Process and apparatus for separating particles by relative density

A particle separation method and apparatus carrying forward the teachings of U.S. Pat. No. 4,148,725 whereby separation of particles by density takes place in a size-classified fluidized bed of particles. Particles are disposed on a supporting surface having a plurality of generally concentric annular vertical reaction surfaces which together forms a plurality of annular channels occupied by the particles to be separated. The supporting surface and annular surfaces are agitated with a gyratory motion so as to induce particles in the fluidized bed to move within channels, and through openings between annular channels, toward a central collection zone. In the improved apparatus, the collection zone includes a plurality of vertically spaced horizontal reaction surfaces which enhance the fluidity of particles within that zone. A vertical barrier surface provides a smaller, annular zone of concentration at the center of the collection zone. Another improvement includes a cover over the top of the annular channels for contacting denser particles dispersed over the top of the fluidized particle bed and driving them downwardly into the channels. Any dispersed particles not driven downwardly are permitted to exit from an aperture as light density waste.

RELATED APPLICATIONS 
This application carries forward the teachings of my earlier U.S. Pat. No. 
4,148,725, issued on Apr. 10, 1979. 
FIELD OF THE INVENTION 
This invention relates to certain improvements in the separation and 
concentration of particles according to relative mass and/or density. In 
particular, it relates to an improved process and apparatus wherein 
particles in an aggregated mass of size-classified particles are contacted 
with various reaction surfaces so as to fluidize the particle bed and 
cause particles within such bed to move in a preferred direction for 
density separation or concentration of the feed material. The process is 
especially useful in the concentration of dry particulate ores and 
minerals, where the process can be applied to upgrading the feed material. 
For example, the invention readily enables the concentration of dense 
particles, such as gold or other metal particulates, from a much larger 
volume of less dense dry sand or gravel of the same general particle size 
classification. 
The invention is remarkably effective in separating dense particles from a 
homogeneous flowable bed of particles of different densities, if the 
particles have been properly classified so as to maintain a difference in 
mass between the selected particles and the remaining, or waste, 
particles. It therefore has promising use in the concentration of placer 
ores which cannot be concentrated by washing and sluicing where water is 
unavailable. Even where such a placer is economic in its raw state, it can 
be made more profitable by using the invention to reduce the volume of raw 
feed material that must be transported and/or conventionally processed. 
Similarly, the invention may be used to recover particles from particulate 
waste according to relative mass or density. 
BACKGROUND OF THE INVENTION 
Known processes for separating and classifying particles contained in an 
aggregate particle mass are truly numerous. Many of these processes are 
limited to separating particles according to size (classifying) as, for 
example, the traditional and common screening and size-separating 
processes. Other processes are effective in separating particles in 
accordance with their weight or shape. The present invention relies 
heavily on differences in density among the classified particles in a dry 
fluid bed, and can be used in combination with other types of separation 
techniques. 
One of the oldest methods for separating heavier materials from lighter 
crushed materials is the riffle board, or riffle pan, in which crushed ore 
is placed upon a corrugated surface set at an incline and flushed with 
water. During separation, the riffle board is moved back and forth in 
directions normal to the corrugations, or is otherwise vibrated so as to 
create relative motion between the particles and the riffled surface. The 
ligher ore tends to carry over the corrugations (riffles) farther from the 
point of feed than the heavier minerals, and the crushed materials 
therefore are carried by the water over the edge of the riffle board at 
different locations. 
A disadvantage in the riffle board separation process is its requirement 
for the continuous flow of fluid over the riffles. In addition, the 
riffles are necessarily restricted in dimension and thus a limit is placed 
upon the amount of material which can be contained by any riffle, and 
thereby upon the amount of material which may be separated in a given 
amount of time. 
Another technique for upgrading crushed ore particles is found in U.S. Pat. 
No. 3,349,904. There a rotating screen in the form of an inverted cone 
receives the aggregate particle mass while air is simultaneously blown up 
through the screen to create an upward pressure. Heavier metal particles 
are intended to overcome the upward air blast pressure and be separated 
out of the mass by falling through the screen, while lighter rock 
particles are thrown upwardly and outwardly to the periphery of the screen 
due to centrifugal force. One major disadvantage in attempting to separate 
particles by this method is the high degree of complexity of the apparatus 
and the requirement for a pressurized air source. An obvious limitation is 
that material sized larger than the screen openings, even if having the 
selected density, cannot be handled. Furthermore, although it may be 
possible to separate particles whose densities are grossly disparate, it 
is believed that particle size must be very carefully controlled where the 
density of the desired material (such as crushed ore) approaches the 
density of the waste material. 
