Method for recovering tin from tin-containing waste

Abstract

The present invention relates to the technical field of waste recycling, and specifically discloses a method for recovering tin from tin-containing waste. In the technical solution provided by the present invention, carboxymethyl chitosan is used as a natural polymer dispersant to ensure that Fe 3+ Evenly distributed on the surface and interlayer of bentonite; then sodium borohydride (NaBH4) was used as a strong reducing agent to reduce Fe 3+ In situ reduction to zero-valent iron, during which carboxymethyl chitosan further prevents the aggregation of nano-iron particles through steric hindrance effect, forming a highly dispersed zero-valent iron / bentonite composite structure; the generated zero-valent iron can serve as a catalyst for the reaction of calcium fluoride (CaF2) and tin oxide, improving the reaction efficiency of tin oxide; at the same time, under a reducing atmosphere, carboxymethyl chitosan is pyrolyzed to generate active gases such as CO, which further promotes the reaction of calcium fluoride (CaF2) and tin oxide, so that tin is effectively recovered and the recovery rate of tin is improved.

Description

Technical Field

[0001] The invention relates to the technical field of waste recycling, and in particular to a method for recovering tin from tin-containing waste materials. Background Art

[0002] Tin-containing waste primarily includes electronic waste, smelting slag, tinplate scrap, and tin foil ash. A significant amount of this waste is disposed of informally, leading to wasted tin resources and heavy metal pollution. The accumulation of difficult-to-treat materials, such as low-grade tin tailings and tin-iron co-existing ores, is particularly problematic. Traditional mineral processing techniques struggle to achieve efficient separation, resulting in a consistently low tin recovery rate. Furthermore, the decentralized recycling system for industrial waste such as tin-coated steel sheets and solder paste is imperfect. A significant amount of this waste remains unresourced due to a lack of large-scale processing technology, exacerbating the over-exploitation of primary tin mines.

[0003] Existing tin recovery technologies primarily include pyrometallurgy, wet leaching, and chlorination processes, but these still have several shortcomings. Pyrometallurgical processes, such as the sulfide volatilization method, require operation at temperatures exceeding 1000°C, consume high energy, and produce large amounts of harmful gases such as SO2 and HCl, leading to equipment corrosion and environmental pollution. While wet processes can process low-grade materials, they are less adaptable to complex tin-containing waste materials. Chemical precipitation methods, which generate high sludge volumes and wastewater treatment costs, limit their economic viability. For example, alkaline leaching methods require multiple separation steps and produce tin recovery rates of less than 85%. These technical challenges hinder the sustainable development of the recycled tin industry. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for recovering tin from tin-containing waste materials.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for recovering tin from tin-containing waste comprises the following steps: grinding and crushing the tin-containing waste, then mixing and agglomerating the tin-containing waste with a binder, drying the granules, calcining the granules in a reducing atmosphere, and recovering volatilized tin compounds; the binder is composed of fluorite and modified bentonite.

[0007] In the technical solution disclosed in the present invention, the tin-containing waste is first ground and passed through a 400-mesh sieve.

[0008] In the technical solution disclosed in the present invention, the mass ratio of tin-containing waste to binder is 10-15:1. For example, 10:1, 11:1, 12:1, 13:1, 14:1, and 15:1 can be selected, but it is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0009] In the technical solution disclosed in the present invention, the binder is composed of the following components in parts by weight: 80-100 parts of fluorite and 20-30 parts of modified bentonite.

[0010] For example, the number of parts of fluorite can be selected as 80 parts, 82 parts, 85 parts, 86 parts, 88 parts, 90 parts, 92 parts, 94 parts, 95 parts, 96 parts, 98 parts, and 100 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0011] For example, the amount of modified bentonite can be 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, or 30 parts, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0012] Specifically, the preparation method of the modified bentonite is as follows:

[0013] S1, immersing bentonite in an acid solution, heating and stirring, and then filtering, washing, and drying to obtain pretreated bentonite;

[0014] S2. Pretreated bentonite is dispersed in deionized water, carboxymethyl chitosan and ferric chloride are added thereto, and the mixture is stirred evenly to obtain a mixed solution. Nitrogen is then introduced to expel the air, and an aqueous sodium borohydride solution is added thereto. The mixture is heated and stirred to react. After the reaction is completed, the mixture is filtered, washed, and vacuum-dried to obtain modified bentonite.

