Sylwia Oleszek-Kudlak

Vaporization of zinc during thermal treatment of ZnO with tetrabromobisphenol A (TBBPA)

In the present work we investigate the vaporization of zinc or its compounds during thermal treatment of ZnO with tetrabromobisphenol A. Samples of 2g of ZnO:TBBPA (3.34:1) were isothermally heated in a laboratory-scale furnace at temperatures from 490 °C to 950 °C, and the solid, condensed and gaseous products formed were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. The results obtained indicate that the vaporization of ZnBr(2) formed strongly depends on heating time and temperature, yet is restrained by char, if formed with sufficient yield (above 15 wt%). Starting from 850 °C, this char commences carbothermic reduction of any remaining ZnO, which from then begins to evaporate as zinc metal vapor. Volatilization of zinc is completed at 950 °C. The presence of 5 vol.% of oxygen has no significant effect on the vaporization of formed ZnBr(2), the carbothermic reduction or the volatilization of metallic zinc. Strongly oxidizing conditions (20 vol.% of oxygen), however, boost the oxidation of char and thus the vaporization of ZnBr(2), but prevent carbothermic reduction of any un-reacted ZnO by depleting this char.

Influence of Temperature and Heating Time on Bromination of Zinc Oxide during Thermal Treatment with Tetrabromobisphenol A

Our prior research indicates that hydrogen bromide (HBr) evolved during thermal decomposition of tetrabromobisphenol A (TBBPA) can be utilized as a reagent for selective bromination and evaporation of zinc oxide. The present work investigated dependency of the bromination reaction on time at selected temperatures using a laboratory-scale furnace. The formed solid, condensed, and gaseous products were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. Results indicate that the bromination rate is strongly dependent on heating time. This dependency is a direct consequence of progress in the decomposition of TBBPA, which provides inorganic bromine suitable for the reaction. The bromination rate increases with time until the bromine source is depleted. The process is shorter at higher applied temperatures and appears instantaneous at 310 degrees C and above. However, the maximum bromination yield is independent of the applied conditions and ranges from 64 to 70%. Additionally, the influence of oxidizing conditions on the bromination reaction and the effect of ZnO on decomposition of TBBPA were investigated in this study.

Alternative Method for Pyrometallurgical Recycling of EAF Dust Using Plastic Waste Containing Tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA) is the largest volume brominated flame retardant (BFR) in production today, used in more than 70% of the world’s electronic and electric (E&E) appliances as well as in many plastics, textiles and so forth. There is constant growth in the production of such products and they become obsolete quickly, this generates huge amounts of BFR-containing wastes and causes significant problems for their safe disposal and recycling. The most common way to use them is in thermal processing. TBBPA easily decomposes during this process, generating significant amounts of gaseous HBr. The HBr is present mostly in the flue gas and can act as a bromination agent for selective bromination-evaporation of heavy metals present in co-combusted metallurgical dusts, like zinc and lead-rich electric arc furnace (EAF) dust. EAF dust, though classified by various government regulatory agencies as hazardous waste, is considered a valuable secondary raw material in the production of zinc. The worldwide generation of EAF dust represents a possible recovery of approximately 1.4 million tons of zinc. Thus the co-combustion of the mixed wastes can be chance for simultaneous recovery of both, energy from waste plastics and inorganic fractions from the dust, while the separated iron oxide-rich residues can be used as iron-making and steelmaking resources. In this study, a laboratory-scale furnace was used to investigate (1) the reactivity of zinc with the product of the thermal decomposition of TBBPA, and effect of (2) temperature on the efficiency of the bromination and vaporization processes.