A method for controlling the crystallization rate of arsenic trioxide

Abstract

The application discloses a method for regulating the crystallization rate of arsenic trioxide, characterized in that: after one-time reduction, the liquid is transported to a settling tank, SO2 is introduced to obtain secondary reduction liquid, the secondary reduction liquid is rapidly cooled to room temperature through a plurality of liquid cooling coils, and then is cooled and crystallized; when the solid content reaches 2-10%, the liquid is transported to a thickener in which crystal seeds are reserved; static nucleation is realized at the upper part of the thickener, and stirring is realized at the bottom of the thickener to promote the growth of crystal nucleus; and finally, coarse arsenic trioxide is obtained through centrifugation. According to the method, the supercooling degree is improved, crystal nucleus is added to reduce nucleation work, and stirring is realized to promote the growth of crystal nucleus, so that the cooling and crystallization efficiency of arsenic trioxide is greatly improved, the production time is shortened, great economic effects are brought to enterprises, and the treatment rate of arsenic-containing wastewater is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of arsenic removal technology, specifically relating to a method for regulating the crystallization rate of arsenic trioxide. Background Technology

[0002] With societal development, the concentration of arsenic in water has increased dramatically due to mining, metallurgy, coal processing, and the use of pesticides. Arsenic in water exists in two forms (As... 3+ And As 5+ Both of these substances are highly toxic, harming not only plants and animals but also posing a significant threat to human health. Arsenic can enter the human body through drinking water, remaining in blood cells, liver, lungs, kidneys, and skin, causing many chronic diseases such as skin cancer, lung cancer, bladder cancer, and cardiovascular disease.

[0003] According to GB5749-2022 standard, the arsenic concentration in drinking water in my country is not allowed to exceed 0.01 mg / L. For metallurgical wastewater with high arsenic concentrations, the most effective method is precipitation, but the resulting slag is difficult to utilize, and stockpiling it can pollute land and water sources. With the rapid development of the metallurgical industry, tens of thousands of tons of arsenic enter copper smelting systems annually in China, making the technology for arsenic recovery from arsenic-containing industrial wastewater an urgent necessity.

[0004] The main method for treating arsenic-containing industrial wastewater is currently cooling crystallization. However, existing technologies are prone to problems such as pipe blockage and slow crystallization rates during the precipitation process, resulting in a slow yield of arsenic trioxide. This invention employs a method of pre-reserving crystal seeds, controlling temperature, and regulating stirring rate to synergistically improve the crystallization rate of arsenic trioxide. Summary of the Invention

[0005] Cooling crystallization is As 5+ After reduction, it exists in solution as HAsO2. Taking advantage of the large temperature-dependent solubility of HAsO2, crude arsenic trioxide can be obtained upon cooling the solution. This invention addresses the problems existing in current cooling crystallization processes of arsenic trioxide by providing a technique to increase the crystallization rate of arsenic trioxide. This technique increases the crystallization rate of arsenic trioxide by pre-reserving seed crystals to provide non-spontaneous nucleation, increasing supercooling, and utilizing mechanical vibration to enhance the nucleation rate.

[0006] To achieve the above objectives, the technical solution of the present invention is a method for controlling the crystallization rate of arsenic trioxide, comprising the following steps:

[0007] 1. Restore As once 5+ The reduced solution is transferred to the arsenic precipitation tank. When the tank level reaches 1 / 3 to 1 / 2, the agitator is started, and sulfur dioxide is introduced for reduction, causing the As... 3+ Concentration increases.

[0008] 2. Start multiple liquid cooling coils to circulate cold water for cooling. Stop feeding the reduced solution after the arsenic precipitation tank reaches 2 / 3 to 3 / 4 full.

[0009] 3. After the temperature of the reduced solution in the arsenic precipitation tank reaches 20~40℃, stop the flow of cold water for cooling, and continue stirring until arsenic trioxide crystals precipitate.

[0010] 4. Transfer the slurry that has begun to crystallize in the settling tank to the thickening tank with reserved seed crystals, stir it evenly, and the stirring frequency is between 20 and 50 Hz.

