Effective Separation and Beneficiation of Iron and Chromium from Laterite Sulfuric Acid Leach Residue

Abstract

The utilization of laterite sulfuric acid leach residue has always been a challenge in the metallurgical industry. The current treatment involves deep-sea landfills, which leads to considerable environmental pollution and resource wastage. In this work, an effective method is proposed to recover iron and chromium from sulfuric acid leach residue. The effects of roasting temperature, reducing agent dosage, and reaction duration on the recovery of iron and chromium were investigated. The optimum conditions were as follows: roasting temperature of 1200 °C, reducing agent dosage of 30%, and reaction duration of 60 min. Results show that the concentrate contains 87% Fe and that only 0.7% S can be obtained with an iron recovery of 82%, indicating suitability for ironmaking. Meanwhile, 85% of chromium can be beneficiated in tailings at a chromium content of 3.5%. The microstructure and composition of reduction products were analyzed by XRD, SEM, and EDS to understand the phase transformation and the aggregation of the reduction products. Hematite in the leach residue is first reduced to FeS and Fe3O4 at low temperature and then reduced to metallic iron with increased temperature. Sulfur is combined with alunite to form FeS at a low temperature, and the decomposition of chromite at high temperature leads to the formation of chromium oxide. In a high temperature and reducing atmosphere, Cr2O3 reacts with FeS to transform Fe and CrS. Through the reduction roasting–magnetic separation process, most of the iron is beneficiated in the concentrate, and nonmagnetic minerals such as FeS and CrS remain in the tailings. Consequently, the separation and beneficiation of iron and chromium occur. The process is economically feasible and environmentally friendly and thus has great potential for the industrial-scale recycling of laterite sulfuric acid leach residue.