Preliminary results on selective surface magnetization and separation of alumina-/silica-bearing minerals

• Selective surface magnetization of alumina containing minerals was investigated.
• Sodium fluoride is favorable for the selective surface magnetization of alumina-/silica-bearing minerals.
• Alumina-/silica-bearing minerals can be separated by selective surface magnetization followed by magnetic separation.

The efficient and economical separation of alumina/silica minerals is critical to alumina production. In this work, selective surface magnetization was adopted to separate alumina-/silica-bearing minerals. The zeta potentials of boehmite, quartz, and magnetite with and without 100 ppm sodium fluoride (NaF) were measured. Results show that NaF could extend the favorable pH range to 7.4–8.5 for the selective magnetic coating of boehmite. X-ray diffraction and scanning electron microscopy analyses indicate that synthesized magnetite particles are preferentially adsorbed onto boehmite in the artificial bauxite of boehmite and quartz, and then aggregate to form a dense magnetic layer during surface magnetization. The magnetic hysteresis loop determined by Vibrating Sample Magnetometer further confirms that the concentrate from magnetic separation contains magnetic substances and the concentrate is weakly magnetic. Based on the separation results for artificial bauxite, experiments were conducted on the selective surface magnetization of gibbsite–boehmite mixed bauxite and low-temperature Bayer red mud. The results demonstrate that alumina-/silica-bearing minerals could also be separated to a certain extent. Selective surface magnetization exhibits the potential to separate alumina/silica minerals for practical applications and thus deserves further study.