Method for treating organic tin waste through low-temperature pyrolysis and synchronously preparing stannous mono-sulphate

Abstract

The invention discloses a method for treating organic tin waste through low-temperature pyrolysis and synchronously preparing stannous mono-sulphate, and belongs to the technical field of organic tin waste treatment. The method comprises the steps that the organic tin waste is placed in a tubular roasting furnace and pyrolyzed in an oxidizing atmosphere with the O2 volume concentration being 15-25% at the temperature of 400-600 DEG C, a solid product obtained through pyrolysis is leached through sulfuric acid, an obtained leachate is subjected to impurity removal and concentration crystallization, and a stannous mono-sulphate product is obtained. The high-purity stannous mono-sulphate product with the high added value is prepared, resource utilization of hazardous waste is achieved, the treatment cost is reduced, meanwhile, the cyclic utilization efficiency of tin resources is improved, and a new way is provided for green and harmless treatment and efficient recycling of organic tin waste.

Description

Technical Field

[0001] The invention relates to a method for treating organic tin waste, in particular to a method for treating the organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate, belonging to the technical field of resource utilization of organic tin waste. Background Art

[0002] Organotin waste is the residue of organotin compounds generated during industrial production and application, which has high toxicity and environmental hazards. n S n X 4-n , n=1~4, R is an alkyl or aromatic group) is a coordination polymer formed by direct bonding of tin atoms and organic groups. Due to its excellent thermal stability and catalytic performance, it is widely used in the fields of organic thermal stabilizers and esterification catalysts. However, under conditions of high temperature, hydrolysis or acidification, organotin compounds are prone to deactivation and decomposition, forming tin-containing hazardous wastes that are difficult to degrade.

[0003] At present, the main treatment methods for organotin waste include wet leaching, biodegradation and high-temperature incineration. Wet leaching usually uses H 2 O 2 Oxidants such as , can achieve detoxification by destroying the Sn-C bond structure, but the reaction rate is slow and is accompanied by the generation of waste gas and waste liquid. Biodegradation relies on the enzymatic action of microorganisms to decompose organic tin compounds, but due to environmental conditions, the degradation efficiency is low. High-temperature incineration is treated by decomposing organic tin compounds into small molecular gases and water. However, the incineration process is difficult to accurately control, and tin resources often exist in the form of primary raw materials, and the added value of the recovered products is low. For example, a Chinese patent application (publication number: CN117023631A) discloses a method for deep detoxification of organic tin waste and simultaneous preparation of sodium stannate. The method is to mix the organic tin waste with a composite additive whose active ingredients are sodium oxalate and hydrogen peroxide, and then spray burn it. The combustion exhaust is dust-removed to recover the tin-rich material, and the tin-rich material is soaked in water to obtain a sodium stannate solution. This method can not only strengthen the thermal conversion process of organic tin compounds by adding sodium oxalate and hydrogen peroxide and other ingredients during the combustion and decomposition of organic tin waste, but also convert its toxic organic functional groups into harmless CO 2 and H 2 O emissions, and can also promote dioxin decomposition, sulfur fixation and inhibit NO x The process can efficiently convert tin into sodium stannate, which is easy to recover by water leaching. However, this process requires a large amount of sodium oxalate and hydrogen peroxide as combustion additives, which greatly increases the cost of tin recovery. In addition, tin is recovered in the form of sodium stannate, which has a low added value. Summary of the invention

[0004] In view of the technical difficulty that existing methods for treating organic tin waste cannot take into account both harmless disposal and resource utilization, the purpose of the present invention is to provide a method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate. The method achieves detoxification of organic tin waste by low-temperature pyrolysis, and then prepares stannous sulfide products that meet national standards through leaching, impurity removal and other processes, providing a new way for the harmless disposal and high-value utilization of organic tin waste.

[0005] In order to achieve the above technical objectives, the present invention provides a method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate, wherein the organic tin waste is placed in a tubular roasting furnace at 0 2 The pyrolysis is carried out in an oxidizing atmosphere with a volume concentration of 15-25% and a temperature of 400-600°C. The solid product obtained by the pyrolysis is leached with sulfuric acid. The obtained leaching solution is subjected to impurity removal and concentrated crystallization to obtain a stannous sulfate product.

[0006] The key to the technical solution of the present invention is to make full use of the characteristics of small-molecule organic tin compounds in organic tin waste that decompose at low temperatures, and by accurately controlling the pyrolysis temperature, the organic groups in the small-molecule organic tin compounds can be fully pyrolyzed and volatilized, while the tin therein is selectively oxidized to metastable stannous oxide under appropriate temperature and oxidizing atmosphere. The metastable stannous oxide is leached with sulfuric acid and the chemical environment of the solution is regulated to achieve efficient removal of impurity elements such as C, Na, Ca, Fe and Si, and finally a stannous sulfate product with high purity and excellent performance is prepared.

