WO2000012192A1

WO2000012192A1 - Apparatus for the separation of solids and liquids

Info

Publication number: WO2000012192A1
Application number: PCT/ZA1999/000079
Authority: WO
Inventors: Malcolm David Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-02
Filing date: 1999-09-02
Publication date: 2000-03-09
Anticipated expiration: 2001-03-02
Also published as: PE20000841A1; AR020368A1; ZA988005B; AU5591999A

Abstract

A liquid/solids separation device is provided in which a tubular feed chamber (5) extends vertically downwards within a container. The feed chamber is open at its lower end (28) which is located well above a central outlet (4) in the bottom of the container to provide for a compacted zone of dewatered solids located below the lower end of the feed chamber. A usually semi-circular furcated mixing rake (26) is positioned within the feed chamber and a dewatering ring (24) is positioned around the lower end of the feed chamber. An inlet to the feed chamber in the upper region directs inlet slurry in a circumferential direction by conveniently making the inlet pipe (9) follow a tangential path or that of an involute, relative to the tubular feed chamber. Means (15) are also provided for introducing clarified liquid from the top region of the container into the inlet slurry. Thickened underflow material is withdrawn from the base of the container through a sleeve and clarified liquor exits from the top of the container.

Description

"APPARATUS FOR THE SEPARATION OF SOLIDS AND LIQUIDS"

TECHNICAL FIELD

This invention relates to an apparatus for the separation of solids and liquids, which term includes a slurry thickener of the type widely used in the mineral processing, ore dressing and metallurgical extraction fields, as well as in the chemical industry, for the purpose of decreasing the volume of a slurry or other suspension of solids in a liquid. This may be done for the purpose of facilitating and handling the slurry and decreasing the size of equipment needed for further processing; for decreasing the volume of slurry constituting tailings and due to be discarded; for recovering water or other liquid from a slurry for re-use; for any combination of such purposes; or for any other process in which a liquid carrier is separated, to some extent, from solids which it contains.

BACKGROUND ART

Originally, and there are many such slurry thickeners still in use to this day, a slurry thickener assumed the form of a large reservoir of generally squat shape and having a squat inverted truncated conical bottom such that solids could gravitate towards an outlet at the lowermost central point. Rotating rakes ensure that solids do not become permanently lodged on the bottom of the reservoir; to maintain a certain degree of mobility of the thickened slurry at the bottom of the reservoir and to accelerate the release of some of the interstitial liquor from between solid particles. Slurry is introduced radially at the top of a central vertical tubular feed chamber. In order to dilute this slurry to a more optimal consistency, clarified liquid from the top of the reservoir is drawn into the feed chamber by a variety of methods usually making use of the density difference between the incoming slurry and the clarified liquor.

The disadvantages of this type of slurry thickener are that, in the first place, it covers a large physical area; because of its size it is expensive to construct; it is not particularly efficient in operation; and, it has moving parts and thus is maintenance intensive.

A number of other constructions have followed of which employ a container in the form of a conical bottom tank having substantially greater height than the conventional slurry thickener; and a substantially smaller diameter, thereby occupying less floor space.

In one form of these, known as the Tasster thickener, which applicant understands is now off the market, paddles are included in an attempt to promote flocculation in the presence of an added flocculent and accordingly, settling of the solids of the slurry to form a denser slurry at the bottom. Another of this type of slurry thickener is known as the E-CAT and has a central tubular feed chamber into which feed slurry is introduced radially, as in the case of the conventional thickener.

However, the lower end of the feed chamber feeds flocculated solids onto a series of axially arranged upwardly directed spaced conical baffles which assist in the de-watering process in consequence of particles and flocculated particles falling thereon and impinging on each other. Partially clarified liquid is caused to pass through a series of cylinders towards the top of the container in each, of which a secondary bed of fluidised flocculating material can be formed, which further clarifies the liquid. Liquor containing some suspended solids is re-circulated back to the feed chamber via the conical baffles for dilution purposes and is driven by an imbalance of hydrostatic forces within the body of the unit.

