Influence of slag temperature on phosphorus enrichment in P-bearing steelmaking slag

Abstract

To effectively recycle the phosphorus in P-bearing steelmaking slag and use it as slag phosphate fertilizer, it is necessary to study the effect of slag temperature on occurrence forms and enrichment behaviour of phosphorus in P-bearing steelmaking slag. In this work, the thermodynamic and kinetic behaviours of the formation of phosphorus-rich phases are systematically investigated. The results show that decreasing of the slag temperature (1473—1823 K) has a little effect on the thermodynamic trend of the formation of the 2CaO·SiO₂ phase (denoted as C₂S) and on the early precipitation of the n2CaO·SiO₂–3CaO·P₂O₅ solid solution (denoted as n C₂S–C₃P). Additionally, the precipitation of C₂S first increases and then decreases, and reaches a maximum value between 1623 and 1653 K. Moreover, the diffusion of phosphorus is a rate-limiting link in the process. The kinetic equation that describes the variation of P₂O₅ content with time in the phosphorus-rich phase is . The composition of the P-bearing steelmaking slag is in the dicalcium silicate (C₂S) primary zone. Controlling the hold temperature and time, and the cooling rate of the P-bearing slag, allows for high-concentration phosphorus enrichment and for the increase of particle size in the n C₂S–C₃P solid solution. Also, when controlling the aforementioned parameters, the phosphorus partition ratio between the phosphorus-rich and matrix phases (L _p’) increases from 1.1–1.5 to 60–130, and the morphology of the former changes from acicular to fine bar to roughing bar. Furthermore, the P₂O₅ content in phosphorus-rich phase is 31%–33% in enriched slag, meeting the requirements for phosphate fertilizer production.