A method for recovering tin dross

Abstract

The application discloses a tin residue recycling method and relates to the technical field of solid waste treatment. The recycling method comprises the following steps: crushing tin residue to be treated to obtain tin residue particles with a preset particle size; placing the tin residue particles in a leaching tank, introducing leaching liquid into the leaching tank according to a preset proportion, stirring and leaching to obtain leaching products, filtering the leaching products to obtain solid products and liquid products, and repeatedly leaching and filtering the solid products for a first preset number of times; under first preset conditions, performing constant-temperature reaction on the liquid products to obtain reaction solutions; under second preset conditions, performing electrodeposition on the reaction solutions to obtain deposition products, filtering the deposition products to obtain valuable metals and deposition liquid; after electrodeposition is performed for a second preset number of times, the deposition liquid is treated to obtain the leaching liquid for recycling, and the second preset number of times is greater than or equal to one. The application can solve the problem of waste liquid recycling in the tin residue wet recycling process.

Description

Technical Field

[0001] This invention relates to the field of solid waste recycling technology, and in particular to a method for recycling tin dross. Background Technology

[0002] Tin is a low-melting-point metallic element with a silvery-white luster. In compounds, it exists in a divalent or tetravalent state, primarily as oxides and various sulfides. From the Bronze Age to today's high-tech era, the importance and application scope of tin have continuously expanded, making it an indispensable material in modern industry and technological development. Tin has a wide range of uses, mainly in the production of tinplate, electroplating, corrosion science, welding, materials, tin chemical products, and other metallurgical products. It possesses characteristics such as a low melting point, good ductility, easy alloying with many metals, non-toxicity, corrosion resistance, and aesthetic appeal, making tin and its alloys widely used in industry and daily life. With the continuous development of the tin industry, tin has gradually become an indispensable key rare metal in modern industry. The amount of tin used in solder production accounts for more than 45% of the world's tin consumption, and about 75% of tin solder is used in the electronics industry (including photovoltaics, computers, and communication systems). While improvements in welding processes have reduced solder usage, the rapid development of the electronics industry has led to a steady increase in solder consumption.

[0003] However, during the production process, the continuous contact between tin solder and air leads to oxidation, producing various metal oxides, known as tin dross. Especially during soldering operations, the high-temperature transition between solid and liquid states of the tin bar significantly accelerates the oxidation of the tin alloy, resulting in a substantial increase in tin dross. This tin dross is rich in tin and other valuable metal oxides, possessing significant recycling value. However, due to the cumbersome secondary resource recovery process and the low economic value of individual recycling efforts, tin dross recycling has not yet been industrialized in my country. Therefore, from both economic and resource perspectives, comprehensive tin dross recycling is of great significance.

[0004] Currently, tin dross recycling mainly employs two methods: pyrometallurgical and hydrometallurgical processes. Pyrometallurgical processes have low recovery rates, high energy consumption, and generate significant gas emissions, leaving behind small amounts of residue. These shortcomings have consistently hindered the advancement of pyrometallurgical tin dross recycling. Hydrometallurgical processes offer relatively higher recovery rates compared to pyrometallurgical processes, but they still suffer from the inability to recycle waste liquid and the residue left by the hydrolysis of tetravalent tin ions.

[0005] In summary, those skilled in the art urgently need to solve the problems of low recovery rate, residual residue and waste liquid recycling in the wet tin slag recovery process. Summary of the Invention

[0006] To solve at least one of the above-mentioned technical problems, the present invention provides a method for recycling tin dross.

[0007] This invention provides the following solution:

[0008] A method for recycling tin dross, comprising:

[0009] The tin dross to be processed is crushed to obtain tin dross particles of a preset size.

[0010] The tin dross particles are placed in a leaching tank, and leaching solution is introduced into the leaching tank according to a preset ratio. The leaching is stirred and leached to obtain a leaching product. The leaching product is filtered to obtain a solid product and a liquid product. The solid product is leached and filtered again, and the process is repeated a first preset number of times.

[0011] Under a first preset condition, the liquid product is subjected to a constant-temperature reaction to obtain a reaction solution;

[0012] Under a second preset condition, the reaction solution is electrodeposited to obtain a deposition product, and the deposition product is filtered to obtain valuable metals and deposition liquid;

[0013] After performing a second preset number of electrodepositions, the deposition solution is treated to obtain a leachate for recycling, wherein the second preset number of electrodepositions is ≥ 1.

[0014] Optionally, the leachate comprises 120–209 g / L of methanesulfonic acid and 10–45 g / L of naphthol.