A further type of thickener of this nature is known as the Ultrasep and is similar to the E-CAT except for the fact that the baffles are truncated conical baffles which are inverted so as to cause the flocculated solids to gravitate towards the centre from where they pass to the next baffle below. In this case too, a secondary bed of fluidised flocculating material can be formed just outside and above the outlet end of the feed chamber. Liquor containing some suspended solids is also recirculated back to the top of the feed chamber via a conical baffle located within the lower region of the feed chamber for dilution purposes and is also driven by an imbalance of hydrostatic forces. In this design, a portion of the overflow liquor can also be redirected back to the feed chamber across the feed chamber wall via the open launder that collects all the overflow liquor at the top of the container.

Also, both of these thickeners lead to a situation in which liquid is partly removed from the slurry within the central body of the unit to give rise to a "hindered" zone in which settling of floe's still take place, but because some liquid has been removed, this causes a great amount of inter particle touching, which dramatically "hinders" or slows down the settling process. This "hindered" zone occurs between the "free settling" and "compaction" zones, and occupies a large portion of the height of these units.

Whilst the latter two types of thickener generally operate effectively, there is still considerable room for improvement. In particular, with relation to the clarity of overflow liquid recovered at the top of the container and more importantly as to the degree of thickening of the slurry is concerned i.e. the liquid content of the product extracted ■τom the bottom of the thickener; and to the amount of flocculent required for effective separation. DISCLOSURE OF THE INVENTION

In accordance with this invention a solids/liquid separation device is provided, comprising a container having a height substantially greater than its diameter; a central tubular feed chamber extending downwardly from the upper end region of the container to a position spaced upwardly of the lower end of the container which converges to an outlet in the lowermost region of the container, and an inlet pipe for inlet slurry communicating with the upper region of the feed chamber, the inlet arrangement being such that slurry entering the feed chamber does so in a substantially circumferential direction to create a swirling movement of slurry within the feed chamber.

Further features of the invention provide for the inlet pipe to communicate with the upper region of the feed chamber by communicating tangentially or along the path of an involute, or alternatively; for a suitable baffle arrangement to be provided in the feed chamber to direct slurry entering the chamber in a substantially circumferential direction when the inlet pipe communicates with the feed chamber in a roughly radial configuration; for the feed chamber to have a usually semi-circular furcated mixing rake extending throughout the entire length or portion of the entire length of the feed chamber; for the feed chamber to have a plurality of vertically spaced flocculent injection points along it's length, and/or in addition to one or more further flocculent injection points associated with the inlet pipe; for the lower end of the feed chamber to preferably be defined by a coaxial reduced diameter zone tapering down at a selected angle, typically 45 degrees; for there to be communication means between the upper region of the container and the inlet pipe or feed chamber for the controlled introduction of clarified liquid from the upper region of the container into the feed slurry; for a further flocculent injection point to be associated with the lower region of this communication means; for a dewatering ring to be positioned between the lower region of the feed chamber and container wall, or just below the lower region of the feed chamber and container wall; for a sleeve usually to be positioned at the truncated part of the conical section; for a porous membrane to form the inner wall of the sleeve; for pump means to be connected to the outlet from the container and for a usually v-notched shaped overflow weir to collect clarified overflow at the top of the container.

Still further features of the invention provide for the slurry inlet to be provided with monitors for monitoring the flow rate and/or density of the feed slurry; for the underflow pipe to be provided with means for monitoring the flow rate and/or density of the underflow from the thickener; an evacuation system to control the underflow relative density; for a level detector to be associated with the container for detecting and controlling the level of the upper limit of the compacted zone of slurry in the device in use; and for the device to include control means for controlling the amount of flocculent fed to the slurry and also the amount of clarified liquid fed to the feed slurry or feed chamber. In order that the invention may be more fully understood one embodiment and a number of variations thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: -

Fig 1 is a schematic elevation of a slurry thickener according to the invention;

Fig 2 is a schematic plan view illustrating the feed arrangements;

Fig 3 is a schematic illustration of the upper end of a container illustrating different arrangements for diluting the feed slurry using clarified liquid in the container;

Fig 4 is a schematic illustration of a semi-circular furcated mixing rake within the feed chamber;

Fig 5 is a schematic illustration of another semi-circular furcated mixing rake within the feed chamber;

Fig 6 is a schematic illustration of the expanded state of the membrane; and

Fig 7 is a schematic illustration of a cluster of porous sleeves attached to the truncated part cf the conical section.

