Project Status: Complete
Project Participants: University of Queensland, University of Newcastle
Project Leader: Graeme Jameson (University of Newcastle)
The recovery of sulfide minerals by flotation is influenced by the particle size. Particles in the range 30 to 120 microns generally float rapidly, but at each end of this range, the rate decreases markedly as particles become smaller or larger. For flotation to occur, a particle must be firmly attached to at least one bubble. The bubble exerts a lift force on the particle, through the action of surface tension acting
on the three-phase contact line on the surface of the particle. Gravity acts in opposition to the surface tension force. With pure homogenous particles of regular geometry, the attachment force depends on the particle geometry and the contact angle. In real systems the particles are seldom homogeneous, and are usually only partially liberated. The degree of liberation generally declines as the particle size increases. Thus when considering the flotation of coarse particles, it is essential to take into account the degree of liberation, the shapes of the hydrophobic mineralisation zones on the surfaces of the particles, as well as the effective contact angle of the composite.
In this project, samples of different ore types were crushed and ground in different ways so as to alter the liberation characteristics. The ground ore was subjected to flotation in the fluidised bed cell. Particles from feed, flotation product and tails were examined by Mineral Liberation Analysis or Cone Beam Tomography, on a size-by-size basis and the recovery were then correlated with the degree of
liberation.
Samples of lead/zinc ore have been crushed and separated into size fractions and a test protocol for coarse flotation was developed for the fluidised bed flotation cell. The test used galena particles in the same size range plus quartz as a gangue mineral to mimic the known lead concentration of the actual ore. The particle size that is recoverable by the new device is about ten times larger than that recoverable in current technologies – however there was an abrupt drop in recovery at about 900 microns.
It was necessary to reconstruct the machine to avoid very large particles from being trapped selectively in a part of the cell. A satisfactory reagent scheme was also developed, together with a method for simple determination of the recovery on a size-by-size basis. A method for measuring the effective contact angle of the floatable particles was developed.
Analysis showed that there was a significant mismatch in the mass balance between particles in the feed and particles reporting to concentrate and tailings. In effect, coarse particles were found to accumulate in a region of the cell that effectively removed them from the flotation process. Accordingly, the design of the cell was altered to overcome this problem. Sized samples of product, feed and tails were sent to the JKMRC for analysis and the results discussed at a sponsors meeting in August 2010.