US20150376735A1 - Tin stripping additive and application thereof - Google Patents

Tin stripping additive and application thereof Download PDF

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Publication number
US20150376735A1
US20150376735A1 US14/702,205 US201514702205A US2015376735A1 US 20150376735 A1 US20150376735 A1 US 20150376735A1 US 201514702205 A US201514702205 A US 201514702205A US 2015376735 A1 US2015376735 A1 US 2015376735A1
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Prior art keywords
tin
tin stripping
solution
additive
stripping
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English (en)
Inventor
Ching-Hsiang Hsu
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UWIN NANOTECH CO Ltd
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UWIN NANOTECH CO Ltd
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Assigned to UWIN NANOTECH. CO., LTD. reassignment UWIN NANOTECH. CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HSU, CHING-HSIANG
Publication of US20150376735A1 publication Critical patent/US20150376735A1/en
Priority to US16/294,043 priority Critical patent/US11180826B2/en
Abandoned legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B25/00—Obtaining tin
    • C22B25/06—Obtaining tin from scrap, especially tin scrap
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B25/00—Obtaining tin
    • C22B25/04—Obtaining tin by wet processes
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/10—Etching compositions
    • C23F1/14—Aqueous compositions
    • C23F1/16—Acidic compositions
    • C23F1/30—Acidic compositions for etching other metallic material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/44—Compositions for etching metallic material from a metallic material substrate of different composition
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/46—Regeneration of etching compositions
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
    • C23F11/04—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in markedly acid liquids
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present disclosure relates to an additive for metal-stripping; especially for Tin-stripping.
  • PCBs printed circuit boards
  • Burning method is to burn the waste PCBs crashed at high temperature to breakdown and to destroy the resin thereof and then obtain the noble metals therefrom.
  • the burning method may cause air pollution because of the bromine-containing waste gas and dioxin resulted from the burning of the PCBs.
  • Acid-washing method is to wash the waste PCBs with strong acid and then obtain a wash-off solution containing noble metals. Then, the noble metals therein are purified via electrolysis or acid-alkaline precipitation process.
  • Mechanical physical recycling method is to crash the waste PCBs and separate the metal materials and non-metal materials by different density. Then, the metal materials are recycled by magnetic manner. The purity of the metal obtained through this method is too low to be ideal.
  • One of the objects of the present invention is to provide a novel tin stripping additive and a tin stripping solution containing the same, which perform good efficiency in tin-stripping while reducing the usage amount of nitric acid; thereby operation thereof is much safer and the impact on environment would be less.
  • Another object of the present invention is to provide a novel method for tin-recycling, which is favorable for recycling tin from waste electronic elements in high efficiency and thereby achieving the goal of metal recycling.
  • Yet another object of the present invention is to provide a novel reaction tank, whose structure is designed particularly for metal recycling and especially for operating the aforesaid method for tin-recycling.
  • the present invention provides a tin stripping additive, comprising: 0.1 to 20 wt % of copper corrosion inhibitor; and 0.1 to 20 wt % of nickel corrosion inhibitor; wherein, remaining wt % of said tin stripping additive is a solvent; wherein, said wt % is based on the total weight of said tin stripping additive.
  • said copper corrosion inhibitor is a phosphate salt.
  • said phosphate salt is potassium phosphate, potassium dihydrogen phosphate, dipotassium phosphate, trisodium phosphate, or a combination thereof.
  • said nickel corrosion inhibitor is sodium oxalate, ammonium chloride, potassium carbonate, sodium metanitrobenzene sulfonate, or a combination thereof.
  • the present invention also provides a tin stripping solution, comprising: 20 to 50%(v/v) of the aforesaid tin stripping additive; and 20 to 50%(v/v) of nitric acid; wherein said %(v/v) is based on the total volume of said tin stripping solution.
  • said nitric acid is of a concentration of 67 to 68 wt %.
  • said tin stripping solution further comprises a solvent.
  • said solvent is water.
  • the present invention yet provides a method for tin-recycling, comprising the following steps: (A) immersing an object to be processed into the aforesaid tin stripping solution to obtain a wash-off solution; (B) adding an alkaline solution to said wash-off solution to obtain a precipitate; (C) heating said precipitate; and (D) conducting a reduction reaction to said precipitate being heated in said step (C) to obtain tin.
  • said immersing is achieved by placing said object to be processed into a bath of said tin stripping solution.
  • said bath is of a temperature of 20 to 60° C.
  • said alkaline solution is sodium hydroxide, potassium hydroxide, or a combination thereof.
