A method for treating chlorine-containing zinc ash

Abstract

This invention relates to a method for treating chlorine-containing zinc ash, belonging to the field of zinc smelting slag treatment technology. The technical solution of this invention includes: (1) slurrying the chlorine-containing zinc ash with water, and adding Cu... 2+ dilute acid solution, using Cu 2+ (1) Suppress the precipitation of arsine gas, control the pH value of the slurry during the process and at the end point to leach zinc; (2) After zinc leaching is completed, add neutralizing agent and oxidizing agent to remove impurities; (3) Concentrate and crystallize the impurity-removed filtrate from step (2), control the specific gravity of the crystallization liquid at the end point, cool the concentrated liquid to room temperature, filter and air dry to produce zinc sulfate heptahydrate product, and return the crystallization mother liquor to the next group for concentration and crystallization. The process of this invention is short, can effectively suppress the generation of high concentration of arsine gas during acid leaching, and can make chlorine enter the zinc sulfate product evenly without dechlorination. It can stably produce first-grade zinc sulfate heptahydrate, and the crystallization mother liquor is recycled and not discharged.

Description

Technical Field

[0001] This invention belongs to the field of zinc smelting slag treatment technology, specifically, it relates to a method for treating chlorine-containing zinc ash. Background Technology

[0002] Zinc sulfate heptahydrate (ZnSO4·7H2O) is generally used industrially as a mordant, wood preservative, animal glue clarifying agent, leather preservative, paper bleaching agent, and mineral processing reagent. In medicine, it is used as an emetic and astringent. It is also used in the manufacture of synthetic fibers, pesticides, and zinc salts (including lithopone), and its demand is gradually increasing with the rapid development of the national economy. Currently, the main raw materials for producing zinc sulfate heptahydrate in my country are metallic zinc and zinc-containing ores, resulting in high production costs.

[0003] In zinc smelting processes, zinc dross is produced when zinc sheets are melted and cast into zinc ingots, and when zinc sheets are used to produce zinc-based alloys and blown zinc powder. After screening and ball milling, the zinc dross produces chlorinated zinc ash, the main component (%wt) of which contains 70-80% Zn and 1-2% Cl. Currently, the utilization of chlorinated zinc ash mainly involves removing chlorine from the pyrometallurgical furnace, using the residue as a raw material for zinc smelting. However, after purification and washing of the flue gas entering the pyrometallurgical furnace, chlorine re-enters the water body. This chlorine must be recovered to NaCl and used for purifying and washing the flue gas from the pyrometallurgical furnace before it can be reused or meet emission standards. This process suffers from problems such as a long treatment time, the need to recover chlorine from the water body, and high production costs. Summary of the Invention

[0004] To overcome the problems existing in the background technology, the present invention provides a method for treating chlorinated zinc ash, which can prepare chlorinated zinc ash into a heptahydrate zinc sulfate product that meets the requirements of industrial first-class products, with a zinc recovery rate of 96-98%. Throughout the zinc recovery process, the generation of high-concentration arsine gas during acid leaching can be effectively suppressed, and chlorine can be evenly introduced into the zinc sulfate product without the need for chlorine removal. This ensures a stable production of first-class heptahydrate zinc sulfate, and the mother liquor is recycled without being discharged.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] The method for treating the chlorine-containing zinc ash includes the following steps:

[0007] (1) Leached zinc

[0008] Chlorine-containing zinc ash is slurried with water, and Cu is added. 2+ Zinc is leached with dilute acid solution, and the pH value of the slurry is controlled during the leaching process and at the end point.

[0009] (2) Removal of impurities

[0010] After zinc leaching is complete, neutralizing and oxidizing agents are added to remove impurities, and liquid-solid separation is performed.

[0011] (3) Concentration and crystallization

[0012] The impurity-removing filtrate from step (2) is concentrated and crystallized. The specific gravity of the final crystallization liquid is controlled. The concentrated liquid is cooled to room temperature under stirring, filtered, and air-dried to obtain first-grade zinc sulfate heptahydrate.

[0013] Furthermore, in step (1), the pH value of the leaching process and the leaching endpoint is controlled to be 2.0-3.0.

[0014] Furthermore, in step (1), the dilute acid solution is dilute sulfuric acid; Cu 2+ The dosage is 0.5-1.0 g / L.

