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.

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

Electrochemical behaviour of copper electrode in concentrated sulfuric acid solutions

The electrochemical behaviour of copper in 6.0 mol 1-1 sulfuric acid at 30°C, was studied by means of the potentiodynamic method. At low potential sweep rates, v < 200 m V s-1, the data reveal that the anodic process is basically constituted of copper dissolution and a film formation which inhibits further metal oxidation and which may undergo further dissolution. For higher potential sweep rates, a modification in the passivation region of the voltammogram is observed. It can be ascribed to a change in the passivation mechanism which possibly involves different surface species. The kineticrelationships derived from the potentiodynamic I/E curves obtained at low v suggest a film formation via a dissolution/precipitation mechanism. © 1993.

The solvent-solvent extraction of uranium from sulfuric acid solutions with oil soluble amines /

Fifty oil soluble amines were screened for possible use as extractants for uranium from sulfuric acid solutions. The most promising of these were studied further to obtain the optimum conditions for operation of such a process. Kerosene was used as the diluent.

Hydraulic performance of geosynthetic clay liners to sulfuric acid solutions

The ability of geosynthetic clay liners (GCLs) to contain acidic mining leachates is examined. The results of saturated hydraulic conductivity (k) of two GCLs permeated with sulfuric acid solutions (H2SO4) at 0.015M, 0.125M and 0.5M concentrations are reported. Also, the saturated k values of consolidated (35kPa) bentonite cakes made from sodium bentonite extracted from both GCLs were compared to a commonly used magnesium-sodium form bentonite. Chemical compatibility and effects of pre-hydration and effective stress were assessed as part of this study. Results indicated that an increased acid concentration (ionic strength) increased the k of all tested specimens. The ratio of the k0.5 values for non-prehydrated specimens permeated with 0.5M H2SO4 to the kw values for specimens permeated with deionized (DI) water (k0.5/kw) ranged from 10 to 110. Pre-hydration (50-140% water content) and increased effective stress (35-200kPa) improved the performance of GCLs (lower k). Strong correlations were observed between k and liquid limit and swell index parameters independent of pre-hydration and effective stress in this study. However, care should still be taken when using these correlations to evaluate hydraulic performance because the intrinsic micro-structure properties of bentonite, such as porosity, should also be considered. This work showed that, for example, high SI of bentonite does not translate necessarily to a better hydraulic performance of GCLs.

Technical note: Organics-induced fluorescence in Raman studies of sulfuric acid aerosols

Fluorescence is a troublesome side effect in laboratory Raman studies on sulfuric acid solutions and aerosol particles. We performed experiments showing that organic matter induces fluorescence in H2SO4/H2O solutions. The intensity of the fluorescence signal appears to be almost independent of the concentration of the organic substances, but depends strongly on the sulfuric acid concentration. The ubiquity of organic substances in the atmosphere, their relatively high abundance, and the insensitivity of the fluorescence with respect to their concentrations will render most acidic natural aerosols subject to absorption and fluorescence, possibly influencing climate forcing. We show that, while fluorescence may in the future become a valuable tool of aerosol diagnostics, the concurrent absorption is too small to significantly affect the atmosphere's radiative balance.

Non-spectral interferences due to the presence of sulfuric acid in inductively coupled plasma mass spectrometry

