GB2187117A - Magnetic analytical method and apparatus - Google Patents

Abstract

Particles are separated into fractions in accordance with their magnetic susceptibility to provide a magnetic analysis of a sample by causing the particles to follow a free falling trajectory, and providing a magnetic field along the path of the trajectory. In an embodiment particles from hopper 13 pass along belt 10 over a magnetic roll 11. The separated particles are decelerated in a liquid 21 maintained by inlet 18 and overflow 19. Detailed consideration of the various forces on the particles is given (Figs. 2 to 4). <IMAGE>

Description

SPECIFICATION Analytical method and apparatus This invention relates to a method of analysing an ore body magnetically, and the apparatus suitable for use in the method.

In magnetic separation processes it is important to monitor the magnetic properties of the ore body to ensure that optimum results are obtained. The magnetic properties of the ore will determine the type of separator required to provide the best results, and also determine feed rates, particle size requirements, etc.

Itisan objectofthe invention to provide a method and meansforproviding an accurate magneticanalysis of an ore sample for the above purpose. It will be appreciated that such an analysis will also be useful in other fields, particularly for prospecting.

According to the invention a method of separating particles into fractions in accordance with their mag- neticsusceptabilityto provide a magnetic analysis of a sample comprises the steps of causing the particles to foliowa free falling trajectory, and providing a magneticfield along the path of the trajectory so thatthe trajectory of particles of different magnetic susceptability is varied according to such susceptability. Thus in one arrangement the trajectory of a para-magnetic particle will be shortened in respect of horizontal travel relative to a non-magnetic ordia-magnetic particle.

Preferably the particles will be launched from the surface of a roll orthe likewith particles of different magnetic susceptability leaving the surface at different positions thereon. Preferably the roll will provide the magnetic force and will rotate during the process of the invention.

With such an arrangement the method provides for the particles to be subjected to the following force viz to gravity; to a magnetic force drawing the particles onto the roll surface; to a centrifugal force opposing the magneticforce; and to a friction force between the particle and roll surface such force opposing theforceof gravity; with all the above forces determining the point atwhich the particles will leave the roll surface two follow a free falling trajectory.

Further according to the inventionthe method includes the step of collection particles at the ends oftheir trajectories at a plurality of catchment zones. It has been found that with the method of the invention the trajectories of particles are predictable and accordingly particles can be grouped accordingly to magnetic susceptability.

Also according to the invention the method includes the step of decelerating the particles preferably in a liquid medium priorto collection at the catchmentzones.

In one arrangement according to the invention it is envisaged that a horizontal velocity will be imparted to the particles by depositing these on and by releasing these from the end of a substantially horizontally disposed moving endless belt, with the roll defining the end zone ofthe belt.

With the above arrangement the method requires thatthe speed of the belt and the strength of a magnetic field generated by the roll will be such that non-magneticand most para-magnetic materials will be propelled and discharged to the front of the leading extremity ofthe roll.

Also included within the scope ofthe invention is apparatus suitable for use in the method comprising a pathway along which particles move to be discharged at an end zone thereofto follow a free falling trajectory, a magnetic device adapted to create a magnetic field to influence the trajectory of the particles, and a plurality of catchment containers wherein particles are collected at the ends oftheirfree falling trajectories.

Preferably the magnetic device will be in the form of a composite magnetic roll while the pathway will be defined by an endless belt orthe like which moves overthe roll, the roll defining the end zone of the pathway.

Preferably also the catchment containers will be housed in a trough structure adapted to contain a liquid medium so that the catchment containers are capable of being submersed in use in the liquid medium.

Furtherfeatures of the invention will be apparent from the preferred embodiment which is described below purely by way of example with reference to the accompanying drawings wherein: Figure lisa schematic representation of analysing equipment in accordance with the invention, Figure2 is a schematic illustration offorces acting on a particle on a surface of a magnetic roll which forms partofthe equipment in Figure 1, Figure 3 is a schematic illustration of the trajectory of a para-magnetic particle leaving the roll as shown in Figure 2, Figure 4 is a schematic view of the various trajectories which are followed by magnetic particles leaving the roll in Figure 2 in accordance with their magnetic susceptability, and Figure 5 is a graph of cumulative percentage reduction by weight against various magnetic separating processes for a particular ore sample.

