Electrolytic reduction of U(VI) to U(IV) in acidic chloride and acidic sulfate solutions

In order to examine the applicability of the electrolytic reduction process of U(VI) (originally developed for the chloride system by PNC) to the sulfate solution system, a fundamental study was made. In this study, the concentrations of various chemical species in the catholytes were calculated at 298 K at various percentages of uranium reduction, taking the chloro-complex and sulfato-complex formation reactions of uranium into consideration. The polarization characteristics of the electrolytic reduction of uranyl chloride and uranyl sulfate were determined, using titanium and platinum cathodes, respectively, at 303 ± 1 K. In conjunction with this process, the electrical conductivity of the catholyte, the electrical resistivity of the cation exchange membrane, and the diffusion coefficient of uranyl sulfate were also determined.     

Contactless electrochemical reduction of titanium (II) chloride by aluminum

Because of the strong affinity between aluminum and titanium, it has not been possible to produce pure titanium by direct aluminothermic reduction of titanium chlorides. Described in this article is a new process for contactless reduction of titanium dichloride by aluminum in which titanium dichloride and the reductant (aluminum or aluminum alloy) were physically separated, but electrochemically connected through molten NaCl and an external circuit. Titanium dichloride was spontaneously reduced to metal by a cathodic reaction with the simultaneous discharge of chlorine ions into the melt. At the anode, metal aluminum was oxidized to form aluminum chloride dissolved in the molten salt. The electrons were transferred between the electrodes through the external circuit. The concentration of aluminum in titanium produced at 1223 and 1273 K varied from values below the detection limit of the X-ray fluorescence analysis (0.01 mass pct) to 4.5 mass pct. The average contamination was 0.76 mass pct Al. When an aluminum-nickel alloy was used as the reductant, nickel was not detected in the titanium obtained by reduction. This observation suggests that aluminum scrap may be used as a cheap reductant in this contactless electrochemical process.     

Sorption recovery of rhodium(III) from multicomponent chloride solutions in the presence of tin(II) chloride

The influence of tin (II) chloride additives on sorption of Rh(III) on the Purolite S920 ion exchange resin with isothiouronium groups, the Purolite S985 weak base anion exchange resin, and the Purolite A500 strong base anion exchange resin is investigated. It is established that the introduction of SnCl₂ leads to a substantial increase in selectivity of all tested ion exchange resins to Rh(III) and in the sorption rate of Rh(III) on S985 and S920 ion exchange resins. The optimal dosage of SnCl₂ (0.01 mol/L) at which the distribution coefficients of Rh(III) during sorption for all tested ion exchange resins reach maximal values is determined. It is shown that almost quantitative recovery of Rh(III) is attained when passing the multicomponent chloride solution of the composition (g/L) 0.2 Rh(III), 72.9 HCl, 53.5 NH₄Cl, 2.7 Al(III), 1.23 Fe(III) and 5.9 Sn(IV) with the SnCl₂ additive through the Purolite S920 ion exchange resin with isothiouronium groups. Desorption of Rh(III) from the Purolite S920 saturated ionite with the acidified thiourea solution is incomplete, no greater than 60%.     

Precipitation of nanosized titanium dioxide from aqueous titanium(IV) chloride solutions by neutralization with MgO

Aqueous titanium (IV) chloride solutions were neutralized to different terminal pH (2.5 to 6.0) with magnesium oxide as base at 95 °C and were found to yield nanosized titanium dioxide. The produced materials were compared to those obtained by simple forced hydrolysis. The techniques of XRD, TGA–DTA, FT-IR, BET, SEM and TEM were applied for the characterization of the produced materials. Honeycomb-shaped uniform nanosized crystalline TiO₂ powders with aggregate particle size of about 50 nm were successfully obtained by neutralization with magnesium oxide. Phase-pure rutile or mixed rutile and anatase crystalline TiO₂ powders were precipitated with proper selection of conditions. It was found that forced hydrolysis at 95 °C favors the formation of rutile TiO₂. Rutile TiO₂ powders with different crystallite sizes between 11 and 18 nm were obtained from aqueous TiCl₄ solutions with Ti concentration ranging from 0.5 mol/L to 2.0 mol/L. Neutralization with MgO at 95 °C, on the other hand, favored the formation of mixed anatase and rutile materials. The anatase fraction (ranging from 0 to 70%) increased with pH elevation (from 2.5 to 6.0). The neutralization method yielded much higher titanium precipitation efficiency (up to 100%) than simple forced hydrolysis. The magnesium content in the TiO₂ products was found to increase with a rise in the final pH due to partial hydrolysis of magnesium. It was less than 0.1% when the final pH was kept at or below 3.3.     

