A Kinetic Study of Manganese Leaching from Low-Grade Psilomelane Ore by Acetic-Tannic Acid Lixiviant

Kinetic leaching of psilomelane using tannic acid as reductant and acetic acid as an acidic
modifier is investigated in terms of tannic acid and acetic acid concentration, solid-liquid ratio,
particle size and temperature. Kinetic modelling using three models: shrinking core, shrinking
particle, and diffusion-interface transfer model revealed that at room temperature leaching (30 °C),
experimental data are best modelled using diffusion-interface transfer model, indicating the
dissolution of Mn is more affected by reaction rate among reactants and their concentration in
bulk volume rather than by transfer across the boundary layer. At higher temperatures (≥ 50 °C),
the shrinking particle model fits the experimental data best, suggesting the prominence of the
diffusion process boundary layer. The apparent activation energy obtained at two temperatures
were 13.1 and 52.7 kJ/mol for lower and higher temperatures. Plot between rate constant and
concentration yields reaction order to be 1.28 for tannic acid and 0.73 for acetic acid. A semi
empirical model for each temperature range is proposed to describe the overall manganese
leaching efficiency.