Thermal decomposition of Bayer precipitates formed at varying temperatures

Bayer hydrotalcites prepared using the seawater neutralisation (SWN) process of Bayer liquors are characterised using X-ray diffraction and thermal analysis techniques. The Bayer hydrotalcites are synthesised at four different temperatures (0, 25, 55, and 75 °C) to determine the effect of synthesis temperature on the thermal stability of the Bayer hydrotalcite structures and the mineralogical phases that form. The interlayer distance increased with increasing synthesis temperature, up to 55 °C, and then decreased by 0.14 Å for Bayer hydrotalcites prepared at 75 °C. The three mineralogical phases identified in this investigation are; (1) Bayer hydrotalcite, (2), calcium carbonate species, and (3) hydromagnesite. The DTG curve can be separated into four decomposition steps; (1) the removal of adsorbed water and free interlayer water in hydrotalcite (30–230 °C), (2) the dehydroxylation of hydrotalcite and the decarbonation of hydrotalcite (250–400 °C), (3) the decarbonation of hydromagnesite (400–550 °C), and (4) the decarbonation of aragonite (550–650 °C).     

Evaluation of the dissolved oxygen-related electrochemical behavior of pure titanium in acidic fluoride-containing solutions

Journal of Solid State Electrochemistry - The effects of dissolved oxygen (DO) on the corrosion behavior of pure titanium in acidic fluoride-containing acids (pH = 0.6–2.0) were...     

Structural study of the solutions of acidic polysaccharides

A study was made of the effect of NaCl on the counterion activity coefficient in solutions of acidic polysaccharide sodium salts. The counterion activity coefficient in the sodium salt solutions of polyuronic acids was shown to be determined by electrostatic interactions only. Consequently it can be supposed that the counterion-polyion interaction is also of an electrostatic nature. A method was proposed for determining the distribution patterns of nonionogenic groups along the polyelectrolyte chain. The structural transition ofχ-carrageenan, depending on NaCl concentration, was found to be accompanied by a nonelectrostatic binding of sodium ions by the polysaccharide.     

Effects of dissolved oxygen on the electrochemical corrosion behavior of pure titanium in fluoride-containing weakly acidic solutions

The effects of dissolved oxygen (DO) on the electrochemical behavior of titanium in fluoride-containing weakly acidic solutions (pH?=?5.0) were evaluated quantitatively by electrochemical methods, such as open circuit potential (OCP) measurements and potentiodynamic polarization tests, combined with corrosion morphology observation. The results showed that the electrochemical behavior changed from spontaneously passive to active-passive behavior with increasing the fluoride concentration irrespective of the DO content. DO was found to increase the critical fluoride concentration for the corrosion of titanium due to the increased limiting diffusion current density of oxygen reduction reaction and decreased maximum anodic current density caused by DO. But the corrosion rate of titanium would be accelerated by DO once the fluoride concentration exceeded the critical value. Moreover, corrosion products were observed on the surface when the fluoride concentrations were high enough and titanium was in the active state, which altered the electrochemical behavior of titanium further, such as facilitating the occurrence of OCP oscillation.

Open image in new window

Graphical abstract ?

     

Characterization of the precipitates formed during the denitration of simulated HRLW

The denitration of several chemical compositions of simulated HRLW (highly radioactive liquid waste) was performed using formic acid as reducing agent. Precipitates formed during the denitration of simulated HRLW were analyzed using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. Goethite and amorphous fraction were the principal phases in these precipitates. It was found that the chemical composition of simulated HRLW and the experimental conditions of denitration have more influence on the crystallinity and the particle size than on the phase composition of the precipitates. Thermal treatment of denitrated precipitates caused the solid state transformation of goethite+amorphous fraction into hematite. The values of hyperfine magnetic field (HMF) of hematite were decreased, thus indicating the substitution of Fe³⁺ ions with other metal cations.     

