Transfer of O2 from air to mineral slurries in a rushton turbine agitated tank

Oxygen transfer from dispersed air in agitated slurries represents an important unit operation in the minerals processing industry. Gold leaching, iron precipitation and especially bio-oxidation come readily to mind. However, little engineering information is available on the effect of mineral solids on such 02 transfer. Engineering literature on the subject, i.e. information which relates slurry density and energy input to 02 transfer, is reviewed and compared to current experimental work. The latter was carried out with minus 50 micron sand/water slurries in a 64 1 laboratory tank of standard proportions, equipped with a standard Rushton turbine and variable speed drive with torque meter. s confirm an increasing impairment of 02 transfer with increasing slurry density. The volumetric mass transfer coefficient, kla, in a 10 vol.% slurry shows a decrease of 30% compared to the kta in water. At 40 vol. % sand this decrease is near 60%, depending somewhat on superficial gas velocities. Power needed for equivalent oxygen transfer increases even more steeply with slurry density. Experimental results are presented and their significance for slurry bio-oxidation discussed.