Particle handling equipment may use a gyratory separator (or "classifier") 
such as that disclosed in U.S. Pat. No. 2,950,819. A particle mixture is 
placed upon a vibratory screen designed to pass particles of all sizes 
smaller than the screen openings and irrespective of the particles' 
densities. Separators of this type are usually operated to cause all 
over-size particles to move to the periphery of the screen to be 
discharged. It is possible, however, to operate such devices so that 
oversize particles do not discharge due to a tendency for them to move 
radially inwardly to the center of the screen where they are retained as 
is shown, for example, in U.S. Pat. No. 3,794,165 (FIGS. 7-10). In certain 
cases, these separators are used to remove or recover particles entrained 
in liquid, the latter flowing through the screen and leaving behind 
particles trapped by the vibratory screen. These particles are flushed 
down an outlet at the screen's center. 
In all cases, so far as is known, gyratory separators have not been adapted 
to or operated for separating particles in accordance with the relative 
densities. Even in cases where particles are retained on the vibratory 
screen, no provision was made for separately segregating or extracting 
those remaining particles according to their densities. 
Still another known separation technique is based upon a mechanical 
concentrator known as the Denver mechanical concentrating pan which 
duplicates the miner's hand-panning motion. This device consists of a 
series of classifying screens under which are placed several pans 
specially coated to trap the fine heavy materials (e.g., gold). The first 
pan is metal-coated with mercury to amalgamate free gold; the remaining 
pans receive the overflow from the first and are coated with a rubber 
matting covered with screening which acts like a riffle. The entire 
assembly is driven with an eccentric motion in order to swirl the material 
in water, which is added along with the particle mixture to settle the 
mineral. Like other processes, this technique requires a flow of water and 
its collection capacity of the heavier fines is limited by the 
amalgamation and riffle capacity of the concentrating pans. It thus must 
be stopped periodically and emptied of the concentrated materials. 
A similar principle is used in devices such as shown in U.S. Pat. No. 
1,141,972 to Muhleman, where a rotary tilting motion is imparted to a pan 
having a riffled floor surface. Concentrated ore is extracted from a hole 
in the center of the pan floor. Again, the motion of the pan is such that 
the waste material swirls about the edge of the pan and is discharged, 
whereas heavier material gravitates toward the center due to the tilting. 
In my U.S. Pat. No. 4,148,725, I disclose a new process and apparatus 
wherein a size-classified bed of particles is fluidized by agitating a 
supporting surface with a gyratory motion to fluidize the particle bed. 
Particles are contacted with vertically projecting annular surfaces 
movable with the supporting surface and defining two or more annular 
channels. Particles within these regions are given sufficient fluidity by 
their reaction against the surfaces to allow them to move within the 
particle bed and distribute themselves according to their relative 
densities. Thus, particles move from one channel to the next through 
restricted openings in the annular surface, the denser particles tending 
to accumulate in one channel and the less dense particles being displaced 
into adjacent channels. The dense particles migrate in the direction of 
the eccentric "throw" toward a collection zone. Their greater energy, or 
momentum, it is thought, is what causes them to remain in the collection 
zone and displace less dense particles there. 
In accordance with the teachings of said U.S. Pat. No. 4,148,725, particles 
may be added to the fluidized particle bed at one of the interior annular 
channels so that waste material (e.g., less dense particles) flows 
outwardly. The denser particles, on the other hand, tend to be given a net 
inward momentum where they collect at the central collection region. 
The foregoing process and apparatus functions effectively when recovering 
dense particles from a bed of coarse sand when operating on either a 
continuous basis or a "batch" basis. In processing by batch, a fixed 
amount of feed material is loaded into the apparatus, which then is 
operated for a given period of time and shut down. Thereupon the 
densified, or upgraded, concentrate is extracted. It was found, however, 
that a problem sometimes arose when attempting to separate dense particles 
from fine sand, e.g., sand finer than -30 mesh. In such case, the sand 
tends to become compacted in the collection zone to such a degree that 
dense particles sought to be recovered cannot move through the compacted 
mass and, accordingly, may not reach the collection zone. 
There are, perhaps, many reasons for the above phenomenon; however, the 
interrelated motion of the particles and the reaction surfaces is so 
complex that a dispositive analysis cannot be readily made. Because the 
net force on all particles tends to drive them toward the collection zone, 
it has been observed that particles tend to be more compacted at the 
center of the bed. Another explanation may be that the vertical 
displacement of the gyratory motion at the center of the bed is at a 
minimum, the maximum vertical displacement occurring at the bed periphery. 
Thus, it is possible that the fluidity of particles moving toward the 
center of the bed diminishes excessively due to a reduction in this 
vertical displacement. 
