engleski

Analysis of Fe-bearing compounds in the manufacture of TiO2 pigment

TiO2 pigment has found various applications, for example in catalysis, printing inks, plastics, papers, ceramics and pharmaceuticals. In the manufacture of TiO pigment two technologies are used. Ilmenite ore is used in the production of TiO2 pigment by sulfate processing, whereas rutile is used in the production of TiO pigment by chloride processing. In the present work we analyse ilmenite ore from Australia which is utilized in the production of TiO2 pigment by sulfate processing in the “Cinkarna“, Celje (Slovenia). In this technology Fe^3+ ions are reduced to Fe^2+ by adding scrap iron. For that reason, it is important to know the Fe^2+/Fe^3+ ratio in ilmenite ore (input material). Generally, natural ilmenite can be associated with hematite, magnetite, rutile, fayalite, zircon, quartz and various aluminosilicates. 57^Fe Mössbauer analysis of ilmenite ore from Australia shows a significant amount of Fe^3+ due to oxidized Fe^2+. In the manufacture of TiO2 by sulfate processing a significant amount of copperas (by-product) is formed by crystallization. In this technology copperas is calcined in order to produce H2SO4 acid from released gases returning to the operation of ilmenite ore digesting. The 57^Fe Mössbauer spectrum of calcined copperas shows the presence of a sextet corresponding to α-Fe2O3, as well as a quadrupole doublet of small relative intensity. In the XRD pattern of calcined copperas the magnetite phase could not be detected with certainty. However, after being magnetically separated, the fraction from calcined copperas in the 57^Fe Mössbauer spectrum showed the presence of hematite and substoichiometric magnetite (Fe3-xO4). A central quadrupole doublet of small intensity could be assigned to Fe^3+ present in solid solutions with associated phases. Sulfur detected by EDS analysis of calcined copperas was a result of incomplete oxidation of copperas.

TiO2 pigment; Sulfate processing; Hematite; Magnetite; Mossbauer spectroscopy; XRD

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