Prominent bulk pinning effect in the MgB_2 superconductor

We report the magnetic-field dependence of the irreversible magnetization of the recently discovered binary superconductor MgB$_{2}$. For the temperature region of $T< 0.9T_c$, the contribution of the bulk pinning to the magnetization overwhelms that of the surface pinning. This was evident from the fact that the magnetization curves, $M(H)$, were well described by the critical-state model without considering the surface pinning effect. It was also found that the $M(H)$ curves at various temperatures scaled when the field and the magnetization were normalized by the characteristic scaling factors $H^\ast(T)$ and $M^\ast(T)$, respectively. This feature suggests that the pinning mechanism determining the hysteresis in $M(H)$ is unique below $T=T_c$.Comment: 4pages and 4 figures. Phys. Rev. B (accepted

Vortex capture in high gradient magnetic separators at moderate Reynolds number

The authors report on an experimental investigation of the effect of increasing the slurry velocity in a single-wire cell to achieve a working-wire Reynolds number, Re, in the range 4-30. Attention is focused on this range because the slurry velocities are high enough for the boundary layer to have detached itself from the wire and for stable standing vortices to have formed at the rear of the wire. The particle-wire interaction and the flow domain around the wire are considered. The possibility of a turbulent contribution to rear wire capture due to the introduction of turbulence generators in the flow regime is explored. The interaction studied is basic to high-gradient magnetic separation<br/

Determination of magnetic susceptibility of loaded micro-organisms in bio-magnetic separation

Microorganisms and microbial products can be highly efficient bioaccumulators of soluble and particulate forms of metals, especially from dilute external concentrations. The authors outline a video imaging technique in which biological particle velocity profiles were obtained as they interacted with a ferromagnetic wire in a single-wire cell. These profiles were further analyzed using a dedicated image processing workstation. The whole process is automated and is suitable for analyzing particles with different magnetic susceptibilities. The bioaccumulation systems investigated were of two categories. The first was an aerobic process in which the microorganisms of Bacillus subtilis and Candida utilis were used to precipitate metal phosphates onto their cell walls as they cleaved glycerol 3-phosphate, their energy source, from a solution containing uranyl ions. The second was an anaerobic process in which Desulfovibrio microbial biomass was used to reduce sulphate to sulphide<br/

Extraction of heavy metals using microorganisms and high gradient magnetic separation

It is pointed out that a large number of microorganisms have affinity to ingest or precipitate ion species onto their surfaces. In the case of magnetic ionic species, magnetic separation methods could be applied to remove the ion-loaded organisms from the surroundings. A wide range of metal ions were studied in the experiments described. The results show that the microorganisms developed an appreciable magnetic moment which lends to their removal by magnetic separation. The biomagnetic separation process was shown to be effective in reducing the concentration of a large number of ions either in multi-ion solutions or in a single metal ion solution. Reduction in most instances was from 10-100 p.p.m. to 10-100 p.p.b., a 90% removal. The single wire technique proved useful in the magnetic characterization of the microorganisms. The results indicate that this procedure is effective in estimating the magnetic susceptibilities of individual particles. The process described will have applications in the mineral processing industry, in the treatment of effluents from the nuclear industry, and in the recovery of precious metals<br/

The evaluation of HGMS for mineral processing with a single wire

In this short communication it is shown that it is possible to undertake inexpensive but useful preliminary mineral studies using single–wire HGMS. Such studies enable an assessment to be made of the viability of HGMS as a large-scale processing technique for particular mineral slurries.<br/