Manganese recovery from hot cake waste from zinc production plants

Abstract

The present invention provides a novel and efficient method for recovering manganese and producing manganese dioxide from hot cake wastes of zinc production industries. In this process, the waste is first subjected to three stages of leaching with sulfuric acid to extract zinc from it. Then, the leaching solution is separated by filtration and by adding lime water, zinc hydroxide precipitate is obtained. These precipitates are used for the next stage, i.e., modified leaching. In the next step, using ferrous sulfate and sulfuric acid, the conditions for manganese extraction are optimized and the purification process is carried out by removing impurities such as iron, nickel and cadmium. Finally, manganese dioxide is produced with high purity using ammonium persulfate as an oxidant. This method is applicable as an economical and sustainable solution for the metal recycling industry by increasing extraction efficiency, reducing costs and reducing environmental impacts.

Description

Description of the invention Title of the invention Manganese recovery from hot cake waste from zinc production plants Technical background of the relevant invention This invention is in the field of mineral processing and metal recovery from industrial waste, and specifically relates to the recovery of manganese from hot cake waste from zinc production plants. Technical problem and stating the objectives of the invention Zinc metal production plants use primary mineral resources containing zinc minerals and other associated metals. The zinc purification process is carried out by hydrometallurgy, during which other metals are separated and accumulated as waste. Waste from zinc production in Iran is divided into three main categories: 1- Leach cake: A product of the leaching treatment stage that is created to separate metals such as lead and iron. 2- Hot cake: A waste product obtained in the cobalt refining process and is also known as cobalt cake. 3- Cold cake: which is produced during the refining process of nickel and cadmium and is also known as nickel-cadmium cake. These wastes contain significant amounts of heavy metals such as cobalt, manganese, nickel, cadmium and lead. Exposure to air, oxygen and moisture can cause these heavy metals to dissolve and leach into groundwater and surface water, posing a serious threat to the environment and human health. Therefore, the recovery and purification of these wastes is important not only from an environmental perspective, but also from an economic perspective. Hot cake waste contains valuable metals such as manganese, cobalt, lead, cadmium, nickel, copper, and zinc. Currently, a significant portion of this waste is disposed of without recycling, resulting in waste of resources, environmental pollution, and increased costs of industrial waste disposal. Conventional methods for recovering manganese from these wastes are usually expensive, inefficient, or environmentally harmful. Therefore, there is a need for an efficient, economical, and environmentally friendly method for extracting manganese from hot cake. The purpose of this invention is to provide a new method for recovering manganese from hot cake waste from zinc production plants, which, in addition to reducing the waste of mineral resources, helps improve the performance of the metal processing industry and reduce environmental impacts. This method is simpler, more economically viable, and has higher efficiency in extracting manganese than existing methods. Among the problems of current methods are the complexity of the process and the need for solvent extraction, the production of secondary waste, and high acid consumption. A description of the state of the prior art and the history of developments related to the claimed invention. Eyazi et al. (2008) investigated the extraction process of zinc, cobalt and manganese metals from Niles zinc factory waste. In this study, cobalt cake dissolution was performed using sulfuric acid and hydrogen peroxide. To separate the desired metals, a solvent extraction method was used using D2EHPA ligand (20%) and TBP (5%) in kerosene solvent. The results showed that at pH 1.5, zinc was separated from cobalt and manganese, and finally, manganese was separated from cobalt at pH 2.9 [1]. In another study, Safrazadeh et al. (2011) investigated the leaching method using phenol as an aromatic reducing agent for the dissolution of cobalt cake. They studied the effect of parameters such as temperature, particle size, phenol content, and sulfuric acid concentration and finally achieved a recovery rate of 97% for cobalt and 100% for manganese [2]. Given that cobalt cake contains significant amounts of manganese dioxide and that potassium permanganate is used to precipitate cobalt in the cobalt refining step (hot refining), it is assumed that manganese dioxide must also be dissolved to dissolve cobalt. Therefore, the possibility of using manganese dioxide dissolution methods for cobalt cake processing has been investigated. In this regard, Mohammad Bafighi et al. (2008) investigated the dissolution process of manganese dioxide ore using iron powder and dilute sulfuric acid. The results of this study showed that by adjusting parameters such as temperature, particle