AU5940400A

AU5940400A - Pulp screen separator

Info

Publication number: AU5940400A
Application number: AU59404/00A
Authority: AU
Inventors: William Norman Cartner
Original assignee: Anglo Operations Pty Ltd
Current assignee: Anglo Operations Pty Ltd
Priority date: 1999-09-13
Filing date: 2000-09-13
Publication date: 2001-03-15
Anticipated expiration: 2020-09-13
Also published as: AU776134B2

Description

52285 GEH:MN P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

*o the best method of performing it known to us: Page 2 FIELD OF THE INVENTION This invention relates to a screen separator for use in mineral processing adsorption cells such as carbon in pulp adsorption tanks, carbon in leach tanks, resin in pulp adsorption tanks and resin in leach tanks which are filled with metal rich solutions or pulps and adsorbent particles such as activated carbon or resin, as well as in water and effluent treatment processes and is an improvement in the modification of the screen separator disclosed in our Australian Patent No.

651160.

SUMMARY OF THE INVENTION A screen separator for separating solid particles from a pulp in a tank according to the invention includes a cylindrical screen which, in use, is submerged in a tank containing pulp with its open end at or adjacent the full pulp surface level in the tank, a pumping impeller which is fixed in the open end of the screen for pumping screened pulp from within the screen to a level above the full surface level of the pulp in the tank as the impeller and so the screen are rotated in the pulp.

The end of the screen opposite the end in which the impeller is fixed is preferably closed by screening material.

Page 3 The impeller is preferably located partially in and out of the pulp in the screen in use and includes a shroud which is fixed in the open mouth of the screen and surrounds the impeller blades over a substantial portion of the length of the impeller with the shroud including at least one pulp outlet which, in use, is located above the full pulp surface level of the pulp in the tank in which the screen separator is to be used.

o The screen and impeller are preferably rotatable by a single motor driven drive shaft. Conveniently the drive shaft extends concentrically into the screen and beyond the impeller and carries on its free end, adjacent the base of the screen, an upflow mixing impeller for keeping the pulp within the screen in suspension oo and for lifting the pulp in the screen towards the impeller in use.

The tank in which the screen separator is to be used includes a moat which surrounds the separator impeller above the full pulp surface level in the tank and which includes at lease one pulp outlet from the tank.

The screen separator may include a housing in which the portion of the impeller which includes the or each outlet is located with the housing including an aperture through which pulp may be pumped from the impeller into the tank moat.

Page 4 The housing preferably additionally includes sweep arms which extend from the housing to and conveniently across the base of the screen with the sweep arms being spaced from and in close proximity to the screening surface of the screen.

Further according to the invention the housing is, in use, supported in the tank on a hollow shaft through which the impeller and screen drive shaft rotatably passes.

Still further according to the invention the housing shaft and the impeller and screen drive shaft are driven in contra-rotation by a suitable motor driven gearbox.

o BRIEF DESCRIPTION OF THE DRAWING The invention is now described by way of example only with reference to the drawing which is a partially schematic sectioned side elevation of one embodiment of the screen separator of the invention, as used as a mineral processing screen separator, in a tank containing pulp.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows a closed adsorption cell tank 10, the screen separator 12 of Page the invention and a portion 14 of a drive arrangement for the screen separator.

The screen separator 12 includes a cylindrical wire, and preferably a wedge wire screen 16, the lower end of which is closed by screening wire mesh, an impeller 18 and a drive shaft indicated generally at The impeller 18 consists of a circular head plate 22, two spaced frusto conical :i elements 24 and 26 and a series of radially arranged impeller blades 28 which are located between and attached to the frusto conical elements and the drive shaft 20. The upper and lower spaces between the impeller elements 24 and 26 are open to provide impeller inlets within the screen and impeller outlets immediately below the impeller head plate 22. The upper end of the screen 16 is fixed to the outer element or shroud 26 of the impeller as shown in the drawing.

The impeller drive shaft extends through the screen 16 to a position adjacent its lower end and carries radially projecting mixing and upflow impeller blades 32.

A volute or housing 34 at the upper end of the tank 10 surrounds the portion of the impeller which projects from the screen 16 and includes, for all practical purposes a continuous aperture which is radially outward of the impeller outlets as shown in the drawing. The underside of the housing, through which the Page 6 screen 16 passes, carries a plurality of sweep arms 36 which are bridged by further sweep arms 38 below the screen 16. All of the sweep arms are spaced from and in close proximity to the outer screening surfaces of the screen 16. The upper end of the housing 34 carries a hollow drive shaft 40 by which it is suspended in the tank 10 and in which the screen and impeller drive shaft 20 is rotatable in guide bearings.

Both guide shafts 20 and 40 are motor driven from a suitable gearbox which is located on the drive arrangement 14 on and above the tank 10. The relative positioning of the housing 34 and its sweep arms 36 and the screen 16 are maintained by the engagement of the upper ends of the drive shafts with the gearbox. The drive shaft 20 is held in alignment and rotated in bearings between it and the drive shaft The upper closure of the tank 10 carries an annular moat 42 which surrounds the housing 34 below the impeller outlets and above the full pulp surface level 44 in the tank 10. An outlet conduit, not shown, leads from the moat 42 and through the wall of the tank 10, at a position above the full pulp surface level 44, to the outside of the tank.

