Mariusz Grabda

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.

Distribution of copper, silver and gold during thermal treatment with brominated flame retardants

The growing consumption of electric and electronic equipment results in creating an increasing amount of electronic waste. The most economically and environmentally advantageous methods for the treatment and recycling of waste electric and electronic equipment (WEEE) are the thermal techniques such as direct combustion, co-combustion with plastic wastes, pyrolysis and gasification. Nowadays, this kind of waste is mainly thermally treated in incinerators (e.g. rotary kilns) to decompose the plastics present, and to concentrate metals in bottom ash. The concentrated metals (e.g. copper, precious metals) can be supplied as a secondary raw material to metal smelters, while the pyrolysis of plastics allows the recovery of fuel gases, volatilising agents and, eventually, energy. Indeed, WEEE, such as a printed circuit boards (PCBs) usually contains brominated flame retardants (BFRs). From these materials, hydrobromic acid (HBr) is formed as a product of their thermal decomposition. In the present work, the bromination was studied of copper, silver and gold by HBr, originating from BFRs, such as Tetrabromobisphenol A (TBBPA) and Tetrabromobisphenol A-Tetrabromobisophenol A diglycidyl ether (TTDE) polymer; possible volatilization of the bromides formed was monitored using a thermo-gravimetric analyzer (TGA) and a laboratory-scale furnace for treating samples of metals and BFRs under an inert atmosphere and at a wide range of temperatures. The results obtained indicate that up to about 50% of copper and silver can evolve from sample residues in the form of volatile CuBr and AgBr above 600 and 1000°C, respectively. The reactions occur in the molten resin phase simultaneously with the decomposition of the brominated resin. Gold is resistant to HBr and remains unchanged in the residue.

Study on simultaneous recycling of EAF dust and plastic waste containing TBBPA.

In the present work we investigated the fates of zinc, lead, and iron present in electric arc furnace dust during thermal treatment of the dust with tetrabromobisphenol A (TBBPA) and tetrabromobisphenol A diglycidyl ether (TBBPADGE). Mixtures of these materials were compressed into pellets and heated in a laboratory-scale furnace at 550 °C for 80 min, under oxidizing and inert conditions. The solid, condensed, and gaseous-phase products were characterized using an array of analytical methods: scanning electron microscopy, X-ray diffraction, electron probe microscopy, inductively coupled plasma, ion chromatography, and gas chromatography. The results indicated that heating the mixtures under specific conditions enabled high separation of zinc and lead from iron-rich residues, by a bromination-evaporation process. In the case of TBBPADGE, a maximum of 85% of zinc and 81% of lead were effectively separated under the above conditions. The process is based on the reaction between the highly reactive HBr gas evolved during thermal degradation of the flame-retarded materials with zinc (ZnO and ZnFe2O4) and lead in the dust, followed by complete evaporation of the formed metallic bromides from the solid residue.

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.

Fate of lead oxide during thermal treatment with tetrabromobisphenol A.

In this paper, the bromination reaction between lead oxide and hydrogen bromide originating from the thermal decomposition of tetrabromobisphenol A (TBBPA), under inert and oxidizing atmospheres, was investigated, using a laboratory-scale furnace. The results obtained under inert conditions indicated that bromination of PbO proceeded simultaneously with debromination of TBBPA, with an average effectiveness of 69% (max. 80%). Volatilization of the formed PbBr2 began at 315°C, intensified at 750°C, and reached 98% at 850°C. The formed organic char served as a source of carbon for reduction of the unreacted lead oxide to metallic lead in the range 315-750°C. Additional experiments conducted at selected temperatures under slightly oxidizing (5 vol% O2) and quasi-atmospheric (20 vol% O2) conditions showed no significant effects on bromination-evaporation of lead in the studied mixture. However, in isothermal treatment under quasi-atmospheric oxygen levels, complete vaporization of the formed lead bromide was obtained at a temperature of only 650°C.

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.

Predictive model for ionic liquid extraction solvents for rare earth elements

The purpose of our study was to select the most effective ionic liquid extraction solvents for dysprosium (III) fluoride using a theoretical approach. Conductor-like Screening Model for Real Solvents (COSMO-RS), based on quantum chemistry and the statistical thermodynamics of predefined DyF3-ionic liquid systems, was applied to reach the target. Chemical potentials of the salt were predicted in 4,400 different ionic liquids. On the base of these predictions set of ionic liquids’ ions, manifesting significant decrease of the chemical potentials, were selected. Considering the calculated physicochemical properties (hydrophobicity, viscosity) of the ionic liquids containing these specific ions, the most effective extraction solvents for liquid-liquid extraction of DyF3 were proposed. The obtained results indicate that the COSMO-RS approach can be applied to quickly screen the affinity of any rare earth element for a large number of ionic liquid systems, before extensive experimental tests.