Comparative adsorption mechanisms of cationic and non-ionic surfactants on biotite surfaces: An electrokinetic and spectroscopic study

This study investigated the surface interactions between selective different type collectors widely employed in industrial feldspar or nepheline beneficiation processes and lithium-bearing biotite contained in nepheline syenites from the Kırşehir region in order to evaluate their suitability for flotation-based lithium recovery. The interactions of Der A4, DAHC, and Derna 7 with biotite were examined through surface tension, contact angle, zeta potential, and FTIR analyses under varying collector concentrations and pH conditions (2.5, 4.0, 6.5, and 9.5). Surface tension measurements showed that both Der A4 and DAHC gradually reduced the surface tension, reaching their critical micelle concentration (CMC) at lower collector concentrations as the pH became more alkaline. In contrast, Derna 7 reached its CMC at approximately 0.5 g/L across all tested pH values, while the lowest surface tension was observed at pH 9.5, where the value remained stable at concentrations ≥0.5 g/L. However, under these conditions, contact angle measurements could not be obtained due to the sudden spreading of the droplet and the formation of a thin film on the biotite surface. Der A4 exhibited the strongest hydrophobic modification, producing contact angles close to 90° even at low concentrations (0.1 g/L) across all pH values. DAHC showed a similar trend to Derna 7 at high pH, where spreading behavior occurred at concentrations near the CMC, indicating a temporary decrease in wettability. For Derna 7, the highest contact angle (∼45°) was obtained at 0.5 g/L and pH 2.5, while higher pH values resulted in reduced contact angles due to spreading effects. Zeta potential measurements revealed that increasing concentrations of Der A4 and DAHC shifted the initially negative biotite surface toward positive values, indicating strong adsorption, whereas Derna 7 made the surface more negatively charged with increasing concentration. Besides, FTIR analyses confirmed that the adsorption mechanisms of all collectors were predominantly physical in nature.