[0015] Optionally, before crushing the tin dross to be processed to obtain tin dross particles of a preset particle size, the method further includes:

[0016] Under the third preset condition, the tin dross to be processed is heated and melted to obtain molten liquid, and the tin dross on the upper layer of the molten liquid is collected as the tin dross to be processed in subsequent steps.

[0017] Optionally, the third preset condition is a heating temperature of 290–320°C and a heating time of 45–60 min.

[0018] Optionally, the preset particle size is 50–300 μm.

[0019] Optionally, the preset ratio is the mass-to-volume ratio of the tin slag particles to the leaching solution of 1g:(1.9~3.8)L.

[0020] Optionally, the first preset number of times is 3 to 5 times;

[0021] The time for obtaining the leaching product by stirring is 5 to 18 hours, the stirring speed is 80 to 250 r / min, and the temperature is room temperature.

[0022] Optionally, the first preset conditions are a reaction temperature of 20–45°C, a reaction time of 45–78 min, and a stirring speed of 251–300 r / min.

[0023] Optionally, the second preset conditions are a deposition voltage of 5–12V and a deposition current density of 270–320A / m. 2 Deposition time: 20–90 min; and / or,

[0024] The anode used in the electrodeposition is a stainless steel plate, stainless steel rod, titanium alloy plate, titanium alloy rod, graphite plate or graphite rod, and the cathode is a tin plate, tin rod, tin alloy plate, tin alloy rod, copper plate or copper rod.

[0025] Optionally, the step of treating the sediment to obtain leachate for recycling includes:

[0026] Hydrogen peroxide was added to the sediment at a volume ratio of 1:(305-389) to carry out the reaction, and the mixture was filtered to obtain the filtered liquid.

[0027] The concentration of the filtered liquid product was determined and the extract was prepared.

[0028] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0029] The recycling method provided by this invention adopts a five-step process of tin dross pretreatment, multiple leaching, isothermal reaction, deposition reaction, and deposition solution recovery to recover valuable metals (mainly tin, with a small amount of lead) from tin soldering dross. This method can achieve a recovery rate of more than 99% of valuable metals. The leaching solution can be directly electrodeposited, and after deposition or purification, it can be directly returned for continued leaching. The entire process does not generate waste discharge, thus achieving green recycling.

[0030] Furthermore, addressing the problem of SnO2 being difficult to dissolve during leaching (SnO2 is chemically stable and poorly soluble in acids and alkalis) and having low reaction efficiency in tin slag, in one example of this application, the leaching solution is a mixture of methanesulfonic acid and naphthol. Preferably, the concentration of methanesulfonic acid is 120–209 g / L, and the concentration of naphthol is 10–45 g / L. Its mechanism of action is as follows:

[0031] 1) The system undergoes a coupling reaction. The products, due to intramolecular hydrogen bonds, accelerate the reaction, further improving the leaching rate of tin dross and the recovery rate of valuable metals. The leaching solution is prepared with methanesulfonic acid and naphthol in a specific ratio. During the multiple leaching process, trace amounts of copper (in some examples, copper accounts for 0.4%–0.8% of the tin dross mass) are leached out by the methanesulfonic acid, forming cuprous ions (which have oxidizing properties). These cuprous ions act as an oxidative coupling catalyst, promoting the coupling reaction of naphthol to form β,β'-binaphthol, rich in intramolecular hydrogen bonds. The reaction formula is as follows:

[0032]

[0033] 2) Organometallic frameworks (MOFs) formed based on β,β'-binaphthol promote the leaching of SnO2. Tin slag has a complex composition, mainly containing elemental Sn and oxides SnO and SnO2. During the multiple leaching process, SnO leaches out to form SnO2. 2+ Trace amounts of SnO2 leaching form Sn 4+ Sn 2+ and Sn 4+ It can undergo a disproportionation reaction with metallic Sn. This reaction is an equilibrium reaction, when Sn in the system 2+ If the temperature is too high, the reaction will proceed in the opposite direction, Sn 2+ If the concentration is too low, the reaction will proceed in the forward direction. In this application, β,β'-binaphthol obtained through a coupling reaction reacts with Sn in the leachate. 2+ The combination forms an organometallic framework compound, which reduces the Sn content in the system. 2+ Concentration promotes the disproportionation reaction in the forward direction, facilitating the leaching of SnO2. During the constant-voltage electrodeposition process, the resulting organometallic framework compound, along with the deposition of Sn, [increases / increases] Sn in the system. 2+ As the concentration decreases, organometallic framework compounds decompose and release Sn. 2+ Improve the recovery rate of metallic tin from tin slag.

