Summary

One way to improve the recycling of by-products from iron and steel production is briquetting, a process in which fine materials unsuitable for use as such are agglomerated to achieve a larger particle size. This work is about the high-temperature properties of auger pressing briquettes mainly consisting of blast furnace sludge and mill scale. The aim was to determine the suitability of the briquettes for blast furnace (BF) ironmaking by studying the reduction, swelling and cracking behavior using blast furnace simulator (BFS) furnace. The BFS, which can perform non-isothermal reduction experiments with changing gas atmospheres, was used to simulate the reducing conditions in a BF. In the BFS experiments, different stages of reduction up to 1100 °C were simulated. A commercial olivine pellet and another industrial blast furnace briquette were used as reference samples. The weight losses were monitored by thermogravimetry, swelling as a change in the external dimensions, and cracking by visual inspection. TG-MS analysis was carried out to study the presence of potentially harmful volatiles. The samples were analyzed using LOM and FESEM to study the phase transformations. The auger pressing briquettes proved to be a promising raw material for BF use. They were of self-reducing type due to their carbon content, and they were reduced to metallic iron faster compared to the reference briquettes. The swelling was slight, and despite minor cracking the auger pressing briquettes did not degrade. No harmful volatile substances were found.