Acidic Chloride Media Research Articles

Adsorption of Palladium(II) from Hydrochloric Acid Solution on Glycidylmethacrylate-Divinylbenzene Copolymers Containing Nitrogen Atoms

Glycidylmethacrylate-divinylbenzene copolymers containing ethylenediamine groups (GD-EDA) and triethylenetetramine groups (GD-TET) were prepared to develop new selective adsorbents for precious metals over base metals. It was found that GD-EDA and GD-TET are highly selective adsorbents for palladium (II), gold (III) and platinum (IV) over base metals such as copper (II), cobalt (II), cadmium (II) and iron (III) . The adsorption equilibrium of palladium (II) was quantitatively studied from acidic chloride media at 303 K using GD-EDA. The effects of the hydrogen ion and chloride ion concentrations on the adsorption of palladium (II) were examined to elucidate the chemical species of adsorbed palladium (II) on GD-EDA.

The dissolution of silver cathodically polarized in acid chloride media

The dissolution of silver cathodically polarized in a 1M HC1 solution is investigated. It occurs only in the presence of oxygen, is independent of the cathodic potential in a range from 0.00 to −0.45 V, and is determined by the convective experimental conditions and the acidity of the solution. It may be assumed that silver can be oxidized at cathodic potentials because of an increase in the concentration of hydroxide ions adsorbed by the electrode, during the reduction of the dissolved oxygen.

Extraction of chromium(VI) by salting-out with a homogeneous, mixed solvent of water and 2-propanol: A laboratory study

Chromium enters into the aquatic environment as a result of effluent discharge from steel works, electroplating, leather tanning industries and chemical industries. As the Cr(VI) is very harmful to living organisms, it should be quickly removed from the environment when it happens to be contaminated. Therefore, the aim of this laboratory research was to develop a rapid, simple and adaptable solvent extraction system to quantitatively remove Cr(VI) from polluted waters. Aqueous salt-solutions containing Cr(VI) as CrO4(2-) at ppm level (4-6 ppm) were prepared. Equal volumes (5 ml) of aqueous and organic (2-PrOH) phases were mixed in a 10 ml centrifuge tube for 15 min, centrifuged and separated. Concentrations of Cr(VI), in both the aqueous and organic phases, were determined by atomic absorption spectrometry. The effects of salt and acid concentrations, and phase-contact time on the extraction of Cr(VI) were investigated. In addition, the extraction of Cr(VI) was assessed in the presence of tetramethylammonium chloride (TMAC) in 2-PrOH phase. Effects of some other metals, (Cd(II), Co(II), Cu(II), Ni(II) and Zn(II)), on the extraction of Cr(VI) were also investigated. The Cr(VI) at ppm level was extracted quantitatively by salting-out the homogeneous system of water and 2-propanol(2-PrOH) using chloride salts, namely CaCl2 or NaCl, under acidic chloride media. The extracted chemical species of Cr(VI) was confirmed to be the CrO3Cl-. The ion-pair complex extracted into the organic phase was rationalized as the solvated ion-pair complex of [2-PrOH2+, CrO3Cl-]. The complex was no longer stable. It implied the reaction between extracted species. Studies revealed that salts and acid directly participated in the formation of the above complex. Use of extracting agents (TMAC) didn't show any significant effect on the extraction of Cr(VI) under high salting-out conditions. There is no significant interference effect on the extraction of Cr(VI) by the presence of other metals. The Cr(VI) in the organic phase was back-extracted using an aqueous ammonia solution (1.6 mol dm(-3)) containing 3 mol dm(-3) NaCl. The extraction mechanism of Cr(VI) is also discussed. Salting-out of homogeneous mixed solvent of 2-propanol can be employed to extract Cr(VI) quantitatively, as an ion-pair of [2-PrOH2+ * CrO3Cl-] solvated by 2-PrOH molecules. Then, the complex becomes 'solvent-like' and is readily separated into the organic phase. The increase of Cl- ion concentration in the aqueous phase favors the extraction. The 2-PrOH, salts and acid play important roles in the extraction process. There is no need to use an extracting agent at a high salting-out condition. Chromium(VI) must be quickly removed before it enters into the natural cycle. As the 2-PrOH is water-miscible in any proportion, ion-pairing between 2-PrOH2+ and CrO3Cl- becomes very fast. As a result, Cr(VI) can easily be extracted. Therefore, the method is recommended as a simple, rapid and adaptable method to quickly separate Cr(VI) from aqueous samples.

