CAVITATION SPARGING SYSTEM

Canadian Process Technologies Inc.

Unit 1-7168 Honeyman Street
Delta, B.C.
Canada V4G 1G1
Tel: +1 604 952 2300
Fax: +1 604 952 2312
Email: cpt@cpti.bc.ca
URL: http://www.cpti.bc.ca
PICOBUBBLE ENHANCED FLOTATION

Effect of Picobubbles on Particle Collision/Attachment

Tiny bubbles, referred to as Picobubbles, naturally exist in liquids such as seawater and distilled water.
Picobubbles attach more readily to particles than large bubbles due to their lower ascending velocity and
rebound velocity from the surface and higher surface free energy to be satisfied. More efficient
attachment of particles and improved flotation rate have been observed when tiny bubbles co-exist with
air bubbles commonly used in flotation cells. Klassen and Mokrousov showed that the combined flotation
by gas nuclei from air supersaturation and by mechanically generated bubbles produced higher flotation
recovery than by either of them alone. Gas nuclei or picobubbles on a particle surface activate flotation by
promoting the attachment of larger bubbles (as shown in Fig. 1) since attachment between gas nuclei or
picobubbles and large bubbles is more favored than bubble–solid attachment.

Bubble

Bubble

Particle
Pico-Bubbles

Figure 1
In other words, picobubbles act as a secondary collector for particles, reducing flotation collector dosage,
enhancing particle attachment probability, and reducing the detachment probability. This leads to
substantially improved flotation recovery of poorly floating fine and coarse particles and reduced reagent
cost, which is often the largest single operating cost in commercial mineral flotation plants. Application of
this process to coal flotation resulted in an increase in flotation yield up to 15 wt%, a frother dose
reduction of 10%, and a collector dose reduction of 90%. Zhou et al. showed that hydrodynamic cavitation
significantly increased flotation kinetics of silica and zinc sulfide precipitates.
 Hydrodynamic Cavitation

Hydrodynamic cavitation is the process of creation and growth of gas bubbles in a liquid due to the
rupture of a liquid–liquid or a liquid–solid interface under the influence of external forces. The bubbles
generated on a particle surface by cavitation naturally attach to the particle, eliminating the collision and
attachment process, which is often the rate-determining step for flotation. Cavitation also improves the
flotation efficiency of coarse particles by reducing the detachment probability during the rise of particle–
bubble aggregate in liquid. This is best illustrated in Fig. 2 where the large bubble represents the one
produced by breaking the external air and smaller ones (picobubbles) are created by cavitation. While the
large bubble may run away from the particle, the cavitation bubbles, particularly those underneath the
particle, will push the particle upward, facilitating particle recovery. Without cavitation-generated bubbles,
particles will detach from the bubble surface when the capillary force and other attachment forces are
exceeded by detachment forces, such as the viscous or drag force (Fd), the gravitational force, and the
hydrostatic pressure. As the drag force is directly proportional to the particle diameter; coarse particles
are more likely to detach from the bubble surface than fine particles. This is the main reason for low
flotation recovery of coarse particles, which is recognized by many researchers.

Bubble

Bubble

Particle Pico-Bubbles

Figure 2

Cavitation takes place in the form of gas supersaturation or hydrodynamic cavitation. Tiny bubbles may
form by gas supersaturation in liquid from preexisting gas nuclei trapped in crevices of solid particles.
Hydrodynamic cavitation occurs when the pressure at a point in a liquid is momentarily reduced below its
vapor pressure due to high flow velocity. Minute air or vapor-filled bubbles are carried on by the flow to
regions of higher pressure.

The CPT Cavitation Tube is shown in Fig. 3. The liquid in the cylindrical throat is higher in flow velocity
and lower in pressure than liquid in the entrance cylinder, resulting in cavitation. The differential pressure
between the entrance cylinder and the cylindrical throat measured by the manometers is indicative of
cavitation behavior. The presence of tiny pockets of undissolved gas in crevices on mineral particles
assists the cavitation as a result of the expansion of these gas pockets under the negative pressure. Holl
found that the cavitation was directly proportional to the dissolved air content in liquid. Addition of organic
chemicals such as frothers produces smaller and more copious cavities by stabilizing the cavity and
preventing cavity collapse and coalescence.
Figure 3 – CPT Cavitation Tube
Fines Circuit (-150 + 20 microns)
Conc
Feed
Air / water Spargers
Assay Dist'n
% P2O5 % P2O5
Feed 13.8 100
Concentrate 31.5 87.6
Scavenger Tail 2.8 12.4

Tails

CavTube Spargers (CT-500)

Assay Dist'n
% P2O5 % P2O5
Feed 14.0 100 Conc
Feed
Concentrate 31.5 90.0
Tailings 2.4 10.0

Tails

Ultrafines Rougher (-20 + 7 Microns)

Column 3m x 5m x 12m H
Conc
Feed
Air / water Spargers
Assay Dist'n
% P2O5 % P2O5
Feed 11.06 100
Concentrate 32.97 62.3 Tails
Tailings 5.27 37.7

CavTube Spargers (CT-350)

Assay Dist'n Conc
Feed
% P2O5 % P2O5
Feed 11.5 100
Concentrate 33.7 84.2
Tailings 2.5 15.8
Tails
Zinc Calamine Flotation Cyclone Overflow (-20 microns)

Feed

Rougher

CavTube Sparg (CT-350)

Tails
Assay Dist'n
% Zn % Zn
Feed 19.37 100
Concentrate 39.12 92.6
Formerly
Tailings 2.64 7.4 Conc
Tailings

Tails
Conc