A method for co-treating and recovering valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag.

Abstract

This invention relates to a method for the co-treatment and recovery of valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag, comprising the following steps: placing the high-arsenic alkaline wastewater in a reaction tank, slowly adding arsenic sulfide slag and a small amount of oxalic acid to the high-arsenic alkaline wastewater to obtain sulfur slag and arsenic-rich wastewater; placing the arsenic-rich wastewater from step 1 in a reaction tank, and then adding oxalic acid to the reaction tank to obtain arsenic trioxide and low-arsenic wastewater; placing the low-arsenic wastewater obtained in step 2 in a reaction tank, and then adding a sulfiding agent to the reaction tank to obtain arsenic sulfide slag and arsenic-removed wastewater; neutralizing the arsenic-removed wastewater with lime to obtain gypsum and reclaimed water. This invention, by co-treating high-arsenic alkaline wastewater and arsenic sulfide slag, can achieve the goal of "using waste to treat waste and turning waste into treasure," and has advantages such as low investment in treatment equipment, reasonable treatment process, high treatment efficiency, and low treatment cost. It has profound significance for improving the economic benefits of enterprises and pursuing a green and sustainable development path.

Description

Technical Field

[0001] This invention relates to a method for the co-processing and recovery of valuable elements from wastewater and solid waste in non-ferrous smelting, particularly a method for the co-processing and recovery of valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag, which belongs to the field of chemical and metallurgical technology. Background Technology

[0002] In the pyrometallurgical treatment of lead anode mud in non-ferrous smelters, the introduction of compressed air for arsenic and antimony smelting generates a large amount of arsenic- and antimony-containing flue dust, resulting in high arsenic and antimony content in the flue dust. The traditional wet process for this flue dust is the alkaline leaching oxygen pressure method, which selectively leaches arsenic under alkaline conditions by pressurizing oxygen, while antimony remains in the slag, achieving arsenic-antimony separation. However, the arsenic concentration in the solution can reach over 30 g / L, constituting high-arsenic alkaline wastewater, which is difficult to treat. Arsenic in wastewater is typically removed using physical or chemical methods, such as lime precipitation, aluminum coagulation, iron coagulation, activated carbon adsorption, and reverse osmosis. For arsenic in acidic wastewater containing heavy metal ions, sulfide precipitation can be used for removal, but sulfide precipitation is not suitable for removing arsenic from alkaline solutions. Lime can be used to remove arsenic from strongly alkaline solutions, but this method is only suitable for treating low-concentration alkaline wastewater containing arsenic. It is not effective for removing arsenic from high-arsenic alkaline wastewater, resulting in high arsenic content in the subsequent liquid. Furthermore, this method produces a large amount of arsenic-calcium slag, which is not only costly but also requires further treatment.

[0003] In the non-ferrous metal smelting industry, pyrometallurgical processes are used to process metal sulfide ores. During the smelting process, some arsenic in the ore volatilizes into sulfur dioxide flue gas as arsenic trioxide. The sulfur dioxide flue gas is then scrubbed with dilute acid to produce arsenic-containing waste acid. This waste acid is treated with sulfiding agents such as sodium sulfide and hydrogen sulfide to precipitate and separate the arsenic, yielding arsenic sulfide slag with a higher arsenic content. Currently, industrial treatment methods for arsenic sulfide slag are broadly divided into pyrometallurgical and hydrometallurgical methods. Pyrometallurgical methods, also known as oxidative roasting, directly recover arsenic trioxide from the flue gas through condensation. This method suffers from a poor production environment, low arsenic recovery rate, and low purity. Hydrometallurgical methods include alkaline leaching, ferric sulfate leaching, and copper sulfate replacement, but these methods generally suffer from cumbersome processes and high production costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for the co-treatment and recovery of valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag. This method combines the treatment of high-arsenic alkaline wastewater and arsenic sulfide slag to turn waste into waste and promote the sustainable and green development of the smelting industry.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for co-treating and recovering valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag includes the following steps:

[0007] Step 1: Place the high-arsenic alkaline wastewater in a reaction tank, and slowly add arsenic sulfide slag to the high-arsenic alkaline wastewater. The amount of arsenic sulfide slag added is based on the molar ratio of arsenic concentration in the high-arsenic alkaline wastewater to sulfur content in the arsenic sulfide slag being 0.7-1.0:1. Then add a small amount of oxalic acid to control the pH value of the solution, which is 8.0 < pH < 10.0. After stirring for 1.0-3.0 hours, filter under pressure to obtain sulfur slag and arsenic-rich wastewater. The sulfur slag is sent to pyrometallurgical ore blending treatment.

