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Roasting reduction kinetics of an Indonesian nickeliferous laterite ore
Abstract
In this work, the kinetics of roasting reduction of an Indonesian nickeliferous laterite ore, both in the form of ore and pellets, with a gaseous reducing mixture -CO:N 2 -, is examined. It is deduced that reduction degree of the ore, in-creases within the first 20 and 60 minutes of re-duction in the case of ore and pellets respec-tively, and then it tends to equilibrium, for all temperatures examined. Maximum reduction degree achieved was approximately 45% at 900 0 C for both ore and pellets. The diffusion controlled mechanism clearly prevails for the reduction of ore, as verified by the low activa-tion energy values, the study of selected reduced sample by SEM-EDS and the negligible effect of temperature on the progress of the reduction. On the contrary, the procedure is chemically controlled up to the first 20 minutes regarding the reduction of pellets. After this time, diffu-sion controlled mechanism prevails, till equilib-rium is attained. The predominant effect of the specific surface area and porosity of the laterite ore on its reducibility is verified.
... Zevgolis y colaboradores en Grecia, en la Universidad Técnica Nacional de Atenas, desarrollaron varios trabajos enfocados en el estudio del comportamiento de lateritas niquelíferas locales y describen algunos mecanismos de reducción que se presentan en el proceso en el calcinador rotatorio (Zevgolis, Zografidis, & Halikia, 2010). Estos autores determinan algunas variables relevantes como el tamaño de partícula, la composición del agente reductor, entre otras y definen diferentes parámetros y características para este tipo de minerales (Zevgolis, Zografidis, Halikia, & Perraki, 2009). ...
... Zevgolis y colaboradores en Grecia, en la Universidad Técnica Nacional de Atenas, desarrollaron varios trabajos enfocados en el estudio del comportamiento de lateritas niquelíferas locales y describen algunos mecanismos de reducción que se presentan en el proceso en el calcinador rotatorio (Zevgolis, Zografidis, & Halikia, 2010). Estos autores determinan algunas variables relevantes como el tamaño de partícula, la composición del agente reductor, entre otras y definen diferentes parámetros y características para este tipo de minerales (Zevgolis, Zografidis, Halikia, & Perraki, 2009). ...
In the present work, a reduction roasting experimental study of Greek nickeliferous laterite samples with a gaseous reducing mixture - CO:N2- is presented. The effect of parameters such as temperature, ore grain size, and composition of the reducing mixture were examined. It is deduced that the reducibility of intermediate type laterite sample, where iron appears mainly in the form of goethite (a-FeOOH), is considerably higher than that of limonitic type laterite samples, where hematite (a-Fe2O3) is the predominant iron mineral phase. The degree of reduction of the limonitic type laterite samples does not exceed 50%, while it reaches 95% in the case of the intermediate-type laterite sample under the same experimental conditions. Increasing the temperature in the range 750-900°C does not considerably favor the reduction of the limonitic type laterites, whereas decrease of ore grain size of the limonitic-type ore samples and more intense reducing conditions increase the reduction. The considerably higher specific surface area values of the intermediate laterite samples, diminishes the effect of the ore grain size and this can be regarded as the critical parameter leading to the higher reducibility of this ore.
Energy required for roasting and smelting of a nickeliferous laterite ore by the rotary kiln -electric furnace process is investigated. From this work it comes that thermal energy is about 65% of the total energy needed and the rest is electrical. Also, 61.3% of thermal energy input in the roasting step (of all combustibles fed into the rotary kilns) is used for pre - heating, 11.6% for pre - reduction and the rest (27.1%) corresponds to the energy of the remaining carbon in the rotary kiln products (i.e., calcine, dust and coatings). Carbon entering the system is used as follows: 57.9% for combustion, 37.1% for reduction and the rest (5.0%) remains unburnt. Exploitation of energy from gases of both furnaces, as well as the higher possible reduction degree, the optimum temperature of the calcine and also elimination of the excess air in the rotary kilns, improve significantly energy balance and economics of the process.
