Pulsation curves strengthen the high gradient magnetic separation process: Experimental study and simulation explanation

The pulsating slurry high gradient magnetic separator (PHGMS) has been widely used for the separation of feebly magnetic materials. As the main competing force, pulsating slurry effectively overcomes matrix blockage and affects the buildup behavior of particles. At present, the used pulse shape in PHGMS constitutes a sinusoidal harmonic vertical motion in which the duration and intensity of the impulsion and suction strokes are similar. However, other pulsation profiles, such as, trapezoidal shape and saw-tooth shape pulses, can also be obtained depending on the stratification mechanism. There is little literature to focus on how pulse shape influences the performance of PHGMS. The change of curve could be a method worth exploring to improve the separation. In this paper, the asymmetry pulsating curves are obtained by switching the velocity of the step motor during one cycle. Then, the single-wire experiments, single-wire 2D numerical simulation and multi-wires experiments are presented to indicate the effect of different pulse shapes. In single-wire experiments, compared with the traditional sinusoidal harmonic curve, the asymmetry pulsating curves have a higher grade, finer particle buildup, but lower accumulation volume. The curves of the rapid downward stroke and slow upward stroke are better than the inverse movement curve in asymmetry pulsation. The results of separating the up and downstream accumulations on the magnetized wire and numerical simulation reveal that these effects can be attributed to the direction of net force and vortex strengthening. The trajectory simulation of multi-component obtains a similar result with single-wire experiments to confirm the superiority of rapid downward stroke and slow upward stroke in selectivity. However, in multi-wires experiments, due to the matrix blockage the curves of rapid upward stroke and slow upward stroke show the greater potential advantages in both grade and weight compared with other curves at condition of high feed velocity.