Wa e Resou ces and Indus y 30 (2023) 100219
A ailable online 22 July 2023
2212-3717/© 2023 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license
(h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
Regene a ion possibili ies and applica ion o magne ically
modi ied biocha o hea y me als elimina ion in eal condi ions
Michaela Toka ˇ
cíko ´
a
a
,
*
, Pa lína Peike o ´
a
a
, Ka la ˇ
Cech Ba abaszo ´
a
a
,
Ondˇ
ej ˇ
Zi o ský
b
, Roman Gabo
a
, Jana Seidle o ´
a
a
a
Nano echnology Cen e, Vˇ
SB-Technical Uni e si y o Os a a, 17. Lis opadu 15/2172, 708 00, Os a a, Po uba, Czech Republic
b
Depa men o Physics, Vˇ
SB-Technical Uni e si y o Os a a, 17. Lis opadu 15/2172, 708 00, Os a a, Po uba, Czech Republic
ARTICLE INFO
Keywo ds:
Biocha
Magne ic p ope ies
Magne ic composi e
So p ion
Reusabili y
Was ewa e
ABSTRACT
Al hough new ypes o composi es wi h magne ic p ope ies and high adso p ion capaci y o
po en ially oxic elemen s elimina ion a e s udied by esea che e s, he in o ma ion abou he
eusabili y, s abili y and emo al e iciency o composi es is s ill sca ce o absen . The e o e, he
aim o ou wo k was applica e he so ben o elimina e Zn(II), Cd(II) and Pb(II) ions om in-
dus ial was e leacha es, and mo eo e , s udy he composi e eusabili y and magne ic sepa a ion
e iciency. Magne ically modi ied biocha was p epa ed om he e men a ion esidue o maise
hyb id by a simple wo-s ep me hod wi h mic owa e assis ance. Composi e p ope ies, as well as
he adso p ion e iciency and magne ic esponse a e depend on he ex ac ion agen . The alkaline
ex ac ion agen showed he bes p ope ies o eusabili y and had no in luence on Fe eleasing
om he composi e, he adso p ion e iciency was highe han 90% e en in he 5
h
ecycling cycle,
and he composi e emained magne ically ac i e. The sepa a ion e iciency o composi e om an
aqueous en i onmen by a magne was highe han 95% wi hin 15 min. Magne ically modi ied
biocha p o ed o be an e ec i e so ben o me al ions elimina ion om was ewa e .
CRediT au ho ship con ibu ion s a emen
Michaela Toka ˇ
cíko ´
a: W i ing-o iginal d a ; W i ing- e iew & edi ing; Concep ualiza ion; Me hodology; In es iga ion. Pa lína
Peike o ´
a: W i ing- e iew & edi ing; Fo mal analysis; Valida ion; In es iga ion. Ka la ˇ
Cech Ba abaszo ´
a; Fo mal analysis; In es i-
ga ion. Ondˇ
ej ˇ
Zi o ský: Fo mal analysis; In es iga ion, Roman Gabo : Fo mal analysis; In es iga ion, Gab iela Mikesko ´
a Resou ces;
Funding acquisi ion. Jana Seidle o ´
a: Supe ision; Resou ces.
1. In oduc ion
Biocha is a p oduc o he py olysis o biomass unde low oxygen condi ions. Biocha p oduc ion educes he amoun o biomass
was e which would be land illed [1]. Biocha s ands ou o i s po osi y, high su ace a ea and he p esence o unc ional g oups such as
C=O, –OH, –COOH and phenolic g oups on he su ace, which enable binding wi h po en ially oxic elemen s (PTEs), making a biocha
p omising ma e ial wi h excellen adso p ion p ope ies [2]. The su ace modi ica ion o biocha using i on oxides leads o he key
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (M. Toka ˇ
cíko ´
a).
Con en s lis s a ailable a ScienceDi ec
Wa e Resou ces and Indus y
jou nal homepage: www.else ie .com/loca e/w i
h ps://doi.o g/10.1016/j.w i.2023.100219
Recei ed 12 Ap il 2023; Recei ed in e ised o m 4 July 2023; Accep ed 10 July 2023
Wa e Resou ces and Indus y 30 (2023) 100219
2
bene i – he composi e becomes e omagne ic and can be, a e he so p ion, easily emo ed – wi h adso bed PTEs – om an aqueous
en i onmen using a magne ic ield. Magne ic sepa a ion becomes a sui able, low-cos and sus ainable ma e ial o was ewa e
ea men o aqueous en i onmen s con aining a ious concen a ions o PTEs [3–6].
