Influence of waste plastic utilisation in blast furnace on heavy metal emissions

Abstract Waste plastics can be utilised in blast furnaces as an alternative reducing agent. However, the use of waste plastics also implies an additional input of heavy metals into the process. The present paper investigates the extent to which this increased input influences the emissions of heavy metals from blast furnaces. A multitude of measurements characterising the input and output flows of a full-scale blast furnace that utilised waste plastics over a period of 4 years have been analysed with respect to their contents of Mercury (Hg), Cadmium (Cd), Zinc (Zn) and Lead (Pb). The results of the study indicate that despite the fact that waste plastics were utilised only at a maximum rate of 35 kg/t HM (Hot Metal) (during the considered time period), they contribute significantly to the total input of Hg ( 54%) into the blast furnace. By contrast, waste plastics are of minor importance ( The results of further analyses indicate that the emissions of heavy metals to the atmosphere and the hydrosphere are completely independent from their input into the blast furnace. Thus, the usage of transfer coefficients to predict emission levels is (at least for minor flows such as emissions) inadequate. It has been shown that constant emission factors (describing the specific emission load of a heavy metal per unit hot metal), which are independent from the input of heavy metals, describe process emissions at least as well as transfer coefficients, which require detailed information about the input flow to predict emissions. This finding also implies that a certain increased input of heavy metals into a blast furnace does not necessarily increase its emissions, and thus, the usage of transfer coefficients would result in a significant overestimation of environmental burdens associated with plastic utilisation.