Waste Printed Circuit Boards and Edge Resource Technology

I. Foreword In response to the continued production of waste printed circuit boards in China and the increase in the number and compliance with the requirements of the Basel Convention, the control of exporting waste printed circuit boards will become increasingly severe in the future. Therefore, this paper will focus on the waste printed circuit board as the main object of discussion, at the same time on its composition, processing methods, etc. to introduce the content, looking forward to interested domestic industry reference.

Second, the characteristics of waste printed circuit board In general, the source of waste printed circuit board may be from the printed circuit board manufacturing process of defective products, edge materials, or may be from the relevant waste information products have been disassembled components of the printed circuit board. Its related composition is shown in Table 1. In addition, since the epoxy resin contains 10-20% of the bromine component, as a whole, waste printed circuit boards contain harmful heavy metals and bromine, and are classified as hazardous waste according to environmental protection laws. Relatively, processing is not easy. thing.

III. Resource-based technologies for the discussion of metal recycling technology for scrap metal scrap recycling can be divided into chemical treatment (such as scrubbing, dissolution, etc.), mechanical physical separation (such as flotation, etc.), and heat treatment (such as incineration, cracking, and treatment). Laws, etc.) If evaluated by technology, a description of each recycling process is given.

1. The squeegee method utilizes the squeegee method to recover the metal in the waste board trim. In the scrubbing method, waste scraps containing noble metals are treated with strong cesium or strong oxidants to obtain stripped precipitates of precious metals, which are then reduced to metal products such as gold, rhodium, and palladium, respectively. Detergents containing high concentrations of ions are obtained. Recyclable sulfur or electrolytic. However, due to the significant decrease in economic value, waste scraps and wastes containing ions that have been recovered from precious metals are dumped or buried arbitrarily, causing serious secondary pollution.

2. Erosion method The chlorination method is mainly used to recover the alloy substrate containing noble metal contacts. It is placed in a chlorinated solution, and the substrate is eroded under the control of the appropriate redox potential, but the precious metal remains insoluble. After recovery, the mother liquor (Chloride chloride) is oxidized by chlorine gas after being dissolved, and the chlorination solution is recycled. After the overflow liquid is recovered by replacing the powder, it is treated to make the tail fluid meet the emission standards. Chloride corrosion is widely used in the recovery of printed circuit boards and the treatment of precious metals should be feasible, and the dissolution rate is high, the only thing to pay attention to is that during the treatment process, the dissolution rate of the multilayer board after crushing and the dissolution efficiency of its inner layer Is the key.

3. Mechanical physical separation method uses mechanical crushing of waste printed circuit boards, followed by physical separation to collect metals and non-metals. The waste printed circuit board is first crushed and then passed through 10 mesh sieves. The metal phase and the non-metallic phase are collected by shaking the table and flotation, or the difference between the specific gravity of metal and non-metal is used in the crushing product, and the floatation method is used ( Float-Sink Method). The metal part of the chemical recovery method, such as the recovery of tin, after recovery, and then magnetic separation of magnetic metal and non-magnetic characteristics of gold, antimony, lead, etc.; non-metallic part can be used as a reinforcing material reuse.

4. The incineration method uses incineration to recover the metal in the waste board trim. Firstly, the waste material of the waste board is mechanically crushed and then sent to the incinerator for burning. The resin containing about 40% is decomposed and destroyed. The remaining waste is exposed metal and glass fiber, and after being crushed, it can be sent to the metal smelting. The factory carries out metal recycling. Because metal and glass fibers are in non-bonded state, they are suitable for recovery by wet or pyrometallurgical smelting. However, due to the waste of scrap as hazardous waste, the incineration process may generate bromine-containing waste gas. Therefore, the requirements for installation of incinerators and air pollution control facilities are more stringent.

5. Pyrolysis Pyrolysis is used to pyrolyze waste printed circuit boards to recover combustible oil and gas and metal materials. Like the incineration method, air pollution prevention and control facilities have high design and installation requirements. At present, the processing technology still needs to be considered again economically. Pyrolysis is the decomposition of organic matter (usually 350 to 900 degrees Celsius) in an oxygen-deficient environment. In the state of high temperature and oxygen deficiency, organic matter cracking reaction occurs. The larger molecule gradually generates molecules with lower molecular weight due to the breakage of intermolecular chemical bonds, forming liquid, gaseous and solid products. The products after thermal cracking are usually produced. There are four phases of gas, oil, carbon and water. After the cracking, the organic substances in the waste printed circuit boards are decomposed and volatilized, and the various components in the waste printed circuit boards are in a single state, and they can be easily separated and recycled by simple powder, magnetic separation, and eddy current separation. According to the type of waste and characteristics of the decision of the next recycling process. The volatile gas generated during the cracking process is discharged through the exhaust pipe of the reactor, and is subjected to oil-gas separation (condensation) to condense the condensable gas to oil. The non-condensable gas can be used as fuel after treatment, and The secondary combustion chamber stays at 1,000°C for 2 seconds, causing it to completely break and discharge.

6. The direct smelting method uses the direct smelting method to recover the metal in the waste board trim. The recycling process is shown in Figure 2. The incinerated waste blanks can be used as Anode Casting or Sintering raw materials, and the non-incinated waste blanks can also be directly used as roasting raw materials. After processing can be sent to the sintering process for processing.
According to the above, chemical waste treatment (such as washing, dissolution, etc.), mechanical and physical separation (such as flotation, etc.), heat treatment (such as incineration, pyrolysis, treatment, etc.), etc. Features. As for the evaluation of various technologies, it can be analyzed from the perspectives of “economic feasibility”, “recycling effect”, and “secondary hazard risk”. The so-called “economic feasibility” mainly focuses on equipment costs, operating costs, and recovery revenue. , environmental protection-related expenditures and other factors are considered; the so-called "re-recycling effect": mainly for the consideration of factors such as the effect of technology recovery and the degree of acceptance of its related resource products; the so-called "secondary hazard risk" is mainly aimed at the potential difficulty in pollution control. The results of the evaluation are shown in Table 2.

IV. Conclusion

In short, there is consensus that there is a need to recycle metals (eg, etc.) from waste printed circuit boards and edge materials. However, for 80-90% of the non-metallic parts, if we look at resources from the perspective of resource design and application, will work hard in the future. According to the analysis of domestic and international technological capabilities, waste printed circuit boards and edge materials can be reused on artificial wood and construction materials as long as they are pre-treated (eg, washed, dried, etc.) and passed the TCLP test standards. Waste and resource reuse purposes.

Source: Zheng Zhihe, China Recycling Metals