A key aspec o magne ically modi ied biocha use is he apid and e ec i e sepa a ion o he composi e con aining adso bed PTEs
om he aqueous solu ion by he magne ; he ime o he whole decon amina ion p ocess will be sho ened, he cos will be educed,
which is desi able in a p ac ical applica ion. Magne ically modi ied biocha can be p epa ed by a ious me hods [7]. The calcina ion
me hod uses hea ing in an au ocla e o he p oduc ion o magne ic biocha ; p ocesses equi e hea y mechanical sys ems, and an ine
a mosphe e [8] o elec omagne ic induc ion echnology [5], o magne ic biocha p oduc ion. On he con a y he co-p ecipi a ion
leads o high-pu i y p oduc by simple eac ion condi ions [9].
I is no only he p epa a ion and so p ion p ope ies o magne ically modi ied biocha a e essen ial. The magne ic p ope ies,
s abili y and egene a ion p ope ies om he sus ainabili y poin a e also impo an . The p ope ies o magne ically modi ied biocha
can be a ec ed by he pH o he en i onmen , ionic s eng h, o he p esence o addi ional elemen s; he e o e, i is necessa y o s udy
i s p ope ies and beha iou in a ious condi ions. The acid en i onmen can block he ac i e si es o he so ben , cause he elease o
i on oxides and change he so ben p ope ies o make he so ben un ecyclable [10].
Absolu e e hanol was used by Yi e al. [11] o he deso p ion o C , Ni and Fe in 3 adso p ion- egene a ion cycles. Remo al o C
and Ni e iciency dec eased o 71.9% a e he 3
d
cycle, while in he 1
s
cycle was eleased o Fe negligible, and in he 2
nd
and 3
d
cycles
was eleased Fe almos 20%. Howe e , de ails conce ning changes in he magne ic p ope ies o magne ic biocha a e missing. Fo he
deso p ion o Cd and Pb and egene a ion o magne ic adso ben , 0.1 M hyd ochlo ic acid and sodium hyd oxide solu ions we e used
[12]. The deso p ion e iciency a e he 5
h
adso p ion/deso p ion cycle eached mo e han 80% and he ollowing adso p ion was
highe han 50%, bu he de e mina ion o eleased Fe om magne ic biocha o s udy o changing o magne ic p ope ies du ing
egene a ion we e no p esen ed [12]. The ba h deso p ion s udy o Pb-loaded magne ic biocha was pe o med by 0.1 M HCl, ace ic
acid, EDTA-2-Na and deionised wa e [13]. HCl and EDTA-2-Na we e e icien solu ions o Pb deso p ion; howe e , mo e han 90% o
Fe was leached om he magne ic biocha . The ace ic acid solu ion eached 50% o Pb deso p ion, and less han 10% o Fe was leached
du ing he deso p ion expe imen . Al hough he so p ion capaci y o magne ic biocha emained 50% a e he 6
h
cycle, 1.1 mg/g o Fe
was eleased in each cycle. The in o ma ion abou magne ic p ope ies a e he ecycling expe imen is missing. EDTA-2-Na (0.1 M)
was used as an e ec i e ex ac ion agen o Pb(II) deso p ion om magne ically modi ied biocha [14]. Remo al and ollowing
adso p ion e iciency emained highe han 70% a e he 5
h
cycle; howe e , in o ma ion abou magne ic p ope ies a e he ecycling
expe imen was no s udied [14].
The e ha e been many s udies dealing wi h so p ion p ope ies and so ben e iciency a he labo a o y scale, howe e , e y li le is
known abou so p ion p ope ies in na u al condi ions (mos expe imen s we e pe o med on single o mul i PTEs in he wa e ) and he
eusabili y possibili ies o composi es. As was men ioned abo e, mos s udies a e ocused on he eusabili y o ma e ials by adso p ion/
deso p ion cycles. S ill, in o ma ion dealing wi h Fe elease o changes in s uc u e o magne ic p ope ies o magne ically modi ied
biocha du ing he eusabili y p ocedu e has no been in es iga ed in de ail.
In con as wi h s udies ocused on so p ion p ope ies o magne ically modi ied biocha om labo a o y-p epa ed solu ion and
ollowing ecycling, he p esen a icle is ocused on he na u al condi ions du ing he so p ion p ocess, changes o composi e p op-
e ies a e eusabili y es s in a ious ex ac ion agen s and he changes in he s abili y and unc ionali y o composi e.