Toluene/ter-Butanol Mixed Solvent for the Selective Extraction of Cr(VI) from Divalent Heavy Metals

A solvent-extraction system comprising toluene/ter-butanol (ter-BuOH) mixed solvent as the organic phase was developed to selectively extract Cr(VI) from acidic chloride media in the presence of divalent metals, namely Cd(II), Co(II), Cu(II), Ni(II) and Zn(II) under 5 M CaCl2 salting-out conditions. Chromium(VI) was selectively extracted as a solvated ion-pair of [ter-BuOH2+ x CrO3Cl-] at ter-BuOH mole fractions of between 0.1 and 0.6 (9.0-57.2% in volume). Divalent metals were extracted at ter-BuOH mole fraction over 0.6 with extraction percents of Co (< 20%), Cu (< 15%), Ni (< 10%) and Zn (< 20%). The concentrations of Ca2+, water and ter-BuOH in the organic phase and ter-BuOH in the aqueous phase were determined to find out the effects on the extraction of Cr(VI). The chemical species of Cr(VI) in acidic chloride media containing 5 M CaCl2 and 0.1 M HCl was confirmed to be the CrO3Cl- species. The effects of the acid, salt concentrations in the aqueous phase and the solvent composition of a mixed organic solvent on the extraction of Cr(VI) were evaluated. Based on the above studies, the extraction mechanism was elucidated and the optimum extraction conditions were determined.

Electrochemical behavior of copper–nickel alloys in acidic chloride solutions

The electrochemical behavior of Cu–Ni alloys in acidic chloride medium was investigated. Commercial Cu–Ni alloys were investigated using potentiodynamic techniques, complemented by electrochemical impedance spectroscopy. The influence of alloy composition, chloride ion concentration and immersion time on the electrochemical response of the alloys was analyzed. Results of present investigations with pure metals (Cu and Ni) are also considered in this paper for the sake of comparison. Potentiodynamic measurements reveal that the increase in nickel content decreases the corrosion rate of the alloy and when the nickel content exceeds 30%, an increase in the corrosion rate was recorded. Also, the corrosion current density increases with increasing the concentration of chloride ions up to 0.6 M. The experimental impedance data were fitted to an equivalent circuit model representing the electrode/electrolyte interface. The relevance of the proposed model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.

Solvent Extraction of Iron(III) from Acidic Chloride Media Using N,N′‐Dimethyl‐N,N′‐dibutylmalonamide

