GB1575056A - Separation and selective recovery of metal ions - Google Patents

Description

(54) SEPARATION AND SELECTIVE RECOVERY OF METAL IONS (71) We, PGP INDUSTRIES, INC., a Corporation organised and existing under the laws of the State of Deleware, United States of America, of 13429 Alondra Boulevard, Santa Fe Springs, California, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the separation and selective recovery of platinum and palladium from aqueous acidic solutions. More specifically, the invention relates to the separation and selective recovery of platinum and palladium from aqueous hydrochloric acid solutions.

The conventional procedures for separation of platinum and palladium values from aqueous leach liquors resulting from ore concentration are tedious and require expensive apparatus. Since these techniques often call for the stepwise treatment of each batch of pregnant liquor in sequence, they are generally unsuitable for operation on a continuous flow basis. A further drawback of the aforementioned procedures is that they frequently require lengthy treatment periods to separate and recover platinum and palladium values from the acidic solutions in which they are dissolved along with other platinum group metals such as rhodium, iridium and ruthenium. This tends to increase the already high cost of these metals.

While the use of tertiary and quaternary amine extractants to win platinum and palladium values from solution is discussed in S. African Patent No. 72/0308, a fairly lengthy and complex technique is required to strip the extracted metal values.

According to the present invention there is provided a process for the separation and selective recovery of platinum and palladium values from an aqueous acidic medium containing platinum and palladium in the presence of at least one other platinum group metal which process comprises: reducing the medium to an emf measured with standard platinum saturatedcalomel electrodes of between -425 and -650 millivolts, contacting the medium with an organic extraction reagent comprising a waterimmiscible solvent having dissolved therein an amine compound of the general formula I::

(wherein each of R1 and R2, which may be the same or different, represents a hydrocarbyl group), the compound being capable of forming complexes with platinum and palladium that are preferentially soluble in the water-immiscible solvent and whereby the contacting results in the formation of an organic extract phase and an aqueous raffinate phase, separating the organic extract phase from the aqueous raffinate phase, and either contacting the said organic extract phase with an acidified aqueous solution of a water-soluble reducing agent to form an aqueous phase loaded with palladium and a platinum-containing organic extract phase, separating the platinum-containing organic extract phase from the palladiumcontaining aqueous phase, and contacting the platinum-containing organic extract phase with at least the stoichiometric quantity of an aqueous alkaline stripping agent solution required for neutralisation of the extract phase, the contacting resulting in the formation of an aqueous phase loaded with platinum and a stripped organic phase, or contacting the said organic extract phase with at least the stoichiometric quantity of an aqueous alkaline stripping agent solution required for neutralisation of the extract phase to form an aqueous phase loaded with platinum and a palladium-containing organic extract phase, separating the palladium-containing organic extract phase and the platinumcontaining aqueous phase, and contacting the palladium-containing organic extract phase with an acidified aqueous solution of a water-soluble reducing agent, the contacting resulting in the formation of an aqueous phase loaded with palladium and a stripped organic phase.

Thus the process of the invention comprises a simple liquid-liquid extraction process of the aqueous acidic medium which is preferably an aqueous hydrochloric acid solution. Following phase separation, palladium may be recovered by contacting the organic phase with an acidified aqueous solution of a water-soluble reducing agent.

Platinum recovery may be effected by contacting the organic phase with at least the stoichiometric quantity of an alkaline stripping agent required for neutralisation of the organic phase. These recovery steps may be carried out in either order.

The secondary amine compounds capable of functioning as the extractant preferably have a solubility of at least 1% O/o by weight in the organic solvent used. The amine compound is of the formula

wherein each of R1 and R2, which may be the same or different, represents a hydrocarbyl group. Suitably R1 is a straight or branched alkyl group (preferably C8 to C30); and R, is alkyl, aryl or fatty alkyl (C8 to C30), and R1 plus R2 preferably contain between 18 and 35 carbon atoms. The term "hydrocarbyl" includes branched chain radicals and alkyl or aryl substituted radicals. The term aryl includes alkyl-substituted aryl radicals.

The amine compounds useful as extractants in the present invention form com plexes with each of the desired metals (i.e., platinum and palladium) which complexes are soluble in at least one of the organic solvents set forth below, permit ready disengagement of the aqueous raffinate and organic extract phases after the extraction, and preferably have a solubility of at least 1% by weight in the solvent of the organic phase. Additionally, the amine compound must be insoluble in water. Amberlite Lea 1, N-dodecyl, N- (trialkylmethyl)amine (made by Rohm & Haas Co.) is an effective extractant preferred for use in the invention.Other secondary amines which are suitable for use as extractants in the present invention include di(2 - propyl - 4methylpentyl) - amine, didecylamine, dilaurylamine, bis(l - isobutyl 3,5 - di methylhexyl) - amine, N - benzyl, N - heptadecylamine, N - benzyl, N - 1 - (3ethylpentyl) - 4 - ethyloctylamine, N - lauryl, N - (trialkylmethyl)amine, di - tridecylamine ("tridecyl" equals mixture of 13 carbon alkyls from tetrapropylene), N-benzyl, N - (1 - nonyl - decyl) - amine, N - benzyl, N - (I - undecyl - lauryl) - amine, di(lheptyl - octyl) - amine, N - (1 - nonyl - decyl), N - lauryl - amine, N - (1 - undecyllauryl), N - lauryl - amine, and di(l - nonyl - decyl) - amine.

