Separation and recovery of iron and scandium from acid leaching solution of red mud using D201 resin

Red mud is a byproduct of alumina refining of bauxite ores, and is a significant source for extracting scandium. However, a large amount of iron in red mud makes it difficult to recover scandium because Fe(III) and Sc(III) have similar physicochemical properties. In this study, a new method was developed for selective separation of iron and scandium in acid leachate of red mud using D201 resin. Theoretical calculations indicate that the ferric species mainly exists as FeCl₃ or FeCl₄⁻ at chloride concentration above 6.65 mol/L, while scandium still exists as ScCl₂⁺, making it possible to selectively separate iron from scandium through anion resin adsorption. The factors affecting the adsorption of iron and scandium such as chloride concentration, resin dosage, adsorption time, and temperature were evaluated in batch experiments. The Langmuir model was successfully applied to both iron and scandium adsorption, and the maximum adsorption capacities of iron and scandium are 147.06 and 0.95 mg/g, respectively, indicating a significant difference between iron and scandium. Raman analysis further demonstrates that the iron is adsorbed onto D201 resin as FeCl₄⁻ anion.     

Oxidative leaching of an offgrade/complex copper concentrate in chloride lixiviants

Laboratory studies have been conducted on chloride leaching as a possible route for the simultaneous recovery of copper, zinc, and lead from an off grade and complex chalcopyrite concentrate (from Sikkim, India) associated with appreciable amounts of sphalerite, galena, and pyrite. The effects of temperature, concentration, and quantity of ferric chloride, stirring speed, and leaching time on metal dissolution have been investigated. Leaching tests have also been conducted with in-dividual (HC1, NaCl, CuCl₂, FeCl₃) and mixed chlorides (two-, three-, and four-component mix-tures). Results show the possibility of recovering not only 99 pct Cu and 89 pct Zn but also 82 pct Pb and 58 pct elemental S by treatment of the concentrate with 4 M FeCl₃ at 383 K (110 °C) for 7.2 ks (2 hours) employing 25 pct excess FeCl₃ and a stirring speed of 700 rev min⁻¹. Though 64 pct iron of the concentrate is found to dissolve, the pyrite seems to remain unattacked. Kinetic studies indicate that the chalcopyrite, sphalerite, and galena of the concen-trate dissolve simultaneously in the FeCl₃ lixiviant as if each mineral is separately leached, and the Cu and Zn dissolution reactions are under chemical control (linear kinetics). The addition of NaCl to the chloride lixiviants is found to be beneficial only up to a common salt concen-tration of 100 g/l. Leaching of the copper concentrate with CuCl₂ or mixed FeCl₃-CuCl₂-NaCl has not been as effective as its direct leaching with 4 M FeCl₃. N.V. NGOC, formerly Visiting Scientist with the Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University.     

The removal of iron from aluminum chloride leach liquors by ion exchange

The sorption behavior of iron onto two anion exchange resins from simulated aluminum chloride leach liquors was studied. Bench-scale sorption isotherm experiments were performed at room temperature. The initial chloride concentrations of the simulated leach liquors ranged from 1 M to 6 M. Iron loading for the Dowex SBR and Dowex MWA-1 resins increased with increasing chloride concentrations. Maximum capacities observed for both resins were approximately 0.95 meq Fe/g dry resin at an initial chloride concentration of 6 M. The Dowex SBR resin sorbed noticeably greater amounts of iron than the MWA-1 resin at initial chloride concentrations of 4 and 5 M. Computer programs were written to predict the equilibrium distribution of species in various aqueous electrolytes. Correlation of computer results with some published experimental data indicated good qualitative correlations. However, strict quantitative conclusions may be suspect due to an inability to predict activity coefficients accurately at the high ionic strengths of this work. Comparison of computer program predictions and sorption isotherm results indicate that the species FeCl_3(aq) may be involved in the sorption of iron from the simulated leach liquors.     

