Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
This invention relates to a method of and apparatus for analysing a
sample of particulate mineral ore from an ore body.
BACKGROUND TO THE INVENTION
Conventionally, the grade of an ore body is measured by periodically
removing a sample of ore from the body, crushing the sample ore and
subjecting the crushed sample to chemical analysis to determine its
gradé. If the grade of the ore is high enough to warrant the processing
of the entire ore body all of the ore and a substantial proportion of
waste material, with perhaps the exception of large particles which
obviously do not contain the mineral being sought and which are removed
by hand from the remainder of the ore, is processed. This method of
ore analysis and processing is, in terms of recovery, efficient as a
very large percentage of the sought after mineral in the ore is
obtained from the ore. However, a major problem with this process is
thatvast quantities of unproductive material are processed to arrive at
a relatively small volume percentage of the mineral and this is achieved
at considerable plant and labour cost.
In deep level gold mining the above problem has been minimised by the use
of automatic sorting machines which sort graded particles of a
particular size or range of sizes, into particles which have a particular
characteristic, such as radio-active emission, which is related to the
gold grade of the ore, from particles which do not have the characteristic
or have the characteristic helow a predetermined threshold. When the ore
has thus been sorted only the accept ore which is the ore having the
characteristic above the threshold level is then processed resulting
in a considerable saving over the previously described process in both
plant utilisation and labour.
In a radiometric sorting process of this type the radiometric
measurement of the ore particles is considerably influenced by parameters
such as the mass, volume and shape of the particles. For example, the
radio-active count of each particle will depend on the shape of the
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particle, the position of the radio-active daughter products in the particle
and the orientation of the particle relatively to the radiation detector when
the radio-activity of the particle is measured. Because of this problem and
the fact that radio-active emission from the particles is not constant many ore
particles which are suitable for processing are rejected by the sorter to waste
so reducing the efficiency of this type of sorting process.
OBJECT OF THE INVENTION
It is the object of this invention to provide a method of and apparatus
for analysing the characteristics of all the particles of a sample of ore from
an ore body to determine the sortability of the ore from the body.
UMMARY OE T~IE INVENTION
The invention provides a method of analysing ore particles from a
representative sample of ore which method includes the step~q of feeding the
particles, spaced fro~n each otller, succe.ssively to a plurality of measuring
stations; and at respective ones of the plurality of mea~suring stations, for
each particle determ;nin~? at lea~t, ~ mea~surelllent which iq <lependent on the
mass of the particle, and D lll(`a.qnrlllellt Wh;C~ q depend~nt on the radioactivity
of the partic]e, and recordilll! the mnqs all(l rad;oactivity m~asur(mentR.
Preferably at lenst at one locat;oll the rrldioactivity of (~ch particle ;s
measured under condi-~ions wh;cll ~pproximDte conditions prevail;ng in a working
ore sorter.
Opt;onally, depending on the analysis required, at least at one location a
measure is made of at least one of a spectral component, reflectivity. X-ray
fluorescence, conductiv;ty or magnetic susceptibility, of each particle.
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In addition the method may include the step, during the movement of
each particle to one of the locations, of measuring the physical dimensions of
the particle.
The measurements may be recorded by means of a computer and once the
characteristic measurements of each particle have been assimilated by the com-
puter the characteristic of the particles are presented in a printout or
other suitable form to enable characteristic tabulations or graphs to be
prepared.
The graphs are drawn in a form appropriate for the purpose of the
analysis, i.e. to determine the ore sortabi]ity, the sorting efficiency of a
sorter, misplacecl particles in a sort, etc.
The invention also provides apparatus for analysing ore particles
from a representative sample of the ore which apparatus comprises conveyor
means for moving a plurality of the particles, spacec! from each other, ial
succession to a plurality of measuring stations, means at a first measuring
station for obtaining a measurement of the mass of each particle, means at a
second measuring station for obt;l-ining a measurelllent of the radio.lctivity ot
each particle, and means for recorcling tlle m;lss alld rilclio;lctivity me.lsuremerlts.
In adclitioll the ullpar;ltus inclucles me;llls at one location ~for measur-
ing the radioactivity ol cucll p;lrticle nllder conclitiolls whicll al)prox:imate
conditions prev;lilillg in a worlcillg ore sorter.
