In order to effect enrichment of phosphorus in converter slag, phosphorus enrichment was researched by Al 2 O 3 melting modification, the Al 2 O 3 modification process is discussed according to the thermodynamic analysis, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that gehlenite (Ca 2 Al 2 SiO 7 ) and high phosphorus solid solution (n9C 2 S-C 3 P) are generated by the continuous reaction of n2CaO.SiO 2 -3CaO.P 2 O 5 (nC 2 S-C 3 P) solid solution precipitated in the slag with Al 2 O 3 at 1623K. The early precipitated solid solution (nC 2 S-C 3 P) is reduced with increasing content of Al 2 O 3 , and even disappeared. If the addition of Al 2 O 3 is increased or excess in the slag, the high phosphorus solid solution (n9C 2 S-C 3 P) that was generated by the above mentioned reaction will continue to react with Al 2 O 3 to produce gehlenite, then the phosphorus content in the phosphorus rich phase is increased. Through magnetic separation the amount of non-magnetic substance of no. 2 slag after modification is raised 26?88% compared to the original slag, the distribution ratio of P 2 O 5 is raised from 0?96 to 4?61, and the amount of separated non-magnetic substance is 68?47% of the total no. 2 slag, 84?57% of the phosphorus in slag is entered into collected non-magnetic substance, thereby most phosphorus element was recycled.
In order to effect enrichment of phosphorus in the converter slag, phosphorus enrichment was researched by slag modification with SiO 2 . The SiO 2 modification process was evaluated thermodynamically, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that n2CaO.SiO 2 -3CaO.P 2 O 5 (nC 2 S-C 3 P) solid solution is generated by the reaction of Ca 3 (PO 4 ) 2 phase in the slag with precipitated Ca 2 SiO 4 phase at 1623 K, and Ca 2 SiO 4 in the solid solution is reduced with increasing SiO 2 ; hence, the phosphorus content in the solid solution is increased. If the addition of SiO 2 is excessive, the amount of Ca 2 SiO 4 precipitation in the slag is decreased remarkably (and even disappeared), CaSiO 3 phase is generated and the generation of nC 2 S-C 3 P 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 P 2 O 5 was increased from 2?71 to 5?48. As 84?57% of the phosphorus in the slag is in the collected nonmagnetic substances, the work demonstrates that most of the phosphorus is able to be effectively recycled.
In order to recycle phosphorus in P-bearing converter slag for slag phosphate fertiliser, the effect of CaF 2 and SiO 2 modification on P-bearing steelmaking slag on phosphorus-bearing phases, P 2 O 5 solubility and magnetic separation behaviour has been researched. The results show that the phosphorus-rich phase is mainly n2CaO?SiO 2 -3CaO?P 2 O 5 (nC 2 S-C 3 P for short) and exists along with fluorapatite phase [Ca 5 (PO 4 ) 3 F] after the addition of CaF 2 . The fluorapatite cannot be dissolved in 2% citric acid solution, which decreases the P 2 O 5 solubility in slag. Although adding CaF 2 can increase the P 2 O 5 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. P 2 O 5 content of phosphorus-rich phase is more than 31% and P 2 O 5 solubility of slag is increased to 96% in fluorine-free modified slag, which can meet the requirement of P 2 O 5 content and P 2 O 5 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.
The surface cleanness of Ti-IF steel, including head, transition, end and normal slabs, was studied by original position analyser. The content, number, size and porosity of inclusions on the surface were obtained. The results showed that: the contents of inclusions in head and end slabs were significantly higher than in normal or transition slabs and fluctuated significantly in nonsteady state slabs within 3.5 mm of the surface; the porosity in 3.5 mm of slab surface was lower than other positions; the surface cleanliness order was normal slab.transition slab.end slab.head slab; a reasonable surface peeling thickness for non-steady state slabs was 3.5 mm. The energy dispersive spectroscopy showed that more lump Al 2 O 3 existed in the head slabs, and slag entrapment inclusions also appeared frequently in the end slabs. The main effect factors for cleanness of the head and end slabs were reoxidation and slag entrapment.
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