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Abstract  

The position of scandium and yttrium within lanthanides in respect to the enthalpies of solution of anhydrous rare earth halides has been discussed. It has been indicated that although the respective shift of Sc(III) as a quasi-heavy lanthanide is less pronounced than for Y(III), the overall covalency within the trivalent ions of the scandium group, Ln(III) and An(III) included, is the most pronounced for Sc(III) due to participation of the empty orbitals in bonding: Sc(III)>An(III)>Ln(III)> Y(III). The irregularity of this trend is produced by the superimposed participation of the 5f (An(III)) and, to a lesser extent, of the 4f (Ln(III)) orbitals in bonding. The crucial factor of a maximum difference between the product and substrate coordination number (CN) of the central ion for covalency, separation factor and isotope effect in chemical exchange is emphasized.

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Abstract  

The extraction behavior of nalidixic acid (HNA) in CH2Cl2 has been studied for various di- and trivalent metal ions such as Cu(II), Fe(II), Ni(II), Mn(II), Sb(II), Co(II), Sc(III), Y(III), Nd(III) and Eu(III) from aqueous buffer solutions of pH 1–7 with 0.1 mol dm−3 nalidixic acid in dichloromethane. Separation factors of Sc(III) from these metals has shown that its clean separation is possible at pH 3.4–4. The parameters affecting the extraction of Sc(III) were optimized. The composition of the extracted adduct was determined by slope analysis method that came out to be Sc(NA)3. Extraction of Sc(III) was studied in the presence of various cations and anions. Among the anions studied only fluoride, citrate and oxalate have significant interference whereas, Fe(III) has reduced the extraction to 53% that can be removed by using ascorbic acid as reducing agent. The proposed extraction system proved good stability up to six extraction-stripping stages for the extraction of Sc(III).

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Abstract  

A rapid, selective and simple method has been developed for the determination of Sc in rock samples by thermal neutron activation analysis, employing substoichiometric solvent extraction of Sc(III) with alizarin into 1-octanol. Two samples and a standard can be processed and counted within three hours.

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Abstract  

The soprtion behaviour of Fe(III), Cr(III), Sc(III), Y(III) and U(VI) toward cationite KU-2 and silica gel under hydrolysis condition has been studied. The role of mononuclear and polynuclear hydroxo complexes in sorption is demonstrated and the mechanism of the sorption process is analyzed.

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The conditions of thermal decomposition of scandium(III) hemimellitate, trimellitate and trimezinate in air and nitrogen atmospheres have been studied. On heating, the benzene-tricarboxylates of Sc(III) decompose in two stages. First, the hydrated complexes lose crystallization water; heating in air finally yields Sc2O3, and heating in a nitrogen atmosphere Sc2O3 and C. The dehydration of the complexes is associated with strong endothermic effects. The decomposition of benzenetricarboxylates in air is accompanied by an exothermic effect and in nitrogen by an endothermic effect.

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Abstract  

The extraction of palladium/II/ with diphenyl-2-pyridylmethane /DPPM/ in benzene has been investigated from thiocyanate-nitrate media and optimized. Thiosulphate ions showed strong interference and reduced the extraction below 1%. Separation factors determined for most of the elements were better than 103. This extraction method affords palladium preconcentration and its separation from Sc/III/, Co/II/, Cu/II/, Zn/II/, Se/IV/, Sr/II/, Ru/III/, Cd/II/, Cs/I/ and Eu/III/. Few possible applications of such separations have been cited.

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Abstract  

The sorption of Cd(II) on Haro river sand from deionized water is reported. The sorption system obeyed according to the Freundlich and Dubinin–Radushkevich (D-R) isotherms. The Freundlich parameters 1/n = 0.67±0.05 and of A = 1.38±1.14 mmole·g-1 have been ascertained. D-R isotherm yields the values of = -0.003741±0.000321 kJ2·mole-2, X m = 0.23±0.21 mole·g-1 and of E = 11.6±0.5 kJ·mole-1. The influence of common anions and cations on the sorption was examined. Trivalent Bi enhances the sorption whereas Fe, Cr, Al and chromate ions reduce the sorption significantly. Hf(IV) and Ag(I) indicate substantial sorption (61–98%) whereas Gd(III), Re(VII) and Sc(III) show low sorption (<5%). The elements having low sorption can be separated from elements indicating higher sorption using Haro river sand column.

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The effect of the central ion of tris- β -diketonato complexes of transition metals on their hR F values in thin layer chromatography (TLC) on silica gel has been investigated for 24 Co(III), Cr(III), and Ru(III) complexes of the types [M(acac) 3− n (phacphac) n ] and [M(acac) 3− n (phacphSac) n ], where n = 0–3, and with four complexes of the type [M(acac) 3 ], where M = Sc(III), Y(III), Nd(III), or La(III), acac is the 2,4-pentanedionato ion, phacphac is the 1,3-diphenyl-1,3-propanedionato ion, and phacphSac is the 3-mercapto-1,3-diphenylprop-2-en-1-one ion. One- and two-component non-aqueous mobile phases were used for the chromatographic separations. The dependence of retention data on the length of ionic radius and on En/r i value is discussed. The mobility ( hR F values) of the tris(acetylacetonato) complexes on thin layers of silica gel is directly proportional to the ionic radius of the central ion. On the basis of the results obtained, adsorption was assumed to be the dominant mechanism of separation under the chromatographic conditions used.

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Abstract  

The sorption of hafnium on hydrous titanium oxide (TiO2·1.94 H2O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g–1·min–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK =6.33·10–2 min–1 and of the rate constant for sorptionk 1=6.32·10–2 min–1 and desorptionk 2=2.28·10–5 min–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10–5 to 9.01·10–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g–1 and of a constant related to sorption energy have been estimated to be 2917 dm3·mole–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.

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