Process of Magnetic Separation and Apparatus Adapted to the Conduct of such Process.
Year: 1893

page_text: Date of Application, 13th June, 1893-Accepted, 15th July, 1893
UBTLEIE DIECIFICATION.
Process of Magnetic Separation and Apparatus Adapted to the
Conduct of such Process.
We, RICHARD HAWES SANDERS, residing at No. 1225 Locust Street, in the
City of Philadelphia, State of Pennsylvania, United States of America, Mining
Engineer, and CHARLES TROTTER THOMPSON, residing at No. 2116 Spruce
Street, in the City of Philadelphia aforesaid, Mechanical Engineer, do hereby
declare the nature of this invention and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
The following is a Specification of our said invention, reference being had to the
accompanying drawings.
Our invention is adapted to the separation of para-magnetic material, generally,
from admixture with non-para-magnetic material, but as we contemplate its use
primarily in connection with the separation of iron ore from its gangue, we shall
use the terms ore and gangue in this Specification as typical respectively of the two
classes of material, the term stock being used to indicate the admixture of the two
which is to be subjected to treatment.
Our invention is based upon the discovery of the peculiar behaviour of ore
particles under the following conditions:-
If an elongated surface presenting a magnetic field of single polarity be inclined
in the direction of its length so as to overhang, say at an angle of about seventy
degrees to the horizontal, and ore particles be fed against said surface at the upper
end of the incline, the particles will, if the intensity of the field be sufficient as
compared with their individual weight, cluster upon the overhanging polarized
surface adjacent to the point of feed. As new accretions are fed on at this same
point the cluster or group of detained particles will grow downward until it has
completely covered the polarized surface, to a depth depending, of course, on the
strength of the magnet. When this depth is attained throughout, the polarized
surface may be appropriately said to be charged; that is to say, the field is
supplied with the maximum number of particles which it is capable of completely
arresting in suspension, against the action of gravity. If now the feed of particles
be continued at the same point as before, the new accretion will surcharge the
polarized surface, and in so doing will displace from the point of arrival a substan-
tially equivalent mass of particles previously in suspension. Instead, however, of
completely dislodging the particles immediately adjacent to the point of feed, so
that they will directly drop clear of the magnetic field, the following phenomenon
will be observed.
The superficial particles previously suspended nearest the point of arrival will
move downwards in a direction practically parallel to the polarized surface,
displacing as they go, the next superficial particles previously suspended below
them, and these in turn affect similarly the superficial particles next below
them, so that a progressive displacement occurs down the entire face of the
suspended group until the lower end thereof is reached, when the particles which
for the time being have been suspended at the lowest point will upon displacement
fall off and pass out of the field. If the feed at the top be intermittent, the
phenomenon will take the form of a series of waves passing down the surface until
the discharge from the bottom occurs; but if the feed be continuous, a constant
stream of particles will appear to flow down the incline and discharge itself at the
ower end thereof.
It will furthermore be seen that as the particles descend, in the manner above
lescribed, they tumble over and over upon each other so as to undergo a thorough

page_text: shaking up and exposure of new surfaces. If now, instead of feeding ore particles,
or other para-magnetic material alone, against a polarized surface in the manner
described, stock be similarly fed, a selective action will take place whereby the ore
will be detained and diverted down in the general direction of said surface, whilst
the gangue will drop out. The maximum escape of gangue will occur immediately
adjacent to the point of arrival, but as the ore particles in their descent tumble
over and over upon one another, in the manner just described, any remaining
gangue, which has been mechanically detained within the cluster of adhering ore
particles, will be permitted to drop out. If the gangue be under the influence of
gravity alone (as distinguished from being acted upon by the air, or water current)
it will of course fall vertically downwards from the point of escape.
For the practical conduct of this process it is necessary that the length of the
polarized surface, as compared with the amount of its overhang, should be sufficient
be afford an opportunity for the travelling ore particles to thoroughly cleanse
themselves of gangue; and this condition on the one hand, and mechanical
convenience on the other, will suffice to determine practically the required length
through which the polarized surface should extend.
