F. Friedlaender

Generalization of HGMS theory: The capture of ultra-fine particles

A generalized HGMS theory describing particle capture of ultra-fine particles is formulated and the conditions for the appearance of the dynamic and static buildup are analyzed. A particle size criterion for the generalized and conventional theories to become coincidental is established. Typical examples of capture of paramagnetic, diamagnetic and ferromagnetic particles are used to illustrate the consequences of the new theory.

Magnetic separation of submicron particles

The application of high gradient magnetic separation to the capture of submicron-sized particles is studied. The steady state solution of the diffusion equation applicable to diffusion processes taking place under the influence of external forces is obtained. The relevance of the critical particle size to the phenomena of dynamic and static capture is discussed for various materials ranging from ferromagnetic to diamagnetic. The experimental results obtained are shown to be in satisfactory agreement with the theoretical predictions.

Application of magnetic susceptibility gradients to magnetic separation

Particle separation in a magnetic colloidal fluid with a susceptibility gradient created by means of a Frantz‐Isodynamic magnet is described. The positions where particles and fluid are in equilibrium are a function of the particle magnetic susceptibility only. This method allows magnetic separation of several materials with a wide range of magnetic susceptibilities in a single separator with multiple dividers. A model separator was constructed. The magnetic gradient of the Frantz magnet and the concentration gradient of the magnetic colloids were calibrated. Separations were carried out using fine particles of Mn2P2O7, CuO, and Al2O3. The results confirm the feasibility of this method. The experimental data agree quite well with calculations based on the calibrated concentration gradient.

Selective seeding for magnetic Separation

Selective seeding utilizes surface chemistry to bond a desired mineral or minerals to introduced ferromagnetic seeds. Experiments were performed using finely ground Al(OH) 3 (gibbsite), SiO 2 (quartz), and Fe 3 O 4 (magnetite). The mineral particles were screened and only those having grain sizes between 20 and 2 μm were used. The materials were dispersed in a water slurry with 5% solid contents by 100 ppm Na 2 S and/or 100 ppm NaF. Two ppm polyacrylamide-acrylate was employed to flocculate Al(OH) 3 and Fe 3 O 4 . Magnetic separation in a HGMS coarse stainless steel wool model filter removed 73% of the SiO 2 and the Al(OH) 3 was upgraded from 40% to 69% with 93% yield. Repeated dispersal both chemically and mechanically with subsequent flocculation resulted in further upgrading of Al(OH) 3 to 79% with 87% recovery after the 3rd stage. Magnetite was finally recovered at 92% purity with 83% yield.

Wall states in a bubble moving in a rotating field gradient

In the rotating gradient experiment, a magnetic bubble is in steady-state circular motion. This experiment is reviewed as a method for determining the dynamical wall structure of a magnetic bubble. New data obtained by this technique on a low damping, unimplanted sample are presented. The bubble is brought to a critical velocity where one or two Bloch curves punch through and form vertical Bloch line pairs of opposite twist. A 0.15 Oe, 5.5 MHz ac tickle field was superposed on the dc bias to make possible domain motion. The experimentally determined values of Bloch curve nucleation and punch-through velocities were 2 and 4 m/s, respectively.

The collection of strongly magnetic particles in HGMS

Abstract The process of collecting strongly magnetic particles is studied both experimentally and theoretically in a single wire arrangement of high gradient magnetic separation. It is found that for such particles the build-up consists of two regions: a compact build-up region close to the collection wire, and a region of particle chains, stretching from the compact build-up along the direction of the magnetic field. The chains are not entirely stable. The separation between them is found to depend on their length, the magnetization and size of the captured particles, and the magnetization of the HGMS collector.

Collection of micron-sized particles at high velocities in HGMS

The collection of micron-sized, strongly magnetic particles is studied at flow velocities ranging from 21 to 73cm/s in different collector arrangements of a model high gradient magnetic separator. The buildup of Fe 3 O 4 particles is compared for different flow velocities, applied magnetic fields and particle concentrations for five different collector geometries. It is found that the longitudinal configuration of parallel nickel wires shows the largest buildup, closely followed by the transverse arrangements and the parallel wires in the axial configuration, while the longitudinal grid has the smallest particle buildup at a given time. At low particle concentrations - where the saturation of the filter cannot be reached during the experiments - a higher flow velocity leads to an increased particle buildup. An increase of the magnetic field has hardly any effect for all concentrations and flow velocities used in our experiments. The results of this research show that the HGMS filter can be used effectively to remove micron-sized, strongly magnetic particles from a liquid flowing through the filter at high velocities.

High gradient magnetic separation II: Single wire studies of shale oils

The single wire high gradient magnetic separation (HGMS) technique was used to investigate the buildup process of solid particles found in several different types of shale oils. The effects of slurry temperature, magnetic field, flow velocity, and solvent concentration on solid removal were determined. The results indicate that the HGMS technique is effective in removing solid particles from shale oil fluids. The efficiency can be further improved by reducing the viscosity of the shale oil slurry by heating and/or solvent dilution.

Controlled generation of stable winding and unwinding vertical Bloch lines in

Generation of pairs of Bloch loops (BL) and vertical Bloch lines (VBL) occurs when the bubble translational velocity is monotonically increased. A magnetic bubble is translated continuously in a circular trajectory by means of the Rotating Gradient Experiment (RGE) and changes in the values of the winding number (S) and the dimensionless momentum (P) are observed. The specific transitions of the bubble wall structure are always found to be repeatable under the same experimental conditions. Increases in S are generally seen for the clockwise (CW) circulation, while decreases in S occur for the CCW sense of circulation. In addition to finding S with the RGE, the Rocking Experiment (RE) is used to independently determine the value of S from the deflection angle of the bubble trajectory. In all cases, the values of S determined from the RGE and from the RE have been found to be the same. Particular cases of transitions of S and P are reviewed for three samples having different compositions and material parameters. Changes in the value of S are caused by the annihilation of pairs of VBLs during a bubble state transition. Any two +π (or -π) VBLs are found to stay together both for moving and stationary bubbles.

Removal of paramagnetic particles from single wire HGMS

The partial removal of paramagnetic particles from a wire in the axial flow configuration was studied. Saturation accumulation radii are larger when the wire is first saturated at a higher field H which subsequently is reduced to H o than when buildup proceeds to H o only. The amount of material collected on the wire depends on the history of the collection process. The results can be explained on the basis of the structural strength of the buildup, and different friction factors.