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 - Funding Information:
This work was supported by the Australian Research Council (ARC). We acknowledge the Pawsey Supercomputing Centre in Perth as well as the National Computational Infrastructure (NCI) in Canberra, Australia for providing grants of computational resources. O. A. thanks the higher committee for education development in Iraq (HCED) for the award of a postgraduate scholarship.
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 -