FIELD OF THE INVENTION

The present invention relates to a solvent extraction settler arrangement adapted for hydrometallurgical liquid-liquid extraction processes.

BACKGROUND OF THE INVENTION

As disclosed in e.g. publications WO 97/40899 and WO 97/40900 a solvent extraction settler arrangement is known which is adapted for hydrometallurgical liquid- liquid extraction processes and which typically com ^¬ prises a mixing unit for preparing a dispersion from mutually immiscible solutions. A settler is arranged to separate solution phases from a dispersion fed from the feed end while the dispersion flows towards the discharge end of the settler. Elongated discharge launders are arranged at the discharge end of the set ^¬ tler to receive from the settler and discharge each solution phase that is separated from the dispersion in the settler. Each discharge launder includes a first end to which an outlet is arranged and a closed second end. In the known technology the discharge launder has a same cross-sectional shape along the entire length of the discharge launder. In operation, as the launder collects solution flows of the solution from the set ^¬ tler along its entire length, and the whole volume is discharged from the launder from the outlet at the first end of the launder, the flow volume increases gradually along the length of the launder as the flow propagates towards the outlet. The discharge launder with a uniform cross-section is normally designed for the greatest flow volume to achieve a certain flow rate. The flow volume is greatest adjacent to the out- let and therefore the cross-section of the discharge launder is optimal only at a very short range of the launder . In a launder with a constant cross-section the flow rate is lower at positions which are distant from the outlet in relation to other positions which are nearer the outlet whereby standing flow zones and eddies may occur. If the solution contains solids, crud accumula- tion may occur in these areas of standing zones and eddies. One disadvantage of the constant cross-section of the launder is also that the structure of the laun ^¬ der includes an excess of material which actually would not be needed.

OBJECT OF THE INVENTION

The object of the invention is to eliminate the disad ^¬ vantages mentioned above. In particular, it is the object of the invention to provide a settler arrangement having a discharge laun ^¬ der, the structure of which may be built with a lesser amount of material than the discharge launders of pri ^¬ or art.

Further, it is the object of the invention to provide a settler arrangement with discharge launders in which the flow rate is constant so that standing zones and eddies, and crud accumulation caused by such non- uniform flow, do not occur.

SUMMARY OF THE INVENTION

According to an aspect of the invention, the present invention provides a solvent extraction settler ar- rangement adapted for hydrometallurgical liquid-liquid extraction processes. The settler arrangement compris ^¬ es a settler having a feed end and a discharge end. The settler is arranged to separate solution phases from a dispersion fed from the feed end while the dis ^¬ persion flows to the discharge end. Elongated dis ^¬ charge launders are arranged at the discharge end of the settler for collecting and discharging each solution phase to be separated from the dispersion. Each discharge launder includes a first end, an outlet ar ^¬ ranged at the first end, and a closed second end. In accordance with the invention at least one of the discharge launders has a form of a conical tube with a cross-section converging from the first end towards the second end, and an inclined bottom descending from the second end towards the first end.

The advantage of the invention is that, due to the conical form of the discharge launder, the cross- section is optimal for the flow rate at each point along the length of the discharge launder. The flow rate remains constant and no standing flow zones and eddies occur. Crud accumulation is small and thus the need for interrupting the process to remove the crud will be reduced. Due to the conical shape, material costs are also reduced in the manufacturing of the discharge launder. The first and second discharge launders are tubular closed compartments which have many advantages. As an essentially closed structure, the inner atmosphere of the launders can be isolated from the outer atmosphere so that mist emissions can- not escape from the interior of the launders to con ^¬ taminate the air and worsen the working conditions. Likewise, the surrounding air and e.g. insects and birds cannot enter the launders. In addition, when the lighter solution is an organic phase, the oxidation degree of the organic phase decreases, whereby solu ^¬ tion costs are reduced. In one embodiment of the settler arrangement, the dis ^¬ charge launders include a first discharge launder for receiving a separated lighter solution phase as an overflow from the settler, and for discharging the lighter solution phase to a first outlet located at the first end of the first discharge launder.

