Kinetics and Rate-Controlling Mechanism of Reductive Acid Leaching of a Beneficiated Madaka Manganese Ore: A Shrinking-Core Model Approach

This study kinetically analysed the reductive acid leaching of a beneficiated manganese ore from Madaka, Niger State, Nigeria, building on a prior experimental investigation. The ore, containing 48.44% MnO, was upgraded via froth flotation and leached in sulfuric acid with glucose as the reducing agent. Time-conversion data collected across five temperatures (323–363 K) and five acid concentrations (0.2–1.0 mol/L) were tested against four heterogeneous kinetic models: chemical reaction control, product-layer diffusion, liquid-film diffusion, and Avrami-Erofeev. Although several models fit individual isotherms well, only the product-layer (Ginstling-Brounshtein) diffusion model produced a rate constant that obeyed the Arrhenius relationship, identifying diffusion through the reacted product layer as rate-limiting. This yielded an apparent activation energy of 40.4 kJ/mol and a reaction order of 1.44 with respect to sulfuric acid concentration. A stirring-speed plateau above 400 rpm confirmed that external liquid-film diffusion was not controlling.