MXPA97005123A - Extract recovery method - Google Patents

Abstract

A method for recovering the extractant from the aqueous effluent that continuously exits from a solvent extraction circuit, where the effluent is contacted with the same immiscible diluent in water that is used in the circuit as a solvent for the extractant of such that the extractant is transferred from the aqueous effluent phase to the diluent phase. The diluent phase, which is now enriched with the extractant, is separated from the aqueous effluent now used as an extractant. The phase of the separated diluent can then be brought back into contact with the effluent or it can be combined with an organic phase of the extraction circuit by solven

Description

"EXTRACTANT RECOVERY METHOD" BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to a method for the recovery of extractant from aqueous effluents from a continuously operating solvent extraction circuit. 2. DESCRIPTION OF THE RELATED TECHNIQUE The operation of a solvent extraction circuit can be exemplified by the following description of a large-scale circuit using mixer-settlers for copper processing. The starting material is an aqueous feed solution, obtained by leaching the copper ions from the ore. The aqueous feed solution is mixed in tanks with an organic solvent comprising an extractant which is dissolved in an organic diluent, e.g., a kerosene. The extractant selectively forms a metal extractant complex with copper ions, in preference to ions of other metals. The step of forming the complex demoninates the extraction or charging stage of the solvent extraction process. The mixer outlet is continuously fed to a large settling tank, where the organic solvent (organic phase), which now contains the copper-extractant complex in solution, is separated from the spent aqueous solution (aqueous phase). This part of the process is called phase separation. Usually, the extraction process is repeated through a total of two or more stages of the mixer-settler, in order to extract more completely the desired metal. When two or more stages of the mixer-settler are used for extraction, the countercurrent flow of the aqueous feed solution and the organic phase or the extractant solution is employed. In a typical three stage extraction system, for example, the aqueous feed solution will flow through the initial stage of the mixer-settler ("E"), subsequently through a second stage ("E2") / and then through the final stage of the mixer-settler ("E3"). The organic phase, in turn, will initially come into contact with the aqueous feed solution at E3, find a subsequent contact at? 2, and a contact As a result, by the time the aqueous feed solution reaches stage E3 of the mixer-settler, considerable amounts of copper will have been extracted from it and will be in contact with a low organic phase in copper. organic phase reaches the mixer-settler, large amount of the extractant will be in the form of the copper-extractant complex and the organic phase will be in contact with the aqueous feed solution when it is in a condition where it has been extracted little in case of having extracted the dissolved copper. After extraction, the spent aqueous solution (extraction or refining effluent) can be passed through a means for the recovery of easily separated organic droplets, and either discharged or recirculated for further leaching. Any of the droplets of the organic phase remaining associated with the effluent leave the system together with the aqueous phase and are not lost. Even in systems where the effluent is recirculated as in the leaching of ore to regenerate a feed solution, any organic phase associated with the effluent tends to be irreversibly absorbed into the ore and does not return to the circuit with the regenerated feed. The loaded organic phase of the extraction containing the dissolved copper-extractant complex is fed to another set of mixer-settler where it is mixed with a relatively concentrated aqueous purification solution of sulfuric acid. The highly acidic purification solution disintegrates the copper-extractant complex and allows the purified and concentrated copper to pass into the aqueous purification phase. As in the extraction process described above, the mixture is fed to another sedimentation tank for phase separation. This process of disintegrating the copper-extractant complex is called the purification step and the purification operation optionally is repeated in a countercurrent manner through a total of two or more stages of the mixer-settler in order to more fully purify the copper from the organic phase. From the depuration tank, the reclaimed purified organic phase is recirculated to the extraction mixers to start the extraction again, and the aqueous phase of purification is usually fed to a tank-electrolytic extraction chamber, where the values of copper metal are deposited on plates by the electrodeposition process. After electrolytically extracting the copper values from the aqueous purification solution, the solution is recycled to the purification blenders to begin debugging again. As with the extraction effluent, any organic material that is associated with the aqueous scrubber that exits the circuit tends to be lost. The organic material retained tends to accumulate in the electrolytic extraction cells where the properties of the organic material can be degraded. For practical