CN103436885A - Method for recycling tin removal waste liquor - Google Patents

Abstract

The invention provides a method for regenerating and recycling the waste liquid of the tin stripping process suitable for the circuit board industry, and is suitable for recycling and recycling the waste liquid of the tin stripping process containing nitric acid as the main component and containing heavy metal compounds such as tin and copper. The invention adopts the complex precipitation method to treat the heavy metal in the tin stripping waste liquid, and precipitates the metal ions in the tin stripping waste liquid. After the waste tin stripping liquid is separated from the solid and liquid, metal resources such as tin and copper can be recovered from the sediment; the composition of the clear liquid and the new tin stripping liquid is close, and it can be used for the tin stripping process after proper adjustment, so as to realize the recycling of the tin stripping waste liquid purpose of use. The invention can realize the recycling of tin stripping waste liquid, efficiently recycle metal resources in the waste liquid, has simple process, small equipment investment, low energy consumption, no waste water and waste gas discharge in the operation process, and realizes clean production in the tin stripping process .

Description

Recycling method of tin stripping waste liquid

technical field

The invention relates to the technical field of resource recycling in the chemical industry, especially in the circuit board industry, and in particular to a method for recycling the waste tin stripping liquid produced in the tin stripping process in the production of printed circuit boards. The invention is preferably suitable for nitric acid type Regeneration and reuse of tin stripping waste liquid.

Background technique

Tin stripping is an indispensable step in the production process of printed circuit boards (PCB, printed circuit board), which is used to strip the tin coating that protects the copper substrate. The currently widely used tin stripping solution is nitric acid + ferric nitrate type, and its tin stripping mechanism is shown in the following formula:

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In the tin stripping solution, both nitric acid and ferric nitrate play the role of tin stripping. Nitric acid mainly strips the tin on the surface of the tin coating, and ferric nitrate is used to strip the tin on the Cu-Sn alloy between the copper and tin layers. The hydrated ion Sn(H ₂ O) ₆ ²⁺ is the initial form of tin after tin stripping, and Fe ³⁺ /Fe ²⁺ , Cu ²⁺ /Cu ⁺ , HNO ₃ /HNO ₂ , For electric pairs such as O ₂ /H ₂ O, their electrode potentials are higher than those of Sn ⁴⁺ /Sn ²⁺ . Among them, Sn(H ₂ O) ₆ ²⁺ is easily oxidized into Sn(H ₂ O) ₆ ⁴⁺ , and when the acidity of the system decreases, it is hydrolyzed into Sn(H ₂ O) ₂ (OH) ₄ (white orthostannic acid Precipitate, amphoteric, soluble in acid or alkali). Orthostannic acid becomes metastannic acid after being left to lose water. There are two types of metastannic acid, α and β. Among them, α-type metastannic acid is amorphous, soluble in acid and alkali, and insoluble in water; β-type metastannic acid is Crystal structure, insoluble in acid and alkali, insoluble in water. In addition, there are nitric acid stabilizers, copper surface protectors, surfactants, accelerators, nitrogen oxide inhibitors (such as various ammonium salts and urea), heavy metal complexing agents (such as ethylenediaminetetraacetic acid, halide amino acids, etc.).

In the current production, the treatment methods for tin stripping waste liquid mainly include neutralization precipitation method, distillation method, diffusion dialysis-ion membrane-electrodeposition method and solvent extraction method.

The neutralization precipitation method uses alkaline substances such as ammonia water, sodium carbonate, sodium bicarbonate and sodium hydroxide to neutralize the nitric acid, and separates the metals in the form of hydroxide precipitation. Although this method can achieve the purpose of treating nitric acid and recycling resources, at the same time, because of the introduction of ammonium nitrate, sodium nitrate and other components, the follow-up treatment is difficult, and it is easy to cause serious nitrate pollution, and there is also a large amount of alkali consumption and high cost. Disadvantages such as difficulty in meeting wastewater discharge standards.

