Effect of calcium carbonate on transformation behavior of phosphorus in iron minerals during direct reduction

Direct reduction followed by magnetic separation (DRMS) is recognized as an efficient method for iron enrichment and phosphorus removal. The effect of calcium carbonate on phosphorus removal from iron minerals during DRMS was thus investigated, and the mechanism of action of calcium carbonate was elucidated from thermodynamic, mineral phase evolution, and microstructural perspectives. The experimental results demonstrated that adding 20 wt.% calcium carbonate reduces the phosphorus content in direct reduced iron from 0.50 to 0.13 wt.%, increasing the dephosphorization rate from 38.64% to 82.28%. Mechanistic analysis revealed that phosphorus in iron minerals reacted with calcite to form apatite, while calcium carbonate reacted with chlorite and silicon components in iron minerals to generate dicalcium silicate, preventing the formation of free silica and inhibiting the reduction of formed apatite.