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By M. D. Gibbs, T. N. Smith, B. Verbaan

When heated in the absence of oxygen, pyrite from refractory gold concentrates decomposes endothermically to pyrrhotite, releasing sulphur. The decomposition starts at the particle surface and progresses inwards, leaving an adhering layer of porous pyrrhotite. Use of the conventional shrinking-core model implicitly assumes a negligible partial pressure of sulphur in the bed, but this pressure is in fact at least equal to the equilibrium vapour pressure of sulphur over pyrite, constituting the principal control of the rate of decomposition. Further experiments showed a decrease in reaction rate as the conversion increased. Both phenomena are attributed to the persistence of non-isothermal conditions in the fluidised bed during pyrolysis, caused by the endothermic nature of the reaction and the relatively slow rates of heat transfer to particles and vapour removal from the bed. Equipment must be developed to maximise these two parameters

Jun 19, 1905

By S. Chander, A. Briceno

The properties of surface films on pyrite have been studied through electrochemical techniques of cyclic voltammetry and AC impedance, measurements. The characteristics of the surface films depend on the conditions of oxidation and the source of pyrite. At potentials near 0.0 V, some pyrites have large values of polarization resistance, showing a certain degree of passivity. Some pyrites show more passivation than others, however. On oxidation, meta- stable phases of Fe(OH)2 and Fe(OH)3 form that transform to more stable phases on aging. The growth of surface films near the corrosion potential of pyrite follows a linear kinetics that is attributed to a chemical (or an electrochemical) reaction as the rate determining step. The surface film is considered to be a hydroxide or an oxide because it is hydrophilic. This study has also demonstrated that AC impedance ,measurements can be used to study the growth characteristics of films at mineral/solution interfaces.

Jan 1, 1988

By S. Chander

The formation of surface films on pyrite has been studied through electrochemical techniques of cyclic voltametry and AC impedance measurements. The characteristics of the surface films depend upon the conditions of oxidation and the source of pyrite. At potentials near 0.0 V, some pyrites have large values of polarization resistance showing a certain degree of passivity. Some pyrites show more passivation than the others, however. On oxidation, metastable phases of Fe(OH2) and Fe(OH3) form which transform to more stable 3 phases on aging. The growth of surface films near the corrosion potential of pyrite follows a linear kinetics which is attributed to a chemical (or an electrochemical) reaction as the rate determining step. The surface film is considered to be a hydroxide or an oxide rather than sulfur because the later is expected to be limited to a monolayer in alkaline solutions. This study has also demonstrated that AC impedance measurements can be used to study the growth characteristics of films at mineral/ solution interfaces.

Jan 1, 1987

By J. A. Arias

The oxidation kinetics of pyrite and refractory gold concentrates in acidified ferrous sulfate solutions in the presence of oxygen-sulfur dioxide gas mixtures has been studied. The effect of temperature, pulp density and gas composition were determined. The optimum oxidation rate was obtained at 80°C and 2 percent sulfur dioxide in the gas mixture. The oxidation of the sulfide minerals is attributed to the presence of ferric ions, which are continuously regenerated by the gas mixture. The objective of this study is to find a new hydrometallurgical method to render sulfidic refractory gold ores amenable to cyanization.

Jan 1, 1993

By Kenneth S. Coley, Michael Pomeroy, Elaine Chen

Recent work on modeling of BOF steelmaking is reviewed, highlighting the critical aspects of each approach. It is concluded that the most successful models should be based on a deep understanding of the mechanisms and kinetics of the critical reactions. The importance of the decarburization mechanism is discussed with particular reference to its role in droplet swelling or bloating which has a profound influence on the droplet residence time in the slag. Conditions which cause bloating are discussed and the rate determining step is proposed to be primarily nucleation of CO bubbles inside the metal droplet with some influence from growth by reaction at the bubble/metal interface. The discrepancy in the super-saturation ratio required for classical nucleation is discussed and an approach using a surface tension modifying parameter is illustrated. Finally, the role of CO nucleation in controlling the driving force for dephosphorization is discussed.

