Selective Depression of Biotite by Carboxymethyl Chitosan in Apatite-Biotite Flotation: Effects of Particle Size

Biotite in mica-bearing phosphate ores is prone to sliming and forms fine intergrowths with apatite, impairing flotation selectivity. Taurine, sodium lignosulfonate, chitosan, hydroxypropyl distarch phosphate, and carboxymethyl chitosan (CMCS) were screened by single-mineral and artificial-mixture flotation tests. Contact angle, adsorption, zeta potential, FTIR, and XPS analyses focused on the −0.023 mm fraction. At pH 9 and a collector dosage of 268 mg/L, CMCS retained selectivity in favor of apatite. In single-mineral tests, CMCS dosages of 30, 60, and 150 mg/L produced apatite–biotite recovery differences of 47.57, 40.51, and 20.59 percentage points for the +0.074, −0.074 + 0.023, and −0.023 mm fractions, respectively. In artificial-mixture tests, selected dosages of 20, 120, and 180 mg/L yielded P2O5 recoveries of 95.50%, 95.58%, and 74.37% and grades of 28.02%, 26.47%, and 21.10%, respectively. As particle size decreased, the required CMCS dosage increased and separation deteriorated. Contact-angle measurements showed that CMCS pretreatment preserved the strong collector-induced hydrophobicity of apatite while slightly weakening that of biotite, thereby increasing the wettability contrast between the two minerals. Biotite showed a larger negative zeta-potential shift and greater CMCS adsorption than apatite; at 180 mg/L, the adsorption amounts were 1.17 and 0.76 mg/g, respectively. Together with the adsorption results, FTIR and XPS suggested stronger CMCS–biotite interfacial interactions involving carboxyl and hydroxyl-containing groups, with possible participation of Mg-related surface sites. These findings demonstrate the particle-size dependence of CMCS-assisted apatite-biotite flotation and reveal preferential CMCS interaction with biotite under fine-particle conditions.