Another problem that has been experienced is the limitation in the flow 
rate through the gyratory apparatus. When the equipment was operated in a 
continuous flow mode, high flow rates had to be avoided in order that the 
dense particles not be carried out of the bed with the less dense waste 
material. Separation times, therefore, could be much longer than is 
ordinarily acceptable for some commercial operations. On the other hand, 
if the equipment were operated on a batch basis to avoid inadvertent loss 
of dense particles, through-put is reduced. This is because particles have 
to be given sufficient residence time in order to penetrate the particle 
bed and collect in the collection zone. The amount of particles that can 
be batch processed at any one time is limited to the bed capacity, as the 
apparatus must be periodically stopped to remove the particles before 
additional particles may be introduced into the bed. 
SUMMARY OF THE INVENTION 
In general, the present invention carries forward the teachings of my prior 
U.S. Pat. No. 4,148,725 with several refinements which enhance their 
efficiency and effectiveness and which extend their usefulness to a 
greater range of feed materials. This is achieved in part by improving the 
fluidity of the particle bed within the collection zone, by providing 
means of adding particles to the bed and dispersing them during a 
continuous separation process, and by acting upon dispersed particles in 
such a way that the more dense particles which are to be separated out are 
caused to enter the fluidized particle bed while permitting the less dense 
particles to be discharged as waste. 
Although each of the foregoing features may be independently incorporated 
into the separation technique advantageously, a synergistic effect is 
realized when employing at least two, and preferably all, of these 
features. 
As noted above, the apparatus includes a plurality of annular concentric 
channels formed by a plurality of rings constituting the vertical reaction 
surfaces. Each ring has a narrow opening therein so that particles may 
move from one channel to the next under the influence of the motion of the 
reaction surfaces. This motion preferably is a gyratory motion having a 
circularly eccentric motion component and a repetitive vertical motion 
component. 
The present invention improves the process and apparatus of my issued 
patent by using additional reaction surfaces that control the behavior of 
particles within the particle bed. Such particle behavior is brought about 
by one or more of the following: 
(1) contacting the particles with a plurality of spaced-apart horizontal 
reaction surfaces disposed in the collection zone so as to enhance the 
fluidity of particles and thereby to increase the ability of particles of 
greater density to move into and remain in the collection zone in 
preference to particles of lesser density; 
(2) dispersing added excess particles over the top of the fluidized bed for 
reception into the annular separation regions; 
(3) contacting excess particles flowing over the top of the bed with a 
laterally extending reaction surface having a repetitive vertical motion 
so as to cause contacted particles to be driven downwardly into the 
fluidized bed; and 
(4) exposing particles in the collection zone to a vertical barrier surface 
against which more dense particles may react to displace less dense 
particles. 
The preferred embodiment employs a concentrate zone associated with the 
collection zone, from which the concentrate may be extracted. Particles 
gain access to this concentrate zone through apertures communicating with 
the collection zone. When operating in the continuous mode, the more dense 
particles entering the concentrate zone can be removed therefrom by 
suction, thus permitting the upgraded concentrate to be continuously 
removed during the separation operation. 
When the foregoing improvements are utilized together, particles can be 
continuously added to the particle bed and dispersed over the top of the 
bed where they are contacted by the laterally extending reaction surface, 
giving the denser particles a net downward momentum into the fluidized bed 
while permitting the less dense particles to disperse away from the point 
of particle addition to an exit aperture for extraction. In the collection 
zone, fluidity of the particle bed is enhanced so as to diminish the 
resistance of the particle bed to movement of the more dense particles 
into the collection zone and ultimately into the concentrate zone. This 
enhanced fluidity is brought about by the spaced-apart horizontal reaction 
surfaces which are more effective in transmitting the vertical reciprocal 
impact of the gyratory motion to the particles in the collection zone. 
For a better understanding of the invention, together with its objects and 
advantages, reference may be made to the following detailed description 
and to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
General Description 
Turning first to FIG. 1, the process of the invention is carried out by 
apparatus which includes a gyratory separator machine, designated 
generally by the numeral 10, and a separation head 12 implementing the 
improvements earlier described. It will be understood that the machine 10 
is a commercial apparatus whose function is to impart a gyratory motion to 
the separation head 12. Separation of the dense particles from the less 
dense particles occurs as a result of the control exerted on the particle 
bed by the improved separation head 12 in response to that motion. 
The vibratory device includes a cylindrical base 11 and a plurality of 
compression springs 13 circumferentially spaced about the upper lip 13a of 
the base for supporting a flat table 14. This table carries at its center 
of cylindrical motor mount 15 that extends down into the center of base 
11. A motor 17 is supported within the mount 15 by a pair of annular 
flanges 18, such that the motor is rigidly affixed to the table 14. 
