Solubility of YF<Subscript>3</Subscript>, CeF<Subscript>3</Subscript>, PrF<Subscript>3</Subscript>, NdF<Subscript>3</Subscript>, and DyF<Subscript>3</Subscript> in solutions containing sulfuric and phosphoric acids

The solubility of YF₃, CeF₃, PrF₃, NdF₃, and DyF₃ in solutions containing 0–4.496% mol/L (0–35 wt %) of H₂SO₄ and 0–27.6 g/L of H₃PO₄ (0–20 g/L of P₂O₅) at 20 °C was determined. Higher solubility in sulfuric acid solutions compared to that in hydrochloric and phosphoric acid solutions was attributed to the formation of fluorosulfate complexes M₂(SO₄)F₄(M = Y, Ce, Pr, Nd, Dy). The effect of minor concentrations of the phosphate ions on the solubility of YF₃, CeF₃, PrF₃, NdF₃, and DyF₃ in sulfuric acid solutions and the effect of fluoride ions on the recovery of lanthanides during sulfuric acid leaching from the phosphohemihydrate were discussed.     

On the emitters of sulfuric acid sonoluminescence

A comparative study of the sonoluminescence spectra of water and argon-saturated aqueous H₂SO₄ solutions was carried out. At an H₂SO₄ concentration of 18 mol L⁻¹, the sulfuric acid sonoluminescence is fifty times more intense than water sonoluminescence. The sulfuric acid luminescence spectrum differs from the water sonoluminescence spectrum caused by the emission of excited water molecules and OH radicals from the gas phase of cavitation bubbles. The sulfuric acid sonoluminescence spectrum exhibits maxima at 330, 420, 500, and 630 nm. Emitters of sonoluminescence of sulfuric acid are the singlet (330–340 nm) and triplet (∼420 nm) excited SO₂ molecules formed by sonolysis of H₂SO₄ molecules. Another product of sonolysis of H₂SO₄, atomic oxygen, is assumed to be responsible for the luminescence at λ = 630 nm. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1742–1745, August, 2005.     

Electrochemical behavior of Ti(IV)/Ti(III) redox couple on dropping mercury electrode in sulfuric acid aqueous and aqueous-organic media

The processes of electrochemical reduction of Ti(IV) and oxidation of Ti(III) in aqueous solutions of H₂SO₄ not containing and containing AcOH or MeCN are studied by the methods of classical and commutation polarography. It is shown that in the absence of organic solvents the heterogenous electron transfer is irreversible in the media with the sulfuric acid concentration up to 9 M, while in aqueous-organic solution the same occurs at the concentration up to 7 M. Organic solvents are involved into the process of complex formation and like H₂SO₄, influence the step of heterogenous electron transfer; this effects weakens with the increase in the concentration of sulfuric acid.     

Solubility of Double Alkali Metal (Na, K) Rare-Earth (La, Ce) Sulfates in Sulfuric-Phosphoric Acid Solutions at 20°C

The dependence of the solubility of NaLa(SO₄)₂·H₂O, NaCe(SO₄)₂·H₂O, KLa(SO₄)₂·H₂O, and KCe(SO₄)₂·H₂O on the concentration of acids in sulfuric, phosphoric, and sulfuric-phosphoric acid solutions containing up to 36 wt % H₂SO₄ and 33.12 g l_-1 H₃PO₄ was studied at 20°C.     

Effect of electrolytes on the sensitivity of thermal-lens measurements in aqueous media

The thermooptical properties of aqueous solutions of strong electrolytes (H₂SO₄, HCl, NaCl, Na₂SO₄, and NaOH) are considered. The thermal lens signal depends on the nature of the electrolyte. The effect of an electrolyte is not the sum of the effects of the constituent ions. The largest gain in the sensitivity of thermal-lens measurements is achieved with sulfuric acid (sensitivity enhancement factor of 2 for 0.6 M H₂SO₄ versus water) and sodium chloride (sensitivity enhancement factor of 1.5 for 3 M NaCl), while the effect of hydrochloric acid is negligible.     

