ZA200503905B - Method and device used for mixing and sedimentation in solvent extraction processes for the recovery of highly-pure products - Google Patents

Description

MIXING AND SETTLING METHOD AND DEVICE IN SOLVENT

EXTRACTION PROCESSES TO RECOVER HIGHK-PURITY PRODUCTS

OBJECT AND FIELD OF APPLICATION

This invention refers to a method and device perfecting the purification systemm used in extraction brocesses using organic solvents (hereinafter, SX) by means of rnixers-settlers, as used for the recovery of metals and other products. The invention includes rew elements I>oth with regards to equ ipment and operative methodology.

Its field of application is the final or intermediate production of any Ihigh-purity producst, preferably metals and their salts, requiring 5X technology with mixers-settlers, in which phases a_re mixed by stirring turbines and/or pumping in one or several wi xing units, reactors or tandem compartmen_ts (hereinafter, compartments).

STATE OF THE ART

SX is a well-known separation teschnique, in which an impure aqueous solution containing -the end product, i on or species (hereinafter, species) cornes into contact wi th an organic solvent showing a specia 1 affinity with sa id species. After the complete mixing of the two phases, and once the matter has been transferred. it is separated f.or extraction of the end product.

The equipment typically used in this type of process consists off mixers and settlers. Each mixer-settler Hs called a “s tage” in SX. The mixer, wlhiich may have several tandem compartments, has the function of dispersing the two phases to be mixed, to form an enulsion in order wo favour tran.sfer and obtain equilibrium. The settler musst be capable of re-separating the two components, organzc phase and aqueous phase, forming the emulsion. The mosst _ important parameters defining the ope=ration are:

In tlhe mixer, stirring intensity is largely

A determined by viscosity, surface tension and density differences between the phases. It is essential to identify the stirring intensity requir-ed, since too little leads to tlme formation of large droplets reducing the contact area and transfer, whereas t oo much causes the formation of stable emulsions and small droplets which are easily entrained by the other phase, with a negative impact on the purity of the end product obtained. Furthermore, is rotating stirrirmg equipment is 1% used, energy is coricentrated on the borders, leading to a non-uniform droplet--size distribution.

In the settler, the separation con ditions depend both on the physical characteristics of the dispersed phases (differences of density, sur—face tension, viscosity, tempera ture, acidity, unitary speed) and on the intensity of the mix and the resulting droplet size.

When the two liquid phases - organic and aqueous - involved in a metal or other product extraction process with organic solverats are mixed, it is not only important to ensure appropriate stirring, to provide a good contact for the mass transfer of the metal of species to be extracted from one phase to the other {chemical transformation), buat for this mix to be swmich that after the reaction it is not difficult to separate the phases in the settler (phy sical transformation) .

The specific design of this equzipment, their combination with other standard agitators, and their distribution in several compartments of an extraction stage, allow for appropriate effects (both chemical and physical) and const itute a clear improvemen t allowing for a faster and clearer phase separation while maintaining all its chemical advantages. This clarity in the separation of non-miscible phases produces less entrainments of orie phase in the other-, leading to greater efficacy Dn the separation of the possible y impurities contained in one of the feed phases.

The agitator in the first compartment of a stage mixer in an SX process normally has a two-fold furaction consisting of stirring and pump ing the phases fro m the settlers in the adjacent stages, so its geometmy is usually s imilar to that of a pump impeller. The degr—ee of agitation and pumping capacity largely depend on the= size of the turbine, its stirring speed and its geometry.

Normally, the organic and aqueous phases involved i n the metal tramsfer reaction are easily and rapidly mixedl with the thorowugh mixing of one phase with the other. One-= type of radial agitation, appropriate for both funct ions, gives thes agitator a shear effect, especially ora the borders of the turbine, and the greater the degree of this shear effect and agitatiori, the smaller are the droplets formed (and therefore the more difficul t to decant) .

The &=gitators in following mixer compartments have the function of maintaining the homogeneity, to preovide time for the reaction according to the specific kinestics of each type of extraction and each phase involved. They can therefore be of the axial agitation (non-shear) ®Eype, with less agitation (size and/or speed).

It i= known that the conditi ons in which the m&Ex is agitated affect its decantation later. Depending ora the conditions , if the type of mix is such that there= are organic pkase droplets dispersed in the aqueous IDhase (aqueous continuous, hereinafter AC) or aqueous pohase droplets in the organic phase (organic continuvious, hereinafte x OC), this causes one Phase or the other t—o be cleaner (Jess entrainment). The organic/aqueous pohase ratio of the mix is another variable which not only affects the type of prior mix but also Creates a de=gree within each type of mix which either improves or himmders phase decantation. It has been shown that there. are y possibilities oof improving the char acteristics and

Operative condit ions of the agitation process which lead, in specific equi pment, to an improvement in decantation, reducing the en trainments from one pha se into another and, consequentlwy, the impurities entrain ed.

The mix obt ained in SX mixers is feed into settlers where the phases are separated by gravit=y, thanks to the different density of each phase. This liquid-liquid separation is a dynamic process in which, since it is continuous, the speed and type of route of each phase affects the ease with which the result ing emulsion is broken, the surf ace area available and consequently the time of residence, temperature, acidity, etc.

For a specific process, settler conditions and geometry, the undtary speed of each phase may vary with the feed flow, including its possible recirculation and control of the position of the interface . The ease with which the emulsion can be broken, for a given liquid temperature and characteristics, is not only affected by unitary speed but also be the type and degree of agitation obtained and the type of “intesrnal elements”, which are especially designed barriers imtroduced in the flow to facilitate its distribution, hommogenisation and lamination throughout the settler’s geometry, or to facilitate an ircrease in the size of the droplets, therefore improvimg the decantation processs.