Jan 1, 2014

By Marcelo B. Mourão

An experimental investigation was carried out to -study the rates of reduction of pellets containing iron oxides by carbon dissolved in liquid iron, at temperatures ranging from 1720 K to 1973 K. Several different pellet types were employed; the materials used in the pellet's manufacture were pure hematite, two kinds of commercial iron ores, and mixtures hematite/silica and hematite/lime: Reaction times were determined employing the constant volume pressure increase technique (CVPI). It has been observed that the reaction rate increases as the temperature and the pellet's specific surface area increases. The reaction rate is also affected by the oxide type: pellets made from commercial ores or from mixtures hematite/silica or hematite/lime show reaction rates lower than those made from pure hematite.

Jan 1, 1996

Kinetics of Reclamation of E-Waste by a Bioleaching Route

Sep 13, 2010

By Lawson F

The Australasian Institute of Mining and Metallurgy is a society of engineers and scientists formed in 1893 (incorporated by Royal Charter in 1955) to advance science and engineering in the mineral industries, and to facilitate the exchange of information and ideas to enhance the professional excellence of its members. The Institute has several grades of members. The professional members are linked with Student and Company Members, as well as an Affiliate grade covering other professionals and non-professionals with experience in the mineral industry. The diverse group covers all sections of the mineral industry, from exploration through production to marketing of minerals and petroleum. Corporate (professional) membership also covers science and engineering professionals from specialisms other than the "traditional" ones in geosciences, mining and petroleum engineering and metallurgy. The Institute has Branches throughout Australia, New Zealand, Papua New Guinea and Oceania, whose activities complement the corporate occasions arranged for the benefit of all members by Headquarters in Melbourne. Members are drawn from all sections of the industry - private enterprise, government, research, education, and the support sector, including consultancies, manufacturers and suppliers. Membership of The Institute allows professionals to contribute to their profession through participation in The Institute's seminars and conferences, its many committees and Branch meetings, and through contribution to its many high standard publications. The Institute is the main body for the accreditation of professionals in the minerals industry. The activities of The Institute are directed towards the achievement of professional excellence. It provides opportunitites for contact with, and professional support from, colleagues, and the interchange of information on the latest industry developments.

Jan 1, 1989

By Manoj Kumar, S. Ranganathan, S. N. Sinha

The reducibility of three different manganese ores with coke was studied. The three ores were reduced to different extents under the same experimental conditions. The investigations showed that in the temperature range of 900-1000 ×C, Fe2O3 in the ore was reduced to metallic iron. MnO2 was reduced to Mn3O4 in all cases except one in which it was reduced to Mn2O3. The kinetics of reduction was controlled by different mechanisms in the different ores. Temperature had a significant influence on the reducibility of the ores.

Jan 1, 2007

By B. S. Terry, C. L. Harris

Reduction kinetics from slags containing CuO(0.5), ZnO, PbO, NiO and SnO into a Cu-based metal phase were subjected to computer simulation using a previously developed model for the kinetics of metal-slag-gas reactions that assumes mass-transfer control in all phases. The effects were examined of changing bulk Fe oxide activity, gas reducing potential, temperature, Fe content of the Cu phase and metal/slag ratio. The results permit practical conclusions to be drawn about industrial slag-cleaning practice, but the model is still limited in terms of thermodynamic inputs and the idealisation of reaction conditions

Aug 1, 1995

By B. S. Terry, C. L. Harris

After measuring the kinetics of Ni reduction from a SiO2-saturated fayalite slag into a Cu-based metallic phase on a laboratory scale, a general model was developed that is capable of simulating mass transfer to and from metal-slag, slag-gas and metal-gas interfaces for multiple species. The model was used to simulate the reactions that occur when Cu and Ni are reduced from fayalite-based slags into a Cu-based metallic phase. Good agreement was achieved between model predictions and experimental data

Aug 1, 1995

By Vincent Canaguier

Methane is increasingly considered as a promising reductant for metal oxides, including chromite. To assess the possibilities of such reduction route, the gas-solid reactions between Ar–CH4–H2 gas mixtures and synthetic chromites are studied between 950 and 1050 °C. The influence of Mg and Al additions on the reduction-caburization of (Fe,Mg)(Cr,Al)2O4 solid solution is investigated thermodynamically, structurally and kinetically. The product phases are examined by x-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The reaction rate is derived from real-time exhaust gas measurements and post-reaction product analyses such as oxygen analysis. Kinetic models are proposed based on the product phase morphologies and confronted with the empirical data.

