Mineralogy and solid-state reduction features of typical ironsands from Indonesia

With over 100 billion tons of reserves, the ironsands resource is mainly distributed along the “Belt and Road” countries, such as Indonesia. It is the second largest marine resource inferior to petroleum and natural gas. Ironsands mainly comprise vanadium, titanium, and iron. With advantages of easy mining, low cost, and abundance in polymetallic minerals, the ironsands resource has attracted extensive attention for its extremely high comprehensive recycling value. According to previous studies, solid-state reduction is an efficient approach to a number of processes in complex mineral resources such as ironsands, especially in vanadium-bearing titanomagnetite treatments. In this paper, the process mineralogy and direct reduction characteristics of typical ironsands from Indonesia were studied based on the classical mineralogy method combined with various characterization techniques such as chemical phase analysis, MLA, X-ray diffraction, particle size analysis, optical microscopy, and SEM-EDS. Results show that the mineral composition of the ironsands is mainly titanomagnetite, followed by a small amount of pseudo-hematite, hematite, ilmenite, pyroxene, plagioclase, and others. Most titanomagnetites exist as compact monomers or iron-rich aggregates with occasional fine ilmenite flakes formed through solid-melt separation. The iron contained in titanomagnetite phase accounts for 89.79% of the total iron in the ironsands, while titanium and vanadium account for 85.42% of the total titanium and 97.97% of the total vanadium content, respectively. Ironsands can achieve high metallization ratio when they are reduced at 1300 ℃ for 60 min with C/Fe mole ration of 1.2. The reduction course is as follows: Fe_2.75Ti_0.25O₄ → FeTiO₃, (Fe, Mg)Ti₂O₅ → (Fe, Mg)Ti₂O₅ → Fe. Results reveal that the stable anosovite ((Fe, Mg)Ti₂O₅) phase is the main factor affecting the final metallization degree of the reduced samples. With solid state reduction treatment, iron is enriched in the metal phase while vanadium and titanium elements are distributed in the titanium-rich phase in the slag. These create favorable conditions for the subsequent separation and extraction process, which consequently lay a firm foundation for the comprehensive utilization of the ironsands.