Solubility in the systems Rb2SO4-H2SO4-H2O and Cs2SO4-H2SO4-H2O at 25°

Conclusions The solubility of rubidium and cesium sulfates in aqueous solutions of sulfuric acid was studied at 25°. Rubidium sulfate forms the compounds 3Rb₂SO₄· H₂SO₄, Rb₂SO₄ · H₂SO₄, Rb₂SO₄·3H₂SO₄ and Rb₂SO₄·7H₂SO₄ with sulfuric acid, while cesium sulfate forms the compounds Cs₂SO₄·H₂SO₄; Cs₂SO₄·3H₂SO₄ and Cs₂SO₄ · 7H₂SO₄.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1166–1170, June, 1968.     

Cyclic Voltammetric Behavior of Uranyl ion in Sulfuric Acid Solutions. Application to Some Nuclear Materials Characterization

Abstract

The U(VI) reduction at mercury electrode in sulfuric acid solutions was examined by cyclic voltammetry (C. V.). A diffusion coefficient, D, was (5.30 ± 0.08) × 10^?6 cm²/sec was obtained for the depolarizer at 25.0±0.2°C in 1 N K₂SO₄ (pH = 2). In 1 N K₂SO₄/1 N H₂,SO₄ systems the disproportionation of U(V) was found to occur with the constant rate of K_d/[H⁺] = 6.500 ± 1.000 M^?2 sec^?1.

In 1 M H₂SO₄ supporting electrolyte pure kinetic control was achieved over the range of scan rates and uranyl concentration (C) investigated, hence linear correlation between cathodic peak current and C (above 5x10^?6 M) was obtained. Strong complexing oxyanions, such as phosphate and pyrosulphate, do not interfere with the cathodic peak current. Rapid determination of O/U ratios in uranium oxides and of U in mixed U-Th materials were performed respectively in 1 M H₂SO₄/1.5 M H₃PO₄ and 1 M H₂SO₄/0.2 M K₂S₂0₄ supporting media, with a reproducibility of ± 1.3% standard deviation.     

Ozone solubility in concentrated aqueous solutions of salts

The effect exerted by the concentration of salts (NaCl, Na₂SO₄, and NaNO₃) on the ozone solubility in aqueous solution at 20, 30, and 40°C was studied. The solubility coefficients of ozone were calculated. The Henry constants and the Sechenov coefficients were determined.     

Phase ratios in the M<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-SO<Subscript>3</Subscript> (M = Rb,Cs) systems and the properties of the compounds formed in these systems

Powder X-ray diffraction and microscopy have been used to study phase ratios of the M₂O-V₂O₅-SO₃ (M = Rb, Cs) systems, which model the active component of rubidium-vanadium and cesium-vanadium catalysts for sulfuric acid production at high sulfur dioxide conversions. We have stated that each system forms four compounds: M₃VO₂(SO₄)₂, MVO₂SO₄, M₄V₂O₃(SO₄)₄, and MVO(SO₄)₂. The thermal properties of these compounds and their interaction with water vapor saturated at room temperature have been studied. The unit cell parameters have been determined for the compounds MVO₂SO₄ (M = K, Rb), MVO(SO₄)₂, and M[VO₂(SO₄)(H₂O)₂] · H₂O (M = Rb, Tl). The reciprocal transformations of the components and phases of the M₂O-V₂O₅-SO₃ systems match the Lux-Flood ideas of the acid-base properties of oxide compounds.     

Hydrogen atoms trapped in acid ices at very low temperatures

The ratios of H_t yield at 4 K to that at 77 K were 8.2 and 1.0 for 0.6 M and 6 M H₂SO₄, respectively, whereas the ratio of the yield for 0.6 M H₂SO₄ to that for 6 M H₂SO₄ was 0.15 at 4 K. The effective number of near neighbor protons, n_eff, and their effective distance, r_eff, to H_t were obtained: n_eff = 3.1 and r_eff = 2.06 for 6 M H₂SO₄, and n_eff = 10.1 and r_eff = 2.46 for 0.6 M H₂SO₄ at 4 K. The results obtained for 6 M H₂SO₄ are interpreted in terms of the relaxation of the environment of H_t, whereas the results for 0.6 M H₂SO₄ imply trapping sites and the trapping mechanism which are different from those for either the glassy or pure ices.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.     

