A method for recycling sulfur-containing waste salt

Abstract

This invention belongs to the field of sulfur-containing waste salt treatment technology, specifically relating to a method for the resource utilization of sulfur-containing waste salt. This invention involves redissolving sulfur-containing inorganic sodium chloride salt with oxidizing sodium hypochlorite, followed by pulping to remove encapsulated organic matter or reducing substances from the salt surface. The filtered salt contains ≤5% water (including sodium hypochlorite), which is then dried, crushed, and sieved. The sieved salt is then subjected to high-temperature pyrolysis before being calcined in a melting furnace. This invention first performs pulping to remove sulfur-containing compounds or organic matter encapsulated during crystallization; simultaneously, it controls the moisture content of the filtered salt to avoid problems such as encapsulation issues in clumped salt and incomplete oxidation of organic matter. The invention also involves sieving the salt and performing secondary pulping on large salt particles to ensure sufficient reaction of the salt entering the melting process. The treatment method provided by this invention can effectively improve the treatment efficiency of sulfur-containing waste salt, resulting in salt with high purity.

Description

Technical Field

[0001] This invention belongs to the field of sulfur-containing waste salt treatment technology, and specifically relates to a method for the resource utilization of sulfur-containing waste salt. Background Technology

[0002] Currently, the production of sulfur-containing technical materials generates high-salt wastewater with sulfur content. After desalination via MVR (Mechanical Vapor Reduction) evaporation, this wastewater yields waste salt containing large amounts of sulfur-containing organic or inorganic compounds. Directly introducing this waste salt into subsequent melting and refining processes severely impacts the quality of the molten salt. Therefore, a technology is needed to pretreat this sulfur-containing waste salt to improve the quality of the recovered salt.

[0003] CN102992514B describes a method for treating and recovering pesticide wastewater with high sulfur and salinity. It primarily uses chlorine gas to oxidize sulfur compounds in the wastewater into yellow elemental sulfur. This technology is mainly applicable to wastewater containing divalent sulfur. However, its applicability is relatively narrow, and the mass transfer efficiency of gas-liquid reactions is lower than that of liquid-liquid reactions, requiring improvements in chlorine utilization.

[0004] CN109293148B describes a treatment device and method for sulfur- and saline wastewater. It primarily targets organosilicon-containing wastewater. The sulfur-containing substances in the wastewater are mainly divalent sulfur. This technology is not suitable for treating waste salts containing organosulfur.

[0005] CN109519938A describes an energy-saving and environmentally friendly emission system for incinerating sulfur- and saline organic waste liquid. The system can physically break down the sulfur- and saline waste liquid into small droplets, which are then fed into an incineration system to thermally decompose the organic matter. The resulting waste salt is then fed into a melting furnace for refining. This method is suitable for systems containing degradable sulfur-containing organic matter.

[0006] CN111646487A describes a resource recovery method for treating chemical waste salt. This method employs a melting process, controlling the moisture content of the feed and adding a certain amount of oxidizing agent to ensure sufficient oxidant to remove organic matter during melting. While this method can address the issue of insufficient oxygen during salt melting to some extent, it is unsuitable for sodium chloride waste salt containing encapsulated sulfites. This is primarily because sodium sulfite undergoes a self-disproportionation reaction at 150℃ to form sodium sulfide. The added solid oxidant cannot react with encapsulated sodium sulfite at this temperature. Furthermore, solid oxidants suffer from uneven mixing, posing a safety risk.

[0007] Currently, in the treatment of sulfur-containing waste salt, it is directly fed into a melting furnace for calcination. After feeding, the material temperature continuously rises. Because the density of liquid sodium chloride is greater than that of solid sodium chloride, the density of sodium chloride increases during the heating process, causing it to continuously sink. This results in insufficient contact between some salt and oxygen, leading to the carbonization of organic matter into inorganic carbon. Under high-temperature conditions, the inorganic carbon reacts with sulfur-containing organic matter to form low-valence sulfur.