size, and molar ratio of iron powder to sulfuric acid, 100% efficiency in dissolution of manganese dioxide can be achieved [3]. Also, Sahu et al. (2001) studied the leaching process of low-grade manganese ore (containing 24.7% Mn and 28.4% Fe) under high temperature and atmospheric pressure, using oxalic acid in a sulfuric acid environment. The results of this study showed that 98.4% Mn and 8.7% Fe were extracted [4]. In another study, Lashin et al. (2009) investigated the leaching of low-grade manganese dioxide ore in dilute nitric acid solution containing molasses. The findings of this study showed that the degree of complete dissolution depends on the concentration of nitric acid and the amount of molasses, and under optimal conditions, the best results were obtained at a concentration of 1.2 M nitric acid and 1.9 M molasses [5]. In patent number 45406 in 2007, Zarrin Madan Asia Company disclosed a plan to extract manganese dioxide and manganese sulfate from the waste cakes of the Alborz zinc sulfate and cobalt oxide production plant, in which the cake waste is first leached using sulfuric acid, then by adding liquid sodium sulfide at a specific percentage and based on temperature, pH, and residence time adjustment, cobalt, zinc, and iron elements precipitate in the form of cobalt sulfide (CoS), zinc sulfide (ZnS), and iron sulfide (FeS), and manganese (Mn2+) remains in the solution. By filtration, the solution containing manganese (Mn2+) is separated, and a caustic soda solution is added to it at a specific percentage to obtain magnesium hydroxide (Mn(OH)2). In patent number 40170 in 2007, Shahnaz Mohammadi Rad and Rasoul Mehrvarzan disclosed a plan to extract cobalt and manganese from waste from zinc producing factories and use it in pigment production. In this, cobalt cake waste from zinc ingot producing factories was first mixed with water in a polyethylene tank at ambient temperature for 2-4 hours, and the zinc sulfate salt present in the waste was dissolved in water by settling and filtration. The remaining sediment was reacted with dilute sulfuric acid and hydrogen peroxide in a polyethylene tank equipped with a stirrer for 4-6 hours. In this reaction, the zinc, iron, cobalt, and manganese compounds present in the waste were dissolved in the form of sulfate salts. Then, the solution and sediments were separated by filtration. Alkaline compounds such as soda or sodium carbonate were added to the resulting solution so that all zinc, iron, cobalt, and manganese precipitated in the form of hydroxide or carbonate. Then, brown precipitates of hydroxide or carbonate of zinc, iron, cobalt, and manganese are used in the process of producing black ceramic pigment in a mixed form after drying. Providing a solution to an existing technical problem along with an accurate, sufficient, and integrated description of the invention Manganese is a key element in various industries, especially in metallurgy, steelmaking, battery manufacturing, and the chemical industry. This metal has a wide range of applications in industry due to its unique properties, including its vital role in improving the mechanical properties of steel. In addition, compounds such as manganese dioxide (MnO₂) are used as a valuable material in the production of rechargeable batteries, catalysts, and water purification processes. Despite the high importance of manganese, one of the main challenges in its extraction and processing is the limitation of primary resources as well as the difficulty in dissolving manganese compounds, especially manganese dioxide, in aqueous and acidic environments. For this reason, leaching has been considered as an efficient method for extracting and recycling this metal from secondary sources such as industrial wastes. Leaching is a hydrometallurgical process in which acidic or alkaline solutions are used to dissolve minerals and extract metal ions. The selection of optimal leaching conditions, including the type of acid, temperature, pH, reaction time, and the presence of reducing agents, plays a decisive role in the dissolution rate of manganese and other valuable metals. One of the most important secondary sources of manganese is the hot cake wastes of zinc production companies. These wastes mainly contain compounds of manganese, cobalt, iron, zinc and other metals that are difficult to extract under normal conditions. Therefore, the development of an efficient and economical process for the recovery of these metals from hot cake, in addition to reducing environmental pollution, can bring significant added value to related industries. In this study, a novel and optimized method for modified hot cake leaching is presented, which not only enables manganese extraction, but also maximizes the recovery of other valuable metals by optimizing operating conditions. In the following, the hot cake leaching process and the role of various parameters in metal dissolution are first examined, then, by introducing the modified method, the effect of adding reducing agents on improving leaching efficiency and effective recovery of manganese dioxide will be explained. 