TWI662135B - Method for recovering gold from waste printed circuit boards - Google Patents

Abstract

The invention discloses a method for recovering gold from a waste printed circuit board. First, the waste printed circuit board is subjected to microwave cracking, and then the solid residue formed by microwave cracking is subjected to acid leaching treatment using a sulfuric acid-based acid immersion liquid, and then, Gold ions are extracted from the solid residue subjected to acid leaching using a thiosulfate mixed solution to obtain a gold ion-containing solution, and finally, an oxidizing agent is added to the gold ion-containing solution to form gold ions into a metal. gold. Thereby, the reuse of gold in the waste printed circuit board can be realized.

Description

Method for recovering gold from waste printed circuit boards

The present invention relates to a method for recycling and recycling metal resources, and more particularly to a method for recovering gold from a waste printed circuit board.

With the development of technology, smart phones have become a necessity in daily life, and it has changed the way people live. According to statistics from International Data Information (IDC), in Taiwan, the average person replaces a mobile phone within two years. At such a high replacement rate, only a few of the eliminated mobile phones are directly recycled; according to the EPA, the waste mobile phone The recovery rate is actually less than 30%, resulting in an increase in the amount of electronic waste (E-Waste). If most of these electronic wastes are disposed of by burial or incineration, the harmful substances generated during the treatment will directly or indirectly cause harm to the human body and the environment.

With the current rare metal content in the world, it will be exhausted in about 20 to 30 years: due to the rapid accumulation of electronic waste, the recycling of electronic waste, and the acquisition of rare metals inside, will become the world's research. An important topic for development, this is the concept of Urban Mining proposed by Professor Nanjo Daofu, Institute of Mineral Processing, Tohoku University, Japan in 1988.

Urban mines mainly refer to the recycling of expired or outdated electronic products and small waste household appliances, such as mobile phones, digital cameras, computers, televisions and other equipment, and use of the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

The part of the waste mobile phone with recycling value is mainly printed circuit board (PCB); the composition of mobile phone printed circuit board generally includes precious metals, general metals, heavy metals and non-metals, among which precious metals (such as gold, silver, platinum, The economic value of palladium, etc. is much higher than other metals (such as copper, lead, aluminum, etc.). Today, the recycling of precious metals becomes very important as mineral resources are declining and demand is rising. Therefore, many literatures propose different process flows for the recovery of precious metals, mainly mechanical processing, pyrometallurgy and wet metallurgy.

The mechanical treatment is mainly based on the machine to discard the waste printed circuit board at high speed, and sorts according to the difference of material density, surface characteristics, electrical conductivity and magnetic properties. The advantage of mechanical treatment is low energy consumption, and the disadvantage is recycling. The obtained metal is not high in purity, and there are problems such as powder layer contamination and noise. Pyrometallurgy mainly uses metal incineration and melting to dissolve and separate metals from waste printed circuit boards. The advantage of pyrometallurgy is that the purity of the recovered metal is high, and the disadvantage is that the recycling process is very energy intensive. Wet metallurgy mainly uses a strong acid or a strong oxidizing solvent to dissolve and separate metal from waste printed circuit boards. The advantage of wet metallurgy is that the recovered metal has high purity, and the disadvantage is that waste acid is generated in the recycling process.

For the Waste Printed Circuit Board (WPCB), the method for recovering precious metals commonly used in factories is mainly combined with the processing steps of mechanical processing and wet metallurgy. However, in the cyanide stripping step, the cyanide used is a highly toxic compound, and a small amount of inhalation may be fatal, and the cyanide-containing waste liquid easily forms a complex with many metalloids, which causes Difficulty in handling; in the acid dissolution step, the solvent used is mostly aqua regia. Since the aqua regia itself is a strong acidic solvent, the pH of the waste liquid is between 1 and 2, and it needs to be treated. Neutralization of waste liquid to neutral, which also causes difficulty in handling; In addition, toxic gases are emitted during the recycling process, causing air pollution problems. Current recycling methods have a negative impact on human health and the environment.

