CN110396596A - Method for gold recovery from waste printed circuit boards - Google Patents

Abstract

The present invention discloses a method for recovering gold from waste printed circuit boards. First, the waste printed circuit boards are subjected to microwave cracking, then, the solid residue formed after the microwave cracking is subjected to acid leaching treatment using a sulfuric acid-based acid leaching solution, then, gold ions are dissolved from the solid residue subjected to the acid leaching treatment using a thiosulfate mixed solution to obtain a gold ion-containing solution, and finally, an oxidant is added to the gold ion-containing solution to convert the gold ions into metallic gold. In this way, the gold in the waste printed circuit boards can be reused.

Description

Method for gold recovery from waste printed circuit boards

technical field

The invention relates to a method for recovering and reusing metal resources, in particular to a method for recovering gold from waste printed circuit boards.

Background technique

With the development of science and technology, smart phones have become a necessity in daily life, which has changed the way of human life. According to the statistics of International Data Information (IDC), in Taiwan, Chinese people replace a mobile phone within two years on average. With such a high replacement rate, only a small number of eliminated mobile phones are directly recycled; according to the data of the Environmental Protection Agency, the recycling of waste mobile phones The rate is actually less than 30%, leading to an increase in the amount of electronic waste (E-Waste). If most of these electronic wastes are disposed of by landfill or incineration, the harmful substances produced during the disposal will directly or indirectly cause harm to the human body and the environment.

As far as the current rare metal content in the world is concerned, it will take only 20 to 30 years for it to be exhausted: as electronic waste is accumulating rapidly, recycling electronic waste and obtaining rare metals inside will become a research topic worldwide. The important subject of development is the concept of urban mining proposed by Professor Michio Nanjo of the Mineral Processing Institute of Tohoku University in Japan in 1988.

Urban mining mainly refers to the recycling of expired or obsolete electronic products and small waste household appliances, such as: mobile phones, digital cameras, computers, televisions and other equipment, and the use of resources such as general metals, precious metals and rare earth elements contained in them to reduce The impact of ore mining, smelting and processing on the environment, while achieving the goals of Reduce, Reuse and Recycle. This concept can not only promote the sustainable development of the environment, but also the amount of precious metals obtained from recycling electronic waste is much higher than that obtained from mining minerals, and has higher economic value.

The recycling value of waste mobile phones is mainly in printed circuit boards (Printed Circuit Board, PCB). The economic value of palladium, etc.) is much higher than that of other metals (such as: copper, lead, aluminum, etc.). Today, when mineral resources are decreasing and demand is increasing, the recovery of precious metals has become very important. Therefore, many literatures propose different methods and processes for the recovery of precious metals, mainly including mechanical treatment, pyrometallurgy and hydrometallurgy.

Mechanical treatment is mainly to use machines to rotate and grind waste printed circuit boards at high speed, and then sort them according to differences in material density, surface characteristics, conductivity, and magnetism. The purity of the obtained metal is not high, and there are problems such as powder layer pollution and noise. Pyrometallurgy mainly uses incineration and melting to dissolve and separate metals from waste printed circuit boards; the advantage of pyrometallurgy is that the recovered metals are of high purity, but the disadvantage is that the recycling process is very energy-intensive. Hydrometallurgy mainly uses strong acid or strong oxidizing solvent to dissolve and separate metals from waste printed circuit boards; the advantage of hydrometallurgy is that the recovered metals are of high purity, but the disadvantage is that waste acid is produced during the recovery process.

For the waste printed circuit board (WPCB) of mobile phones, the method commonly used in factories to recover precious metals mainly combines mechanical treatment and hydrometallurgical treatment steps. However, in the step of cyanide stripping, the cyanide used is a highly toxic compound, which may be fatal if inhaled in a small amount, and the waste liquid containing cyanide is easy to form complexes with many metalloids, which will Difficulty in handling; in the step of acid dissolution, the solvent used is mostly aqua regia, because aqua regia itself is a strong acidic solvent, the pH value of the waste liquid will be between 1 and 2, and it needs to be processed Neutralize the waste liquid to neutral, which will also cause difficulties in disposal; in addition, toxic gases will be emitted during the recycling process, causing air pollution problems. Current recycling methods have adverse effects on human health and the environment.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for recovering gold from waste printed circuit boards, which has both environmental and economic benefits.

