Study on the mechanochemical oxidation of ilmenite

Abstract

The oxidation kinetics and mechanism of ilmenite milled in air and oxygen atmospheres were investigated. Effects of mill spin rate, milling ball/ore mass ratio and oxygen pressure on the oxidation were examined. The results showed that the former two parameters significantly affected the oxidation process while the influence of oxygen pressure was demonstrated only in a low initial O 2 pressure range. An evident O 2 adsorption (macro-adsorption) was observed at high O 2 pressures (≥50 kPa) but it disappeared with decreasing of O 2 pressure. The oxidation was mechanochemically limited at the initial O 2 pressures from 152.0 to 33.4 kPa. With further decreasing of the O 2 pressure to ≤27.4 kPa, the oxidation changed to be controlled by the O 2 adsorption on the active sites of ilmenite particles surface (micro-adsorption). The mechanochemical oxidation occurred mainly at those active sites with the c-axis lattice strain. The mechanism of the oxidation was suggested, upon which a rate equation in kinetic regime was built and derived as follows: − d ( 1 − a ) d t = 2.1 × 10 − 5 R 2.044 a c 2.616 ( 1 − α ) 2 when t > 0.5 h and FeTiO 3 oxidation extent α ≤ 85%. Beyond the extent, the oxidation was limited by O 2 diffusion through the solid products layer.