Field of the invention

The invention relates to a method for mixing first liquid and second liquid into dispersion as defined in the preamble of independent claim 1.

The invention also relates to a mixing device for mixing first liquid and second liquid into dispersion as defined in the preamble of independent claim 12.

In a typical mixer- settler, in a first step, the aqueous and organic phases are pumped into a mixer or mixers in order to achieve uniform liquid-liquid dispersion and a small droplet size. In the VSF® technology (stands for Vertical Smooth Flow) developed by the applicant, this first step is performed in a pump-mixer called Dispersion Overflow Pump (DOP®) (disclosed e.g. in document US 5,662,871) and in a set of one or more SPIROK® helical mixers (disclosed in e.g. document US 5,185,081). After mixing, the dispersion is fed into a settler.

Objective of the invention

The object of the invention is to provide a method and a mixing apparatus enabling mixing two phases of a liquid-liquid extraction process with each other in a single mixing apparatus instead of using a separate pump-mixer and a separate set of one or more helical mixers.

Short description of the invention

The method of the invention is characterized by the definitions of independent claim 1. Preferred embodiments of the method are defined in the dependent claims 2 to 11.

The mixing apparatus of the invention is correspondingly characterized by the definitions of independent claim 12.

Preferred embodiments of the mixing apparatus are defined in the dependent claims 13 to

22.

In an embodiment of the invention the delivery of the first liquid and the second liquid is taken care of by ordinary high pressure centrifugal pumps and all mixing is done in a single mixing apparatus. The mixing of the phases into dispersion takes place in a static mixer consisting of 10-20 pieces of commercial mixer inserts placed inside the vertical shaft of a rotatable mixing device comprising at least two helical bars around the vertical shaft, such as inside the vertical shaft of a rotating helical Spirok type mixer, which vertical shaft is supported in a cylindrical mixing tank of the mixing apparatus at the upper end and at the lower end by a bearing. The liquids are fed into the vertical shaft at its lower end by means of a first feeding means and a second feeding means comprising concentric pipes that induce the primary dispersion of the first liquid and the second liquid. The first feeding means and a second feeding means are placed at least partly inside the cylindrical mixing tank and it is sealed against the shaft by glands due to a high back pressure generated by the static mixers. The static mixers creates a highly turbulent flow pattern resulting in an intense mixing of the dispersion, which produces very fast mass transfer that enables to drive the extraction reaction close to equilibrium within a retention time of only one second of order. The mixed dispersion is discharged from the static mixer from the openings at the top of the vertical shaft to the top region of the cylindrical mixing tank. The dispersion is then drawn downwards in the cylindrical mixing space by the inner axial flow pattern of the rotatable mixing device. When the flow reaches the bottom of the cylindrical mixing tank, its direction is reversed to an upward flow in the annular region near the wall of the cylindrical mixing tank to the lifting force of the rotatable mixing device. The rotatable mixing device and its rather gentle mixing effect provides additional retention time to bring the extraction reaction to completion and also allows the average droplet size of the dispersion to grow large enough so that the phases can effectively disengage in a gravity settler no larger in size than those used with the current mixer-settlers. The dispersion eventually exits the cylindrical mixing tank through a round aperture in the middle of the height of the wall and flows further to the settler through an uptake channel. The cylindrical mixing tank is covered by a partly submerged top lid, which significantly reduces the air liquid interface and prevents harmful air mixing into the dispersion in the cylindrical mixing tank. List of figures

In the following the invention will described in more detail by referring to the figures, which

Figure 1 shows the function principle of a mixing device according to a first embodiment, Figure 2 shows the function principle of a mixing device according to a second embodiment,

Figure 3 shows the function principle of a mixing device according to a third embodiment,

Figure 4 shows the function principle of a mixing device according to a fourth embodiment,

Figure 5 shows the function principle of a mixing device according to a fifth embodiment, and

Figure 6 shows the function principle of a mixing device according to a sixth embodiment. Detailed description of the invention

The figure shows an example of a method and an apparatus for mixing first liquid and second liquid into dispersion. The first liquid can be an aqueous solution containing dissolved copper ions and the second liquid can be an organic hydroxyoxime extractant dissolved in kerosene, capable of extracting the copper by forming a chelate complex.

