Valorização sinérgica de voláteis de biomassa e rejeitos de mineração de ferro

Abstract

The iron and steel production chain is highly dependent on fossil fuels, causing the sector to contribute about 8% of all anthropogenic CO2 emissions. Biomass-based reducing agents are considered an opportunity to reduce fossil CO2 emissions. In addition to greenhouse gases, large amounts of solid waste are also generated in the mining and metallurgical sector, with iron ore beneficiation being responsible for generating approximately 1.4 billion tons of tailings per year, making their recovery crucial and strategic in countries with high iron ore production. In this context, the present Thesis aimed to investigate the reduction of iron oxides using biomass volatiles, focusing on determining the phenomena involved and the synergistic impact on the generated solid and gaseous products. In the first stage of the work, the reduction potential of volatiles from raw eucalyptus and charcoal fines on lump iron ore was evaluated, aiming to understand the phenomena associated with different reducing agents. The results showed that up to 980 ºC a significant mineralogical transformation occurred, with wüstite being the major phase obtained with both biomasses. Interrupted tests at 600 ºC evidenced carbon deposition on the ore surface, especially with raw eucalyptus. The morphological characteristics of wüstite indicated that the ore reduced by volatiles from raw biomass had carbon deposition as the main reducing agent, while the reduction with charcoal volatiles was mainly driven by H2. Based on the first stage, in which high-grade iron ore was used to minimize the influence of impurities and accurately analyze the effects of reducing agents from different biomasses on the mineralogy and morphology of the final product, the second stage expanded the investigation. It explored the synergistic effect of volatiles from sugarcane bagasse (SCB) in combination with the iron oxides present in iron ore tailings (IOT), focusing on iron recovery, carbon deposition in the ferrous material, and the production of biogenic hydrogen. Different SCB/IOT ratios were tested, and it was observed that the lower SCB amount relative to IOT provided a higher H2 yield, mainly resulting from tar catalytic cracking. The tests at 1000 ºC resulted in the production of a reduced material consisting of wüstite, fayalite, and metallic iron, with a higher biomass proportion favoring metallization, reaching 18.9% of Fe0. However, at 600 ºC it was possible to obtain a product rich in magnetite (96.7%) with 3.5% deposited carbon, promoting a magnetic recovery of 98% by mass of the total treated tailings. The results achieved in this work propose a technically viable synergistic approach to valorize the volatile matter resulting from the pyrolysis of different biomasses and as an alternative for recovering iron contained in the amount of tailings from mining activities that supply the steel industry.