mine als
A icle
Cha ac e iza ion o Was e Sludge Pigmen om P oduc ion
o ZnCl2
Hana O ˇcaˇcíko á1,* , Ma ek Veliˇcka 1, Pe a Maie o á1, Joze Vlˇcek 1, Jonáš Toka ský2,3 and Tomᚡ
Cegan 4


Ci a ion: O ˇcaˇcíko á, H.; Veliˇcka,
M.; Maie o á, P.; Vlˇcek, J.; Toka ský,
J.; ˇ
Cegan, T. Cha ac e iza ion o Was e
Sludge Pigmen om P oduc ion o
ZnCl2.Mine als 2021,11, 313.
h ps://doi.o g/10.3390/min11030313
Academic Edi o : Anna Candida
Felici and Lucilla P on i
Recei ed: 14 Feb ua y 2021
Accep ed: 15 Ma ch 2021
Published: 17 Ma ch 2021
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
1
Depa men o The mal Enginee ing, Facul y o Ma e ials Science and Technology, VSB-Technical Uni e si y
o Os a a, 17. Lis opadu 2172/15, 708 00 Os a a, Czech Republic; [email p o ec ed] (M.V.);
[email p o ec ed] (P.M.); [email p o ec ed] (J.V.)
2Nano echnology Cen e, CEET, VSB-Technical Uni e si y o Os a a, 17. Lis opadu 2172/15,
708 00 Os a a, Czech Republic; [email p o ec ed]
3Ins i u e o En i onmen al Technology, CEET, VSB-Technical Uni e si y o Os a a, 17. Lis opadu 2172/15,
708 00 Os a a, Czech Republic
4Depa men o Non-Fe ous Me als, Re ining and Recycling, Facul y o Ma e ials Science and Technology,
VSB-Technical Uni e si y o Os a a, 17. Lis opadu 2172/15, 708 00 Os a a, Czech Republic;
[email p o ec ed]
*Co espondence: [email p o ec ed]; Tel.: +42-05-9732-1523
Abs ac :
This s udy is ocused on he ea men o was e sludge om a zinc chlo ide p oduc ion
in o de o p epa e i on- ich pigmen s usable o a p oduc ion o glazes. In gal anizing plan s,
yellow was e sludge con aining signi ican amoun o ZnO, Cl, and Fe
2
O
3
, is o med. This aw
was e sludge canno be used as a pigmen in glaze. The e o e, h ee me hods o ea ing his
ma e ial we e p oposed: (a) washing wi h H
2
O, (b) calcina ion a 180
◦
C and washing by H
2
O,
and (c) calcina ion a 900
◦
C and washing by H
2
O. These me hods helped o educe Zn and Cl
con en up o 97%. Acco ding o X- ay luo escence analysis pe cen age o Fe
2
O
3
inc eased om
~41% o ~98%. X- ay powe di ac ion analysis con i med he o ma ion o
α
-Fe
2
O
3
(hema i e) in
he pigmen p epa ed. Scanning elec on mic oscopy wi h Ene gy dispe si e X- ay analysis showed
clus e s o ounded pa icles, and also he change in size o pa icles a e calcina ion was obse ed.
Pa icle size, speci ic su ace a ea, and densi y measu emen s oge he wi h he mog a ime ic and
di e en ial he mal analyses we e pe o med. Pigmen s p epa ed om he was e sludge we e added
o anspa en glaze in amoun s o 1, 5, 10, and 15 w .%. Pigmen -con aining glazes we e applied
by sp aying on i ed ce amic iles and hen i ed a 1060
◦
C. Colo o glazes was de e mined by
(Commission In e na ionale de l’Eclai age) CIE L*a*b* coo dina es as colo less, ligh b own shades,
b own- ed, b own-yellow, and deep ed-b own. Compa ison wi h colo s o glazes p epa ed using
comme cial pigmen s was also pe o med. Was e sludge can be used o p epa e pigmen s and glazes
con aining pigmen s as an al e na i e o comme cial p oduc s.
Keywo ds: pigmen ; Fe sludge; ZnCl2; calcina ion; glaze
1. In oduc ion
P epa a ion o glaze and pigmen is an excellen al e na i e o ecycling ma e ials.
The global pigmen consump ion in he indus y is expec ed o be 282.7 housand in
2023/$8 bn, and, in Eu ope, i is expec ed o inc ease o app oxima ely 85 housand .
Pigmen s a e widely applied in nume ous indus ial sec o s, such as ci il enginee ing, p o-
duc ion o pape , pain s, dyes, ce amic ma e ials (18 housand in 2023), plas ic ma e ials,
e c. This is he consump ion o example: o mixed me al oxide pigmen s (60 housand ),
pea lescen pigmen s (71 housand ), o ganic pigmen s (44 housand ), me allic pigmen s
(94 housand ), and special y pigmen s (14 housand ) [
1
]. Pigmen s can be classi ied as in-
o ganic, o ganic, and syn he ic. They mus ul ill h ee main equi emen s: he mal s abili y,
chemical s abili y, and high colo ings powe [2].
Mine als 2021,11, 313. h ps://doi.o g/10.3390/min11030313 h ps://www.mdpi.com/jou nal/mine als
Mine als 2021,11, 313 2 o 16
Ino ganic pigmen s exhibi co e ing p ope ies, colo ing p ope ies, o o he spe-
cial ea u es, and can be di ided as ollows: (a) whi e pigmen s, (b) black pigmen s,
and (c) colo ed pigmen s. Thei o he special ea u es a e he an ico osion p ope ies
( e i e pigmen s) [
3
], bu pigmen s can be also me allic, nac eous, luminescen [
4
], mag-
ne ic [
5
], o an i- us [
6
]. The quali y o pigmen depends on he op ical and physical
p ope ies. Ino ganic pigmen s a e powde subs ances colo ing he en i onmen (binde )
in which whe e hey a e dispe sed, o colo ing he su ace on which hey a e applied.
Ce amic pigmen s a e compounds o ino ganic o igin wi h a ious c ys al s uc u es. Ce-
amic pigmen s a e o med by a he mally s able hos la ice (MgAl
2
O
4
, TiZn
2
O
4
, Z SiO
4
,
TiO
2
, e c.), which is colo less in i s pu e o m, and a ch omopho e de e mining he colo
o he esul ing pigmen and e ac i e indices o indi idual compounds. This p ope y
is e y impo an because high e ac i e index o he pigmen pa icles ela i e o he
e ac i e index o he medium whe e i is dispe sed indica es he quali y o he pigmen .
By changing he amoun o he indi idual compounds, o changing he s oichiome ic
ep esen a ion o he elemen s in he s uc u e, i is possible o p epa e pigmen shades o
colo ing ce amic glaze. Va ying calcina ion condi ions can also be used o achie e di e en
colo shades.