In the present paper, a new, simple, and effective method for iron(III) extraction from acidic chloride solutions is described involving the use of a N,N,N′,N′‐tetrasubstituted malonamide, N,N′‐dimethyl‐N,N′‐dibutylmalonamide (DMDBMA). The behavior of this ligand towards iron(III) extraction was investigated for different experimental conditions with a particular emphasis on the influence of HCl, LiCl, and ligand concentrations. The extraction behavior of DMDBMA is compared with the ones shown by two similar malonamide derivatives, N,N′‐dimethyl‐N,N′‐diphenylmalonamide (DMDPHMA) and N,N′‐dimethyl‐N,N′‐diphenyltetradecylmalonamide (DMDPHTDMA), previously studied. The mechanism involved on iron(III) extraction, the structure of the metal–adducts formed, and also the relationship between the extraction mechanism and the ligand structures are clarified. Therefore, hydrochloric acid extraction, slope analysis, and spectroscopic data—UV and NMR—were used to collect information on the iron(III) extraction reactions. A solvation mechanism involving iron(III) extraction as chlorocomplexes such as HFeCl4 and FeCl3 is proposed. From aqueous feed solutions with HCl concentrations higher than 4 M, iron(III) is mainly extracted as the anionic chlorocomplex, while from solutions with lower HCl concentrations (2 M < CHCl ≤ 4 M) the metal is probably removed as FeCl3. The results also suggest that different malonamides (e.g., DMDBMA, DMDPHMA, and DMDPHTDMA) extract iron(III) through diverse mechanisms, thus showing the important role played by the chemical structure on the metal ion transfer reactions to the organic phase. The efficient extraction of iron(III) from aqueous chloride solutions and the selectivity of the ligand for this metal ion when in the presence of interfering ions such as copper, zinc, nickel, cobalt, lead, and silver, in binary and in multicomponent mixtures, are also reported. The high selectivity towards iron(III), the complete stripping of this metal by simple contact of the loaded organic phase with water and the efficient reutilization of DMDBMA are very promising results that can justify an eventual industrial application.

Mechanism of copper action on pitting phenomena observed on stainless steels in chloride media

The influence of the addition of copper on the resistance to pitting corrosion of stainless steels has been investigated using different experimental techniques––current transient analysis, polarization curves in acidic media, pitting and repassivation potential measurements, XPS and SEM observations––so that pit initiation, propagation and repassivation could be analysed separately. Copper addition is shown to act in three different ways on pitting corrosion. On the one hand, copper reduces steel dissolution rates in acidic chloride media and also pit propagation rates. On the other hand, copper addition in steel is shown to lower repassivation potentials in neutral chloride environments and also to delay pit repassivation. Lastly, when copper is injected into solution as CuCl 2 or when the steel is polarized at anodic potentials so that copper can dissolve from the steel into solution, pit initiation close to sulfide inclusions is prevented. A model is proposed for these three different actions of copper, showing that the role of this element is complex and that no relevant information can be drawn from only considering its effect on the pitting potential.

Pitting Corrosion of Bulk Glass‐Forming Zirconium‐Based Alloys.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Pitting corrosion of bulk glass-forming zirconium-based alloys

The polarization behavior of glassy Zr 59Ti 3Cu 20Al 10Ni 8 alloy samples was investigated in 1N H 2SO 4 solution to understand their passivation characteristics in strongly acidic environment. Pitting corrosion tests were performed in acidic chloride medium of 1N H 2SO 4 containing 0.01–0.2N NaCl. Electrochemical investigations were carried out by potentiodynamic and potentiostatic anodic polarization methods at room temperature. The corroded sample surfaces were examined using scanning electron microscopy, and the alloying element distribution across the pits was analyzed using energy dispersive X-ray analysis. The passive films developed at potentiostatic anodic polarization were examined using Auger electron spectroscopy (AES). The results of the present investigation revealed (i) corrosion resistance of Zr-based amorphous alloys is very high in acidic medium and moderate in acidic chloride medium (ii) structural defects and clustered zones of alloying elements deteriorate the corrosion resistance, and (ii) copper plays a significant role in enriching below the passive film and affecting the corrosion behavior. In conclusion, a localized corrosion mechanism is proposed.

Hexavalent chromium recovery by liquid-liquid extraction with tributylphosphate from acidic chloride media.