In one embodiment of the settler arrangement, the dis ^¬ charge launders include a second discharge launder ar- ranged beside and in parallel with the first discharge launder for receiving a separated heavier solution phase from the settler as an underflow, and for discharging the heavier solution phase to a second outlet at the first end of the second discharge launder.

In one embodiment of the settler arrangement, at least one of the first discharge launder and the second dis ^¬ charge launder is a hollow body made of a fibre- reinforced plastic composite and manufactured by fila- ment winding technology.

In one embodiment of the settler arrangement, at least one of the first discharge launder and the second dis ^¬ charge launder is a hollow body made of steel.

In one embodiment of the settler arrangement, the set ^¬ tler arrangement comprises a plurality of first outlet pipes arranged along the length of the first discharge launder at a distance from each other, each first out- let pipe having a third end opening to the settler to receive the lighter solution phase as an overflow from the settler, and a fourth end opening to the inner space of the first discharge launder. In one embodiment of the settler arrangement, the ar ^¬ rangement comprises a plurality of second outlet pipes arranged along the length of the second discharge launder at a distance from each other, each second outlet pipe having a fifth end opening to the settler to receive the heavier solution phase as an underflow from the settler, and a sixth end opening to the inner space of the second discharge launder at the bottom of the second discharge launder.

In one embodiment of the settler arrangement, the ar ^¬ rangement comprises a level control valve connected to the sixth end of each second outlet pipe inside the second discharge launder.

In one embodiment of the settler arrangement, the lev ^¬ el control valve comprises an extendable and collapsi- ble tube member, such as a bellows tube, having a low ^¬ er end connected to the sixth end of the second outlet pipe, and an upper end; an overflow lip attached at the upper end of the tube member; and an actuator connected to the overflow lip for vertical adjustment of the height position of the overflow lip.

In one embodiment of the settler, the settler consists of one tank having a single uniform flow space; and that all first and second outlet pipes open to said single flow space.

In one embodiment of the settler, the settler is di ^¬ vided into a plurality of mutually separated elongated parallel settler sections each extending from the feed end to the discharge end and forming a plurality of parallel flow spaces. At at least one first outlet pipe and at least one second outlet pipe are connected to each settler section. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to pro ^¬ vide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the de ^¬ scription help to explain the principles of the inven ^¬ tion. In the drawings:

Figure 1 shows a plan view of a settler arrangement according to a first embodiment of the invention,

Figure 2 shows a section II-II from Figure 1,

Figure 3 shows a plan view of a settler arrangement according to a second embodiment of the invention,

Figure 4 shows a section IV-IV from Figure 1,

Figure 5 shows a section V-V from Figure 1,

Figure 6 shows an enlarged detail A from Figure 2, Figures 7 and 8 show a level control valve in two po ^¬ sitions .

DETAILED DESCRIPTION OF THE INVENTION

Figures 1 and 3 show solvent extraction settler ar- rangements which are adapted for hydrometallurgical liquid-liquid extraction processes.

The settler arrangement comprises a mixing unit 24 for preparing a dispersion from mutually immiscible solu- tions. The mixing unit 24 includes, in this case, a pumping unit 25 and two mixers 26. A settler 1 is ar ^¬ ranged to separate solution phases from a dispersion which is fed from the feed end 2 while the dispersion flows towards the discharge end 3. A feeding device 27 is arranged at the feed end 2 for feeding the dis ^¬ persion prepared by the mixing unit 24 to the settler 1. Elongated discharge launders 4 and 5 are arranged at the discharge end 3 to collect and discharge the sepa ^¬ rated solutions. Each discharge launder 4, 5 includes a first end 6, an outlet 7, 8 arranged at the first end 6, and a closed second end 9.

