CA1061282A - Electrolytic recovery of metal from dispersion using cationic ion exchange agent - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A cyclic process for selective recovery of a metal from a material which contains other metal values in addition to the selected metal, comprises leaching the material with an aqueous solution capable of leaching metal values including the selected metal from the material. The resulting aqueous solution, containing the selected metal and other metallic contaminants, is dispersed in an organic medium comprising a cationic exchange reagent which is capable of selectively extracting the selected metal from the aqueous solution while rejecting any other metal values in the aqueous solution. The dispersion, comprising the aqueous solution and the organic medium containing the extracted metal, is passed as a flowing stream through a passageway defined by a conduit in which there are a plurality of mutually spaced, parallel, elongate electrodes. Flow of the dispersion is such that it is distributed uniformly about the electrodes. An alternating current potential is applied to the electrodes to create an A.C. electrical field within the passageway sufficient to electrically coalesce the aqueous phase of the flowing dispersion, and the aqueous phase is separated from the organic phase in a separation zone downstream from the electrodes. The selected metal values are stripped from the organic phase by dispersing the organic phase in an aqueous acidic stripping solution.
This dispersion is then resolved into an organic phase and an aqueous phase by flowing the dispersion through a passageway as described above. The selected metal is recovered in essentially pure form from the aqueous phase, and the organic phase can be used in further selective extraction of metal values from aqueous leach solution.

Description

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~ , ~ K-0447 . _ This invention relates to a cyclic process for the selective re~overy of a metal from a material containing the selected metal as well as other metal values and is described and illustrated herein as applied to an improved integrated process for recovering copper from copper-bearing ,.~, ' materials using selective, solvent extraction techniques.
Applying a high-voltage electric field to an oil-water dispersion to coalesce water droplets has been used in the petroleum industry to remove small amounts of water : 10 from oil distillates and crude oil~ Commercial application of electrical coalescence has generally been limited to dispersions containing only small amounts of water.
The electric field is customarily established by ~; immersing a plurality of electrodes in the dispersion. As the water content of the dispersion increases, coalesced water particles have a tendency to form conduc-ting bridges l between the immersed electrodes. Several early patents 3 (for example U.S. Patent Nos. 1,116,299; 1,980,722; and

2,072,917) suggested utilizing alternating current or ! 20 pulsating direct current to avoid the short circuiting of ~- the electrodes caused by the formation oE the conducting bridges. In U.S. Patent No. 2,000,018, uni-directional, high voltage impulses, having durations of not greater than ten microseconds, with a time interval between impulses of at least ten times the duration of the impulse, were required to be effective in inhibiting the formation of the conducting bridges.

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It has also been suggested (see U.S. Patent Nos.

3,074,870 and 3,567,619) to use a corona wind discharge to prevent the formation of conducting bridges. The iso-lation of the electrodes from the solution eliminates the .
conducting bridges; however, the corona wind discharge has been found to be rather ineffective in coalescing the water ~' particles in the dispersion.
~; Recent developments in the art have been directed to improved apparatus and processes for applying potentials of very high gradients to hydrocarbon dispersions which contain very small amounts of water. U.S. Patent Nos.
3,616,460 and 3,701,723 disclose systems using coaxially arranged electrodes, with the dispersion flowing longitu-dinally through the inter-électrode space. U.S. Patent No. 3,661,746 discloses a system for flowing the dispersion 'i along a vertical flow axis and through an electric field which increases monotonically in potential in the direction ~ of dispersion flow.
,.t In United Kingdom Patent No. 909,485 processes are ' 20 disclosed wherein an aqueous phase and an organic phase are ~- first intimately mixed, and the dispersion or mixture is subsequently separated into lts respective phases in a ; gravity settling tank. Improved settling rates were obtained by producing a high voltage electric field in the s settling tank in the region of the emulsion band separating the aqueous phase from the organic phase.
It is an object of the present invention to provide an improved process of the type above described.

