R.P. Das

Extraction studies of cobalt (II) and nickel (II) from chloride solutions using Na-Cyanex 272. Separation of Co(II)/Ni(II) by the sodium salts of D2EHPA, PC88A and Cyanex 272 and their mixtures

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.

Hydrothermal preparation and characterization of boehmites

Boehmites (Al2O3·xH2O, 1<x<1.5) have been prepared hydrothermally from Al(NO3)3·9H2O and urea. Effect of temperature on preparation was studied in the range of 160°–220°C. No precipitation of boehmite was observed until the attainment of ∼160°C at which temperature a partly amorphous gel started precipitating. With the increase in temperature, transformation of the amorphous precipitate into crystalline boehmites took place as indicated by the X-ray diffraction (XRD) patterns. From the weight loss studies of the samples prepared at different temperatures and for different reaction time intervals, the value of x was estimated to vary between 1.3 and 1.5. The Fourier transform infrared (FTIR) spectra of samples obtained at 180°, 200° or 220°C showed 25–40 cm−1 upward shift in the –OH stretching and bending vibrations assigned to boehmites. γ-Alumina obtained by subsequent calcination of boehmite at 725°C was also characterized by XRD.

Effect of preparation conditions on formation of nanophase Ni-Zn ferrites through hydrothermal technique

Abstract Nanophase Ni 1− x Zn x Fe 2 O 4 ( x = 0 , 0.5, 1.0) samples were prepared by chemically precipitating hydroxides followed by hydrothermal processing. The products were characterized by X-ray diffraction and Mossbauer spectroscopy. Ferrite formation was found to be quite sensitive to the procedures adopted for preparing the hydroxide slurry prior to hydrothermal treatment. Nickel ferrite could be prepared in pure phase by co-precipitation as well as by mixing separately precipitated hydroxides. However, Ni 0.5 Zn 0.5 Fe 2 O 4 could only be prepared by co-precipitation. Leaving small amount of sodium in the slurry seems to obstruct pure phase formation of Ni 0.5 Zn 0.5 Fe 2 O 4 and results in partial formation of α-Fe 2 O 3 . A similar effect is observed in zinc ferrite.

Microstructure-dependent coercivity in monodispersed hematite particles

Microstructure and magnetic properties of monodispersed pseudocubic and trapezoidal particles with varying sizes prepared through the hydrothermal precipitation route are reported. The coercivity for trapezoidal particles was similar to that of reported values. For pseudocubic particles, however, the coercivity is unusually high (∼6 kOe) as compared to the maximum value (3 kOe) reported in the literature. Detailed microstructural analysis revealed that particles with a well-defined shape are, in fact, polycrystalline. The high coercivity and its variation with particle shape and size are correlated to the internal nanostructure of the particles.

Leaching of manganese nodules in ammoniacal medium using glucose as reductant

Polymetallic Indian Ocean nodules can be leached in ammoniacal solution in the presence of glucose. The various parameters chosen for leaching studies were: amount of glucose, time, pH, temperature, concentrations of ammonia and ammonium salt, and particle size. The percentage extraction of copper, nickel and cobalt decreases when the glucose concentration is increased to more than 0.4 gramme per gramme of nodule at 338 K and 0.2 g/g at 358 K. The dissolution of copper has been found to be dependent more on the pH of the solution than on the total molarity of ammonia and the ammonium ion. Leaching temperatures above 373 K are disadvantageous for the extraction of copper and cobalt, whereas nickel extraction is about 95% even at 433 K. The rate of leaching for all three metals is independent of the particle size in the range studied. All the copper, about 90% of the nickel and 60% of the cobalt can be extracted under the following leaching conditions: temperature 358 K, time 4 h, initial ammonia concentration 2.5 M, ammonium chloride concentration 0.37 M and glucose 0.2 gramme per gramme of nodule.

Leaching of metals from Indian ocean nodules in SO2-H2O-H2SO4-(NH4)2SO4 medium

Abstract Studies have been carried out for extraction of Cu, Ni, Co, Zn and Mn with simultaneous avoidance of iron dissolution during leaching of manganese nodules in an aqueous SO2–H2SO4–(NH4)2SO4 system. The leaching parameters such as sulphuric acid concentration, ammonium sulphate concentration, time and pulp density were varied to study their effect on extraction of metals and precipitation of iron. It was observed that the presence of both sulphuric acid and SO2 was required for maximum recovery of Cu, Ni, Co, Zn and Mn. The iron in solution decreased with increase in ammonium sulphate concentration. The optimum conditions established for maximum metal extractions were: pulp density 20%, time 3 h, temperature 363 K, SO2 60 g l−1, sulphuric acid 3.0% (v/v) and ammonium sulphate 100 g l−1. Under these conditions the recoveries from a typical nodule sample were: 88.5% Cu, 99.8% Ni, 91.8% Co, 97.8% Zn, 99.6% Mn with iron extraction of 2.4%. Nodules containing different percentage of metal contents were also tested under the established conditions and it was observed that the dissolution of iron varied between 2.4 and 4.9% with no significant variations in recoveries of Cu, Ni, Co, Zn and Mn.

