A method for oxidative leaching of selenium and mercury from copper smelting acid mud

Abstract

This invention discloses a method for oxidative leaching of selenium and mercury from copper smelting acid sludge, belonging to the field of solid waste comprehensive utilization technology. The leaching system in the oxidative leaching is a ternary synergistic oxidative leaching system of "sulfuric acid-sodium chloride-oxidant". Under the action of the synergistic leaching system, efficient and selective leaching of selenium and mercury from copper smelting acid sludge is achieved. This method avoids the corrosion of equipment by volatile acids and the problem of excessive oxidation of the nitric acid system, and significantly improves the stability of the oxidation process and the efficiency of reagent utilization, ultimately achieving multiple goals such as efficient recovery of valuable metals, low-carbon and energy-saving process flow, and compliant and harmless treatment of hazardous waste.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of solid waste, specifically a method for oxidative leaching of selenium and mercury from copper smelting acid sludge. Background Technology

[0002] As my country's copper smelting industry continues to expand, the amount of copper smelting sludge generated by pyrometallurgical processes is increasing year by year. This sludge, a typical hazardous waste, is primarily composed of lead sulfate (PbSO4), and is also rich in rare and precious metals such as selenium and mercury, often accompanied by gold and silver. Improper disposal can easily cause serious environmental pollution due to the harmful components in the sludge. Given the relative scarcity of selenium and mercury resources in my country and increasingly stringent environmental protection requirements, developing efficient and clean technologies for the resource-based disposal of sludge, achieving stable recovery of valuable metals such as selenium and mercury, and harmless treatment of hazardous waste, is of significant strategic importance for improving the comprehensive utilization of resources by enterprises, enhancing economic benefits, reducing environmental risks, and promoting the green and sustainable development of the industry.

[0003] Currently, the mainstream processes for extracting selenium and mercury from copper smelting sludge both domestically and internationally are mainly divided into two categories: pyrometallurgical processes and hydrometallurgical processes. Pyrometallurgical processes typically rely on high-temperature roasting to volatilize and separate selenium and mercury. While simple in process, they suffer from high energy consumption, heavy flue gas pollution, and low selenium and mercury recovery rates and product purity. Hydrometallurgical processes, particularly oxidative leaching systems using hydrochloric acid as a medium, suffer from drawbacks such as the volatility of hydrochloric acid and severe equipment corrosion. Nitric acid systems, on the other hand, easily lead to excessive oxidation of selenium, forming insoluble selenates, affecting leaching stability. Furthermore, some processes use oxidants (such as sodium hypochlorite) with unstable chemical properties, often requiring excessive dosage to maintain the oxidation effect, resulting in reagent waste and increased difficulty in subsequent processing. Therefore, this invention proposes a novel ternary synergistic oxidative leaching process: sulfuric acid-sodium chloride-oxidant. This process uses potassium chlorate or trichloroisocyanuric acid (TCCA) as the oxidant, achieving efficient and selective leaching of selenium and mercury under the action of the synergistic leaching system. This method avoids the corrosion of equipment by volatile acids and the excessive oxidation of the nitric acid system, while significantly improving the stability of the oxidation process and the efficiency of reagent utilization. Ultimately, it achieves multiple goals, including efficient recovery of valuable metals, low-carbon and energy-saving process flow, and compliant and harmless treatment of hazardous waste. Summary of the Invention

[0004] To address or partially address the problems existing in the prior art, this invention provides a method for oxidative leaching of selenium and mercury from copper smelting sludge. This method focuses on optimizing the leaching stage by adding potassium chlorate or trichloroisocyanuric acid (TCCA) as an oxidant to the oxidative leaching system, forming a new ternary synergistic oxidative leaching process of "sulfuric acid-sodium chloride-stabilizing oxidant". This process synergistically achieves efficient and selective leaching of selenium and mercury, laying the foundation for efficient recovery of valuable metals, low-carbon and energy-saving processes, and compliant harmless treatment of hazardous waste in my country's copper smelting industry.

[0005] The specific steps of the method described in this invention are as follows: (1) Mix sulfuric acid, sodium chloride and oxidant in water to obtain a leaching system.

[0006] (2) Add copper smelting acid mud to the leaching system at a liquid-to-solid ratio of (2-5):1L / kg, mix evenly, and start leaching.