[0034] 3) A reversible sulfonation reaction can occur in the system. Methanesulfonic acid dissociates in aqueous solution into electrophilic methanesulfonate ions and hydrogen ions. In the initial stage of the reaction, due to the high concentration of methanesulfonic acid, naphthol reacts with methanesulfonate ions to form naphthol methanesulfonic acid, releasing free hydrogen protons. These free hydrogen protons gain electrons on the anode plate during constant-pressure deposition to form highly reducing hydrogen atoms, maintaining the reducing atmosphere of the system. This reducing atmosphere can reduce some SnO2 to SnO, which then dissolves into the leachate in an ionic state. During constant-pressure deposition, this ionic state can suppress the growth of Sn. 2+ Oxidized to Sn 4+ Maintain Sn 2+ Stability in solution.

[0035] Of course, the embodiments of the present invention do not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of a method for recycling tin dross according to an embodiment of the present invention;

[0038] Figure 2 This is a composition diagram of the valuable metal obtained by the deposition reaction in Example 1 of the present invention;

[0039] Figure 3 This is the Fourier transform infrared spectrum of the coupling reaction product obtained by multiple leaching in Example 1 of the present invention;

[0040] Figure 4 This is an X-ray photoelectron spectroscopy (XPS) spectrum of the organometallic framework (MOFs) obtained in Example 1 of this invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0042] It should be noted that the descriptions of "left," "right," "left side," "right side," "upper part," "lower part," "top," and "bottom" in this invention are defined based on the orientation or positional relationships shown in the accompanying drawings. They are merely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the described structure must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] In the description of this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0044] To address the technical problems mentioned in the background section, this application provides a green recycling method for tin dross. For example... Figure 1 As shown, the recycling method generally includes the following steps:

[0045] S10: The tin dross to be processed is crushed to obtain tin dross particles of a preset particle size;

[0046] This step can be summarized as tin dross pretreatment. The preset particle size is 50–300 μm, and the crushing method can be any existing method; this application does not limit it. Any method that can achieve the preset particle size of the tin dross particles can be applied to this application.

[0047] S20: Place the tin dross particles in a leaching tank, introduce leaching liquid into the leaching tank according to a preset ratio, stir and leach to obtain leaching product, filter the leaching product to obtain solid product and liquid product, and leach and filter the solid product again, repeating the first preset number of times.

[0048] This step can be summarized as multiple leaching. The preset ratio refers to the mass-to-volume ratio of the tin slag particles to the leaching solution, with a preferred ratio range of 1g:(1.9–3.8)L.

[0049] The first preset number of times is 3 to 5 times, the time for stirring and leaching to obtain the leaching product is 5 to 18 hours, the stirring speed is 80 to 250 r / min, and the temperature is room temperature.

[0050] The solid product typically contains tin, therefore, multiple leaching and filtration processes are required to improve the recovery rate. It is understood that, within a certain range, the more repetitions, the higher the recovery rate. In some preferred examples, the process is repeated until no solid product remains after filtration.

[0051] S30: Under the first preset conditions, the liquid product is subjected to a constant-temperature reaction to obtain a reaction solution;

[0052] This step can be summarized as a constant-temperature reaction. The first preset conditions are a reaction temperature of 20–45°C, a reaction time of 45–78 min, and a stirring speed of 251–300 r / min.

[0053] S40: Under the second preset conditions, the reaction solution is electrodeposited to obtain a deposition product, and the deposition product is filtered to obtain valuable metals and deposition liquid;

[0054] This step can be summarized as a deposition reaction. The second preset conditions are a deposition voltage of 5–12V and a deposition current density of 270–320 A / m. 2 Deposition time: 20–90 min.

[0055] The anode used in the electrodeposition is a stainless steel plate, stainless steel rod, titanium alloy plate, titanium alloy rod, graphite plate or graphite rod, and the cathode is a tin plate, tin rod, tin alloy plate, tin alloy rod, copper plate or copper rod. After electrodeposition, the recovered product is solidified and deposited on the cathode in the form of valuable metal. The cathode can be directly returned to the soldering production process as raw material for direct use. A new cathode is used for each electrodeposition.

[0056] Valuable metals include tin and a small amount of lead.

[0057] S50: After performing a second preset number of electrodepositions, the deposition solution is treated to obtain a leachate for recycling, wherein the second preset number of electrodepositions is ≥ 1.

