Effect of CaO on reducing atmosphere in the direct reduction and magnetic separation process of beach titanomagnetite concentrate

The exploitation of refractory iron ores has become increasingly important around the world because of the rapid depletion of easy-to-process iron ores. Ironsand is extensively distributed in the coastal areas of Indonesia, China, and New Zealand, and can provide an alternative to conventional iron ores. Although the composition of ironsand is partially dependent on its location and position, it approximates that of titanomagnetite (Fe_3-xTi_xO₄) containing ~ 60% total Fe (TFe). However, the conventional smelting route for smelting beach titanomagnetite concentrate with carbon uses a blast furnace to produce pig iron and titanium slag, which has many disadvantages. First, the smelting process requires lots of coke and a high temperature. Second, sinter blend allows for the addition of only a small amount of beach titanomagnetite concentrate to ensure the desired sintering characteristics. Therefore, in order to efficiently utilize beach titanomagnetite, the processes of direct reduction followed by magnetic separation are generally applied to recover iron. In addition, additives such as CaO, CaCO₃, and NaCO₃ are often used in the reduction roasting process. These additives may improve the reduction characteristics or facilitate the growth of iron particles to some extent. In order to study the effect of the additive CaO on the direct reduction and magnetic separation of beach titanomagnetite concentrate which contains 58.58% of TFe and 12.04% of TiO₂, the mechanisms were investigated by gas composition of CO and CO₂, gasification rate of total reaction, CO partial pressure, metallization rate, mineral composition and so on. The results indicate that adding CaO can improve the gasification rate of reductant and facilitate the reduction of titanomagnetite, which improves the generation of CO₂ gas and decreases the CO partial pressure. Besides, CaO can participate in solid-solid reaction, reduce FeO content in Ti-containing mineral and facilitate the migration and enrichment of Ti and Fe components, which promote the growth of metallic iron particles. Thus, adding CaO is good for the separation and recovery of Fe and Ti by grinding and magnetic separation.