The purpose of said “internal elements” is therefore to favour the decantation of the emulsion, preventing each phase from overflowing, obtaining w=them separately and preventing one phase from being contaminated with the other.

Three stages are normally used in SX technology: extraction of thes product or its species by an organic phase from an imp-ure aqueous solution, washing to purify this organic phasse and, finally, re-ext—raction of the y puri fied species or product to a new aqueous pohase. In each. of these stages, there can be several mixers- sett lers (stages) in serial formation, in wh_.ich each phas e (organic or aqueous) circulated against the 5 curr ent.

In SX technology, the need to obtain a high-purity product is not only derived from market condi tions or qual ity-based competition, but it is often an essential techmical condition to obta in this product at later stag=es (such as zinc electrolysis). The current— problem is t hat obtaining high purity, levels requires =a process with the simultaneous combX® nation, within SX, of a selective solvent, of mixers—settlers with a de=sign and internal elements that provi de an appropriate mix and good phase separation, =nd acceptable Operative conddtions.

There are several pro«<esses and systems which reinforce the product purification aspect Ioased on increasing or decreasing the number of mixers —settlers (stages) or the flow conditiorms applicable durincg a stage (washing, for example), or om chemical aspects such as enharicing the selectivity of whe species to be extracted or its purification after extraction, etc., buts not on the internal components of each mixer or set—tler or speciial operative conditions that could drastically reducce the aspects preventirmg the production of pure solutions containing the target species such as, for instance, the entrainments (suspended droplets) of one phase in the other or emulsion s from the two phas-es.

In the former case, docum ents such as Spanissh patent appli cations PCT ES01/00060 amd ES00/0458 or US patents 4,552,629 and 4,572,771, appdied to zinc SX, describe eithe=r a process especially based on reinforcoing the chemi cal aspects of purification and selectivity (the first two presented by this applicant) or varwing the py aqueous medium (sulphuric and hydrochloric solutions) and the extractant system (the third), or processes based on specific purification processes applied before (oxidation with chlorine and settling) or after ( use of additional membranes or diaphragms in the electrol ysis) the SX (the fourth). The same occurs in processes where the selectivity of the extraction is enharced by selecting specific organic solvents, such as the recovery of zirconium and hafnium (EP 154.448 ), gallium (Us 4,559,203), separation of rare-eart h elements (EP 156,735), cadmium (US 4,511,541), separation of nickel and cobalt, copper SX, etc. or others processing specific materials for specific applications such as Spanish patent ES 9701296 (household batteries) and Canadian patent CA 11 98290 (secondary zinc products), presented by this applicant. None of them contemplates either the introduction of special elements in the equipment to be used Or non—generic conventional mixing and decantation conditions erhancing purification.

Within the second group, more irmx line with this invention, involving equipment, methods and apparatus other than conventional mixers-settl ers, there are patents referring to the mixer and/or its agitation turbine, to the settler, or to the two together.

One group of them (Outokumpu, Finland) covers different methods and apparatus acting on the mixing and decantation of phases, but largely on the hydrodynamic aspects of tlie system, proposing special flow chambers or phase recycl ing, or with turbine des igns focused on preventing aeration, or forcing a changes of direction in the mix flow, etc. Thus, US patent 4,7 21,571 defends a mixer-presett ler-settler method in which the presettler acts as arm intermediate chamber enhancing phase separation wi th its corresponding flow buffers. US patent 5,185,081 desscribes a method of mixincg and separating phases with spiral turbines and a sy stem aimed at preventing and avoiding aeration as the pPTincipal source of emulsion. Another method and appamatus for re- circulating part of the decanted heavy phase from the = interface area to tthe mixer is described in US patent 6,083,400 as a design improvement for better phase contact and droplet size in the mixer. Another patent, which complements tthe previous one, is US 6,132,615, defending a method and apparatus to improve phase separation by the advanced design of the flow buffers, improving the conventional system's hyd rodynamics. US patent 6,176,608 acts on the decantabilit y of the phase mix discharge system, subjecting it to sevesral changes of direction before discharge into the settle-r. 15. Another group of patents, such as US 4,925,441 (US

Energy, Usa) contemplates a cascade of centrifuge contactors with intercommunications for phase mixing and separation, applicable to re-processing maclear fuel. US 6,007,237 (Bateman, Canada) defends the action of a mix based on controlling agitation by the creation and propagation of vortex rings with a special agitator. US 4,551,314 (Amax, USA.) covers a mixing system based on two tandem compartments, with different continuity conditions in the phase as an element favouring decantation.

Likewise, US 6,033, 575 (Krebs, France) proposed a pre- separation of the dispersion in two independently decanted fractions.

For each system and reagents used, most of the agitation turbines used principally @&n copper SX (Lightnin, VSF by Ou tokumpu, Nettco, Philadelphia, Krebs, etc.) conceive the p-ump turbine like a pump impeller and, to reduce power conssumption, they usually have curved or fast, small diametexr blades which, in order to reduce pumping consumption_, sacrifices the agitation effect, with tiny droplets of one phase forming in. the other due to the hi gh shear effect on the straight edges of the turbine, this making phase sepsaration very diff icult.

Another gr-oup of turbines or systems (Baterman, Out okumpu spiral, et=c.), on the other hand, have a very gentlee type of agitation, insufficient for appropriate pumpi ng or agitation and requiring additional agitators or systems.

With regards to the decantation systems used =n the settler, and as we have mentioned earlier, ther—e are usually va riations on the design of the flow distrilutors and buffems, or hydrodynamic variations affecting re- circulation to the mixer with the corresponding increase in the flow to be decanted, or wariations in the change of directdon of the mix prior to discharge int o the settler.

