The effect of Fe(II) and Fe(III) on the efficiency of copper electrowinning from dilute acid Cu(II) sulphate solutions with the chemelec cell. Part II. The efficiency of copper electrowinning from dilute liquors

This programme of work forms part of a study into the application of the Chemelec cell for direct electrowinning of copper from dilute leach liquors. A typical liquor is defined as containing less than 2 g l^?1 Cu(II), with an equivalent or greater concentration of iron as Fe(II) and Fe(III). Electrowinning experiments using simulated liquors showed that the current efficiency decreased in proportion to the increase in the Fe(III) concentration. A current efficiency of less than 30% was obtained during the electrowinning of a copper solution (1–2 g l^?1 Cu) with an Fe(III) concentration of 0.5–3.0 g l^?1. Electrowinning from leach liquors (1–2 g l^?1 Cu, 1–2 g l^?1 Fe(III) and 1–5 g l^?1 Fe(II)) showed improved efficiencies. A current efficiency of 47% was obtained for copper removal to less than 50 mg l^?1, with an electrolytic energy cost of about £198 per tonne at 3.3p per kWh. The impurity content of the copper was low, the most significant impurity being lead at 0.012%. This work has shown that the Chemelec cell can achieve reasonable efficiencies for direct electrowinning from dilute leach liquors. Further work is required in order to confirm the efficiency of electrowinning and to assess the operating and capital costs of a commercial cell.     

Cuprous hydrometallurgy : Part II. The electrowinning of copper from cuprous sulphate solutions containing organic nitriles

Copper can be won with low power consumption from an acidified cuprous sulphate solution containing organic nitriles in a one electron process to give smooth non-dendritic copper cathodes and cupric sulphate at the inert anode. A diaphragm is necessary if cupric sulphate is allowed to concentrate in the cell. In the presence of an organic nitrile in water, cuprous sulphate is stable and cupric sulphate oxidises copper to cuprous sulphate. A scheme for refining crude copper to cathode copper without casting anodes is proposed. Various inert anode materials are compared.     

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.     

Effect of manganese(II) and boric acid on the electrowinning of cobalt from acidic sulfate solutions

The effect of Mn(II) and boric acid on the electrowinning of cobalt from acidic sulfate electrolyte was investigated by electrochemical methods. The results indicated that the presence of Mn(II) or boric acid alone increased the current efficiency by 2 to 3 pct but that their combination had no additional effect. The preferred crystal orientation pattern changed from (110) (100) (101) to (100) (110) (101) in the presence of 0.1 to 10 g dm⁻³ Mn(II); an additional change, to (110) as the only preferred orientation, occurred at a very high concentration of Mn(II) (100 g dm⁻³). Boric acid had no effect on the crystal pattern of the cobalt deposits. In general, the presence of boric acid increased the brightness of all the deposits, irrespective of the presence of Mn(II) in the electrolyte, and had no effect on the deposit morphology. The cathode polarization behavior of the cobalt electrocrystallization was affected only marginally by the presence of Mn(II) in the electrolyte, but the presence of boric acid with or without Mn(II) had a significant effect. Boric acid was found to suppress the rate of electroreduction of cobalt on stainless steel by an order of magnitude, irrespective of the presence of Mn(II).     

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.     

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.     

The thermodynamic studies of liquid copper alloys by electromotive force method: Part I. The Cu−O,Cu−Fe−O,and Cu−Fe systems

Oxygen activities in liquid Cu−O and Cu−Fe−O alloys were measured in the temperature range 1100° to 1300°C by the solid oxide electrolyte emf method with mixtures of Ni−NiO and Co−CoO as reference electrodes. The Cu−O and Cu−Fe−O alloys were analyzed for iron and/or oxygen content. The activity coefficient of oxygen at infinite dilution in liquid copper was found to be 0.115, 0.195, and 0.286 at 1100°, 1200°, and 1300°C, respectively. The results are compared with previous investigations on the Cu−O system. Based on this comparison, the best equation for the free energy of solution has been suggested. The standard free energy of formation of CoO(s) has been calculated at the experimental temperatures. In the liquid Cu−Fe−O system at 1200°C, a minima in oxygen solubility is reached at 1.1 at. pct Fe in the alloy. The value of interaction coefficient, , is −565 at 1200°C. Iron activities in the liquid Cu−Fe alloys have been calculated at 1100° and 1200°C, and a strong positive deviation from ideality is observed. Results of this study were combined with literature data at 1550°C to obtain the values of and at infinite dilution in liquid copper. A. D. KULKARNI, formerly with Chase Brass and Copper Co., Cleveland, Ohio     

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.     

Cuprous hydrometallurgy Part IV. Rates and equilibria in the reaction of copper sulphides with copper(II) sulphate in aqueous acetonitrile

Copper(II) sulphate in solutions of aqueous acetonitrile leaches copper from copper sulphides to form stable copper(I) sulphate solutions. Covellite and chalcopyrite are oxidised and leached more rapidly in the early stages of leaching with acidic CuSO₄/CH₃CN/H₂O than with acidic iron(III) sulphate in water. A redox equilibrium between copper(I) sulphate, copper(II) sulphate and partially leached solid copper sulphide, Cu_xS, is established. The equilibrium concentration of Cu₂SO₄ and the value of x in Cu_xS, in solutions saturated with CuSO₄, are interdependent if the acetonitrile concentration is constant. This behaviour is considered in terms of the structural and electrochemical changes which occur, in the solids Cu₂S and CuS, as leaching proceeds. According to the activities of acetonitrile, of copper(I) sulphate and of copper(II) sulphate, i.e. according to the redox potential of the solution, CuS either can be oxidised by copper(II) sulphate to a less copper-rich copper sulphide and even to sulphur, or reduced by copper(I) sulphate to a more copper-rich sulphide, up to Cu₂S, in acidic solutions containing CuSO₄, Cu₂SO₄, CH₃CN and water. This observation leads to an easy method of generating Cu₂S from CuS or from sulphur.     

Zinc,nickel and lead in copper deposited from copper(II) ammine sulphate electrolytes

The influence of electrolytic variables on the content of Zn, Ni and Pb in copper deposited cathodically from ammine solution has been investigated. Solutions spiked with zinc or nickel sulphate were studied using a rotating cylindrical titanium cathode and a lead anode.The nickel and zinc contents in the cathodic deposit increase with increasing current density and their concentration in the electrolyte. A rise in the rotation speed of the cathode increases the lead and nickel contents but diminishes the zinc content in the deposit.To explain these results an attempt has been made to schematically reconstruct polarisation diagrams for each metal. Direct potential measurements are subject to considerable experimental error in the system studied. Polarisation measurements performed on a simplified system were in good agreement with the hypothetical diagram.     

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.     

Uranium sorption from phosphoric acid solutions using selective ion exchange resins: Part II. Kinetic studies

Experiments have shown that the sorption of uranium from strong phosphoric acid solutions onto four D2EHPA/TOPO based ion exchange resins and one aminophosphonic acid resin is particle diffusion controlled in the uranium concentration range 42–780 μM. Interdiffusion coefficients of about 10^?12 m²s^?1 were obtained for D2EHPA/TOPO resins and 0.14 × 10^?12 m²s^?1 with the aminophosphonic acid exchanger at 20°C in 3 M H₃PO₄. Both homogeneous particle diffusion, based on Fick's Law, and the ash layer diffusion model fitted the kinetic measurements.     

Zn-exchange and M?ssbauer studies on the [Fe-Fe] derivatives of the purple acid Fe(III)-Zn(II)-phosphatase from kidney beans

In order to perform M?ssbauer studies, Zn(II) in the Fe(III)-Zn(II) purple acid phosphatase of the red kidney bean has been exchanged by incubating the semiapoenzyme with 57Fe(II). The resulting Fe(III)-57Fe(II) enzyme has 125% activity, compared with that of the Zn(II) enzyme. It can be oxidized by H2O2 or peroxydisulfate to the Fe(III)-57Fe(III) species with a 30-times lower activity. Incubation of the metal-free apoenzyme with 57Fe(II) in the presence of O2 leads to the 57Fe(III)-57Fe(II) species which is stable in dilute solutions, but partially oxidized during the concentration procedure to the 57Fe(III)-57Fe(III) enzyme. Limited reduction of the oxidized enzyme with ascorbate delivers a mixture of the Fe(II)-Fe(II)/Fe(III)-Fe(III) species, but not the mixed valent Fe(III)-Fe(II) species, indicating that after the transfer of the first electron the second electron of the ascorbate radical is immediately transferred to the second Fe(III). The M?ssbauer spectra of the oxidized species show at 4.2 K two quadrupole doublets with delta of 0.51 mm/s and 0.53 mm/s and delta E of 1.46 and 0.96 mm/s indicating high spin Fe(III) in two different binding sites, obviously with a higher asymmetry in the chromophoric Fe(III) site. The values are too low for a mu-oxo bridge. The mixed-valent Fe(III)-Fe(II) species shows two quadrupole doublets with delta values of 0.55 mm/s and 1.14 mm/s and delta E values of 1.43 mm/s and 3.01 mm/s at 70 K for high spin Fe(II) and Fe(III), but the signal of the Fe(II) component shows magnetic patterns at 4.2 K indicating a half-integer spin system with antiferromagnetic coupling. The Fe(II)-Fe(II) system exhibits two quadrupole doublets with delta values of 1.18 mm/s and 1.22 mm/s and with delta E values of 3.69 mm/s and 2.68 mm/s again indicating a higher asymmetry in the originally chromophoric Fe(III)-binding site. Addition of phosphate shows only minor differences in the oxidized enzyme and in the mixed valent Fe(III)-Fe(II) system. Interaction with O2 is discussed.     

Kinetics of leaching of copper metal in copper(II)-ammonium sulphate solutions as determined by the rotating disc method

The influence of the concentration of copper(II)-ammine-sulphate complexes, temperature and the concentration of ammonia on the velocity of the leaching of copper metal in sulphate solutions was investigated by application of the rotating disc method.The results show that the following factors determine the velocity of the process: transport of copper(II) complexes to the reaction surface and the rate of the surface reaction (mixed control).An attempt was made to derive a semi-empirical equation describing the kinetics of the process. The value of the diffusion coefficient, calculated on the basis of the derived formula and the experimental data, is equal to (1.2 ± 0.1) × 10^?9 m² s^?1 (for solutions containing from 0.0012 to about 1 mol/l copper, 6.5 mol/l ammonia and 1.2 mol/l sulphates; temperature 25°C).The diffusion activation energy, determined in the range of temperatures from 15 to 50°C equals 30.1 ± 1.7 kJ/mole. This is surprisingly high especially in comparison with the activation energy of viscous flow determined at the same conditions, which is 15.9 ± 0.4 kJ/mole.Discussion of the results leads to the conclusion that free ammonia (the stoichiometric excess in relation to the amount necessary for a complete bonding of copper in a complex) does not participate in the electrode reaction. However, it diminishes the velocity of transport of copper complexes to the reaction surface.     

The extraction of zinc(II) from sulphate and perchlorate solutions by di(2-ethylhexyl)phosphoric acid dissolved in Isopar-H

The extraction of zinc from sulphate and perchlorate solutions at constant ionic strength, by di(2-ethylhexyl)phosphoric acid, DEHPA, in Isopar-H has been studied at 25°C as a function of metal and DEHPA concentrations. The distribution data have been analyzed both graphically and numerically, using the computer program LETAGROPDISTR [33]. The results showed that the species extracted into the organic phase have the composition ZnA₂HA and ZnA₂H₂A₂ for both perchlorate and sulphate systems. The formation constants for each system are given in Table 2. An estimate of the formation constant of ZnSO₄ in aqueous phase was obtained from the extraction data in sulphate solutions.     

Extraction of Fe(III) from hydrochloric acid solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921)

Ferric ions were efficiently removed from HCl solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921). Iron was removed under the form HFeCl₄ through direct binding on the resin or by extraction with Cyanex 921 involving a solvation mechanism. High concentrations of HCl and intermediary extractant loadings were required for maximum sorption efficiency and rationale use of the extractant. At intermediary extractant loading (in the range 300–450 mg Cyanex 921 g^− 1) the maximum sorption capacity increased with extractant loading. Maximum sorption capacity slightly increased with temperature, the reaction is endothermic and the enthalpy change was found close to − 30.8 kJ mol^− 1. Sorption isotherms were fitted with the Langmuir equation and maximum sorption capacity reached values as high as 20–22 mg Fe g^− 1 in 3 M HCl solutions. Despite the good fit of experimental data with the pseudo second-order rate equation, sorption kinetics was controlled by the resistance to intraparticle diffusion. The intraparticle diffusion coefficient (D_e) varying in the range 1.2 × 10^− 11–4.7 × 10^− 10 m² min^− 1 was found to increase with metal concentration and with temperature, while varying the extractant loading it reached a maximum at a loading close to 453 mg Cyanex 921 g^− 1. The desorption of Fe(III) can be achieved using 0.1 M solutions of nitric acid, sulfuric acid, sodium sulfate and even water, maintaining high efficiencies for sorption and desorption for at least 5 cycles.     

The influence of the diluent on the extraction of iron(III) from aluminium sulphate solutions by the amine primene 81R sulphate

The extraction of iron(III) from aluminium sulphate solutions by the amine Primene 81R sulphate has been studied using 15 diluents of different types. The results are discussed in terms of the composition of the diluent and aggregation of the amine sulphate in solution, the dielectric constant and polar nature of the diluent, and interfacial tensions between aqueous media and amine sulphate solutions in the diluents. The best extraction results were obtained with diluents such as toluene and benzene.     

The interaction of antitumor-active anthraquinones with biologically important redox couples: I. Spectrophotometric investigation of the interaction of carminic acid and mitoxantrone with the iron (II, III) and copper (I, II) redox couples

Studying the interaction of antitumor-active anthraquinones with biologically important redox couples is important in understanding the possible reductive or oxidative mode of metabolism of these antineoplastic agents coupled with the formation of free radicals. The interactions of such anthraquinones, i.e., carminic acid (CA) and mitoxantrone (Mx) with iron(II, III) and copper(I, II) redox couples in oxygenated and deaerated solutions, were investigated by UV-Visible and IR-spectroscopy. The superoxide radical reagent, nitroblue tetrazolium (NBT), was added to the metal and anthraquinone solutions and their binary mixtures at varying pH. Formazan, the reduction product of NBT, was produced mainly as a result of Fe(II)-NBT and Fe(II)-Mx-NBT interactions. The ternary mixtures of the lower valencies of iron and copper with CA and NBT exhibited intensive charge-transfer bands in the visible region, while metal-Mx-NBT combinations did not produce such bands, possibly due to the blockage of the redox-active aminoethanolamine side-chains of Mx through coordination with the metals. Copper-Mx combinations showed an oxygen sensitivity as spectral evidence was obtained for the oxidative transformation of Mx to the cyclic primary metabolite. The results were evaluated in regard to the possible oxidative activation of the studied anthracenediones with iron and copper systems.