Preparation of a Master Fe–Cu Alloy by Smelting of a Cu-Bearing Direct Reduction Iron Powder

Abstract

Generally, the Cu-bearing direct reduction iron powder (CBDRI) obtained from a direct reduction-magnetic separation process of waste copper slag contains a high content of impurities and cannot be directly used to produce Cu-bearing special steel. In this paper, further smelting treatment of CBDRI was conducted to remove its impurities (such as S, SiO2, Al2O3, CaO and MgO) and acquire a high-quality Fe–Cu master alloy. The results show that the Fe–Cu master alloy, assaying 95.9% Fe, 1.4% Cu and minor impurities, can be obtained from the smelting process at 1550 °C for 40 min with 1.0 basicity. Meanwhile, the corresponding iron and copper recoveries are 98.6% and 97.2%, respectively. Theoretical calculations and experimental results show that appropriate basicity (0.9~1.1) is beneficial for the recovery of Fe and Cu from a thermodynamic viewpoint due to the excellent fluidity of the slag in this basicity range. Moreover, the mechanism of desulfurization was revealed by calculating the sulfide capacity and the desulfurization reaction kinetics. Increasing the binary basicity of the slag benefits both the sulfide capacity and diffusion coefficient of the sulfur in the molten slag, resulting in higher desulfurization efficiency and lower S content in the master alloy.