Newly-Patented Technical Solutions for improving the Tribo-Electrostatic Separation of Mixed Granular Solids

The tribo-electric effect consists in the electrification of certain materials after coming into contact with other materials. This effect may be used in conjunction with the electric field forces for electrostatically separating positivelyand negatively-tribo-charged granules that have otherwise similar size, density, magnetic properties and electric conductivities. Although tribo-electrostatic separation has been used for a long time, its larger-scale application is hampered by a multitude of technical problems that need to be solved: sensitivity to environmental conditions, non-homogeneity of material charging, chaotic particle trajectories, electrode clogging, etc. This paper reviews various recent patents that claim innovative solutions of these problems, allowing increasing efficiency and robustness of the separation. The improvements concern each phase of the process: (i) pretreatment and feeding; (ii) tribo-charging of the materials to be separated; (iii) electrostatic separation and particle collection. Most of the new applications were developed for the recycling of plastics from industrial waste and the recovery of unburned carbon from fly ash. The paper concludes with a description of the future developments expected in the field of tribo-electrostatic separation.