Abstract:
A phase splitter ( 14 ) for splitting phases of liquids, the phase splitter ( 14 ) characterized by an elongate body ( 16 ) having a generally convexly curved liquid-facing face ( 28 ) when viewed in transverse cross-section along a longitudinal axis of the elongate body ( 16 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 U.S. National Stage of International Application No. PCT/AU2012/000364, filed on Apr. 11, 2012, and claims priority to Australian Patent Application No. 2011901489, filed on Apr. 20, 2011, the disclosures of which are herein incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     This invention relates to solvent extraction and partitioning. More particularly, the invention relates to a splitter for splitting liquid phases, to a splitter assembly for splitting liquid phases, and to a method of splitting liquid phases. 
     BACKGROUND ART 
     The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgment or admission that any of the material referred to herein is or was part of the common general knowledge as at the priority date of the application. 
     Liquid-liquid extraction, also referred to as solvent extraction or partitioning, is a method used in hydrometallurgy to separate or extract compounds from one liquid phase into another liquid phase. This is accomplished by manipulating the relative solubilities of the compounds to be isolated in two or more liquids having differing characteristics, as is the case with an aqueous phase (such as water), and an organic solvent phase (such as an oil or immiscible organic solvent). 
     The term solvent extraction can also refer to the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. In such a case, a soluble compound may be separated from an insoluble compound or a complex matrix. 
     Although the term partitioning is sometimes used to refer to the underlying chemical and physical processes involved in liquid-liquid extraction, these terms as used herein should be considered synonymous. 
     In the field of solvent extraction or partitioning, several hydrometallurgical systems are known which incorporate systems for manipulating liquid flow streams and phases, and for separating, splitting, or isolating liquids or phases of liquids, and the desired compounds extracted by such systems. Typically, a mixture of an extractant in a diluent is used to extract a desired compound from one phase to another. In solvent extraction techniques this mixture is often referred to as the “organic” phase and entrained organics need to be removed or recovered from the eventual aqueous streams. 
     Many extraction processes make use of so-called mixer-settlers. Mixer-settlers are a type of mineral process equipment used in solvent extraction processes and consist of a first stage that mixes the phases together in an agitated tank (referred to as a mixer) followed by a quiescent settling stage, usually in the form of a gravity settling basin (settler) that allows the phases to separate by gravity. It is difficult to manage the flow of liquid in settlers to achieve sufficient separation and to also minimise the settler area. The flow of liquids needs to be as laminar as possible, as flow interruptions or turbulence can lead to co-mixing of phases and resultant losses in extraction efficiency. The settling stage allows the phases to separate, but achieving high flow velocities can disturb the flow and hamper the process of separation, making it inefficient. Typical settler stages utilise an organic launder at the downstream end of the settler. The organic launder has a vertical liquid-facing face whereby the organic phase passes over the top lip of the vertical liquid-facing face and the aqueous phase passes under the bottom edge of the vertical liquid-facing face of the organic launder. 
     It is one object of the present invention to provide a phase splitter, phase splitter assembly, and method which overcomes substantially one or more of the abovementioned problems associated with the prior art, or at least provides a useful alternative thereto. 
     SUMMARY OF INVENTION 
     In accordance with the present invention there is provided a phase splitter for splitting phases of liquids, the phase splitter characterised by an elongate body having a generally convexly curved liquid-facing face when viewed in transverse cross-section along a longitudinal axis of the elongate body. 
     Preferably, the convex liquid-facing face has a generally curved profile when viewed in transverse section and which curves away from the liquid interface, in the direction of liquid flow. 
     The curve of the liquid-facing face preferably defines an apex which, in use, may be positioned at the interface between an organic phase and an aqueous phase of a liquid stream to be split. 
     Advantageously, the profile of the liquid-facing face prevents the formation of recirculating flow patterns in each of the phases when applied to a settler. It is understood that this arrangement reduces liquid velocities, reducing entrainment and the settler area that may be required when compared to conventional liquid splitters. The resulting reduction in entrainment allows for the settler to be operated at higher specific flow velocities, leading to higher throughput and yield of desired values. 
     In one embodiment, the elongate body may, when viewed in cross-section, define a dome or plane curve of constant radius, when plotted from a centre point of a longitudinal axis extending medially along the length of the splitter body. 
     In another embodiment, the curvature may comprise a plane curve of decreasing radius, when plotted from a centre point of a longitudinal axis extending medially along the length of the splitter body. 
