Conclusions to Chapter 3

1. The discharge of insulating particles in contact with a grounded electrode can be evidenced trough surface potential measurements. The potential decay is strongly dependent on the nature of the granular material; it can be identified with a non-integer model.

2. Coarser particles are characterized by a higher initial value of the surface potential than finer ones, which are also more likely to loose faster their charge.

3. Drying affects to a significant extent the discharging process. As the charging conditions are similar for dried and un-dried samples, superficial moisture accelerates the discharge of the latter. After a certain time lapse, when the charge decay related to this physical mechanism is over, the surface potential variation of the dried and un-dried samples tend asymptotically to the same curve.

4. The difference in the charge decay characteristics of two constituents of a PE/rubber granular mixture was enough to ensure the selective sorting of the constituents. Using a belt-type electrostatic separator allowing particles to spend longer times in contact with the grounded electrode (i.e., the belt) would lead to much better separation results.