Coupled effects of NaOL–MIBC interaction and Ca2⁺ on foam stability

• NaOL–MIBC synergy enhances foam only at low-to-intermediate NaOL concentrations. • Excess NaOL promotes aggregation, reducing oleate availability for foam. • Ca 2 ⁺ destabilizes foam by complexing with oleate and lowering interfacial activity. • Aggregation regimes control interfacial adsorption and concentration effects. • Aggregation and interfacial effects determine foam stability in NaOL–MIBC systems. Froth stability is a critical factor in flotation processes. However, the mechanisms by which Ca 2 ⁺ activation, sodium oleate (NaOL), and methyl isobutyl carbinol (MIBC) jointly influence foam behaviour remain unclear, particularly in the reverse flotation of iron ores. Here, we present a multi-scale investigation systematically varying NaOL concentration, MIBC addition, and Ca 2 ⁺ levels to explore their coupled effects on foam generation and stability under alkaline conditions at 25 ± 1 °C. By integrating macroscopic foam measurements (Dynamic Foam Analysis, FBRM) with interfacial characterization (surface tension, zeta potential) and molecular-scale probes (NMR spectroscopy, SAXS), we connect solution-phase aggregation, interfacial adsorption, and bubble population dynamics. The results indicate that synergy between NaOL and MIBC emerges at intermediate NaOL concentrations. Under these conditions, aggregates can supply oleate efficiently to the interface. At higher NaOL concentrations, excessive collector promotes bulk aggregation and limits interfacial availability. In contrast, Ca 2 ⁺ progressively reduces interfacial activity through complexation with oleate, weakening cooperative surfactant–frother interactions and causing gradual foam destabilization. Molecular-scale analysis further reveals distinct aggregation regimes under collector-deficient and collector-rich conditions, providing mechanistic insight into non-linear foam stabilization. Together, these findings establish a unified framework linking surfactant aggregation, interfacial organization, and electrolyte effects to macroscopic foam behaviour, offering guidance for optimizing NaOL-based reverse flotation processes.