During bioleaching of pyrite particles, acidophilic micro-organisms attack the iron sulfide and use the oxygen of air to oxidize the sulfide to sulfuric acid. This operation is usually done in stirred tanks. To investigate the feasibility of bioleaching in slurry bubble columns, some basic investigations on the hydrodynamics and the gas-liquid mass transfer were made, since the behavior of a typical pyrite flotation pulp (small but very dense particles: rho(s) = 4500 kg/m(3)) in slurry bubble columns is not well known. Two long duration bioleaching experiments were performed in the same small scale (ID 0.1 m; height: 2 m) column as the hydrodynamics and mass transfer investigations. The variations with time of mean oxygen uptake rate and the dissolved oxygen concentration were determined. One of the conclusions of this work is that oxygen mass transfer limitations play an important role in bioleaching in suspended solid bubble columns, even in the small-scale equipment tested here. It is also shown that higher solid loads may be used in this kind of equipment than in the traditional stirred tank reactor.