The separation of Cerium(IV) from nitric acid solutions containing Thorium(IV) and Lanthanides(III) using pure [C(8)mim]PF6 as extracting phase

The extraction behavior of Ce(IV) along with Th(IV) and Ln(III) (Ln = Ce, Gd, Yb) nitrate by pure ionic liquid, [C(8)mim]PF6, was investigated. [C(8)mim]PF6 alone showed good extraction ability for Ce(IV), while it was slight for Th(IV) and negligible for Ln(III). The extraction behavior of Ce(IV) by [C(8)mim]PF6 was particularly studied, and the most probable extraction mechanism proposed was the anion exchange mechanism. Moreover, the stripping of Ce(IV) from IL phase was also investigated. The Ce(IV) in IL phase can be quantitatively recovered by water.

Extraction and separation of cerium(IV) from nitric acid solutions containing thorium(IV) and rare earths(III) by DEHEHP

The extraction behaviour of Ce(IV), Th(IV) and part of RE(III), viz., La, Ce, Nd and Yb, has been investigated using di(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP,B) in heptane as an extractant. Results show that extractability varies in the order: Ce(IV) > Th(IV) much greater than RE(III). Therefore, it is possible to find the appropriate conditions under which Ce(IV) can be effectively separated from Th(IV) and RE(III). Furthermore, stripping Ce(IV) from the loaded organic phase can be carried out by dilute H2SO4 with an aliquot of H2O2.Roasted bastnasite made in Baotou (China) by Na2CO3 and leached by HNO3, there is about 50% Ce mainly as tetravalent nitrate along with other RE(III) and Th(IV) in the leachings. Through fractional extraction, taking nitric acid leachings of roasted Bastnasite as feed and DEHEHP as an extractant, we can obtain the CeO2 products with high purity of 99.9-99.99%, with a yield of >85%, in which ThO2/CeO2 < 10(-4).

Liquid-liquid extraction of cerium(IV) from nitric acid media by di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP)

In this paper, the extraction of Ce(IV) from nitric acid solutions is investigated using di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP, B) in heptane as extractant. Ce(IV) can be extracted effectively from nitric acid solution, whereas it is poorly extracted from sulfuric acid solution. Compared with some other organophosphorus esters, DEHEHP has moderate extractablity for Ce(IV). The extraction efficiency varies with diluent in the order: aliphatic hydrocarbons > nitrobenzene > aromatic hydrocarbons > carbon tetrachloride > chloroform. Regeneration and loading capacities of DEHEHP have also been examined. Ce(IV) extraction in HNO3 solutions as well as extraction of HNO3 and H2O have been systematically studied. The Ce(IV) extraction increases with an increasing of HNO3 concentration and exhibits the maximum distribution ratio at 1-1.5 mol/L HNO3. Nitric acid, as a source of nitrate ion, enhances the extraction of metal ion. But it also competes with metal ions for extractant molecules by its own extraction under high acidities. The proposed extraction process is described by the following equilibrium equations

Microwave-assisted digestion procedures for biological samples with diluted nitric acid: Identification of reaction products

Microwave-assisted sample preparation using diluted nitric acid solutions is an alternative procedure for digesting organic samples. The efficiency of this procedure depends on the chemical properties of the samples and in this work it was evaluated by the determination of crude protein amount. fat and original carbon. Soybeans grains, bovine blood. bovine muscle and bovine viscera were digested in a cavity-microwave oven using oxidant mixtures in different acid concentrations. The digestion efficiency was evaluated based on the determination of residual carbon content and element recoveries using inductively coupled plasma optical emission spectrometry (ICP OES). In order to determine the main residual organic compounds, the digests were characterized by nuclear magnetic resonance (1 H NMR). Subsequently, studies concerning separation of nitrobenzoic acid isomers were performed by ion pair reversed phase liquid chromatography using a C18 stationary phase, water:acetonitrile:methanol (75:20:5, v/v/v) +0.05% (v/v) TFA as mobile phase and ultraviolet detection at 254 nm. Sample preparation based on diluted acids proved to be feasible and a recommendable alternative for organic sample digestion, reducing both the reagent volumes and the variability of the residues as a result of the process of decomposition. It was shown that biological matt-ices containing amino acids, proteins and lipids in their composition produced nitrobenzoic acid isomers and other organic compounds after cleavage of chemical bonds. (C) 2009 Elsevier B.V. All rights reserved.