[0015] Furthermore, Cu in step (1) 2+ It is added in the form of copper sulfate.

[0016] Furthermore, the neutralizing agent added in step (2) is CaO powder or Ca(OH)2 powder.

[0017] Furthermore, the oxidant added in step (2) is hydrogen peroxide or potassium permanganate.

[0018] Furthermore, in step (3), the specific gravity of the crystallization solution at the concentration endpoint is controlled to be 1.56-1.60 g / cm³. 3+ .

[0019] Furthermore, the mother liquor filtered in step (3) is returned to the next group for concentration and crystallization.

[0020] Furthermore, the air drying in step (3) is natural air drying or hot air drying.

[0021] Furthermore, the hot air drying temperature is 50-60℃.

[0022] The beneficial effects of this invention are:

[0023] The method of the present invention can recover zinc from chlorine-containing zinc ash in the form of zinc sulfate heptahydrate, and the purity of the product meets the requirements of first-class product.

[0024] In the zinc recovery process, this invention, through the control of process steps and process indicators, can not only effectively suppress the generation of high-concentration arsine, but also ensure that chlorine enters the zinc sulfate product in a balanced manner, without the need to set up additional chlorine removal or chlorine-containing gas recovery processes or devices.

[0025] The method of this invention not only yields zinc sulfate heptahydrate products that meet the requirements of first-class products, but also ensures the quality requirements of zinc sulfate heptahydrate products even after the mother liquor is recycled. The mother liquor does not require open-circuit treatment, and there is no waste liquid discharge throughout the entire process.

[0026] This invention is a novel process for preparing zinc sulfate from chlorinated zinc ash produced during zinc smelting. It not only achieves zinc recovery but also balances and controls all impurity ions in the chlorinated zinc ash. The entire process produces no wastewater or waste gas discharge, has a short process flow, low processing cost, and has strong industrial application value. Detailed Implementation

[0027] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are all within the scope of protection of this invention.

[0028] The aforementioned treatment of chlorine-containing zinc ash includes the following steps:

[0029] (1) Leached zinc

[0030] Chlorine-containing zinc ash is slurried with water, and Cu is added. 2+ The zinc is leached with a dilute acid solution, and the pH value of the slurry is controlled during the process and at the end point. After the zinc leaching is completed, a neutralizing agent and an oxidizing agent are added to remove impurities and the liquid and solid are separated.

[0031] In addition to Zn and Cl, chlorine-containing zinc ash also contains impurities such as Al2O3, Fe, and a small amount of As.

[0032] Since zinc in chlorinated zinc ash contains 5-15% by weight of zinc in the form of metallic Zn, as well as a small amount of As, it is easy to generate high concentrations of arsine gas when leached under acidic conditions, which endangers the safety of workers.

[0033] By adding Cu to the zinc chloride-containing acid solution 2+ The reaction produces Cu3As precipitate, while almost no or only a very small amount of AsH3 gas is produced. Experimental studies have shown that Cu... 2+ It can be added to dilute sulfuric acid or to the leaching slurry, but when added to dilute sulfuric acid, Cu... 2+ The amount added can be minimized, saving production costs. Therefore, the chlorine-containing zinc ash is first slurried with water, and then mixed with Cu-containing... 2+ The reaction with dilute sulfuric acid.

[0034] This invention controls the Cu content by maintaining a Cu / As mass ratio of 3.5-4.0. 2+ The amount added. Through experimental research, the inventors discovered that Cu... 2+ The interaction between dilute sulfuric acid and chlorine-containing zinc ash is extremely important. If chlorine-containing zinc ash is added to a Cu-containing... 2+In dilute sulfuric acid solution, due to the change in slurry acidity from high to low, arsine gas with a concentration of 4-6 ppm will be generated, seriously affecting operational safety; even if Cu in the dilute sulfuric acid solution... 2+ Even increasing the concentration to 5 g / L could not suppress the generation of high-concentration arsine gas. Therefore, only Cu-containing... 2+ Dilute sulfuric acid solution was added to the zinc ash slurry that had been slurried with water.