1- Warm cake dip Leaching is one of the important parts in the hydrometallurgical industries of metals, including the zinc extraction industry. Various factors, including temperature, pH, residence time, solid to liquid ratio, and type of acid, are effective in leaching. Each of these factors can have many effects on leaching. Therefore, in the present work, conditions that are used in the zinc industry for soil leaching were selected for hot cake leaching. 500 grams of hot cake were transferred into the leaching vessel with one liter of water according to the analysis in Table 1. Then, the pH of the mixture was adjusted to 1.5 by adding sulfuric acid. The volume of the solution was adjusted to 2 liters by adding water. The mixture was allowed to complete leaching for 90 minutes at a temperature of 70-75 °C. Sulfuric, nitric, and hydrochloric acids were used to investigate the effect of the type of acid. After leaching, the amount of metal ions in the solution was measured, and the results are shown in Table 2. It should be noted that all measurements in this study were performed using an atomic absorption spectrometer. The results of leaching hot cake in sulfuric acid, nitric acid and hydrochloric acid in Table 2 showed that the metals in hot cake were classified into two groups. The first group includes nickel, cadmium, copper and lead, whose solubility increases by changing the type of acid from sulfuric acid to nitric acid or hydrochloric acid. The second group includes cobalt, manganese and iron, whose solubility does not change by changing the type of acid. The presence of manganese in the form of manganese dioxide in the hot cake causes the special behavior of cobalt and manganese in the leaching of the hot cake with acid. It can be concluded that the industrial leaching method and the use of sulfuric acid, nitric acid and hydrochloric acid have no effect on the leaching of cobalt and another method must be sought to leach manganese and cobalt from the hot cake. This issue will be discussed below. 2- Zinc leaching As shown in the results of Table 2, a significant amount of zinc can be removed by performing the leaching operation. In this section, by performing the leaching operation three times in succession, the amount of zinc in the hot cake is reduced to the lowest value. First, 1400 grams of hot cake was transferred to the first tank by analyzing Table 3, and by adding 50 ml of sulfuric acid, the pH of the solution was adjusted to 1. By adding water, the volume of the solution was adjusted to 2 liters. By adjusting the temperature of the solution to 70-75, the mixture was stirred for 60 minutes until the leaching was complete. Then, the parts of the hot cake that had not dissolved were separated from the solution by filtering and transferred to the second tank, the pH of the solution was adjusted to 1.5 by adding 10 ml of sulfuric acid, and the volume of the solution was adjusted to 2 liters by adding water. By adjusting the temperature of the solution to 70-75°C, the mixture was stirred for 60 minutes until the leaching was complete. Then, the undissolved parts of the hot cake were separated from the solution by filtering and transferred to the third tank. The pH of the solution was adjusted to 1.5 by adding 10 ml of sulfuric acid, and the volume of the solution was brought to 2 liters by adding water.The mixture was stirred for 60 minutes by adjusting the temperature of the solution to 70-75°C until the leaching was complete. The results are reported in Table 3. The undissolved portions of the hot cake were separated from the solution by filtration. The precipitate from the third leaching step was sent as the initial feed to the next step. Lime water was added to the resulting solution, which contained a large amount of zinc ions, to convert it to zinc hydroxide. Zinc hydroxide not only has significant added value economically, but also acts as a sustainable and effective solution in reducing the negative effects of heavy metals on the environment. Zinc hydroxide production is an important achievement, both helping to increase the economic efficiency of the process and as a new and efficient solution in solving environmental problems. According to Table 4, the highest zinc extraction efficiency is related to the first stage, because the zinc content is the highest and can be extracted more easily. By performing three consecutive leaching stages, 77.42% of the total zinc content in the initial hot cake can be extracted. After three leaching stages, we will reach a stable texture of hot cake with 15.2% manganese, 3.8% zinc and 1.64% cobalt, in which the zinc content has been greatly reduced and the cobalt content in this cake has been concentrated. After the completion of the three leaching stages and the separation of the solution phase and the solid phase, the resulting precipitate is transferred to the modified leaching stage. The schematic diagram of zinc leaching is shown in Figure (A1). 3- Modified hot cake sink In hot cake, manganese is in the form of manganese dioxide, which is insoluble in sulfuric acid, therefore, manganese and cobalt cannot be transferred from hot cake to the solution phase by leaching hot cake. Manganese dioxide has oxidizing properties and is considered a weak oxidizing agent. In this study, this property of manganese dioxide was used in leaching. For this reason, leaching was performed in the presence of iron sulfate as a reducing agent. 