CA1299521C - Screening device - Google Patents
Screening deviceInfo
- Publication number
- CA1299521C CA1299521C CA000520596A CA520596A CA1299521C CA 1299521 C CA1299521 C CA 1299521C CA 000520596 A CA000520596 A CA 000520596A CA 520596 A CA520596 A CA 520596A CA 1299521 C CA1299521 C CA 1299521C
- Authority
- CA
- Canada
- Prior art keywords
- screen element
- screening device
- agitators
- wall
- shaft
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Landscapes
- Separation Of Solids By Using Liquids Or Pneumatic Power (AREA)
- Paper (AREA)
Abstract
ABSTRACT
A screening device for separating suspended solids from a liquid in a container comprises a hollow screen element with walls of a mesh structure. The screen element is submerged in the liquid, which passes from the container into the interior of the element and to an outlet. Agitators and impellers are provided on a shaft passing through the centre of the screen element. The impellers cause an increased flow of liquid past the screen element, while the agitators dislodge solids caking the mesh. The agitators are in the form of a frame which closely surrounds the screen element.
A screening device for separating suspended solids from a liquid in a container comprises a hollow screen element with walls of a mesh structure. The screen element is submerged in the liquid, which passes from the container into the interior of the element and to an outlet. Agitators and impellers are provided on a shaft passing through the centre of the screen element. The impellers cause an increased flow of liquid past the screen element, while the agitators dislodge solids caking the mesh. The agitators are in the form of a frame which closely surrounds the screen element.
Description
~Z~95~1 BACKGROUND OF THE INVENTION
This invention relates to a screening device for separating suspended solids from a liquid.
Metal values may be extracted from their ores by finely grinding the ore, and then leaching the ore with a suitable leaching solution. For example, gold values may be extracted from their ores by leaching finely ground gold-bearing ore with a cyanide solution. The product of the leaching step is a metal-rich leach solution or pulp known as a pregnant solution or pulp. The metal values may be recovered from the pregnant leach solution or pulp using various techniques. One widely used technique is to capture the metal values on a suitable support such a activated carbon by the so-called carbon-in-pulp method.
The carbon-in-pulp method may be carried out in a series of tanks with the pulp flowing in one direction under the influence of gravity and the carbon flowing counter-current to the pulp flow. The lean pulp is withdrawn from one end of the series of tanks while the loaded carbon is withdrawn from the other end.
A screening device is commonly provided at the outlet from each tank, which has a covering mesh or screen to enable the pulp to pass through, but not the carbon. The screens tend to become clogged with carbon during use. Many methods have been proposed and are used for unclogging the screens during use. One such method is to sweep the screens with air. This method is not very efficient and is costly in energy. Problems are encountered with proper air distribution and the method necessitates the use of a multiplicity of air injection nozzles which are subject to wear and choking with solids. Furthermore, it is only possible to attain relatively low throughputs, typically 60m3~h.m2. It is also known to sweep the screens mechanically or to cause the screens to vibrate. These methods again have not proved very efficient.
SUMMARY OF IHE _NY~NTION
According to the invention there is provided a screening device for separating suspended solids from a liquid in a container, comprising a screen element which has a mesh structure and which i5 adapted to be at least partially submerged in the container between an inlet to and an outlet from the container;
at least one agitator arranged to be driven past a surface of the screen element to create turbulence in the liquid adjacent the surface; and at least one impeller arranged to be driven together with the or each agitator to cause the liquid to flow past the surface.
5~Z~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial sectional side view of a screening device according to the invention; and Figure 2 is a partial sectional top view of the device of Figure 1.
DESCRIPTIO~ 0~ ~ PREFER~E~ ~MBODI~E~T
Figure 1 shows a screening device, generally designated by the numeral 14, located with its lower end submerged in a gold-bearing pulp 12. The pulp 12 is contained in a large container or tank (not shown). The screening device 14 has a central housing 16 which defines a vertical bore 18 in which a shaft 20 is rotatably mounted. The shaft is supported near its upper end on bearings 22 and 24, and is arranged to be rotated by an electric motor 26 via a belt drive 28 mounted at the upper end of the screening device. The bore 18 has an opening 54 and an optional overflow pipe 56.
At the lower end of the screening device is a screen element 30 which is in the form of a hollow cage. The screen element 30 has an inner wall 32 which is generally frusto-conical in shape, and an outer wall 34 which is right cylindrical in shape. The inner wall 32 and the outer wall 34 are coaxial, and comprise a relatively coarse grid covered with a fine mesh.
