Factors influencing physical and mechanical properties of direct reduced iron ore pellets

Direct Reduction processes for iron ore employing natural gas or hydrogen are becoming more important. Correspondingly, properties of outgoing products are of importance. Degradation of Direct Reduced Iron (DRI) feedstock greatly influences storage, handling, risk of reoxidation, and following melting operations. The focus of this work has been on the physical properties of DRI, and their effect on mechanical properties. Four types of industrially produced DRI having varying metallization, carbon content, structure and apparent porosity have been studied. Three of the selected DRI types have been reduced using natural gas, and one DRI type has been reduced using pure hydrogen. Cold compression strength and tumbling tests are performed. Qualitative analysis of samples before and after mechanical testing is made using SEM and LOM. Results show that total carbon content has a significant influence on overall mechanical strength of DRI. Degradation of samples in tumbling tests is least significant for the hydrogen-reduced – and hence carbon-free – DRI type. The DRI type containing the most carbon (3 wt%) exhibits the most fines generation and lowest compression strength. Furthermore, apparent porosity and fractures formed during reduction have a small though not as significant impact as carbon content on mechanical properties.