The distillation recovery method is to heat up the system to 70 ℃ for distillation under reduced pressure, and absorb the distilled nitric acid with water to obtain nitric acid with a concentration of 30-40%. After replenishing the regeneration solution, it can be reused in the production line; After alkali neutralization, metals such as tin and copper are separated through precipitation, extraction and other processes. The advantage of this method is that most of the nitric acid can be recycled, and the discharge is small, but the disadvantages are that there is a large energy consumption, the concentration of the recovered nitric acid is low, and the applicable area is narrow.

In addition, there are also literatures that use a simple polymer system to treat waste liquid. For example, Xiao Zuoping of the Shenzhen Hazardous Waste Treatment Station uses the PAM-Na ₂ S system to completely remove tin and copper in the waste tin stripping liquid, basically maintaining the stability of the waste liquid. Regenerate useful acidity and some iron ions. After adding other components, the application performance of the tin stripping solution is the same as that of the newly opened tank. However, hydrogen sulfide and other gases will overflow during the operation, which will also cause many inconveniences in production.

Diffusion dialysis-ion membrane-electrodeposition method uses diffusion dialysis to recover nitric acid to obtain dilute nitric acid, and then the waste liquid after diffusion dialysis is recovered by ion membrane-electrodeposition method to recover tin and copper. The operating conditions of this method are not easy to control, the recovery rate is low and the cost is high.

The solvent extraction method is to use 50% TBP kerosene to extract nitric acid to reduce the acidity, then electrolytically remove copper, and then precipitate and recover tin. Although this method can successfully recover nitric acid and metals, its extraction and precipitation process consumes a large amount of solvent and precipitant.

In recent years, the treatment of tin stripping waste liquid is mainly based on the recovery of metal resources, especially tin resources with high economic value. However, most of the existing recycling technologies for tin stripping waste liquid have some problems, such as the quality of regenerated tin stripping liquid is not high, there are many regeneration processes, the operation is complicated, the recovery rate of free acid value is low, the treatment cost is high, waste liquid or waste gas will be generated, etc. .

Therefore, it is necessary to develop a simple, stable and reliable, economical and environmentally friendly recycling technology for tin stripping waste liquid, and then effectively solve the low recovery rate and environmental pollution of resources such as nitric acid in the tin stripping liquid, and provide better economic and environmental protection. Effective technical solutions appear to be very necessary.

Contents of the invention

The purpose of the present invention is to solve the deficiencies of the prior art, to provide a recycling method for tin stripping waste liquid suitable for the circuit board industry, through the effective recovery of tin, copper and other metal resources in the tin stripping waste liquid, so that the tin stripping waste The liquid can be regenerated into high-quality tin stripping liquid and used in the tin stripping process, so as to achieve the purpose of recycling.

The purpose of the present invention is specifically achieved through the following technical solutions:

The recycling method of tin stripping waste liquid comprises the following steps:

S1. Add a complexing precipitant to the tin stripping waste liquid to mix and stir evenly, so that the metal ions in the complexing precipitant and the tin stripping waste liquid are selectively precipitated; wherein, the reaction complexing precipitant can be mixed with the tin stripping waste Metal ions such as tin and copper in the liquid undergo selective precipitation reactions without affecting the concentration of nitric acid and effective tin stripping components in the tin stripping liquid;

S2. Separating the solid-liquid separation of the tin stripping waste liquid, separating the precipitate containing metal ions in the tin stripping waste liquid, and recovering the tin and copper in the precipitate;

S3. Add new tin stripping liquid to the clear liquid obtained after the solid-liquid separation of the tin stripping waste liquid to form a finished tin stripping liquid, and return the finished tin stripping liquid to the tin stripping process.

The tin stripping waste liquid described in step S1 is a nitric acid type tin stripping waste liquid, wherein the tin content is 30-150 g/L, the copper content is 2-30 g/L, and the mass factor of the nitric acid content is 15-40%.

