International Journal of Nonferrous Metallurgy

Published by Scientific Research Publishing
Online ISSN: 2168-2062
Publications
Article
The study of copper adsorption onto ion exchange resins of anionic type is part of the gold recovery from ammonia-thiosulfate solutions, where copper is the main impurity of the system because it acts as a catalyst of gold dissolution reaction. A study is made of the adsorption and desorption of copper in the form of the complex in an ammonia-thiosulfate media on an ion exchange resin, DOWEX 550A, classified as a strong base, which in its inner structure has a quaternary amine functional group. In the studied pH range copper adsorption increased with increasing pH, while the presence of thiosulfate decreased it, the same as the ammonia content, due to the greater presence of cuprotetramine, . Elution of the copper complexes from the resin was more efficient with sulfite than with perchlorate.
 
Chemical structure of LIX 84-ICNS [18]. 
Influence of O/A ratio on nickel and cobalt extractions. 
McCabe-Thiele Diagram constructed for nickel extraction at pH 8.75, temperature of 55˚C and LIX 84-ICNS of 40% (v/v). 55˚C and O/A ratio 0.5. This investigation results demonstrate the advantage of LIX 84-ICNS in comparison to other extractants used previously for extracting nickel in ammoniacal solutions [8] [9]. Kumar et al. reported that by using LIX 84 of 10% (v/v), maximum Ni extraction was obtained at two stage extraction under O/A ratio of 2 [8]. Parija et al. that used LIX 84-I 30% (v/v) reported three stage of extraction to obtain a maximum nickel extraction from the ammonium sulphate solution containing 20 g/l Ni at O/A ratio of 0.8 [9]. In industrial practice, QNI Yabulu that used LIX 87-QN at 30% (v/v) and O/A 1.5 requires three stage extraction to get a maximum Ni extraction [14]. 
Article
In the present paper, separation of nickel and cobalt in ammonia-ammonium carbonate solution that simulates pregnant leach solution of Caron Process by solvent extraction using LIX 84-ICNS was studied. LIX 84-ICNS is a novel extractant which is still being studied, especially for nickel and cobalt separation in ammonia-ammonium carbonate solution. A series of solvent extraction tests were performed at various equilibrium pH, temperature, extractant concentration, and volume ratio of organic to aqueous solution (O/A ratio). The investigation results show that the highest nickel and cobalt extraction percentages of 99.8% and 90.3% were obtained from the extraction test at equilibrium pH of 8.75, temperature of 55˚C, extractant concentration of 40% (v/v) and O/A ratio of 1/1, respectively. Oxidation of cobalt in aqueous solution prior to extraction is needed to minimize co-extraction of cobalt. Co-extracted cobalt can be decreased from 90.3% to 30.3% by mixing 1% (v/v) H2O2 in aqueous solution prior to the extraction stage. It was found that nickel and cobalt extractions by LIX 84-ICNS are endothermic processes with enthalpy changes of +171.03 and +7.64 kJ/mole, respectively. Based on constructed McCabe-Thiele Diagram, nickel extraction level of more than 99.9% can be obtained in 2 stages at O/A ratio of 0.5. The highest stripping percentages of nickel and cobalt of 98.82% and 3.16%, respectively were obtained at 200 g/l H 2 SO 4 as stripping agent.
 
Chemical structure of (a) Carrier and (b) Surfactant. 
Effect of treat ratio on palladium extraction. 
Article
The extraction of palladium from hydrochloric acid solutions into emulsion liquid membranes (ELMs) using LIX 984N-C as the extractant was investigated. The influential factors and the total capacities of palladium extraction were determined by a batch method. The behavior of palladium extraction by ELMs under the operational conditions-pH of the external feed phase, surfactant and extractant concentration, internal stripping phase concentration, treat ratio and agitation speed were reported. Using LIX 984N-C, palladium was effectively extracted from the external acidic chloride feed phase into the internal receiving phase of W/O emulsions. More than 92% of palladium could be extracted at a feed pH of 2 with 3% Span 80, 9% LIX 984N-C and 7M HCl at a stirring speed of 300 rpm.
 
