Effect of CaF2 and SiO2 modification on phosphorus utilisation in P-bearing slag

Abstract

In order to recycle phosphorus in P-bearing converter slag for slag phosphate fertiliser, the effect of CaF2 and SiO2 modification on P-bearing steelmaking slag on phosphorus-bearing phases, P2O5 solubility and magnetic separation behaviour has been researched. The results show that the phosphorus-rich phase is mainly n2CaO·SiO2–3CaO·P2O5 (nC2S–C3P for short) and exists along with fluorapatite phase [Ca5(PO4)3F] after the addition of CaF2. The fluorapatite cannot be dissolved in 2% citric acid solution, which decreases the P2O5 solubility in slag. Although adding CaF2 can increase the P2O5 content of phosphorus-rich phase, it can improve its metallisation and magnetisation of RO phase, increase the amount of recovered magnetic substances, and separate incompletely phosphorus and iron, therefore it is adverse to the phosphorus recovery from P-bearing slag by magnetic separation. P2O5 content of phosphorus-rich phase is more than 31% and P2O5 solubility of slag is increased to 96% in fluorine-free modified slag, which can meet the requirement of P2O5 content and P2O5 solubility of the phosphate fertiliser. Meanwhile, 87.1% of the phosphorus in the fluorine-free modified slag is contained in non-magnetic substance, and most of the phosphorus was recycled.