This invention affects these last aspects = new designs, n_ew internal elements =nd specific condit-ions.

The purpose of this invention As to obtain a dr-astic reduction in the entrainments of one phase in the other by reducing, depending on the pha se, contamination of the organic ph ase with entrainments from the impure acueous phase (aqueous entrainment im organic phase) or entrainmentcs from the organic phase in the purified aqueous phase (organic entrainment in aqueous phase) .

BRIEF DESCRIPTION OF THE INVENTION

The p-roposed invention acts directly on one of the principal causes of impurity: entrainments from one Phase in the other. This is reduced by acting both orm the agitation system that provokes the emulsion createed in the mixer and on the destruction of its consistency which persists amlong the dispersion band in the inte=rface (settler). Thus, in the mixer, a reduction in the quantity arid consistency of the emulsion is obtain-ed by jointly actcing on the special des ign of the primary: pump agitator (first compartment) and on its treatment due to the way of reducing this consistency throughout the rest of the compartments and, later, on the dispersion band in the settler with the introduction of systems ard apparatus to reduce the quantity and persistence of thie band. The se aspects are not approached in any of the aforementi oned documents.

Both in the mixers and the settlers, we add a series of espec-ially designed elements. In each mixer compartmerat, we install turbines with blunt edged bladess, eliminatirmg points and sharp edges, to avoid a type oof shear mix which produces agitation with excessively smal l droplets. This, together with an appropriate combinaticsn of the mixing and overflow operative condition.s . throughout the series of compartments, obtains an easily decanted emulsion. As an additional solution, we recommend a compartment geometry in which they are communicat ed and connected by wide communication channel s which do not provoke additional agitation and favour droplet gr coups in each phase. Agitation should also be of a type to reduce the level of occasional turbulences .

Although it is also possible to employ cylindrical mixing units or c ompartments, the use of square compartments im the mixers , connected by communi cation channels betweem contiguous compartments and superficial counter currents to avoid vortices, also has a postitive impact.

In the conventionally designed settler, we introduce two new “internal elements” located cross-wise to the flow after the flow buffers and im the interface area: - A firsst baffle located in the interface area, of = size such as to allow for the upper and lower overf Mow of part of each decanted non-emulsified phase, by allowing the compressed evacuation of this emulsion towards the centre of the interface. - A second baffle, later in the direction of the flow and s imilar to the first, but without a windows (blind), retaining all the remaining emulsion and

«decanted areas, allowing the overflow pihases to later maintain a clearly «defined and clear =interface dine.

Their position in the settl er varies dependimg on the mixer -settler considered, in order to ensure the best possible conditions.

On the other hand, the o perative condition s in the organDc and aqueous phase mix and decantation affect the type eof mix formed and the degree of difficulty involved in its eventual separation.

In the mixing process, a decreasing sequence of the degree of agitation in which it progressively decreases in time mixer’s series of cormpartments, has advantages over decantation. More intense agitation produces smaller droplets which are more difficult to separate, and consequently more entrainment of one phase in tlme other, making the product impure.

Xt has been shown that, tollowing general li nes, the achievements obtained with r egards to later physical behaviour (speed, clear decantation anc less entrai nments) are clearly positive starting with a degree of agi tation in the first compartment in the seri es which is appropriate for pumping purposes, and then reducing this degree in the followirag compartments. This is complesmented by making the mix overflow fr om each compar-tment in the series famll through wide channels forcirag a change of direction in the mix.

The mix thus obtained owerflows into the settler from the last compartment ef the mixer th rough a ~ 30 commurmication channel. The two phases are sepamated in the sesttler by means of a Physsical process in which the periodi of decantation until t he emulsion becomes clear separa ted phases will depencd, besides the specific operat ive conditions for each 8X system selected (different density, temperatures, type of mix, ew®c.), on the approp riate selection of unitary velocities for each

Phase and certain operative conditio ns which speed up the process. These conditions are not ne cessarily the same im all SX systems or in all settlers. The emulsion is brokem due to the collision and intersection of the disperse droplets, which break and grow in size when they moves from the irmterface to the surface or bottom, according to the relati<ve density of each phase. More unitary velocity= could cause more contacts, but raot many because no turbulence is generated, whereas the re would also be mucla less time for decantation, running the risk of overflows before this process is completed.

Therefore, the process applied both to the mixincg and phase separation devices is summ-arised as: a) Mix ing: © Special agitation-pump turbine © Appropriate combination of types of turbine im the different mixing compartments of a stage © Mixer geometry b) Set tling:

O Use of specific internal a«cessories © Appropriate combination and distribution of t—hese accessories

The appropriate selection of the operative- conditions of the devices completes the efficacy of the proposed method, affecting: a) Mix. ing: © Type and degree of agitatieon in each mixer © Their combination in the sesries of agitators in_ the compartments © Specific operative conditions in mixers b) Settling: © Decantation velocity desi_gn, appropriate and. different for each phase ard each stage. © Specific operative conditions in settlers.

This improves the quality of the separat ions, decreasing the sedimentation surface required and, consequently, enhancing the qua lity of the end product obtained.

BRIEF DESCR IPTION OF THE DRAWING=S

To complete the previous d escription, and in order to provide a better understandirag of the characteri stics of the inve ntion, following is & detailed descripti on of a preferred embodiment, based om a set of drawings which is attache-d to this description and where, im an illustrative and non-restricted way, the following has been represe=nted:

Figure 1 shows a diagram of an SX install ation which, in this case, shows e ight stages or mi xers- settlers, grouped into three typsical stages of this type of installa®ion: extraction, wash and re-extraction, with their interconnection and flows.

