Particle-Bubble attachment

  
Motivation

In froth flotation, hydrophobized target particles attach to the fluidic interface of gas bubbles rising in a suspension (Fig. 1). The efficiency of the froth flotation process depends on the encounter of particle and bubbles based on the hydrodynamics within the cell and the surface chemistry of the bubble and particle surface.

We focussed on novel methods to observe and quantify the collision and attachment process directly. Therefore, we employ optical 4D particle tracking velocimetry (PTV), Positron Emmission Particle Tracking (PEPT), High-Speed imaging, and X-ray radiography.

4D Particle-Tracking Velocimetry

The 4D PTV measures simultaneously particle and bubble trajectory in 3D with a high temporal resolution. We applied this measurement technique to a bubble column. The majority of particles attaches to the leading edge of the bubble. Additionally, trailing edge collisions were discovered, that could be caused by the bubble vortices within the bubble wake [1,2].

Optical attachment quantification

A new experimental approach based on particle attachment dynamics is proposed to evaluate particle floatability, a parameter critical to predicting flotation performance and designing a flotation flowsheet prior to industrial application. This is to minimize industrial trials and to reduce cost and effort. Our method allows precise control of hydrodynamic conditions, visualization of attachment processes, and direct observation of bubble surfaces. This innovative technique provides a faster, more versatile means of studying particle floatability and attachment dynamics.

X-ray radiographic attachment quantification

The depletion of existing high grade ore deposits has shifted the current mining standards towards the exploitation of lower grade mineral deposits. These low-grade ores must be finely ground to release the finely dispersed valuable minerals, which can lead to various problems and challenges associated with fine/ultra-fine particles. Besides the influence these particles have on the recovery rate of the flotation cell, their high number density per unit mass makes optical investigations quite challenging. Therefore, we developed advanced X-ray tomography methods to research the sorption of particles in the presence of ultrafines.

Positron Emmision Particle Tracking

In collaboration with the Imperial College London and the University of Cape Town we have researched the trajectory of particles in the vicinity of a stagant bubble using PEPT. Collision events and the corresponding trajectories were defined and analysed [3]. 

Publications

[1] Sommer, A. E., Nikpay, M., Heitkam, S., Rudolph, M., & Eckert, K. (2018). A novel method for measuring flotation recovery by means of 4D particle tracking velocimetry. Minerals Engineering, 124, 116-122.

[2] Sommer, A. E., Heitkam, S., & Eckert, K. (2024). Wake effect on bubble–particle collision: An experimental study using 4D particle tracking velocimetry. International Journal of Multiphase Flow, 179, 104903.

[3] Sommer, A. E., Ortmann, K., Van Heerden, M., Richter, T., Leadbeater, T., Cole, K., ... & Eckert, K. (2020). Application of Positron Emission Particle Tracking (PEPT) to measure the bubble-particle interaction in a turbulent and dense flow. Minerals Engineering, 156, 106410.