The mos impo an p ope y o he pigmen is he colo ( he abili y o pigmen a ion),
and he abili y o ge dispe sed in a ma ix. The he mal s abili y o pigmen s in a ce amic
ma e ial o engobe is de e mined o be be ween 1200 and 1300
◦
C. The pigmen in he
glaze and he pigmen o deco a ion mus be s able a empe a u es o 1000–1200
◦
C and
625–775 ◦C, espec i ely [7–9].
I on pigmen s, bo h na u al and syn he ic, ha e low cos o p oduc ion and signi ican
ad an ages o indus ial pu poses. The ea men o i on pigmen can esul in changes
in colo , such as black/magne i e, ed/hema i e, b own/maghemi e, yellow/goe hi e,
and o ange/lepidoc oci e [
10
,
11
]. The na u al i on pigmen s comp ise he ollowing
compounds: limoni e (Fe
2
O
3
.xH
2
O) om yellow o ed oche , goe hi e (Fe
3+
O(OH))— ed-
b own, hema i e (
α
-Fe
2
O
3
)—me allic g ey e ous mica. Na u ally-hyd a ed Fe
3+
oxides
we e used as pigmen s al eady in an Ea ly S one Age.
Many ino ganic pigmen s a e p epa ed wi h me allic oxides o sal s. In e es ing is
he p epa a ion o e ous pigmen s by chemical means om was e aw ma e ials, us-
ing p ecipi a ion eac ions, in he o m o e ous p ecu so s, e.g., magne i e (Fe
3
O
4
) [
12
,
13
],
goe hi e
α
-FeO (OH), hema i e (
α
-Fe
2
O
3
) [
14
–
16
], and maghemi e
γ
-Fe
2
O
3
[
17
,
18
].
α
-Fe
2
O
3
,
which can be u he p epa ed, e.g., by he hyd o he mal app oach [
19
], sol-gel p ocess,
chemical p ecipi a ion, high- empe a u e he mal oxida ion, e c. [20].
The pa h o he p epa a ion o i on- ich pigmen s begins wi h he p ocessing o ZnCl
2
.
The ZnCl
2
is a c ys alline and hyg oscopic powde exhibi ing he moch omic p ope ies.
ZnCl
2
is anhyd ous wi h a densi y o 1400–1700 kg/m
3
, wi h pH alue o 5. The colo o he
powde is whi e o sligh ly g eyish. Hea ed o a empe a u e o 500–700 ◦C, mol en anhy-
d ous ZnCl
2
dissol es me allic zinc. When his mel is apidly cooled, yellow diamagne ic
glass is o med. Raman spec oscopy analyses show ha he yellow glass o med con ains
zinc ions. As he empe a u e inc eases, he colo changes om whi e o yellow. This change
in colo is caused by la ice impe ec ions. Oxygen molecules a e los . The eac ion o ZnO
wi h acids p oceeds as ollows Equa ion (1) and in alkaline medium, and he ollowing
eac ion occu s, as in Equa ion (2) [21]:
ZnO + 2HCl = H2O + ZnCl2, (1)
ZnO + 2NaOH + H2O→Na2[Zn(OH)4]]. (2)
ZnCl
2
is used in indus y o me al su ace ea men and elec opla ing, as an elec-
oly e o ion exchange , in chemical syn heses, e c. [
22
–
25
]. Indus ially, ZnCl
2
is p epa ed
om so-called o e haul acids, which a e ob ained in gal anizing plan s by dissol ing
zinc coa ing on poo ly gal anized objec s (and aids and ools) in HCl. The Fe con en
Mine als 2021,11, 313 3 o 16
in o e haul acids hus p epa ed is usually >1.5%. A he beginning o p oduc ion, Fe is
neu alized by he so-called zinc ash, which is also a was e p oduc om gal anizing plan s.
Subsequen ly, he i on ions a e oxidized by H
2
O
2
. Because Fe
2+
ions hyd olyze a
highe pH han Zn
2+
ions, i is necessa y o achie e oxida ion o all Fe o he oxida ion s a e
III. Hyd oly ic p ecipi a ion is based on he di e en s abili y o he hyd oxide p ecipi a es
depending on he pH o he solu ion. The hyd oly ic p ecipi a ion o Fe can be desc ibed
as ollows in Equa ion (3):
Fe3+ +3H2O→Fe(OH)3+ 3H+. (3)
The p ecipi a e o med is il e ed on a sludge il e p ess. Subsequen ly, me als noble
han Zn a e emo ed om ZnCl
2
solu ion by cemen a ion p ocess. Zn powde is used as
a cemen ing agen . The e iciency and kine ics o he cemen a ion p ocess inc ease wi h
inc easing empe a u e, and he solu ion pH equi ed lies in he ange o 4 o 5. The eac ion
can be desc ibed by he ollowing gene al mechanism in Equa ion (4):
Zn + Me2+ →Me + Zn2+. (4)
This s udy is ocused on he ea men o was e sludge om he ZnCl
2
p oduc ion
in o de o p epa e i on pigmen s usable o a p oduc ion o glazes. The was e sludge
p ima ily con ains ZnO, Cl, and Fe
2
O
3
. In i s o iginal o m, i is yellow, due o he high
pe cen age o Cl. To ob ain pigmen o good quali y, he was e sludge calcina ion a 180
◦
C
and 900
◦
C, and subsequen washing in wa e was p oposed. The choice o empe a u es is
based on p e ious expe imen s pe o med by ou esea ch g oup. The ma e ials s udied in
his wo k we e cha ac e ized by a wide ange o me hods (X- ay powde di ac ion (XRPD),
he mog a ime ic analysis (TG), di e en ial he mal analysis (DTA), scanning elec on
mic oscopy (SEM), ene gy dispe si e X- ay analysis (EDAX), X- ay luo escence analysis
(XRF), B unaue -Emme -Telle (BET) su ace a ea analysis). Pa icle size dis ibu ion and
densi y we e also de e mined. I on- ich pigmen s success ully p epa ed om he was e
sludge we e added o a anspa en glaze and sp ayed on ce amic iles. The i ing was
pe o med a 1060
◦
C. The desc ibed p ocedu e led o ob aining glazes wi h di e en
colo and in ensi y, wi h a compac appea ance, gloss and wi hou isible de ec s on he
su ace. Colo ime ic analysis was used o compa e colo s o glazes p epa ed using ou
pigmen s wi h colo s o glazes p epa ed using comme cial pigmen s. This s udy shows
how he was e sludge can be used o p epa e p oduc s—pigmen s and pigmen -con aining
glazes—al e na i e o comme cial p oduc s.
