Influence of SiO 2 modification on phosphorus enrichment in P bearing steelmaking slag

Abstract

In order to effect enrichment of phosphorus in the converter slag, phosphorus enrichment was researched by slag modification with SiO₂. The SiO₂ modification process was evaluated thermodynamically, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that n2CaO.SiO₂–3CaO.P₂O₅ (nC₂S–C₃P) solid solution is generated by the reaction of Ca₃(PO₄)₂ phase in the slag with precipitated Ca₂SiO₄ phase at 1623 K, and Ca₂SiO₄ in the solid solution is reduced with increasing SiO₂; hence, the phosphorus content in the solid solution is increased. If the addition of SiO₂ is excessive, the amount of Ca₂SiO₄ precipitation in the slag is decreased remarkably (and even disappeared), CaSiO₃ phase is generated and the generation of nC₂S–C₃P solid solution is reduced, which is not favourable to phosphorus enrichment. Through magnetic separation, the non-magnetic fraction was increased by 10–74·68% compared with the original slag. The distribution ratio of P₂O₅ was increased from 2·71 to 5·48. As 84·57% of the phosphorus in the slag is in the collected non-magnetic substances, the work demonstrates that most of the phosphorus is able to be effectively recycled.