Figure 2 shows a diagram of one of the mi xers- settlers fr-om figure 1. In thos case, it is a mixer formed by f our parallelopipedic tandem compartments , and a settler woth details referring both to the position and shape of t-he traditional elem ents (distributor, flow buffers, re-circulation system, and organic and ag-ueous phase overf lows) and of new el ements (baffle with and without window).

Figure 3 shows a cross-sect ion diagram of a pr imary agitator.

Figure 4 shows a cross—section diagram of a secondary radial agitator.

Figure 5 shows a cross—section diagram of a secondary ax><ial agitator.

Figure 6 shows a cross-section diagram of the m ixer- settler froru figure 2, with details of the evolution of the emulsiorn in the mixer and how it is affected bx the different iraternal elements in tlie settler.

Figure 7 shows a front view of the baffles with windows.

Figure 8 shows a front view of the baffles without windows.

In these figures, the numerical references correspond to the fol. lowing parts and eleme=nts: 1 Extraction stage 2 Wash stage 3 Re-extraction stage 4 Mixer, consisting of a series of several compartments 5 Settler 6 Organic phase inte-rconnection 7 Impure solution (f ertile liquid) feed 8 Residual (refined) impure solution as 9 Aqueous phase feed to wash stage 10 Aqueous phase feed to re-extraction stage 11 Purified aqueous solution with product species (agueous extract) 12 Primary agitator =20 13 Secondary radial agitator 14 Secondary axial ag itator

Communication chanmels between mixer comapartments 15’ Communication chamnel upper overflow 15” Communication chamnel lower overflow 25 16 Turbine blades 17 Blunt edges on plates 18 Blunt edges on blades 19 Flow distributor

Flow buffer 3 0 21 Baffle with window 22 Window 23 Baffle without window 24 Emulsion

Upper overflow collection channel for the decanted 3 5 organic phase

26 Lower overflow collection channel for the decanted aqueous phase 27 Final interface 28 Interface level control valve system 29 Recirculation system 30 Organic phase 31 Aqueous phase

DETAILED DESCRIPTION OF A PREFERRED EMBODIM ENT

Figure 1 shows an installation to obtain a high- purity product by me ans of SX technology, consisting of three fundamental stages: extraction stamge (1), wash stage (2) and re-extraction stage (3), each formed by a series of several mixers (4) -settlers( 5). In this installation, the series of mixers-settlers are connected 45 by organic phase (3) interconnections (6) c irculating and loading with the target product in the ext-raction stage (1), being washed in the wash stage (2) and unloading in the re-extraction stage (3). The different &gueous phases fed to each stage flow in the opposite dir-ection to the organic phase: an impure solution (7) (fertile liquid) containing the produc t of interest, which i= extracted by the organic phase (30), leaving a residual impure solution (8) (refined); an aqueous phase to wash (10) which washes this lo aded organic phase, amd an aqueous phase to re-extraction (10), recovering the purified product from this organic phase (30) to obt=in a purified aqueous solution (11) (aqueous extract).

Figure 2 shows & diagram of this mixesr (4) -settler (5) in which, in this case, the mix of the organic phase (30) with the aqueous phases (31) and recirculation system (29) takes place in a mixer (4) comsisting of a series of 4 compartments equipped with the=ir respective primary agitators (12), secondary radial a_gitators (13) and secondary axial agitators (14), plus successive communication channels (15) consisting of successive mixer (4) compartments, with tlie fluid penetratimg the communication channels (15) over— an upper overflows (15') located on the output side of the previous compar—tment, and benea th a lower overflow (1 5") located on the input side of the following compartmment, which channels the mixture o-f the two phases from each compartment to the next indepoendently. The secondary agitators (13) armd (14) have turloines which keep the wmixture agitated An the desired c onditions for an appro-priate material transfer and for the eventual separation process. The Perimary agitator (12) turbine not only agitates, but also a.cts as a pump, a.spiring each phase from the contiguous se=ttlers and, if required, re-circulation from the settler i tself.

The secon dary agitator (13) and. (14) turbines keep the phases mizxed to complete this unit's function, wi-th the possibility of varying mixing conditions for a better separatiora process. The agitat ion conditions have to progressively decrease in the series of compartment s with a view to-, keeping the two phasses agitated, reduce its intensity and aggressiveness, thuas preparing the emulsion to facilit-ate settling and the grouping together oof the smaller dr-oplets. In this respect=, these compartmen ts can be inter=communicated with wi-de overflows (15) to facilitate the gradual reduct_don of the degre=e of agitation. The settler (5) has both conventional. flow distributor (19) systems, flow buffers (20), upper overflow collection channel for the decanted organic phase (25), lower overflow colZlection channel for the decanted &queous phase (26), re- circulation system (29), interface level control valve system (28) ancl new elements consisting of a baffle with (21) and without a window (23 ).

The t-ype of mixture with a view to eventual phase separation. is improved on the one hand by avoidi_ng or reducing t.he shear rate and the formation of excesssively small droplets by the use of appropriate tu-rbines and, on the other, by Pp rogressively reducing the degree of agitaticn throughout the series of agitamtors in each mixer-settler. As figures 3, 4 and 5 stiow, both the > primary agitator (12) and the secondary emgitators (13) and (14) are equipped with blunt edges on tke blades (18) and blunt edges on the plates (17), and this is irrespective of the number and arrangement of the blades (16) . These turbines avoid an excessive shear rate during 0 agitation, inhibiting the secondary dispersion responsible for tlie formation of small droplets created from the large droplets originally produced during primary dispersion .

