Bioleaching of molybdenite

Molybdenum was bioleached from molybdenite-containing mine waste samples and from high purity molybdenite in solutions amended with ferrous sulfate. Bioleaching of Mo occurred when solution Eh exceeded 750 mV to 800 mV (s.h.e.). The rate of bioleaching of high purity molybdenite increased with decreasing particle size, averaging 3.22 mg Mo/m2/d at 24 °C. This surface area-based rate is less than 1% of the bioleaching rate of pyrite. Molybdenite bioleaching increased with temperature by a factor of approximately 2.5 for each 10 °C increase in leaching temperature up to 40 °C. Apparent activation energies were 61.2 to 73.4 kJ/mol for bioleaching of high purity molybdenite and for molybdenite from mineral processing waste streams, respectively. Thermophilic bioleaching at 65 °C did not improve the rate or extent of Mo extraction. Molybdenum extraction was about 50% from mineral process waste stream samples after the first month of bioleaching, and slowed thereafter. Ultimate Mo extraction was approximately 85% after 6 months of bioleaching. High concentrations of ferric iron in bioleach solutions allowed iron-oxidizing microorganisms to grow, oxidize iron and bioleach molybdenite at dissolved Mo concentrations as high as 4.4 g/L. There was no evidence for selection of microbial populations with increased Mo resistance.