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 ${\displaystyle \frac{{\left[\text{\%}{\mathrm{P}}_2{\mathrm{O}}_5\right]}_{SS}}{{\left[\text{\%}{\mathrm{P}}_2{\mathrm{O}}_5\right]}^0}=-2.11472e^{-\frac{t}{51.04047}}+3.04849}$. 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.

KEYWORDS:

• P-bearing steelmaking slag
• solid solution
• temperature control
• enrichment
• dynamics

Acknowledgements

This work was supported by the National Natural Science Foundation of China under Grant number 51704080 & 51874102 & 51704085; Key Laboratory of Metallurgical Emission Reduction & Resources Recycling, Ministry of Education Foundation under Grant KF17-01; and the State Key Laboratory of Refractories and Metallurgy Foundation under Grant G201804.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China: [Grant Number 51704080]; the National Natural Science Foundation of China: [Grant Number 51874102]; the State Key Laboratory of Refractories and Metallurgy Foundation: [Grant Number G201804]; Key Laboratory of Metallurgical Emission Reduction & Resources Recycling, Ministry of Education Foundation: [Grant Number KF17-01]; Foundation for the Author of National Excellent Doctoral Dissertation of the People’s Republic of China (CN): [Grant Number 51704085].