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.

Liquid–Vapor Interface of Formic Acid Solutions in Salt Water: A Comparison of Macroscopic Surface Tension and Microscopic in Situ X-ray Photoelectron Spectroscopy Measurements

The liquid–vapor interface is difficult to access experimentally but is of interest from a theoretical and applied point of view and has particular importance in atmospheric aerosol chemistry. Here we examine the liquid–vapor interface for mixtures of water, sodium chloride, and formic acid, an abundant chemical in the atmosphere. We compare the results of surface tension and X-ray photoelectron spectroscopy (XPS) measurements over a wide range of formic acid concentrations. Surface tension measurements provide a macroscopic characterization of solutions ranging from 0 to 3 M sodium chloride and from 0 to over 0.5 mole fraction formic acid. Sodium chloride was found to be a weak salting out agent for formic acid with surface excess depending only slightly on salt concentration. In situ XPS provides a complementary molecular level description about the liquid–vapor interface. XPS measurements over an experimental probe depth of 51 Å gave the C 1s to O 1s ratio for both total oxygen and oxygen from water. XPS also provides detailed electronic structure information that is inaccessible by surface tension. Density functional theory calculations were performed to understand the observed shift in C 1s binding energies to lower values with increasing formic acid concentration. Part of the experimental −0.2 eV shift can be assigned to the solution composition changing from predominantly monomers of formic acid to a combination of monomers and dimers; however, the lack of an appropriate reference to calibrate the absolute BE scale at high formic acid mole fraction complicates the interpretation. Our data are consistent with surface tension measurements yielding a significantly more surface sensitive measurement than XPS due to the relatively weak propensity of formic acid for the interface. A simple model allowed us to replicate the XPS results under the assumption that the surface excess was contained in the top four angstroms of solution.

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.

Water activity in aqueous amino acid solutions containing ammonium sulfate at 298.2 K

Water activity in aqueous solutions of DL-alanine, glycine, or L-serine, with ammonium sulfate, molality ranging from 0.5 to 5.0, have been measured at 298.2 K. The new experimental data was correlated using three different theoretical schemes such as Zdanovskii-Stokes-Robinson, its extension, or the Clegg-Seinfeld-Brimblecombe approach, with global average absolute deviations in the calculation of the osmotic coefficient of 3.46 %, 0.93 % and 1.95 %, respectively. The extended Zdanovskii-Stokes-Robinson method also enabled the prediction of unsymmetric molal activity coefficients of the electrolyte, in fair agreement with the experimental values found from literature measured by an electrochemical method. It is evidenced the usefulness of the experimental ternary data measured to extend the capabilities of thermodynamic models to higher salt and amino acid concentrations.

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.

Corrosion behaviour of direct current and active screen plasma carburised AISI 316 stainless steel in boiling sulphuric acid solutions

Active screen plasma is a recently developed plasma surface alloying technique, which has shown potential for addressing some drawbacks associated with conventional direct current plasma processes. In this study, the corrosion performance of untreated, direct current and active screen plasma carburised AISI 316 was investigated by immersion in a boiling solution of sulphuric acid. The experimental results show that the corrosion behaviour of expanded austenite produced by low temperature plasma carburising is controlled by the type and density of surface defects; the corrosion properties of the active screen plasma carburised material are superior to that produced by direct current plasma because of the significantly reduced edge effect and surface defects; and the bias level used in the active screen carburising treatment has a profound effect on the corrosion performance of the material. Based on the experimental results, the corrosion mechanisms involved are discussed.

The equivalent conductance of solutions of picric acid

Picric acid possesses the property, which is rare among strong electrolytes, of having a convenient distribution ratio between water and certain organic solvents such as benzene, chloroform, etc. Because of this property, picric acid offers peculiar advantages for studying the well known deviations of strong electrolytes from the law of mass action, for; by means of distribution experiments, the activities of picric acid in various aqueous solutions may be compared.

In order to interpret the results of such distribution experiments, it is necessary to know the degree of ionization of picric acid in aqueous solutions.

At least three series of determinations of the equivalent conductance of picric acid have been published, but the results are not concordant; and therefore, the degree of ionization cannot be calculated with any degree of certainty.

The object of the present investigation was to redetermine the conductance of picric acid solutions in order to obtain satisfactory data from which the degrees of ionization of its solutions might be calculated.

BDST modelling of sodium ion exchange column behaviour with strong acid cation resin in relation to coal seam water treatment

Reverse osmosis is the dominant technology utilized for desalination of saline water produced during the extraction of coal seam gas. Alternatively, ion exchange is of interest due to potential cost advantages. However, there is limited information regarding the column performance of strong acid cation resin for removal of sodium ions from both model and actual coal seam water samples. In particular, the impact of bed depth, flow rate, and regeneration was not clear. Consequently, this study applied Bed Depth Service Time (BDST) models to reveal that increasing sodium ion concentration and flow rates diminished the time required for breakthrough to occur. The loading of sodium ions on fresh resin was calculated to be ca. 71.1 g Na/kg resin. Difficulties in regeneration of the resin using hydrochloric acid solutions were discovered, with 86% recovery of exchange sites observed. The maximum concentration of sodium ions in the regenerant brine was found to be 47,400 mg/L under the conditions employed. The volume of regenerant waste formed was 6.2% of the total volume of water treated. A coal seam water sample was found to load the resin with only 53.5 g Na/kg resin, which was consistent with not only the co-presence of more favoured ions such as calcium, magnesium, barium and strontium, but also inefficient regeneration of the resin prior to the coal seam water test.