In the present study, the reductive behavior of nickeliferous dust from rotary kilns, during Greek laterite treatment in ferronickel production is investigated. The study concerns dust of various origins, i.e. washing towers, electrostatic filters and polycyclones. Laboratory made pellets from these dusts were also examined. Reducibility was studied in the temperature range of 700°C to 850°C in a laboratory tube furnace. Experimental results showed that the reduction degree reaches maximum values of 28% and 26% percentage for dusts and pellets respectively within the first twenty minutes of the process, and then reaction tends to equilibrium for all cases examined. The rate of reduction increases significantly during the first ten minutes of reaction and then it becomes lower until it diminishes to zero after twenty minutes of roasting. Temperature favors the reduction process, the reduction percentage being increased as a function of temperature up to about 800°C. Rates and reduction degrees are higher for the dusts than for the corresponding pellets, for all experimental conditions examined. Kinetic analysis of the results showed that at low temperature values the mixed kinetic model verifies the experimental results of dust and pellet samples. At higher temperatures (800°C and 850°C), diffusion becomes the rate determining step. The change in the controlling mechanism is attributed to the formation of silicate compounds around the grains as temperature rises. The calculated activation energy values verify the above mentioned results.
for wastes from iron and steel mills. These wastes consist of slags, dusts and sludges, mill scales, spent pickle liquor, and other iron-bearing materials. Accurate determination of metallic iron in these wastes will provide the vital information for the recycling or reuse of these wastes. The new procedure for the determination of metallic iron (Fe0) was developed and various factors that could affect the test result were determined. Pure metallic iron powders were mixed with pure iron oxides with various ratios and then were tested using this method. Testing results had excellent agreement with actual concentration. Samples from several sites have been tested.
The reduction behaviour of hematite compacts by H-2-CO gas mixtures was investigated at 1073-1223 K. The total porosity, pore size distribution and surface area of the compact was measured using mercury pressure porosimeter, The reduction tests were carried out using Cahn balance. The reduction behaviour could not be described in terms of a single rate-determining step; the reduction process was initially controlled by the chemical reaction at the oxide/iron interface, controlled by the intraparticle diffusion through the reduced layer towards the end of reduction, and the mixed control, in between. Over the whole range, the reduction rate decreased with CO content in the gas mixture. The chemical reaction rate constants were two to three times higher for H-2 reduction than those of CO reduction, and the effective diffusivities of H-2 reduction were three to four times higher than those of CO reduction. Values of activation energy for chemical reaction were found to be 19.8-42.1 kJ/mol depending on the gas compositions; 100% CO showing the lowest.
A simple mathematical model is proposed for the reduction of hematite pellets in a counter-current moving bed shaft reactor under non-isothermal conditions. Oxygen removal is assumed to be controlled at the iron-Wustite interface with transport occurring through the other oxide layers and reduced iron shell. Hydrogen, carbon monoxide and mixtures of the two gases are employed for reduction in small quantities of the product gases, water vapor and carbon dioxide. A parametric study of the effect of reactor length, gas and solid flow rates, inlet gas temperature and inlet gas composition on the reduction has been undertaken. Solid flow rate and solid inlet temperature were found to be the most important parameters influencing the reduction.
In this heterogeneous multi-reaction system, kinetic steps in each group of heat transfer, mass transfer and chemical reactions are investigated first to identify the slowest step based on a validated mathematical model of 19 independent equation.2, 3) They are conductive heat transfer, convective mass transfer and carbon gasification by CO2 and H2O. The overall reaction of metallization of iron ore by coal with heat supplied by an external source is largely limited by the conduction of heat though the sponge iron shell of an ore/coal composite.
