Study On Emission Characteristics Of Polybrominated Diphenyl Ether From The Thermal Disassembly Of Waste Printed Circuit Boards

Waste printed circuit boards（WPCBs）,as the core components of almost all electronic and electrical waste（e-waste）,contain high recovery value but high harmfulness.Thermal disassembly is prevalently applied for the removal of electronic components on WPCBs.However,the harmful substances released from the WPCBs will limit the environmental development of e-waste recycling.Existing studies have mainly investigated the pollution of polybrominated diphenyl ethers（PBDEs）and heavy metals in the environmental media near the e-waste dismantling area,few studies were conducted on their emission characteristics.In this study,the emission characteristics of PBDEs and heavy metals from the thermal disassembly of WPCBs were studied by conducting bench-scale and pilot-scale experiments.Firstly,the thermal characteristics of different materials on WPCBs were investigated,and the PBDEs released from different materials at a same temperature were studied.The substrate,slot and the plastic skin of capacitor with poor thermal stability were important source of PBDEs during WPCBs dismantling.The concentration level of PBDEs emitted from the substrate was higher than the other two,which was main source of PBDEs.The released of PBDEs distributed in flue gas,liquid oil and solid residue,and flue gas was the main carrier for migration of PBDEs from WPCBs to the environment.The influence of temperature and structural changes on the emission level and composition of PBDEs was studied by taking the substrate as an example.PBDEs emission factors（EFs）increased with the increase of temperature.The EFs for∑₃₉PBDEs at 260^oC for the substrate fragments and substrate powder increased by 13 and 98 times compared to that observed at 100^oC,respectively.The EFs for∑₃₉PBDEs from substrate powder was 243.13～3365.44g/g,which was 4～30 times of the corresponding EFs from substrate fragments without structural damage.Mono-to tri-BDEs predominated the emission at each temperature and size,and higher proportion for those released from powders.A pilot-scale device was used to perform the thermal disassembly of complete WPCBs,and the emission characteristics of PBDEs and heavy metals（Sb,Pb,Zn,Cu,Cr,Cd）in the flue gas were studied.The particulate PBDEs dominated the generated flue gas.At 260^oC,the EFs for the gaseous∑₃₉PBDEs is 25.00ng/g,but the EFs for the particulate∑₃₉PBDEs is 649.08 ng/g.A bimodal distribution pattern for the particulate matter（PM）with peaks at 0.4-0.7 and 5.8-9.0μm was observed.At 100 and 150^oC,∑₃₉PBDEs were concentrated in coarse particles,while at 200 and 260^oC,∑₃₉PBDEs had a unimodal distribution pattern at 0.7-1.1μm.The highly brominated PBDEs（hexa-and hepta-BDEs）had a mass median aerodynamic diameter（MMAD）greater than 2.5μm,while the lightly brominated PBDEs（mono-to penta-BDEs）were mainly distributed in finer particles.The particle size distribution of PBDEs was significantly correlated with the distribution of semi-volatile and volatile organic carbon in PM.Heavy metal emission was increased with increasing temperature.The pollution status of Sb and Pb at high temperature was more prominent than that of other heavy metals.At 260℃,the total heavy metal emission level in PM₁₀ was 33.53g/m³,and the concentration from high to low was Sb>Pb>Zn>Cu>Cr>Cd.Pb,Cu and Cd were mainly distributed in fine particles,while Zn,Cr and Sb were concentrated on coarse particles.All these results can provide basic data and reference for the control measures of PBDEs and heavy metals from the thermal disassembly of WPCBs.