Vibrations induced by the motor are therefore transmitted directly to the 
table. A cylindrical spacing frame 20, secured by clamping ring 21 at the 
periphery of the table, extends upwardly for supporting the separation 
head 12. The entire upper section 12 is clamped by a ring 27 to the rim of 
the lower frame 20. 
A shaft 30 extends from each end of the motor to which weights 31, 32 are 
affixed. These weights project horizontally outwardly from the shaft, and 
the radial angle between the axes of the two weights is adjustable by 
shifting and locking the angular position of one of the weights on the 
shaft relative to the other weight. In this manner, the upper weight 31 
can be made to lead or lag the position of the lower weight 32 by an 
adjustable angle. Adjustment of these weights alters the characteristics 
of the resultant gyratory motion, as is well understood. 
I have found that the best results are obtained when the weights are set to 
provide an angle of 180.degree. between weights with the lower weights 32 
being heavier than the top weights 31. In practice this was accomplished 
by inverting the motor of an 18-inch Kason vibratory machine. This brings 
about the maximum fluidity in the particle bed by causing the table 14 to 
exhibit the maximum vertical displacement. At the same time, of course, 
this weight setting imparts a substantial eccentric motion to the table 14 
(to which the separation head 12 is affixed) and, specifically, induces an 
inward thrust (or "throw") to particles contained within the separation 
head 12. 
As already mentioned, the table 14, and thereby the frame 20 and head 12, 
assume a gyratory motion when the motor is in operation. Such gyratory 
motion has both a circularly eccentric component and an oscillatory, or 
repetitive, vertical component. The combination of these two motion 
components enables energy to be imparted to the particle bed in such a way 
as to achieve the desired separation action. Fluidization occurs as a 
result of the instantaneous spacing between individual particles of the 
bed. The lead angle of 180.degree. between the upper and lower weights 
provides the maximum vertical oscillatory component consistent with 
optimum fluidization of the particle bed. The motion components result in 
the lateral, or translational, movement of the particles within the 
particle bed, this being possible due to the diminished resistance of the 
fluidized particle bed to individual particles moving within the bed. 
Separation Head 12 
The separation head 12, implementing the improvements according to the 
invention, will now be described. A description of the elements which are 
common to the present invention and to the invention of U.S. Pat. No. 
4,184,725 is given first. 
As described in the earlier patent, the separation head comprises a 
particle-supporting plate, or table 22, and an upstanding cylindrical wall 
23. Securely mounted to the table 22 are five substantially concentric 
annular rings 36, 37, 38, 39 and 40. These rings provide reaction surfaces 
which act directly upon the particles to impart a net movement to them. 
The spaces between the rings form a plurality of generally concentric 
annular regions, or annular channels. The rings have restricted openings 
in the form of slots 43-47 in the vertical wall so as to permit radially 
directed migration of the particles in the fluidized bed, with the 
openings in adjacent ring being circumfrentially displaced by, for 
example, 180.degree.. 
With the foregoing configuration, particles filling the annular channels 
follow a generally spiral migratory path which is radially inward if the 
"throw" of the motor weights is directed inwardly, and which is radially 
outward if this "throw" is outwardly directed. I have found that the most 
efficient results are achieved when the throw of the eccentric motor is 
inwardly directed and the collection zone is at the center of the particle 
bed. In this case, the vertical ring 43 provides a reaction surface which 
defines the collection zone. 
Inside the collection zone is a plurality of spaced-apart horizontal plates 
in the form of round disks designated 50a-50e. The spaced disks are 
mutually separated by cylindrical spacing elements 52. These disks 50a-50e 
surround an upstanding narrow cylinder or pipe 60 at the center of the 
particle bed. The stand pipe 60 is supported in a flange 64 that is bolted 
to the particle supporting plate 22, as best seen in FIG. 5. The interior 
of this pipe 60 constitutes a zone for the removal of densified particle 
concentrate. The plates 50a-50e and spacing element 52 are held firmly in 
position by a cylindrical collar 65 of larger diameter at the top of the 
plate stack, and by a threaded nut 66 which is threaded onto the pipe 60 
at the top. As will be explained shortly, the function of the collar 65 is 
to provide an auxiliary reaction surface to aid in the dispersion of 
excess particles over the top of the fluidized particle bed. Particles 
enter the interior of the pipe 60 through passageways 68 (FIG. 5) in the 
flange. 
Affixed to the wall 23 is a cover 70 in the form of an inverted conical 
section. It is separated from the wall's rim by spacing washers 71 (FIG. 
2) to form a horizontal aperture 77 about substantially the entire 
periphery of the wall 23 near the top of the particle bed. The cover 70 
has an opening 73 of larger diameter than the collar 65, and supports a 
particle-receiving hopper 75 that encompasses both the aperture 73 and the 
pipe 60. 