Referring to the drawing, apparatus for analysing an ore body in respect of magnetic susceptabilitycomprises a dry feed hopper 13 which is adapted to feed ore particles onto an endless belt conveyor. The upper surface ofthe belt conveyor 10 provides a pathway along which the ore particles are accelerated forsubse- quent discharge at the end zone thereof. The end zone ofthe pathway is defined by a magnetic roll 11 around which the belt 10 reverses its direction of movement. It has been found that the particles will leave the periphery of the roll 11 at predetermined launching positions in accordance with their magneticsuscept ability,fora given belt speed.Upon leaving the peripheryofthe roll 11 the particles will follow a pred- etermined trajectory and the particles can therefore be graded in accordance with their magnetic suscept- ability. The apparatus which is shown schematically in Figure 1 accordingly provides for a series a catchment containers which is designed to collect such graded particles.Thus a catchmentzone 14 located in a position furthestfrom the magnetic roll 11 will be adapted to collect non-magnetic and diamagnetic particles which will havethe longest trajectory being unaffected by the magnetic field of the roll 11.A plurality ofcatchment zones 16 will be adapted to collect para-magnetic material in accordance with the magnetic susceptability of these, while a zone 15 which is located upstream from the roll 11 will be adapted to collect highly magnetic particles which will tend to adhere to the roll 11 until the belt 10 separates the particles from the roll 11.

In orderto minimise rebounding and jumping of particles during the collection process the invention providesforthe catchmentzones 14,15 and 16to besubmersed in a liquid medium with the liquid level shown at21.An inlet for liquid is provided at 18 and an opposed overflow zone at 19. When the particlesstnke the liquid level 21 they are decelerated and tend to reportto the correct predetermined catchment container, floating downwardly substantially vertically.

As mentioned above applicant has determined that particles will leave the surface ofthe roll 11 from various launching positions according to magneticsusceptability and follow a predeterminedtrajectory which is in turn determined bythe point atwhich a particle leaves the surface 11.

With reference to Figure 3, the trajectory 50 of a non-magnetic particle is illustrated. The particle will leave the surface ofthe roll from a launching position P. Thetrajectory is parabolic and described bythefollowing formula.

1 X2 -- Sina Y = 2R 3 Cosa Paramagnetic particles will leave the roll from different launching positions designated by P1.With reference to Figure 4 the forces acting on a paramagnetic particle are illustrated and these forces arethefollowing: Gravity force Fg Radial Component of Gravity Fgr Tangential Component of Gravity Fgt Centrifugal Force Fc Magnetic Force Fmr Friction Force Ff Reaction Thrust T When the friction force Ff is smallerthan the tangential component ofthe gravity force Fgtthe paramagnetic particle will accelerate down the surface of the roll leaving the roll at point P1. Location ofthe point P1 is determined by the angle al.Since cos a1 for paramagnetic material is smaller than cos afornonmagnetic material the point P1 is vertically lowerthan the point p as shown in Figure 5. Howeverthetrajectories in both cases are parabolic and the formula I applies in both cases.

With highly magnetic material the magnetic force substantially overcomes the effects of both centrifugal force and gravity and such particles are accordingly trapped on the belt and carried around the roll until the belt separates from the roll whereupon the particles are removed from the magnetic influence of the roll to fall downwardly underthe influence of gravity.

In Figure 4the trajectory of non-magnetic material is shown at 50. Paramagnetic material will range be tween trajectories 51 and 52 shown by the bracket 55, magnetic material will range between the trajectories 52 and 53 as shown by the bracket 56, while highly magnetic material will followtrajectories ranging between 53 and 54shown bythe bracket 57.

The invention will enable a detailed analysis ofthe magnetic characteristics of the particles in the sample to be made. Such an analysis can be made quickly and with a high degree of efficiency and will be useful in the selection of the optimum magnetic separation equipment for ore treatment.