It will be noted that in the foregoing description of our process, we have specified
the use of a surface which exhibits polarity of only a single kind. By this we
mean that said surface should be so isolated from its correlative polar surface,
(cither by distance, or by the interposition of a screen between the two fields), that
the sensible accretion of the correlative pole should not be sufficient to build the
detained particles up in the form of closed circuits or chains, from pole to pole.
In such case the particles assume the form of very dense and compact masses and
their displacement will not occur to any substantial extent in the organized manner,
which we have just described as characteristic of our invention. Hence while, as
will hereafter appear, we are able in some form of apparatus to utilize both poles,
or both legs of a magnet, they are to be understood as really being independent of
each other and as having substantially no combined action upon the particles.
Furthermore, we desire to note at this point that, although a continuous polarized
surface constitutes the preferred type of apparatus for our invention, a series of
surfaces possessing similar polarity may be so combined as to exhibit the action
described, the particles appearing to fall from one surface to the next, when the
latter are properly arranged with relation to one another. As, however, such
arrangement is in reality nothing more than an aggregation of similar polarized
surfaces, each one of which operates upon the material in the manner characteristic
of our discovery, we do not deem it necessary to do more than allude to the
possibility of such arrangement in order to prevent a misunderstanding of terms
hereafter used in the singular number.
We will now proceed to describe, by reference to the drawings, a typical or
elementary apparatus, and some convenient variations thereof, for the conduct of
our process.
In said drawings
Figure 1 represents a front elevation of the clementary apparatus and comprises
also a diagrammatic representation of the action thereof upon the material;
Figure 2 is a vertical section on the line X X of Figure 1, and
Figure 3 is a transverse section through the magnet.
Figures 4 and 5 represent a modified apparatus, in which both poles of the
magnet are separately employed, said figures being respectively a front elevation
and a transverse section through the magnet.
Figures 6, 7 and 8 are, respectively, a vertical section, a partial front view and
a transverse section through the magnet, in a third variety of apparatus, employing
two separately acting polarized surfaces.
Referring to the type shown in Figure 1, A represents an open rectangular
frame work, in which is suspended, by means of the rods, a a, an elongated flat
plate, B, of soft iron or steel capable of being magnetized by means of the coil C,
whose strands are wound at right angles to the shortest axis of the plate B. The

page_text: terminals D E of said coil are placed in circuit with a dynamo, or other suitable
current generator. When energized the plate will of course have two polar
surfaces NS respectively, and it is so suspended as that the surface S shall
overhang, as indicated in Figure 1, at an angle of about seventy degrees to a
horizontal line. We preferably apply along each edge of the overhanging polar
surface, a shield F, which may conveniently be made of wood, slotted to receive
the projecting edge of the plate B, and extending outwards for some distance as
indicated in Figures 1 and 3, so as to protect the coil C, from contact with ore, and
limit the movement of particles in a direction back of the plane of the surface S.
Such shield is, however, only a convenient adjunct which we do not regard as
essential to the conduct of the process.
G represents a hopper to contain stock, terminating at its lower end in a spout, g,
whose delivery orifice is immediately beneath and in close proximity to the upper
end of the inclined polar surface S, so as to deliver the stock directly to said
surface.
At the bottom of the framework A, a transverse partition i, divides the area
beneath the polar surface, into two compartments or receptacles H I, respectively,
the plane of said partition being such that if upwardly prolonged it would intersect
the polar surface at a point quite near to the lower end thereof, as indicated clearly
in the side elevation seen in Figure 1.
The operation of the device is as follows
:―
The magnet being energized, stock is fed to the overhanging polar surface at the
upper end thereof and the phenomenon previously described occurs. The cluster
of detained ore particles grows downwards, as indicated at J, along the face of the
pole, whilst the gangue particles fall off in a shower, indicated at K.
By the time the ore particles J, have travelled down the polar surface to a point
coinciding with the plane of the partition, i, all, or substantially all of the gangue
has dropped off and been received at k, in the compartment 1. The ore particles,
on the other hand, travel past the plane of the partition i, and on reaching the
lower end of the polar surface S, are dislodged into the compartment H as indicated
at j.
