A method for separating zinc and magnesium in a wet-process zinc electrolyte frozen crystallization product

Abstract

This invention discloses a method for separating zinc and magnesium from the frozen crystallization product of waste electrolyte in hydrometallurgical processes, belonging to the field of hydrometallurgical technology. The frozen crystallization product of the waste electrolyte in hydrometallurgical processes is heated to 950-1050℃ and held for 2-4 hours, causing zinc sulfate heptahydrate to decompose into zinc oxide and magnesium sulfate heptahydrate to dehydrate into anhydrous magnesium sulfate. Both are transferred as pyrolysis solid products to the next process. Then, the pyrolysis solid products are added to an aqueous leaching solution at a liquid-to-solid ratio of 2-10:1, maintaining the temperature at 20-60℃, and leaching with stirring for 10-60 minutes. Solid-liquid separation yields magnesium-rich solution and zinc-rich slag, achieving zinc-magnesium separation. This method, through thermodynamic transformation, converts ion-selective separation into a solid-liquid leaching separation process based on the differences in the physical properties of the phases, resulting in more efficient, thorough, and cleaner separation. The process flow is shorter, and energy consumption is lower, improving resource utilization while reducing processing costs.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a method for separating zinc and magnesium from the frozen crystallization products of waste electrolyte in hydrometallurgical zinc smelting. Background Technology

[0002] In the hydrometallurgical zinc smelting process, magnesium from the zinc concentrate accumulates in the waste electrolyte as the process continues. After the waste electrolyte undergoes freeze crystallization treatment, the resulting crystallized product is mainly zinc sulfate heptahydrate (ZnSO4). . 7H2O) and magnesium sulfate heptahydrate (MgSO4) . The efficient separation of these two substances (7H2O) is crucial for the recycling of zinc and the resource utilization of magnesium.

[0003] Currently, the main methods for separating such mixed salts are chemical precipitation and solvent extraction. Chemical precipitation involves adding neutralizing or precipitating agents to cause metal ions to precipitate in steps. However, zinc and magnesium have similar chemical properties, resulting in poor separation selectivity and often causing significant losses of zinc through co-precipitation. Furthermore, the precipitate products have complex compositions, making secondary processing difficult.

[0004] Solvent extraction separates zinc and magnesium by selectively binding specific extractants. However, this method suffers from problems such as organic phase entrainment, emulsification, and regeneration, resulting in a lengthy process and high costs for reagent consumption and wastewater treatment. Therefore, developing a novel zinc-magnesium separation method that is highly efficient, has a short process, and is environmentally friendly is of significant practical importance for cleaner production and industrial upgrading in the hydrometallurgical zinc smelting industry. Summary of the Invention

[0005] The purpose of this invention is to provide a method for separating zinc and magnesium from the frozen crystallization products of waste electrolyte in wet zinc smelting.

[0006] The objective of this invention is achieved as follows: the method for separating zinc and magnesium from the frozen crystallization product of the waste electrolyte in wet zinc smelting includes the following steps: High-temperature directional conversion: The frozen crystallization product of the waste electrolyte of wet zinc smelting is heated to 950~1050℃ and kept at the temperature for 2~4h, so that zinc sulfate heptahydrate is decomposed into zinc oxide and magnesium sulfate heptahydrate is dehydrated into anhydrous magnesium sulfate. Both are transferred to the next process as pyrolysis solid products. Selective water leaching separation: Pyrolysis solid products are added to water leaching solution at a liquid-to-solid ratio of 2~10:1, the temperature is maintained at 20~60℃, and the solution is stirred and leached for 10~60 min; solid-liquid separation yields magnesium-rich solution and zinc-rich slag, thus achieving zinc-magnesium separation.

[0007] Compared with the prior art, the technical solution described in this invention has the following advantages: 1. Selective thermal decomposition: By precisely controlling the temperature window of 950~1050℃, the difference in thermal stability between zinc sulfate heptahydrate and magnesium sulfate heptahydrate is utilized to decompose zinc salt into insoluble zinc oxide, while magnesium salt is only dehydrated into soluble anhydrous magnesium sulfate. This achieves the activation and passivation of the phases, creating conditions for water leaching separation.

[0008] 2. Green separation process: Through thermal conversion, the separation becomes a physical dissolution process. There is no need to add chemical reagents to promote precipitation or complexation. Instead, the separation is achieved by relying on the differences in thermal stability and water solubility of the substances themselves, thus avoiding secondary pollution. The gas produced by thermal decomposition can be recovered and treated, and the water leaching solution can be recycled.