The major constituent of the extraction organic phase is a weter immiscible carrier solvent in which the secondary amine extractant is dissolved to form the organic phase.

Conventional organic solvents including, for example, aliphatic hydrocarbons such as petroleum derived liquid hydrocarbons, either straight chain or branched chain, kerosene, and fuel oil are useful as the carrier solvent in the present invention. A wide variety of aromatic solvents and chlorinated aliphatic solvents may also be employed including, for example, benzene, toluene, xylene, carbon tetrachloride, perchloroethylene. The organic carrier solvent must be substantially water-immescible and capable of dissolving the secondary amine extractant. Moreover, the solvent should not interfere with the extraction of the desired platinum and palladium metal values from acid solution by the amine. The secondary amine constituent of the organic extractant mixture preferably has a solubility of at least 1% O/o by weight in the solvent of the organic phase.Kerosene, available as AMSCO 175 from the American Mineral Spirits Co., is the preferred solvent.

A phase modifier is usually admixed with the carrier solvent and the extractant to increase the solubility of platinum and palladium and help prevent the formation of a third phase during extraction and when platinum and palladium are stripped from the metal laden organic extract phase. Water-insoluble straight or branched chain aliphatic alcohols containing at least 6 carbon atoms in the hydrocarbon chain may generally be used as phase modifiers. Examples of suitable phase modifiers include isodecanol which is preferred, 2-ethyl-hexanol and tridecanol.

The aqueous phase from which platinum and palladium are extracted in the present invention is ordinarily an aqueous mineral acid leach solution of the type normally resulting from the fusion and leaching of platinum metal ore concentrates. For purposes of illustration the invention will be further described by reference to separation and recovery of platinum and paladium from aqueous hydrochloric acid solutions since these are most commonly employed in the processing and recovery of platinum group metals. In aqueous acid chloride solutions, the soluble platinum and palladium compounds are generally present as complex chloro salts. Typically, such leach solutions range between 0.1 to 5 N HCI, and up to about 250 grams per liter Cl- and higher.In addition to the platinum group metals (i.e., platinum, palladium, rhodium, ruthenium and iridium), the solutions may contain other impurities such as silver, silica and base metals such as lead, copper, bismuth, nickel, aluminium, and barium. The aqueous acid solutions from which platinum and palladium are to be extracted should preferably be substantially free of gold and iron. Since these metals are frequently found in association with platinum and palladium they may be removed from solutions beforehand by conventional techniques well known in the art. To promote optimum separation of platinum and palladium during the extraction operation, the aqueous solution should preferably contain less than about 0.5 grams per litre of gold or iron.

It has been discovered that platinum and palladium can be effectively extracted from the foregoing aqueous hydrochloric acid solution in a conventional liquid-liquid extraction process employing the secondary amine organic extractant mixtures outlined above. In order to prevent simultaneous extraction of rhodium and iridium which are often present along with platinum and palladium, the aqueous leach liquors are reduced to an emf of between -425 mv.* and - 650 mv., and preferably about -525 mv.

prior to the contact with the amine extractant. This is usually accomplished by the addition of a water-soluble reducing agent, as for example, hydroquinone. In addition to preventing the extraction of rhodium and iridium, maintenance of the aqueous chloride solution in the reduced condition has been found to provide increased loading of the organic phase with platinum and palladium. In most instances the platinum and palladium extraction is carried out under acid conditions in which the pregnant leach solution is approximately pH 1, although the extraction will proceed satisfactorily with solutions up to about 2 N HCI or higher. Under the preceding conditions, platinum and palladium will ordinarily exist as anions.

Generally the organic extraction phase of the present invention will contain 1 to 25 volume percent (%) of the secondary amine extractant, and 0.05 to 15 volume percent (%) of phase modifier diluted in carrier solvent.

Based upon the maximum metal loading characteristics of a particular solvent, the metal bearing characteristics of the leach liquor to be extracted and the number of extraction stages to be employed, either the concentration of extractant and phase modifier in the solvent may be adjusted or the organic/aqueous (O/A) ratio for any particular extraction concentration may be varied to achieve a desired level of metal loading. In one effective version of the platinum/palladium extraction process of the present invention, the organic phase used to extract platinum and palladium from the preferred pH 1 aqueous hydrochloric acid solution comprises 10 volume percent (%) Amberlite LA-i, 3-volume percent (%) isodecanol and 87 volume percent (%) kerosene.As a measure of economy, it is normally preferred to employ the lowest organic/ aqueous ratio that will provide efficient separation for platinum and palladium values from an aqueous chloride solution. However, the most efficient organic to aqueous ratio for the extraction of platinum and palladium can be arrived at in accordance with procedures well known in the art.

