AU2010329807A1

AU2010329807A1 - Method and apparatus to create uniform mixing in connection with a hydrometallurgical process

Info

Publication number: AU2010329807A1
Application number: AU2010329807A
Authority: AU
Inventors: Launo Lilja; Juhani Lyyra; Bror Nyman; Pertti Pekkala; Teemu Ritasalao; Jussi Vaarno
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2009-12-08
Filing date: 2010-12-08
Publication date: 2012-06-21
Also published as: FI20096296A; CA2780852A1; ZA201203911B; WO2011070219A1; FI20096296A0; FI20100318A0; BR112012013894A2; FI124092B; CL2012001477A1; WO2011070219A8; EA201290405A1; AU2010329807A8; FI123597B; CN102665887A; FI20100318A; EP2509709A1; PE20130300A1; EP2509709A4; EA022724B1; WO2011070218A1

Abstract

The invention relates to a method and apparatus for mixing one or several solutions in a reactor (3) in conjunction with a hydrometallurgical process, such as precipitation, crystallisation or forming a suspension in solvent extraction. Mixing with a vertical circulation flow is created in the reactor by means of a multi-part mixer (1), so that the primary mixing zone in which the mixer rotates is over 70 % of the effective volume of the reactor, whereby the homogenous, low-intensity mixing needed for precipitation, crystallisation and/or the mixing stage of solvent extraction is achieved.

