Effect of preoxidation and sintering on properties of ilmenite concentrates

The paper examines the effects of preoxidation and sintering on the phase composition, specific surface area, morphology and reducibility of ilmenite concentrates. Samples were preoxidised in air or sintered in argon by temperature-programmed heating to temperatures of 600-1400degreesC at a ramping rate of 300degreesC/h. In the concentrates preoxidised at temperatures up to 800degreesC, ilmenite formed an intermediate product, Fe2O3.2TiO(2), which decomposed into Fe2O3 and TiO2. At temperatures above 800degreesC, pseudorutile was transformed into ferric pseudobrookite and rutile. Haematite recombined with rutile to form pseudobrookite at temperatures above 1000degreesC. When samples were heated in an argon atmosphere, ferric-ferrous pseudobrookite solid solution was formed from ilmenite and pseudorutile. Preoxidation and sintering at temperatures above 600degreesC caused a sharp decrease in the specific surface area of samples. The specific surface area decreased by more than 97% when samples were heated to 1200degreesC. Preoxidation enhanced while sintering retarded the reduction of iron oxides in ilmenite concentrates by methane-hydrogen gas mixtures in the temperature range of 550-800degreesC. Both preoxidation and sinteting increased the temperature required to reduce titanium oxides. At high temperatures, such as 1200degreesC, the effects of preoxidation and sintering on isothermal reduction of ilmenites were negligible. (C) 2002 Elsevier Science B.V. All rights reserved.