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Influence and role of potassium in the reduction of hematite with CO/CO 2
Author(s) -
Roederer Jeanne,
Jeannot François,
Dupré Bernard,
Gleitzer Charles
Publication year - 1987
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.198700875
Subject(s) - wüstite , hematite , magnetite , potassium , chemistry , pellets , mineralogy , inorganic chemistry , chemical engineering , metallurgy , analytical chemistry (journal) , materials science , composite material , chromatography , organic chemistry , engineering
In most shaft furnaces, there is some overlap between hematite‐magnetite and magnetite‐wustite single reactions, due to thermodynamic conditions prevailing during burden movement and to the texture of pellets and/or sinters. Hence, we have investigated the action of potassium on hematite ore and pure crystal reduction with CO—CO 2 , from 700°C to 1000°C, and with CO/CO 2 = 30/70 and 50/50. With or without potassium reduction proceeds in two successive steps, where the first seems to be much faster than the second. But actually the recorded kinetic data correspond to the same order of magnitude for the two reduction rates, especially at high temperatures. Consequently the usual Bessières model does not apply. This is partly due to the nontopochemical interface in the magnetite‐wustite step. As care has been taken to avoid any reactant starvation, a hypothesis which would encompass all results in a consistent picture is the drop of CO partial pressure in the very outer part of the magnetite layer. The action of potassium on the hematite‐magnetite step is in agreement with oberservations reported in the preceding article: finer texture, greater surface and reactivity, easier gas access. Consequently these features favour an easier reaction in the second step, which proceeds within the Uniform Internal Reaction regime.