The Chemistry of Fuming Zinc from Oxide Slags using Coke
The thermodynamics and kinetics of the reactions involved in fuming zinc from oxide slags using coal or coke were first studied in 1955 and have been the subject of many investigations since that time. The key reaction is ZnO(in slag) + CO = Zn(g) + CO2. This paper will review the some of the recent work, and will add new insights obtained in experiments carried out by the authors. In the first series of experiments it was shown that the reaction 2Fe2+ + ZnO = 2Fe3+ + Zn(g) or 2FeO + ZnO = Fe2O3 + Zn(g) does not occur at an appreciable rate, as is expected from thermodynamic considerations. In the second series of experiments it was shown that zinc does not fume from the slag at a significant rate unless a reductant has been added. This again is in accord with thermodynamic considerations, but is in contradiction to some of the experimental results reported in the literature. A third series of experiments was carried out with excess coke being present, so that the rate of supply of reductant was not in any way controlling the rate. The kinetics of zinc oxide reaction were then found to be independent of the zinc oxide concentration, but increased with increasing basicity, and temperature. The presence of high concentrations of FeO in the slag also improves the kinetics. At low zinc oxide concentrations iron oxide reduction occurred in parallel with zinc oxide reduction. We propose that (under the conditions of this work) the kinetics were controlled by a chemical step, namely the rate of desorption of an adsorbed CO2 species. This is the same mechanism as reported by Belton and co-workers for the kinetics of the reduction of FeO. This explains why the reduction of metal oxides in slags by hydrogen is often faster than by CO.
D. G. Robertson et al., "The Chemistry of Fuming Zinc from Oxide Slags using Coke," Yazawa International Symposium Proceedings, vol. 1, pp. 647-657, Wiley-Blackwell, Mar 2003.
Yazawa International Symposium: Metallurgical and Materials Processing: Principles and Technologies; Materials Processing Fundamentals and New Technologies (2003: Mar. 2-6, San Diego, CA)
Materials Science and Engineering
Keywords and Phrases
Adsorption; Alkalinity; Carbon dioxide; Coke; Desorption; Metal recovery; Reaction kinetics; Thermal effects; Thermodynamics; Reduction kinetics; Zinc oxide slag,
Article - Conference proceedings
© 2003 Wiley-Blackwell, All rights reserved.
06 Mar 2003