194
10.3.2.4.2 Mechanical Processing
Mechanical processing, also called physical processing, aims to segregate metals,
polymers, and ceramic materials using milling, classification based on grain size,
and separation (Gerbase and Oliveira 2012).
For Moraes (2011), the mechanical treatment of printed circuit boards may
require milling, grain size classification, magnetic segregation, electrostatic segregation, and heavy medium separation, amid other processes.
Other authors, like Ventura (2014), include disassembly and screening as stages
of the mechanical processing of waste. The other stages are milling, grain size classification, magnetic segregation, electrostatic segregation, and gravimetric
separation.
Milling is the mechanical fragmentation of rare earth elements with or without
the electronic components on the board (Ventura 2014). The operation involves the
controlled reduction of the size of the material. Milling is carried out in a vertical or
horizontal knife, hammer, or ball mills (Veit 2001). At this stage, the material is
milled using the combination of impact, compression, abrasion, and attrition to
appropriate particle size (CETEM 2004). According to Richter (2009), the objective
of mechanical processing is to redefine the shape and size of particles, increasing
surface area to promote chemical reactions and release metals from the part that has
no use after ore fragmentation. Milling also influences the segregation of organic
from inorganic materials, improving the efficiency of the process. This separation is
carried out based on the differences in density or grain size. This stage is carried out
using a hammer, knife, or cryogenic mills (Veit 2005). After milling, materials are
separated based on grain size or magnetic, electrostatic, and gravimetric methods or
even leaching (de Moraes 2011). The classification and sieving of milled material
are carried out to obtain two or more factions of particles of different sizes. In sifting, the material is segregated based on particle size, while in classification the
material is segregated based on the speed at which particles cross a liquid medium
(CETEM 2004). Grain size classification is carried out using shaking screens of different meshes to retain particles. Although this process segregates materials based
only on particle size (Hayes 1993; Kasper 2011), Oliveira (2012) claims that components that are attached to boards may be separated by efficient milling.
A given material has its own magnetic characteristics, which depend on a few
factors like chemical composition, atom arrangement (electron spin), and crystalline structure, among others (de Moraes 2011). The magnetic properties of materials are also influenced by atomic arrangements and the electronic structure of the
elements. Magnetism is influenced by the constituting elements, the concentrations
of these elements, and the crystalline structure in the solid (Ribeiro 2013). Materials
and minerals are classified based on magnetic susceptibility, which determines the
response of a material to a magnetic field. This affords to classify minerals as ferromagnetic, which are attracted by magnetic fields, or paramagnetic, which are only
weakly attracted. Materials and minerals repelled by a magnetic field are called
diamagnetic (CETEM 2004).
T. A. da Silveira et al.
10.3.2.4.2 Mechanical Processing
Mechanical processing, also called physical processing, aims to segregate metals,
polymers, and ceramic materials using milling, classification based on grain size,
and separation (Gerbase and Oliveira 2012).
For Moraes (2011), the mechanical treatment of printed circuit boards may
require milling, grain size classification, magnetic segregation, electrostatic segregation, and heavy medium separation, amid other processes.
Other authors, like Ventura (2014), include disassembly and screening as stages
of the mechanical processing of waste. The other stages are milling, grain size classification, magnetic segregation, electrostatic segregation, and gravimetric
separation.
Milling is the mechanical fragmentation of rare earth elements with or without
the electronic components on the board (Ventura 2014). The operation involves the
controlled reduction of the size of the material. Milling is carried out in a vertical or
horizontal knife, hammer, or ball mills (Veit 2001). At this stage, the material is
milled using the combination of impact, compression, abrasion, and attrition to
appropriate particle size (CETEM 2004). According to Richter (2009), the objective
of mechanical processing is to redefine the shape and size of particles, increasing
surface area to promote chemical reactions and release metals from the part that has
no use after ore fragmentation. Milling also influences the segregation of organic
from inorganic materials, improving the efficiency of the process. This separation is
carried out based on the differences in density or grain size. This stage is carried out
using a hammer, knife, or cryogenic mills (Veit 2005). After milling, materials are
separated based on grain size or magnetic, electrostatic, and gravimetric methods or
even leaching (de Moraes 2011). The classification and sieving of milled material
are carried out to obtain two or more factions of particles of different sizes. In sifting, the material is segregated based on particle size, while in classification the
material is segregated based on the speed at which particles cross a liquid medium
(CETEM 2004). Grain size classification is carried out using shaking screens of different meshes to retain particles. Although this process segregates materials based
only on particle size (Hayes 1993; Kasper 2011), Oliveira (2012) claims that components that are attached to boards may be separated by efficient milling.
A given material has its own magnetic characteristics, which depend on a few
factors like chemical composition, atom arrangement (electron spin), and crystalline structure, among others (de Moraes 2011). The magnetic properties of materials are also influenced by atomic arrangements and the electronic structure of the
elements. Magnetism is influenced by the constituting elements, the concentrations
of these elements, and the crystalline structure in the solid (Ribeiro 2013). Materials
and minerals are classified based on magnetic susceptibility, which determines the
response of a material to a magnetic field. This affords to classify minerals as ferromagnetic, which are attracted by magnetic fields, or paramagnetic, which are only
weakly attracted. Materials and minerals repelled by a magnetic field are called
diamagnetic (CETEM 2004).
T. A. da Silveira et al.