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.
Quadratic nonlinear models for optimizing electrostatic separation of crushed waste printed circuit boards using response surface methodology.
The electrostatic separation has proved to be an effective and environment-friendly treatment for the recovery of crushed waste printed circuit boards (PCBs). In this paper a more sophisticated response surface methodology was applied to build quadratic models and optimize the three main factors on a roll-type electrostatic separator. The sample of granular mixture got from crushed PCB wastes (size 0.3-0.45 mm, containing 25% metal and 75% nonmetal). According to the analysis of the experiment data, some quadratic effects were found, and two quadratic models for conductor production (C) and middling production (M) were established. The results indicated that the high voltage level and roll speed are the most important factors for the process. Because of the existence of the quadratic effect, the highest efficiency can also be achieved at a lower voltage level (27-29 kV) compared with a maximum voltage level.
Electrostatic Charge Separation at Metal‐Insulator Contacts
An investigation has been made of the electrostatic charge produced in vacuum on several inorganic insulators when they are put into rolling contact with nickel, platinum, and copper surfaces. The primary role of relative motion is to increase the area on the insulator that ultimately undergoes contact, thereby increasing the total charge separated. With quartz, all evidence favors electron transfer which occurs because the nonconductor has a higher effective work function than the metal. Field emission‐induced back leakage of electrons during separation of the charged surfaces is considered to reduce the charge originally separated to that actually measured. Little difference is seen between the charging properties of quartz cleaned chemically in room air and quartz subsequently outgassed at 700°C in vacuo better than 10−8 mm Hg. No difference in electron affinity is found between fused and monocrystalline quartz. No evidence directly supporting electron transfer is found for the other insulators tested,...