The liquid-liquid extraction may be carried out by continuous counter-current, or batch processing procedures. As is well known in the liquid-liquid extraction art, greater separation may be achieved with multi-stage extraction processes. Typical apparatus for * all measurements made with standard platinum saturated-calomel electrodes use in a multi-stage embodiment of the present invention could include a multiple stage counter-current mixer-settler system in which the barren organic solvent and a pregnant aqueous stream are mixed together for a predetermined time period following which they are permitted to separate in a settling reservoir. The solvent and aqueous phase then flow in opposite directions to the next stage of contact.

Following extraction and separation of the organic extract phase and the aqueous raffinate, platinum and palladium are selectively stripped by sequentially contacting the organic extract phase with an aqueous solution of an alkaline reagent (to recover platinum) and an aqueous acidified reducing reagent (to recover palladium). The preceding values need not be stripped from the loaded organic phase in any particular sequence, except in those instances described below where a chelating agent is used in conjunction with the alkaline stripping solution, in which case palladium is desirably stripped first.

The alkaline stripping reagent used in the present invention must be a watersoluble compound which will convert the extracted values in the organic solvent into reaction products which are readily soluble in aqueous solution. Stripping efficiency (i.e., the ability to remove a large quantity of metal salts per unit volume of strippant) is an important criteria for selection of an alkaline stripping agent. Suitable alkaline stripping reagents include water-soluble alkali and alkaline earth metal carbonates, bicarbonates and hydroxzdes, e.g., sodium and potassium hydroxide, carbonate or bicarbonate, although sodium bicarbonate (NaHCO3) is preferably employed as the alkaline stripping reagent in most instances.The quantity of alkaline strippant required is at least the amount which will neutralize the acid salt (usually the chloride) form of the secondary amine compound and desirably includes in excess of the stoichiometric amount (preferably about 50%) of the alkaline reagent in order to ensure efficient stripping within the shortest possible contact times. The aqueous alkaline stripping solutions used in the invention are fairly strong and usually contain between 5 and 100 grams per liter (g/l) of the alkaline stripping reagent and fall within the range of 0.5 N to 2.5 N. By contacting the loaded organic solvent with the alkaline stripping agent, the organic soluble, aqueous insoluble platinum amine complexes are converted to aqueous soluble/organic insoluble platinum salts.

A common problem encountered in stripping platinum from loaded organic solvents containing platinum group metals is the formation of an insoluble scum believed to consist primarily of base metal impurities and which results in poor phase separation.

To solubilize the emulsion-forming scum, a chelating agent, suitably an amino carboxylic acid chelating agent (e.g., ethylenediaminotetraacetic acid (EDTA), or diethylenetriaminopentaacetic acid) is added to the strip solution, usually in the form of its sodium salt, prior to contact with the metal laden organic extract phase. The disodium salt of ethylenediaminotetraacetic acid (i.e., NaEDTA) is the preferred chelating agent for use in the present process. The quantity of chelating agent required to solubilize the scums will vary depending upon the composition of a particular liquor, but will generally be equal to at least 10% by weight of the alkaline reagent in the aqueous stripping solution.While addition of the chelating agent reduces the scum formation to trace levels and eliminates the physical problem of phase separation, analysis of the aqueous platinum strip solution revealed a corresponding increase in the quantity of palladium stripped along with platinum thereby reducing the platinum/palladium ratio in the strip solution. As an example, a loaded organic extract phase having a platinum/ palladium ratio of 0.3 and stripped with an aqueous NaHCO3 solution yielded an aqueous strip solution containing platinum and palladium in the ratio of 450/1 platinum/palladium. However, when the same solution of NaHCO3 was used as the strippant in conjunction with a solution of sodium EDTA, the aqueous strip solution from the same loaded organic phase had a platinum/palladium ratio of 11/1.Hence, the use of a chelating agent (e.g., NaEDTA) in the stripping solution was found to increase the amount of palladium accompanying platinum into the aqueous strip solution.

Accordingly, palladium is preferably stripped first from the loaded organic to a low level with an acidified reductant solution followed by platinum stripping using alkaline NaEDTA solution.

Palladium is stripped from the loaded organic using a water-soluble reducing agent in an acidified aqueous solution. An important criterion in selecting a suitable reductant reagent is that it should not contribute any foreign metals to the organic which might eventually cause fouling or a reduction in loading capacity. Satisfactory reductant stripping agents for use in the present invention include acidified solutions of hydrazine salts, hydroxylamine salts, and thiourea. The reductant stripping solutions are generally acidified to between 0.1 to 3 N HC1 and are preferably employed as 0.5 N solutions.