BEST MODES FOR CARRYING OUT THE INVENTION

In the embodiment of the invention illustrated in Figure 1, a slurry thickener, generally indicated by numeral (1), comprises a container (2), which may assume a substantially standard form of tank or pachuca. The lower end (3) of the container is formed into an inverted truncated conical shape with an outlet (4) at the lower end thereof.

A tubular feed chamber (5) is arranged co-axially within the container, the lower end of the feed chamber terminating above the ultimate desired upper level of the thickened sludge compaction zone indicated by numeral (6) in use. The feed chamber also terminating above or within the inner region of the dewatsring ring (24). The upper end (7) of the feed chamber is above the upper level (8) of liquid in the container in use. Whilst being of constant diameter along its length in this particular case, the feed chamber may also diverge or converge by 10 degrees or less. In the case of a divergent feed chamber an extra tubular wall would be vertically positioned around the outside of the feed chamber. This would effect to maintain a constant cross sectional area in the clarified liquor region thereby preventing the clarified liquor passing from a high velocity region to a progressively lower velocity region as would be the case if the extra tubular wall was not used. In the case of a convergent feed chamber this extra wall would not be required, as the clarified liquor would pass from a low velocity region to a progressively higher velocity region. In consequence of this a floe structure would not report to the region of low velocity and therefore would not report to the upper region of higher velocity.

A generally horizontal feed pipe (9) communicates from the exterior of the container with the feed chamber (5), and in this embodiment; the feed pipe (9) communicates tangentially with the feed chamber as shown clearly in Figure 2. As an alternative it may also communicate in a path corresponding to that of an involute indicated by dotted lines (10) or radially (10a) when baffles are used to ensure that the feed material enters the feed chamber in a circumferential direction.

Located within the feed chamber (5) is a usually semi-circular furcated mixing rake (26), and in this embodiment, the mixing rake extends throughout the entire length of the feed chamber. Alternatively, the length of the mixing rake may be shorter than the length of the feed chamber and one or more, shorter mixing rakes could be positioned at any point inside and along the length of the feed chamber as shown in Figure 4.

The lower end of the feed chamber (5) would preferably reduce, as indicated by numeral (27) at an angle of about 45 degrees, to a coaxial reduced diameter outlet (28) located centrally up the height of the tubular baffle. In this case, the lower end of the reduced diameter zone (28) of the feed chamber may terminate above or within the inner region of the dewatering ring (24).

Along the length of the feed chamber (5), both above and below the point of communication between the inlet pipe (9) and feed chamber (5) are a series of vertically spaced injection points (11 ) for flocculent solution supplied by a flocculent pump (12) and a further injection point/s (13) for flocculent is provided in the inlet pipe (9) and/or branch (15).

In this embodiment of the invention an outlet pipe (14) for clarified liquid in the top of the container has a branch (15) controlled by a valve (16) communicating with the inlet pipe (9) so that the feed slurry can be diluted as and when may be required with clarified liquid. With the use of branch (15) and valve (16) the dilution of the incoming feed suspension can be controlled very accurately ensuring that the optimum relative density of the slurry inside the feed chamber, is kept constant, at a desired set point. The use of branch (15) and valve (16) is in contrast to other designs. The value of the relative density set point will be determined for each application, as it can vary for different applications depending on particle size, shape, density and surface chemistry, amongst others. The dilution of a liquid/solid suspension to a very narrow predetermined range of liquid/solid ratios has numerous advantages. This range occurs when the solids settling rate and dewatering characteristics are maximised whilst simultaneously the flocculent demand is minimised. In order to ensure smooth operation and assist the flow of the clarified liquid the branch is preferably smooth and parabolically curved. The branch joins the feed pipe (9) at an angle of only about 15 degrees usually at the throat of a restriction creating a venturi effect. The point at which the branch (15) joins the inlet (9) may be either inside or outside the container.

In use the thickener is used in substantially conventional way with feed slurry being pumped or gravity fed into the thickener by way of the inlet pipe (9). In this way, the necessary energy is supplied to the suspension to cause the solid particles to collide with one another.