2. Ma e ials and Me hods
2.1. Ma e ials
All ma e ials we e ob ained om he Czech Republic. Ce amic whi e slu y (la-
beled as CS) was ob ained om Pá ek Ke amika, spol. s .o. (Doub a ice nad S i a ou,
Czech Republic). T anspa en glaze (labeled as TG) is a comme cial whi e powde p o-
duced by Glazu a s. .o. company (Dobˇ ín, Czech Republic). In he expe imen , h ee ypes
o comme cial pigmen (labeled as SP1, SP2, SP3) wi h isible di e en colo SP1 ( ed),
SP2 (ligh b own), and SP3 (da k b own) we e used (Figu e 1). Ma e ials desc ibed abo e
we e used o ecipe o glazes shown in Table 1, and chemical composi ion o hese aw
ma e ials is p esen ed in Table 2, pa 3.1.
These pigmen s we e applied in hei o iginal o m. These a e syn he ic ine pigmen s,
wi hou any o he addi i es ( ille s), e y inely g ound, wi h e y good colo abili y, opaci y,
and pa icles dis ibu ion, esis an o wea he ing and chemicals, non- oxic, and he mally
s able up o 800
◦
C. Pigmen s a e de e mined acco ding o ˇ
CSN EN 12878—Pigmen s o
he colou ing o building ma e ials based on cemen and/o lime. (Eu opean S anda d
speci ying equi emen s and es ing me hods o pigmen in ended o use in he colo ing
o building ma e ials based on cemen and cemen lime combina ions. Lis o ele an
pigmen s o his applica ion is a ailable in Eu opean S anda ds EN 459 1 and EN 459 2).
Mine als 2021,11, 313 4 o 16
Pigmen s ypically belong o one o he ollowing classes: syn he ic oxides, na u al oxides,
o i on hyd oxides.
Mine als 2021, 11, 313 4 o 16
Figu e 1. Comme cial pigmen s in powde o m used o p epa a ion o glazes.
Table 1. Recipe o glazes p epa ed om was e Fe sludge (WFS) and comme cial pigmen (SP,
s anda d pigmen ).
Recipe Samples Amoun o he Ma e ials (w .%)
T anspa en Glaze (TG) Was e Fe Sludge (WFS) S anda d Pigmen s (SP)
WFS/0 WFS/180 WFS/900 SP1 SP2 SP3
R1
GP01 99 1
GP02 95 5
GP03 90 10
GP04 85 15
GPX 90 10
GOKP 90 10
R2
GPF1 90 10
GPF2 90 10
GPF3 90 10
Table 2. Chemical composi ion o ma e ials.
Amoun o Oxides in Raw Ma e ials (w .%)
Oxides Ce amic
Slu y (CS)
Was e
Fe Sludge
(WFS)
Was e
Fe Sludge
(WFS/0)
Was e
Fe Sludge
(WFS/180)
T anspa en
Glaze
(TG)
SP3
(Da k
B own)
SP2
(Ligh
B own)
SP1
(Red)
Na
2
O 1.22 5.61 4.61 5.50
MgO 2.83 1.12 0.18 <0.3 0.58 0.44 <0.001
Al
2
O
3
12.42 0.20 0.74 0.49 9.10 <0.001 0.44 <0.001
SiO
2
69.57 80.10 0.16 0.80 <0.001
P
2
O
5
<0.0012 0.06 0.16 <0.01 0.022 0.073 <0.001
SO
3
0.19 0.15 0.19 0.71 0.12 0.27 0.33 0.20
K
2
O 2.08 0.88 <0.001 <0.001 <0.001
CaO 4.52 0.02 <0.001 0.30 0.05 0.31 0.01
TiO
2
0.56 <0.001 0.13 0.67 0.59 1.311
MnO 0.07 <0.001 0.006 1.06 0.75 0.13
Fe
2
O
3
4.09 40.92 90.09 97.56 0.22 96.97 95.22 97.807
BaO 0.05 0.05
Cl 22.08 2.47 0.49 0.006 0.017 <0.001
ZnO 29.87 1.52 0.24 0.15 0.13 0.03
PbO 0.05 0.12 <0.001
V
2
O
5
<0.001 0.03 <0.001
C
2
O
3
0.14 <0.001 0.12 <0.001
NiO 0.028 0.10 <0.001
CuO <0.001 0.047 <0.001
These pigmen s we e applied in hei o iginal o m. These a e syn he ic ine pig-
men s, wi hou any o he addi i es ( ille s), e y inely g ound, wi h e y good colo abil-
i y, opaci y, and pa icles dis ibu ion, esis an o wea he ing and chemicals, non- oxic,
and he mally s able up o 800 °C. Pigmen s a e de e mined acco ding o ČSN EN 12878—
Pigmen s o he colou ing o building ma e ials based on cemen and/o lime. (Eu opean
Figu e 1. Comme cial pigmen s in powde o m used o p epa a ion o glazes.
Table 1. Recipe o glazes p epa ed om was e Fe sludge (WFS) and comme cial pigmen (SP, s anda d pigmen ).
Recipe Samples Amoun o he Ma e ials (w .%)
T anspa en Glaze (TG) Was e Fe Sludge (WFS) S anda d Pigmen s (SP)
WFS/0 WFS/180 WFS/900 SP1 SP2 SP3
R1
GP01 99 1
GP02 95 5
GP03 90 10
GP04 85 15
GPX 90 10
GOKP 90 10
R2
GPF1 90 10
GPF2 90 10
GPF3 90 10
Table 2. Chemical composi ion o ma e ials.
Amoun o Oxides in Raw Ma e ials (w .%)
Oxides Ce amic
Slu y (CS)
Was e Fe
Sludge(WFS)
Was e Fe
Sludge
(WFS/0)
Was e Fe
Sludge
(WFS/180)
T anspa en
Glaze (TG)
SP3 (Da k
B own)
SP2 (Ligh
B own) SP1 (Red)
Na2O 1.22 5.61 4.61 5.50
MgO 2.83 1.12 0.18 <0.3 0.58 0.44 <0.001
Al2O312.42 0.20 0.74 0.49 9.10 <0.001 0.44 <0.001
SiO269.57 80.10 0.16 0.80 <0.001
P2O5<0.0012 0.06 0.16 <0.01 0.022 0.073 <0.001
SO30.19 0.15 0.19 0.71 0.12 0.27 0.33 0.20
K2O 2.08 0.88 <0.001 <0.001 <0.001
CaO 4.52 0.02 <0.001 0.30 0.05 0.31 0.01
TiO20.56 <0.001 0.13 0.67 0.59 1.311
MnO 0.07 <0.001 0.006 1.06 0.75 0.13
Fe2O34.09 40.92 90.09 97.56 0.22 96.97 95.22 97.807
BaO 0.05 0.05
Cl 22.08 2.47 0.49 0.006 0.017 <0.001
ZnO 29.87 1.52 0.24 0.15 0.13 0.03
PbO 0.05 0.12 <0.001
V2O5<0.001 0.03 <0.001
C 2O30.14 <0.001 0.12 <0.001
NiO 0.028 0.10 <0.001
CuO <0.001 0.047 <0.001
Mine als 2021,11, 313 5 o 16
The ma e ial s udied was a was e Fe sludge ob ained as a seconda y p oduc du ing
p oduc ion o ZnCl
2
. Un ea ed o m o he was e sludge (labeled as WFS) om he
p oduc ion o zinc oxide (see Figu e 5, yellow colo samples) is no sui able as a pigmen .
