Ammonia zinc leaching process for cloth bag ash of blast furnace

Abstract

The invention discloses a process for extracting zinc from blast furnace cloth bag ash by ammonia leaching. The process comprises the steps of preparation, ammonia leaching, ammonia distillation and calcination, ammonia leaching dezincification is achieved under the condition of low temperature, the problem of cyclic accumulation of harmful elements is solved, the energy-saving, efficient and clean blast furnace ironmaking method is constructed, resource utilization of the blast furnace cloth bag ash is achieved in the most economical mode, beneficial elements such as iron, carbon and calcium are efficiently recycled, and the economic benefit is increased. Harmful elements such as zinc are removed at a time through ammonia water reaction, high-purity zinc oxide can be obtained by calcining the produced basic zinc carbonate and can be directly exported, remarkable economic benefits and social and environmental benefits are achieved, and demonstration is provided for efficient utilization of metallurgical circulating materials in China.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of metallurgical solid waste, and particularly relates to a process for leaching zinc from blast furnace bag ash with ammonia. Background Art

[0002] Blast furnace gas dust is a coarse dust produced during the gas purification process in blast furnaces. It primarily includes dust from gravity dust collectors, bag filters, and electrostatic precipitators. Its production and chemical composition are influenced by blast furnace raw material conditions, process flow, equipment, and management. According to statistics, dust generated by steel companies accounts for over 10% of steel production, of which zinc-containing dust accounts for approximately 30%. This zinc-containing dust is both a solid waste and an important secondary resource, rich in valuable elements such as iron, zinc, and carbon. The content of some rare metals is even higher than the industrial grade of some primary ores.

[0003] A steel mill's main office has a pig iron production capacity of 6.4 million tons and produces approximately 120,000 tons of blast furnace dust annually. Its branch has an ironmaking capacity of 1.45 million tons and produces 30,000 tons of blast furnace dust annually. This dust has a complex composition. While it can be recycled as an iron-containing material, its high zinc content limits its direct application in metallurgical systems. Currently, much of it is stored or exported, resulting in resource waste. Therefore, developing new technologies to efficiently process and utilize dust dust and other solid waste resources, and to recover valuable metals such as iron and zinc, has become a top priority for steel companies.

[0004] Currently, the primary method for treating blast furnace bag ash is high-temperature roasting in a rotary kiln while simultaneously collecting zinc oxide. However, this process is energy-intensive. There are also cases where bag ash is injected into the blast furnace, but this does not address the issue of recycled zinc enrichment. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for leaching zinc from blast furnace bag ash with ammonia, so as to solve the problems of low resource recovery rate and high energy consumption in the existing blast furnace bag ash treatment process.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A process for extracting zinc from blast furnace bag ash with ammonia, comprising the following steps: S1. Preparation: Place the blast furnace bag ash in a grinder and grind it to below 200 mesh; S2, ammonia leaching: The blast furnace bag ash obtained in S1 is placed in a beaker, and ammonia water, ammonium bicarbonate and distilled water are prepared into a mixed solution. The mixed solution is added to the beaker and mixed with the blast furnace bag ash to obtain a total ammonia amount of 5 mol / L, an ammonia-liquid ratio of 2:1-1:4, and a solid-liquid ratio of 1:3-1:7. Then, ammonia leaching dezincification is performed in a constant temperature water bath under the condition of an ammonia leaching temperature of 30-70°C, a stirring time of 30-70 min, and a stirring rate of 100-500 r / min; S3, ammonia distillation: The mixed solution obtained in S2 after ammonia leaching and zinc removal is subjected to solid-liquid separation, the filter residue is returned to the sintering process to participate in the batching, the filtrate is evaporated with ammonia at a temperature of 60-100°C for 50-70 minutes, aged for 40-80 minutes and precipitated to prepare basic zinc carbonate solid; S4. Calcination: The basic zinc carbonate solid obtained in S3 is calcined at 200-400° C. and kept warm for 30-150 minutes.

