INVENTORY OF WASTE MATERIALS FROM SILICON INGOT AND WAFER MANUFACTURING FOR A
CIRCULAR PV VALUE CHAIN
Yijiang Xua, Gau e S okkana, Anne-Ka in Søilandb, Bi gi Ryningena, I ene B ags ada, Ma in Bellmanna
a SINTEF Indus y, b ReSiTec AS
a Richa d Bi kelands ei 3, 7034 T ondheim, No way. b Se esdals eien 110, 4617 K is iansand, No way.
ABSTRACT: Pho o ol aics (PV) is one o he mos impo an enewable ene gy. Du ing he p oduc ion o Si-based
PV panels, la ge esou ce lows a e gene a ed, and many was e ma e ials a e gene a ed. The challenge o ecycling is
connec ed o he ma e ial p ope ies: The composi ion, pu i y and mo phology will de e mine how he cu en was e
should be p ocessed in o de o ealize he po en ial alue. We ha e he e o e pe o med a was e in en o y o h ee
impo an ma e ial lows occu ing om monoc ys alline silicon ingo and wa e manu ac u ing in he PV p oduc ion
alue chain: Si ke om sawing o wa e s, silica om c ucibles used in CZ-Si ingo pulling and g aphi e om CZ
c ys al g ow h u naces. A se ies o cha ac e iza ion and analysis me hods, ha e been used o in es iga e he chemical
composi ion, phases, size and mo phology e c. o he h ee was e ma e ials. Possible con amina ion sou ces we e
discussed. The was e in en o y esul s gi e an o e iew o he ma e ials quali y and p ope y, and hei po en ial o
ecycling and e-use in he PV sec ion and o he applica ion ields.
Keywo ds: Si ke , Recycling, Ma e ials cha ac e iza ion
1 INTRODUCTION
The PV module ma ke in 2021 [1] showed a
signi ican g ow h o 183 GW, whe e 95% is based on he
c-Si echnology. Among c-Si module, mono-Si is he
dominan in he ma ke while mc-Si p oduc s educed o
13%. The ups eam silicon ingo and wa e
manu ac u ing p ocess is e y ene gy in ensi e, and
consume la ge quan i y o aw ma e ial and pa s, and
gene a e la ge was e. In he silicon wa e slicing
p ocesses, diamond wi e sawing, nea ly 40% o he high
pu i y silicon become ke loss was e. The amoun o Si
ke was e is es ima ed o be a a ound 160, 000 me ic
on in 2021. Besides, in he silicon ingo p oduc ion
p ocess, ancilla y ma e ials, such as g aphi e used as
c ys al g ow h u nace pa s, and silica om used qua z
c ucibles u n o was e. Acco ding o he ecen epo
[2], he global isos a ic g aphi e consumed in PV iled is
es ima ed a ound 50, 000 me ic ons in 2021. And he
silica was e olume eached 205,400 m in 2019.
The diamond wi e sawing (DWS) p ocess has
eplaced he adi ional slu y p ocess o silicon wa e
manu ac u ing. The s eel wi e a e co e ed wi h diamond
g i s by elec opla ed nickel coa ing. Silicon b icks which
a e moun ed o a beam a e ed in o he mo ing wi e web
while being ba hed in wa e -based cu ing luid.
Depending on he wi e hickness, a ound 35% o silicon
is los as Si-ke which is dispe sed in he wa e -based
cu ing luid. The cu ing luid and he Si-ke a e la e
sepa a ed h ough a il e p ess p o iding a liquid and a
solid ac ion (Si-ke il e cake). The in es iga ion and
esea ch on ecycling hese Si ke o di e en
applica ion has s a ed since 2013 [3], bu i is s ill a i s
in an s age. I is sho o a sys ema ic cha ac e iza ion
and in en o y o hese ma e ials, o cla i y he
composi ion, phases, impu i ies, mo phology e c.
In silicon ingo g ow h u nace, such as Czoch alski
single c ys al u nace, he e a e abou 30 kinds o high
pu i y isos a ic g aphi e pa s [4], including o ex,
hea e , hea shields and insula ion componen s,
suscep o s, bases o o a ion. G aphi e used in he ho es
sec ions o he u nace has a li e ime o only abou a ew
mon hs, ei he due o he s uc u e and p ope y
deg ada ion o due o he impu i y deposi ion and
o ma ion. This ma e ial is cu en ly down-cycled as low-
alue ca bon o example as a educing agen in smel ing
ope a ions. In o de o ecycle i as a high- alue ma e ial,
such as euse in exis ing g aphi e p oduc ion plan s and
use o anode ma e ials in li hium-ion ba e ies, a de ailed
analysis o hese g aphi e is demanded.