Description

WO 2011/070219 PCT/F12010/000074 1 METHOD AND APPARATUS TO CREATE UNIFORM MIXING IN CONNECTION WITH A HYDROMETALLURGICAL PROCESS FIELD OF THE INVENTION 5 The invention relates to a method and apparatus, enabling the mixing of one or several solutions in a hydrometallurgical process in a reactor to bring about the desired crystallisation, precipitation or suspension in solvent extraction. The apparatus consists of a reactor and a multi-part helical rotor mixer placed in it, in the helical rotors of which there are helical bars rotating 10 around the shaft and supported to it. BACKGROUND OF THE INVENTION Non-homogenous mixing is a problem for many hydrometallurgical unit processes. In conventional solutions a blade or turbine type mixer often 15 rotates in a volume in which the primary mixing zone is at most around 3 % of the total volume of the reactor that is used. This means that the shaft power produced by the mixer is directed very strongly on the immediate vicinity of the mixer. As a consequence, the volume-specific mixing intensity around the shaft is several tens of kilowatts per cubic metre, but falls 20 dramatically going towards the edges of the reactor. A spiral mixer has been developed for providing homogenous mixing in a reactor when two liquids that are insoluble in each other or a liquid and a solid are mixed together, which is described for instance in US patent 25 publications 5,185,081, 5,248,485 and 5,182,087. The diameter of the mixer in the apparatuses described is around 0.7 times the diameter of the reactor. However, for instance in solvent extraction, when treating solutions with a low interface tension, the mixing intensity achieved with this kind of mixer also may be too high. 30 When solids precipitation or salt crystallisation is carried out using a mixer, in which the mixing intensity is high, very fine precipitates or very small crystals WO 2011/070219 PCT/F12010/000074 2 are formed. A fine precipitate or crystal size does not create a base for further growth of the precipitate or crystal, and instead the product may become problematic due to its fineness. A high mixing intensity may also bring about mechanical wear on the precipitates or crystallisations that have 5 already formed, resulting in the crystals being ground fine again. PURPOSE OF THE INVENTION The purpose of the method and apparatus accordant with the invention is to achieve a more homogenous mixing than earlier in conjunction with various 10 hydrometallurgical unit processes such as during precipitation or crystallisation or in the mixing section of solvent extraction. The purpose of the invention is to reduce the total power used in various unit processes while nevertheless achieving a more homogenous mixing than previously in the reactor space used. When mixing is uniform throughout the entire reactor 15 space, neither localised peak power points nor almost dead spots will be formed. SUMMARY OF THE INVENTION The invention relates to a method for mixing one or several solutions in a 20 reactor in conjunction with a hydrometallurgical process, such as precipitation, crystallisation or forming a suspension in solvent extraction. Mixing with a vertical circulation flow is formed in the reactor by means of a multi-part mixer, so that the primary mixing zone is over 70 % of the effective volume of the reactor in order to achieve the homogenous, low-intensity 25 mixing needed for precipitation, crystallisation and/or the mixing stage of solvent extraction. According to one preferred embodiment of the invention, the primary mixing zone is over 80 % of the effective volume of the reactor. 30 WO 2011/070219 PCT/F12010/000074 3 It is typical of the method accordant with the invention that uniform mixing is achieved in the reactor using a helical rotor mixer consisting of at least three helical rotors. 5 In accordance with the method described in the invention, the primary mixing zone consists of the area remaining on the inside of the helix rotor as well as an area about the size of the cross-sectional area of the helix rotor outside the helix rotor and the height of the primary mixing zone in terms of elevation is at least the same as the height of the helix rotor. 10 It is typical of the method accordant with the invention that the primary mixing zones of the helix rotors merge with each other outside the helix rotors. According to one embodiment of the invention, a flocculant is used as an 15 agent in precipitation and/or crystallisation to flocculate the solid. The invention also relates to an apparatus for mixing one or several solutions in conjunction with a hydrometallurgical process, such as precipitation, crystallisation or forming a suspension in solvent extraction. The apparatus 20 comprises a reactor, which consists of a base and a cylindrical sidewall rising upwards from the base, as well as a mixer placed in the reactor. The mixer is a multi-part helix rotor mixer, which is adapted to provide homogenous mixing with a vertical circulation flow, creating a low mixing intensity, where the primary mixing zone is over 70 % of the effective volume of the reactor. 25 It is typical of the apparatus accordant with the invention that the helix rotor mixer comprises at least three helix rotors, which are arranged in the reactor, a power device to rotate the helix rotors, and several elongated vertical baffles projecting from the sidewall of the reactor. 30 It is further typical of the apparatus accordant with the invention that the helix rotor comprises a vertical rotation shaft, which is connected to a power WO 2011/070219 PCT/F12010/000074 4 device, and two or three helix members, which are fixed to the rotation shaft with support arms that are a radius away from the rotation shaft. 5 In one configuration of the apparatus accordant with the invention, the helix member is circular in cross-section. In another configuration of the apparatus, the helix member is oval in cross section. 10 According to one configuration of the apparatus, the baffles are at an angle of 5 - 15 degrees to the radius of the reactor. The baffles are preferably placed in the vicinity of each helix rotor, downstream of its rotation direction. 15 According to one configuration of the apparatus, when the number of helix rotors is three, their diameter is at least 0.33 times the diameter of the reactor. According to another configuration of the apparatus, when the number of 20 helix rotors is five, their diameter is at least 0.23 times the diameter of the reactor, so that one helix rotor is located in the centre of the reactor and the four others symmetrically around the central helix rotor. According to a third configuration of the apparatus, when the number of helix 25 rotors is five, one helix rotor is located in the centre of the reactor and the four others symmetrically around the central helix rotor, so that the diameter of the central helix rotor is greater than that of the rotors surrounding it. It is typical of the apparatus accordant with the invention that the rotation 30 shafts of the helix rotors are arranged radially in relation to the vertical central shaft of the reactor.