500 grams of hot cake leached three times, containing (15.2% manganese, 1.64% cobalt, 3.8% zinc, 450 ppm cadmium, and 130 ppm nickel with 45% moisture), were weighed, and iron sulfate as a reducing agent and one liter of water were added. The pH of the solution was adjusted to 1.5 using sulfuric acid. The mixture was stirred at 70-75°C for 90 minutes. The amount of materials and metals released in the solution was measured and is given in Table 5. The data in Table 5 show that leaching in the presence of ferrous sulfate has a very large effect on leaching efficiency. In this process, divalent iron is converted to trivalent iron by oxidation by manganese dioxide. The color of the solution changes from green (divalent iron) to a yellow-brown solution (trivalent iron). Also, the high amount of manganese and cobalt in the solution indicates the effectiveness of ferrous sulfate on the leaching efficiency. An increase of more than 150 grams of ferrous sulfate reduces the efficiency of the process. Because trivalent iron has a viscous characteristic and tends to retain a lot of moisture, the solution becomes gel-like with increasing iron content, making it difficult to filter and reduce moisture. This experiment shows that 150 grams of ferrous sulfate per 500 grams of hot cake can introduce the highest amount of metal ions into the solution. With increasing ferrous sulfate, the amount of cobalt in the solution increases, but the volume of the solution obtained decreases greatly (Table 5). Leaching in the presence of ferrous sulfate also causes the amount of iron in the solution to increase. Therefore, the iron in the solution must be precipitated.Since trivalent iron forms a very insoluble precipitate with hydroxide ion, it is sufficient to raise the pH of the solution to 4 by adding lime. All the iron in the solution will be precipitated. It is better to add lime in the form of dry lime rather than lime water, because lime water is much more active than dry lime and causes a reduction in zinc, cobalt and manganese in the solution. Table 6 shows the amount of metal ions in the solution before and after the addition of lime. To increase the pH of the above solution, 30 grams of lime was added. According to Table 6, by increasing the pH to 4-4.5, iron can be completely removed. Complete removal of iron shows that iron in the presence of manganese dioxide has been converted to trivalent iron, which forms a precipitate rapidly with increasing pH. The schematic diagram of the modified hot cake leaching is shown in Figure (B1). 4- Removal of nickel and cadmium from leached aqueous solution To remove nickel and cadmium, the industrial cementation method was used. For this reason, zinc powder was added to the desired solution because the reduction potential of nickel and cadmium is slightly larger than zinc and they can oxidize zinc metal and settle at the bottom of the container as a precipitate. For this purpose, first 200 ml of a solution containing cobalt(II), cadmium(II), nickel(II), zinc(II) and manganese(II) metal ions (with an initial concentration of cobalt ppm2640, cadmium ppm64, nickel ppm32, zinc ppm4430 and manganese ppm17000) was transferred into the beaker. The solution was heated to 80°C. Then a few drops of sulfuric acid were added to bring the pH of the solution to between 3.5-4. Since the surface of the zinc powder used may be oxidized and deactivated, it is more activated by placing it in an acidic environment. Excessive use of acid will result in excessive use of zinc powder, so care must be taken to use the required amount of acid. After adjusting the pH and temperature, 100 times the molar amount of nickel and cadmium zinc powder was added.In this solution, after adding 4 grams of zinc powder, cadmium removal occurs very quickly, but it takes another 60 minutes to remove nickel. Due to the high concentration of cobalt, some of it is also removed along with nickel and cadmium. Table 7 shows the amount of metal ions in the leached aqueous solution before and after this step. In Table 7, you can see that by adding zinc powder to the solution, nickel and cadmium impurity ions are removed to a significant extent, and cobalt is also removed at this stage by 16%. After removing nickel and cadmium from the leached solution and separating the precipitate from the solution, the solution is transferred to the next step to remove manganese. The schematic diagram of nickel and cadmium removal is shown in Figure (C 1). 5- Removing manganese from solution Potassium permanganate has sufficient power to remove manganese, but it also removes cobalt, so in the present work, another oxidant called ammonium persulfate was used. To conduct the first experiment, 200 ml of a solution from which nickel and cadmium had been removed in the previous stage and containing cobalt(II), zinc(II) and manganese(II) metal ions (with an initial concentration of cobalt ppm 2200, zinc ppm 6930 and manganese ppm 16800) was transferred to a two-liter beaker. At this stage, temperature regulation is very important and the higher it is, the more effective the method will be. The solution was heated to the boiling point. Then, ammonium persulfate was gradually added to the boiling solution. It should be noted that the addition of ammonium persulfate must be gradual because adding it all at once will remove a larger amount of other ions. 20 