<p>The efficient separation of chromite from olivine remains a critical challenge in mineral processing due to their industrial significance and frequent co-occurrence in ultramafic deposits. Conventional gravity separation methods are ineffective for fine-grained ores, leading to chromite losses and reduced concentrate grades, thereby necessitating alternative approaches such as froth flotation. However, selective flotation is impeded by the minerals’ similar surface charge characteristics and isoelectric points (IEP; pH_iep). Fatty acid-based collectors, particularly oleic acid, are commonly used, yet their adsorption mechanisms are complex and often obscured in mixed-mineral systems. To address this issue, micro-flotation tests were carried out on high-purity chromite and olivine samples to examine their flotation behavior as a function of collector concentration, conditioning time, air flow rate (AFR), and particle size. These experiments were complemented by zeta potential and surface tension measurements to elucidate the pH-dependent adsorption mechanisms. The results identified two pH intervals, 5–6 and 9–10, exhibiting enhanced recoveries above 90%, particularly for olivine. Increasing conditioning time had a more positive effect on olivine, while higher AFR and finer particle sizes significantly improved flotation performance (e.g. from 40% to about 90%). Surface characterization indicated that mineral–collector interactions strongly depend on pH, consistent with the observed flotation trends. Near the IEP (pH 5–6), where electrostatic effects are minimal, flotation likely proceeds through non-electrostatic mechanisms such as hydrophobic interactions or weak chemical adsorption. Under alkaline conditions (pH 9–10), enhanced collector ionization and specific chemical interactions between oleate species and surface metal ions enable effective adsorption and flotation despite the overall negative surface charge.</p> Graphical Abstract <p></p>