GB2097293A - High gradient magnetic separation - Google Patents

Abstract

In a process in which magnetic material is trapped in a filter disposed in a magnetic field, and is unloaded by passing a fluid through the filter in the absence of the initial magnetic field, the magnetic field is first reduced to an intermediate value to allow unloading of the more weakly magnetic particles, the more strongly magnetic particles being retained and subsequently unloaded by further reduction of the magnetic field. Stage by stage reduction of the magnetic field during unloading allows separation of different species from the mixture.

Description

SPECIFICATION High gradient magnetic separation The present application relates to high gradient magnetic separation (HGMS) in which a magnetic material can be trapped by passing it through a filter placed between the poles of a magnet. The filter is fabricated from a ferromagnetic material usually in the form of wire, balis or rods. A strong magnetic force exists at the surface of the filter material and this enables the filter to trap magnetic particles. The material can subsequently be unloaded by passing a fluid through the filter in the absence of a magnetic field.

For some applications however it is required to isolate a magnetic species which exists in association with another species which is more strongly magnetic and possibly with other species which are non-magnetic. The above technique can achieve this only by passing the feed through a number of magnets of different strength or passing the feed several times through the same magnet, and varying the field and cleaning the filter between passes. In either case the process is complex and extra plant is required.

In the present scheme these disadvantages are eliminated by using the unloading stage to achieve separation between magnetic species.

In the proposed scheme, the following sequence is carried out: i. The feed is supplied into the magnet in the usual way, thus separating the non-magnetic (i.e. diamagnetic) and very weakly magnetic constituents from the magnetic part of the feed.

ii. The filter is then unloaded, but with the magnet partly energised. With the correct choice of unloading magnetic field and cleaning fluid flow rate the moderately magnetic particles will be detached from the filter while the strongly magnetic particles remain held.

iii. The filter is then unloaded with the magnet completely de-energised, thus releasing the strongly magnetic particles from the filter.

Hence a detailed classification of the feed into un-magnetised, weakly magnetised and strongly magnetised species can be achieved using one magnet system and a loading/unloading sequence. This process can obviously be extended to achieve a more detailed classification by using an unloading sequence with progressively reduced magnetic field.

Thus, in summary, this invention provides a method of obtaining a partial separation of strongly magnetic from weakly magnetic particles trapped on an HGMS filter by unloading the filter in two stages; the first stage being in the presence of a residual magnetic field, and the second stage in the absence of magnetic field.

A number of unloads can be carried out with the magnetic field being progressively reduced.

The magnetic field may be generated by an electromagnetic winding, in which case variation of the magnetic field is achieved by altering the excitation in the winding. Alternatively the magnetic field may be generated by a permanent magnet, and here the field variation is achieved by physically moving the filter relative to the pole pieces of the permanent magnet.

The fluid used for unloading may be either liquid (including water) or gas (including air).

As an example the method can be applied to the separation of uranium compounds from mine ores. The uranium compounds are magnetic, while most of the other constituents of the ore are non-magnetic. The ore can be fed in when the ambient magnetic field at the filter is about 2 Tesla. The filter can be subsequently unloaded when the magnetic field at the filter is reduced in steps to 1.6 Tesla, 1.2 Tesla, 0.8 Tesla and 0.4 Tesla. In this way, the uranium recovery is made as large as possible and a substantial part of this uranium is collected in a more concentrated form.

The starting material is a suspension of the ore. Water is used for unloading. The filter material in this case is stainless steel balls.

1. A method of high-gradient magnetic separation wherein the material to be separated is fed through a filter disposed in a magnetic field and the magnetic material trapped in the filter is unloaded by the passage of a fluid through the filter in the absence of the magnetic field characterized in that the initial unloading is carried out with a reduced magnetic field to remove particles which are less magnetic while leaving the more magnetic particles to be removed in the absence of the magnetic field.

2. A method as claimed in claim 1 in which the magnetic field is progressively reduced during the unloading.

3. A method as claimed in claim 2 in which the magnetic field is reduced in stages.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION High gradient magnetic separation The present application relates to high gradient magnetic separation (HGMS) in which a magnetic material can be trapped by passing it through a filter placed between the poles of a magnet. The filter is fabricated from a ferromagnetic material usually in the form of wire, balis or rods. A strong magnetic force exists at the surface of the filter material and this enables the filter to trap magnetic particles. The material can subsequently be unloaded by passing a fluid through the filter in the absence of a magnetic field. For some applications however it is required to isolate a magnetic species which exists in association with another species which is more strongly magnetic and possibly with other species which are non-magnetic. The above technique can achieve this only by passing the feed through a number of magnets of different strength or passing the feed several times through the same magnet, and varying the field and cleaning the filter between passes. In either case the process is complex and extra plant is required. In the present scheme these disadvantages are eliminated by using the unloading stage to achieve separation between magnetic species. In the proposed scheme, the following sequence is carried out: i. The feed is supplied into the magnet in the usual way, thus separating the non-magnetic (i.e. diamagnetic) and very weakly magnetic constituents from the magnetic part of the feed. ii. The filter is then unloaded, but with the magnet partly energised. With the correct choice of unloading magnetic field and cleaning fluid flow rate the moderately magnetic particles will be detached from the filter while the strongly magnetic particles remain held. iii. The filter is then unloaded with the magnet completely de-energised, thus releasing the strongly magnetic particles from the filter. Hence a detailed classification of the feed into un-magnetised, weakly magnetised and strongly magnetised species can be achieved using one magnet system and a loading/unloading sequence. This process can obviously be extended to achieve a more detailed classification by using an unloading sequence with progressively reduced magnetic field. Thus, in summary, this invention provides a method of obtaining a partial separation of strongly magnetic from weakly magnetic particles trapped on an HGMS filter by unloading the filter in two stages; the first stage being in the presence of a residual magnetic field, and the second stage in the absence of magnetic field. A number of unloads can be carried out with the magnetic field being progressively reduced. The magnetic field may be generated by an electromagnetic winding, in which case variation of the magnetic field is achieved by altering the excitation in the winding. Alternatively the magnetic field may be generated by a permanent magnet, and here the field variation is achieved by physically moving the filter relative to the pole pieces of the permanent magnet. The fluid used for unloading may be either liquid (including water) or gas (including air). As an example the method can be applied to the separation of uranium compounds from mine ores. The uranium compounds are magnetic, while most of the other constituents of the ore are non-magnetic. The ore can be fed in when the ambient magnetic field at the filter is about 2 Tesla. The filter can be subsequently unloaded when the magnetic field at the filter is reduced in steps to 1.6 Tesla, 1.2 Tesla, 0.8 Tesla and 0.4 Tesla. In this way, the uranium recovery is made as large as possible and a substantial part of this uranium is collected in a more concentrated form. The starting material is a suspension of the ore. Water is used for unloading. The filter material in this case is stainless steel balls. CLAIMS

1. A method of high-gradient magnetic separation wherein the material to be separated is fed through a filter disposed in a magnetic field and the magnetic material trapped in the filter is unloaded by the passage of a fluid through the filter in the absence of the magnetic field characterized in that the initial unloading is carried out with a reduced magnetic field to remove particles which are less magnetic while leaving the more magnetic particles to be removed in the absence of the magnetic field.

2. A method as claimed in claim 1 in which the magnetic field is progressively reduced during the unloading.

3. A method as claimed in claim 2 in which the magnetic field is reduced in stages.