Manganese extraction from pyrometallurgy slags mediated by endemic microbial communities

Manganese represents a key metal in our modern industries being mainly used in the production of steel and alloy as well as batteries and chemicals like fertilizers. The growing issue of declining deposits and their depletion requires improved recovery from waste residues including industrial slags. In recent years, there has been a growing interest in bio-assisted extraction techniques that offset the energetic and environmental costs associated with high temperature as well as acid and reductive leaching processes. However, these approaches involve acidic conditions that limit their scope of application. By using elemental and mineralogical analyses combined with high-throughput DNA sequencing of 16S ribosomal RNA-encoding gene, we show here that manganese oxyhydroxides can be produced from ferro-magnesian pyrometallurgical slags as a result of the in situ activity of endemic slag-hosted microbial communities at alkaline and saline surface conditions. While microbially-produced reactive oxygen species likely contributed to the formation of Mn oxides accompanying slag alkalinizing biological and chemical alteration, we propose an important role of Alphaproteobacteria, notably members of the Erythrobacter genus, in the precipitation of Mn oxyhydroxides from slags.