  • said heating of said step (C) is conducted at a temperature of 600 to 800° C.
  • said reduction reaction is conducted by heating said precipitate of step (C) in a gas mixture atmosphere of hydrogen and nitrogen.
  • said gas mixture comprises: 20 to 30%(v/v) of hydrogen; and 70 to 80%(v/v) of nitrogen; wherein said %(v/v) is based on the total volume of said gas mixture.
  • said gas mixture is supplied to said reduction reaction as a gas flow with a flow speed of 100 to 500 ml/min.
  • said reduction reaction is conducted at a temperature of 200 to 800° C.
  • said method further comprises a filtration step after said step (A) and before said step (B).
  • said filtration step is a filter-paper filtration, a bag filtration, a filter-press filtration, a vane filtration, a cross-flow filtration, a centrifugal filtration, a Don filtration, a hydraulic cyclone filtration, a membrane filtration, or a combination thereof.
  • said method further comprises a washing step after said step (B).
  • the present invention further provides a reaction tank, comprising a body, comprising an inlet, an outlet, a sidewall, and a gas inlet; wherein said sidewall defines an inner space; wherein an area of said inner space adjacent to said outlet is a collection area; a first heating apparatus, positioned to surround at least parts of said sidewall; and a sieve, positioned inside said inner space to separate said inner space into two spaces.
  • the shape of said body is a tapered structure at said collection area and is connection with said outlet.
  • a collection tray is position inside said body at said collection area.
  • said first heating apparatus is at a relative position to said sieve inside said inner space.
  • said reaction tank further comprises a second heating apparatus; wherein the position of said second heating apparatus is corresponding to the position of said collection area.
  • said heating apparatus is a furnace, a heating tape, or a combination thereof.
  • said sieve has plural pores with an average diameter of 0.1 to 1 mm.
  • said reaction tank further comprises a gas supply device; wherein said gas supply device is connection with said gas inlet for supplying gas into said inner space.
  • said reaction tank is used for the purification of tin.
  • the present invention provides a tin stripping additive, which can be used together with nitric acid (what is conventionally used for metal stripping) as the present tin stripping solution.
  • the usage of the present tin stripping additive can favorably reduce the usage amount of nitric acid while maintain the tin-stripping efficiency in a desired level; therefore is more friendly to the environment.
  • the present invention also provides a method for tin-recycling by using said tin stripping additive/tin stripping solution as well as a reaction tank, which can operate correspondingly with said method for tin-recycling. Said method for tin-recycling has the advantages of ease in operation and being friendly to the environment.
  • the present reaction tank has a structure particularly designed for operating the metal recycling procedure more smoothly.
  • FIG. 1 shows an embodiment of the reaction tank of the present invention.
  • FIG. 2 shows another embodiment of the reaction tank of the present invention.
  • FIG. 3 shows the results of the Experiment 1 of the Example 1 of the present invention.
  • A Before the tin-stripping process;
  • B After the tin-stripping process.
  • FIG. 4 shows the results of the Experiment 2 of the Example 1 of the present invention.
  • A Before the Tin-stripping process, front side;
  • B Before the tin-stripping process, back side;
  • C After the tin-stripping process, front side;
  • D After the tin-stripping process, back side.
  • FIG. 5 shows the results of the Experiment 3 of the Example 1 of the present invention.
  • A Before the tin-stripping process, front side;
  • B Before the tin-stripping process, back side;
  • C After the tin-stripping process, front side;
  • D After the tin-stripping process, back side.
  • FIG. 6 shows the results of the Experiment 4 of the Example 1 of the present invention.
  • A After the tin-stripping process, process time: 20 minutes;
  • B After the tin-stripping process, process time: 1,000 minute.
  • FIG. 7 shows the strip ratio of samples 1, 3, and 4 of the Example 2 of the present invention.
  • FIG. 8 shows the change in concentration of the hydrogen inside said reaction tank during the reduction reaction of the Example 3 of the present invention.
  • FIG. 9 shows the XRD spectrum of the tin mass obtained in the Example 3 of the present invention.
  • the present invention is related to a tin stripping additive and a tin stripping solution containing the same.
  • the present invention is also related to a method for tin-recycling by using said tin stripping solution and a reaction tank, which is particularly suitable for tin-recycling.
  • the first aspect of the present invention is a tin stripping additive, which can be used together with nitric acid (which is conventionally used for metal stripping) and thereby the usage amount of nitric acid can be reduced.
