Microbiological Beneficiation of Low Grade Manganese Ores: A Review

Manganese is a transition element like iron. However, it exists in different valencies like 2, 3, 4 and 7. Of these, Mn 2+ is highly water soluble, but is rarely found in natural conditions. Mn 4+ is the least water soluble and under different pH and redox conditions it can slowly become colloidal in natural water. It exists naturally as a very common mineral called pyrolusite and is used for pyrometallurgical processes in ferro‐alloys industries. However, in order to have such beneficial application, the manganese content should be more than 80% in the ore. Anything less than this is treated as low grade ore and is usually dumped on land with cultivable soil, in order to reach deeper for the high grade ores. This is highly ecotoxic to the environment and over a period of time can be very damaging to agriculture and the biodiversity which includes human health as it finds its way to ground water table like wells and ponds. As time went by and high grade ore started depleting, miners started going deeper in the ground, with the result of dumping lower grade ores over surface soils. In this study, such low grade ores were examined and found to contain a mixture of Mn 3+ and Mn 4+ oxides. When such ores were subjected to microbial oxidation, it was found that under certain conditions of growth, Arthrobacter sp could not only convert the Mn 3+ to Mn 4+ and 67% of the Mn 4+ oxides had the ramsdellite γ‐ crystalline structure, which could be used as a depolarizer in the dry cell batteries. This was considered as a very important biotechnological discovery which not only could save the biodiverse environment but also gave a value added product for commercial exploitation.