Current situation of e-waste recycling technology

2022-08-14
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Current situation of "e-waste" recycling and treatment technology at home and abroad

at present, e-waste has posed a great threat to the environment of various countries. Most European countries have established corresponding recycling systems. In Germany, the scale of electronic waste recycling and treatment enterprises is generally small, most of which are professional recycling and treatment companies of municipal systems, professional recycling and treatment companies of manufacturers, professional recycling and treatment companies of society, professional hazardous waste recycling companies, etc. In the United States, the recycling industry of electronic waste has been formed, with a total of more than 400 companies, mainly including specialized companies, non-ferrous metal smelters, municipal solid waste treatment enterprises, electronic product manufacturers (OEMs) and dealers

the treatment process of electronic waste is as follows:

classified recycling and disassembly

classified recycling and disassembly of electronic waste usually means that electronic waste is transported to the disassembly company after classified recycling, and then disassembled into various fragments by the disassembly company. At the sterman technology center in Sweden, electronic waste is first roughly divided into five parts: large metal parts, polychlorinated biphenyls, packaging materials, plastic parts and cathode ray tubes, and then further divided into more than 70 different fragments. In the process of disassembly, those that can be repaired or upgraded, such as memory chips and integrated circuit boards, will extend their service life and be reused; The parts containing harmful substances, such as mercury switches, nickel cadmium batteries and capacitors containing polychlorinated biphenyls, can be removed in advance and treated separately after passing the reliability test. The content of precious metals is the basis to measure the value of electronic waste. Electronic waste with high value has more precious metals, such as polychlorinated biphenyls in computers; Low value electronic waste contains less precious metals, such as polychlorinated biphenyls in televisions and video recorders. However, regardless of the value of electronic waste, the treatment process is basically the same

recovery of metals in electronic waste

the recovery process of metals in electronic waste is relatively complex. Usually, metals and impurities are separated through high temperature, and then various metals are refined through several corresponding processing processes. Precious metals such as copper, gold, silver, platinum and palladium in electronic waste are generally recycled through converter processing. The recycling process of electronic waste containing precious metals from Boliden company in Sweden and Noranda company in Canada is [Zhang Weigang, Wu Fengshun, Wu Yiping, an Bing, he Jinqiang, 2006]:

1) melting:

different electronic waste after sampling is evenly mixed and added to the furnace as raw materials. Some fuel needs to be added at the beginning of incineration. When the furnace temperature is 1200 ℃ ~ 1250 ℃ and the energy contained in polychlorinated biphenyls is 35 ~ 36gj/T, the processing process can be maintained by the energy released by the organics contained in polychlorinated biphenyls. In the smelting process, the combustion of plastics and the oxidation of metal aluminum will release heat. In order to control the smelting temperature not to be too high, silicate needs to be added, and the amount of plastic needs to be controlled at the same time. In the smelting process, the top layer of molten electronic waste is slag and the bottom layer is copper. Copper and a little slag flow into the converter, and the remaining slag and ore are used to recover some precious metals through flotation. Finally, the remaining slag is stacked in the residue, which can be further concentrated and refined to recover precious metals

2) refining:

copper from the furnace is added to the converter for mixed refining, and the iron and sulfur in the copper are melted by blowing oxygen, so as to purify the copper, and silicate is added to form slag, with a temperature of about L200 ℃. The refining process of the converter is an exothermic process, and the oxidation process can provide enough heat to make the converter operate. The upper slag mainly includes iron and zinc; The lower layer is blister copper or white copper. The slag can be further purified to get by-products iron sand and zinc slag, and then iron and zinc can be obtained by processing iron sand and zinc slag in electric furnace. The metal dust obtained from the industrial waste gas produced in the converter after treatment can be recycled

3) electrolysis:

anode copper is cast from blister copper (98% copper) obtained in the converter, that is, the so-called anode casting is convenient to use, and the formed anode copper contains 99% copper and 0.5% precious metal. The copper electrode is purified by electrolysis, using sulfuric acid and copper sulfate as electrolyte, and the DC current during processing is about 20000 amps. Generally, 99.99% pure copper can be obtained on the cathode plate, while precious metals and impurities remain on the anode plate as attachments of the anode, which can be further refined. Precious metals are refined in refineries, and gold, silver, platinum and palladium are renewable

in the processing process, the anode attachment is leached, and the copper sulfate and tellurium are obtained from the solution containing copper telluride and nickel sulfate. The residue is dried and then refined in the precious metal furnace. In the smelting process, selenium is first recycled, and the rest is cast into a silver anode and then electrolyzed under high-strength current to obtain high-purity silver and gold slime. Filtering the gold slime can precipitate the impurities containing gold, palladium and platinum. Recovery process of tin and lead in the smelting process, 75% - 80% of lead comes from solder. In the process of ant solder, 15% - 20% of lead evaporates with industrial waste gas, and about 5% of lead remains in slag with the continuous improvement of environmental protection requirements of the government and the public. It can be obtained when copper and other precious metals are recovered by flotation. In Kaldor furnaces (lead furnaces), lead is present in industrial waste gas or slag. Lead in slag can be captured in copper process; Most of the lead in the industrial waste gas is directly or indirectly introduced into the converter through the gas processing plant. With the evaporation of the industrial waste gas, 99.9% of the lead will be captured in the gas filtration device as dust. About 90% of tin is fed into the copper converter from the Kaldor furnace, and most of it will be discharged with industrial waste gas. The recovery path of tin in industrial waste gas is the same as that of lead, and most tin is captured by the filter as dust

