Research On The Recycling And Reutilization Of Printed Circuit Board Scraps

Information technology innovation and market expansion continue to accelerate the replacement of the equipment, which led to a significant increase of waste electric and electronic equipment (WEEE). The ever-increasing amount of WEEE exerts great impact on the ecological environment and has become a common problem facing to modern civilized society. As the primary components of electronic industry, printed circuit boards (PCB) are commonly found in almost all kinds of electronic products. Recently large quantities of PCB scraps have been generated at the fast rate of obsolescence of WEEE. Research on the reutilization and safe disposal of waste PCB has a great practical significance for its potential high value and environmental pollution.In this paper, the recycling process and reutilization of waste PCB have been studied. An effective and environmental friendly mechanical process including dismantling, crushing and classification has been developed to realize the metals and nonmetals in waste PCB reclaimed. In addition, the recovery of PCB substrate resin by hydrothermal treatment has also been preliminary explored.Based on the analyze of the structure and interface characteristics of PCB, a high speed hammer mill was employed to achieve metals liberation from waste PCB by the impact stress and shearing force of the crushing rings. The crushed products from the hammer mill were analyzed by sieving analysis and microscopic examination. The results show that when the discharge screen size is 2.0 mm, about 80 % of total metal contained in PCB is primarily distributed in the size range from 0.125 to 1.0 mm, while nonmetals are enriched in the fine fractions below 0.50 mm. Metal liberation degree increases with particle size decrease and the metals achieve satisfactory liberation at particle size below 0.80 mm. Selective comminution occurs in the crushing process, which provides an appropriate feed material for the subsequent separation.Metals recovery from crushed PCB powders has been studied using the specially designed gas-solid fluidization separation apparatus. The fluidization and separation characteristics of metals and nonmetals in crushed PCB powders were described in the fluidized bed. According to the particles separation principle in the fluidized bed, two operation modes including pneumatic separation and fluidization separation in bubble-fluidized bed were employed. The influence of the operating variables on separation effect such as feedstock amount, gas velocity has also been discussed.Relatively high metal concentrate and approximately 90% metal recovery can be obtained from the main size 0.125-0.80 mm fraction by pneumatic separation for the optimal operating conditions. Good fluidization could be achieved for the fine particles below 0.50 mm. For the fractions of 0.25-0.50 mm and 0.074-0.25 mm respectively, when the bed aspect ratio is 1.2 and separation time is 5min, the fluidized bed posses the best separation performance with a total metal recovery excess 90% at the gas velocity of 0.424 m/s, 0.226 m/s.The disposal status and reutilization technology of nonmetal material reclaimed from waste PCB are introduced. A physical method has been developed for reusing nonmetal powders as fillers for polymer. Polypropylene (PP) composites filled with nonmetal powders were prepared. The effects of filler size and content, the compatibilizer content on the mechanical performance and some physical properties of the composites were investigated. The composites with smaller filler size display better mechanical performance than those with larger filler size. The results show that maleic anhydride-grafted polypropylene (MAH-g-PP) could enhance the interfacial compatibility and adhesion between PP matrix and nonmetal fillers, leading to higher mechanical performance. Compared with the composites filled with traditional fillers, such as talc and CaCO₃ powder, composites filled with nonmetal powders exhibit light gravity, waterproof and high hardness besides the equivalent mechanical performance, which have a good application perspective.The decomposition behavior of PCB substrate resin in subcritical and supercritical water was explored in a batch reactor under N₂ atmosphere. The depolymerization products were analyzed by GC-MS, HPLC, TOC, SEM, respectively. The epoxy resin was decomposed to its monomers such as phenol, cresols, p-isopropylphenol by reactions in hot water in the temperature from 240 to 400℃. The solid residue contains glass-fiber and resin residue. The effect of catalyst concentration, temperature, reaction time and water volume on the yields of phenol, o-cresol, p-cresol and p-isopropylphenol were investigated. According to the resin molecular structure and the depolymerization products, the decomposition path for resin in hydrothermal condition has also been discussed.2-bromophenol has been chosen as the model component in order to explore the details of decomposition of brominated flame retardants in waste PCB during the hydrothermal process. Decomposition reaction and kinetics of 2-bromophenol in hot water were studied in the temperature from 250 to 350°C with a batch reactor. The results show that the debromination rate of 2-bromophenol can be accelerated significantly by increasing temperature and adding alkaline materials. With a first-order kinetics equation, the activation energies evaluated is 114.7 kJ/mol for the decomposition of 2-bromophenol in 0.1MNa₂CO₃ solution. This work demonstrates the possible use of hydrothermal treatment for the dehalogenation of waste halogen-containing plastics in WEEE recycling.