An improved determination of ammonia in kjeldahl digests and acidic solutions with a buffered berthelot reaction

The addition of trisodium citrate to acidic samples and sodium carbonate to an alkaline hypochlorite reagent ensures that up to 100 μmol of hydrogen ion in the sample does not significantly affect the absorbance. Calibration was linear from 0.05–3 μg of ammonia-N. For aliquots (2.5 μg N) of a Kjeldahl digest from gorse leaves, the relative standard deviation was 0.38% (n = 10).     

Dehydration of zinc hydroxide precipitate produced by neutralization of weakly concentrated zinc sulfate solutions with aqueous ammonia

Method for dehydration of zinc-containing products is suggested. The method makes lower the energy expenditure in filtration, drying, and calcination, diminishes the expenditure of reagents, and improves ecological characteristics of the process.     

Kinetic study and analytical application of the iodate-arsenite reaction in strongly acidic solutions

The iodate-arsenite reaction in strongly acidic solutions was studied by stopped-flow spectrophotometric techniques. The molar absorptivity of iodine and the activation energy of the reaction were determined. A method for determining arsenite was developed on the basis of this reaction. The method was checked in the concentration range 5.0·10^-4–1.0·10^-2M, the mean error being about 3%.     

Kinetic study and analytical application of the iodate-hypophosphite reaction in strongly acidic solutions

The iodate—hypophosphite reaction in strongly acidic solutions was studied spectrophotometrically. Reaction rate constants and the activation energy of the reaction are reported. A method for determining hypophosphite on the basis of this reaction is described. Hypophosphite in the range 0.06–4 mg (10^-3–6·10^-2 M) can be determined with a relative error and relative standard deviation of 2—3%.     

Characteristic features of the crystallization of carbonate precipitates in alkaline solutions

The results of studies of the mechanism of action of sodium polyacrylate on the nucleation and crystal growth for carbonate salts under precipitation-simulating conditions are considered.     

A study of some cations formed in the ammonia chemical ionization of ketones using mass analysed ion kinetic energy spectrometry

The structures of the major adduct ions formed in ammonia chemical ionization of thirteen aliphatic and aromatic ketones have been studied by mass analysed ion kinetic energy spectrometry. The [M+NH₃+H]⁺ ion is shown to have a protonated carbinolamine structure, [M+2NH₃+H]⁺ to be a protonated carbinolamine with hydrogen-bonded ammonia and [2M+NH₃+H]⁺ to be, at least in part, a protonated carbinolamine with hydrogen-bonded ketone. These structures may imply a nucleophilic addition of ammonia at the carbonyl of the ketone-ammonium ion complex. An unusual hydroxy migration is seen in the internal rearrangement of the [2M+NH₃+H]⁺ ion leading to the formation of a protonated imine.     

Change in the volume of orthophosphoric acid solutions in the neutralization with solutions of various bases

Volume changes in the reactions of orthophosphoric acid neutralization with solutions of NaOH, NH₄OH, and tris(hydroxymethyl)methanamine in the mixed solvent H₂O-dimethylformamide were studied by dilatometric titration. Volume effects of the reaction depending on the mixed solvent composition and base strength were discussed.     

Kinetic study on hydrolysis and oxidation of formamidine disulfide in acidic solutions

Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chromatography(HPLC) and mass spectrometry(MS) at 25 °C.By controlling the slow reaction rate and choosing appropriate mobile phase,HPLC provides the unique advantages over other methods(UV-Vis,chemical separation) in species tracking and kinetic study.In addition to thiourea and formamidine sulfinic acid,two unreported products were also detected in the hydrolysis reaction.Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyanogen with mass weights of 92.28 and 116.36,respectively.In the oxidation of formamidine disulfide by hydrogen peroxide,besides thiourea,formamidine sulfenic acid,formamidine sulfinic acid,thiocyanogen and urea,formamidine sulfonic acid and sulfate could be detected.The oxidation reaction was found to be first order in both formamidine disulfide and hydrogen peroxide.The rate constants of hydrolysis and oxidation reactions were determined in the pH range of 1.5-3.0.It was found both rate constants are increased with the increasing of pH.Experimental curves of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation,including hydrolysis equilibrium of formamidine disulfide and irreversible hydrolysis of formamidine sulfenic acid.     