  • the present tin stripping additive comprises 0.1 to 20 wt % of copper corrosion inhibitor; and 0.1 to 20 wt % of nickel corrosion inhibitor; wherein, remaining wt % of said tin stripping additive is a solvent; wherein said wt % is based on the total weight of said tin stripping additive.
  • Said solvent includes but not limited to water.
  • said tin stripping additive further comprises a solvent for favorably mixing said copper corrosion inhibitor and said nickel corrosion inhibitor. Preferable, said solvent is water.
  • said copper corrosion inhibitor is a phosphate salt.
  • said phosphate salt includes but not limited to potassium phosphate, potassium dihydrogen phosphate, dipotassium phosphate, trisodium phosphate, or a combination thereof.
  • said nickel corrosion inhibitor includes but not limited to sodium oxalate, ammonium chloride, potassium carbonate, sodium metanitrobenzene sulfonate, or a combination thereof.
  • present tin stripping additive is particularly suitable to be used together with nitric acid, said tin stripping additive being used is not limited in this way. In other words, the present tin stripping additive can also be used together with other conventional working solution for metal stripping to obtain the desired metal stripping effect.
  • the second aspect of the present invention is a tin stripping solution, comprising 20 to 50%(v/v) of said tin stripping additive and 20 to 50% (v/v) of nitric acid; wherein said %(v/v) is based on the total volume of said tin stripping solution.
  • the ratio of said tin stripping additive and said nitric acid is 1:1 in volume; that said, in this preferable embodiment, the present tin stripping additive can replace half usage amount of the nitric acid and therefore significantly reduce the impact on the environment as well as the risk in operation.
  • the nitric acid used for preparing said tin stripping additive is at a concentration of 67 to 68 wt %; usually, the commercially available nitric acid is at the concentration of 68 wt %.
  • said tin stripping solution further comprises a solvent.
  • said solvent is water.
  • a solvent such as: to obtain a better mixing of said tin stripping additive and said nitric acid, and/or to increase the total volume of said tin stripping solution for favorably immersing an object to be processed therein.
  • the third aspect of the present invention is a method for tin-recycling, comprising the following steps: (A) immersing an object to be processed into said tin stripping solution to obtain a wash-off solution; (B) adding an alkaline solution to said washing to obtain a precipitate; (C) heating said precipitate; and (D) conducting a reduction reaction to said precipitate being heated in said step (C) to obtain tin.
  • said immersing is achieved by placing said object to be processed into a bath of said tin stripping solution.
  • said object to be processed is shaken in said bath in said step (A) to facilitate the reaction.
  • a circulating fluid flow is generated in said bath to facilitate the reaction.
  • said bath is of a temperature of 20 to 60° C.
  • said object After being processed in said step (A), said object is discarded from said bath and said wash-off solution is collected.
  • the resulting wash-off solution contains said tin stripping solution and metal materials stripped from said object.
  • an alkaline solution is added to said wash-off solution to conduct said step (B).
  • a precipitate, composed mainly of tin (II) hydroxide, can be obtained while the reaction between said alkaline solution and said wash-off solution are sufficiently conducted.
  • said alkaline solution is sodium hydroxide, potassium hydroxide, or a combination thereof.
  • step (C) said precipitate is collected and heated in the air (step (C)).
  • tin (II) hydroxide interacts with air resulting the generation of tin dioxide.
  • said heating of said step (C) is conducted at a temperature of 600 to 800° C.
  • step (D) a reduction reaction is conducted to said tin dioxide to obtain tin step (D)).
  • hydrogen is supplied into during said step (D) to let said tin dioxide react with hydrogen as the following chemical equation and generate tin:
  • said reduction reaction is conducted by heating said precipitate of step (C) in a gas mixture of hydrogen and nitrogen.
  • Said gas mixture comprises: 20 to 30%(v/v) of hydrogen; and 70 to 80%(v/v) of nitrogen; wherein said %(v/v) is based on the total volume of said gas mixture.
  • said gas mixture is supplied to said reduction reaction as a gas flow with a flow speed of 100 to 500 ml/min.
  • said gas mixture is continuously supplied into said reduction reaction so that the starting chemicals (the left hand side of the aforesaid chemical equation) are maintained in saturation and the reaction is forced toward the right hand side where the product is generated to achieve balance in the equation.
  • said reduction reaction is conducted at a temperature of 600 to 800° C.
  • the present method further comprises a filtration step after said step (A) to filter out the impurity in said wash-off solution.
  • Said impurity may comprise silver-containing precipitate.
  • the present method further comprises a washing step after said step (B).