recycling and treatment of non-metallic materials in electronic waste

the non-metallic components contained in electronic waste are mainly resin fibers, plastics and glass. The organic substances contained in the PCB substrate, including resin fibers, are used as fuel in the Kaldor furnace to generate calorific value to maintain the furnace temperature, and the final slag can be used as road building materials. Plastic mainly comes from the shell parts of computers, televisions, washing machines, etc. after melting, it can be used as raw materials for new products, or as fuel. Glass mainly comes from cathode ray tube displays. Because it contains lead, glass is classified as dangerous goods. Some companies use broken display glass to make new cathode ray tubes. Landfill, incineration or pyrolysis gasification technology is often used in non-metallic treatment

landfill technology

landfill technology is a simple waste treatment method, which can treat all kinds of waste, and it has been a scene for a time. But with the passage of time and the development of technology, its shortcomings began to be exposed one by one. Landfilling takes up a lot of land, and most landfills do not have strict anti leakage measures of more than 7 floors, and are exposed to relatively open spaces for a long time. With the infiltration of rainwater, the exudate of electronic waste will pollute groundwater and soil, including non chlorinated aromatic compounds such as naphthalene, chlorinated aromatic compounds, phosphates, phenolic compounds and aniline compounds that are difficult to degrade at the 2016 National Conference on scientific and technological innovation; It also contains a large number of metal ions, including iron ion concentration of 2050mg/l, lead ion concentration of 12.3 mg/l, zinc ion concentration of 130 mg/l and calcium ion concentration of 4200 mg/L. [Wang Jinhui, Wang Yonghui, 2005 2] at the same time, the gas generated by garbage stacking seriously affects the air quality around the site. In recent years, some cities have recognized these problems and established a number of high-level landfill plants, which have better solved the problem of secondary pollution, but it has brought other problems - large construction investment, high operating costs. The most critical thing is that the treatment capacity of the landfill is limited. After the service period expires, it still needs to invest in the construction of a new landfill to further occupy land resources. For these reasons, since the 1980s, the landfill facilities in foreign countries have gradually reduced and become an auxiliary method of other treatment processes, mainly used to deal with substances that can not be reused

incineration technology

incineration is a traditional waste treatment method. From the ancient Mayans to today's society, incineration still occupies an important position in waste treatment methods. By incinerating garbage to generate electricity, the volume of garbage is minimized and new energy is generated. Modern waste incineration technology was born several decades ago and was once the first choice of many big cities in the world. In Japan, the Netherlands, Switzerland, Denmark, Sweden and other countries, it has become the main means of waste treatment. 80% of Swiss waste is incinerated, and more than 70% of Japanese and Danish waste is incinerated. But decades after incineration plants bloomed everywhere in developed countries, people found dioxin, which is more terrible than garbage disaster. This toxic gas caused people and animals to suffer from cancer. Dioxin is a kind of chlorinated organic compounds, namely polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzo furan (PCDF) and their homologues (PCDDs and PCDFs). It can exist in gas and solid forms, with high chemical stability, difficult to dissolve in water, stable to acid and alkali, not easy to decompose, not easy to burn, easy to dissolve in fat, almost no excretion after entering the human body and accumulated in fat and liver. It is not only carcinogenic, but also reproductive toxicity, immunotoxicity and endocrine toxicity. Among them, the most toxic is 2,3,7,8-TCDD, which is 500 times more toxic than brucine and 1000 times more toxic than cyanide. [Gao Ningbo, Li Aimin, Chen Ming, 2006]

so in the late 1980s, researchers in Europe and Japan began the research and development of "third generation" waste treatment technology. The governments of many developed countries have announced new and stricter waste discharge standards, and the Japanese government has decided to gradually close more than 1800 existing incineration plants within a few years. [Zhang Qinghong, 2006]

pyrolysis and gasification technology

the third generation of waste treatment technology - pyrolysis and gasification technology is a new waste disposal method developed on the basis of incineration, which combines pyrolysis and gasification with melting and solidification. It has achieved harmlessness, significant volume reduction, extensive material adaptability and efficient energy and material recovery. In the mid-1990s, it began to be popular in developed countries

gasification and melting technology is to vaporize garbage in a reducing atmosphere of 450 ~ 600 ℃, produce combustible gas and residues that are easy to recover iron, aluminum and other metals, and then burn combustible gas to melt carbonaceous ash at 1350 ~ 1400 ℃. The whole process combines low-temperature gas and high-temperature melting. It is different from incineration in the traditional sense. It decomposes a large number of urban domestic waste - waste electrical appliances, computers, batteries, printer cartridges, ink cartridges, disposable infusion and injection products discarded in hospitals, and a large amount of domestic waste into steam at high temperature, thereby generating new heat energy to generate electricity and heat

compared with traditional incineration technology, gasification and melting technology has many advantages: first, it can minimize the volume and quantity. The gasification and melting technology enables the combustible components in the garbage to be decomposed at high temperature, and the compactness of the slag is greatly improved, which can reduce the volume by about 70% and the weight by more than 85%; Secondly, low dioxin emissions can be achieved. At present, the dioxin emission standard of the world's most advanced incineration facilities

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