[0011] 5. Cooling and Crystallization: 60%–80% of the arsenic trioxide is discharged into a centrifuge. The underflow from the thickener is continuous and uniform. The specific gravity of the underflow is measured periodically and should not exceed 2. Then, it is transferred to further centrifugation to finally obtain crude arsenic trioxide.

[0012] Compared with the prior art, the advantages of this invention are:

[0013] 1. Adding seed crystals to increase yield: Compared with traditional methods, due to the presence of pre-reserved arsenic trioxide seed crystals, HAsO2 requires less nucleation work on the seed crystal surface, resulting in smaller structural and energy fluctuations for nucleation. This makes it more likely for HAsO2 to nucleate and grow on the seed crystal surface, thereby increasing the crystallization rate.

[0014] 2. Increased Subcooling for Increased Production Rate: This invention employs a multi-inlet liquid-cooled coil, which increases cooling efficiency and, compared to traditional methods, increases subcooling. With greater subcooling, the nucleation rate increases, crystal nuclei grow faster, and the crystallization rate is thus faster.

[0015] 3. Stirring accelerates crystal growth: The bottom stirring of the thickener provides shear force, which inhibits the formation of more small crystal nuclei and promotes the continued growth of larger crystal nuclei. Meanwhile, the upper part is in a relatively static state, which is conducive to spontaneous nucleation. After nucleation, the crystals settle to the bottom stirring area and continue to grow.

[0016] This invention provides a technology for regulating the crystallization rate of arsenic trioxide, thereby increasing the yield of arsenic trioxide and the rate of treating arsenic-containing wastewater, achieving both economic and social benefits for enterprises. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] The following are examples of improvements made using the technical solutions of the present invention, which will be described in more detail. It should be clearly pointed out that the scope of protection of the present invention includes, but is not limited to, the following examples.

[0019] Example 1:

[0020] A. Take 144 m of the reduced solution on a certain day in July. 3 Its main component is: As 5+ 34.45 g / L, As 3+ 32.54 g / L, Cu 3.68 g / L, Fe 2.27 g / L, H2SO4 118.17 g / L. This was transferred to an arsenic precipitation tank. When the tank level reached 1 / 2, the agitator was started at 40 Hz, and SO2 was introduced for secondary reduction. When the tank level reached 2 / 3, the primary reduction solution was stopped, and the multi-port liquid cooling coils were cooled to room temperature with water. Stirring continued until crystallization. At this point, the slurry in the arsenic precipitation tank was the secondary reduction solution, whose main components were: As... 5+ 13.66 g / L, As 3+ When the solid content is 5% (40.26 g / L, Cu 3.45 g / L, Fe 2.84 g / L, H2SO4 116 g / L), it is transported to a thickener with 100 kg of arsenic trioxide seed crystals reserved.

[0021] B. Start the agitator at the bottom of the thickener, with a stirring frequency of 45 Hz, crystallize for 4 hours, monitor the underflow of the thickener, and ensure that the underflow specific gravity does not exceed 2.

[0022] C. After crystallization, about 70% of the bottom liquid is taken into a centrifuge. The centrifuged liquid is the arsenic-free liquid, which is recycled. The precipitate is arsenic trioxide. During the shift (8h), the material was unloaded four times, producing a total of 2395kg of crude arsenic trioxide. After two centrifugations, the content was found to be 97.72%.

[0023] Example 2:

[0024] A. Take 162 m of the reduced solution on a certain day in August. 3 Its main component is: As 5+ 23.31 g / L, As 3+ 35.29 g / L, Cu 3.51 g / L, Fe 1.29 g / L, H2SO4 83 g / L. This mixture was transferred to an arsenic precipitation tank. When the tank level reached 1 / 2 full, the agitator was started at 40 Hz, and SO2 was introduced for secondary reduction. When the tank level reached 2 / 3 full, the primary reduction solution was stopped, and the multi-port liquid cooling coils were cooled to room temperature with water. Stirring continued until crystallization. At this point, the slurry in the arsenic precipitation tank was the secondary reduction solution, whose main components were: As... 5+ 14.97 g / L, As 3+When the solid content is 7% (41.04 g / L, Cu 3.04 g / L, Fe 1.62 g / L, H2SO4 104 g / L), it is transported to a thickener with 124 kg of arsenic trioxide seed crystals reserved.

