Surfactant-driven atmospheric leaching of cobalt from limonitic lateritic ore: CTAB effects and kinetic modeling

The increasing global demand for cobalt has driven interest in processing limonitic laterite ores, particularly in Indonesia, which hosts substantial laterite resources. Unlike saprolitic ores, which are typically processed by pyrometallurgical routes such as ferronickel smelting, limonitic laterites are predominantly treated by hydrometallurgical processes, particularly high-pressure acid leaching (HPAL) at industrial scale. Atmospheric nitric acid leaching (NAAL), while not yet widely implemented commercially, has emerged as a promising alternative due to its potential for lower capital intensity and improved process controllability. However, cobalt recovery from limonitic laterite is often constrained by mass transfer resistance and diffusion limitations, especially at high acid concentrations due to silica gel formation. This study investigates the use of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), to enhance cobalt recovery during the NAAL process. Leaching experiments were conducted using 1–4 M nitric acid at 50–90 °C with CTAB addition. The limonitic laterite contained 0.19 % Co, 1.37 % Ni, and 57.08 % Fe. The results show that cobalt recovery increased with acid concentration up to an optimum of 2 M HNO 3 at 90 °C and 240 min, beyond which recovery declined due to diffusion hindrance. Under optimal conditions, CTAB increased cobalt recovery from 43.8 % to 93.6 %, with additional improvements observed for nickel, while iron dissolution remained essentially unchanged. Kinetic analysis using the Shrinking Core Model revealed a shift in the rate-controlling step to ash layer diffusion under surfactant-assisted conditions, confirming that CTAB enhances mass transfer and enables efficient cobalt recovery under milder leaching conditions.