In addi ion, in Czoch alski p ocess o silicon ingo
g ow h, high pu i y used qua z c ucible is ano he key
componen [5]. I is used o hold he silicon mel du ing
ingo p oduc ion. The c ucible has wo laye s, a bubble
con aining laye wi h ce ain mechanical s eng h and a
bubble- ee inne laye . Du ing he CZ-p ocess, he silica
goes h ough a phase change, o ming c is obali e on he
su aces. A he same ime, bubbles could o m and g ow
in he bubble- ee laye a e se e al uns, which is
de imen al o he g owing ingo . The e o e, he li e ime
o hese c ucibles is e y limi ed. A e cooled down, he
emaining silicon is s icked o he bo om pa o he
c ucible, and he c ucibles canno be eused. This was e
ma e ials is being land illed. Some esea ch has been
epo ed [6] o s udy he silica c ucible was e om he
mul ic ys alline silicon ingo g ow h, and he me hod o
ecycling. Howe e , hose c ucibles a e di e en om he
high pu i y used qua z c ucibles o CZ mono-
c ys alline silicon ega ding he o iginal s a e, pu i y and
he using condi ion e c.. Un il now, he e is no
in es iga ion on he used c ucibles om CZ Si g ow h
p ocess, ega ding he phases, impu i y and i s po en ial
o ecycling e c.
In his wo k, he ma e ials' quali y o h ee impo an
was e ma e ial om silicon-ingo and wa e
manu ac u ing in he PV p oduc ion alue chain: Si ke
om sawing o wa e s, silica om c ucibles used in
c ys al pulling and g aphi e om c ys al g ow h u naces,
has been in es iga ed. The quali y is mainly consis ed o
chemical composi ion and impu i y con en , phases, size
and mo phology o pa icles in powde o m e c.
2 EXPERIMENTAL
2.1 Ma e ials
The ma e ials in es iga ed a e summa ized in Table I.
Si ke samples wi h di e en sou ce and condi ion a e
labled wi h di e en ID numbe . While g aphi e and
silica c ucible sc ap a e only om No way.
1636
Table I: Type, o igin, ID and condi ion o was e
ma e ials in es iga ed in his s udy.
Was e
yp
e O i
g
in ID Condi ion
Si-ke d y
(1x)
No way RST-ODIN-0921 D ied
Si-ke d y
(3x)
Asia RST-HAN-0120/-
MING-020/-
SONG1-0721
D ied
Ho -zone
g aphi e
No way RST-ODIN-C c ushed
Silica
c ucible
sc ap
No way RST-ODIN-Q-
0921
c ushed
Fo he c ushed g aphi e samples, hey ha e been
so ed acco ding o hei isual appea ance: 1: “clean”
samples, 2: yellow su ace, 3: sil e -g ey su ace, 4:
sil e wi h d ople . He e in his wo k, sample ype
1& ype 4 will be s udied.
Fo he silica c ucible samples, hey we e ca ego ized
as well by 4 di e en ypes, as shown in Fig. 1. 1: Clean
samples wi h a whi e laye on he c ucible inne and ou e
su ace, 2: Inne su ace wi h o ange and b own do s,
while ou e su ace is whi e, 3: Ou e su ace wi h o ange
do s and a eal sp eading, while inne su ace is whi e, 4:
Non- la inne su ace wi h sil e -like pa icles.
Figu e 1: Silica samples and ca ego iza ion in di e en
ypes: ype 1: whi e inne and ou e su ace, ype 2: small
yellow and black do s a he inne su ace, ype 3: yellow
do s and sp ead on he ou e su ace, ype 4: sil e -like
pa icles on he non- la inne su ace.
2.2 Analysis and Cha ac e iza ion me hods
A se ies o chemical analysis and ma e ials
cha ac e iza ion, such as Induc i ely coupled plasma
mass spec ome y (ICP-MS), LECO, X- ay
pho oelec on spec oscopy (XPS), X- ay di ac ion
analysis (XRD), ligh mic oscopy and scanning elec on
mic oscopy, and lase di ac ion has been pe o med.
3 RESULTS
3.1 Silicon ke
Fig. 2 shows he concen a ion (in ppmw) o common
dopan elemen s (B, Ga and P) in di e en Si-ke
samples measu ed by ICP-MS. The B con en in ODIN
sou ce samples and mos o he sou ce samples is a ound
0.35 o 0.4 ppm. Ming-0120 has sligh ly highe B, which
eaches 0.6 ppm. The Ga con en is in he ange o 0.05 o
0.65 ppm depending on he sou ce. Gene ally, ODIN
sou ce has highe Ga concen a ion. Fo P, he highes
con en is 15 ppm while lowes is 4 ppm, which is much
highe han B and Ga. Compa ing he d y samples om
di e en sou ces, i can be seen ha o Asian sou ces he
P con en is highe han o he ODIN sou ces.