First the method for mixing first liquid and second liquid into dispersion and some embodiments and variants thereof will be described in greater detail.

The method comprises feeding first liquid into a static mixer 5 by means of a first feeding means 6 and feeding second liquid into the static mixer 5 by means of a second feeding means 7.

The method comprises mixing first liquid and second liquid into primary dispersion by means of the static mixer 5 and discharging mixed primary dispersion from the static mixer 5 into a mixing space 2 of a mixing cell.

The method comprises mixing mixed primary dispersion by means of the rotatable mixing device 1 arranged in the mixing space 2 to form mixed dispersion, and discharging mixed dispersion from the mixing space 2.

The method comprises rotation the rotatable mixing device 1 by means of a motor means

19.

The method may, as shown in the figures, comprise discharging mixed primary dispersion from the static mixer 5 into a mixing space 2 of a mixing cell, which mixing space 2 is a cylindrical mixing space 2 limited by a vertical cylindrical inner wall 22 and a bottom 10, and which mixing space 2 have a vertical axis A, and using a rotatable mixing device 1 comprising mixing means 23 supported at a vertical shaft 4 that is arranged at the vertical axis A of the mixing space 2. In the cylindrical mixing space 2, the ratio of the height of the cylindrical mixing space 2 to the diameter of the cylindrical mixing space 2 can be 1 to 4. The ratio of the diameter of the rotatable mixing device 1 to the diameter of the cylindrical mixing space 2 can be 0.7 to 0.8.

If the method comprises using mixing cell having a cylindrical mixing space 2 and a rotatable mixing device 1 as described above, the method may comprise by using a rotatable mixing device 1 comprising mixing means 23 comprising at least two helical bars 3 supported along the verticals shaft 4 by means of supports such as by means of support rods or support rings. Each helical bar 3 can ascend around the vertical shaft 4 for 1 to 3 revolutions. The diameter of each helical bar 3 can be 0.03 to 0.07 the diameter of the rotatable mixing device 1.

If the method comprises using mixing cell having a cylindrical mixing space 2 and a rotatable mixing device 1 as described above, said discharging mixed dispersion from the mixing space 2 may comprise discharging mixed dispersion from the cylindrical mixing space 2 of the mixing cell through an exit 9 arranged at an level 0.25h to 0.75h as measured from the bottom 10 of the cylindrical mixing space 2, where h is the height of the cylindrical mixing space 2.

If the method comprises using mixing cell having a cylindrical mixing space 2 and a rotatable mixing device 1 as described above, the method may comprise using a rotatable mixing device 1 comprising mixing means 23 supported at a vertical shaft 4 that is hollow, and arranging the static mixer 5 inside the vertical shaft 4 of the rotatable mixing device 1. In such case said feeding first liquid into the static mixer 5 by means of a first feeding means 6 includes feeding first liquid from the outside of the cylindrical mixing space 2 of the mixing cell into the vertical shaft 4 at a level below said static mixer 5 by means of a first feeding means 6 and in such case said feeding second liquid into the static mixer 5 by means of a second feeding means 7 includes feeding second liquid from the outside of the cylindrical mixing space 2 of the mixing cell into the vertical shaft 4 at a level below said static mixer 5 by means of a second feeding means 7, and in such case said discharging mixed primary dispersion from the static mixer 5 into a mixing space 2 of a mixing cell includes discharging mixed dispersion into the cylindrical mixing space 2 from the vertical shaft 4 of the rotatable mixing device 1 through an outlet 8 of the vertical shaft 4, which outlet 8 is provided at an level above the static mixer 5. In such case, the method may comprise supporting the vertical shaft 4 rotatable in the cylindrical mixing space 2 at a level below the static mixer 5 and at a level above the static mixer 5. In such case, the method may comprise providing a deflector 12 at the top end of the vertical shaft 4, and directing mixed dispersion emerging from the outlet 8 of the vertical shaft 4 downwards into the cylindrical mixing space 2 by means of the deflector 12. The deflector 12 may be in the form of a tube surrounding the upper end of the vertical shaft 4 so that an annular space is formed between the tube and the upper end of the vertical shaft 4, wherein the method comprises feeding mixed dispersion from the outlet 8 of the vertical shaft 4 into the annular space.

