Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/30—Oximes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/38—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds containing phosphorus
  • C22B3/384—Pentavalent phosphorus oxyacids, esters thereof
  • C22B3/3846—Phosphoric acid, e.g. (O)P(OH)3
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• This invention relates to the solvent extraction of metals and, more particularly, to a method for the removal of metal cation species in solvent extraction by galvanic stripping with added metals.
• Aqueous solutions that contain one or more dissolved metals in ionic form may be subjected to solvent extraction for the recovery of one or more desired metals.
• the desired metal ions are usually extracted from aqueous solution into an organic solvent containing an extractant and are recovered from the loaded solvent by stripping with a suitable aqueous strip solution.
• the other metals, present as ions in the aqueous solution as impurities, must often be removed from the process as they may cause difficulties in the stripping of the desired metal, and often increase in concentration in the circulating solvent to an extent that affects the efficiency of the extraction process.
• Methods that are used alone and in combinations for removing desired and impurity cations present in solvent extraction processes include the conventional stripping or selective stripping with acidic or basic solutions and the more recently developed hydrogen reductive stripping, hydrolytic stripping and electrolytic stripping. Stripping is often accomplished with acids or bases under ambient or elevated conditions. Hydrogen reductive stripping is carried out at temperatures between 150 and 350°C under elevated pressure and usually in the presence of seed metal particles to produce a metal powder. In hydrolytic stripping, loaded solvent is subjected to elevated temperatures (100-250°C) in the presence of water whereby metal oxides or hydroxides are formed. Hydrogen reductive stripping and hydrolytic stripping have been reviewed by Monhemius, A.J., Mintek 50, pp. 599-609. Electrolytic stripping has been applied to a loaded solvent by subjecting the solvent to electrolysis with electrodes placed in the loaded solvent (Wan, R.Y., etal., J. of Metals, Dec. 1986, pp. 35-40).
• Ferric iron may also be stripped from various loaded organic solvents into the aqueous phase with an acid alone or combined with the introduction of sulfur dioxide or hydrogen sulfide to reduce ferric to ferrous.
• the stripping may be carried out at ambient or elevated temperatures and pressures. It is noted that iron is usually present in solvent extraction processes as ferric and that, in many cases, ferrous is the stable form in the aqueous phase.
• the Shibata et al. method is operable with zinc powder or metals other than iron and zinc.
• the Shibata et al. method is operable with organics other than D2EHPA, or that actual deposition of a metal species dissolved in an organic liquid would occur in the organic phase onto an added solid metal.
• addition of a solid metal to an organic phase would make it possible to reduce metal ions other than ferric ions in the organic phase from a higher to a lower state of oxidation.
• the present invention seeks to provide an excellent and simple way to separate a wanted cation species from another one in an organic liquid, the species being either a desired or an undesired species.
• many metal cations can be readily reduced in a loaded organic liquid by contacting loaded organic liquid with a suitable solid metal or solid metal alloy causing a galvanic reaction.
• aqueous solutions containing metal cations that may include cations of both desired metal and impurity or secondary metal, are treated with an organic liquid extractant or solvent suitable for the extraction of cations of the desired metal, cations of at least one secondary metal being co-extracted.
• the loaded organic phase containing either cations of a desired metal or cations of desired metal together with cations of secondary metal is contacted with a solid metal or solid metal alloy capable of reducing in the organic phase either cations of a desired metal or cations of a secondary metal from a higher to a lower state of oxidation.
• the cations of an extracted metal are reduced to the lower state of oxidation and are either deposited (cemented) in the metallic state onto the solid metal or solid metal alloy, or are partially reduced in the organic phase to a lower oxidation state, which is easily stripped, with the solid metal or solid metal alloy being oxidized in part.
• the method of galvanic stripping is carried out at ambient pressures and at ambient or slightly elevated temperatures. It is understood that the term solid metal will De used hereinafter to denote and is hereby defined to include joth solid metals and solid metal alloys.
• alvanic stripping is useful for the removal of cations of a esired metal, or cations of a secondary metal, from an organic iquid into which it has been extracted from an aqueous
• Galvanic stripping is also useful for the partial reduction to a lower state of oxidation and for the removal of cations of secondary metals from an organic liquid.
• cations of the secondary metal are reduced to a lower state of oxidation and are removed by stripping into an aqueous phase. Reduction and stripping may be carried out selectively and separately in two steps or simultaneously in one step.
