Separation of rhodium from iridium with sodium borohydride and standardization of rhodium(III) solutions

Of the platinum group metal separations, that of rhodium from iridium is the most difficult. The existing gravimetric methods are too lengthy or make use of organic reagents which ultimately need to be removed before iridium can be determined. The proposed method of separation is rapid, needs no pH control, and easy to carry out. Rh(III) ions are quantitatively reduced to Rh(0) by the action of aqueous sodium borohydride. The separation is best achieved in perchlorate medium in the presence of hydroxylamine. The separation is dependent on the concentration ratio of iridium to rhodium; if this is high, some iridium is co-precipitated; if low, the rhodium obtained is free from even spectrographic traces of iridium. A new method for standardization of Rh(III) solutions with sodium borohydride is proposed.     

Distribution of Pu(VI) from nitric acid to tri-n-butyl phosphate saturated with uranium(VI)

Solvent extraction of plutonium(VI) from nitric acid (1 to 5M) into 20% and 30% TBP in dodecane saturated with uranium(VI) (0% to 80%) has been studied. For a particular nitric acid concentration, the distribution coefficient (K _d ) is found to decrease with the increase in saturation of organic phase with uranium(VI). At a fixed organic phase the saturationK _d increased with increase in nitric acid concentration, however, the magnitude of this increase inK _d decreased with the increase in saturation.     

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)₄ ^2– and the cationic potassium complex of dicyclohexyl-18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)4(2-) and the cationic potassium complex of dicyclohexyl- 18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

Reversed-phase extraction chromatography of iron(III) with tri-n-butyl phosphate on silica gel

Iron(III) is separated by reversed-phase extraction chromatography with TBP as the stationary phase on a column of silica gel, with 2-6M hydrochloric acid as the mobile phase. From knowledge of the distribution coefficients, several separations have been devised, such as separation of Fe(III) from alkali and alkaline earth metals, chromium, manganese, cobalt, nickel, copper, vanadium zirconium, thorium, uranium, yttrium and titanium.     

Extraction of rhodium(III) with sulfoxides from hydrochloric acid solutions

Extraction of rhodium(III) from hydrochloric acid solutions with dihexyl sulfoxide (DHSO) and with petroleum sulfoxides (PSOs) was studied, and the optimal conditions for its recovery were found. At a phase contact time of up to 0.5 h, the extraction of rhodium(III) with sulfoxides occurred mainly by an ionassociation scenario. If the phase contact time exceeds 0.5 h, a mixed extraction scenario predominated to form the extracted complexes (L · H⁺) · [RhCl₄L₂]-(DHSO)_o and PSO (LH⁺) · [RhCl₄(H₂O) · L]⁻. The protonation of the extraction agents occurred at the donor oxygen atoms of the sulfoxide group. When rhodium was extracted with PSOs, the coordination of the extractant molecule in the inner coordination sphere of the acido complex to the metal ion occurred through the donor sulfur atom of the sulfoxide group, while with the use of DHSO, through the donor atoms of sulfur and oxygen of the sulfoxide group. Electronic, ¹H NMR, and IR spectroscopy and elemental analysis were used to determine the composition of the extracted compounds and suggest their structure.     

Separation and determination of trace amounts of beryllium(II), aluminium(III) and chromium(III) with chromotrope 2C chelates by RP-HPLC

A reversed-phase high-performance liquid chromatographic separation and determination of beryllium(II), aluminium(III) and chromium(III) with chromotrope 2C chelates on a C18-bonded stationary phase is reported. Methanol-water (45:55 v/v) containing 6 x 10(-3)M tetra-n-butylammonium bromide (TBAB) and 2 x 10(-2)M acetate buffer solution (pH 6.0) as mobile phase and with spectrophotometric detection at 530 nm was applied. The method has high sensitivity, the detection limits being 0.2 ppb for beryllium(I), 1 ppb for aluminium(III) and 2 ppb for chromium(III). Under the optimum conditions, most other metal ions did not interfere, e.g. up to 2 mg of Hg(II), Sn(II, IV), Pb(II), Bi(III), Ag(I), Zn(II), Cd(II), Cu(II), 1.5 mg of Fe(II), Co(II), Ni(II), 1.2 mg of Ca(II), Mg(II), Sr(II), Ba(II), 1 mg of Ga(III), In(III), 0.5 mg of Fe(III), 1 mg of Ga(III), In(III), 0.5 mg of Fe(III), 0.4 mg of Th(IV), Zr(IV). The method can be applied to the simultaneous determination of trace amounts of beryllium(II), aluminium(III) and chromium(III), in water, rice, flour and human hair samples.     

