Method for recycling desulfurized liquid of acid-making tail gas from zinc hydrometallurgy

Abstract

The invention relates to the technical field of acid-making tail gas treatment and leaching systems of zinc hydrometallurgy, and discloses a zinc hydrometallurgy acid-making tail gas desulfurized liquid recycling method which comprises the following steps: performing two-stage absorption desulfurization on acid-making tail gas by using a sodium hydroxide solution to generate sodium nitrite absorption liquid; carrying out aeration oxidation on the sodium nitrite absorption liquid to obtain oxidized liquid mainly containing sodium sulfate; the oxidized liquid is sent to a leaching process to wash zinc-containing filter residues; and finally, returning the slag washing liquid to the alum precipitation process, so that sodium ions in the slag washing liquid are utilized as a alum precipitation agent. The two-stage sodium hydroxide desulfurization process is adopted, the desulfurization efficiency is high, meanwhile, the sodium nitrite absorption liquid generated through desulfurization is completely oxidized and reused in the production process, external discharge of the wastewater is thoroughly eliminated, zero discharge of the desulfurized liquid is achieved from the source, and the pressure of tail-end sewage treatment of enterprises and the environmental protection risk are greatly relieved.

Description

Technical Field

[0001] This invention relates to the technical field of acid production tail gas treatment and leaching systems in zinc hydrometallurgy, specifically to a method for recovering and utilizing desulfurized liquid from acid production tail gas in hydrometallurgical zinc production. Background Technology

[0002] Hydrometallurgical zinc smelting plants typically employ desulfurization processes such as hydrogen peroxide, zinc oxide, lime, and sodium alkali to treat the sulfuric acid tail gas. The desulfurized slurry is then directly discharged into the plant's water treatment system for compliant treatment before being released into the environment. In recent years, with the continuous expansion of hydrometallurgical zinc smelting operations and the increasing stringency of environmental standards for emissions, such as particulate matter concentration in flue gas and heavy metal ion concentration in wastewater, the original environmental protection facilities of these plants are no longer sufficient to meet current production and environmental requirements. Optimizing the process technology based on existing equipment and facilities is a crucial production challenge that these established enterprises must address. Summary of the Invention

[0003] The purpose of this invention is to provide a method for recovering and utilizing the liquid after desulfurization of the tail gas from wet zinc smelting and acid production, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for recovering and utilizing the liquid residue from the desulfurization of tail gas in a wet zinc smelting process includes the following steps:

[0006] S1. Two-stage desulfurization treatment of the tail gas from wet zinc smelting and acid production is carried out using sodium hydroxide solution to generate sodium sulfite absorbent.

[0007] S2. The sodium sulfite absorbent is oxidized to convert sodium sulfite and sodium bisulfite into sodium sulfate and sodium bisulfate, resulting in an oxidized solution.

[0008] S3. The oxidized liquid is transported to the leaching workshop of the wet zinc smelting process to rinse the lead-silver slag produced in the leaching process, and the slag-washed liquid is obtained.

[0009] S4. The slag washing liquid is returned to the leaching and alum precipitation process of wet zinc smelting; wherein, the sodium ions in the slag washing liquid participate in the reaction as an alum precipitation agent, and its water is used as makeup water for the production system.

[0010] In step S1, the absorption desulfurization is a two-stage desulfurization process, and both stages of desulfurization are completed in the same desulfurization tower.

[0011] In the two-stage desulfurization process, the first stage of desulfurization adopts an internal circulation method, while the second stage of desulfurization is carried out through an external circulation tank of sodium sulfite located outside the desulfurization tower.

[0012] The sodium nitrite circulation tank is connected to the spray systems of the first-stage desulfurization and the second-stage desulfurization, respectively. During operation, freshly prepared sodium hydroxide solution is continuously added to the sodium nitrite circulation tank, while the sodium nitrite absorbent is continuously discharged from the circulation system of the desulfurization tower to maintain the liquid balance of the system.

[0013] The concentration of the sodium hydroxide aqueous solution is 10% to 15%.