• the stripping of cations of the desired metal may be carried out either before or after the contacting with solid metal and the removal of cations of the reduced secondary metal from the organic phase.
• the solid metal is preferably used in particulate form.
• the use of a solid metal reductant makes it possible to directly reduce cations of a metal, especially cations of those metals that may be difficult to transfer from the organic phase in their normal oxidation state, into the solid state or in a partially reduced form (but usually still in cationic form) to allow easy stripping.
• the method according to the invention eliminates the use of high temperatures and/or pressures, and the need to deal with stripping solutions that are not easily treated, or are chemically or environmentally undesirable.
• a method for the extraction of cations of at least one metal from an aqueous solution with an organic liquid capable of extracting cations of said at least one metal in a higher state of Oxidation from said solution said aqueous solution containing cations of metals chosen from the group consisting of a) cations of a desired metal and b) cations of a desired metal together with cations of at least one secondary metal, cations of said at least one secondary metal being co-extracted from the aqueous solution by the organic liquid
• said method comprising the steps of: (1) mixing said aqueous solution with said organic liquid for the formation of an aqueous raffinate phase and an organic phase containing cations of said at least one metal; (2) separating said aqueous raffinate phase from said organic phase; (3) contacting separated organic phase with a solid metal capable of reducing in said organic phase at least a portion of said cations of metals from said higher state of oxid
• a method wherein said cations of metals comprise both cations of a desired metal and cations of at least one secondary metal, cations of said desired metal and cations of said at least one secondary metal are extracted into said organic phase, cations of said desired metal are stripped from separated organic phase with a stripping solution capable of stripping cations of said desired metal from separated organic phase prior to said contacting with solid metal while substantially leaving cations of said at least one secondary metal in said organic phase, and cations of said at least one secondary metal are reduced to said lower state of oxidation in said contacting.
• a method wherein said cations of metals comprise cations of a desired metal and cations of at least one secondary metal, cations of said desired metal and cations of said at least one secondary metal are extracted into said organic phase, cations of said at least one secondary metal are reduced to a lower state of oxidation in said contacting while substantially leaving cations of said desired metal in said organic phase to provide organic liquid having a reduced content of cations of secondary metal and having left cations of the desired metal therein, and stripping cations of said desired metal from said organic liquid having a reduced content of cations of secondary metal with a stripping solution capable of stripping cations of said desired metal from said organic liquid prior to returning liquid having a reduced content of cations of secondary metal to said mixing of step (1).
• cations of metal comprise cations of a desired metal, and wherein cations of said desired metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited desired metal is removed from said organic liquid.
• Solvent extraction or liquid-liquid extraction is a versatile method for the selective separation of metals.
• the separation involves the mass transfer of metal cations across boundary interfaces between two contacting, insoluble phases, i.e. an organic phase and an aqueous phase.
• the degree of extraction is influenced by the selectivity among various cations in the solution and the pH.
• the process functions very well using straight-forward, reversible loading and stripping.
• reactions are less easily attained by simple shifts in chemical equilibria, and it is in these cases that the galvanic stripping method of the present invention finds particular application.
• the galvanic stripping of this invention is particularly valuable for the recovery of certain desired cations and for the removal of co-extracted cations of impurity, unwanted or secondary metals, especially iron.
• an added solid metal reductant provides an electrochemical driving force to alter the oxidation state or, in general, modify the equilibrium of inorganic ions dissolved in organic liquids.
• Equation (1) shows the reduction of the M j ion to metal j , s » by added solid metal
• M , x This reduction is similar to but by no means the same as the displacement (or cementation) reactions commonly encountered in aqueous chemical processes.
• the M j ion is only partially reduced by solid metal M 2(s « to a lower oxidation state, altering the equilibrium and allowing easier stripping into an aqueous phase. In both cases, M 2 remains in the organic phase as an oxidized stable species.
• M 2 as a reactant for j in such a system then requires that a) added solid metal 2 is capable of forming a stable R-M 2 species, and b) the potential of the half cell M 2 /R-M 2 is less noble than that of M/R-M j .
• These conditions are necessary, but not necessarily sufficient, to insure reaction.
• the added solid metal must be capable of reducing a metal extracted into an organic liquid to a lower state of oxidation.
• Aqueous solution containing one or more dissolved metal species, in the form of cations or, in some cases, complexed as anions, is mixed with an amount of an organic liquid capable of extracting cations or complexed anions of a desired metal.
