Abstract
The reduction behavior of raw and prior-oxidized magnetite iron ore ultra-fines with hydrogen was investigated. Reduction tests were conducted with a thermogravimetric analyzer in a temperature range from 873 K to 1098 K at 1.1 bar absolute, using hydrogen as reducing gas. The experimental results show that a prior oxidation of the magnetite has a positive effect on the reduction behavior because of changing morphology. The apparent activation energies show a turnaround to negative values, depending on the prior oxidation and degree of reduction. A multi-step kinetic analysis based on the model developed by Johnson–Mehl–Avrami was used to reveal the limiting mechanism during reduction. At 873 K and 948 K, the reduction at the initial stage is controlled by nucleation and chemical reaction and in the final stage by nucleation only, for both raw and pre-oxidized magnetites. At higher temperatures, 1023 K and 1098 K, the reduction of raw magnetite is mainly controlled by diffusion. This changes for pre-oxidized magnetite to a mixed controlled mechanism at the initial stage. Processing magnetite iron ore ultra-fines with a hydrogen-based direct reduction technology, lower reduction temperatures and a prior oxidation are recommended, whereby a high degree of oxidation is not necessary.
Highlights
INTRODUCTIONTHE iron and steel industry is one of the biggest single emitters of CO2 emissions, accounting for one third of the global industrial CO2 emissions.[1,2,3,4] The conventional ore-based iron- and steelmaking production route, blast furnace and basic oxygen furnace, emits in the range of 1700 to 1900 kg of CO2 per ton of liquid steel.[4,5]
The findings in this study show that a porous iron morphology is achieved when the reduction proceeds mainly corresponding to the chemical reaction mechanism at the initial stage, given at low reduction temperatures of 873 K and 948 K for both raw and oxidized magnetite ultra-fine iron ores
The apparent activation energy was studied according to the modelfree method as a function of the degree of reduction
Summary
THE iron and steel industry is one of the biggest single emitters of CO2 emissions, accounting for one third of the global industrial CO2 emissions.[1,2,3,4] The conventional ore-based iron- and steelmaking production route, blast furnace and basic oxygen furnace, emits in the range of 1700 to 1900 kg of CO2 per ton of liquid steel.[4,5]. METALLURGICAL AND MATERIALS TRANSACTIONS B halved compared to those emitted from the blast furnace and basic oxygen furnace.[5] A further reduction is achievable using hydrogen generated from electrolysis with renewable energies towards 100 to 250 kg of CO2 per ton of liquid steel.[4]. Besides the trend of lowering the CO2 emissions, new innovative ore-based iron- and steel production technologies must be able to process any type of iron oxide in the form of ultra-fines due to their steadily increasing availability. The change in the controlling mechanisms with the reduction degree is discussed along with the prevailing iron morphology
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