Pretreatment method for evaporating and crystallizing zinc sulfate from liquid after arsenic precipitation

Abstract

The invention discloses a pretreatment method for evaporating and crystallizing zinc sulfate in arsenic precipitation post-liquid, which comprises the following steps: carrying out acid leaching on zinc smelting smoke dust to obtain leachate; zinc oxide is added into the leachate to adjust the initial pH value of the leachate to 1-2, then ferrous sulfate heptahydrate is added, oxygen is introduced, oxidation arsenic precipitation is conducted, and liquid obtained after arsenic precipitation is obtained; adding zinc oxide into the arsenic-precipitated liquid to adjust the pH value to 4-6, and neutralizing and purifying to obtain a neutralized and purified liquid; and carrying out evaporative crystallization on the neutralized and purified liquid to obtain a zinc sulfate heptahydrate product. According to the method, the pH value of the leachate is adjusted in a gradient mode, oxygen oxidation and a specific additive ratio are combined, efficient precipitation of arsenic is achieved, and then residual arsenic, iron, copper and other impurity elements are removed through further neutralization; in the whole process, an endogenous regulator is adopted to replace a traditional exogenous chemical agent, introduction of additional impurity elements is avoided, meanwhile, the neutralization slag is converted into a material capable of being directly returned to a pyrogenic copper smelting system to be recycled, and resource recycling is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a pretreatment method for zinc sulfate crystallization by evaporation of liquid after arsenic precipitation. Background Art

[0002] Smelting dust generated during the recycling of secondary non-ferrous metals contains significant amounts of valuable metals such as lead, tin, zinc, copper, iron, germanium, and indium, which are of significant recycling value. However, it also contains significant amounts of the toxic and hazardous element arsenic. The indiscriminate discharge and storage of arsenic-containing materials pose a serious threat to the environment and human health. Acid leaching is currently the primary treatment method for smelting dust, as it is relatively low-cost and can largely extract the arsenic and valuable metals. The acidic environment creates favorable conditions for the subsequent separation of the valuable metals from the arsenic. Smelting dust is leached with sulfuric acid, extracting the majority of the arsenic and valuable metals into the leachate. To achieve harmless treatment of the arsenic and cascade recovery of the valuable metals, iron salts are added to the leachate to precipitate the arsenic as ferric arsenate for harmless treatment. Due to incomplete arsenic precipitation and the addition of excessive iron during the precipitation process, the post-precipitation solution contains small amounts of arsenic, iron, and copper. Direct evaporation of the post-precipitation solution for zinc sulfate crystallization results in a high impurity content in the resulting zinc sulfate heptahydrate product, impacting sales. Currently, research has been conducted on the preparation of various zinc sulfate products by removing impurities from the post-arsenic precipitation solution. However, the resulting products are prone to exceeding the standard for impurities, failing to meet the requirements for high-purity zinc sulfate products. Furthermore, research on deep removal of impurities is limited, and arsenic removal is difficult and expensive. Deeply removing impurities from the post-arsenic precipitation solution to produce higher-purity zinc sulfate products remains a challenge both domestically and internationally. Therefore, pre-treating the post-arsenic precipitation solution for evaporation and crystallization of zinc sulfate is essential.

[0003] Currently, the pretreatment methods for evaporated crystallized zinc sulfate include chemical precipitation, solvent extraction, ion exchange, adsorption and reduction.

[0004] ① Neutralization precipitation method: By adding alkaline substances, such as sodium hydroxide, the pH value of the arsenic precipitation solution is adjusted, so that the metal ions form hydroxide precipitation and the arsenic forms arsenate precipitation. However, the addition of sodium hydroxide to adjust the pH introduces impurity sodium ions, which affects product quality.

[0005] ②Sulfide precipitation method: sulfiding agents (such as sodium sulfide and hydrogen sulfide) react with impurity ions to form insoluble sulfide precipitates. However, after adding the sulfiding agent to precipitate arsenic, some zinc in the solution will also form zinc sulfide precipitates. At the same time, hydrogen sulfide gas will be generated under acidic zinc conditions, causing environmental pollution and harm to the human body.

[0006] ③Solvent extraction: Acidic extractants such as P204 and P507 can be used to extract impure metal ions from the arsenic precipitation solution. However, the selectivity of the extractant for arsenic is low, and metal ions such as zinc will also be extracted, resulting in zinc loss during the crystallization of zinc sulfate.

