John S. Preston

Solvent extraction of cobalt and nickel by organophosphorus acids I. Comparison of phosphoric, phosphonic and phosphonic acid systems

The solvent extraction of cobalt(II) and nickel(II) by xylene solutions of commercial dialkyl-phosphoric (D2EHPA), phosphonic (Shell RD 577) and phosphinic acids (Cyanex CNX) has been investigated. In each case, cobalt is extracted at lower pH values than nickel; under comparable conditions, the cobalt-nickel separation increases in the order phosphoric < phosphonic < phosphinic acids. Application of the slope analysis technique indicates stoichiometries of Co(HA2)2 and NiHA2)2(H2A2)x(H2O)2−x for the cobalt and nickel complexes, respectively, where H2A2 represents the dimerized extractant molecule and x = 0, 1, or2. The effect of a range of organic phase additives has been examined. Typical emulsion inhibiting reagents such as isodecanol and tributyl phosphate cause the cobalt—nickel separations to decrease significantly. A novel synergistic effect has been found with mixtures of D2EHPA and 2-ethylhexanal oxime (EHO); the synergism is so marked in the case of nickel as to reverse the selectivity for cobalt over nickel shown by D2EHPA alone. The electronic spectra of the organic extracts show that the organophosphorus acids examined from complexes of tetrahedral structure with cobalt and octahedral structure with nickel. In the D2EHPA—EHO system, however, the deep blue tetrahedral cobalt-D2EHPA complex is transformed into a pink octahedral complex, presumably of the type Co(HA2)2(EHO)2, whilst the green octahedral nicke—D2EHPA complex is converted to a bright blue species of similar geometry, in which the neutral oxygen-donor ligands (H2A2 and/or H2O) have been displaced by the nitrogen-donor oxime ligands.

The recovery of rare earth oxides from a phosphoric acid by-product. Part 1: Leaching of rare earth values and recovery of a mixed rare earth oxide by solvent extraction

The development of a process for the recovery of a mixed rare earth oxide from calcium sulphate sludges obtained in the manufacture of phosphoric acid from a South African apatite ore is described. The leaching of the rare earth values from the sludges by dilute nitric acid is considerably enhanced by the addition of calcium nitrate to the lixiviant, enabling recoveries of up to 85% to be achieved. The rare earth values can be recovered from a leach liquor containing 1.0 M nitric acid and 0.5 M calcium nitrate by the addition of 2.5 M ammonium nitrate and extraction into 33 vol%v dibutyl butylphosphonate in Shellsol 2325. The organic phase can be stripped with water, preferably at temperatures above ambient, to yield a solution of rare earth nitrates from which the mixed oxide can be recovered by the addition of oxalic acid, and calcination of the precipitate. In a continuous counter-current laboratory trial of the process, a total of 140 kg of sludge was processed to produce 265 1 of leach liquor, which was treated in five extraction and five stripping stages to give a strip liquor from which 4 kg of mixed rare earth oxide of 98% purity was recovered. In a pilot-plant evaluation, the organic phase was changed to 40 vol% tributyl phosphate in order to enhance the stripping characteristics (as well as for economy), and the leach liquor was changed to 1.0 M nitric acid plus 3.0 M calcium nitrate, the addition of ammonium nitrate then being unnecessary. Some 3200 kg of mixed rare earth oxalates were prepared and calcined in a rotary kiln to give 1600 kg of mixed oxide of 89–94% purity. In all of the continuous trials the raffinate from the solvent-extraction process was recycled to the leaching stage, without any deleterious effect on the leaching efficiency being apparent.

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).

Solvent extraction of nickel and cobalt by mixtures of carboxylic acids and non-chelating oximes

Abstract The effect of non-chelating oximes on the solvent extraction of nickel(II) and cobalt(II) by solutions of carboxylic acids (H 2 A 2 ) in xylene has been studied. Synergistic enhancements of extraction were found with aldoximes, but not with ketoximes. The synergistic effects are larger for nickel than for cobalt, with the result that the selectivities of the carboxylic acids for nickel over cobalt are considerably enhanced in the presence of aldoximes. The influence of the molecular structure of the oxime and carboxylic acid components upon the synergistic effects is rationalized in terms of the prevailing stereochemical and electronic effects. The extracted complexes were shown to be octahedral in structure, with the compositions NiA 2 (oxime) 4 and CoA 2 (oxime) 4 . The mixed reagent systems may prove useful for the selective extraction of nickel in the presence of cobalt.