The e o e, h ee me hods ha e been p oposed o p epa e a pigmen applicable o glazes:
(a) was e Fe sludge washed by H
2
O (labeled as WFS/0 and in an expe imen called as
he o iginal o m), (b) was e Fe sludge washed by H
2
O and calcined a 180
◦
C (labeled as
WFS/180), and (c) was e Fe sludge washed by H
2
O and calcined a 900
◦
C (labeled as
WFS/900).
2.2. Sample P epa a ion
Two ecipes o p epa ed glazes (Table 1) we e mixed. Recipe 1 con ains 6 di e en
mix u es o glazes. As a pigmen , 1, 5, 10, o 15 w .% o he was e Fe sludge was added in o
he anspa en glaze (Table 2). Recipe 2 can be called “compa a i e” because o mixing
anspa en glaze wi h 10 w .% o comme cial (s anda d) pigmen s. Indi idually p epa ed
mix u es (WFS/0; WFS/180; WFS/900 + TG) and (SP1; SP2; SP3; + TG) we e homogenized
in ball mill de ice wi h con ain he con en o 50% alumina balls by we milling (5% H
2
O)
o 30 min. The we mix u e was sie ed h ough a 0.2 mm sie e. The ob ained suspension
was mixed wi h wa e o each he composi ion exp essed by weigh o glaze. The ange
o li e weigh was de e mined o be om 1442 o 1550 g.L
−1
. The li e g a i y o glaze
was de e mined in a 1 L g adua ed cylinde . Fi s , he weigh o he emp y con aine was
de e mined. Subsequen ly, he con aine wi h he glaze in i was weighed and he weigh
o he emp y con aine was sub ac ed.
Ce amic iles we e p epa ed by cas ing in o gypsum o m ha ing dimensions
10 ×10 cm2
( i eclay slu y wi h a wa e con en o app oxima ely 34%). The ce amic iles
we e d ied a 105
◦
C and i ed in an elec ic esis ance u nace (LAC M125/13HTCe amic,
CZ) a a maximum empe a u e o 900
◦
C o 60 min. The glazes we e applied by sp aying
me hod o ensu e o compac laye s on he su aces o iles.
In his expe imen , he inal i ing was g adually speci ied. Fi ing I: This was o iginally
designed o a empe a u e o 1060
◦
C, a a a e o 3
◦
C/min, and i was wi hou a dwell a
his empe a u e. The samples glazed in his way showed c a e s on he su ace. C a e s a e
usually o med due o gas leakage om he glaze. In his case, he eason migh ha e been
he p esence o ZnO in he pigmen . Fi ing II: The op imal i ing cu e o his ype o
pigmen was wi h wo dwells: 30 min/600 ◦C and 60 min/1060 ◦C.
2.3. Cha ac e iza ion Techniques
•
Chemical composi ion o aw ma e ials was de e mined using ene gy dispe si e
luo escence spec ome e SPECTRO XEPO (SPECTRO Analy ical Ins umen s GmbH,
Kle e, Ge many), equipped wi h 50 Wa Pd X- ay ube.
•
The phase composi ion o samples was cha ac e ized using a B uke D8 Ad ance X-
ay powde di ac ome e (B uke AXS GmbH, Ka ls uhe, Ge many). The di ac ion
pa e ns in he ange o 5
◦
o 70
◦
2
θ
we e eco ded unde CoK
α
(
λ
= 1.78897 Å,
U = 35 kV
, I = 25 mA) i adia ion wi h scanning a e 2
◦
/min using as posi ion-
sensi i e de ec o VÅNTEC1.
•
The mo phology o he pa icles was cha ac e ized using he scanning elec on mic o-
scope (SEM) QUANTA 450 FEG, (FEI, Hillsbo o, OR, USA); he images we e collec ed
using a seconda y elec on de ec o .
•
The pa icle size dis ibu ion (PSD) was analyzed using Mas e size (Mal e n Panaly -
ical L d., Mal e n, UK). Measu emen s we e pe o med in an aqua ic en i onmen ,
and ul asound was used o homogeniza ion o he suspension.
•
The cha ac e iza ion o he he mal beha io was pe o med on TG/DTAanalyze
STA504 (TA Ins umen s, New Cas le, Delawa e, USA). The sample o scale placed
in alumina c ucible was analyzed in a empe a u e ange om 21 o 1100
◦
C in he
dynamic a mosphe e o N2(5 L·h−1), and he hea ing a e was 10 K·min−1.

Mine als 2021,11, 313 6 o 16
•
The e lec ance spec a o he inal glazes in he spec al ange 400–700 nm we e ob ained
using MiniScan EZ0828 spec ome e (Hun e Lab, Res on, VA, USA), model 45
◦
/0
◦
,
small obse a ion a ea. The colo o he glazes was exp essed using CIE L*a*b*
coo dina es calcula ed o 10◦obse e and D65 illuminan .
•
Speci ic su ace a ea was de e mined by BET me hod-equipmen (Quan ach ome No-
aWin Ins umen -Acquisi ion and Reduc ion o NOVA ins umen , analysis gas
ni ogen, G az, Aus ia).
•
Densi y o samples was de e mined by Pycnoma ic and Pycnoma ic ATC (Helium py-
cnome e ) POROTEC GmbH, Coconu C eek, FL, USA.
3. Resul s and Discussion
3.1. Chemical Composi ion
Chemical composi ion o o iginal ma e ials (CS, WFS, FWS/0, WFS/180, and TG)
used in expe imen s is p o ided in Table 2. The main oxides in he ce amic slu y (CS) a e
SiO
2
and Al
2
O
3 (
o e 83 w .%), and ~4 w .% o Fe
2
O
3
and CaO was also ound. T anspa en
glaze (TG) con ains ~80 w .% o SiO
2
, 9 w .% o Al
2
O
3
and 5 w .% o Na
2
O. The was e Fe
sludge (WFS) in o iginal o m (p esen ed as yellow colo in Figu e 5) con ains 41 w .% o
Fe
2
O
3
and high con en o chlo ine (22 w .%) and zinc oxide (up o 29 w .%). A e washing
he was e sludge by H
2
O (WFS/0), he amoun o chlo ine and ZnO signi ican ly dec eased
o 2.4 w .% and 1.5 w .%, espec i ely (Table 2). On he con a y, he amoun o i on oxide
eached 90 w .% a sample WFS/0 and mo e han 97 w .% a sample WFS/180 (Table 2).
