pH-responsive depressant enables efficient CuFeS2-MoS2 flotation separation at near-neutral pH: Performance and mechanism

The flotation separation of chalcopyrite (CuFeS 2 ) and molybdenite (MoS 2 ) is hindered by similar surface properties, typically requiring environmentally detrimental high-alkalinity conditions (pH > 10.0). Herein, we introduce 3,4,5-Trihydroxy-N,N-bis(2-hydroxyethyl)benzamide (TBHB), a gallic acid-derived surfactant, as an efficient selective depressant for chalcopyrite under near-neutral conditions (pH 6.0–8.0). Notably, chalcopyrite recovery is reactivatable via pH adjustment (pH > 9.0). Micro-flotation tests demonstrated TBHB's high selectivity, achieving 91.81% molybdenite recovery while suppressing chalcopyrite recovery to 12.61% at pH 8.0, outperforming conventional depressants (e.g., sodium thioglycolate). Artificial mixed minerals flotation further confirmed TBHB's efficacy, with a dosage of 75 mg/L achieving Mo recovery exceeding 80%, Cu recovery below 20%. Mechanistic investigations revealed TBHB chemisorbs on the chalcopyrite surface via phenolic hydroxyl-Fe coordination, supported by high adsorption capacity (> 1.6 mg/m 2 ), reduced hydrophobicity, and FTIR/XPS analyses, which showed Fe–O bond formation and red-shifted C=O/benzene ring vibrations. Zeta potential measurements affirmed pH-dependent adsorption/desorption. DFT calculations confirmed spontaneous adsorption ( ΔE = −1.8206 eV) and short O–Fe bond (1.99 Å), verifying Fe-site affinity. Conversely, TBHB showed negligible adsorption on the molybdenite surface, with values below 0.4 mg/m 2 and a contact angle of approximately 70°, preserving its floatability. This work establishes TBHB as a sustainable alternative for Cu-Mo separation, eliminating high-alkalinity requirements while advancing green reagent design through integrated experimental and computational insights.