Studies in the polarography of metal-amino acid complexes - Part I. Cadmium

1. A detailed polarographic study of cadmium has been made employing glycine, α-alanine, β-alanine, valine, aspartic acid, glutamic acid and asparagine as complexing agents at various pH values. The effect of incorporating sodium hydroxide, sodium carbonate and ammonium nitrate + ammonium hydroxide, on the polarographic behaviour of amino acid complexes of cadmium has also been investigated. 2. The reduction process has been found to be reversible in all systems. 3. The small shifts in the half-wave potentials noticed due to increase in the concentration of sodium hydroxide and sodium carbonate in presence of amino acids have been explained on the basis of formation of mixtures of pure and mixed amino acid complexes of cadmium. Mixed complexes have also been noticed in presence of ammonium hydroxide and ammonium nitrate and amino acids. 4. Polarographic evidence has been obtained for the formation of over 30 pure and mixed complexes. The dissociation constant Kd, the Δ F° value for the dissociation, and standard potential value for the formation, of each complex have been computed. 5. It has been found that cadmium can be polarographically estimated in amino acid solutions.

Volume Change behaviour in Calcitic Soil influenced with Sulphuric Acid using Artificial Neural Networks

This paper elucidates the methodology of applying artificial neural network model (ANNM) to predict the percent swell of calcitic soil in sulphuric acid solutions, a complex phenomenon involving many parameters. Swell data required for modelling is experimentally obtained using conventional oedometer tests under nominal surcharge. The phases in ANN include optimal design of architecture, operation and training of architecture. The designed optimal neural model (3-5-1) is a fully connected three layer feed forward network with symmetric sigmoid activation function and trained by the back propagation algorithm to minimize a quadratic error criterion.The used model requires parameters such as duration of interaction, calcite mineral content and acid concentration for prediction of swell. The observed strong correlation coefficient (R2 = 0.9979) between the values determined by the experiment and predicted using the developed model demonstrates that the network can provide answers to complex problems in geotechnical engineering.

Extraction mechanism of La3+ from hydrochloric acid solution using Cyanex 302

The solvent extraction of La3+ from hydrochloric acid solutions was investigated using his (2, 4, 4-trimethylpentyl) monothiophosphinic acid (Cyanex 302, HL) as an extractant. The effect of equilibrium of aqueous acidity on extraction of La3+ using Cyanex 302 In different diluents was discussed. The effects of extractant concentration and chloride ion on the extraction reaction were also studied. Stoichiometry of the extraction reactions and the nature of metal complexes formed were determined using slope analysis technique and IR measurement.

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

Solvent extraction of scandium(III), yttrium(III), lanthanides(III), and divalent metal ions with sec-nonylphenoxy acetic acid

Such physicochemical properties of sec-nonylphenoxy acetic acid (CA-100) as the solubility in water, acid dissociation constant in water, dimerization constant in heptane, and distribution constant in organic solvent-water were measured by two-phase titration. The extraction behaviors of scandium (III), yttrium (III), lanthanides (III), and divalent metal ions from hydrochloric acid solutions with CA-100 in heptane have been investigated, and the possibilities of separating scandium (yttrium) from lanthanides and divalent metal ions have been carefully discussed. The stoichiometries of the extracted metal complexes were investigated by the slope-analysis technique. The effect of the nature of diluent on the extraction of yttrium (III) with CA100 has been studied and correlated with the dielectric constant.

Separation of heavy rare earth elements with extraction resin containing 1-hexyl-4-ethyloctyl isopropylphosphonic acid

This paper presents the results of the adsorption of heavy rare earth ions (Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III)) from hydrochloric acid solutions at 30 degreesC by the extraction resin containing 1-hexyl-4-ethyloctyl isopropylphosphonic acid (HEOPPA), which has higher steric hindrance, higher selectivities and lower extraction and stripping acidity than di(2-ethylhexyl)phosphoric acid (DERPA) or 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH/EHP). The dependence of acid concentration, flow rate and amounts of rare earth ions sorbed on the separation of Er-Tm, Tm-Yb and Er-Tm-Yb mixtures has been studied. The baseline chromatographic separation of Er-Tm-Yb mixture has been observed. Satisfactory results with purity and yield of Tm2O3>99.71% and >71.25%, Er2O3>99-81% and >94.17%, and Yb2O3>99.74% and >89.83%, respectively, have been obtained. The parameters such,as resolution, separation factors and efficiencies have been determined as a function of acidity, loading of rare earth elements and flow rates. The stoichiometry of the extraction of rare earth ions has been suggested as well.