Solubilities,densities and electrical conductivities of aqueous copper(I) and copper(II) chlorides in solutions containing other chlorides such as iron,zinc, sodium and hydrogen chlorides

With a view to industrial applications, solubilities, densities and electrical conductivities of aqueous copper(I) and copper(II) chlorides were measured in solutions containing other chlorides like those of iron, zinc, sodium and hydrogen.In these solutions copper(I) chloride shows a behaviour similar to that observed in pure CuClNaClHCl solutions. Increasing the FeCl₂ concentration decreases the solubility of CuCl less than increasing the ZnCl₂ concentrations does. Moreover, increasing total Cl^? concentration increases CuCl solubility if Cl^? is added as FeCl₂ and decreases CuCl solubility if Cl^? is added as ZnCl₂. NaCl solubility remains unchanged by FeCl₂ additions and is increased by ZnCl₂ additions.Copper(II) chloride also shows in these solutions a behaviour similar to that observed in pure CuCl₂NaClHCl solutions. FeCl₃ additions decrease CuCl₂ · 2 H₂O solubility in a more drastic manner than ZnCl₂ additions. However, NaCl additions have a much higher effect.These results can be qualitatively interpreted when taking into account the relative Cl^? donor or acceptor character of the constituent chloride salts of the solution.FeCl₂ additions slightly decrease the electrical conductivity of Cu(I) solutions. However, this can easily be compensated by a slight increase in temperature or in acidity.     

Calculation of phase diagrams for the FeCl2, PbCl2, and ZnCl2 binary systems by using molecular dynamics simulation

Recently, molecular dynamics (MD) simulation has been widely employed as a very useful method for the calculation of various physicochemical properties in the molten slags and fluxes. In this study, MD simulation has been applied to calculate the structural, transport, and thermodynamic properties for the FeCl₂, PbCl₂, and ZnCl₂ systems using the Born—Mayer—Huggins type pairwise potential with partial ionic charges. The interatomic potential parameters were determined by fitting the physicochemical properties of iron chloride, lead chloride, and zinc chloride systems with experimentally measured results. The calculated structural, transport, and thermodynamic properties of pure FeCl₂, PbCl₂, and ZnCl₂ showed the same tendency with observed results. Especially, the calculated structural properties of molten ZnCl₂ and FeCl₂ show the possibility of formation of polymeric network structures based on the ionic complexes of ZnCl ₄ ²⁻ , ZnCl ₃ ⁻ , FeCl ₄ ²⁻ , and FeCl ₃ ⁻ , and these calculations have successfully reproduced the measured results. The enthalpy, entropy, and Gibbs energy of mixing for the PbCl₂-ZnCl₂, FeCl₂-PbCl₂, and FeCl₂-ZnCl₂ systems were calculated based on the thermodynamic and structural parameters of each binary system obtained from MD simulation. The phase diagrams of the PbCl₂-ZnCl₂, FeCl₂-PbCl₂, and FeCl₂-ZnCl₂ systems estimated by using the calculated Gibbs energy of mixing reproduced the experimentally measured ones reasonably well.     

Equilibria between ferrous and ferric chlorides in molten chloride salts

Equilibria between ferrous and ferric chlorides in molten salts have been studied for improving magnesium electrolysis and molten salt chlorination. The apparent equilibrium constants,K, of reaction FeCl_2(melt)+0.5Cl_2(gas)=FeCl_3(melt) were obtained. Measured values ofK were in good agreement with computed ones from regression equations. The composition of the melts, the partial pressure of chlorine, and the temperature were found to have important effects onK, and the effect of dissolved iron was smaller than that of other factors. At identical other conditions, the largest values ofK were observed in system 3, which suggested that the current efficiency for electrolysis of MgCl₂ should be lower when carnallite was used as electrolyte and that catalysis of iron species in molten salt chlorination would be better when molten salt systems containing high potassium chloride were used.     