In ou wo k we we e ocused on he eal condi ions du ing he adso p ion p ocess, changes o magne ic p ope ies a e eusabili y
es s in a ious ex ac ion agen s and he changes in he s abili y and unc ionali y o composi e. The aim o his wo k is he e o e
s udy: 1) he e ec o he en i onmen in which he composi e will be used on he s abili y and magne ic esponse o he p epa ed
composi e, 2) he applica ion o magne ically modi ied biocha o he emo al o hea y me als ca ions om an en i onmen close o
na u al condi ions, 3) he eusabili y o he p epa ed magne ically modi ied biocha and obse a ion o changes du ing egene a ion
p ocedu e, 4) e i ica ion o he magne ic esponse o he composi e a e eusabili y es s, 5) e iciency o emo ing he composi e
emo al om solu ion using he magne .
2. Ma e ials and me hods
2.1. Biocha and chemicals
The eco- iendly biocha (BCH) was p epa ed om he e men a ion esidue o maise hyb id g own up in he Czech Republic. The
e men a ion esidue was d ied a 80 ◦C o 2 h o emo e wa e and hea ed a 200–400 ◦C. The cha ac e is ic o BCH, including he
bio oxici y es s, was desc ibed in de ail in he s udy o Ma ouˇ
sek [15]. Be o e he p epa a ion o he composi e, he biocha was milled
in a FRITSCH mill o ob ain he pa icle size 90–200
μ
m.
Chemicals used in expe imen s we e analy ical g ade om MACH CHEMIK´
ALIE s. .o. (Os a a, Czech Republic) i no s a ed
o he wise. The p ecu so o he p epa a ion o he Fe
x
O
y
pa icles was FeSO
4
⋅7H
2
O. NaOH, HCl, ace ic acid (HAc) and e hyl-
enediamine e ace ic acid disodium (bo h: LACHEMA, B no, Czech Republic) we e used o p epa a ion o ex ac ion agen s.
2.2. P epa a ion o magne ically modi ied biocha
A wo-s ep me hod was used o he p epa a ion o magne ically modi ied biocha (MBCH). The i s s ep, a suspension con aining
Fe
x
O
y
pa icles was p ecipi a ed om he i on hyd oxide solu ion. SO
4
2−
ions we e decan ed ( e i ying using BaCl
2
solu ion) om he
suspension, and he suspension was dilu ed wi h deionised wa e and BCH. The p epa ed mix u e was sepa a ed by il a ion and d ied
M. Toka ˇ
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a e al.
Wa e Resou ces and Indus y 30 (2023) 100219
3
a labo a o y empe a u e he nex day. The MBCH p epa a ion may be summa ised as ollows:
Fe2++H2O→
NaOH Fe(OH)2−x
x
Fe3++H2O→
NaOH Fe(OH)3−y
y→
mic owa e FexOy+BCH→
il a ion MBCH (1)
The calcula ion o he p ice o 1 kg o p epa ed MBCH is due o he a iabili y o ene gy and chemicals p ice di icul . The
manu ac u ing cos o p epa a ion o biocha by py olysis can be es ima ed as 273.30 Eu o pe on [16], which can be op imised by
was e hea , which b ings signi ican sa ings [15]. The cos o biocha magne isa ion was calcula ed o be 17.12 Eu o pe 1 kg.
2.3. Cha ac e isa ion o biocha and magne ically modi ied biocha
The chemical composi ion o BCH and MBCH was de e mined using he SPECTRO XEPOS ene gy dispe si e X- ay luo escence
spec ome e (EDXRF) (SPECTRO A. I., Ge many). The BCH and MBCH we e decomposed in he mix u es o acids o de e mine he
o al con en o Fe using a lame a omic abso p ion spec ome e (AAS-FL) (UNICAM 969, AA Spec ome e ). FeO in solid samples was
de e mined acco ding he alida ion p ocedu e [17].
The ib a ing-sample magne ome e (VSM) Mic osense EZ9 was used o measu e (a oom empe a u e) he magne isa ion cu es
o na i e BCH and MBCH bo h be o e and a e egene a ion expe imen s. “Maximal applied magne ic ield was se o ±1600 kA/m
(±2 T). Basic magne ic pa ame e s we e de e mined om he measu ed cu es” [6].
The pa icle size alues (PS) and pa icle size dis ibu ion (PSD) we e de e mined by he “HORIBA Lase di ac ion pa icle size
analyse (LA-950 ins umen ) wi h a wo 405 nm sho -wa eleng h blue and 650 nm ed-ligh lase sou ce in conjunc ion wi h o wa d
and backsca e de ec ion” [6]. Pa icle size analyses we e pe o med wi h e ac i e indices o 2.90 ( o expe imen al samples) and
1.33 ( o wa e ).