Figure 6 shows how the emulsion (24 ) of the two

B5 phases flows from the last mixer (4) compa rtment and is finally fed into the settler (5). This emu lsion (24), a mixture of the organic phase (30) and the aqueous phase (31), is subject t« a conventional flow disstributor (19) system and another with the same purpose, homogeneously distributed over tohe surface of the settlem, and one or two flow buffers (20) which buffer the flow. The emulsion (24) behaves like a third phase with disappe=ars over time inside the settler (5). Although for the de canted phases (30) and (31), a low unitary velocity is comvenient, this is not the case for the emulsion (24), due to the convenience of generating the possibiliity of more contacts between the disperse droplets, leacding to their coalescence and separation. This is achieved with the window (22) “tubing and compressing” this em_.ulsion on the 3 0 interface, and mitzgating its increase in welocity with barriers lengthening or hindering their movement, such as the baffle without a window (23) which eliminates the prolongation of the emulsion in the vicinity of the collection channels (25) and (26). This minimises the final entrainments of one phase in the other and obtained a7 a totally clear final phase (27). These two new addit- ional elements, the ba ffle with a window (21) and, furth.er downstream, the ba ffle without a wimndow (23), both around 500 mm high, are installed cross-w-ise to the flow along the width of thie settler, in the interface area and, as indicated by t-he evolution of th. e emulsion (24) in the interface, this improves phase sepamration and reduc es entrainment. These new units consist of indep-endent elements aligned or installed on posts or columms anchored in the settler in order to fa vour their installation and maintenance in large settlerss. Several of tliese units can even I»e installed in parallel if required by the specific coraditions of the ins tallation.

Their relative position can also vary according to the stage (mixer-settler) cons idered, to obtaim maximum efficacy.

The baffles (21) and ( 23) made up of a series of modular units as shown in fi qures 7 and 8, and supported from beneath, are positioned cross-wise to the flow, covering the entire width of the settler (5).

I'n a preferred embodiment, the agitator turbines have & diameter of between 0.2 and 0.7 of the circular diametzer equivalent to the cross section (of t=he circle of thes same cross section) of the mixer compartrment, with the de=gree of agitation decreasing from 50 rps®//sq.ft. to 0.5 rpos®/sq.ft.. The height of the baffles is between 10% and 9-0% of the total height of the phases, and the opening of the baffles with windows is betweemn 10% and 90% of their total surface area.

F inally, each stage of the same process (extraction (1), wwash (2) or re-extracti«on (3)), and even each step within the same stage, can require different d egrees of agitat don of the above solutions, adapted to the= concrete purposes in question, using, if necessary, several units in parallel, with these elements located at an appropriate height and distance in the settler (5), conveniently poszitioning the final irterface (27) and applying the mosst appropriate operat ®ve conditions in each case. Each SX process, and each stage in particular,

S requires optimisation for its specific objectives.

EXAMPLES

A - AGITATION

Several effects are analysed, with an example of the extraction o% a metal ion in each. For each example, in each case tested, the metal wass analysed in each phase, and the phase separation time until the dispersion b and disappeared was d_etermined, taking the mean vamlue of at least fi=ve different and independent r-eadings.

Al - Effect of the type of turbine with blunt blades

Comparison of the chemical extrac®ion and eventual physical separation in a mixer with typical vertical blade turbines and with a blunt blade tuarbine, with other conditions remaining unaltered.

Example No 1:

Mixer: 1 or 2 tandem compartments (one turbine in each, the first a pump turbime), cylindrical geometry witch diameter = useful height (D=H), transparent, with upper baffle

Typical turbines: (one for each comepartment) a) pump, 8 flat vertical Iolades, straight bladess, diameter d = %¥ D of the compartment b) pump, d = % D, blunt blade=s and 8 straight flat vertical blades wi th curve r = 0.1%*e‘ ®%% (where x is blade width and r the curve radius). (see figure 3)

Cc) 4 bl ades with 45° inclination, axial agitatzion, diameter d = 1/3 D of the compartment (see figure 5) d) 4 straight blades, racial agitation,

F diametter d = 1/3 D of the compartment

Reagents (feed):

Case A: Orgamxic: D2EHPA (Di-2 ethyl he Xyl phosphoric acid) 40% v/v in kerosene

Aqueous (impure solution feed): =inc sulphate solution with 32.7 g/L of Zn and pH = 4.0

Case B: Organic: 5-nonyl-salicyl-aldoxime (Acorga

M5640) 30% v/v in kerosene

Aqueous (impure solution feed): copper sulphate 0 solution with 15.0 g/L of Cu and pH = 1.5

Conditions: Temperature 30°C, totzal time of residence 3 min., organic/aqueous rat3dios 2 (organic continuous) or 1 (aqueous continuous).

Results: 1.1 .- Case A reagents (Zinc) :

Type of Type of Degree of Zn g/L i_.n phase Table agitation turbDdine agitation separatio (rps'sq.f t.)

Loo [a9 [aia | aes | es

PA EC I ve

Aqueous a) + c) 2.3 (c) 11.1 15.0 82 continuous 19(b) +

ME: a) + d) | 2.3 /4) 11.0 19.1

IRE EV b) + d) 2.3(d) 10.9 19.1 74 » [1 | ean | 167 | es » [1 | so | 168 | e1

FA a) + c) 2.3(c) 16.7

Organic eo] 19(b) + continuous |b) + c¢) | 2.3(c) 8.1 16.8 63 a) + d) 2.3(d) 16.7 75

LET b) + 4d) 2.3(d) 8.1 16.6 67

1.2 .- Case B reagents (Coppe x) :

Tywpe of Type of Degree of Cu g/L in phase Table agd@ tation turbine agitation separation (sec.)