The complex precipitation agent is an organic acid substance, an organic acid salt substance or a combination of an organic acid and an organic acid salt. The composition of the complex precipitation agent includes but is not limited to citric acid, malic acid, lactic acid, maleic acid, tartaric acid, Oxalic acid, malonic acid, benzoic acid, salicylic acid, sodium citrate, potassium citrate, magnesium citrate, sodium malate, potassium malate, magnesium malate, sodium lactate, potassium oxalate, potassium hydrogen oxalate, potassium tetraoxalate, One or more of sodium oxalate, ammonium oxalate, dimethyl oxalate, diethyl oxalate and sodium malonate. Wherein, when the complex precipitation agent is a mixture, each component can be combined in any proportion.

The complex precipitating agent has a strong chelating ability for some metal ions, can form insoluble precipitates in a strongly acidic environment, and can precipitate metal ions such as tin and copper in the tin stripping waste liquid. Using the difference in solubility product, the complex precipitant can selectively precipitate Cu(Ⅱ) and Sn(Ⅱ/Ⅳ) without destroying the existing form of Fe(Ⅲ) in the solution. Wherein, the complexing precipitating agent chelates with metal ions, but does not react with the organic additives in the tin stripping waste liquid, so the organic additives in the tin stripping waste liquid will not be consumed substantially; the organic additives are mainly Corrosion inhibitors commonly used in the tin stripping process, such as benzotriazole, methylbenzotriazole, pyrrolidone, etc.

In practical application, the use method of the complexing precipitant is simple, easy to operate, and does not require additional processing equipment. It is applicable to most nitric acid waste liquids containing heavy metals such as copper, iron, tin, and lead, and does not affect the nitric acid in the tin stripping liquid. Concentration, can maximize the recovery of nitric acid. At the same time, the chemical precipitation reaction in which the complex precipitation agent participates can be carried out at normal temperature and pressure, the reaction conditions are mild, only simple stirring is required, the reaction time is short, and the kinetic energy consumption is small, so the application effect is very good.

In the above step S1, in order to speed up the precipitation, a sedimentation aid can be added at the same time as the complex precipitation agent, and the sedimentation aid is polycarboxylate, polyacrylamide or a combination of the two.

In the above step S1, the concentration of the total amount of the added complexing precipitation agent in the tin stripping waste liquid is 0.1-1mol/L.

In the above step S1, the reaction time of the selective precipitation reaction is not less than 10 minutes.

In the above step S1, after adding a complexing precipitating agent into the tin stripping waste liquid for mixing, the mixture is uniformly stirred at a speed of 200-400 rpm. In addition, during the stirring process, processes such as aeration or ultrasonic oscillation can be performed as required.

In the above step S1, a selective precipitation reaction occurs between the complexing precipitant and the metal ions in the tin stripping waste liquid at a constant temperature of 23°C to 26°C.

In the above step S2, the precipitate containing metal ions in the tin stripping waste liquid is separated by ammonia leaching or alkali leaching, and the tin and copper resources in the precipitate are recovered.

In the above step S2, the sediment separation methods include but not limited to gravity sedimentation, filtration and centrifugation.

In the above step S3, in order to maintain the balance between the amount of tin stripping waste liquid produced and the amount of tin stripping waste liquid reused, the mass coefficient of the added tin stripping liquid in the finished tin stripping liquid is 5-50%.

In the above step S3, the reference amount of the compound in the clear liquid obtained after the solid-liquid separation of the tin stripping waste liquid is: tin content 1-10 g/L, copper content 0.1-4 g/L, iron content 5-35 g /L, the concentration of nitric acid is 30%~40%, while the content of organic additives remains basically unchanged. Generally speaking, the composition of the clear liquid obtained in step S3 is similar to that of the new tin stripping liquid. After adding a small amount of new tin stripping liquid, the tin stripping ability can be restored and become a finished tin stripping liquid, which can be effectively reused in the tin stripping process .

The present invention has little effect on the concentration of free nitric acid in the waste liquid of tin stripping. When the concentration of nitric acid in the waste liquid is less than 20%, it has no effect on the precipitation effect of the complex precipitation agent. The agent is more suitable for use in a strong acid environment, and has a better recovery effect on nitric acid.

