Kinetics and Mechanism of Sulfation Reactions during roasting of Sulfides

ROASTING of sulphidic minerals is one of the very important steps in the extraction metallurgical practice of most of the non-ferrous metals from their concentrates. In recent times, the technique of roasting has undergone substantial changes leading to higher production and better products, more suitable for subsequent operations. Some of these processes have developed on the basis of our understanding of the kinetic limitations of the old proc-esses and elimination of such kinetic bottlenecks like diffusion in the roasting processes. These new processes like flash roasting or fluidized roasting are being increasingly utilised in production units. However, our present state of knowledge on the kinetics of roasting reaction lacks certain fundamental understanding of the process which is explained in the following paragraphs

Kinetics and Mechanism of Sulfation Reactions

Roasting of metallic sulfides have been studies by a large number of investigators in recent years. Wadsworth, McCabe in U.S.A. and Smirnov and his group have contrib-uted to our understanding of the roasting mechanism to a very considerable extent. On the basis of these works, two kinds of mechanisms have been proposed for the formation of metallic sulfate from metallic sulfide and oxygen. One of the theory suggests a direct formation of metallic sulfate, whereas the other theory assumes prior formation of metallic oxide of SO2 to SO3, which combines with metallic oxide to give sulfate. Present investigation is aimed at further clearing up the mechanism of sulfate formation and estabilishing the role of individuality of the system on a more generalised basis

Effect of Ce and Sb on Primary Graphite Growth in Cast Irons

It is well-known that if certain trace elements are present in cast iron melts the morphology of the graphite precipitates can be altered. In order to understand the effect of doping elements on primary growth of graphite, pure Fe–Sb alloys were prepared by induction melting. They were then placed in graphite crucibles and heated to a temperature above the Fe–C eutectic so that the charge became saturated in carbon and melted. To obtain Fe–Ce alloys, metallic Ce was added at the bottom of a graphite crucible and covered with iron, and then heated as for the Fe–Sb charge. In both cases, the melt was then cooled and held slightly above the eutectic temperature so that primary graphite crystals, which had nucleated on the crucible walls and then detached from it, could grow freely in the melt. The influence of the added elements on graphite growth was revealed by the change in the shape and distribution of the crystals compared to those obtained in similar experiments carried out with pure Fe. The experiments were made in air and vacuum so as to point out possible interactions between the elements present in the melt and oxygen

Processing of aluminum-graphite particulate metal matrix composites by advanced shear technology

Copyright @ 2009 ASM International. This paper was published in Journal of Materials Engineering and Performance 18(9) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.To extend the possibilities of using aluminum/graphite composites as structural materials, a novel process is developed. The conventional methods often produce agglomerated structures exhibiting lower strength and ductility. To overcome the cohesive force of the agglomerates, a melt conditioned high-pressure die casting (MC-HPDC) process innovatively adapts the well-established, high-shear dispersive mixing action of a twin screw mechanism. The distribution of particles and properties of composites are quantitatively evaluated. The adopted rheo process significantly improved the distribution of the reinforcement in the matrix with a strong interfacial bond between the two. A good combination of improved ultimate tensile strength (UTS) and tensile elongation (e) is obtained compared with composites produced by conventional processes.EPSR

Smelting reduction of prereduced iron ore

Investigations have been made to study the reduction kinetics of iron oxide in molten slag by dissolved carbon in liquid iron melt, and the behaviour of phosphorus transport at the slag/metal interface during smelting of prereduced iron ore (PRI). The experimental work included laboratory and large scale smelting of the PRI, While the laboratory studies were carried out in a Tamman furnace using a carbon saturated iron bath, the latter were carried out in a 500 kVA submerged are furnace. The data generated under controlled conditions have been subjected to kinetic analysis. A study of simultaneous effects of the major process variables during smelting reduction of the PRI on the phosphorus distribution between slag and metal is presented, The variables studied were: reduction period, temperature of the molten slag, and the major constituents (%FeO, %CaO, and %SiO2) in the molten slag. A series of statistically planned isothermal experiments has been carried out to quantitatively assess the effects of these variables on the phosphorus transport across the slag/metal interface. The paper describes the phosphorus distribution as a function of the governing process parameters obtained from two level factorial experiments and mathematical statistical models. The predicted distribution ratio, expressed as (P)/[P], is successfully compared with the controlled experimental results for the smelting of PRI. Within the range of the variables studied, the (P)/[P] distribution ratio has been correlated with the process variables and their interactions, and the model predictions are compared with the laboratory and large scale experimental data. Attempts have also been made to compare and correlate the smelting reduction phenomena of the PRI on a laboratory scale with the large scale conditions. (C) 1997 The Institute of Materials

On the infiltration behavior of Al, Al-Li, and Mg meltas through SiC<SUB>p</SUB> bed

Aluminum, Al-Li(8090), and Mg matrix composites with uniform distributions of SiC<SUB>p</SUB> reinforcement have been prepared by the vacuum infiltration technique. The infiltration kinetics have been found to increase in the order of Al, Al-Li, and Mg. The Al-Li alloy and Mg as matrix materials have shown improved wettability with SiC<SUB>p</SUB> in comparison to Al, leading to enhanced infiltration kinetics and reduced reinforcement degradation in the former cases. The infiltration kinetics are insensitive to preheat temperature beyond a critical temperature, which is close to the melting point of the matrix. A marginal improvement in infiltration kinetics could be obtained with Cu and Ni coating on SiC and on its dynamic oxidation. The improvement is significant at a higher preheat temperature of SiC. The Vickers hardness, measured on the SiC particles, has been shown to be an index of the strength of the interface between the matrix and reinforcement in the composite

Modelling and Experimental Characterization of Processing Parameters in Vertical Twin Roll Casting of Aluminium Alloy A356

Production of near net shape thin strips using vertical twin roll casting method has been studied. In a typical VTRC process, the simultaneous action of solidification and rolling makes the process quite attractive as well as complicated. An industrially popular alloy A356 has been chosen for the VTRC processing. It is challenging to identify VTRC processing parameters for the alloy to produce thin strips because of its freezing range and complex composition. In the present work processing parameters of VTRC like roll speed, roll gap, melt superheat and the interface convective heat transfer coefficient have been investigated through modelling of the process. The mathematical model was developed which simultaneously solves the heat transfer, fluid flow and solidification, using commercial software COMSOL Multiphysics 5.4. VTRC sheets of alloy A356 were produced in an experimental set up and attempts were made to correlate the microstructures of VTRC A356 alloy to that predicted from the numerical studies to validate the model