The Effect of Pre-Roasting on the Atmospheric HCl and HNO<sub>3</sub> Leaching of Ni, Co, and Fe from Sorowako Limonite Ore, Sulawesi, Indonesia

An atmospheric leaching of a limonite ore from Soroako, Sulawesi, Indonesia, has been performed using hydrochloric acid (HCl) and nitric acid HNO 3 solutions. The study's objectives are to determine the effect of pre-roasting the laterite ore sample on the dissolution behavior and to compare the leaching efficiency of metals (Ni, Co, and Fe) from limonite under HCl and HNO 3 lixiviants. The sample was characterized using optical microscopic, X-ray diffraction (XRD), X-ray fluorescence (XRF), and atomic absorption spectrometry (AAS) methods. Heating the ore at 300 °C has transformed goethite into proto-hematite, resulting in the highest Ni and Fe leaching efficiency. However, Co leaching efficiency attains the maximum at a roasting temperature of 750 °C. It is shown that HCl leaching for Ni and Fe is more efficient than HNO 3 . The higher leaching rate of Fe under HCl indicates low selectivity of iron relative to nickel.