purposes, this constitutes a lost organic material. In addition, the extractant tends to accumulate in the liquid surface of the electrolytic extraction cells causing the deterioration of the quality of the deposited copper. A similar loss of the organic material can be made from the solvent extraction circuit, where any aqueous phase leaves the circuit after coming into contact with the organic phase. For purposes of this invention, this aqueous phase leaving a solvent extraction circuit is referred to as an effluent, whether it is an extraction effluent or a purification effluent, a wash effluent or any other aqueous phase of departure. For the most part, the organic phase associated with the effluent does not dissolve in the aqueous phase, but consists of a retained organic material, that is, droplets suspended from the insoluble organic phase that did not bind in the volumetric organic phase during the phase separation. The losses of the organic material can be worsened by several means: the organic phase can be absorbed in undissolved solids in the aqueous phase, which is frequently referred to as impurities, and can be discharged with the effluent; non-ideal flow patterns in a settler can lead to locally fast liquid velocities, sweeping organic droplets that would otherwise have settled and bound; or disturbances that disturb the interface of the organic / aqueous material that may result in the organic phase having been carried out with the aqueous phase. An analytical method has been used to determine the level of the organic material retained in the aqueous effluent from a copper solvent extraction circuit, where a known volume of the effluent is first agitated in a separating funnel with another known volume. of a solvent immiscible in water, wherein the retained organic material is known to be soluble. The separated solvent phase now containing the retained organic material is then contacted with an excess of an aqueous copper solution to load the contained extractant at its maximum loading capacity. The copper level of the charged solvent phase can then be determined to very low levels by atomic absorption spectroscopy and the level of the extractant can be recalculated on the basis of the known stoichiometry of copper with respect to the extractant.

For most circuits, a large portion of the cost of the organic phase that is lost is due to the extractant content, since the extractant is often much more expensive than the diluent. For example, in solvent extraction of copper, the extractant can cost 25 to 35 times more per .454 kilogram of the diluent. This organic phase of the circuit formulated with 20 percent extractant in the diluent can therefore cost as much as 10 times more than the diluent alone. In other circuits the cost of the reagent in relation to the diluent can be much higher. The diluent often tends to get lost from the circuit more quickly than the extractant due to evaporation. Because the diluents tend to be nonpolar materials of relatively low viscosity, they have higher vapor pressures than the extractants, and evaporate more rapidly. Therefore, the replacement of the organic material in a circuit will typically require a greater amount of diluent in proportion than the extractant. Solvent Extraction, Principles and Applications to Process Metallurgy, Part II, pages 642-650, by Ritcey & Ahsbrook cites several techniques that have been applied in the solvent extraction industry to recover the organic phase retained. Flotation involves dispersing air into the aqueous phase to generate small bubbles that absorb organic droplets and transport them to the surface where they join. A variant of this technique dissolves the air in the aqueous phase under pressure, and then suddenly releases the pressure; the air bubbles form a nucleus on the organic droplets and carry them to the surface. However, flotation techniques have limited recovery capacity of the organic material and require significant energy input to disperse or dissolve the air. Alternatively, the aqueous effluent can be passed through a coalescence vessel containing a solid with hydrophilic surfaces. Organic droplets tend to bind and accumulate on the solid surface; these can then be collected by backwashing and returned to the circuit. The coalescence containers, however, can be ineffective if the aqueous phase is not free of solids. The absorption with carbon can be effective to remove the organic droplets by absorption, but the absorption capacity is relatively low, and regeneration can be expensive. Centrifuges can remove organic retention material effectively but are very expensive to operate and maintain. Cyclone separators can also be effective, but the high speed of the liquid required means increased pumping costs, and the shear stresses involved in pumping may actually cause finer dispersion of the retained organic droplets. Therefore it would be desirable to have a method for recovering the extractant lost in the solvent extraction effluents in order to reduce costs. It would be especially desirable if there were a method that recovered both the extractant in the retained organic material and any extractant dissolved in the aqueous phase, which simply operated with a minimum energy requirement.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a diagrammatic representation of a specific embodiment of the method of the invention.

