TY - JOUR
T1 - Recycling of zincite (ZnO) via uptake of hydrogen halides
AU - Ahmed, Oday H.
AU - Altarawneh, Mohammednoor
AU - Al-Harahsheh, Mohammad
AU - Jiang, Zhong Tao
AU - Dlugogorski, Bogdan Z.
N1 - Publisher Copyright:
© 2018 the Owner Societies.
PY - 2018
Y1 - 2018
N2 - Hydrogen halides (HCl/HBr) represent major halogen fragments from the thermal decomposition of halogen laden materials, most notably PVC and brominated flame retardants (BFRs). Co-pyrolysis of halogen-containing solid waste with metal oxides is currently deployed as a mainstream strategy to treat halogen content as well as to recycle the valuable metallic fraction embedded in electric arc furnace dust (EAFD) and e-waste. However, designing an industrial-scale recycling facility necessitates accurate knowledge on mechanistic and thermo-kinetic parameters dictating the interaction between metal oxides and hydrogen halides. In this contribution, we investigate chemical interplay between HCl/HBr and zincite surfaces as a representative model for structures of zinc oxides in EAFD by using different sets of functionals, unit cell size and energy cut-off. In the first elementary step, dissociative adsorption of the HCl/HBr molecules affords oxyhalide structures (Cl/Br-Zn, H-O) via modest activation barriers. Conversion of the oxyhalide structure into zinc halides occurs through two subsequent steps, further dissociative adsorption of HCl/Br over the same surface Zn atom as well as the release of a H2O molecule. Evaporation (or desorption of zinc halide molecules) signifies a bottleneck for the overall halogenation of ZnO. Our simplified kinetic model on the HCl + ZnO system concurs very well with experimentally reported TGA weight loss profiles on two grounds: accumulation of oxyhalides until ∼700 K and desorption of ZnCl2 at higher temperatures. The thermo-kinetic and mechanistic aspects reported herein could be useful in the pursuit of a design of a large-scale catalytic upgrading unit that operates to extract valuable zinc loads from EAFD.
AB - Hydrogen halides (HCl/HBr) represent major halogen fragments from the thermal decomposition of halogen laden materials, most notably PVC and brominated flame retardants (BFRs). Co-pyrolysis of halogen-containing solid waste with metal oxides is currently deployed as a mainstream strategy to treat halogen content as well as to recycle the valuable metallic fraction embedded in electric arc furnace dust (EAFD) and e-waste. However, designing an industrial-scale recycling facility necessitates accurate knowledge on mechanistic and thermo-kinetic parameters dictating the interaction between metal oxides and hydrogen halides. In this contribution, we investigate chemical interplay between HCl/HBr and zincite surfaces as a representative model for structures of zinc oxides in EAFD by using different sets of functionals, unit cell size and energy cut-off. In the first elementary step, dissociative adsorption of the HCl/HBr molecules affords oxyhalide structures (Cl/Br-Zn, H-O) via modest activation barriers. Conversion of the oxyhalide structure into zinc halides occurs through two subsequent steps, further dissociative adsorption of HCl/Br over the same surface Zn atom as well as the release of a H2O molecule. Evaporation (or desorption of zinc halide molecules) signifies a bottleneck for the overall halogenation of ZnO. Our simplified kinetic model on the HCl + ZnO system concurs very well with experimentally reported TGA weight loss profiles on two grounds: accumulation of oxyhalides until ∼700 K and desorption of ZnCl2 at higher temperatures. The thermo-kinetic and mechanistic aspects reported herein could be useful in the pursuit of a design of a large-scale catalytic upgrading unit that operates to extract valuable zinc loads from EAFD.
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U2 - 10.1039/c7cp06159e
DO - 10.1039/c7cp06159e
M3 - Article
C2 - 29243754
AN - SCOPUS:85040182854
SN - 1463-9076
VL - 20
SP - 1221
EP - 1230
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 2
ER -