Anna C. du Preez

Solvent extraction of platinum-group metals from hydrochloric acid solutions by dialkyl sulphoxides

ABSTRACT The solvent extraction of palladium(II), platinum(II), platinum (IV), rhodium(III), iridium(III) and iridium(IV) from hydrochloric acid solutions by some dialkyl sulphoxides of the types R2SO, RR′SO and R2′SO, where R=alkyl and R′=cycloalkyl, was investigated. The order of extraction of these metals by 0.50 M di-n-hexyl sulphoxide in xylene from solutions containing 1 to 6 M hydrochloric acid was found to be Pd(II)> Pt(II)> Ir(IV)>Pt(IV)>Rh(III)>Ir(III). Metal-distribution studies suggest that iridium(IV) and platinum(IV) are extracted in the form of ion-pairs such as (L3ċH3O+)2IrCl6 2- and (L2ċH3O+) (L3ċH3O+)PtCl6 2-, where L=dialkyl sulphoxide. In the case of palladium(II), and probably platinum(II) also, the sulphoxide apparently displaces one or two of the chloride ligands from the chlorometallate anion (MCl4 2-), and the distribution data are consistent with the extraction of PdCl2L2 at low hydrochloric acid concentrations (1–2 M) and (L2ċH3O+)PdCl3L− at higher concentrations (4–6 M). The slow rates of extraction of rhodium (III) and iridium(III) from solutions containing the MCl6 3- species suggests a ligand substitution reaction for these metals also, with the probable formation of species such as (L2ċH3O+) RhCl4L2 − and (LċH3O+)2IrCl5L2− in the organic phase. Comparison of the uv-visible spectra of the metal-loaded organic phases with those obtained using tri-n-octylammonium chloride as extractant confirms that simple chlorometallate anions are present in the dialkyl sulphoxide extracts only for platinum(IV) and iridium(IV).

THE SOLVENT EXTRACTION OF NICKEL AND COBALT BYMIXTURES OF CARBOXYLIC ACIDS AND PYRIDINECARBOXYLATE ESTERS

ABSTRACT A series of fifteen pyridinecarboxylate esters has been synthesized with the structure C5H4N.CO.OR, in which the carboxylate group is situated at the 2-, 3-, or 4-position on the pyridine ring, and R = n-octyl, 2-ethylhexyl, 2-octyl, cyclooctyl, or cyclohexyl. The presence of these compounds causes substantial synergistic shifts in the pH50 values for the extraction of nickel (up to about 2 pH units) and cobalt (up to about 1.5 pH units) by solutions of carboxylic acids in xylene. The extent of the synergistic shift depends on the nature of the carboxylic acid, and increases in the order: n-octanoic < 2-ethylhexanoic < Versatic 10 < 2-bromodecanoic < 3,5-diisopropylsalicylic acid (DIPSA). The synergistic shifts depend to a lesser extent on the identity of the pyridinecarboxylate ester, except that they are smaller for the sterically hindered 2-carboxylates than for their 3- and 4- isomers. Studies using the methods of continuous variation and saturation loading indicate that the metal complexes e...

The separation of europium from a middle rare earth concentrate by combined chemical reduction, precipitation and solvent-extraction methods