DESCRIPTION OF THE INVENTION In this description, except where explicitly stated otherwise, all numbers describing the amounts of ingredients to the reaction conditions should be understood as modified by the word "approximately" when describing the broader scope of the invention. Generally, however, the practice of the invention is preferred within the exact numerical limits. This invention provides a method for recovering the extractant from an aqueous effluent leaving continuously from a solvent extraction circuit., wherein the effluent is contacted with the same diluent that is being used in the circuit, in such a way that the extractant is transferred from the aqueous effluent phase to the diluent phase. The aqueous effluent now exhausted from the extractant is then separated from the diluent phase enriched now with the extractant. The separated diluent phase can then be brought back into contact with the effluent to recover the extra extractant, or it can be combined with the organic phase of the solvent extraction circuit. The extractant in this invention may be any organic molecule or combination of molecules that is preferably soluble in a water immiscible diluent, and which exhibits an ability to form a complex or associate with a solute initially present in an aqueous solution. Examples of extractants include, but are not limited to, ortho-phenolic oxides, primary, secondary and tertiary amines, quaternary ammonium compounds, substituted guanidines, phosphine oxides, esters and partial esters of phosphoric, phosphonic or phosphinic acid, aliphatic carboxylic acids and esters, sulfonic acids and esters of carboxylic acids of pyridine. Preferred extractants for use in the invention include those that contain one or more aryloxy a, hydroxyl extractants of the hydroxyl-aryl oxime, aldoxy a or ketone type. The hydroxy-aryl ketoxime extractants, which can be used in reagents for the practice of the invention, are those of Formulas I and II which are presented below: wherein R and R1 may be individually similar or different and are saturated aliphatic groups of 1 to 25 carbon atoms, ethylenically unsaturated aliphatic groups of 3 to 25 carbon atoms or -OR1 ', where R "is a saturated aliphatic group or ethylenically unsaturated as defined; n is O or l; and a and b each is 0, 1, 2, 3, 4, with the exception that both are not 0 and the total number of carbon atoms in Ra and R'jj is 3 to 25, wherein R are already as defined with respect to Formula I and R1 '°' is a saturated aliphatic group of 1 to 25 carbon atoms, or an ethylenically unsaturated aliphatic group of 3 to 25 carbon atoms, with the exception of that the total number of carbon atoms in Ra and R "'is from 3 to 25. Preferred compounds of Formula I are those wherein a is 1, b is 0, R is a branched straight-chain alkyl group which it has from 7 to 12 carbon atoms and wherein R is fixed at a para position with respect to the hydroxyl group, among which, especially preferred are those wherein R is a mixture of isomers The preferred compounds of Formula II are those in which R '•' is methyl and R are already as designated as being preferred for the compounds of Formula I.