[0058] This step can be summarized as leachate recovery. It's important to note that, to improve the utilization rate of the leachate, treatment is not required after each leaching; instead, it can be reused. The timing of treatment can be determined by measuring the impurity content.

[0059] The treatment of the sediment solution may include purification and preparation. In one example, S50 includes:

[0060] Hydrogen peroxide was added to the sediment at a volume ratio of 1:(305-389) to carry out the reaction, and the reaction was carried out by filtration to obtain the filtered liquid product.

[0061] The concentration of the filtered liquid product was determined and the extract was prepared.

[0062] The reaction conditions can be as follows: at 28-38℃, the reaction is stirred at 150-250 r / min for 25-39 min. After the reaction, the filtered liquid product can be left to stand at 20-25℃ in a ventilated place for 10-12 h. Then, the filtered liquid product after standing is filtered to separate the solid and liquid. The concentration of the obtained liquid is measured and adjusted to obtain the leachate.

[0063] The above-mentioned recycling method uses a five-step process of tin dross pretreatment, multiple leaching, isothermal reaction, deposition reaction, and deposition solution recovery to recover valuable metals (mainly tin, with a small amount of lead) from tin soldering dross. This method can achieve a recovery rate of more than 99% of valuable metals. The leaching solution can be directly electrodeposited, and after deposition or purification, it can be directly returned for continued leaching. The entire process does not generate waste discharge, thus achieving green recycling.

[0064] To address the problem of SnO2 being difficult to dissolve during leaching (SnO2 is chemically stable and poorly soluble in acids and alkalis) and having low reaction efficiency in tin slag, in one example of this application, the leaching solution is a mixture of methanesulfonic acid and naphthol. Preferably, the concentration of methanesulfonic acid is 120–209 g / L, and the concentration of naphthol is 10–45 g / L. Its mechanism of action is as follows:

[0065] 1) The system undergoes a coupling reaction. The products, due to intramolecular hydrogen bonds, accelerate the reaction, further improving the leaching rate of tin dross and the recovery rate of valuable metals. The leaching solution is prepared with methanesulfonic acid and naphthol in a specific ratio. During the multiple leaching process, trace amounts of copper (in some examples, copper accounts for 0.4%–0.8% of the tin dross mass) are leached out by the methanesulfonic acid, forming cuprous ions (which have oxidizing properties). These cuprous ions act as an oxidative coupling catalyst, promoting the coupling reaction of naphthol to form β,β'-binaphthol, rich in intramolecular hydrogen bonds. The reaction formula is as follows:

[0066]

[0067] 2) Organometallic frameworks (MOFs) formed based on β,β'-binaphthol promote the leaching of SnO2. Tin slag has a complex composition, mainly containing elemental Sn and oxides SnO and SnO2. During the multiple leaching process, SnO leaches out to form SnO2. 2+ Trace amounts of SnO2 leaching form Sn 4+ Sn 2+ and Sn 4+ It can undergo a disproportionation reaction with metallic Sn. This reaction is an equilibrium reaction, when Sn in the system 2+ If the temperature is too high, the reaction will proceed in the opposite direction, Sn 2+ If the concentration is too low, the reaction will proceed in the forward direction. In this application, β,β'-binaphthol obtained through a coupling reaction reacts with Sn in the leachate. 2+ The combination forms an organometallic framework compound, which reduces the Sn content in the system. 2+ Concentration promotes the disproportionation reaction in the forward direction, increasing the leaching rate of SnO2. During the constant-voltage electrodeposition process, the Sn concentration in the resulting organometallic framework compound increases with Sn deposition.2+ As the concentration decreases, organometallic framework compounds decompose and release Sn. 2+ Improve the recovery rate of metallic tin from tin slag.

[0068] 3) A reversible sulfonation reaction can occur in the system. Methanesulfonic acid dissociates in aqueous solution into electrophilic methanesulfonate ions and hydrogen ions. In the initial stage of the reaction, due to the high concentration of methanesulfonic acid, naphthol reacts with methanesulfonate ions to form naphthol methanesulfonic acid, releasing free hydrogen protons. These free hydrogen protons gain electrons on the anode plate during constant-pressure deposition to form highly reducing hydrogen atoms, maintaining the reducing atmosphere of the system. This reducing atmosphere can reduce some SnO2 to SnO, which then dissolves into the leachate in an ionic state. During constant-pressure deposition, this ionic state can suppress the growth of Sn. 2+ Oxidized to Sn 4+ Maintain Sn 2+ Stability in solution.