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In accordance with the invention, the phases of an aqueous-organic dispersion, wherein the aqueous phase is dispersed in an organic continuum, are resolved by passing ,,~
the dispersion through a flow passageway comprising a conduit having a plurality of spaced, parallel elongate electrodes positioned therein. The electrodes are insulated elec--~ trically from the conduit and positioned therein so that the flow of dispersion through the conduit is distributed , uniformly about the electrodes. An alternating currént 10 potential is applied to the electrodes to produce an electric field th~ugh which the dispersion passes. The potential applied to the electrodes is of sufficient voltage to produce an electric field which electrically coalesces the ., aqueous phase of the dispersion as the dispersion passes ~; through the conduit. The voltage applied to each electrode ~, may range from 250 volts to 20,000. A major advantage of ~A~ the invention is that voltages in the range of 250 to 7500 volts are essentially as effective as higher voltages in the range of 7500 to 20,000 volts. The coalesced aqueous phase 20 is separated from the organic phase in a gravity separation~
zone downstream from the electrodes.
The process according to this invention is useful in separating the phases of emulsions or dispersions produced in liquid-liquid contact operations. In such operations, two immiscible liquids, generally a liquid, organic ion exchange medium and an aqueous exchange solution are intimately contacted in a mixing device to effect an inter-facial transfer of a solute from one of the liquids to the other. The emulsion or dispersion produced by the intimate ~0~ 28Z

contact of the iwo liquids in the mixing device is intro-duced into a settling tank wherein the quiescent emulsion or suspension is allowed to separate into two separate liquid phases under the influence of gravity. The emulsion or dispersion formed in the mixing apparatus is continually passed through a flow passageway which has a plurality of electrodes disposed therein. An alternating current potential in the range of 250 to 20,000 volts is applied to ; --the electrodes to create an electric field which coalesces *' 10 the aqueous phase of the dispersion as it passes through the flow passageway, and the coalesced aqueous phase is separated from the organic phase in the settlin~ tank.
In practicing the process according to the invention,for selective solvent extraction of a metal, such as copper, from a material containing the same, an aqueous leach solution is used to leach the selected metal together with other metal-bearing material. The resulting pregnant leach solution, containing dissolved metal values, is mixed with an organic medium carrying a cationic hydrogen exchange reagent, which has a high affinity for seIected cationic metal ions and a low affinity for other contaminating metal ions contained in the pregnant leach solution. The selected cationic metal ions, such as copper ions, in the pregnant leach solution are exchanged for the hydrogen ions of the cationic exchange reagent, thereby producing a dispersion comprising an aqueous phase containing exchanged hydrogen ions and an organic phase containing the selected metal ions and the cationic exchange reagent. The dispersion is then passed through an electrically conductive, grounded conduit having a plurality of mutually spaced, parallel elongate , z~

electrodes disposed in the conduit so that the flow of dispersion is distributed uniformly about the electrodes.
The flowing dispersion is subjected to an electric field by applying an alternating current potential to the electrodes in the conduit. The potential applied to the electrodes is o~ sufficient voltage to produce an electric field which electrically coalesces the aqueous phase of the dispersion.
The electrically-treated dispersion is forwarded to a gravity settling tank, wherein the coalesced aqueous phase is separated by gravity from the organic phase which contains the metal-bearing organic exchange reagent. The aqueous phase i5 recycled as leach solution for further leaching the metal-bearing materials.
The organic phase containing the metal-bearing cationic exchange reagent is forwarded to a stripping stage, wherein it is intimately contacted with an aqueous acid stripping solution,. The hydrogen ions of the stripping solution are exchanged for metal ions of the cationic exchange reagent, thereby producing a dispersion comprising an aqueous portion containing exchanged ions of the selected metal and an organic portion containing the cationic hydrogen ion exchange reagent. The dispersion is passed through another electrically grounded conduit and subjected to an electrical field treatment in the same manner as hereinfore described for treating the dispersion formed from the pregnant leach solution. The resulting electrically treated dispersion is forwarded to a gravity settling tank wherein the coalesced aqueous metal-bearing phase is separated from the organic phase which contains the cationic ".,, . .

