099 g / L Fe. By mass percentage, the zinc carbonate contained 44.52% Zn, 0.001% Cl, 0.001% F, and 0.0001% Fe, with a purity of 85.4%. 6. Place the sedimentation filtrate from step 5 into a reaction tank, add hydrochloric acid to lower the pH to 3.0, and evaporate at 90℃ for 80 min. In the first cooling crystallization process, cool the temperature from 90℃ to 20℃ (cooling rate 7℃ / h) and crystallize for 10 h. After filtration, obtain the mother liquor and zinc chloride crystals. Add the zinc chloride crystals to a dilute hydrochloric acid solution with pH 3.0 and dissolve at 85℃. In the second cooling crystallization process, cool the temperature to 20℃ again (cooling rate 4℃ / h) and crystallize for 21 h. After filtration, obtain the mother liquor and zinc chloride crystals. Dry the zinc chloride crystals at 95℃ for 5 h to obtain the zinc chloride product. The mother liquor contained 4.3 g / L Zn and 40.7 g / L Cl, and the purity of zinc chloride was 97.4% by mass percentage.

[0075] Example 3 Raw materials: The zinc oxide powder contains elements such as zinc, chlorine, fluorine, lead, iron, and indium. After testing, its main components and contents are as follows: by mass percentage, the zinc oxide powder contains Zn 58.48%, Cl 4.62%, Pb 4.16%, F 0.47%, Fe 6.24%, and indium 150g / t.

[0076] The zinc oxide powder undergoes dechlorination treatment; the specific process flow is as follows: Figure 2 As shown: 1. Add zinc oxide powder and water to a high-pressure reactor (liquid-to-solid ratio of 3 L / kg). At 30°C and 400 rpm, add CO2 with a purity greater than 95% at a speed of 600 Nm³ / min. 3 A flow rate of / h is fed into the high-pressure reactor, and the reactor pressure is controlled at 1.0 MPa for a single washing operation at room temperature and high pressure for 5 hours. After flash evaporation, the slurry is washed, stirred in a closed system, and desorbed at room temperature and pressure for 1.5 hours to obtain CO2 and the first-washed slurry. The CO2 content of the tail gas at the outlet of the absorption tower is 0.3%. 2. The primary washing slurry is filtered through a filter press to obtain primary washing liquid and primary washing residue. The primary washing liquid is returned to step 1 for a second washing to enrich chlorine. The pH of the first washing solution (after enrichment) was 6.62, and it contained Zn 30.4 g / L, Cl 37.2 g / L, F 0.17 g / L, and Fe 0.099 g / L. 3. Add the primary washing residue from step 2 to water for secondary washing (liquid-solid ratio of 1 L / kg), wash at 30℃ for 5 hours, filter by pressure to obtain secondary washing liquid and secondary washing residue, and return the secondary washing liquid to step 1 for primary washing. The secondary washing solution had a pH of 6.87 and contained Zn 3.42 g / L, Cl 4.2 g / L, F 0.051 g / L, and Fe 0.018 g / L. 4. Add the secondary washing residue from step 3 to water for three washings (liquid-solid ratio of 1 L / kg), wash at 30℃ for 5 hours, filter by pressure to obtain the three washing solutions and the washed zinc oxide powder, and return the three washing solutions to step 3 for a second washing. The pH of the three washing solutions was 7.01, containing 2.14 g / L Zn, 2.4 g / L Cl, 0.020 g / L F, and 0.009 g / L Fe. By mass percentage, the secondary zinc oxide powder after washing contained 53.52% Zn, 0.17% Cl, 4.08% Pb, 0.4% F, 6.01% Fe, and 147 g / t indium. 5. The washing solution from step 2 was allowed to stand at 30°C for 12 hours to settle, and then filtered to obtain the sediment filtrate and zinc carbonate. The sedimentation filtrate had a pH of 6.58 and contained 22.8 g / L Zn, 35.7 g / L Cl, 0.18 g / L F, and 0.01 g / L Fe. By mass percentage, the zinc carbonate contained 45.41% Zn, 0.001% Cl, 0.001% F, and 0.0001% Fe, with a purity of 87.1%. 6. Place the sedimentation filtrate from step 5 into a reaction tank, add hydrochloric acid to lower the pH to 3.0, and evaporate at 100℃ for 60 minutes; in the first cooling crystallization process, cool the temperature from 100℃ to 20℃ (cooling rate 5℃ / h), crystallize for 16 hours, and filter to obtain mother liquor and zinc chloride crystals; add the zinc chloride crystals to a dilute hydrochloric acid solution with pH 3.0, dissolve at 85℃, and in the second cooling crystallization process, cool the temperature to 20℃ again (cooling rate 5℃ / h), crystallize for 13 hours, filter to obtain mother liquor and zinc chloride crystals, and dry the zinc chloride crystals at 100℃ for 4 hours to obtain the zinc chloride product; The mother liquor contained 3.4 g / L Zn and 40.1 g / L Cl, and the purity of zinc chloride was 97.6% by mass percentage.