The conduc i i y was de e mined by a nanopa icle analyse (“HORIBA Nanopa ica SZ-100, Kyo o, Japan”). 0.05 g o BCH and
MBCH was mechanically mixed wi h 15 mL o dis illed wa e . 0.1 mL o he suspension was placed in o he disposable Ze a po en ial
cell. Each measu emen was epea ed h ee imes a 23 ◦C.
The images o BCH and MBCH we e ob ained using he “JEOL JSM-7610F Plus (JEOL L d., Japan) wi h EDS mic oanalyse Az ec
Line S anda d Mic oanalysis sys em wi h Ul im Max 65 Analy ical Silicon D i De ec o (SDD) (Ox o d Ins umen s, High Wycombe,
UK)” [6]. Sample image de ails we e ob ained by a seconda y elec on de ec o in he b igh ield mode.
“FT-IR spec a in he mid-in a ed ange (400–4000 cm
−1
) we e eco ded on he Nicole iS50 FT-IR de ice (The mo Fishe Sci-
en i ic, USA). ATR echnique wi h diamond c ys al and 64 scans we e used. Spec a we e analysed in he OMNIC (OMNIC 8) and O igin
(O iginP o 9.1) so wa e” [6].
2.4. Ba ch adso p ion expe imen s
So p ion expe imen s we e done using 0.1 ±0.01 g o BCH and MBCH and 50 mL o me allu gical was e leacha e in a plas ic lask.
The mix u es we e blended in a o a ion con aine a a cons an speed (45 pm) a labo a o y empe a u e in 0.25–48 h in e als,
sepa a ed (0.23
μ
m po e il e , P agopo 8, PRAGOCHEMA spol. s. .o.) and pH o inal ex ac s we e de e mined (G y 158). The
concen a ions o Zn(II), Cd(II), Pb(II) and Fe(II) ions we e de e mined by AAS-FL.
Fo a kine ic expe imen , con e o dus o igina ing om an elec o il e o cas i on p oduc ion (Slezský K´
amen, Czech Republic)
was shaken wi h a solid- o-liquid a io o 1:100 in he o a ion con aine a labo a o y empe a u e o 24 h. The solid phase was
sepa a ed, he pH and concen a ions o Zn(II), Cd(II), Pb(II) ions we e de e mined in he ex ac s by AAS-FL.
Va ious solid- o-liquid a ios o con e o dus leacha e we e used o he adso p ion iso he ms s udy. Adso p ion s udies we e done
in a solid- o-liquid a io o 0.1 g o MBCH o 50 mL o con e o dus leacha e, shaken a labo a o y empe a u e, and, be o e analysis,
sepa a ed by il a ion.
2.5. Regene abili y o MBCH
To e alua e MBCH eusabili y, 0.1 g o sample and 50 mL o liquid we e used in each s ep. Based on ou p e ious expe imen s, he
con e o dus leacha e (0.25 g/100 mL) was used o he adso p ion s udy. 50 mL o ou a ious ex ac ion agen s we e used in he
deso p ion s ep: 0.1 M HCl deno ed as EAI, 0.1 M ace ic acid (HAc) deno ed as EAII, 0.1 M EDTA-2-Na deno ed as EAIII, 0.5 M NaOH
deno ed as EAIV and deionised wa e a 298.15 K o 24 h. A e he adso p ion es , he MBCH was washed wi h deionised wa e o
neu al pH, d ied a labo a o y empe a u e, weighed, and used o e i ying adso p ion p ope ies. The adso bed/deso bed expe i-
men s we e pe o med wice, and he concen a ions o Zn(II), Cd(II), Pb(II) and Fe(II) we e de e mined in inal ex ac s by AAS-FL.
The Zn(II), Cd(II) and Pb(II) emo al e iciency Re (%) and he equilib ium me al up ake capaci y we e calcula ed acco ding o
Equa ions (2) and (3):
qe=V(c0−ce)
m(2)
Re =V(c0−ce)
m•100 (3)
M. Toka ˇ
cíko ´
a e al.
Wa e Resou ces and Indus y 30 (2023) 100219
4
The adso p ion capaci y a ime :
q =V(c0−c )
m(4)
whe e q
e
(mg/g) and m (g) deno e he adso p ion capaci y and he mass o BCH and MBCH, espec i ely. c
0,
c
,
c
e
(mg/L) a e he
concen a ions o he Zn(II), Cd(II) and Pb(II) in he ini ial solu ion, a ime and a he equilib ium a e he adso p ion expe imen s. V
(L) e e s o solu ion olume in he adso p ion expe imen s.
