Zinc ferrite formation

Feltz, A. Martin, A. (1987) Solid-state reactivity and mechanisms in oxide systems. 11 Inhibition of zinc ferrite formation in zinc oxide - a-iron(lll) oxide mixtures with a large excess of a-iron(lll) oxide. In Schwab, G.M. (ed.) Reactivity of solids. Elsevier, 2 307—313 Fendorf, S. Fendorf, M. (1996) Sorption mechanisms of lanthanum on oxide minerals. Clays Clay Miner. 44 220-227 Fendorf, S.E. Sparks, D.L. (1996) X-ray absorption fine structure spectroscopy. In Methods of Soil Analysis. Part 3 Chemical Methods. Soil Sd. Soc. Am., 377-416 Fendorf, S.E. Eick, M.J. Grossl, P. Sparks, D.L. (1997) Arsenate and chromate retention mechanisms on goethite. 1. Surface structure. Environ. Sci. Techn. 31 315-320 Fendorf, S.E. Li,V. Gunter, M.E. (1996) Micromorphologies and stabilities of chromiu-m(III) surface precipitates elucidated by scanning force microscopy. Soil Sci. Soc. Am. J. 60 99-106... 

Reaction 3 also occurs on cooling since the concentration of SO is very low at roaster temperatures of 950°C and approaches zero at 1000°C. Another important reaction that occurs during roasting is the formation of zinc ferrite, Zn0-Fe2 03 above 650°C (see Ferrites). Zinc ores contain 5—12% iron. Zinc ferrite forms soHd solutions with other spinels, such as Fe0-Fe203, and therefore the zinc—iron compositions formed are of indefinite stoichiometry. Ferritic zinc is difficult to solubilize in hydrometaHurgical leaching but several recovery processes are discussed below. 

A limited number of laboratory results of varied nature will be cited for perspective. The mechanism of formation of zinc ferrite,... 

Baranchikiv AE, Ivanov VK, Muraveva GP, Oleinikov NN, Tretyakov Yu D (2004) Kinetics of the formation of zinc ferrite in an ultrasonic field. Dokl Chem 397(Part I) 146-148... 

In a natural gas fueled PAFC, water is condensed out of the fuel stream going to the fuel cell to increase the partial pressure of hydrogen. In a coal gasification MCFC, water often is added to the fuel stream prior to the fuel cell to prevent soot formation. The addition of excess steam not only prevents the soot formation, but also causes a voltage drop of approximately 2 mV per each percentage point increase in steam content (45). The use of zinc ferrite hot gas cleanup can aggravate the soot formation problem because of the catalytic effect of the sorbent on carbon formation, and requires even higher moisture levels (46). 

Figure 7.23 Schematic diagram of spray drying process for the formation of calcined magnesium zinc ferrite. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John Wiley and Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The main phase in the ZIC is zinc-ferrite, while other phases include ZnO, Zn2Si04, gypsum, Pb-K jarosite, PbS04, ZnS and Fe-hydroxide. Silica (gel) can be formed as described in Equations 2 to 4. The zinc ferrite is free of silica. The mineralogical assays, however, do not provide enough information to correlate the formation of ZIC with the composition of the calcine. 

Systems in which two simple oxides react to form a complex oxide are usefiil models for investigating the production of single-phase ceramics by reaction sintering because of the available data on the reaction mechanisms (91) and the relative simplicity of the reactants and product. Two examples are the formation of zinc ferrite by Eq. (11.67) and the formation of zinc aluminate spinel by the reaction between ZnO and AI2O3 powders. 

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