<p>This study investigates the effect of Ca²⁺ and Mg²⁺ ions on the performance of hybrid binders composed of anionic polyacrylamide (APAA) and montmorillonite in magnetite systems. Zeta potential measurements showed that both cations reduce surface charge, promoting heteroaggregation and flocculation. DLVO modeling and SEM imaging confirmed increased montmorillonite attachment onto magnetite in the presence of divalent cations. However, these cations interfered with hybrid binder’s interactions with magnetite. Molecular dynamics simulations revealed distinct coordination mechanisms: Ca²⁺ forms both inner- and outer-sphere complexes, whereas Mg²⁺ remains more fully hydrated, forming weaker associations. These findings highlight the importance of water chemistry, especially cation composition that influences hybrid binder performance and stability. Understanding these interactions is essential for optimizing binder formulations in mineral processing, particularly under variable water quality conditions encountered in iron ore pelletizing and more because it is possible the use of negative charged binders although magnetite has negative charges.</p> Graphical abstract <p></p>