The technical problem to be solved by the present invention is to provide a method for recovering gold from a waste printed circuit board which has both environmental and economic benefits in view of the deficiencies of the prior art.

In order to solve the above technical problem, one of the technical solutions adopted by the present invention is: a method for recovering gold from a waste printed circuit board, comprising: performing microwave cracking on a waste printed circuit board; using a sulfuric acid-based acid immersion liquid for microwave The solid residue formed after the cracking is subjected to an acid leaching treatment to remove the copper component in the solid residue; the gold ion is dissolved from the solid residue subjected to the acid leaching treatment using a thiosulfate mixed solution to obtain a gold ion-containing solution; and an oxidizing agent added to the gold ion-containing solution to form gold ions to form metal gold.

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

In an embodiment of the invention, the number of times of the acid leaching treatment using the sulfuric acid-based acid immersion liquid is two, and the conditions of the acid immersion treatment each time include: the reaction temperature is 25-35 ° C, Preferably, it is 30 ° C, and the reaction time is 3-5 hours, preferably 3 hours.

In an embodiment of the invention, the sulfuric acid acid leaching solution comprises sulfuric acid and hydrogen peroxide.

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

In an embodiment of the invention, the conditions for dissolving the gold ions using the thiosulfate mixed solution include: the reaction temperature is 50-70 ° C, preferably 60 ° C, and the reaction time is 2-4 hours, preferably 2 hours.

In an embodiment of the invention, the thiosulfate mixture comprises thiosulfate, copper sulfate, and aqueous ammonia.

In an embodiment of the invention, the concentration of the thiosulfate is 0.05 to 0.15 M, preferably 0.1 M, the copper sulfate concentration is 0.01 to 0.02 M, preferably 0.015 M, and the aqueous ammonia concentration is 0.10 to 0.25 M, preferably 0.2 M.

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

In an embodiment of the invention, the oxidizing agent is hydrogen peroxide or perchloric acid, wherein a volume ratio of the oxidizing agent to the gold ion-containing solution is 1:45-55, preferably 1:50.

In an embodiment of the invention, before the step of performing microwave cracking on the discarded printed circuit board, the method further comprises: first cleaning the discarded printed circuit board, and then cutting the discarded printed circuit board into an appropriate one. size of.

One of the beneficial effects of the present invention is that the method for recovering gold from a waste printed circuit board provided by the present invention can be carried out by "micro-cracking a waste printed circuit board first, and then removing the microwave cracking by using a sulfuric acid-based acid immersion liquid. Forming the copper component in the solid residue, then using the thiosulfate mixture to dissolve the gold ions from the solid residue from which most of the copper component is removed, and finally using the oxidizing agent to reduce the gold ions in the gold-containing solution to metal The technical solution of “Golden” is beneficial to non-polluting, low cost, low energy consumption and high recovery rate. It is suitable for large-scale recycling of waste printed circuit boards and has industrial application prospects.

For a better understanding of the features and technical aspects of the present invention, reference should be made to the detailed description and drawings of the invention.

S1 to S6‧‧‧ steps

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing the steps of a method for recovering gold from a waste printed circuit board of the present invention.

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

Figure 3 shows the waste printing after cracking at 150W and 350W microwave power. SEM photograph of the solid residue of the board.

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

Figure 5 is a SEM photograph of a precipitate formed by the recovery of gold ions using hydrogen peroxide.

Fig. 6 shows the results of EDS component analysis of a precipitate formed by recovering gold ions using hydrogen peroxide.

Fig. 7 is a SEM photograph of a precipitate formed by recovering gold ions using perchloric acid.

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

From the metal content point of view, the printed circuit board is like a piece of ore. In the case of a decreasing amount of ore, if valuable metals such as gold, palladium and other precious metals can be recovered from discarded printed circuit boards, environmental and economic benefits can be created at the same time. Accordingly, the present invention provides an innovative method that both reduces environmental pollution and increases gold recovery.

