Xiayu Zheng

Particle capture of elliptic cross-section matrices for parallel stream high gradient magnetic separation

Purpose – The purpose of this paper is to model the particle capture of elliptic magnetic matrices for parallel stream type high magnetic separation, which can be a guidance for the development of novel elliptic cylinder matrices for high-gradient magnetic separation (HGMS). Design/methodology/approach – The magnetic field distribution around the elliptic matrices is investigated quantitatively and the magnetic field and gradient were calculated. The motion equations of the magnetic particles around the matrices were derived and the particle capture cross-section of elliptic matrices was studied and was compared with that of the conventional circular matrices. Findings – Elliptic matrices can present larger particle capture cross-section than the conventional circular matrices and can be a kind of promising matrices to be applied to HGMS. Originality/value – There is little literature investigating the magnetic characteristics and the particle capture of the elliptic matrices in HGMS, the study is of grea...

Particle capture efficiency of elliptic cylinder matrices for high-gradient magnetic separation

ABSTRACT 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.

Magnetic Field Simulation and Experimental Tests of Special Cross-Sectional Shape Matrices for High Gradient Magnetic Separation

The cross-sectional shape has great influence on the magnetic field characteristics of magnetic matrices in high gradient magnetic separation (HGMS). Suitable cross-sectional matrices can improve the recovery of fine weakly magnetic minerals and reduce mineral processing energy consumption. The performance of four types of cross-sectional shape matrices in the axial configuration of HGMS was studied through numerical simulation combined with experimental tests. The magnetic field generated by the matrices was simulated with ANSYS software, and the magnetic field strength, gradient, and magnetic force were analyzed and compared. The simulation results showed that diamond shaped, elliptical, square, and circular steel matrices reach magnetization saturation successively with increasing the magnetic induction, and the required magnetic induction is approximately 0.7, 0.8, 1, and 1.1 T, respectively. The magnetic field gradient increases with increasing the magnetic induction and then keeps constant when the matrices reach magnetization saturation. Within a wide range of the magnetic induction, the elliptical and square matrices present good magnetic field characteristics. The magnetic force near the surface of the square matrices is the largest but decreases rapidly and consequently has a small effect depth. The magnetic force near the surface of the elliptical matrices is relatively lower but decreases slowly and has a larger effect depth. The diamond-shaped matrices are easy to reach magnetization saturation, and the magnetic force decreases most rapidly. Magnetic matrices were manufactured, and magnetic separation experiments were conducted to verify the simulation results. The experimental results show that the elliptical and square matrices can obtain higher recovery in a wide range of magnetic induction, and the recovery of the elliptical matrices is the highest. The experimental results correspond well with the numerical simulation results, and the results indicate that the magnetic force effect depth is a very important factor influencing the performance of the matrices.

Effect of Matrix Shape on the Capture of Fine Weakly Magnetic Minerals in High-Gradient Magnetic Separation

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 Lh/Lv (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 Lfh/Lv value at which the capture radius and efficiency reach the maximum. The optimal Lh/Lv value increases with the increase in particle size and the decrease in matrix size. Within the Lh/Lv range of 1/3-3, the maximum particle capture efficiency (at the optimal Lh/Lv or at Lh/Lv = 3) under some arrangements can be much higher than the circular matrix (at Lh/Lv = 1), but the increment decreases with the increase in matrix size, the arrangement parameter d/Lv, 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.

Flotation separation of limonite from quartz with sodium oleate: effects of limonite dissolution and addition of sodium hexametaphosphate

The utilisation of limonite ore is potentially important to China as the high quality iron resource, such as magnetite and hematite of high grade, are rapidly depleting, but many detrimental impurities, such quartz and calcite etc, are difficult to upgrade to make suitable concentrates for the blast furnace. The flotation behaviour of limonite, quartz and their mixture by using sodium oleate as collector were studied systematically in this paper. Single-mineral flotation tests showed that the flotation recovery of limonite was much higher than that of quartz in a broad range of pH. However, flotation tests for the mixture of limonite and quartz showed rather poor mineral separation efficiency with the flotation recovery of both minerals being high in froth products. The flotation separation efficiency of limonite from quartz was substantially improved by adding sodium hexametaphosphate (SHMP) as a depressant for quartz flotation. To elucidate these phenomena, the solution species calculation of limonite dissolution and the measurements of iron ions content were carried out. It was found that iron ions or its species released into the pulp from the dissolving of limonite could effectively activate the flotation of quartz but have little influence on the flotation of limonite. In the presence of SHMP, iron ions or its species lost their activating power on quartz flotation which caused by the chemical reaction between SHMP and iron ions or its species, and then removed iron ions or its species from quartz surface into the solution.