The function of the outwardly sloping cover 70 is to provide a laterally 
extending reaction surface which, being directly mounted to the wall 23, 
has the same motion as the particle supporting table 22. During the 
repetitive vertical excursions of the cover 70, its undersurface contacts 
excess particles at the top of the particle bed and thereby imparts a 
downwardly directed momentum to those particles to urge at least the 
denser particles into the annular channels between rings 36-40. Any 
particles which are not received by the channels are permitted to flow 
outwardly as waste through the aperture 77 at the periphery of the bed. 
Particles are loaded into the apparatus by filling them into the hopper 
75, from which they enter the particle bed via the aperture 73. The 
particle concentrate is extracted from the center of the stand pipe 60. 
Operation 
The operation of the apparatus will now be more completely described. 
First, as explained in my earlier U.S. Pat. No. 4,148,725, particles 
occupying the annular channels formed between rings 36-40 are given a net 
radially inward momentum, as well as a circular motion, by virtue of the 
eccentric component of motion of the rings. The primary effect of the 
vertical component of the gyratory motion is to fluidize the bed. The 
circumferential displacement of the restricted openings in the rings 
requires particles migrating within the fluidized bed to follow a circular 
path before reaching an opening interconnecting an adjacent annular 
channel. As a result, particles are given a longer residence time in the 
fluidized bed. Moreover, this multiple ring configuration appears to 
result in an increased fluid pressure which is exerted in the direction of 
radial thrust or, in this example, toward the center of the particle bed. 
Thus, generally speaking, the inwardly directed pressure is, in part, a 
function of the number of concentric rings that are used, several rings 
tending to be more effective than fewer rings in driving denser particles 
into the collection zone. The generally spiral paths of the denser 
particles in the particle bed is shown by the dark arrows 78 in FIG. 4. 
Particles reaching the collection zone at the interior of the ring 43 
encounter the plurality of horizontal plates 50a-50e. Because these plates 
are affixed to the table 22 and move with it, they too have a fluidizing 
influence on the particles. Specifically, they maintain the fluidity of 
the particles within the collection zone so that the denser particles may 
enter into this zone. As earlier noted, there is a general tendency of 
particles, particularly the fines, to become compacted in the collection 
zone, and compaction retards or precludes entirely the further inward 
advancement of particles. The spaced horizontal plates prohibit or greatly 
diminish this compaction by keeping the particles more fluid inside of the 
collection zone. 
While the precise explanation for the general preference of more dense 
particles to migrate into the collection zone and there displace particles 
of lesser density is subject to some debate, one can think in terms of the 
inwardly directed kinetic energy or momentum of the particles. Since 
particles of greater density (i.e., greater mass for particles of same 
size) have greater momentum, they tend to displace out of the way any less 
dense particles, this displacement generally taking place at any surface 
providing resistance to the denser particle's movement. The less dense 
particles, on the other hand, ultimately find their way outwardly and/or 
upwardly to the top of the bed where they are free to flow over the tops 
of the rings or through the slots 43-49 to the aperture 77 at the upper 
periphery of the rim 23. In FIG. 4, this outward migration of the less 
dense particles over the tops of the rings is shown diagrammatically by 
the light arrows 79 pointing generally radially outwardly. The dark arrows 
78 in FIG. 4 depict the motion of the denser particles. 
The foregoing separation action is also pictorially represented in the 
enlarged view of the collection zone in FIG. 5, wherein the dark arrows 
78a represent the path of removal of more dense particles and the light 
arrows 79a represent the net movement of the less dense particles during 
operation. Referring to FIG. 5, there is a preponderance of dense 
particles adjacent the barrier surface formed at the spacers 52. These 
dense particles are free to move vertically downwardly through small 
apertures 80a-80d in the plates 50a-50d. These apertures in adjacent 
horizontal plates are preferably circumferentially displaced to avoid 
excessive gravity effects. The dense particles, which displace less dense 
particles at the center of the collection zone, ultimately move to the 
lower level where they encounter the plurality of circumferentially spaced 
passageways 68 in the flange 65. These passageways provide access for the 
more dense particles into the center of stand pipe 60 during withdrawal of 
the concentrate. This concentrate within the pipe 60 is advantageously and 
preferably removed by suction applied either continuously or periodically 
at the top of the pipe 60 by a flexible coupling (not shown). Particle 
withdrawal is depicted by the dark arrow 86 in FIGS. 1 and 3. 
From the foregoing, it should be realized that the more dense particles, 
which are desired to be separated out from the aggregate mass of 
size-classified particles in the particle bed, follow a generally spiral 
path into the collection zone at the center of the particle bed and tend 
to remain in the collection zone in preference to particles of less 
density. Moreover, such dense particles will displace less dense particles 
in the collection zone (and elsewhere in the particle bed) in the event 
that such less dense particles impede their radially inward migration. 