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hydrogen ion exchange reagent. The organic phase i5 recycled as the reagent used to extract metal ions from ~ the pregnant aqueous leach solution. The enriched aqueous ', solution containing the selected metal is an essentially impurity-free solution which can be further treated to recover metal therefrom in essentially pure form. When the selected metal is copper, the impurity-free solution is electrolyzed to produce high quality cathode copper, and ` the aqueous acid solution which is produced during the ` 10 electrolysis is recycled for use as the stripping solution in the stripping stage.
i The invention and the best mode of carrying it into practice will~ now be descri~ed in detail with xeference to the accompanying drawings, in which:
Fig. 1 is a flowsheet illustrating the invention as applied in an integrated cyclic process for extraction of copper from copper-bearing materials using solvent extraction techniques;
Fig. 2 is a perspective view of apparatus for use 20 in the practice of the process according to the present invention;
Fig. 3 is a vertical section taken along the line 3-3 of Fig. 2; and Fig. 4 is a fragmentary horizontal section taken along the line 4-4 of Fig. 3.
The present invention is particularly adapted to be used in combination with liquid-liquid contact operations wherein two immiscible liquids, generally an '"
organic liquid and an aqueous solution, are intimately contacted, preferably in continuous fashion in a mixing device to produce a dispersion of the aqueous phase in the organic liquid and to effect interfacial transfer of a solute from one of the liquids to the other. In such operations, the aqueous portion of the so formed dispersion is present in substantial amounts i.e. 10 percent or more by volume. Customarily, the aqueous portion is present in about equal proportions with the organic liquid.

The dispersion is withdrawn from the mixer, preferably as a continuous flowing stream, and passed through a passageway having a plurality of electrodes dis-posed therein as hereinbefore described. The dispersion is subjected to an electric field by applying an alternating current potential to the electrodes, and the electrically-treated dispersion is delivered to a settler wherein the coalesced aqueous phase separates from the organic phase.
The flowsheet of Fig. 1 illustrates the invention as applied to an integrated cyclic process for recovering high quality copper from a copper-bearing material. The copper bearing material, such as mine ore, ore concentrates, the waste dump of a mine, and scrap metals containing copper, is contacted with an aqueous, leach solution, e.g. a weakly acidic solution of sulfuric acid and ferric sulfate. The leach solution dissolves copper and other metallic materials, such as iron, from the material being leached, and the pregnant leach solution is collected in a catch basin.

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The pregnant leach solution containing copper i values and other metal ions is forwarded to a mixer wherein -~ it is intimately mixed with and dispersed in an organic, ;, liquid medium containing a cationic, hydrogen ion exchange , reagent which has a high degree of affinity for copper ions and a low affinity for the other metallic ions. The copper ions are selectively transferred from the aqueous , phase to the organic phase of the dispersion, and hydrogen , ions are transferred from the organic phase to the aqueous phase.
The resulting dispersion is withdrawn from the -' mixer and is passed as a flowing stream through a coalescer passageway defined by a conduit in which a plurality of mutually spaced, paralle~ elongate electrodes are positioned.
, The electrodes are electrically isolated from the conduit and disposed in the conduit so that the flow of aispersion is distributed uniformly about the electrodes. The dispersion is subjected to an electric field as it flows through the conduit. The electric field is established by applying an alternating current potential to each of the electrodes in the conduit. The potential is of sufficient voltage to electrically coalesce the aqueous phase of the dispersion as the dispersion passes through the electric field. Preferably, the conduit is made of an electrically conducting ma~erial and is grounded. The potential is then applied to the electrodes to create an electrical field between the electrodes and the conductive grounded condui~. When the conduit is made of a non-conductive material the potential is applied to the electrodes to create an electrical field between alternating electrodes.