[0007] In order to further realize the present invention, the temperature in S3 is 80° C., ammonia is evaporated for 60 minutes, and aging is performed for 80 minutes.

[0008] In order to further realize the present invention, the calcination temperature in S4 is 250° C. and the temperature is kept for 90 minutes.

[0009] The beneficial effects of the present invention compared to the prior art are: The zinc element in blast furnace bag dust exists primarily in the form of zinc oxide, with smaller amounts in the form of zinc ferrite and zinc sulfide. Zinc oxide is an amphoteric oxide, soluble in both acidic and alkaline solutions. In aqueous ammonia, zinc oxide reacts to form soluble ammonia compounds, while insoluble compounds such as zinc ferrite and zinc sulfide do not participate in the reaction. The main reaction equation for zinc oxide in the aqueous ammonia-ammonium bicarbonate system is: ZnO+NH4HCO3+3NH3→Zn(NH3)4CO3+H2O The reaction shows that in the ammonia-ammonium bicarbonate system, zinc oxide dissolves to form Zn(Π)-ammonia complex ions, mainly in the form of Zn(NH3)4 2+ exists in ionic form.

[0010] The ammonia leaching unit of the present invention includes steps such as grinding, mixing, ammonia leaching, and filtration of bag ash. In order to make the ammonia leaching zinc reaction more complete and reduce the reaction time, the bag ash is ground to less than 200 mesh before the experiment. The appropriate amount of ammonia water, ammonium bicarbonate, and water are mixed with the bag ash by calculation. Different variables are controlled and the reaction is carried out in a constant temperature water bath. The influence of conditions such as the total ammonia amount, ammonia-liquid ratio, solid-liquid ratio, leaching temperature, leaching time, and stirring rate on the leaching effect of zinc in blast furnace bag ash is explored. After the reaction is completed, the solution is filtered through a suction filtration device for solid-liquid separation. The leachate obtained under different leaching conditions is detected by atomic absorption spectrometry for the concentration of zinc element, and the leaching rate is calculated. By comparing the leaching rate, the optimal experimental parameters for ammonia leaching zinc are finally obtained. At the same time, the bag ash filter residue after ammonia leaching is dried and XRD phase detection is performed again. The phase results are compared with the blast furnace ash phase results before leaching to further verify the leaching of metal ions.

[0011] The ammonia distillation unit of the present invention includes steps such as evaporation and precipitation of the filtrate and steam recycling. After the ammonia-leached zinc solution is filtered to achieve solid-liquid separation, a zinc complex solution is obtained. The filtrate needs to be subjected to ammonia distillation to obtain basic zinc carbonate solid and separate it from the solution. The ammonia distillation process mainly examines the effects of the ammonia distillation temperature, ammonia distillation time, and the standing time after ammonia distillation on the precipitation rate of basic zinc carbonate.

[0012] The calcination unit of the present invention includes the calcination of basic zinc carbonate solid, ammonia recycling and finished product bagging for export. After the basic zinc carbonate precipitate is separated from the leachate, it needs to be calcined at high temperature to obtain the final product zinc oxide. The influence of factors such as calcination temperature and calcination time on the zinc oxide yield is mainly investigated.

[0013] The present invention realizes the resource utilization of blast furnace bag dust in the most economical way, efficiently recovers beneficial elements such as iron, carbon, and calcium, and removes harmful elements such as zinc at one time through ammonia reaction. The produced basic zinc carbonate can be calcined to obtain high-purity zinc oxide, which can be directly exported.