A method is introduced for recuperation of chromium(VI) in water samples by liquid-liquid extraction with tributylphosphate PO(C4H9O)3 (TBP) from acidic chloride media. The optimum conditions for quantitative extraction of Cr(VI) were evaluated by varying the experimental parameters, such as the shaking period, the pH of the aqueous phase, the hydrochloric acid concentration, the hydrogen and chloride ion concentrations, the extractant concentration and the ratio of aqueous-to-organic phase. The probable extracted species of hexavalent chromium in organic phase, deduced from log-log plots, were H2CrO4 in acid media in absence of chloride and HCrO3Cl in acidic chloride media. Chromium(VI) was found to be extracted with tributylphosphate from acidic chloride media according to the following reaction: HCrO4-(aq), + 2H+(aq) + Cl-(aq) + 2TBP(org) <==> [HCrO3Cl, 2TBP](org) + H2O(aq). Since the tributylphosphate (TBP) exhibited a high selectivity for chromium(VI), this method can be applicable to the extraction and the determination of chromium in both oxidation states [Cr(VI) and Cr(III)] in water samples.

Prediction and measurement of mild steel corrosion inhibition by alkyl pyridinium chloride and alkyl trimethyl ammonium bromide surfactants in acidic chloride media

Surfactants are important corrosion inhibitors that are used in different applications. This paper utilizes the recently developed methodology and formulae to predict mild steel corrosion inhibition by alkyl pyridinium chloride and alkyl trimethyl ammonium bromide compounds. By utilizing different surfactants of varying chain lengths in different acidic media and determining the associated corrosion inhibition, the relationship between surfactant concentration, surfactant hydrocarbon chain length, surfactant critical micelle concentration, and corrosion inhibition can be evaluated. The results from this study can be used to improve relevant industrial uses of surfactants for corrosion inhibition.

New pyridinecarboxamides for rapid extraction of palladium from acidic chloride media

The extraction of palladium(II) from hydrochloric acid solutions of various concentrations in the presence of different amounts of sodium chloride with various defined alkylpyridinecarboxamides having one or two alkyl groups in the amide substituents at positions 2, 3 or 4 was studied. The hydrophobicity of the studied reagents was characterized by various parameters, including octanol/water distribution coefficient. It was found that the extraction of palladium(II) with monoalkylpyridinecarboxamides depends upon the number, length and position of the alkylamide group. Higher extractions are observed for the derivatives with the alkylamide group at position 3. The extraction of palladium(II) from aqueous 0.1 M HCl with N-dodecylpyridine-3-carboxamide (3-C 12) is rapid and the equilibrium is achieved in 30–60 s. The replacement of HCl with NaCl has only a minor effect on the extraction of palladium(II). During the extraction of palladium(II) from acidic solutions, HCl is also transferred to the organic phase. High transfer of HCl is observed for N-dodecylpyridine-3-carboxamide. A spontaneous transfer of palladium(II) to the organic phase is observed. The Vosburgh and Cooper method and the Job method were used to determine the composition of the complexes formed. Complexes with the molar ratio of palladium(II) to the extractant equal to 1:2 (PdCl 2L 2) and 1:1 (Pd 2Cl 4L 2) are extracted.

The Effect of Oxygen on Copper Dissolution during Cathodic Polarization

The effect of oxygen on the anomalous dissolution of copper in acidic chloride media is studied. An increase in the copper corrosion rate during cathodic polarization in the potential range from –0.4 to –0.7 V is attributed to stirring of the near-electrode layer by evolving hydrogen bubbles. An addition of surface-active tetrabutylammonium iodide shifts the overpotential of hydrogen evolution and eliminates this effect. The copper dissolution rate during cathodic polarization is shown to be directly proportional to the reduction rate of dissolved oxygen. It is shown experimentally that H2O2 does not affect the dissolution rate of copper during cathodic polarization. The latter fact makes it possible to assume that oxygen reduction stages, which involve hydrogen peroxide, do not affect the anomalous dissolution of copper.