TllC ;l~ a:l`;ltlls IlI.ly .llS(l illCIlldC IllC;IllS ;It OllC loc;ltiol~ for mCaSIJring
at least OllC`, of the rel`lectivity, X--ray fluorescence, condllctivity, magnetic
susceptibility, or a spectral coml)onent, ol each particle.
Use may be made of a computer programmed to assimilate the measured
characteristics oF each particle. 'rhe computer may be connected to each
measuring station or location of the apparatus.
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The conveyor means of the apparatus may be adapted to deposit the
particles sequentially orl beds at selected locations, where the
particles are maintained for predetermined time periods.
BRIEF DESCRIPTION OF THE DRAWINGS .
An embodiment of the invention is described by way of example
with reference to the drawings in which:
Figure 1 is a partially schematic side elevation of apparatus
according to the ;nvention,
Figure 2 is a fragmentary perspective view of a station pad of the
apparatus of Figure 1, and
Figures 3 and 4 depict typical graphs produced by means of the
apparatus of Figure 1.
DETAILED DESCRIPTION OF THE DRAWINGS
The analyser apparaius of the invention is shown in the drawings to
consist of a frame indicated generally at 10, a conveyor 12, and ore
particle receiving and measuring stations 14, 16, 18, 20, 20A, 22 and
24.
The conveyor 12 consists of a substantially rectangular frame 26 which
is bridged froln one short end to the other by a plurality of parallel
closely spaced and tensioned piano wires 28.
The conveyor is adapted for movement relatively to the frame 10 by means
of a first hydraulic or pneumatic jack, not shown, which is connected to
act between the frame 10 and a linkage arrangement for lifting the
conveyor to the position shown in dotted lines,and a second jack which is
adapted to move the raised conveyor to the right from the position shown
in dotted lines and~back,again. The length of stroke of the second jack
is equal to the distance separating the receiving and measuring stations
14 to 22 of the apparatus.
The stations 14, 18 and 22 each include a particle receiving pad 30
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which, as is illustrated in Figure 2, includes a plurality of grooves in which
the wires 28 of the eonveyor are located clear of both the upper surfaee of
the pad and the bases of the grooves when the frame 26 is in the position
illustrated in solid lines in the drawing. The pads at the stations l~ and 22
are fixed to the frame 10 and the pad at the station 18 is loeated on a load
cell transducer 32 which is fixed to the frame 10.
The measuring station 16 eonsists of an open frame which carries on
its inner periphery a plurality of opposed light emitters and sensors whieh
establish in use a closely spaced grid of vertical and horizontal light beams.
An arrangement of this kind and the electronies assoeiated therewith for
processing the light signals are deseribed in the applieant's Canadian Patent
Application Serial No. 372,590 entitled "Volumetric Measurement of Particles"
and filed March 3, 1982. Such an arrangement proves information on the dimen-
sions of a particle e.g. its height, projected area, or volume.
The measuring station 20 consists of a housing having walls made Erom
radiation free lead. The up and downstream walls o~ the housing are door
slabs 36 and 38 which are located for vert;caI movement ;n gnicIes on the
housing. Tho uI)per end of the doors are connectecI to a Iifting bridge ~0
which is raisecI.Ind loworocl by means ol a jaek, not shown in the cIrawing.
The lower edges o~ the doors in t1Ieir IowerecI positioIl rest Oll sills which are
grooved like the p;lC15 3() to ;ICCOllllt)OCI;ltc thc w;res 2X ol the conveyor. rIIe
lowor ~ortions o-f the cIoors are l;ikewise groove(I. SeintiII;Ition sensorsJ not
shown, are located ill the housilIg below thc wires 28 in the lowered positior
of the conveyor aIld above and spaced Erom the wires in a ~attern to Ineasure
raclio-active emission fI~olll a I)article in the housing -from all directions.
The arrangement of the sensors could be similar to that described in the
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applicant's Canadian Patent Application Serial Nos. 367 157 and 367 J 158 both
entitled "Radiometric Methods and Means" and both filed December 19 1980. In
the station 20 the particle rests on a pad similar to the pad 30. The sensors
located above the conveyor are located i.n a framework which is attached to
the doors 36 and 38 so that they are raised and lowered with the doors to
permit passage of an ore particle through the housing.
