Effect of Na_2SO_4 on the Embedding Direct Reduction of Beach Titanomagnetite and the Separation of Titanium and Iron by Magnetic Separation

摘要

A novel process for separating iron and titanium from Indonesian beach titanomagnetite (TTM) concentrates is proposed. This process involves several steps, including mixing the TTM concentrate and additive, pressing the mixture into pellets, embedding direct reduction of the pellets, and magnetic separation. Given that coal and additives are the main factors influencing the coal-based direct reduction of beach TTM, this study employed embedding reduction, where pellets are embedded under the coal to be reduced, and Na_2SO_4 was used as an additive. The best result was obtained when the Na_2SO_4 dosage was 4%, and the direct reduction iron powder (DRI powder) with an iron grade of 94.45%, iron recovery of 85.18%, and TiO_2 content of 0.44% were obtained. Titanium concentrate assay yielded 40.43% TiO_2 containing main titanium minerals of ilmenite and ferrous pseudobrookite. The results showed that a suitable Na_2SO_4 addition (4-6%), DRI powder and titanium concentrate presented better iron recovery and TiO_2 grade as compared without addition, while this advantage disappeared as Na_2SO_4 addition increased (＞6%). The characteristics of roasted pellets were analyzed through X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. Results showed that FeS and nepheline are formed by addition of Na_2SO_4, thereby benefiting the migration and growth of metallic iron particles in the redox system and separation of titanium and iron. While a suitable dosage of Na_2SO_4 could promote porosity and induce a reducing atmosphere, but more liquid phase formed by an excessive Na_2SO_4 was unfavorable and caused expansion of the pellets.