Abstract
In order to recycle the phosphorus in P-bearing converter slag and make it used as slag phosphate fertilizer, the effect of Na2O in P-bearing steelmaking slag on phosphorus existence form, P2O5 solubility and magnetic separation behavior was researched systematically. The results show that the melting point of slag decreases obviously with the increasing of Na2O content in slag, and high phosphorus solid solution (Ca2SiO4–Ca3(PO4)2 and Na2Ca4(PO4)2SiO4) are generated by the continuous reaction of 6Ca2SiO4–Ca3(PO4)2 (for short 6C2S–C3P) solid solution precipitated in the slag with Na2O under the condition of 1623 K. The early precipitated 6C2S–C3P solid solution is reduced with the increasing content of Na2O even disappeared. If the addition of Na2O is increased or excess in the slag, the high phosphorus solid solution (Na2Ca4(PO4)2SiO4) that generated by the above mentioned reaction will continue to react with Na2O to produce Na3PO4, then the phosphorus content in the phosphorus-rich phase is heightened. Na2Ca4(PO4)2SiO4 and Na3PO4 have almost same good citric acid solubility with 6C2S–C3P solid solution. Therefore, adding appropriate Na2O content into slag can improve the slag P2O5 solubility, but the effect of different amounts of Na2O on the P2O5 solubility has little difference. Meanwhile, Added Na2O into slag can improve the metallization of slag and magnetism of iron-rich phase, make the magnetic substances content increased and separation of phosphorus and iron is incomplete, so it is adverse to phosphorus resources recovery from P-bearing slag by magnetic separation method. In order to recycle the phosphorus in P-bearing converter slag, adding appropriate Na2O content (<6%) into slag can be used as a flux to instead of fluorite for slag forming in steelmaking process.