Compared with prior art, technical effect of the present invention is:

1. The metal resources in the waste liquid are basically fully recovered. Compared with the new tin stripping liquid, the acid value of the regenerated tin stripping liquid is basically not lowered, and effective tin stripping components such as nitric acid, iron, and organic corrosion inhibitors are retained;

2. The operation process is simple, the process is short, and it is convenient for large-scale production;

3. No waste liquid and waste gas are produced, less power consumption, energy saving and environmental protection;

4. The separated clear liquid can be used in the tin stripping process after simple treatment, and the tin stripping effect is basically the same as that of the new tin stripping agent, which effectively realizes the recycling of the tin stripping waste liquid.

Detailed ways

Embodiment one

Add sodium oxalate to the tin stripping waste liquid containing 18% nitric acid, and after uniform stirring, the chemical precipitation reaction is completed. Among them, the tin content in the tin stripping waste liquid is 132 g/L, the copper content is 25 g/L, the concentration of sodium oxalate is 0.6 mol/L, the reaction temperature is 25 °C, and the reaction time is 30 min. After the precipitation reaction is completed, gravity sedimentation separation is carried out. After separation and precipitation, 700 mL of clear liquid was obtained, in which tin content was 14.4 g/L, copper content was 2.1 g/L, and nitric acid content was 17.5%, and 300 mL of new tin stripping waste liquid was added to obtain regenerated tin stripping liquid. Place the tin-clad circuit board in the regenerated tin stripping solution. It takes 15 seconds to strip the tin. After stripping the circuit board, the surface is clean, the copper metal is bright in color, and the tin stripping effect is good.

The tin stripping speed of the regenerated tin stripping solution is less than 30 s, and the tin stripping capacity is greater than 150 g/L, which is basically the same as the new tin stripping solution, meeting the production requirements of the tin stripping process.

Put the tin-clad circuit board in the waste tin stripping solution, and it takes 65 s to strip the tin. After stripping the tin, there is dirt on the surface of the circuit board, the surface finish of the board is poor, and the tin stripping effect is not good.

Place the tin-clad circuit board in the regenerated tin stripping solution. It takes 15 seconds to strip the tin. After stripping the circuit board, the surface is clean, the copper metal is bright in color, and the tin stripping effect is good.

Embodiment two

Add oxalic acid, sodium oxalate and dimethyl oxalate (complexing precipitant) to the tin stripping waste liquid containing 18% nitric acid, and complete the chemical precipitation reaction after uniform stirring. Among them, the tin content in the tin stripping waste liquid is 132 g/L, the copper content is 25 g/L, and the concentrations of oxalic acid, sodium oxalate and dimethyl oxalate are 0.25 mol/L, 0.20 mol/L and 0.20 mol/L respectively , the reaction temperature was 25 °C, and the reaction time was 30 min. Carry out centrifugation after the precipitation reaction is completed, in the separated precipitate, the tin content is 26.5%, the tin recovery rate is 92%, the copper content is 5%, and the copper recovery rate is 95%. /L, 24 g of copper powder was obtained by electrolysis, and 121 g of tin was obtained by electrolysis after the solid phase product was dissolved in strong alkali after ammonia immersion, and the recovery rates of tin and copper were 99% and 100% respectively. After separation and precipitation, the clear liquid is 700 mL, in which the tin content is 4.2 g/L, the copper content is 1.8 g/L, and the nitric acid content is 19%. Add 300 mL of new tin stripping waste liquid, the tin stripping speed is less than 20 s, and the tin stripping capacity is greater than 150g /L, which is basically the same as the new tin stripping solution, which meets the production requirements of the tin stripping process.

