Chemistry of rhenium sulfide deposition from sulfuric acid solutions

Rhenium sulfi de deposition from sulfuric acid solutions of sodium thiosulfate was examined.     

Vanadium(V) extraction from sulfuric acid solutions

We studied vanadium(V) extraction by di-2-ethylhexylphosphoric acid (DEHPA) from 1.0–12.0 M sulfuric acid. Optimal extraction parameters were determined. IR, ⁵¹V NMR, and electronic spectroscopy was used to determine the stoichiometry of the extracted complex and the reaction equation for vanadium(V) extraction by DEHPA. The equilibrium constant of vanadium(V) extraction by DEHPA was determined.     

Recovery of rhenium from sulfuric acid solutions with activated coals

Equilibrium and kinetic characteristics of rhenium sorption from sulfuric acid solutions (pH 2) by activated coals produced from coal raw materials (China) were studied. Constants of the Henry equation describing isotherms of rhenium sorption by activated coals were calculated. The effective diffusion coefficients of rhenium in the coals were determined. The dynamic characteristics of rhenium sorption and desorption were determined for the activated coal with the best capacity and kinetic characteristics.     

A note on the distillation of permanganic acid from sulphuric acid solutions

1. If solutions which contain XXX periodic acid and sulphuric acid are boiled, permanganic acid is found in the XXX concentration of permanganate in the steam is negligibly small until the sulphuric acid concentration of the solution exceeds about 6 M. It is at a maximum when the sulphuric acid is to M and then rapidly decreases as the sulphuric acid concentration further increases. 2.The'distillation of permanganic acid from nitric acid solutions is inappreciable even from the concentrated acid. 3. A brief account is given of the analytical application of the distillation from IoM sulphuric acid.     

Reaction of sphene with sulfuric acid solutions

The kinetics of titanium(IV) extraction from sphene with boiling 4–6 M sulfuric acid was studied. The rate constants of the sphene dissolution were determined. The influence of the particle size of the starting mineral on the rate of its dissolution was established. The feasibility of performing sphene dissolution by a liquid-phase procedure yielding stable titanium-containing sulfate solutions suitable for the synthesis of multifunctional composite materials was examined.     

Extraction recovery of vanadium(V) from sulfuric acid solutions

The IR and electronic absorption spectra of di-2-ethylhexyl hydrogen phosphate (HDEHP) extracts of vanadium(V) and sulfuric acid and of vanadium(V) solutions in sulfuric acid were studied. The composition of the extractable complex was determined, and the equation of vanadium(V) extraction with HDEHP was suggested. The equilibrium constant of vanadium(V) extraction from concentrated sulfuric acid solutions was found.     

Recovery of rhenium(VII) with triisooctylamine from sulfuric acid solutions

Extraction recovery of rhenium(VII) with triisooctylamine from model sulfuric acid solutions was studied. The effect of the composition of the organic and aqueous phases on the recovery of rhenium(VII) was analyzed, and the composition of rhenium(VII) complexes in the organic phase was determined. The possibility of effective re-extraction of rhenium(VII) from triisooctylamine with ammonia solutions was demonstrated.     

Sonoluminescence of aqueous solutions of sulfuric acid and sulfur dioxide

Sonoluminescence (SL) of aqueous solutions of sulfuric acid and sulfur dioxide enhances with an increase in their concentration and reaches a maximum at 16 and 0.05 mol L^–1, respectively. The further increase in the concentration of these substances decreases the SL intensity. The SL spectra of the solutions have a broad maximum at 450 nm. Excited SO₂ molecules formed in sulfuric acid due to sonolysis are luminescence emitters. The proposed mechanism of bright SL in these systems is based on the energy transfer from the electron-excited sonolysis products to the SO₂ molecules in cavitation bubbles.     

Direct contact membrane distillation of humic acid solutions

Direct contact membrane distillation process has been conducted for the treatment of humic acid solutions using microporous polytetrafluoroethylene and polyvinylidene fluoride membranes. The membranes were characterized in terms of their non-wettability, pore size and porosity. Water advancing and receding contact angles on the top membrane surfaces were measured. Experiments were also carried out employing pure water as feed at different mean temperatures and the water vapor permeance of each membrane was determined. Different humic acid concentrations in the feed solution, pH values and transmembrane temperature difference were tested. The direct contact membrane distillation technique is more adequate for the treatment of humic acid solutions than the applied pressure-driven separation processes, as lower membrane fouling was detected.     