  • Said washing step is to add a large amount of water into said wash-off solution and mix them sufficiently so that the Sodium salt contained in said wash-off solution can dissolve in the water.
  • another filtration step can be conducted to separate the solid components and the liquid components of said wash-off solution.
  • said filtration step is a filter-paper filtration, a bag filtration, a filter-press filtration, a vane filtration, a cross-flow filtration, a centrifugal filtration, a Dorr filtration, a hydraulic cyclone filtration, a membrane filtration, or a combination thereof.
  • the fourth aspect of the present invention is a reaction tank.
  • the present reaction tank is particularly designed to co-operate with the present method for tin-recycling and therefore is particularly suitable for the recycle and purification of Tin.
  • FIG. 1 and FIG. 2 respectively show the two embodiments of the present reaction tank.
  • the present reaction tank illustrated in the aforesaid figures comprises: a body 100 comprising an inlet 101 , an outlet 102 , a sidewall 103 , and a gas inlet 104 ; wherein said sidewall 103 defines an inner space 110 ; wherein an area of said inner space 110 adjacent to said outlet is a collection area 111 ; at least a heating apparatus (first heating apparatus 201 and second heating apparatus 202 ); and a sieve 300 positioned inside said inner space 110 and divides said inner space 110 into two spaces.
  • the two bodies 100 are different in the structure of said collection area 111 .
  • said body 100 is configured as a tapered structure 105 at said collection area; wherein the width of said tapered structure 105 is gradually reduced along with the vertical axis of said body and the end of said tapered structure 105 is configured to connect with said outlet 102 .
  • said body 100 is configured as a collection tray 106 at said collection area; wherein said collection tray is positioned at said outlet 102 for collecting products (ex. tin) and can be taken away separately from said body 100 for delivery of products.
  • the two present reaction tanks both have two heating apparatus 201 and 202 .
  • the configuration is favorable for meeting different requirements of reaction temperature in different reaction sections.
  • those having ordinary skill in the art can also use single heating apparatus to satisfy the heating purposes in the procedure by adjusting the temperature thereof.
  • said first heating apparatus 201 and said second heating apparatus 202 seems to be configured at the bilateral sides of the body from the angle of view in the FIGS. 1 and 2 , they are actually positioned to surround at least parts of said sidewall 103 .
  • said first heating apparatus 201 is positioned corresponding to the position of said sieve 300 in said inner space 110 .
  • said second heating apparatus 202 is positioned corresponding to the position of said collection area 111 .
  • said heating apparatus is a furnace, a heating tape, or a combination thereof.
  • said sieve 300 has plural pores with an average diameter of 0.1 to 1 mm (said pores are not shown in the figures).
  • said reaction tank further comprises a gas supply device; said gas supply device is connection with said inlet 104 for introducing the gas into said inner space 110 .
  • the precipitate obtained from said step (B) of the present method for tin-recycling is placed on said sieve 300 for following processes.
  • the size of said precipitate is larger than the pores of said sieve 300 and would not fall through it; whereas, upon heating in said step (C) and introducing gas mixture (H 2 /N 2 ) through said gas inlet 104 in said step (D) for reduction reaction, the melted tin can fall onto said collection area 111 through said pores.
  • the tin stripping additive of the present invention was prepared.
  • a copper corrosion inhibitor and a nickel corrosion inhibitor was mixed in a solvent in accordance with the following table 1 to obtain the present tin stripping additives of this example.
  • FIG. 3A showed a picture took before tin stripping treatment and FIG. 3B showed a picture took after. According to the figures, the tin stripping solution of the sample 1 successfully stripped the tin of the motherboard in 30 minutes.
  • FIGS. 4A , 4 B, 4 C, and 4 D respectively showed a picture took before tin stripping treatment and FIGS. 4C and 4D respectively showed a picture took after.
  • the tin stripping solution of the sample 2 successfully stripped the tin of the motherboard in 20 minutes.
  • the copper layer on the motherboard, the nickel layer on the connector, and the legs of the fillet weld of the IC elements were not stripped by the tin stripping solution.
  • the present tin stripping solution exhibited specificity in stripping tin and would not strip other metals on the object to be processed. In other words, the tin can be recycled in better purity in the tin-recycling procedures thereafter.
  • FIGS. 5A , 5 B, 5 C, and 5 D respectively showed a picture took before tin stripping treatment (front side and back side respectively) and FIGS. 5C and 5D respectively showed a picture took after treatment.
  • the tin stripping solution of the sample 2 successfully stripped the tin of the motherboard in 20 minutes.