Compounds of Formula I wherein n has a value of 0 (ie, hydroxybenzophenone oxime compounds) can be appropriately prepared according to the methods disclosed in the Swanson US Patents Nos. 3,592,775 and 3,428,449. Due to the ease and economy of the synthesis of the available starting materials, the easy solubility in organic diluents that is commonly employed in solvent extraction and the desirable properties of complexes of the compounds with copper, the preferred benzophenone oxime compounds of Formula I include those having a single alkyl substituent ring having from 7 to 12 carbon atoms in a para position relative to the hydroxy group whose alkyl substituent is a mixture of isomers. Examples of these compounds are 2-hydroxy-5-nonylbenzophenone oxime and 2-hydroxy-5-dodecylbenzophenone oxime which are obtained as mixtures of alkyl isomeric forms when commercial nonylphenol and dodecylphenol are used respectively in their synthesis. The compounds of Formula I wherein n has a value of 1 (ie, hydroxyphenyl-benzyl ketone oxime compounds) can be appropriately prepared according to the methods described in Anderson's North American Patent Number 4,029,704. Preferred phenylbenzyl ketone oximes as well as the aforementioned benzophenone oximes are those having an isomeric mixture of alkyl groups of 7 to 12 carbon atoms, as the sole substituent in the para position of the ring with respect to the hydroxyl group. These preferred compounds are exemplified by the 2-hydroxy-5-nonylphenolbenzyl ketone oxime compound, as manufactured from a commercial nonylphenol comprising a mixture of nonyl isomeric forms. Compounds of Formula II (ie, hydroxyphenylalkyl ketone oxime compounds) can be appropriately prepared according to the methods disclosed in U.S. Patent No. 1,322,532. As mentioned with respect to benzophenone oxime and phenylbecyl ketone oxime compounds of Formula 1, the preferred phenyl alkyl ketone oxime compounds of Formula II are those having an isomeric mixture of alkyl groups of 7 to 12 atoms. of carbon, as a single substituent in the para position of the ring with respect to the hydroxyl group. Also preferred are compounds wherein the alkyl group R '' 'is methyl. Accordingly, illustrative of the preferred phenyl alkyl ketone oxime compounds is the 2-hydroxy-5-nonylphenylmethyl ketone oxime manufactured through the use of commercial nonylphenol. The hydroxy aryl aldoxime extractants that can be used in the reagents for the practice of the invention are those of Formula III wherein R is as defined above with respect to Formulas I and II, c has a value of 1, 2, 3 or 4, and the total number of carbon atoms in Rc is from 13 to 25. Preferred compounds of Formula III are those wherein c is 1, R is a branched straight chain alkyl group having 7 to 12 carbon atoms and wherein R is attached at a para position to the hydroxyl group. Among these, the especially preferred ones are those wherein R is a mixture of isomers. Compounds of Formula III (ie, hydroxybenzaldoxime compounds, which are sometimes referred to as "salicylaldoximes") can be properly prepared according to the methods described in the Ackerley US Patent and other Nos. 4,020,105 or 4,020,106 or by oximation of aldehydes prepared according to US Pat. No. 4,085,146 of Beswick. Again, the preferred compounds are those having an isomeric mixture of alkyl groups of 7 to 12 carbon atoms as a single substituent in the para position with respect to the hydroxyl group. The mixed isomeric alkyl forms of 2-hydroxy-5-heptylbenzaldoxime, 2-hydroxy-5-octyl, 2-hydroxy-5-nonylbenzaldoxime and 2-hydroxy-5-dodecylbenzaldoxime are therefore preferred. The extractants can print a single extractant chemical substance, as illustrated above may comprise mixtures of different extractants of aldoxime or ketoxime of the type illustrated in US Patent Nos. 4,507,268, 4,544,532 and 4,582,689. In addition to the extractant, the organic phase may also include modifiers to improve the operating properties of the system. Examples of modifiers include, but are not limited to, nonylphenol, isotridecyl alcohol, 2,2,4-trimethylpentan-1,3-diisobutyrate and 5,8-diethyl-7-hydroxy-6-dodecanone oxime.

The extractant in this invention is dissolved in a diluent to provide the organic phase used in the solvent extraction circuit. The diluent is a liquid solvent immiscible in water that can dissolve the extractant and the associated complex of extractant and extracted solute. The selection of the diluent will depend on a number of factors, including the nature of the contact equipment used, the characteristics of the extractant and the solute to be extracted, the value and desired properties of the final product of the extraction, and similar factors. Examples of diluents include toluene, xylene, ethylendichloride and kerosenes. Kerosenes are the preferred diluents, several types of which can be obtained. Examples of commercially available kerosene include the Ion Exchange Solver Chevron (obtainable from Standard Oil of California flammability temperature of 91 ° C), Escaid 100 and 110 (obtainable from Exxon-Europe - flammable temperature 820C), Exxon Aromatic 150 (an aromatic kerosene obtainable from Exxon-USA - flammability temperature 71 ° C), Phillips SX 1 and 7 (obtainable from Phillips Petroleum - flammability temperature of 71 ° C) and Conoco 170 Exempt Solvent (obtainable from Conoco - flammability temperature of 77 ° C).

