AU681182B2 - Parallel array mineral sorting apparatus - Google Patents

Description

01/87 '97 12:21 2 03852B027 AST MELBOURNE Parallel Array Mineral Sorting Apparatus This invention relates to improvements in mineral sorting through use of parallel arrays of tubular electromagnetic sensors which are fixed below an integral vibrating screen, with rocks fed through these sensors under gravity. The system allows for sorting of run-of-mine (ROM) material at high rates without the need for screening plants. This results in reduced capital cost of infrastructure and in reduced scale of sorting installation, making it suitable for both underground deployment to minimise mining waste haulage to the surface and subsequent treatment and tailings disposal on the surface.

Mineral sorting equipment which uses electromagnetic sensing to identify mineralised rock from barren rock is well known. However its use in mineral industry is almost non-existent despite offering large potential performance gains in metallurgical plants. There are a number of substantial reasons for this which the present invention overcomes, viz 1. difficulty in obtaining high sensitivity from conventional sensor configurations which have been, typically, planar coils similar to prospecting metal detector search coils, the difficulty being largely due to the use of the fringing fields of the coils; 2. linked to 1) is the difficulty of avoiding interference from metal structures adjacent to the coils which have conventionally caused unwanted perturbations in output which can be difficult to separate from true signals; 3. conventional electromagnetic sorting practice requires closely sized feed material to suit a particular configuration for detector, entailing large and costly screening plants to produce size fractions of typically 2:1, with consequent need to supply storage capability to buffer sorting streams against fluctuating ROM size distribution; 4. in order to attempt to increase capacity in a One-by-one rock sorting system, it has been conventional practice to increase the linear speed of the rocks, accelerating them in single streams, either on inclined slide plates or high speed conveyor belts, so that speeds of up to 5 rn/sec are achieved through the detector zone. This minimise the number of sensors required, but means that rocks have a large and sometimes unanageable momentum and high rotational energy, It also means that the machines are large and inflexible, and require optical synchronisation between detection and deflection systems, with ensuing problems of the need to maintain clean optics in a dirty environment.

The invention described here overcomes these drawbacks by using a 2-dimensional array of sensor/deflector modules. The sensors have special properties as described in Australian Patent Number 673076 A Tubular Mineral Detector which ideally suit this form of deployment, integrated into a sorter based around a linear vibrating V. screen with progressively larger Woe sizes as the material advances.

In effect this produces a parallel rather then serial rock sensing and separating stream.

A larger number of detectors and deflectors are required, bu~t the speed requirements are accordingly lower, and in production the sensing/deflection modules are relatively low in cost. The system lends itself to modularity and so can be cheaply added to, if *increased throughput is required, by adding more modules in the direction of material flow. No optical elements are required to synchronise detector with deflector. The system uses the electromagnetic sensor signal itmelf to trigger deflector action) thus giving considerable gain in terms of robustness and reliability.

A deflector plate is used in each channel instead of blast valves, conserving air and causing minimum disruption by acting as a bounce plate rather than imparting large momentum to the rock via a high pressure air pulse. This further allows for the use of a "blast waste" feature, even though no optics are present, in the event that waste rock is the smaller fraction in the sorter feed requiring to be removed. This is becaus Ou: pneumatically extended weaT plate can remain in the stream causing deflection of undetected and unmineralised waste without optical synchronising signals, The deflector would then revert to open state when mineral ised rock passes through. Air RA4/ 2-t w 0 01/87 197 12:22 el/a?'97 2:22Z 3B520027 95T MIELBOURNE blast valves arc unable to provide this option as they need high velocity pressure front to impart initial particle change of direction.

Because of the lower speed of the rock through each of the parallel channels, the lower actuating speed of the wear plate (due to its greater inertia compared with air blast valves) is sufficient to keep up with the particle flow rate through the tube, The key to the above is to construct the sorter structure as part of a vibrating screen with non-blinding decks, with hole size progressively increasing from fines to large sizes. A second, and lower, deck delivers sized rock to arrays of holes immediately above arrays of detector/deflector modules, Material in the lower deck that doesn't pass through its intended holes is carried forward to the nextt largest size range, and so is easily accommodated without significpnt loss in detectability. Throughput is limited by the number of modules fitted, and the maximum advancement rate available for the vibrating stream, This allows a full size range of typically ex-primary crusher material to be fed to the single sorter, with slimes/fines removed in the first increment, through to top size which would normally be around I150mmn in a practical implementation. If necessary, oversize carry over could be discharged and returned to the crusher, or diverted to join either the accept or reject sorted product.

In this way a full size range sorter can be rcaliscd without a separate costly aind space- 5 consuming screening plant. This makes underground sorting a real possibility, but also increases flexibility and reduces capital cost in above ground treatment plants.

The invention utilises the tubular electromagnetic sensors disclosed in our patent 673076, which, because of coil deployment and electromagnetic shielding, can be located in harsh areas near large metallic masses such as beams and frames. The fields relating to the coils are confined to a small internal region, virtually completely within the tube housing of length typically -34 times the diameter of the opening aperture. This also means that groups of detectors can be deployed in close proximity without crosstalk, giving rise to the ability to use them in closely packed ar-rays.

Sensor sizes are then apportioned according to the nominal size range split, but if 01/07 '97 12123 Z 0385203027 AST MIELBOURNE there is some carry over to large screen regions then not a lot of performance is lost, and consequently fluctuating feed size distribution is not a problem, This compares with conventional sorting plants where storage would be needed to allow a bank of sorters to run at the limniting rate of the one fed with the most abundant size range.

The description below, together with the diagrams, is intended to illustrate further both the principles and practical form of this invention.