Thermo physical properties of Al 0.12 wt.% Cu 0.11 wt.% Si Alloy.
Computed solidification profile for (g = 9.81 m/s 2 ) and B = 0.0 T.
Computed velocity magnitudes for (g = 9.81 m/s 2 ) and B = 0.0 T.
Computed velocity magnitudes for (g = 9.81 m/s 2 ) and B = 0.05 T.
Article
With the purpose of obtaining compositionally uniform ingots during Ohno continuous casting of a dilute industrial aluminum alloy through eliminating segregation due to convection, a magnetic field strength required to damp natural convection and suppress macrosegregation was numerically determined. This was achieved by solving conservation equations of continuity, momentum, energy and Maxwell’s equations in order to predict the magnetic field effects on flow field (determining macrosegregation). The electromagnetic field was applied orthogonally to the natural convection flow. Through this approach, the optimum magnetic field strength required to damp natural convection and establish diffusion controlled solute transport of the alloy during solidification was established.
 
Thermodynamic parameters and activation energy for Cd 2+ sorption onto MANC.
Freundlich isotherm plot for adsorption of Cd 2+ onto MANC. 
Article
Magnetic alumina nano composite (MANC) was prepared for combination of the adsorption features of nano activated alumina with the magnetic properties of iron oxides to produce a nano magnetic adsorbent, which can be separated from the medium by a simple magnetic process after adsorption. MANC was characterized using XRD, SEM, TEM, EDX and surface area (BET). Quantum design SQUID magnetometer was used to study the magnetic measurement. The present study was conducted to evaluate the feasibility of MANC for the removal of cadmium ions from aqueous solutions through batch adsorption technique. The effects of pH, adsorbent dose, temperature, contact time and initial Cd2+ concentration on cadmium ions adsorption were studied. Equilibrium data were fitted to Langmuir, Freundlich and Temkin isotherms. The equilibrium data were best represented by the Langmuir isotherm. The kinetic data were fitted to pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models, and it was found to follow closely the pseudo-second-order model. Thermodynamic parameters were calculated for the Cd2+ ion-MANC system and the positive value of ΔH° showed that the adsorption was endothermic in nature. Furthermore, a single-stage batch adsorber was designed for the removal of Cd2+ ions by MANC based on the equilibrium data obtained.
 
Isotherm and kinetic constants of different models for the adsorption of copper(II) ions onto SB.
FTIR spectrum of SB. 
Effect of agitation time on the removal of copper(II) ions by SB. 
Pseudo first-and pseudo second-order plots for the removal of copper(II) ions with SB. 
Article
The Schiff base, 4-[(2-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1H-pyrizol-3(2H)-one (SB), was used for the first time to adsorb copper(II) ions in aqueous solution. Various parameters such as initial pH, agitation period and different initial concentration of copper(II) ions which influenced the adsorption capacity were investigated. The equilibrium adsorption data for copper(II) ions were fitted to Langmuir, Freundlich and Dubinin-Radushkevish isotherm models. The maximum monolayer adsorption capacity of SB as obtained from Langmuir isotherm was 5.64 mg/g. Kinetic data correlated well with the pseudo second-order kinetic model indicating that chemical adsorption was the rate limiting step.
 
degree reduction-time curve at different temperatures. 
activation energy in different temperature ranges.
Article
Using high temperature carbon tube furnace, reduction of manganese ore pellets containing carbon was investigated. The reaction was divided into two stages at five minutes after reaction, and the kinetics model of reduction process was established. The experimental results showed that, the reaction rate in the earlier stage was controlled by the chemical reactions between FeO, MnO and carbon reductant, and the activation energy was 28.85 KJ/mol. In the later stage, as the carbon reductant replaced by CO, the reaction rate was controlled by CO-diffusing in solid products, and the cor- responding activation energy was 86.56 KJ/mol. Reaction rate of the later stage was less than the earlier one.
 
Article
In this paper, prediction of copper and molybdenum grades and their recoveries of an industrial flotation plant are investigated using the Artificial Neural Networks (ANN) model. Process modeling has done based on 92 datasets collected at different operational conditions and feed characteristics. The prominent parameters investigated in this network were pH, collector, frother and F-Oil concentration, size percentage of feed passing 75 microns, moisture content in feed, solid percentage, and grade of copper, molybdenum, and iron in feed. A multilayer perceptron neural network, with 10:10:10:4 structure (two hidden layers), was used to estimate metallurgical performance. To obtain the optimal hidden layers and nodes in a layer, a trial and error procedure was done. In training and testing phases, it achieved quite correlations of 0.98 and 0.93 for Copper grade, of 0.99 and 0.92 for Copper recovery, of 0.99 and 0.92 for Molybdenum grade and of 0.99 and 0.94 for Molybdenum recovery prediction, respectively. The proposed neural network model can be applied to determine the most beneficial operational conditions for the expected Copper and Molybdenum grades and their recovery in final concentration of the industrial copper flotation process.
 
