2014 Volume 54 Issue 12 Pages 2746-2753
In order to recycle the phosphorus in P-bearing steelmaking slag and make it used as slag phosphate fertilizer, the citric acid solubility of P-bearing steelmaking slag was researched. The research results show that the citric acid solubility of P-bearing steelmaking slag is decreased with the increasing of P2O5 and Fe2O3 content for the CaO–SiO2–Fe2O3–P2O5 slag system. Added CaF2 into slag can easily form the fluorapatite (Ca5(PO4)2F) that can’t be dissolved in 2% citric acid solution, which makes citric acid solubility of the slag decreased obviously. And added MgO, MnO or Na2O into slag can prevent the precipitation of β-Ca3(PO4)2 phase with low citric acid solubility, which makes the citric acid solubility of slag increased. While for the CaO–SiO2–Fe2O3–P2O5–X (MgO, MnO or Na2O) slag system, MgO and MnO in slag mainly enters into RO phase, which has no effect on the phosphorus existence form in slag and has little influence on citric acid solubility of the slag. The Na2O in slag changes the phosphorus existence form in slag, but the generated Na2Ca4(PO4)2SiO4 and Na3PO4 also have good citric acid solubility, which also has little effect on citric acid solubility. Al2O3 and TiO2 modification only increases the phosphorus content in phosphorus-rich phase, does not change the phosphorus existence form in slag, which makes the citric acid solubility increased slightly. While SiO2 modification prevents the precipitation of β-Ca3(PO4)2 phase with low citric acid solubility, which makes citric acid solubility of the slag increased significantly. The modified slag without fluoride makes the citric acid solubility increased to 95% and meets the requirement of producing slag phosphate fertilizer.
