Marcelo Breda Mourão

Kinetics and catastrophic swelling during reduction of iron ore in carbon bearing pellets

AbstractThe rate of reaction between iron oxides and charcoal, agglomerated together as pellets, has been correlated with the swelling of the pellets and with the morphology of the iron formed. The experimental techniques employed were thermogravimetric analysis, X-ray diffraction analysis, and microscopic examination of partially reduced pellets. The experiments were performed in the temperature range 1223–1423 K. The conditions that favour the growing of iron in the form of whiskers, and hence lead to catastrophic swelling, have been determined.

Experimental investigation of dissolution rates of carbonaceous materials in liquid iron-carbon melts

Interactions of carbonaceous materials in liquid Fe-C melts have been investigated experimentally by determining the rates of dissolution at temperatures ranging from 1623 to 1935 K. The rates of dissolution of spectroscopic graphite and an industrial coke obeyed the correlation for natural convection under turbulent conditions. The experimental data for the graphite suggested that the rate of dissolution was controlled by mass transfer in liquid boundary layer adjacent to the solid sample. The value of the empirical parameter correlating the dissolution coefficient and the operating variables was found to be 0.19, which was close to that reported in the literature. The comparison of the results obtained for coke and low-volatile coal char samples with those for the graphite revealed that impurities and porosity of the samples can effect the dissolution rates. The values ofk1, for coke decreased with increasing the dissolution time. The examination of some of the partially dissolved coke samples by electron micro-scopy revealed that a thin, viscous ash layer was forming on the sample surface, which must be the main reason for the behavior. The dissolution rates were controlled by both mass transfer and phase boundary reactions when sulfur was present in the bath. The extent of devolatilization and dissolution of coal particles when they were injected into an Fe-C melt depended on the particle size and location.

SELF-REDUCING PELLETS FOR IRONMAKING: REACTION RATE AND PROCESSING

Self-reducing pellets bearing iron oxides and carbonaceous material are considered as an efficient way of promoting the carbothermic reduction of iron ore or iron-containing wastes, as several processes already employ this technology. This paper discusses the reaction rates obtained when this kind of agglomerate is heated at different temperatures. To take advantage of the kinetic features presented by self-reducing pellets, any process has to solve the problem of furnishing a high heat load to the charge without compromising its physical integrity. This paper also presents a discussion on how the different existing or proposed processes tackle this problem.

Effect of slag composition on iron nuggets formation from carbon composite pellets

®cement, silica and alumina the slag composition was varied to adjust the expected liquidus temperature to 1573 and 2273 K. It has been shown that the formation of iron nuggets is favored for slags presenting low liquidus temperature. In order to further investigate this phenomenon, pellets containing iron powder and carbonaceous material, together with previously prepared slags, were also submitted to high temperature, and it has been shown that iron carburization depends on slag composition.

SELF-REDUCING PELLETS FOR IRONMAKING: MECHANICAL BEHAVIOR

Self-reducing technology has shown a process that presents advantages due to the flexibility of using different low-cost raw materials (fines, dusts, sludge, etc.) and low investment cost, resulting in a competitive one. The main technical advantage is the rate of reaction due to closeness of reactants resulting in a process with high productivity. The development started at MTU (Goksel 1977), and presently there are many processes based on these principles: PTC process (Goksel et al. 1991), Tecnored process (Contrucci and Spearman 1997), Itmk3 (Tsuge 2002), Fastmet (McClelland 2002), Inmetco (Koros 2001), and others. This paper discusses the behavior of self-reducing pellets usable in the self-reducing processes. Mechanical properties such as cold strength, strength after heating, decrepitation, and swelling are analyzed.