The di e ences in he composi ion o he WFS/180 and WFS/900 samples did no exceed
0.5 w .%.
Comme cial pigmen s a e p epa ed by syn he ic ways. La ge amoun o Fe
2
O
3
ex-
pec ed in hese pigmen s was con i med by chemical analysis (Table 2). The ed colo
pigmen (SP1) con ains o e 97 w .% o Fe
2
O
3
. The ligh b own pigmen SP2 con ains
95 w .% o Fe2O3, and he las one, da k b own pigmen SP3, con ains 96 w .% o Fe2O3.
3.2. Phase Composi ion o Comme cial Pigmen s
X- ay di ac ion analysis showed (Figu e 2) showed he mos in ense e lec ions o
hema i e (
α
-Fe
2
O
3
) [
26
–
28
] in all h ee pigmen s. Mo eo e , magne i e was de ec ed in
samples SP2 (Figu e 2b) and SP3 (Figu e 2c). Only one phase was ound in he pigmen SP1
(Figu e 2a), i.e., hema i e wi h he mos in ense e lec ion a he posi ion o 38
◦
2
θ
. In he
case o ligh b own pigmen SP2, he p esence o h ee phases was ound:
α
-hema i e and
magne i e a posi ion 42
◦
2
θ
, and maghemi e (
γ
-Fe
2
O
3
) a posi ion 13
◦
2
θ
. The colo o
maghemi e co esponds o he colo o he SP2 pigmen . In he case o he da k b own
pigmen SP3, dominan e lec ions o hema i e and magne i e a he posi ion 42–44
◦
2
θ
a e
p esen . In addi ion, e lec ions o wüs i e (FeO) can be obse ed a he ollowing posi ions:
42◦, 50◦, and 74◦2θ.
3.3. G anulome y o Comme cial Pigmen s
The syn he ic pigmen s SP1, SP2, and SP3 a e e y ine powde s. All cu es on
(
Figu e 3
) e eal e y simila g ain size. Red pigmen s SP1 ha e g ained size
D (10) = 0.95 µm
,
D (50) = 9.38 µm
, and D
(90)
= 66.7
µ
m. The pa ame e s o ligh b ow pigmen SP2 a e
D
(10)
= 0.47
µ
m, D
(50)
= 5.83
µ
m, and D
(90)
= 19.4
µ
m, while he pa ame e s o he
dis ibu ion cu e o da k b own pigmen SP3 a e D
(10)
= 0.43
µ
m, D
(50)
= 7.02
µ
m,
and
D (90) = 28.4 µm
. The op imum size o pigmen pa icles o mos applica ions is
0.1–10 µm
. F om he measu ed da a, i can be concluded ha he syn he ic pigmen s SP1,
SP2, SP3 ha e he p ope ies decla ed by he manu ac u e .
3.4. SEM Analysis o Comme cial Pigmen s
Comme cial pigmen s show exhibi a conside able he e ogenei y o he pa icles,
as shown by SEM analysis (Figu e 4). The pa icles o hese pigmen s ha e an i egula
shape (see Figu e 4B,C-1, wi h scale 20
µ
m). Image wi h scale 200
µ
m (Figu e 4C-2) also
Mine als 2021,11, 313 7 o 16
do no show he p esence o sphe ical g ains. Based on SEM analysis, i can be s a ed
ha , in e ms o pa icle shape (a ec ing pigmen dispe sibili y), comme cial pigmen s SP1
(Figu e 4A) SP2 (Figu e 4B), and SP3 (Figu e 4C-1,C-2) a e no ideal powde sys ems.
Mine als 2021, 11, 313 7 o 16
Figu e 2. XRD pa e ns o (a) SP1 pigmen ( ed colo ); (b) SP2 pigmen (ligh b own colo ); and (c) SP3 pigmen (da k
b own colo ).
3.3. G anulome y o Comme cial Pigmen s
The syn he ic pigmen s SP1, SP2, and SP3 a e e y ine powde s. All cu es on (Fig-
u e 3) e eal e y simila g ain size. Red pigmen s SP1 ha e g ained size D
(10)
= 0.95 µm,
D
(50)
= 9.38 µm, and D
(90)
= 66.7 µm. The pa ame e s o ligh b ow pigmen SP2 a e D
(10)
= 0.47 µm, D
(50)
= 5.83 µm, and D
(90)
= 19.4 µm, while he pa ame e s o he dis ibu ion
cu e o da k b own pigmen SP3 a e D
(10)
=
0.43 µm, D
(50)
=
7.02 µm, and D
(90)
= 28.4
µm. The op imum size o pigmen pa icles o mos applica ions is 0.1–10 µm. F om he
measu ed da a, i can be concluded ha he syn he ic pigmen s SP1, SP2, SP3 ha e he
p ope ies decla ed by he manu ac u e .
Figu e 3. G ain size dis ibu ion o pigmen : 1) SP1 ( ed); 2) SP2 (ligh b own); 3) SP3 (da k
b own).
3.4. SEM Analysis o Comme cial Pigmen s
Comme cial pigmen s show exhibi a conside able he e ogenei y o he pa icles, as
shown by SEM analysis (Figu e 4). The pa icles o hese pigmen s ha e an i egula shape
(see Figu es 4B and 4C-1, wi h scale 20 µm). Image wi h scale 200 µm (Figu e 4C-2) also
do no show he p esence o sphe ical g ains. Based on SEM analysis, i can be s a ed ha ,
in e ms o pa icle shape (a ec ing pigmen dispe sibili y), comme cial pigmen s SP1
(Figu e 4A) SP2 (Figu e 4B), and SP3 (Figu e 4C-1 and 4C-2) a e no ideal powde sys ems.
Figu e 2.
XRD pa e ns o (
a
) SP1 pigmen ( ed colo ); (
b
) SP2 pigmen (ligh b own colo ); and (
c
) SP3 pigmen
(da k b own colo ).
Mine als 2021, 11, 313 7 o 16
Figu e 2. XRD pa e ns o (a) SP1 pigmen ( ed colo ); (b) SP2 pigmen (ligh b own colo ); and (c) SP3 pigmen (da k
b own colo ).
3.3. G anulome y o Comme cial Pigmen s
The syn he ic pigmen s SP1, SP2, and SP3 a e e y ine powde s. All cu es on (Fig-
u e 3) e eal e y simila g ain size. Red pigmen s SP1 ha e g ained size D
(10)
= 0.95 µm,
D
(50)
= 9.38 µm, and D
(90)
= 66.7 µm. The pa ame e s o ligh b ow pigmen SP2 a e D
(10)
= 0.47 µm, D
(50)
= 5.83 µm, and D
(90)
= 19.4 µm, while he pa ame e s o he dis ibu ion
cu e o da k b own pigmen SP3 a e D
(10)
=
0.43 µm, D
(50)
=
7.02 µm, and D
(90)
= 28.4
µm. The op imum size o pigmen pa icles o mos applica ions is 0.1–10 µm. F om he
measu ed da a, i can be concluded ha he syn he ic pigmen s SP1, SP2, SP3 ha e he
p ope ies decla ed by he manu ac u e .