Solvent extraction of base metals by mixtures of organophosphoric acids and non-chelating oximes

Abstract The effect of non-chelating oximes on the extraction of several transition and nontransition metals by solutions of organophosphoric acids (H 2 A 2 ) in xylene has been investigated. Synergistic enhancements of extraction of divalent transition metal ions were found with the oximes of aliphatic aldehydes, the enhancements of extraction increasing in the order VO 2+ 2+ 2+ 2+ 2+ 2+ 2+ . Large synergistic effects were also found for copper(I) and silver(I). Among the divalent non-transition metals studied (Mg, Ca, Zn, Cd, Sn, and Pb), only cadmium showed a synergistic effect. No significant synergism was found for any of the trivalent metal ions studied (Fe, Cr, V, Al, Bi, La, Ce, and Nd). The extracted complexes of copper, cobalt, and nickel were shown to be octahedral in structure, with the compositions Cu(HA 2 ) 2 (oxime) 2 , Co(HA 2 ) 2 (oxime) 2 , and NiA(HA 2 )(oxime) 3 , respectively, in which HA 2 − acts as a bidentate ligand. Extraction rates were found to be rapid, even for nickel, and complete stripping of metal-loaded organic phases was effected by contact with 0.5 M mineral acid. Some practical applications, such as the recovery of nickel from acidic leach liquors, are envisaged.

Separation of nickel and calcium by solvent extraction using mixtures of carboxylic acids and alkylpyridines

Abstract The solvent extraction of some base metals by mixtures containing a carboxylic acid and an alkylpyridine synergist was studied, with particular reference to the separation of nickel from calcium in sulphate media. The dependence of the synergistic shift in the pH 50 value (ΔpH 50 ) and the Ni–Ca separation (pH 50 Ca –pH 50 Ni ) on the identities of the carboxylic acid, the alkylpyridine and the organic diluent was examined. The effect of extractant concentration in the organic phase and the nature of the anion present in the aqueous phase (nitrate, chloride and sulphate) was also investigated. Large synergistic shifts were found for nickel, whereas antagonistic shifts were found for calcium, resulting in marked enhancement of the Ni–Ca separation, e.g. from 1.04 pH units for Versatic 10 acid (0.50 M in an aliphatic diluent) to 3.48 pH units for its mixture with 4-(5-nonyl)pyridine (0.50 M). The selectivity series for the extraction of divalent metals from sulphate media by the above-mentioned mixture lies in the order (pH 50 values in parentheses): Cu (3.16)>Ni (4.73)>Zn (4.94)>Co (5.41)>Fe (5.65)>Mn (6.45)>Ca (7.96)>Mg (8.43). This series suggests that in the recovery of nickel from laterite leach liquors, the mixed extractant systems would allow the early rejection of manganese, ferrous iron, calcium and magnesium to the raffinate, whilst the more valuable impurity metals (copper, cobalt and zinc) would report to the nickel strip liquor, from which they could be subsequently recovered. In batch countercurrent experiments, a simulated leach liquor containing (in g L −1 ): Ni 5, Mg 5, Mn 2, Co 0.5, Ca 0.5, Cu 0.1 and Zn 0.1 was contacted with the mixed extractant in three stages at unit organic-to-aqueous phase ratio and an equilibrium pH of 5.8. The recovery of nickel was 99.9% and that of cobalt was 98.8%, with co-extractions of manganese, calcium and magnesium of only 4.2%, 1.3% and 0.04%, respectively. Stripping of nickel with 0.25 M sulphuric acid was essentially complete (≥98%) in a single stage at an organic-to-aqueous phase ratio of 3.33, uptake of acid by the alkylpyridine component of the mixed extractant being avoided by operating the stripping stage in the equilibrium pH range of 3–4. The nickel-containing strip liquor can be purified by removal of the co-extracted cobalt, copper and zinc using a commercial organophosphinic acid extractant.

THE SOLVENT EXTRACTION OF RARE-EARTH METALS BY CARBOXYLIC ACIDS

ABSTRACT The solvent extraction of the trivalent lanthanides and yttrium from nitrate media by solutions of carboxylic acids in xylene has been studied. Commercially available carboxylic acids such as Versatic 10 and naphthenic acids were used, as well as model compounds of known structure, such as 2-ethylhexanoic and 3-cyclohexylpropanoic acids. In a few cases, extraction of the metals from sulphate and chloride solutions was also investigated. The dependence of the extraction properties of the carboxylic acids on the atomic number of the lanthanide shows a definite relationship to the steric bulk of the carboxylic acid molecule quantified by means of the steric parameter, Es′ of the substituent alkyl; group. For sterically hindered acids (− Es′ > 2) the pH0.5 of extraction decreases more or less continuously from lanthanum through to lutetium, and the behaviour of yttrium most closely resembles that of the middle lanthanides, such as gadolinium or terbium. For straight-chain and other non-hindered acids...