[0014] The oxidation treatment includes aeration oxidation in the first-stage desulfurization process and hydrogen peroxide oxidation in the second-stage desulfurization process. The aeration oxidation in the first-stage desulfurization process is carried out in an independent aeration oxidation tank, which is connected to the internal circulation tank in the desulfurization tower used for the first-stage desulfurization.

[0015] It is possible to selectively operate only the first stage of the two-stage desulfurization process based on the concentration of sulfur dioxide in the acid production tail gas.

[0016] A system for recovering and utilizing the desulfurized tail gas from the wet zinc smelting acid production process includes: a desulfurization tower for desulfurizing the acid production tail gas with sodium hydroxide solution; a sodium sulfite circulation tank connected to the desulfurization tower for preparing and circulating sodium hydroxide solution and temporarily storing sodium sulfite absorbent; an aeration oxidation tank, the inlet of which is connected to the sodium sulfite absorbent discharge pipeline for oxidizing the sodium sulfite absorbent; and a conveying pipeline for connecting the outlet of the aeration oxidation tank to the slag washing point in the wet zinc smelting leaching process.

[0017] The desulfurization tower is equipped with multiple spray layers, of which at least one spray layer and the sodium sulfite circulation tank form an external circulation loop.

[0018] The concentration of sulfur dioxide in the acid production tail gas entering the integrated desulfurization tower is 100–500 mg / Nm³. 3 .

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0020] 1) This invention employs a two-stage sodium hydroxide desulfurization process, achieving high desulfurization efficiency and ensuring that the sulfur dioxide concentration in the outlet exhaust gas remains consistently below 10 mg / Nm³. 3 Strict standards. More importantly, by completely oxidizing the sodium sulfite absorbent produced during desulfurization and reusing it in the production process, the discharge of this wastewater to the outside world is completely eliminated, achieving "zero discharge" of the desulfurized liquid from the source, greatly reducing the pressure on the company's end-of-pipe wastewater treatment and environmental risks;

[0021] 2) This invention uses sodium sulfate solution as a process medium to rinse lead-silver slag, which can reduce the zinc content in the slag and increase the total zinc recovery rate. At the same time, the rinsing liquid is returned to the alum precipitation process, where the sodium ions can be directly used as alum precipitation agent, replacing part of the purchased sodium salt, while the water is retained in the system, replacing the fresh process water replenishment, thus realizing "waste treatment" and multi-level utilization of resources.

[0022] 3) This invention achieves a dynamic balance between system liquid volume and alkalinity by using a design that connects two stages of desulfurization via a sodium sulfite circulation tank, combined with a continuous replenishment of fresh alkali solution and continuous discharge of waste liquid, thus ensuring stable desulfurization efficiency. Furthermore, this invention allows for flexible selection of the operating mode based on the inlet flue gas load, achieving energy conservation and consumption reduction while ensuring compliance with standards, and improving metal recovery rate, resulting in significant economic benefits.

[0023] 4) This invention focuses on sodium hydroxide desulfurization and its products, avoiding the complexity of separation of multi-metal systems. The equipment involved are all mature industrial devices, requiring little investment for modification and easy to promote and apply in existing hydrometallurgical zinc smelting enterprises. It provides an efficient and practical technical solution for solving common environmental problems in the industry. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention.

[0025] Figure 2 This is a schematic diagram of the desulfurization tower in this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0028] To better understand this invention, the following description is provided:

[0029] A hydrometallurgical zinc plant uses a fluidized bed roasting process to produce zinc calcined sand. The flue gas produced during the fluidized bed roasting process is processed into sulfuric acid using a dynamic crushing and washing + two-stage conversion and two-stage absorption process. The sulfuric acid tail gas volume is 60,000–7,000 Nm³. 3 / h, SO2 concentration 100mg / Nm 3 ~500mg / Nm 3 Particulate matter 10-20 mg / Nm 3 The emissions do not meet the requirements of the "Emission Standard of Pollutants for Lead and Zinc Industry" (GB25466-2010) and its amendments. The company's original design used a two-stage desulfurization process of zinc oxide and sodium hydroxide. The zinc oxide desulfurized slurry was returned to the roasting furnace after pressure filtration, while the sodium hydroxide desulfurized liquid was directly discharged to the water treatment workshop. This process design has several drawbacks: first, it increases the load on the roasting furnace and water treatment workshop, increasing the company's operating costs; second, with increasingly stringent environmental standards, the company's wastewater discharge is limited, and during the rainy season, the company faces the risk of exceeding wastewater discharge standards, making the realization of water resource utilization and waste reduction urgent; third, with increasingly stringent environmental standards, the concentration of particulate matter in the discharged flue gas does not meet the requirements (10 mg / Nm³). 3 The company's primary zinc oxide desulfurization process introduces additional particulate matter, increasing the particulate matter concentration in the flue gas to 15–30 mg / Nm³ after desulfurization. 3 To meet environmental standards, companies may even need to reduce their production load.