The device just described presents what may be called an elementary apparatus
for the conduct of our process in that the surface employed is the actual pole
of the magnet and that only one pole is utilized.
We will now proceed to describe, by reference to the remaining figures, an
apparatus in which both poles of the magnet are independently used, and another
in which the polarized surfaces utilized are not the actual poles themselves.
Thus in the type shown in Figures 4 and 5 two plates, B₁, B', are employed,
united by a back plate, 61, so as to form in conjunction with the coils, C, C₁,
a borseshoe magnet having elongated overhanging poles N', S¹, respectively,
which may be appropriately provided with a shield F. The distance between
the polar surfaces N', S', is such that the ore within the field of one, is not
sensibly acted upon by the other, and thus any permanent aggregation of particles
in close circuits is prevented.
The feed takes place, if desired, from the same hopper, G', but by different
spounts g, each delivering in the proper relation to one polar surface, and the
operation is precisely the same as that before described.
In the form of apparatus shown in Figures 6, 7 and 8, a horseshoe magnet
is employed, consisting of a pair of plates B' B*, connected by means of a
transverse bar at one end, said bar being wound with the coil C. Instead
of utilizing the extreme polar surfaces N' S³ as was done in the previous instance,
we incline the legs of the magnet so that the edges n² ² of each leg, instead of
the ends thereof, shall constitute the overhanging polarized surface against which
the stock is to be fed. The projecting shield F may be employed as in the
previous instance, and the distance apart of the legs should be such as to prevent
the sensible action of one upon the ore detained by the other.
The stock being fed by independent spouts g arranged in the described relation

page_text: to the polarized surfaces n³ ³ the operation above set forth takes place and the ore
and gangue fall respectively, as indicated at kon opposite sides of the
partition.
Having thus described our invention, we wish to point out certain features which
distinguish it from previously known processes of separation and apparatus
employed therefor.
We are of course aware that it is not new to carry stock along an inclined
magnetic field by means of a belt or other conveyer, and we are also aware that
the use of horseshoe magnets in an inclined chute, or behind an inclined screen, is
not new, these latter devices having been used to clean grain and similar material
from accidentally mixed para-magnetic particles. Our invention, however, differs
from the former type of apparatus in that we absolutely dispense with the use of a
conveyer by reason of the new principle of operation involved in our discovery.
Our invention obviously differs from the latter type of apparatus, in which both
poles of the magnet or magnets co-act upon para-magnetic material, in that we
subject the ore to the action of but a single polarized surface and thus obviate the
practically permanent clustering which takes place where closed circuits can be
formed of the ore particles between the two adjacent and co-operative poles.
We desire also to note that although we prefer to feed the stock into direct
contact with the polarized surface, yet we do not desire to exclude the use of a
diaphragm covering the surface, provided such diaphragm does not substantially
interfere with the projection of the lines of force from such polarized surface to
form a magnetic field, in which the material can be subjected to the treatment
above described. Hence in using the words polarized surface in our claims, we
must not be understood as limiting ourselves to a process which involves the direct
contact between the ore particles and the magnet itself.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. The hereinbefore described process of magnetic separation, which consists in
feeding stock to the upper portion of an overhanging surface of substantially single
polarity, whereby the ore is detained and gangue permitted to drop off; causing
the ore to descend along said surface by new accretions fed at the upper portion
thereof, permitting the remaining gangue to drop out during the period of descent
and finally causing the discharge of the cleaned ore by surcharging the polar
surface, substantially as set forth.
2. The combination of a magnet having an overhanging elongated polarized
surface; a shield arranged along each side of said surface; a feeding device
arranged to deliver stock to the upper end of said surface and separate receptacles
for gangue and ore subjacent respectively to the upper and lower ends of said
surface, substantially as set forth.
Dated this 13th day of June 1893.
CARPMAEL & CO.,
Agents for the Applicants.