The chemical reduction of pure europium(III) chloride solutions was investigated using reagents comprising reactive metals (Zn and Mg), metal amalgams (Zn-Hg, Na-Hg and Eu-Hg), metal hydride (NaBH4) and nitrogenous reductants (N2H4 and NH2OH). Using 100% excess of reducing agent and of ammonium sulphate, efficient precipitation of europium(II) sulphate was obtained with the metal amalgams (99·7–99·9%) and with zinc metal (99·8%), whereas only partial precipitation was obtained with magnesium metal (69%), and no precipitation was observed with the other reagents. Application of the method to synthetic rare earth chloride solutions containing europium 7·5, neodymium 5, samarium 35 and gadolinium 20 g dm−3 gave efficient precipitation of europium(II) sulphate with zinc and europium amalgams, but no selective precipitation with sodium amalgam. Reduction of an authentic middle rare earth chloride solution with zinc amalgam gave 97·5% recovery of europium(II) sulphate containing (as a percentage of the total rare earths) europium 92, samarium 3·5, neodymium 2, cerium 1, praseodymium 0·6 and gadolinium 0·5%. Conversion of the europium(II) sulphate to europium(II) chloride, followed by re-precipitation of the sulphate increased the europium content only to 96·5%, whereas replacement of the re-precipitation by solvent extraction of the trivalent rare earth impurities into solutions of commercial organophosphorus or carboxylic acids in xylene increased the europium content to > 99·98%. The zinc ions introduced into the middle rare earth mother liquor during the reduction procedure can be removed by solvent extraction into a commercial phosphine oxide (Cyanex 925), without loss of rare earth values.

Solvent extraction of nickel from acidic solutions using synergistic mixtures containing pyridinecarboxylate esters. Part 1. Systems based on organophosphorus acids

The solvent extraction of nickel from acidic solutions by pyridinecarboxylate esters (2-, 3- and 4-C 5 H 4 N.CO.OR) mixed with organophosphorus acids (R 2 POOH, (RO)RPOOH and (RO) 2 POOH) in toluene was investigated for both series of compounds in which R = n-octyl, 2-ethylhexyl and cyclooctyl. Substantial synergistic effects were observed, which increased in the orders : pyridine 2-ester Ni > Zn > Co > Ca > Mg. In a batch countercurrent experiment, a simulated leach liquor containing Ni 2.1, Cu 0.5, Ca 0.4 and Mg 5.0 g dm -3 (initial pH 3.00) was extracted with the mixed reagent (0.50 M) in four stages at unit phase ratio, without pH adjustment.

SYNERGISTIC EFFECTS IN SOLVENT-EXTRACTION SYSTEM BASED ON ALKYLSALICYLIC ACIDS. PART 2. EXTRACTION OF NICKEL, COBALT, CADMIUM AND ZINC IN THE PRESENCE OF SOME NEUTRAL N-, O- AND S-DONOR COMPOUNDS.

ABSTRACT Nine alkyl- and dialkyl-substituted salicylic acids were prepared and their solvent extraction behaviour towards divalent nickel, cobalt, cadmium and zinc in nitrate media was examined, both in the absence and in the presence of some neutral N-, O- and S-donor compounds (n-octyl 3-pyridinecarboxylate and octanal oxime as N-donors, tri-n-butylphosphine oxide as O-donor, and tri-n-butylphosphine sulphide as S-donor). It was found that the pH50 values for extraction of these metals by the salicylic acids themselves can be correlated with the respective pKa and steric parameters of the extractants. Addition of the N-donor compounds caused synergistic shifts in the pH50 values for all four metals, these being especially marked for nickel (up to almost 3 pH units). Addition of the S-donor compound caused substantial shifts only for cadmium (up to 2.5 pH units), and the O-donor only for zinc and cadmium (up to 1.5 pH units). The size of the synergistic shift depends on the identity of the alkylsalicylic...

SYNERGISTIC EFFECTS IN SOLVENT-EXTRACTION SYSTEMS BASED ON ALKYLSALICYLIC ACIDS. IV. EXTRACTION OF THE TRIVALENT RARE-EARTH METALS IN THE PRESENCE OF BIFUNCTIONAL C=0, P=0 AND S=0 COMPOUNDS

ABSTRACT Several bifunctional compounds of different types (diamides, diphosphonates and disulphoxides) were synthesized, and their effect on the extraction of the trivalent rare-earth metals from chloride media by solutions of some alkylsalicylic acids (HA) in xylene was investigated. Appreciable synergistic shifts in the individual pH50 values were observed in most cases, the shifts generally increasing in the order S=0 ≤ C=0 < P=0 for comparable bifunctional compounds containing these donor groups. For compounds with C=0 or P=0 groups, the synergism is greater when the two groups are separated by a one-carbon bridge (-CH2-) than by a two-carbon bridge (-CH2-CH2-), whereas the opposite is true for compounds containing S=0 groups. For a given bifunctional compound, the synergistic shifts were found to increase with increasing steric bulk of the alkylsalicylic acid The synergistic shifts produced by the addition of a given bifunctional compound generally decrease across the lanthanide series (La to Lu), w...