Thermodynamic parameters of the Pt-Sb system a . 
Article
The Pt-Sb system was critically assessed by means of CALPHAD technique. Based on the experimental data in the literature, the excess Gibbs energies of the solution phases (liquid, rhombohedral, fcc) were modeled with the Redlich-Kister equation. The five intermetallic compounds, Pt7Sb, Pt3Sb, Pt3Sb2, PtSb, and PtSb2 were treated as stochiometric compounds and expressed as the formula (Pt)m(Sb)n. The intermetallic compound, Pt5Sb with a homogenerity ranges 0.155 - 0.189 Sb, were treated as the formula (Pt,Sb)m(Pt,Sb)n. A set of self-consistent thermodynamic parameters of the Pt-Sb system was obtained.
 
Article
Abstract Considering the geographical location and one of the very densely populated countries in the world, Bangladesh is very vulnerable to climate change and its adaptability. This paper has been designed with an attempt to inform the policy maker of Bangladesh regarding the potentiality of MSW as a renewable source of energy in Bangladesh. It deals with modern waste collection, management and incineration practices based on densely populated cities or towns like Bogura Municipality and Chattogram City Corporation. Waste to Energy (WtE) conversions not only reduce the land pressure problem in urban areas, but also generate electricity and heat to supply to the surrounding urban areas. The increase in generation of methane (CH4) from municipal solid wastes (MSW) alarms the world to take suitable initiative for the sustainable management of MSW, as it is stronger than carbon dioxide (CO2). By burning one mole of CH4, 890 kJ∙mol−1 heat is produced which is a major source of energy. This treatment technology is used in destruction of solid waste by controlled burning at high temperatures. With the release of heat, it can be accompanied and this heat from combustion can be converted into energy. This type of incineration is a high-quality treatment for Municipal or City Corporation solid waste like Bangladesh where were over crowded cities, towns and it can reduce the quantity and volume of a large amount of waste to landfill, which can recover energy and dispose in the compact zone. The results also examined that the total amount of solid waste produced in Bogura municipality is lower than that of Chattogram City Corporation. The percentage compositions of waste patterns are shown in both the Cities. The paper discusses these problems, analyses and finally, a recommendation has been proposed in order to understand the industrial situation enhanced. Keywords Population Distribution, Chattogram, Bogura Municipal or City Waste, Management, Waste to Energy, Incineration, Compact Zone How
 
Schematic diagram of experimental elutriator. Numbers 1 and 2 refer to first and second elutriators.
Gold head essay for different particle size of the minerals tested.
Chemical composition and X-ray difraction analysis for the different minerals tested.
Article
Conventional methods for precious metals gravimetric concentration involve equipment such as shaking tables, centrifuging concentrators, jigs, trommels, or a combination of those. A less commonly used technique is elutriation, which represents an efficient, safe and low-cost method of separation. The goal of the present investigation was to make a comparative study of gold concentration by elutriation from different precious metal bearing ores: an oxide ore, a mineral consisting of a sulfide matrix, a mineral in which the precious metals are free and disseminated and a slimy and clayey black sand material. The best recoveries of precious metals by elutriation were attained for the free disseminated ore and for the black sands, obtaining gold recoveries of 70% and 96% respectively, with appreciable ratios of concentration as well.
 
HRB400 steel standard (add vanadium nitrogen alloy and micro nitrogen alloy).
Inclusion morphology and energy spectrum images of samples at 25 mm diameter.
Inclusion morphology and energy spectrum images of samples at 32 mm diameter.
Article
The analysis of the crack on the HRB400 screw-thread steel surface has been carried out by means of metallographic microscope, scanning electron microscope and EDAX. It is shown that the type of inclusions in the crack steel samples is mainly class B oxide, C silicate, and the inclusion size of the majority below 10 μm, and a small number of large inclusions are observed. The content of oxygen in the steel is high, and the carbon segregation is the main reason of the crack formation of HRB400 screw-thread steel. The measures to improve the crack formation of HRB400 screwthread steel are put forward, which provides a powerful basis for the practical production.
 
