Dr. Roland Rzehak

Head Flotation and reactive multiphase flows
Phone: +49 351 260 3475

Modelling and simulation of threephase flow in flotation equipment

Sketch of a flotation column

Flotation is a method for the separation of particles based on the different hydrophobicity of their surfaces. It play a vital role in resource technology to separate valuable mineral particles from the surrounding rock and thereby to secure the supply with base metals such as copper, lead, zinc, tin, aluminum and nickel as well as so-called critical raw materials like e.g. rare earth metals. While present flotation processes give relatively good results in the range of particle sizes between 50 and 250 µm, the importance of selective separation of mineral ores in the range of both fine and coarser particles is increasing recently.

In addition to the chemo-physical surface properties, the attachment of the particles to the bubbles and the stability of the formed aggregates are particularly determined by the local hydrodynamics. The optimisation of existing or the development of new flotation equipment with systematically improved hydrodynamics therefore has a huge potential to yield more efficient separation with higher selectivity. Applying methods from multiphase CFD can provide a useful complement to experimental techniques. To this end suitable closure models for three-phase flows and the attachment of particles to bubbles have to be developed.

As first steps in this direction, already available models for two-phase flows in bubble-columns were extended and validated also for stirred tanks [1]. Likewise a base set of models was proposed and validated for two-phase particulate flows in such apparatuses [2]. Presently, the combination of both model sets for three-phase flows is being worked on. A validation also for this case requires further experimental work, since hardly any suitable data for this purpose are found in the literature.


  1. Shi, P., Rzehak, R.,
    Solid-liquid flow in stirred tanks: Euler-Euler/RANS modeling,
    Chemical Engineering Science 227 (2020), 115875.
  2. Shi, P., Rzehak, R.,
    Bubbly flow in stirred tanks: Euler-Euler/RANS modeling,
    Chemical Engineering Science, 190 (2018), 419-435.