[0030] Based on the above background and reasons, and considering that the SO2 concentration in the exhaust gas is not high but fluctuates significantly, and also taking particulate matter into account, the company adopted a two-stage sodium hydroxide desulfurization process to replace the original zinc oxide + sodium hydroxide two-stage desulfurization process. The company's original design process was as follows:

[0031] The desulfurization tower has five layers: layers 1-3 are zinc oxide desulfurization, and layers 4-5 are sodium hydroxide desulfurization. Zinc oxide desulfurization uses internal circulation within the tower, while sodium hydroxide desulfurization uses external circulation. The sodium hydroxide aqueous solution has a concentration of 10%–15%, and the pH of the desulfurization solution after failure is controlled at 4–5 before being directly discharged to the water treatment workshop.

[0032] The system and process optimizations are as follows:

[0033] 1. An additional unit with an effective volume of 50m³ was added to the existing desulfurization tower system. 3 The aeration oxidation tank (including aeration components) has an effective volume of 30m³. 3 The sodium nitrite circulation tank is connected to the desulfurization tower and is used to prepare and circulate sodium hydroxide solution and temporarily store sodium nitrite absorbent. The inlet of the aeration oxidation tank is connected to the sodium nitrite absorbent discharge pipeline of the inner circulation tank and is used to oxidize the sodium nitrite absorbent.

[0034] 2. Install a liquid transport pipeline and supporting facilities from the aerated oxidation tank to the leaching workshop. The transport pipeline is used to connect the outlet of the aerated oxidation tank to the slag washing point of the wet zinc smelting leaching process.

[0035] 3. Replace the desulfurizing agent with a two-stage sodium hydroxide desulfurization process. Desulfurization tower layers 1-3 constitute the first-stage desulfurization stage, using internal circulation within the tower. Layers 4-5 constitute the second-stage desulfurization stage, using external circulation. The desulfurization tower is equipped with an internal circulation tank and multiple spray layers. At least one spray layer, together with the internal circulation tank and the sodium hydroxide circulation tank, forms an internal circulation loop; at least one spray layer, together with the sodium hydroxide circulation tank, forms an external circulation loop.

[0036] 4. During normal production, the newly prepared sodium hydroxide aqueous solution is continuously sent to the sodium nitrite circulation tank, which then sends it to the internal circulation tank of the desulfurization tower. The liquid in the internal circulation tank is continuously discharged to the aeration oxidation tank to achieve overall volume balance.

[0037] 5. Aeration oxidation mainly involves further oxidizing NaHSO3, Na2SO3, etc. in the desulfurization solution into NaHSO4 and Na2SO4. After aeration oxidation is completed, the solution is sent to the intermediate tank of the leaching workshop.

[0038] 6. The leaching workshop uses the desulfurized liquid after aeration and oxidation to wash the lead-silver slag, further reducing the zinc content in the lead-silver slag and improving the company's total zinc recovery rate; the slag washing liquid is returned to the leaching alum precipitation process; sodium ions are used as a leaching alum precipitant in the potassium (sodium) iron alum slag to realize resource utilization; water can partially replace the normal slag washing water in wet zinc smelting, reducing water waste.

[0039] 7. During normal production, if the sulfur dioxide concentration in the flue gas at the front end is low, only the first-stage desulfurization stage needs to be activated to reduce energy and resource waste.

