Study On Reutilization Of Nonmetals Reclamed From Crushing-Separating Waste Printed Circuit Boards

Waste printed circuit boards (WPCBs) are an important part of electronic waste (e-waste). The recycling of WPCBs is valuable as the purity of precious metals in WPCBs is more than 10 times higher than that of rich-content minerals. Mechanical process including crushing and separating is the main method for recycling WPCBs. A large number of nonmetals are generated when recycling metals. The treating methods for the nonmetals include incineration, landfill, or open dumping, resulting in environmental load and environmental pollution. Based on the principle of"waste-resource-product", this paper studied the reuse of the nonmetals reclaimed from crushed WPCBs by physical filling method. According to the components, particle sizes, shapes and other physical properties of the nonmetals, the nonmetals replacing wood flour or other materials were used to prepare 4 kinds of nonmetal products successfully, including phenolic molding compounds (PMC), wood plastic composites (WPC), nonmetallic plate (NMP), and nonmetals modified asphalt (NMA). The paper provided a theoretical basis and experimental data by investigating reaction mechanism, reinforcing mechanism, micro-interfacial morphology, and solidification of hazardous materials.The nonmetals mainly consisted of reinforcing materials and resin powder. Glass-nonmetals with particle size 0.3-0.15 mm, 0.15-0.125 mm and <0.07 mm were in the form of sheet, long rod, short-cut glass fibers and resin powder, respectively. Paper-nonmetals with particle size 0.3-0.125 mm and <0.07 mm were in the form of sheet and powder, respectively. The reinforcing characteristics of glass fibers and paper in the nonmetals provided the possibility of treating the nonmetals with filling methods.1. PMC filled with nonmetalsGlass-nonmetals and paper-nonmetals reclaimed from laboratory crushing and separating were used to replace wood flour in the production of PMC. Kinetic mechanism of curing process of PMC was studied by differential scanning calorimetry (DSC). Effects of filling content and particle size of the nonmetals on the properties of PMC were also studied. The results show the PMC with 40 wt % glass-nonmetals qualified the standard. To ensure sufficient properties of PMC, the optimal added content of paper-nonmetals is 20 wt %, which results in a flexural strength of 70 MPa, a charpy notched impact strength of 2.3 kJ/m2, a heat deflection temperature of 168°C, a dielectric strength of 3.9 MV/m, and a rasching fluidity of 103 mm, all of which meet the national standard data.2. WPC filled with nonmetalsThe nonmetals were used to replace wood flour in the production of WPC. The results show that filling of the nonmetals in WPC improves the flexural strength and tensile strength, and reduces screw withdrawal strength. The filling content of nonmetals in WPC can be up to 40 wt %. To evaluate property durability against weather exposure, the effects of accelerated aging process on the properties of WPC are investigated. After solid WPC with 40 wt % nonmetals (S-40-WPC) underwent aging process, S-40-WPC had a flexural strength of 21.6 MPa (before aging 23.4 MPa), a tensile strength of 7.7 MPa (before aging 9.6 MPa), a charpy impact strength of 4.35 kJ/m2 (before aging 3.03 kJ/m2), and face/edge screw withdrawal strength of 109/104 N/mm (before aging 121/115 N/mm).3. NMP made from nonmetalsA new kind of NMP was produced by adding unsaturated polyester resins and other additives into the nonmetals using a self-made hot-press former. Kinetic mechanism of resin curing was studied by DSC method, and molding parameters are determined. Effects of content and particle size of the nonmetals on the properties of NMP were also studied. The results show that the optimum molding conditions are as follows: top/bottom molding temperature are 140/135°C, molding time is 5 min. When the filling content of the nonmetals with particle size less than 0.07 mm was 20 wt %, NMP had a flexural strength of 68.8 MPa and impact strength 6.4 kJ/m2.4. Asphalt modified with nonmetalsThe nonmetals were reused as a new modifier to improve the performance of asphalt. The classical and rheological properties of unmodified asphalt and NMA were determined. Specifically, the effects of content and particle size on these properties were studied. When the filling content of the nonmetals with particle size from 0.09 to 0.07 mm was 25 wt %, the NMA had a viscosity of 1225 cP at 135°C, a penetration of 53.7 dmm at 15°C, a ring and ball softening point of 54°C, a ductility of 43.5 cm at 15°C, a G*/sinδof 3995.27 Pa at 60°C, and an upper limit temperature (G*/sinδ= 1 kPa) of 69.4°C, all of which showed that the high temperature performance of asphalt was improved significantly.Tests of volatile compounds (VOCs) released from nonmetal products show that the VOCs, such as phenol and styrene, were mainly originated from added compounds when producing nonmetal products. Leaching tests on nonmetal products show that Cu and Pb concentrations in the leachates were far below the standard limits. It indicates that filling method was safe and environmentally friendly for treating the nonmetals as the hazardous materials could be well solidified in the resin matrix.Nonmetal products with potential applications such as decking boards and sewage lids were successfully produced. The paper not only tackled the environmental problems caused by treating nonmetals with the methods of landfill, incineration or open dumping, but also achieved the comprehensive utilization of the nonmetals.