In use, as a mineral processing screen separator, the tank 10 is charged through an opening at or towards its upper end, not shown, on the outside of the screen Page 7 with metal absorbent particles and the tank is filled with a metal-rich pulp to the full pulp level 44 in the tank. The gearbox is now driven to counter-rotate the two drive shafts 20 and 40 to cause the screen and impeller and the sweep arms 36 and 38 to rotate in the pulp in the tank. As the screen is rotated the leaner pulp which has entered the screen is driven upwardly and outwardly on the impeller blades 28 by centrifugal and cyclonically induced forces towards the upper portions of the blades to be thrown from the impeller outlets 30 into the moat or launder 42. In so doing, a negative pressure is generated in the screen 16 which causes pulp in the tank to be drawn through the screening with metal loaded absorption particles above the screen size of the screen being trapped by the outer screening surface of the screen. The leaner pulp in the launder 42 is fed through the outlet conduit under gravity from the tank 10 to an adjacent tank in a series for further processing. Metal rich pulp is fed into the tank 10 at the rate at which the lean pulp is pumped from it by the impeller 18 to maintain the level 44 in the tank The metal rich pulp particles which accumulate on the outside surface of the screen 16 are dislodged from the screen and reintroduced into suspension in the pulp by the sweep arms 36 causing a pulsing disturbance in the space between themselves and the outer screening surface of the screen.

When the precalculated saturation time of the adsorbent particles in the tank Page 8 has been reached the inlet valve to the tank is closed and an outlet valve, which is attached to the tank outlet in the base of the tank, is opened to discharge the now metal rich particles in the tank on the outside of the screen from the tank into a receiver tank.

The lean pulp, which still contains commercial metal values, is fed from the launder 42 to an adjacent tank 10 in a series of the tanks for further processing as described above.

The advantages of the separator of the invention over prior art separators is that the contra-rotating screen and sweep arms together with the enhanced screen area provide a more efficient and uniform discharge of material from the outer surface of the screen than is capable with the prior art devices and, as the drive shaft 20 is not supported from the base of the screen by a hydraulic leg high particle densities cannot build up within the shaft 20 in the screen to cause serious degradation of the walls of the leg and the bearings in it as is the case with known screen separators.

The screen and tank arrangement described above finds equal application in conventional carousel or counter current resin or carbon advance mineral processing processes and, as mentioned above, as well as in water and effluent treatment processes.

Page 9 The invention is not limited to the precise details as herein described with reference to the drawing. For example a shaft with a lifting impeller at its lower end could be fixed to the sweep arms 38 at their junction on the axis of the screen 16 to agitate and keep in suspension solids in the pulp on the outside of the screen. Alternatively the pulp on the outside of the screen could be air agitated.

@0O *0 6 oo @600 0 S i

Claims

1. A screen separator for separating solid particles from pulp in a tank comprising a cylindrical screen which, in use, is submerged in a tank containing pulp with its open end at or adjacent the full pulp surface level in the tank, a pumping impeller which is fixed in the open end of the screen for pumping screened pulp from within the screen to a level above the full surface level of the pulp in the tank as the impeller and so the screen are rotated in the pulp.

2. A screen separator as claimed in claim 1 wherein the end of the screen opposite the end in which the impeller is fixed is closed by a screening material.

3. A screen separator as claimed in either one of claims 1 or 2 wherein the impeller is located partially in and out of the pulp in the screen, in use, and includes a shroud which is fixed in the open mouth of the screen and surrounds the impeller blades over a substantial portion of the length of the impeller with the shroud including at least one pulp outlet which, in use, is located above the full pulp surface level of the pulp in the tank in which the screen separator is to be used. A screen separator as claimed in any one of claims 1 to 3 wherein Page 11 the screen and impeller are rotatable by a single motor driven drive shaft. A screen separator as claimed in claim 4 wherein the drive shaft extends concentrically into the screen beyond the impeller and carries on its free end, adjacent the base of the screen, an upflow mixing impeller for keeping the pulp within the screen, in use, in suspension and for lifting the pulp in the screen towards the impeller.

6. A screen separator as claimed in any one of claims 3 to 5 including a moat which is, in use, fixed to the tank to surround the impeller above the full pulp surface level in the tank and which includes at least one pulp outlet to the outside of the tank.

7. A screen separator as claimed in claim 6 having a housing in which the portion of the impeller which includes the or each outlet is located with the housing having an aperture which substantially surrounds the impeller and through which pulp may be pumped from the or each impeller outlet into the tank moat, in use.

8. A screen separator as claimed in claim 7 wherein the housing is, in use, supported in the tank on a hollow drive shaft through which the impeller and screen drive shaft rotatably passes. Page 12

9. A screen separator as claimed in claim 8 wherein the housing includes downwardly directed sweep arms which extend from the housing to and across the base of the screen with the sweep arms being spaced from and in close proximity to the screening surfaces of the screen. A screen separator as claimed in either one of claims 8 or 9 wherein the housing shaft and the impeller and screen drive shaft are, in use, driven in contra-rotation by a suitable motor driven gearbox. *oo

11. A screen separator for separating solid particles from a pulp in a tank substantially as herein described with reference to the drawing. Dated this 13th day of September 2000 ANGLO AMERICAN CORPORATION OF SOUTH AFRICA LIMITED By their Patent Attorneys COLLISON CO