Selective bromination-volatilization of PbO from ZnO-PbO mixtures using bromine-containing plastic: A promising approach for recycling hazardous wastes

This study explores the potential of acrylonitrile butadiene styrene (ABS) resin, a bromine-containing plastic, for selectively separating PbO from a ZnO-PbO mixture. Thermodynamic calculations suggested the susceptibility of both PbO and ZnO to bromination by HBr from ABS resin. Initial trials showed limited PbO and ZnO volatilization. Combusting ABS resin and dust mixtures converts approximately 40 wt% of PbO to PbBr₂, but PbO volatilization selectivity remains below 30% due to concurrent ZnO volatilization. This low selectivity is due to the inhibiting effect of char and CO gas on PbBr₂ volatilization and the enhancement of ZnO volatilization. To improve PbO volatilization selectivity, operational parameters were varied. Increasing ABS resin size, decreasing pellet size, and altering the heating method raised PbO volatilization selectivity by over three times, with more than 60 wt% PbO volatilized. Microscopic analysis confirmed PbO bromination and volatilization as lead bromide compound (e.g., PbBr₂), while ZnO underwent direct volatilization through a carbothermic reaction. This study shows that optimizing operational parameters can selectively separate heavy metals using bromine-containing plastics. For practical application in steelmaking dust, it is crucial to examine the effects of coexisting Fe compounds.