Results of a systematic study concerning non-spectral interferences from sulfuric acid containing matrices on a large number of elements in inductively coupled plasma–mass spectrometry (ICP-MS) are presented in this work. The signals obtained with sulfuric acid solutions of different concentrations (up to 5% w w− 1) have been compared with the corresponding signals for a 1% w w− 1− nitric acid solution at different experimental conditions (i.e., sample uptake rates, nebulizer gas flows and r.f. powers). The signals observed for 128Te+, 78Se+ and 75As+ were significantly higher when using sulfuric acid matrices (up to 2.2-fold for 128Te+ and 78Se+ and 1.8-fold for 75As+ in the presence of 5 w w-1 sulfuric acid) for the whole range of experimental conditions tested. This is in agreement with previously reported observations. The signal for 31P+ is also higher (1.1-fold) in the presence of sulfuric acid. The signal enhancements for 128Te+, 78Se+, 75As+ and 31P+ are explained in relation to an increase in the analyte ion population as a result of charge transfer reactions involving S+ species in the plasma. Theoretical data suggest that Os, Sb, Pt, Ir, Zn and Hg could also be involved in sulfur-based charge transfer reactions, but no experimental evidence has been found. The presence of sulfuric acid gives rise to lower ion signals (about 10–20% lower) for the other nuclides tested, thus indicating the negative matrix effect caused by changes in the amount of analyte loading of the plasma. The elemental composition of a certified low-density polyethylene sample (ERM-EC681K) was determined by ICP-MS after two different sample digestion procedures, one of them including sulfuric acid. Element concentrations were in agreement with the certified values, irrespective of the acids used for the digestion. These results demonstrate that the use of matrix-matched standards allows the accurate determination of the tested elements in a sulfuric acid matrix.

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.

Further studies on the recovery of uranium from sulfuric acid leach solutions by anion exchange resins /

"Date Declassified: September 23, 1955."

Room Temperature, Electrochemical Generation of Ozone with 50% Current Efficiency in 0.5M Sulfuric Acid at Cell Voltages <3V.

The electrochemical generation of ozone by Ni/Sb-SnO2 anodes immersed in 0.5M H2SO4 was assessed in both flow and recycle systems using the same electrochemical cell. The anodes were found to exhibit current efficiencies of up to 50% for ozone generation under flow conditions at room temperature, with an optimum mole ratio in the precursor solutions of ca. 500:8:3 Sn:Sb:Ni and optimum cell voltage of 2.7V. A comparison of the data obtained under flow and recycle conditions suggests that the presence of ozone in the anolyte inhibits its formation. The minimum electrical energy cost achieved, of 18 kWh kg1 compares favorably with estimated costs for Cold Corona Discharge generally reported in the literature, especially when the very significant advantages of electrochemical ozone generation are taken into account.

Structural and phenomenological characterization of the thermoreversible sol-gel transition of a zirconyl aqueous precursor modified by sulfuric acid

The thermoreversible sol-gel transition is well-known in biological and organic polymeric systems but has not been reported for inorganic systems. In this paper we put in evidence a thermoreversible sol-gel transition for zirconyl chloride aqueous solutions modified by sulfuric acid in the ratio 3:1 Zr:SO4. The synthesis conditions are detailed and a variety of experimental techniques (turbidimetry, dynamic rheology, and EXAFS) have been employed for investigating the thermal reversibility and the chemical structure of this new material. Turbidimetric measurements performed for solutions containing different concentrations of precursor have evidenced that the sol-gel transformation temperature increases from 50 to 80 degrees C as the concentration of zirconyl chloride decreases from 0.22 to 0.018 mol L-1. A more detailed study has been done for the sample with [Zr] = 0.156 mol L-1, in which the sol-gel-sol transformation has been repeated several times by a cyclic variation of the temperature. The mechanical properties of this sample, evaluated by measuring the storage and the loss moduli, show a change from liquid like to viscoelastic to elastic behavior during the sol-gel transition and vice versa during the gel-sol one. In situ EXAFS measurements performed at the Zr K-edge show that no change of the local order around Zr occurs during the sol-gel-sol transition, in agreement with the concept of physical gel formation. We have proposed for the structure of the precursor an inner core made of hydroxyl and oxo groups bridging together zirconium atoms surrounded in surface by complexing sulfate ligands, the sulfate groups act as a protective layer, playing a key role in the linking propagation among primary particles during sol-gel-sol transition.