By C. Dorfling

Experimental work was performed using a bench scale autoclave to evaluate the effects that leaching temperature, pressure, initial acid concentration, and the solid to liquid ratio have on the behaviour of base metals and platinum group metals in a high-pressure sulphuric acid oxygen leaching system. The concentrations of metals in the leach solution were measured over time at different leaching conditions. At the conditions investigated, the initial acid concentration had the largest influence on the copper leaching kinetics, while the leaching rates of the other precious metals (OPMs: rhodium, ruthenium, and iridium) were highly dependent on the leaching temperature. A set of chemical reactions that can be used to describe the leaching chemistry was proposed, and the associated reaction kinetics were quantified. As a first estimation, the rate expressions were considered first order, and the rate constants were determined using the method of least squares, considering the experimental and predicted concentrations obtained for the different leaching conditions. Of the OPM compounds, the sulphides showed the fastest dissolution rate, followed by OPM alloys, and finally the OPM oxides. During the initial leaching stages, base metals and OPMs competed for the available dissolved oxygen, with oxygen being preferentially used for copper leaching. Precipitation of OPMs during the initial leaching stages can be ascribed to copper and nickel dissolution according to exchange reactions between dissolved OPMs and copper present as digenite or nickel present as polydymite. Control of the autoclave residence time is of particular importance to enhance the selectivity of this leaching step, given the dependence of the PGM leaching rates on the extent of copper dissolution.

Sep 1, 2012

By Omid Marzoughi

In this research, both the kinetics and the mechanisms of the roasting of a sphalerite concentrate from the Bafgh mining complex in Iran were investigated. The oxidation process was performed in a muffle furnace in air and the effects of time and temperature on the degree of oxidation of the zinc sulfide sample were quantitatively studied. The experimental data were fitted to the shrinking core model. In the temperature range of 650–800 °C, the rate-controlling step was the chemical reaction between the zinc sulfide and oxygen with an activation energy of 103 kJ mol−1. On the other hand, in the temperature range of 850–950 °C, the rate-controlling step was oxygen diffusion with an activation energy of 50 kJ mol−1. Also, the roasting process was studied using thermogravimetric (TGA) and derivative thermogravimetric (DTGA) techniques.

By Zenjiro Asaki

The copper concentrate particles dissolve quickly into the molten matte in the smelting furnace of Mitsubishi Process, which indicates that the sulfide smelting is essentially a gas/liquid reaction. In this paper, theoretical calculation has been made on the rate of oxidation of FeS component in the matte to form FeO by rising gas bubbles using the penetration theory. The results showed that all the oxygen in the bubble of 1.2 cm in diameter, which is the maximum stable diameter, is consumed in 3 ms. This time required is sufficiently short, and it results in the actual operation of smelting furnace of 1100% oxygen-efficiency. These calculations indicate that most smelting reactions are completed just under the lance, except slag formation.