The preferred reducing solution is 50 g/l hydrazine dihydrochloride (N2H4 2HCl) acidified to 0.5 N HC1. Although suggested concentrations of strippant solutions have been described herein, those skilled in the art will appreciate that these may be varied depending up on the organic volumes to be treated, metal stripping efficiency of a particular strippant, to adjust the quantity and concentration of strip to yield solutions containing significant quantities of dissolved metal values and to avoid the handling of weak and/or large volumes of solution.The latter criterion is important because a significant advantage of the present process lies in its use as a means of producing highly concentrated aqueous solutions of either platinum or palladium from aqueous leach liquors in which the metals are present at substantially lower concentrations.

The stripping contact time required for a given strippant solution will vary from one loaded organic to another depending upon the particular solvent system, the quantity of platinum or palladium sought to be stripped from the organic extract phase and the temperature at which the stripping operation is conducted. In most instances stripping contact times of between 1 and 10 minutes will strip about 90% or more of the respective metals from the loaded organic phase.

The invention is further illustrated in the following examples: EXAMPLE I.

This example illustrates that a secondary amine may be used to selectively extract platinum and palladium from aqueous hydrochloric acid solutions also containing iron, iridium, ruthenium and rhodium.

An aqueous hydrochloric acid solution analyzing (in grams per liter) (g/l) platinum 0.40, palladium 3.30, iridium 1.10, rhodium 3.80, ruthenium 4.1 and iron 0.002 and having a measured emf of - 525 millivolts was contacted and mixed with an organic extractant at an organic to aqueous (O/A) ratio of 1.5 to 1 for two minutes at 2S"C to form an organic extract phase and an aqueous raffinate phase. Following phase disengagement, the aqueous and organic phases were separated and analyzed.The organic extractant utilized in this example contained 10 volume percent (%) Amberlite-LA-1, 3 volume percent (%) isodecanol and 87 volume percent (%) kerosene (as AMSCO 175) and was conditioned to the chloride form of the organic by two contacts with a solution of 200 g/l NaCI in 1N HC1 at an O/A ratio of 2 to 1, followed by washing with a solution of 20 grams per liter NaCI adjusted to pH 1.5 with HCI. The results of the extraction are summarized in the following table.

TABLE 1 Assay, g/1 Grams Amount Product in ml. Pt Pd Ir Rh Ru Fe Pt Pd Aqueous feed 1050 0.40 3.30 1.10 3.80 4.10 0.002 0.42 3.5 Raffinate 1050 0.04 1.00 1.10 3.78 4.05 0.002 0.04 1.1 Loaded Organic 1575 0.24 1.58 0.02 0.003 0.05 0.004 0.38 2.5 It will be seen from the above Table that platinum and palladium were selectively extracted from an aqueous hydrochloric acid solution containing iridium, rhodium, ruthenium and iron by an organically substituted secondary amine. The minute quantities of iridium, rhodium, ruthenium and iron which are extracted along with platinum and palladium are relatively insignificant.

EXAMPLE II.

The tests in this Example illustrate that a variety of alkaline reagents at different concentrations may be used to selectively strip platinum from an organic extraction solvent loaded with platinum and palladium.

A ten percent (%) by volume Amberlite-LA-1 solution in kerosene (AMSCO 175) containing 3% by volume isodecanol (and conditioned to chloride form as in Example I) was loaded with platinum and palladium by contacting with an aqueous hydrochloric acid solution assaying (g/l) gold 0.007, platinum 2.86, palladium 8.40, iridium 0.031, rhodium 0.038 and ruthenium 1.13. The loaded orgaic assayed (g/l) platinum 1.12 and palladium 3.55. Predetermined quantities of the loaded organic were treated with solutions of Na2CO3, NaHCO3 and NaOH in separatory funnels at room temperature approximately 25 C) or approximately 40 C at an O/A ratio of 2 to 1. The contact times and alkaline concentration of the stripping solution were varied as noted in Table II.Following each contact period, the phases were separated, filtered and assayed for platinum distribution, Results of the respective assays are indicated in Tables II and IIA below.

TABLE II Loaded organic: 1.12 g/1 Pt + 3.55 g/1 Pd Stripping: O/A = 2/1 Contact Assays1 "K" applrox Strip Org. Strip Soln, (concentration) Ratio Test Strip Volumes Taken, ml Time Temp g/l g/l Stripped O/A4 Pt/Pd No. Solution Organic Aqueous min C Pt Pd Pt Pd Pt Pd Pt Pd in Strip 1 50 g/l Na2CO3 30 15 5 25 0.03 3.30 2.19 0.49 97 7 < 1 7 4.5/1 2 50 g/l NaCH 30 15 5 25 0.03 2.80 2.06 0.91 97 21 < 1 3 2/1 3 11 g/1 Na2CO3 30 15 15 25 1.17 3.45 0.007 0.002 < 1 < > 100 > 100 4 50 g/1 NaHCO3 30 15 15 25 0.18 0.80 0.004 84 < 1 < 1 > 100 450/1 5 50 g/1 NaHCO3 50 25 15 40 0.25 3.52 1.80 0.038 78 1 < 1 93 47/1 6 50 g/1 NaHCO3+ 30 15 15 25 0.20 2.45 1.91 0.17 82 3 < 1 20 11/1 5 g/1 NaEDTA2 7 75 g/1NaHCO3+ 50 25 15 25 0.21 3.40 1.87 0.18 81 4 < 1 19 10/1 5 g/1 EDTA3 8 50 g/1NaHCO3+ 50 25 15 25 0.28 3.44 1.76 0.17 75 3 < 1 20 10/1 5 g/ 1 EDTA 1All assays were on filtered products and do not include losses, if any, in scum products.

