Application of betaine surfactant in flotation separation of macerals and interfacial mechanism: An eco-friendly and tunable strategy

Separation and application of macerals have become key research focus in materials and mineral processing fields. This study employed eco-friendly surfactant 3-sulfopropyl tetradecyl dimethyl betaine (STDMB) as collector, combined with Ca2+ to achieve floatation of different macerals. Interfacial interaction mechanism was elucidated through Zeta potential measurement, atomic force microscopy (AFM) test, molecular docking, contact angle measurement, and particle-bubble adhesion angle measurement. Results indicated that using STDMB alone favored vitrinite flotation. With 1.2 mM·L-1 STDMB, vitrinite content increased from 55.60% to 72.53%; after adding 3 mM·L-1 Ca2+, inertinite content rose by 13.11%, reaching 57.51%. Further analysis revealed that Ca2+ changed surface charge difference between vitrinite and inertinite; meanwhile adsorbing to STDMB molecule terminal, converting STDMB electronegativity to positive; the C-NH-C in vitrinite and abundant C-O-C in inertinite are the key structural factors influencing interactions among STDMB, Ca2+, and macerals. Thereby influencing the adsorption of collector on macerals surface, regulating hydrophobicity difference between vitrinite and inertinite and particle-bubble interaction process. This work reports the first application of betaine surfactant in macerals separation. Its non-toxic, easily degradable, and highly efficient characteristics make it sustainable collector. Moreover, the regulatory effect of STDMB and Ca2+ synergy on macerals flotation grants broader application significance.