In order to solve the above-mentioned technical problems, one of the technical solutions adopted in the present invention is: a method for recovering gold from waste printed circuit boards, which includes: microwave cracking of waste printed circuit boards; The solid residue formed after microwave cracking is subjected to acid leaching treatment to remove the copper component in the solid residue; a thiosulfate mixed solution is used to dissolve gold ions from the solid residue treated by acid leaching to obtaining a solution containing gold ions; and adding an oxidant to the solution containing gold ions, so that the gold ions form metallic gold.

In an embodiment of the present invention, the waste printed circuit board is subjected to microwave cracking under the microwave power of about 200W to about 400W.

In one embodiment of the present invention, the number of acid leaching treatments using the sulfuric acid-based acid leaching solution is twice, and the conditions of each acid leaching treatment include: the reaction temperature is 25-35°C, the reaction The time is 3-5 hours.

In one embodiment of the present invention, the sulfuric acid-based pickling solution includes sulfuric acid and hydrogen peroxide.

In an embodiment of the present invention, the concentration of the sulfuric acid is 2-3M, and the concentration of the hydrogen peroxide is 30-35wt%.

In an embodiment of the present invention, the conditions for using the thiosulfate mixed solution to extract gold ions include: the reaction temperature is 50-70° C., and the reaction time is 2-4 hours.

In an embodiment of the present invention, the thiosulfate mixed solution includes thiosulfate, copper sulfate and ammonia water.

In one embodiment of the present invention, the concentration of the thiosulfate is 0.05-0.15M, the concentration of the copper sulfate is 0.01-0.02M, and the concentration of the ammonia water is 0.10-0.25M.

In one embodiment of the present invention, the thiosulfate is sodium thiosulfate, potassium thiosulfate or ammonium thiosulfate.

In one embodiment of the present invention, the oxidizing agent is hydrogen peroxide or perchloric acid, wherein the volume ratio of the oxidizing agent to the mixed solution of thiosulfate is 1:45-55.

In an embodiment of the present invention, before the step of microwave cracking the waste printed circuit board, the method for recovering gold from the waste printed circuit board further includes: first cleaning the waste printed circuit board, Then cut the waste printed circuit board into proper size.

One of the beneficial effects of the present invention is that the method for recovering gold from waste printed circuit boards provided by the present invention can be achieved by "first performing microwave cracking on waste printed circuit boards, and then using sulfuric acid acid dipping solution to remove gold after microwave cracking. The copper component in the solid residue formed, and then use a thiosulfate mixture to dissolve gold ions from the solid residue from which most of the copper component has been removed, and finally use an oxidizing agent to reduce the gold ions in the gold-containing solution to metal Gold" technical solution to achieve beneficial effects such as no pollution, low cost, low energy consumption, and high recovery rate. It is suitable for mass recovery of waste printed circuit boards and has industrial application prospects.

In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings related to the present invention. However, the provided drawings are only for reference and description, and are not intended to limit the present invention.

Description of drawings

Fig. 1 is a flowchart of steps of the method for recovering gold from waste printed circuit boards of the present invention.

FIG. 2 is a graph showing the relationship between weight loss rate and temperature obtained by thermogravimetric analysis of waste printed circuit boards.

Fig. 3 is a SEM photograph of the solid residue of the waste printed circuit board obtained after pyrolysis under the microwave power of 150W and 350W.

Fig. 4 is a graph showing the relationship between copper dissolution rate and time obtained by acid leaching treatment of solid residues of waste printed circuit boards.

Figure 5 is a SEM photo of the precipitate formed by using hydrogen peroxide to recover gold ions.

Figure 6 shows the EDS component analysis results of the precipitate formed by using hydrogen peroxide to recover gold ions.

Fig. 7 is a SEM photo of the precipitate formed by using perchloric acid to recover gold ions.

Figure 8 shows the EDS component analysis results of the precipitate formed by recovering gold ions using perchloric acid.

Detailed ways

From the perspective of metal content, the printed circuit board is like a piece of ore. In the case of decreasing raw ore content, if valuable metals (such as gold, palladium and other precious metals) can be recovered from waste printed circuit boards and reused, environmental and economic benefits can be created at the same time. Therefore, the present invention provides an innovative method that can both reduce environmental pollution and increase gold recovery.

