Reducing the greenhouse gas emissions from steel production can be done through direct reduction inside a shaft furnace using hydrogen gas as a reductant, generating water as an off gas. The temperature varies along the height of the shaft furnace, and studying the non-isothermal reduction is therefore necessary. In this work, industrial hematite pellets were non-isothermally reduced in a vertical tube furnace. Different gas mixtures containing water and hydrogen were used for reduction. The reduction gas used contained water vapor contents of 5%, 10%, and 20%, respectively, and the remaining gas was hydrogen. The experimental setup was carefully designed for the reductions to be carried out under well-controlled experimental conditions. It was clear that the water present in the reduction gas significantly decreased the reduction rate, especially at the lower temperatures. Moreover, the onset temperature of reduction was increased to around 525°C when water was present, compared to 450°C when pure hydrogen was used. Water contents above 5% lead to a low-rate stage at reduction degrees between 0.11 to 0.15. The low-rate stage ended when the wüstite phase became stable, changing the mechanism of reduction, which altered the chemical reaction rate. The reduction rate was less affected by water when the heating rate increased, since an increasing heating rate led to the reduction occurring at a higher temperature. Finally, the present study showed that the kinetics of non-isothermal reduction, using different water vapor contents, are very different from isothermal reduction.

The reaction mechanisms during melting of hydrogen direct reduced iron pellets (H-DRI) with different degrees of reduction were studied experimentally at 1773 K to 1873 K at different times (60 to 600 seconds), focusing on the autogenous slag formation. It was found that an autogenous slag is formed inside the pellets prior to the melting of the metal phase. The formation of the autogenous slag started with the melting of FeO, initially located in the center of the iron grains. The liquid FeO flowed into the pore network of the pellet. While flowing, the liquid FeO dissolved parts of the residual oxides, forming an autogenous slag. The slag stayed in the pore network until the iron was molten. Upon melting of the iron, the slag coalesced into spherical droplets. The final state is reached upon the separation of the metal and slag phases by flotation, as a bulk slag was formed on the surface of the liquid iron. In addition, since the iron ore used in this study contains vanadium, the behavior of V was discussed separately based on the experimental observations to build a basis for future studies on V extraction.

In order to obtain a realistic view of the foam in metallurgical slag, high temperature experiments where the foaming heights of FeO-CaO-SiO2-MgO slags containing precipitated MgO center dot FeO particles were measured. The foaming height slightly increased when small amounts of particles were present in the slag, but decreased to half height already when approximately 8 vol% particles were present in the liquid phase of the foam. To help the understanding, the foaming heights of silicone oil and food oil containing liquid insoluble droplets and non-reacting particles were also studied at room temperature. In these experiments, insoluble oil droplets were found to stabilize the foam, increasing the foaming height, while the addition of water droplets or solid particles had very little effect on foaming height. In line with the literature, it is believed that the interfacial energy between the droplets or particles and the bulk liquid as well as the interfacial energy between the droplets or particles and gas plays an important role. When the interfacial energy between the different phases becomes too high, the foaming height decreases, while when it's low enough, the foaming height increases.

A novel experimental setup for simultaneous weight, surface temperature, and center temperature tracking of a single iron ore pellet under reducing conditions has been utilized. Studies conducted in the setup indicate that the reduction of iron ore pellets in a pure hydrogen atmosphere is controlled by several transport steps inside the pellet. It is further shown that for a period of time during reduction, the reduction rate is limited by the heat transfer inside the sample. Any attempt to make accurate and robust models of the hydrogen based iron ore reduction process must therefore consider heat transfer in the pellet. The reduction is observed to take place in a reduction zone extending along the pellet radius, consisting of a mix of different phases. The amount of the different phases varies with radial position and time, as does the observed temperature gradient between the surface and the center of the pellet. Representative literature data on actual transfer coefficients of this system is therefore not available. Apparent thermal conductivities for the different experimental temperatures are evaluated based on the experimental data and found to be significantly lower than the corresponding value for dense iron.

The development of new materials and their production processes along with the environmental constraints demand new data of high quality, especially thermodynamic and physical property data. As slags play a crucial role in metallurgical processes and recycling, the need of better understanding of the reaction mechanisms between slag and metal is also increasingly felt. High precision data and better understanding of the reaction mechanism require efficient collaboration between the researchers in the laboratory and in the industries. Unfortunately, in some cases, the reported data are not obtained in well-controlled experimental conditions. Without the knowledge of the experimental conditions, the use of the data in industrial practice would possibly lead to unintended results. In other cases, the measurements themselves, even their principles, are questionable. This review article addresses how to make the laboratory investigation more relevant to the industrial reality. Some existing uncertainties in the laboratory studies are also discussed. To help a sensible discussion, some specially designed experiments are conducted to support the argument. The review is focused on slag properties (namely, sulfide capacity, phosphate capacity, apparent viscosity, and apparent interfacial tension) and studies of interfacial slag phenomena.

