Recovery of Fe and P from CaO-SiO ₂-Fe _tO-P ₂O ₅ slag by microwave treatment

In order to optimize the recovering process of Fe and P from steelmaking slag by the microwave irradiation, heating rates of various substances and recovery ratios of iron and phosphorus from slag-graphite mixtures were investigated. The heating rates of the examined substances are in the order of graphite Fe ₃O ₄ Fe ₂O ₃ > the synthesized CaO-SiO ₂-Fe _tO-P ₂O ₅ slag > the industrial slag. From the maximum heating rates, it was considered that the microwave absorption ability of graphite was 40 times greater than that of the industrial slag. Consequently, it was considered that the heating rate of the graphite-slag mixture was dominantly determined by graphite. In the reduction of the synthetic slag (15 g) by graphite (0.816 g), the weight of the recovered metal was maximized at 900 s under the present experimental condition (1.7 kW, 2.45 GHz). At a fixed microwave processing time of 900 s, the recovery ratio of iron increased with increasing the carbon equivalent (C _eq.: the mole ratio of carbon to oxygen to reduce Fe ₂O ₃ and FeO, yielding CO gas), and reached 0.97 when C _eq. = 1.69. The recovery ratio of phosphorus also increased with C _eq., and showed 0.89 at the same condition. From the chemical analysis of the slag and metal after experiments, it was found that the phosphorus distribution ratio (L _p) strongly depended on T. Fe content in slag, namely, as FeO content decreased, L _p value decreased.