[0008] Furthermore, some encapsulated sulfur-containing inorganic salts, such as sodium sulfite, will melt and disproportionate at 150°C to form sodium sulfide and sodium sulfate. This results in the salt product absorbing moisture, developing a rotten egg odor, and easily discoloring. This situation cannot be resolved even by adding a solid oxidant beforehand. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a method for the resource utilization of sulfur-containing waste salt. This invention involves redissolving sulfur-containing inorganic sodium chloride salt with oxidizing sodium hypochlorite, followed by pulping to remove encapsulating organic matter or reducing substances from the salt surface. The filtered salt contains ≤5% moisture (including sodium hypochlorite). This salt is then dried, crushed, and sieved. Larger salt particles are returned to the front end for redissolving and pulping. The sieved salt is then subjected to high-temperature pyrolysis before being calcined in a melting furnace. This method avoids the problem of encapsulation caused by clumped salt and incomplete oxidation of organic matter.

[0010] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0011] This invention provides a method for the resource utilization of sulfur-containing waste salt, comprising the following steps:

[0012] 1) Pulping: Sulfur-containing waste salt is added to a sodium hypochlorite solution for pulping;

[0013] 2) Filtration: The pulped material is transferred out for solid-liquid separation to obtain solid salt;

[0014] 3) Drying, grinding and screening: Dry the solid salt, grind the dried material and then screen it to obtain sieved salt; unscreened salt is returned to the pulping process.

[0015] 4) Melting and calcining: The sieved salt is calcined at a constant temperature, and then cooled. The resulting salt is qualified salt.

[0016] The resource utilization method provided by this invention mainly treats sulfur-containing waste salts generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials. The total sulfur (inorganic sulfur and organic sulfur) TS in the waste salt is ≤10000mg / kg, and the total organic carbon TOC is ≤5000mg / kg.

[0017] Furthermore, in step 1), the mass fraction of the sodium hypochlorite solution is 0.1-10%; and the solid content of the sodium hypochlorite solution is controlled to be 20%-50%.

[0018] Furthermore, in step 1), the pulping is performed at a temperature of 0~60℃ for 30min~150min.

[0019] Furthermore, in step 2), the water content of the solid salt is ≤5%.

[0020] Furthermore, in step 3), the drying temperature is 100℃; the moisture content of the dried material is ≤1%; and the mesh size of the vibrating screen used for screening is 80~100 mesh.

[0021] Furthermore, in step 4), the melting and calcining involves calcining the sieved salt at a constant temperature of 800℃~1000℃ for 1~5 hours.

[0022] The beneficial effects of this invention are as follows:

[0023] 1) The present invention first slurries the salt containing sulfur-containing organic matter to remove the sulfur-containing compounds or organic matter encapsulated during the crystallization process; at the same time, it controls the moisture content of the filtered salt to avoid problems such as encapsulation of clumps of salt and incomplete oxidation of organic matter.

[0024] 2) This invention proposes to use a vibrating screen with a mesh size of 800-1000 to screen the salt and to perform secondary pulping on large salt particles to ensure that the salt entering the melting process can react fully and that there is no encapsulation.

[0025] 3) The processing method provided by the present invention can effectively improve the processing efficiency of sulfur-containing waste salt and obtain salt with high purity. Attached Figure Description

[0026] Figure 1 A flowchart of the resource utilization method provided by the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further explained and described below through specific embodiments. The flowchart of the resource utilization method provided by the present invention is as follows: Figure 1 As shown, the sulfur-containing waste salts treated in the examples mainly come from the sulfur-containing waste salts generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials. The total sulfur (inorganic sulfur and organic sulfur) TS in the waste salts is ≤10000mg / kg, the total organic carbon TOC is ≤5000mg / kg, and the sodium chloride content is ≥80%.

[0028] Example 1

[0029] 500g of sulfur-containing waste salt generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials was taken and dissolved in a 0.1% sodium hypochlorite solution at room temperature (20-30℃). After slurrying for 60 minutes, solid-liquid separation was performed by vacuum filtration, and the moisture content of the obtained salt was determined to be 4%. The salt was then dried at 100℃ for 2 hours, and its moisture content was determined to be 0.4%. The salt was then ground, sieved through an 800-mesh vibrating sieve, and then calcined in a muffle furnace at 850℃ for 1 hour. After natural cooling, qualified salt was obtained.

[0030] The calcined salt is white in appearance, and the sodium chloride purity is determined to be 99.3%. A small amount of sample is dissolved in an acidic solution, and no sulfur is detected. 2- TOC: 5 mg / kg.