The method may be carried out continuously. This is achieved by loading 
particles (represented by arrow 84 in FIGS. 1 and 3) into the hopper 75 at 
the top of the apparatus at a rate compatible with the separation and 
extraction of both concentrate and waste. Particles added to the hopper 
(arrow 84) enter into the region above the fluidized particle bed via the 
cover aperture 73 and encounter the cylindrical collar 65. Since this 
collar has the same eccentric component of motion as the other components 
of the apparatus, it contacts the entering particles and disperses them 
outwardly toward the exit aperture 77 (see arrow 79 in FIG. 4). 
As depicted by the white arrows in FIG. 3, feed material entering the 
particle bed through the aperture 73 will first fill up the inner channels 
between rings and then overflow into the outer channels. As more feed 
material is introduced, it will occupy the space between the tops of the 
rings and the underside of the cover 70. These particles, which are termed 
"excess" particles, are dispersed radially outwardly by the eccentric 
motion of the auxiliary reaction surface of the annular collar 65. Excess 
particles moving outwardly over the tops of the rings are contacted by the 
laterally extending reaction surface of the underside of the cover 70. As 
already mentioned, this reaction surface has a reciprocal vertical 
displacement which contacts the particles and drives the denser excess 
particles downwardly. If the rate of flow of particles through the 
apparatus is properly adjusted, the residence time of excess particles in 
the space between the cover and the fluidized bed within the channels is 
such to permit a great majority of the denser particles to enter into the 
channels before exiting from the aperture 77. These denser particles have 
a preponderant tendency to enter into the channels due to the combined 
effect of gravity and their greater kinetic energy upon being struck by 
the cover. 
I have found that the outwardly sloping pitch of the cover 70 is desirable 
in obtaining satisfactory operation. Attempts to achieve high throughput 
with a horizontal cover spaced above the channels were not consistently 
effective. The sloping cover, on the other hand, provides a larger 
cross-sectional material flow area per unit of circumference adjacent the 
point of addition of particles into the bed, this cross-sectional area 
gradually decreasing as the particles disperse toward the perimeter of the 
bed. It also places the cover's reaction surface closer to the top of the 
particle bed at the periphery of the bed, thus greatly enhancing the 
downward thrust exerted on more dense particles near the perimeter. 
Table I below lists the mechanical specifications of a preferred embodiment 
of the apparatus which has proved effective in trial field separation of 
heavy metal particles from sand and gravel. 
TABLE I 
______________________________________ 
Element Dimension or Specification 
______________________________________ 
Diameter of wall 23 
17 in. 
Width of each channel 
between rings 36-40 
.5 in. 
Diameter of rings 36-40 
Selected to yield .5 in channel width 
Width of slots 43-47 
.5 in. 
Height of rings 36-40 
2 in. 
Number of plates 50 
6 
Diameter of plates 50 
5 in. 
Spacing between plates 50 
.25 in. 
Diameter of stand pipe 60 
1 in. 
Height of stand pipe 60 
5 in. 
Diameter of aperture 73 
4 in. 
Diameter of collar 65 
3 in. 
Height of collar 65 
1-1 in. 
Diameter of hopper 75 
9 in. 
Slope pitch of cover 70 
1/4 in.-3/4 in. rise per 
7 in. radius 
Motor 1/3 hp, 1140 rpm 
Weights 31 5.125 lbs. 
Weights 32 5.875 lbs. 
Weight Lead Angle 
180.degree. 
Aperture 77 Variable 
______________________________________ 
Generally speaking, the width of the aperture 77 will vary according to the 
size of the particles in the feed material. As a rule, the aperture has a 
dimension about of 2-3 times the dimension of the largest particle in the 
feed material. For example, where the largest particle in the feed 
material has a nominal diameter of 1/4 in., the aperture 77 is selected to 
be about 1/2 in.-3/4 inch. 
The width of the channels, i.e., the spacing between adjacent annular rings 
may be similarly varied. I have found, for example, that a channel with a 
3/8 in. works best for -30 +50 mesh ore, a channel width of 1/2 in. 
performs well with -1/8 in. +16 mesh and -16 +30 mesh ores, and that a 5/8 
in. width is preferred for -1/4 +1/8 ore. Also, the rate of flow through 
the apparatus can vary considerably according to the feed material, as 
well as the entrance and exit aperture dimensions. 
Best results are achieved when all particles in the bed have a narrow size 
classification. Exemplary particle classifications for good separation are 
as follows: 
(a) 1/2 in.-1/4 in., (b) 1/4 in.-1/8 in., (c) -16 +30 mesh, (d) -30 +40 
mesh, and (e) -50 +100 mesh. Particle classification is generally achieved 
at low cost by common screening methods familiar to those in the art. 
