No abstract

To meet the future environmental challenges, hydrogen direct reduced iron (H‐DRI) is expected to constitute the principal material for virgin steel production. For an efficient value chain, knowledge of the melting mechanism and dephosphorization mechanism of H‐DRI is needed. The in situ melting behavior, the melting mechanism, and the dephosphorization mechanism during heating of H‐DRI are investigated experimentally at 1773 and 1873 K. It is found that the melting rate of H‐DRI varies with the reduction degree (91–99.5%), increasing with decreasing reduction degree. An autogenous slag forms during heating and flows through the pores of the H‐DRI, thus increasing its effective thermal conductivity. The fraction of filled pores varies with reduction degree explaining the difference in melting rate. At this stage, the dissolution of apatite is initiated and completed upon melting of the metal phase. A gradual reversion of phosphorus from the autogenous slag to the liquid metal is observed after complete melting. The rate of reversion is discussed based on the properties of the H‐DRI, for example, reduction degree and carbon addition.

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.

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.