Mechanism of Ion-Diffusion Solid-Phase Reduction of Iron Oxides of Technogenic Origin in the Presence of the Liquid Phase and without it

Abstract

The processes of iron oxides’ reduction have a complex physicochemical mechanism, with the participation of solid, liquid, and gaseous substances. The article discusses the existing models for the reduction of iron oxides and provides data on the thermodynamic possibility of carrying out the reactions of their reduction through the solid and gas phases. Experimental data on the reduction of iron from industrial scale, obtained by the DSC (differential scanning calorimetry) method, show the kinetic dependence of the rate and completeness of recovery on external factors: pressing pressure during sample preparation and the reagents’ composition. The pressing pressure, under conditions of iron ions’ solid-phase diffusion, has the significant effect by increasing the reagents’ contact area. Under conditions of iron ions’ comprehensive diffusion, the pressing pressure does not affect the reduction processes rate. The introduction of 10 mass.% flux into the raw mixture composition leads to a partially liquid-phase diffusion of iron ions and weakens the effect of the pressing pressure in this process. An ion diffusion-catalytic mechanism is proposed to describe the observed effects during the reduction of iron oxide of technogenic origin.

Carbothermal reduction of mill scales formed on steel billets during continuous casting

“…This cementite reacts with carbon dioxide (generated in step I) following Eq. ( 5) [10]. In this step, fewer gases than in the previous step would be formed, which is reflected in a lesser mass loss.…”

“…This process is accompanied with gasification of carbon via the Boudouard reaction which promotes the sudden mass loss through Eq. ( 3) [4,10]. This reaction controls the overall process of the reduction.…”

Mechanochemical Activation Effect on Technogenic Iron Oxide Reduction Kinetics

“…It is established that the reduction proceeds in the sequence Fe 3 O 4 -FeO-Fe 3 C-α-Fe. In [ 5 ], the MCA influence (the briquetting pressure of the initial reagents) on the reduction in kinetics of scale of iron oxides during heating is considered. It was found that the reduction of iron oxides in scale proceeds in a solid-phase manner in three modes: diffusion-free, intermediate and diffusion.…”

“…In [ 5 ], only one of the MCA methods was considered (pressing). However, preliminary grinding is important for scale secondary processing.…”

“…To explain the effects observed during the scale iron oxide reduction, an ion-diffusion-catalytic mechanism of solid-phase technogenic (scale) iron oxide reduction was proposed in [ 5 ]. In accordance with this mechanism, at the first stage there is a solid-phase interaction of hematite located on the scale surface with solid carbon located in the intergranular space, with the formation of CO according to Equation (2): Fe 2 O 3 + C = 2FeO + CO↑ …”