Adso p ion o Zn(II), Cd(II) and Pb(II) om con e o dus leacha es was in es iga ed by F eundlich [18] and Langmui [19]
iso he ms in non-linea o m.
2.6. Remo al a e o magne ically modi ied biocha
The emo al a e o MBCH and MBCH om solu ion by he neodymium magne (5 ×1 ×1 cm, s eng h ~15 kg), a e eusabili y
expe imen s in ex ac ion agen s (EAI-EAII), was s udied using u bidime e 2100 N TURBIDIMETER (HACH LANGE s. .o., Czech
Republic). The u bidi y o solu ions was measu ed be o e and a e he magne ic sepa a ion o MBCH. The yield o MBCH magne ic
sepa a ion was de e mined as well.
3. Resul s and discussion
3.1. Biocha cha ac e isa ion
To al Fe con en inc eased om 3.99 w % in BCH (4.82 w % FeO and 0.35 w % Fe
2
O
3
) o 7.35 w % in MBCH (7.15 w % FeO and
2.57 w % o Fe
2
O
3
). The speci ic su ace a ea o 13.79 m
2
/g o MBCH did no inc ease signi ican ly compa ed wi h 13.22 m
2
/g o BCH.
The chemical composi ion o BCH and MBCH exp essed in oxides is lis ed in Table 1.
3.2. Adso p ion expe imen s
3.2.1. Adso p ion kine ic
De e mining adso ben /adso ba e con ac ime enables he adso p ion kine ic and adso ben applica ion desc ip ion. Con ac ime
consequence o emo al o Zn(II), Cd(II) and Pb(II) om con e o dus leacha e by BCH and MBCH is p esen in (Fig. 1a and b). The
adso p ion a e was as a he beginning o he adso p ion, and he equilib ium o Zn(II), Cd(II) and Pb(II) was achie ed o MBCH
as e han o BCH (Fig. 1c and d). The equilib ium o adso p ion on o MBCH was achie ed du ing 6 h (Cd(II) and Pb(II)) and 24 h (Zn
(II)).
Pb(II) shows he highe emo ed pe cen age (>95%) han Zn(II) (20%) and Cd(II) (13%) by MBCH om he leacha e. The highes
pe cen age o ca ion adso p ion on o MBCH is in he o de o Pb(II) >Zn(II) >Cd(II), which co esponds wi h he esul s o Pa k e al.
[20]. A easonable explana ion may be ha i is due o hyd a ed adii o adso bed ions: Cd
2+
(4.26 Å) ≈Zn
2+
(4.30 Å) >Pb
2+
(4.01 Å)
and hus, g ea e Pb(II) a ini y o mos unc ional g oups in o ganic ma e . Mo eo e , lead has a highe elec onega i i y han
cadmium and zinc; Pb (2.33) >Cd (1.69) ~ Zn (1.65). Based on p e ious p esump ions, Pb(II) is mo e a ou ably adso bed han Cd(II)
and Zn(II), which is in good co espondence wi h he esul s o Inyang e al. [21].
Al hough Pb(II) shows he highes pe cen age o emo al om leacha e, he highes adso bed amoun was de e mined o Zn(II),
he main eason is he a ious ini ial concen a ion o ca ions and, he e o e, he highe concen a ion g adien o Zn(II) (see Table 2.).
The kine ic pa ame e s de i ed om (Fig. 1e and ) a e p esen ed in Table 2. The co ela ion coe icien s (R
2
) esul ing om he
pseudo-second-o de (PSO) kine ic model o BCH and MBCH a e highe han he co ela ion coe icien s (R
2
) esul ing om he
pseudo- i s -o de (PFO) kine ic model. The PSO kine ic model is a con enien exp ession o he desc ip ion o Zn(II), Pb(II)
adso p ion on o BCH and Zn(II), Cd(II) and Pb(II) adso p ion on o MBCH om con e e dus leacha e.