[0007] (3) After leaching, the slurry is obtained, filtered and washed to separate the leachate and mercury-free acid sludge.

[0008] (4) The mercury-free acid sludge is washed a second time.

[0009] Preferably, the leaching system of the present invention has a sulfuric acid concentration of 20-60 g / L, a sodium chloride concentration of 30-80 g / L, and an oxidant concentration of 30 g / L.

[0010] Preferably, the oxidant in the leaching system of the present invention is one of potassium chlorate or trichloroisocyanuric acid.

[0011] Preferably, the copper smelting acid sludge of the present invention has a selenium content of 1.5%-1.9% and a mercury content of 0.65%-0.74%; the acid sludge needs to be sealed and stored to avoid contact with air and maintain a stable moisture content.

[0012] Preferably, the leaching process described in this invention involves a leaching temperature of 80-90℃, a stirring speed of 220-300 rpm, and a leaching time of 3 hours.

[0013] Preferably, the rinsing in this invention uses water with a liquid-to-solid ratio of 1.2:1 L / kg to separate a leachate containing selenium and mercury and mercury-free acid sludge.

[0014] Preferably, the washing process described in this invention uses water or a 0.1-1 mol / L NaCO3 solution with a liquid-to-solid ratio of 2:1 L / kg to ensure that the mercury leaching concentration in the mercury-removed acid sludge is ≤0.1 mg / L, meeting the requirements of GB5085.3-2007 Hazardous Waste Identification Standard - Leaching Toxicity Identification.

[0015] The mechanism of the method described in this invention is as follows: Selenium and mercury in acid sludge mainly exist in the form of sulfides. Using potassium chlorate as an oxidant in a sulfuric acid-sodium chloride system, selenium and mercury are oxidized to soluble selenate / selenite and soluble mercury chloride complexes, thereby achieving the leaching of valuable metals. The reaction equation is as follows (taking potassium chlorate as an example): 3Se+3H2O+2KClO3=3H2SeO3+2KCl (1) Se+H2O+KClO3=H2SeO4+KCl (2) 2HgSe+2KClO3+2NaCl+2H2SO4=2H2SeO3+2HgCl2+K2SO4+Na2SO4 (3) 3HgSe+4KClO3+2NaCl+3H2SO4=3H2SeO4+3HgCl2+2K2SO4+Na2SO4 (4) This invention utilizes a ternary synergistic process involving sulfuric acid, sodium chloride, and trichloroisocyanuric acid / potassium chlorate to forcibly convert various forms of selenium and mercury in acid sludge that are difficult to treat into soluble high-valence selenates and soluble mercury chloride complexes, thereby achieving separation from the solid sludge.

[0016] Beneficial effects of this invention: (1) Improve the leaching rate of selenium and mercury in copper smelting acid mud with selenium content of 1.5%-1.9% and mercury content of 0.65%-0.74%. The potassium chlorate system has a leaching rate of ≥98%, and the TCCA system has a selenium ≥96% and mercury ≥98%.

[0017] (2) Avoid excessive selenium oxidation caused by oxidizing acids and reduce the risk of corrosion of equipment by leachate.

[0018] (3) Select an oxidant (potassium chlorate or TCCA) to improve process stability.

[0019] (4) The optimal leaching effect can be achieved with a molar ratio of potassium chlorate to selenium of 1:1. The concentration of TCCA is 30g / L, and there is no need to add excessive amounts, which reduces the reagent cost by more than 20%.

[0020] (5) The method described in this invention does not affect the subsequent recovery of valuable elements such as Pb, Au, and Ag in acid sludge. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below, but the scope of protection of the present invention is not limited thereto.

[0022] Example 1 (1) Sulfuric acid, sodium chloride and trichloroisocyanuric acid are mixed in 1L of water to obtain a trichloroisocyanuric acid leaching system. The concentration of sulfuric acid in the system is 40g / L, the concentration of sodium chloride is 50g / L and the concentration of trichloroisocyanuric acid is 30g / L.

[0023] (2) Take 100g of sealed copper smelting acid mud. The acid mud is a gray-black blocky wet mud with a dry basis moisture content of 14.33%. The main phase is lead alum (PbSO4), with a selenium content of 1.5% and a mercury content of 0.65%. Add the copper smelting acid mud to the trichloroisocyanuric acid leaching system at a liquid-to-solid ratio of 5:1 L / kg and mix evenly at 220 rpm.

