GB2066456A

GB2066456A - Analyser

Info

Publication number: GB2066456A
Application number: GB8039632A
Authority: GB
Original assignee: General Mining Union Corp Ltd
Current assignee: General Mining Union Corp Ltd
Priority date: 1979-12-12
Filing date: 1980-12-10
Publication date: 1981-07-08
Also published as: DE3046807A1; AU542927B2; DE3046807C2; AU6506680A; JPS56100338A; CA1150966A; FR2472188B1; FR2472188A1; GB2066456B

Abstract

A method of and apparatus for producing data useful for the statistical analysis of ore particles to establish sorting criteria. The samples are moved individually by a conveyor in succession to a plurality of measuring stations (14 to 22). At each station the particle is held stationary and the appropriate measurement is made. This method enables the radioactivity of a particle to be accurately related to its mass or physical dimensions. <IMAGE>

Description

SPECIFICATION Analyser This invention relates to a method of and apparatus for analysing a sample of particulate mineral ore from an ore body.

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 grade. 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 that vast 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 below a predetermined threshold. When the ore has thus been sorted only the accept ore which is the ore having the characteristic above and 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 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.

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.

The invention provides a method of analysing ore particles which includes the steps of moving a plurality of the particles which are spaced from one another successively between a plurality of locations, maintaining each particle stationary for a predetermined period at each of the locations, measuring, for each particle at each location, a characteristic of the particle, and recording the measurements.

Further according to the invention at least at one location the mass of each particle is measured.

Also at least at one location the radioactivity of each particle is measured.

Preferably at least at one location the radioactivity of each particle is measured under conditions which approximate conditions prevailing in a working ore sorter.

Optionally, depending on the analysis required, at least at one location a measure is made of at least one of a spectral component, reflectivity, Xray fluorescence, conductivity or magnetic susceptibility, of each particle.

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 computer 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 sortability, the sorting efficiency of a sorter, misplaced particles in a sort, etc.

The invention also provides apparatus for analyzing ore particles which comprises conveyor means for moving a plurality of the particles, spaced from one another, in succession between a plurality of locations, means, at each location, for measuring a characteristic of the particle at the location while the particle is stationary, and means for recording the measurements.

Preferably the apparatus includes at one location means for measuring the mass of each particle and, at a second location, means for measuring the radioactivity of each particle.

In addition the apparatus includes means at one location for measuring the radioactivity of each particle under conditions which approximate conditions prevailing in a working ore sorter.

The apparatus may also include means at one location for measuring at least one of the reflectivity, X-ray fluorescence, conductivity, magnetic susceptibility, or a spectral component, of each particle.

Use may be made of a computer programmed to assimilate the measured characteristics of each particle. The computer may be connected to each measuring station or location of the apparatus.

The conveyor means of the apparatus may be adapted to deposit the particles sequentially on beds at selected locations, where the particles are maintained for predetermined time periods.

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 invention, 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.

The analyser apparatus 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, 1 6, 18, 20, 20A, 22 and 24.

The conveyor 12 consists of a substantially rectangular frame 26 which is bridged from 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, 1 8 and 22 each include a particle receiving pad 30 which, as is illustrated in Figure 2, includes a plurality of grooves in which the wires 28 of the conveyor are located clear of both the upper surface 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 14 and 22 are fixed to the frame 10 and the pad at the station 18 is located on a load cell transducer 32 which is fixed to the frame 10.

The measuring station 1 6 consists of an open frame which carries on its inner periphery a plurality of opposed light emitters and sensors which establish in use a closely spaced grid of vertical and horizontal light beams. An arrangement of this kind and the electronics associated therewith for processing the light signals are described in the applicant's South African Patent Application No. 80/4250 entitled "Volumetric Measurement" the disclosure of which is herein incorporated. Such an arrangement provides information on the dimensions of a particle e.g. its height, projected area, or volume.

The measuring station 20 consists of a housing having walls made from radiation free lead. The up and downstream walls of the housing are door slabs 36 and 38 which are located for vertical movement in guides on the housing. The upper ends of the doors are connected to a lifting bridge 40 which is raised and lowered by means of a jack, not shown in the drawling. The lower edges of the doors in their lowered position rest on sills which are grooved like the pads 30 to accommodate the wires 28 of the conveyor. The lower portions of the doors are likewise grooved.