[0025] B. Start the agitator at the bottom of the thickener at a frequency of 50 Hz, crystallize for 4 hours, monitor the underflow of the thickener, and ensure that the underflow specific gravity does not exceed 2.

[0026] C. After crystallization, 80% of the bottom liquid is taken into a centrifuge. The centrifuged liquid is the arsenic-free liquid, which is recycled. The precipitate is arsenic trioxide. During the shift (8h), 2551kg of crude arsenic trioxide is produced by unloading four times. After two centrifugations, the content is 98.29%.

[0027] Example 3:

[0028] A. Take 156ml of the reduced solution on a certain day in August. 3 Its main component is: As 5+ 19.47 g / L, As 3+ 31.74 g / L, Cu 4.34 g / L, Fe 2.37 g / L, H2SO4 105 g / L. This mixture was transferred to an arsenic precipitation tank. When the tank level reached 1 / 2, the agitator was started at 45 Hz, and SO2 was introduced for secondary reduction. When the tank level reached 2 / 3, the primary reduction solution was stopped, and the multi-port liquid cooling coils were cooled to room temperature with water. Stirring continued until crystallization. At this point, the slurry in the arsenic precipitation tank was the secondary reduction solution, whose main components were: As... 5+ 12.82 g / L, As 3+ When the solid content is 36.28 g / L, Cu 3.58 g / L, Fe 1.88 g / L, H2SO4 105 g / L, it is transported to a thickener with 124 kg of arsenic trioxide seed crystals reserved.

[0029] B. Start the agitator at the bottom of the thickener at a frequency of 48 Hz, crystallize for 4 hours, monitor the underflow of the thickener, and ensure that the underflow specific gravity does not exceed 2.

[0030] C. After crystallization, about 75% of the bottom liquid is taken into a centrifuge. The centrifuged liquid is the arsenic-free liquid, which is recycled. The precipitate is arsenic trioxide. During the shift (8h), the material was unloaded four times, producing a total of 2246kg of crude arsenic trioxide. After two centrifugations, the content was found to be 98.2%.

[0031] Finally, it should be noted that the above examples have illustrated the technical solutions and data of the present invention, and do not limit them. Those skilled in the art should understand that changes, modifications, or substitutions to the technical parameters without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the crystallization rate of arsenic trioxide, characterized in that, Specifically, it includes the following steps: (1) Temperature control: The liquid after primary reduction is transported to the arsenic precipitation tank. When the liquid level reaches 1 / 3 to 2 / 3, the agitator is started, and SO2 is introduced to reduce it to obtain the liquid after secondary reduction. The temperature of the liquid after secondary reduction in the arsenic precipitation tank is controlled. Multiple liquid cooling coils are circulated with water to cool the liquid after secondary reduction to 20 to 35°C. Stirring is carried out continuously during the cooling process. The liquid after primary reduction contains: As 5+ 20~30g / L, As 3+ 10~30g / L, Cu 2+ 5~15g / L, Fe 3+ H₂SO₄: 5~15g / L; H₂SO₄: 90~120g / L; The solution after secondary reduction contains: As 5+ 5~20g / L, As 3+ 20~40g / L, Cu 2+ 5~15g / L, Fe 3+ :5~15g / L, H2SO4: 90~120g / L; (2) Seed crystal control: When the solid content of the liquid after secondary reduction reaches 1%~15%, it is transported to a thickener with reserved seed crystals, wherein the reserved seed crystals account for 20%~40% of the yield; (3) Stirring control: Start the bottom stirrer of the thickener and stir at a frequency of 30~50Hz to keep the bottom in a flowing state and the upper part in a static state. Control the bottom flow specific gravity to 1~2. After the crystal nuclei are formed in the upper static zone, they settle down to the bottom stirring zone for growth.

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