grams of ammonium persulfate was added to the solution and heated for one hour. The results of this step are given in Table 8. By adding ammonium persulfate, manganese is converted to manganese dioxide and forms a precipitate. This precipitate also precipitates some of the cobalt in the solution. The amount of cobalt removed is about 12%. The precipitated manganese is separated from the solution by filtration. The precipitate obtained is manganese dioxide, the analysis of which is given in Table 9. Manganese dioxide is used as an oxidant in the zinc industry, for this reason, a comparison of a production sample with an industrial sample is also given in Table 9. As can be seen in Table 9, the manganese dioxide produced during the manganese removal process has a much higher percentage than the industrial sample. It has much lower levels of iron, nickel and cadmium impurities than the industrial sample, which is also a feature. The schematic diagram of manganese removal is shown in Figure (D1). The overall schematic diagram of the manganese production process from hot cake waste is shown in Figure 1. As a result, in this research, a new, efficient and economical method for the production of manganese dioxide was presented, which is simple and highly feasible. This method is not only cost-effective, but also provides high efficiency due to the use of optimal operating conditions. The main advantage of this process is the reduction of production costs, increased productivity and ease of implementation on an industrial scale. The results obtained show that this method is a very efficient and effective solution for producing manganese dioxide from hot cake wastes of zinc production companies. In addition to reducing environmental problems caused by the accumulation of industrial wastes, this technology plays an important role in sustainable development by converting waste materials into a valuable product. On the other hand, the production of manganese dioxide from these wastes not only creates significant economic added value, but can also meet the needs of related industries for this vital material and reduce dependence on primary resources. The findings of this research have high potential for development, commercialization, and industrial exploitation and can be used as a practical and innovative solution to optimize industrial processes related to manganese dioxide production. This innovation can create a new path in the metallurgical, steelmaking, electronics, and battery manufacturing industries and be an important step towards intelligent resource management and the development of green technologies. Explanation of shapes, maps and diagrams Table 1 - This table is the result of the analysis of the consumed hot cake (digestion by the Sultani acid method). Table 2 - This table is the result of hot cake leaching analysis using different acids. Table 3 - This table shows the results of successive hot cake leaching using sulfuric acid. Table 4 - This table is the result of the zinc extraction efficiency from hot cake in the leaching process with sulfuric acid. Table 5 - This table shows the results of the modified leaching of the hot cake leached waste in the previous stage. Table 6 - This table shows the results of the effect of increasing pH using lime on the precipitation of iron ions. Table 7 - This table shows the results of nickel and cadmium removal from the leached aqueous solution. Table 8 - This table shows the result of manganese removal from the leached aqueous solution. Table 9 - This table shows the results of the analysis of manganese dioxide produced in the present work and an industrial sample. Figure 1- This figure is a schematic diagram of the manganese production process from hot cake waste. (a) Schematic diagram of zinc leaching. (b) Schematic diagram of modified hot cake leaching. (c) Schematic diagram of nickel and cadmium removal. (d) Schematic diagram of manganese removal. A clear and precise statement of the advantages of the claimed invention over prior inventions. Advantages of the claimed invention over previous inventions The method presented in this invention is a novel, economical and efficient process for recycling manganese and producing manganese dioxide from hot cake wastes of zinc production companies. Compared to conventional methods, this process has significant advantages, including: 1- Increasing extraction efficiency: In traditional methods, manganese dioxide leaching using common mineral acids such as sulfuric, nitric, and hydrochloric acid has low efficiency due to the insolubility of manganese dioxide. However, in this method, the use of iron sulfate as a reducing agent increases the leaching efficiency and effective dissolution of manganese. 2- Optimization of operating conditions: This process improves leaching performance by carefully controlling operating parameters (such as pH, temperature, type and amount of reductant), thereby enabling maximum extraction of manganese and other valuable metals. 3- Reducing production and processing costs: Compared to traditional methods that require complex processes and expensive chemicals such as extracting ligands and organic solvents, the proposed method significantly reduces the costs of manganese dioxide production by using cheaper materials and simpler processes. 