GB2174020A

GB2174020A - Magnetic separation

Info

Publication number: GB2174020A
Application number: GB08505948A
Authority: GB
Inventors: Richard Gerber; Mark Harold Watmough
Original assignee: British Nuclear Fuels PLC
Current assignee: Sellafield Ltd
Priority date: 1985-03-07
Filing date: 1985-03-07
Publication date: 1986-10-29
Also published as: GB8505948D0

Abstract

A feed of material 3, comprising weakly magnetic and non-magnetic particles, falls under gravity through a high magnetic field gradient created by a pair of oppositely energised superconducting coils 7,8. The weakly magnetic particles in the feed are deflected radially towards the coils and are separated from the non-magnetic particles which fall vertically without deflection. An adjustable throat 4 is provided on the hopper 2. In another embodiment (Fig. 2), the material falls under gravity around the outside of the coils. The optimum ratios of inner and outer radii of the coils, their height and separation are given. <IMAGE>

Description

SPECIFICATION Improvements in and relating to magnetic separation The present invention relates to magneticseparation and in particularto open gradient magnetic separators.

It is known to effectthe separation of magentic materials from non-magnetic materials by means of magnetism. As an example mention can be made of the purification of iron ore to separate the ferromagnetic and non-ferromagneticconstituents. However difficulties can arise in the magnetic separation of weakly magnetic particles from non-magnetic particles on a large scale industrial process.

According to the present invention there is provided an open gradient magnetic separatorforthe separation of weakly magnetic particles from non-magnetic particles in a material supply, the separator comprising means for directing a flow ofthe material to fall under gravity between or about a pair of oppositely energised horizontal superconducting solenoid coils, the coils being spaced apart and arranged whereby overa region therebetween the magnetic density is a maximum.

The invention will be described further, by way of example, with reference to the accompanying drawings; in which: Figure lisa diagrammatic representation of a first embodiment of an open gradient magnetic separator; Figure 2 is a diagrammatic representation of a second embodiment of an open gradient magnetic separator; and Figure 3 is a schematic view ofthe arrangement of magnetic coils aboutthe axial and radial centre lines ofthe separator in Fig. 1 or Fig. 2.

With reference to Fig. lan open gradient magnetic separator comprises a steel vessel 1 having a hopper2 from which a feed material 3 can fall under gravity into the vessel 1. The hopper 2 is provided with an adjustable throat 4 whereby to selectively control the rate of flow of material into the vessel. A conical deflector5 is positioned symmetrically on the centre line ofthe vessel 1 such that material falling into the vessel from the hopper is deflected substantially uniformlytowardsthesidewall orwallsofthevessel.

The vessel 1 is surrounded by two horizontally mounted superconducting solenoid coils 7 and 8 which are symmetrically position above and below the transverse centre line ofthe vessel. The coils 7 and 8 are energised such that current in the coils flows in opposite directions. By energising the coils in opposite direction a high magnetic field gradient is obtained throughout the central region of the separatorin which the opposing magneticfields cross. The magnetic field strength is maximised by appropriate selection ofthe dimensions ofthe coils 7 and 8. Thus high values of both the magnetic field and themagnetic gradient are obtained over the central region.

Asplitter9, adjustable both in heightand radius, is located within the lower region of the vessel 1.

Fig. 2 differs from Fig. 1 inthatthefeed material is directed outside upper and lower horizontally mounted coils 10 and 11 respectively. As before the coils 10 and 11 are symmetrically positioned relative to the axial and transverse axes of the separator. For convenience a substantially uniform distribution of feed material is obtained aboutthe coils by means of a frusto-conical deflector 12 positioned beneath a plur ality offeed hoppers 13. A splitter 14, again adjustable both in height and radius, is located outsidethecoils andwithinanouterwall 15.

The feed material comprises a mixture of weakly magnetic particles and non-magnetic particles. The performance of the separator can be optimised by maximising the values ofthe magnetic field and the magnetic gradient overthe central region of the separator.

In operation and with reference to Fig. 1, feed particles in the hopper 2 fall under gravity on to the conical deflector 5. The deflector 5 forms a curtain of particles which fall through the interiorofthe coils 8.

Duetothe oppositeenergisation ofthecoilsthe magnetic gradient is a maximum at the central region.

As a resultthe magnetic particles in the feed experience a radial force in a direction towards the coils and are attracted to fall through an annular outer zone within the separator. The non-magnetic particles being unaffected fall vertically through the vessel from the deflector and are not attracted towards the coils. The splitter 9 within the vessel below the central region provides an annular outer channel 16forthe weakly magnetic particles and a central passage 17 for the non-magnetic particles.

The separator functions by utilising a magnetic traction force to extract or divert magnetic particles from a flow of magnetic and non-magnetic particles.

This depends on the magnetic force density experienced bythe particles in a separating zone and the magnetic force density is proportional to the product of the magnetic field strength and the magnetic gradient acrossthe separating zone. The performance ofthe separator is enhanced by maximising the product ofthe magnetic field and the magnetic gradient and extensive analysis of many different coil configurations and separator geometries has demonstrated the superiority ofthe following relationships.

1. For a predetermined radius ofseparatorvessel, the inner and outer radii of the coils, the extent ofthe coils and the distance between the coils is an optimum when at ratios indicated below. Reference is made to Fig. 3foridentification ofthe dimensions.

Ratio of Dimensions

Outer radius | 1.38 x Inner radius Extent of Coil 0.63 x Inner radius Start of Coil 0.25 x Inner radius 2. Forthe optimum configuration of the coils and a given feed material the radial distance between the edge of the deflector and the splitter is chosen such that the magnetic separation is independent of particle size.

Claims

1. An open gradient magnetic separatorforthe separation of weakly magnetic particles from nonmagnetic particles in a material supply comprising meansfor directing a flow ofthe material to fall under gravity tb rough a magnetic field created by a pair of oppositely energised superconducting coils, the coils being substantially co-axial and spaced apart such that over a region therebetween the magnetic density is a maximum.

2. Amagneticseparator as claimed in claim 1 in which the directing means comprises a deflector positioned and arrangedto permitthe supply mate rialtofallthrough the coils.

3. A magnetic separator as claimed in claim 1 in which the directing means comprises a deflector positioned and arranged to permitthesupplymate- rial to fall aboutthe coils.

4. A magnetic separator as claimed in claim 2 or 3 including means arranged at a position belowthe region of maximum magnetic density defining re spective flow paths for the separated weakly magnetic and non-magnetic particles.

5. A magneticseparatoras claimed in claim 4in which the flow path means is axially and radiaily adjustable.

6. An open gradient magnetic separator substantially as herein described with reference to and as illustrated in Figures 1 or 2 ofthe accompanying drawings.