Patent ID: 8276761

Claim:
An apparatus for extracting a valuable substance from a slurry comprising a mixture of solid phase, liquid phase and said substance, the apparatus comprising: a flotation vessel having an inlet feeding slurry into the flotation vessel; a gas dispersion mechanism for delivering gas into the slurry to infuse gas bubbles into the slurry said gas bubbles being for capturing said substance from the slurry and forming a froth phase above the slurry phase; means for removing froth from the flotation vessel by overflow; and means for mechanically generating continuously moving negative pressure zones in the froth phase in the flotation vessel before the overflow so that the negative pressure zones extend from the froth phase to the slurry phase and so that said negative pressure zones capture unwanted slurry and liquid pockets entrained from the slurry phase to the froth phase and form paths for guiding said unwanted slurry and liquid pockets via said paths from the froth phase downwardly back to the slurry phase, wherein the means for mechanically generating continuously moving negative pressure zones comprises a helical rotor having a plurality of sloped rake blades extending in the froth phase and partly into the slurry phase, each rake blade having a spiral shape twisted around a vertical center axis of rotation and the rake blades being arranged at different radial distances from the center axis of rotation, and means for rotating said rake blades whereby the negative pressure zones are formed behind the rake blades by the movement of the rake blades through the froth phase.