4- Improving the quality of the produced manganese dioxide: The manganese dioxide produced in this process has a higher purity than existing industrial samples, and the percentage of impurities such as iron, nickel, and cadmium in it is minimized. 5- Environmental benefits and reduction of industrial waste: In addition to reducing pollution caused by the disposal of hot cake waste, this method prevents the waste of resources and contributes to sustainable development by recycling valuable materials from this waste. 6- Industrial scale implementation capability: Due to its simplicity, low cost, and high effectiveness, the presented process has the capability of being implemented on an industrial scale and can be used as a commercialized technology in the metallurgy and metal recycling industry. 7- Reducing dependence on primary manganese sources: Given the limited manganese mineral resources, this method can be used as an alternative solution to meet the needs of dependent industries, reduce dependence on imports, and increase the security of raw material supply. By combining hydrometallurgical technologies and optimal resource management, this innovation enables effective recycling of manganese and could revolutionize the mining and processing industry of this metal. Description of at least one implementation method for implementing the invention 1- First, 500 grams of hot cake waste is combined with one liter of water in a leaching vessel. Then, by adding sulfuric acid, the pH of the mixture is adjusted to 1.5. Then, water is added until the volume of the solution reaches 2 liters. The mixture is stirred at a temperature of 70 to 75 degrees Celsius for 90 minutes until the leaching is complete. The solution and the remaining precipitate are separated, and then the leaching is repeated with the remaining precipitate, and this operation is finally done three times. The precipitate is used for the next step, i.e., the modified leaching, and lime water is added to the resulting solution, and zinc hydroxide precipitate is obtained. 2- In this step, 500 grams of thrice-washed hot cake is combined with 150 grams of iron sulfate and one liter of water, and the pH of the mixture is adjusted to 1.5 by adding sulfuric acid. The mixture is stirred at 70 to 75 degrees Celsius for 90 minutes. Then the solution is increased to 4.5 by adding lime to separate the iron as a precipitate. The cementation method using zinc powder is used to remove nickel and cadmium. Finally, ammonium persulfate is used as an oxidant to separate manganese. Explicit mention of the industrial application of the invention This invention impacts various industrial fields by providing a novel method for recovering manganese from hot cake waste. This method not only efficiently recovers manganese, but also helps reduce the waste of mineral resources and improve the performance of the metal processing industry. The following are industrial applications of the invention: 1- Steel and metallurgy industry: Manganese recovered in this method can be used as an important raw material in steel production. Manganese plays a vital role in improving the mechanical properties of steel, such as increasing strength and ductility. 2- Battery industry: The manganese dioxide produced by this process can be used in the production of rechargeable batteries. These batteries are used in electronic devices and electric vehicles. 3- Chemical industry: Manganese and its compounds are used in the production of catalysts and various chemicals. These materials are used in industrial processes and water purification.

Claims

Claim What is claimed: Claim 1) What is claimed is a method of recovering manganese from hot cake waste from zinc production industries, which includes the following steps: a) leaching the waste in a sulfuric acid solution of a certain concentration, b) adding iron sulfate as a reducing agent to facilitate the dissolution of manganese, c) separating metal impurities such as iron, nickel, and cadmium from the solution by adjusting pH and temperature, d) oxidizing the dissolved manganese using ammonium persulfate to produce a manganese dioxide precipitate, e) recovering by-products including zinc hydroxide. Claim 2) According to claim 1, in the zinc leaching step, sulfuric acid is used at a concentration between 1 and 2 molar and at a controlled temperature between 50 and 70 degrees Celsius. Claim 3) According to claim 1, in the modified hot cake leaching step, iron(II) sulfate is added to the solution as a reducing agent, so that the resulting Fe²⁺ ions reduce manganese dioxide (MnO₂) and convert it into divalent manganese ion (Mn²⁺). Claim 4) According to claim 1, to remove metal impurities from the solution, the pH of the solution is adjusted to about 4 with caustic soda and heated at a certain temperature for a certain period of time to form a selective precipitate. Claim 5) According to claim 1, in the final oxidation step, ammonium persulfate is added at a ratio of 1.5 to 1 to Mn²⁺ ions to form a high-purity manganese dioxide precipitate. Claim 6) According to claim 1, the by-product of the process, which includes zinc ions, is precipitated by adding sodium hydroxide to a pH of about 9 to 10 and is recycled as zinc hydroxide.

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