However, just the collision of two or more particles generally does not form a bigger structure especially under high-energy conditions and hence the need to agglomerate the particles with or without breaking down the electrostatic repulsive forces between the solid particles.

The use of coagulants and/or flocculents is employed to provide a structure onto which solid particles can adhere, forming agglomerates with faster settling rates than the individual particles.

As a result of the provision of this invention, the slurry on entering the feed chamber travels in a roughly helical or spiral path. This has been found to have a highly beneficial effect in the flocculating procedure giving rise to larger and more denser floe structures forming, when compared to the conventional mixing procedure, both under high and low energy conditions. In practice it has been found that the best results are yielded under conditions of high energy or high rotational velocities. This flow pattern that encourages floe growth causes each solid particle or floe structure to rotate within the carrier liquor, as the solid/liquid suspension is travelling in a rotational direction. In practice it has been observed that the floe structures follow a downward spiral path and therefore the flow could be described as laminar in a rotational direction, but could also be turbulent in a rotational direction. This is in contrast to the conventional mixing procedure which effects turbulent type flow with random direction, ensuring that the solid particles collide without conforming to any specific direction or motion pattern. The creation and maintaining of rotational flow is intentional and is considered desirable which is a significant difference between the method of this invention and prior art thickeners. In prior art devices such flow is considered undesirable so baffles within the feed chamber or counter-directional feed inlets are used to halt the rotational flow pattern yielding quiescent conditions.

In addition to this, a usually semi-circular furcated mixing rake (26) of varying geometry could be used to further increase the rate at which large and dense floe structures are formed. The arcs of the mixing rake serve to create several different rotational paths of varying diameter within the feed chamber. This in turn would lead to the suspension having varying angular and rotational velocities.

The arcs (29) of the mixing rake can vary in number; be in the horizontal or near horizontal planes; and be of the same or varying lengths in the same vertical plane as shown clearly in Figure 4 or be of the same or varying lengths in different vertical planes as shown clearly in Figure 5. The number, length and position of the arcs will be determined for each application usually by effect of pilot plant test work as each application would respond in a different manner to a fixed set of geometric arrangements.

Flocculent is pumped in at a rate determined by the controller (17) through the injection points (11) and/or (13) so that a substantially staged increase in flocculent level can be achieved. Simultaneously the valve (16) is controlled to allow a quantity of clarified liquid to mix with the feed slurry in order to achieve an optimal relative density of the feed material which is usually of the order of ten weight percent solids, or a solids/liquid weight ratio of 1 :9. Viscosity measurements of the feed suspension could also be used as the control basis.

Particles collide with rotational motion, adhere, agglomerate and flocculate into substantially larger and denser agglomeration of particles, commonly known as floes, as they proceed down the feed chamber and, by the time they reach the bottom of the feed chamber, the flocculated particles are dense and heavy enough to fall substantially through the inner confines of the dewatering ring (24) and directly onto the compaction zone (6).

As a result of the enhanced flocculation method used, it is believed, at least in part, by the rotational or centrifugal action imposed on the slurry particles, that the particles become part of a floe structure which is large enough and heavy enough to possess a settling velocity greater than the upflow velocity of the clarified liquor reporting to the overflow exit. Also, each floe structure exiting the feed chamber is still travelling in a rotational direction, the rotational velocity of which decreases progressively upon exit, and in conjunction with gravitational forces is therefore biased to settle to the bottom of the unit. Hence the flocculated particles do not get carried up into the region outside and above the feed chamber termination point and hence a fluidised bed of flocculating material is not formed.

Floes exiting the feed chamber immediately settle into the inner confines of the dewatering ring (24) where the "hindered settling" zone in the unit occurs as the floe structures hinder one another in the settling process as liquor is continually being removed which continually increases the solids/liquid ratio. This short hindered settling zone contrasts quite distinctly with other devices. In this invention the mixing, floe formation and clarification of the carrier liquor is done within the feed chamber using the "snowball" effect to produce large and dense floe structures. Smaller sized particles and/or floe structures will have been captured by bigger sized floes via the snow ball effect within the feed chamber due to the rotational movement of the solids/liquid suspension.

