Particle-Size-Dependent Effects of Sodium Carboxymethyl Cellulose on the Flotation Separation of Apatite from Chlorite and Biotite

To address the challenge of separating fine-grained apatite from layered silicate gangue minerals (chlorite and biotite) in medium- and low-grade collophane ores in China, this study systematically investigated the effects and mechanisms of sodium carboxymethyl cellulose (CMC-Na) as a selective depressant on the flotation behavior of different particle-size fractions. Pure mineral and artificially mixed mineral flotation tests demonstrated that, at pH 9, using a mixed collector composed of sodium oleate, oxidized paraffin soap, and sodium fatty acid methyl ester sulfonate at a total dosage of 250 mg/L, CMC-Na enabled selective separation of apatite from gangue minerals; however, the optimal dosage exhibited significant particle-size dependence. For the −0.5 + 0.074 mm fraction, effective separation was achieved with collector alone. For the −0.074 + 0.023 mm fraction, the optimal CMC-Na dosages were 10 mg/L for single-mineral flotation and 100 mg/L for artificially mixed mineral flotation. The maximum apatite recovery in the single-mineral flotation was 87%, while the artificially mixed mineral flotation achieved a P2O5 grade of 23.7% with a recovery of 41.8%. For the −0.023 mm fraction, 30 mg/L CMC-Na maintained an apatite recovery of 66.5% in the single-mineral flotation. In the artificially mixed mineral system, increasing the CMC-Na dosage improved apatite enrichment to some extent, and at 300 mg/L a recovery of 24.8% was obtained at a P2O5 grade of 13.2%; however, the degree of upgrading remained limited. Contact-angle measurements showed that CMC-Na decreased the contact angles of chlorite and biotite while increasing that of apatite, thereby increasing the wettability contrast between apatite and the two gangue minerals. Zeta-potential measurements further showed larger negative potential shifts for chlorite and biotite than for apatite. FTIR and XPS analyses indicated that the carboxyl groups of CMC-Na participated in the interactions with the mineral surfaces, with more pronounced spectroscopic responses observed for biotite and chlorite than for apatite. Changes in the Mg 1s and K 2p spectra further suggest that Mg-containing sites in chlorite and K-containing sites in biotite may participate in these interactions. These interfacial differences are consistent with the stronger depression of chlorite and biotite observed in the flotation tests. The results provide model-system evidence for the particle-size-dependent role of CMC-Na in the flotation separation of apatite from layered silicate gangue minerals.