[0014] This method achieves ammonia leaching dezincification under relatively low temperature conditions, solves the problem of cyclic accumulation of harmful elements, and constructs an energy-saving, efficient and clean blast furnace ironmaking method with significant economic and social and environmental benefits, providing a demonstration for the efficient utilization of recycled materials in my country's metallurgy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a process flow chart of the present invention; Figure 2 The curve of zinc content in the solution changing with time at different ammonia distillation temperatures in the present invention; Figure 3 It is the decomposition product of the experimental example of the present invention when the calcination temperature is 250°C and the holding time is 90 minutes; Figure 4 This is the XRD spectrum of the decomposition product in the experimental example of the present invention at a calcination temperature of 250°C and a holding time of 90 min. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0017] A process for extracting zinc from blast furnace bag ash with ammonia, comprising the following steps: S1. Preparation: Place the blast furnace bag ash in a grinder and grind it to below 200 mesh; S2, ammonia leaching: The blast furnace bag ash obtained in S1 is placed in a beaker, and ammonia water, ammonium bicarbonate and distilled water are prepared into a mixed solution. The mixed solution is added to the beaker and mixed with the blast furnace bag ash to obtain a total ammonia amount of 5 mol / L, an ammonia-liquid ratio of 2:1-1:4, and a solid-liquid ratio of 1:3-1:7. Then, ammonia leaching dezincification is performed in a constant temperature water bath under the condition of an ammonia leaching temperature of 30-70°C, a stirring time of 30-70 min, and a stirring rate of 100-500 r / min; S3, ammonia distillation: The mixed solution obtained in S2 after ammonia leaching and zinc removal is subjected to solid-liquid separation, the filter residue is returned to the sintering process to participate in the batching, the filtrate is evaporated with ammonia at a temperature of 60-100°C for 50-70 minutes, aged for 40-80 minutes and precipitated to prepare basic zinc carbonate solid; S4. Calcination: The basic zinc carbonate solid obtained in S3 is calcined at 200-400° C. and kept warm for 30-150 minutes.

[0018] Example 1: S1. Preparation: Place the blast furnace bag ash in a grinder and grind it to below 200 mesh; S2, ammonia leaching: The blast furnace bag ash obtained in S1 was placed in a beaker, and ammonia water, ammonium bicarbonate and distilled water were prepared into a mixed solution. The mixed solution was added to the beaker and mixed with the blast furnace bag ash to obtain a total ammonia amount of 5 mol / L, an ammonia-liquid ratio of 2:1, and a solid-liquid ratio of 1:3. Then, the ammonia immersion dezincification was carried out in a constant temperature water bath at an ammonia immersion temperature of 30°C, a stirring time of 30 minutes, and a stirring rate of 100 r / min. S3, ammonia distillation: The mixed solution obtained in S2 after ammonia leaching and zinc removal is subjected to solid-liquid separation, the filter residue is returned to the sintering process to be mixed with the ingredients, the filtrate is evaporated with ammonia at 60°C for 50 minutes, aged for 40 minutes and precipitated to prepare basic zinc carbonate solid; S4. Calcination: The basic zinc carbonate solid obtained in S3 was calcined at 200°C and kept warm for 30 minutes.

[0019] Test results: The zinc leaching rate is 78.71%.

[0020] Example 2: S1. Preparation: Place the blast furnace bag ash in a grinder and grind it to below 200 mesh; S2, ammonia leaching: The blast furnace bag dust obtained in S1 was placed in a beaker, and ammonia water, ammonium bicarbonate and distilled water were prepared into a mixed solution. The mixed solution was added to the beaker and mixed with the blast furnace bag dust to obtain a total ammonia amount of 5 mol / L, an ammonia-liquid ratio of 1:4, and a solid-liquid ratio of 1:7. Then, the ammonia leaching dezincification was carried out in a constant temperature water bath under the condition of an ammonia leaching temperature of 70°C, a stirring time of 70 minutes, and a stirring rate of 500 r / min; S3, ammonia distillation: The mixed solution obtained in S2 after ammonia leaching and zinc removal is subjected to solid-liquid separation, the filter residue is returned to the sintering process to participate in the batching, the filtrate is subjected to ammonia evaporation at 100°C for 70 minutes, aged for 80 minutes and precipitated to prepare basic zinc carbonate solid; S4. Calcination: The basic zinc carbonate solid obtained in S3 was calcined at 400°C and kept warm for 150 minutes.