[0009] 3. High separation efficiency: Due to the complete transformation of the solid phase, the magnesium leaching rate is ≥99.9% and the zinc residue rate in the slag is ≥99.8%, which far exceeds the traditional chemical separation method, providing high-purity raw materials for subsequent resource utilization.

[0010] 4. Comprehensive Resource Recovery: The separated zinc oxide is a direct return material from the zinc electrolysis system. After dissolving, it is returned to the electrolyte, forming a closed-loop cycle without the need for additional conversion steps. Magnesium is separated in the form of magnesium sulfate solution to prepare industrial-grade MgSO4·7H2O, improving the comprehensive utilization rate of resources. The gaseous products obtained from pyrolysis can be used as basic raw materials for sulfuric acid production and directly incorporated into the acid production system, realizing the closed-loop utilization of sulfur resources.

[0011] 5. Short process: The form of the separated product is highly compatible with the subsequent recycling process, which greatly shortens the process flow.

[0012] 6. Low energy consumption and simple process: The thermal decomposition temperature is lower than that of magnesium sulfate, resulting in lower energy consumption; only two steps are required: thermal decomposition and water immersion, requiring less equipment investment and simple operation.

[0013] 7. Environmentally friendly: No chemical reagents are introduced throughout the process. Pyrolysis gases (SO3, water vapor) are absorbed to produce acid, and the crystallization mother liquor can be recycled, which meets environmental protection requirements.

[0014] In summary, the technical solution of this invention utilizes the difference in thermal stability and the difference in water solubility of the thermal decomposition products between zinc sulfate heptahydrate and magnesium sulfate heptahydrate. By precisely controlling the thermal decomposition temperature, the zinc salt is directionally converted into water-insoluble ZnO, while the magnesium salt is retained as water-soluble MgSO4. The selective dissolution of magnesium and retention of zinc are achieved by using water leaching. Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the technical solution described in this invention. Detailed Implementation

[0016] The present invention will be further described below, but this is not intended to limit the invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the scope of protection of the present invention.

[0017] The method for separating zinc and magnesium from the frozen crystallization product of waste electrolyte in wet zinc smelting according to the present invention includes the following steps: High-temperature directional conversion: The frozen crystallization product of the waste electrolyte of wet zinc smelting is heated to 950~1050℃ and held for 2~4h to obtain pyrolysis solid and gas products. During this process, zinc sulfate heptahydrate decomposes into zinc oxide and magnesium sulfate heptahydrate is dehydrated into anhydrous magnesium sulfate. Both are transferred to the next process as pyrolysis solid products. Selective water leaching separation: Pyrolysis solid products are added to water leaching solution at a liquid-to-solid ratio of 2~10:1, and the temperature is maintained at 20~60℃. Stirring and leaching are carried out for 10~60 min. Solid-liquid separation yields magnesium-rich solution (i.e., filtrate containing magnesium sulfate) and zinc-rich slag (i.e., zinc oxide filter residue), thus achieving zinc-magnesium separation.

[0018] The frozen crystallization product has a ZnSO4·7H2O content >30% and a MgSO4·7H2O content >60%.

[0019] The high-temperature directional conversion is carried out in a slightly negative pressure air environment of -50 to -10 Pa.

[0020] The preferred conversion temperature is 950~1000℃.

[0021] The liquid-to-solid ratio is preferably 5:1.

[0022] The pH value of the aqueous extract is 5.5~7.

[0023] When the pH value of the aqueous extract is <7, sulfuric acid is used for adjustment.

[0024] The preferred leaching temperature is 50~60℃.

[0025] The leaching time is preferably 30-45 minutes.

[0026] The magnesium-rich solution is concentrated and crystallized to prepare industrial-grade MgSO4·7H2O, and the crystallization mother liquor is returned to the magnesium-rich solution; the zinc-rich slag is returned to the zinc electrolysis process to prepare zinc sheets; the pyrolysis gas products can be used to produce acid.

[0027] Example 1

[0028] The composition of the frozen crystallization product to be processed is as follows: ZnSO4·7H2O 35.01%, MgSO4·7H2O 63.78%.

[0029] Take 100.00g of the frozen crystallization product and place it in a muffle furnace. Under a slightly negative pressure air environment of -10Pa, heat it to 950℃ and keep it at that temperature for 4 hours to obtain pyrolysis solid and gaseous products. During this process, zinc sulfate heptahydrate decomposes into zinc oxide and magnesium sulfate heptahydrate dehydrates into anhydrous magnesium sulfate. Both are transferred to the next process as pyrolysis solid products.