Also, the upflow velocity of the liquor reporting to the overflow exit at different points up the length of the annulus between the feed chamber of constant diameter and cylinder remains the same, as no reductions in the cross sectional area are made. This is also in contrast to other units.

The dewatering ring or tubular baffle (24) which can be solid or have slotted or perforated side walls could be positioned just below the lower region of the feed chamber and the container wall or between the lower region of the feed chamber (5) and the container wall. The dewatering ring being concentric and being held in position by radially orientated fins (25) secured to the inside wall of the cylinder and to the outside surface of the dewatering ring. The effect of this is that clarified liquid associated with the floes in the "hindered zone" tends to flow through the slots in the side wall and/or around the lower region of the side wall and up between the dewatering ring and the container wall.

The driving force for this movement of clarified liquor is due to the difference in density of the slurry on the inside region and the liquor on the outside regions of the dewatering ring.

The hindered settling zone occurs within the confines of the tubular baffle.

In a sophisticated version of the invention automatic controls are envisaged and a control unit (17) will be connected to a monitor (18) associated with the feed inlet for monitoring the flow rate and density of the feed slurry. The control unit (17) is also connected to the outlet (4) to monitor the flow rate and density of the thickened slurry and is connected to both the pump (12) for flocculent solution dosing and the valve (16) controlling the quantity of clarified liquid being mixed with the feed in order to control the density of same.

It should be understood that, in use, the controller (17) will automatically control the addition of clarified liquid to the feed slurry in order to adjust the solids content to an optimum value and will automatically control the supply of flocculent to achieve the desired objective. Because the relative density of the feed suspension would be kept constant, due to the control system employed, the flow rate of the flocculent solution would usually be controlled on a fixed fraction basis of the diluted slurry flow rate, thereby yielding a constant flocculant solution dosage when expressed in parts per million (ppm) and/or grams of flocculant per dry ton of solids (g/ton).

A "feed forward" control philosophy is used whereby a potential disturbance to the system e.g. variations in feed density, is corrected before entering the system. This also contrasts with existing units on the market in which the usual "feed back" philosophy is used where the disturbance is first felt by the system and then corrected. This can result in instability. In this invention, the fluid dynamics within the unit are more stable and the continuing process of under and over flocculation resulting from the "feed back" philosophy are eliminated, and the overall flocculent consumption is reduced.

Whilst the addition of clarified liquid is illustrated in Figure 1 as taking place externally of the container and from the clarified liquor overflow exit pipe, it is also possible, as shown in Figure 3, to have a clarified liquid inlet (19) controlled by a valve (20) communicating with the feed pipe (9) within the container itself. In this case the overflow is collected in a launder (21) or drawn from the clarified liquor overflow pipe (14). Alternatively the inlet (19) could communicate directly with the interior of the container in the upper region thereof (30) with the valve (20) been inside or outside the container.

As a general principle, flocculation is a technique used simply to cause fine particles to agglomerate together in order to increase the settling rate of the solids within the carrier liquid. However, once settled into the compaction zone, the floe structures still possess entrained liquor even after inter-granular forces between the particles would have caused them to deform. This entrained liquor as well as liquor present between the floe structures is usually unwanted and the primary purpose of a thickener unit is to remove as much liquor from the solids as possible.

In order to release the liquor entrained within the floe structure this would usually be effected by breaking the structure using mechanical parts such as rotating rakes etc.

In accordance with a feature of this invention a sleeve forms the wall to the outlet duct (4) as indicated by numeral (22). The inner wall of the sleeve could be made of a flexible or in-flexible membrane. The pore size of the membrane would usually be chosen to allow for the passage only of liquor through it thereby decreasing the pore water pressure.

In the use of a flexible membrane the membrane would be supported by a flexible diaphragm and fixed support in which air or water is pumped between the flexible diaphragm and fixed support to expand the flexible diaphragm pushing the porous flexible membrane into the outlet duct (4) occupied by the thickened sludge. The flexible membrane may be made of a natural or synthetic textile or fabric.