Specific features of disposal of sulfuric acid solutions resulted from magnesium silicate decomposition

The photocatalytic activity of crystalline titania nanopowders synthesized in a stream of ultrahigh-frequency discharge oxygen-containing low-temperature plasma was assessed. To this end, oxidation of an organic dye was carried out in UV-irradiated aqueous suspensions of TiO₂ at different concentrations and varied irradiation times.     

Protonation equilibria of rauwolfia alkaloids in sulfuric acid solutions

The pK_a values for the indole ring protonation equilibria of the Rauwolfia alkaloids, yohimbine, ajmalicine, reserpine and reserpiline have been measured in strongly sulfuric acid solutions. The alkaloids obey the H_I acidity function stablished by Hinman and Lang for indole ring protonation, but they are considerably weaker bases than alkylindoles. Evidences indicating that these compounds behave as carbon bases are reported.     

Ab initio simulations of sulfuric acid solutions

Ab initio molecular dynamics simulations are presented for a solution consisting of a single H₂SO₄ molecule in a periodic box with 63 water molecules. Three trajectories lasting 35–55 ps were calculated at temperatures in the 320–326 K range, for two functionals, and double- and triple-zeta quality basis sets. All three trajectories displayed prompt ionization of the first proton. The ion displayed varying extents of ionization in the different trajectories. Proton hopping was observed between the oxygen atoms. Moreover, hopping of the solvating water molecules also occurred between the different oxygen atoms of the anions, with bidentate water, hydrogen bonding to two different oxygen atoms, serving as an intermediate.     

Anodic dissolution of cobalt suicides in sulfuric acid solutions

Anodic dissolution of suicides Co₂Si, CoSi, and CoSi₂ in 0.5 M H₂SO₄ solutions with and without NaF is studied by polarization methods coupled with an atomic-absorption analysis. In the absence of NaF, anodic stability of cobalt silicides is higher than that of cobalt itself by 3–6 orders of magnitude and increases in the series Co₂Si < CoSi < CoSi₂. Cobalt selectively dissolves from the lattice of silicides, while silicon simultaneously oxidizes to SiO₂. The process is controlled by the diffusion of elemental and oxidized cobalt in the suicide and the SiO₂ surface layer, respectively. The anodic dissolution rate of silicides markedly increases in the presence of NaF, while their anodic stability becomes less different.     

Effect of extractant on arsenic(V) recovery from sulfuric acid solutions

Extraction of arsenic(V) from sulfuric acid solutions with various extractants in multistage counter-current extraction-stripping systems was compared. The extraction ability of the extractants studied showed the following order: ENIM 100>TBP=CYANEX 923>2-methylhexanol. The extraction depends significantly on the number of extraction stages and the phase ratios in extraction. The effects of the number of stripping stages and the phase ratio in stripping are less important.     

Interaction of ethyl alcohol vapor with sulfuric acid solutions

We investigated the uptake of ethyl alcohol (ethanol) vapor by sulfuric acid solutions over the range approximately 40 to approximately 80 wt % H2SO4 and temperatures of 193-273 K. Laboratory studies used a fast flow-tube reactor coupled to an electron-impact ionization mass spectrometer for detection of ethanol and reaction products. The uptake coefficients (gamma) were measured and found to vary from 0.019 to 0.072, depending upon the acid composition and temperature. At concentrations greater than approximately 70 wt % and in dilute solutions colder than 220 K, the gamma values approached approximately 0.07. We also determined the effective solubility constant of ethanol in approximately 40 wt % H2SO4 in the temperature range 203-223 K. The potential implications to the budget of ethanol in the global troposphere are briefly discussed.     

Interaction of activated carbon electrodes with sulfuric acid solutions

Impedance and potentiodynamic studies have been carried out to investigate reversible processes on the surface of electrodes based on activated carbon (AC). Relationships have been found between the reversible capacity and true resistance, on the one hand, and the potential, on the other. Stoichiometric characteristics of AC charging in sulfuric acid have been obtained. A mechanism of the reversible surface process is suggested. It is concluded that Faraday pseudocapacity makes a considerable contribution to charging of AC electrolytes. The amount of gas liberated in the course of AC wetting in electrolyte has been measured. It is assumed that the amount of liberated gas depends on the amount of active oxygen involved in the current-forming reaction. Based on the data obtained, a redox surface reaction is substantiated in general form.     

Vanadium(V) complexes in sulfuric acid solutions

The ionic state of vanadium(V) is studied spectrophotometrically over a wide range of sulfuric acid concentrations from 1.0 to 16.8 mol/l. Existence regions for monomeric and dimeric vanadium(V) complexes are determined. The equilibrium constant of vanadium(V) dimerization in 12 M H₂SO₄ is determined.