WO 2011/070219 PCT/F12010/000074 5 According to one configuration of the apparatus accordant with the invention, all the helix rotors rotate in the same direction and the rotation direction of the helix members around the shaft is the same as the rotation direction of the helix rotor. 5 According to another configuration of the apparatus accordant with the invention, all the helix rotors rotate in the same direction and the rotation direction of the helix members around the shaft differs from the rotation direction of the helix rotor. 10 According to a third configuration of the apparatus accordant with the invention, the central helix rotor rotates in a different direction from the helix rotors surrounding it. 15 LIST OF DRAWINGS Figure 1 presents a cross-section of one configuration of a helix rotor mixer accordant with the invention, Figure 2 presents the profile II - II of the mixer in Figure 1, Figure 3 presents the corresponding profile to Figure 2 of another helix rotor 20 mixer configuration. DETAILED DESCRIPTION OF THE INVENTION Homogenous mixing with low mixing intensity in accordance with the invention that nevertheless extends across the reactor volume is achieved by 25 means of a helix rotor mixer, which consists of at least three separate helix rotors. The mixer is placed in a reactor that is generally an upright cylinder in shape. A solution to be crystallised, a liquid containing solids, or two liquids insoluble in each other are mixed in the reactor to bring about crystallisation, precipitation or a suspension in solvent extraction. The primary mixing zone 30 of the helix rotor mixer covers over 70 %, preferably over 80 %, of the effective volume of the reactor. Effective volume means the volume in the reactor between the bottom of the reactor and the surface of the liquid. In the WO 2011/070219 PCT/F12010/000074 6 case of helix rotors, the primary mixing zone consists of the area remaining within the helix rotor plus an area outside it about the size of the cross sectional area of the helix rotor. In terms of elevation the height of the primary mixing zone is at least the same as the height of the helix rotor. 5 Clearly, mixing also occurs outside the primary mixing zone even though the mixing intensity is lower. The individual helix rotors of the helix rotor mixer are grouped so that their primary mixing zones merge with each other outside the helix rotors. When 10 the helix rotor is up-pumping, it means that in this case a flow pattern is formed in which the direction of the flow within the rotor is downward and outside the rotor it is upward. The flows that come from the inside of the helix rotors turn obliquely upwards outside the helix rotors and interact with each other so that they merge with each other in the space between the helix 15 rotors. The operating speed of the helix rotors is adjusted to be such that the formation of turbulence is prevented in the space between the helix rotors, but at the same time the desired effects are brought about by laminar mixing. When the mixing power is divided in this way to be uniform throughout the reactor, we can state that this arrangement reduces the overall energy 20 consumption used in mixing. With this arrangement locally occurring powerful mixing forces can also be avoided and low-intensity mixing can be directed on the entire cross-section of the reactor. One apparatus accordant with the invention, consisting of a reactor and a 25 mixer with three separate helix rotors, is described in more detail in Figures 1 and 2. The figures show one configuration as an example, where helix rotor mixer 1 comprises three double helix rotors 7. The helix rotor mixer 1 consists of reactor 3, whose interior 4 is bounded laterally by cylindrical sidewall 5 and beneath by base 6. The double helix rotors 7 are arranged in 30 interior 4 a radius away from the central shaft of the reactor in a triangular formation, as shown in Figure 2. Each helix rotor 7 is rotated by a power device 8. Several elongated vertical baffles 9 protrude from sidewall 5 of WO 2011/070219 PCT/F12010/000074 7 reactor 3. Each helix rotor 7 comprises a vertical rotating shaft 10, which is connected to a power device 8, and two identical helical tubes 11, which are circular in cross-section and are attached to rotation shaft 10 by support arms 12. The helical tubes are symmetrically opposite each other at a 5 distance of one radius from the shaft. The solution or solutions to be treated can be introduced into the reactor at desired points and the result of the generated reactions removed from desired points of the reactor (not shown in detail in the drawing). 10 In the solution accordant with Figure 1 the diameter of the helix rotors is at least 0.33 times the diameter of the reactor and preferably around 0.35 times the diameter of the reactor. All the helix rotors preferably rotate in the same direction either up-pumping or down-pumping, and in this case the direction that the helical tubes rotate around the shaft is also the same as the rotation 15 direction. Therefore the helix rotors rotate either clockwise or anticlockwise. In most cases it is more advantageous to use a up-pumping mixing direction, so that outside the helix rotors a strong upward zone is generated at each point downstream of the baffles. The upward zones merge with each other in the manner described above and intensify mixing. The upward zones can be 20 further intensified by placing the baffles closer to the helix rotors. It is advantageous to place the baffles 9 at a distance that is 0.04 - 0.08 times the diameter of the reactor from the sidewall of the reactor and their width is preferably 0.1 - 0.13 times the diameter of the reactor. It is typical of 25 the baffles accordant with the invention that instead of placing them radially, they are at an angle of 5 - 15 degrees from the radius. The baffles are placed in the vicinity and downstream of each helix rotor, as shown in Figure 2. In this way an intensifying effect is attained on the homogenous mixing across the entire reactor. 30 By means of the three helix rotors and the three baffles described above, an arrangement is obtained providing mixing with a vertical circulation flow, WO 2011/070219 PCT/F12010/000074 8 whereby the primary mixing zone is over 80 % of the effective volume of the reactor. The primary mixing zone of each helix rotor is shown by a dashed line in Figure 2. This brings about the homogenous low-intensity mixing required for precipitation, crystallisation and/or the mixing stage of solvent 5 extraction. Distribution can be affected by means of the size and location of the mixer and by the size, location and alignment of the baffles. When the mixing intensity is made fairly uniform throughout the entire reactor space in this way, the motor power used for mixing can be reduced. Depending on the mixing requirement, the mixing intensity can be adjusted for example to the 10 range of 0.05 - 1.5 kW/m 3 . The advantage of the arrangement accordant with the invention is that localised strong primary mixing is no longer required thanks to the homogenous mixing that covers the whole reactor area. Figure 3 is an illustration of a further mixer accordant with the invention, in 15 which there are five helix rotors 7. One of the helix rotors is situated in the centre of the reactor and the four others symmetrically around the central helix rotor on the circumference of the reactor. The diameter of the helix rotors is at least 0.23, preferably 0.25 - 0.3 times the diameter of the reactor. There are four baffles 9 in number and they are located in the vicinity of the 20 helix rotors on the circumference on the same principle as described in conjunction with Figures 1 and 2. The arrangement accordant with Figure 3 can achieve a situation where as much as 85 % of the mixing in the reactor space is primary mixing. 25 The structural configuration accordant with Figure 3 can be changed further so that the diameter of the helix rotor situated in the central part of the reactor is greater than the diameter of the helix rotors located on the circumference of the reactor. In this case the rotation direction of all the helix rotors can be selected to be the same or the rotation direction of the centrally 30 placed helix rotor can be selected to differ from the rotation direction of the helix rotors located on the circumference.