Effect of tellurium on supersaturation in aluminum deoxidized liquid iron

The effect of tellurium addition on supersaturation observed in aluminum deoxidized liquid iron was studied at 1873 K, using CaO-Al₂O₃ slags in an alumina crucible. Supersaturated oxygen content for a given aluminum level decreased with the addition of tellurium as a result of lowering the interfacial energy between liquid iron and alumina and promoting the elimination of precipitated alumina by flotation. Furthermore, the degree of lowering of oxygen content was found to increase with a decrease in cooling rate. Tellurium distribution ratio between liquid iron and CaO-Al₂O₃ slags was determined as a function of aluminum content.     

The precipitation of hematite from ferric chloride media at atmospheric pressure

The precipitation of hematite from ferric chloride media at temperatures <100 °C and at ambient pressure was studied as part of a program to recover a marketable iron product from metallurgical processing streams or effluents. Hematite (Fe₂O₃) can be formed in preference to ferric oxyhydroxides (e.g., β-FeO·OH) at temperatures as low as 60 °C by controlling the precipitation conditions, especially seeding. The hematite product typically contains >66 pct Fe and <1 pct Cl, and its composition does not change appreciably on repeated recycling. The amount of product formed increases significantly with increasing FeCl₃ concentrations to ∼0.2 M FeCl₃, but nearly constant product yields are obtained thereafter; the precipitates consist only of hematite, provided that an adequate amount of seed is present. The contamination with Zn, Ca, and Na is <0.1 pct, even for high concentrations of dissolved ZnCl₂, CaCl₂, or NaCl. The extent of the precipitation reaction depends principally on the temperature and the free-acid concentration; accordingly, the controlled addition of a base allows the nearly complete elimination of the iron from metallurgical processing streams or effluents, as readily filterable Fe₂O₃.     

A mathematical model for calculation of equilibrium solution speciations for the FeCl3-FeCl2-CuCl2-CuCl-HCl-NaCl-H2O system at 25 ‡C

Equilibrium solution speciation computations were performed for the FeCl_-FeCl3-CuCl₂-CuCl-HCl-NaCl-H₂O system at 25 ‡C. In dilute solutions, complexation of Fe(III), Fe(II), and Cu(II) is insignificant but the major Cu(I) species is CuCl₂ ^-. In concentrated solutions, FeCl ₃ ⁰ , FeCl ₂ ⁰ , and CuCl ₂ ⁰ are the major Fe(III), Fe(II), and Cu(II) species, and CuCl ₃ ^2- is the most important cuprous complex. High Cu(I)/Cu(II) ratios are apparently more readily attainable in CuCl₂ than in FeCl₃ media. The Cu(I)/Cu(II) ratio is increased by making the solution more concentrated in any component except FeCl₃ or CuCl₂. Neither the ionic strength nor the total chloride concentration is a good predictor of the Cu(I)/Cu(II) ratio.     

The solubility of silver chloride in ferric chloride leaching media

The solubility of silver chloride in various FeCl₃-FeCl₂-HCl solutions has been measured over the temperature range 20–100°C; the densities of the associated saturated solutions have also been determined. The solubility increases systematically with either rising temperature or increasing concentrations of the constituent chlorides. The solubility is higher in a ferrous chloride medium than in an equivalent ferric chloride solution. The presence of CuCl₂ systematically raises the AgCl solubility, but increasing ZnCl₂ concentrations cause the solubility to decrease slightly to about 1.5 M ZnCl₂ and subsequently to increase gradually. The addition of NaCl to the iron chloride media substantially increases the AgCl solubility under all conditions. Although the solubility of AgCI is only a few mg/L in cold water, this increases to over 1 g/L in hot, moderately concentrated chloride media. Silver chloride solubilities at elevated temperatures are sufficiently high that silver solubility limitations should not be a problem in most commercial ferric chloride leaching processes.     

