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

Abstract

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.