Linking physicochemical properties with flotation strategy for Baganuur and Shivee-Ovoo lignites

This study investigates the relationship between physicochemical properties and flotation strategy selection for two Mongolian lignites, Baganuur and Shivee-Ovoo, and provides insight into the physicochemical basis for flotation strategy differentiation of low-rank coals based on physicochemical characteristics rather than applying a uniform beneficiation approach. Proximate and ultimate analyses, XRD, XRF, XPS, zeta potential, induction time, and contact angle measurements revealed significant differences in surface oxygenation, mineral dissemination, and hydrophobicity between the two lignites. Baganuur showed a more oxygen-rich surface and stronger mineral association, whereas Shivee-Ovoo exhibited relatively higher hydrophobicity and carbon content. The results indicate that flotation performance is influenced not only by intrinsic hydrophobicity but also by ultrafine particle behavior, gangue entrainment, and coal–gangue hydrophobic contrast under the conditions investigated. For Baganuur lignite, pre-desliming-assisted direct flotation using Collector 2 produced a clean coal yield of 39.52% at 12.62% ash. In contrast, direct flotation of Shivee-Ovoo lignite remained ineffective despite its higher contact angle, owing to poor selectivity and entrainment effects. Reverse flotation with dodecyltrimethylammonium bromide (DTAB) proved more suitable for Shivee-Ovoo, yielding a retained coal stream of 69.89% at 10.37% ash. The study demonstrates that flotation strategies for low-rank coals should be differentiated according to physicochemical characteristics rather than applied uniformly.