Product Diffusion-Controlled Leaching of Nickel Laterite using Low Concentration Citric Acid Leachant at Atmospheric Condition

Abstract

This work studies the leaching kinetics of nickel laterite in a citric acid solution. A new kinetics model that considers a reversible chemical reaction and internal diffusion of a product is proposed. The experiment was conducted at various temperatures (303, 333, and 358 K) and particle sizes (< 70 to 250 ?m). Whereas acid concentration, pulp density, and leaching time were constant at 0.1 M, 20% w/v, and 120 min, respectively. The experimental results showed that the leaching process was dependent on temperature and particle size. In the case of Ni, Al, and Fe leachings, the formation of complex molecules might lead to a steric hindrance of product diffusion; however, this was not observable for Mg. The proposed model was found to be much better than the conventional shrinking core models (SCM). Using the proposed model, the activation energy for nickel was found to be 121.38 ± 0.0324 kJ/mol, 78.98 ± 0.4157 kJ/mol, 1,022.62 ± 9.6507 J/mol for forward reaction, backward reaction, and diffusion, respectively.

Keywords

• citric acid
• diffusion model
• leaching kinetics
• nickel laterite
• shrinking core model