• the organic liquid is usually premixed with a diluant, a modifier may be added, and the organic liquid may be equilibrated or conditioned prior to mixing with aqueous solution.
• Aqueous solution and organic liquid are mixed to form a loaded organic raffinate phase and an aqueous phase, which are subsequently separated. If desired, the loaded organic phase may be scrubbed with a scrub solution.
• a scrub raffinate is separated and loaded (scrubbed) organic phase is stripped with a strip solution to form a strip liquor and a stripped organic liquid. Cations of the desired metal are recovered from the separated strip liquor and the stripped organic liquid is regenerated, purified and recycled to the extraction.
• an amount of suitable solid metal is added to the loaded organic phase, after separation from the aqueous raffinate phase.
• the suitable solid metal must be capable of reducing cations of the metal to a lower oxidation state, either to its elemental form, i.e. the metallic state, or to a partly lowered oxidation state.
• the amount of added solid metal should be at least stoichio etric to accomplish the reactions, but is added preferably in excess of the stoichiometrical amount required to effect the reduction.
• the solid metal may be added in the form of sheets or coupons but is preferably added in a particulate form such as chips, pellets, granules or powders. Although coarse reductant effects the reduction, small particle sizes increase the rate and efficiency considerably. A broad range of particle sizes may be used, such as in the range of from about 44 to 6000 microns. The particle sizes are preferably in the range of from about 44 to 600 microns.
• the reduction may be carried out in an oxidizing, neutral or reducing atmosphere to suit the needs of the desired reaction. The reduction is preferably carried out in the absence of oxygen, as, in the case of some metals, oxygen (air) tends to re-oxidize cations of the reduced metal and to lower the efficiency. If desired, the reduction may be carried out in the presence of nitrogen, which is essential in some cases to avoid re-oxidation.
• the galvanic stripping is carried out at ambient pressures and at ambient temperatures.
• the rate of reduction may be increased by using elevated temperatures.
• slightly elevated temperatures such as, for example, up to about 60°C may be used.
• the temperature may, therefore, be in the range of from ambient to about 60°C. Efficiency is increased with good mixing during the contacting and stripping steps.
• the loaded organic phase is contacted with the solid metal for a period of time sufficent to reduce at least a portion of cations of the metal in the organic phase.
• Contact times may be in the range from about 1 to 90 minutes, preferably about 15 to 60 minutes.
• the contacting - may be carried out continuously or intermittently in a column loaded with reductant by passing the loaded organic phase through the column. Alternatively, the contacting may be carried out by mixing reductant with the loaded organic phase in a suitable vessel provided with agitation.
• D2EHPA di-2-ethylhexylphosphoric acid
• Aliquat ⁇ 336 is tri-(C 8 C 10 ) methylammonium chloride
• LIX TM 622 is a mixture of LIX TM 860 (5-dodecylsalicylaldoxime) with tride- canol
• LIX TM 864 is a mixture of LIX TM 64N, which is 1 vol % LIX TM 63 (5, 8-diethyl-7-hydroxy-6-dodecanone oxime) in LIX TM 65N (2-hydroxyl-5-nonylbenzophenone oxime)
• iron denotes low carbon steel or electrolytic iron.
• the resulting organic phase contains, in addition to cations of the desired metal, the above-noted ferric complexes which are strongly stable.
• a suitable solid metal that is capable of reducing the ferric to the ferrous form.
• Suitable solid metals are selected from the group consisting of zinc, manganese and magnesium, the use of zinc being preferred. Certain alloys, such as, for example, low carbon steel or zinc containing a small amount of lead (e.g. 0.2%) may also be used.
• Cations of the desired metal may be stripped from the organic phase with a stripping solution capable of stripping cations of the desired metal from the organic phase, either before or after the contacting with solid metal, and removing cations of the secondary metal in its partially reduced state of oxidation.
• galvanic stripping reactions of iron with the preferred solid metal i.e. activated zinc
• the galvanic stripping reactions of iron with the preferred solid metal may be represented by the equations (5), and (6) and (7):
• *Zinc may remain in the organic phase if solution is dilute.
• Equation (5) illustrates the reduction and stripping being accomplished simultaneously in one step, and equations (6) and (7) sequentially in two separate steps.
• the contacting may be carried out as described above and with similar conditions of time, temperature, pressure and particle sizes to reduce at least a portion of cations of the secondary metal in the organic phase from a higher to a partially reduced lower state of oxidation, i.e. ferric to ferrous ion.
