Heavy metals dispersion during thermal treatment of plastic bags and its recovery

One of the main worries for thermal treatment of plastic bag (PB) is the air pollution resulting from heavy metal (HM) evaporation and emission. The quest of the study was to investigate their fate during thermal treatment varying with temperature and atmosphere to explore the appropriate treatment technology. Four commonly consumed polymer bags such as PE, HDPE, LDPE and PVC were selected for the analysis. The elemental compositions, heating values and total metal contents of the samples were measured by an elemental analyzer, a sulphur/halogen analyzer, a bomb calorimeter and an ICP-OES, respectively. Thermal treatments of the samples were conducted in a tube furnace at 350, 550, 650, 750, and 850 °C with 1 L/min air or N₂ gas flow, respectively. 5% HNO₃/10% H₂O₂ solution was used for absorbing metals from gas phase, and then HM distributions both in flue gas and bottom ash were determined. Results revealed that the lower heating values of HDPE, LDPE, PVC and PE bags were 33.32, 34.28, 24.82 and 36.7 MJ/kg, respectively indicating energy recovery potential. Thermal treatment showed the maximum mass reduction (>90%) of PB at 850 °C. The higher percentage of metals was distributed in ash at initial temperature that promoted to gas with rise of temperature. The used absorption solution exhibited tremendous quantity of metals recovery. However, there was no significant difference between using air and N₂ gas flow during treatment of PB.