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Abstract

Photovoltaic (PV) modules contain both valuable and hazardous materials, which makes their recycling meaningful economically and environmentally. The recycling of the waste of PV modules is being studied and implemented in several countries. Current available recycling procedures include either the use of high-temperature processes, the use of leaching agents or a combination of both. In this study, waste of silicon-based PV modules are separated using an electrostatic separator after mechanical milling. An empirical study is used to verify if the separation works and to select and fix several parameters. Rotation speed of the roller and DC voltage are evaluated as a result of the separation of metals (silver and copper), silicon, glass, and polymers. The efficiency of metals’ separation is determined by acid leaching of the corresponding fractions followed by inductively coupled plasma optical emission spectrometry (ICP-OES); that of polymer separation is determined by mass difference due to combustion of the corresponding fractions; and those of glass and silicon quantities are determined by X-ray diffraction (XRD) followed by characterization using Rietveld quantitative phase analysis (RQPA). It is shown that the optimal separation is obtained under different operating voltages of 24 and 28 kV and a rotation speed of 30 RPM or higher. Furthermore, it is shown that there is no significant difference among the tested parameters. Results provide a new option in the recycling of waste of silicon PV modules that can and should be optimized.
INNOVATIONS IN WEEE RECYCLING
Recycling Waste Crystalline Silicon Photovoltaic Modules
by Electrostatic Separation
Pablo Dias
1,2
Lucas Schmidt
1
Lucas Bonan Gomes
3
Andrea Bettanin
1
Hugo Veit
1
Andre
´a Moura Bernardes
1
The Minerals, Metals & Materials Society 2018
Abstract
Photovoltaic (PV) modules contain both valuable and hazardous materials, which makes their recycling meaningful
economically and environmentally. The recycling of the waste of PV modules is being studied and implemented in several
countries. Current available recycling procedures include either the use of high-temperature processes, the use of leaching
agents or a combination of both. In this study, waste of silicon-based PV modules are separated using an electrostatic
separator after mechanical milling. An empirical study is used to verify if the separation works and to select and fix several
parameters. Rotation speed of the roller and DC voltage are evaluated as a result of the separation of metals (silver and
copper), silicon, glass, and polymers. The efficiency of metals’ separation is determined by acid leaching of the corre-
sponding fractions followed by inductively coupled plasma optical emission spectrometry (ICP-OES); that of polymer
separation is determined by mass difference due to combustion of the corresponding fractions; and those of glass and
silicon quantities are determined by X-ray diffraction (XRD) followed by characterization using Rietveld quantitative
phase analysis (RQPA). It is shown that the optimal separation is obtained under different operating voltages of 24 and
28 kV and a rotation speed of 30 RPM or higher. Furthermore, it is shown that there is no significant difference among the
tested parameters. Results provide a new option in the recycling of waste of silicon PV modules that can and should be
optimized.
Keywords Crystalline silicon Electrostatic separation Material separation optimization Recycling Solar panel
Introduction
Waste Electric and Electronic Equipment (WEEE)
The demand for cleaner energy sources to overcome the
use of fossil fuels and to slowdown climate change due to
human activities creates a favorable scenario for photo-
voltaic technologies, which is considered a promising
technology [1]. Photovoltaic (PV) modules are devices that
can convert sunlight into electricity without any other
source of energy; they can be made of numerous semi-
conductors materials [2]. However, PV modules have a
technical lifespan of 20–30 years and will become elec-
tronic waste (WEEE) in the next few years, since the
commencement of broad PV installation occurred in the
1990s [3]. End-of-life modules are expected to reach 5.5–6
million tons by the 2050s [4]. Therefore, it is essential to
develop recycling technologies to reduce the amount of this
The contributing editor for this article was Bernd Friedrich.
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s40831-018-0173-5) contains supplementary
material, which is available to authorized users.