If the method comprises arranging the static mixer 5 inside the vertical shaft 4 of the rotatable mixing device 1, the method may comprise arranging a first outlet 17 of the first feeding means 6 to concentrically surround a second outlet of the second feeding means 7, and feeding first liquid into the vertical shaft 4 from the first outlet 17 of the first feeding means 6, and feeding second liquid into the vertical shaft 4 from the second outlet of the second feeding means 7.

The method may comprise feeding first liquid into the static mixer 5 by means of a first pump means 13 such as a centrifugal pump of the first feeding means 6. In such case, the method may comprise providing a first non-return valve 14 downstream of the first pump means 13 in the first feeding means 6.

The method may comprise feeding second liquid into the static mixer 5 by means of a second pump means 15 such as a centrifugal pump of the first feeding means 6. In such case the method may comprise providing a second non-return valve 16 downstream of the second pump means 15 in the second feeding means 7.

If the method comprises using mixing cell having a cylindrical mixing space 2 and a rotatable mixing device 1 as described above, the method may comprise providing baffles 21 in the annular space between the cylindrical inner wall 22 and the rotatable mixing device 1.

If the method comprises providing baffles 21 in the annular space between the cylindrical inner wall 22 and the rotatable mixing device 1, the method may comprise arranging the static mixer 5 in the mixing space 2 of the mixing cell in the annular space between the cylindrical inner wall 22 and the rotatable mixing device 1, as is shown in figures 5 and 6. The method may comprise providing the cylindrical mixing space 2 with a top lid 20 for reducing the air-liquid- interface to prevent air dissolution into the dispersion in the cylindrical mixing space 2.

Next the mixing device for mixing first liquid and second liquid into dispersion and some embodiment and variants thereof will be described in greater detail.

The mixing device comprises a mixing cell having a mixing space 2, and a rotatable mixing device 1 in the mixing space 2.

The mixing device comprises a static mixer 5 configured to form mixed dispersion of first liquid and second liquid.

The mixing device comprises first feeding means 6 configured to feed the first liquid into the static mixer 5 and second feeding means 7 configured to feed the second liquid into the static mixer 5.

The mixing device comprises an outlet 8 configured to feed mixed primary dispersion from the static mixer 5 into the mixing space 2, wherein the rotatable mixing device 1 in the mixing space 2 is configured to mix mixed primary dispersion to form mixed dispersion.

The mixing device comprises an exit 9 configured to feed mixed dispersion from the mixing space 2 of the mixing cell.

In the mixing devices shown in the figures, the mixing space 2 is a cylindrical mixing space limited by a cylindrical inner wall 22 and a bottom 10 and wherein the cylindrical mixing space having a vertical central axis A, and the rotatable mixing device 1 comprising mixing means 23 supported at a vertical shaft 2 arranged at the vertical central axis of the cylindrical mixing space. In the cylindrical mixing space 2, the ratio of the height of the cylindrical mixing space 2 to the diameter of the cylindrical mixing space 2 can be 1 to 4. The ratio of the diameter of the rotatable mixing device 1 to the diameter of the cylindrical mixing space 2 can be 0.7 to 0.8.