N3g? Organic {Aqueou (rps’sq. Ft. s ) 19

Lo» | 39 [ae | aes | es weal Se [ae [aw | ow

Aqueous a) + c) 2.3 (cD 12.0 2.95 91 continuous 19(b) —

I A

: a) + 4) 2.3 /A> 11.9 3.08 19(b) + ov | ie [oa | oso | er

A a) + c¢) 2.3(c) 7.0 0.95 82

Organic 19 (b) + cont inuous | b) + ¢) 2.3 (c) 7.1 0.95 78 a) + 4d) 2.3(d4) 7.1 0.93 83

A

Conc’lusion: As we can see, irrespective of the metal extracted, the use of a pump turbine with blunt edgres (b) hardly affects the chemical extraction process, bout it always improves the veloci ty of liquid-liquid phase sepawation, both independent ly and in combinatior with othew turbines. This effect is more marked in casses of aqueous continuous agitation.

A2.- Bffect of the decreasing degree of agitation

Comparison of the chemical extraction and eventual physical separation Din a mixer with a series of compartments with the same degree of agitation or with decreasing agitation, with the other conditions remaining unaltered.

Example No 2:

Mixer: 3 tandem compartments (one turb-ine in each, the first a pump turbine), cylindrical shape as in example No 1, tran sparent, with upper ba ffle

Typical turbines: (one for each compartment) b)- as in example No 1, pump, d = ¥ D, blunt blades and 8 straight, flat, vertical blades wi th curve r = 0.1%e ©%¥ (yheree x is the blade widt h and r the curve radius) c)- as in example No 1, axial agitation , diameter d = 1/3 D of the mixer with 4 blades incli ned 45° e)- plate, d = 1/3 D, radial agitation, blunt blades and 6 flat, straight, vertical blades wi th curve r = 0.1% ©°% (where x is the blade width and r is the curve radius) (see figure 4)

Reagents:

Case E: Organic: DZ2EHPA (Di.2 ethyl hexy—1 phosphoric acid) 40% v/v in kerosene, loaded with 12.1 g/l of zn®* and 0.3 g/1 of Fe’, in equilibrium v~ith

Aqueous: zinc sulp hate solution (20 g/l zn, 18 g/1

H,S0,)

Case B: Organic: _Ald-oxy-oxime (Acorga M5640) 30% v/v in kerosene

Aqueous: copper su lphate solution with 15.0 g/l of

Cu and pH = 1.5

Conditions: Temperature 30°C, total resicience time 3 min., organic/aquecus rations 2 (organic continuous) or 1 (aqueous continuous), recy cling the corresponding phases in equilibrium, when necessary.

Results: 2.1.- Casse A reagents (Zinc)

~ «<< 200°C "g9z0p5

Type of “Type of Degree of Zn «g/L in phase Table agitation turbine agitation separaticon

Nd? Orgari | Aqueous (sec.) (rps’sq. ft. c ) 19 (b) +

Aqueous Bb) + c¢) 12(c) + 11. © 19.1 continuous + C) 8 (c)

Org/Ac = 1 19(b) +

ERE EEE

+ C) 8(c) 19(b) + >) + ¢) 8(c) + 11. 1 18.9 53 + C) 2.3(c) pS [ee [er

Organic =) + c¢) 12 (c) + 8.1 16.7 79 continuous + C) 8 (c)

Org/Ac = 2 19(b) + b=) + c) B(c) + 16.8 71 + C) 8(c) 19(b) + b) + ¢) 8(c) + 8.1. 16.8 62 - + C) 2.3 (c)

2 4 2.2.- Case B reagents (Copper) oo

Type of Type of Cu g/L in phase Table agitat—ion turbine | agita-tiocra separation

Ng? Organic | Aqueouss (sec.) (rps’sq. E£ t.) 19 (b) + b) + c) 8(c) + 12.0 3.02 79

Aqueous + C) 8 (c)

A TB oe [om

Org/Ac = 1| Db) + ¢) 8% 4 12.1 2.85 73 + C) 2.3¢ 19{(b) + b) + e) B{e) + 12.0 2.95 81 + C) 8(c) 19(b) + + Cc) 2.3(c) mp ee [en b) + c) 8(c) + 7.0 0.93 76

Orgariic + C) 8 (c)

Si

Org/Ac= = 2| b) + c) 8% 4 7.1 73 + C) 2.3¢ are |e b) + e) 8{e) + 7.0 0.95 77 + C) 8 (c) 19(b) + b) + e) 8(e) + 7.0 0.98 75 + Cc) 2.3(c)

Concluwmsion: A decreasing sequence in the degree of agitatzion through the ser ies of mixing ceompartments improwes the liquid-liquid phase separation ~selocity in solverat extraction.

B.~- SETTLING

In a prototype mixer-settler, we analyse the effect of internal elementts on settling, with =n example in each. For each example, in each case tested, the organic phase entrainments in the aqueous phase, arid vice versa, were analysed at the end of the settling process, determining the height of the dispersion band or the distance at which it disappeared, taking t_he mean value of five different and independent readings.

Bl.- Effect of the baffle with window in the settler, with the same type o f mix

Comparison of the emulsion conssistency and entrainment of aqueous phase in orgamic phase and organic phase in aqueous phase, in a prototype settler, with amd without a baffle with a window.