&Pablo Dias
pablo.dias@ufrgs.br
Andre
´a Moura Bernardes
amb@ufrgs.br
1
Programa de Po
´s-Graduac¸a
˜o em Engenharia de Minas,
Metalu
´rgica e de Materiais (PPGE3M), Universidade Federal
do Rio Grande do Sul (UFRGS), Av. Bento Gonc¸alves, 9500,
Porto Alegre, RS 91509-900, Brazil
2
Faculty of Science and Engineering, Macquarie University,
Sydney, NSW 2109, Australia
3
X-Ray Diffraction Laboratory, Geosciences Institute, Federal
University of Rio Grande do Sul (UFRGS), Av. Bento
Gonc¸alves, 9500 - Pre
´dio 43126 - Sala 211,
Caixa Postal 15001, Porto Alegre, RS 91501-970, Brazil
123
Journal of Sustainable Metallurgy
https://doi.org/10.1007/s40831-018-0173-5(0123456789().,-volV)(0123456789().,-volV)
waste, taking into consideration the dimensions that it will
acquire in the next years. It is also necessary to evaluate the
risks of disposing the WEEE, which can generate envi-
ronmental impacts [5], given that the waste contains haz-
ardous materials that require special handling and can
cause possible detrimental effects on human health.
Moreover, recycling can recover reusable components and
base materials such as copper [6], precious metals [7,8],
and reserves of carbon [9].
Photovoltaic Modules
The composition of PV modules varies according to the
technology used. The modules are basically a layer of a
semiconductor material placed between tempered glass
and/or glass or a polymer as back sheet. Lead, chromium,
cadmium, and nickel are among the hazardous metals
usually used [10]. Currently, silicon (Si)-based PV mod-
ules, such as single-crystalline Si (sc-Si), multicrystalline
Si (mc-Si), and hydrogenated amorphous Si (a-Si) PV
modules, are playing a vital role in the PV market [11]. A
general quantification of the materials present in silicon-
based PV modules is shown in Table 1.
Modules are encapsulated with various materials to
protect the cells and the electrical connectors from the
environment [14]—the most common being ethylene–vinyl
acetate (EVA). The removal of these encapsulating mate-
rials is an important step in the recycling of PV modules
[15] (Fig. 1).
Thermal and hydrometallurgical processes are prevalent
in most of the PV recycling methods, and the encapsulating
material can be removed with the aid of thermal decom-
position and nitric acid [16]. Jung et al. [17] used a thermal
treatment to decompose the EVA layer and to separate the
different layers of solar panels. Doi et al. [18] used various
organic solvents aiming to dissolve the EVA layer.
Radziemska et al. [19] used a thermal process to decom-
pose the EVA, followed by a chemical treatment for the
solar cell, which they refer to as a second primary step in
PV modules’ recycling. Kang et al. [20] employed a mix-
ture of acid solvents in the process of etching Si solar
panels. Zhang and Xu [21] used pyrolysis in a nitrogen
atmosphere to remove the EVA layer, and recycle glass
and gallium from thin-film solar modules. However, as
shown in earlier studies [5], the use of mechanical pro-
cesses, such as shredding/milling, and sieving, may assist
in the recycling of PV panels and reduce the cost of
recycling, given that these processes are able to concentrate
metals in different fractions according to particle size.
Moreover, mechanical processes may be used prior to the
thermal and hydroprocesses as a pretreatment step that aids
the following recycling steps and upgrades material content
[22,23].
Electrostatic Separation
Electrostatic separation is frequently used in the separation
of equipment containing copper, aluminum, and insulating
materials, which is also the case of WEEE. It represents a
Table 1 Typical composition of materials in a silicon-based photovoltaic module. Source: [5,8,12,13]
Material Content/wt% Purpose
Silicon 2–3 Photovoltaic effect
Glass 69–75 Module protection, allowing light to reach PV cell
Polymers (EVA, Tedlar) 7 Module protection, encapsulating PV cell, isolating module from surroundings
Copper 0.6–1 Current conductor
Silver 0.006–0.06 Current conductor
Aluminum 10–20 Module frame, p-doping silicon, current conductor
Boron \0.1 p-doping of silicon
Phosphorus \0.1 n-doping of silicon
Tin dioxide \0.1 Anti-reflection (AR) coating
Lead \0.1 Copper coating
Tin \0.1 Copper coating
Fig. 1 Arrangement of components in a typical silicon-based solar
module. Adapted from [13] (Color figure online)
Journal of Sustainable Metallurgy
123
modern and useful technology for the recycling of indus-
trial waste materials [24,25]. Electrostatic separation sorts
substances with different electrical conductivities, which
are typically charged before exposure to electrostatic and
gravitational forces. In a roll-type separator (Fig. 2), the
materials go through a grounded roller and are subjected to
electric charge ionization from an electrode; conductive
particles discharge due to physical contact with the roller,
while nonconductive particles are attracted to the roller due
to Coulomb forces. Thus, the particles are eventually sep-
arated due to the differences in conductivity and electro-
static properties [26].