2NaEDTA = Ethylenediaminotetraacetic acid disodium salt.

3EDTA = Ethylenediaminotetraacetic acid.

K" (concentration) O/A refers to the concentration of platinum or palladium in the organic phase over that in the aqueous phase.

TABLE IIA Test No. Physical Observations 1 Emulsion-forming scum suspended throughout the aqueous phase. Poor phase separation.

2 Emulsion-forming scum suspended throughout the aqueous phase. Poor phase separation.

3 Scum in aqueous phase Poor Dhase senaration.

4 r Scum suspended in aqúeous phase, settles in aqueous phase, clear organic S t phase. Same problem, botch tests.

6 Trace scum, no phase separation problem.

7 Clear organic + aqueous phases, no scums.

8 Clear organic + aqueous phases, no scums.

The results of the tests illustrated in Table II indicate that a variety of alkaline reagents can be used selectively to strip platinum from an amine organic loaded with platinum and palladium. The poor stripping action of Test No. 3 is attributable to use of a weak alkaline solution (11 g/l). The insoluble scums formed in Tests Nos. 1 to 5 resulted in poor phase separation. The emulsion forming scum was solubilised by addition of a chelating agent [NaEDTA; ethylenediamino-tetraacetic acid disodium salt] to the alkaline stripping solution prior to contact with the loaded organic. As indicated in the results of Tests Nos. 6 to 8, this entirely eliminated the scum formation in most instances or reduced it to trace levels and also alleviated the physical problem of phase separation.A 50 g/l solution of Na HCOa provided optimum selective stripping of platinum from palladium as illustrated in the results of Test No. 5. In all instances it was possible to obtain strip solutions in which platinum was at a relatively high concentration with respect to palladium as compared to the original aqueous solutions from which they were separated.

EXAMPLE III.

The extraction and selective stripping tests in Example III were performed to illustrate that the sequence of stripping platinum and palladium from a loaded secondary amine organic is not important and either metal may be stripped first through the process of the present invention.

To carry out Example III a 10% by volume solution of Amberlite LA-1 in 3 volume percent (%) isodecanol and 87 volume percent (%) kerosene (AMSCO 175) was loaded with platinum and palladium in a single contact with a hydrochloric acid solution assaying (g/l) gold 0.004, platinum 2.90, palladium 8.20, iridium 0.024, ruthenium 1.13 and rhodium 0.036. Prior to the extraction the emf of the aqueous solution was reduced to - 525 millivolts by the addition of hydroquinone. The extraction organic was preconditioned to chloride form by two contacts at an O/A ratio of 2 to 1 with 100 grams per liter NaCI in 1N HC1 followed by washing with 20 grams per liter NaC1 adjusted to pH 1.5 with HCI.The extraction was carried out by allowing the aqueous solution to contact the organic for three minutes at 24"C and at an O/A ratio of 2 to 1. Following the contact period the phases were separated and the loaded organic phase scrubbed by contacting with pH 1 HCI for three minutes at 240C at an O/A ratio of 2 to 1. The phases were again separated and the scrubbed platinum and palladium loaded organic was analyzed, and assayed (g/l) platinum 1.06, palladium 3.52, iridium 0.002, ruthenium 0.002 and rhodium less than 0.001.The loaded organic solution was then divided into three approximately equal portions (labeled organic 1, 2 and 3) which were each contacted once with an aqueous strip solution containing 50 g/l NaHCO, for a period of 5 minutes at 25 C. After contacting the first loaded organic portion, the phases were separated and sufficient NaHCO3 added to the aqueous phase to restore it to 50 grams per litre NaHCO3, and the restored solution used to contact the second and third portions of loaded organic in sequence. All contacts were carried out at an O/A ratio of 2 to 1 and the phases separated and analysed after each contact. The platinum pregnant aqueous strip solution was then acidified to pH 1 with 12N HCl. Analyses of the scrubbed-loaded organic, each stripped organic portion and the acidified platinum pregnant strip solution were carried out and the results found to be as follows: TABLE III Assay, g/1 Grams Amount Product ml O/A Au Pt pd Ir Ru Rh Pt pd S@rubbed organic 1400 0.005 1.06 3.52 0.002 0.002 < 0.001 1.48 4.9 Stripped organic 1 440 2.0 0.05 3.52 0.02 1.5 Stripped organic 2 470 # 0.06 3.52 0.03 1.6 Stripped organic 3 490 0.09 3.52 0.04 1.7 Pt pregnant strip 232 0.002 6.00 0.004 < 0.001 0.001 < 0.001 1.39 < 0.001 (acidified) 1.48 4.8 Pt Pd %stripped 94 0.03 Ratio Pt/Pd in pregnant strip = 1000/1 Table III indicates that 94% of the platinum was stripped from the loaded organic while less than 0.03% of the palladium was removed. The ratio of platinum to palladium in the pregnant strip solution was greater than 1,000 to 1.Platinum stripped organic portions (Nos. 1, 2 and 3) were combined and assayed (g/l) platinum 0.070 and palladium 3.48. The platinum stripped organic was then scrubbed with 1N HCl for 3 minutes at 25 C at an O/A ratio of 2 to 1. After phase separation, the scrubbed organic phase was analyzed and found to assay (g/l) platinum 0.070 and palladium 3.50. The scrubbed organic was then contacted three times in succession with a fresh solution of 50 g/l N2H4 # 2HCl in 0.5N HCl at an organic aqueous ratio of 2 to 1 for a period of 5 minutes, the phases being separated after each contact. The separated aqueous strip solutions were combined and an analysis of the aqueous strip solution revealed that 75% of the palladium present in the scrubbed organic and less that 2% of the platinum had been stripped into the aqueous solution by the acidic strip treatment.

