Abstract
The formation mechanism of deposits in commercial gas-fired magnetization-reduction roasting rotary kiln was studied. The deposits ring adhered on the kiln wall based on the bonding of low melting point eutectic liquid phase, and the deposit adhered on the air duct head by impact deposition. The chemical composition and microstructure of the deposits sampled at different locations varied slightly. Besides a small amount of quartz and limonite, main phases in the deposits are fayalite, glass phase and magnetite. The formation of the deposits can be attributed to the derivation of low melting point eutectic of fine limonite and coal ash, and the solid state reaction between them. Coal ash, originated from the reduction coal, combining together with fine limonite particles, results in the accumulation of deposits on the kiln wall and air duct. Fayalite, the binder phase, was a key factor for deposit formation. The residual carbon in limonite may cause an over-reduction of limonite and produce FeO. Amid the roasting process, SiO2, originated from limonite and coal ash, may combine with FeO and reduce the liquefaction temperature, therewith liquid phase generates at high temperature zone, which can significantly promote the growth of deposits.
Highlights
Due to the depletion of easy-processing iron ores, much attention has been paid to the utilization of refractory ores in recent years [1,2,3,4,5]
SiO2, originated from limonite and coal ash, may combine with FeO and reduce the liquefaction temperature, therewith liquid phase generates at high temperature zone, which can significantly promote the growth of deposits
The limonite ore becomes porous, easy-to-be-reduced and the iron grade can be naturally enriched by the removal of crystal water which was banded with iron oxide after roasting process, qualified iron concentrate can be obtained by the sequential magnetic separation [10]
Summary
Due to the depletion of easy-processing iron ores, much attention has been paid to the utilization of refractory ores in recent years [1,2,3,4,5]. Limonite ore is a common refractory iron oxide ore with low grade, weak magnetic property and high gangue content. Limonite ore is poorly responsive to conventional beneficiation techniques, magnetizing roasting-magnetic separation approach has been proved a promising solution for such refractory iron oxide ore beneficiation [1,6,7,8,9]. The limonite ore becomes porous, easy-to-be-reduced and the iron grade can be naturally enriched by the removal of crystal water which was banded with iron oxide after roasting process, qualified iron concentrate can be obtained by the sequential magnetic separation [10]. The MRR technology mainly include shaft furnace MRR, rotary kiln MRR, fluidized
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