Removal of phosphorus from steel-making slag by carbothermic reduction

Abstract

Basic oxygen furnace (BOF) slag is a main byproduct in steelmaking and the growth rate of slag generation is increasing as steel production increases Due to most of the elements in the converter slag are beneficial components it can be reused as a raw material in the steelmaking process However the high phosphorus content in the basic oxygen furnace slag limits its recycling in the steel-making process Most of phosphorus in BOF slag is incorporated with Ca2SiO4 to form a Ca2SiO4?Ca3(PO4)2 solid solution Therefore it is necessary to find a method to remove phosphorus in slag without causing other harmful effects in order to activate BOF slag recycling In this work the reduction of P2O5 from the BOF slag was investigated Graphite SiO2 CaCl2 and Al2O3 were used as dephosphorization agents under conditions of different temperatures (1500°C and 1600°C) The chemical compositions of the slag are analyzed with XRF The crystalline phases of the slag are obtained by XRD The phosphorus contents in the iron particles and solution are analyzed by ICP-OES Elemental mapping and compositional analysis of P-phase of the slags are quantitatively characterized using EMPA and WDS analysis The experimental results show that SiO2 favors reduction of phosphorus in the slag but excess SiO2 may cause re-dephosphorization The Al2O3 is good for reduction of iron but it decreases the reduction of phosphorus due to the formation of Ca2Al2O7 Due to the dissociation of CaCl2 into CaO at 800-900°C the increased basicity inhibits the dephosphorization The best phosphorus vaporization rate is carried out at1500°C with the graphite and SiO2 mixing ratio of 7 wt % and 5 wt % respectively Moreover the best dephosphorization rate under conditions of 7 wt % C and 10 wt % SiO2 at 1600°C EPMA observation of the slag after the experiment showed that most of phosphorus concentrated in the metal phase and the content of phosphorus in the metal phase increase with the increasing of graphite content

Date of Award	2020
Original language	English
Supervisor	Shou-Heng Liu (Supervisor)