     In one embodiment, the body of the splitter may comprise a so-called bull-nose profile. The bull-nose profile of the body of the splitter is intended to allow sufficient space behind the liquid-facing face to incorporate a crud decant system should such be required. 
     A top lip of the splitter body may define a further arc which curves back upon the body of the splitter, thereby defining an overhang or skirt at the operative rear of the splitter. This serves to smooth the flow of liquid in the system. 
     A bottom lip of the splitter body preferably defines a further arc that curves rearwardly to provide a bottom surface of the splitter body. The bottom lip and bottom surface are arranged so as to allow the aqueous phase to pass therebelow at a sufficient velocity. 
     It is to be understood that the curvature may be varied so as to allow for the use of the splitter in various liquids having varying characteristics. This may be consequential upon the flow requirements in the organic launder, the organic operating depth, and the aqueous operating depth. It is envisaged that the curvatures of both the liquid facing face of the splitter and the top lip may be varied. 
     The splitter may be provided as part of an organic launder splitter assembly. Accordingly, in accordance with the present invention there is further provided an organic launder splitter assembly, the assembly characterised by a phase splitter as described hereinabove attached to, or present in, an organic launder. 
     The phase splitter is preferably attached to the organic launder by way of an attachment means. The attachment means may be provided in the form of one or more arms which are attached or attachable to the liquid splitter. Preferably, the or each arm is attached at a corresponding longitudinal end of the splitter body, or at the top, bottom, or both, of the splitter body. 
     Alternatively, or additionally, the or each arm is attached or attachable centrally to the body of the splitter, or anywhere along the length of the splitter body. 
     Typically, the splitter or splitter assembly is provided internally to an organic launder or is located in a settler area in a mineral processing plant. 
     Preferably, the organic launder is arranged to transmit separated organic out of the settler. 
     In accordance with the present invention there is still further provided a method of splitting a liquid, or phases of a liquid, the method characterised by the steps of: 
     bringing a liquid splitter or liquid splitter arrangement of the invention into contact with a liquid stream, and entraining the respective liquids which have been split by the liquid splitter or liquid splitter arrangement. 
     Preferably, flow velocity of the liquid stream is between about 0.001 m/s and 0.05 m/s. Still preferably, flow velocity of the liquid stream is between about 0.001 m/s and 0.03 m/s. It is to be understood however that flow velocities may be dictated by the properties of the liquids/phases to be separated and the desired throughput rate. 
     Examples of liquids/phases which may be separated using the splitter of the invention include: an organic phase being a combination of narrow cut kerosene (diluent)(for example Shellsol 2052™) and a dissolved extractant (for example Cyanex 272™); aqueous including water, salts and dissolved metals (for example Cobalt sulphate). Further examples include loaded organic and raffinate, and barren organic and barren strip liquor combinations. 
     The splitter, system, and method of the present invention are considered to be especially useful in solvent extraction processes for the extraction of non-ferrous values such as copper, uranium, nickel, cobalt, zinc, rare earths and vanadium. 
     Further aspects of the invention will now be described with reference to the following non-limiting examples and drawings. 
     Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 
     As used herein, the term “liquid” means a liquid or a phase or phases of a liquid. 
     As used herein, the term “splitter” means any device or liquid flow arrangement which allows for the partial or substantial division, isolation, separation, or splitting-out of liquid flow streams or phases of liquids from one another into differential streams or phases which may have characteristics or properties different to each other and/or from the original feed stream or phase. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which: 
         FIG. 1  is an upper perspective part sectional view of a liquid phase splitter in accordance with one aspect of the present invention; 
         FIG. 2  is an upper perspective view of the liquid phase splitter of  FIG. 1 , showing the splitter body in detail; 
         FIG. 3  is an upper plan view of the liquid phase splitter of  FIG. 1 , shown in use in a settling area; and 
         FIG. 4  is a diagrammatic representation of a sectional side view of the liquid facing face of the liquid phase splitter (organic launder) of  FIG. 1 , shown with dimensions indicating the curvature, and dimensions relative to the settler area. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the drawings, reference numeral  10  refers generally to a splitter arrangement in accordance with one aspect of the invention, the splitter arrangement  10  being located in a settler area  12 , whilst reference numeral  14  refers generally to a phase splitter in accordance with the present invention. 