The cu es o he in apa icle di usion (IPD) model a e p esen ed in (Fig. 1g and h). The plo s o Cd(II) and Pb(II) did no pass
h ough he o igin. The adso p ion o Cd(II) s a s a e 24 h o con ac ime wi h BCH; he e o e, he slope o he 1
s
s age o Cd(II)
adso p ion on o BCH indica ed a slow adso p ion p ocess [22]. The i s slope o he linea pa – Cd(II) adso p ion on o MBCH and Pb
(II) adso p ion on o BCH and MBCH – indica ed he as adso p ion a e, which possibly will be caused due o he exis ence o many
adso p ion si es on he BCH and MBCH su aces. The slope o he linea pa indica es he adso p ion a e. The bounda y laye
in luenced adso p ion o Pb(II) on o BCH and MBCH sligh ly mo e han Cd(II), while he in e cep alue desc ibed adso p ion o Cd(II)
on o MBCH p edic ha ilm di usion was he a e-con olling mechanism du ing he i s 60 min o adso p ion [23]. The second s age
was p obably in luenced by he di usion o Pb(II) in o BCH and MBCH mesopo es. The second pa was slowe han he i s due o he
Table 1
Chemical composi ion o biocha exp essed in oxide (in w . %); LOI – los on igni ion.
Oxides Na
2
O MgO Al
2
O
3
SiO
2
P
2
O
5
K
2
O CaO TiO
2
MnO Fe
2
O
3
LOI
BCH 0.88 2.66 0.35 6.20 2.69 4.85 3.19 0.014 0.04 0.35 77.78
MBCH 0.36 2.89 0.04 6.80 3.45 2.58 3.38 0.014 0.06 2.57 71.33
M. Toka ˇ
cíko ´
a e al.
Wa e Resou ces and Indus y 30 (2023) 100219
5
Fig. 1. Adso p ion kine ics o Zn(II), Cd(II) and Pb(II) ions on he BCH and MBCH. Remo al e iciency by a) BCH and b) MBCH, he e ec o con ac
ime c) BCH and d) MBCH, PSO kine ic model e) BCH and ) MBCH, in apa icle di usion model g) BCH and h) MBCH.
Table 2
The pseudo- i s -o de and pseudo-second-o de kine ic pa ame e s o he adso p ion o Zn(II), Cd(II) and Pb(II) om con e o dus leacha e; pH =
4.95, solid- o-liquid a io 0.1 g/50 mL, c
0
(Zn) =553 mg/L, c
0
(Cd) =10.9 mg/L, c
0
(Pb) =1.72 mg/L.
Ion PFO PSO In apa icle di usion
q
e
(mg/g) k
1
(1/min) R
2
q
e
(mg/g) k
2
(g/(mg⋅min)) R
2
k
ID
(mg/g⋅min
1/2)
C R
2
BCH Zn(II) 20.23 4.61⋅10
−4
0.0148 26.82 0.227⋅10
−3
0.9954 – – –
Cd(II) – – – – – – 0.001 −0.007 0.8288
Pb(II) 7.06 1.38⋅10
−4
0.3931 0.849 70.1⋅10
−3
0.9985 0.043 0.4408 0.9866
MBCH Zn(II) 3.123 0.92⋅10
−4
0.0148 55.74 29.8⋅10
−3
0.8859 – – –
Cd(II) 2.105 4.61⋅10
−4
0.4937 0.705 5.95⋅10
−3
0.7891 0.105 −0.32 0.9942
Pb(II) 9.681 0.014⋅10
−4
0.3931 0.839 0.379 0.9999 0.012 0.7531 0.9496
M. Toka ˇ
cíko ´
a e al.

Wa e Resou ces and Indus y 30 (2023) 100219
6
dec easing concen a ion o ions in he solu ion and he low mass ans e a e. The hi d s age was he a ea o equilib ium. The
limi ing s ep o Pb(II) and Cd(II) adso p ion om con e e dus leacha e was pe haps he di usion in o BCH and MBCH mesopo es
[24].
3.2.2. Adso p ion iso he ms
The in luence o ini ial hea y me al ions concen a ion on he adso p ion p ope ies o BCH and MBCH was s udied using con e e
dus leacha es. The leacha es we e p epa ed using di e en solid- o-liquid a ios; he concen a ions o Zn(II), Cd(II) and Pb(II) a e
p esen ed in Table 3. The adso p ion capaci y o MBCH inc eased wi h inc easing o ini ial hea y me als concen a ion, especially Zn
(II) (Fig. 2). The same esul s we e achie ed in he esea ch o Yu e al. [25], which may be esul o a g ea inhibi o y e ec .
The Langmui iso he m model desc ibes he adso p ion o Zn(II) and Cd(II) ca ions on BCH be e han he F eundlich adso p ion
iso he m model. These esul s sugges ed he monolaye adso p ion o Zn(II) and Cd(II) on BCH and he physical in e ac ion be ween
he Zn(II) and BCH (due o he low b alue =0.387) [26]. The sepa a ion ac o R
L
(which is no Langmui cons an ) was calcula ed o
examine he p og ession o he adso p ion cons an by ollowing equa ion [27]:
RL=1
1+bC0
(5)
whe e b and C
0
we e de i ed om he Langmui iso he m. R
L
alues we e ound o be 0 ≤R
L
≤1, which p edic ed he a ou able
adso p ion o Zn(II), Cd(II) and Pb(II) on o BCH.
