Investigation of the effect of chlorine in different additives on dioxin formation during high temperature processing...

Ironmaking can have an important role in the circular economy by utilising alternative carbon bearing materials, which are otherwise of low value in use or landfilled. Biomass and plastic wastes have been proposed as alternatives for coke and coal in sintering, blast furnace ironmaking and direct iron ore reduction processes. However, introduction of the alternative carbon sources with higher chlorine contents may influence the formation of some pollutants, most notably, dioxins. This study investigated the effects of carbon bearing materials, i.e., coke, biomass and polyvinyl chloride (PVC), on formation of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) during high temperature processing of iron ore. The effect of copper (Cu) as a known dioxin synthesis catalyst, on formation of the dioxins was also investigated. The study found an exponential increasing relationship between the chlorine content in the fuel source and the dioxin emissions. The addition of both biomass and PVC materials contributed to significantly increased dioxin formation, especially for the case of plastics. PCBs had higher concentrations than PCDD/Fs in all cases except when CuCl₂ was added due to its catalytic properties to synthesise PCDD/Fs. PCDF concentrations far outweighed the PCDDs, suggesting that de novo reaction mechanism, where carbon particles are oxidised by a transition metal in presence of chlorine, dominated the formation of the dioxins in the process.