[0007] ④ Ion exchange method: Cation exchange resins can be used to remove cationic impurities from the solution after arsenic precipitation. For example, when treating iron-containing solutions, cation exchange resins can be used to adsorb iron ions onto the resin, thereby removing iron. Anion exchange resins can be used to remove anionic impurities from solutions. For example, when treating acid leaching solutions containing chloride ions, anion exchange resins can be used to adsorb chloride ions onto the resin. However, ion exchange resins are expensive, resulting in high production costs and hindering industrialization.

[0008] ⑤ Adsorption method: Activated carbon has a large specific surface area and adsorption capacity, and can be used to adsorb arsenic in the acid leaching solution. However, its adsorption capacity for iron and copper is weak, and it cannot remove impurity ions in the solution after arsenic precipitation.

[0009] ⑥ Reduction method: By adding a reducing agent, such as iron powder or zinc powder, the addition of iron powder reduces the impure copper ions to elemental copper, but this also produces divalent iron ions, introducing new impurities. Adding zinc powder reduces the impurity copper and iron ions to elemental copper and iron, but due to the high reactivity of zinc powder, it produces highly toxic arsine gas in acidic arsenic solutions. Summary of the Invention

[0010] In view of the deficiencies in the prior art, the present invention provides a pretreatment method for evaporating and crystallizing zinc sulfate in a liquid after arsenic precipitation.

[0011] The present invention discloses a pretreatment method for evaporating zinc sulfate crystallized from a post-arsenic precipitation solution, comprising: Step 1, acid leaching zinc smelting dust to obtain a leachate; Step 2: adding zinc oxide to the leachate to adjust the initial pH of the leachate to 1-2, then adding ferrous sulfate heptahydrate and introducing oxygen to oxidize and precipitate arsenic to obtain an arsenic precipitation solution; Step 3: adding zinc oxide to the arsenic precipitation solution to adjust the pH to 4-6 for neutralization and purification to obtain a neutralized and purified solution; Step 4: Evaporating and crystallizing the neutralized and purified liquid to obtain zinc sulfate heptahydrate product.

[0012] As a further improvement of the present invention, the step 1 specifically includes: Mix zinc smelting fume and dilute sulfuric acid and stir them evenly, heat and stir them in a water bath with a magnetic stirring pot, and react at 60-80°C for 1.5-2.5 hours; After the reaction is completed, liquid-solid separation is performed to obtain leaching residue and leaching liquid, and the pH value of the leaching liquid is less than 1.

[0013] As a further improvement of the present invention, the step 2 specifically includes: Zinc oxide was added to the leachate to adjust the initial pH to 1.50; ferrous sulfate heptahydrate was added at a molar ratio of Fe / As to 1 and oxygen was introduced. The reaction time was 2 hours and the reaction temperature was 90°C. After the reaction is completed, liquid-solid separation is performed to obtain arsenic iron slag and arsenic precipitation liquid.

[0014] As a further improvement of the present invention, oxygen with a purity of 99.9% is introduced into the leachate at a flow rate of 250 mL / min and a stirring speed of 400 r / min.

[0015] As a further improvement of the present invention, the step 3 specifically includes: Add zinc oxide to the arsenic precipitation solution to adjust the pH to 5, stir at 400 r / min, react for 1 hour, and at 90°C. After the reaction is completed, the neutralization and purification residue is removed by liquid-solid separation to obtain a neutralization and purification liquid.

[0016] As a further improvement of the present invention, the separated neutralized and purified slag is returned to the pyrometallurgical copper smelting system.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention achieves efficient precipitation of arsenic by gradient-adjusting the pH of the leachate, combining oxygen oxidation with a specific additive ratio, and then further neutralizes and removes residual arsenic, iron, copper and other impurity elements. Endogenous regulators are used throughout the process to replace traditional exogenous chemical agents to avoid the introduction of additional impurity elements. At the same time, the neutralized slag is converted into a material that can be directly returned to the pyrometallurgical copper smelting system for reuse, thereby realizing resource recycling.