[0024] (3) Control the leaching temperature to 85℃, the stirring speed to 220rpm, and leach at a constant temperature for 3h.

[0025] (4) Filter and rinse the mercury-removing acid sludge with water at a liquid-to-solid ratio of 1.2:1 L / kg.

[0026] (5) The mercury-free acid sludge is washed twice with water at a liquid-to-solid ratio of 2:1 L / kg.

[0027] Analysis of the treated mercury-removed acid sludge revealed a selenium leaching rate of 96.8% and a mercury leaching rate of 98.3%. After two washes with water, the mercury leaching concentration of the mercury-removed acid sludge was 0.1 mg / L, meeting the hazardous waste identification standard.

[0028] Example 2 (1) Mix sulfuric acid, sodium chloride and potassium chlorate in 1L of water to obtain a potassium chlorate leaching system. The concentration of sulfuric acid in the system is 20g / L, the concentration of sodium chloride is 80g / L and the concentration of potassium chlorate is 30g / L.

[0029] (2) Take 100g of sealed copper smelting acid mud. The acid mud is a gray-black blocky wet mud with a dry basis moisture content of 14.33%. The main phase is lead alum (PbSO4), with a selenium content of 1.7% and a mercury content of 0.7%. Add the copper smelting acid mud to the trichloroisocyanuric acid leaching system at a liquid-to-solid ratio of 3:1 L / kg and mix evenly at 220 rpm.

[0030] (3) Control the leaching temperature to 80℃, the stirring speed to 300rpm, and leach at a constant temperature for 3h.

[0031] (4) Filter and rinse the mercury-removing acid sludge with water at a liquid-to-solid ratio of 1.2:1 L / kg.

[0032] (5) The mercury-free acid sludge was washed twice with 0.1 mol / L NaCO3, with a liquid-to-solid ratio of 2:1 L / kg.

[0033] Analysis of the mercury-removed acid sludge obtained in this embodiment showed that the selenium leaching rate was 98.0% and the mercury leaching rate was 98.1%. After two washings with water, the mercury leaching concentration of the mercury-removed acid sludge was 0.034 mg / L, which meets the hazardous waste identification standard.

[0034] Example 3 (1) Sulfuric acid, sodium chloride and trichloroisocyanuric acid are mixed in 1L of water to obtain a trichloroisocyanuric acid leaching system. The concentration of sulfuric acid in the system is 60g / L, the concentration of sodium chloride is 30g / L and the concentration of trichloroisocyanuric acid is 30g / L.

[0035] (2) Take 100g of sealed copper smelting acid mud. The acid mud is a gray-black blocky wet mud with a dry basis moisture content of 14.33%. The main phase is lead alum (PbSO4), with a selenium content of 1.9% and a mercury content of 0.74%. Add the copper smelting acid mud to the trichloroisocyanuric acid leaching system at a liquid-to-solid ratio of 2:1 L / kg and mix evenly at 220 rpm.

[0036] (3) Control the leaching temperature to 90℃, the stirring speed to 250rpm, and leach at a constant temperature for 3h.

[0037] (4) Filter and rinse the mercury-removing acid sludge with water at a liquid-to-solid ratio of 1.2:1 L / kg.

[0038] (5) The mercury-free acid sludge was washed twice with 0.5 mol / L NaCO3, with a liquid-to-solid ratio of 2:1 L / kg.

[0039] Analysis of the mercury-removed acid sludge obtained in this embodiment showed that the selenium leaching rate was 96.7% and the mercury leaching rate was 98.2%. After two washings with water, the mercury leaching concentration of the mercury-removed acid sludge was 0.041 mg / L, which meets the hazardous waste identification standard.

[0040] Example 4 (1) Sulfuric acid, sodium chloride and trichloroisocyanuric acid are mixed in 1L of water to obtain a trichloroisocyanuric acid leaching system. The concentration of sulfuric acid in the system is 40g / L, the concentration of sodium chloride is 30g / L and the concentration of trichloroisocyanuric acid is 30g / L.

