| Summary: | Based on the results obtained from a previous study investigating the dissolution of Mn from marine nodules with the use of sulfuric acid and foundry slag, a second series of experiments was carried out using tailings produced from slag flotation. The proposed approach takes advantage of the Fe present in magnetite contained in these tailings and is believed to be cost-efficient. The surface optimization methodology was used to evaluate the independent variables of time, particle size, and sulfuric acid concentration in the Mn solution. Other tests evaluated the effect of agitation speed and the MnO<sub>2</sub>/Fe<sub>2</sub>O<sub>3</sub> ratio in an acid medium. The highest Mn extraction rate of 77% was obtained with an MnO<sub>2</sub>/Fe<sub>2</sub>O<sub>3</sub> ratio of 1/2 concentration of 1 mol/L of H<sub>2</sub>SO<sub>4</sub>, particle size of −47 + 38 μm, and 40 min of leaching. It is concluded that higher rates of Mn extraction were obtained when tailings instead of slag were used, while future research needs to focus on determination of the optimum Fe<sub>2</sub>O<sub>3</sub>/MnO<sub>2</sub> ratio to improve dissolution of Mn from marine nodules.
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