Preparation and Crystal Structure of Copper(I) Carbonyl Hydrogensulfate,obtained by Carbonylation in Sulphuric Acid

The hydrogensulfato‐carbonyl derivative [Cu(CO)(SO₄H)]_n, as obtained from the Cu₂O/ H₂SO₄/CO system and recrystallized from H₂SO₄/(CH₃O)₂SO₂ has been shown to possess a crystal structure organised in infinite chains built up by corner sharing of {CuO₃(CO)} and {S(OH)O₃} tetrahedra. The chains are connected by hydrogen bonds in layers, with CO groups leaning out on both sides. The absorption of CO by CuSO₄/Cu or by Cu₂O in sulfuric acid was quantified as a function of concentration. The CuSO₄/Cu system in water absorbs carbon monoxide (CO/Cu molar ratio = 1.0).     

Extraction of uranium (VI) from sulfuric acid solution with TOPO

The extraction of uranium(VI) from sulfuric acid medium with tri-octylphosphine oxide (TOPO) in n-heptane was studied. Accompanied with the increase in the concentration of H₂SO₄, the distribution coefficient of uranium(VI) increased in the region of dilute sulfuric acid. When the concentration of H₂SO₄ surpassed 3.5 mol·dm⁻³, the distribution coefficient of uranium(VI) was at maximum. This result was due to the competition extraction between uranium(VI) and H₂SO₄. From the data, the composition of extracted species and the equilibrium constant of extraction reaction have been evaluated, which were (TOPOH)₂UO₂(SO₄)₂ (TOPO) and 10^7.6±0.15, respectively.     

Ozone generation on the lead dioxide electrodes in a sulfuric acid solution at potentials of 2 to 3 V

The electrochemical synthesis of ozone is studied on lead dioxide electrodes in sulfuric acid solutions. The two maximums of the current efficiency for ozone (CEO) observed at 2–3.5 V are largely due to the participation of various chemisorbed particles in the ozone synthesis. In the vicinity of the first CEO maximum at lead dioxide, ozone forms only in a discharge of water molecules with the participation of adsorbed oxygen-containing radicals. In the potential range of the second maximum, the adsorbed anion radicals, e.g., ·HSO₄ and ·SO₄, also take part in the reaction of ozone generation. At the electrode not subjected to anodic polarization, CEO is considerably higher than that on the preliminarily polarized electrode. On the basis of the experimental data, schemes for the ozone evolution at PbO₂ in sulfuric acid at 2 to 3 V are proposed.     

Reaction of dolomite with dilute solutions of sulfuric acid and Iron(II), Copper (II), and Zinc(II) sulfates

We study how the composition of dolomite changes in its reaction with 0.1 N solutions of H₂SO₄, FeSO₄, CuSO₄, and ZnSO₄, using X-ray diffraction and differential thermal analysis (DTA). The MgCO₃ concentration in the mineral decreases; the maximal decrease is observed in the reaction of dolomite with aqueous sulfuric acid.     

Anodic Oxidation of Silver Alloys in Concentrated Sulfuric Acid Solutions

Anodic oxidation of Ag–Cu and Ag–Pd alloys in concentrated sulfuric acid solutions is studied by cyclic voltammetry. Influence of electronegative (Cu) and electropositive (Pd) constituents on the rate and mechanism of the silver electrooxidation in non-steady-state conditions is revealed. The maximum silver oxidation current increases with the copper content due to a decreased H₂SO₄ concentration in the near-electrode layer and increased solubility of passivating phase Ag₂SO₄. The mechanism of ionization of palladium-doped silver is complicated by two electrochemical reactions involving the formation of Ag₂SO₄ and Ag⁺ _solv.     