The Recovery of a Mixed Rare-Earth Oxide and the Preparation of Cerium, Europium and Neodymium Oxides from a South African Phosphoric Acid Sludge by Solvent Extraction

Abstract A novel process based largely on solvent-extraction methods has been developed for the recovery of rare-earth oxides from waste calcium sulphate sludges obtained during the manufacture of phosphoric acid from a South African apatite ore. A mixed rare-earth oxide (90-98% purity) was first recovered from calcium nitrate leach liquors by extraction with TBP or DBBP, after which it was dissolved in nitric acid to enable pure cerium dioxide (99.98%) to be prepared by selective extraction of cerium(IV) nitrate into TBP. The heavy (yttrium), middle, and light rare-earth fractions were then separated by sequential extraction into D2EHPA at controlled pH values. Pure europium oxide (99.98%) was isolated from the middle fraction by reductive precipitation of europim(II) sulphate, followed by conversion to soluble europium(II) chloride and removal of trivalent rare-earth impurities by extraction with D2EHPA or Versatic 10 acid. Finally, magnet-grade neodymium oxide (95-96%) was obtained from the light rare-...

SYNERGISTIC EFFECTS IN SOLVENT-EXTRACTION SYSTEMS BASED ON ALKYLSALICYLIC ACIDS. III. EXTRACTION OF THE TRIVALENT LANTHANIDES AND YTTRIUM FROM CHLORIDE MEDIA IN THE PRESENCE OF DIALKYL AND DIARYL SULPHOXIDES

ABSTRACT DialkyI and diaryl sulphoxides were found to cause synergistic shifts in the pH50 values for the extraction of the trivalent lanthanides and yttrium from sodium chloride media by solutions of alkylsalicylic acids in xylene. The extent of the synergistic shift for a given sulphoxide increases with increasing steric bulk of the alkylsalicylic acid used. With the homologous series of dialkyl sulphoxides R2SO, where R = n-butyl, n-hexyl, and n-octyl, there is little variation in the size of the synergistic shift for a given alkylsalicylic acid. For a series of sulphoxides containing similar numbers of carbon atoms, the extent of the shift increases with the introduction of alicyclic rings, but decreases when aromatic rings are introduced, for example, in the order of R: cyclohexyl > n-hexyl > phenyl, although the effect is not very marked. For a given extractant mixture, the pH50 values decrease from lanthanum to samarium and then increase from samarium to lutetium. The separation between the pH50 va...

SOLVENT EXTRACTION OF NEODYMIUM(III) AND ERBIUM(III) FROM CHLORIDE MEDIA BY MIXTURES OF 3,5- DIISOPROPYLSALICYLlC ACID AND NEUTRAL ORGANOPHOSPHORUS COMPOUNDS

ABSTRACT Neutral organophosphorus compounds containing a phosphoryl donor group were found to cause synergistic shifts in the extraction of neodymium(III) and erbium(III) from chloride media by solutions of 3,5-diisopropylsalicyUc acid in xylene. With the series of compounds containing n-butyl substituent groups (R), the extent of the synergistic effect for both metals follows the order of increasing basicity caused by the progressive replacement of alkoxy groups by alkyl groups through the series: (RO)3PO < (RO) 2RPO < (RO)R2PO < R3PO. For the series of compounds with R = isobutyl, irregularities occur in this order, presumably because of steric effects. Both steric and electro-inductive effects appear to play a role in determining the extent of the synergistic shifts caused by the series of isomeric phosphonates, (n-C4H9O) 2RPO, where R = n-butyl, isobutyl, sec-butyl and tert-butyl. Treatment of distribution data by slope analysis and by the method of continuous variation suggests that the extracted neo...