[0077] Example 4 The zinc oxide powder was dechlorinated according to the method in Example 1, except that in step 1, CO2 with a purity greater than 95% was used at 200 Nm 3 A flow rate of / h is introduced into the autoclave.

[0078] Experimental results showed that in a single wash (unenriched), Zn was 3.2 g / L and Cl was 5.4 g / L. The CO2 flow rate was too low, resulting in a slow increase in carbonic acid concentration, a high pH, ​​and insufficient chloride ion dissolution. Under the same 4-hour washing time, the amount of F entering the liquid phase in a single wash was significantly lower. - Cl - The dechlorination efficiency is reduced, and the residual chlorine in the zinc oxide powder is too high; the pressure inside the reactor is too low, making it difficult to maintain a stable lower limit, resulting in insufficient reaction kinetics; the holding time needs to be extended during the washing cycle to achieve a better dechlorination effect, although the energy consumption is low, the treatment effect is worse.

[0079] Example 5 The zinc oxide powder was dechlorinated according to the method in Example 1, except that in step 1, CO2 with a purity greater than 95% was used at 700 Nm 3 A flow rate of / h is introduced into the autoclave.

[0080] Experimental results showed that in a single wash (without enrichment), Zn was 5.9 g / L and Cl was 7.4 g / L. Excessive CO2 flow rate led to rapid carbonic acid formation and high acidity in the solution. Within the same washing time of 4 hours, a single wash resulted in the dissolution of F... - Cl- More, faster circulation enrichment rate, and for the same number of cycles, the washing solution F - Cl - With higher concentrations, the zinc loss from the zinc oxide powder increases slightly; the pressure in the reactor can rise rapidly, exceeding the rated range, requiring frequent depressurization; excess CO2 escapes before fully reacting, resulting in significant gas loss and increased raw material costs; although the reaction rate is fast and the dechlorination effect is better, the zinc recovery rate decreases.

[0081] Example 6 The zinc oxide powder was dechlorinated according to the method in Example 2, except that in step 1, the pressure in the autoclave was controlled at 0.2 MPa and a single high-pressure wash was performed at room temperature for 3 hours.

[0082] The experimental results showed that the initial washing solution (unenriched) contained 2.9 g / L Zn and 4.1 g / L Cl. The pressure in the vessel was too low, the solubility of CO2 decreased, the concentration of carbonic acid in the solution was insufficient, and the pH of the reaction was too high. The chloride ion dissolution was incomplete, the dechlorination rate was low, and there was a lot of residual chlorine in the secondary zinc oxide powder. The reaction driving force was weak, so the washing time needed to be extended, which reduced the dechlorination efficiency. The zinc dissolution loss was low, and the material loss was low.

[0083] Example 7 The zinc oxide powder was dechlorinated according to the method in Example 2, except that in step 1, the pressure in the autoclave was controlled at 1.5 MPa and a single high-pressure wash was performed at room temperature for 3 hours.

[0084] Experimental results showed that the primary washing solution (unenriched) contained 4.7 g / L Zn and 6.9 g / L Cl. When the pressure in the reactor was too high, the solubility of CO2 increased and the acidity of the solution increased rapidly. Chlorine leaching from the secondary zinc oxide powder was thorough, and the dechlorination effect was good. However, excessively high reactor pressure could easily aggravate the dissolution of zinc elements, and the zinc loss would increase significantly. The higher the reactor pressure, the more CO2 gas was consumed, and the operating cost increased accordingly.

[0085] Example 8 The zinc oxide powder was dechlorinated according to the method in Example 3, except that in step 1, the temperature of 20°C was replaced with a temperature of 15°C.

[0086] Experimental results showed that in the primary washing solution (unenriched), Zn was 3.1 g / L and Cl was 6.7 g / L. When the reaction temperature was too low, CO2 solubility increased, the carbonic acidity of the solution was stronger, and chlorine in the secondary zinc oxide powder dissolved more completely, resulting in better dechlorination. However, the reaction rate was slower and lower than usual for the same amount of time. There was less zinc dissolution loss and less material loss. The viscosity of the slurry increased, which was not conducive to the subsequent filtration process.

[0087] Example 9 The zinc oxide powder was dechlorinated according to the method in Example 3, except that in step 1, the temperature of 20°C was replaced with a temperature of 35°C.

[0088] Experimental results showed that in the primary washing solution (unenriched), Zn was 5.2 g / L and Cl was 4.6 g / L. Excessive reaction temperature decreased CO2 solubility and reduced solution acidity, leading to poorer chloride ion leaching capacity from the zinc oxide powder and higher residual chlorine levels. Higher reaction temperatures accelerated reaction kinetics and shortened reaction time, but also increased zinc dissolution rate and significant zinc loss. Higher temperatures also accelerated side reactions and decreased material stability.

[0089] Comparative Example 1 The specific process of alkaline washing and dechlorination of zinc oxide powder in the existing technology is as follows: Raw materials: The zinc oxide powder contains elements such as zinc, chlorine, fluorine, lead, iron, and indium. After testing, its main components and contents are as follows: by mass percentage, the zinc oxide powder contains Zn 58.48%, Cl 4.62%, Pb 4.16%, F 0.47%, Fe 6.24%, and indium 150g / t.