Referring to FIG. 1, the present invention provides a method for recovering gold from a waste printed circuit board, comprising at least a cleaning step S1, a cutting step S2, a microwave cracking step S3, an acid leaching step S4, and a gold extraction step S5. And gold recovery step S6. The sources of discarded printed circuit boards mentioned in this article are mainly "electronic waste" or "e-waste", such as: computers, smart phones, cameras, digital cameras, multi-function machines, game consoles, players. Etc., has reached the end of its useful life or has been disposed of due to other factors.

The following is a description of an embodiment of the present invention relating to a "method of recovering gold from a waste printed circuit board" by a specific embodiment, and those skilled in the art can understand the advantages and effects of the present invention from the contents disclosed in the present specification. The invention may be embodied or applied by other different embodiments, the details of the specification. The various modifications and changes can be made without departing from the spirit and scope of the invention. In addition, the drawings of the present invention are merely illustrative and are not intended to be stated in the actual size. The following embodiments will further explain the related technical content of the present invention, but the disclosure is not intended to limit the scope of the present invention.

The cleaning step S1 is for removing the dirt (such as fine dust particles) attached to the discarded printed circuit board, and the cutting step S2 is for cutting the cleaned printed circuit board to an appropriate size, for example, 2.4 cm × 3 cm. Sheet, but not limited to this. In this embodiment, the clean printed circuit board is cleaned by using clean water (such as deionized water), so the residual moisture needs to be removed after cleaning; the residual moisture can be removed by first soaking the discarded printed circuit board. In high volatile organic solvents, such as: isopropanol (IPA), methanol, ethanol, acetone, etc., and applying ultrasonic vibration to the organic solvent to accelerate the replacement rate between the solvent and the clean water, and then to waste printing The board is dried, for example, by placing the waste printed circuit board in an oven at 105 ° C to evaporate the organic solvent. Incidentally, the above organic solvent contributes to carrying away residual moisture on the waste printed circuit board because the surface tension is lower than that of clean water and the volatility is higher than that of high-purity water.

The microwave cracking step S3 is used to separate the layered structures of the waste printed circuit boards, so that the layers are clearly separated from each other, thereby improving the effect of subsequent acid leaching. In order to find a better microwave condition, the inventors first conducted a Thermal Gravimetric Analysis (TGA) on a waste printed circuit board to understand the cracking temperature of the organic matter in the plate, and the results are shown in Fig. 2, among which three weight loss curves The change rate of weight loss rate (wt%/°C) at a heating rate of 10 ° C / min, 20 ° C / min and 30 ° C / min, respectively. It can be seen from Fig. 2 that the maximum peak value of the three weight loss curves occurs between about 340 ° C and 360 ° C, which means that the thermal cracking reaction of organic matter mainly occurs in this temperature range.

Referring to Table 1 below, the inventors further analyzed the temperature rise of the discarded printed circuit boards at 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 first temperature. Linear regression values from minutes to 10 minutes. As shown in Table 1, when the microwave power is 150 W, the temperature of the discarded printed circuit board rises only slowly, and the highest temperature is about 280 °C. When the microwave power reaches 200W or more, the temperature rise of the discarded printed circuit board is obviously improved, and the temperature tends to be stable within 10 minutes, no sharp change occurs; thus, it can be inferred that the minimum wattage required for cracking That is 200W.

Referring to FIG. 3(a), the solid residue of the discarded printed circuit board obtained after cracking at a microwave power of 150 W is still intact, and the interlayer separation phenomenon is not obvious. Referring to Figure 3(b), the solid residue of the discarded printed circuit board obtained after cracking at a microwave power of 350 W has a very significant interlayer separation. It is worth noting that the temperature of the waste printed circuit board can be raised to about 400 ° C under the microwave power of 350 W. It can be known from the previous thermogravimetric analysis that this temperature can ensure the stable thermal cracking reaction; therefore, 350 W The microwave power is a preferred condition for the microwave cracking step S3.