[0021] Example 3: S1. Preparation: Place the blast furnace bag ash in a grinder and grind it to below 200 mesh; S2, ammonia leaching: The blast furnace bag ash obtained in S1 was placed in a beaker, and ammonia water, ammonium bicarbonate and distilled water were prepared into a mixed solution. The mixed solution was added to the beaker and mixed with the blast furnace bag ash to obtain a total ammonia amount of 5 mol / L, an ammonia-liquid ratio of 1:1, and a solid-liquid ratio of 1:5. Then, the ammonia immersion dezincification was carried out in a constant temperature water bath at an ammonia immersion temperature of 40°C, a stirring time of 50 minutes, and a stirring rate of 300 r / min. S3, ammonia distillation: The mixed solution obtained in S2 after ammonia leaching and zinc removal is subjected to solid-liquid separation, the filter residue is returned to the sintering process to be mixed with the ingredients, the filtrate is subjected to ammonia evaporation at 80°C for 60 minutes, aged for 80 minutes and precipitated to prepare basic zinc carbonate solid; S4. Calcination: The basic zinc carbonate solid obtained in S3 was calcined at 250°C and kept warm for 90 minutes.

[0022] Test results: The zinc leaching rate is 81.82%.

[0023] Under the same conditions as in Example 1-3, when the ratio of ammonia solution was 1:3, the zinc leaching rate was 67.25%.

[0024] Experimental example: Blast furnace bag dust collector ash (composition see Table 1) contains a high zinc content, of which Zn exists mainly in the form of ZnO and ZnFe2O4, with a small amount in the form of zinc sulfide (ZnS). Iron exists mainly in the form of hematite, with a small amount of magnetite. In the ammonia-ammonium bicarbonate system, zinc oxide in blast furnace bag dust collector ash dissolves to form Zn(Π)-ammonia complex ions, mainly in the form of Zn(NH3)4 2+After the basic zinc carbonate precipitate is separated from the leachate, it is calcined at high temperature to obtain the final product, zinc oxide.

[0025] Table 1 Chemical composition of blast furnace bag ash (wt.%) like Figure 1 As shown in the figure, a blast furnace bag ash injection zinc extraction process includes the following practical processes: (1) Place the blast furnace bag ash in a grinder and grind it to below 200 mesh.

[0026] Blast furnace bag dust is a black powder with a particle size range of 40-240 μm, with an average particle size of 124.12 μm, which is considered coarse. To ensure a more complete ammonia-zinc leaching reaction and reduce reaction time, the bag dust was ground to a size of less than 200 mesh before the experiment.

[0027] (2) Place the beaker containing the ground blast furnace bag ash in a constant temperature water bath, and prepare a mixture with an appropriate amount of ammonia water, ammonium bicarbonate and a certain amount of distilled water. Then add the mixture into the beaker for ammonia leaching and dezincification.

[0028] In the previous experimental research, the influence of total ammonia amount, ammonia-liquid ratio, solid-liquid ratio, leaching temperature, leaching time, stirring rate and other conditions on the leaching effect of zinc element in bag ash has been explored.

[0029] Taking all factors into consideration, the suitable ammonia leaching conditions for blast furnace bag ash are: total ammonia content of 5 mol / L, ammonia-liquid ratio of 1:1, solid-liquid ratio of 1:5, ammonia leaching temperature of 40°C, stirring time of 50 min, stirring rate of 300 r / min, and the zinc leaching rate reaches 81.94%.

[0030] (3) The mixed solution after ammonia leaching and zinc removal is subjected to solid-liquid separation by filter pressing, the filter residue is returned to the sintering process to participate in the mixing, and the filtrate is prepared into basic zinc carbonate by ammonia evaporation precipitation.

[0031] At different ammonia evaporation temperatures and over time, the zinc in the solution will completely react to form a precipitate. The time required for the zinc in the solution to completely react varies at different ammonia evaporation temperatures, with higher temperatures requiring less time.