     Liquid/Liquid Splitter and Splitter Arrangement 
     In  FIGS. 1 to 3  there is shown a splitter arrangement  10  comprising a splitter  14  having a generally convex splitter body  16  which is located in a settler area  12 . There are a number of means whereby the splitter  14  may be located or arranged in the settler area  12 . For example, such may be achieved through one or more attachment means (not shown). The attachment means may include arms which are attached to respective ends  18  and  20  of the splitter body  16 , or other attachment means which are attached to the operative upper or lower surfaces of the body  16 , to be described hereinafter (indicated generally by reference numerals  22  and  24 , respectively). The attachment means serve to maintain the splitter body  16  in position at a desired height in a liquid stream  26 , discussed below. 
     The splitter body  16  has a liquid-facing convex face  28 , which is generally of a so-called bullnose design or profile, as is best seen in  FIGS. 1 and 2 . In the embodiment shown, the splitter body  16  curves at a continuous radius both Upwardly and downwardly away from a longitudinal axis  30 , best seen in  FIG. 2 , and which is defined along the centre of the convex face  28 . At an upper end thereof, the body  16  is further curved upon itself so as to define an inverted U-profile, which terminates in a top lip  32 . At a bottom end thereof the body  16  is curved back on itself at a bottom lip  34  and from which a lower surface  36  extends rearwardly. 
     The inventors have experimented with several configurations of splitter faces and shapes, and have found that the configuration of the present invention can split phases of liquids from each other at relatively high flow speeds and provides useful build-up of an intermediate phase or interface  38  (see below) between an upper organic/solvent phase  40  and a lower aqueous phase  42 , without unnecessary dispersion. The intermediate phase  38  can then be extracted separately from the remaining phases  40  and  42 , should this be required. 
     In  FIG. 4  there is shown the curvature of the splitter face as defined by the following general equation:
 
 X=c ·( a   2   +Y   2   /b   2 ) 1/2  
 
     where a,b and c are chosen for the specific system, and Y, the vertical plane, is the organic and aqueous depth, and X, the horizontal plane, describes the profile of the curvature. Specifically, the example shown in  FIG. 4  describes an organic depth of 0.6 m and an aqueous depth of 0.7 m. The factors a, b and c being selected as 0.7, 0.3 and 0.2, respectively. Variable a is adjusted based on the organic plus aqueous depth (the deeper the solution in the settler the larger this figure). Variables b and c are adjusted based on the width of the launder (to be described hereinbelow). This width is dependent in turn on the flow rate of organic processed through the system. 
     Splitter Operation 
     As mentioned hereinbefore, a liquid stream  26  emanating from an upstream mixer or processing area, by way of a feed tank  44  and flow distributing devices or baffles  46 , shown in  FIG. 3 , will generally comprise a lower aqueous phase  42 , a solvent-based upper phase  40  and, depending on the liquid characteristics and flow kinetics, an intermediate phase  38 . In operation, that is when the splitter  14  is in a liquid stream  26  in a settler area, the splitter body  16  is positioned such that the longitudinal axis  30  defining a furthest upstream protrusion  48  aligns generally with the phase interface  38  of the liquid stream  26  to be split. In other words, the splitter body  16  is placed in the settler area  12  at a depth such that the upper solvent/organic phase  40  passes over the upper surface of the body  16 , over the top lip  32  and passes into an organic launder  50 . The lower aqueous phase  42  passes underneath the splitter body  16 , past the bottom lip  34  and the lower surface  36  and into an aqueous launder  52 . In certain embodiments, the aqueous may be channelled via an alternative flow path out of the settler area  12 . 
     The splitter  14  of the present invention assists in maintaining relatively high flow velocities. Typically rates of between about 0.001 m/s and 0.03 m/s can be utilised in solvent extraction applications. However, in stripping applications rates of as high as about 0.05 m/s can be utilised. Referring again to application in solvent extraction, generally, flow velocities of up to 0.03 m/s would make the formation of an intermediate layer impossible to see or isolate, but using the splitter  14  of the present invention, this is achievable at these flow velocities. The splitter body  16  is placed in the liquids  26  at a height such that it is aligned with the interface between the organic and aqueous phases. Following splitting, the organic, and aqueous phases and their various contents can be subjected to further treatment or scrubbing. 
     The Applicant is of the opinion that, advantageously, the profile of the liquid-facing face prevents the formation of recirculating flow patterns in each of the phases when applied to a settler, thereby reducing re-circulating liquid velocities, reducing entrainment and the settler area that may be required when compared to conventional liquid splitters, and reducing dispersion of the intermediate liquid phase at high flow velocities. The resulting reduction in entrainment allows for the settler to be operated at higher specific flow velocities, leading to higher throughput and yield of desired values. Similar improvements relative to the prior art are envisaged when the present invention is applied to stripping applications. 
     Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.