Figu e 2: Con en o common dopan s (B, Ga and P) in
di e en Si-ke samples measu ed by ICP-MS.
The me al con amina ions, such as Al, Fe, and Ni,
de e mined by ICP-MS a e shown in Fig. 3. ODIN sou ce
sample has he highes Al (~0.72 w .%), while he h ee
Asian samples ha e much lowe Al (<1000 ppm),
especially SONG1 only has 10 ppm. Al con amina ion in
ODIN sou ce should be mainly om aluminium i-
hyd oxide used as beam ma e ial in he DWS p ocess.
Ming has a e y high Fe concen a ion (~1000 ppm),
while o he samples ha e less han 100 ppm Fe. The Fe
con en in ODIN sou ce samples is lowe han ha in
Asian samples. Fe con amina ion could come om he
s eel wi e o o he s eel-made equipmen / ools in he
il a ion and d ying p ocess. In addi ion, Ni is a common
con amina ion elemen , due o he use o elec opla ed
nickel coa ing on he s eel wi e. Typical Ni con en is
100-200 ppm.
Figu e 3: Con en o me al impu i ies (Al, Fe, Ni) in
di e en Si-ke samples measu ed by ICP-MS.
Table II shows he ca bon and oxygen con en
measu ed by LECO. The ypical ca bon con en o mos
o he samples is a ound 1-2 w .%, while SONG1 is mo e
han double his. Ca bon may come om he o ganic
compound in he cu ing luid. The oxygen con en is
abou 4-5 w .%.
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Table II Ca bon and oxygen con en in di e en Si ke
samples measu ed by LECO.
Sa
mple-
ID
R
ST-
ODIN
-0921
R
ST-
HAN
-0120
RS
T-
MING
-0120
RS
T-
SONG1
-0721
(w
.%
)
Ca bon 2.
0
2.
0
1.0 4.4
Oxygen 4.
2
4.
3
4.8 5.6
Fig. 4 shows an SEM image o RST-ODIN-0921-d y
Si-ke sample. I is seen ha he Si-ke consis s o
ibbon-like, i egula shaped angula pa icles,
agglome a es, and nano-sized pa icles. The ibbon
shaped pa icles a e up o a ound 4 µm long.
Figu e 4: SEM images o RST-ODIN-0921-d y Si-ke
sample.
The pa icle size dis ibu ion (sphe ical equi alen ) o
wo ep esen a i e Si ke samples om No way and
Asia measu ed by lase di ac ion analysis is shown in
Fig. 5. As can be seen, ODIN-0921 has mo e small
pa icles wi h size below 0.34 µm, and mo e pa icles in
he ange o 0.66-1.8 µm, bu less big pa icles la ge
han 2 µm.
Figu e 5: Pa icle size dis ibu ion o 2 Si-ke samples
(RST-ODIN-0921 and RST-HAN-0120) measu ed by
lase di ac ion me hod.
3.2 G aphi e
The ash con en o g aphi e sample is 0.16% and
4.1% espec i ely o sample 1 and sampel4. The me al
impu i y con en in he g aphi e was calcula ed om he
impu i y con en measu ed in he ash by ICP-MS, and he
esul s a e lis ed in Table III. I can be seen ha he
highes impu i y is Si, which is a 0.39 w .% and 10.9
w .% in g aphi e sample 1 and sample 4. O he impu i ies
a e in ppm le el. Ca and Co a e sligh ly highe in sample
4.
Table III: Impu i y con en in he g aphi e measu ed by
ICP-MS o ash samples.
Si
w
%
Cap
pmw
Alp
pmw
Fep
pmw
Cop
pmw
Nip
pmw
T
i
Bp
pm
w
Ppp
mw
#
1
0.
39
4.7 1.3 2.0 5.5 0.2 0
.
2
0.1 6.
7
#
4
10
.9
21.
8
0.6 2.1 41.
1
0.7 0
.
3
0.2 10
.2
Fig. 6 shows he XRD esul s o g aphi e sample 4.
Bo h Si and SiC a e iden i ied on he su ace. The su ace
is u he cha ac e ized by SEM. Two ep esen a i e
Seconda y elec on images a e shown in Fig. 7. In Fig.
7a, we see a egion wi h la su ace and a egion wi h
ough su ace. The la egion is consis ed o Si g ains.
While in he ough egion, he e a e se e al phases wi h
di e en mo phologies. F om magni ied images o Fig.
7b, i shows ha some ace ed pa icles a e imbedded
inside some ma ix, while only exposing some su aces,
which is SiC. A he same ime, he e a e some small
sphe ical shaped phases and i egula pa icles on he
su ace.
Figu e 6: XRD esul s o he su ace o g aphi e ype 4.
Figu e 7: SEM seconda y elec on image o g aphi e
ype 4 sample su ace.
