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

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 ۳۵-۹۵°C for AL and ۲۲۰-۲۵۰°C for HPAL. Nickel and cobalt contents were found to be ۰.۷% and ۰.۰۴%, respectively. AL achieved an ۸۹% yield of Al with a pH of ۰.۲ and a ۱۴-hour leaching time, while nickel and iron recoveries reached ۹۲% and ۸۷% after ۲۰ hours, with an acid consumption of ۱.۲ kg H۲SO۴ per ۱۰۰ kg laterite (dry) at pH ۰.۲. Leaching experiments at ۲۲۰-۲۵۰°C for ۲ hours showed similar nickel recovery rates, indicating no improvement beyond ۲۴۰°C. Hematite, a stable compound associated with nickel, hindered its release during HPAL due to its resistance to leaching. Nickel yields remained around ۹۰% 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 ۱.۵ with activation energies of ۳۶.۲۳ and ۲۵.۰۹ kJ/mol for Ni and Fe, respectively.

Laterites, Nickel, Atmospheric leaching, HPAL, Environmental friendly