GB2130109A - Inclined screen - Google Patents

Abstract

An inclined screen separator 12, 14 is used to separate adsorbent particles from a slurry, which is being treated in vessel 1 by countercurrent contact with the adsorbent particles, so that the separated particles may be conveyed from one chamber 3 to the next chamber 4. The chambers are separated by a sieve 5 which allows the slurry to pass through but not the adsorbent. The slurry may be finely divided ore containing Cu, Au or U which is picked up by the adsorbent, the adsorbent loaded with the metal being discharged at 22 and depleted ore at 8. The separator comprises a level detector 23 which acts in conjunction with a timer 20 to control the flow of adsorbent-slurry mixture up line 11 and/or the return of separated slurry and adsorbent through lines 17 and 19, intermittently or continuously. <IMAGE>

Description

SPECIFICATION Control device This invention relates to a control device, more particularly to a device for controlling the transfer of adsorbent to and from stages of a resin-in-pulp or a carbon-in-pulp contactor.

In a resin-in-pulp process a metal ore in finely divided form is leached with a suitable lixiviant and then contacted with a solid ion exchange resin having dependent substituent groups capable of adsorbing metal values from the loaded lixiviant.

Typically the ore is a uranium ore or tailings from a gold mine and the metal to be recovered is uranium. In such a process the ion exchange resin usually bears amino substituents, whilst the lixiviant is normally sulphuric acid. The resin-inpulp process is also applicable to the recovery of other metals, e.g. copper and gold, from their ores, A related process is the carbon-in-pulp process which was developed for the recovery of gold from cyanide leach liquors.

A description of the resin-in-pulp process appears, for example, in British Patent Specification No. 807094 and in United States Patent Specification No. 2743154. A review of both the resin-in-pulp process and the carbon-inpulp process will be found in a paper "Alternative processes to filtration: carbon-in-pulp and resinin-pulp in the metallurgical industry", by C. A.

Fleming and M. J. Nicol, Hydrometallurgy 81, pages C 2/1 to C 2/16, published by Society of Chemical Industry. This paper was presented at a Society of Chemical Industry symposium held at the University of Manchester Institute of Science and Technology, Ma#nchester, England from 30th June to 3rd July 1981.

In either case the process is usually carried out in several stages and involves the problem of retaining the loaded adsorbent (i.e. the loaded resin or carbon) in each stage whilst allowing the metal value-depleted pulp to flow on to the next stage. Perhaps the most commonly adopted expedient involves providing each stage with a screen whose perforations are of a size such that the particles of ore in the pulp can pass through but the adsorbent particles cannot. In the apparatus of the afore-mentioned British and United States patent specifications the screen forms essentially a complete wall of each stage. In the apparatus of Figure 1 of the afore-mentioned paper by Fleming et al. the screen is provided at the upper end of one or more of the side walls of each stage.

In the course of operation the adsorbent becomes loaded with metal values. British Patent Specification No. 807094 describes in relation to Figure 4 thereof an arrangement in which an Archimedes screw 15, operating in a cylinder 16 provided with a screen section 17, is used to transfer resin solids from one stage to the next in order to allow countercurrent flow of pulp and resin through the various stages of resin-in-pulp contactor. Figures 5 to 8 of the same specification illustrate an arrangement with 8 cells or stages which operate on the so-called carousel principle; in this case the resin is not moved from cell to cell but the supply of fresh pulp and of eluant for the loaded resin is switched from cell to cell in turn.

More recent designs, however, have involved air-lifting of the resin (or carbon) and the pulp on to an external screen, with the resin overflow from the screen being diverted to the next stage up the line, while the pulp underflow from the screen returns to the stage of origin. Problems, however, arise in practice with such designs in that careful supervision is required of all stages to ensure that the resin is evenly distributed throughout the pulp in every stage.

The present invention accordingly seeks to provide an improved means of controlling the amount of adsorbent in each stage, and the transfer of resin between stages, in a resin-in-pulp or carbon-in-pulp contactor.

According to the present invention there is provided a control device for controlling the transfer of adsorbent to and from stages of an adsorbent-in-pulp contactor comprising a vessel for receipt of an adsorbent-pulp mixture and having an inclined screen for retention of adsorbent particles and passage of pulp, means for transferring adsorbent-pulp mixture to the vessel, means for measuring the volume of adsorbent or of adsorbent-pulp mixture in the vessel, and outlet means adjacent the lower end of the screen for recovery of drained adsorbent solids.