Of the typical differences between extractants and diluents, two are of special importance in this invention. First, the diluents tend to have a higher vapor pressure and evaporate much more quickly than the extractants. This leads to an unequal loss regime so that it needs to be added to a proportionally more diluent than extractant circuit to maintain its organic phase at a constant composition. Second, extractants tend to be considerably more expensive than diluents, so that extractant recovery is much more cost effective than diluent recovery. This invention uses these two differences using the least expensive diluent that would have to be added to the circuit anyway in order to recover the most expensive extractant from the aqueous effluent. This invention does not eliminate organic retention because typically some organic extractant remaining in the effluent after contacting the diluent has been achieved. Nevertheless, the composition of the organic retention agent after being brought into contact with the diluent, is substantially lower at the level of the extractant than the retention of the organic phase directly from the circuit. In fact, this invention replaces the retention of the organic phase containing the expensive extractant and the retention of the organic phase which predominantly contains the less expensive diluent. Therefore, the greater the cost difference between the extractant and the diluent, the greater the economy capable of achieving this invention. As indicated above, the separate diluent phase of this invention can be added to the solvent extraction circuit or can be recycled by contacting once or more times with more effluent to increase the concentration of the recovered extractant to a higher level. Normally, all of the diluent that is added to the solvent extraction circuit to replenish the diluent in order to replace the lost diluent by retention to evaporation, or a considerable portion thereof, will first be used in the process of this invention to recover the extractant from the solvent. effluent and then it will be added to the circuit. In this manner, the amount of the diluent used to contact the effluent is essentially equal to or less than a quantity of diluent required to replace the diluent lost from the continuous solvent extraction circuit. When the separated diluent is recycled, the volume ratio of the diluent to the effluent can be varied acceptably between as low as 1 / 30,000 and as high as 5/1, preferably between 1/100 and 2/1 and so especially preferred between 1/20 and 1/1. In total, the number of reuses of the diluent phase can vary acceptably between zero, in the case where the diluent separated after being contacted with the effluent is added directly to the solvent extraction circuit and approximately 30,000. Preferably, the number of reuses of the diluent phase will be between about 500 and about 15,000, and especially preferably between about 1,000 and about 10,000. The portion of the separated diluent that is added to the solvent extraction circuit can be acceptably varied from about 0.003 percent to 50 percent, preferably from about 0.007 percent to 0.2 percent and especially preferably from 0.01 percent to 0.1 percent. hundred. Correspondingly, the portion of the separated diluent that is reused can range acceptably from about 50 percent to 99.997 percent, preferably from about 99.8 percent to 99.993 percent, and especially preferably from about 99.9 percent to 99.99 percent. The type of equipment used to contact the aqueous effluent with the diluent may vary. The main consideration is that the interfacial surface area generated between the aqueous effluent and the diluent during the contact step is large enough and is maintained for a period sufficient for the droplets of the retained organic phase to bind with the diluent phase before The mixture of the organic-aqueous phase is separated again. Fortunately, this coalescence process is rapid so that a high energy input is not necessary for the mixing of the phases. Useful contact means include mixers mechanically agitated with turbines, typically passing to a gravity settler. This mixer-settler combination is preferably operated with a direct recycle of the diluent phase separated from the settler back to the mixer, effectively providing multiple contacts of the diluent phase with the aqueous effluent phase. Figure 1 is a digramatic representation of a recycling system of the continuous mixer-settler with organic recycling. The mixer-settler unit 1 consists of a mixer compartment 2 equipped with an agitator 3, and a compartment 4 of the settler for coalescence of the mixed phases. The aqueous effluent from the solvent extraction circuit and a combination of a fresh and recycled diluent are continuously added to the mixer 2 where the stirrer 3 disperses the phases to produce an emulsion. During the time that the phases are in the mixer, the organic retained phase in the aqueous effluent phase dissolves in the diluent phase. The emulsion of the two mixed phases is passed from the mixer 2 to the settler 4 where a sufficient residence time is provided to allow separation in aqueous and diluent phases. The separated aqueous phase continuously leaves the settler as a treated aqueous effluent. The separated diluent phase continuously leaves the settler and is divided, a portion of which is recycled to the mixer 2 to be contacted with an additional amount of the aqueous effluent, and a portion of which is removed from the recovery