[0035] The inventors also discovered that after slurrying chlorine-containing zinc ash with water, adding Cu... 2+ When leaching zinc with dilute sulfuric acid at temperatures of 60-80℃, pH control during the leaching process is equally important. If the process pH is less than 2.0, high concentrations of arsine gas will still be produced, with the concentration increasing as the pH decreases. When the process pH is stable at 2.0 or above, the instantaneous peak concentration of arsine gas is less than 0.1 ppm. However, if the process pH is greater than 3.0, zinc leaching is slow, and the leaching time will be prolonged. Therefore, controlling the process pH between 2.0 and 3.0 can simultaneously control both the concentration of arsine gas produced and the leaching rate of zinc. Thus, the pH value during and at the end of the leaching process must be strictly controlled between 2.0 and 3.0.

[0036] By controlling the acid leaching process and the pH value at the end of the acid leaching process (2.0-3.0), the zinc leaching rate in chlorine-containing zinc ash can reach 96-98%, resulting in relatively thorough zinc leaching.

[0037] (2) Precipitation and impurity removal

[0038] During zinc leaching, Cl, Al₂O₃, and Fe are also leached. At the final pH of 2.0-3.0, Al₂O₃ exists as Al(OH)₃ colloidal form after leaching, severely affecting the clarification and filtration of the slurry and impacting product quality. The leached iron exists as FeSO₄, also affecting product quality. Therefore, after acid leaching, a neutralizing agent needs to be added to adjust the slurry pH to precipitate Al(OH)₃ into the slag, eliminating its impact on clarification and filtration. When the pH of the leached slurry is adjusted to 4.5-5.0, the Al(OH)₃ colloidal precipitation is complete, without affecting clarification and filtration. The neutralizing agent is CaO powder or Ca(OH)₂ powder. After adding the neutralizing agent, an oxidizing agent needs to be added to oxidize FeSO₄ and precipitate it; the oxidizing agent is hydrogen peroxide or potassium permanganate. Liquid-solid separation is then performed.

[0039] (3) Concentration and crystallization

[0040] The filtrate from step (1) is concentrated, and the concentrated solution is cooled to room temperature under stirring and then filtered to produce zinc sulfate heptahydrate crystals and crystallization mother liquor. The upper group of crystallization mother liquor is added to the lower group of concentrated crystallization.

[0041] Zinc sulfate heptahydrate crystals, after being air-dried, yield industrial grade 1 product (HG / T2326-2005). Air drying can be done by natural drying or hot air drying, wherein the hot air temperature is 50-60℃ during hot air drying.

[0042] During concentration and crystallization, a large amount of the leached Cl enters the zinc sulfate heptahydrate product, while a small amount remains in the mother liquor. Controlling the specific gravity of the final crystallization solution is extremely important during concentration and crystallization. If the specific gravity of the final crystallization solution is <1.56 g / cm³... 3 This will cause chlorine to gradually accumulate in the crystallization mother liquor. When the mother liquor is returned for concentration and crystallization, it will result in excessive chlorine content in the product, failing to meet the requirements for first-grade products. The crystallization mother liquor must be periodically discharged to ensure product quality, leading to zinc loss and chlorine leakage. If the specific gravity of the final crystallization solution is greater than 1.60 g / cm³, 3 This can result in insufficient solution volume in the concentrated liquid after cooling, making it difficult to remove zinc sulfate crystals. Therefore, it is necessary to control the specific gravity of the final crystallization solution.

[0043] 1.56-1.60 g / cm³ 3 .

[0044] Table 1 shows the product quality requirements for "Industrial Zinc Sulfate" (HG / T2326-2005).

[0045] Table 1 Quality Requirements for Industrial Zinc Sulfate (HG / T2326-2005)

[0046]

[0047] To illustrate the present invention more clearly, the following embodiments will be described in detail.

[0048] Example 1

[0049] The chlorine-containing zinc ash used in this embodiment has the following composition: Zn 76.38%wt, Cl 1.86%wt, As 0.0050%wt, Fe 0.076%wt, and Al2O3 2.53%wt.

[0050] ① Leached zinc

[0051] Take 500g of zinc ash containing chlorine, slurry it with water, and then add Cu. 2+ Leaching was performed using 1.0 g / L dilute sulfuric acid at 80℃. The acid addition rate was controlled to maintain the leaching pulp pH at 3.0. The highest instantaneous concentration of AsH3 gas during leaching was measured to be 0.05 ppm. The final leaching pH was controlled at 2.5. After leaching, CaO powder was added to adjust the pulp pH to 5.0, followed by hydrogen peroxide oxidation to remove iron. The leached pulp underwent liquid-solid separation, yielding 1850 mL of filtrate.