In order that the invention may be clearly understood and readily carried into effect, a preferred embodiment thereof will now be described, by way of example only, with reference to the accompanying diagrammatic drawing, which is a vertical section through a control device constructed according to the invention.

Referring to the drawing, which is diagrammatic only and is not drawn to scale, a resin-in-pulp contactor 1 comprises a rectangular plan tank 2 which is divided into first staye 3 and second stage 4 by means of a vertical screen 5.

For the sake of simplicity two stages only are shown but it will be appreciated by those skilled in the art that in practice it will usually be desirable to include 3, 4 or more stages, e.g. up to about 7 or more.

Resin of controlled bead size, e.g. a +22 mesh (British Standard Test Sieve) resin, i.e. a resin with a particle size of 699 micrometres or larger, is supplied to first stage 3 as indicated by line 6 whilst a uranium ore pulp containing, for example, -200 mesh (British Standard Test Sieve) ore particles (i.e. particles with a diameter of less than 76 micrometres) is supplied by way of line 7 to second stage 4. Pulp passes from second stage 4 to first stage 3, in countercurrent to the resin as will be described hereafter, through screen 5, the apertures in which are intermediate in size between the particle sizes of the resin and of the ore particles in the pulp. Lean pulp exits first stage 3 by way of line 8.Impellers 9 on vertical shafts 10 are driven by variable speed motors (not shown) so as to cause mass circulation of the resin-pulp mixture in each of the stages.

A mixture of resin and pulp is withdrawn from first stage 3 as indicated by line 11 and passed to a control device 12. An air lift or Archimedes screw can be used for raising the resin-pulp mixture from first stage 3 to control device 12.

Control device 12 is illustrated at a much larger scale than the remainder of the apparatus. It is in the form of a rectangular section box having a sloping bottom 13 and fitted with an inclined screen 14, the apertures in which are intermediate in size between the resin particle size and the ore particle size. For example when using +22 mesh resin particles and a pulp with~200 mesh ore particles, the screen may be an 80 mesh screen.

(Mesh sizes relate to British Standard Test Sieve.) Pulp passes through screen 14 into a sump between screen 14 and the sloping bottom 13 of the box but resin particles are retained on screen 14, as indicated by reference numeral t 5.

Underflow pulp from screen 14 is returned from the sump by way of valve 16 and line 17 to first stage 3. Resin collected at 15 is discharged intermittently from device 12 by way of valve 1 8 and passed as indicated by line 19 to second stage 4 or returned to stage 3 by line 27.

A timing device 20 is used to control a valve 21 in line 11 as well as valves 16 and 18. Loaded resin is removed from second stage 4 by way of line 22.

The device 12 is fitted with a detector 23 for measuring the volume of resin-pulp mixture in the device 12 and/or the volume of the drained resin 15. Detector 23 can be, for example, a microwave detector of the type described in co-pending Patent Application No. (Case No.

81324) filed simultaneously herewith.

Alternatively detector 23 can be a contact probe, an ultrasonic detector or a nucleonics detector arranged to feed data to a control device 24, such as a microprocessor, linked to timer 20.

Alternatively detector 23 may comprise a pair of conducting plates arranged to dip into the resinpulp mixture with a measuring circuit arranged to measure the capacitance between the plates and hence the volume of pulp and/or resin between the plates and hence the corresponding volume thereof in the device 12.

The invention may be used to control the transfer of resin from one stage to the next in the following way: In operation of the illustrated control device resin-pulp mixture is air lifted via line 11 to device 12. During this step valve 16 is left open so that pulp drains continuously through screen 14 and back into first stage 3 by way of line 17. When the level of resin in the device 12 has reached a predetermined level the flow of resin-pulp mixture to device 12 by way of line 11 is stopped, the body of resin 1 5 is allowed to remain on the screen 14 until the pulp has drained below the resin surface (e.g. for a further 1 to 2 minutes), whereupon valve 18 is opened by timer 20 and the resin mass 1 5 is flushed, using water or barren solution from line 28, into second stage 4 as indicated by line 19.The cycle can then be repeated at fixed intervals depending on the rate of resin transfer required.