system and it is added to the solvent extraction circuit from where the aqueous effluent came. The removal rate of the diluent phase is essentially the same as the addition rate of the fresh diluent. The volume ratio of the phase of the recycled diluent to the phase of the removed diluent is related to the average number of reuses experienced by the diluent phase. For example, a ratio of 100 to 1 would result in an average recycled number of approximately 100. In this way, to achieve 2,000 recycled diluent phase, the volume of fresh diluent added, which is essentially the same as the volume of The phase of the removed diluent would be approximately 0.05 percent of the volume recycled. To achieve a single recycling of the diluent phase, the volume of fresh diluent added and that of the phase of the removed diluent would be equal to the volume recycled. In this way the number of reuses or recycling can be controlled by adjusting the volume ratio of the recycled diluent to the phase of the removed diluent. The number of reuses can vary acceptably between one and 20,000, preferably between 500 and 15,000 and more preferably between 1,000 and 10,000. Another preferred means of contact is the injection of the diluent phase into a pipe that carries the aqueous effluent phase preferably upstream in an aligned mixer. A convenient point for this injection of the diluent is the case of the aqueous landfill of the last mixer-settler before the effluent leaves the solvent extraction circuit. The aqueous agent typically overflows continuously from the settler into the box of the spillway and then flows out at the bottom of the spillway through a pipe. The continuous addition of the diluent at this point allows the mixing of the two phases in view towards the pipe. Even when not required, the aligned mixer uses the velocity of the liquid past the stationary mixing blades in the pipe to impart a mixing action, thereby dispersing one phase with the other. The pipeline or transfer line then supplies the two-phase mixture to a still zone, where the two phases can be separated. The still zone can be a settler or in the case of large scale mining operations, it can be a "refining pond" where the effluent accumulates before being reused in leaching. The separated diluent phase is defoamed from the surface. In any case, the separated diluent phase is recycled for further contact with the effluent phase or is added to the solvent extraction circuit. In another embodiment of the invention, the diluent phase can be used to contact more than one stream of the effluent from the same solvent extraction circuit. Typically, a circuit will produce at least one extraction effluent and a purification effluent. The process usually results in the concentration of the extracted material, such as the copper in the aqueous feed solution to the cleaning solution so that the volume of the cleaning solution is considerably smaller than the volume of the aqueous feed solution. It is preferred to contact the diluent first with the purification effluent to recover the retained organic phase, and then to contact said separated diluent with the extraction effluent before adding the final separated diluent to the solvent extraction circuit. Therefore, the ratio to the volume of the diluent to the aqueous effluent will be higher during contact with the purification effluent resulting in higher dilution of the recovered extractant towards the diluent and a lower concentration of the extractant remaining in the treated purification effluent. In the case of electrolytic copper extraction, this provides the added benefit of minimizing "organic singeing" in the cathodes and allows the production of a higher quality copper deposit. The diluent separated from the treatment effluent is then brought into contact with the extraction effluent, where the volume ratio of the diluent to the aqueous effluent will be lower but where a considerable recovery of the retained organic phase is still possible. Of course, the diluent separated from the treatment of the extraction effluent is added to the solvent extraction circuit. A preferred option in this embodiment is the treatment of the purification effluent to recycle a predominant portion of the separated diluent to be brought into additional contact with the purification effluent, and transfer a small portion of the separated diluent to the treatment of the extraction effluent. Similarly, it is preferred that, in the treatment of the extraction effluent, a predominant portion of that separate diluent be recycled to be brought into additional contact with the extraction effluent, and a small portion of that separate diluent is added to the extraction circuit by solvent. The process of this invention can also be used in conjunction with other means to recover the retention of the organic phase from the effluents. Devices such as post-settlers, absorption columns or flotation columns can be used to recover a portion of the retained organic phase, and the effluent leaving this device can then be treated by the process of this invention. In this way, the concentration of the extractant accumulated in the phase of the separated diluent will be lower, and the loss of the extractant in the treated effluent will be reduced. To further illustrate the various objects and advantages of the present invention, the following example is provided. It will be understood that its object is entirely illustrative and is in no way intended to limit the scope of the invention.

