STUDY OF PHASE INTERACTIONS IN PROCESS ENGINEERING

1
Project 46897
STUDY OF PHASE INTERACTIONS IN PROCESS ENGINEERING
Effect of hydrophobicity and time dependency on
particle-bubble interactions
Nóra Schreithofer, Kari Heiskanen
Helsinki University of Technology, Laboratory of
Mechanical Process- and Recycling Technology,
P.O. Box 6200, 02015 HUT, Finland http//www.hut.f
i/Yksikot/Mekpros/
Objective
Experimental observations jump-in study
Observation of time dependency of adhesion and
jump-in force between air bubbles and particles
having different degree of hydrophobicity.

• Results of measurements show (fig. 3 and 4.) time
  dependency of jump-in force measured.

Experimental apparatus and procedures

• Apparatus
• unique home-made instrument based on AFM force
  measurement principle
• designed and built at HUT 1 (Fig. 1)

• Materials and methods
• Particles
• 10 ?m silica spheres, heat treated at 200 and
  1050 C, hydrophobized in trimethyl-chlorosilane
  (TMCS) vapour, then kept at 110 C.
• Procedure
• force measurements between particles (10 ?m) and
  air bubbles (600-800 ?m)
• the measurements conducted during an extended
  time period (up to 12 days).

Experimental observations adhesion study
Jump-off distance of particles from air bubbles
measured for particles treated at 70, 200, 1050
C with TMCS, and at 1050 C without TMCS (Fig.
2) measured during extended time
period. Adhesion was time
dependent in most of the experiments. The
jump-off force decreased significantly during the
first 5 hours. No clear dependency of bubble age
can be observed.
Conclusions

• Time dependent phenomena takes places on both,
  particle and bubble surfaces.
• Adhesion of particle to air bubble decreases
  significantly with time.
• Bubble age has no effect on adhesion.
• Jump-in force decreases with time.
• Bubble age has an effect on jump-in force.
• Particle-bubble interaction is a dynamic
  phenomena and it has to be taken into
• account when building more precise flotation
  models 2.
• The reasons for the dynamic effects are largely
  unknown.
• Present theories of colloidal interactions do
  not explain the the observed
• phenomena.
• There are few hypothesises 3, but there is no
  established theory available.

Figure 2. Maximum adhesion values (jump-off
force) vs. time
References 1 Schreithofer, N., Heiskanen, K.,
2001. New experimental design for direct force
measurements between particles and air bubbles,
with special interest on natural mineral
particles. Proceedings of 6th World Congress of
Chemical Engineering, September 23-27,
Melbourne, Australia. 2 Yoon, R.-H., 2000. The
Role of Surface Forces in Flotation Kinetics,
Proceedings of XXI Int. Min. Proc. Congr., July
23-27, Rome, Italy. 3 J. Laskowski, J.A.
Kitchener, 1969. The Hydrophilic-Hydrophobic
Transition of Silica, J. of Colloid and Interface
Sci., Vol. 29, No. 4, 670-679.