Use of colemanite and ulexite as additives in iron ore pelletising

Colemanite and ulexite are boron-containing minerals with about 45% B₂O₃, along with gangue components such as CaO, MgO, SiO₂, Al₂O₃, etc. While the use of colemanite has been studied as an additive in iron ore pelletisation, ulexite has not been investigated. This study compares the effects of colemanite and ulexite on haematite ore pellets. Varying amounts of both minerals were added, and the pellets were compared with pellets without those minerals, under acidic and basic conditions. The results show that increasing colemanite or ulexite improves pellet quality by increasing cold crushing strength (CCS) and reducing the reduction degradation index (RDI). While the acidic pellets without these additives exhibited a CCS of 257 kg/pellet and an RDI of 35.2%, adding 0.4% colemanite increased CCS to 357 kg/pellet and decreased RDI to 12%. Similarly, with 0.4% ulexite, CCS reached 335 kg/pellet, and RDI fell to 10.5%. The required induration temperature also decreased by 25–50°C. However, reducibility decreased slightly by about 2 percentage points, while swelling increased by about 3 percentage points. Overall, 0.4% calcined colemanite under acidic or basic conditions and 0.3% calcined ulexite under basic conditions were found to be optimal. Colemanite showed better performance than ulexite.