Coordination reactions in the extraction of cerium(IV) and fluorine(I) by DEHEHP from mixed nitric acid and hydrofluoric acid solutions

The coordination reactions during the solvent extraction of cerium(IV) and fluorine(l) from mixed nitric acid and hydrofluoric acid solutions by di-(2-ethylhexyl)-2-ethylhexylphosphonate, L (DEHEHP) in heptane have been investigated. The extraction data have been analyzed by graphical methods taking into account all plausible species extracted into the organic phase. Different variables influencing the extraction of Ce(IV), such as the concentrations of nitrate ions, hydrofluroric acid, nitric acid, and extractant have been studied. The results demonstrate that DEHEHP can extract not only Ce(NO3)(4) as Ce(NO3)4.2L and HF as HF (.) H2O (.) L, but both together as Ce(HF)(NO3)(4) (.) L. The extraction equilibrium equations are determined according to slope analysis and IR spectra. The equilibrium constants of the extracted complexes have been calculated, taking into account complexation between the metal ion and inorganic ligands in the aqueous phase and all plausible complexes extracted into the organic phase. It is also shown that boric acid, which was added into the mixed solutions to complex with F(I) is not extracted by DEHEHP, and neither does it affect the extraction of cerium(IV) and HF, nor change the extraction mechanism.

Solubility of sulfur dioxide at low partial pressures in dilute sulfuric acid solutions

Equilibrium of dissolution of sulfur dioxide at ppm levels in aqueous solutions of dilute sulfuric acid is analyzed, and a general expression is derived relating the total concentration of sulfur dioxide in the liquid phase to the partial pressure of SO2 in the gas and to the concentration of sulfuric acid in the solution. The equation is simplified for zero and high concentrations of the acid. Experiments at high concentrations of sulfuric acid have enabled the direct determination of Henry’s constant and its dependency on temperature. Heat of dissolution is -31.47 kJ/mol. Experiments in the absence of sulfuric acid and the related simplified expression have led to the determination of the equilibrium constant of the hydrolysis of aqueous sulfur dioxide and its temperature dependency.The heat of hydrolysis is 15.69 kJ/mol. The model equation with these parameters predicts the experimental data of the present work as well as the reported data very well.

Solvent extraction of scandium(III), yttrium(III), lanthanum(III) and gadolinium(III) using Cyanex 302 in heptane from hydrochloric acid solutions

The extractions of the selected rare earths (Sc, Y, La and Gd) from hydrochloric acid solutions have been investigated using bis(2,4,4-trimethylpentyl)-mono thiophosphinic acid (Cyanex 302, HL) in heptane as an extractant. The results demonstrate that the extractions of rare earths occur via the following reaction: Sc(OH)(2+) + 2[(HL)(2)]((O)) double left right arrow [Sc(OH)L-2 (.) 2(HL)]((O)) + 2H(+) Y3+ + 3[(HL)(2)]((O)) double left right arrow [Y(HL2)(3)]((O)) + 3H(+) La(OH)(2)(+) + 3[(HL)(2)](O) double left right arrow [La(OH)(2)L (.) 5(HL)]((O)) + H+ Gd(OH)(2+) + 3[(HL)(2)]((O)) double left right arrow [Gd(OH)L-2 (.) 4(HL)]((O)) + 2H(+) The pH(1/2) values and equilibrium constants of the extracted complexes have been deduced by taking into account the aqueous phase complexation of the metal ion with hydroxyl ligands and plausible complexes extracted into the organic phase. According to the pH(1/2) values, it is possible to realize mutual separation among Sc(III), Y(III), La(III) and Gd(III) with Cyanex 302 by controlling aqueous acidity.