[0015] In the technical solution disclosed in the present invention, in step S1, the acid solution is selected from sulfuric acid solution, nitric acid solution or hydrochloric acid solution.

[0016] The concentration of the acid solution is 0.5-2 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L can be selected, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] In the technical solution disclosed in the present invention, in step S1, the temperature of the heating and stirring treatment is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C, and 80°C can be selected; the time of the heating and stirring treatment is 1-2h, for example, 1h, 1.5h, and 2h can be selected, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] In step S1, the bentonite is immersed in an acid solution and heated and stirred. The hydrogen ions can replace the impurity ions such as calcium and magnesium between the bentonite layers, expand the interlayer spacing of the bentonite and increase its specific surface area; at the same time, the organic and inorganic pollutants adsorbed by the bentonite are removed, making the internal channels of the bentonite more unobstructed, and providing a larger reaction interface for the subsequent loading of metal particles.

[0019] In the technical solution disclosed in the present invention, in step S2, the mass ratio of pretreated bentonite, carboxymethyl chitosan, ferric chloride and sodium borohydride aqueous solution is 4-8:4-8:2-4:20-30.

[0020] The mass fraction of the sodium borohydride aqueous solution is 5-10%, for example, 5%, 6%, 7%, 8%, 9%, 10% can be selected, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] In the technical solution disclosed in the present invention, in step S2, the temperature of the heating and stirring reaction is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C, and 60°C can be selected; the time of the heating and stirring reaction is 1-2h, for example, 1h, 1.5h, and 2h can be selected; but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] In step S2, the present invention uses bentonite as an additive to mix with tin-containing waste to form agglomerates. Its high melting point property can maintain the structural stability of the agglomerates. The present invention loads carboxymethyl chitosan on bentonite through hydrogen bonding. Carboxymethyl chitosan is a natural polymer dispersant. The hydroxyl (-OH) and amino (-NH2) on its molecular chain can chelate Fe 3+ , ensuring Fe 3+ Evenly distributed on the surface and interlayer of bentonite; then, nitrogen was introduced to expel the air, and sodium borohydride aqueous solution was added. Sodium borohydride (NaBH4) acts as a strong reducing agent to reduce Fe 3+ In situ reduction to zero-valent iron, during which carboxymethyl chitosan further prevents the aggregation of nano-iron particles through steric hindrance effect, forming a highly dispersed zero-valent iron / bentonite composite structure; the generated zero-valent iron can serve as a catalyst for the reaction of calcium fluoride (CaF2) and tin oxide, improving the reaction efficiency of tin oxide; at the same time, under a reducing atmosphere, carboxymethyl chitosan is pyrolyzed to generate active gases such as CO, which further promotes the reaction of calcium fluoride (CaF2) and tin oxide, so that tin is effectively recovered and the recovery rate of tin is improved.

[0023] In the technical solution disclosed in the present invention, the reducing atmosphere consists of CO and N2.

[0024] Among them, the volume percentage concentration of CO in the reducing atmosphere is 10-20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20% can be selected, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] In the technical solution disclosed in the present invention, the calcination temperature is 600-700°C, for example, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, and 700°C can be selected; the calcination time is 60-90min, for example, 60min, 65min, 70min, 75min, 80min, 85min, and 90min can be selected, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The method for recovering tin from tin-containing waste provided by the present invention is suitable for treating difficult-to-treat tin-containing waste such as tin-containing electronic waste, tin iron ore, and tin smelting slag, and has the characteristics of simple operation and low energy consumption.

