Reductive leaching of Co and Mn from laterite ore in nitric acid solution

Creating a reducing environment is essential for greatly enhancing the leaching efficiency of Mn 4+ and Co 3+ in laterite ores, as their reduction to divalent states significantly improves solubility in acidic media. This study examines the effects of ferrous iron (Fe 2+ ) and nitrite ion (NO 2 − ) as reductants on the leaching behaviour of Mn and Co under atmospheric nitric acid conditions. The temperature at which these reductants are introduced markedly influences the leaching efficiency. Leaching tests conducted at temperatures ranging from 70 to 110 °C show a notable decline in Mn and Co dissolution at higher temperatures. This decrease is attributed to the more reduction of nitric acid by the added reductants, which competes with the reduction of Mn and Co species, as well as direct losses of reductant by excessive NOx gas evolution. Under the test conditions in this bench scale leaching test, 90 °C was identified as the optimal temperature for reductant addition to maximise Co recovery under industrially favourable conditions. Further tests varying the amount of reductants are conducted to optimise leaching conditions. Additionally, X-ray absorption spectroscopy reveals increased structural disorder during leaching, suggesting the formation of crystal defects or oxygen vacancies around metal atoms. These findings could provide an insight into the leaching mechanisms and may help optimise commercial and industrially significant leaching processes.