Figu e 3. G ain size dis ibu ion o pigmen : 1) SP1 ( ed); 2) SP2 (ligh b own); 3) SP3 (da k
b own).
3.4. SEM Analysis o Comme cial Pigmen s
Comme cial pigmen s show exhibi a conside able he e ogenei y o he pa icles, as
shown by SEM analysis (Figu e 4). The pa icles o hese pigmen s ha e an i egula shape
(see Figu es 4B and 4C-1, wi h scale 20 µm). Image wi h scale 200 µm (Figu e 4C-2) also
do no show he p esence o sphe ical g ains. Based on SEM analysis, i can be s a ed ha ,
in e ms o pa icle shape (a ec ing pigmen dispe sibili y), comme cial pigmen s SP1
(Figu e 4A) SP2 (Figu e 4B), and SP3 (Figu e 4C-1 and 4C-2) a e no ideal powde sys ems.
Figu e 3.
G ain size dis ibu ion o pigmen : (1) SP1 ( ed); (2) SP2 (ligh b own); (3) SP3 (da k b own).
Mine als 2021, 11, 313 8 o 16
Figu e 4. SEM images o comme cial pigmen s (A) ed pigmen SP1 wi h scale 20 µm; (B) ligh b own pigmen SP2 wi h
scale 20µm; (C-1) da k b ow pigmen SP3 wi h scale 20 µm and (C-2) da k b own pigmen SP3 wi h scale 200 µm..
3.5. The T ea men o Was e Fe Sludge.
The was e Fe sludge (Figu e 5, labeled as WFS/0) was deli e ed in piece o m con-
aining o e 23% o mois u e. The aim was no only o achie e as much i on con en in he
mix u e as possible bu also o elimina e chlo ine con en . Th ee me hods we e designed
o his p ocess, wi h he esul ing colo e ec o indi idual pigmen s (see Figu e 5):
1. WFS/0—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS,
2. WFS/180—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS and calcined a
180 °C a he mode o 15 °C/min o 10 h/180 °C, and
3. WFS/900—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS and calcined a
900 °C a he mode o 15 °C/min o 3 h/900 °C.
Figu e 5. Fo m and colo o he un ea ed was e Fe sludge (WFS), was e Fe sludge washed in wa e (WFS/0), was e Fe
sludge calcined a 180 °C (WFS/180), and was e Fe sludge calcined a 900 °C (WFS/900).
Figu e 5 show un ea ed (labeled as WFS) and ea ed pigmen s (labeled as WFS/0,
WFS/180, and WFS/900). Washing he was e wi h wa e emo es soluble impu i ies.
Washing and calcina ion lead o a pa ial educ ion o he Zn and Cl amoun con ained in
he sludge. A e calcina ion, he amoun o H
2
O dec eased. WFS/180 and WFS/900 con-
ained 2.2 w .% and 0.2 w .% o H
2
O, espec i ely. Densi y o WFS/0, WFS/180, and
WFS/900 was 3.85 g/cm
3
, 4.95 g/cm
3
, and 4.46 g/cm
3
, espec i ely. Du ing calcina ion o
WFS/180, i on oxyhyd oxides dehyd a ed o Fe
2
O
3
. This sludge mus be well washed o
emo e mos o he ZnCl
2
con ained in he sludge.
As men ioned be o e, he highe he calcina ion empe a u e, he mo e signi ican
dehyd a ion occu ed. By calcina ion a 900 °C, he washed sludge was s abilized. The
p epa ed pigmen s WFS/180 and WFS/900 a e e y ine powde s. This is p o en by hei
speci ic su ace a ea (SSA) and be e abso p ion o loose mois u e compa ed o he WFS/0
sample, which was sligh ly coa se . Cl
−
bound in he s uc u e and α-FeOOH we e e-
leased du ing hea ea men s as HCl. A he same ime, he amoun o Zn is educed by
up o 97%. Du ing calcina ion o he WFS/900 sample, he Cl
−
in he mix u e was signi i-
can ly elimina ed (by almos 99%). While he o iginal was e Fe sludge WFS/0 con ained
~41 w .% o Fe
2
O
3
, usable was e sludge con aining up o 90 w .% o α-Fe
2
O
3
was ob ained
by he calcina ion.
Figu e 4.
SEM images o comme cial pigmen s (
A
) ed pigmen SP1 wi h scale 20
µ
m; (
B
) ligh b own pigmen SP2 wi h
scale 20µm; (C-1) da k b ow pigmen SP3 wi h scale 20 µm and (C-2) da k b own pigmen SP3 wi h scale 200 µm.
3.5. The T ea men o Was e Fe Sludge
The was e Fe sludge (Figu e 5, labeled as WFS/0) was deli e ed in piece o m con-
aining o e 23% o mois u e. The aim was no only o achie e as much i on con en in he
mix u e as possible bu also o elimina e chlo ine con en . Th ee me hods we e designed
o his p ocess, wi h he esul ing colo e ec o indi idual pigmen s (see Figu e 5):
1. WFS/0—Was e Fe sludge washed by H2Oby1LH2O/300 g o WFS,
2.
WFS/180—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS and calcined
a 180 ◦C a he mode o 15 ◦C/min o 10 h/180 ◦C, and
Mine als 2021,11, 313 8 o 16
3.
WFS/900—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS and calcined
a 900 ◦C a he mode o 15 ◦C/min o 3 h/900 ◦C.
Mine als 2021, 11, 313 8 o 16
Figu e 4. SEM images o comme cial pigmen s (A) ed pigmen SP1 wi h scale 20 µm; (B) ligh b own pigmen SP2 wi h
scale 20µm; (C-1) da k b ow pigmen SP3 wi h scale 20 µm and (C-2) da k b own pigmen SP3 wi h scale 200 µm..
3.5. The T ea men o Was e Fe Sludge.
The was e Fe sludge (Figu e 5, labeled as WFS/0) was deli e ed in piece o m con-
aining o e 23% o mois u e. The aim was no only o achie e as much i on con en in he
mix u e as possible bu also o elimina e chlo ine con en . Th ee me hods we e designed
o his p ocess, wi h he esul ing colo e ec o indi idual pigmen s (see Figu e 5):
1. WFS/0—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS,
2. WFS/180—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS and calcined a
180 °C a he mode o 15 °C/min o 10 h/180 °C, and
3. WFS/900—Was e Fe sludge washed by H
2
O by 1 L H
2
O/300 g o WFS and calcined a
900 °C a he mode o 15 °C/min o 3 h/900 °C.