EXAMPLE 1 A laboratory solvent extraction circuit was assembled with two extraction stages, a depuration stage and a recovery phase of the organic phase. The aqueous feed solution was a copper leaching solution containing 2.8 grams per liter of Cu and 0.3 gram per liter of Fe at a pH of 1.80. The purification solution was a spent copper electrolyte containing 30 grams per liter of Cu and 193 grams per liter of H2SO4. The organic phase for the extraction and purification steps was 8.3 percent (volume / volume) of LIX®984N (a mixed oxime extractant, obtainable from Henkel Corporation) in an exempt Conosol® 170 solvent (a kerosene obtainable from Conoco) The aqueous and organic feed phases were then pd at a rate of 45 milliliters per minute, while the purification solution was pd at a rate of 7.8 milliliters per minute. An aqueous recycle was used in the purification step to maintain a ratio of the organic phase to the aqueous phase (O / A) of 1 to 1 in the mixer. The stream of the aqueous raffinate from the second extraction stage was advanced to the stage of recovery of the organic phase. The organic phase in the recovery phase of the organic phase was 350 milliliters of Conosol® 170 exempt solvent, which was recycled by png from the settler back to the mixer at a rate of 45 milliliters per minute. In this way, the organic phase recovery blender was operated at 1/1 O / A. The concentration of LIX®984N in the organic phase of the recovery phase of the organic phase was monitored by removing 5 milliliters of the organic phase from the settler and adding 5 milliliters of the Conosol® 170 exempt solvent to the mixer. The sample of the organic phase of the organic phase recovery stage was then charged to the maximum by successive contacts with the aqueous solution of a pH of 1.9 containing a large excess of copper, and the copper concentration of the charged organic phase was determined by atomic absorption spectroscopy. The average parts per million of the organic phase of the circuit recovered in the recovery phase of the organic phase during each increment of time was calculated from the copper concentration based on a comparison of the organic phase concentration of the original circuit of the increase in the concentration of the extractant in the recovery stage. The results of the experiments are shown below.

Total Hours Total Liters Maximum Load Percentage ppm of the performance of Organic Refining (in vol / vol) Retention of circuit E2 (ppm of Cu) LIX®984N of Recuperada 3. 25 8.78 14.5 .0276 133 8. 08 21.82 23.8 .0453 88 13. 08 35.32 30.9 .0589 70 17. 75 47.93 36.0 .0686 60 23. 00 62.10 45.3 .0863 59 The data show that the recovery phase of the organic phase effectively accumulates the retained organic phase, the level of which continues to rise through a prolonged operation. According to the present invention, when the concentration of the extractant in the phase of the separated diluent reaches a desired level, additional diluent would be added to the mixer and a similar volume of the diluent separated from the settler would be removed and added to the solvent extraction circuit.