[0008] Step 2: Place the arsenic-rich wastewater from Step 1 into a reaction tank, then add oxalic acid to the reaction tank to adjust the pH value of the solution in the reaction tank to 3.0 < pH < 6.0. After stirring for 1.0 h to 3.0 h, filter under pressure to obtain arsenic trioxide and low-arsenic wastewater. The arsenic trioxide can be sent to the arsenic purification workshop for further purification to obtain refined arsenic trioxide.

[0009] Step 3: Place the low-arsenic wastewater obtained in Step 2 into a reaction tank, and then add a sulfiding agent to the reaction tank. The amount of sulfiding agent added is based on a molar ratio of sulfur content in the sulfiding agent to arsenic content in the low-arsenic wastewater of 1.5 to 2.0:1. After stirring for 0.5 to 1 hour, filter under pressure to obtain arsenic sulfide slag and arsenic removal wastewater, wherein the arsenic sulfide slag is returned to Step 1.

[0010] Step 4: Place the arsenic-removed wastewater obtained in Step 3 into a reaction tank, then add lime to the reaction tank, stir for 0.5h to 1h, and then filter under pressure to obtain gypsum slag and neutralized water. The gypsum slag is used for ore blending in the refractory process, and the neutralized water is returned to the workshop for reuse.

[0011] Preferably, in step 1, the main reaction is that sodium arsenate in the high-arsenic alkaline wastewater reacts with arsenic sulfide to produce elemental sulfur and sodium arsenite, and a small amount of oxalic acid is added to react with sodium hydroxide in the solution to produce sodium oxalate and water. The solution pH is controlled to be 8.0 < 10.0. The main chemical reaction equations are as follows:

[0012] Reaction 1: 3Na3AsO4 + As2S3 + 2H2O = 5NaAsO2 + 3S↓ + 4NaOH;

[0013] Reaction 2: H₂C₂O₄ + 2NaOH = Na₂C₂O₄ + 2H₂O;

[0014] Preferably, in step 1, the main components of the sulfur residue are: S content ≥ 80% and As content ≤ 1.0%;

[0015] In step 2, the main reactions are: oxalic acid reacts with sodium hydroxide in the solution to produce sodium oxalate and water; under weakly acidic conditions, oxalic acid reacts with sodium arsenate in the high-arsenic alkaline wastewater to produce sodium oxalate, carbon dioxide, water, and arsenous acid; oxalic acid reacts with sodium arsenous acid to produce sodium oxalate and arsenous acid; and arsenous acid precipitates out as solid arsenic trioxide under weakly acidic conditions, promoting reactions four and five towards the formation of arsenous acid. The main chemical reaction equations are as follows:

[0016] Reaction 3: H₂C₂O₄ + 2NaOH = Na₂C₂O₄ + 2H₂O;

[0017] Reaction 4: 5H₂C₂O₄ + 2Na₃AsO₄ = 2HAsO₂ + 3Na₂C₂O₄ + 4CO₂↑ + 4H₂O;

[0018] Reaction 5:

[0019] Reaction 6: 2HAsO2=As2O3↓+H2O (under acidic conditions);

[0020] Preferably, in step 2, the purity of arsenic trioxide is: As₂O₃≥95%; and the As ion concentration in the low-arsenic wastewater is ≤15g / L.

[0021] Preferably, in step 3, the concentrations of As ions in the arsenic removal wastewater are ≤3 mg / L, Cd ions are ≤5 mg / L, and Pb ions are ≤1 mg / L.

[0022] The concentrations of each component in the high-arsenic alkaline wastewater are as follows: As ion concentration 30–50 g / L, Cd ion concentration 10–100 mg / L, Zn ion concentration 10–100 mg / L, Pb ion concentration 1–5 mg / L, and pH 10–13. The contents of each component in the arsenic sulfide slag are as follows: As content 30%–55%, S content 20%–45%, Cu content 0.1%–2.0%, Pb content 0.1%–1.0%, Zn content 0.1%–1.0%, and Fe content 0.1%–1.0%.

[0023] The beneficial effects of this invention are: by combining the chemical properties of high-arsenic alkaline wastewater and arsenic sulfide slag, the two are treated together, which reduces the production cost of treating high-arsenic alkaline wastewater and arsenic sulfide slag separately; on the other hand, it achieves the goal of "using waste to produce waste and turning waste into treasure". It has the advantages of low investment in treatment equipment, reasonable treatment process, high treatment efficiency and low treatment cost; it has profound significance for improving the economic benefits of enterprises and taking the path of green and sustainable development. Attached Figure Description

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

[0025] Example 1:

[0026] The concentrations of each component in the high-arsenic alkaline wastewater are as follows: As ion concentration 30 g / L, Cd ion concentration 10 mg / L, Zn ion concentration 10 mg / L, Pb ion concentration 1 mg / L, and pH 10.