[0041] (2) Take 100g of sealed copper smelting acid mud. The acid mud is a gray-black blocky wet mud with a dry basis moisture content of 14.33%. The main phase is lead alum (PbSO4), with a selenium content of 1.5% and a mercury content of 0.65%. Add the copper smelting acid mud to the trichloroisocyanuric acid leaching system at a liquid-to-solid ratio of 5:1 L / kg and mix evenly at 220 rpm.

[0042] (3) Control the leaching temperature to 85℃, the stirring speed to 220rpm, and leach at a constant temperature for 3h.

[0043] (4) Filter and rinse the mercury-removing acid sludge with water at a liquid-to-solid ratio of 1.2:1 L / kg.

[0044] (5) The mercury-free acid sludge was washed twice with 1 mol / L NaCO3, with a liquid-to-solid ratio of 2:1 L / kg.

[0045] Analysis of the mercury-removed acid sludge obtained in this embodiment showed that the selenium leaching rate was 96.7% and the mercury leaching rate was 98.5%. After two washings with water, the mercury leaching concentration of the mercury-removed acid sludge was 0.031 mg / L, which meets the hazardous waste identification standard.

[0046] Comparative Example 1 The difference between this embodiment and embodiment 1 is that the leaching system in step (1) uses hydrochloric acid with a concentration of 60 g / L and potassium chlorate with a concentration of 6 g / L.

[0047] The remaining steps are the same as in Example 1.

[0048] Analysis of the mercury-removed acid sludge obtained in this embodiment revealed that the selenium leaching rate was 86.4% and the mercury leaching rate was 97.1%. During the leaching process, hydrochloric acid volatilized significantly, the equipment was severely corroded, and a large number of bubbles were generated in the solution in the early stage of the reaction, which easily led to material overflow. The mercury leaching concentration of the mercury-removed sludge was 0.3 mg / L, which did not meet the hazardous waste identification standard.

[0049] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that in step (1), the concentration of sulfuric acid in the leaching system is 50 g / L, the concentration of sodium chloride is 50 g / L, and no external oxidant is added.

[0050] The remaining steps are the same as in Example 1.

[0051] Analysis of the mercury-free acid sludge obtained in this embodiment showed that the selenium leaching rate was 0.45% and the mercury leaching rate was 6.0%, indicating that effective leaching of selenium and mercury was not achieved.

[0052] By comparing the examples with Comparative Example 1, it can be seen that without the addition of an oxidant, selenium and mercury in acid sludge cannot be oxidized to form soluble selenate / selenite and soluble mercury chloride complex, indicating that selenium and mercury can be efficiently leached in a reaction system with the participation of an oxidant.

Claims

1. A method for oxidative leaching of selenium and mercury from copper smelting acid sludge, characterized in that, Includes the following steps: (1) Mix sulfuric acid, sodium chloride and oxidant in water to obtain a leaching system; (2) Add copper smelting acid mud to the leaching system at a liquid-to-solid ratio of (2-5):1L / kg, mix evenly, and start leaching; (3) After leaching, the slurry is obtained, which is then filtered and washed to separate the leachate and mercury-removing acid sludge. (4) The mercury-free acid sludge is washed a second time.

2. The method for oxidative leaching of selenium and mercury from copper smelting acid mud according to claim 1, characterized in that: In step (1), the leaching system contains sulfuric acid at a concentration of 20-60 g / L, sodium chloride at a concentration of 30-80 g / L, and oxidant at a concentration of 30 g / L.

3. The method for oxidative leaching of selenium and mercury from copper smelting acid mud according to claim 1, characterized in that: The oxidant mentioned in step (1) is either potassium chlorate or trichloroisocyanuric acid.

4. The method for oxidative leaching of selenium and mercury from copper smelting acid sludge according to claim 1, characterized in that: The leaching in step (2) is carried out at a temperature of 80-90℃ and a stirring speed of 220-300rpm.

5. The method for oxidative leaching of selenium and mercury from copper smelting acid mud according to claim 1, characterized in that: The rinsing in step (3) is carried out using water with a liquid-to-solid ratio of 1.2:1 L / kg.

6. The method for oxidative leaching of selenium and mercury from copper smelting acid mud according to claim 1, characterized in that: The washing step (4) uses water or a 0.1-1 mol / L NaCO3 solution with a liquid-to-solid ratio of 2:1 L / kg.