A method for pyrolyzing organic tin waste at low temperature and simultaneously preparing stannous sulfate

Abstract

The invention discloses a method for pyrolyzing organotin waste at low temperature and simultaneously preparing stannous sulfate, belonging to the technical field of organotin waste treatment. The method is to place the organotin waste in a tube roasting furnace, pyrolyze it under an oxidation 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 leaching solution is subjected to impurity removal and concentrated crystallization to obtain a stannous sulfate product. This method uses organotin waste as a raw material to prepare a high-purity stannous sulfate product with high added value, realizing the resource utilization of hazardous waste, reducing the treatment cost while improving the recycling efficiency of tin resources, and providing a new way for the green and harmless disposal and efficient recovery of organotin waste.

Description

Technical Field

[0001] The present invention relates to a method for treating organotin waste, and particularly to a method for pyrolyzing organotin waste at low temperature and simultaneously preparing stannous sulfate, belonging to the technical field of organotin waste resource utilization. Background Art

[0002] Organotin waste is the residue of organotin compounds generated during industrial production and application, and has high toxicity and environmental hazards. Organotin compounds (general formula: R n S n X 4-n , n = 1-4, R is an alkyl group or an aromatic group) are coordination polymers formed by the direct bonding of tin atoms with organic groups. Due to their excellent thermal stability and catalytic performance, they are widely used in fields such as organic heat stabilizers and esterification reaction catalysts. However, under conditions such as high temperature, hydrolysis, or acidification, organotin compounds are prone to inactivation and decomposition, forming tin-containing hazardous waste that is difficult to degrade.

[0003] At present, the main treatment methods for organotin waste include wet leaching, biodegradation, and high-temperature incineration, etc. Wet leaching usually uses oxidants such as H2O2 to achieve detoxification by destroying the Sn-C bond structure, but the reaction rate is slow and accompanied by the generation of waste gas and waste liquid. Biodegradation relies on the enzymatic action of microorganisms to decompose organotin compounds, but is limited by environmental conditions and has low degradation efficiency. High-temperature incineration treats organotin compounds by decomposing them into small molecule gases and water. However, the incineration process is difficult to precisely 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, Chinese Patent Application (Publication No.: CN117023631A) discloses a method for deeply detoxifying organotin waste and simultaneously preparing sodium stannate. In this method, organotin waste is mixed with a composite additive with sodium oxalate and hydrogen peroxide as the active ingredients and then subjected to spray combustion. The combustion tail gas is dust-removed to recover tin-rich materials, and the tin-rich materials are leached with water to obtain a sodium stannate solution. By adding components such as sodium oxalate and hydrogen peroxide during the combustion decomposition process of organotin waste, this method can not only strengthen the thermal conversion process of organotin compounds, making their toxic organic functional groups transform into harmless CO2 and H2O emissions, but also promote the decomposition of dioxins, sulfur fixation, and inhibit the generation of NO x generation, and enable tin to be efficiently converted into sodium stannate, which is easy to leach and recover. However, this process requires a large amount of sodium oxalate and hydrogen peroxide as combustion additives, greatly increasing the cost of tin recovery, and tin is recovered in the form of sodium stannate, with low added value. Summary of the Invention

[0004] Aiming at the technical problem that the existing methods for treating organotin waste cannot balance harmless disposal and resource utilization, the purpose of the present invention is to provide a method for pyrolyzing organotin waste at low temperature and simultaneously preparing stannous sulfate. This method detoxifies the organotin waste through low-temperature pyrolysis, and then prepares stannous sulfate products that meet national standards through processes such as leaching and impurity removal, providing a new way for the harmless disposal and high-value utilization of organotin waste.

[0005] To achieve the above technical purpose, the present invention provides a method for pyrolyzing organotin waste at low temperature and simultaneously preparing stannous sulfate. In this method, the organotin waste is placed in a tubular roasting furnace and pyrolyzed under an oxidative atmosphere with an O2 volume concentration of 15 - 25% and a temperature of 400 - 600 °C. The solid product obtained from pyrolysis is leached with sulfuric acid, and the resulting leachate is subjected to impurity removal and concentrated crystallization to obtain stannous sulfate products.