Richard et al. [28] applied electrostatic separation to sort
out granular metals and plastics from electric wire waste.
Recently, the same authors evaluated the use of three dif-
ferent configuration of roll-type electrostatic separation in
order to optimize the segregation of PVC (Polyvinyl chlo-
ride), aluminum and copper from electronic waste. The
three configurations included the use of an (i) elliptical
static electrode with corona effect, an (ii) s-shaped plate
with plastic trap and (iii) an s-shaped plate with plastic trap
and corona effect. They have found that the corona elec-
trode (or ionizing electrode) is necessary for the separation
of PVC and copper [29]. Veit et al. [30] also used this
method to recover metals from circuit boards and concluded
that the use of electrostatic separation was efficient in
obtaining high concentrated fractions of metals, in partic-
ular, he was able to concentrate 50% of copper, 25% of tin,
and 7% of lead. This method has been further improved by
adding a second roll and creating a two-step process [31].
Electrostatic separation is considered an efficient low cost
mechanical process that requires little energy in comparison
to thermal processes [32] and does not generate byproduct
effluents, unlike hydrometallurgical processes [33].
As demonstrated, thermal and hydrometallurgical
methods are largely implemented in the recycling of waste
PV and the combination of both is currently presenting
optimal outputs [15,19,20]. The use of electrostatic sep-
aration in PV recycling has not yet been studied despite the
great potential this method has in assisting the recycling
through the segregation of different materials present in the
modules. Moreover, the use of electrostatic separation
could potentially reduce the cost of PV recycling, which is
one of the biggest barriers keeping the recycling of WEEE
from expanding [34]. Therefore, in this study, the use of
electrostatic separation is assessed in order to segregate the
main materials of PV panels.
Materials and Methods
The objective of this study is to evaluate the use of elec-
trostatic separation technique to segregate some of the
main materials present in silicon-based photovoltaic mod-
ules: silver, copper, silicon, glass, and polymers from the
back sheet and encapsulating material. The schematic
diagram (Fig. 3) outlines the principle of investigations
performed in this study.
The experiments were performed with five different
crystalline silicon modules (c-Si modules). The aluminum
frames were manually removed from all modules. The
modules were then milled with a SRB 2305 knife mill
(Rone, Sa
˜o Paulo, Brasil) with the experimental parameters
based on previous works [8]. The milling was repeated four
times, the first two using a screen with 4-mm openings and
the second two using a screen with 2-mm openings; the
output powder weighed approximately 5 kg.
The output powder was quartered and separated in 300-g
samples. These samples were named F1, F2, F3, F4, F5,
and F6. In the first part of the experiment, empirical studies
were performed by attempting to separate the different
materials from the sample by varying several parameters at
random starting points. The equipment used for all the
electrostatic separations was a MMPM-618C (Eriez, Erie,
USA) high-tension roll separator (Fig. 4).
Visual inspection was adopted to determine the perfor-
mance of a given parameter. A sample considered great
would have the majority of polymers on output C, the
majority of silicon on output B, and the majority of glass
and metals in output A. The changeable parameters are
listed in Table 2, which also presents the parameters that
were fixed (pinned down) after repetitive attempts of sep-
arating the materials and observing the results.
It is important to notice that there are only three col-
lection pans (Fig. 4—item 9): conductor, middling, and
nonconductor: A, B, and C, respectively. Samples F1, F2,
and F3 were used in the empirical study.
Fig. 2 Diagram illustrating the electrostatic separation principle in a
roll-type electrostatic separator. Adapted from [27] (Color figure online)
Journal of Sustainable Metallurgy
123
The results obtained from the empirical study led to the
restriction of the degrees of freedom related to the variables
in the separation process. As a result, it was chosen to vary
the electric potential difference and the rotation speed and
keep the other parameters fixed. The electric potential
difference (voltage hereafter) is given in volts and is the
difference in electric potentials between wired electrodes
(lifting and ionizing) and the roll (grounded). The selected
voltages were 24 and 28 kV; the selected rotation speeds
were 50, 65, and 80 RPM.