The results of this test indicated that a secondary amine organic phase loaded with platinum and palladium may be selectively stripped from a loaded secondary amine organic in a stripping sequence in which platinum is first removed followed by palladium.

EXAMPLE IV.

This test was conducted to illustrate that platinum and palladium may be stripped from a loaded secondary amine organic in the order (1) palladium, (2) platinum.

An organic extraction solution was prepared and preconditioned to chloride form as in Example III and used to contact an aqueous hydrochloric acid solution assaying (g/l) gold less than 0.001, platinum 1.70, palladium 4.59, iridium 0.025, ruthenium 1.10, and rhodium, 0.036. The emf of the aqueous solution was reduced to - 525 millivolts by the addition of dry hydroquinone prior to contacting the extraction organic.

A single organic/aqueous contact was then carried out for three minutes at 25"C at an O/A ratio of 1/1. Following phase separation the organic extract phase was scrubbed by contacting with pH 1 HCl for three minutes at an organic to aqueous ratio of 2 to 1.

Analysis of each of the respective phases gave the following results.

TABLE IV Assay. g/l Amount Product ml O/A Pt Pd Aqueous 850 1.7:0 4.59 Raffinate 850 1.Q 0.710 1.70 Loaded Organic 850 1.04' 260 Aqueous Scrub 412 2.0 0.009 0.02 Scrubbed Organic 825 1.04 2.60 The scrubbed loaded organic (assaying g/l) platinum 1.04 and palladium 2.60 was then subdivided into two separate portions. The first portion was contacted with a 50 g/l aqueous solution of N2H4 # 2 HCl acidified to 0.5N with HCl for 3 minutes at O/A ratio of 2 to 1.Following phase separation the aqueous raffinate phase was used to contact the second portion of scrubbed organic (at an O/A ratio 1.5 to 1) for 3 minutes at 25"C. The palladium pregnant aqueous raffinate was separated from the organic extract phase which was then combined with the previously stripped first organic portion.As in the initial test, the percentages and amounts of platinum and palladium stripped were determined by analysis of the respective separated phases as indicated in the following table: TABLE IVA Assay, g/l Grams % Stripped Amount Product ml Pt Pd Pt Pd Pt Pd Scrubbed organic 700 1.04 2*60 0.7:28 1.82 stripped Combined Pd/organic 700 1.00 0.56 0.7i00 0.3'9 < 1 78 Pd pregnant strip 200 0.1-0 6.90 0.020 1.3-8 0t720 1.77 The combined palladium stripped organic was then contacted with pH 1 HC1 at an O/A ratio of 2 to 1 for 3 minutes at 250C to scrub the organic phase.Following phase separation, the scrubbed organic phase was analyzed and found to assay (g/l) platinum 1.00, and palladium 0.56. The scrubbed organic phase was then contacted with a 50 g/l solution of NaHCO3 containing 5 g/l EDTA which was prepared by adjusting an EDTA suspension in water to pH 8 with NaOH solution to dissolve the EDTA, adding NaHCO3 and diluting with water to final volume. The organic was divided into two equal aliquots. The first aliquot was contacted with the alkaline stripping solution for 10 minutes at 25 C. Following phase separation, 5.1 grams of NaHCO3 was dissolved in the aqueous phase to restore the alkaline solution to 50 g/l NaHCO,.The restored strippant solution was then used to contact the second aliquot for 10 minutes at 25 C. Both of the preceding contacts were carried out at an organic to aqueous ratio of 2 to 1. No scum was observed during the first contact and only trace scums were apparent at the interface of the second stripping contact. After phase separation following the second stripping contact, the stripped organic phases were combined and the platinum pregnant strip solution was adjusted to pH 1 by addition of 12N HCI to stabilize the solution.As in the preceding test, the percentage of platinum and palladium stripped was determined by analysis of the separated phases as indicated below: TABLE IVB Assay, g/l Grams % Stripped Amount Product ml Pt Pd Pt Pd Pt Pd Pd stripped organic 600 1.00 0.56 0.60 0.336 (scrubbed) Pt stripped organic 600 0.15 0.55 0.09 0.330 85 < 2 Pt pregnant strip 151 3.20 0.071 0.48 0,011 0.57 0.3:41 The tabulated data indicate that the initial stripping operation resulted in the strip of 78% of the palladium and less than 1% of the platinum from the loaded organic.