Please refer to Fig. 1, the present invention provides a method for recovering gold from waste printed circuit boards, which at least includes: cleaning step S1, cutting step S2, microwave cracking step S3, acid leaching step S4, gold extraction step S5 and gold recovery step S6. The sources of waste printed circuit boards mentioned in this article are mainly "electronic waste" or "e-waste", such as: computers, smart phones, video cameras, digital cameras, multifunction devices, game consoles, players etc., have reached the end of their service life or have been discarded due to other factors.

The following is a description of the implementation of the "method for recovering gold from waste printed circuit boards" disclosed by the present invention through specific specific examples. Those skilled in the art can understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and various modifications and changes can be made to the details in this specification based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are only for simple illustration, and are not drawn according to the actual size, which is stated in advance. The following embodiments will further describe the relevant technical content of the present invention in detail, but the disclosed content is not intended to limit the protection scope of the present invention.

The cleaning step S1 is used to remove the dirt (such as: dust particles) attached to the waste printed circuit board, and the cutting step S2 is used to cut the cleaned waste printed circuit board to an appropriate size, such as 2.4cm×3cm sheets, but not limited to this. In this embodiment, clean water (such as: deionized water) is used to clean the waste printed circuit board, so the residual water needs to be removed after cleaning; the way to remove the residual water can be to soak the waste printed circuit board first In highly volatile organic solvents, such as: isopropanol (IPA), methanol, ethanol, acetone, etc., and apply ultrasonic vibration to the organic solvent to speed up the replacement rate between the solvent and clean water, and then clean the waste printing The circuit board is dried, for example, placing the waste printed circuit board in an oven at 105° C. to evaporate the organic solvent. As a side note, the above-mentioned organic solvents help to remove residual moisture on discarded printed circuit boards due to lower surface tension and higher volatility than clean water.

The microwave cracking step S3 is used to separate the layered structure of the waste printed circuit board, so that the layers are clearly separated, thereby improving the effect of the subsequent acid leaching. In order to find out the optimal microwave conditions, the inventor first carried out thermal gravimetric analysis (Thermal Gravimetric Analysis, TGA) on the waste printed circuit board, thereby understanding the cracking temperature of the organic matter in the board, the results are shown in Figure 2, and three of them lost weight The curves respectively present the changes in the weight loss rate (wt%/°C) at the heating rates of 10°C/min, 20°C/min and 30°C/min. It can be seen from Figure 2 that the maximum peaks of the three weight loss curves occur between 340°C and 360°C, which indicates that the thermal cracking reaction of organic matter mainly occurs in this temperature range.

Please refer to Table 1 below, the inventors further analyzed the temperature rise of waste printed circuit boards under different microwave powers. The average temperature in Table 1 is the average temperature from the 40th minute to the 50th minute when the microwave cracking reaches stability; the heating rate in Table 1 is the linear regression value from the 1st minute to the 10th minute. As shown in Table 1, when the microwave power is 150W, the temperature of the waste PCB only rises slowly, and the highest temperature is about 280°C. When the microwave power reaches more than 200W, the temperature rise of the waste printed circuit board is significantly improved, and its temperature tends to be stable within 10 minutes, and no drastic changes occur; it can be deduced that the minimum wattage required for cracking That is 200W.

Table I

Please refer to Fig. 3(a), the solid residue of the discarded printed circuit board obtained after pyrolysis under the microwave power of 150W, the main body is still intact, and the interlayer separation phenomenon is not obvious. Please refer to FIG. 3( b ), the solid residue of the waste printed circuit board obtained after pyrolysis under the microwave power of 350W has very obvious interlayer separation phenomenon. It is worth noting that under the microwave power of 350W, the temperature of the waste printed circuit board can rise to about 400°C. According to the previous thermogravimetric analysis results, this temperature can ensure the stable progress of the pyrolysis reaction; therefore, 350W The microwave power is a better condition for the microwave cracking step S3.

