Selective flotation separation of spodumene and feldspar under low alkalinity enabled by a sulfonate-based organic depressant

• A novel polyanionic depressant (ODA-1) enables selective spodumene-feldspar flotation. • The ODA-1 system with NaOL/DDA mixed collectors achieves efficient separation at pH 8.5 ± 0.1. • ODA-1 adsorbs on feldspar via bidentate Al-Si coordination, forming a hydrophilic film. • On spodumene, ODA-1 binds monodentately and can be displaced by NaOL/DDA collectors. • The low-alkali strategy offers a cleaner and more sustainable spodumene beneficiation route. The flotation separation of spodumene from feldspar under low-alkaline conditions remains challenging due to their similar aluminosilicate surface characteristics and the limited selectivity of conventional reagent schemes. In this study, a sulfonate-based polyanionic organic depressant with aromatic backbone and sulfonate (−SO 3 - ) functional groups, denoted as ODA-1, was introduced for spodumene-feldspar separation in the sodium oleate/dodecylamine (NaOL/DDA) mixed collector system under low-alkaline conditions (pH = 8.5 ± 0.1). Micro-flotation experiments on single minerals and binary mixtures were combined with zeta potential measurements, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations to elucidate the underlying adsorption mechanism. The flotation results show that at 100 mg/L ODA-1 and pH 8.5, efficient separation of spodumene from feldspar was achieved. Surface analyses revealed that ODA-1 preferentially adsorbed on feldspar with surface Al and Si atoms via its sulfonate groups, forming a hydrophilic layer that suppresses NaOL/DDA adsorption. In contrast, ODA-1 interacts weakly with spodumene and is readily displaced by NaOL/DDA, leading to surface hydrophobization. This work provides fundamental insights into the interfacial regulation mechanism of selective organic depressants under low-alkalinity conditions.