Chemical compositions of anthracite and calcium hydroxide.
Chemical compositions of metal particles and the yield of nickel and iron (wt%).
Article
Based on the process of coal-based self-reduction and melting separation at high temperature, it was investigated that the effect of process factors on the reduction of iron and nickel oxide, the metal yield and the nickel content in ferronickel about the laterite nickel ore, was from Philippines and contented low nickel, high iron and aluminum. The results showed that if the C/O mole ratio was not higher than 0.5 and the reduction temperature was kept as 1200˚C and then increased up to 1500˚C, the metal could not separate from molten slag for the A series of experiments, which were only added CaF2. However, when the C/O ratio was added up to 0.6 - 0.8, the metal could separate well from the slag, and the yields of Fe and Ni increased gradually. But the nickel content in the metal declined from 1.79% to 1.34%. When the C/O ratio increased to 1.2, and the temperature of melting products obtained at 1200˚C and rose to 1550˚C, the separation of metal from slag could not be realized in B group of tests, which were only added hydrated lime. However, when both of CaF2 and hydrated lime were added, the metal could separate from slag in C group. In order to increase the content of nickel in the metal, it is necessary to restrain the reduction of iron oxide. When the C/O mole ratio is 0.6, the nickel content of metal could be 1.79%, which was higher than the theoretical ratio 1.65% of Ni/(Ni + Fe) of the latcritic nickel ore , but the yield of nickle was only 71.3%.
 
Article
Unlike the reported leaching technologies of waste superalloys, the process of the “atomized spray-sulfuric acid leaching nickel and cobalt” technology was put forward in the present work according to the compositions of waste superalloys. The effects of sulfuric acid temperature, concentration, leaching time, stirring speed and size of superalloys on leaching of Ni and Co from waste superalloys have been mainly investigated, and the optimum leaching conditions were determined and reported. The leaching rates for nickel and cobalt were 96.68% and 96.63%, respectively, and the contents of nickel and cobalt in leaching slag were 6.77% and 0.96%, respectively. The obtained leaching solution containing Ni and Co could be used for production of Ni and Co products after removal.
 
The integral molar volume of TBP-kerosene binary solution as a function of measured at room temperature. kerosene X
Activity coefficient of kerosene as a function of concentration. 
Article
Results of the experimental measurements on the partial molar volume of kerosene used as a medium for dissolving TBP are utilized to determine the activity of TBP in the binary kerosene-TBP solution through the application of Gibbs-Duhem equation. The treatment is based on combination of the experimental data with the thermodynamic values available on the compressibility factor of pure kerosene at room temperature. It is shown that the activity of TBP in kerosene has a positive deviation from ideality with an activity coefficient derived as follows: 1) at TBP 0.01 X  : TBP 42.530   , 2) at the TBP
 
Unit for research of electrochemical behavior of elemental sulfur in water solutions (а) front view; (b) rear view): 1-composite sulfur-graphite electrodes, 2-compressor, 3-bipolar membrane BM, 4-gas trap unit for entrapping of hydrogen sulfide gas, 5 – cathode chamber, 6-anode chamber. 
shows a cyclic anode-cathode potentiodynamic polarization curve for sulfur-graphite electrode in 1.0 M solution of sulfuric acid. On sulfur-graphite electrode before the potential of oxygen release at "+" 1625 mV oxidation current is registered. According to our hypothesis (or expectations), reactions of sulfur oxidation with formation of sulfite and sulfate ions according to the Equations (1-3) are indicative for the stated values of potential. The results of electrolysis carried out under galvanostatic conditions indicate that during anode polarization in sulfurous environment oxidation of sulfur-graphite electrodes runs with formation of sulfite and sulfate ions: 2 2 3 S 3H O 4e SO 6H − + + − → + 
Article
Method and mechanism for the formation of sulfur compounds during the process of sulfur electrochemical dissolution has been studied, including a technique for the production of composite sulfur-graphite electrode. Along with these, a 3D design is presented in the unit that was used to perform electrolytic reduction, using composite sulfur-graphite electrode. For the first time, a study was carried out for the simultaneous reactions of electroreduction and electrooxidation of sulfur at the sulfur-graphite electrode in sulfurous environment in the same electrolytic bath, with separate electrode spaces. Influences of current density, acid concentration and electrolyte temperature were studied, and it was demonstrated that sulfur is reduced in cathode chamber with formation of hydrogen sulfide gas, and is oxidized in the anode chamber with formation of sulfite and sulfate ions. It has been shown that the methods we propose can be used to produce important sulfur compounds through electrochemical dissolution of specially designed sulfur-graphite electrode.
 