Seen from above, the screen element has an annular cross section which decreases towards the bottom of the element. The interior of the screen element 30 is in communication with the interior of the housing 16, which defines an outlet flow path from the tank or container.
Towards the lower end of the shaft 20 are mounted impellers 36 and 38. Each impeller comprises four equally radially spaced blades which extend laterally from the shaft 20 and which are inc]ined at an angle of 45 relative to the axis of the shaf-t 20. An agitator assembly, shown more clearly in Figure 2, is 5~
also attached to the shaft 20. A circular plate 40 i8 fixed to the shaft 20 a-t the same heigh-t as the impeller 36. Eight agitator elements 42, comprising sections of angle iron, extend downwardly from the plate 40 to respective radially extending legs 44 which extend from a hub 46 at the bottom end of the shaft 20. The agitator members 42 are angled so as to be parallel to the inner surface 32 of the screen element 30. The radial legs 44 extend beyond the outer wall 34 of the screen element 30 and carry respective vertical agitator members 48 which extend parallel to the outer surface 34 of the screen element 30. Strengthening hoops 50, 52 and 58 reinforce the agitator assembly.
As can be seen more clearly in Figure 2, adjacent agi-ta-tor elements 42 are rotated through 180 about their respective longitudinal axes, and the orientation of adjacent vertical agitator members 48 is similarly reversed. On one flange of each agitator member 42, 48 and running the entire length thereof is a reinforced flat rubber blade 51, one edge of which extends beyond the edge of the respective flange.
The operation of the screening device is as follows. Gold bearing pulp is introduced to the tank or container via an inlet 60, where it is mixed with carbon present in the tank.
The shaft 20 is caused to rotate, and the impellers 36 and 38 cause a flow of pulp through the center of the screen element 30 in the direction of the arrows.The pulp is drawn into the central bore 18 through the opening 54 and passes down through the centre of the screen element 30 back into the tank or container, flowing from the apical end to the basal end of the inner wall 32. Screened liquid which has passed through the mesh of the screen element 30 passes via the interior of the housing 16 and an outlet (not shown) to a successive container or pipeline. Clearly, suspended particles smaller than the mesh size will pass through the screen element. Solid material in the pulp tends to collect on the inner and outer mesh walls of the screen element 30 as liquid crosses the mesh into the s~
interior of the screen element. However, the agita-tion caused by the rotating agitator elements 42, 48 tends to dislodge this solid matter by creating pressure waves or -turbulence adjacent the surfaces. The rubber blades 51 pass close to the respective surfaces of the screen element but do not contact the surfaces.
The exact configuration of the blades, their distance from the walls of the screen element, and the rotational speed of the agitator assembly will depend on the characteristics of the pulp in the tank or container.
If the orienta-tion of the blades of the impellers 38 and 40 is reversed, or if the direction of rotation of the shaft 20 is reversed, the pulp will flow through the screening device in the opposite direction to that shown by the arrows in Figure 1.
In the event that the shaft 20 is rotated too rapidly, causing an excessive flow of pulp through the central bore 18, an overflow pipe 56 diverts the excess flow back into the tank or container, and prevents the pulp from rising up to the level of the bearings 22 and 24.
It has been found in use, however, that clogging of the inner surface 32 of the screen element 30 is minimised by causing the pulp to flow downwards through the screen element 30 as described earlier.
It has been found that the improved pulp flow caused by the use of the impellers 36 and 38 together with the agitator assembly improves the throughput of the screening device over prior devices.
This invention relates to a screening device for separating suspended solids from a liquid.
Metal values may be extracted from their ores by finely grinding the ore, and then leaching the ore with a suitable leaching solution. For example, gold values may be extracted from their ores by leaching finely ground gold-bearing ore with a cyanide solution. The product of the leaching step is a metal-rich leach solution or pulp known as a pregnant solution or pulp. The metal values may be recovered from the pregnant leach solution or pulp using various techniques. One widely used technique is to capture the metal values on a suitable support such a activated carbon by the so-called carbon-in-pulp method.
The carbon-in-pulp method may be carried out in a series of tanks with the pulp flowing in one direction under the influence of gravity and the carbon flowing counter-current to the pulp flow. The lean pulp is withdrawn from one end of the series of tanks while the loaded carbon is withdrawn from the other end.
