Metal Removal from Contaminated Soils Through Bioleaching with Oxidizing Bacteria and Rhamnolipid Biosurfactants

The use of surfactants as a method for solubilization and removal of heavy metal contamination from soil has been reported before. Biosurfactants produced by some microorganisms are able to modify the surface of various metals and aggregate on interphases favoring the metal separation process from contaminated environments. We evaluated the feasibility of enhancing the removal of metal ions from mineral waste/contaminated soils using alternate cycles of treatment with rhamnolipid biosurfactants and bioleaching with a mixed bacterial culture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. Bioleaching alone removed 50% Zn and 19% Fe. When rhamnolipids were used at low concentration (0.4mg/mL), 11% Fe and 25% Zn were removed, while at 1mg/mL 19% Fe and 52% Zn removal were achieved. When using a cyclic treatment combining bioleaching and biosurfactants, metal removal reached up to 36% for Fe and 63% to 70% for Zn.