The station 20A is substantially similar in construction and working
to the station 20. Ilowever it contains only a single radiation detector of
the type employed in a radiometric ore sorter and is intended to provide under
laboratory conditions a measure of the count which would be recorded on a
working ore sorter by an ore particle.
The measur;ng stati.on 22 includes a fixed particle receiving pad 30
and a spectrum analyser or like instrument 42 which is attached to the lift;ng
bridge 40.
The parti.cle discharge station 24 includes an arm 44 which includes
a plurality of spaced plates 46 whi.cll in the position shown in tl)e drawing
:Eol-m a pad sim:i]ar to the pads 30. Thc .11`111 44 is rotatllble by means ol a jack
not shown a.bout a ~:ivot point 50 at which :it is secured to a -I`ixed support.
As tlle arm is ra:i.sed From the illllstr;lted posi.t:ion the pl;ltes 46 pclSS ~:reely
between the w:ires 28 iUld in this way a Inlrt.icle call rcadily he ejected f:rom
the conveyor l2
A comll~ter 52 is connectc(l to tllc app.lratlls to rccorcl and analyse
tlle cl.l.ta gelle:rlltecl ;at eacll ol the st.lt:iOllS 16 18 20 20A and 22.
:[n llse an OI`C` paI`t:i.ClC iS p~ ced on the pad 30 at the station 14.
Tlle conveyor is tllen lifted to the position shown in dottecl lines with the
particle resting on the wires 28 of the conveyor. The conveyor is then moved
to the right in the drawing and lowered until the particle rests for a pre-
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determined time on the pad 30 of the station 18 free of the conveyor wires.
In its passage fronl station 14 to 18 the particle is moved through the light
grid at the station 16. The particle, in its passage through the grid,
blanks off a number of both the vertical and horizontal light beams of the grid
and this information together with the known speed of movement of the
particle enables the computer to determine and record the length, breadth and
height of the particle and so its volume, all in the manner described in
the applicant's Canadian Patent Application Serial No. 372,590 already
referred to. At the station 18 the mass of the particle is determined by the
transducer 32 and recorded in the computer.
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The conveyor 12 is then moved, without lifting, back to the position
indicated in solid lines-while-the particle remains resting on the pad
30 at the station 18. A second particle is then placed on the station
14 and the conveyor transport process is repeated. As the second
particle is moved to the station 18 the first is moved to the station
- - 20. As the conveyor moves the first particle towards the station 20
the lifting bridge 40 raises the doors 36 and 38 until the particle is
in the housing. Whèn the frame 26 settles the particle is left on the
pad in the housing and the doors are closed to shield the inside of the
housing. The pad in the housing is made from a material which does not
inhibit the passage of radio-active waves and the sensors surrounding the
particle on the pad in the lowered position of the doors 36 and 38
measure, for the period of rest of the particle on the pad, radio-active
emission from the particle in all directions. Using this method of
radio-active transmission measurement errors due to background e.g.
cosmic radiation and transient emission effects are eliminated. In
addition the transmission of the radio-active waves is not significantly
attenuated due to shielding of the waves by the bulk of the mass of the
particle which may be located between the radio-active daughter products
in the particle and one or more sensors located in a fixed plane. Thus
the station 20 produces to a considerable degree of accuracy, a measure of
the true radioactivity of the particle inside the housing.
The particle radio-active emission is recorded by the cornputer and the
cycle of the conveyor is again repeated with a third particle located on
the station 14.
On the next cycle the leading particle is moved into the station 20A and
a count of the particle's radioactivity is recorded by means of the single
detector. The station 20A approximates the physical conditions
prevailing on a working model ore sorter but as shielding is provided tne
effects of following and preceding particles which manifest themselves
under practical conditions are eliminated.
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The count recorded in this way thus provides a good basis on which
to correlate the laboratory derived data to the data produced in
the field.
As the first particle is moved from the station 20 the doors 36 and 38
are lifted to permit the second particle to enter the housing and the
first to leave it in its passage to the station 20A. On the successive
cycle the leading particle is moved to the station 22, in the manner
described. Each time the doors of the station 20A are closed, the
analyser 42 is lowered to just above the particle at the station 22.
1~ The first particle is thus analysed at the station 22 in respect of its
content of one or more specific minerals or elements by means of the
spectrum analyser 42.