[0069] To improve recycling efficiency and reduce the number of subsequent multiple leaching operations, in one example of this application, the step of crushing the tin dross to be processed to obtain tin dross particles of a preset particle size further includes:

[0070] Under the third preset conditions, the tin dross to be processed is heated and melted to obtain molten liquid. The tin dross on the top layer of the molten liquid is collected as tin dross to be processed in subsequent steps. The tin dross after this processing can also be called secondary tin dross, which is subjected to various treatments in subsequent steps.

[0071] The third preset condition is a heating temperature of 290–320°C and a heating time of 45–60 min.

[0072] To better illustrate this application, the solution of this application will be described in more detail below with reference to embodiments and comparative examples.

[0073] Example 1

[0074] Tin dross remelting: The tin dross to be treated scraped from the surface of the tin furnace in the tin coating production line is put into the tin remelting furnace for tin dross remelting. After that, the lower layer of tin alloy is returned to the production line for use, and the upper layer of secondary tin dross that cannot be remelted is collected for later use. The tin dross remelting temperature is 290℃ and the remelting time is 45min. The secondary tin dross contains unremelted elemental metal Sn, oxides SnO and SnO2, trace amounts of copper (copper accounts for 0.4% of the mass percentage of the secondary tin dross) and a small amount of lead.

[0075] Tin dross pretreatment: The collected secondary tin dross is crushed to obtain uniform and fine tin dross particles. The particle size range of the treated tin dross particles is about 50μm.

[0076] Multiple leaching: 10.01g of tin dross particles were placed in the leaching tank, and leaching solution was introduced according to a specific solid-liquid ratio. The leaching solution (aqueous solution) was stirred and leached. The formula of the leaching solution (aqueous solution) was: 120g / L of methanesulfonic acid and 10g / L of naphthol. The leaching conditions were: solid-liquid ratio: 1:1.9g / L (i.e., 1g of tin dross particles were added to every 1.9L of leaching solution), stirring speed: 80 rpm, leaching time: 5 hours, and leaching temperature: room temperature.

[0077] Isothermal reaction: The leached product is filtered to separate the solid product and the liquid product. The solid product is returned to the previous process for leaching, and the liquid product is placed in the reaction vessel for isothermal reaction. In this example, leaching is performed 4 times and filtered to obtain 1.43g of leached solid product (mainly composed of poorly soluble impurities). The isothermal reaction conditions are: temperature 20℃, reaction time 45min, and stirring speed 251 rpm.

[0078] Deposition reaction: The liquid product was transferred into a deposition tank, followed by electrodeposition at the cathode and anode. The constant voltage deposition conditions were: deposition voltage 5V and deposition current density 270A / m. 2 The deposition time was 20 minutes, the anode was a stainless steel plate, and the cathode was a tin plate.

[0079] Product removal: The cathode and anode are removed from the deposition tank. The anode is returned to the deposition tank for continued use, while the cathode is returned to the soldering production process as raw material for direct use (the cathode is a tin plate with deposited valuable metal; calculations show that 7.51g of valuable metal was deposited on the tin plate in this embodiment. This cathode can be directly returned to the soldering production process as raw material for direct use. When the deposition reaction is carried out again under constant pressure, a new tin plate is used as the cathode). Deposition yields a deposition product, which is then filtered to obtain valuable metal and deposition liquid.

[0080] Sediment recovery: The concentration of the sediment is measured and adjusted to a suitable concentration for leaching, then returned to the leaching tank as leachate for continued use. In this embodiment, the sediment can be returned to the leaching tank as leachate for continued use, i.e., reflux.

[0081] The amount of valuable metals in the tin dross particles of this embodiment was determined by an SH-ICP1100 inductively coupled plasma atomic emission spectrometer. Calculations showed that 10.01g of tin dross particles contained 7.55g of valuable metals.

[0082] In this embodiment, the methanesulfonic acid in the sediment is a monoprotic acid, which is titrated with a standard sodium hydroxide solution. The content of methanesulfonic acid in the sediment is quantitatively calculated based on the amount of sodium hydroxide consumed. After determining the content of methanesulfonic acid in the sediment, methanesulfonic acid is added until its final concentration is 120 g / L.

[0083] In this embodiment, the naphthol content in the sediment was determined by high performance liquid chromatography in the HJ1073-2019 standard "Determination of Naphthol in Water". After determining the naphthol content in the sediment, naphthol was added to a final concentration of 10 g / L and returned to the leaching tank as leachate for continued use.

[0084] The method in this embodiment is green and environmentally friendly, with a high tin dross recycling rate and no waste liquid, waste gas, or waste residue emissions during the process.

[0085] The method in this embodiment achieves a recovery rate of over 99% for valuable metals in tin dross.