Expe imen al da a o Zn(II) and Pb(II) adso p ion on MBCH co ela ed well wi h he F eundlich adso p ion model, assuming he
exis ence o so p ion si es wi h a ious ene gies enabling mul ilaye and he e ogeneous so p ion [28], which may be ela ed o he
p esence o Fe
x
O
y
pa icles. The F eundlich iso he m cons an 1/n was lowe han 1; he e o e, he adso p ion o Zn(II) and Pb(II) on
he MBCH we e a ou able.
The expe imen al q
e
alues and he q
m
alues showed signi ican ly highe adso p ion capaci y o Zn(II), Cd(II) and Pb(II) on MBCH
han BCH. Based on he expe imen al da a, i can be concluded ha he p esence o Fe
x
O
y
on he MBCH su ace caused he c ea ion o
mo e ac i e si es; he e o e, he adso p ion capaci y inc eased.
The p ocess o M
2+
adso p ion, which subs i u es Zn(II), Cd(II) and Pb(II) ca ions, can be complexed and ixed wi h Fe
3
O
4
(6),
≡FeOH p esence on he MBCH su ace can in e ac wi h M
2+
o o m complexes (7) [29], Fe-R-OH and Fe-R-COOH g oups on o MBCH
su ace enable ion exchange o complexa ion wi h hea y me als ca ions (Fo mulas 8 and 9) [30]. Gene ally, he emo al o hea y
me als ca ion by MBCH by adso p ion, p ecipi a ion o educ ion can be summa ised by he ollowing Fo mulas (10–14) [31–33].
Fe
3
O
4
+M
2+
→ M
2+
-Fe
3
O
4
(6)
M
2+
+2(≡FeOH) → ≡(FeO)
2
M +2H
+
(7)
2Fe-R-COOH +M
2+
→ 2Fe-R-COOM +2H
+
(8)
2Fe-R-OH +M
2+
→ (Fe-R-O)
2
M +2H
+
(9)
Fe
2+
+H
2
O → FeOH
+
+H
+
(10)
FeOH
+
+M
2+
→ MOH
+
+Fe
2+
(11)
MOH
+
+H
2
O → M(OH)
2
+H
+
(12)
≡FeOH +M
2+
+H
2
O → ≡FeOMOH +H
+
(13)
2Fe
0
+3M
2+
+4H
2
O → 3M
0
+2FeOOH +2H
+
(14)
Func ion g oups such as ca boxylic, amino, and hyd oxyl g oups all play impo an oles in Zn(II), Cd(II) and Pb(II) so p ion. Due o
he simila i y o di alen me al ca ions in aqueous solu ion, he so p ion mechanisms, i.e., ca ion exchange, su ace complexa ion,
p ecipi a ion, and elec os a ic in e ac ions, a e simila [34]. Ne e heless, me al so p ion mechanisms depend on he ype o biocha
T akal e al. [35]. Due o he insigni ican shi o bands in FTIR spec a (Fig. 4b), i can be p esumed ha he mechanism o
Table 3
The ini ial concen a ion o con e o dus leacha e o di e en solid- o-liquid a ios and emo al e iciency o Zn(II), Cd(II) and Pb(II), 24 h con ac
ime.
leacha e s (g):l (L) pH c
Zn
(mg/L) c
Cd
(mg/L) c
Pb
(mg/L)
1 0.3125:0.5 4.26 8.2 0.193 0.461
2 0.625:0.5 4.6 15.5 0.361 0.510
3 1.25:0.5 4.95 29.6 0.667 0.534
4 2.5:0.5 5.15 58.7 1.30 0.945
5 5:0.5 4.96 111 2.60 1.35
6 10:0.5 4.97 262 5.16 1.48
7 20:0.5 5.15 430 9.12 1.98
M. Toka ˇ
cíko ´
a e al.
Wa e Resou ces and Indus y 30 (2023) 100219
7
complexa ion wi h ca boxylic g oups is no signi ican in Pb(II), Zn(II) and Cd(II) so p ion. Howe e , –OH g oups esponsible o
coo dina ing a me al d-elec on and p oducing single bond O-M bond [36] we e de ec ed. P e ious s udies showed ha he slow
elease o nega i ely cha ged ions (ca bona e and phospha e) om biocha could p ecipi a e me al ions, especially Pb(II), which can be
comple ely emo ed a low concen a ions om an aqueous solu ion [21].