The acid leaching step S4 is used to dissolve copper ions from the solid residue of the discarded printed circuit board, so as to remove the copper component in the solid residue as thoroughly as possible, so as to improve the subsequent gold extraction effect. In this embodiment, the sulfuric acid acid leaching solution is used to carry out acid leaching treatment on the solid residue; during the acid leaching treatment, the reaction temperature may be 25-35°C, preferably 30°C, and the reaction time may be 3-5 hours, which is relatively It is preferably 3 hours, but not limited thereto. In order to find out better acid leaching conditions, the inventors tested the effect of different sulfuric acid-based acid leaching solutions on the dissolution of copper components in solid residues, and the results are shown in Table 2 below. As can be seen from Table ₂ , hydrogen peroxide (H2O2) can promote the copper stripping reaction of sulfuric acid, and under the synergistic effect of 2M sulfuric acid and 30wt% hydrogen peroxide, the stripping rate of copper can reach more than 95%. That is, more than 95% of the copper in the solid residue can be effectively separated into solution. In this embodiment, the concentration of sulfuric acid contained in the sulfuric acid dipping solution may be 2-3M, and the concentration of hydrogen peroxide may be 30-35wt%.

Table II

Furthermore, please refer to FIG. 4 , after 30 minutes of the acid leaching treatment, the dissolution rate of copper reaches about 72%, and the final dissolution rate can reach more than about 86%. It can be known from this that hydrogen peroxide can also accelerate the reaction rate of sulfuric acid, and can have a good copper removal effect in the initial stage of the reaction.

The gold extraction step S5 is used to dissolve gold ions from the solid residue treated by acid leaching, so as to facilitate subsequent gold recovery. In this embodiment, a thiosulfate mixture is used to dissolve gold ions; when dissolving gold ions, the reaction temperature may be 50-70°C, preferably 60°C, and the reaction time may be 2-4 hours, preferably 2 hours, but not limited to this. Further, the thiosulfate mixed solution contains thiosulfate, copper sulfate and ammonia water, wherein the thiosulfate can be sodium thiosulfate, potassium thiosulfate or ammonium thiosulfate, etc., and preferably thiosulfate Ammonium. The concentration of thiosulfate can be 0.05-0.15M, the concentration of copper sulfate can be 0.01-0.02M, and the concentration of ammonia can be 0.10-0.25M. It is worth noting that under the synergistic effect of 0.1M ammonium thiosulfate, 0.015M copper sulfate and 0.2M ammonia water, the dissolution rate of gold can reach 99%, that is to say, more than 99% of the solid residue Gold can be effectively separated into the solution, and gold ions can form stable gold thiosulfate ions (Au(S ₂ O ₃ )2 ^3- ) with thiosulfate ions. Extractants, such as: two (2-ethylhexyl) phosphoric acid (D2EHPA), tributyl phosphate (TBP), dibutyl carbitol (DBC), trioctylamine, etc., also cannot extract gold ions from the solution. Extraction and separation.

As a side note, although aqua regia can also be used to dissolve gold ions from solid residues, this method will cause gold ions to exist in the form of AuCl4-, that is, gold ions will exist in a positive trivalent ion state, which is less stable and easy to be extracted. The extractant is adsorbed by bonds. In addition, because aqua regia is too corrosive, there are great difficulties in subsequent treatment.

Preferably, in this method, the gold extraction step S5 is performed after the acid leaching step S4 is performed twice, so as to avoid the influence of the presence of copper ions on the subsequent gold extraction. Experiments have shown that there is a nearly five-fold difference in the concentration of gold ions dissolved after only one acid leaching for copper removal and two acid leaching for copper removal.

The gold recovery step S6 is used to make the gold ions extracted into the solution form metallic gold and precipitate out of the solution, so as to facilitate separation and purification to obtain high-purity gold. In this embodiment, a strong oxidizing agent is used to break the bond of the gold thiosulfate ion, so that the gold ion cannot exist in a positive monovalent ion state, but can be reduced to a solid state. In this embodiment, the oxidizing agent can be hydrogen peroxide or perchloric acid, but not limited thereto; the volume ratio of the oxidizing agent and the thiosulfate mixed solution can be 1:45-55, preferably 1:50, and the oxidizing agent can be It is hydrogen peroxide or perchloric acid, but not limited thereto; when reducing gold ions, it can be reacted at room temperature for half an hour, and left to stand for 24 hours until the reaction reaches equilibrium, but not limited thereto.

