Abstract
Abstract The presence of potassium oxide (K2O) and sodium oxide (Na2O) causes high reduction swelling of pellets of Bayan Obo iron concentrate during reduction and thus affects the permeability of blast gases during blast furnace operations. The influencing mechanism of K2O and Na2O on the swelling behavior of reduction reactions (1) Fe2O3 → Fe3O4, (2) Fe3O4 → Fe x O, and (3) Fe x O → Fe was researched by adding (K2O + Na2O) to Australian fine ore briquettes. The mineral composition and structure of the briquettes, as well as the reduction swelling after the three reactions coupled with the morphology and lattice parameters of the reduced products, were studied. From the results, the swelling index with 0.6% (K2O + Na2O) added was 8.52%, 7.91%, and 33.81%, respectively, and without were 12.36%, 3.27%, and 12.61%, respectively, for the three reactions. The swelling index of the first reaction (Fe2O3 → Fe3O4) is reduced because alkali metal suppresses crystal cracking. The swelling mainly occurs at the third stage (Fe x O → Fe), because K2O and Na2O enhance the oriented growth of iron whiskers, as well as make them smaller. Crystal transformation does not occur at the second stage (Fe3O4 → Fe x O) and the reduction swelling is small, but the swelling index of the briquettes with added with K2O and Na2O increases (7.91% compared to 3.27%). The main reason is that the alkali metal reduces the melting point of the slag phase and promotes the cascade crystallization of FeO. Therefore, the abnormal swelling of briquettes caused by K and Na is mainly caused by the growth of iron whiskers at the third stage.
Highlights
With the rapid development of China’s iron and steel industry, the output of iron and steel has increased significantly, which creates an iron ore supply issue
The samples used in the reduction and swelling experiments included: (1) Laboratory briquettes of Australian ore: The Bayan obo ore was simulated by adding (K2O + Na2O) into Australian ore
According to the water immersion method: V = m2 − m1 × 100%, ρ where V is the volume of briquette, m1 is the mass of briquette in water, m2 is the mass of briquette in the air after water immersion, and ρ is the density of water at the current temperature, and the reduction swelling rate calculation formula is as follows: RSI% = V1 − V0 × 100%
Summary
With the rapid development of China’s iron and steel industry, the output of iron and steel has increased significantly, which creates an iron ore supply issue. Studying the effect of potassium and sodium on the metallurgical properties of the pellets has great significance for the utilization of Bayan Obo ore. When alkaline metals (as Na2O, K2O) were added to Fe2O3 pellets, abnormal swelling occurred during reduction. The effect of alkali metal on the swelling index, slag phase properties, and mineralogy of the iron oxides in the three different reduction stages of briquettes has been investigated, as well as exploring the mechanism of reduction swelling. The main reason for abnormal reduction swelling of Bayan Obo ore has been recommended based on the experimental results. The samples used in the reduction and swelling experiments included: (1) Laboratory briquettes of Australian ore: The Bayan obo ore was simulated by adding (K2O + Na2O) into Australian ore. The proportion of (K2O + Na2O) added is 1.00 and 5.00 wt% in pure reagents
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