[0006] The key to the technical solution of the present invention lies in: making full use of the characteristics of the decomposition of small-molecule organotin compounds in organotin waste at low temperature. By precisely controlling the pyrolysis temperature, the organic groups in the small-molecule organotin compounds can be fully pyrolyzed and volatilized, while promoting the selective oxidation of tin in them to metastable stannous oxide (SnO) under appropriate temperature and oxidative atmosphere. The metastable stannous oxide can efficiently remove impurity elements such as C, Na, Ca, Fe, and Si through sulfuric acid leaching and regulating the chemical environment of the solution, and finally prepare stannous sulfate products with high purity and excellent performance.

[0007] As a preferred scheme, the mass content of Sn in the organotin waste is 5% - 15%, the mass content of C is not less than 40%, the mass content of H is not higher than 15%, and the total mass content of Na, Ca, Fe, and Si is not higher than 1%. The organotin waste of the present invention is, for example, a deactivated organotin catalyst. In a low-temperature environment and a weak oxidative atmosphere composed of oxygen and the pyrolysis products of organic groups, 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 mass content of C is too low, part of the tin will be oxidized to tin oxide (SnO2). 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 the product yield and economic benefits.

[0008] As a preferred scheme, the pyrolysis time is 60 - 90 min. During the pyrolysis process of the present invention, the preferred temperature range can effectively promote the oxidation of metallic Sn to SnO. If the temperature is too low, the oxidation of Sn is incomplete, and if the temperature is too high, Sn is further oxidized to SnO2. At the preferred pyrolysis temperature, the pyrolysis time is not less than 60 min, which can ensure the full conversion of metallic Sn to SnO and improve the stability of the process and the product quality.

[0009] As a preferred embodiment, the conditions for leaching are as follows: the concentration of H2SO4 is 1 - 5 mol / L, the solid-liquid ratio is 1 g : 3 - 8 mL, and the leaching temperature is 40 - 100 °C. Under the preferred leaching conditions, stannous oxide (SnO) reacts with sulfuric acid (H2SO4) to form stannous sulfate (SnSO4) and water. If the sulfuric acid concentration is too high, it may cause the oxidation of Sn 2+ to form Sn 4+ , resulting in the incorporation 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 SO3 gas, which not only increases the risk of equipment corrosion but also may further promote the oxidation of Sn 2+ . Meanwhile, at too high a leaching temperature, residual oxygen or oxidizing substances generated by sulfuric acid will further oxidize Sn 2+ , affecting the purity of the target product.

[0010] As a preferred embodiment, the impurity removal process includes filtering to remove insoluble carbon and silicon impurities, hydrolytic precipitation to remove iron ions, and sulfate coprecipitation to remove calcium ions. Among the solid products generated by the pyrolysis of organotin waste, there are often impurities such as carbon, silicon, iron, calcium, and sodium. If these impurities are not removed, they will affect the purity of the stannous sulfate product. In the present invention, the leaching solution is filtered to directly remove carbon and silicon impurities that are insoluble in sulfuric acid, while iron ions can be removed by hydrolytic precipitation, and then calcium ions are precipitated using sulfate. The final sodium ions can be retained in the crystallization mother liquor during the subsequent crystallization and precipitation of stannous sulfate.

[0011] As a preferred embodiment, during the hydrolytic precipitation process, NaOH is used to adjust the pH to 3.5 - 4.0. Under the preferred hydrolysis conditions, Fe 3+ is prone to hydrolysis reaction with water in a weakly acidic environment to form iron hydroxide (Fe(OH)3) precipitate, thereby achieving effective removal of iron impurities. Adjusting the pH to the range of 3.5 - 4.0 is the key to ensuring the selective precipitation of iron impurities. At this time, Fe(OH)3 has a low solubility and can precipitate out quickly, while Sn 2+ remains in a good dissolved state under this pH condition, avoiding the loss of tin and coprecipitation phenomena.

[0012] As a preferred embodiment, the sulfate used in the sulfate coprecipitation process is Na2SO4. Using sodium sulfate for impurity removal can utilize the sulfate ion (SO4 2- ) in Na2SO4 to react with Ca 2+ in the solution to form insoluble CaSO4 precipitate, thereby achieving efficient removal of calcium impurities. Selecting Na2SO4 as the sulfate source can not only effectively promote Ca 2+Precipitation separation also avoids the introduction of other impurity elements, ensuring the purity of Sn in the solution. 2+ In the remaining solution, SO4 2- Based on the common ion effect, it can promote the precipitation of stannous sulfate subsequently.

