Transfer of O_2 from air to mineral slurries in a Rushton turbine agitated tank

摘要

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 O_2 transfer. Engineering literature on the subject, i.e. information which relates slurry density and energy input to O_2 transfer, is reviewed and compared to current experimental work. The latter was carried out with minus 50 micron sand/water slurries in a 64 l laboratory tank of standard proportions, equipped with a standard Rushton turbine and variable speed drive with torque meter. Results confirm an increasing impairment of O_2 transfer with increasing slurry density. The volumetric mass transfer coefficient, k_la, in a 10 vol. percent slurry shows a decrease of 30 percent compared to the k_la in water. At 40 vol. percent sand this decrease is near 60 percent, 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.