[0027] The contents of each component in the arsenic sulfide slag are as follows: As 30%, S 20%, Cu 0.1%, Pb 0.1%, Zn 0.1%, and Fe 0.1%.

[0028] Step 1: Place a certain amount of high-arsenic alkaline wastewater in a reaction vessel, and slowly add arsenic sulfide slag to the high-arsenic alkaline wastewater. The amount of arsenic sulfide slag added is based on a molar ratio of arsenic concentration in the high-arsenic alkaline wastewater to sulfur content in the arsenic sulfide slag of 0.7:1. Then add a small amount of oxalic acid to control the pH of the solution to 8.5. After stirring for 1.0 h, filter under pressure to obtain sulfur slag and arsenic-rich wastewater. The sulfur slag is sent to pyrometallurgical ore blending treatment. The main components of the sulfur slag (dry basis) are: S content of 85% and As content of 0.9%.

[0029] Step 2: Place the arsenic-rich wastewater from Step 1 into a reaction tank, then add oxalic acid to the reaction tank to adjust the pH of the solution in the reaction tank to 3.5. After stirring for 1.0 h, filter by pressure to obtain arsenic trioxide and low-arsenic wastewater. The arsenic trioxide can be sent to the arsenic purification workshop for further purification to obtain refined arsenic trioxide. The purity of arsenic trioxide (dry basis) is: As2O3 is 96.52%, and the As ion concentration in the low-arsenic wastewater is 10.25 g / L.

[0030] Step 3: Place the low-arsenic wastewater obtained in Step 2 into a reaction tank, and then add a sulfiding agent to the reaction tank. The amount of sulfiding agent added is based on a molar ratio of sulfur content in the sulfiding agent to arsenic content in the low-arsenic wastewater of 1.5:1. After stirring for 0.5 hours, filter under pressure to obtain arsenic sulfide slag and arsenic removal wastewater. The arsenic sulfide slag is returned to Step 1, and the concentration of As ions in the arsenic removal wastewater is 2.25 mg / L, the concentration of Cd ions is 3.85 mg / L, and the concentration of Pb ions is 0.25 mg / L.

[0031] Step 4: Place the arsenic-removed wastewater obtained in Step 3 into a reaction vessel, then add lime to the reaction vessel, stir for 0.5 hours, and filter under pressure to obtain gypsum slag and neutralized water. The gypsum slag is used for ore blending in the refractory smelting process, and the neutralized water is reused in the workshop.

[0032] Example 2:

[0033] The concentrations of each component in the high-arsenic alkaline wastewater are as follows: As ion concentration 50 g / L, Cd ion concentration 100 mg / L, Zn ion concentration 100 mg / L, Pb ion concentration 5 mg / L, and pH 13.

[0034] The contents of each component in the arsenic sulfide slag are as follows: As 55%, S 40%, Cu 2.0%, Pb 1.0%, Zn 1.0%, and Fe 1.0%.

[0035] Step 1: Place a certain amount of high-arsenic alkaline wastewater in a reaction tank, and slowly add arsenic sulfide slag to the high-arsenic alkaline wastewater. The amount of arsenic sulfide slag added should be based on a molar ratio of arsenic concentration in the high-arsenic alkaline wastewater to sulfur content in the arsenic sulfide slag of 1.0:1. Then add a small amount of oxalic acid to control the pH of the solution to 9.5. After stirring for 3 hours, filter under pressure to obtain sulfur slag and arsenic-rich wastewater. The sulfur slag is sent to pyrometallurgical ore blending treatment. The main components of the sulfur slag (dry basis) are: S content of 95% and As content of 0.21%.

[0036] Step 2: Place the arsenic-rich wastewater from Step 1 into a reaction tank, then add oxalic acid to the reaction tank to adjust the pH of the solution in the reaction tank to 5.5. After stirring for 3.0 hours, filter by pressure to obtain arsenic trioxide and low-arsenic wastewater. The arsenic trioxide can be sent to the arsenic purification workshop for further purification to obtain refined arsenic trioxide. The purity of arsenic trioxide (dry basis) is: As2O3 is 98.21%, and the As ion concentration in the low-arsenic wastewater is 8.25 g / L.

[0037] Step 3: Place the low-arsenic wastewater obtained in Step 2 into a reaction tank, and then add a sulfiding agent to the reaction tank. The amount of sulfiding agent added is based on a molar ratio of sulfur content in the sulfiding agent to arsenic content in the low-arsenic wastewater of 2.0:1. After stirring for 1 hour, filter under pressure to obtain arsenic sulfide slag and arsenic removal wastewater. The arsenic sulfide slag is returned to Step 1, and the concentration of As ions in the arsenic removal wastewater is 2.25 mg / L, the concentration of Cd ions is 3.85 mg / L, and the concentration of Pb ions is 0.25 mg / L.