The following examples are illustrative of the operative results from 
laboratory and field experiments. Except as otherwise noted the apparatus 
used possessed the physical specifications of Table I. 
EXAMPLE A 
The separation head was filled with 16.4 pounds of sand which had been 
classified to -30 +50 mesh. A feed batch was made by admixing 16.7 grams 
of -40 +50 mesh iron shot with 30 pounds of -30 +50 mesh sand. The motor 
was turned on and the sand shot mixture was poured into the hopper 75 at a 
rate of 12 pounds per minute. The separation head was operated for a 
period of about three minutes until no further waste material was 
discharged from the aperture 77. Thereupon, vacuum was applied to the open 
end of the pipe 60 and the motor turned off. Next, the cover 77 was 
removed in order to gain access to the interior of the separation head. 
Particulate material was removed from various sections of the separation 
head and separately weighed. The results are reported in Table A below. 
TABLE A 
______________________________________ 
Weight of 
Location of Material Weighed 
Weight of Sand 
Iron Shot 
______________________________________ 
Feed material 30.0 lbs. 16.7 grams 
Total separation head 
at start 16.4 lbs. 0 grams 
Discharged waste material 
36.0 lbs. 2.4 grams 
Material in outer 
channels 5.0 lbs. 2.6 grams 
Material in collector 
channel .4 lbs. .7 grams 
Material between horizontal 
plates 50 1.0 lbs. 4.7 grams 
Concentrate removed by 
vacuum from pipe 60 
4.0 lbs. 6.0 grams 
Total separation head at 
finish 10.4 lbs. 14.0 grams 
______________________________________ 
The foregoing results show a recovery of iron shot of 14.0/16.7=0.84 (84%). 
Moreover, of the 14 grams of shot recovered, 11.4/16.7 (68%) was 
concentrated in the collection and concentrate zones of the separation 
head. Continued operation of the separation head, as would normally occur 
during a continuous separation operation, would result in essentially all 
of the shot ending up in the collection zone. 
For purposes of comparison, the same tests were run on the separation head 
with the cover 70 removed in order to evaluate the contribution of the 
cover to the separation process. Start-up conditions were 16.4 lbs. of 
sand in the separation head at the beginning of the test. Once again, 16.4 
grams of -40 +50 iron shot was admixed with 32 pounds of -30 +50 sand. The 
motor was turned on and the sand/iron shot mixture was poured into the 
center of the collection zone at a rate of 6.5 pounds per minute. The 
separation head was operated about five minutes, until no waste material 
flowed over the wall 23. As before, vacuum was applied to the open end of 
the pipe 60 and the motor turned off. Next, the lid was removed and the 
material at various sections of the separation head was weighed. The 
results are listed below in Table B. 
TABLE B 
______________________________________ 
Location of Material 
Weight of Sand 
Weight of Iron Shot 
______________________________________ 
Feed material 32.0 lbs. 16.4 grams 
Total separation head 
at start 16.4 lbs. 0 grams 
Discharged waste material 
32.0 lbs. 6.8 grams 
Material in outer 
channels 10.0 lbs. 6.0 grams 
Material in collector 
channel .4 lbs. .5 grams 
Material between hori- 
zontal plates 50 
1.3 lbs. 1.5 grams 
Concentrate removed by 
vaccum via pipe 60 
4.7 lbs. 2.0 grams 
Total separation head 
at finish 16.4 lbs. 10.0 grams 
______________________________________ 
The rate of recovery in this test was 10.0/16.7=0.64, or 64% recovery of 
the iron shot from the 30 lbs. mixture. Of the recovered shot, 4.0/16.4, 
or 24%, was found in the collection and concentration zones. 
Example B evidences the positive effect of the cover upon the separation 
process. With the cover in place, a faster through-put was realized--12 
lbs/min. as opposed to only 6.5 lbs./min. without the cover. In addition, 
a higher rate of recovery was realized with the cover in place--84% 
(cover) as compared with 63% (no cover). Finally, a higher concentration 
of the iron shot was found within the collection and concentrate zones of 
the apparatus with the cover in place--68% (cover) vs. 24% (no cover). 
A quantity of dry gold-bearing placer ore was classified -16 +30 mesh and 
divided into batches of from 60 lbs. to 70 lbs. for processing through the 
separator head. The ore was not assayed. Each batch was fed through the 
separator at a rate of from 10 lbs./min. to 15 lbs./min., and the motor 
was allowed to run until no further waste was ejected from the exist 
aperture. The lid was removed and the total contents of the separator head 
were panned by hand to locate any free gold particles. The waste was 
collected and similarly panned by hand. The gold recovered from the 
separator head was weighed separately from any gold recovered from the 
waste. Based on the weight of the panned gold, the recovery rate for the 
gold particles ranged from about 90% to 100%, with average in excess of 
about 95%. 