  • the copper layer on the motherboard, the nickel layer on the connector, and the legs of the fillet weld of the IC elements were not stripped by the tin stripping solution.
  • the present tin stripping solution exhibited specificity in stripping tin and would not strip other metals on the object to be processed. In other words, the tin can be recycled in better purity in the tin-recycling procedures thereafter.
  • Strip ⁇ ⁇ ratio ⁇ ⁇ ( S ⁇ ⁇ R ) Number ⁇ ⁇ of ⁇ ⁇ the ⁇ ⁇ electronic ⁇ ⁇ elements ⁇ ⁇ being ⁇ ⁇ stripped . Total ⁇ ⁇ number ⁇ ⁇ of ⁇ ⁇ the ⁇ ⁇ electronic ⁇ ⁇ elements ⁇ ⁇ of ⁇ ⁇ the ⁇ ⁇ board ⁇ 100 ⁇ %
  • the present tin nitric acid Sample stripping additive (68%) water Total volume 1 300 mL 300 mL 400 mL 1000 mL 3 500 mL 500 mL 0 mL 1000 mL 4 0 mL 1000 mL 0 mL 1000 mL
  • FIG. 7 respectively showed the strip ratio of samples 1, 3 and 4.
  • the strip ratio of sample 3 was higher than that of sample 4.
  • Sample 4 did not add the present tin stripping additive; that said, the results of this experiment indicated that adding the present tin stripping additive to replace half of the usage amount of nitric acid can not only reduce the usage amount of nitric acid but also increase the stripping efficiency.
  • the present tin stripping solution of sample 1 was not ranked as the best performance in the experiment, it was expected to be the safest in operation as containing the least usage of nitric acid. Therefore, the example further tested the strip ratio of sample 1 by extending the treatment period to see if it can provide liable performance.
  • the following table 4 showed that after extending, the treatment period to 10, 20, or 30 minutes, the strip ratio of the sample 1 of the Tin stripping solution was gradually raised to 100%. It proved that an excellent strip ratio can also be achieved for sample 1 upon a slight increase in the treatment period.
  • Example 2 This example was conducted in follow of the above Example 2 to use the wash-off solution obtained by using sample 1 for stripping PCB board in the present method for tin-recycling.
  • step (A) of the present method had been completed in Example 2
  • said wash-off solution was analyzed by SEM-EDS and determined to contain the following components: Sn (contained 85.58 wt %), Cu (contained 0.46 wt %), Ag (contained 8.92 wt %), and Na (contained 5.04 wt %).
  • a filtration step filter-paper filtration
  • Sodium hydroxide was then added into said wash-off solution until achieving the equivalent point and a precipitate was generated accordingly.
  • Tin (II) hydroxide was the main component of said precipitate.
  • said precipitate shall also contain a significant amount of sodium component.
  • said precipitate was mixed with a large amount of water and another filtration step (filter-paper filtration) was conducted to remove the sodium component therein and obtain purified precipitate.
  • a further SEM-EDS confirmed that the precipitate contained: Sn (contained 94.76 wt %), Cu (contained 0.43 wt %, and Na (contained 4.81 wt %). That said the aforesaid procedures indeed removed the silver component, reduced the Sodium component, and enriched the Tin component therein.
  • said precipitate was dried to obtain a tin-containing crude product.
  • the main component of said precipitate was tin (II) hydroxide
  • the main component of said Tin-containing crude product would be tin dioxide upon the heating of said step (C). It was noted that the heating of said step (C) can also be conducted in the reaction tank of the present invention.
  • a reduction reaction to the tin dioxide was conducted at high temperature by using the first heating apparatus (that is said step (D) of the present invention).
  • Said tin-containing crude product was melted into liquid metal droplets in the reduction reaction of high temperature and dropped from the pores of said sieve to the collection area of the present reaction tank.
  • the procedures were tested in accordance with the conditions listed in the following Table 5 to determine the optimal conditions.
  • FIGS. 9A and 9B respectively showed the XRD spectrum of the tin mass obtained in said condition 1 and condition 2.
  • the XRD spectrum there was tin dioxide remained in the product of condition 1 showing that the time of reaction was not sufficient to complete the reaction.
  • there was no tin dioxide remained in the product of condition 2 indicating the reaction was completed.
  • the tin mass of said condition 2 was further analyzed by SEM-EDS and the results showed that the tin mass contained 99.68 wt % of tin and a small amount of copper (0.32 wt %).
  • the present method for tin-recycling was proved to be able to obtain tin of high purity.

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