The present work is a fundamental study of reduction in mixtures of iron ore concentrate and pulverized coal by indirect heating. Cylindrical steel crucibles, 118 mm i.d. and 150 mm height, with full-load of mixtures were placed in a muffle furnace which was controlled to be at a constant temperature of 1 200-degrees-C for predetermined times of reaction. The profile of temperature and degree of reduction, and distribution of residual carbon were measured by embedded tiny thermocouples during the course of reaction and sampling and chemical analysis of reacted solids. It has been found that reducing gas generated in higher temperature regions by devolatilization and Boudouard reaction plays a role in convective heat transfer and indirect reduction for benefits of interior regions. The likely rate-controlling step of the overall reaction is considered to be heat transfer.
Experimental measurements of the rate of reduction of particles of Carol Lake and Kiruna ores have been made using pure hydrogen and pure carbon monoxide and mixtures of these two gases. The temperature range covered was 773–1143 K and throughout this range the reduction rate with hydrogen was greater than that with carbon monoxide. A retracting core model was found to best fit the experimental data even when granules of 9 × 10−4 m diameter were used. Reduction with gas mixtures of hydrogen and carbon monoxide give rates intermediate between those of the pure gases.
Thermogravimetric analysis (TGA) of the reduction of Fe2O3 in a continuous stream of 100% CO was conducted at temperatures ranging from 800 to 900 °C. X-ray diffraction analysis of solids identified the presence of iron, graphite and a carbide of iron as the products of reactions. A kinetic model based on the first-order irreversible rate kinetics was developed and fitted to the TGA data so as to estimate the rate constants for each reduction reaction. The reaction pathways considered in this analysis involved reduction of iron oxides, Boudouard reaction and iron-carbide formation. The rate parameters were calculated and compared with data reported in literature.
This study deals with the reduction of Fe2O3 by H2 in the temperature range of 220–680 °C. It aims to examine the rate controlling processes of Fe2O3 reduction by H2 in the widest and lowest possible temperature range. This is to be related with efforts to decrease the emission of CO2 in the atmosphere thus decreasing its green house effect.Reduction of hematite to magnetite with H2 is characterized by an apparent activation energy ‘Ea’ of 76 kJ/mol. Ea of the reduction of magnetite to iron is 88 and 39 kJ/mol for temperatures lower and higher than 420 °C, respectively. Mathematical modeling of experimental data suggests that the reaction rate is controlled by two- and three-dimensional growth of nuclei and by phase boundary reaction at temperatures lower and higher than 420 °C, respectively.Morphological study confirms the formation of compact iron layer generated during the reduction of Fe2O3 by H2 at temperatures higher than 420 °C. It also shows the absence of such layer in case of using CO. It seems that the annealing of magnetite's defects around 420 °C is responsible for the decrease of Ea.The rate of reduction of iron oxide with hydrogen is systematically higher than that obtained by CO.
Reduction of iron ore lumps by coal and carbon monoxide was investigated under a variety of temperature-time schedules. The rate law has been established using isothermal experiments in the range 800–1000 °C. Non-isothermal experiments were carried out with constant and variable heating rates using large samples. Some additional experiments have been carried out under fluctuating temperature conditions. It is shown that non-isothermal kinetic data can easily be analysed to obtain values of kinetic parameters even when the rate of heating is not constant. The course of a reaction under any temperature-time schedule can be predicted provided the kinetic parameters are first evaluated through some test runs.
Reductive Roasting of Iron-Nickel Ore Using Greek Lignite Thermodynamic and Kinetic Approach, ed. NTUA, In honor of Professor Emeritus of NTUA A
- I Halikia
- P Neou-Syngouna
- M Katapotis
Halikia, I., P. Neou-Syngouna and M. Katapotis, 1998.
Reductive Roasting of Iron-Nickel Ore Using Greek
Lignite Thermodynamic and Kinetic Approach, ed.
NTUA, In honor of Professor Emeritus of NTUA A.Z.
Fragiskos, Athens, (Greek Text).
Test Method for Total Iron in Iron Ores by Stannous Chloride Reduction and Dichromate Titration
- Astm Standard
ASTM Standard E277, 1988. Test Method for Total Iron
in Iron Ores by Stannous Chloride Reduction and Dichromate Titration.