Minerals and iron-making reactions in blast furnaces

We investigated the effect of flux (lime) addition on the reduction behavior of iron oxide in copper slag by solid carbon at 1773 K (1500 °C). In particular, we quantified the recovery of iron by performing typical kinetic analysis and considering slag foaming, which is strongly affected by the thermophysical properties of slags. The iron oxide in the copper slag was consistently reduced by solid carbon over time. In the kinetic analysis, we determined mass transfer coefficients with and without considering slag foaming using a gas holdup factor. The mass transfer of FeO was not significantly changed by CaO addition when slag foaming was ignored, whereas the mass transfer of FeO when slag foaming was considered was at a minimum in the 20 mass pct CaO system. Iron recovery, defined as the ratio of the amount of iron clearly transferred to the base metal ingot to the initial amount of iron in the slag phase before reduction, was maximal (about 90 pct) in the 20 mass pct CaO system. Various types of solid compounds, including Mg2SiO4 and Ca2SiO4, were precipitated in slags during the FeO reduction process, and these compounds strongly affected the reduction kinetics of FeO as well as iron recovery. Iron recovery was the greatest in the 20 mass pct CaO system because no solid compounds formed in this system, resulting in a highly fluid slag. This fluid slag allowed iron droplets to fall rapidly with high terminal velocity to the bottom of the crucible. A linear relationship between the mass transfer coefficient of FeO considering slag foaming and foam stability was obtained, from which we concluded that the mass transfer of FeO in slag was effectively promoted not only by gas evolution due to reduction reactions but also by foamy slag containing solid compounds. However, the reduced iron droplets were finely dispersed in foamy and viscous slags, making actual iron recovery a challenge.

Effect of CaO Addition on Iron Recovery from Copper Smelting Slags by Solid Carbon

The reduction of CaO-SiO2-Al2O3-FeO slags containing less than 10 wt pct FeO by solid carbonaceous materials such as graphite, coke, and coal char was investigated at reaction temperatures of 1400 °C to 1450 °C. The carbon monoxide evolution rate from the system was measured using stationary and rotating carbon rods, stationary horizontal carbon surfaces, and pinned stationary spheres as the reductants. The measured reaction rate ranged from 3.25 × 10−7 mol cm−2 s−1 at 2.1 pct FeO under static conditions to 3.6 × 10−6 mol cm−2 s−1 at 9.5 pct FeO for a rotating rod experiment. Visualization of the experiment using X-ray fluoroscopy showed that gas evolution from the reduction reaction caused the slag to foam during the experiment and that a gas film formed between the carbon surface and the slag at all times during experimentation. The reaction rate increased with increased slag FeO contents under all experimental conditions; however, this variation was not linear with FeO content. The reaction rate also increased with the rotation speed of the carbon rod at a given FeO content. A small increase in the reaction rate, at a given FeO content, was found when horizontal coke surfaces and coke spheres were used as the reductant as compared to graphite and coal char. The results of these experiments do not fit the traditional mass transfer correlations due to the evolution of gas during the experiment. The experimental results are consistent, however, with the hypothesis that liquid phase mass transfer of iron oxide is a major factor in the rate of reduction of iron oxide from slags by carbonaceous materials. In a second article, the individual rates of the possible limiting steps will be compared and a mixed control model will be used to explain the measured reaction rates.

Reduction of FeO in smelting slags by solid carbon: Experimental results

Recovery of iron and removal of hazardous elements from waste copper slag via a novel aluminothermic smelting reduction (ASR) process

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/106363/2/hdl_106363.pdf

Potential use of liquid metal oxides for chemical looping gasification: A thermodynamic assessment

An idea of vacuum suction through a porous graphite tube has been applied to maintain direct contact between FeO bearing molten slag and graphite by continuous removal of CO gas generated by the reduction In this way examination of relative importance of the direct and indirect reductions has become possible The primary slag had the composition of 205%Li2O-384%CaO-414%SiO2 (molar ratio 1:1:1) The initial concentration of FeO in the molten slag was varied between 15 and 125% Experiments were made at 1300°C under argon gas stream The rotation speed of the porous graphite tube was kept constant at 100 rpmThe net effect of vacuum suction is the resultant of two opposing effects of enhancement by interfacial agitation by CO bubble evolution and interference by gas bubbles around the graphite tube These two effects balance each other when the initial FeO concentration is below about 2% For concentrations high than 2%, the rate of reduction is larger when the gas is removed by vacuum suction The positive net effect indicates that the indirect reduction by CO gas is not so important as the direct reduction by graphiteA possible mechanism has been proposed to explain how the direct reduction can be responsible for the reduction of iron oxide in molten slag by graphite

Effect of CO Gas Formation on Reduction Rate of Iron Oxide in Molten Slag by Graphite.

A kinetic study has been made on the reduction of iron oxide in molten slag with graphite. The composition of the primary slag was changed so that SiO2 concentration varied between 0.33 and 0.50 mole fraction, and slag basicity between 1 and 2. The experimental temperature was 1300°C. The reaction rate is significantly affected by the slag composition. From values of the mass transfer coefficient, calculated by using penetration theory, it is presumed that for the slags with basicity of 2, the reaction rate is controlled by mass transfer in the slag phase, but chemical reaction resistance is predominant in slags with lower basicities. By applying a mixed-control model to the latter case, the apparent chemical reaction rate constant was calculated. The rate constant decreases largely with increasing the silica activity. The reaction rate also decreases with the presence of phosphorus in the slag. These behaviors indicate that the reaction rate is very sensitive to the interfacial chemisorption of the surface active agents.

Yoshiki Ito

Papers

Effect of CO Gas Formation on Reduction Rate of Iron Oxide in Molten Slag by Graphite.

Effect of slag composition on the kinetics of the reduction of iron oxide in molten slag by graphite