Using the procedure described above a uniform quantity of resin can be transferred in each cycle from one stage to the next. In addition it will be readily apparent to those skilled in the art that devices similar to device 12 can equally be used to transfer resin to first stage 3 and to remove loaded resin by way of line 22. In this way the rate of resin transfer to and from each stage can be controlled at all stages of operation of the process.

Alternatively the device 12 can be used to calculate the quantity of resin transferred in each transfer period and to make adjustments as required. In this case valves 16 and 18 both remain closed during the initial transfer operation of resinpulp mixture to the device 12. Detector 23 then measures the volume of resin-pulp mixture in the device, the upper level of which is indicated at 25 at this stage, whereupon valve 16 is opened and the resin allowed to drain for a set period. The detector 23 measures the volume of the drained resin mass 15 and so calculates the resin concentration in the resin-pulp slurry.This information can then be used by microprocessor 24 to vary the time for which valve 21 remains open or to vary the air supply to the air lift device (not shown) in line 11 so as to adjust the volume of resin-pulp mixture transferred on the next cycle, and hence to vary the volume of resin transferred in each cycle until the system re-adjusts itself to the desired conditions. In this way the resin-inpulp contactor can be run with a minimum of supervision.

Instead of using device 12 to effect bulk transfer of resin from stage to stage it can alternatively be used to monitor the resin concentration in the relevant stage. In that case a recycle line 26 may be provided to provide, together with line 11 and its associated air lift device (not shown) a small continuously recycling sampling system for first stage 3. A separate air lift (not shown) is in this case provided to enable resin transfer to second stage 4. In this case device 12 is relatively small.

In operation of this modification of the invention valves 16 and 18 are closed and valve 21 is opened until a predetermined volume of resin-pulp mixture has been transferred from first stage 3 to device 12. When a Dreselected sample size has been collected, as monitored by the detector 23 and indicated at 25, valve 16 is opened or the underflow pulp is allowed to drain back to first stage 3 by way of line 17. The volume of drained resin 15 is then measured by detector 23 and the result used by microprocessor 24 to calculate the resin concentration. This information is then used as necessary to adjust automatically the air supply to the main air lift device used for inter-stage resin transfer. In this way the amount of resin in each stage can be controlled to a desired value. The drained sample 15 of resin can be dumped back in first stage 3 by way of line 27.

It is of course within the scope of the invention to utilise within the same resin-in-pulp contactor apparatus both one or more large resin control devices 12 as illustrated for inter-stage resin transfer and also one or more small control devices 12, modified as described above and each fitted with a detector 23 connected to a microprocessor 24, for controlling the resin concentration in the stages and hence the amount of resin in each stage.

Instead of using mesh, screen 14 can alternatively comprise closely spaced bars.

Although the invention has been specifically illustrated in relation to a resin-in-pulp contactor, it is equally within the scope thereof to utilise it in a carbon-in-pulp contactor.

Claims (9)

1. A control device for controlling the transfer of adsorbent to and from stages of an adsorbentin-pulp contactor comprising a vessel for receipt of an adsorbent-pulp mixture and having an inclined screen for retention of adsorbent particles and passage of pulp, means for transferring adsorbentpulp mixture to the vessel, means for measuring the volume of adsorbent or of adsorbent-pulp mixture in the vessel, and outlet means adjacent the lower end of the screen for recovery of drained adsorbent solids.

2. A device according to claim 1, in which the outlet means comprises a timer-operated valve for intermittent discharge of drained adsorbent solids.

3. A device according to claim 1 or claim 2, in which the vessel includes a sump below the screen for retaining pulp that has passed through the screen and means for intermittent discharge of pulp from the sump.

4. A device according to claim 3, in which the means for intermittent discharge of pulp from the sump comprises a timer-operated valve.

5. A device according to any one of claims 1 to 4, in which the means for transferring adsorbentpulp mixture to the vessel comprises an air-lift pump.

6. A device according to any one of claims 1 to 5, in which the means for transferring adsorbentpulp mixture to the vessel includes a timeroperated valve.

7. A device according to any one of claims 1 to 6, in which the means for measuring the volume of adsorbent or adsorbent-pulp mixture in the vessel comprises a microwave detector.

8. A device according to any one of claims 1 to 7, further including means for flushing adsorbent solids retained on the screen out of the vessel.

9. A control device for controlling the transfer of adsorbent to and from stages of an adsorbentin-pulp contactor constructed and arranged substantially as herein described with particular reference to the accompanying drawing.