[0040] 8. After the upgrade, the sulfur dioxide concentration in the desulfurization tail gas remained stable at 10 mg / Nm³. 3 Within this range, the particulate matter concentration remained stable at 10 mg / Nm³. 3 Within; the discharge volume of desulfurized liquid is 10-15 m³. 3 / day; Sodium hydroxide dosage 400-800 kg / day.

Claims

1. A method for recovering and utilizing the liquid after desulfurization of tail gas from wet zinc smelting acid production, characterized in that, Includes the following steps: S1. Two-stage desulfurization treatment of the tail gas from wet zinc smelting and acid production is carried out using sodium hydroxide solution to generate sodium sulfite absorbent. S2. The sodium sulfite absorbent is oxidized to convert sodium sulfite and sodium bisulfite into sodium sulfate and sodium bisulfate, resulting in an oxidized solution. S3. The oxidized liquid is transported to the leaching workshop of the wet zinc smelting process to rinse the lead-silver slag produced in the leaching process, and the slag-washed liquid is obtained. S4. The slag washing liquid is returned to the leaching and alum precipitation process of wet zinc smelting; wherein, the sodium ions in the slag washing liquid participate in the reaction as an alum precipitation agent, and its water is used as makeup water for the production system.

2. The method for recovering and utilizing the desulfurization liquid from the tail gas of wet zinc smelting acid production according to claim 1, characterized in that, In step S1, the absorption desulfurization is a two-stage desulfurization process, and both stages of desulfurization are completed in the same desulfurization tower.

3. The method for recovering and utilizing the desulfurization liquid from the tail gas of wet zinc smelting acid production according to claim 2, characterized in that, In the two-stage desulfurization process, the first stage of desulfurization adopts an internal circulation method, while the second stage of desulfurization is carried out through an external circulation tank of sodium sulfite located outside the desulfurization tower.

4. The method for recovering and utilizing the desulfurization liquid from the tail gas of wet zinc smelting acid production according to claim 3, characterized in that, The sodium nitrite circulation tank is connected to the spray systems of the first-stage desulfurization and the second-stage desulfurization, respectively. During operation, freshly prepared sodium hydroxide solution is continuously added to the sodium nitrite circulation tank, while the sodium nitrite absorbent is continuously discharged from the circulation system of the desulfurization tower to maintain the liquid balance of the system.

5. The method for recovering and utilizing the desulfurization liquid from the tail gas of wet zinc smelting acid production according to claim 4, characterized in that, The concentration of the sodium hydroxide aqueous solution is 10% to 15%.

6. The method for recovering and utilizing the desulfurization liquid from the tail gas of wet zinc smelting acid production according to claim 4, characterized in that, The oxidation treatment includes aeration oxidation in the first-stage desulfurization process and hydrogen peroxide oxidation in the second-stage desulfurization process. The aeration oxidation in the first-stage desulfurization process is carried out in an independent aeration oxidation tank, which is connected to the internal circulation tank in the desulfurization tower used for the first-stage desulfurization.

7. The method for recovering and utilizing the desulfurization liquid from the tail gas of wet zinc smelting acid production according to claim 2, characterized in that, It is possible to selectively operate only the first stage of the two-stage desulfurization process based on the concentration of sulfur dioxide in the acid production tail gas.

8. A system for implementing the method according to any one of claims 1-7, characterized in that, include: A desulfurization tower is used to desulfurize acid production tail gas with sodium hydroxide solution. A sodium sulfite circulation tank, connected to the desulfurization tower, is used to prepare and circulate sodium hydroxide solution and temporarily store sodium sulfite absorbent. The aeration oxidation tank has its inlet connected to the sodium sulfite absorbent discharge pipeline of the inner circulation tank, and is used to oxidize the sodium sulfite absorbent. A conveying pipeline is used to connect the outlet of the aerated oxidation tank to the slag washing point in the wet zinc leaching process.

9. The system according to claim 8, characterized in that, The desulfurization tower is equipped with an internal circulation tank and a multi-stage spray layer, wherein at least one stage of the spray layer, together with the internal circulation tank and the sodium sulfite circulation tank, forms an internal circulation loop; wherein at least one stage of the spray layer, together with the sodium sulfite circulation tank, forms an external circulation loop.

Images