Effect of B2O3 and Na2B4O7 on phosphorus enrichment in Ca2SiO4–Ca3(PO4)2 solid solutions
摘要
To separate the phosphorus-containing phase from steel slag, the effects of B2O3 and Na2B4O7 on the enrichment of phosphorus-containing phases in Ca2SiO4–Ca3(PO4)2 (C2S–C3P) solid solution were comparatively analyzed through theoretical calculations and experimental investigations. The results indicate that the optimum reaction temperature between B2O3 and C2S–C3P is 800 °C. The phase compositions of C2S–C3P equilibrium system with 5 wt.% B2O3 at 800 °C included Ca3(PO4)2, CaSiO3 and Ca11B2Si4O22, among which the content of Ca3(PO4)2 was the highest. For C2S–C3P with 5 wt.% Na2B4O7 equilibrium system, Ca3(PO4)2, CaSiO3, Ca11B2Si4O22 and Na2Ca2P2O8 were independent at 390–690 °C. Ca3(PO4)2 and Ca2SiO4 precipitated in the solid solution when the addition of B2O3 was more than 6 wt.%, and the content of Ca3(PO4)2 raised with the increase in the addition of B2O3. The main phases in the C2S–C3P solid solution with Na2B4O7 were (Ca2SiO4)0.05[Ca3(PO4)2], Ca2SiO4 and Na3Ca6(PO4)5 at 650 °C. And when the addition of Na2B4O7 exceeded 6 wt.%, the content of Na3Ca6(PO4)5 increased significantly. There was no precipitation of Ca3(PO4)2 or boron-containing phase in the samples with Na2B4O7, but a small proportion of Ca3(PO4)2 transformed into (Ca2SiO4)0.05[Ca3(PO4)2], and Ca2+ was partially replaced by Na+ to generate Na3Ca6(PO4)5. As a result, the temperature for Na2B4O7 to enrich the phosphorus-containing phase in C2S–C3P solid solution was lower than that for B2O3. However, the grade of the phosphorus-containing phase for Na2B4O7 was lower than that for B2O3.