As the thickened suspension flows through the sleeve, liquor and solids would migrate to the membrane surface but only the passage of liquor will be allowed through the membrane. Solids would adhere to the flexible membrane and would pack closely together forming a matrix as the liquor previously associated with the solids, permeates through the membrane. The flow of further liquor through the matrix would also cause solids to adhere to the membrane. The thickness of the matrix would with time increase and would eventually be thick enough to not allow the passage of liquor through it. Therefore the flux (rate of liquor removed per unit area) would constantly decrease. Hence the necessity to decrease the rate at which this matrix forms and/or to remove this matrix. The flexible diaphragm would alternate between expand and contract modes. In this way the layer of solids that have formed on the surface of the porous membrane will be sheared away when the porous membrane expands. The advantage of this is that the flux is kept at a maximum. Another feature of this invention is that liquor will still be extracted from the outlet duct when the flexible diaphragm is in the expanded state. The flexible diaphragm could be made of polypropylene and would have drainage grooves inscribed into it. The extracted liquor would pass through the matrix layer and membrane and exit the system via the drainage grooves. The extracted liquor could be discarded or returned to the feed chamber. The solids once sheared away from the membrane would exit the system via the underflow withdrawal pump.

The flexible diaphragm, to get into the expanded state, would have to overcome the static pressure head exerted on it due to the weight of the solids and liquor within the container. This expansion can be effected by means of a pump. An advantage of the expanded state is that the pressure difference across the membrane would be greater when the flexible diaphragm is in the expanded state, which would further increase the flux. Another advantage of the expanded state is that the cross sectional area of the outlet duct will be decreased and hence the compacted material velocity increased. This would help to remove the matrix layer. A vacuum system may also be attached to the sleeve and used to further enhance the liquor removal rate.

In the use of a in-flexible membrane conveniently made of sintered metal, ceramic compound or any other porous compound which is wear resistant, the passage of liquor through it would usually be effected via capillary action. In this case, the in-flexible porous membrane or in-flexible filter media would be manufactured on top of the support and therefore cannot be expanded.

A vacuum/pressure system (23), which would usually consist of a liquid ring vacuum pump or a vacuum receiver and vacuum pump, would be used to withdraw liquor from the in-flexible porous sleeve at a faster rate than when not used and can be used to control the underflow density. The vacuum system may operate in continuous mode, withdrawing liquor from the material passing through the outlet continually, or preferably, operating as alternating between withdrawal and backwash modes. The withdrawn liquor could be discarded or returned to the feed chamber.

The backwash mode would operate to re-inject liquor that has previously been withdrawn, back into the sleeve and usually be effected by the use of compressed air forcing the liquor back into the sleeve and through the underside of the membrane. This backwash would remove the layer of solids that will have formed on the inner surface of the membrane. This backwash mode could also be used periodically when using a flexible membrane and flexible diaphragm. The sleeve would usually be cylindrical and could be divided into different vertical segments by spacers thereby allowing expansion of each segment. The sleeve would usually be of constant cross-sectional area. The area would be chosen to give a specific range of thickened sludge downward velocities, which would be great enough to substantially maintain a minimum amount of solids adherence to the inner wall of the sleeve. The downward velocity and hence the diameter would vary for different applications. The use of this sleeve in contrast to other thickener units, and assists to further the process of increasing the solids to liquid ratio.

The porous sleeve would usually be attached to the truncated part of the conical section. If one porous sleeve is used it would usually be vertical or could be near vertically positioned. Alternatively to increase the flux, two or more sleeves can be used and could assume the form of a cluster arrangement and each sleeve being positioned usually near vertically. A shut-off valve may also be positioned between the truncated part of the conical section and the upper region of the porous sleeve/s, when mounted vertically, so that if any maintenance has to be carried out on the porous sleeve, it can be done with ease and the tank does not have to be emptied. The porous sleeve or cluster of sleeves could also be horizontally or vertically positioned before and/or after the underflow withdrawal pump and in which case a shut-off valve would be positioned on the underflow pipeline between the truncated part of the conical section and the porous sleeve. An added advantage of positioning the porous sleeve/s after the underflow withdrawal pump is that the delivery pressure of the pump can be used to further increase the flux.