EQUILIBRIUM OF PALLADIUM(II) EXTRACTION WITH 1-OCTYLTHEOBROMINE

ABSTRACT 1-Octyltheobromine was synthesized to study extraction equiliburium of palladium(II). To evaluate its efficiency as an extractant, the extraction of palladium(II) from acidic chloride media was studied at 303K using toluene. The extraction of palladium(II) from hydrochloric acid media by 1-octyltheobromine exhibited high selectivity for palladium(II) over the platinum group metals. The stoichiometrics of the extraction of palladium(II) with 1-octyltheobromine was elucidated by examining the effects of hydrochloric acid, chloride ion, hydrogen ion, extractant and metal ion concentrations on its extractability. Palladium(II) was found to be extracted as two molecules of 1-octyltheobromine reacted with PdCl2 as follows: PdCl2 +{2}¯RN ⟺ ¯PdCl2(RN)2. The extraction equilibrium constant was K=2.72 × 108(mol dm−3)−2. The complex of 1-octyltheobromine with PdCl2 was confirmed by mass spectrometric analysis. The stripping of palladium(II) was performed over 60% by a single batchwise treatment with an aqueous solution of thiourea or ammonia.

Crystal structure and kinetics of the acid-catalysed decomposition of ( N, N′-bis(2-pyridylmethylene)-1,3-diamino-2,2-dicarboxyethylpropane)copper(II)perchlorate

The crystal structure of the complex [CuL(OH) 2](ClO 4) 2·H 2O; L= N, N′-bis(2-pyridylmethylene)-1,3-diamino-2,2-dicarboxyethylpropane, determined for the first time, reveals a penta-coordinated copper(II) centre in a distorted square-pyramidal geometry with a weakly bonded axial water molecule. In order to assess possible routes to the putative free ligand N, N′-bis(2-pyridylmethylene)-1,3-diaminopropane-2-carboxylic acid the behaviour (stability) of the complex towards both acid and alkaline aqueous solution has been investigated. In 1.0 M acidic chloride media at 25 °C the complex undergoes slow decomposition in two stages giving 2-pyridylmethylammonium chloride, formaldehyde and diethylmalonate in addition to aqueous Cu 2+. The initial fast stage has both H +-dependent (5.32±0.18×10 −5 M −2 s −1) and independent (1.59±0.10×10 −5 s −1) paths, the latter believed to reflect rapid chloride equilibration at the labile axial site followed by rate determining isomerisation to place a CuNH bond at the axial site leading to CuN bond cleavage. The rate constant for the H +-dependent faster stage carries a [H +] 2 dependence suggesting that here protonation of both secondary NH groups occurs within the rate-determining step prior to decomposition. Assistance from the axial site is also proposed. Absorbance changes monitored as a function of [H +] for the ∼10× slower second stage suggest that it may involve intermediates resulting from the H +-independent initial step.

Interfacial chemistry of powdered barium ferrites immersed in aqueous solutions: leaching in acidic chloride media

The kinetics of leaching and dissolution of barium mono- and hexa-ferrite in acidic chloride media are presented and discussed. The monoferrite is appreciably more reactive, and dissolves in a nearly congruent way in low pH media. In the case of barium hexaferrite, iron and barium dissolution are independent processes. Initially, fast barium leaching is observed, which is followed by a slower process controlled by diffusion through a growing iron oxide layer. Iron dissolves at nearly constant rates that are a function of pH; the apparent kinetic order on H+ is 0.66, typical of acid dissolution mechanisms. The differing reactivities of the mono- and the hexa-ferrite relates to their crystal chemistry.

Selective extraction of palladium(II) with theophylline derivatives.

Theophylline derivatives with some kinds of alkyl chains were synthesized and used in extraction experiments involving metal ions. Theophylline derivatives have exhibited a high selectivity for palladium over other precious metals and base metals. The extraction of palladium from acidic chloride media has been investigated using theophylline derivatives (= RN) as extractants. Palladium(II) was found to be extracted with 7-octyltheophylline according to the following reaction: PdCl2 + 2RN <==> PdCl2(RN)2. The extraction equilibrium constant was determined to be K = 2.67 x 10(8) ( moldm(-3))(-2). In addition, the stripping of palladium was performed to an extent of 100% by a single batchwise treatment with a 1.0 mol dm(-3) ammonia solution. The stoichiometric relation in the extraction of palladium was supported by an analysis using mass spectrometry.