In performing the runs of Example C, all elements of the apparatus had the 
dimensions and specifications set forth above in TABLE I. 
FIG. 6 shows an alternate embodiment of the collection and concentrate 
sections of the apparatus. The fundamental difference of the alternate 
embodiment resides in a relocation of the zone from which concentrate is 
removed. Instead of extracting particles via the column 60, a 
concentrate-accumulating region is established beneath the gyratory 
support table 22, and particles in the collection region are permitted to 
fall through one or more apertures in the table into this lower region. 
As clearly illustrated in FIG. 6, the collection zone of the apparatus 
remains substantially unchanged, the zone being defined by the annular 
ring 36 and including the stack of horizontal plates 50a-50e, spaces 52 
and column 60'. In this case, however, the column extends through the 
center of a circular aperture 90 in the table 22 and mounts to a flange 
64' affixed to the bottom of a cylindrical concentrate box 92. This box is 
constructed of heavy guage aluminum, such as 1/8 in.-1/4 in. having a 
diameter of about 3 in., and includes a horizontal flange 93 about its 
upper edge for the purpose of securely bolting the box 92 to the underside 
of the table. The horizontal plate stack in the collection zone is located 
at the desired vertical position by an extended spacer 95 which is 
supported at the top of the flange 64'. Thus, the horizontal plate stack 
is supported by the floor of the concentrate box 92, and an annular 
opening formed between the spacer 95 and the aperture 90. 
Operation of the embodiment shown in FIG. 6 is substantially the same as 
that described above, except that the more dense particles arriving at the 
collection zone do not enter the interior of the column 60 but, rather, 
are permitted to enter by gravity into the interior of the concentrate box 
92. This box may be periodically emptied of its contents by withdrawing 
the particles through the exit conduit 97. I have found that a vacuum 
applied to the conduit 97 removes most of the particles from concentrate 
box, as well as most of the particles between the horizontal plate 50a-50b 
in the collection zone. 
The embodiment of FIG. 6 is highly effective in upgrading or densifying 
particulate ore at a through-put rate greater that that achieved by 
extracting the concentrate through the interior of the column 60. The 
embodiment of FIG. 6 makes possible the use of a larger aperture for the 
entry of particles into the zone of concentration and also permits the 
more dense particles to enter this zone aided by the influence of gravity. 
It should be noted, with respect to FIG. 6, that the particles passing 
through aperture 90 need not necessarily be collected in the box 92. For 
example, particles entering aperture 90 may be conveyed via a conduit to 
remote locations which, if such conduit is flexible, can be disassociated 
from the moving components of the separation head. 
The present invention provides a significant improvement in the separation 
of dry particles according to density. Through the use of the several 
refinements described and claimed herein, separation of dense particles 
from less dense particles may be carried out faster, with a higher rate of 
recovery and with improved concentration within the collection zone. In 
addition, the invention can be applied to both coarse and fine particle 
feed material and, especially, material having a particle size of -50 mesh 
or finer. In addition to the other advantages, the configuration of the 
apparatus permits convenient and effective continuous feeding and 
withdrawal of the material without shutting down the apparatus. 
It is an important aspect of the invention that it can effectively upgrade 
raw particulate ores and thereby render economic certain particulate ores 
which heretofore have been uneconomic. For example, a gold placer, having 
an assay value of 0.01 ounce of recoverable free gold per ton of 
particulate ore at a gold price of $400.00 per ounce, contains gold valued 
at $4.00 per ton. If such ore must be transported to a source of water for 
conventional recovery processing, the transportation costs alone can 
approach the value of the ore. The present process and apparatus is 
capable of concentrating the raw ore from 0.01 ounce per ton to to 0.10 
ounce per ton concentrate. In other words, this ore can be upgraded by a 
factor of ten, to reduce transportation costs by the same factor. An ore 
which is fundamentally uneconomic or only marginally economic may thus be 
concentrated to a degree permitting the concentrated ore to be transported 
at economic cost to a remote location for further processing. 
It is to be understood that the foregoing description of the preferred 
embodiments of the invention is illustrative only and that certain 
modifications and variations can be implemented in both the process and 
the apparatus without departing from the invention. As one example, ore 
concentrate may be removed from the so-called concentrate region by any 
suitable means, and by paths other than those specifically disclosed 
herein. Additionally, changes in the relative dimensions of the elements 
may be made according to the requirements of the feed material. 
Furthermore, the term "adjacent annular regions" as used herein does not 
connote regions that are necessarily continguous but, rather, annular 
regions that communicate for the movement of particles.