How do acidic ores and basic ores affect manganese recovery in ferromanganese production?

In the production of ferromanganese, the acidity or basicity of the ore significantly influences the efficiency of metal recovery and the composition of the resulting slag.1

• Acidic Ores: These ores contain high levels of silica, an acidic compound that can combine with manganous oxide (MnO) during smelting. This reaction prevents the manganese from being reduced into the metal, thereby lowering recovery rates. When using acidic ores, recovery typically ranges from 70 to 80 percent, resulting in a slag that contains 30 to 42 percent manganese.12
• Basic Ores: To counteract the negative effects of silica, producers may use ores high in basic constituents like lime and magnesia, or add basic fluxes such as roasted limestone. This approach facilitates higher metal recovery, typically between 85 and 90 percent, and produces a slag low enough in manganese to be discarded.12

While basic conditions improve manganese recovery, they require higher energy consumption to calcine the fluxes and sustain the smelting process. Additionally, the acidity or basicity of the slag influences whether silica is reduced to silicon and enters the molten metal.21