3264 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
without chemical waste. The aluminum frame and junction
box were removed first, followed by heating the remaining
module to peel off the back sheet. A laser with a wavelength
not absorbed by the encapsulant scanned across the module
to debond the encapsulant layer from the silicon cell. The
encapsulant layer was then peeled off after a corner of the
layer was separated from the silicon cell by scratching it with
a knife. This process should be applicable to debonding of
the front encapsulant layer from silicon cells as well since
the glass is also transparent to the laser wavelength. One
question is about the throughput: how long does it take to
process an entire module as the laser is a point source?
Metal Recovery
Nitric acid is the most common leaching agent for sil-
ver, but there are two alternative chemicals for silver leach-
ing now. One is methanesulfonic acid (CH2SO2OH) (Yang
et al., 2017). The other is hydrofluoric acid (Tao, 2023).
Both leaching agents require hydrogen peroxide (H2O2) to
facilitate silver leaching as they alone do not dissolve sil-
ver. With a 90:10 ratio of 99 wt% methanesulfonic acid
and 30 wt% hydrogen peroxide, complete silver dissolu-
tion is achieved within 4 hours at room temperature. The
dissolved silver is recovered through precipitation of silver
chloride (AgCl). Additional steps and chemicals are used to
recover metallic silver of a 99.9% purity.
With hydrofluoric acid leaching, complete silver dis-
solution is achieved within 60 min. Electrowinning is per-
formed on the hydrofluoric leachate to recover metallic
silver without additional steps or chemicals. After 12 hours,
a 95% silver recovery rate is achieved. This represents a sig-
nificant improvement over the nitric leachate, 65% after 24
hours of electrowinning (Hwang et al., 2017). The recov-
ered silver is 99.9% pure. However, the hydrofluoric acid
recipe is complicated by the presence of silicon in the source
material, as hydrofluoric acid plus hydrogen peroxide etch
silicon and silver simultaneously. A similar problem exists
for methanesulfonic acid, as it dissolves lead, tin, copper,
along with silver. More innovations are needed to improve
the selectivity of these recipes.
Limited efforts have been devoted to lead recovery from
silicon cells. Besides nitric acid, acetic acid (CH3COOH)
plus hydrogen peroxide is an effective and mild leaching
agent for lead (Click et al., 2023). Complete lead dissolu-
tion is achieved within minutes. 24-hour electrowinning of
the acetic leachate results in 99% lead recovery. However,
the recovered lead includes various lead oxides and acetates
in addition to metallic lead. Further processing is needed to
obtain all the lead in the metallic form.
There are also proprietary technologies for metal recov-
ery by startup companies. These are claims so no details
are available. ROSI, a French startup, claims “soft chem-
istry” to recover solar-grade silicon and silver from silicon
cells (ROSI Solar, 2023a). TG Companies, a startup in
Arizona, claims a regenerative chemistry for sliver recovery
(TG Companies, 2023a), i.e., the acid for silver leaching
is regenerated later in the process and then reused in silver
leaching. These claims, if true, are certainly noteworthy as
they would minimize the quantity and hazard of the chemi-
cals used in silicon cell recycling.
CONCLUSIONS
This paper reviews the current recycling technologies for
silicon solar modules, analyzes the major technical barri-
ers in silicon module recycling, and summarizes significant
progress to achieve a 90–95 wt% circularity for silicon
modules. The major technical barriers to silicon module
recycling include polymer removal (encapsulant and back
sheet) and high metal recovery rates with minimum amount
of less hazardous chemicals. Some of the significant prog-
ress includes: 1) laser debonding of encapsulant from sili-
con cells 2) dissolution of encapsulant with a base 3) mild
chemicals for silver and lead recovery and 4) regenerative
chemistry to minimize chemical waste. More innovations
are needed to develop an environmentally and financially
sound recycling process and create a circular economy in
the solar industry.
ACKNOWLEDGMENT
This material is based upon work supported by the US
Department of Energy’s Office of Energy Efficiency and
Renewable Energy under Award Number DE-EE0007897
awarded to the REMADE Institute, a division of
Sustainable Manufacturing Innovation Alliance Corp.
REFERENCES
Bruton, T.M., Scott, R.D.W., and Nagle, J.P. 1994.
Recycling of high value, high energy content com-
ponents of silicon PV modules. In Proceedings of
12th European Photovoltaic Solar Energy Conference.
Amsterdam:303–304.
Click, N., Adcock, R., Chen, T., et al. 2023. Lead leach-
ing and electrowinning in acetic acid for solar mod-
ule recycling. Solar Energy Materials and Solar Cells
254:112260.