Retardation of intermetallic phase formation in experimental superferritic stainless steels

While superferritic stainless steels containing 29 pct chromium possess excellent resistance to corrosion, they may, under certain conditions, be embrittled by the precipitation of intermetallic phases. The extent to which the precipitation reactions can be retarded by alloying additions of aluminum and copper has been evaluated. It was found that additions of aluminum to an Fe-29 pct Cr-4 pct Mo-1.5 pct Ni base alloy suppress the precipitation of the undesirable sigma and chi intermetallic phases, but additions of up to 3 pct aluminum promote 475 ‡C embrittlement. Additions of copper slightly reduce the precipitation of sigma and chi phases under most conditions but enhance 475 ‡C embrittlement. The resistance to corrosion in 10 pct H₂SO₄ and 10 pct FeCl₃ was assessed. All the aluminum-containing alloys performed significantly better in H₂SO₄ than the base alloy; however, large additions of aluminum had a deleterious effect on the pitting resistance in FeCl₃. Additions of copper improved the resistance to FeCl₃ and lowered the rate of corrosion in the H₂SO₄ solution used.     

Leaching of CuFeS2 by aqueous FeCl3, HCl,and NaCl: Effects of solution composition and limited oxidant

Batch leaching experiments were performed in which the initial amounts of chalcopyrite and ferric chloride were selected to ensure that the oxidant was significantly depleted over the course of an experiment. Solution samples were analyzed for Cu(II) and Fe(III) by visible spectrophotometry and for total copper and total iron by atomic absorption, making it possible to measure changes in the solution component concentrations as leaching progressed. For selected samples, the solution potential was also measured. In all experiments, the Cu(II) concentration passed through a maximum and, simultaneously, the Cu(I) concentration increased very sharply. An acceleration in the total rate of leaching was normally observed at the same time. Early in a leach, the solution potential was too high for the reduction of Cu(II) to Cu(I) to take place at the time of the increase in the overall leaching rate, however, the solution potential dropped sharply during a span of a few hours, reaching a value low enough that reduction of cupric ion became possible. The amount of Cu(I) present at the completion of a leach was dependent on the total chloride concentration of the system. The highest Cu(I)/Cu ratios were observed in systems with the highest chloride concentrations. The ultimate extent of CuFeS₂ leaching was dependent on the initial FeCl₃ and total chloride concentrations; the FeCl₃ was virtually completely consumed and the total chloride concentration controlled the extent to which Cu(II) was reduced by reaction with chalcopyrite.     

Copper removal from carbon-saturated molten iron with Al2S3-FeS flux

Copper removal from carbon-saturated molten iron to Al₂S₃-FeS flux was experimentally investigated in the temperature range from 1473 to 1573 K. The maximum copper distribution ratio between the Al₂S₃-FeS flux and the ferrous alloy was about 28 at the composition where the molar ratio of Al to Fe in the flux was around 2. The distribution ratio was no less than 25 as long as the copper content of the flux was less than 10 mass pct. The sulfur content in the ferrous alloy in equilibrium with the Al₂S₃-FeS flux was higher than that obtained by using Na₂S-FeS flux, and it was concluded that the high copper distribution ratio of the Al₂S₃-FeS flux was brought about by the high activity coefficient of FeS in the flux. In experiments for recovering copper from the flux, copper in Al₂S₃-FeS-Cu₂S flux was reduced by metallic aluminum at 1473 K. The FeS in the flux was primarily reduced and, after that, the copper was recovered in the form of Cu-Al-Fe alloy. The residual copper content in the flux could be decreased to less than 1 mass pct when the aluminum content in the alloy was higher than 40 mass pct. A process for copper removal from molten iron is proposed, which uses successive contacts between the Al₂S₃-FeS flux and molten iron at several stages with counterflow operation. It is suggested that 1 mass pct Cu in molten iron can be reduced to approximately 0.1 mass pct Cu using 100 kg flux/ton iron; the amount of aluminum required for the iterative use of the flux is about 10 kg/ton iron. By the recycling use of this Al₂S₃-FeS flux, it is suggested that copper removal from molten iron using the sulfide flux can be more effective.     

Separation of iron and nickel from a spent FeCl3 etching solution by solvent extraction

Solvent extraction experiments were conducted to separate iron and nickel from a spent FeCl₃ etching solution. Alamine336, MIBK and PC88A were tested as extractants and the highest extraction percentage of iron was obtained with Alamine336. It was possible to separate iron and nickel by extracting the spent etching solution with Alamine336. In the operation of mixer-settler, seven extraction stages with 1.0 M Alamine336 led to 99% extraction of iron at an O / A ratio of 7. Ten stripping stages with 0.01 M HCl solution resulted in an aqueous solution with 133 g/L of iron at an O / A ratio of 7.     