[0086] like Figure 2 The figure shows the composition of the valuable metals obtained by the deposition reaction in this embodiment. As can be seen from the figure, the valuable metals are mainly Sn, Pb and Cu. That is, the left figure is a picture of the valuable metals, and the right figure is an elemental analysis chart of the valuable metals.

[0087] like Figure 3 The figure shows the Fourier transform infrared spectrum of the coupling reaction product obtained by multiple leaching in this embodiment. As can be seen from the figure, the coupling product has the characteristic peak of naphthol and the hydrogen bond association peak formed by the hydroxyl group in naphthol, indicating that the product is binaphthol.

[0088] like Figure 4 The figure shows the X-ray photoelectron spectroscopy (XPS) spectra of the organometallic framework (MOFs) obtained in this embodiment. As can be seen from the figure, the MOFs are mainly composed of carbon, nitrogen, oxygen, and tin. The electron binding energy corresponding to the tin characteristic peak indicates the presence of Sn in the MOFs. 2+ This indicates that β,β'-binaphthol and Sn 2+ They combine to form organometallic framework compounds.

[0089] Example 2

[0090] Tin dross remelting: The tin dross to be treated scraped from the surface of the tin furnace in the tin coating production line is put into the tin remelting furnace for tin dross remelting. After that, the lower layer of tin alloy is returned to the production line for use, and the upper layer of secondary tin dross that cannot be remelted is collected for later use. The tin dross remelting temperature is 305℃ and the remelting time is 52min. The secondary tin dross contains unremelted elemental metal Sn, oxides SnO and SnO2, trace amounts of copper (copper accounts for 0.6% of the mass percentage of the secondary tin dross) and a small amount of lead.

[0091] Tin dross pretreatment: The collected secondary tin dross is crushed to obtain uniform and fine tin dross particles. The particle size range of the treated tin dross particles is about 150μm.

[0092] Multiple leaching: 10.08g of tin dross particles were placed in the leaching tank, and leaching solution was introduced at a specific solid-liquid ratio. The leaching was carried out with stirring. The leaching solution (aqueous solution) formula was: 165g / L methanesulfonic acid and 25g / L naphthol. The leaching conditions were: solid-liquid ratio 1:2.5g / L (i.e., 1g of tin dross particles were added to every 2.5L of leaching solution), stirring speed 120 rpm, leaching time 10 hours, and leaching temperature room temperature.

[0093] Isothermal reaction: The leached product is filtered to separate the solid product and the liquid product. The solid product is returned to the previous process for leaching, and the liquid product is placed in the reaction vessel for isothermal reaction. In this example, leaching is performed 3 times and filtered to obtain 1.48g of leached solid product. The isothermal reaction conditions are: temperature 30℃, reaction time 60min, and stirring speed 275 rpm.

[0094] Deposition reaction: The liquid product was transferred into a deposition tank, followed by electrodeposition at the cathode and anode. The constant voltage deposition conditions were: deposition voltage 10V and deposition current density 300A / m. 2 The deposition time is 50 minutes, the anode is a titanium alloy plate, and the cathode is a tin alloy plate;

[0095] Product removal: The cathode and anode are removed from the deposition tank. The anode is returned to the deposition tank for continued use, while the cathode is returned to the soldering production process as raw material for direct use. The deposition product is obtained by filtration of the deposition product to obtain valuable metals and deposition liquid.

[0096] Sediment purification: Add hydrogen peroxide at a volume ratio of 1:305 to sediment, stir at 150 r / min for 25 min at 28℃, and let the sediment stand at 20℃ in a ventilated place for 10 h. Filter the sediment after standing to separate the solid and liquid. The obtained liquid is the purified sediment.

[0097] Sediment recirculation: The concentration of the purified sediment is measured and adjusted to a suitable concentration for leaching, then returned to the leaching tank as leachate for continued use.

[0098] In this embodiment, the methanesulfonic acid in the sediment is a monoprotic acid, which is titrated with a standard sodium hydroxide solution. The content of methanesulfonic acid in the sediment is quantitatively calculated based on the amount of sodium hydroxide consumed. After determining the content of methanesulfonic acid in the sediment, methanesulfonic acid is added until its final concentration is 165 g / L.

[0099] In this embodiment, the naphthol content in the sediment was determined by high performance liquid chromatography in the HJ1073-2019 standard "Determination of Naphthol in Water". After determining the naphthol content in the sediment, naphthol was added to a final concentration of 25 g / L and returned to the leaching tank as leachate for continued use.

