Shahrood University of Technology Journal of Mining and Environment 2251-8592 15 4 2024 10 01 Environmental Friendly Approach: Atmospheric and High-Pressure Acid Leaching Studies, Low-Grade Laterites Nickel Processing 1591 1606 3198 10.22044/jme.2024.14230.2656 EN Ahmad Abbasi Gharaei Department of Mining Engineering, Science and Research Branch of Islamic Azad University, Tehran, Iran Bahram Rezai Department of Mining Engineering, Amirkabir University of Technology, Tehran, Iran. Hadi Hamidian Shormasti Department of Mining Engineering, Qaem Shahr Branch Islamic Azad University, Qaem Shahr, Iran Journal Article 2024 02 23 This paper examines the performance of Atmospheric Leaching (AL) and High-Pressure Acid Leaching (HPAL) on nickel laterite, classified as limonite. The study, conducted on a laboratory scale, involved temperatures of 35-95°C for AL and 220-250°C for HPAL. Nickel and cobalt contents were found to be 0.7% and 0.04%, respectively. AL achieved an 89% yield of Al with a pH of 0.2 and a 14-hour leaching time, while nickel and iron recoveries reached 92% and 87% after 20 hours, with an acid consumption of 1.2 kg H₂SO₄ per 100 kg laterite (dry) at pH 0.2. Leaching experiments at 220-250°C for 2 hours showed similar nickel recovery rates, indicating no improvement beyond 240°C. Hematite, a stable compound associated with nickel, hindered its release during HPAL due to its resistance to leaching. Nickel yields remained around 90% in both AL and HPAL tests. Iron behavior differed significantly between the two methods, with HPAL dissolving iron initially but transforming it into hematite in situ, leading to lower net acid consumption compared to AL. The leaching mechanism for iron oxides followed empirical power law kinetics of order 1.5 with activation energies of 36.23 and 25.09 kJ/mol for Ni and Fe, respectively. https://jme.shahroodut.ac.ir/article_3198_fbbc30baa6d6d11412ca0fa3aef80f40.pdf