Extraction of rhodium(III) with petroleum sulfoxides from hydrochloric acid solutions

Extraction of rhodium(III) from hydrochloric acid solutions with petroleum sulfoxides was studied. The optimal conditions of its recovery were found. The composition and structure of the compound being extracted was determined by electronic absorption, ¹H NMR, and IR spectroscopies and elemental analysis.     

The speciation of rhodium(III) in hydrochloric acid media by capillary zone electrophoresis

A fast and effective method to study the aquation of rhodium(III) chlorocomplex in hydrochloric solutions using capillary zone electrophoresis (CZE) is developed. At least five species, some of which seem to be oligomeric, are formed in solution during the aquation process at pH>1. The fast hydration of RhCl₆³⁻ makes this species impossible to detect. The first species detected in the optimised conditions is RhCl₅(H₂O)²⁻ although RhCl₄(H₂O)₂⁻ is the main species during the first stage of the aquation process. When equilibrium is reached either RhCl₃(H₂O)₃ or a cationic complex, RhCl₂(H₂O)₄⁺, is formed as the main species. Matrix Assisted Laser Desorption Ionisation Time of Flight Mass Spectrometry (MALDI-TOF MS) is used as a novel technique to elucidate the structure of the rhodium aqua/chloro complexes formed in solution. Results obtained by CZE are confirmed by spectrophotometry.     

Fluorimetric trace determination of cerium(III) with sodium triphosphate

Sodium triphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III). The purpose of this study was to investigate the spectrofluorimetric determination of trace amounts of Ce(III) in sodium triphosphate solution. The excitation and emission wavelengths are 303.5 nm and 353 nm respectively. Optimum sodium triphosphate concentration is found to be 0.074 g l(-1) at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range 0.001-45 mug ml(-1). The detection limit is 9.4 x 10(-4)mug ml(-1). The relative standard deviations for 30 mug ml(-1) and 0.05 mug ml(-1) Ce(III) in 0.074 g l(-1) sodium triphosphate solution are 1.1% and 0.72% respectively. Quenching effects of other lanthanides and some inorganic anions are described. This method is a direct and rapid analytical method for the determination of Ce(III) in rare earth mixtures and cerium concentrates.     

Separation of cerium from other lanthanides by leaching with nitric acid rare earth(III) hydroxide-cerium(IV) oxide mixtures

A simple operational method for separating cerium from other lanthanides in natural mixtures of cerium dioxide with lanthanide(III) hydroxides, obtained from Vietnamese parisite and Mongolian bastnasite, has been developed. The method is based on drying crude Ln(OH)₃×H₂O material in air at about 200°C within 6h, followed by leaching Ln(III) with concentrated nitric acid added carefully with stirring to the dried material/water 11.5 slurry. Under optimum conditions cerium (and Th, if present) virtually does not pass into solution while the yield of leaching and the sum of REE oxides (REO) concentration in the after-leach solution reach the maximum values of 97% (mass) and 0.18 kg·dm^–3, respectively. Besides an expected decrease of the leaching yield, roasting the starting material at 600°C results in over 7% Ce content in the Ln leached.     