Chemical composition of copper sulfide concentrate (wt%).
Effect of roasting time on copper extraction (500˚C, 1% Na 2 SO 3 ).
Effect of Na 2 SO 3 amount on copper extraction (roasting time: 2 h).
Article
Sulfation roasting was studied to extract copper from the copper sulfide concentrate. Sodium sulfite was added as sulfation agent to the copper sulfide concentrate during roasting in this study. Sulfur removal rate at different roasting temperatures was investigated, and the effects of roasting temperature, roasting time, and the amount of sodium sulfite on copper extraction were studied. Copper extraction higher than 96% was achieved at optimum roasting conditions.
 
Surface species and their atomic concentrations (%) on galena determined by XPS analysis. 
Effect of grinding conditions on the amount of EDTA extracted iron products and their influence on galena flotation recovery. 
Article
This study has been done to determine the galvanic interaction between five types of grinding media (mild steel, cast iron, 10% chromium, 20% chromium, and ceramic media) and galena, in situ of the mill. The ceramic media has a significantly not galvanic interaction with galena and high chromium media has a significantly weaker galvanic interaction with galena, and produces a very much lower amount of oxidize iron species in the mill discharge than mild steel medium. The investigation of the various reactions occurring on the galena surface were investigated by ethylene diamine-tetra acetic acid disodium salt (EDTA) extraction and Xray photoelectron spectroscopy (XPS) measurements. The floatability of galena is dependent on the galvanic current between grinding media and galena during grinding because the current is relative to the amount of iron oxidation species and the reduction rate on galena. Iron oxidation species depressed galena flotation. The optimum galena flotation was achieved by selecting grinding conditions that enabled iron oxidation to be controlled.
 
XRD pattern of the sample.
The lower and upper limits of five parameters.
Designed experiments by DX7 software.
Article
This study was carried out to investigate the interaction of oxalic acid with hydrochloric acid to attain the better performance for iron dissolution in comparison to absence of oxalic acid. The effects of oxalic acid on ratio of hydrochloric acid, acid concentration, ratio of liquid to solid, temperature and dissolution time are investigated for the dissolution of Fe and Ti from ilmenite to produce synthetic rutile. The DX7 software basing on an experimental design method with the central composite of response surface design is applied to specify the effects of the parameters and to optimize the leaching process. The optimum condition was determined by analysis of variance (ANOVA), indicating that the ratio of oxalic acid to hydrochloric acid for Fe dissolution and acid concentration for Ti dissolution were the most effective parameters. The results showed that the dissolution of Fe and Ti in 30% (w/w) hydrochloric acid solution was only 48.65% and 5.14%, respectively, while at the same condition and in the presence of oxalic acid with twice the ratio, these values are increased to 78.65% and 12.06%, respectively. The optimum values of parameters were as follows: oxalic acid to hydrochloric acid ratio (2:1), acid concentration (30%), ratio of liquid to solid (10), temperature (160˚C), and dissolution time (3 h). By applying the optimized parameters, Fe and Ti dissolution of 97.15% and 2.8% were predicted by the software with a desirability of 0.745. The results of leaching tests indicated that the Fe and Ti dissolution of 97.58% and 2.43%, were achieved, respectively, which are very close to the predicted value.
 
Article
Hydrometallurgical technology offers a unique possibility for developing countries to exploit their mineral resources locally instead of shipping them as concentrates. Production plants may start on a small scale with small capital investment then increase productivity later when the economy permits without financial penalty. This is in contract to smelt-ing operations which necessitates large scale production from the start with high capital investment that may not be available locally.
 
Article
Grain-size class redistribution of non-ferrous, precious metals and iron in copper-nickel ores tailings from Norilsk industrial region was after artificial weathering investigated. Possible mechanisms of metal redistribution were suggested.
 
