Effect of Retrofit Design Modifications on the Macroturbulence of a Three-Phase Flotation Tank—Flow Characterization Using Positron Emission Particle Tracking (PEPT)

Turbulence in stirred tank flotation tanks impacts the bulk transport of particles and has an important role in particle–bubble collisions. These collisions are necessary for attachment, which is the main physicochemical mechanism enabling the separation of valuable minerals from ore in froth flotation. Modifications to the turbulence profile in a flotation tank, therefore, can result in improvements in flotation performance. This work characterized the effect of two retrofit design modifications, a stator system and a horizontal baffle, on the particle dynamics of a laboratory-scale flotation tank. The flow profiles, residence time distributions, and macroturbulent kinetic energy distributions were derived from positron emission particle tracking (PEPT) measurements of tracer particles representing valuable (hydrophobic) mineral particles in flotation. The results show that the use of both retrofit design modifications together improves recovery by increasing the rise velocity of valuable particles and decreasing turbulent kinetic energy in the quiescent zone and at the pulp–froth interface.

: Key to figures of azimuthal slices of the vessel (a) the geometry in terms of vertical position z and radial position r and (b) the relative proportions of z to the vessel height H and r to vessel radius R. The voxels outlines are plotted relative to features of the vessel geometry including the rotor impeller, stator, mesh, interface and lip level. See the main article for further information.
S-2 Figure S2: Particle size distribution of a sample of the silica solids in size +75 -150 µm used for flotation experiments. Measured using a Mastersizer 3000. Figure S3: Radial velocity U r from PEPT measurements of a hydrophobic tracer particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The horizontal axis of each azimuthal slice corresponds to the radial position 0 ≤ r < 90 mm and the vertical axis is the vertical position -60 ≤ z < 160 mm; refer to Figure S1 for the geometry of the voxel configuration. The lip and approximate interface levels are indicated with dashed lines and the impeller, stator and mesh with dotted lines.
S-3 Figure S4: Azimuthal angular velocity U θ from PEPT measurements of a hydrophobic tracer particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The horizontal axis of each azimuthal slice corresponds to the radial position 0 ≤ r < 90 mm and the vertical axis is the vertical position -60 ≤ z < 160 mm; refer to Figure S1 for the geometry of the voxel configuration. The lip and approximate interface levels are indicated with dashed lines and the impeller, stator and mesh with dotted lines. Figure S5: Vertical velocity U z from PEPT measurements of a hydrophobic tracer particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The horizontal axis of each azimuthal slice corresponds to the radial position 0 ≤ r < 90 mm and the vertical axis is the vertical position -60 ≤ z < 160 mm; refer to Figure S1 for the geometry of the voxel configuration. The lip and approximate interface levels are indicated with dashed lines and the impeller, stator and mesh with dotted lines.
S-4 Figure S6: Magnitude of velocity U from PEPT measurements of a hydrophobic tracer particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The horizontal axis of each azimuthal slice corresponds to the radial position 0 ≤ r < 90 mm and the vertical axis is the vertical position -60 ≤ z < 160 mm; refer to Figure  S-8 Figure S10: Contours of the radial component of the turbulent kinetic energy per unit mass (u r 2 ) derived from PEPT measurements of a hydrophobic particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The lip and approximate interface levels are indicated with dashed lines and the impeller, stator and mesh with dotted lines. Figure S11: Contours of the angular component of the turbulent kinetic energy per unit mass (u θ 2 ) derived from PEPT measurements of a hydrophobic particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The lip and approximate interface levels are indicated with dashed lines and the impeller, stator and mesh with dotted lines.

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Figure S12: Contours of the vertical component of the turbulent kinetic energy per unit mass (u z 2 ) derived from PEPT measurements of a hydrophobic particle for each design: (a) rotor, (b) rotor + mesh, (c) rotor + stator and (d) rotor + stator + mesh. The lip and approximate interface levels are indicated with dashed lines and the impeller, stator and mesh with dotted lines. S-10