Electrostatic Separation of Fine Particles in Vibrated Fluidized Beds
Very fine particles which cannot be fluidized by means of a flowing gas alone because of entrainment may be effectively individualized and retained in the bed through a combination of gas at low rate flow and mechanical vibrations of selected frequency and amplitude. A mixture of very fine particles may be fluidized and successfully separated and/or concentrated by means of electrostatic fields. Results are presented of a factorial experiment in which the conditions of temperature, humidity, and voltage were investigated for the separation of a (50-50 by weight) synthetic mixture of iron and glass powder of particle size ranging from 15-45¿m. A new and highly efficient particle collection mechanism is introduced, and mathematical models of the process are presented as part of the optimization work.
On electrostatic effects in fluidized beds
The classical theory of fluidization does not take into consideration the possibility of the occurrence, in fluidized beds, of electrical forces conditioned by static electricity. The electric charges which accumulate on solid particles may cause: 
1. 
the adhesion of a layer of solid particles to the walls of the fluidizing equipment. 
 
2. 
the agglomeration of particles into larger aggregates. 
 
3. 
the change of a fluidized bed into a chanelling bed. 
 
 
 
 
Between metal elements which are in contact with the fluidized bed there may arise considerable potential differences, reaching even more than 15 kV.
Frictional Electrification and Gaseous Discharge
IT is well known that the leakage of charge from high-voltage static generators, such as the Van de Graaff machine, is controlled by use of high pressure or other suitable atmospheres which increase the dielectric strength of the medium in which they operate. The results reported below suggest that in a study of the mechanism of frictional electrification, quantitative measurements may be of doubtful value, because a similar leakage is apt to take place between the rubbing surfaces and to control the process of charge separation.