[0032] When the ammonia evaporation temperature is between 60℃ and 100℃, the zinc element in the solution can be completely precipitated as long as the reaction time is sufficient. The higher the temperature, the less time is required to precipitate all the zinc elements. Figure 2 shown.

[0033] The time the ammonia solution is left in the air after ammonia distillation is called the aging time. Prolonging the aging time can reduce the zinc content in the solution to a certain extent, allowing the basic zinc carbonate grains to fully grow.

[0034] Table 2 Quality of ammonia evaporation products at different ammonia evaporation temperatures Table 3 Leaching results of zinc element at different ammonia evaporation time and aging time (mg / L) Taking all factors into consideration, the optimal precipitation conditions for the ammonia leaching solution were an ammonia distillation temperature of 80°C, a distillation time of 60 minutes, and an aging time of 80 minutes. Under these optimal process parameters, the zinc precipitation rate was 100%, and the resulting basic zinc carbonate had the highest purity, facilitating the subsequent calcination process to produce zinc oxide.

[0035] (4) The basic zinc carbonate solid is calcined at high temperature, the ammonia is recycled, and the finished zinc oxide is bagged and exported.

[0036] After basic zinc carbonate precipitate is separated by ammonia evaporation, it needs to be calcined at high temperature to obtain the final product zinc oxide. The main focus is on the influence of factors such as calcination temperature and calcination time on the zinc oxide yield.

[0037] When the calcination temperature is 200℃, basic zinc carbonate begins to decompose. When the calcination temperature rises to 250℃, the basic zinc carbonate is basically decomposed. When the holding time is longer, such as 90min, the basic zinc carbonate crystal structure can be completely formed, and the yield reaches 96.90%. Figure 3-4 shown.

[0038] This invention solves the core technical problem of recycling blast furnace dust containing valuable elements such as potassium and zinc. It eliminates the problem of large-scale storage of blast furnace bag dust in steel mills, while also recovering valuable metals such as iron, carbon, and zinc, thereby realizing the resource utilization of blast furnace bag dust. It generates an annual economic benefit of over 50 million yuan and has great promotional value in the industry.

Claims

1. A process for extracting zinc from blast furnace bag ash with ammonia, characterized in that The steps include: S1. Preparation: Place the blast furnace bag ash in a grinder and grind it to below 200 mesh; S2, ammonia leaching: The blast furnace bag ash obtained in S1 is placed in a beaker, and ammonia water, ammonium bicarbonate and distilled water are prepared into a mixed solution. The mixed solution is added to the beaker and mixed with the blast furnace bag ash to obtain a total ammonia amount of 5 mol / L, an ammonia-liquid ratio of 2:1-1:4, and a solid-liquid ratio of 1:3-1:

7. Then, ammonia leaching dezincification is performed in a constant temperature water bath under the condition of an ammonia leaching temperature of 30-70°C, a stirring time of 30-70 min, and a stirring rate of 100-500 r / min; S3, ammonia distillation: The mixed solution obtained in S2 after ammonia leaching and zinc removal is subjected to solid-liquid separation, the filter residue is returned to the sintering process to participate in the batching, the filtrate is evaporated with ammonia at a temperature of 60-100°C for 50-70 minutes, aged for 40-80 minutes and precipitated to prepare basic zinc carbonate solid; S4. Calcination: The basic zinc carbonate solid obtained in S3 is calcined at 200-400° C. and kept warm for 30-150 minutes.

2. The process for extracting zinc from blast furnace bag ash using ammonia as claimed in claim 1, wherein: The temperature in S3 is 80° C., ammonia evaporation is 60 minutes, and aging is 80 minutes.

3. The process for extracting zinc from blast furnace bag ash using ammonia as claimed in claim 1, wherein: The calcination temperature in S4 is 250° C. and the temperature is kept at this temperature for 90 minutes.

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