Jan 1, 2002

By E. Asselin, P. Sauve, H. Salomon-de-Friedberg

"Residues from the CESL Copper process were leached using the CESL Gold process. The kinetics of reaction were confirmed to be fast with over 50% of the gold consistently extracted within 2 minutes of leaching. Final gold extractions under the conditions tested here were between 80-90% obtained within 90 minutes. A model for the CESL Gold process was developed. This model is slightly different based on whether the copper concentrate leach residue was ground or unground prior to leaching: the gold leaching rate constant is approximately twice as fast for the ground samples. Unground residues had a P80 of 13 ?m whereas ground residues had a P80 of 10 ?m. The model predicts a 43% decrease in leaching time for ground residue versus unground residue to achieve the same extraction under otherwise identical conditions. The model was more accurate for the ground samples. INTRODUCTIONTeck's CESL Process (Jones, 1996) was developed to provide an economically attractive alternative to traditional copper smelting. It has since evolved to also deal with copper concentrates containing valuable impurities such as nickel and undesirable ones, such as arsenic, while reducing downstream costs. Effective recovery of gold and silver is essential to the economics of the CESL Process. The Brook Hunt 2007 copper concentrate assay data (Wood-Mackenzie, 2007) were examined to determine the ratio of gold plus silver value relative to the contained copper. As indicated in Figure 1 below, nearly two-thirds of concentrates have 10% or more of their total value tied up in their precious metals content.CESL has extensively examined the recovery of gold and silver at bench, pilot and demonstration scale, which has culminated in the present CESL Gold Process (Barr et al., 2007). The process targets the precious metal contained in the leach residues produced in the copper portion of the flowsheet. This residue has two primary components which influence downstream processing. The major iron-rich fraction (-75 wt%) of the residue is a mixture of various forms of iron oxide precipitates including hematite and jarosite (Sahu and Asselin, 2011). The iron fraction ranges from amorphous to crystalline in nature depending on the compound precipitated, upstream operating conditions and feed material composition. The lesser, but by no means less important, fraction is a mixture of elemental sulphur and unreacted sulphides (principally pyrite).Elemental sulphur formed during the oxidative leach of the copper concentrate reacts with cyanide to form thiocyanate (SCN-) making a traditional cyanide leach approach too costly. Since the SCN formation reaction strongly depends on contact time with the CESL residues (Po, 2007) short contact times were preferred. This factor guided the development work towards the eventual room temperature, pressure cyanidation process which results in near complete gold dissolution in 90 minutes. A recent CESL gold demonstration campaign treating 1.5 t/d of residue from the copper oxidation step achieved an average gold extraction of 91% (96% maximum)."

Jan 1, 2012

By Clarence Zener

[ ] THE present investigation started in an attempt to understand certain details of the decomposition of austenite, and of the effect of alloying elements thereon. As the investigation proceeded it became apparent that not only these details, but all the general features of austenite decomposition, could be understood in terms of fundamental physical principles. Since the direct applicability of these physical principles has not been previously recognized, it was decided to incorporate the original results of the investigation into a review of the general subject of the kinetics of austenite decomposition. This review constitutes the present article. An extended summary of the results is given on pages 27 to 30. This article, which deals with the kinetics of phase transformations, may appropriately be considered as a sequel to two recent articles1,2 from this laboratory on the equilibrium relations in medium alloy steels.

Jan 1, 1946

By J. B. Austin, R. L. Rickett

MEASUREMENTS Of the rate of decomposition of austenite at constant temperature are commonly represented by plotting the percentage transformed on linear coordinates against time on either a linear or a logarithmic scale, a method that yields a curve that in shape resembles an integral sign (Fig. 1). A graph of this kind is not always convenient because extrapolation to the beginning or end of the transformation, or even interpolation, may be uncertain unless there are a large number of observations, which seldom happens; furthermore, the degree of consistency of a set of measurements is difficult to judge from such a curve. It is desirable therefore to find some mode of plotting, or even better to find a standard variety of graph paper, that gives a straight line instead of the integral shape. The straight line has many advantages; the number of readings required to fix the position of the curve is greatly reduced, interpolation is easy and rapid, extrapolation can be carried out with greater confidence and, finally, the consistency of the measurements is readily estimated from the scatter of the points. The last advantage is particularly valuable when the data are obtained by direct microscopic examination alone, because they are influenced by the skill of the observer in estimating the relative size of areas, possibly also by undetected inhomogeneity of the specimen. A search for ways of representing the observations as a straight line yielded two methods which are described in this paper. The paper also includes an account of some interesting relations brought to light in applying these methods to the available experimental data. Usually the best way to derive such a method of plotting is to base it on established principles of chemistry and physics, as has been done, for example, for the temperature variation of the equilibrium constant of a chemical reaction. But so little is known of the mechanism of the decomposition of austenite, and so little is available in the way of well established background for changes of this kind, that it is simpler to rely upon purely empirical means. The general plan therefore is to study existing data with a view to finding some function of the direct observations that will

