The flotation separation of spodumene from feldspar was investigated using a new type of mixed anionic/cationic collector, sodium oleate/tributyl tetradecyl phosphonium chloride (NaOL/TTPC). Microflotation experiments, fluorescence spectroscopy measurements, microcalorimetric analysis, and Fourier transform infrared analysis were performed. Microflotation experiments show that the highest flotation separation performance can be achieved at the NaOL:TTPC molar ratio of 5:1 at the pH of 4.0. Fluorescence spectroscopy measurements show that the critical micelle concentration (CMC) of the mixed collector NaOL/TTPC is smaller than either of its components alone. Microcalorimetric results indicate that the difference in adsorption reaction heat between spodumene and feldspar is larger for the mixed collector than either single collector, confirming the former's separation advantage. Fourier transform infrared analyses show that in the mixed collector, both NaOL and TTPC adsorb on the spodumene surface through chemical interaction and electrostatic attraction, respectively; while only trace amounts of them are adsorbed on the feldspar surface.