Separation of thorium(IV) and extracting rare earths from sulfuric and phosphoric acid solutions by solvent extraction method

The bastnasite of Baotou (China) was roasted in concentrated sulfuric acid at 250-300 degreesC and the calcined products were leached by water. Almost all rare earths (RE) were moved into solutions in trivalent along with some radioactive impurity thorium(IV) (Th(IV))which accounts for 0.4% of RE and other impurities such as Fe(III), Ca, F, P, etc. Through fractional extraction (seven stages for extraction and nine for scrubbing), the mass ratio of Th(IV) and RE (ThO2/REO) in solution has decreased to 5 x 10(-6). The purity of ThO2 product recovered from organic phase is above 99%. The iron(III) in solutions can be removed in the form of precipitation by adding some magnesia into the solutions. Then RE can be concentrated by solvent extraction with 2-ethylhexyl phosphinic acid 2-ethylhexylester (P-507). The results of fractional extraction show that the concentration of total RE in aqueous solutions stripped by hydrochloric acid is over 200 g REO/I with the yield of RE above 99%. Individual RE can be attained by solvent extraction with P507 in the following process.

EXTRACTION MECHANISM OF SC(III) AND SEPARATION FROM TH(IV),FE(III) AND LU(III) WITH BIS(2,4,4-TRIMETHYLPENTYL)PHOSPHINIC ACID IN N-HEXANE FROM SULFURIC-ACID-SOLUTIONS

The extraction equilibrium data of sulphuric acid and scandium(III) with bis(2,4,4-trimethylpentyl)phosphinic acid (H[BTMPP]) from sulphuric acid solutions have been obtained. There are two extraction mechanisms of scandium(III) with H[BTMPP] at different

The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative

The title compound 1-(4,5-dihydro-3-phenylpyridine-1-yl)-2-(1H-1,2,4-triazole-1-yl)ethyl ketone (DTE) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electronic microscope (SEM). Results obtained revealed that DIE performed excellently as a corrosion inhibitor for mild steel in 1 M hydrochloric acid media and its efficiency attains more than 90.9% at 1.0 x 10(-3) M at 298 K. Polarization curves indicated that the inhibitor behave mainly as mixed-type inhibitor. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. And the values of the free energy of adsorption Delta G(ads) indicated that the adsorption of DTE molecule was a spontaneous process and was typical of chemisorption. (c) 2008 Elsevier B.V. All rights reserved.

OXIDATION OF RUTHENIUM(II) TRIS(2,2'-BIPYRIDINE) IONS BY THALLIC IONS IN NITRIC-ACID, MEDIATED BY RUTHENIUM DIOXIDE HYDRATE - AN EXAMPLE OF REVERSIBLE HETEROGENEOUS REDOX CATALYSIS

The kinetics of the oxidation of Ru(bpy)32+ to Ru(bpy)33+ by T13+ ions, catalyzed by a dispersion of RuO2-xH2O in 3 mol dm-3 HNO3, are reported as a function of [Ru(bpy)32+], [Tl3+], [Tl+], [RuO2.xH2O], and temperature. The kinetics of Ru(bpy)32+ oxidation fit an electrochemical model of redox catalysis involving electron transfer between the two electrochemically reversible redox couples, i.e. Ru(bpy)33+/Ru(bpy)32+ and Tl3+/Tl+, mediated by the dispersion of microelectrode particles of RuO2.xH2O. In this model, the rate of reaction is assumed to be controlled by the diffusion of Ru(bpy)32+ toward, and Ru(bpy)33+ away from, the catalyst particles. The Arrhenius activation energy for the catalyzed reaction is 25.9 +/- 0.7 kJ mol-1, and the changes in enthalpy and entropy for the reaction are 36 +/- 2 kJ mol-1 and 127 +/- 6 J mol-1 K-1, respectively. This work describes a rare example of reversible heterogeneous redox catalysis.