Kamala Kanta Sahu

Dependence on cation distribution of particle size, lattice parameter, and magnetic properties in nanosize Mn–Zn ferrite

In Mn1−xZnxFe2O4 (x=0 to 1) nanosize particles prepared through hydrothermal precipitation we observe a decrease in particle size from 13 to 4 nm with increasing Zn concentration from 0 to 1. The lattice constant, a, for all Mn/Zn concentrations is found to be less than that for the corresponding bulk values. At specific compositions within x=0.35 and 0.5, the temperature dependence of the magnetization exhibits a cusp-like behavior below the temperature at which the nanoparticles undergo a ferri- to para-magnetic transition (Tc). The Curie temperatures, Tc, of the nanoparticles are in the range of 175–500u200a°C, which are much higher than their corresponding bulk values. To explain these unusual features, the strong preferential occupancy of cations in chemically inequivalent A and B sites and the metastable cation distribution in nanoparticles are invoked.

PREPARATION AND CHARACTERIZATION OF NANOSIZE MN-ZN FERRITE

Abstract Synthesis of nanosize (9–12xa0nm) Mn 0.65 Zn 0.35 Fe 2 O 4 particles from metal chloride solution through a hydrothermal precipitation route using aqueous ammonia, and their characterization by XRD, TEM and VSM are reported. Chloride ion concentration in the solution and the pH of precipitation are shown to play a crucial role in retaining the initial stoichiometry of the solution in the nanoparticles. While at lower pH, precipitation of Mn was incomplete, higher pH of precipitation led to Zn loss in the particles. The optimum pH for stoichiometric precipitation was found to lie around 10. The coercive force, H c and the transition temperature, T c (from ferrimagnetic to paramagnetic state) were high as compared to reported bulk values and confirm the nanosize nature of the particles. The M versus T curve, instead of showing a monotonic drop of magnetization, showed a cusp before T c . This cusp-like feature is shown to arise due to an irreversible phase transition involving cationic redistribution in the unit cell of the nanoparticles.

Appearance of superparamagnetism on heating nanosize Mn0.65Zn0.35Fe2O4

Nanosize particles (average size ∼12 nm) of mixed ferrite Mn0.65Zn0.35Fe2O4 were prepared by the hydrothermal precipitation route and studied using x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, magnetization measurements, and Mossbauer spectroscopy. The as-prepared sample was largely ferrimagnetic and, as the sample was annealed at temperatures above 250u2009°C, it gradually became superparamagnetic. This unexpected behavior is explained by assuming that the cation distribution in the nanosize as-prepared sample is in a metastable state and, as the sample is heated, this distribution changes to a more stable state while the grain size remains nearly the same.

An overview on the production of pigment grade titania from titania-rich slag

To recover pigment grade TiO2, operating plants all over the world use chemical processes. Slag-based technology is considered to be attractive because of low waste generation and low chemical cost due to high titanium content and is poised to replace the conventional technology. This paper provides a review of the slag-based technology with the specific aim to produce leachable slag and achieving high titania yield from recovered wastes. Leachable oxides of the lower oxidation state, such as TiO and Ti2O3, facilitate the leaching process. However, during smelting these oxides increase the viscosity of the slag. Formation of titanium carbide or carbonitride is also not desirable as it leads to resistance to the leaching of titanium. This report highlights the problems and their possible solutions to obtain leachable slag.

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.

Nickel recovery from spent nickel catalyst.

A process for nickel recovery from a spent catalyst of definite composition has been developed using the hydro-metallurgical route. The processing steps includes direct sulphuric acid leaching followed by separation of iron as well as silica and other impurities. For a 152 μm particle size catalyst, extraction of about 98% nickel was achieved at 363 K in 2 h using a sulphuric acid concentration (v/v) of 8% and a pulp density of 10%. The dissolution of nickel followed diffusion-controlled leaching kinetics. Increase in temperature and sulphuric acid concentration resulted in increase in the nickel recovery. The activation energy for nickel dissolution was calculated to be 62.8 kJ mol-1. Finally, nickel was recovered as value-added products such as sulphide and oxalate with overall recovery of 90 and 88% of nickel, respectively.

Recent trends and current practices for secondary processing of zinc and lead. Part I: lead recovery from secondary sources.

Implementation of stricter environmental laws and economic reasons has forced all the metallurgical industries to go for eco-friendly technologies to produce metal and other related products. However, generation of wastes is an integral part of metallurgical industries. If the wastes/residues are hazardous in nature, they generally have to be treated or/and disposed of in safe and designated dumping sites. If these wastes/residues are non-hazardous in nature, then they may be suitable for use as secondary raw material to recover metals such as lead, copper etc., which are in growing demand all over the world. The processing of lead secondaries is important because of their relative high metal content, as well as the low energy and cost involved in recovering the metal. This paper mainly focuses on the current practices and recent trends in the secondary processing of lead. Various processes, particularly hydrometallurgical ones, already developed or in the development stages, are discussed. Attempts made by various Council of Scientific and Industrial Research (CSIR) Laboratories including the National Metallurgical Laboratory (NML) and industries such as Binani Zinc to develop eco-friendly processes for the recovery of lead from secondary raw materials are also described.

Adsorption Kinetics for the Removal of Co(II) and Zn(II) from Wastewater by Indion BSR — A Chelating Ion-Exchange Resin

A comparative study on the adsorption of zinc(II) and cobalt(II) from aqueous solutions onto Indion BSR, an indigenous cation-exchange resin, was undertaken in the present work. Various parameters for the removal of Co(II) and Zn(II) such as the initial solution pH, contact time, resin and metal ion concentration were optimized. The equilibrium data obtained were well fitted by both the Langmuir adsorption isotherm at pH 6.0 for 500 mg resin and the Freundlich adsorption isotherm under optimum conditions of contact time and pH 5.0 for 250 mg resin at 30°C. The adsorption of Zn(II) and Co(II) on this cation-exchange resin followed first-order reaction kinetics. Film diffusion of Co(II) and Zn(II) in this ion-exchange resin was shown to be the main rate-limiting step over the concentration range studied. The studies showed that the resin could be used as an efficient adsorbent for the removal of Co(II) and Zn(II) from aqueous solutions.