A screening device is commonly provided at the outlet from each tank, which has a covering mesh or screen to enable the pulp to pass through, but not the carbon. The screens tend to become clogged with carbon during use. Many methods have been proposed and are used for unclogging the screens during use. One such method is to sweep the screens with air. This method is not very efficient and is costly in energy. Problems are encountered with proper air distribution and the method necessitates the use of a multiplicity of air injection nozzles which are subject to wear and choking with solids. Furthermore, it is only possible to attain relatively low throughputs, typically 60m3~h.m2. It is also known to sweep the screens mechanically or to cause the screens to vibrate. These methods again have not proved very efficient.
SUMMARY OF IHE _NY~NTION
According to the invention there is provided a screening device for separating suspended solids from a liquid in a container, comprising a screen element which has a mesh structure and which i5 adapted to be at least partially submerged in the container between an inlet to and an outlet from the container;
at least one agitator arranged to be driven past a surface of the screen element to create turbulence in the liquid adjacent the surface; and at least one impeller arranged to be driven together with the or each agitator to cause the liquid to flow past the surface.
5~Z~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial sectional side view of a screening device according to the invention; and Figure 2 is a partial sectional top view of the device of Figure 1.
DESCRIPTIO~ 0~ ~ PREFER~E~ ~MBODI~E~T
Figure 1 shows a screening device, generally designated by the numeral 14, located with its lower end submerged in a gold-bearing pulp 12. The pulp 12 is contained in a large container or tank (not shown). The screening device 14 has a central housing 16 which defines a vertical bore 18 in which a shaft 20 is rotatably mounted. The shaft is supported near its upper end on bearings 22 and 24, and is arranged to be rotated by an electric motor 26 via a belt drive 28 mounted at the upper end of the screening device. The bore 18 has an opening 54 and an optional overflow pipe 56.
At the lower end of the screening device is a screen element 30 which is in the form of a hollow cage. The screen element 30 has an inner wall 32 which is generally frusto-conical in shape, and an outer wall 34 which is right cylindrical in shape. The inner wall 32 and the outer wall 34 are coaxial, and comprise a relatively coarse grid covered with a fine mesh.
Seen from above, the screen element has an annular cross section which decreases towards the bottom of the element. The interior of the screen element 30 is in communication with the interior of the housing 16, which defines an outlet flow path from the tank or container.
Towards the lower end of the shaft 20 are mounted impellers 36 and 38. Each impeller comprises four equally radially spaced blades which extend laterally from the shaft 20 and which are inc]ined at an angle of 45 relative to the axis of the shaf-t 20. An agitator assembly, shown more clearly in Figure 2, is 5~
also attached to the shaft 20. A circular plate 40 i8 fixed to the shaft 20 a-t the same heigh-t as the impeller 36. Eight agitator elements 42, comprising sections of angle iron, extend downwardly from the plate 40 to respective radially extending legs 44 which extend from a hub 46 at the bottom end of the shaft 20. The agitator members 42 are angled so as to be parallel to the inner surface 32 of the screen element 30. The radial legs 44 extend beyond the outer wall 34 of the screen element 30 and carry respective vertical agitator members 48 which extend parallel to the outer surface 34 of the screen element 30. Strengthening hoops 50, 52 and 58 reinforce the agitator assembly.
As can be seen more clearly in Figure 2, adjacent agi-ta-tor elements 42 are rotated through 180 about their respective longitudinal axes, and the orientation of adjacent vertical agitator members 48 is similarly reversed. On one flange of each agitator member 42, 48 and running the entire length thereof is a reinforced flat rubber blade 51, one edge of which extends beyond the edge of the respective flange.
The operation of the screening device is as follows. Gold bearing pulp is introduced to the tank or container via an inlet 60, where it is mixed with carbon present in the tank.
The shaft 20 is caused to rotate, and the impellers 36 and 38 cause a flow of pulp through the center of the screen element 30 in the direction of the arrows.The pulp is drawn into the central bore 18 through the opening 54 and passes down through the centre of the screen element 30 back into the tank or container, flowing from the apical end to the basal end of the inner wall 32. Screened liquid which has passed through the mesh of the screen element 30 passes via the interior of the housing 16 and an outlet (not shown) to a successive container or pipeline. Clearly, suspended particles smaller than the mesh size will pass through the screen element. Solid material in the pulp tends to collect on the inner and outer mesh walls of the screen element 30 as liquid crosses the mesh into the s~
interior of the screen element. However, the agita-tion caused by the rotating agitator elements 42, 48 tends to dislodge this solid matter by creating pressure waves or -turbulence adjacent the surfaces. The rubber blades 51 pass close to the respective surfaces of the screen element but do not contact the surfaces.
