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.