Claims (19)

1. R E I V I N D I CAC I O N S: 1. A method for recovering extractant from an aqueous efflufrom a continuous solvextraction circuit containing the extractant dissolved in a dilu comprising the steps of (a) contacting the effluwith a dilufor a sufficiperiod of time to allow the extractant to dissolve in the diluand (b) to separate the efflufrom the dilu which now contains an increased level of extractant. The method according to claim 1, wherein at least a portion of the separated diluis recycled by contacting an additional portion of the effluin step (a). 3. The method according to claim 2, wherein the separated diluis recycled for an average of one to about 30,000 times. . The method according to claim 1, wherein at least a portion of the separated diluis added to the solvextraction circuit. 5. The method according to claim 4, wherein the portion of the separated diluthat is added to the solvextraction circuit is more than 0.003 perc but not more than 50 perc 6. The method according to claim 1, wherein the diluis contacted with the effluby in-line mixing. The method according to claim 1, wherein the diluis contacted with the effluin a mixer-settler. The method according to claim 7, wherein the mixer-settler is operated with at least partial recycling of the separated dilu The method according to claim 8, wherein the portion of the separated diluwhich is recycled is greater than 50 percand less than 99.997 perc The method according to claim 1, wherein the diluis used to contact two or more aqueous efflu from the same solvextraction circuit. The method according to claim 10, wherein the diluis first contacted with a scrubbing effluand subsequy contacted with an extraction efflu 12. The method according to claim 1, wherein the extractant comprises a phenolic oxime. 13. The method according to claim 1,?. wherein the extractant is a hydroxyaryl oxime comprising (a) one or more hydroxyaryl ketone oxime compounds of Formula I or II, wherein R and R 'may be individually similar or differand are saturated aliphatic groups of 1 to 25 carbon atoms, ethylenically unsaturated aliphatic groups of 3 to 25 carbon atoms, or -OR1', wherein R '* is a group ethylenically unsaturated saturated aliphatic as defined; n is O or l and a and b are each 0, 1, 2, 3, 4 with the proviso that both are not zero and that the total number of carbon atoms in Ra and R'b is from 3 to 25, where R are already as defined with respect to Formula I and R '' 'is a saturated aliphatic group of 1 to 25 carbon atoms or an ethylenically unsaturated 3-alpha group of 3 to 25 carbon atoms, with the exception of that the total number of o ^ - s cs.rbon in Ra and R '' 'is from 3 to 25; and / or one or more hydroxy aryl aldoxime compounds of Formula III, wherein R is as defined in the foregoing with respect to Formulas I and II, b has a value of 1, 2, 3 or 4, and the total number of carbon atoms in Rc is from 3 to 25. 14. The method according to claim 12, wherein the oxime is selected from the group consisting of a 2-hydroxy-5-alkylbenzophenone oxime wherein the alkyl group contains from about 7 to about 2 carbon atoms; a 2-hydroxy-5-alkylbenzaldoxime wherein the alkyl group contains from about 7 to about 12 carbon atoms; a 2-hydroxy-5-alkylphenylmethyl ketone oxime wherein the alkyl group contains from about 7 to about 12 carbon atoms; an oxime of 2-hydroxy-5-nonylphenylbenzyl ketone; and mixtures thereof. 15. The method according to claim 14, wherein the benzophenone oxime is 2-hydroxy-5-nonylbenzophenone oxime. 16. The method according to claim 14, wherein the benzaldoxime is 2-hydroxy-5-nonylbenzaldoxime. 17. The method according to claim 14, wherein the benzaldoxime is 2-hydroxy-5-dodecylbenzaldoxime. 18. The method according to claim 14, wherein the alkylphenylmethyl ketone oxime is 2-hydroxy-5-nonylphenylmethyl ketone oxime. 19. The method according to claim 1, wherein the diluent is kerosene. HO. The method according to claim 1, wherein the amount of the diluent used to contact the effluent in step (a) is essentially equal to or less than a quantity of diluent required to replace the lost diluent of the extraction circuit by continuous solvent.