Effect of sodium hexametaphosphate on the separation of fine quartz-magnetite by magnetic separation: A study of dispersion properties and mechanism

Iron minerals and gangue minerals in iron ore are often embedded as microfine grains, making the effective separation during grinding and beneficiation processes challenging and leading to high impurity content in the iron ore concentrate. This study investigates the mechanism of sodium hexametaphosphate (SHMP) in promoting the separation of fine-grained quartz from magnetite through dispersion-sedimentation and dispersion-magnetic separation experiments. Scanning electron microscopy (SEM), zeta potential measurements, extended DLVO (EDLVO) theoretical calculations, and Fourier transform infrared spectroscopy (FTIR) were employed to systematically analyze the dispersion mechanism of SHMP on fine-grained quartz and magnetite. The experimental results show that under optimized conditions, the addition of SHMP effectively removes the coating of finegrained quartz, significantly improves the dispersion rate of both magnetite and quartz, and reduces the impurity content in the iron ore concentrate. The concentrate achieved a TFe grade of 71.29 % and a recovery rate of 98.48 %, while the SiO2 content was reduced to 0.62 %. Furthermore, zeta potential measurements reveal that SHMP substantially improves the electrical properties of mineral surfaces. E-DLVO theoretical calculations further demonstrate that SHMP strengthens the electrostatic repulsion between minerals, while FTIR analyses reveal that SHMP interacts with magnetite through both chemisorption of hydroxyl groups and electrostatic adsorption, whereas its interaction with quartz is only chemisorption of hydroxyl groups.