Data
The extraction of chromium(III) from a model waste solution and also from a waste solution of an Indian tannery with Amberlite IR 120 resin is described, and the performance of this resin is compared with other similar resins. The pa-rameters that were optimized include effect of mixing time, pH, loading and elution behaviours of chromium(III) for this resin. Sorption of chromium(III) on Amberlite IR 120 followed Freundlich isotherm and Langmuir isotherm model, and the maximum sorption capacity was determined to be 142.86 mg Cr(III)/g of the resin. Higher Freundlich constant (K f) values (6.30 and 13.46 for aqueous feed of 500 and 1000 ppm Cr(III)) indicated strong chemical interaction through ion exchange mechanism of the metal ion with the resin. The kinetic data showed good fit to the Lagergren first order model for extraction of chromium(III). Desorption of chromium(III) from the loaded resin increased with the in-crease in concentration of eluent (5-20% H 2 SO 4). With 20% (v/v) sulphuric acid solution 94% chromium(III) was eluted in three stages. Elution of the Cr(III) in the column experiments was however, found to be lower (82%) than that of the shake flask data. In case of Indian tannery's waste solution, it was observed that almost total chromium was ex-tracted in four stages with Amberlite IR 120.
 
Effect of [Ni(II)] (ini) on flux [Ac − ] = 0.25 mol/L, Temp. = 303 K,     2 4 SO  = 0.042 mol/L, C.H = 0.66 m. (), pH (ini) = 6.70, [H 2 A 2 ] (o,ini) = 0.025 mol/L; (), pH (ini) = 6.00, [H 2 A 2 ] (o,ini) = 0.025 mol/L; (), pH (ini) = 6.70, [H 2 A 2 ] (o,ini) = 0.30 mol/L.
Effect of pH (ini) on flux. [Ni 2+ ] (ini) = 1.3405 g/L,     2 4 SO  = 0.05 mol/L, C.H = 1.2/0.9/0.66 m. (), [H 2 A 2 ] (o,ini) = 0.025 mol/L; (), [H 2 A 2 ] (o,ini) = 0.10 mol/L; (), [H 2 A 2 ] (o,ini) = 0.30 mol/L. Other parameters are as in Figure 2. −5.80 (for 0.30 mol/L [H 2 A 2 ] (o,ini) system) and 10 6.32 is a proportionality constant resulting from non-linear curve fitting. Its unit is L/mol. I-values of the asymptotic lines are embodied in figure. It is concluded that the rate of Ni 2+ extraction is independent of [H + ] in lpHr; whereas, inversely proportional to [H + ] in hpHr. In other words, the reaction order wrt [H + ] is −1 (b = 1) and 0 (b = 0) in lpHr and hpHr, respectively. Figure 4 displays logF f vs log[H 2 A 2 ] (o,ini) plots. For each pH system, the plot is a straight line whose s and I are given. The s-values indicate that the rate of forward extraction is directly proportional to the square root of the extractant concentration (i.e., c = 0.5). The nature and extent of variations of F f with
The log{(F f h/kT), kmol/m 2 s} vs (1/T) plots. Legends are as in (), logf(R) = −2.4679; (), logf(R = −3.2299; (), logf(R) = −2.9834; (), logf(R) = −2.4682; (), logf(R) = −3.4670. 
The logF f vs logf(R) plot at 303 K. 
Article
The kinetics of extraction of Ni(II) in the Ni2+-SO4 2_AC- (Na+, H+)-Cyanex 272 (H2A2)-kerosene-3% (v/v) octan-1-ol system using the single falling drop technique have been reported. The flux of Ni2+ transfer (F) at 303 K in presence of 3% (v/v) octan-1-ol (de-emulsifier) can be represented as:.Depending on reaction parameters, the activation energy (Ea) and enthalpy change in activation (DH±) varies within 17 - 58 kJ/mol and 17 - 67 kJ/mol, respectively. Entropy change in activation (DS±) is always negative. Based on the empirical flux equation, Ea and DS± values, mechanisms of extractions in different parametric conditions are proposed. At low and [Ac-], and pH, the chemical controlled step is: Ni2+ + A- → NiA+; and this reaction occurs via an SN2 mechanism. But in most parametric conditions, the process is under intermediate control; and at high SO42- and [Ac-], and pH, the extraction process is under diffusion control.
 