[0007] As a preferred solution, the organotin waste has a Sn content of 5% to 15%, a C content of not less than 40%, a H content of not more than 15%, and a total Na, Ca, Fe and Si content of not more than 1%. The organotin waste of the present invention is, for example, a deactivated organotin catalyst. In a low temperature environment and a weakly oxidizing atmosphere composed of oxygen and organic group pyrolysis products, the Sn in the organotin waste can be selectively converted into metastable stannous oxide (SnO), which is beneficial to the subsequent sulfuric acid leaching process. If the C content is too low, part of the tin will be oxidized to tin oxide (SnO 2 ). In addition, if the content of inorganic impurities is too high, it will significantly increase the burden of the subsequent impurity removal process and reduce product yield and economic benefits.

[0008] As a preferred solution, the pyrolysis time is 60 to 90 minutes. In the pyrolysis process of the present invention, the preferred temperature range can effectively promote the oxidation of metal Sn to SnO. If the temperature is too low, the oxidation of Sn will be incomplete. If the temperature is too high, Sn will be further oxidized to SnO. 2At the preferred pyrolysis temperature, the pyrolysis time is not less than 60 min, which can ensure that the metal Sn is fully converted into SnO and improve the process stability and product quality.

[0009] As a preferred solution, the leaching conditions are: H 2 SO 4 The concentration is 1~5mol / L, the solid-liquid ratio is 1g:3~8mL, and the leaching temperature is 40~100℃. Under the optimal leaching conditions, tin oxide (SnO) and sulfuric acid (H 2 SO 4 ) to generate stannous sulfate (SnSO 4 ) and water. If the sulfuric acid concentration is too high, it may cause Sn 2+ Oxidation to form Sn 4+ , resulting in the mixing of tetravalent tin compounds into the product, thereby reducing the purity of stannous sulfate. At the same time, too high a leaching temperature will accelerate the decomposition of sulfuric acid to generate SO 3 Gas not only increases the risk of equipment corrosion, but may also further promote Sn 2+ At the same time, the residual oxygen or oxidizing substances produced by sulfuric acid at too high a leaching temperature will further oxidize Sn. 2+ , affecting the purity of the target product.

[0010] As a preferred solution, the impurity removal process includes filtering to remove insoluble carbon and silicon impurities, hydrolysis precipitation to remove iron ions, and sulfate coprecipitation to remove calcium ions. The solid product generated based on the pyrolysis of organic tin waste often contains impurities such as carbon, silicon, iron, calcium and sodium. If these impurities are not removed, the purity of the stannous sulfate product will be affected. The present invention filters the leachate to directly remove carbon and silicon impurities that are insoluble in sulfuric acid, and the iron ions can be removed by hydrolysis precipitation, and the calcium ions therein are then precipitated by sulfate, and the final sodium ions can be retained in the crystallization mother liquor in the subsequent stannous sulfate crystallization and precipitation process.

[0011] As a preferred solution, NaOH is used to adjust the pH to 3.5-4.0 during the hydrolysis precipitation process. Under the preferred hydrolysis conditions, Fe 3+ In a weakly acidic environment, it is easy to hydrolyze with water to generate iron hydroxide (Fe(OH) 3 ) precipitation, thereby achieving effective iron impurity removal. Adjusting the pH to the range of 3.5~4.0 is the key to ensure the selective precipitation of iron impurities. At this time, Fe(OH) 3 It has low solubility and can be precipitated quickly, while Sn 2+ Under this pH condition, it still maintains a good solubility state, avoiding the loss and co-precipitation of tin.

[0012] As a preferred solution, the sulfate used in the sulfate coprecipitation process is Na 2 SO 4 . Using sodium sulfate to remove impurities can utilize Na 2 SO 4 The sulfate ions (SO 4 2- ) and Ca in solution 2+ Reaction to form insoluble CaSO 4 Precipitation, thus achieving efficient removal of calcium impurities. Select Na 2 SO 4 As a sulfate source, it can not only effectively promote Ca 2+ The precipitation of Sn in the solution is avoided, and the introduction of other impurity elements is avoided. 2+ purity. At the same time, the residual SO 4 2- Based on the common ion effect, the subsequent precipitation of stannous sulfate can be promoted.

[0013] The oxygen content in the oxidizing atmosphere of the present invention is preferably controlled at O 2 The volume concentration is 15~25%. If the oxygen concentration is too high, tin will be oxidized to tin oxide. If the oxygen concentration is too low, tin oxidation will be incomplete. The remaining gases in the oxidizing atmosphere are non-reactive gases, such as nitrogen and argon. The oxidizing atmosphere can be replaced by air, and the oxygen content in the air meets the requirements.