[0100] The method in this embodiment is green and environmentally friendly, with a high tin dross recycling rate and no waste liquid, waste gas, or waste residue emissions during the process.

[0101] The method in this embodiment achieves a recovery rate of over 99% for valuable metals in tin dross.

[0102] Example 3

[0103] Tin dross remelting: The tin dross to be treated scraped from the surface of the tin furnace in the tin coating production line is put into the tin remelting furnace for tin dross remelting. After that, the lower layer of tin alloy is returned to the production line for use, and the upper layer of secondary tin dross that cannot be remelted is collected for later use. The tin dross remelting temperature is 320℃ and the remelting time is 60min. The secondary tin dross contains unremelted elemental metal Sn, oxides SnO and SnO2, trace amounts of copper (copper accounts for 0.8% of the mass percentage of the secondary tin dross) and a small amount of lead.

[0104] Tin dross pretreatment: The collected secondary tin dross is crushed to obtain uniform and fine tin dross particles. The particle size range of the treated tin dross particles is about 300μm.

[0105] Multiple leaching: 10.02g of tin dross particles were placed in the leaching tank, and leaching solution was introduced according to a specific solid-liquid ratio. The leaching solution (aqueous solution) was stirred and leached. The formula of the leaching solution (aqueous solution) was: 209g / L of methanesulfonic acid and 45g / L of naphthol. The leaching conditions were: solid-liquid ratio of 1:3.8g / L (i.e., 1g of secondary tin dross particle powder was added to every 3.8L of leaching solution), stirring speed of 250 rpm, leaching time of 18 hours, and leaching temperature of room temperature.

[0106] Isothermal reaction: The leached product is filtered to separate the solid product and the liquid product. The solid product is returned to the previous process for leaching, and the liquid product is placed in the reaction vessel for isothermal reaction. In this example, leaching is performed 5 times and filtered to obtain 1.47g of leached solid product. The isothermal reaction conditions are: temperature 45℃, reaction time 78min, and stirring speed 300 rpm.

[0107] Deposition reaction: The liquid product was transferred into a deposition tank, followed by electrodeposition at the cathode and anode. The constant voltage deposition conditions were: deposition voltage 12V, deposition current density 320A / m³. 2 The deposition time was 90 minutes, the anode was a titanium alloy plate, and the cathode was a tin plate.

[0108] Product removal: The cathode and anode are removed from the deposition tank. The anode is returned to the deposition tank for continued use, while the cathode is returned to the soldering production process as raw material for direct use. The deposition product is obtained by deposition, and the deposition product is filtered to obtain valuable metals and deposition liquid.

[0109] Sediment purification: Add hydrogen peroxide at a volume ratio of 1:389 to sediment, stir at 250 r / min for 39 min at 38℃, and let the sediment stand at 25℃ in a ventilated place for 12 h. Filter the sediment after standing to separate the solid and liquid. The obtained liquid is the purified sediment.

[0110] Sediment recirculation: The concentration of the purified sediment is measured and adjusted to a suitable concentration for leaching, then returned to the leaching tank as leachate for continued use.

[0111] In this embodiment, the methanesulfonic acid in the sediment is a monoprotic acid, which is titrated with a standard sodium hydroxide solution. The content of methanesulfonic acid in the sediment is quantitatively calculated based on the amount of sodium hydroxide consumed. After determining the content of methanesulfonic acid in the sediment, methanesulfonic acid is added until its final concentration is 209 g / L.

[0112] In this embodiment, the naphthol content in the sediment was determined by high performance liquid chromatography in the HJ1073-2019 standard "Determination of Naphthol in Water". After determining the naphthol content in the sediment, naphthol was added to a final concentration of 45 g / L and returned to the leaching tank as leachate for continued use.

[0113] The method in this embodiment is green and environmentally friendly, with a high tin dross recycling rate and no waste liquid, waste gas, or waste residue emissions during the process.

[0114] The method in this embodiment achieves a recovery rate of over 99% for valuable metals in tin dross.

[0115] Comparative Example 1

[0116] The only difference from Example 1 is that naphthol is replaced with phenol, and the leaching time is 48 hours each time.

[0117] Comparative Example 2

[0118] The only difference from Example 1 is that methanesulfonic acid is replaced with hydrochloric acid, and the leaching time is 48 hours each time.

[0119] Comparative Example 3

[0120] The only difference from Example 1 is that naphthol is replaced with phenol and methanesulfonic acid is replaced with hydrochloric acid; the leaching time for each leaching is 48 hours.