Comparative example: Add 0.65 mol/L oxalic acid to the tin stripping waste liquid containing 18% nitric acid, stir evenly, and form a complex precipitate. The tin content in the precipitate separated by centrifugation is 25.2%, the recovery rate of tin is 88%, the copper content is 4.8%, and the recovery rate of copper is 89%. After separating and precipitating, 700 mL of the supernatant liquid contains 12.6 g/L of tin, 3.9 g/L of copper, and 21% of nitric acid. Add 300 mL of new tin stripping waste liquid, the tin stripping speed is less than 20 s, and the tin stripping capacity is greater than 150 g/L, which is basically the same as the new tin stripping solution, which meets the production requirements of the tin stripping process.

Under the same conditions, compared with adding only one complex precipitant (oxalic acid), the method in this example improves the recovery rate of tin and copper.

Embodiment Three

Add oxalic acid, sodium oxalate, dimethyl oxalate and polycarboxylic acid to the tin stripping waste liquid containing 18% nitric acid. After uniform stirring, the chemical precipitation reaction is completed. Among them, the tin content in the tin stripping waste liquid is 132 g/L, the copper content is 25 g/L, and the concentrations of oxalic acid, sodium oxalate and dimethyl oxalate are 0.25 mol/L, 0.20 mol/L and 0.20 mol/L respectively , the dosage of polycarboxylic acid was 1 g/L, the reaction temperature was 25°C, and the reaction time was 30 min. After the precipitation reaction is completed, gravity sedimentation is used for separation. The tin content in the separated precipitate is 26.1%, the tin recovery rate is 95%, the copper content is 5%, and the copper recovery rate is 95%. The supernatant after separation and precipitation was 700 mL, in which the tin content was 9.4 g/L, the copper content was 1.5 g/L, and the nitric acid content was 20%. The separated clear liquid can restore the tin stripping function after adding a certain amount of new tin stripping liquid, so as to realize the regeneration of the tin stripping waste liquid.

Embodiment Four

Add tartaric acid and polycarboxylic acid to the tin stripping waste liquid containing 18% nitric acid, and after uniform stirring, the chemical precipitation reaction is completed. Among them, the tin content in the tin stripping waste liquid is 132g/L, the copper content is 25 g/L, the dosage of tartaric acid and polycarboxylic acid are 95g/L and 1g/L respectively, the reaction temperature is 25°C, and the reaction time is 30min. After the precipitation reaction is completed, it is centrifuged, and the separated precipitate has a tin content of 29.7%, a tin recovery rate of 94%, a copper content of 5.7%, and a copper recovery rate of 96%. The supernatant after separation and precipitation was 750 mL, in which the content of tin was 10.7g/L, the content of copper was 1.3g/L, and the content of nitric acid was 22%. The separated clear liquid can restore the tin stripping function after adding a certain amount of new tin stripping liquid, so as to realize the regeneration of the tin stripping waste liquid.

Embodiment five

Add maleic acid and polycarboxylic acid to the tin stripping waste liquid containing 18% nitric acid, and after uniform stirring, the chemical precipitation reaction is completed. Among them, the tin content in the tin stripping waste liquid is 132g/L, the copper content is 25 g/L, the dosage of maleic acid and polycarboxylic acid are 73.5g/L and 1g/L respectively, the reaction temperature is 25°C, and the reaction time for 30min. After the precipitation reaction is completed, it is centrifuged, and the separated precipitate has a tin content of 20.5%, a tin recovery rate of 92%, a copper content of 5.8%, and a copper recovery rate of 92%. The supernatant after separation and precipitation was 750 mL, in which the tin content was 13.3 g/L, the copper content was 2.6 g/L, and the nitric acid content was 22%. The separated clear liquid can restore the tin stripping function after adding a certain amount of new tin stripping liquid, so as to realize the regeneration of the tin stripping waste liquid.

Embodiment six

Add maleic acid and polycarboxylic acid to the tin stripping waste liquid containing 10% nitric acid, and after uniform stirring, the chemical precipitation reaction is completed. Among them, the tin content in the tin stripping waste liquid is 121g/L, the copper content is 14g/L, the dosages of maleic acid and polycarboxylic acid are 73.5g/L and 1g/L respectively, the reaction temperature is 25°C, and the reaction time is 30min. After the precipitation reaction is completed, it is centrifuged, and the separated precipitate has a tin content of 41.4%, a tin recovery rate of 96%, a copper content of 4.7%, and a copper recovery rate of 94%. The supernatant after separation and precipitation was 860 mL, in which the content of tin was 6g/L, the content of copper was 0.9g/L, and the content of nitric acid was 13.7%. The separated clear liquid can restore the tin stripping function after adding a certain amount of new tin stripping liquid, so as to realize the regeneration of the tin stripping waste liquid.