[0014] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0015] 1) The present invention not only achieves deep detoxification of organic tin waste and effectively eliminates its environmental hazards, but also successfully prepares a high-value-added stannous sulfate product that meets the requirements of industrial production, providing a new way for the harmless disposal and resource utilization of organic tin waste.

[0016] 2) The present invention can use hazardous solid waste organic tin waste as a tin source for preparing stannous sulfate, which significantly reduces the cost of raw materials and reduces dependence on primary tin resources. It has good economic and environmental benefits and further promotes the recycling of tin resources and the development of green manufacturing.

[0017] 3) The present invention makes full use of the low-temperature decomposition characteristics of small-molecule organic tin compounds in organic tin waste. Through precise temperature control, the organic small molecules are volatilized and decomposed during the pyrolysis process, and the generated inorganic tin is selectively converted into metastable stannous oxide (SnO) under a low-temperature oxidizing atmosphere. Subsequently, impurity elements such as C, Na, Ca, Fe and Si are effectively removed by acid leaching and regulating the chemical environment of the solution. Under optimized process conditions, the impurity removal rate is high and the purity of the stannous sulfate product is significantly improved. The final stannous sulfate product not only has excellent chemical purity, but also has good physical properties, meeting the requirements of high-standard industrial applications. DETAILED DESCRIPTION

[0018] The following examples are intended to further illustrate the present invention in detail, but are not intended to limit the scope of protection of the claims of the present invention.

[0019] In the following examples and comparative examples, the organic tin waste used was derived from organic tin waste of a chemical enterprise in Jiangsu, with a Sn content of 5.5 wt.%, a C content of 54.6 wt.%, a N content of 8.3 wt.%, a S content of 0.5 wt.%, and a total content of Na, Ca, Fe and Si of 0.2 wt.%.

[0020]

[0021] Comparative Example 1

[0022] Compared with Example 1, the only difference is that the pyrolysis is carried out at 300°C.

[0023] Since the pyrolysis temperature is too low, it is not conducive to the formation of SnO and some organic matter is not completely decomposed and volatilized.

[0024] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 89.1%, and the SnSO 4 The content is 96.8wt.%, and the purity does not meet the national standard. Due to the low pyrolysis temperature, a small amount of incompletely converted volatile organic matter remains in the solid product, affecting the final purity of the stannous sulfate product.

[0025] Comparative Example 2

[0026] Compared with Example 1, the only difference is that the pyrolysis is carried out at 700°C.

[0027] Due to the high pyrolysis temperature, Sn may be further oxidized to SnO during the oxidation process. 2 .

[0028] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 91.5%, and the SnSO 4The content is 98.3wt.%, and the purity does not meet the national standard. Due to the high pyrolysis temperature, the solid product contains a small amount of SnO 2 generated, and converted into Sn(SO 4 ) 2 , affecting the final purity of the stannous sulfate product.

[0029] Comparative Example 3

[0030] Compared with Example 1, the only difference is that the solid product obtained by pyrolysis is heated to 8 mol / L H 2 SO 4 , solid-liquid ratio of 1g:5mL, leaching conditions at 80℃.

[0031] Due to the high concentration of sulfuric acid, Sn 2+ Oxidation to form Sn 4+ .

[0032] The obtained stannous sulfate product was analyzed and the recovery rate of tin was 94.2%. 4 The content is 98.1wt.%, and the purity does not meet the national standard. 2+ Oxidation to form Sn 4+ , resulting in the mixing of tetravalent tin compounds into the product, thereby reducing the purity of stannous sulfate.

[0033] Comparative Example 4

[0034] Compared with Example 1, the only difference is that the solid product obtained by pyrolysis is heated to 5 mol / L H 2 SO 4 , solid-liquid ratio of 1g:5mL, leaching conditions at 120℃.

[0035] Due to the high leaching temperature, Sn 2+ of oxidation.

[0036] The obtained stannous sulfate product was analyzed and the recovery rate of tin was 91.5%. 4 The content is 98.5wt.%, and the purity does not meet the national standard. Due to the high leaching temperature, sulfuric acid decomposes to generate SO 3 Gas not only increases the risk of equipment corrosion, but also further promotes Sn 2+ Oxidation results in the mixing of tetravalent tin compounds into the product, thereby reducing the purity of stannous sulfate.