• the organic liquid may be one of a number of extractants into which iron is co- extracted such as, for example, phosphoric acids such as di-2-ethylhexylphosphoric acid (D2EHPA), mono-2-ethylhexylphosphoric acid (M2EHPA) and mixtures thereof, phosphonics such as the mono-2-ethylhexyl ester of 2- ethylhexylphosphonic acid (PC88A, tradename), phosphinics such as bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex TM 272) , and (LIX 64N) which is a mixture of LIX 65N ( 2-hydroxy-5- nonylbenzophenone oxime) and 1% LIX 63 (5, 8 -diethyl-7- hydroxy-6-dodecanone oxime).
• phosphoric acids such as di-2-ethylhexylphosphoric acid (D2EHPA), mono-2
• the loaded organic phase is contacted with particulate zinc under the appropriate conditions, as described.
• the solution is stripped with an acid such as sulfuric or hydrochloric acid.
• an acid such as sulfuric or hydrochloric acid.
• the strength of the acid may range from 20 to 100 g/L H 2 S0 4 or 30 to 100 g/L HC1, dependent on the organic.
• the reduction of ferric in the loaded organic phase with zinc powder then allows stripping with a sulfuric acid solution at a value of the pH of about 3. At this pH value the zinc remains in the organic phase, providing a selective separation from the iron. At a pH below about 3.5, no iron or zinc hydroxides precipitate.
• the pH should also have a value of below about 3.5.
• zinc metal and acid stripping solution are both added to the loaded organic phase. After the desired contact time under the desired conditions, as described, the phases are separated, the ferrous iron reporting to the aqueous phase. If desired," using the appropriate conditions, a portion or virtually all of the iron can be removed from the organic phase using either the one-step or the two-step method. It is noted that the reduction substantially takes place in the organic phase, as ferric ions do not readily strip into the aqueous phase.
• an aqueous solution contains cations of a desired metal together with cations of a secondary metal
• the method is carried out as follows.
• the aqueous solution is mixed with an organic liquid capable of extracting cations of the desired metal and co-extracting cations of the secondary metal to form an aqueous phase and a loaded organic phase containing both cations of the desired metal and cations of the secondary metal.
• the secondary metal is substantially present in a higher oxidation state.
• the loaded organic phase is separated from the aqueous raffinate phase.
• Cations of the desired metal are then stripped, if desired after scrubbing, from the loaded organic phase with a stripping solution capable of stripping cations of the desired metal from the organic phase while substantially leaving cations of the secondary metal in the higher oxidation state in the organic phase.
• the organic liquid is subsequently contacted, batch-wise, continuously or intermittently, with a solid metal for the reduction of at least a portion of cations of the secondary metal from the higher state of oxidation to a partially reduced state of oxidation.
• Cations of the secondary metal in the partially reduced state of oxidation are stripped from the organic liquid with a stripping solution capable of stripping cations of partially reduced secondary metal from the organic liquid with the formation of a regenerated organic liquid having a reduced content of cations of the secondary metal.
• the regenerated organic liquid is returned to the extraction step.
• cations of the secondary metal in the higher state of oxidation in the separated loaded organic phase are first partially reduced and stripped from the organic liquid without substantially reducing or stripping cations of the desired metal in the organic, and cations of the desired metal are then stripped from the organic phase, leaving a regenerated organic liquid with a reduced content of cations of secondary metal for return to the mixing step for extraction of metal.
• This embodiment may, for example, be applied to a solution containing indium as desired metal and iron as secondary metal, and using commercial grade di-2-ethylhexylphosphoric acid, which contains mono-2-ethylhexylphosphoric acid, dissolved in kerosene. Cations of both metals are substantially extracted into the organic liquid.
• the indium is stripped from the loaded organic phase with dilute hydrochloric acid (1-3 normal) substantially leaving the iron in the organic phase.
• the organic phase is then contacted, as described, with zinc having particle sizes from about 44 to 6000 microns, preferably about 74 to 150 microns, in the presence of nitrogen and at temperatures of from ambient to about 60°C.
• the ferrous iron is stripped from the organic phase with a sulfuric acid stripping solution containing 20 to 100 g/L sulfuric acid.
• the organic liquid with a reduced iron content is returned to the extraction.
• the reduction and the stripping of ferrous iron may be carried out simultaneously in one step or separately in two steps.
