Tracking particles in froth flotation using positron emission

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					Waters et al
Tracking particles in froth flotation using positron emission particle tracking




       105 Tracking particles in froth flotation using positron
                    emission particle tracking
                           K.E.Waters1, N.A.Rowson2, X.Fan3, J.J.Cilliers1

1 Royal School of Mines, Department of Earth Science and Engineering, Imperial College
London, Prince Consort Road, South Kensington, London, SW7 2BP, UK
k.waters@imperial.ac.uk

2Department of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham,
B15 2TT, UK

3School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15
2TT, UK

                                                  Abstract

Understanding the motion of particles in froths and foams is vital for a number of applications,
not least froth flotation where hydrophobic and hydrophilic particles are separated by an
overflowing froth. Positron emission particle tracking (PEPT) is a method by which particles
                                                              18
can be tracked in engineering equipment. A radionuclide ( F, with a half-life of approximately
                                                                 3
110 minutes), generated by irradiating deionised water in a He beam from the Birmingham
University MC40 cyclotron, is adsorbed onto a tracer particle. As the F decays through 
                                                                            18                 +

decay positrons annihilate with electrons to produce a pair of back-to-back 511 keV -rays.
These -rays are detected using an ADAC Forte positron camera and the position of the
particle at the point of positron emission can be inferred at a rate of up to 250 Hz.

This work followed the motion of a hydrophobic and a hydrophilic particle in a froth flotation
cell. Prior to any air flowing in the Denver cell, i.e. no froth being formed, and with the
impeller set at 1500 rpm, there was little difference in the flow of the different particles. When
the air flow into the cell was switched on, the flow patterns were completely different.

The hydrophobic particle moved into the froth and overflowed, attached to bubbles. The
hydrophilic particle did not overflow, and very rarely entered the froth phase at the sides of the
flotation cell, appearing to follow the flow of the water rather than the bubbles. Using PEPT,
the movement of particles in the flotation cell was observed, and the behaviour. These
included the moment of attachment of the hydrophobic particle to an air bubble in the liquid,
indicated by a significant decrease in the particle velocity and a change in trajectory. The
occasional downward movement of the hydrophobic particle inside the froth also implied
detachment of the particle from a bubble, probably due to coalescence, and reattachment
prior to overflowing. PEPT has been shown to be a powerful tool in following particles in a
foam, and has considerable potential in assisting the generation and validation of
computational models of particle motion in froths.




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Waters et al
Tracking particles in froth flotation using positron emission particle tracking




Figure 1: Occupancy plot of the hydrophobic particle when the air into the cell has been switched on. The
particle enterer the froth and overflowed. Iit was then re-inserted into the cell and overflowing re-occurred




Figure 2: Occupancy plot for the hydrophilic particle once the air flow into the cell had been switched on.
The particle does not overflow, and only enters the froth at the side of the cell following the path of the liquid




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