Development of composite briquettes of iron ore and coal hardened by heat treatment

Abstract Innovative energy saving technologies have been developed to improve the efficiency of coal usage, especially in ironmaking. One of these technologies is a product known as the carbon composite iron ore hot briquette (CCB) – a self-reducing iron ore–carbon composite that uses the thermal plasticity of coking coals as a binder to enhance mechanical strength. This paper proposes an alternative method for manufacturing self-reducing briquettes which consists of pressing a mixture of the fine particles from coking coal and pellet feed iron ore in a cylindrical die followed by a heat treatment. The effects of the coal particle size, heating rate, coal/ore ratio and briquetting pressure were investigated with regard to the compressive strength and bulk density of the briquettes. Optimal results were obtained using a fine coal particle size (0.053–0.103 mm), a high heating rate, 25% coal content in the briquetting mixture, and a briquetting pressure of 53 MPa.

Prereduction of self-reducing pellets of manganese ore

Abstract A brief review of alternative processes for production of high C Fe–Mn is presented. Experimental results of the reduction behaviour of charcoal bearing pellets with manganese concentrate at temperatures up to 1400°C are discussed. At temperatures up to 1000°C iron and manganese oxides are reduced to MnO, Fe and some Fe–Mn. At temperatures between 1000 and 1250°C, there is the formation of a liquid phase (Fe–Mn) by dissolution of reduced Mn into Fe. At temperatures between 1250 and 1350°C, manganese continues to be reduced and incorporated into Fe–Mn, and the composition of the metallic phase is similar to that of commercial Fe–Mn. The results have also shown that it is possible to obtain a Fe–Mn alloy with good recovery yield of Mn at temperatures within 1300 and 1400°C, without disintegration of the charcoal bearing pellet, but obtaining a liquid metallic phase inside it, favouring the coalescence of Fe–Mn. This result allows the prospect of new processes for Fe–Mn production with low energy consumption.

Recovery of Cr, Ni and Fe from dust generated in stainless steelmaking

Abstract During stainless steel production in an electric arc furnace, the dust generated amounts to around 1% of the charge weight. This dust contains chromium, zinc and other heavy metal oxides; therefore, its final disposal in special landfill sites is expensive. On the other hand, the content of chromium oxide (∼9 wt%), nickel oxide (∼2·5 wt%) and iron oxides (∼47 wt%) can be recovered by reduction with carbon or Fe–Si. In this paper, the dust was physically and chemically characterised, and used in the manufacture of composite pellets with carbon and Fe–Si. These pellets were added to iron–carbon melts at a temperature around 1600°C. After smelting-reduction, the recovery yields of Cr, Ni, and Fe were determined. These yields were: (i) with Fe–75%Si as reductant – Ni ∼90%, Cr ∼90%, Fe ∼90%; and (ii) with coal as reductant – Ni ∼12%, Cr ∼35%, Fe ∼90%). A preliminary economic evaluation for Brazilian conditions showed that the process is sustainable depending on the landfill cost for dusts and the availability of inexpensive Fe–Si. When coal is used as reductant, the electric energy becomes the main cost component and the above recycling process becomes economically feasible with landfill costs higher than US

Fundamental aspects of sintering of chromites concentrates

150 t−1.

Reaction rate and product morphology in carbon composite iron ore pellets with and without Portland cement

Abstract Brazilian chromite ores need to be crushed to a size below 1 mm to allow concentrations that decrease the content of gangues. The concentrate particle size distributions therefore are not favourable for sintering. The chromite concentrates are mainly composed of chromite grains and gangues of magnesium silicates. Because of its refractoriness and low rate of dissolution in gangue, the chromite minerals participation in liquid phase formation during the sintering process is low, and the gangue also shows a solidus temperature of ∼1400°C. This paper attempts to analyse these fundamental aspects by characterising chromites, with estimates of the liquidus temperatures of chromite grains and gangue. To improve permeability, fines of lump ore (not concentrate) were added to the charging sintering mixture, and some slag forming agent was also added to facilitate the liquid phase formation. With these changes, the results of the industrial runs demonstrated improved sintering yields.