Synergistic extraction of uranium(VI) with tri-n-butyl phosphate and i-butyldodecylsulfoxide

Summary The synergistic extraction of uranium(VI) from aqueous nitric acid solution with a mixture of tri-n-butyl phosphate (TBP) and i-butyldodecylsulfoxide (BDSO) in toluene was investigated. The effects of the concentrations of extractant, nitric acid, sodium nitrate and sodium oxalate on the distribution ratios of uranium(VI) have been studied. The values of enthalpy change for the extraction reactions with BDSO, TBP and a mixture of TBP and BDSO in toluene were -23.2±0.8 kJ/mol, -29.2±1.4 kJ/mol and -30.6±0.6 kJ/mol, respectively. It has been found that the maximum synergistic extraction effect occurs when the molar ratio of TBP to BDSO is close to 1. The composition of the complex of the synergistic extraction is UO₂(NO₃)₂ ^. BDSO ^. TBP.     

Extractive spectrophotometric determination of trace amounts of iron(III) with benzyltriethylammonium chloride

The ion-association complex formed between a thiocyanato-iron(III) ion and a benzyltriethylammonium ion is extracted into 1,2-dichloroethane, and its absorbance at 476 nm is used for determination of the iron. Beer's law is obeyed up to about 4 mug/ml iron concentration in the final solution. The molar absorptivity is 2.79 x 10(4) l.mole(-1).cm(-1).     

Liquid-liquid extraction of rhodium(III) from hydrochloric acid solutions with 1,2,4-triazole derivative

Liquid-liquid extraction of rhodium(III) from hydrochloric acid solutions with a 1,2,4-triazole derivative was studied. Optimal conditions for its recovery were found. Rhodium(III) was shown to be recovered in extraction system by ion-exchange reaction at the time of phase contact not longer than 5 min. When phase contact time increased, rhodium(III) is extracted by a mixed mechanism with simultaneous insertion of two extractant molecules into the inner coordination sphere of rhodium(III) ion. Composition of coordination species of recovered compounds was established by electronic, IR, ¹H and ¹³C NMR spectroscopy and functional analysis, the structure of the coordination species is proposed.     

Complex rhodium(III) salts with isonicotinic acid: Synthesis and study

A method for the synthesis of complex rhodium(III) salts of the trans-dichlorotetramine series with isonicotinic acid (iso-NicH) was developed. Three new compounds were isolated: [Rh(iso-NicH)₃(iso-Nic)Cl₂] (I), [Rh(iso-NicH)₄Cl₂]Cl · 4H₂O (II), and Na3[Rh(iso-Nic)₄Cl₂] · 9H₂O (III). The compounds synthesized were characterized by elemental analysis, X-ray phase analysis, and IR spectroscopy. The crystal structures of salts II and III were determined by X-ray diffraction analysis. The thermal properties of all compounds were studied by the DTA method. The intermediate and final thermolysis products were isolated and characterized.     

State of rhodium(III) in sulfuric acid solutions

The formation of rhodium(III) sulfate complexes under moderately rigorous temperature conditions was studied by ¹⁰³Rh and ¹⁷O NMR spectroscopy. The complexes [Rh₂(μ-SO₄)₂(H₂O)₈]²⁺, [Rh₂(^*μ-SO₄)(H₂O)₈]⁴⁺, and [Rh₃(μ-SO₄)₃(μ-OH)(H₂O)₁₀]²⁺ were found to be the most stable species in aged solutions.     

Spectrophotometric determination of trace amounts of iron(III) with norfloxacin as complexing reagent

The complexation of iron(III) with norfloxacin in acidic solution at 25 degrees C, at an ionic strength of about 0.3 M and a pH of 3.0 has been studied. The water-soluble complex formed, which exhibits an absorption maximum at 377 nm, was used for the spectrophotometric determination of trace amounts of iron(III). The molar absorptivity was 9.05 x 10(3) I mol-1 cm-1 and the Sandell sensitivity 6.2 ng cm-2 of iron(III) per 0.001 A. The formation constant (Kf) was determined spectrophotometrically and was found to be 4.0 x 10(8) at 25 degrees C. The calibration graph was rectilinear over the range 0.25-12.0 p.p.m. of iron(III) and the regression line equation was A = 0.163c - 0.00042 with a correlation coefficient of 0.9998 (n = 9). Common cations, except cerium (IV), did not interfere with the determination. The results obtained for the determination of iron(III) using the described procedure and the thiocyanate method were compared statistically by means of the Student t-test and no significant difference was found.