Fig I shows a side view representation of the general detector and deflector modules, which would form one channel of a typically 2-dimensional array (in plan view), comprising broadly of a cramic-lined (or similar hard wearing/impact/pit resistance) delivery tube, coil, shielding and field-shaping electromagnetic system as described in Australian Patent Number 673076, together with pro-processing electronics, exit tube for continued rock transport under gravity into deflection zone, with deflector pneumatic cylinder and toggle mechanism mounted on frame causing rapid positioning of deflector plate with replaceable wear surface which is triggered by sensor signals when niineraliscd rock passes through the coil.

If the minority fraction is expected to be ore, the detection-to -deflection timing is set in the iiormai way such that the deflector is forced into an oblique position just before the rock arrives, causing the oie piece to be expelled out opening the detector returning to the vertical position after a very short time in the path of material failing through the tube. Waste pieces typically are so low in response as to not be seen by the coil detector system, and thus pass unreflected through to the bottom tube openinlg By this means, the wear on the deflector plate is mininised.

Ccriversely, if the deflected (minority) fraction is waste, the opposite procedure occurs, with the deflector which is normally forced open, moving to closed (vertical) position when an ore piece is detected, then returning to the open position, This is an important aspect, as normal sorting systems require optical synchronisation in order to deflect barren rock. The avoidance of optics is a major feature enabling the system to operate in dirty conditions.

-1c RA, 4 Fig 2 shows typical disbursement of a group of 3 detector modules with associated deflector modules In order to effect full area coverage, it would be normal to stagger alternate rows. This allows the deflectors (being narrower than the diameter of the coil system, and about the same width as the delivery tube cross section) to operate in a way that allows deflected material liom one row to pass through chutes placed between adjacent deflector modules. In this way, several rows can be built up with separate chute systems combining streams of accept and reject rocks and passing them to discharge belts (24) on alternative sides of the machine.

Fig 3 shows in diagrammatic form a side section of a typical machine in accordance with this invention. Vibrating screen system consisting basically of an existing double deck system with eccentric drive provides the basis for the sorting machine. The top deck is provided with non-blinding screen in several sections the initial section to allow for slinmes and lines removal a second section (16) passes the smallest rock size fraction for sorting (typically +1-25mmi), which may be fed to detectors in such a way as to provide a bulk prcsentation of small sized material through the tubes. A series of additional sections (25) etc, 110llow for successively larger size fractions.

Slines/fines are discharged via removal chute whilst the sized rock in each stage passes through the top deck (12) and vibrates across the second deck to over the 2- dimensional sorting tubes It is a feature that if any material fails to pass through its normal tube array, it would pass on to the next array of larger sized tubes and so pass tough the sorting system without much reduction in detectability. A slight reduction would expect to take place due to the larger sized coil relative to the rock piece, After the sorting module, rocks are discharged through the accept and r-eject product chutes (19) as appropriate for each size, which direct material on to appropriate conveyor belt (24) collecting accept material on one side and another belt collecting reject material along the other side of the sorter.

7<ARAT -IVT 0' 01/07 '97 12:24 Z 038520027 AlST MELBOURNE Oversized material from either deck falls on to the oversize exit chute (26) a~nd is available for return to primary crusher, or for combining with either accept or reject streams, The sorting arrmy modules (2 3) are constructed in such a way that the coil system is enclosed and sealed, with the inside of the tube being the only part exposed to the outside environment, The complete module slides out to the side of the machine for maintenance.

Claims (1)

1. 01.-07 '97 12:24 X 03B520027 AlST MELBOUR14E The claims vf this invenfion are as follows; 1. An electronic rock sarting system which incorporates the dual functions of size screening and ore/waste rock separation into a single sorting machine, such system comprising: a linea vibrating screen, which has progressively larger holes in the direction in which rock material to be electronically sorted advances, tubular electromagnetic sensors arranged in a two-dimensional array below said screen, each sensor controlling the angular position of a deflector plate arranged below it, where each deflector plate can move between a first position which deflects the rock which has passed through its corresponding sensor, and a second position which does rnot deflect rock material which has passed through its corresponding sensor, where the diameter of the aperture of each sensor is correlated with the size of the screen hole above it. An electronic rock sorting system according to, and using the characteristic featurcs of claim 1, in which such sensors are tubular shielded electromagnetic sensors as described in Australian Patent No. 673076. An electronic rock sorting system according to, and using the characteristic features of claim I1, where a pneumatically driven deflector plate under corresponding sensor is positioned by the sensor control signal in the first position to deflect all undetected rocks, and which moves rapidly to a second position by the sensor control signal in responds to mineralised rock, such signal being sufficient to control the timing of the said deflector movement without requirement for any external synchronising means such as would be provided by an separate optical station in electronic ore sorting equipment of a conventional nature. 4, An electronic rock sorting system according to, and using the characteristic features of, claim 1, where the rocks are presented to said parallel array of sensors by means of a sizing process achieved by a double deck vibrating screen with top deck having progressively larger holes in the direction of rock advance, and the lower deck OL/07 '97 12:25 Z 038520027 PST MELBOURNE having sets of longitudinal grooved channels in 7ones corresponding to the different screen size regions in the upper deck, these channels having exit holes such that appropriately sized rocks will generally fall through the top deck screen opening, into said longitudinal channels and through vibration action, be made to singulate along these grooved channels, discharge through said exit holes and hence fall through corresponding tubular sensors for ore/waste separation. Dated this 27th day of June, 1997 APPLIED SORTING TECHNOLOGIES PTY LTD (Name of Applicant) Ge a p S 0*C a a a a a.,