Effective separation and recovery of iron and chromium from laterite residue in the presence of calcium chloride

Abstract

In nitric acid pressure leaching (NAPL) for the treatment of limonitic laterite ores, the comprehensive utilization of leach residue is significant for resource recovery and environmental protection. In this work, the recovery and separation of iron and chromium from NAPL residue by metallization reduction roasting−magnetic separation with calcium chloride as additive was studied. The following optimum parameters were obtained: 1100 °C roasting temperature, 25 % reductant dosage, 40 min roasting time, 7 % calcium chloride dosage, 200 mT magnetic field intensity, and 40 s rod mill time (D50 = 7.20 µm). Under these optimum conditions, 81 wt% iron content in the concentrate and 7.4 wt% chromium in the tailings were obtained. The corresponding recovery rates of iron and chromium were 95 % and 64 %, respectively. The microstructure and composition of leach residue and process products were investigated by SEM, EDS, and XRD to study the phase transition and polymerization of substances during roasting. The results showed that iron was mainly enriched in the magnetic concentrate, and chromite and silicate minerals dominated the tailings. Analysis of the action of calcium chloride in the reduction roasting revealed that calcium chloride was beneficial for the liberation of Fe from fayalite and the migration and polymerization of iron.