WO 2011/070219 PCT/F12010/000074 9 The examples above have referred to a helix rotor with two helical members only as an example. Depending on the requirements of the application the helix rotor may have two or three helical members. Three helical members together in the rotor makes the rotor more solid structurally and achieves a 5 more even distribution of mixing power compared with two helical members. As for the helical member, it may be some other shape than round in cross section. A round bar may also be flattened, so that the profile of the helical member is oval in shape. 10 As stated above, the properties of the solid to be precipitated or crystallised can be improved with homogenous mixing. Growth in particle size during solid precipitation and crystallisation can be controlled better than in apparatus where there is a powerful, narrow primary mixing. In addition to the equipment selection, a flocculant can also be used to aid the flocculation 15 of solids. An example of this is the fact that using a helix rotor mixer accordant with the invention consisting of three helix rotors with the aid of a flocculating agent in the feedwell of the thickener caused the solids content of the thickener overflow to fall from a value of 50 mg/L to 15 mg/L. 20 The method and apparatus accordant with the invention are particularly advantageous when the diameter of the reactor is large, in the region of tens of metres. The invention is not restricted to the example configurations presented 25 above; many modifications are possible while remaining within the framework of the concept of the invention as specified in the claims.

Claims

1. A method for mixing one or several solutions in a reactor (3) in conjunction with a hydrometallurgical process, such as precipitation, 5 crystallisation or forming a suspension in solvent extraction, characterised in that mixing with a vertical circulation flow is formed in the reactor b y means of a multi-part mixer (1 ), whereby the primary mixing zone is over 70 % of the effective volume of the reactor in order to achieve the uniform mixing of low intensity required for precipitation, 10 crystallisation and/or the mixing stage of solvent extraction.