[0013] In the oxidation atmosphere of the present invention, the oxygen content is preferably controlled such that the volume concentration of O2 is 15 - 25%. If the oxygen concentration is too high, tin will be oxidized to tin oxide, and if the oxygen concentration is too low, the oxidation of tin will be incomplete. The remaining gases in the oxidation atmosphere are non-reactive gases, such as nitrogen and argon. The oxidation atmosphere can be replaced by air, and the oxygen content in the air meets the requirements.

[0014] Compared with the prior art, the beneficial technical effects brought by the technical solution of the present invention are as follows:

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

[0016] 2) The present invention can use hazardous solid organotin waste as the tin source for preparing stannous sulfate, significantly reducing the raw material cost, reducing the dependence on primary tin resources, having good economic and environmental benefits, and further promoting the development of the recycling of tin resources and green manufacturing.

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

[0018] The following examples are intended to further illustrate the content of the present invention in detail, rather than limiting the protection scope of the claims of the present invention.

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

[0020]

[0021] Comparative Example 1

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

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

[0024] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 89.1%, the content of SnSO4 in the product was 96.8 wt.%, and the purity did not reach the national standard. Due to the too low pyrolysis temperature, a small amount of organic matter that was not completely converted and volatilized remained 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 pyrolysis is carried out at 700 °C.

[0027] Due to the too high pyrolysis temperature, Sn may be further oxidized to SnO2 during the oxidation process.

[0028] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 91.5%, the content of SnSO4 in the product was 98.3 wt.%, and the purity did not reach the national standard. Due to the too high pyrolysis temperature, a small amount of SnO2 was formed in the solid product and was converted to Sn(SO4)2 during the sulfuric acid leaching process, 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 leached under the conditions of 8 mol / L H2SO4, solid-liquid ratio of 1 g:5 mL, and 80 °C.

[0031] Due to the too high sulfuric acid concentration, it will cause the oxidation of Sn 2+ to form Sn 4+ .

[0032] The obtained stannous sulfate product was analyzed. The recovery rate of tin was 94.2%, the content of SnSO4 in the product was 98.1 wt.%, and the purity did not reach the national standard. Due to the oxidation of Sn 2+ caused by the too high sulfuric acid concentration, forming Sn 4+ , resulting in the mixing of tetravalent tin compounds in the product, thus 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 leached under the conditions of 5 mol / L H2SO4, solid-liquid ratio of 1 g:5 mL, and 120 °C.

[0035] Due to the too high leaching temperature, it may further promote the oxidation of Sn 2+ .

[0036] The obtained stannous sulfate product was analyzed. The recovery rate of tin was 91.5%, the content of SnSO4 in the product was 98.5 wt.%, and the purity did not meet the national standard. Due to the too high leaching temperature, it accelerated the decomposition of sulfuric acid to generate SO3 gas, which not only increased the risk of equipment corrosion, but also further promoted the oxidation of Sn 2+ , resulting in the mixing of tetravalent tin compounds in the product, thereby reducing the purity of stannous sulfate.

[0037] Example 1

[0038] First, 10 g of organic tin waste was loaded into an alumina crucible and placed in a tubular roasting furnace with an oxygen-containing atmosphere where the volume concentration of oxygen was 21% (the remaining gas was nitrogen); pyrolysis was carried out at 400 °C to decompose and volatilize the organic components and promote the formation of SnO; subsequently, the solid product obtained by pyrolysis was leached under the conditions of 4 mol / L H2SO4, solid-liquid ratio of 1 g:5 mL, and 80 °C to make the tin element enter the solution; first, insoluble substances C and SiO2 were filtered out; NaOH was added to adjust the solution pH = 3.8 to convert Fe 3+ into Fe(OH)3 precipitate; then 1 mol / L Na2SO4 solution was slowly added until all Ca was converted into CaSO4 precipitate and no precipitate was formed. Utilizing the solubility difference between stannous sulfate and sodium salts, separation was carried out by the crystallization method. Under acidic conditions, stannous sulfate crystallized preferentially, while sodium sulfate remained in the mother liquor and was separated by filtration.

[0039] The obtained stannous sulfate product was analyzed: the recovery rate of tin was 98.6%, the content of SnSO4 in the product was 99.2 wt.%, and the purity met the national standard.

