Ultrafine particle separation based on multiple particle properties by means of froth-flotation and their characterization using MLA and flow cytometry

The separation of fine particles is a challenging task for which a fundamental understanding of the interfacial properties is inevitable. One of the most important techniques in the mining sector to separate fine particles (10 μm to 200 μm) from unwanted gangue material is froth flotation, which is based on the difference in particle wettabilities. As nowadays, particles need to be milled down to finer size fractions to obtain sufficient liberation of the valuable minerals as well as the fact that particles used in electronic devices become finer, existing techniques need to be adapted. For that reason, this project, which is part of the German research foundation priority programme DFG-SPP 2045 “MehrDimPart”, aims at developing a method for the separation of ultrafine particles based on multiple particle properties, such as size, morphology, surface energy or state of dispersion.
In this study, a system consisting of ultrafine size fractions of glass particles as the valuable material and magnetite as the gangue material is used for testing and the particle properties of wettability and state of gangue dispersion are modified. Said glass particles are hydrophobised via an esterification reaction using alcohols with differing chain length and the resulting wettability states are analysed using inverse gas chromatography as well as analytic particle solvent extraction. The particle properties of size and shape (multiple shape factors) are characterised via a combination of laser diffraction and microscopic analysis. Flow cytometry is introduced as a new method for multidimensional particle characterization, as it allows for size and shape analysis, as well as wettability analysis via fluorescent marking of particles with dyes. Selective flocculation of magnetite is carried out using macromolecules as flocculants. For all flotation tests, a novel flotation apparatus, specifically designed for the flotation of ultrafine particles, is used, which combines advantages from machine-type froth flotation and column flotation. Flotation tests are run in batch mode to study the influence of certain particle properties on the outcome, as well as in continuous stationary mode to study the behaviour of the particles during the process in more depth. For this, samples will be taken at different heights along the flotation column to analyse in which parts certain particles accumulate.
The investigation of the separation of ultrafine particles based on multiple particle properties by means of froth flotation will help to further understand how certain particle properties influence flotation, as well as other separation processes. In this way, the separation of ultrafine particles can be optimized and adjusted to be more efficient, which will play an important role in the recycling of secondary materials.