Please refer to Fig. 5 to Fig. 8, in order to prove that hydrogen peroxide and perchloric acid can reduce gold ions in the solution to metallic gold, the inventor observed the precipitate after the reaction through a scanning electron microscope (Scanning Electron Microscope, SEM), And further use energy dispersive spectrometer (Energy Dispersive Spectrometer, EDS) to analyze the metal components in the precipitate. First, it can be seen from Figures 5 and 7 that there are many granular solids with metallic luster in the sediment; the brightness of metallic gold in the solid phase is much higher than that of metallic silver or copper, and most of them are in the form of tiny particles. form exists. Furthermore, it can be seen from Figure 6 and Figure 8 that the precipitate does contain metal components such as copper, silver, and gold, so it can be known that both hydrogen peroxide and perchloric acid can destroy the gold thiosulfate ion bond and reduce gold ions to metallic gold.

Beneficial effects of the embodiment

One of the beneficial effects of the present invention is that the method for recovering gold from waste printed circuit boards provided by the present invention can be achieved by "first performing microwave cracking on waste printed circuit boards, and then using sulfuric acid acid dipping solution to remove gold after microwave cracking. The copper component in the solid residue formed, and then use a thiosulfate mixture to dissolve gold ions from the solid residue from which most of the copper component has been removed, and finally use an oxidizing agent to reduce the gold ions in the gold-containing solution to metal Gold" technical solution to achieve beneficial effects such as no pollution, low cost, low energy consumption, and high recovery rate. It is suitable for mass recovery of waste printed circuit boards and has industrial application prospects.

The content disclosed above is only a preferred feasible embodiment of the present invention, and does not therefore limit the protection scope of the claims of the present invention. Therefore, all equivalent technical changes made by using the description of the present invention and the contents of the accompanying drawings are included in this document. within the protection scope of the claims of the invention.

Claims (10)

1. A method of recovering gold from waste printed circuit boards, characterized in that, the described method of recovering gold from waste printed circuit boards comprises: Microwave cracking of waste printed circuit boards; Using a sulfuric acid-based acid leaching solution to carry out acid leaching treatment on the solid residue formed after microwave cracking, so as to remove the copper component in the solid residue; Using a thiosulfate mixed solution to dissolve gold ions from the solid residue treated by acid leaching to obtain a gold ion-containing solution; and An oxidizing agent is added to the gold ion-containing solution, so that the gold ions form metallic gold. 2. The method for recovering gold from waste printed circuit boards as claimed in claim 1, wherein the waste printed circuit boards are subjected to microwave cracking at a microwave power of about 200W to about 400W. 3. the method for reclaiming gold from waste printed circuit boards as claimed in claim 1, is characterized in that, the number of times of using the described acid leaching treatment of described sulfuric acid acid leaching solution is twice, and each time described acid leaching The conditions of the immersion treatment include: the reaction temperature is 25-35° C., and the reaction time is 3-5 hours. 4. The method for recovering gold from waste printed circuit boards as claimed in claim 1, wherein the sulfuric acid-based pickling solution comprises sulfuric acid and hydrogen peroxide. 5. The method for recovering gold from waste printed circuit boards as claimed in claim 4, wherein the concentration of the sulfuric acid is 2-3M, and the concentration of the hydrogen peroxide is 30-35wt%. 6. The method for recovering gold from waste printed circuit boards as claimed in claim 1, wherein the conditions for using the thiosulfate mixed solution to dissolve gold ions include: the reaction temperature is 50-70°C, and the reaction temperature is 50-70°C. The time is 2-4 hours. 7. The method for recovering gold from waste printed circuit boards as claimed in claim 1, wherein said thiosulfate mixed solution comprises thiosulfate, copper sulfate and ammoniacal liquor. 8. the method for recovering gold from waste printed circuit boards as claimed in claim 7, is characterized in that, the concentration of described thiosulfate is 0.05-0.15M, and the concentration of described copper sulfate is 0.01-0.02M, The concentration of the ammonia water is 0.10-0.25M. 9. the method for recovering gold from waste printed circuit boards as claimed in claim 8, is characterized in that, described thiosulfate is sodium thiosulfate, potassium thiosulfate or ammonium thiosulfate. 10. the method for recovering gold from waste printed circuit boards as claimed in claim 9, is characterized in that, described oxidizing agent is hydrogen peroxide or perchloric acid, and wherein, described oxidizing agent and described thiosulfate mixed solution The volume ratio is 1:45-55.