The magnetic matrix is the core component of the high-gradient magnetic separation (HGMS) system and plays a decisive role in the operation of the HGMS system. The cylindrical matrix is the most commonly used matrix in HGMS. The matrix shape is a very important parameter influencing the performance of the HGMS system. The special cross-section matrix may have better magnetic characteristics and present better performance in HGMS. However, previous studies of the basic principles of HGMS are basically limited to those employing a circular cross-section matrix. Investigations into the magnetic characteristic and performance of a special cross-section shape matrix are scarce. In this paper, the effect of matrix shape on the capture of fine weakly magnetic minerals in HGMS is investigated with the particle capture model. The matrix shape varies between circular cross section and elliptical cross section. The magnetic field and the flow field around the elliptic matrix are analytically calculated. The motion equations of particles around the elliptic matrix under different circumstances are derived and the particle motion trajectories are depicted. The particle capture radius and efficiency of the matrix with shape coefficient L_h/L_v (ratio of the horizontal axis to the vertical axis of the matrix cross section) ranging from 1/3 to 3 are calculated and compared, providing that the matrix area facing the incoming fluid is the same. The results indicate that there exists the optimal L_fh/L_v value at which the capture radius and efficiency reach the maximum. The optimal L_h/L_v value increases with the increase in particle size and the decrease in matrix size. Within the L_h/L_v range of 1/3-3, the maximum particle capture efficiency (at the optimal L_h/L_v or at L_h/L_v = 3) under some arrangements can be much higher than the circular matrix (at L_h/L_v = 1), but the increment decreases with the increase in matrix size, the arrangement parameter d/L_v, and the decrease in particle size. The results provide a theoretical basis for the application of the elliptical matrix in HGMS as well as a reference for the development of other novel magnetic matrices in HGMS.

High-gradient magnetic separation (HGMS) is an effective method to recover fine weakly magnetic minerals or remove ferromagnetic and paramagnetic particles from aqueous solution. The most commonly used matrices are circular cylinders of high magnetic permeability. However, special cross-section matrices may present better magnetic characteristics and improve the separation efficiency. In this paper, the magnetic field and flow field characteristics of elliptic cross-section matrix were studied in the elliptic coordinate system. The particle capture of the elliptic matrix in the longitudinal configuration of HGMS was modelled and the motion equations of the magnetic particles were derived. The particle capture radius and efficiency were calculated and were compared with those of the circular matrix. Two circumstances were considered to investigate the particle capture of elliptic matrix: the short axis of the elliptic matrix is equal to the diameter of the circular matrix and the cross-section area of the elliptic matrix is equal to that of the circular matrix. The influence of λ (ratio of long axis to short axis) of the elliptic matrix on the capture efficiency of micron-sized paramagnetic particles in the two circumstances was also studied. The results showed that for all the conditions considered, there exists an optimum λ at which the particle capture efficiency reaches the maximum. With the matrices of the optimum λ and suitable d values, the capture efficiency of the 10 μm and 2 μm haematite particles can be improved by 6 ~ 22% and 1 ~ 3% compared with the circular matrices, respectively. Both approaches can be adopted to utilize elliptic matrices in HGMS to improve the particle capture efficiency. The results reveal the higher particle capture efficiency of the elliptic matrix and its application possibility in HGMS.

This study investigates the negative impact of temperature on spodumene flotation from the perspective of the gas–liquid interface of sodium oleate (NaOL) solutions. Micro-flotation tests revealed a significant decrease in the flotation recovery of spodumene when NaOL was employed as a collector, dropping from 55.3% at 305.4 K to 5.1% at 277.3 K as the temperature decreased. A strong linear correlation between the surface tension of the NaOL solution and temperature was established. As the temperature decreased, the surface tension of 6 × 10⁻⁵ mol/L NaOL increased from 37.88 mN/m at 294.9 K to 40.71 mN/m at 281.9 K, while its critical micelle concentration decreased from 9.49 × 10⁻⁴ mol/L at 305.0 K to 6.85 × 10⁻⁴ mol/L at 288.0 K. Additionally, molecular dynamics (MD) simulations indicated that a decrease in temperature resulted in an enhancement of intermolecular action forces, a more compacted interfacial structure, and weakened molecular thermal motion at the gas–liquid interface of the NaOL solution. These variations were found to be the main reason for the rise in the surface tension of the NaOL solution as the temperature decreased, which in turn lowered its efficiency, resulting in a decrease in the flotation efficiency of spodumene.

Traditional dry magnetic separation has poor separation efficiency for fine-grained materials, and combining airflow and a magnetic field may be one of the most effective means to improve it. Based on the pneumatic drum magnetic separator developed by our team, an improved pneumatic magnetic separator with a segmented flow field is proposed, which pushes materials to move along the separation surface. Analysis of flow field in the separation zone and the forces on particles show that the improved pneumatic magnetic separator makes it easier to collect fine magnetic particles, while nonmagnetic particles are more easily removed by airflow. Separation test results also show that the iron grade and the recovery of concentrate improved from 37.89% and 74.75% to 51.76% and 91.79%, respectively. The separation efficiency of the pneumatic drum magnetic separator has been remarkably improved by optimizing airflow field in the separation zone.