To sum up, the method for regenerating and reusing tin stripping waste liquid provided by the embodiment of the present invention has been described in detail above, but the contents of this description should not be understood as limiting the present invention. For those of ordinary skill in the art, According to the ideas of the embodiments of the present invention, there will be changes in specific implementation methods and application ranges.

Claims (10)

1. The recycling method of tin stripping waste liquid is characterized in that comprising the following steps: S1. Add a complexing precipitant to the tin stripping waste liquid to mix and stir evenly, so that the metal ions in the complexing precipitant and the tin stripping waste liquid undergo a selective precipitation reaction; S2. Separating the solid-liquid separation of the tin stripping waste liquid, separating the precipitate containing metal ions in the tin stripping waste liquid, and recovering the tin and copper in the precipitate; S3. Add tin stripping liquid to the clear liquid obtained after the solid-liquid separation of the tin stripping waste liquid to form a finished tin stripping liquid, and return the finished tin stripping liquid to the tin stripping process. 2. The recycling method of tin stripping waste liquid according to claim 1, characterized in that the tin stripping waste liquid described in step S1 is nitric acid type tin stripping waste liquid, wherein tin content is 30 ~ 150 g/L, copper The content is 2~30g/L, and the mass factor of nitric acid content is 15~40%. 3. The recycling method of tin stripping waste liquid according to claim 1, characterized in that the complex precipitation agent is an organic acid, an organic acid salt, or a combination of an organic acid and an organic acid salt. 4. the recycling method of tin stripping waste liquid according to claim 3, described complex precipitation agent is made of citric acid, malic acid, lactic acid, maleic acid, tartaric acid, oxalic acid, malonic acid, benzoic acid, lattice Salicylic acid, sodium citrate, potassium citrate, magnesium citrate, sodium malate, potassium malate, magnesium malate, sodium lactate, potassium oxalate, potassium hydrogen oxalate, potassium tetraoxalate, sodium oxalate, ammonium oxalate, dimethyl oxalate At least one component of ester, diethyl oxalate and sodium malonate. 5. The recycling method of tin stripping waste liquid according to claim 1, is characterized in that in the described step S1, adds the sedimentation aid while adding the complex precipitation agent, and the sedimentation aid is polycarboxylate, Compositions of polyacrylamide or polycarboxylate and polyacrylamide. 6. The recycling method of tin stripping waste liquid according to claim 1, characterized in that in the step S1, the concentration of the added complexing precipitant in the tin stripping waste liquid is 0.1-1mol/L. 7. The recycling method of tin stripping waste liquid according to claim 1, characterized in that in the step S1, after adding a complexing precipitation agent in the tin stripping waste liquid and mixing, at 200-400 rpm/min Stir evenly at a high speed; and at a constant temperature of 23 ℃ ~ 26 ℃, the complex precipitation agent and the metal ions in the tin stripping waste liquid undergo a selective precipitation reaction, and the reaction time of the selective precipitation reaction is not less than 10 minutes. 8. The recycling method of tin stripping waste liquid according to claim 1, characterized in that in the step S2, the sediment separation method is gravity sedimentation, filtration or centrifugation. 9. The recycling method of tin stripping waste liquid according to claim 1, characterized in that in said step S2, the precipitate containing metal ions in the tin stripping waste liquid is separated by ammonia leaching or alkali leaching, and the precipitate is reclaimed tin and copper in. 10. The recycling method of tin stripping waste liquid according to claim 1, characterized in that in the step S3, the mass coefficient of the added tin stripping liquid in the finished tin stripping liquid is 5-50%.