[0028] (2) In the technical solution provided by the present invention, carboxymethyl chitosan is used as a natural polymer dispersant, and the hydroxyl (-OH) and amino (-NH2) on its molecular chain can chelate Fe 3+ , ensuring Fe 3+ Evenly distributed on the surface and interlayer of bentonite; then, nitrogen was introduced to expel the air, and sodium borohydride aqueous solution was added. Sodium borohydride (NaBH4) acts as a strong reducing agent to reduce Fe 3+ In situ reduction to zero-valent iron, during which carboxymethyl chitosan further prevents the aggregation of nano-iron particles through steric hindrance effect, forming a highly dispersed zero-valent iron / bentonite composite structure; the generated zero-valent iron can serve as a catalyst for the reaction of calcium fluoride (CaF2) and tin oxide, improving the reaction efficiency of tin oxide; at the same time, under a reducing atmosphere, carboxymethyl chitosan is pyrolyzed to generate active gases such as CO, which further promotes the reaction of calcium fluoride (CaF2) and tin oxide, so that tin is effectively recovered and the recovery rate of tin is improved. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0030] It should be noted that, unless otherwise specified, all chemical reagents involved in the present invention were purchased through commercial channels.

[0031] The bentonite used in the embodiment of the present invention is calcium-based bentonite with a mesh size of 400 mesh;

[0032] The CaF2 content in fluorite is 95% and the CaCO3 content is 0.74%.

[0033] Example 1

[0034] A method for recovering tin from tin-containing waste comprises the following steps:

[0035] Tin-containing electronic waste (tin content of 7.6%) was ground and pulverized through a 400-mesh sieve, and then mixed with a binder to form agglomerates, wherein the mass ratio of the tin-containing electronic waste to the binder was 12:1, and the binder consisted of 80 parts of fluorite and 20 parts of modified bentonite. After drying, the agglomerates were placed in a reducing atmosphere composed of CO and N2, with a CO volume percentage concentration of 15%. The calcination temperature was 600°C and the calcination time was 90 minutes. After the calcination, the volatilized tin compounds were recovered.

[0036] Wherein, the preparation method of modified bentonite is as follows:

[0037] S1. Immerse 10 g of bentonite in 100 mL of 1 mol / L sulfuric acid solution, heat and stir at 80° C. for 1 h, then filter, wash, and dry to obtain pretreated bentonite;

[0038] S2. 6 g of pretreated bentonite was dispersed in 100 mL of deionized water, and then 6 g of carboxymethyl chitosan and 3 g of ferric chloride were added thereto, and the mixture was stirred evenly to obtain a mixed solution. Subsequently, nitrogen was introduced to expel the air, and 20 g of a 10 wt% aqueous solution of sodium borohydride was added thereto. The mixture was heated and stirred at 40° C. for 2 h. After the reaction was completed, the mixture was filtered, washed, and vacuum-dried to obtain modified bentonite.

[0039] The tin content in the volatilized tin compound was analyzed. The tin recovery rate (%) = tin content in the volatilized tin compound / tin content in the tin-containing electronic waste × 100%. The tin recovery rate was calculated to be 98.3%.

[0040] Example 2

[0041] A method for recovering tin from tin-containing waste comprises the following steps:

[0042] Tin-containing electronic waste (tin content of 7.6%) was ground and pulverized, passed through a 400-mesh sieve, and then mixed with a binder to form agglomerates, wherein the mass ratio of the tin-containing electronic waste to the binder was 10:1, and the binder consisted of 85 parts of fluorite and 25 parts of modified bentonite. After drying, the agglomerates were calcined in a reducing atmosphere consisting of CO and N2, with a CO volume percentage concentration of 15%. The calcination temperature was 600°C and the calcination time was 90 minutes. After the calcination, the volatilized tin compounds were recovered.

[0043] Wherein, the preparation method of modified bentonite is as follows:

[0044] S1. Immerse 10 g of bentonite in 100 mL of 1 mol / L sulfuric acid solution, heat and stir at 80° C. for 1 h, then filter, wash, and dry to obtain pretreated bentonite;

[0045] S2. 6 g of pretreated bentonite was dispersed in 100 mL of deionized water, and then 6 g of carboxymethyl chitosan and 3 g of ferric chloride were added thereto, and the mixture was stirred evenly to obtain a mixed solution. Subsequently, nitrogen was introduced to expel the air, and 20 g of a 10 wt% aqueous solution of sodium borohydride was added thereto. The mixture was heated and stirred at 40° C. for 2 h. After the reaction was completed, the mixture was filtered, washed, and vacuum-dried to obtain modified bentonite.

