Red mud as a green dephosphorization agent: Co-reduction with high phosphorus oolitic hematite for iron extraction and dephosphorization

The large utilization of red mud (RM) presents many challenges due to its high alkalinity, which is attributed to the presence of CaO and Na2O. High phosphorus oolitic hematite (HPOH) is a typical refractory ore for Fe and P separation. During the direct reduction of HPOH to produce direct reduced iron (DRI) and achieve simultaneous dephosphorization, sodium or calcium salts are typically added as dephosphorization agents. This study investigated the feasibility of using RM as a green dephosphorization agent. Co-reduction of RM with HPOH was conducted to prepare DRI. By adding 60 % RM and using a reductant dosage of 17 %, a DRI with 90.89 % Fe and 0.095 % P was obtained. The corresponding total iron recovery was 87.79 %. This indicated that the addition of RM facilitated effective simultaneous iron extraction and dephosphorization. The co-reduction mechanisms were analyzed using X-ray diffraction (XRD), thermodynamic analysis, and scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS). In the absence of RM, the reduction of fluoroapatite occured, leading to the incorporation of P into metallic iron. However, with adding RM, albite and anorthite were generated, hindering the reduction behavior of fluoroapatite and reducing P content in DRI. Thus, RM effectively served as a green dephosphorization agent in the co-reduction process.