[0018] This invention develops a process system that synergizes deep purification and metal recovery, significantly improving impurity removal efficiency, ensuring efficient zinc recovery, and significantly reducing overall processing costs. This method, compatible with conventional wet processing equipment, overcomes the secondary pollution and safety risks associated with traditional processes while also breaking through the industrial bottleneck of high-cost technologies. Ultimately, it achieves the goal of producing high-purity zinc sulfate products and achieving a green process throughout. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention discloses a flow chart of a pretreatment method for evaporating zinc sulfate crystallization in a post-arsenic precipitation liquid. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0021] When zinc smelting dust is dearsenified through sulfuric acid leaching, arsenic, iron, copper, and zinc enter the leachate together. Ferrous sulfate heptahydrate is added to the leachate and oxygen is introduced to oxidatively precipitate the arsenic. If the pH is adjusted too high during oxidative precipitation, the loss of valuable metal zinc is large and the arsenic precipitation rate is high. If the pH is adjusted too low, the loss of valuable metal zinc is small and the arsenic precipitation rate is low. To achieve a high arsenic precipitation rate while reducing zinc loss, an appropriate pH is required. Even when oxidative precipitation is performed at the optimal pH, the solution after arsenic precipitation still contains small amounts of impurity elements such as arsenic, copper, and iron, with concentrations of 3.42g / L, 1.21g / L, and 3.47g / L, respectively. If the solution after arsenic precipitation is directly evaporated to crystallize zinc sulfate, the resulting product will contain the harmful element arsenic and impurities iron and copper. How to remove impurity elements from zinc sulfate solution at a low cost and in depth to obtain a high-purity zinc sulfate product is a difficult problem both domestically and internationally. In order to solve the above problems, the present invention adds zinc oxide to the liquid after arsenic precipitation to adjust the pH to 5, and reacts at 90°C for 1 hour for neutralization and purification, thereby pre-treating the subsequent evaporation and crystallization of zinc sulfate.

[0022] The present invention is described in further detail below with reference to the accompanying drawings: like Figure 1 As shown, the present invention provides a pretreatment method for evaporating and crystallizing zinc sulfate in a liquid after arsenic precipitation, comprising: S1. Mix zinc smelting fume and dilute sulfuric acid and stir them evenly. Heat and stir them in a water bath with a magnetic stirring pot. React at 60-80°C for 1.5-2.5 hours.

[0023] S2. After the reaction is completed, liquid-solid separation is performed to obtain leaching residue and leaching liquid, and the pH value of the leaching liquid is less than 1.

[0024] S3. Add zinc oxide to the leachate to adjust the initial pH to 1.50; add ferrous sulfate heptahydrate at a molar ratio of Fe / As = 1 and introduce oxygen; the reaction time is 2 hours and the reaction temperature is 90°C.

[0025] S4. After the reaction is completed, liquid-solid separation is performed to obtain arsenic iron slag and arsenic precipitation liquid.

[0026] S5. Add zinc oxide to the solution after arsenic precipitation to adjust the pH to 4-6 for neutralization and purification. Stir at 400 r / min, react for 1 hour, and set the reaction temperature at 90°C.

[0027] S6. After the reaction is completed, liquid-solid separation is performed to remove the neutralization and purification residue to obtain a neutralization and purification liquid.

[0028] S7. Evaporating and crystallizing the neutralized and purified liquid to obtain zinc sulfate heptahydrate product. Example

[0029] The present invention provides a pretreatment method for evaporating and crystallizing zinc sulfate from a post-arsenic precipitation solution, comprising: mixing zinc smelting fume with 75 g / L dilute sulfuric acid at a liquid-to-solid ratio of 3:1 and stirring uniformly; heating and stirring in a magnetically stirred water bath at 70°C and a stirring speed of 400 r / min; and reacting at 70°C for 2 hours. After the reaction, liquid-solid separation is performed to obtain a leachate and a leachate, with a pH of 0.75. Zinc oxide is added to the leachate to adjust the initial pH to 1.50, followed by the addition of ferrous sulfate heptahydrate at a molar ratio of Fe / As of 1, and the introduction of 99.9% pure oxygen at a flow rate of 250 mL / min, a stirring speed of 400 r / min, a reaction time of 2 hours, and a reaction temperature of 90°C. After the reaction, liquid-solid separation is performed to obtain ferrosargenous slag and a post-arsenic precipitation solution. Zinc oxide is added to the post-arsenic precipitation solution to adjust the pH to 5, and the stirring speed is 400 r / min. The reaction time is 1 hour, and the reaction temperature is 90°C. After the reaction is complete, the neutralization and purification residue is removed through liquid-solid separation to obtain a neutralized and purified liquid (zinc sulfate solution). This treatment method achieves a 100% As and Fe removal rate and an 87.76% Cu removal rate in the arsenic precipitation liquid. The removal of impurity elements is significant. Zinc sulfate heptahydrate is obtained by evaporation and crystallization of the neutralized and purified liquid. The neutralized and purified residue can be returned to the pyrometallurgical copper smelting system for copper recovery and reuse. This achieves a zero-waste residue discharge scenario.