Deng, R., Chang, N.L., Ouyang, Z. et al. 2019. A techno-
economic review of silicon photovoltaic module
recycling. Renewable and Sustainable Energy Reviews
109:532–550.
without chemical waste. The aluminum frame and junction
box were removed first, followed by heating the remaining
module to peel off the back sheet. A laser with a wavelength
not absorbed by the encapsulant scanned across the module
to debond the encapsulant layer from the silicon cell. The
encapsulant layer was then peeled off after a corner of the
layer was separated from the silicon cell by scratching it with
a knife. This process should be applicable to debonding of
the front encapsulant layer from silicon cells as well since
the glass is also transparent to the laser wavelength. One
question is about the throughput: how long does it take to
process an entire module as the laser is a point source?
Metal Recovery
Nitric acid is the most common leaching agent for sil-
ver, but there are two alternative chemicals for silver leach-
ing now. One is methanesulfonic acid (CH2SO2OH) (Yang
et al., 2017). The other is hydrofluoric acid (Tao, 2023).
Both leaching agents require hydrogen peroxide (H2O2) to
facilitate silver leaching as they alone do not dissolve sil-
ver. With a 90:10 ratio of 99 wt% methanesulfonic acid
and 30 wt% hydrogen peroxide, complete silver dissolu-
tion is achieved within 4 hours at room temperature. The
dissolved silver is recovered through precipitation of silver
chloride (AgCl). Additional steps and chemicals are used to
recover metallic silver of a 99.9% purity.
With hydrofluoric acid leaching, complete silver dis-
solution is achieved within 60 min. Electrowinning is per-
formed on the hydrofluoric leachate to recover metallic
silver without additional steps or chemicals. After 12 hours,
a 95% silver recovery rate is achieved. This represents a sig-
nificant improvement over the nitric leachate, 65% after 24
hours of electrowinning (Hwang et al., 2017). The recov-
ered silver is 99.9% pure. However, the hydrofluoric acid
recipe is complicated by the presence of silicon in the source
material, as hydrofluoric acid plus hydrogen peroxide etch
silicon and silver simultaneously. A similar problem exists
for methanesulfonic acid, as it dissolves lead, tin, copper,
along with silver. More innovations are needed to improve
the selectivity of these recipes.
Limited efforts have been devoted to lead recovery from
silicon cells. Besides nitric acid, acetic acid (CH3COOH)
plus hydrogen peroxide is an effective and mild leaching
agent for lead (Click et al., 2023). Complete lead dissolu-
tion is achieved within minutes. 24-hour electrowinning of
the acetic leachate results in 99% lead recovery. However,
the recovered lead includes various lead oxides and acetates
in addition to metallic lead. Further processing is needed to
obtain all the lead in the metallic form.
There are also proprietary technologies for metal recov-
ery by startup companies. These are claims so no details
are available. ROSI, a French startup, claims “soft chem-
istry” to recover solar-grade silicon and silver from silicon
cells (ROSI Solar, 2023a). TG Companies, a startup in
Arizona, claims a regenerative chemistry for sliver recovery
(TG Companies, 2023a), i.e., the acid for silver leaching
is regenerated later in the process and then reused in silver
leaching. These claims, if true, are certainly noteworthy as
they would minimize the quantity and hazard of the chemi-
cals used in silicon cell recycling.
CONCLUSIONS
This paper reviews the current recycling technologies for
silicon solar modules, analyzes the major technical barri-
ers in silicon module recycling, and summarizes significant
progress to achieve a 90–95 wt% circularity for silicon
modules. The major technical barriers to silicon module
recycling include polymer removal (encapsulant and back
sheet) and high metal recovery rates with minimum amount
of less hazardous chemicals. Some of the significant prog-
ress includes: 1) laser debonding of encapsulant from sili-
con cells 2) dissolution of encapsulant with a base 3) mild
chemicals for silver and lead recovery and 4) regenerative
chemistry to minimize chemical waste. More innovations
are needed to develop an environmentally and financially
sound recycling process and create a circular economy in
the solar industry.
ACKNOWLEDGMENT
This material is based upon work supported by the US
Department of Energy’s Office of Energy Efficiency and
Renewable Energy under Award Number DE-EE0007897
awarded to the REMADE Institute, a division of
Sustainable Manufacturing Innovation Alliance Corp.
REFERENCES
Bruton, T.M., Scott, R.D.W., and Nagle, J.P. 1994.
Recycling of high value, high energy content com-
ponents of silicon PV modules. In Proceedings of
12th European Photovoltaic Solar Energy Conference.
Amsterdam:303–304.
Click, N., Adcock, R., Chen, T., et al. 2023. Lead leach-
ing and electrowinning in acetic acid for solar mod-
ule recycling. Solar Energy Materials and Solar Cells
254:112260.
Deng, R., Chang, N.L., Ouyang, Z. et al. 2019. A techno-
economic review of silicon photovoltaic module
recycling. Renewable and Sustainable Energy Reviews
109:532–550.