[0037] Example 1

[0038] First, 10 g of organotin waste was placed in an alumina crucible and placed in a tubular calcining furnace with an oxygen atmosphere of 21% by volume (the rest was nitrogen); pyrolysis was performed at 400 °C to decompose volatile organic components and promote the formation of SnO; then, the solid product obtained by pyrolysis was heated to 4 mol / L H 2 SO 4 , solid-liquid ratio 1g:5mL, leaching at 80℃, so that the tin element enters the solution; first filter to remove the insoluble C and SiO 2 ; Add NaOH to adjust the solution pH to 3.8 to make Fe 3+ Converted to Fe(OH) 3 Precipitation; then slowly add 1 mol / L Na 2 SO 4 solution until all Ca is converted into CaSO 4 Precipitation, no precipitation. Using the difference in solubility between stannous sulfate and sodium salt, separation is done by crystallization. Under acidic conditions, stannous sulfate crystallizes first, while sodium sulfate remains in the mother liquor and is separated by filtration.

[0039] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 98.6%, and the SnSO 4 The content is 99.2wt.%, and the purity meets national standards.

[0040] Example 2

[0041] First, 10 g of organotin waste was placed in an alumina crucible and placed in a tubular roasting furnace with an oxygen volume concentration of 24% (the rest of the gas was nitrogen); pyrolysis was performed at 500 °C to decompose the volatile organic components and promote the formation of SnO; then, the solid product obtained by pyrolysis was heated to 4.5 mol / L H 2 SO 4 , solid-liquid ratio 1g:5mL, leaching at 90℃, so that the tin element enters the solution; first filter to remove insoluble C and SiO 2 ; Add NaOH to adjust the solution pH to 3.8 to make Fe 3+ Converted to Fe(OH) 3 Precipitation; then slowly add 1 mol / L Na 2 SO 4 solution until all Ca is converted into CaSO 4 Precipitation, no precipitation. Using the difference in solubility between stannous sulfate and sodium salt, separation is done by crystallization. Under acidic conditions, stannous sulfate crystallizes first, while sodium sulfate remains in the mother liquor and is separated by filtration.

[0042] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 99.1%, and the SnSO 4The content is 99.3wt.%, and the purity meets national standards.

[0043] Example 3

[0044] First, 10 g of organotin waste was placed in an alumina crucible and placed in a tubular roasting furnace with an oxygen volume concentration of 18% (the rest of the gas was nitrogen); pyrolysis was performed at 600 °C to decompose the volatile organic components and promote the formation of SnO; then, the solid product obtained by pyrolysis was heated to 5 mol / L H 2 SO 4 , solid-liquid ratio 1g:5mL, leaching at 100℃, so that the tin element enters the solution; first filter to remove the insoluble C and SiO 2 ; Add NaOH to adjust the solution pH to 3.8 to make Fe 3+ Converted to Fe(OH) 3 Precipitation; then slowly add 1 mol / L Na 2 SO 4 solution until all Ca is converted into CaSO 4 Precipitation, no precipitation. Using the difference in solubility between stannous sulfate and sodium salt, separation is done by crystallization. Under acidic conditions, stannous sulfate crystallizes first, while sodium sulfate remains in the mother liquor and is separated by filtration.

[0045] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 99.3%, and the SnSO 4 The content is 99.5wt.%, and the purity meets national standards.

Claims

1. A method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate, characterized in that: The organic tin waste is placed in a tubular roasting furnace and pyrolyzed in an oxidizing atmosphere with an O2 volume concentration of 15-25% and a temperature of 400-600°C. The solid product obtained by pyrolysis is leached with sulfuric acid, and the obtained leachate is subjected to impurity removal, concentration and crystallization to obtain a stannous sulfate product.

2. The method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate according to claim 1, characterized in that: The organotin waste has a Sn content of 5% to 15%, a C content of not less than 40%, a H content of not more than 15%, and a total Na, Ca, Fe and Si content of not more than 1%.

3. A method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate according to claim 1 or 2, characterized in that: The pyrolysis time is 60 to 90 minutes.

4. The method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate according to claim 1, characterized in that: The leaching conditions are: the concentration of H2SO4 is 1~5mol / L, the solid-liquid ratio is 1g:3~8mL, and the leaching temperature is 40~100℃.

5. The method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate according to claim 1, characterized in that: The impurity removal process includes filtering to remove insoluble carbon and silicon impurities, hydrolyzing and precipitating to remove iron ions, and co-precipitating with sulfate to remove calcium ions.

6. The method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate according to claim 5, characterized in that: During the hydrolysis precipitation process, NaOH is used to adjust the pH to 3.5-4.

0.

7. The method for treating organic tin waste by low-temperature pyrolysis and simultaneously preparing stannous sulfate according to claim 5, characterized in that: The sulfate used in the sulfate co-precipitation process is Na2SO4.

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