The acid leaching step S4 is for extracting copper ions from the solid residue of the waste printed circuit board to remove the copper component in the solid residue as completely as possible, thereby improving the effect of subsequent gold extraction. In this embodiment, the solid residue is subjected to acid leaching treatment using a sulfuric acid-based acid immersion liquid; in the acid leaching treatment, the reaction temperature may be 25-35 ° C, preferably 30 ° C, and the reaction time may be 3-5 hours. Good for 3 hours, but not limited to this. In order to find a better acid leaching condition, the inventors tested the dissolution effect of different sulfuric acid-based acid immersion liquids on the copper component in the solid residue, and the results are shown in Table 2 below. It can be seen from Table 2 that hydrogen peroxide (H ₂ O ₂ ) can promote the copper dissolution reaction of sulfuric acid, and the dissolution rate of copper can reach 95% under the synergy of 2M sulfuric acid and 30wt% hydrogen peroxide. Above, that is, more than 95% of the copper in the solid residue can be effectively separated into the solution. In the present embodiment, the concentration of sulfuric acid contained in the sulfuric acid-based acid immersion liquid may be 2-3 M, and the concentration of hydrogen peroxide may be 30-35 wt%.

Furthermore, referring to FIG. 4, after 30 minutes from the start of the acid leaching treatment, the dissolution rate of copper is about 72%, and the final dissolution rate can reach about 86% or more. It can be seen 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 for extracting gold ions from the acid residue-treated solid residue to facilitate subsequent gold recovery. In this embodiment, the thiosulfate mixed solution is used to dissolve the gold ions; when the gold ions are dissolved, the reaction temperature may be 50-70 ° C, preferably 60 ° C, and the reaction time may be 2-4 hours, preferably. It is 2 hours, but is not limited to this. Further, the thiosulfate mixture solution comprises thiosulfate, copper sulfate and ammonia, wherein the thiosulfate may be sodium thiosulfate, potassium thiosulfate or ammonium thiosulfate, and preferably thio. Ammonium sulfate. The concentration of thiosulfate may be from 0.05 to 0.15 M, the concentration of copper sulfate may be from 0.01 to 0.02 M, and the concentration of aqueous ammonia may be from 0.10 to 0.25 M. It is worth noting that the synergistic effect of 0.1M ammonium thiosulfate, 0.015M copper sulfate and 0.2M ammonia water can achieve a dissolution rate of 99%, that is, more than 99% of the solid residue. Gold can be effectively separated into solution, and gold ions can form stable thiosulfate gold mision (Au(S ₂ O ₃ ) ₂ ^3- ) with thiosulfate ion, even if it is commonly used to extract and separate precious metals. Extractants such as di(2-ethylhexyl)phosphoric acid (D2EHPA), tributyl phosphate (TBP), dibutyl carbitol (DBC), trioctylamine, etc., are also unable to extract gold ions from solution. Extraction separation.

Incidentally, although gold water can be extracted from the solid residue by using aqua regia, the gold ion exists in the form of AuCl ₄ ^- , that is, the gold ion exists in a positive trivalent ion state, and its stability is poor and it is easy to be The extractant is adsorbed by a bond. In addition, because of its corrosiveness, Wangshui has great difficulties in subsequent processing.

Preferably, the method performs the gold extraction step S5 after performing the acid leaching step S4 twice to avoid the presence of copper ions to cause subsequent gold extraction. Experiments have shown that the concentration of gold ions eluted by acid leaching only two times and two times after acid leaching of copper has a concentration difference of nearly five times.