[0052] ② Concentration and crystallization

[0053] The filtrate from step ① is concentrated and crystallized until the specific gravity of the concentrated crystallization solution is 1.56-1.58 g / cm³. 3 When the concentration was stopped, the mixture was stirred and cooled to room temperature. The liquid and solid were separated to obtain 300 mL of crystallization mother liquor. After the crystals were naturally air-dried for 10 h, 1416.3 g of first-grade zinc sulfate heptahydrate was obtained.

[0054] Repeat the above steps for 10 more sets of zinc sulfate preparation process using chlorine-containing zinc ash. The mother liquor from the previous set is returned to the next set for concentration and crystallization. The product quality of each set is shown in Table 2.

[0055] Table 2. Quality of Zinc Sulfate Product When the Crystallization Mother Liquor is Used Continuously

[0056]

[0057]

[0058] Table 3. Volume of mother liquor and Cl content for each group of crystallization samples

[0059] serial number Volume (mL) Cl(g / L) Group 1 300 5.62 Group 2 280 6.32 Group 3 300 5.82 Group 4 290 6.12 Group 5 310 5.93 Group 6 300 5.72 Group 7 300 5.83 Group 8 280 6.33 Group 9 290 6.22 Group 10 270 7.01 Group 11 290 6.03

[0060] As can be seen from Tables 2 and 3, when the zinc ash Cl content is 1.96% wt, the specific gravity of the concentrated crystallization solution should be maintained at 1.56-1.58 g / cm³. 3 When the mother liquor is continuously returned for use without being discharged, chlorine is evenly distributed into the zinc sulfate product, and all the produced zinc sulfate meets the requirements of first-class product. The chlorine in the mother liquor is stable and does not accumulate, so there is no need to discharge the mother liquor to balance the chlorine.

[0061] Comparative Example 1

[0062] Using the chlorine-containing zinc ash from Example 1, take 500g of the chlorine-containing zinc ash, slurry it with water, and then add Cu-containing... 2+ The leaching process was carried out using 1.0 g / L dilute sulfuric acid at a temperature of 80 °C. The acid addition rate was controlled by the pH of the leaching pulp at 1.2. The highest instantaneous concentration of AsH3 gas during leaching was measured to be 4.86 ppm, with a fluctuation range of 1.92-3.91 ppm. The concentration gradually decreased to below 0.1 ppm after 40 minutes. The final pH value of leaching was 2.5.

[0063] Comparative Example 1 shows that even with the addition of Cu 2+ The pH value of the leaching process must also be controlled; otherwise, the release of high concentrations of arsine gas cannot be suppressed.

[0064] Example 2

[0065] The chlorine-containing zinc ash used in this embodiment has the following composition: Zn 74.27%wt, Cl 1.12%wt, As 0.0020%wt, Fe 0.082%wt, and Al2O3 2.23%wt.

[0066] ① Leached zinc

[0067] Take 500g of zinc ash containing chlorine, slurry it with water, and then add Cu. 2+ The leaching process used 0.5 g / L dilute sulfuric acid at a temperature of 60°C. The acid addition rate was controlled to maintain the leaching pulp pH at 2.0. The highest instantaneous concentration of AsH3 gas during leaching was measured to be 0.08 ppm. The leaching gas was exhausted outdoors through a fume hood. The final leaching pH was controlled at 3.0. After leaching, Ca(OH)2 powder was added to adjust the pulp pH to 4.5, followed by the addition of potassium permanganate to remove iron. The leached pulp underwent liquid-solid separation, yielding 1950 mL of filtrate.

[0068] ② Concentration and crystallization

[0069] The filtrate from step ① is concentrated and crystallized until the specific gravity of the concentrated crystallization solution is 1.58-1.60 g / cm³. 3 When the concentration was stopped, the mixture was stirred and cooled to room temperature. The liquid and solid were separated to obtain 300 mL of crystallization mother liquor. After the crystals were dried with hot air at 55 °C, 1310.7 g of first-grade zinc sulfate heptahydrate was obtained.

[0070] Repeat the above steps for 10 more groups of zinc sulfate preparation using chlorine-containing zinc ash. The mother liquor from the previous group is returned to the next group for concentration and crystallization. The product quality of each group is shown in Table 4, and the chlorine content of the mother liquor changes as shown in Table 5.