Solvent extraction of copper(II) with ortho-hydroxyoximes—I kinetics and mechanism of extraction

The preparations and properties of a number of ortho-hydroxyoximes are described. Several of the compounds have not previously been characterised. The kinetics of extraction of copper(II) from acidic perchlorate media into toluene solutions of these reagents has been investigated by means of a single drop technique. A mechanism consistent with the rate data is presented in which the importance of interfacial concentration terms is emphasised. Variations in the rates of extraction observed for compounds of different structures are rationalised in terms of the mechanism proposed.

The recovery of rare earth oxides from a phosphoric acid byproduct. Part 4. The preparation of magnet-grade neodymium oxide from the light rare earth fraction

Abstract The development of a solvent-extraction process for the recovery of magnet-grade neodymium oxide (95% Nd 2 O 3 ) from a light rare earth nitrate liquor is described. In a continuous counter-current mini-plant trial, 1901 of feed liquor containing 16–17 gl −1 Nd, 3.5 g l −1 Pr, 7 gl −1 Ce and 7.5 g l −1 La were processed in two separate passes with a combined duration of 220 h. In the first pass, 95% of the lanthanum and 75% of the cerium contained in the feed liquor were removed, whilst in the second pass the residual cerium and most of the praseodymium were extracted, leaving a purified neodymium solution as the raffinate. Both circuits used a 0.50 M solution of Aliquat 336 nitrate (tfcaprylmethylammonium nitrate) in Shellsol AB in 8 extraction and 6 scrubbing stages. Stripping of the loaded organic phase was carried out with water in 6 stages, part of the resulting strip liquor being recycled as the aqueous feed to the scrubbing circuit. Under conditions of sufficient reflux of strip liquor (ca. 40%), the raffinate from the second pass contained up to 75% of the neodymium present in the original feed at a purity of 95–96% Nd 2 O 3 (with 2% Pr 6 O 11 ; 1.5% Sm 2 O 3 ; 0.7% CeO 2 ; and 0.2% La 2 O 3 ). From the strip liquors produced in the first pass was obtained a lanthanum concentrate containing 51% La 2 O 3 (with 36% CeO 2 ; 7% Pr 6 O 11 ; and 6% Nd 2 O 3 ), whilst from the strip liquors produced in the second pass was obtained a praseodymium concentrate containing 32% Pr 6 O 11 (with 41% Nd 2 O 3 ; 22% CeO 2 ; and 4% La 2 O 3 ).

The recovery of rare earth oxides from a phosphoric acid by-product. Part 3. The separation of the middle and light rare earth fractions and the preparation of pure europium oxide

Abstract The development and operation of a continuous solvent extraction process for the separation of the middle (Sm, Eu, Gd, Tb) and light rare earth fractions (La, Ce, Pr, Nd) from a nitrate feed liquor is described. The process consists of extraction of the middle rare earths into a 15 vol% solution of D2EHPA in Shellsol AB in 8 counter-current stages, followed by scrubbing with 1 M nitric acid in 2–4 stages, and stripping with 1.5 M hydrochloric acid in 6–8 stages. Residual rare earth values in the organic phase (mainly Dy, with some Tb and Gd) were removed in a secondary stripping circuit using 2.5 M hydrochloric acid in 4 stages. More than 1000 1 of feed liquor were processed in two continuous counter-current trials lasting a total of 630 h. From a feed containing Sm 3.5, Gd 2.4, Eu 0.8 and Nd 20 g l −1 (together with 4–8 g l −1 each of the lighter rare earths), strip liquors containing Sm 35, Gd 20 and Eu 8 g l −1 were obtained, with neodymium (5 g l −1 ) as the main impurity. Recoveries of the middle rare earths to the strip liquors were high (95–100%), whereas losses of the light rare earths were low (0–4%). Addition of oxalic acid to the strip liquors, followed by calcination of the precipitated oxalate, gave a middle rare earth oxide containing 45% Sm 2 O 3 , 29% Gd 2 O 3 , 13% Eu 2 O 3 and 6% Nd 2 O 3 . This oxide was dissolved in acetic acid and electrolysed in 1 M potassium citrate solution, using a mercury cathode and a platinum anode, to give a europium amalgam containing a small amount of samarium (Eu:Sm ≈ 66:1). The amalgam was treated with acetic acid, and the resulting acetate solution was again electrolysed to give a purified amalgam from which was recovered a final europium oxide product containing only traces of other rare earths ( −1 Sm, −1 Nd and −1 each of Gd, Pr, Ce and La).