Self-fluxing hematite pellets are reduced by hydrogen to different degrees. The reduced pellets are melted in closed MgO crucibles at 1873 K to study the effect of reduction degree on the characteristics of slag formed. The results reveal that the phosphorus content in the metallic phase can be brought down to 130 ppm merely by the self-fluxing slag, even though the slag weighs only about 8% of the metal. It shows a great potential in reducing the amount of slag formers in the steelmaking process. The slag compositions obtained by melting the reduced pellets are used to prepare small synthetic slag samples for identifying the phases after melting. The use of the small samples is to ensure efficient quenching. Microscopic examination reveals that all the self-fluxing slags contain mainly three phases, namely, magnesiowüstite, spinel, and a liquid phase. Most of vanadium is found to be in the spinel and magnesiowüstite phases. The liquid phase only contains 1–2 wt% V2O3. Decreased FeO content of the slag increases the vanadium oxide contents in the spinel and magnesiowüstite phases. The fact that vanadium concentrates in the solid oxide phases provides essential information for sustainable extraction of vanadium from the steelmaking slag.

A novel setup of fluidized bed was developed to study the reduction of iron oxides by pure hydrogen. The setup enabled the introduction of powder directly to pure hydrogen atmosphere at experimental temperature. The arrangement was to minimize the experimental uncertainties due to gas switching. Hematite and magnetite powders were studied in the temperature range of 768-888 K. Reduction rates of the two powders were found to be similar. For both powders, the reduction rates were very high before the O/Fe ratio reached 0.5. Thereafter, the reduction was sluggish. SEM analyses revealed that the later stages of reaction was controlled by diffusion through the product layer on bigger particles, irrespective of the type of oxide powder. The results have indicated that both hematite and magnetite powder could be employed in fluidized bed. The results have also suggested that process optimization is essential regarding the sluggish reaction below 0.5 O/Fe ratio.

The solubility of calcium in liquid iron as a function of aluminum content and calcium potential, at compositions relevant to production of aluminum killed steels, was studied experimentally at 1 873 K. The measurements were made using a closed molybdenum chamber in which iron-aluminum alloys were held. The calcium potential was fixed using pure liquid calcium held at different temperatures. The calcium contents in the iron varied between 6 and 22 ppm by weight and the aluminum contents varied between 70 and 1 900 ppm by weight. The results indicate that the effect of aluminum on the solubility of calcium in iron is very low in the composition ranges studied.

The composition ranges of the phases in the pseudo binary system MgO-V2O3 were studied between 1661 and 1873 K and at controlled oxygen partial pressures of (3.55 +/- 0.2) x 10(-6) and (3.55 +/- 0.3) x 10(-5) Pa. The phase relationship was determined by equilibrating MgO-V2O3 pellets in a CO-CO2 mixture followed by quenching and electron-probe microanalysis. To ensure sufficient quenching, a new setup was designed and developed, so that the equilibrated samples can be quenched in oil directly under the same atmosphere inside the experimental setup. Three different phases were found in the samples, namely MgO, MgO-V2O3 spinel and V2O3. The phase boundaries were determined with good reproducibility. The solubility of V2O3 in the MgO phase increased with temperature and was significantly higher than literature data. The spinel as well as the V2O3 composition range were found to change only a little with temperature in the investigated temperature range. Decreased oxygen potential led to a slight increase of the V2O3 content in the spinel phase and V2O3 phase. Furthermore, decreased oxygen potential resulted in a significant increase of the solubility of V2O3 in the MgO phase at the higher temperatures, especially at 1873 K.

The paper presents a study on the decarburization of pig iron droplets in synthetic BOF slag. The effects of droplet size and slag composition were studied. The results show evidently that the decarburization is very fast in general. One gram of pig iron is mostly decarburized within one minute. The reaction is shown to be faster when many small droplets were employed instead of one big droplet with equal total mass. This is explained by the bigger interfacial area between the liquid slag and the pig iron of the many small particles. It is also interesting to see that the decarburizing reaction in the slag having lower dynamic viscosity and higher FeO activity is slower than in the slag with higher viscosity and lower FeO activity. The slower reaction could be explained by the longer incubation time in this slag.