Interaction parameters and (solid + liquid) equilibria calculation for KCl–H2O–HCl–C2H5OH,K2SO4–H2O–H2SO4 and K2SO4–H2O–C2H5OH mixed solvent-electrolyte systems

This work deals with the prediction and experimental measurements of the (solid + liquid) equilibrium (SLE) in acid medium for industrial purposes. Specific systems including KCl–ethanol–water–HCl and K₂SO₄–water–H₂SO₄ were analyzed. At first, a critical discussion of SLE calculations was given, based on the well-known UNIQUAC extended and LIQUAC models. Two new proposals were derived, considering the explicit necessity of a new reference state for SLE calculations for the studied (solvents + acid) mixtures. The solubility of KCl in water–ethanol–HCl mixed solvents was measured in the temperature range of 300.15 to 315.15 K using an analytical gravimetric method. These results combined with some other experimental data reported in the open literature let us to propose a set of parameters for the new models. They included the interaction parameters between ethanol and the H⁺ ion. The prediction capability of the new models, for calculations in acid medium, was illustrated. Experimentally, it was observed that the (K₂SO₄ + water + H₂SO₄) system presented the unusual behavior of increasing K₂SO₄ solubility with an increase in the sulfuric acid concentration. This was accurately predicted by the newly proposed models.     

Fe2(SO4)3·H2SO4·28H2O,a low‐temperature water‐rich iron(III) sulfate

The title compound, diiron(III) trisulfate–sulfuric acid–water (1/1/28), has been prepared at temperatures between 235 and 239 K from acid solutions of Fe₂(SO₄)₃. Studies of the compound at 100 and 200 K are reported. The analysis reveals the structural features of an alum, (H₅O₂)Fe(SO₄)₂·12H₂O. The Fe(H₂O)₆ unit is located on a centre of inversion at (, 0, ), while the H₅O₂⁺ cation is located about an inversion centre at (, , ). The compound thus represents the first oxonium alum, although the unit cell is orthorhombic.     

Hydrolysis of HNSO2: A potential route for atmospheric production of H2SO4 and NH3

The hydrolysis of sulfonylamine (HNSO₂) results in the formation of sulfuric acid along with ammonia, and is of significant interest due to their negative impact on environment and life on Earth. The formation of H₂SO₄ through the reaction of HNSO₂ with (H₂O)_2-4 has been studied using high level electronic structure calculations. This hydrolysis reaction is a step-wise process, in the first step a H-atom from H₂O is transferred to the N-atom of HNSO₂ which results in the formation of NH₂, and in the next step, H₂SO₄, NH₃ and water molecule(s) are formed. The results show that the energy barrier associated with the formation of intermediates and product complexes is reduced by 7 to 10 kcal/mol when the number of water molecules is increased from 2 to 4. The rate constant was calculated using canonical variational transition state theory with small curvature tunneling correction over the temperature range of 200 to 1000 K. At 298 K, the calculated rate constant for the formation of intermediate in the first step is 2.24 × 10⁻¹⁶, 1.03 × 10⁻¹², and 2.10 × 10⁻¹¹ cm³ mol⁻¹ s⁻¹, respectively, for the reaction with water dimer, trimer and tetramer. The calculated enthalpy and free energy show that the reaction corresponding to the formation of H₂SO₄ is highly exothermic and exoergic in nature.     

Solubility and stability of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript>·H<Subscript>2</Subscript>O<Subscript>2</Subscript> in organic and aqueous-organic media

Solubility and stability of (NH₄)₂SO₄·H₂O₂ in organic solvents (glycerol, ethylene glycol, TOSOL-A40 OM antifreeze), in mixtures of an organic solvent and water, and in pure water was studied. Crystallographic properties of the ammonium sulfate precipitating from aqueous-organic solvents and aqueous solutions in various time intervals and differing from ordinary (NH₄)₂SO₄ in solubility and one of crystallographic parameters were analyzed.