With the use of a sleeve/s the removal of a portion of liquor that is still associated with the solids in the compaction zone is enhanced and the thickening capability of the unit no longer relies heavily on the residence time of the solids in the compaction zone, as is the case with other units. In consequence of this, the residence time of the sludge in the compaction zone may be substantially reduced. In addition, the downward velocity of the sludge in the compaction zone can be increased, thereby substantially reducing the chance of solids adhering to the wail of the conical section forming a rathole.

Therefore, a smaller compaction zone volume can be used as well as a lower overall internal volume, giving rise to cost and space reductions, compared to other units, in obtaining a certain underflow relative density.

The cross-section of the sleeve could take the form of many different shapes, including shapes providing multiple passages to increase the available area and hence the withdrawal rate of the liquor.

Not all applications would require the use of this porous sleeve to extract additional liquor e.g. where further extraction of liquor would result in the underflow material not being pumped. It is an added feature of the invention that since the downward velocity of the material in the compaction zone is increased along with the removal of liquor, that the conical end wall could be inclined at an angle of less than 60 degrees to the horizontal, but usually at 60 degrees.

It will be understood that numerous variations may be made to the embodiments and variations thereof which are described above with reference to the drawings.

It is to be noted that the invention apparently results in a much purer overflow, to the extent that the thickener can serve as a clarifier as well.

INDUSTRIAL APPLICABILITY

The object of this invention is to provide a solids/liquid separation device, which can be used to provide improved performance when compared to the prior art thickeners. This device could be used in the metallurgical industry to dewater cyclone overflow, leach feed and tailings and be used in counter current decantation, water management, filtrate clarification, settling of fine carbon and clarification of conventional thickener overflow applications, amongst others.

Claims

1. A liquid/solids separation device of the general type characterised by a container having a height substantially greater than its diameter; a central tubular feed chamber extending downwardly from the upper end region of the container to a position spaced upwardly of the lower end of the container which converges to an outlet in the lowermost region of the container, and an inlet pipe for inlet slurry communicating with the upper region of the feed chamber. The inlet arrangement being such that slurry entering the feed chamber does so in a substantially circumferential direction to create a swirling movement of slurry within the feed chamber.

2. A device as claimed in claim 1 characterised by the inlet pipe communicating with the upper region of the feed chamber, either tangentially or along the path of an involute.

3. A device as claimed in claim 1 characterised by the inclusion and adaptation of a baffle arrangement to direct slurry entering the chamber in a substantially circumferential direction when the inlet pipe communicates with the feed chamber in a roughly radial configuration.

4. A device as claimed in any one of the preceding claims characterised by the feed chamber having a usually semi-circular furcated mixing rake extending throughout the entire length, or a portion of the length, of the feed chamber that could be positioned at any point inside and along the length of the feed chamber.

5. A device as claimed in any one of the preceding claims characterised by the arcs of the mixing rake varying in number, be it in the horizontal or near horizontal planes; be of the same or varying lengths in the same vertical plane; or be of the same or varying lengths in different vertical planes.

6. A device as claimed in any one of the preceding claims characterised by the feed chamber having a plurality of vertically spaced flocculent injection points along its length so that a substantially staged increase in flocculent level can be achieved.

7. A device as claimed in any one of the preceding claims characterised by one or more flocculent injection points that are associated with the inlet pipe.

8. A de ice as claimed in any one of the preceding claims characterised by the feed chamber diverging or converging by 10 degrees or less. In the case of a divergent feed chamber an extra tubular wall would be vertically positioned around the outside of the feed chamber.

9. A device as claimed in any one of the preceding claims characterised by the lower end of the feed chamber which would preferentially reduce at an angle of about 45 degrees, to a coaxial reduced diameter outlet.

10. A device as claimed in any one of the preceding claims characterised by a communication system between the upper region of the container and the inlet pipe or feed chamber. This communication, by means of a branch and valve, is for the controlled introduction of clarified liquid from the upper region of the container into the feed slurry for dilution purposes.

11. A device as claimed in any one of the preceding claims characterised by the addition of clarified liquid to the feed pipe being effected externally or internally of the container and from the clarified overflow exit pipe or overflow launder. Alternatively the inlet could communicate directly with the interior of the container in the upper region thereof with the valve and/or branch being inside or outside the container.

