Recovery of low phosphorus iron from steel slag using secondary aluminum dross as the reductant

Abstract

Iron extraction by carbothermic reduction is a promising technique for the recycling and valorization of steel slag, but phosphorus reduction and dissolution are inevitable and limit the value of the metal products. To solve this issue, in this work, a novel smelting reduction method was proposed to produce low phosphorus iron from steel slag by using secondary aluminum dross (SAD) as the reductant. The roles of modified basicity and SAD/slag in the iron recovery and phosphorus distribution behavior were investigated by various characterization and theoretical approaches, such as ICP-AES, XRD, SEM-EDX, FTIR, and FactSage. Owing to the fluxing action of Al2O3 and the supply of abundant free (O2-), the slag shows a fully melted and highly depolymerized state during reduction even when no slag modification is made, contributing to a high iron recovery (92.8 %). This is an advantage compared to other traditional reduction methods. Besides, the higher basicity under no modification significantly suppresses the reduction of P2O5 by reducing its activity coefficient, resulting in a decrease of 50 % in P content in the separated metals. It is also found that phosphorus recovery presents a power growth law with SAD/slag. The P content in the metals can be as low as 0.16 wt% by decreasing this ratio from 0.28 to 0.26. Although a sacrifice of iron recovery (∼6 %) is required for this purification, it shows great potential in producing high-quality metals from steel slag.