Novel metallic Fe recovery from copper smelting slag by the deep reduction method with renewable biochar reducing agent: Phase transformation process and Fe particle growth optimization

Abstract

The land stockpiling of copper smelting slag causes serious environmental pollution and resource waste. It contains a large amount of Fe, which is difficult to recover by traditional methods. In this paper, a novel metallic Fe recovery method was presented by deep reduction with renewable biochar as a reducing agent. It not only recovers metallic Fe but also relieves the pressure of iron ore with a sustainable and eco-friendly method. It was found that the metallization ratio variation trend was explored by the temperature, time, CaO content and C/O molar ratio increasing. When biochar was used as a reducing agent, the metallization ratios of Fe under different reduction conditions were better than the traditional reducing agent coal, which indicated that biochar could replace coal as a reducing agent. The phase transition and microstructure change during the deep reduction process were analyzed by XRD, XPS and SEM-EDS. The metallic Fe particles were formed from the copper smelting slag particle outside and spread to the inside gradually, distinguishing the slag phase and metal phase eventually. The growth kinetic equations of the two stages were obtained after calculation and simulation. There's a certain amount of truth to the predicted value because R2 is 0.9745 with experimental measurements. This study demonstrates that the deep reduction is a green and effective technology for copper smelting slag utilization.