Example No 3:

Typical mixer/agitation:

Mixer with a series of three identical FGRP parallelopipedi< 350 L compartments, communicated by channels consis ting of independent dowtable overflow- bottom walls, with the following characteristics:

Oo Parallelop ipedic, square based, s-ide = 0.89 of height H, transparent

Oo Agitation in aqueous continuous and organic/agqueous ratio = 1 in all rmixers o Conditions : 30°C, total residence- time 3 min., organic/agueous ratio = 1

Turbine: 1° compartment: case Db) from ex-ample No 1, agitation with N’d*® = 19 (rps®sq.ft.) 2" and 3™ compartment: case c) from example No 1, agitation Nd? = 8 (rps’sq.ft.)

Reagents: Case E: organic: D2EHPA (Di—2 ethyl hexyl phosphoric acid) 40% v/v in kerosene , loaded with 12.1 g/1 of 2zZn®=* and 0.3 g/l of Fe in equilibrium with

Aqueous: zinc sulphate solution (20 g/l zn, 18 g/1

H;S0,)

Contiriuous operation in industrial prototype mi=xer- settler. Centralised control

Typical settler:

Of transparent methacrylate, 22 x 0.25 x 1.1m «L x

W x Hm» (length x width x hezdight). Internal elements positi_oned perpendicularly to the direction of the flow: distributor, laminator-buffer and, wvhen indica ted, 1 0.5 m high baf fle with central 0.225 m windows, centred on the axis of the interface and positi oned at a distance (variable) from the mixer outlet .

The specific flow of each phase was 2.5 m*/hm?. The unitary velocity values were 2.5 m/min in organic and 1. 8 m/min in aqueous.

Results:

Posi - Dispersion band (m) Entrainment (opt)

Baffle t ion of with an-d/or Organic window dime=nsio Height Height At final in Aque=ous n,m before after- overflow | aqueous im wards orga nic

No 0.18 | 27 19-1 ves | wo | 0.26 | 023 | oar | 20 | 130

Conclusion: In the conditions tested, the presence of a baffle with a window improves the efficacy of the liqu id- liquid deca ntation process, consi derably decreasing the entrainmentss of one phase in the «other. This improvem-ent is more effective the greater t_he dispersion band on which it i s applied (less advanced position in the directzion of the flow), without overflowing ab-ove and/or beneath the baffle.

B2. - Effect of the bafflee without a window in the settlexr, with the same type of mix

Comparison of the consistency of the emialsion and entrainment of aqueous phase in organic phase and

Vv-ice versa, in a prototype settler, with amd without a baffle without a window.

Exampl e No 4:

Reagen ts, operation, mixer, agitation and condZitions: as in the previous example

Type of settler: as in t he previous example (No 3)

Imternal elements located perpendicularl—y to the ddrection of the flow: distributor, laminat=or-buffer arid, when indicated, a 0.5 high baffle -without a wodindow, centred on the axis of the inte—rface and located at a distance (variable) from t=he mixer outlet. Unitary velocities and specific flows: as in exzample No 3

Results:

Position Dispersion band (m) Entrairmment (ppt)

Baffle and/or of without dimensio Organic= window n, m Height Height At final in Aqueous : before afterwar | overflow aqueous in ds organic 20 [oer oo | 13 | 025 | wote | 30 207 26 | 022 | on ves | 13 | 035 | 000 | 13 | 1s | 130] 16 | 022 | 000 | 16 | 20 | 15

Note (* ): At the end of the settler the disperssion bang was still 0.19 m

Conclusion: In the conditions tested, the presemnce of a baffle without a window improves the efficacy of the liquid-liquid phase decantation process, considerably decreasing the entrainments of one phase in the other.

This improvement is more effective thie smaller the dispersion band on which it is applied (more advanced position in the d&drection of the flow), pr-oviding it does not overflow above and/or beneath the baffFEle.

C.- MIXING AND SETTLING

Combined effect of special turbirmes, decreasing a0 degree of agitation and the two baffles (with and without a window) , on decantation speed and entrainments of one phase in the othe r

Cl.- Symergic effect of all the new device s and methods

Comparison between the application or not of the new as inventions introduced (blunt ecdged turbine, decreasing degree of agitation, bafffle with window and baffle without window) and -their synergic effect, and their behaviour in the doifferent stages of the SX installation.

Example No 5:

Reagents:

Case E (extraction): see previous examples No 3 and

No 4

Case W (wash): organic: D2EHPA (Di—2 ethyl hexyl phosphoric acid) 40% v/v in kerosene=, loaded with 12.1 g/1 of zm* and 0.3 g/l of Fe’.

Aqueous: zinc sulphate solution (27 g/l zn, 17 g/l

H,S0,)

Case R (re-extraction): organic: D2EH_PA (Di-2 ethyl hexyl phospho ric acid) 40% v/v in ke=rosene, loaded with 1.5 g/1 of zZn*" and 0.3 g/1 of Fe™'

Aqueous: zinc sulphate solution (85 9/1 Zn, 17 g/1

H>S0,)

Continuous opesration, in industrial prototype mixer- 3s settler. Centralised control

Type of mixer-set-tler:

Mixer: three compartments as in examples No 3 and No 4

Agitation: Cases E and W: aqueous continuous organ/ac ratio = 1 in the three compa rtments. Case

R: organic conti nuous organ/ac- ratio = 3 in both mixers

Conditions: 30°C, total residence time 3 min.

Turbines: © Test without. application of the in vention: " 1°" compartment: type a) fresm example No 1, agitation N’d® = 19 (rps?sqg .ft.) = 2" ang 3% compartments: t ype c¢) from example No 1, agitation Nd? = 8 (rps’sqg .ft.) © Test with application of the inven-tion: * 1°° compartment : type b) from example No 1, agitation N’d* = 19 (rps’sqg .ft.) « om compartment: type cc) fromm example No 1, agitation N’d® = 8 (rps’sq.=ft.) * 3" compartment: type c) fromm example No 1, agitation N°@® = 2.3 (rps’scy. ft.)

