3 Chemical method
Chemical treatment technology is an extracting process based on different chemical stability for various components of PCB.
3.1 Heat treatment
Heat treatment is the separation of organic matter and metal by means of high temperature.It mainly includes incineration method, vacuum cracking method, microwave method and so on.
3.1.1 Incineration method
The incineration method is to break up the electronic waste to a certain particle size and send it to an incinerator for burning. The organic components are decomposed to separate the gas from the solid. The residue after incineration is the exposed metal or its oxide and glass fiber, which can be recovered by physical and chemical methods after being crushed. The gases containing organic components are discharged after combustion treatment in a secondary incinerator. The disadvantage of this method is producing a lot of waste gas and toxic substances.
Pyrolysis, also known as dry distillation in industry, is to heat the electronic waste in the container under the condition of air isolation, control the temperature and pressure, so that the organic material is decomposed into oil and gas, which can be recovered after condensation collection. Unlike the incineration of electronic waste, the vacuum pyrolysis process is carried out in the absence of oxygen, so the waste gas production is small and the environmental pollution is small.
3.1.3 Microwave processing technology
Microwave recovery method is to break up electronic waste, and then heat it by microwave to make organic decomposition. Heated to 1400 ℃ or so make glass fiber and metal melting to glass material, after this kind of material cooling,gold, silver and other metals are separated in the form of beads, recycling of the rest of the glass material can be used as building materials. This method is significantly different from the traditional heating method and has obvious advantages such as high efficiency, fast, high resource recovery rate and low energy consumption.
Hydrometallurgy technology is mainly to use the metal can be dissolved in nitric acid, sulfuric acid and royal water and other acid characteristics, metal is removed from electronic waste and recover from liquid phase. It is currently widely used in the treatment of electronic waste methods. Compared with fire metallurgy, hydrometallurgy has the advantages of less exhaust gas emission, easy disposal of metal residues after extraction, significant economic benefits and simple process flow.
Biotechnology is the utilization of microbial adsorption on mineral surface and microbial oxidation to solve the problem of metal recovery.Microbial adsorption can be divided into two types: fixation of metal ions by microbial metabolites and direct fixation of metal ions by microorganisms. The former is fixed by hydrogen sulfide generated by bacteria. When ions are absorbed on the surface of bacteria and reach saturation state, flocs can be formed and settle down.The latter is to use the oxidation of ferric iron ions to make other metals in precious metal alloys such as gold oxidize into soluble substances and enter the solution, so that the precious metal is exposed to facilitate recovery. Biotechnological extraction of gold and other precious metals has the advantages of simple process, low cost and convenient operation, but the extraction time is long and the extraction rate is low, so it has not been put into use