Thermodynamic studies on selective oxidation of Nb, P and C in dephosphorization of low niobium hot metal

The main problem with the efficient utilization of Nb resource in the Boyan Obo Ore lies in the selective oxidation of [Nb], [P] and [C]. In this work, thermodynamic studies have been conducted to determine the conditions of selective oxidation of [Nb], [P] and [C] in low niobium hot metal in the process of oxidizing dephosphorization. The thermodynamic condition for dephosphorization was determined as: Ig alpha((P2O5)) <= 38754/T -27.82 + 5Ig alpha([O]) + 2Ig alpha([P]) The condition for retaining Nb from oxidation is: Ig alpha([O-Nb]) <= 1/5Ig alpha((Nb2O5)) -2/5Ig f([nb]) -2/5Ig[%Nb] -70425/T + 28.14 The oxygen activity for oxidation of Nb, C and P is relevant to the initial [C] content in hot metal. The equilibrium oxygen activity of Nb-O reaction increases with an increase of the [C] content, whereas the equilibrium oxygen activity of C-O and P-O reactions varies oppositely with the [C] content. The reduction of (alpha P2O5) results in a decrease of the [C] content required for removing P and retaining Nb, as well as makes the process of dephosphorization more feasible. The increase of temperature decreases the [C] content of selective oxidation of Nb and P, but is unfavorable to dephosphorization.