Bioleaching for tailings valorisation.

An assessment of old and current mine tailings in Finland has shown that they have economic potential, with the metallic value being hundreds of millions of euros. Samples of acidic waters from the Pyhasalmi mine were analysed for bioleaching microorganisms and then used in bioleaching experiments using pyrite and pyrrhotite tailings from four Finnish mines. A high bacterial and fungal diversity was found in the mine water: Acidithiobacillus and Leptospirillum dominated the mine water 240 m below the surface, Leptospirillum dominated at 500 m below the surface, and Ferrovum and Metallibacter were dominant at 600 m below the surface. The bioleaching experiments showed that three of the tailings samples had rapid decrease of pH and increase of redox-potential, suggesting sulphide mineral dissolution, and resulting in iron oxidation and sulphuric acid production. For Tailing 4, no major pH decrease or redox-potential increase was observed, even though the material contained several wt% of pyrrhotite. Zn yields for Tailings 1 were 85% in 5 days, with low Ni and Co. Tailings 2 had a Zn yield of 100% in 18 days, and Tailing 3 had a Zn yield of 78% in 32 days.
An assessment of old and current mine tailings in Finland has shown that they have economic potential, with the metallic value being hundreds of millions of euros. Samples of acidic waters from the Pyhasalmi mine were analysed for bioleaching microorganisms and then used in bioleaching experiments using pyrite and pyrrhotite tailings from four Finnish mines. A high bacterial and fungal diversity was found in the mine water: Acidithiobacillus and Leptospirillum dominated the mine water 240 m below the surface, Leptospirillum dominated at 500 m below the surface, and Ferrovum and Metallibacter were dominant at 600 m below the surface. The bioleaching experiments showed that three of the tailings samples had rapid decrease of pH and increase of redox-potential, suggesting sulphide mineral dissolution, and resulting in iron oxidation and sulphuric acid production. For Tailing 4, no major pH decrease or redox-potential increase was observed, even though the material contained several wt% of pyrrhotite. Zn yields for Tailings 1 were 85% in 5 days, with low Ni and Co. Tailings 2 had a Zn yield of 100% in 18 days, and Tailing 3 had a Zn yield of 78% in 32 days.