The influence of iron and aluminum on the precipitation of metastable Ni3Nb phases in the Ni-Nb system

The effect of additions of aluminum and iron on the formation of transitional phases has been examined for alloys of the Ni-Nb system. It has been established that metastable phases of approximate composition Ni₃Nb will not form in binary Ni-Nb alloys under normal conditions of quenching and aging, but that iron or iron and aluminum additions promote their formation when certain size and electronic factors are satisfied. In Ni-Nb-Fe alloys containing more than ≈ 12 at. pct Nb, iron promotes the formation of a bct (DO₂₂) Ni₃Nb precipitate. Aluminum additions to these Ni-Nb-Fe alloys promote the precipitation of fcc (L1₂) Ni₃Nb γ’, initially together with the bct phase, but at higher aluminum concentrations the tetragonal phase disappears. The appearance of both precipitates followed the Hagel-Beattie requirement for interfacial mismatch of < or ～ 1 pct between the matrix and the precipitate. The presence of both precipitating phases can be predicted on the basis of the Engel-Brewer correlations. The preferrede/a ratio for the stability of the bct (DO₂₂) phase is 2.50 to 2.62. In the present investigation this phase precipitates only in the presence of iron (bcce/a ratio = 1.5), and only when the lattice constant of the matrix is greater than 3.600Å. The preferrede/a ratio for the stability of the γ’ having a fcc L1₂ structure is between ～2.75 and 3.0. Precipitation of this phase occurred only when aluminum(e/a) ratio = 3.0) was present, and when the matrix lattice constant was greater than 3.589Å.     

The rate of chlorination of metals and oxides: Part I. Fe,Ni, and Sn in chlorine

The rates of chlorination of Fe (528 to 921 K), Ni (890 to 1249 K), and Sn (340 to 396 K) in Cl₂-He andCl₂-Ar mixtures were measured. In the temperature range of the respective investigations the overall reaction products are gaseous: (FeCl₃)₂, NiCl₂, and SnCl₄. Transport through the gas film boundary layer at the surface of the sample plays a major role in controlling the rate of the reactions over large temperature ranges for all three metals. In the high-temperature range for iron (> 680 K) and nickel (> 993 K) as well as for the entire temperature range studied for tin, the transport of Cl2₂(g) through the gas film boundary layer to the surface of the sample controlled the rates for the experimental conditions in the present work. The transport of NiCl₂(g) controlled the rate of the Ni-Cl₂ reaction at lower temperatures. The rate of the Fe-Cl₂ reaction at lower temperatures is controlled by a slow surface reaction between Cl₂(g) and FeCl₂(s) which covers the surface of the iron. The overall activation energy for the formation of the activated complex (FeCl₃)₂‡ is 23 kcal/g-atom Fe.     

Use of the bromley equation for the analysis of ionic equilibria in mixed ferric and ferrous chloride solutions at 25 °C

The ionic equilibria in the mixed ferric and ferrous chloride solution were analyzed by considering the complex formation reactions as well as the mass and charge balance equations. The activity coefficients of the ions were calculated using the Bromley equation. The equilibrium constants for the formation of ferrous complexes were determined from the reported thermodynamic data. The interaction parameters of the ferric species were estimated from the reported values of FeCl₃ in an HCl solution. By applying the ionic equilibria, the speciation of the ferric and ferrous species with the composition was obtained. The predicted pH values of the FeCl₃-FeCl₂-HCl-H₂O system agreed well with the measured values at 25 °C in the ionic strength range of up to 9.34 m.     

