Development and theory of centrifugal flotation cells

Rotating fluids occur in a very wide range of applications. The dramatic, large-scale effects of rotating flows on flowfields have stimulated flotation cell designers to make use of them for his particular purpose: improve the processing of fine particles. In this thesis, the author offers a personal view of the applicability of various rotating fluids to flotation cell and mechanism design. Three types of rotating flows, namely, Rankine's combined vortex, externally-forced vortex, and internally-forced vortex, are considered to be applicable to flotation and their features of interest are illustrated and discussed. As a result, two new types of centrifugal flotation cells, CFC-Q1 and CFC-Q2, were developed. Both models introduce the reactor/separator concept in their designs and use an external in-line air sparger made of porous stainless steel to aerate the pulp. The operating mechanism of the CFC-Q1 cell uses a rotating drum or bowl to create a centrifugal force on the feeding slurry. Froth concentrate is collected on the central top of the cell and tailing is discharged along the top edge of the rotating drum or bowl. The CFC-Q2 cell utilizes a vertical rotating feeder to introduce the feeding slurry into a stationary structure. A centrifugal force is created by the rotating feeder for the feeding slurry. Froth concentrate floats over the cell and tailing is discharged through the bottom of the cell. The major operating variables of the CFC-Q1 and CFC-Q2 models include the rotating speed, the air flow rate into the air sparger, and the slurry feeding rate. The metallurgical performances of the CFC-Q1 and CFC-Q2 cells were compared with that of a conventional laboratory Denver mechanical cell. Flotation tests were carried out with two artificial mixtures and two natural base metal ore samples. The test results clearly indicate the advantages possessed by the CFC-Q1 and CFC-Q2 cells in the processing of fine particles. The grade-recovery curves produced from the CFC-Q1 and CFC-Q2 cells are generally better than or equivalent to that from the Denver cell. The study coincides with the prior theories that strong force fields such as centrifugal force fields would increase the particle-bubble collision efficiencies in the flotation process and consequently the recovery of fine particles would be improved.