Each 300-g group (F4, F5, and F6) was quartered and
separated in six 50-g samples—one for each combination
of parameters. 50-g samples were chosen based on previ-
ous WEEE electrostatic separation studies [29]. The end
result after electrostatic separation is a total of 18 samples
(six combinations of parameters with output fractions A, B
and C), which were replicated three times (F4, F5 and F6)
for further statistical analyses. To evaluate the efficiency of
each combination of voltage and rotation speed, a series of
experiments were performed: First, each sample was lea-
ched in nitric acid (65% concentration) solution using a
10:1 liquid–solid ratio, under magnetic stirring, at room
Fig. 3 Schematic diagram
illustrating the procedures used
in this study.
Fig. 4 Schematic illustration of the electrostatic separator equipment
setup. Adapted from [35]
Journal of Sustainable Metallurgy
123
temperature. The solid part from the leaching was filtered,
rinsed, dried, and put aside. The solutions containing the
leached metals were analyzed by inductively coupled
plasma optical emission spectroscopy (ICP-OES) to
determine the amount of silver and copper in each sample.
The equipment used was a 5110 ICP-OES (Agilent Tech-
nologies, California, USA). The filter residue was then
weighed and placed in a crucible, which was placed inside
a furnace in order to eliminate the polymers in each sam-
ple. The dwell temperature was set to 500 C based on
previous works [15]. The heating ramp was 15 C/min and
the dwell time was 5 h per sample. The samples were
weighed again and the mass difference was assumed to be
the mass of the polymeric fraction contained in each
sample.
Finally, the samples were milled in an alumina mortar
and sieved through a mesh 400 sieve (37 lm). Each sample
was weighted and analyzed by X-ray diffraction (XRD)
using a Siemens (Bruker AXS—Germany) D-5000
diffractometer with Cu Ka1,2 radiation (1.54178 A
˚
´) and
equipped with curved graphite monochromator in the sec-
ondary beam. The data were collected in the Bragg–
Brentano (h/h) geometry between 10 and 75(2h) in 0.05
steps, at 1 s/step using a 1divergence, and anti-scattering
slits, and a detector slit of 0.6 mm.
After initial analysis, an internal standard of hexagonal
(P63 mc) ZnO (99.9%) was added to the sample. The
internal standard was added so that it would represent 10%
in weight of the sample. For Rietveld quantitative phase
analysis (RQPA), the same angular interval was analyzed
in 0.02steps, at 15 s/step using a 1divergence and anti-
scattering slits, and a detector slit of 0.2 mm. The X-ray
tube was operated at 40 kV and 40 mA [36]. The Si and
ZnO contents were determined by RQPA using a free-code
software MAUD (Materials Analysis Using Diffraction
[37]. After RQPA, the amorphous content was determined
using Eq. (1).
A¼1Ws
Rs
100 Ws 104%;ð1Þ
where (%) is the weighted concentration of the internal
standard and (%) is the Rietveld-analyzed concentration of
the internal standard [36,38]. The amorphous phase is
assumed to be glass, while the crystalline phase is assumed
to be silicon.
The optimal parameter to separate materials from waste
PV modules is given by the analysis of the distribution of
material in A, B and C (Fig. 4). In the interest of evaluating
the effectiveness of electrostatic separation and the optimal
parameter combination, a variance analysis was performed,
and p-values were generated to determine significance for a
confidence level of 95% (a= 0.05). The variance analysis
was performed for the silver, copper, and polymer sepa-
ration. Because of the cost of XRD and RQPA analysis, it
was not possible to perform a variance analysis for glass
and silicon as this requires replicated measurements.
Results
In the first part of the experiment, an empirical study was
carried out in order to restrain the degrees of freedom
related to the electrostatic separation. Initially, all param-
eters varied, and the output of each combination was
analyzed by visual inspection. As a result, the fixed
parameters were the two splitter angles, the vibratory fee-
der speed, and the position of the ionizing electrode, the
brush and the lifting electrode. The visual inspection
Table 2 Relationship between parameters and variation for the electrostatic separator used in this study
Parameters Variation Position in Fig. 4Fixed? Pinned at
Splitter angle (conductor) [-45to ?45] 7 Yes 10
Splitter angle
(nonconductor)
[-45to ?45] 8 Yes 22
Vibratory feeder speed 0–100% 2 Yes 25%
Preheating 0–60 C 12 Not used Room
temperature
Rotation speed 0–300 RPM 4 No
Electric potential difference 0–40 kV 3, 4, 5 No
Ionizing electrode position Position in a 650 9720 mm
2
area having the roll electrode
on the center, Xas the horizontal axis, and Yas the vertical
X=[-200 to ?450 mm]
Y=[-450 to ?270 mm]
3 Yes x[90;240]
y[110;260]
Lifting electrode position 5 Yes x[255; 450]
y[95; 160]
Brush position 11 Yes x[– 200; – 170
y[– 70; 35]]
Journal of Sustainable Metallurgy
123
revealed a clear separation among the main materials
present in waste PV modules. As can be seen in Fig. 5, the
nonconductor fraction (C) contains mostly polymers (white
particles), the middling fraction (B) contains mostly silicon
(gray and blackish particles) and the conductor fraction
(A) mostly contains glass. Although glass is an electrical
insulating material [39], its particles fall into the first pan
along with the metals (conductive fraction: A). This may
be due to particles being too heavy (speed gained during
rotation is superior to the electrostatic forces acting) and/or
due to the influence of metallic particles, which can attach
to the glass particles through the encapsulating material.
The following experiments determined which would be
the values for voltage and rotation speed used in this study.
Rotation speed varied from 15 to 85 RPM and the voltage
from 10 to 30 kV (voltages higher than 30 kV were not
tested because electrical discharges start taking place at this
point). Each output was evaluated by visual inspection and
classified as poor, fair, good, and great. The results are
displayed in Table 3.
Table 3shows two results classified as ‘‘great’’: 28 kV
with 30 RPM and 28 kV with 55 RPM. The table also
shows that the best results are obtained with a voltage of
24 kV or higher and a rotation speed of 30 or higher. Thus,
two voltage values (24 and 28 kV) and three rotation speed
values (50, 65, and 80 RPM) were chosen to quantitatively
evaluate the separation of materials from waste PV
modules.
The distributions of silver and copper for each parameter
combination obtained by ICP-OES are displayed in Figs. 6
and 7, respectively.
Both Figs. 6and 7indicate that metals tend to concen-
trate in the first fraction (A), followed by the second and
third (B and C). It should be highlighted that the metal
concentration in C is around 5% on average. Therefore, the
electrostatic separation concentrates about 95% of silver
and copper in fractions A and B. The copper did not follow
this distribution for the combination 24 kV-65 RPM nor
28 kV-50 RPM. While 100% of separation was not
achieved at this point, these results indicate that
electrostatic separation is able to separate the metal content
from photovoltaic waste, but also show that there is no
significant difference between the treatments (combina-
tions of parameters) tested in this study in regard to metal
separation. Figure 8supports the statement that there is a
significant difference between the three fraction outputs.
The detailed distributions of silver and copper are available
in Supplementary Tables 1 and 2, respectively.
The polymer distribution was measured by gravimetric
analysis. The mass differences before and after combustion
are assumed to be the mass of polymers present in a certain
sample. The variance analysis for the polymer distribution
is shown in Fig. 9, and the average polymer distributions in
pans A, B, and C are displayed in Fig. 10. Figure 9indi-
cates that the combinations of parameters tested for the
electrostatic separation do not differ significantly among
each other.
Moreover, Fig. 10 shows that it was not possible to
segregate the polymers in any of the separation pans. It has
been reported that photovoltaic panels may have polyvinyl
chloride (PVC) in its substrate [15]. Richard et al. [29]
have stated that the use of a reverse s-shaped electrode
assists in the separation of PVC by this method. The
presence of PVC in waste PV may have influenced the
separation process. The detailed distribution of polymers is
available in supplementary Table 3.
The silicon and glass distributions were measured by
XRD with Rietveld’s refinement. The amorphous phase
was assumed to be glass, while the crystalline phase was
assumed to be silicon. The distributions of glass and silicon
in the three pans for all tested parameters are displayed
Fig. 10, while the uncertainties associated with the Riet-
veld’s refinement for the analysis of this study are pre-
sented in Supplementary Table 6.
Figure 10 suggests that glass tends to concentrate in the
first fraction (conductor: A) as predicted from the empirical
study. Moreover, for a significance of p\0.001, fraction
sA and B concentrate approximately 95% of the glass. A
similar behavior is found with the silicon, given it con-
centrated mainly in A, followed by B and C. The standard
Fig. 5 Visual analysis comparing the three different outputs from the electrostatic separation during the empirical study. Conductor (a),
middling (b) and nonconductor (c) (Color figure online)
Journal of Sustainable Metallurgy
123
deviations suggest that it is possible to concentrate silicon
in the second fraction (middling) with the appropriate
combination of parameters. The influences of each com-
bination of parameters on the material distribution for glass
and silicon are displayed in Figs. 11 and 12.
The detailed distributions of glass and silicon are
available in Supplementary Tables 4 and 5, respectively.
Figure 11 shows that for all the combination of parame-
ters tested, glass mostly stays in the first fraction. This is
probably due to its weight, i.e., most of the glass particles
have a mass such that the gravitational force has a greater
influence than the electrostatic force from the process. The
smaller glass particles are the ones found in the last fraction
(nonconductor: C). As for the silicon, Fig. 12 shows that for
different combination of parameters (particularly for 24.50
and 28.80), it is possible to concentrate this material in the
second fraction (middling: B), but for the combinations of
this study, it tends to remain on the first fraction (conductor:
A). Silicon particles in PV waste are distributed in fine par-
ticles that can remain attached to particles of other material.
This may affect the distribution of silicon particles during the
electrostatic separation. The assessment of the different
combination of parameters is limited given that a single
analysis for each combination of parameters was made for
glass and silicon. Therefore, a statistical analysis is not
possible for these given parameters. Moreover, the mass
distributions in the three pans as a function of the tested
parameters are shown in Supplementary Table 7.
Fig. 6 Average distribution of
silver in each fraction for a
given combination of chosen
parameters (p-values for A, B,
and C distribution are 0.662,
0.789, and 0.856, respectively).
There were three replicates per
parameter
Table 3 Qualitative results from empirical study to determine key values of voltage and rotation speed
Voltage (kV) Rotation speed (RPM) Classification Comment
10 15 Poor No separation. All in B
10 30 Poor No separation. All in B
10 45 Poor Little improvement, glass in A, the rest in the B
10 55 Poor No separation. All in C
10 85 Poor No separation. All in C
12 30 Poor Almost all sample in B
14 30 Fair Glass in A, the rest in B
16 30 Fair Improvement. Some polymer in C
18 30 Fair Improvement. Most of it still in B
20 30 Fair Improvement. Better distribution among the three pans
22 30 Fair Same as previous
24 30 Good Most of the glass in A, polymers in C
26 30 Good Little improvement from previous
28 30 Great Most of the glass in A, most of the polymer in C, silicon, and polymers mixed in B
30 30 Electrical discharge (arcing) observed at this voltage
28 15 Good Nonconductive material concentrated in C
28 45 Good Most of the glass in A, most of the polymer in C, silicon in B and C
28 55 Great Similar to previous, but most of the silicon in B
28 70 Good Similar to previous, but silicon did not concentrate in B as much
Journal of Sustainable Metallurgy
123
Fig. 7 Average distribution of
copper in each fraction for a
given combination of chosen
parameters (p-values for A, B,
and C distribution are 0.606,
0.552, and 0.209, respectively).
There were three replicates per
parameter
Fig. 8 Electrostatic separation’s influence on silver and copper
content distributions (pvalue for silver and copper distribution
is \0.001)
Fig. 9 Average distribution of
polymer in each fraction for a
given combination of chosen
parameters (p-values for A, B,
and C distributions are 0.834,
0.051, and 0.933, respectively).
There were three replicates per
parameter
Fig. 10 Electrostatic separation’s influence on polymer, glass, and
silicon content distributions (p-values of polymer, glass, and silicon
distribution are 0.146, \0.001, and \0.001, respectively)
Journal of Sustainable Metallurgy
123
Conclusions
The key conclusions from this study are as follows:
Electrostatic separation is able to segregate the metallic
fraction of waste photovoltaic panels. Metals tend to
concentrate in the first separation fraction (conductor).
About 95% of the metals in waste silicon photovoltaic
modules concentrate in output pans A and B (conductor
and middling, respectively) combined.
The studied combination of parameters have no statis-
tical differences among each other for the separation of
metals. The influence of the parameters was not
significant for either silver or copper.
Electrostatic separation was not able to concentrate the
polymers present in photovoltaic panels. The presence
of PVC as one of the polymers present in photovoltaic
panels may have contributed to the failure of the
electrostatic separation method [15,29].
The studied combination of parameters have no statis-
tical difference among each other for the separation of
polymers. The influence of the parameters was not
significant.
The glass present in waste PV tends to concentrate in
the conductive fraction, followed by the middling and
nonconductor (p\0.001).
For the majority of tested combination of parameters,
silicon tends to concentrate in the first output fraction
(conductor). However, it was shown that it is possible
to concentrate silicon in the second output fraction
(middling) by varying the parameters.
Among the tested combination of parameters
(24 kV.50RPM; 24 kV.65RPM; 24 kV.80RPM;
28 kV.50RPM; 28 kV.65RPM; 28 kV.80RPM), it is
Fig. 11 Distribution of glass in
each fraction for a given
combination of chosen
parameters
Fig. 12 Distribution of silicon
in each fraction for a given
combination of chosen
parameters
Journal of Sustainable Metallurgy
123
not possible to determine the optimal combination of
parameters for separating metals and polymers from
photovoltaic modules at this stage.
Electrostatic separation has an influence in most of the
materials present in waste silicon photovoltaics. This
process may assist in the recycling of waste PV.
This study can be improved by means of samples with
higher masses for each parameter combination (e.g.,
300 g), by evaluating the separation at a lower rotation
speed (e.g., 20, 30, and 40 RPM); by using a reversed
s-shaped plate so that materials such as PVC are more
influenced by the separation (as stated by Richard et al.
[29]); and by heating the samples before the separation to
reduce the humidity. The improvement of this study is
encouraged by the results observed. Electrostatic separa-
tion can assist in the recycling of waste photovoltaics, but
the parameters for an optimal separation are still uncertain.
Acknowledgements The authors are grateful to Capes, CNPq, FINEP,
and FAPERGS (Brazil) for their financial support.
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Many countries have gained benefits through the solar cells industry due to its high efficiency and non-polluting power generation associated with solar energy. Accordingly, the market of solar cell modules is expanding rapidly in recent decade. However, how to environmentally-friendly and effectively recycle waste solar cell modules is seldom concerned. Based on nitrogen pyrolysis and vacuum decomposition, this work can successfully recycle useful organic components, glass and gallium from solar cell modules. The results were summarized as follows: (i) nitrogen pyrolysis process can effectively decompose plastic. Organic conversion rate approached 100 % in the condition of 773 K, 30 min and 0.5 L/min N2 flow rate. But, it should be noted that pyrolysis temperature should not exceed 773 K, and harmful products would be increased with the increasing of temperature, such as benzene and its derivatives by GC-MS measurement; (ii) separation principle, products analysis, and optimization of vacuum decomposition were discussed. Gallium can be well recycled under temperature of 1123 K, system pressure of 1 Pa and reaction time of 40 min. This technology is quite significant in accordance with the "Reduce, Reuse and Recycle Principle" for solid waste, and provides an opportunity for sustainable development of photovoltaic industry.
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Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and non-conductive granular materials. The aim of this work is to identify the optimal operating conditions of such equipment, when employed for separating copper and plastics from either flexible or rigid electric wire wastes. The experiments are performed according to the response surface methodology, on samples composed of either "calibrated" particles, obtained by manually cutting of electric wires at a predefined length (4mm), or actual machine-grinded scraps, characterized by a relatively-wide size distribution (1-4mm). The results point out the effect of particle size and shape on the effectiveness of the electrostatic separation. Different optimal operating conditions are found for flexible and rigid wires. A separate processing of the two classes of wire wastes is recommended.