[0030] The advantages of the present invention are: 1. The method of the present invention is used to directly remove impurities such as As, Fe, and Cu from the liquid after arsenic precipitation. The removal effect is significant and can be achieved in one go, enabling industrial application. This fundamentally avoids the problem of incomplete As and Fe removal during the arsenic precipitation process, which leads to excessive impurity elements in the produced zinc sulfate product. The As and Fe removal rates of the liquid after arsenic precipitation can reach 100%, and the Cu removal rate can reach 87.76%.

[0031] 2. The raw material used in the method of the present invention is zinc oxide, which is easy to purchase, economical and efficient, and will not introduce other harmful impurities. It is suitable for removing impurity elements in the liquid after arsenic precipitation.

[0032] 3. The main component of the neutralization and purification slag produced by the present invention is Cu(OH)2, which can be returned to the pyrometallurgical copper smelting system to recycle the copper in the neutralization and purification slag. The whole process does not introduce impurity elements, and no waste slag, waste liquid or harmful gas is generated. The operation is simple, the operating cost is low, the whole process is green and efficient, and it has good application prospects.

[0033] 4. The conventional hydrometallurgical equipment used in the present invention has a simple structure, low cost and is easy to maintain.

[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A pretreatment method for evaporating and crystallizing zinc sulfate after arsenic precipitation, characterized in that: include: Step 1, acid leaching zinc smelting dust to obtain a leachate; Step 2: adding zinc oxide to the leachate to adjust the initial pH of the leachate to 1-2, then adding ferrous sulfate heptahydrate and introducing oxygen to oxidize and precipitate arsenic to obtain an arsenic precipitation solution; Step 3: adding zinc oxide to the arsenic precipitation solution to adjust the pH to 4-6 for neutralization and purification to obtain a neutralized and purified solution; Step 4: Evaporating and crystallizing the neutralized and purified liquid to obtain zinc sulfate heptahydrate product.

2. The pretreatment method for evaporating and crystallizing zinc sulfate after arsenic precipitation according to claim 1, wherein: The step 1 specifically includes: Mix zinc smelting fume and dilute sulfuric acid and stir them evenly, heat and stir them in a water bath with a magnetic stirring pot, and react at 60-80°C for 1.5-2.5 hours; After the reaction is completed, liquid-solid separation is performed to obtain leaching residue and leaching liquid, and the pH value of the leaching liquid is less than 1.

3. The pretreatment method for evaporating and crystallizing zinc sulfate after arsenic precipitation according to claim 1, wherein: The step 2 specifically includes: Zinc oxide was added to the leachate to adjust the initial pH to 1.50; ferrous sulfate heptahydrate was added at a molar ratio of Fe / As to 1 and oxygen was introduced. The reaction time was 2 hours and the reaction temperature was 90°C. After the reaction is completed, liquid-solid separation is performed to obtain arsenic iron slag and arsenic precipitation liquid.

4. The pretreatment method for evaporating and crystallizing zinc sulfate after arsenic precipitation according to claim 3, characterized in that: Oxygen with a purity of 99.9% was introduced into the leachate at a flow rate of 250 mL / min and a stirring speed of 400 r / min.

5. The pretreatment method for evaporating and crystallizing zinc sulfate after arsenic precipitation according to claim 1, wherein: The step 3 specifically includes: Add zinc oxide to the arsenic precipitation solution to adjust the pH to 5, stir at 400 r / min, react for 1 hour, and at 90°C. After the reaction is completed, the neutralization and purification residue is removed by liquid-solid separation to obtain a neutralization and purification liquid.

6. The pretreatment method for evaporating and crystallizing zinc sulfate after arsenic precipitation according to claim 5, characterized in that: The separated neutralized and purified slag is returned to the pyrometallurgical copper smelting system.

Images