Triboelectric separators

Triboelectric Separators There are currently two industrial forms of triboelectric separators installed commercially to treat minerals and recycled plastics ... 

Triboelectric separators for plastics have been described in detail (46,47). The separation efficiency in a triboelectric separator can be enhanced by adding media against which the components of the mixture will charge. As a result, random charging between the components of the mixture is reduced and controlled, and a predictable charging is achieved (47). 

FIG. 19-57 Triboelectric separators. V-Stat electrostatic separator for silica removal from industrial minerals. Courtesy ofCarpco, Inc.)... 

FIG. 19-58 Triboelectric separators. Belt-type electrostatic separator for separation of carbon from fly ash. Courtesy of Separation Technolo es, Inc.)... 

Electrostatic-type separation is being tested as an alternative to the presently used process of flotation of pebble phosphates for coarser-size fractions. Advantages sought include reduced reagent costs, a lower water requirement, and fewer tailings-disposal problems when a part of the flotation circuit is eliminated. The largest application of triboelectric separation is in the salt industry where sodium and potassium salts are separated after preconditioning. 

A new application of triboelectric separation involves the separation of PVC from PET and other plastics. Recent developments in precharging technology permit PVC to assume a strong negative charge and be removed efficiently from properly protected mixed plastic feedstocks (Fig. 19-62). 

FIG. 19-62 New Triboelectric separator for separation of PVC from other plastics. Courtesy Carpco, Inc.)... 

Plastic-Plastic Separation Both dry and wet processes can be used to separate one plastic from another in a recycling operation. The most common wet separation methods are based on differences in density between particles of different plastics [1, 2, 10, 49], Density is a bulk property of the plastic. Unfortunately, many factors beyond polymer type affect density. Plastic particles can also show differences in surface properties. Plastic-plastic separation methods based on surface property differences include triboelectric separation [75] (a dry process) and froth flotation [75] (a wet process). Density-based and surface-property-based methods for separating a stream of mixed plastics are covered in the following sections. 

Figure 14.21. Triboelectric separator bnilt by Plas-Sep and nsed by APC and MBA polymers for R D on mixed plastics. Photo courtesy of MBA Polymers, Inc.

Figure 14.22. Schematic showing the operating principles for a triboelectric separator [42],...

Hamos GmbH of Penzberg, Germany, has developed triboelectric separation systems for plastic/plastic separations, and electrostatic separators for plastic/metal separation. ... 

Figure 1. Approach, contact, and separation of two dissimilar solid materials leads to triboelectric charge separation. Here, the particle of material A is assumed to have lower work function and much higher electrical resistivity than the material B.

R. Kohnlechner, Triboelectric charging and electrostatic separation of diverse, non-conductive mixed waste, especially plastic, employs enclosed vibro-conveyor followed by in-flight separation influenced by non-linear electrostatic field, DE Patent 19 901 743, assigned to Hamos GmbH Recycling und Separ, July 20, 2000. 

The peak current and the total area under the curve for the contact current and for the separation eurrent are nearly identical, differing only in the sign. From the contact and separation current value a triboelectric series, which shows not only the position but also quantitative separation between two positions, is constructed as shown in Table 24.1. Triboelectric series based on the average current on contact and separation is given in Table 24.2, in which the zero point is set at nylon. 

Table 24.2 Triboelectric Series Based on Contact Electrification/Separation Current...

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