• this embodiment may also be used for the partial reduction of other multivalent metal cations such as Ce, Mn and Cr.
• the method of the invention may be used in a number of applications.
• the method is suitable for the selective removal of cations of a metal from an aqueous solution by solvent extraction, the metal cation being of a desired metal or of a secondary metal; for the removal of cations of a metal from an organic liquid that is difficult to remove in its normally occurring oxidation state; for the removal of cations of one or more co-extracted secondary metals from an organic liquid being used for the recovery of a desired metal; or for the coating of a metal on the added solid metal as a substrate.
• solvent-solid metal combinations especially designed to effect such applications may be used.
• This example illustrates that the galvanic stripping can be carried out in two stages to achieve 100% iron stripping and removal.
• An organic liquid loaded with 1.0 g/L iron was mixed with zinc granules for 30 minutes under nitrogen. Metallic zinc was then removed, and the resulting organic phase was stripped with 10 g/L sulfuric acid for five minutes. Analysis showed that complete reduction and stripping of iron was achieved.
• Example 2 To examine the effects of reoxidation of the ferrous iron, the nitrogen was removed from above the organic and aqueous strip solutions obtained in Example 2. The two phases were allowed to mix in a vessel open to the air. After 30 minutes, it was found that 20% of the stripped iron was re-extracted back into the organic phase.
• the galvanic stripping was carried out in one step with the addition of 99.8% pure zinc granules having particle sizes of 1000 to 2000 microns and a total surface area in the range between 15 and 35 cm 2 .
• the galvanic stripping was carried out at temperatures between 20°C and 60°C with the addition of from 2 to 7 g of zinc granules which is in excess of the amount stoichiometrically required for the reduction of the ferric present to ferrous, and in a solution containing from 20 to 100 g/L sulfuric acid.
• Example 5 The loaded organic phase was heated to the desired temperature, sparged with nitrogen for five minutes and zinc and preheated sulfuric acid solution were added. The mixture was then agitated in a closed vessel for 30 minutes. The desired number of samples were taken and analyzed.
• Example 5 The loaded organic phase was heated to the desired temperature, sparged with nitrogen for five minutes and zinc and preheated sulfuric acid solution were added. The mixture was then agitated in a closed vessel for 30 minutes. The desired number of samples were taken and analyzed.
• This example illustrates that iron can be effectively removed in a one-step galvanic stripping from different organic phases using different solid metals added in particulate form.
• the ratio of organic to aqueous phase was 1:1, and the mixing time was 50 minutes.
• Test data are presented in Table VII.
• This example illustrates that an organic liquid loaded with indium and iron can be selectively stripped of indium, and the iron remaining in the liquid can then be at least partly stripped of iron using added solid metal to yield a regenerated organic liquid with a reduced iron content.
• a feed solution containing iron and 0.94 g/L indium, and an organic extractant containing one volume % M2EHPA, three volume % D2EHPA, and two volume % TBP in kerosene were used.
• a loaded organic phase was obtained that contained 0.89 g/L indium and 0.52 g/L iron.
• the indium was stripped from the loaded organic liquid with 3N hydrochloric acid.
• the organic liquid was washed with sodium sulfate solution to remove chloride and found to contain ⁇ 0.003 g/L indium and 0.51 g/L iron.
• the washed organic liquid was split in two portions. The first portion was treated with 100 g/L sulfuric acid solution in a 1:1 volume ratio, with 10 g activated zinc dust (0.2% Pb) per litre of organic liquid, at ambient temperature, and with the addition of nitrogen. All iron was removed from the organic liquid after 15 minutes.
• the second portion was similarly treated with 10 g activated zinc dust (0.2% Pb) per litre of organic liquid but with the addition of 150 g/L return acid (obtained from a zinc electrowinning process) in a ratio of organic to acid solution of 30:1. Substantially all iron had been removed after 30 minutes.
• This example illustrates that iron can be at least partly stripped from an organic phase in a one-step process by continuous circulation of organic phase mixed with stripping solution through a column filled with a solid metal.
• a vessel containing a mixture of 6.5 L of an organic phase consisting of 4% EHPA, 2% TBP and 94% Exxsol TH D80 by volume, and 6.5 L of a regenerated raffinate containing sodium sulfate and 60 g/L sulfuric acid 0.5 L/min of the mixture was continuously circulated through a column containing zinc granules.
• the column was 2 m high with a diameter of 1.9 cm, and was filled with 860 g zinc (0.2% Pb) granules, the void volume being 0.47 L.