Effect of [HA] (o,eq) on extraction. (), pH (ini) = 2.00; (), pH (ini) = 1.50; (), pH (ini) = 1.40, [ ] = 1.50 mol/L. Other parameters are as in Figure 1. 2 4 SO 
Effect of [ ] on extraction. pH (ini) = 2.00 = pH (eq) , [HA] (o,ini) = 0.225 mol/L = [HA] (o,eq). Other parameters are as in Figure 1. Experimental points fall on a curve represented by: log C D = constant + log(1 + ]). The curve possesses two asymptotes: at lcr of : log C D = constant (represented by horizontal line) and at hcr of : log C D = constant + log + log[ ] (represented by inclined line). At the point of intersection of two asymptotes: log + log[ ] = 0; or, log −log[ ] = −(−0.20) = 0.20; or, log = 1.58. Intercept of asymptote at hcr is 1.08 and that at lcr is 0.95. 
Loading of HA with V(IV). [V(IV)] (ini) = 1000 mg/L, [ ] = 0.10 mol/L, pH (ini) = 2.60, [HA] = 0.20 mol/L, Stage equilibration time = 15 min, Temp. = 303 K, O/A = 1 (O = 100 mL). 2 4 SO 
Article
The equilibrium of extraction of V(IV) in the V(IV)- SO42- (H+, Na+)-Cyanex 301 (HA)-kerosene system has been studied. Significant extraction occurs above pH 1 within 10 min. CD (extraction ratio at constant pH(eq) and [HA](o,eq)) value is slightly decreased with increasing [V(IV)](ini). CD is found to be directly proportional to [H+]-n (n ≤ 2), [HA] 2 and (1+1.58 [SO42-]). The process is endothermic (DH = 16 kJ/mol). Apparent Kexvalues at 303 K are 10-1.419 and 10-0.94 in 0.10 and 1.50 mol/L SO42- medium, respectively. The loading capacity is calculated to be7.87 gV(IV) per100 g Cyanex 301. Kerosene appears as the best diluent. Stripping to the extents of 100%, 94% and 97.7% are possible in single stage by 1 mol/L H2SO4, HCl and HNO3, respectively. Separations of V(IV) from Cu(II) (at pH 0), Zn(II) (at pH 0.5) and Fe(III) (at pH 1.0) by Cyanex 301 are possible.
 
Effect of [V(IV)]on C D·[ ] = 0.02 mol/L, Temp. = (303  0.5) K, Equilibration time = 20 min, O/A = 1 (O = 20 mL). () [Cyanex 302] = 0.10 mol/L, pH (ini) = 4.30, pH (eq) const. = 3.41; () [Cyanex 302] = 0.20 mol/L, pH (ini) = 3.80, pH (eq) const. = 3.10. 2 4 SO  
Loading of V(IV) in the organic phase. [V(IV)] (ini) = 2000 mg/L, [Cyanex 302] = 0.20 mol/L, pH = 6.0, [ 2 4 SO  ] = 0.04 mol/L, Equilibration time = 20 min, Temp. = (303  0.5) K, O/A = 1 (O = 100 mL). 
Article
The title system has been investigated from the equilibrium point of view. Significant extraction occurs above pH 2. Equilibration time is 20 min. The extraction ratio (D) remains constant with increasing [V(IV)] of at least 0.50 g/L. It is inversely proportional to [H+]2, [H+] and [H+]0.3 in the lower pH (<2.25), medium pH (~2.90) and higher pH (~4.0) regions, respectively. Moreover, it is proportional to [Cyanex 302]2; and [SO42-]0 and [SO42-]-1 in the lower [SO42-] (<0.05 mol/L) and higher [SO42-] (>1 mol/L) regions, respectively. The apparent extraction equilibrium constant (Kex) in 0.02 mol/L SO42- medium and at 303 K is found to vary from 10-3.447 to 101.508 with increasing equilibrium pH from 2.25 to 4.00. Various sulphated, hydrolyzed, hydrated and mixed sulphated hydrolyzed species of V(IV) have been considered at different extraction conditions to propose the extraction equilibrium reactions to form always [VO(HA2)2] as the extractable species. The system is highly temperature dependent with ?H value of ~90 kJ/mol and ~25 kJ/mol in lower and higher temperature regions, respectively. The calculated loading capacity is low (4.05 g V(IV)/100 g Cyanex 302). Kerosene is a better diluent over CHCl3, Cyclo-C6H12 and CCl4; but much better solvents are C6H6, C6H5CH3, n-C7H16,C6H4(CH3)2, petroleum benzin, 1,2-C2H4Cl2, C6H5Cl. Mineral acids (1 mol/L) are able to strip off V(IV) from the organic phase in a single-stage. Using Cyanex 302, almost complete separations of V(IV) from Cu(II) at pH 1.0 and from Ni(II) at pH(eq) 4.5 are possible in a single-stage of extraction; whereas, its separation from Zn(II) at pH(eq) 2.5, Co(II) at pH(eq) 3.5, Fe(III) at pH(eq) 2.0 and Ti(IV) at pH(eq) 2.5 will require counter-current multi-stage extractions.
 