[0031] Example 2

[0032] 500g of sulfur-containing waste salt generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials was taken and dissolved in a 2% sodium hypochlorite solution at 50-60℃. After slurrying for 150 minutes, solid-liquid separation was performed by vacuum filtration, and the moisture content of the obtained salt was determined to be 2%. The salt was then dried at 100℃. The moisture content of the dried salt was 0.8%. The salt was then sieved, and the material passing through a 1000-mesh vibrating screen was transferred to a muffle furnace for melting and calcination at 900℃ for 3 hours. It was then allowed to cool naturally.

[0033] The calcined salt is white in appearance, and the sodium chloride purity is determined to be 99%. A small sample is dissolved in an acidic solution, and no sulfur is detected. 2- TOC: 5.6 mg / kg.

[0034] Example 3

[0035] 500g of sulfur-containing waste salt generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials was taken and dissolved in a 5% sodium hypochlorite solution at 30-40℃. After slurrying for 30 minutes, solid-liquid separation was performed by vacuum filtration, and the moisture content of the obtained salt was determined to be 1%. The salt was then dried at 100℃ for 2 hours, and its moisture content was determined to be 0.2%. The salt was then ground, sieved through a 1000-mesh vibrating sieve, and then calcined in a muffle furnace at 1000℃ for 5 hours. After natural cooling, qualified salt was obtained.

[0036] The calcined salt is white in appearance, and the sodium chloride purity is determined to be 99.3%. A small amount of sample is dissolved in an acidic solution, and no sulfur is detected. 2- TOC: 4.8 mg / kg.

[0037] Comparative Example 1

[0038] 500g of sulfur-containing waste salt generated during the synthesis of pesticides using thioacryl chloride or thionyl chloride as raw materials was taken without pulping. The moisture content of the salt was determined to be 4%. The salt was then melted and calcined in a muffle furnace at 900℃ for 1 hour. After natural cooling, the salt was obtained with a light yellowish-brown appearance, a purity of 91%, and a TOC of 4890mg / kg.

[0039] Comparative Example 2

[0040] 500g of sulfur-containing waste salt generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials was taken. The waste salt was pulped with tap water at room temperature (20-30℃) and separated into solid and liquid components by filtration. The resulting salt had a moisture content of 4%. It was then calcined in a muffle furnace at 1000℃ for 5 hours. After natural cooling, the resulting salt was pale yellowish-brown in appearance, with a sodium chloride purity of 90% and a TOC of 4996 mg / kg.

[0041] Comparative Example 3

[0042] 500g of sulfur-containing waste salt generated during the synthesis of pesticides using thiocyanate chloride or thionyl chloride as raw materials was taken and dried at 100℃ for 2 hours, with a moisture content of 0.4%. Then, 6.5g of sodium hypochlorite solid was added and mixed evenly, followed by grinding, sieving, and then calcining in a muffle furnace at 850℃ for 1 hour. After natural cooling, a white salt with a sodium chloride purity of 96.5% and a TOC of 3860mg / kg was obtained.

Claims

1. A method for the resource utilization of sulfur-containing waste salt, characterized in that, Includes the following steps: 1) Pulping: Sulfur-containing waste salt is added to a sodium hypochlorite solution for pulping; The sodium hypochlorite solution has a mass fraction of 0.1% to 10%. 2) Filtration: The pulped material is transferred out for solid-liquid separation to obtain solid salt; The moisture content of the solid salt is ≤5%. 3) Drying, grinding and screening: Dry the solid salt, grind the dried material and then screen it to obtain sieved salt; unscreened salt is returned to the pulping process. The moisture content of the dried material is ≤1%; the vibrating screen used for screening has a mesh size of 800~1000 mesh; 4) Melting and calcining: The sieved salt is calcined at a constant temperature and then cooled down to obtain qualified salt.

2. The resource utilization method according to claim 1, characterized in that, In step 1), the sodium hypochlorite solution has a solid content of 20% to 50%.

3. The resource utilization method according to claim 2, characterized in that, In step 1), the pulping is performed at a temperature of 0~60℃ for 30min~150min.

4. The resource utilization method according to claim 1, characterized in that, In step 3), the drying temperature is 100°C.

5. The resource utilization method according to any one of claims 1-4, characterized in that, In step 4), the melting and calcining involves calcining the sieved salt at a constant temperature of 800℃~1000℃ for 1~5 hours.

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