Kinetics of chloridization of nickel-bearing lateritic iron ore by hydrogen chloride gas

The selective chloridization of nickel in a lateritic iron ore by gaseous HCl is based on the principle of relative thermal stability of iron and nickel chlorides. This aspect has been discussed with differential thermal analysis (DTA) and thermogravimetric (TG) data of the hydrated chlorides of iron and nickel. The kinetics of chloridization of nickel in a lateritic nickel ore from Orissa, India, have been studied by using both pure HCl (g) and the HCl (g) + N₂ mixture. The sharp decrease in the rate of chloridization of nickel at temperatures above 250 °C is attributed to the rapid decomposition of molten ferric chloride hydrate (FeCl₃ · 3H₂O), which blocks the pores of the reactant solid. Therefore, kinetics of chloridization follow both the pore-blocking model (logarithmic rate law) and diffusion-controlled mechanisms. Very low values of apparent activation energy and effective diffusivity derived from the rate constants of the diffusion-controlled process suggest that diffusion of HCl (g) takes place either in a dissolved state in the molten ferric chloride (at 100 °C to 150 °C) or through cracks and fissures formed on the surface due to rapid decomposition of ferric chloride at 200 °C to 250 °C. Because of the complexity of the reaction system, the rate of chloridization of nickel is almost independent of grain size.     

Upgrading Titanium Ore Through Selective Chlorination Using Calcium Chloride

To develop a simple and effective process for upgrading low-grade titanium ore (ilmenite, mainly FeTiO₃), a new selective chlorination process based on the use of calcium chloride (CaCl₂) as the chlorine source was investigated in this study. Titanium ore and a titanium ore/CaCl₂ mixture were placed in two separate crucibles inside a gas-tight quartz tube that was then positioned in a horizontal furnace. In the experiments, the titanium ore in the two crucibles reacted with either HCl produced from CaCl₂ or CaCl₂ itself at 1100 K (827 °C), leading to the selective removal of the iron present in the titanium ore as iron chlorides [FeCl _x (l,g) (x = 2, 3)]. Various kinds of titanium ores produced in different countries were used as feedstock, and the influence of the particle size and atmosphere on the selective chlorination was investigated. Under certain conditions, titanium dioxide (TiO₂) with purity of about 97 pct was directly obtained in a single step from titanium ore containing 51 pct TiO₂. Thus, selective chlorination is a feasible method for producing high purity titanium dioxide from low-grade titanium ore.     

Selection of the Optimum Electrolysis Bath Composition for the Synthesis of Holmium–Iron Triad Metal Intermetallics

The results of high-temperature electrochemical synthesis of holmium–iron triad metal intermetallics in chloride melts are presented. The influence of the current density, the composition of an electrolysis bath, and the synthesis time on the electrolysis processes and the composition of the end product is studied. The electrolysis of the molten KCl–NaCl mixture containing 0.5–2.5 mol % holmium trichloride and 0.1–2.5 mol % nickel (cobalt) dichloride at a current density of 0.5–2.0 A/cm², a temperature of 973–1073 K, and an electrolysis time of 30–90 min is shown to cause the formation of a cathode deposit in the form of a “metal–salt pear” on a tungsten electrode. This pear consists of a mixture of metallic nickel (cobalt) and HoNi, HoNi₅, and HoNi₃ (HoCo₂, HoCo₃, HoCo₅, Ho₂Co₁₇) intermetallics. The intermetallic compound content in the cathode deposit is found to increase at a constant current density (1.2 A/cm²) and when the holmium chloride content in a melt or the ratio of the holmium chloride concentration to the nickel (cobalt) chloride concentration increases. Only a mixture of holmium–nickel (cobalt) intermetallics can exist in the cathode deposit if the electrolysis bath composition and the electrolysis parameters are controlled. The electrochemical synthesis of holmium–iron intermetallics was performed under galvanostatic conditions in molten KCl–NaCl–HoCl₃. Iron ions are introduced in a melt via the anodic dissolution of metallic iron. The results of X-ray diffraction analysis of the electrolysis products demonstrate the fundamental possibility of synthesizing holmium–iron intermetallics. The optimum conditions of electrosynthesis of holmium–iron triad metal intermetallics are determined.