Continuous biooxidation of a refractory gold concentrate

Biooxidation of a refractory gold concentrate in a continuous culture opera tion utilising a Thiobacillus ferrooxidans strain was studied. The experime nts were conducted in a 5 I, bioreactor using a 6% (w/v) pulp density in th e feed stream, dilution rate of solids between 0.088 and 0.92 d(-1), pH 1.5 and 33 degrees C. Main sulphur compounds of the concentrate were 41% enarg ite and 43% pyrite. Cell, ferric ion and sulphate productivity present a ma ximum at a solids dilution rate in the range of 0.6 - 0.8 d(-1). The presen ce of iron and negligible amounts of arsenic in solution are indicative tha t cells utilises pyrite as energy source rather than enargite. Specific gro wth rate and cell yield associated to solids present a saturation type curv e as a function of solids dilution rate. The increment of cell growth and m ineral dissolution as consequence of step changes, either lowering particle size or air enrichment with CO2, reflect a condition of a double limitatio n of the continuous culture, energy and carbon sources respectively.