The palladium containing aqueous strip solution had a palladium/platinum ratio of 69/1. The platinum stripped organic contained 0.15 g/l platinum and 0.55 g/l platinum (85% and less than 2% stripped, respectively) and the aqueous platinum containing strip solution had a platinum/palladium ratio of 46/1. Compared to the starting feed liquor of the process, the Pd/Pt ratio was increased from 2.7/1 to 69/1 and the Pt/Pd ratio was increased from 0.4/1 to 46/1. Overall recovery from the loaded organic was 85% for platinum and 79% for palladium.

The platinum and palladium values may be won from the respective aqueous stripping solutions using techniques well known in the art (e.g., precipitation of ammonium chloroplatinate with NO4 CM to recover platinum, or precipitation of dichlorodiamino-palladium by sequential addition of ammonium hydroxide and hydrochloric acid solutions to recover palladium).

The words "Amberlite " and" Amsco " are registered Trade Marks.

WHAT WE CLAIM IS: 1. A process for the separation and selective recovery of platinum and palladium values from an aqueous acidic medium containing platinum and palladium in the presence of at least one other platinum group metal which process comprises: reducing the medium to an emf measured with standard platinum saturatedcalomel electrodes of between -425 and -650 millivolts, contacting the medium with an organic extraction reagent comprising a waterimmiscible solvent having dissolved therein an amine compound of the general formula I:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. The combined palladium stripped organic was then contacted with pH 1 HC1 at an O/A ratio of 2 to 1 for 3 minutes at 250C to scrub the organic phase. Following phase separation, the scrubbed organic phase was analyzed and found to assay (g/l) platinum 1.00, and palladium 0.56. The scrubbed organic phase was then contacted with a 50 g/l solution of NaHCO3 containing 5 g/l EDTA which was prepared by adjusting an EDTA suspension in water to pH 8 with NaOH solution to dissolve the EDTA, adding NaHCO3 and diluting with water to final volume. The organic was divided into two equal aliquots.The first aliquot was contacted with the alkaline stripping solution for 10 minutes at 25 C. Following phase separation, 5.1 grams of NaHCO3 was dissolved in the aqueous phase to restore the alkaline solution to 50 g/l NaHCO,. The restored strippant solution was then used to contact the second aliquot for 10 minutes at 25 C. Both of the preceding contacts were carried out at an organic to aqueous ratio of 2 to 1. No scum was observed during the first contact and only trace scums were apparent at the interface of the second stripping contact. After phase separation following the second stripping contact, the stripped organic phases were combined and the platinum pregnant strip solution was adjusted to pH 1 by addition of 12N HCI to stabilize the solution.As in the preceding test, the percentage of platinum and palladium stripped was determined by analysis of the separated phases as indicated below: TABLE IVB Assay, g/l Grams % Stripped Amount Product ml Pt Pd Pt Pd Pt Pd Pd stripped organic 600 1.00 0.56 0.60 0.336 (scrubbed) Pt stripped organic 600 0.15 0.55 0.09 0.330 85 < 2 Pt pregnant strip 151 3.20 0.071 0.48 0,011 0.57 0.3:41 The tabulated data indicate that the initial stripping operation resulted in the strip of 78% of the palladium and less than 1% of the platinum from the loaded organic. The palladium containing aqueous strip solution had a palladium/platinum ratio of 69/1. The platinum stripped organic contained 0.15 g/l platinum and 0.55 g/l platinum (85% and less than 2% stripped, respectively) and the aqueous platinum containing strip solution had a platinum/palladium ratio of 46/1. Compared to the starting feed liquor of the process, the Pd/Pt ratio was increased from 2.7/1 to 69/1 and the Pt/Pd ratio was increased from 0.4/1 to 46/1. Overall recovery from the loaded organic was 85% for platinum and 79% for palladium. The platinum and palladium values may be won from the respective aqueous stripping solutions using techniques well known in the art (e.g., precipitation of ammonium chloroplatinate with NO4 CM to recover platinum, or precipitation of dichlorodiamino-palladium by sequential addition of ammonium hydroxide and hydrochloric acid solutions to recover palladium). The words "Amberlite " and" Amsco " are registered Trade Marks. WHAT WE CLAIM IS:

1. A process for the separation and selective recovery of platinum and palladium values from an aqueous acidic medium containing platinum and palladium in the presence of at least one other platinum group metal which process comprises: reducing the medium to an emf measured with standard platinum saturatedcalomel electrodes of between -425 and -650 millivolts, contacting the medium with an organic extraction reagent comprising a waterimmiscible solvent having dissolved therein an amine compound of the general formula I:

(wherein each of R1 and R2, which may be the same or different, represents a hydrocarbyl group), the compound being capable of forming complexes with platinum and palladium that are preferentially soluble in the water-immiscible solvent and whereby the contacting results in the formation of an organic extract phase and an aqueous raffinate phase, separating the organic extract phase from the aqueous raffinate phase, contacting the said organic extract phase with an acidified aqueous solution of a water-soluble reducing agent to form an aqueous phase loaded with palladium and a platinum-containing organic extract phase, separating the platinum-containing organic extract phase from the palladiumcontaining aqueous phase, and contacting the platinum-containing organic extract phase with at least the stoichiometric quantity of an aqueous alkaline stripping agent solution required for neutralisation of the extract phase, the contacting resulting in the formation of an aqueous phase loaded with platinum and a stripped organic phase.

2. A process according to claim 1 wherein the aqueous alkaline stripping agent solution contains a metal chelating agent.

3. A process according to claim 2 wherein the metal chelating agent is an amino carboxylic acid compound.

4. A process for the separation and selective recovery of platinum and palladium values from an aqueous acidic medium containing platinum and palladium in the presence of at least one other platinum group metal which process comprises: reducing the medium to an emf measured with standard platinum saturatedcalomel electrodes of between - 425 and 650 millivolts, contacting the medium with an organic extraction reagent comprising a waterimmiscible solvent having dissolved therein an amine compound of the general formula I::

(wherein each of R1 and R2, which may be the same or different, represents a hydro carbyl group), the compound being capable of forming complexes with platinum and palladium that are preferentially soluble in the water-immiscible solvent and whereby the contacting results in the formation of an organic extract phase and an aqueous raffinate phase, separating the organic extract phase from the aqueous raffinate phase, contacting the said organic extract phase with at least the stoichiometric quantity of an aqueous alkaline stripping agent solution required for neutralisation of the extract phase to form an aqueous phase loaded with platinum and a palladium-containing organic extract phase, separating the palladium-containing organic extract phase and the platinum containing aqueous phase, and contacting the palladium-containing organic extract phase with an acidified aqueous solution of a water-soluble reducing agent, the contacting resulting in the formation of an aqueous phase loaded with palladium and a stripped organic phase.

5. A process according to any one of the preceding claims wherein, in the com pound of formula I, R1 represents an alkyl group.

6. A process according to any one of the preceding claims wherein, in the com pound of formula I; R1 and R2 together contain between 18 and 35 carbon atoms.

7. A process according to any one of the preceding claims wherein the aqueous acidic medium is aqueous hydrochloric acid.

8. A process according to any one of the preceding claims wherein the aqueous alkaline stripping agent solution contains between 5 and 100 grams per litre of alkaline reagent

9. A process according to claim 8 wherein the alkaline reagent is a water-soluble carbonate, bicarbonate or hydroxide of an alkali or alkaline earth metal.

10. A process according to any one of the preceding claims wherein the acidified aqueous reducing agent solution is an acidified aqueous solution of a hydrazine salt, hydroxylamine salt or thiourea.

11. A process according to claim 10 wherein the acidified reducing agent is hydrazine dihydrochloride.

12. A process according to claim 10 or 11 wherein the acidified reducing agent solution is between 0.1 and 3.0 NHC1.

13. A process according to any one of the preceding claims wherein the aqueous medium is extracted a plurality of times by contacting the aqueous raffinate phase and subsequent raffinates with the organic extraction reagent.

14. A process according to any one of the preceding claims which is operated continuously.

15. A continuous process for the separation and selective recovery of platinum and palladium dissolved in an aqueous acidic chloride solution containing platinum and palladium and at least one other platinum group metal which process comprises: reducing the medium to an emf measured with standard platinum saturatedcalomel electrodes of between -- 425 and - 650 millivolts, contacting the aqueous chloride solution with an organic extraction reagent comprising a water-immiscible organic solvent having dissolved therein an amine compound of the general formula I::

(wherein each of R1 and R2, which may be the same or different, represents a hydrocarbyl group), the compound being capable of forming complexes of platinum and palladium that are preferentially soluble in the organic solvent and whereby the contacting results in the formation of an organic extract phase and an aqueous raffinate phase, separating the organic extract phase from the aqueous raffinate phase, contacting the organic extract phase with an aqueous solution containing sodium bicarbonate and the disodium salt of ethylenediaminotetraacetic acid to strip platinum values from the organic extract phase and form a platinum stripped organic extract phase and an aqueous platinum strip solution, contacting the platinum stripped organic extract phase with an aqueous solution containing hydrazine dihydrochloride to remove palladium from thestripped organic extract phase, and adding the platinum and palladium stripped organic extract phase to a fresh platinum and palladium containing aqueous chloride solution.

16. ,Platinum separated and recovered by the process claimed in any preceding claim.

17. Palladium separated and recovered by the process claimed in any one or claims 1 to 15.