• This example illustrates that four-valent cerium (Ce 4+ ) can be effectively galvanically reduced to the two-valent state (Ce ) in solvent extraction and subsequent stripping.
• aqueous nitric acid solution containing 15 g/L Ce 4+ as ammonium cerium nitrate ( (NH 4 ) 2 Ce (N0 3 ) 6 ) was mixed with 99% tributylphosphate (TBP) in an aqueous to organic volume ratio of 1:1. After 10 minutes, the loaded organic phase was separated from the aqueous phase. The loaded organic phase was then mixed with zinc either as pieces or as powder having particle sizes of 74 to 150 microns in an amount of 1 gram per 10 ml of organic phase and an amount of a dilute acid containing 10 g/L H 2 S0 4 or HN0 3 added either together with the addition of zinc or after the galvanic reduction was completed.
• TBP tributylphosphate
• the galvanic reduction was carried out for times ranging from 30 seconds to 30 minutes.
• the reduction and stripping were carried out in a closed vessel under a flow of nitrogen. During the reduction the colour of the solution changes from dark orange to colourless.
• the Ce concentrations in the solutions were determined with x-ray fluorescence, and additional analyses were made using atomic absorption spectometry. All cerium analyses have been transformed into g/L Ce.
• a series of tests were made including a comparative non-reductive stripping.
• the test data and analytical results were as follows. Test 1: Comparative nonreductive stripping
• the loaded organic phase contained 14.8 g/L Ce, and was split in two equal portions. One portion was mixed for 30 minutes with an equal volume of a 10 g/L HN0 3 solution.
• the resulting aqueous solution contained 1.1 g/L Ce, and the stripped organic contained 13.7 g/L Ce for a stripping efficiency of only 8%.
• the other portion was mixed for 30 minutes with an equal volume of a 10 g/L H 2 S0 4 solution.
• the resulting aqueous solution contained 2.5 g/L Ce, and the stripped organic contained 12.3 g/L Ce for a stripping efficiency of 17% into the aqueous phase.
• Test 2 One-stage galvanic reduction and separate stripping The loaded organic phase containing 14.6 g/L Ce was mixed with 3 g zinc powder for 30 minutes. After removal of zinc, the reduced organic phase was split in two equal portions which were stripped of cerium as in Test 1. After the nitric acid strip, the aqueous phase contained 7.0 g/L Ce and the stripped organic phase contained 7.6 g/L Ce for a 48% stripping efficiency. For the sulfuric acid stripping, these figures were, respectively, 11.1 g/L Ce, 3.5 g/L Ce and 76%.
• Test 3 Simultaneous one-stage galvanic reduction and stripping
• the loaded organic phase containing 14.1 g/L Ce was separated in two equal portions. One portion was mixed for 10 seconds with an equal volume of a 10 g/L HN0 3 solution and 1 g Zn powder.
• the resulting aqueous phase contained 9.4 g/L Ce and the stripped organic phase contained 4.7 g/L Ce for a 62% efficiency.
• the second portion was treated in the same manner but mixed for 30 minutes. The stripping efficiency was 60%.
• Test 4 Simultaneous multi-stage galvanic reduction and stripping
• the loaded organic phase containing 14.6 g/L Ce was mixed in a first stage with a volume of a 10 g/L HN0 3 solution and -zinc pieces with a total surface area of 5.6 cm 2 . Mixing was continued until the solution was colourless. After separation, the aqueous phase was found to contain 12.2 g/L Ce for stripping efficiency of 83%.
• the separated organic phase was then treated in a second stage under the same condition for twice as long a period.
• the separated aqueous phase contained 2.05 g/L Ce and the stripped organic phase contained 0.35 g/L Ce for a stripping efficiency of 85%.
• the cumulative efficiency was 97%.
• Test 5 Multistage stripping using simultaneous and separate stages A first portion of a loaded organic phase containing 14.5 g/L Ce was mixed with an equal volume of a 10 g/L HN0 3 solution and zinc pieces with a total surface area of 5.2 cm 2 until the solution had turned colourless. After separation, the aqueous phase contained 12.2 g/L Ce, and the organic phase was mixed in a second stripping stage with an equal volume of a 10 g/L HN0 3 solution for twice as long but no zinc was present. Separated aqueous phase contained 2.0 g/L Ce and separated twice-stripped organic phase contained 0.3 g/L Ce.

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