Leaching of manganese nodules at elevated temperature and pressure in the presence of oxygen

Abstract Indian Ocean polymetallic nodules were leached with dilute sulphuric acid at elevated temperature and pressure in the presence of oxygen. Conditions were established for treating the nodules for the extraction of three metals, i.e. copper, nickel and cobalt, with minimum iron and manganese contamination of the leach solution. By leaching the nodules for 4 h at 423 K using 0.46 g of H 2 SO 4 per g of nodule and keeping the oxygen partial pressure at 0.55 MPs, almost all the copper and nickel and 88% of the cobalt could be extracted. Under these leaching conditions 28% manganese and 5.7% iron were also leached. To achieve the extraction of four metals, i.e. copper, nickel, cobalt and manganese, charcoal was used as the reductant for reducing the manganese dioxide and rendering it soluble as manganese sulphate. The extraction of copper, nickel, cobalt and manganese were 77, 99.8, 88 and 99.8% respectively under the following leaching conditions: time 4 h, temperature 423 K, H 2 SO 4 0.66 g of nodule and oxygen partial pressure 0.55 MPa. The studies showed that the conditions employed for leaching copper, nickel and cobalt could be extended to the extraction of manganese too, simply by increasing the acid concentration from 0.46 g to 0.66 g per g of nodule and with the addition of 0.05 g of charcoal per g of nodule to the initial slurry.

Reduction-roasting and ferric chloride leaching of copper converter slag for extracting copper, nickel and cobalt values

Abstract In a previous investigation the optimum conditions for recovering copper, nickel and cobalt from converter slag through ferric chloride leaching have been described. The study of various parameters revealed that nickel and cobalt recovery could not be improved beyond 24 to 26% respectively from converter slag, though more than 90% of the copper could be extracted. Further attempts were made to bring the metal values completely into solution through reduction-roasting followed by ferric chloride leaching of the slag. The present work comprises a study of various experimental conditions such as concentration of ferric chloride, duration of leaching, duration of reduction-roasting, temperature and nature of reducing agent, to arrive at the optimal recovery of the metal. Under identical experimental conditions a decrease in copper recovery, but an increase in nickel and cobalt recovery has been observed above a roasting temperature of 750°C. The decrease in copper recovery has been attributed to copper ferrite formation which has been confirmed both by leaching experiments with synthetic mixtures and by X-ray diffraction studies with both slag samples and synthetic mixtures. Recovery of nickel has also shown little decline when solid reductants were used above 850°C whereas cobalt recovery remains nearly the same even above 850°C. Under optimum conditions 80% copper, 95% nickel and 80% cobalt could be recovered by reducing the slag at 850°C with 10 wt % furnace oil, followed by leaching with ferric chloride.

Jarosites: A Review

Abstract Jarosites are known to be potential compounds for the Fe(III), SO4 2− and impurities control in hydrometallurgical processes. Due to inherent association of Na, K, Fe, Al with the oxidic and sulphidic ores, these metal ions dissolve during sulphuric acid leaching and subsequently reprecipitate as varieties of ferric hydroxysulphates. The formation of jarosites is favoured in the temperature range of 80- 100°C and pH 200°C. In this paper, various aspects related to jarosites are briefly reviewed emphasising mineralogy, structure, precipitation, formation at elevated temperatures, stability and utilization.

Effect of anions during hydrothermal preparation of boehmites

Boehmites were precipitated hydrothermally from different inorganic aluminum salt solutions under similar conditions using urea as the precipitating agent. It was observed that the hydrolysis of Al2ŽSO4.3starts at a lower temperature due to formation of hydroxy sulfates in comparison to AlCl3and AlŽNO3.3 solutions. The boehmite obtained from Al2ŽSO4.3 has a lower water content, and a higher surface area than the boehmites obtained either from AlCl3or AlŽNO3.3. The boehmite obtained from Al2ŽSO4.3was lighter giving lower tap density value. Depending on the nature of anion present during synthesis, the TG-DTA showed the endothermic peak between 460 and 480 8C, characteristic of transformation of boehmite to g-Al2O3. No other phase transformation occurred up to 1000 8C, indicating enhanced thermal stability of g-Al2O3 prepared through the present hydrothermal route. q2002 Elsevier Science B.V. All rights reserved.