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-The electrically-treated dispersion flowing from the ;~,; conduit is introduced into a gravity settling tank, wherein the coalesced aqueous phase is separated from the organic phase, which contains the copper-bearing cationic exchange reagent. The aqueous phase is recycled as leach solution .;
; for further leaching of copper-bearing materials in the ~' leach step.
The organic phase, containing the copper-bearing cationic exchange reagent is forwarded to a second mixer wherein it is intimately mixed with an aqueous acidic stripping solution to form a dispersion of the aqueous solution in the organic continuum. The aqueous solution - strips copper from the cationic exchange reagent by exchanging hydrogen ions from the aqueous solution with copper ions from the cationic exchange reayent. The resulting dispersion comprises an aqueous phase containing exchanged copper ions and an organic phase containing the hydrogen form of the cationic exchange reagent, A dispersion is withdrawn from the second mixer and is passed as a flowing s~ream through a second coalescer ! passageway which is of the same construction as the first mentioned coalescer passageway described hereinbefore. The flow of dispersion is subjected to an electric field in a -' manner similar to that described hereinbefore. The electrically treated dispersion, flowing from the second coalescer, is fed to a second gravity settling tank wherein the coalesced, copper-bearing, aqueous phase separates from the organic phase, which contains the hydrogen form of the cationic ion exchange reagent.

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`~ The organic phiase is withdrawn from the second settling tank and is recycled as the organic medium to be , mixed with the pregnant leach solution coming -from the catch basin. The impurity-free copper-bearing aqueous phase is further treated to recover the copper values therefrom. As shown, the aqueous solution can be subjected to electrolysis whereby high quality copper and an acidic :.-; aqueous solution are produced. The acidic aqueous ., .
"- solution is advantageously recycled for use as the stripping solution in the second mixer.
Apparatus suitable for use in carrying out the process according to the present invention is shown in Figs. 2-4. The apparatus comprises a mixing chamber 10 connected by a flow passageway 11 to a settling tank 12.
The mixing chamber 10 is adapted to intimately mix an aqueous liquid and an organic liquid to produce a dispers~n of the aqueous phase in the organic continuum. The organic and aqueous liquids are introduced continuously into the mixing chamber through inlet pipes 13. The mixing chamber , 20 is equipped with means such as the mixing impeller 14 and drive motor 15, for mixing the organic and aqueous liquids to continuously form a disper~on thereof.
,, The aqueous-organic dispersion is withdrawn con-, tinuously from the top of the mixing chamber and flows ~;~ throu~h the passageway 11 to the settling tank 12. The t~- passageway is defined by an electrically-conductive conduit which connects t~e top of the mixing chamber to the top of ,~ the settling tank 12. A plurality of mutually spaced elongate electrodes 16 are supported in the passageway 11 in electrical isolation therefrom. As shown, the electrodes 16 comprise ~, .

an electrically conductive probe 17 encapsulated by an electrical insulating material 18, the probe 17 extending .~ from the top end of the encapsulating material (see Figs. 3 and 4). The electrodes are inserted into the passageway 11 . through openings therein so that the insulating material 18 contacts and seals the openings in the passageway. The the electrodes are disposed in/passageway so that the flow of dispersion therethrough is uniformly distributed about the electrodes. Means are provided for applying an alternating current potential to the.ends of probes 17 and for grounding the conductive conduit which forms the passageway 11. The potential applied to the probes 17 is of sufficient voltage to electrically coalesce the aqueous phase of the dispersion i` the . as the dispersion flows through~passageway.
The electrically coalesced dispersion flows into ., the settling.tank 12, wherein the coalesced aqueous phase 19 separates from the organic phase 20 under the influence of gravity. The organic phase is withdrawn from the settling tank 12 through an outlet pipe 21 located near the top of the tank, and the aqueous phase is withdrawn through an outlet pipe 22 located near the bottom of the tank. If the organic phase has a density greater than that of water, it -, would settle to the bottom of the tank and withdraw through outlet pipe 22. In such case, the aqueous phase would be withdrawn from the settling tank through outlet pipe 21.
~s shown in FIGS. 2-4, the electrodes 16 are preferably disposed in passageway 11 with their longitudinal ii128Z