[0046] The tin content in the volatilized tin compound was analyzed, and the recovery rate of tin was calculated to be 98.7%.

[0047] Example 3

[0048] A method for recovering tin from tin-containing waste comprises the following steps:

[0049] Tin-containing electronic waste (tin content of 7.6%) was ground and pulverized through a 400-mesh sieve, and then mixed with a binder to form agglomerates, wherein the mass ratio of the tin-containing electronic waste to the binder was 15:1, and the binder consisted of 100 parts of fluorite and 30 parts of modified bentonite. After drying, the agglomerates were placed in a reducing atmosphere composed of CO and N2, with a CO volume percentage concentration of 15%. The calcination temperature was 700°C and the calcination time was 60 minutes. After the calcination, the volatilized tin compounds were recovered.

[0050] Wherein, the preparation method of modified bentonite is as follows:

[0051] S1. Immerse 10 g of bentonite in 100 mL of 1 mol / L sulfuric acid solution, heat and stir at 80° C. for 1 h, then filter, wash, and dry to obtain pretreated bentonite;

[0052] S2. 6 g of pretreated bentonite was dispersed in 100 mL of deionized water, and then 6 g of carboxymethyl chitosan and 3 g of ferric chloride were added thereto, and the mixture was stirred evenly to obtain a mixed solution. Subsequently, nitrogen was introduced to expel the air, and 20 g of a 10 wt% aqueous solution of sodium borohydride was added thereto. The mixture was heated and stirred at 40° C. for 2 h. After the reaction was completed, the mixture was filtered, washed, and vacuum-dried to obtain modified bentonite.

[0053] The tin content in the volatilized tin compound was analyzed, and the recovery rate of tin was calculated to be 97.9%.

[0054] Comparative Example 1

[0055] A method for recovering tin from tin-containing waste comprises the following steps:

[0056] Tin-containing electronic waste (tin content of 7.6%) was ground and pulverized, passed through a 400-mesh sieve, and then mixed with a binder to form agglomerates, wherein the mass ratio of the tin-containing electronic waste to the binder was 12:1, and the binder consisted of 80 parts of fluorite and 20 parts of bentonite. After drying, the agglomerates were calcined in a reducing atmosphere consisting of CO and N2, with a CO volume percentage concentration of 15%. The calcination temperature was 600°C and the calcination time was 90 minutes. After the calcination, the volatilized tin compounds were recovered.

[0057] Compared with Example 1, Comparative Example 1 did not perform any modification treatment on the bentonite.

[0058] The tin content in the volatilized tin compounds was analyzed, and the tin recovery rate was calculated to be 63.4%.

[0059] Comparative Example 2

[0060] A method for recovering tin from tin-containing waste comprises the following steps:

[0061] Tin-containing electronic waste (tin content of 7.6%) was ground and pulverized through a 400-mesh sieve, and then mixed with a binder to form agglomerates, wherein the mass ratio of the tin-containing electronic waste to the binder was 12:1, and the binder consisted of 80 parts of fluorite and 20 parts of modified bentonite. After drying, the agglomerates were placed in a reducing atmosphere composed of CO and N2, with a CO volume percentage concentration of 15%. The calcination temperature was 600°C and the calcination time was 90 minutes. After the calcination, the volatilized tin compounds were recovered.

[0062] Wherein, the preparation method of modified bentonite is as follows:

[0063] S1. Immerse 10 g of bentonite in 100 mL of 1 mol / L sulfuric acid solution, heat and stir at 80° C. for 1 h, then filter, wash, and dry to obtain pretreated bentonite;

[0064] S2. Disperse 6 g of pretreated bentonite in 100 mL of deionized water, then add 6 g of carboxymethyl chitosan, stir evenly, filter, wash, and vacuum dry to obtain modified bentonite.

[0065] Compared with Example 1, in Comparative Example 2, zero-valent iron is not loaded on the bentonite.

[0066] The tin content in the volatilized tin compounds was analyzed, and the tin recovery rate was calculated to be 72.1%.