Petrological micrograph of copper ore (at 100×) [C-chalcopyrite, P-pyrite]. 
XRD Phase analysis of copper ore.
Copper recovery at different pulp densities using unadapted culture at 35˚C, <50 µm particles, pH 2.0. [BL-Bio-leaching, CL-Chemical Leaching].
Article
A low-grade ore containing ~0.3% Cu, remains unutilized for want of a viable process at Malanjkhand Copper Project (MCP), India in which copper is present as chalcopyrite associated with pyrite in quartz veins and granitic rocks. In order to extract copper from this material, bioleaching has been attempted on bench scale using Acidithiobacillus fer-rooxidans (A. ferrooxidans) isolated from the native mine water. The enriched culture containing A. ferrooxidans when adapted to the ore and employed for the bioleaching at 5% (w/v) pulp density, pH 2.0 and 25˚C with three particle sizes viz.150 -76 μm, 76 -50 μm and <50 μm, resulted in recovery of 38.31%, 29.68% and 47.5% Cu respectively with a maximum rise in redox potential (E SCE) from 530 to 654 mV in 35 days. Under similar conditions, the unadapted strains gave a recovery of 44.0% for <50 μm size particles with a rise in E SCE from 525 to 650 mV. On using unadapted bacte-rial culture directly in shake flask at pH 2.0 and 35˚C temperature and 5% (w/v) pulp density (PD) for <50 μm size par-ticles, 72% Cu bio-dissolution was achieved in 35 days. Copper biorecovery increased to 75.3% under similar condi-tions with a rise in bacterial count from 1 × 10 7 cells/mL to 1.13 × 10 9 cells/mL in 35 days. The higher bio-recovery of copper with the adapted bacterial culture may be attributed to the improved iron oxidation (Fe 2+ to Fe 3+) exhibiting higher E SCE as compared to that of unadapted strains.
 
Linear polarization curves for a gold electrode in the presence of different additives (a), and of the concentration of sodium sulfite (b).
Article
In this work the dissolutive behavior of gold in alkaline medium using thiou-rea (TU), under different variables, was studied in a theoretical and experimental way, in order to determine the conditions under which it is feasible to dissolve gold in thiourea-alkaline medium. A thermodynamic study was conducted by chemical speciation using the method of Rojas-Hernández, together with an electrochemical study where the electric potential was swept in the anodic direction. The main results of the thermodynamic study were that formamidine disulfide (FDS) and sulfinic compounds (S.C.) prevail at alkaline pH; by increasing the initial concentration of thiourea at alkaline pH, the presence of the gold complex is almost zero for any initial concentration of thiourea. By including sodium sulfite in the gold-thiourea system, it was possible to obtain the Au(I)-TU complex at alkaline pH, with a presence of 95.13%. Electrochemical tests allowed verifying that in the absence of sodium sulfite the dissolution of gold in an alkaline medium is very slow but adding sodium sulfite improvements become evident in the dissolution of the metal. Therefore, sodium sulfite catalyzes the gold dissolution process and stabilizes the thiourea. With this study it was possible to establish the feasibility of using thiourea in an alkaline medium for the dissolution of gold, and the conditions under which it is possible to dissolve the gold in that medium. With these fundamentals and conditions, it is now possible to move forward to test this system for minerals and/or concentrates containing gold.
 
Top-cited authors
Aneek Krishna Karmakar
  • University of Rajshahi
Ranjit Kumar Biswas
  • University of Rajshahi
Davood Moradkhani
  • University of Zanjan
E. Keshavarz Alamdari
  • Amirkabir University of Technology
Alireza Eivazihollagh
  • Mid Sweden University