The spectrum analyser 42 could be replaced, if desired, by suitable
instrumentation for measuring the reflectivity, X-ray fluorescence,
conductivity, magnetic susceptibility, or other defined characteristic
of each particle, or such information could be used in addition to the
analyser, being located at an additional measuring station or stations
provided for the purpose.
The analyser of the invention is employed principally to determine
the characteristics of a representative sample of ore.
It has been established by the applicant that the radioactivity count
of an ore particle recorded by a detector in an ore sorting machine is
dependent on the true radioactivity content of the particle and at least
on one or more of the physical dimensions of the particle, including
its height or volume, the mass of the particle and its density. The
analyser, in conjunction with the computer, is designed to provide the
relevant data in the manner described from representative ore samples so
that these relationships can be statistically determined.
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For example for sorting purposes it is essential to determine, for
a given sample, the number c)f particles within defined mass fractions, and the
mass of the particles within the defined mass fractions, on a percentage basis.
This information is readily obtained by means of the analyser which provides
the mass of each particle at the station 18. It is a simple matter to progratnme
the computer to total the masses and to allocate the mass of each particle into
one of the defined mass fractions. The computer can output the information in
the form of a graph of the type shown in Figure 3 which gives the number of
particles, as a percentage, as a function of particle mass fractions. A
similar curve is obtained for the particle mass, again expressed as a per-
centage, as a fraction of particle mass.
By sizing the ore sample prior to its analysis the maximum and
minimum masses, and the distribution or spread of the particle's masses, can
readily be obtained from the computer as a function of the screen sizes.
The volume measuring device at the station 16 provides the shape,
dimensions and volume of each particle and the distribution of shapes, and
average dimensions of the particles can he ohtained .Incl relate-l to the par-
ticle masses, and raclioactivity. Illis informntioll i.s employcd for count
compensation purposes in tho nl.lllller descriled in the applicallt's Canadian
Patent Application Seri;ll Nos. 366,0()2 alld 33G,()()I, entitle-l "I)isl~ celllent
Error Correctioll in Sorting Systellls" .llld Crade l)etermill.ltion" respectively ~ncl
both filed l~ecenlber 3, l')~().
rl`he station 20 provi~les an accutate measure o~ the radioactive con-
tent of each particle .nlld since this is correlated with the mass of the par-
ticLe the computer can readily determine and represent graphically or
otherwise the mineral content and the grade, on a percentage basis, of the ore
sample as a function of mass. Maximum and average values can be produced.
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Once again it should be pointed out that these parameters are critical in the
efficient working of a radiometric particle sorter.
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Figure 4 illustrates graphically for a representative ore sample
the reject and accept fractions expressed as a percentage, as a
function of cut off grade, with curve A giving the mineral distribution
and curve B the mass distribution. This information is vital in
determining the viability of a sorting machine and is produced from the
data generated by the analyser of the invention.
In a practical situation the cost of processing a unit mass of ore
to recover its mineral content is known. A decision can thus be made
on the cut off grade of the ore which should be processed. The sorting
machine can then be set to accept or reject at this cut off grade.
If this is at point X, in Figure 4, then curve A gives the percentage of
the mineral recovered, and lost, while curve B gives the corresponding
mass percentages of the ore body accepted and rejected. Situtations
which completely justify the use of a sorter in economic terms occur
when the curves A and B are well separated (horizontally) from each
other. Ideally, a large percentage of the mineral content should be
recovered, with a large percentage of the ore body, in mass terms, being
rejected. This implies that a relatively small ore mass has to be
processed to recover the bulk of the mineral content.
Finally, it should be pointed out that the analyser of the invention
can be used in the described manner to analyse ore particles sampled
from the reject or accept fractions of a working ore sorter. The
analyser may, if desired, be installed on site, to provide the information
more or less in real time.
Since, in the analyser, the various measurements are taken over periods,
up to 40 seconds or more, which are long compared to the measurement
periods in a working ore sorter, the information obtained from the
analyser is accurate and the sorting efficiency of the working sorter
can be assessed.
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Inall the analyser measurements.,. to assist in recovering the.particles
falling into the different categories e.g. of mass, shape, volume,
etc, the arm 44 can be replaced, or followed, by one or more flap gates
which are mechanically actuated to sort the particles into the various
categories. The categorised particles may then be subjected to
additional tests, e.g. by assaying, for verification purposes.
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