Effect of slag basicity and reduction time on carbothermal reduction behaviour of P-bearing steelmaking slag

Abstract

ABSTRACT To realize the efficient reduction and recycling of phosphorus resources in P-bearing steelmaking slag, it is necessary to study slag composition and phase changes during carbothermal reduction under different conditions (slag basicity and reduction time). The thermodynamic and kinetic behaviours of carbothermal reduction dephosphorization of P-bearing steelmaking slag are systematically discussed as well. The results show that the reduction rate of FeO and P2O5 show an upward trend with the increase of reduction time at 1823 K. However, the reduction rate of FeO does not change much within 50 minutes. In the range of slag basicity from 0.5 to 2.5, the formation of Ca3(PO4)2 increases with the increase of slag basicity. However, the increase of slag basicity is not good for the occurrence of carbothermic reduction gasification dephosphorization reaction. Taking into account the higher formation of Ca3(PO4)2 and the better dephosphorization effect of carbothermic reduction gasification, the appropriate slag basicity for carbothermic reduction gasification dephosphorization is 1.0–1.5. Carbothermal reduction gasification dephosphorization reaction of P-bearing steelmaking slag is a second-order reaction, and the mass transfer of P2O5 in the slag is the rate-limiting step of the whole process. The kinetic equations that describe the variation of P2O5 content in slag with time are yielded through regression. At 1823 K, by controlling the appropriate slag basicity (1.0–1.5) and reduction time (at least 20 minutes), the gasification dephosphorization rate of the carbothermal reduction can reach more than 80%, which can realize efficient recovery of phosphorus resources in P-bearing steelmaking slag.