Thermal decomposition of ammonia in shock waves

The thermal decomposition of ammonia was studied by means of the shock-tube and vacuum ultraviolet absorption spectroscopy monitoring the concentration of atomic hydrogen. The rate constants of both the initiation reaction and the consecutive reaction were determined directly as and respectively.     

Chemical synthesis of gold nanowires in acidic solutions

High aspect ratio gold nanowires with single crystalline surface have long been a missing piece in the toolbox of plasmonics metal nanostructures. Such wires are now made with a room temperature, surfactant assisted chemical synthesis in acidic aqueous solution. The diameters and lengths of the multiply twinned gold nanowires can be tuned by varying the amount of seed particles and acid in the growth solution. Nanowires with diameters around 35 nm and lengths up to 10 micron were made with a low seed concentration in pH approximately 1 solution.     

Anodic behavior and pore growth of n-InP in acidic liquid ammonia

In this paper, we report on the anodic behavior of n-InP (100) in acidic liquid ammonia at 223 K. Electrochemical, morphological and optical characterizations have been performed on InP after galvanostatic polarizations in different ranges. Prior to any dissolution processes, the formation of a stable anodic passivating thin film with a chemical composition close to “HNP–NH₂” (phosphinimidic amide) is observed. Depending on the current, two different phenomena occur: at low current density a thick amorphous film is formed, while tortuous current line oriented pores are grown when a high current is applied. For high coulometric charges, this last porous film can exhibit a multilayered structure. A decrease of the photoluminescence intensity without any peak shifts is observed whatever the applied current. This has been ascribed to the absorbent property of the layers.     

A study by voltammetry and the photocurrent response method of copper electrode behavior in acidic and alkaline solutions containing chloride ions

The electrochemical behavior of Cu electrodes in Cl⁻ solutions was studied in a wide range of pH. The results were compared with those obtained in solutions containing F⁻, Br⁻, I⁻ and So²⁻₄ ions at pH 8.5, and discussed in terms of the competitive formation of Cu₂O and CuCl films on the Cu surface and the influence of CuCl on the properties of Cu₂O. At pH 8.5 or higher, Cu₂O was formed first, whereas at pH 5.7 or lower the Cu₂O film was formed on the Cu surface under the CuCl layer which was formed initially. It is believed that the Cu₂O films doped with Cl⁻ ions exhibited poor protective properties against Cu corrosion.     

Recovery of cadmium and change in properties of a fibrous carbon electrode in electrolytic processing of ammonia washing solutions formed in cadmium plating

The possibility of recovering cadmium deposited on fibrous carbon electrodes from ammonium washing solutions formed in cadmium plating via operation of a short-circuited electrochemical system or anodic dissolution was examined. A polarization study of electrode processes that occur on a renewable graphite microelectrode in ammonium solutions of varied composition was carried out. The change in the properties of fibrous carbon electrodes in their cyclic use in electrodeposition-recovery of cadmium and the possibility of their repeated use were analyzed.     

Uncommon behavior of the p-GaAs electrode during the reduction of oxygen in liquid acidic ammonia

In liquid acidic ammonia, the mechanism of oxygen reduction begins as in acidic aqueous solutions, by the successive contribution of the conduction band and then of the valence band (doubling effect). However, unlike in the acidic aqueous solutions, soon after the oxygen photoreduction, an activation process of the p-GaAs surface is initiated, tied to the presence of protons in the solution. This activation of the surface allows the passage from a reduction mechanism via a conduction band to a reduction mechanism via a valence band (oxygen reduction in the dark).