Figu e 5. Fo m and colo o he un ea ed was e Fe sludge (WFS), was e Fe sludge washed in wa e (WFS/0), was e Fe
sludge calcined a 180 °C (WFS/180), and was e Fe sludge calcined a 900 °C (WFS/900).
Figu e 5 show un ea ed (labeled as WFS) and ea ed pigmen s (labeled as WFS/0,
WFS/180, and WFS/900). Washing he was e wi h wa e emo es soluble impu i ies.
Washing and calcina ion lead o a pa ial educ ion o he Zn and Cl amoun con ained in
he sludge. A e calcina ion, he amoun o H
2
O dec eased. WFS/180 and WFS/900 con-
ained 2.2 w .% and 0.2 w .% o H
2
O, espec i ely. Densi y o WFS/0, WFS/180, and
WFS/900 was 3.85 g/cm
3
, 4.95 g/cm
3
, and 4.46 g/cm
3
, espec i ely. Du ing calcina ion o
WFS/180, i on oxyhyd oxides dehyd a ed o Fe
2
O
3
. This sludge mus be well washed o
emo e mos o he ZnCl
2
con ained in he sludge.
As men ioned be o e, he highe he calcina ion empe a u e, he mo e signi ican
dehyd a ion occu ed. By calcina ion a 900 °C, he washed sludge was s abilized. The
p epa ed pigmen s WFS/180 and WFS/900 a e e y ine powde s. This is p o en by hei
speci ic su ace a ea (SSA) and be e abso p ion o loose mois u e compa ed o he WFS/0
sample, which was sligh ly coa se . Cl
−
bound in he s uc u e and α-FeOOH we e e-
leased du ing hea ea men s as HCl. A he same ime, he amoun o Zn is educed by
up o 97%. Du ing calcina ion o he WFS/900 sample, he Cl
−
in he mix u e was signi i-
can ly elimina ed (by almos 99%). While he o iginal was e Fe sludge WFS/0 con ained
~41 w .% o Fe
2
O
3
, usable was e sludge con aining up o 90 w .% o α-Fe
2
O
3
was ob ained
by he calcina ion.
Figu e 5.
Fo m and colo o he un ea ed was e Fe sludge (WFS), was e Fe sludge washed in wa e
(WFS/0), was e Fe sludge calcined a 180
◦
C (WFS/180), and was e Fe sludge calcined a 900
◦
C
(WFS/900).
Figu e 5show un ea ed (labeled as WFS) and ea ed pigmen s (labeled as WFS/0,
WFS/180, and WFS/900). Washing he was e wi h wa e emo es soluble impu i ies.
Washing and calcina ion lead o a pa ial educ ion o he Zn and Cl amoun con ained in he
sludge. A e calcina ion, he amoun o H
2
O dec eased. WFS/180 and WFS/900 con ained
2.2 w .% and 0.2 w .% o H
2
O, espec i ely. Densi y o WFS/0, WFS/180, and WFS/900
was 3.85 g/cm
3
, 4.95 g/cm
3
, and 4.46 g/cm
3
, espec i ely. Du ing calcina ion o WFS/180,
i on oxyhyd oxides dehyd a ed o Fe
2
O
3
. This sludge mus be well washed o emo e
mos o he ZnCl2con ained in he sludge.
As men ioned be o e, he highe he calcina ion empe a u e, he mo e signi ican
dehyd a ion occu ed. By calcina ion a 900
◦
C, he washed sludge was s abilized. The p e-
pa ed pigmen s WFS/180 and WFS/900 a e e y ine powde s. This is p o en by hei
speci ic su ace a ea (SSA) and be e abso p ion o loose mois u e compa ed o he WFS/0
sample, which was sligh ly coa se . Cl
−
bound in he s uc u e and
α
-FeOOH we e e-
leased du ing hea ea men s as HCl. A he same ime, he amoun o Zn is educed by
up o 97%. Du ing calcina ion o he WFS/900 sample, he Cl−in he mix u e was signi i-
can ly elimina ed (by almos 99%). While he o iginal was e Fe sludge WFS/0 con ained
~41 w .%
o Fe
2
O
3
, usable was e sludge con aining up o 90 w .% o
α
-Fe
2
O
3
was ob ained
by he calcina ion.
3.6. G anulome y o Was e Fe Sludge
Ino ganic pigmen s a e la gely p esen in he powde o m. The ideal powde ma e ial
con ains only pa icles o he same size; howe e , he ac ual sys em consis s o pa icles o
di e en sizes. Pa icle size dis ibu ion is a e y impo an c i e ion o powde pigmen s,
as he g ain size has a undamen al e ec on he op ical p ope ies o pigmen s. I is
associa ed wi h he sca e ing o ligh on he pa icles, so i highly a ec s he esul ing
opaci y and colo . The sample was measu ed in an aqueous medium, and wi h ega d o he
p esence o clumps in he in es iga ed pigmen s, ul asound was used o be e dispe sion.
The esul s a e p esen ed by dis ibu ion cu es in Figu e 6. Cu es 2 and 3 ha e
a iable g ain size. Pigmen WFS/0 has g ain sizes D
(10)
= 6.14
µ
m, D
(50)
= 13.8
µ
m,
and D
(90)
= 30.3
µ
m. The pa ame e s o WFS/180 a e D
(10)
= 0.898
µ
m,
D (50) = 2.61 µm
,
and D
(90)
= 7.7
µ
m, while he pa ame e s o he dis ibu ion cu e o pigmen WFS/900
a e D
(10)
= 1.98
µ
m, D
(50)
= 44.4
µ
m, and D
(90)
= 1950
µ
m. The pa icles can be di ided
in o coa se—o e 10
µ
m; la ge—10 o 3
µ
m; medium—3 o 1
µ
m; ine—1 o
0.3 µm
;
and e y ine—below 0.3 µm.
3.7. SEM Analysis o Was e Fe Sludge
The pa icle size was changed by calcina ion. The mos common mo phology o
hema i e pa icles ob ained by pep iza ion me hod and calcined a 500
◦
C was unca ed
hombohed ons, cubes, and oc ahed ons [29].
Mine als 2021,11, 313 9 o 16
Mine als 2021, 11, 313 9 o 16
3.6. G anulome y o Was e Fe Sludge
Ino ganic pigmen s a e la gely p esen in he powde o m. The ideal powde ma e-
ial con ains only pa icles o he same size; howe e , he ac ual sys em consis s o pa i-
cles o di e en sizes. Pa icle size dis ibu ion is a e y impo an c i e ion o powde
pigmen s, as he g ain size has a undamen al e ec on he op ical p ope ies o pigmen s.
I is associa ed wi h he sca e ing o ligh on he pa icles, so i highly a ec s he esul ing
opaci y and colo . The sample was measu ed in an aqueous medium, and wi h ega d o
he p esence o clumps in he in es iga ed pigmen s, ul asound was used o be e dis-
pe sion.