[0040] Example 2

[0041] First, 10 g of organic tin waste was loaded into an alumina crucible and placed in a tubular roasting furnace with an oxygen volume concentration of 24% (the remaining gas was nitrogen); pyrolysis was carried out at 500 °C to decompose and volatilize the organic components and promote the formation of SnO; subsequently, the solid product obtained by pyrolysis was leached under the conditions of 4.5 mol / L H2SO4, solid-liquid ratio of 1 g:5 mL, and 90 °C to make the tin element enter the solution; first, insoluble substances C and SiO2 were filtered out; NaOH was added to adjust the solution pH = 3.8 to convert Fe 3+It is converted into Fe(OH)3 precipitate; then 1 mol / L Na2SO4 solution is slowly added until all Ca is converted into CaSO4 precipitate and no precipitate is formed. Utilizing the solubility difference between stannous sulfate and sodium salts, separation is carried out by crystallization method. Under acidic conditions, stannous sulfate preferentially crystallizes while sodium sulfate remains in the mother liquor and is separated by filtration.

[0042] The obtained stannous sulfate product is analyzed: the recovery rate of tin is 99.1%, the content of SnSO4 in the product is 99.3 wt.%, and the purity meets the national standard.

[0043] Example 3

[0044] First, 10 g of organic tin waste is loaded into an alumina crucible and placed in a tube furnace with an oxygen volume concentration of 18% (the remaining gas is nitrogen); pyrolysis is carried out at 600 °C to decompose and volatilize organic components and promote the formation of SnO; subsequently, the obtained solid product after pyrolysis is leached under the conditions of 5 mol / L H2SO4, solid-liquid ratio of 1 g:5 mL, and 100 °C to make the tin element enter the solution; insolubles C and SiO2 are first filtered off; NaOH is added to adjust the solution pH to 3.8 to make Fe 3+ It is converted into Fe(OH)3 precipitate; then 1 mol / L Na2SO4 solution is slowly added until all Ca is converted into CaSO4 precipitate and no precipitate is formed. Utilizing the solubility difference between stannous sulfate and sodium salts, separation is carried out by crystallization method. Under acidic conditions, stannous sulfate preferentially crystallizes while sodium sulfate remains in the mother liquor and is separated by filtration.

[0045] The obtained stannous sulfate product is analyzed: the recovery rate of tin is 99.3%, the content of SnSO4 in the product is 99.5 wt.%, and the purity meets the national standard.

Claims

1. A method for pyrolyzing organic tin waste at low temperature and simultaneously preparing stannous sulfate, characterized in that: Place the organotin waste in a tubular roasting furnace and carry out pyrolysis under an oxidation atmosphere with an O2 volume concentration of 15 - 25% and at a temperature of 400 - 600 °C. The solid product obtained by pyrolysis is leached with sulfuric acid, and the resulting leaching solution is subjected to impurity removal and concentration crystallization to obtain stannous sulfate products; The Sn mass content in the organotin waste is 5% - 15%, the C mass content is not less than 40%, the H mass content is not higher than 15%, and the total mass content of Na, Ca, Fe, and Si is not higher than 1%; The process of impurity removal includes filtering to remove insoluble carbon and silicon impurities, hydrolyzing and precipitating to remove iron ions, and co-precipitating with sulfates to remove calcium ions.

2. The method for pyrolyzing organic tin waste at low temperature and simultaneously preparing stannous sulfate according to claim 1, wherein: The pyrolysis time is 60 - 90 min.

3. A method for pyrolyzing organic tin waste at low temperature and simultaneously preparing stannous sulfate according to claim 1, characterized in that: The leaching conditions are as follows: the concentration of H2SO4 is 1 - 5 mol / L, the solid-liquid ratio is 1 g:3 - 8 mL, and the leaching temperature is 40 - 100 °C.

4. A method for pyrolyzing organotin waste at low temperature and simultaneously preparing stannous sulfate according to claim 3, characterized in that: During the process of hydrolyzing and precipitating, NaOH is used to adjust the pH to 3.5 - 4.

0.

5. A method for pyrolyzing organotin waste at low temperature and simultaneously preparing stannous sulfate according to claim 3, characterized in that: The sulfate used during the process of co-precipitating with sulfates is Na2SO4.

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