[0030] 500 ml of deionized water was used as the leaching solution. The pyrolysis solid product was added, and the temperature was maintained at 50 °C. The mixture was stirred and leached for 45 min. Solid-liquid separation yielded a magnesium-rich solution and a zinc-rich slag. Analysis showed that the filter residue contained 0.031% magnesium, with a magnesium leaching rate of 99.95%. The Zn ion concentration in the filtrate was 0.012 g / L, and the zinc recovery rate was 99.92%.

[0031] Magnesium-rich liquid is concentrated and crystallized to prepare industrial-grade MgSO4·7H2O; zinc-rich slag is returned to the zinc electrolysis process; and pyrolysis gas products are used to produce acid, thus realizing zinc-magnesium separation and comprehensive resource recovery.

[0032] Example 2

[0033] The composition of the frozen crystallization product to be processed is as follows: ZnSO4·7H2O 30.12%, MgSO4·7H2O 68.66%.

[0034] Take 200.00g of frozen crystallization product and place it in a tube furnace. Under a slightly negative pressure air environment of -50Pa, heat it to 1000℃ and hold it for 2 hours to obtain pyrolysis solid and gaseous products. During this process, zinc sulfate heptahydrate decomposes into zinc oxide and magnesium sulfate heptahydrate dehydrates into anhydrous magnesium sulfate. Both are transferred to the next process as pyrolysis solid products.

[0035] 1000 ml of an aqueous solution adjusted to pH 5.5 with dilute sulfuric acid was used as the leaching solution. The pyrolysis solid product was added, and the temperature was maintained at 60℃. The mixture was stirred and leached for 30 min. Solid-liquid separation yielded a magnesium-rich solution and a zinc-rich slag. Analysis showed that the filter residue contained 0.031% magnesium, with a magnesium leaching rate of 99.95%; the Zn ion concentration in the filtrate was 0.012 g / L, and the zinc recovery rate was 99.92%.

[0036] Magnesium-rich liquid is concentrated and crystallized to prepare industrial-grade MgSO4·7H2O; zinc-rich slag is returned to the zinc electrolysis process; and pyrolysis gas products are used to produce acid, thus realizing zinc-magnesium separation and comprehensive resource recovery.

Claims

1. A method for separating zinc and magnesium from the frozen crystallization product of waste electrolyte in wet zinc smelting, characterized in that, The process includes the following steps: High-temperature directional conversion: The frozen crystallization product of the waste electrolyte of wet zinc smelting is heated to 950~1050℃ and kept at the temperature for 2~4h, so that zinc sulfate heptahydrate is decomposed into zinc oxide and magnesium sulfate heptahydrate is dehydrated into anhydrous magnesium sulfate. Both are transferred to the next process as pyrolysis solid products. Selective water leaching separation: Pyrolysis solid products are added to water leaching solution at a liquid-to-solid ratio of 2~10:1, the temperature is maintained at 20~60℃, and the solution is stirred and leached for 10~60 min; solid-liquid separation yields magnesium-rich solution and zinc-rich slag, thus achieving zinc-magnesium separation.

2. The method for separating zinc and magnesium from the frozen crystallization product of wet zinc smelting waste electrolyte according to claim 1, characterized in that, The frozen crystallization product has a ZnSO4·7H2O content >30% and a MgSO4·7H2O content >60%.

3. The method for separating zinc and magnesium from the frozen crystallization product of wet zinc smelting waste electrolyte according to claim 1, characterized in that, The high-temperature directional conversion is carried out in a slightly negative pressure air environment of -50 to -10 Pa.

4. The method for separating zinc and magnesium from the frozen crystallization product of wet zinc smelting waste electrolyte according to claim 1, characterized in that, The conversion temperature is 950~1000℃.

5. The method for separating zinc and magnesium from the frozen crystallization product of waste electrolyte in wet zinc smelting according to claim 1, characterized in that, The liquid-to-solid ratio is 5:

1.

6. The method for separating zinc and magnesium from the frozen crystallization product of wet zinc smelting waste electrolyte according to claim 1, characterized in that, The pH value of the aqueous extract is 5.5~7.

7. The method for separating zinc and magnesium from the frozen crystallization product of wet zinc smelting waste electrolyte according to claim 6, characterized in that, When the pH value of the aqueous extract is <7, sulfuric acid is used for adjustment.

8. The method for separating zinc and magnesium from the frozen crystallization product of waste electrolyte in wet zinc smelting according to claim 1, characterized in that, The leaching temperature is 50~60℃.

9. The method for separating zinc and magnesium from the frozen crystallization product of waste electrolyte in wet zinc smelting according to claim 1, characterized in that, The leaching time is 30-45 minutes.

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