Properties of electrolyte solutions relevant to high concentration chloride leaching. III. Solubility of pertinent solids and iron(III)/iron(II) redox potential measured in concentrated magnesium chloride solutions

Results of solubility measurements of nickel chloride, manganese chloride, iron(II) chloride, hematite and akaganeite in aqueous solutions of MgCl₂ (0.5–3.5 mol L^− 1) at temperatures of 60 and 90 °C are reported. Solubilities of metal(II) chlorides decrease almost linearly with MgCl₂ concentration due to the common ion effect. Nickel chloride and iron(II) chloride solubilities are very similar, while manganese chloride is about 30% more soluble.Hematite is more stable (i.e. less soluble) than akaganeite under all conditions investigated in this study, while ferrihydrite is considerably less stable. In other words, there is no change in the relative stabilities of these phases effected by the presence of high magnesium chloride concentrations. The solubility of all of these phases decreases with temperature and, for each temperature, the solubility constants increase linearly with the MgCl₂ concentration. The present results allow the prediction of the iron concentration as a function of the H⁺ and MgCl₂ molality at equilibrium with hematite or akaganeite.The Fe(III)/Fe(II) redox behaviour has been characterized in concentrated aqueous solutions of MgCl₂ (1.5–3.5 mol L^− 1) at a temperature of 25 °C. Standard redox potentials are ca. 100 mV lower than at infinite dilution and change linearly by only 13 mV in the range 2–4 mol L^− 1 MgCl₂.     

Electrical conductivity of acidic chloride solutions

The electrical conductivities of aqueous solutions in the system HCl-MCl_n (where M = K, Na, Mg, Ni, or Cd) were measured at different temperatures. The equivalent electrical conductivity of H⁺ was calculated on the basis of simple assumptions for these solutions, and show an inverse relationship with water activity in these solutions. The results obtained by varying temperatures, solute ratios, and ionic strength on the electrical conductivity were found to be consistent with a proton jump mechanism for the H⁺ ion, where the activity of water is the most significant parameter affecting its equivalent conductance, and a viscous (Stokes’ law) drag mechanism (i.e., Walden’s rule is obeyed) for other ions found in acidic solutions.     

The extraction of copper(II) and iron(III) from chloride and sulphate solutions with LIX 64N in kerosene

A comparison has been made of the extraction of Cu(II) and Fe(III) from chloride and sulphate solutions with LIX 64N in kerosene. The effects on extraction of pH, anion concentration, and temperature were examined, and attention was paid to the ionic strength of the aqueous media, some of which contained aluminium and magnesium; extraction was carried out under ‘practical’ rather than ‘ideal’ conditions. Extraction of both Cu and Fe was enhanced from chloride solutions compared with sulphate; although separation of Cu from Fe was slightly reduced, extraction of Cu from chloride liquors appears to be applicable to commercial leach solutions.     

Behavior of antimony(III) during copper electrowinning in chloride solutions

Contamination of cathodic copper by Sb during electrowinning in chloride solutions is a surface phenomenon. A digitized scanning electron microscopy (SEM) micrograph indicates that the Sb is concentrated on the surface of the cathode. Energy-dispersive X-ray (EDX) analysis reveals that the Sb-containing layer is a complex salt of Cu, Sb, Cl, and O. Electrochemical measurements show-that the adsorption of Sb or Cu species decreases with the increase of acidity of the solution when the solution contains antimony chloride or cuprous chloride. The adsorption increases with the increase of the acidity when the solution contains both Sb and Cu. The discharge of cuprous ions in the adsorbed complex salt releases antimonious ions and then forms a new layer of the complex salt with cuprous ions from the solution. This newly formed complex salt is readsorbed on the surface of the cathode. Thus, Sb concentrates on the surface of the cathode instead of being evenly distributed throughout the copper product. This suggested mechanism also explains the fact that the presence of Sb in the electrolyte enhances the electrodeposition of Cu.     

Kinetics of gold(III) chloride complex reduction using sulfur(IV)

In this article, the effect of different kinetic parameters such as pH, temperature, gold, and reductant concentrations on the rate of Au reduction from aqueous chloride solutions by NaHSO₃ is investigated. On the basis of available experimental data, the possible mechanism of [AuCl₄]⁻ reduction by sulfur(IV) is also assumed. The suggested mechanism yields the rate equation for reduction of [AuCl₄]⁻, which is given in the form

The extraction of Fe(III) from ammonium chloride solutions with capric acid

Extraction equilibria in the FeCl₃NH₄Clcapric acidCCl₄ system were investigated. Using slope analysis the results were interpreted in terms of the formation of the binuclear species [Fe(OH)R₂]₂ and [Fe(OH)₂R·HR]₂ in the organic phase. From calculations of the complex formation function and the experimental data it was shown that the effect of Fe(III) hydrolysis in the aqueous phase on metal extraction may be neglected.     