Such an analysis can further bye updated virtually continuously to ensure efficient operation of theequipment. For example, where the choice of separation equipment is between wet and dry processes utilising barium ferrite orsamarium cobalt permanent magnetic rolls, a analysis of an ore sample by means ofthe method ofthe invention will enable a suitable selection to be made. Thus the curve 20 shown in Figure5 couid be obtained for a given sampleforthe purposes of making the selection.By weighing each fraction separated from the ore sample a cumulative percentage reduction value is obtained on theY co-ordinate. On the horizontalXco-ordinatethe magnetic processes above are indicated with the numeral 1 indicating a wet BaFe process, numeral 2 indicating a dry BaFe process, numeral 3 a wetSmCo process, numeral 4a dry SmCo process, and numeral 5 a H.l.M.S process. Thus with the sample represented in Figure 2, where an 80% to 100% reduction is required, a wet SmCo or a dry SmCo process would be suitable.

As previously mentioned the method of the invention will also be suitable in detecting ore bodies, such as kimberlite bodies, where use is made of indicator minerals in the detection process. The invention will enable indicator minerals to be separated from an ore samplewith relative ease.

Doubtless variations of the invention existwithout departing from the principles set out in the consistory clauses.

Claims (15)

1. A method of separating particles into fractions in accordance with their magnetic susceptabilityto provide a magnetic analysis of a sample comprising the steps of causing the particlestofollowafreefalling trajectory, and providing a magneticfield along the path ofthe trajectory so that the trajectory of particles of different magnetic susceptability is varied according to such susceptability.

2. The method according to claim 1 including the step of launching the particles from the surface of a rotating roll or the likewith particles of different magnetic susceptability leaving the surface of such roll at different positions thereon.

3. The method according to claim 2wherein the particles are subjected to a pluralityofforceswhich determine the pointatwhich the particles will leave the surface of the roll to follow a free falling projectory, such forces comprising gravity; a magnetic force drawing the particles onto the roll surface; a centrifugal force opposing the magneticforce; and a friction force between the particles and the roll surface, such force opposing theforceofgravity.

4. The method according to any one of claims 1 to 3 including the step of collection particles atthe ends of their trajectories at a plurality of catchment zones.

5. The method according to claim 4includingthe step of decelerating the particles priorto collection at the catchmentzones.

6. The method according to claim 5 wherein the particles are decelerated in a liquid medium.

7. The method according to any one of claims 1 to 6 including the step of imparting a velocitytothe particles in a horizontal direction.

8. The method according to claim 7 wherein the velocity in a horizontal direction is imparted tothe particles by releasing these from the end of a substantially horizontally disposed moving endless belt with a roll or the like defining the end zone of such belt.

9. The method according to claim 8wherein the magnetic field is provided in the zone of the roll, and the speed of the belt and the strength of such magneticfield is such that non-magnetic materials are propelled and discharged to the front of the leading extremity of the roll.

10. A method of separating particles into fractions in accordance with a magnetic susceptability to provide a magnetic analysis of a sample, substantially as herein described with reference to the accompanying drawings.

11. Apparatus suitable for use in the method claimed in any one of claims 1 to 10 comprising a pathway along which particles move to be discharged at an end zone thereof to follow a free falling trajectory, a magnetic device adapted to create a magnetic field to influence the trajectory ofthe particles, and a plurality of catchment containers wherein particles are collected at the ends oftheirfree falling trajectories.

12. Apparatus according to claim 11 wherein the magnetic device is in theform of a composite magnetic roll orthe like.

13. Apparatus according to claim 11 orclaim 12 wherein the pathway is defined by an endless beltorthe like which moves over a roll orthe like, the roll defining the end zone of the pathway.

14. Apparatus according to any one of claims 11 to 13 wherein the catchment containers are housed in a trough structure adapted to contain a liquid medium sothatthe catchmentcontainers are capable of being submerged in use in the liquid medium.

15. Apparatus suitableforuse inthe method claimed in any one of claims 1 to 10 substantially as herein described with reference to the accompanying drawings.