Role of the surface state and structural feature in the thermoreversible sol-gel transition of a zirconyl aqueous precursor modified by sulfuric acid

The sols produced by admixture of ZrOCl2 acidified solutions to hot H2SO4 aqueous solutions were studied to clarify the effects of Cl- and SO42- ions on the kinetic stability of nanoparticles and to obtain some new evidence concerning the mechanism of a thermoreversible sol-gel transition observed in this system. The study of suspensions prepared with different molar ratios R-S = [Zr]/[SO42-] and R-Cl = [Zr]/[Cl-] revealed domains of composition of formation of thermoreversible gels, thermostable sols, and powder precipitation. The effects of R-S and R-Cl on the structural features of nanoparticles and on the particle solution interface were systematically analyzed for samples of thermoreversible and thermostable sol domains. Small-angle X-ray scattering measurements revealed the presence of small fractal aggregates in all samples of thermoreversible domains, while compact packing aggregates of primary particles are present in the thermostable sol. Extended X-ray absorption fine structure and elemental chemical analysis revealed that irrespective of the nominal value of R-S and R-Cl all studied samples of the thermoreversible domain are constituted by a well-defined compound possessing an inner core made of hydroxyl and oxo groups bridging together zirconium atoms surrounded on the surface by complexing sulfate ligands. zeta potentials of powders extracted by freeze-drying from the thermoreversible gel revealed a point of surface charge inversion attributed to the specific adsorption of SO42- ion. Thermoreversible gel formation is rationalized by considering the effect of the specific adsorption on the electrical double-layer repulsion together with the temperature dependency of the physical chemical properties of ions in solution.

Quantum Chemical Studies on Tropospheric Nucleation Mechanisms Involving Sulfuric Acid

Nucleation is the first step of the process by which gas molecules in the atmosphere condense to form liquid or solid particles. Despite the importance of atmospheric new-particle formation for both climate and health-related issues, little information exists on its precise molecular-level mechanisms. In this thesis, potential nucleation mechanisms involving sulfuric acid together with either water and ammonia or reactive biogenic molecules are studied using quantum chemical methods. Quantum chemistry calculations are based on the numerical solution of Schrödinger's equation for a system of atoms and electrons subject to various sets of approximations, the precise details of which give rise to a large number of model chemistries. A comparison of several different model chemistries indicates that the computational method must be chosen with care if accurate results for sulfuric acid - water - ammonia clusters are desired. Specifically, binding energies are incorrectly predicted by some popular density functionals, and vibrational anharmonicity must be accounted for if quantitatively reliable formation free energies are desired. The calculations reported in this thesis show that a combination of different high-level energy corrections and advanced thermochemical analysis can quantitatively replicate experimental results concerning the hydration of sulfuric acid. The role of ammonia in sulfuric acid - water nucleation was revealed by a series of calculations on molecular clusters of increasing size with respect to all three co-ordinates; sulfuric acid, water and ammonia. As indicated by experimental measurements, ammonia significantly assists the growth of clusters in the sulfuric acid - co-ordinate. The calculations presented in this thesis predict that in atmospheric conditions, this effect becomes important as the number of acid molecules increases from two to three. On the other hand, small molecular clusters are unlikely to contain more than one ammonia molecule per sulfuric acid. This implies that the average NH3:H2SO4 mole ratio of small molecular clusters in atmospheric conditions is likely to be between 1:3 and 1:1. Calculations on charged clusters confirm the experimental result that the HSO4- ion is much more strongly hydrated than neutral sulfuric acid. Preliminary calculations on HSO4- NH3 clusters indicate that ammonia is likely to play at most a minor role in ion-induced nucleation in the sulfuric acid - water system. Calculations of thermodynamic and kinetic parameters for the reaction of stabilized Criegee Intermediates with sulfuric acid demonstrate that quantum chemistry is a powerful tool for investigating chemically complicated nucleation mechanisms. The calculations indicate that if the biogenic Criegee Intermediates have sufficiently long lifetimes in atmospheric conditions, the studied reaction may be an important source of nucleation precursors.