In-process online oxidisability regulation of BOF slag enabled by carbon-containing dust

Abstract

Carbon-containing dust, a solid waste from steelmaking, has inherent carbon that can reduce the iron oxide in both the dust itself and BOF slag. Efficient recovery of iron resources contained in BOF slag and dust can be achieved through online control of the slag's oxidisability, thereby minimising iron loss. This study investigated the oxidisability variation of BOF slag during carbothermal reduction by adjusting the ratio of BOF slag to carbon-containing dust and reduction time. The research employed FactSage simulations, complemented by XRD, SEM-EDS and other analytical techniques. The results indicate that MgO and MnO react with incompletely reduced Fe³⁺ and Fe²⁺ to form an intermediate phase, (Mg, Mn)_yFe_3−yO₄, which subsequently combines to form a mixture comprising (Mg, Mn)_xFe_1−xO, (Mg, Mn)O, and metallic iron. Under conditions where iron oxides are fully reduced in the mixed slag, as the reduction reaction time increases, the FeO content initially rises from 12.05 wt% to 14.32 wt%, followed by a decrease to 3.70 wt%. Concurrently, the metallic iron content increases from 5.23 wt% to 27.06 wt%, forming iron blocks that separate from the slag phase, and subsequently declines to 2.22 wt%. Under sufficient reduction time, the FeO content continuously decreases from 14.27 wt% to 10.02 wt%, 3.70 wt% and finally to 1.57 wt% as the proportion of carbon-containing dust increases. When the C/O ratio is 0.8 (corresponding to a carbon-containing dust proportion of 11.31 wt%), the FeO content and iron block mass are measured at 10.02 wt% and 24.10 g. This method demonstrates the potential for online regulation of the oxidisability of Basic Oxygen Furnace slag and the efficient recovery of iron resources.