Classifying – separating – and assorting solids – Magnetic – Paramagnetic
Reexamination Certificate
1999-02-08
2001-12-18
Jillions, John M. (Department: 3653)
Classifying, separating, and assorting solids
Magnetic
Paramagnetic
C209S225000, C209S228000, C209S231000, C209S232000
Reexamination Certificate
active
06330946
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of prior PCT International Application No. PCT/AU97/00496 which has an International filing date of Aug. 6, 1997 which designated the United States of America.
The present invention relates to apparatus and a method for separating particles such as minerals. More specifically the invention relates to apparatus and a method which utilises a rotating magnetic field for effecting separation of particles by rotation of individual particles in the rotating magnetic field.
Separators which utilize a magnetic field which rotates are known, but in prior art separators particle separation is primarily effected by magnetic attraction of magnetised particles in a magnetic field gradient, and is not significantly effected by particle rotation in a rotating magnetic field.
Prior art wet drum magnetic separators utilise rotations of a magnetic field to release entrapped non-magnetic and other adhering particles from magnetic flocs. In these prior art separators particle separation is not effected by particle rotation, and particles experience only a small number of rotations (between 2 and 4 complete rotations) before passing out of the separator.
Induced-roll types of magnetic separators are sometimes referred to as employing a rotating magnetic field. In these prior art separators, the field may rotate with the drum, but around any particular circumference the field is always in the same direction relative to the drum surface, and particle rotation plays no part in the actual separation process. Some separators which balance centrifugal forces against buoyancy in a magnetically controlled heavy liquid have also been referred to as employing a rotating magnetic field, but this field is not designed to produce particle rotations, and particle separation is not effected by particle rotations.
Modern eddy-current separators do use a rotating magnetic drum and a particle above the drum surface does experience a field which rotates. This rotation may cause non-ferrous metallic particles to rotate, and such particle rotation has been documented. However such particle rotations have previously been regarded as an undesirable side effect and a limiting factor which detracts from separator performance rather than as a means of aiding or accomplishing the separation. The rotations have been documented in order to determine ways to minimise them (eg. by flattening or squashing smaller particles). Modern eddy-current separators are designed to emphasise a magnetic field which rapidly changes direction radial to their magnetic drums rather than a magnetic field which rotates at a constant angular velocity. Particle rotation is not used as the means of accomplishing the separation.
The separator of the present invention utilizes a magnetic field such that the field direction or vector rotates. Mineral particles that are caused to rotate by rotation of the magnetic field are those particles that are separated. The rolling or spinning motion that is induced in particles by rotation of the magnetic field is used to influence those particles to move along a different path to that taken by particles that do not rotate as a result of the magnetic field rotations. In at least some embodiments of the present invention movement and magnetic separation of particles may be assisted by non-rotating magnetic or gravitational forces. In some embodiments of the invention movement and magnetic separation of the particles may be assisted by centrifugal forces. The particles to be separated may be delivered to the separator in any convenient fluid and by any convenient means. The rottating magnetic field may be generated by either mechanical or electrical means.
A convenient way of generating the effect of a rotating magnetic field is to use alternate magnetic poles spaced around the circumference of a rotating drum, as illustrated in
FIGS. 2
,
4
,
5
and
7
. This arrangement is similar to that employed in some present eddy current separators. The physical mechanism by which rotary motion is induced in a particle may be explained with reference to
FIG. 1. A
metal particle
10
supported on a stationary surface
11
is exposed to a rotating magnetic field set up via magnetic drum
12
. Magnetic drum
12
includes magnetic poles
13
which rotate in the direction shown via arrow A. Particle
10
experiences a moving magnetic field
14
which from the frame of reference of particle
10
rotates within a plane in the direction shown via arrow B. If particle
10
is metallic, the rotating magnetic field generates eddy currents in particle
10
which react with the rotating field to produce a rotating torque. If particle
10
is magnetic and non-metallic, the rotating magnetic field interacts with particle
10
to produce a rotating torque. Particle
10
experiences a torque in the direction in which the magnetic field rotates. This torque in combination with friction between particle
10
and surface
11
causes the particle to roll to the left along surface
11
in FIG.
1
.
For this separator to operate, particles must be sufficiently held to a surface in order for any particle rotation to cause it to roll. This is accomplished by using either gravity (as in
FIGS. 6
,
8
and
9
), particle attraction in a field gradient (the dominant force in FIGS.
2
and
3
), centrifugal force, or a combination of these forces. The arrangement shown in
FIGS. 6 and 7
, when used on weakly ferrimagnetic minerals, employs attraction in a field gradient as a means of reducing but not quite overcoming, the force of gravity. This allows weakly rotating particles to be rotated but still retain sufficient interaction with a surface so that their spinning will cause them to roll to one side.
The separator of the present invention is adapted to separate minerals on the basis of the magnetic and/or conductive properties of those minerals. These properties include magnetic susceptibility, the degree and type of magnetic ordering within the particles, the crystal structure of the particles, and the conductivity of the particles. Separation of particles may be controlled by several factors including some or all of the following: magnetic field strength of the rotating field; gradient of the magnetic field and its direction; variation of field strength as the magnetic field rotates; and frequency of rotation of the magnetic field.
Movement of mineral particles may be predominantly due to spin or rolling induced in the particles by the rotating magnetic field. The rotating field may be generated by mechanical and/or electronic means. Mechanical field generators may include permanent magnets and rotating elements such as drums, cylinders and the like. The latter may be rotatably driven via motive means such as electric motors or chemical engines or other sources of rotational power.
Electronic field generators may include a plurality of static windings adapted to be energized by alternating electric currents so as to generate a rotating magnetic field not unlike that in a stator of a rotating electric machine. In at least some embodiments of the present invention movement of the particles may be assisted by non-rotating or bulk magnetic forces exerted on particles to be separated.
The separator of the present invention can make particles spin continuously and individually, and this can have advantages over prior art methods for separating ferromagnetic and ferrimagnetic minerals. Individual spinning of particles may break up or prevent formation of magnetic flocs, and may prevent entrapment of non-magnetic particles and interaction between paramagnetic and ferromagnetic or ferrimagnetic minerals.
Separation of conductive particles may take place either in the dry or in a slurry. This is in contrast to prior art conductive minerals separation which requires drying of minerals before separation. No close screening may be required for input material to be separated.
The separator of the present invention may make use of crystallography of particles or degree of magnetic ordering within pa
Birch & Stewart Kolasch & Birch, LLP
Jillions John M.
KA PTY Ltd.
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