As can be seen in Figures 1, 2, 4 and 5, both dis ^¬ charge launders 4, 5 have a form of a conical tube with a cross-section converging from the first end 6 towards the second end 9 and an inclined bottom 10, 11 descending from the second end 9 towards the first end 6. The discharge launders 4, 5 have a form of a coni ^¬ cal tube which has substantially a form of a square pyramid with cambered edges.

The discharge launders include a first discharge laun ^¬ der 4 for receiving a separated lighter solution phase (typically organic solution phase) as an overflow from the settler 1. The first discharge launder 4 discharges the lighter solution phase to a first outlet 7 lo ^¬ cated at the first end 6 of the first discharge laun ^¬ der 4. The discharge launders further include a second dis ^¬ charge launder 5 arranged beside and in parallel with the first discharge launder 4 for receiving a separat ^¬ ed heavier solution phase (typically aqueous solution phase) from the settler 1 as an underflow. The second discharge launder 5 discharges the heavier solution phase to a second outlet 8 at the first end 6 of the second discharge launder.

Preferably the first discharge launder 4 and the sec- ond discharge launder 5 are hollow bodies made of a fibre-reinforced plastic composite and manufactured by filament winding technology. As can be seen in Figures 6 to 8, the cross-section of the discharge launders is substantially rectangular with cambered corners. Such a form allows it to be easily detached from the man ^¬ drel on which it is wound.

A plurality of first outlet pipes 12 are arranged along the length of the first discharge launder 4 at a distance from each other. Each first outlet pipe 12 has a third end 13 which opens to the settler 1 to re- ceive the lighter solution phase as an overflow from the settler 1. A fourth end 14 of each first outlet pipe 12 opens to the inner space of the first dis ^¬ charge launder 4 to conduct the lighter solution phase to the first outlet pipe.

A plurality of second outlet pipes 15 are also ar ^¬ ranged along the length of the second discharge laun ^¬ der 5 at a distance from each other. Each second out ^¬ let pipe 15 has a fifth end 16 which opens to the set- tier 1 to receive the heavier solution phase as an underflow from the settler 1. A sixth end 17 of each second outlet pipe 15 opens to the inner space of the second discharge launder 5 at the bottom 11 of the second discharge launder to conduct the heavier solu- tion phase to the second discharge launder.

In the embodiment shown in Figure 1 the settler 1 con ^¬ sists of one large tank which has a single uniform flow space which extends widthwise over the whole area of the tank and lengthwise from the feed end 2 to the discharge end 3. In this case, all first and second outlet pipes 12, 15 open to said single flow space.

In the embodiment shown in Figure 3 the settler 1 con- sists of a plurality of widthwise mutually separated elongated parallel settler sections 1' each extending from the feed end 2 to the discharge end 4 and forming a plurality of parallel flow spaces. At least one first outlet pipe 12 and at least one second outlet pipe 15 are connected to each settler section 1' . As shown in Figures 6 to 8, the arrangement comprises a level control valve 18 connected to the sixth end 17 of each second outlet pipe 15 inside the second dis ^¬ charge launder 5. The level control valve 18 comprises an extendable and collapsible tube member 19, such as a bellows tube, having a lower end 20 connected to the sixth end 17 of the second outlet pipe 15. An overflow lip 22 is attached at the upper end 21 of the tube member 19. An actuator 23 is connected to the overflow lip for vertical adjustment of the height position of the overflow lip.

Figure 7 shows the level control valve 18 in a posi ^¬ tion in which the overflow lip 22 is adjusted to a certain level which determines the level of the heavi- er phase in the settler. The heavier solution flows from the second outlet pipe 15 over the overflow lip 22 into the inner space of the second discharge laun ^¬ der 5. Figure 8 shows the level control valve 18 being ad ^¬ justed so that the overflow lip 22 is at a higher po ^¬ sition than in Figure 7.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The in ^¬ vention and its embodiments are thus not limited to the examples described above; instead, they may vary within the scope of the claims.