Separation electrostatic

Methods involving physical separation depend on a difference between the physical properties (size, electromagnetics) of the abrasive and those of the paint debris. Sieving requires the abrasive particles to be different in size and electrostatic separation requires the particles to have a different response to an electric field. 

Tapscott et al. [7] and Jermyn and Wichner [8] have investigated the possibility of separating paint particles from a plastic abrasive by sieving. The plastic abrasive media presumably has vastly different mechanical properties than those of the old paint and, upon impact, is not pulverized in the same way as the coating to be 

The boundary used in these studies was 250 microns material smaller than this was assumed to be hazardous waste (paint dust contaminated with heavy metals). The theory was fine, but the actual execution did not work so well. Photomicrographs showed that many extremely small particles, which the authors beheve to be old paint, adhered to large plastic abrasive particles. In this case, sieving failed due to adhesive forces between the small paint particles and the larger abrasive media particles. 

A general problem with this technique is the comparative size of the hazardous and nonhazardous particulate. Depending on the abrasive used and the condition of the paint, they may break down into a similar range of particle sizes. In such cases, screening or sieving techniques cannot separate the waste into hazardous and nonhazardous components. 

Tapscott et al. [7] have also examined electrostatic separation of spent abrasive. In this process, spent plastic abrasive is injected into a high-voltage, direct-current electric field. Material separation depends on the attraction of the particles for the electric field. In theory, metal contaminants can be separated from nonmetal blasting debris. In practice, Tapscott and colleagues reported, the process sometimes produced fractious with heavier metal couceutratious, but the separatiou was iusufficieut. Neither fractiou could be treated as uouhazardous waste. lu geueral, the results were erratic. 

Monazite Bastnasite Scheelite Magnetite Ferberite Wolframite Gold 

Xenotime Epidote (3.5) Zircon Ilmenite Ilmenite Columbite- Copper (8.9) 

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The heavy mineral sand concentrates are scmbbed to remove any surface coatings, dried, and separated into magnetic and nonmagnetic fractions (see Separation, magnetic). Each of these fractions is further spHt into conducting and nonconducting fractions in an electrostatic separator to yield individual concentrates of ilmenite, leucoxene, monazite, mtile, xenotime, and zircon. Commercially pure zircon sand typically contains 64% zirconium oxide, 34% siUcon oxide, 1.2% hafnium oxide, and 0.8% other oxides including aluminum, iron, titanium, yttrium, lanthanides, uranium, thorium, phosphoms, scandium, and calcium. 

To avoid generation of waste brines and the associated serious problem of brine disposal, the potash industry in the former FRG began converting some operations to electrostatic separation, a dry process for separating potassium salts from other soluble salts (24,25). 

Induced-roU separators have also been used in the concentration and cleaning of heavy minerals found in beach sands. Examples are the mtUe and ilmenite beach sands of Florida and New Jersey. Induced-roU separators are frequently used in combination with high tension or electrostatic separators. 

A variable-speed drive is usually used on the feed and cross-belt drives to exercise control in separator operation, although the speed is not usually changed once the optimum operating condition is estabUshed. Feed rates and the selection of the number of magnetic poles are usually deterrnined by preliminary laboratory tests. The mineral types involved in the feed largely determine the number of poles selected. High intensity cross-belt separators are frequendy used in combination with induced-roU or electrostatic separators. 

Dry Coal Cleaning. Developments in the areas of magnetic and electrostatic separation as a means of cleaning coals in the dry state include high gradient magnetic separation (HGMS), triboelectrostatic separation (TESS), and dry coal purifier (D-CoP). 

Frank Knoll/ M S / Min Proc / President, Carpco, Inc., Jacksonville, EL. (Super Conducting Magnetic Separation and Electrostatic Separation)... 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

Ion Bombardment fFig. 19-55c) The most positive and strongest method of charging particles for electrostatic separation is ion bombardment. Use of ion bombardment in charging materials of... 

Electrostatic-Separation Machines The first electrostatic machines to be used commercially employed the principle of contact elec trification. These were free-fall devices incorporating large vertical plates between which an electrostatic field was maintained. Tribo-elec tric separation (contact charging) has experienced an increase in apphcations due to advances in mechanical self-cleaning and electrical design as well as the development of efficient precharging techniques. 

The common types of other industrial electrostatic separators employ charging bv conductive induction anchor ion bombardment. Figure 19-56 illustrates the principles of application,... 

Conductive-Induction Machines Electrostatic separators exploiting the principle of conductive induction will generally use the follovv -ing electrode designs ... 

FIG. 19-57 TriiKK lectric separators, -S tat electrostatic separator for silica removal from industrial minerals, (Courtesy of Carpeo., Inc.)... 

FIG. 19-58 Tril)oelectric separators, Belt-tvpe electrostatic separator for separation of caibon from flv ash, (Coniiesy of Separation Ceehnoloeie.s, Ine.)... 

FIG. 19-59 Condiictivoindiiction platc-tvpc electrostatic separator. (Conr-IcHij of Mincm] TechnoJoi jj, Lid.)... 

Power Supplie.s Iligh-voltage ac and dc power supplies for electrostatic separators are iisiiallv of solid-state construction and feature variable outputs ranging from 0 to 30,()()() for ac wiper transformers to 0 to 60,000 for the dc supply The maximum current requirement is approximately 1,0 to 1,5 rnA/rn of electrode length. Powder supplies for industrial separators are typically oil-insulated, but smaller diw-epoxv-insulated supplies are also available. 

TABLE 19-25 Machine Capacities of Electrostatic Separators for Mineral Applications... 

Plastic and Metals Recycling Electrostatic separation has been inereasinglv applied to recover nonFerroiis metals From industrial plasties (telephone and eornrniinieation scrap). It also is an important step in the reeveling oF beverage bottles to reject anv remaining nonFerroiis metals. Both oF these reeveling applications make use oF roll-type ion-bornbardrnent separators (Fig, 19-61/ ),... 

Typical Operating Conditions Table 19-26 presents some typical values oF important operating conditions For the separation oF several diFFerent types oF Feed materials. In considering candidate processes For a given separation job, the table can sometimes be help-Fiil in showing that materials oF similar properties and/or economic v ahie can be treated bv electrostatic separation. 

TABLE 19-26 Typical Operating Conditions for Electrostatic Separations... 

Magnetic separation for ferrous materials eddy-current separation for aluminum electrostatic separation for glass from wastes free of ferrous and aluminum scrap magnetic fluid separation for uouferrous materials from processed wastes... 

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