Scintillation sensors, not shown, are located in the housing below the wires 28 in the lowered position of the conveyor and above and spaced frorn the wires in a pattern to measure radioactive emission from a particle in the housing from all directions. The arrangement of the sensors could be similar to that described in the applicant's South African Patent Application No.

79/6989, entitled "Radiometric Methods and Means", the disclosure of which is also herein incorporated. In the station 20 the particles rests on a pad similar to the pad 30. The sensors located above the conveyor are located in 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.

However 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 measuring station 22 includes a fixed particle receiving pad 30 and a spectrum analyser or like instrument 42 which is attached to the lifting bridge 40.

The particle discharge station 24 includes an arm 44 which includes a plurality of spaced plates 46 which in the position shown in the drawing form a pad similar to the pads 30. The arm 44 is rotatable by means of a jack, not shown, about a pivot point 50 at which it is secured to a fixed support. As the arm is raised from the illustrated position the plates 46 pass freely between the wires 28 and in this way a particle can readily be ejected from the conveyor 12.

A computer 52 is connected to the apparatus to record and analyse the data generated at each of the stations 16, 18, 20, 20A and 22.

In use, an ore particle is placed on the pad 30 at the station 14. The conveyor is then lifted to the position shown in dotted 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 predetermined time on the pad 30 of the station 18 free of the conveyor wires. In its passage from station 14 to 1 8 the particle is moved through the light grid at the station 1 6. 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 South African Patent Application No.

80/4250 already referred to. At the station 1 8 the mass of the particle is determined by the transducer 32 and recorded in the computer.

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 1 8. 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 1 8 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 untii the particle is in the housing.

When 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 computer 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 the effects of following and preceding particles which manifest themselves under practical conditions are eliminated.

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. 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 radioactivSity 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.

For example for sorting purposes it is essential to determine, for a given sample, the number of 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 1 8. It is a simple matter to programme 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 percentage, 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 1 6 provides the shape, dimensions and volume of each particle and the distribution of shapes, and average dimensions of the particles can be obtained and related to the particle masses, and radioactivity. This information is employed for count compensation purposes in the manner described in the applicant's South African Patent Application Nos. 80/4248, 80/4249 and entitled "Displacement Error Correction in Sorting Systems" and "Grade Determination" respectively.

The station 20 provides an accurate measure of the radioactive content of each particle and since this is correlated with the mass of the particle 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. Once again it should be pointed out that these parameters are critical in the efficient working of a radiometric particle sorter.

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. Situations 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 smali 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.

In all 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.

Claims

1. A method of analysing ore particles which includes the steps of moving a plurality of the particles which are spaced from one another successively between a plurality of locations, maintaining each particle stationary for a predetermined period at each of the locations, measuring, for each particle at each location, a characteristic of the particle, and recording the measurements.

2. A method according to Claim 1 wherein at least at one location the mass of each particle is measured.

3. A method according to Claim 1 or 2 wherein at least at one location the radioactivity of each particle is measured.

4. A method according to any one of Claims 1 to 3 wherein at least at one location the radioactivity of each particle is measured under conditions which approximate conditions prevailing in a working ore sorter.

5. A method according to any one of Claims 1 to 4 wherein at least at one location a measure is made of at least one of a spectral component, reflectivity, X-ray fluorescence, conductivity of magnetic susceptibility, of each particle.

6. A method according to any one of Claims 1 to 5 including the step, during the movement of each particle to one of the locations, of measuring the physical dimensions of the particle.

7. Apparatus for analysing ore particles which comprises conveyor means for moving a plurality of the particles, spaced from one another, in succession between a plurality of locations, means, at each location, for measuring a characteristic of the particle at the location while the particle is stationary, and means for recording the measurements.

8. Apparatus according to Claim 7 which includes at one location means for measuring the mass of each particle and, at a second location, means for measuring the radioactivity of each particle.

9. Apparatus according to Claim 7 or 8 which includes means at one location for measuring the radioactivity of each particle under conditions which approximate conditions prevailing in a working ore sorter.

10. Apparatus according to any one of Claims 7 to 9 which includes means for measuring the physical dimensions of each particle during its movement to a given location.

11. Apparatus according to any one of Claims 7 to 10 which includes means at one location for measuring at least one of the reflectivity, X-ray fluorescence, conductivity, magnetic susceptibility, or a spectral component, of each particle.

12. A method of analysing ore particles substantially as herein described with reference to the accompanying drawings.

1 3. Apparatus for analysing ore particles substantially as herein described with reference to the accompanying drawings.