Lead electrowinning in an acid chloride medium

The results of an investigation of the electrowinning of lead employing a chloride medium are reported. The electro-deposition lead reaction was studied by voltammetric methods and scanning electron microscope (SEM) microphotographs of the electro-deposited lead were taken. The effects of current density, temperature, catholyte flow and H + concentration were investigated at laboratory scale to optimise operating conditions in order to found adequate values for industrial purposes of the parameters energetic cost and production. For a working current density of 100 mA/cm 2 the current efficiency, energy consumption and production were 90%, 1.32 kW h/kg Pb and 83.4 kg Pb/m 2 per day, respectively.

Electrochemical Route for the Synthesis of New Nanostructured Magnetic Mixed Oxides of Mn, Zn, and Fe from an Acidic Chloride and Nitrate Medium

New nanostructured magnetic Mn−Zn−Fe oxides are electrochemically synthesized as precipitates from chloride + nitrate solutions of pH 1.5 with Mn2+, Zn2+, and Fe2+, or Fe3+ at temperatures between 40 and 80 °C using electrodes of commercial iron. The process has been studied using an undivided cell of 100 mL and a stirring batch tank of 700 mL with electrodes of 20 and 140 cm2 area, respectively. Fe2+ is continuously supplied to the solution from oxidation of the sacrificial Fe anode, although this ion can be transformed into Fe3+ by reaction with Mn3+, previously formed by anodic oxidation of Mn2+. An energy cost of ca. 5 kWh kg-1 is found for the batch tank at 35 mA cm-2. For solutions up to 30 mM Mn2+ and 15 mM Zn2+, magnetic precipitates richer in Fe than in Zn and Mn, with Cu impurity proceeding from the anode, are obtained. These materials have an inverse cubic spinel structure, being composed of nanoparticles formed by solid solutions of iwakiite, franklinite, magnetite, and maghemite. Magnetically...

Thermal and photochemical reduction of aqueous chlorine by ruthenium(II) polypyridyl complexes.

Studies are reported on the reactions of aqueous chlorine with a series of substitution-inert, one-electron metal-complex reductants, which includes [Ru(bpy)3]2+, [Ru(4,4'-Me2bpy)3]2+, [Ru(4,7-Me2phen)3]2+, [Ru(terpy)2]2+, and [Fe(3,4,7,8-Me4phen)3]2+. The reactions were studied by spectrophotometry at 25 degrees C in acidic chloride media at mu = 0.3 M. In general the reactions have the stoichiometry 2[ML3]2+ + Cl2-->2[ML3]3+ + 2Cl-. In the case of [Ru(bpy)3]2+, the reaction is quite photosensitive; the thermal reaction is so slow as to be practically immeasurable. The reactions of [Ru(4,4'-Me2bpy)3]2+ and [Ru(4,7-Me2phen)3]2+ are also highly photosensitive, giving pseudo-first-order rate constants that depend on the monochromator slit width in a stopped-flow instrument; however, the thermal rates are fast enough that they can be obtained by extrapolation of kobs to zero slit width. The reactions of [Ru(terpy)2]2+ and [Fe(3,4,7,8-Me4phen)3]2+ show no appreciable photosensitivity, allowing direct determination of their thermal rate laws. From the kinetic effects of pH, [Cl2]tot, and [Cl-] it is evident that all of the thermal rate laws have a first-order dependence on [ML3]2+ and on [Cl2]. The second-order rate constants decrease as Eo for the complex increases, consistent with the predictions of Marcus theory for an outer-sphere electron-transfer mechanism. Quantum yields at 460 nm for the reactions of [Ru(4,4'-Me2bpy)3]2+ and [Ru(4,7-Me2phen)3]2+ exceed 0.1 and show a dependence on [Cl2] indicative of competition among spontaneous decay of *Ru, nonreactive quenching by Cl2, and reactive quenching by Cl2.