Papers by Keyword: Chromite

Abstract: Nature has blessed Pakistan with abundant reserves of various ores/minerals. Among these; ores of Chromium, Manganese and Silicon like; Chromite, Manganite, Hausmannite, Braunite and Quartz are phenomenal in metallurgical perspective particularly for ferroalloys production, metals extraction and steel making industry. Unfortunately, Pakistan has been unable to realize the potential associated with these natural assets and therefore adequate mining, ore-beneficiation and value-additive measures are still missing. This paper briefly describes the locations, size and concentration of aforementioned ore/minerals in the country, local and international market trends, potential associated with value-addition of these raw materials and emphasizes the crucial and strategic need for the establishment of a ferroalloy production facility in the country.

Abstract: This study was conducted to determine the non-isothermal and isothermal reduction of chromium ores in the solid-state by reductants like solid carbon under argon and hydrogen-argon atmosphere. Two different chromite ores from local sources , sandy chromite ore from Opol, Misamis Oriental (SCO) and lumpy chromite ore from Manticao, Misamis Oriental (LCM) were used in the study. Isothermal and non-isothermal experiments were conducted in a fixed bed reactor heated in a vertical tube furnace in the temperature range 800 to 1000°C. Raw chromite and reduced samples were subjected to phase analysis and morphology characterization using X-ray flourescence (XRF), X-ray diffraction (XRD), and energy dispersive x-ray spectroscopy (EDX). It was found that reduction does not go to completion at this temperature range. The early stage of reduction of iron was controlled by nucleation and the later by nucleation or chemical reaction or both. The activation energy at the early stage of reduction is estimated to be 44.76 kJ/mol and the later stage of reduction is 144 kJ/mol for SCO and 76.5 kJ/mol for LCM. The reduction of chromium was controlled by chemical reaction.

Abstract: Chromite and laterite ores from local sources were smelted in a vertical tube furnace with activated carbon as reducing agent at 1400°C to 1550°C using graphite crucible under argon atmosphere. It is shown that the grade and composition of the ore are the main factors determining the feasibility of smelting a mixture of chromite and laterite ores to produce a Fe-Ni-Cr crude alloy. The high recovery of iron and nickel in the alloy indicates the highly reducing condition prevailing in the smelting reduction experiments. It is also shown that the solubility of Ni in the slag increases with Ni concentration in the alloy and the FeO concentration in the slag. The chromium content of the slag increases with increasing iron content of the slag.

Abstract: Utilizing Pakistan chromite as raw material, the rapid leaching of chromium and iron could be realized by the sulfuric acid leaching process on the condition of atmospheric pressure and the addition of oxidant A. And the leaching rate of chromium and iron would be 98.5% and 71.9%, respectively. The sulfuric acid leaching processes with different temperature were systematically studied by chemical analysis and phase analysis. The results showed that, with the increase of reaction temperature, the leaching rate of chromium would increase gradually, but the leaching rate of iron increased at first and then decreases and reached its maximum at 140°C. When the temperature > 160°C, the phases of the leaching residue were magnesium iron silicate and a few of silica, no chromohercynite, chrompicotite and magnesioferrite existed in the chromite. The leaching solution of sulfuric acid leaching process could be used for preparing the basic chrome sulfate, and there is no Cr⁶⁺ in the leaching residue and solution. The results would provide theoretical guidance for solving environmental pollution problem of Cr⁶⁺ in traditional chromate production process.

Abstract: The boundary constants between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were calculated in order to clarify the formation mechanism of fayalite scale (Fe₂SiO₄) or chromite scale (FeCr₂O₄), which can form as a “sub-scale” in Si or Cr containing steels. The diffusion coefficient of oxygen in the alloy, Do, and the oxygen concentration at the specimen surface, N_O^(s), which are constituents of the internal oxidation rate constant, (2D_ON_O^(s)/N_B^(O)n), were calculated for various oxidation conditions, and the rate equation for internal oxidation was derived. By comparing the calculated and measured values of (2D_ON_O^(s)/N_B^(O)n), we confirmed that the rate equation determined for internal oxidation was reasonable. The boundary condition between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were also calculated by substituting the calculated values of D_O and N_O^(s) into the rate equation.

Abstract: In this article, Turkish chromite concentrate was reduced with metallurgical coke at temperature between 1000-1500 °C with variables reducing times. The reduction mechanism and the microstructure of the reduced chromite were investigated. There were closer relationships between the reduction of chromite and the sample morphology, such as, the surface area and the porosities and cracks of the particle have positive effect on the metallization of iron and chromium oxides. The reduction of the iron chromite spinel started at 1000 °C, but picrochromite started to reduce at temperature around 1300 °C. At lower temperature, the formation of iron carbide phases was affected on the formation of ferro alloy and accelerates the reduction of chromium. The formation of carbon monoxide was also affected on the reduction of chromite spinel, especially around imperfections of grain where porosity, cracks and fractures act as diffusion channel for the reducing gas. For the charecterisation of the reaction products, X-ray diffraction techniques, SEM and EDAX were used.

Abstract: Transition-metal spinels are efficient catalysts in a number of heterogeneous processes, such as CO oxidation, catalytic combustion of hydrocarbons and oxychlorination of methane. The properties of catalytic materials are highly dependent on the synthesis route. Spinels are often produced at high temperatures by the calcination of precursors such as powder mixtures, slurries or resins. Combustion synthesis is a cost-efficient method used to produce homogeneous and fine particles with high reproducibility. Cu0.8Ni0.2Cr2O4 spinel was obtained by the combustion of metallic nitrates using urea as fuel. The resulting powders were calcinated at different temperatures and characterized by thermogravimetric and particle size analyses, X ray diffraction, and scanning electron microscopy. The effect of urea on the control of the process and particle morphology was investigated. The results revealed the formation of porous powders with increasing crystallinity as the calcination temperature increased. Crystallization of spinel started at 700 oC.