The gold recovery step S6 is for forming gold metal extracted into the solution to form metal gold, and precipitating from the solution to facilitate separation and purification to obtain a high purity gold element. In this embodiment, a strong oxidizing agent is used to destroy the bond of the thiosulfate gold mision, so that the gold ion cannot exist in the positive monovalent ion state, and can be reduced to a solid state. In this embodiment, the oxidizing agent may be hydrogen peroxide or perchloric acid, but is not limited thereto; the volume ratio of the oxidizing agent to the gold ion-containing solution may be 1:45-55, preferably 1:50, and the oxidizing agent may be Hydrogen peroxide or perchloric acid, but is not limited thereto; when the gold ion is reduced, it can be reacted at room temperature for half an hour, and allowed to stand for 24 hours until the reaction reaches equilibrium, but is not limited thereto.

Referring to FIG. 5 to FIG. 8 , in order to prove that hydrogen peroxide and perchloric acid can reduce gold ions in the solution to metal gold, the inventors observed the precipitate after the reaction by Scanning Electron Microscope (SEM). And further analyzing the metal component in the precipitate by using an Energy Dispersive Spectrometer (EDS). First, as can be seen from Fig. 5 and Fig. 7, there are many granular solids with metallic luster in the precipitate; in the solid phase, the brightness of metallic gold is much higher than that of metallic silver or copper, and mostly with fine particles. Form exists. Furthermore, as can be seen from Fig. 6 and Fig. 8, the precipitate does contain metal components such as copper, silver, gold, etc., and it can be known that both hydrogen peroxide and perchloric acid can destroy the gold thiosulfate ion. Bond, The gold ions are reduced to metal gold.

[Advantageous Effects of Embodiments]

One of the beneficial effects of the present invention is that the method for recovering gold from a waste printed circuit board provided by the present invention can be carried out by "micro-cracking a waste printed circuit board first, and then removing the microwave cracking by using a sulfuric acid-based acid immersion liquid. Forming the copper component in the solid residue, then using the thiosulfate mixture to dissolve the gold ions from the solid residue from which most of the copper component is removed, and finally using the oxidizing agent to reduce the gold ions in the gold-containing solution to metal The technical solution of “Golden” is beneficial to non-polluting, low cost, low energy consumption and high recovery rate. It is suitable for large-scale recycling of waste printed circuit boards and has industrial application prospects.

The above disclosure is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Therefore, any equivalent technical changes made by using the present specification and the contents of the drawings are included in the application of the present invention. Within the scope of the patent.

Claims (3)

A method for recovering gold from a waste printed circuit board, comprising: performing microwave cracking on a waste printed circuit board using a microwave power of about 200 W to about 400 W; and performing acid on a solid residue formed by microwave cracking using a sulfuric acid-based acid immersion liquid Immersing to remove the copper component in the solid residue, wherein the sulfuric acid-based acid leaching solution comprises sulfuric acid having a concentration of 2-3 M and hydrogen peroxide having a concentration of 30-35 wt%, and the conditions of the acid leaching treatment include The reaction temperature is 25-35 ° C, and the reaction time is 3-5 hours; the gold ion is dissolved from the solid residue of the acid leaching treatment using a thiosulfate mixed solution to obtain a gold ion-containing solution, wherein The thiosulfate mixture solution comprises a thiosulfate having a concentration of 0.05-0.15 M, a copper sulfate having a concentration of 0.01-0.02 M, and an aqueous ammonia having a concentration of 00.10-0.25 M, and the conditions for extracting the gold ions include: a reaction temperature. a reaction time of 2-4 hours at 50-70 ° C; and an oxidizing agent added to the gold ion-containing solution to form gold ions, wherein the oxidizing agent is hydrogen peroxide or perchloric acid, and Oxidant and The volume ratio of the gold ion-containing solution is 1:45-55. A method of recovering gold from a waste printed circuit board according to claim 1, wherein the number of times of said acid leaching treatment using said sulfuric acid-based acid immersion liquid is two. A method of recovering gold from a waste printed circuit board according to claim 1, wherein the thiosulfate is sodium thiosulfate, potassium thiosulfate or ammonium thiosulfate.