[0071] Table 4. Quality of Zinc Sulfate Products When the Crystallization Mother Liquor is Used Continuously

[0072]

[0073] Table 5. Volume of mother liquor and Cl content for each group of crystallization samples.

[0074]

[0075]

[0076] As can be seen from Tables 4 and 5, when the zinc ash Cl content is 1.12% wt, the specific gravity of the concentrated crystallization solution should be maintained at 1.58-1.60 g / cm³. 3 When the mother liquor is continuously returned for use and not discharged, chlorine enters the zinc sulfate product in a balanced manner, and all the produced zinc sulfate meets the requirements of first-class product; the chlorine in the mother liquor is stable and does not accumulate, so there is no need to periodically discharge the mother liquor to balance the chlorine.

[0077] Comparative Example 2

[0078] The chlorine-containing zinc ash from Example 2 and the technical conditions of step ① in Example 2 were used.

[0079] The filtrate from step ① is concentrated and crystallized until the specific gravity of the concentrated crystallization solution is 1.50-1.55 g / cm³. 3When the concentration was stopped, the mixture was stirred and cooled to room temperature. The liquid and solid were separated to obtain 800 mL of crystallization mother liquor. After the crystals were dried with hot air at 55 °C, 1026.2 g of first-grade zinc sulfate heptahydrate was obtained.

[0080] Repeat the above steps for 10 more groups of zinc sulfate preparation using chlorine-containing zinc ash. The mother liquor from the previous group is returned to the next group for concentration and crystallization. The product quality of each group is shown in Table 6, and the chlorine content of the mother liquor changes as shown in Table 7.

[0081] Table 6 shows the specific gravity of the concentrated crystallization solution as 1.50-1.55 g / cm³. 3 Zinc sulfate product quality

[0082]

[0083] Table 7 shows the specific gravity of the concentrated crystallization solution as 1.50-1.55 g / cm³. 3 The volume of the mother liquor for each crystallization group and its Cl content

[0084]

[0085]

[0086] As can be seen from Tables 6 and 7, when the zinc ash Cl content is 1.12% wt, the specific gravity of the concentrated crystallization solution should be maintained at 1.50-1.55 g / cm³. 3 Chlorine gradually accumulates in the mother liquor during crystallization. If the mother liquor is continuously reused, from group 9 onwards, the main content and chlorine content in the zinc sulfate product will fail to meet the first-grade standard. It is necessary to periodically discharge the mother liquor to maintain product quality, or lower the product standard. Therefore, controlling the specific gravity of the concentrated crystallization solution is crucial.

[0087] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for treating chlorine-containing zinc ash, characterized in that, Includes the following steps: (1) Leaching zinc Chlorine-containing zinc ash is slurried with water, and Cu is added. 2+ Zinc is leached with a dilute acid solution, and the pH value of the slurry is controlled at 2.0-3.0 throughout the process and at the end point to suppress the concentration of arsine and inhibit zinc leaching; wherein, the dilute acid solution is dilute sulfuric acid, Cu 2+ The dosage is 0.5-1.0 g / L; (2) Removal of impurities After zinc leaching is completed, neutralizing and oxidizing agents are added to remove impurities, and liquid-solid separation is performed. (3) Concentration and crystallization The impurity-removed filtrate from step (2) is concentrated and crystallized, with the final crystallization solution specific gravity controlled at 1.56-1.60 g / cm³. 3 This allows chlorine to enter the zinc sulfate product evenly without accumulating in the mother liquor; after the concentrated solution is cooled to room temperature under stirring, it is filtered and air-dried to obtain first-grade zinc sulfate heptahydrate.

2. The method according to claim 1, characterized in that, Cu in step (1) 2+ It is added in the form of copper sulfate.

3. The method according to claim 1, characterized in that, The neutralizing agent added in step (2) is CaO powder or Ca(OH)2 powder.

4. The method according to claim 1, characterized in that, The oxidant added in step (2) is hydrogen peroxide or potassium permanganate.

5. The method according to claim 1, characterized in that, Step (3) The filtered mother liquor is returned to the next group for concentration and crystallization.

6. The method according to claim 1, characterized in that, The air drying process described in step (3) is either natural air drying or hot air drying.

7. The method according to claim 6, characterized in that, The hot air drying temperature is 50-60℃.

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