In this case, as can be seen, all the turbines have blunt blades and there is a decreasing distribution of the degree of agitation throughout the series of compartmen ts.

Type of settler: as in examples No 3 anc No 4

Internal elements: in all cases, at least distributor and 1 aminator-buffer, and —in the tests applying the inveration, a baffle with a window (BV) as indicated in example No 3, located Dn all cases at 6 m and a baffle without a windew (BC), as indicated in example No 4, located at 15 m in cases

E and W, or at 11 wm in case R, all measu.red from the mixer outlet.

The specific flows and unitary velocities u sed for each phase were:

Flow (w/mw) | velocity (m/min)

Case rowan an Tas es

Results: we compare the three stages: extraction (e), wash (W) and re-extract ion (R) in their behaviour with and without the indicated inventions. In all the cases where the invention was applied, there was no final dispersion band after the BC.

Dispersion band height Entraimment

Reagent (m) (ppt) of

Baffle | s case Organi 5 Before BV Before c in Aqueous

After BC agueou in

BV s organic

E 0.29 (*) 0.23 28

No (*) (*)

BREEN A A

(*)

Yes ® J 027 | 01s [0as | 5 | ase (*) Measured at the same distance at which the kaffles would be located, although they are not used here.

Conclusions: In the conditions tested, where the inventions in question are used (type of turbines ang decreasing degree of agitation, together with the presence of a baffle with a window and a baffle wit hout a window), it has been seen that in all cases, withim each stage, there is a clear improvement in the efficacy of the liquid/l-dquid decantation processs and, surprisingly, an evident and clear synergic effect, with the fimal dispersion b and decreasing considerably, together wi th the entrainments of one phase in thes other (compare casse

E with similar cases in examples No 4 and No 5).

Their concrete application both in agitation metho=ds and as internal parts in the resp ective settlers, c an vary accordirag to the behaviour of each step, dependi ng on the mixing and decantation characteristics require d, such as the height and consistency of the emulsion ba nd generated.

This improvement is general for each and every ome of the typical stages of a solvenk extraction process and, in relat ive terms with regards to its absence, mo—re effective thee more difficult is the natural decantaticon of the system on which it is applied —

Claims (8)

1. Mixing and settling device in solvent extra ction Processes to recover high-puri ty products in which mixers-ssettlers are used that are characterised in that they corisist of: in each mixer, several tanderm compartments, wit h the first containing a primary agita tor with a blunt edged agitation-pumping turbine, and the following with secondary agitators with blunt e=dged agitators, wi_th a decreasing degree of agitation throughout the series of compartments, so that, maintaining the chermical characteristics of the transfer of matter between. the phases, there is a minimal disper sion of droplets off one phase in the other, at least one baffle with a window located in. the interfac e area of the settler and perpendicularly to the flow, equipped with a central hole or window that retains, compresses and directs t—he emulsion area, also allowing for the upper and lower— overflow of the non- emulsified phases, respectively 1 ess heavy and heawsier, and positioned at a certain distan ce after one or several flow buf fers, at Zleast one baffle without = window located in. the interface area of the settler, at .a certain distance from the baffle with a window, and perpendicularly to the flow, so that it retains the fina 1 emulsion area of the interface, also allowing for the upoper and lower over—flow of the non-emulsified phases, respectively less heavy- and heavier.

2. Devi.ce according to claim 1, characterised in that the pumps and agitation turbines have a diameter of between ©.2 and 0.7 of the circul ar diameter equiva lent to the cross section of the reagent compartment or respective mixing unit, with a number of blades between 2 and 12.

3. Device accoxding to claim 1, characte rised in that the blunt edges of the turbines preferably correspond to function r = 0.1%e!®%% yhere x is the blade width and r is the curve radi us applied.

4, Device according to claim 1, charactemxised in that the decreasing degree of agitation varies f rom a maximum of 50 rps’sq.ft to a minimum of 0.5 rpsisq.ft=

5. Device according to claim 1, character—ised in that the baffles with and without windows are po sitioned, the former after the flow buffers and the latter before the final collection channels for the two decanted phases.

6. Device according to claim 1, character-ised in that the baffles with windows have a window covering between 10% and 90% of their surface area.

7. Device according to claim 1, character-ised in that the height of the baffles is from 10% to 90% of the total height of the two phases in the settler.

8. Mixing and settling method in solvent extraction processes for the recovery of high-purity products, characterised in that it inhibits the secondary dispersion of small droplets, so that the ent-rainments of aqueous phase in organic phase and vice versa are considerably reduc ed.

SUMMA _RY MIE XING AND SETTLING METHOD AND DEVICE IN SOLV"ENT EXTRACTION PROCESSES TO RECOVER HIGH-PURITY PROPDUCTS The device of the invent ion includes the following new elements in each mixer-set&ler:

ald Agitators with blunt ed ged turbines,

bD Decreasing degree of agitation throughout the series of mixing compar tments,

c»® Baffle with a central window in the settler interface, located afte r the flow buffers,

d) Baffle without a windo WwW, centred in the settler interface, located after the baffle with a window.

TInese elements allow for an operative metho d which inhibits secondary dispersion, reducing the forma tion of micro-Aroplets, without affeccting the mass transfer betweerm the phases.

Consequently, this obtains = phase separation process with entrairments so small that it is possibl e to drastically increase the quality of the product , by obtaining an ult-ra-pure aqueous e xXtract, simulta neously reducing the set tling surface requi xed.

Fi gures 3, 4, 5 and 6.