Recovery of Al(III) and Fe(III) from mixed chloride solutions containing platinum(IV)

The sorption of Fe(III), Al(III) and Pt(IV) from the individual and mixed chloride solution was investigated by using PC88A resin. With the increase of HCl concentration to 5 M, the distribution coefficient of Fe decreased slowly, while that of Al decreased rapidly and the distribution coefficient of Pt was nearly zero in our experimental range. Batch experiments showed that it was possible to extract both Fe and Al simultaneously by adjusting HCl and PC88A resin concentrations. However, continuous extraction chromatographic experiments indicated that simultaneous sorption of Al as well as Fe was difficult in our experimental range. Two extraction chromatographic steps would extract most of Fe and 90% of Al from the mixed solution, while Pt was not extracted. Extraction chromatography of the mixed chloride solution with PC88A resin was found to be fast and simple.     

The coprecipitation behavior of Co(II) and Ni(II) with Fe(III), Cr(III) and Al(III) from aqueous ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with iron(III), chromium(III) and aluminum(III) from ammoniacal solutions has been investigated. The coprecipitation behavior was found to be very sensitive to the solution pH and total ammonia concentration. Co(II) and Ni(II) can be precipitated from low ammonia concentration solutions but are readily redissolved at higher ammonia concentrations. The coprecipitate of divalent and trivalent species was found to contain very large amounts of the divalent metals (up to a mole ratio M M(II)/M(III) of 2.5) when aluminum was the trivalent species, whereas with iron(III) or chromium(III), the ratio was only 0.5.     

Solvent extraction-separation of La(III), Eu(III) and Er(III) ions from aqueous chloride medium using carbamoyl-carboxylic acid extractants

N,N-dibutyldiglycol amic acid(HLI) and N,N-dioctyldiglycol amic acid(HLII) were synthesized and characterized by conventional spectroscopic methods. These molecules were examined as extractants for extraction-separation of La(III), Eu(III) and Er(III), as representative ions of light, middle and heavy rare earths, from aqueous chloride solutions. The analysis of the extraction equilibria revealed that the extracted species of lanthanum and europium ions by both of the extractants had a 1:3 metal to ligand ratio. It was suggested that erbium ions were extracted into the organic phase via the formation of Er(LI or II)2Cl complexes. The effect of the organic diluents on the extraction-separation efficiency of the studied rare earths by HLI and HLII was investigated by comparing the results obtained in dichloromethane and carbon tetrachloride. Regardless to the diluent used, the order of selectivity presented by the investigated extractants was Er(III)Eu(III)La(III). It is noteworthy that, a significant enhancement in separation of the studied rare earths by the extractants was achieved in their competitive extraction experiments with respect to that obtained in single component extraction experiments. Applicability of the extractants for the removal of rare earth ions from spent Ni-MH batteries was tested by removal of La(III), Eu(III) and Er(III) ions from simulated leach solution of such batteries.     

Kinetics of Cu(II) cementation on a pure aluminum disc in acidic sulphate solutions

Abstract

The rates of copper cementation on pure aluminum discs were studied as a function of (a) initial copper ion concentration, (b) temperature, (c) initial hydrogen ion concentration, and (d) the effect of the peripheral velocity of the Al disc.

At low initial copper ion concentration (1 × 10^?4M), there are two rate-controlling processes: ionic diffusion control at temperatures. above 40°C, and surface reaction control at temperatures below 40° C. At higher initial copper ion concentrations (5 × 10^?3 M), the rate is controlled by a chemical (surface) reaction.

When the-hydrogen ion concentration is increased to 0.7 M, the cementation rate increases. The pH remains constant during the reaction.

The cemented deposit is pure copper. The structure. of the deposit is dependent on both temperature and the initial copper ion concentration. At high initial copper ion concentration (5 × 10^-3 M) and at high temperatures (75° C), the rate, which was constant initially, increases with increasing deposition.

Résumé

Les taux de cémentation du cuivre sur des disques d'aluminium pur ont été étudié en fonction (a) de la concentration initiale des ions cuivres, (b) de la température, (c) de la concentration initiale des ions hydrogene et (d) de l'effet de la vitesse tangentielle du disque d'aluminium.

Pour une faible concentration initiale d'ions cuivre (1 × 10^?4 M) il y a deux processus régulateurs : à des températures supérieures à 40°C un côntrale de diffusion ionique et à moins de 40°C un côntrale de la réaction de surface. Pour des concentrations d'ions cuivre plus élevées (5 × 10^?3 M), le taux est contrôlé par une réaction chimique (de surface).

Quand la concentration des ions hydrogène est augmentée à 0.7M Ie taux de cémentation augmente, lp. pH demeure constant pendant la réaction.

Le dépôt est du cuivre pur et sa structure dépend à la fois de la température et de la teneur initiale en ions cuivre. A haute concentration initiale d'ions cuivre (5 × 10^-3M) et à haute temperature (75°C), le taux, constant du début, augmente quand le dépôt augmente.     

Extraction of chromium(III) from sodium chloride solutions by means of carboxylic acids

Studies of Cr(III) extraction with carboxylic acids showed that the extraction process takes place at a pH of the aqueous phase ranging from 4 to 5. It was shown that sodium chloride is active with respect to chromium(III) as a salting-out agent. For extraction of Cr(III) with hexanoic acid it was shown that in the organic phase trinuclear complexes of the [Cr(OH)R₂·HR]₃ formula are formed.     

Electrochemical reduction of arsenic (III) with cadmium metal

The kinetics of aqueous arsenic (III) reduction to amorphous arsenic with cadmium metal are presented. Two reaction mechanisms are observed in this system. With arsenic concentrations greater than approximately 0.2 gm/1 in solutions containing one molar sulfuric acid, the reduction of arsenyl ion on the cadmium surface is rate controlling. When arsenic concentrations are less than this value, reaction rate is mass-transport controlled. The reduction of arsenic (III) with cadmium powder at pH 2 is also presented.     

The extraction of Zinc(II) from sulphate and chloride solutions with kelex 100 and versatic 911 in kerosene

Zinc(II) is extracted from sulphate or chloride solutions by Kelex 100 (HX) in kerosene, comparable extraction taking place under more acid conditions from chloride media. The addition of Versatic 911 (HA) leads to synergistic enhancement of extraction; equilibrium studies with the mixed extractants indicate that a mixed complex of the form ZnX₂ · (HA)₂ is extracted, and infra-red spectra suggest that Versatic is present as a solvating agent. The effect of chloride ion concentration on extraction was examined, and tracer studies showed that chloride takes no part in the constitution of the extracted zinc complex.     

The behaviour of lix 63 in the extraction of Cu(II) and Fe(III) from chloride media

Investigation of the extraction of copper from chloride solutions using the commercial Lix reagents has shown that Lix 64N extracts small amounts of chloride whereas Lix 65N does not. The extraction of chloride is due to a minor component of the Lix 64N, the aliphatic α-hydroxyoxime Lix 63. This latter reagent extracts copper as a neutral chlorocomplex, probably of the form CuCl₂ · HCl or CuCl₁ · 2HCl₁ at low pH values and extracts the metal ion directly at higher pH. Under similar conditions iron is apparently extracted as the mono-chloro complex, entering the organic phase as FeCl · Lix₂. Following this behaviour, it appears that, in a solvent extraction operation involving chloride leach solutions, Lix 65N, which exhibits no tendency to extract chloride ions, might be a preferable extractant.     

Efficient extraction and stripping of Nd(III), Eu(III) and Er(III) by membrane dispersion micro-extractors

The extraction of low concentration rare earth elements at high phase ratio was investigated. The traditional extraction set-up, such as mixer-settler, have drawbacks of easy emulsification, difficult separation and low efficiency if operated at the above condition. Membrane dispersion micro-extractor, owing to its well-dispersed, high surface-to-volume ratio and fast mass transfer rate, was employed in our work. Nd(III), Eu(III), Er(III) were chosen to represent light, medium, heavy rare earth elements (REEs). The extraction process of REEs with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) was investigated by membrane dispersion micro-extractors. Firstly, the extraction equilibrium of these three elements was explored in the stirred conical flasks, and it is indicated that the extraction efficiencies can be 0.95, 0.97 and 0.98, respectively within 40 min at phase ratio of 100:1. Then the effects of operational conditions such as the residence time, organic and aqueous flow rates on extraction efficiency were also explored in micro-extractors. The results indicate that the efficiency decreases and then increases if increasing aqueous phase flow rate, residence time and droplets' diameter are the key factors of this process. Increasing the phase ratio reduces the extraction efficiency significantly. When the REEs solution has an initial pH of 4.00, the flow rates of continuous and dispersed phase are 40 and 1.6 mL/min, respectively, and 90 mg/L Nd (III), Eu(III) and Er(III) is extracted by 1 mol/L P507 at the out-let length of 8 m. The extraction efficiencies are 0.978, 0.983 and 0.991, respectively. Finally the stripping process was also studied with the micro-extractor. The stripping efficiencies of Nd(III), Eu(III) and Er(III) can reach 0.99, 0.96 and 0.91, respectively when the out-let length is 8 m and the concentration of hydrochloric acid is 1 mol/L. The developed approach offers a novel and simple strategy on the fast extraction and enrichment of low concentration rare earth elements from waste water.