3.3 Silica
Fig. 8 shows he XRD esul s o powde sample o
silica ype 4, which is simila o he pa e n ob ained o he
o he h ee ypes. A sha p c is obali e peak is obse ed,
which is he only c ys alline phase been de ec ed. Si phase
was no de ec ed by cu en XRD, p obably due o he
small olume ac ion. The e is a bump a 2θ=23o, which
co esponds o he amo phous silica phase.
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Figu e 8: XRD esul s o milled powde sample o silica
sample ype 4. Same pa e n was ob ained o he o he 3
sample ypes as well.
The impu i y con en de e mined by ICP-MS is shown
in Table IV. The highes impu i y is Ca, which is much
highe han he ypical amoun in he new c ucibles o CZ
p ocess. Co is a ound 21.4 ppm, which is also highe han
he ypical alue (<0.01 ppm), which could be a esul om
con amina ion du ing he milling p ocess. Simila o Fe,
he samples could ha e been con amina ed du ing c ushing
p ocess i s eel ools ha e been used. Compa ing he 4
samples, i can be seen ha ype 3 has much highe Al
con en han he o he 3, which a e almos he same as in
he o iginal qua z sand and new c ucible.
Table IV Impu i y con en (ICP-MS) in he 4 ca ego ized
silica samples. All alues in ppmw.
# Na Al P Ca Ti Fe Co Ba B
1 11.8 16.7 1.4 518.4 6.7 10.1 25.2 2.1 0.2
2 13.4 10.6 0.6 433.7 6.2 2.4 24.0 1.4 0.6
3 30.1 135.4 1.5 403.5 2.7 37.0 17.4 1.1 <0.2
4 25.0 7.5 1.1 431.2 2.0 26.6 19.0 1.1 <0.2
4 DISCUSSION
Fo ecycling o Si ke back in o he PV alue chain
as new eeds ock, he con amina ion le el is an impo an
pa ame e . A u he e ining p ocess is needed o educe
he impu i y le el o he equi ed amoun . Besides, he
o iginal wa e sawing p ocess could be op imized o
educe and a oid he con amina ion o some impu i y
such as Al and Fe.
Use o Si-ke in o he applica ion o p oduc s can be
ano he way o ecycle. Fo example, as eeds ock o
me allu gical Si p oduc ion, alloying in o Al-Si alloys,
and Li-ion ba e y. The p ocessabili y will also depend on
mo phology and su ace condi ions. I is seen ha some
di e ences exis be ween ma e ials in e ms o pa icle
size and su ace a ea.
The g aphi e is commonly con amina ed wi h Si, SiC
e c. The ash con en wi h ela i ely clean su ace g aphi e
is accep able, while he one wi h con amina ed su ace is
ela i ely high. The gene ally low le els o Ni and Co a e
p omising o ypical g aphi e uses, such as isos a ic
g aphi e p oduc s and Li-ion ba e y applica ion.
The di e ences in impu i y concen a ion be ween
he ypes a e no signi ican , excep ype 3 which has an
o de o magni ude highe Al concen a ion. The o iginal
o high Al in ype 3 needs o be u he in es iga ed. Ca is
also e y high in all samples. The ecycling and euse o
hose was e ma e ials a e less explo ed.
5 CONCLUSIONS
A de ailed cha ac e iza ion and analysis o 3 was e
ma e ials om sola cell CZ-Si ingo and wa e
p oduc ion p ocess ha e been pe o med, including Si
ke , g aphi e and silica c ucibles.
Si-ke is consis ed o ibbon like, i egula shaped
angula pa icles, agglome a es, and nano-sized pa icles.
In Si ke , he Si concen a ion is abou 92 w .%, while
he main impu i ies a e C (~1-2 w .%), O (~4-5 w .%),
me allic elemen s (Al, Ca, Ni, Fe e c.) and doping
elemen s (P, B, Ga).
G aphi e con ains mainly Si and su ace in il a ions
o SiC o igina ing om he chemical eac ions inside he
u nace. The ash con en o ype 1 g aphi e is 0.16 %,
which is qui e low. O he de ec ed impu i ies a e a much
lowe le els, Ca and Co could each 20-40 ppm in ype 4
and a e ~5ppm in ype 1. P is abou 10 ppm. O he
elemen like Al, Fe Ni, Ti B a e below 1ppm.
Silica is mainly p esen in he o m o amo phous
silica and c ys alline c is obali e. In ype 4, i can con ain
silicon. Ca has he highes le el (~500 ppmw) among
o he impu i ies. O he impu i ies like Na, Al, P, Ti, Fe,
Co, Ba and B a e also p esen bu a much lowe le els
(1-40 ppmw).
6 ACKNOWLEDGMENT
This p ojec has ecei ed unding om he Eu opean
Union’s Ho izon 2020 esea ch and inno a ion
p og amme unde g an ag eemen numbe 958365.
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