Hydrometallurgical Synthesis of Cuboidal Manganese Sulfide (MnS) from Low-Grade Manganese Ores and Their Application as Energy Material

Low-grade ores have received great attention from an economic and environmental perspective due to the shortage of high-grade manganese ore resources. However, it is worth mentioning that the final value of the recovery process must be cost-effective. The extracted Mn²⁺ ions from the low-grade manganese ore were purified and converted to the desired manganese salt which is used as a Mn²⁺ source for the synthesis of manganese sulfide nanostructures (MnS). The low-grade oxide ore was treated by reduction roasting using chemically pure sulfur as a reductant. Then, the roasted samples were subjected to selective leaching conditions to extract manganese (Mn). The effects of the roasting and leaching parameters on the leaching efficiencies of Mn and Fe are investigated. The Mn leaching efficiency of 90.67% is obtained under the optimized conditions, whereas the Fe leaching efficiency is <0.01%. Additionally, the electrocatalytic application towards the oxygen evolution reaction (OER) of the hydrothermally synthesized MnS was studied in 1 M KOH using nickel foam (NF) as the substrate. The MnS-NF electrode material exhibits an overpotential of 285 mV at a standard current density of 10 mA/cm² and a Tafel slope of 75 mV/dec, respectively.