The exact configuration of the blades, their distance from the walls of the screen element, and the rotational speed of the agitator assembly will depend on the characteristics of the pulp in the tank or container.
If the orienta-tion of the blades of the impellers 38 and 40 is reversed, or if the direction of rotation of the shaft 20 is reversed, the pulp will flow through the screening device in the opposite direction to that shown by the arrows in Figure 1.
In the event that the shaft 20 is rotated too rapidly, causing an excessive flow of pulp through the central bore 18, an overflow pipe 56 diverts the excess flow back into the tank or container, and prevents the pulp from rising up to the level of the bearings 22 and 24.
It has been found in use, however, that clogging of the inner surface 32 of the screen element 30 is minimised by causing the pulp to flow downwards through the screen element 30 as described earlier.
It has been found that the improved pulp flow caused by the use of the impellers 36 and 38 together with the agitator assembly improves the throughput of the screening device over prior devices.
Claims (14)
1. A screening device for separating suspended solids from a liquid in a container comprising, a screen element which has a mesh structure having a generally vertically aligned inner wall of annular form which defines a central volume in the centre of the screen element, said screen element being adapted to be at least partially submerged in the container between an inlet to and an outlet from the container; at least one agitator arranged to be driven past a surface of the screen element to create turbulence in the liquid adjacent the surface; and at least one impeller arranged to be driven together with the or each agitator to cause the liquid to flow either generally up or generally down the central volume and past the surface.
2. A screening device according to claim 1 in which the screen element is hollow and includes an annular outer wall, the inner and outer walls defining between them an annular volume which is in communication with the outlet from the container, the central volume being in communication with the interior of the container.
3. A screening device according to claim 2 in which the outer wall of the screen element is right cylindrical in shape and the inner wall is frusto-conical in shape, the inner and outer walls being coaxial.
4. A screening device according to claim 2 in which the or each impeller is mounted on a shaft which passes through the central volume defined by the inner wall of the screen element.
5. A screening device according to claim 3 in which the or each impeller is mounted on a shaft which passes through the central volume defined by the inner wall of the screen element and which is coaxial therewith.
6. A screening device according to claim 4 in which the or each agitator is mounted on the shaft on which the or each impeller is mounted.
7. A screening device according to claim 5 in which the or each agitator is mounted on the shaft on which the or each impeller is mounted.
8. A screening device according to claim 7 in which an inner set and an outer set of agitators are provided adjacent the inner and outer walls of the screen element respectively, the inner set of agitators being disposed at an angle to the shaft and parallel to the inner wall of the screen element, the outer set of agitators being disposed parallel both to the shaft and to the outer wall of the screen element.
9. A screening device according to claim 8 in which the inner and outer sets of agitators are coaxial, the inner set of agitators comprising a plurality of elongate members each of which is connected at one end to the shaft and at the outer end to a support member extending radially from the shaft, the outer set of agitators comprising a plurality of elongate members each of which is connected at one end to the end of a support member remote from the shaft, the inner and outer sets of agitators forming an agitator frame which closely surrounds the screen element.
10. A screening device according to claim 9 in which the agitators comprise angle sections.
11. A screening device according to claim 10 in which the orientation of the angle sections of adjacent agitators about their longitudinal axes is reversed.
12. A screening device according to claim 10 in which a planar rubber blade is fixed to a flange of each angle section, with an edge of the blade extending beyond the edge of the flange.
13. A screening device according to claim 11 in which a planar rubber blade is fixed to a flange of each angle section, with an edge of the blade extending beyond the edge of the flange.
14. A screening device according to claim 3 in which the or each impeller is arranged to cause the liquid to flow through the volume defined by the frusto-conical inner wall of the screen element from the apical end of the inner wall to the basal end.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000520596A CA1299521C (en) | 1986-10-16 | 1986-10-16 | Screening device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000520596A CA1299521C (en) | 1986-10-16 | 1986-10-16 | Screening device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1299521C true CA1299521C (en) | 1992-04-28 |
Family
ID=4134155
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000520596A Expired - Lifetime CA1299521C (en) | 1986-10-16 | 1986-10-16 | Screening device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1299521C (en) |
-
1986
- 1986-10-16 CA CA000520596A patent/CA1299521C/en not_active Expired - Lifetime
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |