Hydrometallurgy

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Online ISSN: 0304-386X
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Article
Solubility determinations of gypsum were conducted on simulated process liquors containing 0–72 g/kg solution Mn2+ (as sulfate) and 0–72 g/kg solution H2SO4 from 30 °C to 105 °C. At temperatures ≤ 80 °C gypsum solubility was shown to increase with increasing H2SO4 concentration and temperature in accord with the dissociation equilibrium of the bisulfate ion, while the addition of Mn2+, as sulfate, decreased the solubility. Above 80 °C the conversion of gypsum to anhydrite was shown to be dependent on Mn2+ and H2SO4 concentrations. In water alone hemihydrate was produced at 105 °C. Several empirical models were developed from solubility data at temperatures ≤ 80 °C and correctly predicted gypsum solubility in the experimental acidic manganese solutions.
 
Article
The extraction of manganese(II), iron(III), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium (II) from 1.0 M sodium sulphate by LIX 1104 (a hydroxamic acid) was investigated at various aqueous pH values. The extraction order is: Fe(III)>Cu(II)>Zn(II)>Ni(II)≈Co(II)>Cd(II)>Mn(II).Slope analysis and non-linear least-squares regression showed that LIX 1104 formed chelates of the nature ML2 with manganese, cobalt, zinc and cadmium and ML2 (HL) with nickel and copper. LIX 1104 appears particularly useful for the removal of iron (III) from other base metals as it functions in strongly acidic media and does not co-extract acid significantly. It can also be used to separate copper from other base metals.
 
Article
Di(2-ethylhexyl)phosphoric acid (D2EHPA) was fixed on the Amberlite XAD-1180 solid support by extractant impregnated resin technique (EIR). The quantity of the adsorbed extractant in the resin was in function of the polarity of the impregnation solvent. Thus, the optimal loading of the monomeric D2EHPA was 6 g/g of dry resin using acetone as solvent. The kinetics measurements on the extraction of bismuth (III) ions from nitrate aqueous solution were conducted while varying the initial pH of aqueous solution, initial bismuth concentration, D2EHPA content in the Amberlite XAD-1180 resin, stirring speed and equilibrium time. The extraction yield of bismuth was determined at 98.5% equivalent to 490.7 mg of Bi/g of resin, so the D2EHPA–Bi complex was suggested. Also, the complete regeneration of resin was realized in two stages in the presence of concentrate hydrochloric acid. The increase of the immersion aqueous volume, slightly decreases the sorption of Bi(III). The antagonistic effect on the sorption of Bi(III) was observed by adding sodium chloride. 33 factorial designs were employed for screening the factors that would influence the overall optimization of a batch procedure of sorption.
 
Article
The microbiology of water draining two abandoned mines in the UK and of a pilot-scale-constructed wetland site at one of the mine sites has been studied. The oxidation of ferrous iron in the acid mine drainage (AMD) of both mines is controlled by indigenous microbes and oxygen concentration, and is limited by the availability of nutrients, especially phosphate. A group of isolates that catalyse the oxidation of ferrous iron at pH >3 (“moderate acidophiles”) were obtained from these samples; these outnumbered the more familiar extremely acidophilic iron oxidisers such as Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans. As in the feed AMD, moderate acidophiles outnumbered the more familiar extremely acidophilic iron-oxidising microbes in the surface water and sediment samples of the aerobic wetlands. Novel heterotrophic microorganisms were also isolated from the wetlands. Phylogenetic analysis based on 16S rRNA gene sequence showed that the moderately acidophilic iron oxidisers are unrelated to other more extremely acidophilic iron oxidisers, and revealed that the most dominant heterotrophic microorganisms include a novel Acidobacterium species and Propionibacterium acnes. These results suggest an important role for previously unknown moderately acidophilic iron-oxidising bacteria in the bioremediation of acidic mine drainage waters.
 
Article
The extraction of copper(II) from its solutions containing varying amounts of ammonium sulphate (1–4 M) over a pH range of 2 to 10 using Hostarex DK-16 in kerosene has been studied. Extraction seems to be less at higher pH due to the formation of free ammonia, which subsequently gives rise to non-extractable copper ammine complexes. The amount of copper extracted against pH is shown in the distribution curves. Theoretically calculated distribution values have been compared with the experimental ones. The results were further substantiated with the FTIR spectra of the extracts.
 
Article
Hostarex DK-16 was introduced by Hoechst, Germany. This paper concerns the extraction of zinc from aqueous ammoniacal solutions using Hostarex DK-16 as the extractant. The effect of the pH of the aqueous solution, and subsequent zinc ammine complex formation, on the extraction of zinc were examined. The effect of temperature on the extraction of zinc was also studied. Stripping was carried out at various temperatures and acid concentrations. Arrhenius plots were drawn for extraction as well as stripping studies. The extraction and stripping rates and their distribution isotherms have been examined. The loading capacity and temperature effect for Hostarex DK-16 were compared with other extractants.
 
Article
The solvent extraction and trasnfer through a bulk liquid membrane of chromic acid in sulphate media by dicyclohexano 18 crown 6 (DC18C6,L) in dichloromethane takes place due to the formation of the complex ion pair [(H3O+L] [HCr2O] in the organic phase. In spite of the presence of a large excess of sulphuric acid, the co-extraction and co-transport of sulphuric acid is very slight.The extraction and transport are also selective with respect to Ni2+, Cr3+ and Fe3+ cations. The selectivity of the transfer process characterizes the semi-permeability of the liquid membrane, which is able to concentrate chromic acid according to the Donnan equilibrium. The transport kinetics are explained by the two-film theory, applied to the liquid membrane (diffusion through the stagnant films, reaction equilibrium at the interfaces).
 
Article
Results are presented of laboratory-scale experiments designed to evaluate a solvent extraction process for recovering titanium from the liquor produced in the sulphuric acid leach of a titaniferous magnetite. The solvent extraction of titanium was optimized in batch tests using 10 vol.% tri-n-octylphosphine oxide (TOPO) in the aliphatic diluent Kerosol 200 at 25°C. This extractant system could be loaded to a maximum concentration of 1.1 g l−1 Ti. Up to 3% of the iron and 4% of the vanadium in the leach liquor were co-extracted, loading to 1.2 g l−1 Fe and 0.3 g l−1 V, respectively, on the organic phase. The kinetics of extraction were slow, with 15 to 20 min required to achieve equilibrium. The extent of extraction decreased with increasing temperature. Stripping performance improved with decreasing acid concentration of the strip liquor, and was optimised at 10 mass % H2SO4. The kinetics of stripping were also slow, requiring an equilibration time of 15 min.
 
Article
The extraction of iron(III) from aqueous nitrate solutions by bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272=HA) dissolved in Isopar-H was studied at 25°C and 0.1 ionic strength. The distribution of the metal was measured as a function of pH and metal and extractant concentration.The data have been analyzed both graphically and numerically to determine the stoichiometry of extracted species and their equilibrium constants. It was found that iron (III) was extracted into the organic phase by the formation of the species FeA3, FeA3(HA)3 and Fe(NO3)3(HA)3.
 
Article
This article reviews the proceedings of the 17th International Biohydrometallurgy Symposium held in Frankfurt, Germany from September 2–6, 2007. Topics included, but were not limited to: microbiology and engineering of bioleaching, bioremediation, microbe–mineral interfacial processes, biosorption and nano-biotechnology. This review highlights aspects of biotechnological relevance. The various papers amply demonstrate that an ancient biotechnology has come of age with the commissioning of the world's largest microbial bioreactor at Escondida in Chile sending a strong message that bioleaching is a practical technology. A Special Edition of Hydrometallurgy later this year will feature selected papers from this Symposium that have been peer reviewed.
 
Article
A sequential extraction procedure was used to characterize the geochemical forms of 226Ra retained by mixtures of quartz sand and a variety of fine-grained rock and mineral species. These mixtures had previously been exposed to the sulfuric acid milling liquor of a simulated acid-leach uranium milling circuit. For most test cases, the major fraction of the 226Ra was extracted with 1 mol/1 NH4Cl and was deemed to be exchangeable. However, 226Ra retained by the barite-containing mixture was resistant to both 1 mol/1 NH4Cl and 1 mol/HCHCl extraction.
 
Article
Adsorption of 226Ra on freshly precipitated hydrous oxides of Fe, Mn, Zr and Ti are investigated at pH 1 and 10. Radium removal is found to be highly sensitive to the solution pH and all oxides effectively adsorb Ra2+ at higher pH. Radium adsorption is observed even at pH 1 on these oxides even though the zeta potentials at this pH are unfavourable. However, significant radium adsorption is observed only on manganese dioxide. Desorption of 226Ra from the oxides is found to be difficult in alkaline solutions of EDTA.
 
Article
A flow-through yttria-stabilized zirconia (FTYSZ) electrode has been employed for pH measurements at 250 °C in concentrated electrolyte systems relevant to hydrometallurgical processing of nickeliferous laterites. Experiments were conducted using a custom-made flow-through titanium electrochemical cell specially designed for high-temperature potentiometric pH measurements. In the present work, we assess the accuracy and validity of pH measurements with theory at 250 °C on concentrated sulfate process solutions. First, binary sulfuric acid–water solutions were measured at concentrations ranging from 0.05 to 0.5 mol kg−1 and showed 0.3 pH unit increase on the average between 25 and 250 °C. The measurements were then extended to ternary and quaternary systems containing 0.0076–0.038m Al2(SO4)3 and 0.0276–0.276m MgSO4, respectively. Autoclave passivation against corrosion was successfully achieved using sodium chromate or hydrogen peroxide. In this technique, the potentials are measured against a Ag/AgCl flow-through external reference electrode (FTEFE). A reference solution of 0.1 mol kg−1 NaCl(aq) flows permanently through the electrode at a constant flow rate, so that the thermal liquid junction and streaming potentials are kept constant. The experimental results were compared with theory using available thermodynamic data for estimating the quality of pH measurements. An average difference of 0.15 pH unit was observed between measured and theoretical values at temperature.
 
Article
Thiosulphate leaching of precious metals has been developed as an alternative and non-toxic technique to the conventional cyanidation. This process has advantages over cyanide in a decreased interference from foreign cations and a lower environmental impact. Ammoniacal thiosulphate solution allows the solubilization of gold as stable anionic complex. Leaching of gold occurs at appreciable dissolution rates.The aim of this work is devoted to a preliminary evaluation of the feasibility of thiosulphate leaching for the extraction of gold from precious metals ores on a laboratory scale. The experimental work has allowed the authors to point out the influence of temperature, thiosulphate concentration, ammonia concentration and copper sulphate concentration on the gold dissolution from an ore (51.6 g/t Au) that originated from the Dominican Republic.Gold was recovered from the leach liquors by adsorption onto activated carbon or by electrowinning. With the optimisation of the process parameters about 80% gold recovery has been attained, as in the case of conventional cyanidation.
 
Article
The mechanisms of copper(II) solvent extraction by Cyanex 272, Cyanex 302 and Cyanex 301 are discussed. Extraction from sulfate media is strongly dependant upon sulfur substitution in the phosphinic acid and complete extraction of copper by Cyanex 302 and Cyanex 301 occurs below pH 0. Since conventional slope analysis is not possible under these conditions, the complex stoichiometries and geometries are inferred from analysis of the electronic, 31P-NMR and FAB-MS spectra of the complexed species. Cu(II) is reduced to Cu(I) on extraction by the sulfur-containing ligands, accompanied by the corresponding oxidation of the extractant. It is shown that copper combines in a 1:1 stoichiometric ratio with these ligands to form multinuclear oligomeric complexes, in which the ligands bridge between metal centers. The enhanced stabilities of the complexes formed with the sulfur-containing ligands are explained in terms of the Hard-Soft Acid-Base concept and pi bonding between the d orbitals of the metal center and the donor atoms.
 
Article
Solvent extraction of divalent zinc and manganese from sulphate solutions was carried out using the sodium salt of Cyanex 272. Extraction of metal ions increased with increasing equilibrium pH and extractant concentration. The extracted species were ZnA2 · 3HA for zinc and MnA2 · 3HA for manganese. One mole of hydrogen ion was released for one mole of metal extracted under the experimental conditions used in this work. The zinc and manganese loading capacity of 0.1 M Na-Cyanex 272 was determined. The influence of NaCl, NaNO3, Na2SO4 and NaSCN on the extraction of metal ions was studied. The presence of Na2SO4 in solution had a remarkable depressing effect on extraction systems. The separation factor was pH dependent.
 
Article
Synergistic effects of Cyanex 272 mixed with D2EHPA and Cyanex 302 mixed with D2EHPA were investigated for the separation of cobalt and nickel from a dilute sulfate media with the aim of reducing the reagent cost. Selective extraction of cobalt over nickel improved with respect to D2EHPA, but worsened with respect to Cyanex 272. By the application of the slope analysis method, the stoichiometric coefficient of the extractant was found to be four for cobalt and five for nickel, in a mixture of D2EHPA with Cyanex 302. However, it was four for both cobalt and nickel in a mixture of D2EHPA with Cyanex 272. Fourier Transform Infrared Spectroscopy (FT-IR) was utilized to examine the organo-metallic complexes containing cobalt and nickel. Increasing the ratio of Cyanex 272 or Cyanex 302 to D2EHPA did not reveal a significant effect on the extraction curve of cobalt, but caused an increase in pH of the nickel extraction curve. Increasing the ratio of Cyanex 272 or Cyanex 302 to D2EHPA increased the pH50 difference (ΔpH50(Ni–Co)). Optimum separation was found with a Cyanex 302 to D2EHPA ratio of 0.3:0.3 when the pH50 difference (ΔpH50(Ni–Co)) was 0.9. Results showed that extraction of cobalt is more endothermic than that of nickel. Improved separation was hence achieved with a warm mixture.
 
Article
Gas chromatography (GC) analysis of organic solutions in Murrin Murrin Operations' cobalt and zinc solvent extraction (SX) circuits revealed the presence of the same, prominent, unidentified foreign impurity in both circuits. This species, which was both isolated and synthesised, was characterised and identified as the n-butyl ester of the Cyanex 272 phosphinic acid, namely n-butyl-bis(2,4,4-trimethylpentyl)phosphinate. This species is formed in the SX circuits by reaction, either directly or indirectly, of the phosphinic acid with tributylphosphate (TBP). It was found to be present at 3.7–4.1% v/v in the Murrin Murrin Operations' organic solutions. Notwithstanding poisoning by chromium (III), this is the first example of chemical degradation of phosphinic acid under SX operating conditions. This species could potentially be acting as an acid extractant.
 
Article
Cyanex 301, Cyanex 302 and Cyanex 272 were used to extract cobalt(II) and nickel(II) from a sulphate medium in order to elucidate any separation properties these phosphinic acid extractants display. All the reagents extracted cobalt selectively, Cyanex 302 exhibiting better separation characteristics than Cyanex 272, which in turn showed a higher selectivity than did Cyanex 301. The separation (pH0.5Ni-pH0.5Co) found for Cyanex 302 was 2.6 pH units, compared to 1.7 pH units for Cyanex 272 and 1.1 pH units for Cyanex 301. Based on these results and the fact that Cyanex 301 would need strong acid to strip it, an experiment was conducted using Cyanex 302 and Cyanex 272 to separate cobalt(II) and nickel(II) from a solution containing 100 g/l NiSO4·6H2O and 2 g/l CoSO4·7H2O with favourable results.Vapour pressure osmometry was used to determine the degree of aggregation of the extractants in toluene. Both Cyanex 272 and Cyanex 302 are dimeric and Cyanex 301 exists as a monomer. Slope analysis methods were used to determine the nature of the cobalt(II) and nickel(II) complexes extracted.
 
Article
Solvent extraction studies of cobalt and nickel have been carried out from 1 M chloride solutions using the sodium salt of Cyanex 272 as extractant diluted with kerosene with tri-n-butyl phosphate (TBP) employed as a phase modifier. Extraction of metal ions increases with increasing aqueous phase pH. The pH0.5 value difference of 1.25 with Na-Cyanex 272 indicates the possible separation of cobalt and nickel. Increasing the concentration of Na-Cyanex 272 increased the percentage extraction of both metal ions. The species extracted into the organic phase appears to be associated with 2 mol of extractant. The observed loading capacity of 99.5% for cobalt and 83.7% for nickel with 0.025 M Na-Cyanex 272 indicates that the extractant is pure in form. Increase of temperature increases the percentage extraction of nickel while for cobalt, the percentage extraction increased up to 303 K, beyond which the extraction decreased. Separation factors obtained with binary mixture of extractants gave a value 5.6 times higher in the case of Na-PC88A as extractant and Na-Cyanex 272 as synergist than that for Na-Cyanex 272 alone.
 
Article
Extraction of cadmium (II) from sulphate solutions using organophosphorous-based extractants—TOPS 99, PC 88A and Cyanex 272 has been studied. Percent extraction of cadmium (II) increased with increasing equilibrium pH of the aqueous phase and extractant concentration. Extraction of Cd (II) by organophosporus extractants involves cation exchange mechanism with the formation of 1:3 metal to reagent complex. Characterization of the solid complex of cadmium with TOPS 99 by FTIR, 31P NMR supported metal complex formation with the phosphorus-hydroxyl (P-OH) group. Finally, the extraction behavior and possible separation of cadmium and nickel from the mixture of metals was studied.
 
Article
The extraction and separation of Mn(II) and Co(II) from sulphate solutions have been carried out using sodium salts of di-(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC 88A) and bis-(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) in kerosene. The percentage extraction for the metal ions was increased with increasing equilibrium pH in the case of all the extractants. Manganese was preferentially extracted over cobalt with the extractants and NaD2EHPA was found to be the most suitable extractant for separation, the separation factor being maximum with 0.05 M NaD2EHPA at equilibrium pH 4.45. Manganese and cobalt extractions were carried out at O:A ratio of 9:8 and 1:1, respectively, followed by their strippings at O:A ratio of 2:1 and 4:3 using 0.02 M H2SO4.
 
Article
A technique for the colorimetric estimation of purified Cyanex 272 has been developed. The technique consists of the digestion of pure sample or its aqueous solution with concentrated nitric acid (70%)–perchloric acid (70%) mixture for 1 h. The oxidizing mixed acid quantitatively converts Cyanex 272 to a clear solution of orthophosphate that can be easily estimated by the molybdenum-blue colorimetric method at 830 nm. The method is sensitive with a molar extinction coefficient of ∼2.6×104 and reproducible within ±2%. Applying this technique of analysis, the dimerization constant (K2), distribution or partition coefficient (Kd) and ionization constant (Ka) of the purified Cyanex 272 (bis-2,4,4-trimethylpentylphosphinic acid, BTMPPA) have been estimated to be 190, 53 and 5.52×10−4, respectively.
 
Article
The extraction and separation of aluminium from cobalt, nickel and magnesium sulphate solutions have been carried out using the organo-phosphinic extractant Cyanex 272. Statistical design and analysis of experiments were used in order to determine the main effects and interactions of extraction pH at equilibrium, temperature, extractant concentration and organic to aqueous phase ratio. A statistically designed experiment was also carried out in order to study the stripping of the aluminium loaded Cyanex 272 organic phase by sulphuric acid solution. The number of stages required for both extraction and stripping processes of aluminium was also evaluated. The results of the continuous counter current, mini plant tests demonstrated the recovery of aluminium from cobalt, nickel and magnesium sulphate solution.
 
Article
Separation and recovery of divalent cobalt and nickel ions from sulphate solutions containing 0.01 M metal ions each and 0.1 M Na2SO4 have been carried out using 0.03, 0.05 and 0.06 M sodium salts of D2EHPA, PC 88A and Cyanex 272 in kerosene. The percentage extraction of metal ions increased with increasing equilibrium pH. Cobalt was preferentially extracted over nickel with the extractants; however, 0.05 M NaPC 88A and NaCyanex 272 were found to be suitable for the separation study. The highest separation factor was achieved with 0.05 M NaCyanex 272 at equilibrium pH 6.85. Recovery of cobalt from cobalt–nickel bearing solution was achieved with 0.05 M Cyanex 272 and PC 88A at equal phase ratio followed by their stripping with 0.02 M H2SO4 at O:A ratio of 2:1. Nickel was extracted from the cobalt-free raffinate in two stages at equal phase ratio with PC 88A and Cyanex 272 followed by their stripping with 0.02 M H2SO4 at O:A ratio of 4:3 and 2:1, respectively.
 
Article
Extractive purification of macroquantities of NiSO4 from microquantities of Co(II), Zn(II), Cu(II), Mn(II) and Fe(III) using Cyanex 272 was studied. The optimum conditions of Co(II) removal depending on equilibrium pH value, phase ratio and extraction temperature were determined. The most effective results were obtained using a two-stage extractive purification of Ni(II) sulphate from Co(II) at a phase ratio of 1:1, equilibrium pH > 6 and 323 K. Under these conditions the Co(II) content in the purified NiSO4 decreases several hundred times compared to the initial content. Nickel sulphate purified in this way contains <0.001% Co, <0.0001% Zn, <0.00005% Fe, <0.00005% Cu and <0.00005% Mn.
 
Article
The separation of Co(II) and Li(I) from simulated solution of lithium ion battery (LIB) industry wastes has been studied by a supported liquid membrane (SLM) process. The synergistic effect of mixture of the extractants Cyanex 272 and DP-8R on the permeation rate and separation factor of Co(II) and Li(I) from dilute aqueous sulfate media using a supported liquid membrane (SLM) technique has been examined. A microporous hydrophobic PVDF film was used as the solid support for the liquid membrane. The extractants Cyanex 272 and DP-8R and mixture of those were used as mobile carriers. The effects of different parameter such as stirring speed, pH of the feed solution, extractant concentration in the membrane phase, Co(II)/Li(I) concentration in the feed solution, and H2SO4 strip acid concentration, on Co(II) flux (JCo(II)) and Li(I) flux (JLi(I)) have been studied and compared. For all of the systems studied, Co/Li are optimally separated in the acidic pH region of 5.0−6.0. The best separation factor of 497 was achieved at pH 5.00 using a mixture of Cyanex 272 and DP-8R at a concentration of 750 mol/m3 in the membrane phase, a strip acid concentration of 100 mol/m3, and a stirring speed of 350 rpm. The separation factors for all three systems under the respective optimum experimental conditions have been calculated and compared. Qualitatively, they follow the order: mixed-extractant system > Cyanex 272 > DP-8R. This sequence may be quantitatively expressed as: mixed-extractant system ≈ 3 × Cyanex 272 ≈ 15 × DP-8R.
 
Article
Extraction of cobalt(II) from an acidic sulphate solution has been studied using sodium salts of D2EHPA, PC-88A and Cyanex-272 in benzene; the corresponding pH0.5 values are 6.0, 6.25 and 6.6, respectively. The extracted species appear to be CoA2(HA)2. The electronic spectra of the extracted organic phase support the nature of the species extracted. The loading capacity of 0.1 M extractants in benzene has been determined. The influence of NaCl, NaNO3, Na2SO4 and NaSCN on the extraction systems has been investigated. Synergism has been observed with the binary mixture of all the three extractants used. Of the three extractants, sodium salt of Cyanex-272 has been found to be the best synergist and sodium salt of D2EHPA the least.
 
Article
The speciation in solution of a number of metallurgically important iron-bearing systems are calculated from critically reviewed data. In acidic solution, Fe2+ and Fe3+ are the predominant iron species, although ferric ion hydrolyses to Fe(OH)2+ above pH 2. For sulphate and arsenate, HSO4− and H3AsO4 predominate up to pH ∼2 where deprotonation occurs and sulphate and dihydrogen arsenate ions become predominant. For arsenite, the major species is H3AsO3 for all acidic pH. In ferric systems where complexing anions are present, the situation is somewhat different, although all systems are substantially dependent upon the concentration of the anions. In the presence of arsenate and sulphate, ferric ion readily complexes to form charged anions, arsenate complexes being more favourable than sulphate in mixed solutions. Chloride plays only a minor role with complexation only occurring at concentrations close to unity. The importance of the solution speciation is discussed with reference to both leaching of iron minerals and in oxidative leaching using ferric ions.
 
Article
The standard thermodynamic properties of Zn2+, its hydrolysis reactions and hydroxo-complex formation are critically evaluated on the basis of published experimental studies and specific interaction theory (SIT) for activity coefficient modelling. A set of thermodynamic data and interaction coefficients are recommended.
 
Article
The standard thermodynamic properties of Ni2+, its hydrolysis reactions and hydroxo-complex formation are critically evaluated on the basis of published experimental studies and the specific interaction theory (SIT) for activity coefficients modelling. A set of thermodynamic functions and interaction coefficients are recommended.
 
Article
The effects of 200 mM copper ions on the synthesis of membrane and periplasmic proteins were investigated in iron-grown cells of Acidithiobacillus ferrooxidans (At. ferrooxidans). Total membrane protein profiles of cells grown in the absence of copper ions (unadapted cells) and in the presence of copper ions (copper-adapted cells) were compared by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Crude preparations of outer membrane and periplasmic proteins were analyzed by SDS-PAGE. The synthesis of proteins was diminished or increased in the presence of copper ions. Low molecular weight proteins (<14 kDa) were significantly repressed by copper. These proteins are probably acidic proteins located in the outer membrane. An over-expression of a periplasmic protein of about 17 kDa was detected in the copper-adapted cells and was assumed to be rusticyanin, a 16.5-kDa periplasmic copper protein present in At. ferrooxidans cells and involved in the electron-transport chain of the iron oxidation pathway. To our knowledge, this is the first report of a possible involvement of the rusticyanin and outer membrane proteins in the mechanism of copper resistance in At. ferrooxidans.
 
Calculated speciation at 25 and 50 °C for an aqueous solution containing: [H 2 SO 4 ] = 2.22 m (200 g/L); [Fe(II)] = 0.543 m (27 g/L); [Fe(III)] = 0.437 m (23 g/L). 
Standard diffusivities of ionic species at 25 °C
Article
This work presents theoretical and experimental results on the speciation of the Fe(II)–Fe(III)–H2SO4–H2O system in concentrated solutions (up to 2.2 m H2SO4 and 1.3 m Fe). The aim was to study the chemical equilibria of iron at 25 and 50 °C in synthetic aqueous sulphuric acid solutions that contain dissolved ferric and ferrous ion species. Raman spectroscopy, volumetric titration and conductivity measurements have been carried out in order to study the presence of specific ions and to characterize the ionic equilibrium. A thermochemical equilibrium model incorporating an extended Debye–Hückel relationship was used to calculate the activities of ionic species in solution. Model calculations were compared with experimental results. Model simulations indicate that anions, cations and neutral complexes coexisted in the studied system, where the dominant species were HSO4−, H+, Fe2+ and FeH(SO4)20. This indicated that these solutions showed a high buffer capacity due to the existence of bisulphate ions (HSO4−), which presented the highest concentration. A decrease in the concentration of H+ and Fe3+ took place with increasing temperature due to the formation of complex species. Standard equilibrium constants for the formation of FeH(SO4)20 were obtained in this work: log Kf0 = 8.1 ± 0.3 at 25 °C and 10.0 ± 0.3 at 50 °C.
 
Article
The simultaneous extraction and separation of Co(II) and Ni(II) from manganese and mgnesium sulfate solutions have been carried out using the thio-organophosphinic extractant Cyanex 301, diluted in Exxsol D-80. Statistical design and analysis of experiments were used in order to determine the main effects and interactions of the solvent extraction factors, which were the extraction pH at equilibrium, temperature, extractant concentration and organic to aqueous phase ratio. A statistically designed experiment was also carried out in order to study the stripping of the cobalt- and nickel-loaded Cyanex 301 organic phase by hydrochloric acid solution. The Slope analysis method was used to determine the nature of the cobalt and nickel complexes extracted. The number of stages required for both extraction and stripping processes of cobalt and nickel was also evaluated. The results of the continuous counter current, mini plant tests demonstrated the simultaneous recovery of cobalt and nickel from manganese and magnesium sulfate solution.
 
Article
The partition of zinc(II) between aqueous hydrochloric acid/chloride solutions and solutions of Cyanex 302 (bis (2,4,4-trimethylpentyl] monothiophosphinic acid), in kerosene was studied at various aqueous pH values, extractant and zinc concentrations, different temperatures and equilibration times. The behaviour of the extraction system with different organic diluents and aqueous ionic strengths, in relation to other organophosphorus extractants and to the selectivity of the extractant in systems containing zinc(II) and other metallic ions was also investigated. The zinc(II) extraction mechanism is discussed on the basis of the experimental results.
 
Article
The extraction of Cd (11) from chloride media of 1.0 M ionic strength by the commercial extractant Cyanex 302 in kerosene has been studied over a range of pH and reagent concentrations. The data have been analyzed both graphically and numerically to determine the stoichiometry of the extracted complexes and their extraction constants. The species CdR2(HR) and CdR2(HR)2, HR being the active component in the commercial extractant, bis(2,4,4-trimethylpentyl)thiophosphinic acid, have been found to be responsible for the extraction behaviour observed.
 
Article
Among the bioleaching microorganisms, Acidithiobacillus ferrooxidans is one of the most studied. The bioleaching and bioremediation properties of this obligate chemolithoautotroph originate from its energetic metabolism. Even though several electron-transfer proteins have been identified, there is no convincing argument to tell in which respiratory chain these proteins are involved. Rusticyanin is the A. ferrooxidans redox protein which has been the most extensively studied. This periplasmic blue copper protein is widely considered to play an important role in ferrous oxidation mainly because of its higher concentration in iron-grown cells compared to sulfur-grown cells. To gain more insight on which conditions rusticyanin is synthesized, we have studied the rus gene expression all along the growth in iron- and sulfur-supplemented media at the translational level by immunodetection and at the transcriptional level by Northern blot analyses and quantitative RT-PCR experiments. In the A. ferrooxidans ATCC 33020 strain, rusticyanin was present in ferrous iron-grown cells throughout all the growth phases. In sulfur-grown cells, rusticyanin was present only during the exponential phase, but to a lower level than in iron conditions, and disappeared at the stationary phase. In cultures switched from sulfur- to iron-medium, there was a correlation between iron oxidation and the rusticyanin level. Strikingly, the de novo synthesis of rusticyanin was observed in sulfur-grown cells. All these data agree with a control on rusticyanin level in the cells depending on the electron donor present in the medium and on the growth phase in sulfur-grown cells. Furthermore, they are consistent with the involvement of rusticyanin in iron oxidation.
 
Article
The transport of niobium(V) in chloride medium through a supported liquid membrane (SLM), using Alamine 336 and tributyl phosphate (TBP) as carriers, has been investigated. The work has been undertaken by first determining the liquid–liquid extraction distribution of niobium(V) between aqueous solution and different organic solutions. Optimum conditions for both extraction and stripping were established. The mixture of Alamine 336 and TBP provided the best extraction in high chloride medium, while low HCl concentration stripped the ion from the loaded organic phase. Transport experiments were carried out with a permeation cell having a continuous flow system and constant agitation. The study of the liquid membrane included the chemical conditions, i.e. carrier concentration and hydrochloric acid concentration in the feed solution. Maximum niobium recovery at 10% of Alamine 336 in TBP was obtained at HCl concentration between 6 and 7 mol/dm3. The mechanism postulated is referred to a synergistic extraction of Nb(V) by means of a co-transport process. Nb(V) can be concentrated in the stripping solution and the SLM showed a good performance for Nb–Ta separation.
 
Article
The wide electrochemical window and ion exchange properties of a room-temperature ionic liquid (RTIL) have been exploited for the extraction of palladium from nitric acid medium into ionic liquid phase — followed by direct electrodeposition of the metal from the organic phase. Extraction of palladium by commercial Aliquat 336 ionic liquids, tri-n-octylmethylammonium chloride (TOMAC) and tri-n-octylmethylammonium nitrate (TOMAN), was studied as a function of [HNO3], [NO3−] and [TOMAN]. The distribution ratio (DPd(II)) of palladium in TOMAN increased with an increase in the concentration of nitric acid and passed through a maximum at 1.0 M nitric acid. In contrast, the DPd(II) value of palladium in TOMAC decreased continuously with an increase in the concentration of nitric acid. Substantial amounts of water and nitric acid were also co-extracted into the organic phase with palladium.The redox behavior of a solution of Pd2+ extracted in 0.1 M TOMAN/CHCl3 and 0.1 M TOMAC/CHCl3 at glassy carbon working electrode was studied using cyclic voltammetry. The voltammogram consisted of a single reduction and an oxidation wave indicating that Pd2+ was reduced to palladium metal by a single-step two-electron transfer at the working electrode. Controlled potential deposition of palladium on platinum electrode gave a black deposit, which was characterized to be metallic palladium. Interference of other fission products during extraction and electrodeposition of palladium is also reported.
 
Article
The appropriate experimental conditions of Mo(VI) ion transport across a supported liquid membrane containing Alamine 336 as the mobile carrier dissolved in kerosene solvent have been investigated. The molybdenum flux has been studied as a function of the extraction solution acidity, the sodium carbonate concentration in the stripping solution and the carrier concentration in the liquid membrane. Suitable conditions for both feed and stripping solutions were achieved from analysis of experimental results of molybdenum transport through the liquid membrane. The permeation experiments showed that, at pH 2 with sulfuric acid in the extraction solution and at pH 11.5 with Na2CO3 in the stripping solution, an efficient transfer of the metal ion can be obtained. Furthermore, a maximum molybdenum transport was achieved at around 0.02 M of Alamine carrier in the organic phase. From these results, the extraction-stripping interface reactions for Mo(VI) permeation are proposed. An equation describing the permeation rate, taking into account the aqueous stagnant layers and liquid organic resistance as simultaneous controlling factors, has been derived. The validity of this model is evaluated with experimental data of mass transfer coefficient measured at different stirring rates.
 
Article
The synergistic solvent extraction of 13 lanthanoids with mixtures of thenoyltrifluoroacetone (HTTA) and the quaternary ammonium salt Aliquat 336 in chloride (QCl) or perchlorate (QClO4) forms in C6H6 has been studied. The composition of the extracted species was determined as Q+[Ln(TTA)4]− (Q+ is a quaternary ammonium cation). The values of the equilibrium constant and the separation factor were calculated. The effect of the synergistic agent (QCl or QClO4) on the extraction process has been discussed. Additionally, the values of the equilibrium constant have been used to examine the tetrad effect.
 
Article
A uranyl leach liquor obtained by uranium leaching of a technological sample of Gattar GII ore was subjected to uranium extraction using the liquid emulsion membrane (LEM) technique. The solvent used was methyl trioctyl ammonium chloride commercially known as Aliquat 336 [(C8 H17)3NCH3Cl].This technique yielded much higher degrees of extraction than conventional solvent extraction processes using the same amount of the solvent. Like ion-exchange processes, the technique is particularly suited for dilute solutions such as leach and wash solutions of uranium ores.The effects of the relevant parameters on the permeation rate and percent permeation of uranium were studied. The organic phase in the working LEM was composed of 0.02 M Aliquat 336 with 5% Span 80 in kerosene as diluent (a local aliphatic hydrocarbon product assaying 0.3% aromatic). The internal phase was composed of 1M Na2CO3 aqueous solution. The parameters studied included the effects of H2SO4 acid concentration in the external phase and the effect of uranium concentration in the feed solution, the effect of volume ratio of emulsion to feed solution, the effect of mixing speed on the extraction rate of uranium and finally, the effect of various internal solutions.
 
Article
In the solvent extraction of Pt(IV), Pd(II), and Rh(III) from chloride solution, most of Pt and Pd was extracted into Alamine 336 phase, while extraction percentage of Rh was low. In this study, separation of Pt and Pd from the loaded Alamine 336 solution was investigated as a function of the concentration of stripping agents. HClO4, Na2CO3 and a mixture of HCl and thiourea were tested as stripping agents. In our experimental range, a mixture of HCl and thiourea led to the highest stripping percentage of Pd (> 99%) while the stripping percentage of Pt was less than 8%. The low stripping percentage of Pt by the mixture was related to selective stripping of Pd from the loaded Alamine 336. Our results can be utilized in developing a process to separate Pt, Pd, and Rh from chloride solution by solvent extraction.Research highlights► In the separation of Pt(IV), Pd(II), and Rh(III) from chloride solution by Alamine336, most of Pt and Pd was extracted into Alamine336. ► Stripping experiments were done to separate Pt and Pd from the loaded Alamine336. ► A mixture of HCl and thiourea led to complete stripping of Pd while striping percentage of Pt was low.
 
Article
Extraction of Zn(II) from its aqueous hydrochloric acid solutions into Alamine 336–m-xylene systems was studied. Extraction data were obtained with three different initial metal concentrations of 3, 7 and 15 g L− 1 each at aqueous phase acidic molarities of 1, 5 and 10 mol L− 1. It was observed that the increase in acidic molarity slightly increases the extractability of Zn(II). Alamine 336–m-xylene mixtures were found promising organic solvent systems for the Zn(II) extraction from aqueous media. 2-D, 3-D and 4-D mathematical model equations simulating metal extractability in terms of organic phase Alamine volume content, aqueous phase acidic molarity and initial metal concentration were developed. 4-D model equation was used to develop a performance index function in order to optimize the principal key inputs of the extraction operation.
 
Article
Extraction of Co(II) and Ni(II) from aqueous HCl solutions into organic Alamine 336–m-xylene systems were studied. Extraction experiments were repeated for three initial metal concentration ratios with total initial metal concentration of 7 g L− 1, each at 1, 5 and 10 M HCl. The extraction percentage, E, in terms of volume percentage of Alamine content, Ve, in solvent mixture, were determined for each metal. Optimal Alamine 336 contents were reported for a single stage extraction. The amine loading factor and separation factor values were also determined in terms of Ve. Alamine 336 was found to be a suitable extracting and separating agent for Co(II)–Ni(II) containing solutions at 5 M HCl.
 
Article
Zinc and cadmium solvent extraction separation from cobalt and nickel was studied using 30% Aliquat 336 in either the chloride (R4NCl) or thiocyanate (R4NSCN) forms, and in a mixed aromatic-aliphatic diluent. With NaCl solutions good separation was achieved using R4NCl. Separation improved with decreasing NaCl concentration, but was still effective with 200 g/L NaCl. Zinc and cadmium loaded principally as [MCl4]2− complexes. The maximum loading was 18 g/L for zinc and 28 g/L for cadmium. There was a small selectivity for cadmium over zinc. The mole ratio of organic reagent to metal (R4N:M) was about 2. Separation with R4NSCN was studied with NaCl, NaNO3 and Na2SO4 solutions. Zinc extraction was favored over cadmium in each case and cadmium extraction decreased markedly in the order NaCl>NaNO3>Na2SO4. Maximum zinc loadings were, respectively, 20 g/L, 9 g/L and 6 g/L. The selectivity for zinc over cadmium was rationalized on the basis of the different types of thiocyanate complexes formed by zinc and cadmium. From chloride solution the loaded complexes contained chloride and thiocyanate. The R4N:M ratio was about 2. From nitrate solution, [M(SCN)4]2− species loaded. With chloride or nitrate medium, separation of zinc from cobalt and nickel was good, but separation of cadmium from cobalt was only moderate at best. Thiocyanate losses from the organic phase in these two systems were generally low with zinc loading (<1%), but high for cadmium loading. In the case of sulfate medium, zinc loaded predominantly. However, nickel loaded up to 0.14 g/L even at the highest zinc loading. Ammonia stripping of zinc and cadmium loaded R4NCl was also studied and was found to be effective.
 
Article
The increasing demand for batteries of higher performance characteristics has led to the development of several types of manganese dioxides with optimal battery characteristics. One of these types is produced by a partial leach of a manganese ore, to remove the non-manganese metals to a level acceptable for direct use in batteries. The resulting leach solution must, however, undergo treatment to remove the impurity metals. This paper reports the uptake of copper, nickel, cobalt, lead, iron and manganese from manganese chloride leach solution onto the chelating resin Dowex M-4195 in column experiments. The results demonstrate the ability to remove contaminants to an extent satisfying the quality criteria required for the utilization of the manganese chloride solution for preparing manganese chemicals. Column elution tests demonstrated that a two-stage elution scheme whereby sulfuric acid is first used to elute iron, nickel and cobalt from the resin, then a subsequent ammonium hydroxide elution recovers almost all of the copper is superior to a scheme in which ammonium hydroxide is used before sulfuric acid. However, neither of these elution schemes fully eluted all the metals tested in the study.
 
Article
Solvent extraction of copper from acidic sulphate solutions was carried out using the new oxime extractant, MOC 45 diluted in distilled kerosene. Increase of aqueous phase pH and extractant concentration in the organic phase increases the percentage extraction of metal. Increase of temperature during extraction resulted in an increase in percentage extraction whereas the reverse was observed during stripping. The process was tested for the recovery of copper from converter slag leach solution. The extraction and stripping efficiencies were >98% and 100%, respectively.
 
Article
Silver(I) extraction from nitrate solutions by Cyanex 471 X (triisobutylphosphine sulphide) was investigated. The optimal conditions of silver(I) removal were determined depending on the concentration of purified salts, concentration of nitric acid, concentration of Cyanex 471X, kind of diluent and modifier, as well as phase contact time. Silver(I) extraction isotherms, using 2.5 and 5% Cyanex 471X and D2EHPA or TBP, were determined depending on nitric acid concentration. In the case of a 6 M HNO3 solution a rapid decomposition of Cyanex 471X was observed. The removal of Ag(I) from solutions containing Cu(II), Zn(II), Bi(III) and Fe(III) was studied. It was found that Cyanex 471X could reduce the silver content in the purified salts to below 10−5%.
 
Article
The effectiveness of Cyanex 471X as extractant of gold(III) from hydrochloric acid solutions is demonstrated. The extraction system is endothermic and experimental variables, such as extractant concentration, organic diluent and hydrochloric acid concentration, influence it. Maximum gold extraction is obtained in the range of 1–3 M HCl concentrations. Equilibrium loading isotherms showed that the [Cyanex 47lX]/[Au (III)] molar relationship in the organic phase is near l.5, which is the probable stoichiometry of the extracted species defined by HAUCl4L (log Kext° = 3.79) and HAUCI4L2 (log Kext° = 6.34), L representing the organic extractant. The system seems to be suitable for the selective extraction of gold. Stripping of the metal can only be accomplished using sodium thiosulphate solutions, the corresponding reaction also being endothermic.
 
Top-cited authors
Francesco Veglio
  • Università degli Studi dell'Aquila
David Bruce Dreisinger
  • University of British Columbia - Vancouver
C. Y. Cheng
  • The Commonwealth Scientific and Industrial Research Organisation
Helen Watling
  • The Commonwealth Scientific and Industrial Research Organisation
Francisco jose Alguacil
  • Spanish National Research Council