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Triboelectrostatic separation is a promising method used to separate non-conductive minerals. However, the knowledge about the underlying triboelectrification mechanisms is still very limited. Thus, predicting the separation results and finding proper separation parameters are challenging tasks. This article presents a comprehensive summary of phenomena and factors which play a decisive role in the charging behavior of non-conductors and, by implication, the efficiency of the separation process, such as water and adsorbents layers on the surface, surface roughness, humidity, type of contact, etc. The authors hope that this article opens a way for a systematic approach through basic experiments dedicated to a better understanding of triboelectrification processes.

Electrification of insulators has been applied for years in the triboelectrostatic separation of minerals. However, the knowledge of the charge exchange during particle contact is still limited. Here, the electric charging of calcite single crystals upon contact with atomic force microscopy (AFM) probes was studied through different contact types. A combination of contactmode AFM and Kelvin probe force microscopy was employed to verify the local surface potentials before and after charging, and focused on the influence of contact time, load force, and applied bias on the charge transfer. a) b) Figure 6. KPFM measurements presenting the surface potential distribution for the calcite surface after repeated charging on an area of 4 × 4 lm 2 , wherein the AFM tip was pressed to the surface with a force of ∼3 lN and bias applied to the AFM tip was (a) -10 V and (b) +10 V. Corresponding curves of charge development and decay are also shown. Crosses (x) between KPFM images indicate charging events. The diagrams in the bottom show the evolution of surface potential with time: symbols D, ᮀ, and ᭜ represent maximum, minimum, and average values, respectively, of the surface potential collected from an area of 10 × 10 lm 2 .

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