[0121] Leaching rate = [(tin dross particles - amount of solid product after leaching) / tin dross particles] × 100%;

[0122] Recovery rate = (valuable metal deposited on the tin plate / amount of valuable metal contained in the tin dross particles) × 100%.

[0123] The leaching rates and recovery rates of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 below.

[0124] Table 1 Comparison of leaching rate and recovery rate between Examples 1-3 and Comparative Examples 1-3

[0125]

[0126]

[0127] By comparing the examples and comparative examples, it can be found that the present application selects a mixture of methanesulfonic acid and naphthol as the leaching solution to treat tin dross, which is superior to the scheme using phenol and / or hydrochloric acid as the leaching solution in terms of both the leaching rate of tin dross and the recovery rate of valuable metals.

[0128] The technical solution provided by this invention has been described in detail above. Specific examples have been used to illustrate the structure and implementation of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for recycling tin dross, characterized in that, include: Under the third preset condition, the tin dross is heated and melted to obtain molten liquid, and the tin dross on the upper layer of the molten liquid is collected as tin dross to be processed in subsequent steps; The tin dross to be processed is crushed to obtain tin dross particles of a preset particle size; the tin dross particles contain SnO and SnO2; The tin dross particles are placed in a leaching tank, and leaching solution is introduced into the leaching tank according to a preset ratio. The leaching is stirred to obtain a leaching product. The leaching product is filtered to obtain a solid product and a liquid product. The solid product is then leached and filtered again, and the process is repeated a first preset number of times. The leaching solution includes 120~209 g / L of methanesulfonic acid and 10~45 g / L of naphthol. During the leaching process, the SnO is leached to form Sn 2+ The SnO2 leaching forms Sn 4+ The copper in the tin slag is leached by the methanesulfonic acid to form cuprous ions; the cuprous ions catalyze a coupling reaction of naphthol to form β,β'-binaphthol containing intramolecular hydrogen bonds; the β,β'-binaphthol reacts with the Sn... 2+ The combination generates an organometallic framework compound, which reduces the Sn content in the system. 2+ The concentration is adjusted to promote the leaching of SnO2 and drive the Sn... 4+ The disproportionation reaction between Sn and metallic Sn leads to the formation of Sn. 2+ Proceed in the direction of; Under a first preset condition, the liquid product is subjected to a constant-temperature reaction to obtain a reaction solution; Under a second preset condition, the reaction solution is electrodeposited to obtain a deposition product, and the deposition product is filtered to obtain valuable metals and deposition liquid; During the electrodeposition process, the hydrogen protons dissociated from the methanesulfonic acid gain electrons at the cathode to form hydrogen atoms, thus maintaining a reducing atmosphere. This reducing atmosphere reduces some SnO2 to SnO and inhibits the growth of Sn. 2+ Oxidized to Sn 4+ ; After performing a second preset number of electrodepositions, the deposition solution is treated to obtain a leachate for recycling, wherein the second preset number of electrodepositions is ≥ 1.

2. The recycling method according to claim 1, characterized in that, The third preset condition is a heating temperature of 290~320℃ and a heating time of 45~60min.

3. The recycling method according to claim 1, characterized in that, The preset particle size is 50~300µm.

4. The recycling method according to any one of claims 1-3, characterized in that, The preset ratio is the mass-to-volume ratio of the tin slag particles to the leaching solution of 1g:(1.9~3.8)L.

5. The recycling method according to claim 1, characterized in that, The first preset number of times is 3 to 5 times; The time for obtaining the leaching product by stirring is 5-18 hours, the stirring speed is 80-250 r / min, and the temperature is room temperature.

6. The recycling method according to claim 1, characterized in that, The first preset conditions are a reaction temperature of 20~45℃, a reaction time of 45~78min, and a stirring speed of 251~300r / min.

7. The recycling method according to claim 1, characterized in that, The second preset conditions are a deposition voltage of 5~12V and a deposition current density of 270~320A / m. 2 Deposition time: 20–90 min; and / or, The anode used in the electrodeposition is a stainless steel plate, stainless steel rod, titanium alloy plate, titanium alloy rod, graphite plate or graphite rod, and the cathode is a tin plate, tin rod, tin alloy plate, tin alloy rod, copper plate or copper rod.

8. The recycling method according to claim 1, characterized in that, The step of processing the sediment to obtain a leachate for recycling includes: Hydrogen peroxide was added to the sediment at a volume ratio of 1:(305~389) to carry out the reaction, and the mixture was filtered to obtain the filtered liquid. The concentration of the filtered liquid product was determined and the extract was prepared.

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