[0067] Comparative Example 3

[0068] A method for recovering tin from tin-containing waste comprises the following steps:

[0069] Tin-containing electronic waste (tin content of 7.6%) was ground and pulverized through a 400-mesh sieve, and then mixed with a binder to form agglomerates, wherein the mass ratio of the tin-containing electronic waste to the binder was 12:1, and the binder consisted of 80 parts of fluorite and 20 parts of modified bentonite. After drying, the agglomerates were placed in a reducing atmosphere composed of CO and N2, with a CO volume percentage concentration of 15%. The calcination temperature was 600°C and the calcination time was 90 minutes. After the calcination, the volatilized tin compounds were recovered.

[0070] Wherein, the preparation method of modified bentonite is as follows:

[0071] S1. Immerse 10 g of bentonite in 100 mL of 1 mol / L sulfuric acid solution, heat and stir at 80° C. for 1 h, then filter, wash, and dry to obtain pretreated bentonite;

[0072] S2. 6 g of pretreated bentonite was dispersed in 100 mL of deionized water, and then 3 g of ferric chloride was added thereto and stirred evenly to obtain a mixed solution. Subsequently, nitrogen was introduced to expel the air, and 20 g of a 10 wt% aqueous solution of sodium borohydride was added thereto. The mixture was heated and stirred at 40° C. for 2 h. After the reaction was completed, the mixture was filtered, washed, and vacuum-dried to obtain modified bentonite.

[0073] Compared with Example 1, in Comparative Example 3, carboxymethyl chitosan was not loaded on the bentonite.

[0074] The tin content in the volatilized tin compounds was analyzed, and the tin recovery rate was calculated to be 86.7%.

[0075] From the above results, it can be seen that in Comparative Example 1, the bentonite was not modified, in Comparative Example 2, the bentonite was not loaded with zero-valent iron, and in Comparative Example 3, the bentonite was not loaded with carboxymethyl chitosan. The tin recovery rates were all lower than those in the examples of the present invention.

[0076] Finally, it should be noted that the above embodiments do not limit the present invention in any form. Those skilled in the art will appreciate that modifications and improvements can be made based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are intended to fall within the scope of protection claimed in the present invention.

Claims

1. A method for recovering tin from tin-containing waste, characterized in that: The method comprises the following steps: grinding and crushing tin-containing waste, mixing with a binder to form agglomerates, drying, calcining in a reducing atmosphere, and recovering volatilized tin compounds; the binder is composed of fluorite and modified bentonite; Wherein, the preparation method of the modified bentonite is as follows: S1, immersing bentonite in an acid solution, heating and stirring, and then filtering, washing, and drying to obtain pretreated bentonite; S2. Pretreated bentonite is dispersed in deionized water, carboxymethyl chitosan and ferric chloride are added thereto, and the mixture is stirred evenly to obtain a mixed solution. Nitrogen is then introduced to expel the air, and an aqueous sodium borohydride solution is added thereto. The mixture is heated and stirred to react. After the reaction is completed, the mixture is filtered, washed, and vacuum-dried to obtain modified bentonite.

2. The method according to claim 1, characterized in that The mass ratio of tin-containing waste to binder is 10-15:

1.

3. The method according to claim 1, characterized in that In parts by weight, the binder is composed of the following components: 80-100 parts of fluorite and 20-30 parts of modified bentonite.

4. The method according to claim 1, wherein In step S2, the mass ratio of pretreated bentonite, carboxymethyl chitosan, ferric chloride and sodium borohydride aqueous solution is 4-8:4-8:2-4:20-30, wherein the mass fraction of the sodium borohydride aqueous solution is 5-10%.

5. The method according to claim 1, wherein In step S2, the temperature for the heating and stirring reaction is 40-60° C., and the time for the heating and stirring reaction is 1-2 h.

6. The method according to claim 1, characterized in that The reducing atmosphere consists of CO and N2.

7. The method according to claim 6, characterized in that The volume percentage concentration of CO in the reducing atmosphere is 10-20%.

8. The method according to claim 1, characterized in that The calcination temperature is 600-700°C, and the calcination time is 60-90 minutes.