axes generally transverse to the flow of dispersion in the passageway. However, the electrodes may be positioned with their axes at an angle to the path of flow of dispersion.
The electrodes are shown as extending from the top to the bottom of the flow passageway; however, they could just as well extend from one side to the other of the flow passageway.
The electrodes are also preferably positioned in .
rows which extend generally transversely across the path of flow of the dispersion. ~owever, the rows of electrodes can be positioned at an angle with respect to the path of flow of the dispersion. The electrodes are preferably positioned in three or more rows with the electrodes in the odd-numbered rows staggered with respect to the electrodes in the even-numbered rows. The electrcdes may have any cross-sectional shape, but the cylindrical shape shown in the drawings is preferred. The electrodes may be spaced ap~t at any desirable distance.
The passageway 11 may be made of a non-conductive conduit, in which case the alternating current potential is applied to the elongate electrodes to create an electrical field between alternating electrodes.
The invention will further be described with reference to the following examples:

~ n aqueous leach solution containing dissolved copper values was obtained from a commercial operation for leaching copper values from the waste dumps of a copper mine .. . . . ~ . . .

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` with an aqueous acidic leach solution. The copper-bearing : ~, leach solution was dispersed in an equal volume of an organic liquid made by dissolving in kerosene a cationic hydrogen exchange reagent. The so formed dispersion was continuously withdrawn from the mixing tank and passed as a flowing stream through a passageway to a gravity settling tank. The dispersion separated into its aqueous and organic phases, and the two phases were withdrawn separately from the settling tank so as to maintain steady-state conditions therein. The aqueous and organic phases withdrawn from the settling tank were returned to the mixer.
The apparatus was essentially similar to that shown in Fig. 2 with the exception that there were no electrodes positioned in the passageway 11.
The capacity i.e., throughput, of the settling tank was~ found to be approximately two gallons per minute per square foot of horizontal cross-section of the settling tank.

The procedure ofE~ample 1 was repeated with the exception that several separate modifications were made to the passageway connecting the mixing tank and the settling tank, so that the dispersion flowing through the passageway was subjected to an electric field.
One modification consisted of wrapping an electrical coil around the passageway. The electrical field produced by the coil, when a potential of 7000 volts was connected , .~ . . . . .. . .. . - , . . . . . . .. . . ..

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thereto, improved the coalescence of the aqueous phase, and the capacity of the settling tank was increased to : ;
approximately 7 gallons per minute per square foot.
A second modificationconsisted of positioning a series of insulated, plate electrodes in the passageway.
Each electrode consisted of a copper conductor sealed between two pieces of plastic, thus insulating the electrode from the flow of dispersion in the passageway. Alternating plates were connected to an electrical potential and the remaining plates were grounded. The plates were positioned in longitudinal alignment with the path of flow of dispersion in the passageway, and the plates were equally spaced from each other and the sides of the passageway so that the flow of dispersion was distributed uniformly about the plates.
The electric field produced when a potential of 7000 volts was connected to the alternating plates improved the coalescence of the aqueous phase, and the capacity of the settling tank was increased to approximately 8 gallons per minute per square foot.
Another modification consisted of positioning three rows of insulated electrodes in the passageway. The electrode configuration was essentially the same as that shown in Figs. 2-4. The electrodes comprised plastic dowels i.e., tubes, which were inserted through openings in the top of the passageway. The dowels fit tightly in the holes so as to form a seal, and an electrically conducti~e wire was positioned coaxially inside each dowel. Results obtained with this modification were superior to the results obtained with either - . . . - ~ . . . ; :, .