If the mixing space is a cylindrical mixing space as described above and if the mixing device comprises a rotatable mixing device 1 as described above, the rotatable mixing device 1 may comprise mixing means 23 comprising at least two helical bars 3 supported along the verticals shaft 4 by means of supports such as by means of support rods and/ or support rings. Each helical bar 3 can ascend around the vertical shaft 4 for 1 to 3 revolutions. The diameter of each helical bar 3 can be 0.03 to 0.07 the diameter of the rotatable.

If the mixing space is a cylindrical mixing space as described above and if the mixing device comprises a rotatable mixing device 1 as described above, the exit 9 configured to feed mixed dispersion from the cylindrical mixing space 2 of the mixing cell may be arranged at an level 0.25h to 0.75h as measured from the bottom 10 of the cylindrical mixing space 2, where h is the height of the cylindrical mixing space 2.

If the mixing space is a cylindrical mixing space as described above and if the mixing device comprises a rotatable mixing device 1 as described above, the rotatable mixing device 1 may have a vertical shaft 4 that is hollow, and the static mixer 5 may be arranged inside the vertical shaft 4 of the rotatable mixing device 1. In such case the first feeding means 6 configured to feed the first liquid into the static mixer 5 is configured to feed first liquid from the outside of the cylindrical mixing space 2 of the mixing cell into the vertical shaft 4 at a level below said static mixer 5 and the second feeding means 7 configured to feed the second liquid into the static mixer 5 is configured to feed second liquid from the outside of the cylindrical mixing space 2 of the mixing cell into the vertical shaft 4 at a level below said static mixer 5. In such case the outlet 8 configured to feed mixed primary dispersion from the static mixer 5 into the mixing space 2 is arranged at a level above said static mixer 5 and configured to feed mixed primary dispersion from the vertical shaft 4. In such case the vertical shaft 4 may be rotatable supported in the cylindrical mixing space 2 at a level below the static mixer 5 and at a level above the static mixer 5. In such case a deflector 12 may be provided at the top end of the vertical shaft 4, wherein the deflector 12 is configured to direct mixed dispersion emerging from the outlet 8 of the vertical shaft 4 downwards into the cylindrical mixing space 2. Such deflector 12 may be in the form of a tube surrounding the upper end of the vertical shaft 4 so that an annular space is formed between the tube and the upper end of the vertical shaft 4, and the outlet 8 of the vertical shaft 4 may be configured to feed mixed dispersion into the annular space.

If the static mixer 5 is arranged inside the vertical shaft 4 of the rotatable mixing device 1, as described above, the first feeding means 6 may have a first outlet 17 that concentrically surrounding a second outlet of the second feeding means 7, wherein the first outlet 17 of the first feeding means 6 is configured to feed first liquid into the vertical shaft 4, and second outlet of the second feeding means 7 is configured to feed second liquid into the vertical shaft 4.

If the mixing space is a cylindrical mixing space as described above and if the mixing device comprises a rotatable mixing device 1 as described above, the mixing device may comprise baffles 21 in the mixing space 2 between the cylindrical inner wall 22 and the rotatable mixing device 1.If the mixing device comprises baffles 21 in the mixing space 2 between the cylindrical inner wall 22 and the rotatable mixing device 1, the static mixer 5 may, as shown in figures 5 and 6, be arranged in the mixing space 2 of the mixing cell in the annular space between the cylindrical inner wall 22 and the rotatable mixing device 1.

The first feeding means 6 may comprise a first pump means 13 such as a centrifugal pump. In such case the first feeding means 6 may comprise a first non-return valve 14 downstream of the first pump means 13.

The second feeding means 7 may comprise a second pump means 15 such as a centrifugal pump. In such case, the first feeding means 6 may comprise a second non-return valve 16 downstream of the second pump means 15.

The cylindrical mixing space 2 may be provided with a top lid 20 for reducing the air- liquid-interface to prevent air dissolution into the dispersion in the cylindrical mixing space 2.

It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.