[0090] 1. Add the zinc oxide powder and water to the reaction tank (liquid-solid ratio of 5 L / kg), add Na2CO3 at 80℃ to adjust the pH to 10-11, react for 1.5 h, and filter to obtain the washing solution and washed zinc oxide powder.

[0091] The washing solution had a pH of 10.2 and contained Zn 3.55 g / L, Cl 6.28 g / L, F 0.68 g / L, and Na 8.67 g / L. By mass percentage, the zinc oxide powder after washing contained Zn 55.55%, Cl 1.26%, Pb 4.15%, F 0.14%, and Fe 6.22%. 2. Place the washing solution obtained in step 2 into a reaction tank, add sulfuric acid, and after the pH drops to 7.0, carry out MVR evaporation and crystallization at a temperature of 80℃ to obtain mother liquor and crystalline salt (NaCl≥96%).

[0092] Conventional alkaline washing methods use wastewater with high chlorine, high fluoride, and high zinc content and salinity. The alkaline washing process consumes a large amount of sodium carbonate, introduces sodium ions as impurities into the solution, and leaves a residue of 1.26% chlorine in the slag after washing, failing to meet dechlorination standards and making it unsuitable for direct use in the electrolysis process. Evaporation and crystallization of the washing solution yields industrial salt, a process with high energy consumption and low selling price. During the alkaline washing stage, 3%–5% of zinc dissolves into the liquid phase; after evaporation and concentration, the zinc accumulates in the mother liquor and cannot be recovered, resulting in permanent loss of zinc resources and reducing the overall metal recovery rate.

[0093] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0094] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for removing chlorine from zinc oxide powder, characterized in that, include: (1) The zinc oxide powder is mixed with water and CO2 gas is introduced for the first washing to obtain the first washed slurry; (2) The first washing slurry is subjected to a first pressure filtration treatment to obtain a first washing liquid and a first washing residue; (3) The first washing residue is washed with water to obtain a second washing solution and a second washing residue; (4) The second washing residue is washed with water for a third time to obtain a third washing solution and washed zinc oxide powder; The chlorine content in the washed zinc oxide powder is less than 0.2%.

2. The method according to claim 1, characterized in that, In step (1), after the first washing, the process further includes: The first washing product is subjected to flash evaporation treatment; The flash evaporation product is analyzed to obtain the first washed slurry and CO2 gas.

3. The method according to claim 2, characterized in that, Step (1) satisfies at least one of the following conditions: The temperature of the first wash is 20~30℃; The first washing cycle takes 3-5 hours. The pressure of the first wash is 0.3~1.0 MPa; The CO2 gas flow rate is 300~600 Nm³. 3 / h; The liquid-to-solid ratio in step (1) is 3~5 L / kg; The purity of the CO2 gas is greater than 95%; The parsing process takes 0.5 to 2 hours; The analytical process was carried out under stirring conditions.

4. The method according to claim 1, characterized in that, The first washing solution is returned to step (1) to perform the first washing.

5. The method according to claim 1, characterized in that, The zinc ion concentration in the first washing solution is 10~50 g / L, and the method further includes: The first washing solution was subjected to sedimentation treatment and second pressure filtration treatment in sequence to obtain sedimentation filtrate and zinc carbonate. Hydrochloric acid was added to the sediment filtrate, and the mixture was then evaporated, cooled to crystallize, and dried to obtain zinc chloride.

6. The method according to claim 5, characterized in that, The temperature for the sedimentation treatment is 25~30℃; Optionally, the settling time is 8 to 12 hours.

7. According to claim 5, after adding hydrochloric acid, the pH value of the sediment filtrate is 3.0~3.5; Optionally, the evaporation time is 60-90 min; Optionally, the evaporation temperature is 80~110°C; Optionally, the cooling crystallization includes: The evaporation product is subjected to a first cooling crystallization, the first cooling crystallization product is redissolved, and the redissolved product is subjected to a second cooling crystallization. Optionally, the drying temperature is 90~100℃; Optionally, the drying time is 4 to 6 hours.

8. The method according to claim 1, characterized in that, Step (3) satisfies at least one of the following conditions: The liquid-to-solid ratio in step (3) is 1~2 L / kg; The temperature for the second washing is 20-30℃; The second washing time is 3-5 hours; The second washing solution is returned to step (1) to perform the first washing.

9. The method according to claim 1, characterized in that, Step (4) satisfies at least one of the following conditions: The liquid-to-solid ratio in step (4) is 1~2 L / kg; The temperature of the third wash is 20-30℃; The third washing cycle takes 3-5 hours. The third washing solution is returned to step (3) for the second washing.

10. A dechlorinated zinc oxide powder, characterized in that, The dechlorinated zinc oxide powder is obtained by treating the zinc oxide powder to be treated by the method described in any one of claims 1-9.

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