12. A device in any one of the preceding claims characterised by the clarified liquid branch being smooth and parabolically curved and which joins the feed pipe, usually at the throat of a restriction, at an angle of only about 15 degrees creating a venturi effect. The branch could also communicate with the feed pipe at the throat of a restriction on the feed pipe.

13. A device as claimed in any one of the preceding claims characterised by a further flocculent injection point being associated with the lower region of the communication system, as claimed in claim 10.

14. A device as claimed in any one of the preceding claims characterised by a dewatering ring positioned between the lower region of the feed chamber and container wall or just below the lower region of the feed chamber and the container wall.

15. A device as claimed in claim 14 characterised by the dewatering ring being solid or having slotted or perforated side wails.

16. A device as claimed in any one of the preceding claims characterised by a usually v-notched shape overflow weir that is associated with the top of the container to collect clarified liquor.

17. A device as claimed in any one of the preceding claims characterised by the lower outlet from the container that has pump means associated therewith.

18. A device as claimed in any one of the preceding claims characterised by the slurry inlet, which is provided with monitors for monitoring the flow rate and/or density of the feed slurry.

19. A device as claimed in any one of the preceding claims characterised by the underflow pipe, which is provided with means for monitoring the flow rate and/or density of the underflow.

20. A device as claimed in any one of the preceding claims characterised by a level detector for detecting and/or controlling the level of the upper limit of a compacted zone of slurry in the device.

21. A device as claimed in any one of the preceding claims characterised by control means for controlling the amount of flocculent fed to the diluted slurry or the amount of clarified liquid fed to the feed slurry or feed chamber, or both.

22. A device as claimed in any one of the preceding claims characterised by the flow rate of the flocculent solution usually being controlled on a fixed fraction basis of the diluted slurry flow rate.

23. A device as claimed in any one of the preceding claims characterised by the outlet from the container communicating with a sleeve/s whose inner wall could be made of a flexible or in-flexible membrane for removing additional liquid from the thickened solids.

24. A device as claimed in any one of the preceding claims characterised by the pore size of the membrane usually being chosen to allow for the passage only of liquor through it.

25. A device as claimed in any one of the preceding claims characterised by a flexible membrane which is supported by a flexible diaphragm and fixed support in which air or water is pumped between the flexible diaphragm and fixed support, pushing the porous flexible membrane into the outlet duct occupied by the thickened solids.

26. A device as claimed in any one of the preceding claims characterised by solids which are sheared away from the surface of the membrane while liquor is still being removed when the flexible diaphragm is in the expanded state.

27. A device as claimed in any one of the preceding claims characterised by the porous flexible membrane usually being made of a natural or synthetic textile or fabric.

28. A device as claimed in any one of the preceding claims characterised by a flexible diaphragm being made of polypropylene that would have drainage grooves inscribed into it. The flexible diaphragm usually being expanded by means of a pump.

29. A device as claimed in any one of the preceding claims characterised by an in- flexible membrane being conveniently made of sintered metal or ceramic compound or any other porous compound which is also wear resistant.

30. A device as claimed in any one of the preceding claims characterised by the sleeve which is associated with an evacuation and/or pressure system for drawing liquor from thickened solids therein and to control the underflow relative density.

31. A device as claimed in claim 23 which is characterised by an evacuation system that has a reverse cycle for periodic "backwashing" of the membrane of the sleeve.

32. A device as claimed in any one of the preceding claims characterised by a porous sleeve which would usually be cylindrical, but could take the form of many different shapes, including those providing multiple passages to increase the available area and hence the withdrawal rate of the liquor.

33. A device as claimed in any one of the preceding claims characterised by a single porous sleeve that may be attached vertically, or near vertically, to the truncated part of the conical section.

34. A device as claimed in any one of the preceding claims characterised by two or more sleeves that may be used and that could assume the form of a cluster arrangement, each sleeve which is usually positioned near vertically.

35. A device as claimed in any one of the preceding claims characterised by a porous sleeve/s which could also be positioned before and/or after the underflow withdrawal pump in either the horizontal or vertical positions or at an angle.

36. A device substantially as herein described and exemplified with reference to Figures

1 , 2, 3, 4, 5, 6 or Figure 7; of the accompanying drawings.