2. A method according to claim 1, characterised in that the primary mixing zone is over 80 % of the effective volume of the reactor. 15 3. A method according to claim 1, characterised in that uniform mixing is achieved in the reactor using a helix rotor mixer consisting of at least three helix rotors.

4. A method according to claim 1, characterised in that the primary mixing 20 zone comprises the area remaining inside the helix rotor and an area about the size of the cross-sectional area of the helix rotor outside the helix rotor and, in terms of elevation, the height of the primary mixing zone is at least the same as the height of the helix rotor. 25 5. A method according to claim 1 or 4, characterised in that the primary mixing zones of the helix rotors merge with each other outside the helix rotors.

6. A method according to claim 1, characterised in that a flocculant is used 30 to aid the flocculation of solids in precipitation and/or crystallisation.

7. An apparatus for mixing one or several solutions in conjunction with a hydrometallurgical process such as precipitation, crystallisation or forming WO 2011/070219 PCT/F12010/000074 11 a suspension in solvent extraction, whereby the apparatus comprises a reactor (3), which consists of a base (6) and a cylindrical sidewall (5) rising upward from the base, and a mixer (1) located in the reactor, characterised in that the mixer (1) is a multi-part helix rotor mixer, which 5 is adapted to provide mixing with a vertical circulation flow forming a homogenous, low mixing intensity, in which the primary mixing zone is over 70 % of the effective volume of the reactor.

8. An apparatus according to claim 7, characterised in that the helix rotor 10 mixer (1) comprises at least three helix rotors (7), which are arranged in a reactor, a power device (8) to make the helix rotors (7) rotate, and several elongated vertical baffles (9) protruding from the sidewall of the reactor.

9. An apparatus according to claim 8, characterised in that the helix rotor 15 (7) comprises a vertical rotation shaft (10), which is connected to a power device (8), and two or three helical members (11), which are fixed to the rotation shaft (10) by support arms (12) at a distance of a radius from the rotation shaft. 20 10.An apparatus according to claim 9, characterised in that the helical member (11) is circular in cross section.

11.An apparatus according to claim 9, characterised in that the helical member (11) is oval in cross section. 25

12.An apparatus according to claim 8, characterised in that the baffles (9) are at an angle of 5 - 15 degrees to the radius of the reactor.

13.An apparatus according to claim 8, characterised in that the baffles (9) 30 are located in the vicinity of each helix rotor (7), downstream of its rotation direction. WO 2011/070219 PCT/F12010/000074 12

14.An apparatus according to claim 8, characterised in that when the number of helix rotors (7) is three, their diameter is at least 0.33 times the reactor diameter. 5 15.An apparatus according to claim 8, characterised in that when the number of helix rotors (7) is five, and their diameter is at least 0.23 times that of the reactor diameter, one helix rotor is located in the centre of the reactor and the four others symmetrically around the central helix rotor. 10 16.An apparatus according to claim 8, characterised in that when the number of helix rotors (7) is five, one helix rotor is located in the centre of the reactor and the four others symmetrically around the central helix rotor, so that the diameter of the central helix rotor is greater than that of the rotors surrounding it. 15

17. An apparatus according to claim 8, characterised in that the rotation shafts (10) of the helix rotors (7) are arranged radially in relation to the vertical central shaft of the reactor (3). 20 18.An apparatus according to claim 9, characterised in that all the helix rotors (7) rotate in the same direction and the direction of rotation of the helical members (11) around the shaft (10) is the same as the rotation direction of the helix rotor. 25 19.An apparatus according to claim 9, characterised in that all the helix rotors (7) rotate in the same direction and the rotation direction of the helical members (11) around the shaft (10) differs from the rotation direction of the helix rotor. 30 20.An apparatus according to claim 15 or 16, characterised in that central helix rotor (7) rotates in a different direction to the helix rotors surrounding it.