Influence of cooling rate on the crushing efficiency of solidified iron ore for recycled aggregates

• The influence of the cooling rate of ores on the crushing efficiency was investigated.
• Crystallization temperature decreased as the cooling rate was increased.
• The activation energy is 677 kJ/mol, a lower value than the blast furnace slag.
• Surface cracks and voids increased with the increase of the cooling rate.
• The optimal cooling rate as an aggregate for cement, was confirmed at 20 °C/min.

Solidified iron ore has been utilized as raw material for aggregates of cement after crushing. Therefore, to confirm the crushing efficiency of recyclable solidified iron ore, the microstructural, thermal, and mechanical properties were analyzed as a function of cooling rate. When the cooling rate was increased from 5 to 20 °C/min, the density of the iron ore decreased from 5.391 to 5.271 g/cm3, and the Fe2O3 phase formed. Additionally, the Fe2SiO4 phase formed when the cooling rate was more than 27 °C/min; and, as a result of water quenching (953 °C/min), mixed crystalline (Fe2SiO4) and amorphous phases formed, the density was decreased to 4.714 g/cm3, and crack and void density increased. Thermal analysis showed that crystallization temperature decreased from 1390 to 1357 °C as the cooling rate was increased from 5 to 20 °C/min and the activation energy was 677 kJ/mol for the Fe2O3 phase. When the cooling rate was increased above 27 °C/min, only minor exotherms were observed. Therefore, when the cooling rate was increased from 5 to 953 °C/min, the Vickers hardness and flexural strength decreased by about 41% and 59%, respectively. Consequently, to produce a solidified iron ore having a Fe2O3 crystalline phase without a heterogeneous element, while increasing its crushing efficiency, the optimum cooling rate was confirmed to be 20 °C/min.

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