[0038] Step 4: Place the arsenic-removed wastewater obtained in Step 3 into a reaction vessel, then add lime to the reaction vessel, stir for 1.0 h, and filter under pressure to obtain gypsum slag and neutralized water. The gypsum slag is used for ore blending in the refractory smelting process, and the neutralized water is reused in the workshop.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the co-treatment of high-arsenic alkaline wastewater and arsenic sulfide slag to recover valuable elements, characterized in that: The method comprises the following steps: Step 1, the high-arsenic alkaline wastewater is placed in a reaction tank, arsenic sulfide slag is slowly added into the high-arsenic alkaline wastewater, the amount of the arsenic sulfide slag is added according to the molar ratio of the arsenic concentration in the high-arsenic alkaline wastewater to the sulfur content in the arsenic sulfide slag, which is 0.7-1.0:1, a small amount of oxalic acid is further added, the pH value of the solution is controlled, 8.0 Step 2, the arsenic-rich wastewater in step 1 is placed in a reaction tank, then oxalic acid is added into the reaction tank, the pH value of the solution in the reaction tank is adjusted, 3.0 Step 3, the low-arsenic wastewater obtained in step 2 is placed in a reaction tank, then a sulfidizing agent is added into the reaction tank, the amount of the sulfidizing agent is added according to the molar ratio of the sulfur content in the sulfidizing agent to the arsenic content in the low-arsenic wastewater, which is 1.5-2.0:1, after stirring for 0.5-1 hours, pressure filtration is conducted, arsenic sulfide slag and arsenic-removing wastewater are obtained, and the arsenic sulfide slag is returned to step 1. Step 4, the arsenic-removing wastewater obtained in step 3 is placed in a reaction tank, then lime is added into the reaction tank, after stirring for 0.5-1 hours, pressure filtration is conducted, gypsum slag and neutralization water are obtained, the gypsum slag is used for fire smelting and ore blending, and the neutralization water is returned to the workshop for reuse.

2. The method for the cooperative disposal of high-arsenic alkaline wastewater and arsenic sulfide slag to recover valuable elements according to claim 1, characterized in that: In step 1, the main reaction is that sodium arsenate in the high-arsenic alkaline wastewater reacts with arsenic sulfide to generate elemental sulfur and sodium arsenite, a small amount of oxalic acid reacts with sodium hydroxide in the solution to generate sodium oxalate and water, the pH value of the solution is controlled to be 8.0 Reaction one: 3Na3AsO4+As2S3+2H2O=5NaAsO2+3S↓+4NaOH Reaction two: H2C2O4+2NaOH=Na2C2O4+2H2O.

3. The method for co-treating high-arsenic alkaline wastewater and arsenic sulfide slag to recover valuable elements according to claim 1 or 2, characterized in that: In step 1, the main components of the sulfur slag account for: S content≥80%, As content≤1.0%.

4. The method for treating and recovering valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag according to claim 1 or 2, characterized in that: In step 2, the main reaction is that oxalic acid reacts with sodium hydroxide in the solution to generate sodium oxalate and water, under weak acid conditions, oxalic acid reacts with sodium arsenate in the high-arsenic alkaline wastewater to generate sodium oxalate, carbon dioxide, water and arsenite, oxalic acid reacts with sodium arsenite to generate sodium oxalate and arsenite, arsenite is precipitated to generate diarsenic trioxide solid under weak acid conditions, the reactions of reactions four and five are promoted to proceed in the direction of generating arsenite, and the main chemical reaction equations are as follows: Reaction three: H2C2O4+2NaOH=Na2C2O4+2H2O Reaction four: 5H2C2O4+2Na3AsO4=2HAsO2+3Na2C2O4+4CO2↑+4H2O Reaction five: Reaction six: 2HAsO2=As2O3↓+H2O.

5. The method for treating and recovering valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag according to claim 1 or 2, characterized in that: In step 2, the purity of diarsenic trioxide is: As2O3≥95%; the concentration of As ions in the low-arsenic wastewater is≤15 g / L.

6. The method for treating and recovering valuable elements from high-arsenic alkaline wastewater and arsenic sulfide slag according to claim 1 or 2, characterized in that: In the step 3, the concentration of As ions in the arsenic removal wastewater is less than or equal to 3 mg / L, the concentration of Cd ions is less than or equal to 5 mg / L, and the concentration of Pb ions is less than or equal to 1 mg / L. In the step 3, the concentration of As ions in the arsenic removal wastewater is less than or equal to 3 mg / L, the concentration of Cd ions is less than or

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