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-of the first two modifications. The coalescence of the i aqueous phase was markedly increased with a decrease in potential being applied to the electrodes. When a 4000 ,- volts alternating current potential was applied to the r electrodes positioned within the dowels, with the passage-way grounded, the capacity of the settling vessel was increased to 10 gallons per minute per square foot.
'-` It was found that direct current has no coalescing effect on the dispersion and that alternating current must be applied to the electrodes to create an electrical field j between the electrodes and the grounded conduit, or, when - a non-grounded or non-conducting conduit is employed, to create an electrical field between alternating elongate electrodes.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cyclic process for selectively recovering a metal from a material containing the selected metal and other metallic values, comprising the steps of:
(a) leaching said material with an aqueous leach solution;
(b) recovering a pregnant, aqueous, leach solution containing the selected metal and other metallic con-taminants dissolved therein;
(c) intimately mixing the recovered aqueous leach solution with an organic medium containing a cationic hydrogen ion exchange reagent which is capable of selectively extracting the selected metal from the aqueous solution by exchanging hydrogen from the exchange reagent for the selected metal ions in the aqueous solution, thereby producing a dispersion comprising (1) an aqueous portion containing-said other metallic contaminants and exchanged hydrogen ions, and (2) an organic portion containing the cationic exchange reagent and the selected metal values;
(d) passing the dispersion from step (c) through a conduit having a plurality of spaced parallel elongate electrodes disposed therein so that the flow of dispersion in the conduit is distributed uniformly about the electrodes;

(e) subjecting the flow of dispersion in step (d) to an alternating current electric field by applying a potential to the electrodes in the conduit,of sufficient voltage to electrically coalesce the aqueous phase of the dispersion as it flows through the conduit;
(f) feeding the electrically treated dispersion from step (e) to a gravity settling tank wherein the coalesced aqueous phase is separated from the organic phase;
(g) recycling the aqueous phase as leach solution for further leaching of the material;
(h) intimately mixing the organic phase from step (f) with an aqueous acid stripping solution, whereby hydrogen ions of said stripping solution are exchanged for the selected metal ions of said organic phase, thereby producing a dispersion comprising an aqueous portion con-taining the selected metal and an organic portion containing the cationic hydrogen ion exchange reagent;
(i) passing the dispersion from step (h) through a second conduit having a plurality of mutually spaced parallel elongate electrodes disposed therein so that the flow of dispersion in the conduit is distributed uniformly about the electrodes;
(j) subjecting the flow of dispersion in step (i) to an alternating current electric field by applying to each of the electrodes in said second conduit a potential of sufficient voltage to electrically coalesce the aqueous phase of the dispersion as it flows through said second conduit;
(k) feeding the electrically treated dispersion from step (j) to a gravity settling tank wherein the coalesced aqueous phase which contains the selected metal values is separated from the organic phase which contains the cationic hydrogen ion exchange reagent;

(l) recycling the organic phase from step (k) as the organic medium containing a cationic hydrogen ion exchange reagent to be mixed with further leach solution as in step (c); and (m) recovering the selected metal values from the aqueous phase obtained in step (k).

2. A process according to claim 1, wherein the selected metal is copper recovered from a copper-bearing material.

3. A process according to claim 1, wherein the aqueous leach solution recovered in step (f) contains dissolved copper ions, and hydrogen ions of the organic exchange medium are exchanged for said copper ions during the mixing of the organic medium and the aqueous solution in step (c).

4. A process according to claim 1, wherein said organic exchange medium comprises a liquid organic medium containing a cationic copper ion exchange reagent, said aqueous solution contains hydrogen ions, and said copper ions are exchanged for said hydrogen ions during the mixing of the organic medium and the aqueous solution in step (c).

5. A process according to claim 1, wherein the voltage of the alternating current potential applied to the electrodes in step (e) is in the range of 250 to 20,000 volts.

6. A process according to claim 5, wherein said potential is in the range of 250 to 7000 volts.

7. A process according to claim 2, wherein the copper is recovered from the aqueous phase obtained in step (k) by passing an electrical current through said aqueous solution to deposit the copper as high quality cathode copper and produce an acidic aqueous solution which is recycled for use as acid stripping solution in step (h).