Jan 1, 1938

By J. B. Austin

MEASUREMENTS of the rate of decomposition of austenite at constant temperature are commonly represented by plotting the percentage trans-formed on linear coordinates against time on either a linear or a logarith-mic scale, a method that yields a curve that in shape resembles an integral sign (Fig. 1). A graph of this kind is not always convenient because extrapolation to the beginning or end of the transformation, or even inter-polation, may be uncertain unless there are a large number of observations, which seldom happens; furthermore, the degree of consistency of a set of measurements is difficult to judge from such a curve. It is desirable therefore to find some mode of plotting, or even better to find a standard variety of graph paper, that gives a straight line instead of the integral shape. The straight line has many advantages; the number of readings required to fix the position of the curve is greatly reduced, interpolation is easy and rapid, extrapolation can be carried out with greater confidence and, finally, the consistency of the measurements is readily estimated from the scatter of the points. The last advantage is particularly valu-able when the data are obtained by direct microscopic examination alone, because they are influenced by the skill of the observer in estimating the relative size of areas, possibly also by undetected inhomogeneity of the specimen. A search for ways of representing the observations as a straight line yielded two methods which are described in this paper. The paper also includes an account of some interesting relations brought to light in applying these methods to the available experimental data. Usually the best way to derive such a method of plotting is to base it on established principles of chemistry and physics, as has been done, for example, for the temperature variation of the equilibrium constant of a chemical reaction. But so little is known of the mechanism of the decom-position of austenite, and so little is available in the way of well established background for changes of this kind, that it is simpler to rely upon purely empirical means. The general plan therefore is to study existing data with a view to finding some function of the direct observations that will

Jan 1, 1938

By R. B. Anderson

As a part of a Bureau of Mines program on the conversion of coal to liquid and gaseous fuels, the kinetics of the Fischer-Tropsch synthesis on iron catalysts was investigated. Nitrided catalysts were studied at 21.4 atmospheres using feed gases ranging from 2H2+1CO to 0.25H2+1CO, and at 7.8 to 21.4 atmospheres using 1H2+1CO gas. The overall apparent activation energy increased with increasing carbon monoxide content of the feed gas from 19.5 kcal/mole for 2H2+1CO to 23.7 for 0.7H2+1CO. The rate of synthesis with 1H2+1CO feed increased linearly with operating pressure from 7.8 to 21.4 atmospheres. A semifundamental rate equation of the form [r=a'PH2 0.6pco 0.4- ?r0.5PH200.5] was shown to fit the data satisfactorily. The relative usage of hydrogen to carbon monoxide decreased with increasing conversion, passed a minimum, and then increased. Apparently water is the principal primary product and carbon dioxide is produced by subsequent water-gas shift reaction. In another group of experiments water, carbon dioxide, argon, and methane were added to 1H2+1CO feed to a nitrided iron catalyst. Argon and methane were only diluents. Carbon dioxide was a slight inhibitor and water vapor was a strong inhibitor to the rate of synthesis. Water accelerated the water-gas shift and usually increased methane production. Important factors of catalyst geometry in determining rate were found to be particle size and extent of reduction. Apparently the active portion of the catalyst is confined to a layer of 0.01 to 0.02 cm from the external surface of particles. A special solution was made of differential equations relating re¬action at the catalyst surface to diffusion in pores of the catalyst for spherical particles with an active layer surrounding an inert core. The equation derived expressed the experimental data reasonably well. Diffusivities determined by this equation varied from 3 to 24X10-6 cm2/sec; these values are of the same magnitude as observed for the diffusion of gases in liquid. The appendix presents a group of synthesis experiments at pressures of 21.4 to 103 atmospheres. In this range the rate of synthesis on nitrided iron catalysts increased with pressure to the 0.74 to 0.84 power.

Jan 1, 1964