The esul s a e p esen ed by dis ibu ion cu es in Figu e 6. Cu es 2 and 3 ha e
a iable g ain size. Pigmen WFS/0 has g ain sizes D (10) = 6.14 µm, D (50) = 13.8 µm, and
D (90) = 30.3 µm. The pa ame e s o WFS/180 a e D (10) = 0.898 µm, D (50) = 2.61 µm, and
D (90) = 7.7 µm, while he pa ame e s o he dis ibu ion cu e o pigmen WFS/900 a e
D (10) = 1.98 µm, D (50) = 44.4 µm, and D (90) = 1950 µm. The pa icles can be di ided in o
coa se—o e 10 µm; la ge—10 o 3 µm; medium—3 o 1 µm; ine—1 o 0.3 µm; and e y
ine—below 0.3 µm.
Figu e 6. G ain size dis ibu ion o pigmen was e Fe sludge: 1) o iginal (WFS/0); 2) calcined a 180
°C (WFS/180); 3) calcined a 900 °C (WFS/900).
3.7. SEM Analysis o Was e Fe Sludge
The pa icle size was changed by calcina ion. The mos common mo phology o hem-
a i e pa icles ob ained by pep iza ion me hod and calcined a 500 °C was unca ed hom-
bohed ons, cubes, and oc ahed ons [29].
Fo ino ganic pigmen s, i is sui able ha pa icle sizes ange om 0.1 o 10 µm [30],
so he pigmen s ha e good co e ing and abso p ion quali ies. Figu e 7 shows WFS/0 sam-
ple mo phology as de e mined by SEM by all samples and EDAX by (Figu e 7A-1). SEM
images show a no qui e egula ound pa icle sys em (Figu e 7C-2). Mo eo e , pa icles
la ge han 1000 µm a e also included in his sample, as de e mined by g anulome y
(Figu e 6). Figu e 7A-1 shows mo e clea ly ha he e a e ound pa icles o di e en sizes,
o med by clus e s o smalle ound pa icles o app oxima ely 20 µm. Thus, i he pa i-
cles a e clus e ed in o e en smalle objec s, he g anulome ic cu es may be so a iable
on his basis.
Figu e 6.
G ain size dis ibu ion o pigmen was e Fe sludge: (1) o iginal (WFS/0); (2) calcined a
180 ◦C (WFS/180); (3) calcined a 900 ◦C (WFS/900).
Fo ino ganic pigmen s, i is sui able ha pa icle sizes ange om 0.1 o 10
µ
m [
30
],
so he pigmen s ha e good co e ing and abso p ion quali ies. Figu e 7shows WFS/0
sample mo phology as de e mined by SEM by all samples and EDAX by (Figu e 7A-1).
SEM images show a no qui e egula ound pa icle sys em (Figu e 7C-2). Mo eo e , pa i-
cles la ge han 1000
µ
m a e also included in his sample, as de e mined by g anulome y
(Figu e 6). Figu e 7A-1 shows mo e clea ly ha he e a e ound pa icles o di e en sizes,
o med by clus e s o smalle ound pa icles o app oxima ely 20
µ
m. Thus, i he pa icles
a e clus e ed in o e en smalle objec s, he g anulome ic cu es may be so a iable on
his basis.
The chlo ine p esen in he WFS/0 (see Figu e 7A-2) comes om he ZnCl
2
pu i ica ion
p ocess. The minimum amoun o Al p obably comes om a e y di e en compound con-
ained in he sludge p ecipi a e (Figu e 7A-2). The highes densi y, 4.95 g/cm
3
, was ound
o he WFS/180 sample, while he o iginal un ea ed WFS/0 sample had he lowes den-
si y o all. The mal calcina ion led o an inc ease in densi y by 28%. Wi h an inc ease o he
empe a u e, he SSA changes om 6.89 m
2
/g ( o WFS/0) o 23.6 m
2
/g (WFS/180) and
14.86 m
2
/g (WFS/900). The SSA o comme cial samples was de e mined o be 23.67 m
2
/g.
The SSA alue o all i on oxides p epa ed in his s udy is compa able o he comme cial
pigmen s used in his expe imen .
3.8. Phase Analysis o Was e Fe Sludge
Resul s o he XRPD phase analysis a e shown in Figu e 8. The pa e n o he sample
WFS/0 (see Figu e 8a) does no show any e lec ions. This sample con ains Fe
2
O
3
in
amo phous o m. Wide e lec ions o hema i e phase we e ound in he case o sample
WFS/180; dominan e lec ion is in he posi ion 38
◦
2
θ
(PDF-2 ca d no. 00-033-064-64).
F om he poin o iew o he XRPD measu emen , he sample WFS/180 (see Figu e 8b)
is compa able wi h he sample SP1. XRPD pa e n o he sample WFS/900 (see
Figu e 8c
)
con ains c ys alline phase o he
α
-Fe
2
O
3
(hema i e) (PDF-2 ca d no.01-076-45-79) wi h
he mos in ensi e e lec ion in he posi ion 39
◦
2
θ
. Wi h inc easing empe a u e o cal-
cina ion, he e lec ions a e na owe . In some cases, he goe hi e
α
-FeOOH ans o ms
in o c ys alline phase o hema i e, p esen as na owly shaped peaks [
31
]. Bu he goe hi e
phase was no ound in es ed pigmen s (Figu e 8). When mixing he pigmen s wi h he
anspa en glaze, ce ain phase changes occu ed. The
α
-Fe
2
O
3
o m is s able up o
800 ◦C
,
as decla ed by he manu ac u e . When i ed a 1060
◦
C, he magne i e o m changes o
hema i e, which is s able up o 1000 ◦C [24].
3.9. TG and DTA o Was e Fe Sludge
TG a DTA cu es o WFS/0 sample a e shown in Figu e 9. Signi ican endo he mic
eac ions a e p esen on he empe a u e a 110
◦
C, and 562
◦
C can be connec ed wi h
mois u e decomposi ion. Hema i e o m unde a mosphe ic condi ions and o en he
end o oxida i e ans o ma ion o o he i on oxides. Then, wi h empe a u e ising,
goe hi e can ans o m o
α
-Fe
2
O
3
o he peak is a ibu ed o he oxida ion o FeO o Fe
3
O
4
Mine als 2021,11, 313 16 o 16
40.
Pekkan, K.; Ka asu, B. E alua ion o bo ax solid was es in p oduc ion o i s sui able o as single- i ed wall ile opaque
glass-ce amic glazes. Bull. Ma e . Sci. 2010,33, 135–144. [C ossRe ]
41.
Be na din, A.M. The in luence o pa icle size dis ibu ion on he su ace appea ance o glazed ile. Dyes Pigmen .
2009
,80,
121–124. [C ossRe ]