3.2.3. Reusabili y s udy
The ex ac ion agen s in luenced he deso p ion o Zn(II), Cd(II) and Pb(II) di e en ly (Fig. 3a–d). Mo e han 65% o Zn(II), Cd(II)
and Pb(II) was emo ed by EAI in he 1
s
deso p ion s ep; howe e , wi h inc easing adso p ion/deso p ion s eps, he deso bed pe -
cen age o Zn(II), Cd(II) and Pb(II) dec eased. The ollowing adso p ion dec eased o Zn(II) and Cd(II) and in he las adso p ion s ep
was adso bed 12% o Zn(II) and 20% o Cd(II). The elimina ion e iciency o Pb(II) by MBCH was unchanged in all adso p ion s eps,
which is compa able o he esul s o Zahedi a e al. [12]. A simila cou se o Zn(II) and Cd(II) adso p ion/deso p ion p ocess as in EAI
was also obse ed in EAII. Wi h inc easing adso p ion/deso p ion s eps in EAII bo h he deso p ion o Zn(II) and Cd(II) and emo al
e iciency dec eased. Deso p ion o Pb(II) in EAII inc eased wi h inc easing adso p ion/deso p ion s eps, which could be caused by
inc easing amoun s o Pb(II) adso bed on o MBCH. Al hough he EAIII was an e ec i e eagen o he deso p ion/adso p ion o Pb(II),
Fig. 2. Adso p ion iso he m models o a) Zn(II), b) Cd(II) and c) Pb(II) emo ed om con e e dus leacha e by BCH and MBCH.
Fig. 3. Zn(II), Cd(II) and Pb(II) adso p ion (column)/deso p ion (do -line) e iciency and Fe (line) eleased om MBCH o a ious ex ac ion agen s:
a) EAI, b) EAII, c) EAIII, d) EAIV.
M. Toka ˇ
cíko ´
a e al.
Wa e Resou ces and Indus y 30 (2023) 100219
8
in he 5
h
s ep he deso p ion dec eased o 35%, and Pb(II) adso p ion was unchanged. The EDTA-2-Na was used in Re s. [13,25] as an
e ec i e adso p ion/deso p ion eagen o Pb(II) and Cd(II) as well, he e ec on he s abili y o Fe was no men ioned. Almos 70% o
Fe was eleased om MBCH o he EAIII in he 1
s
deso p ion s ep and MBCH los i s magne ic esponse in he magne ic ield. Mo eo e ,
EAIII nega i ely a ec ed he elimina ion e iciency o Zn(II) and Cd(II) a e 1
s
adso p ion/deso p ion s ep. The e iciency o he
ollowing adso p ion s ep was lowe han 10% o Zn(II) and 30% o Cd(II), bu he e was an inc ease in he 5
h
and 6
h
adso p ion
s eps o 20% o Zn(II) and 43% o Cd(II). The elimina ion o Pb(II) by MBCH was e ec i e in each adso p ion/deso p ion s ep and
was highe han he e iciency in he s udy [13]. The Pb(II) deso p ion dec eased o 34% in he 5
h
deso p ion s ep, bu he ollowing
adso p ion e iciency was unchanged. The EAIV was mo e e ec i e han o he EAs. Wi h inc easing adso p ion/deso p ion cycles, Zn
(II) and Pb(II) deso p ion also inc eased. This was possibly caused by hei inc easing concen a ion on he MBCH su ace du ing he
adso p ion/deso p ion cycles. The emo al o Zn(II), Cd(II) and Pb(II) om con e e dus leacha es by MBCH emained highe han
90% in all cycles. Cd(II) deso p ion was low; howe e , he adso p ion e iciency was p ese ed. This cou se may ha e been a ec ed by
he basic en i onmen o he used ex ac ion agen , al hough he MBCH was washed wi h deionised wa e . The pH alues o solu ions
a e adso p ion p ocedu es did no change signi ican ly a e adso p ion s eps when EAI-EAIII we e used o deso p ion (see Fig. S1 in
he Supplemen a y ile). The pH alues we e de e mined o be 3.9 ±0.2 o he EAI, 4 ±0.2 o he EAII and 4.5 ±0.5 o he EAIII.
The EAIV in luenced he pH o ex ac s a e he ollowing adso p ion mo e signi ican ly han o he EAs. The pH alue inc eased o 7.5
±0.5 and did no change signi ican ly du ing each s ep o he adso p ion/deso p ion p ocedu e. The e iciency o EAIV on he
adso p ion p ope ies o MBCH du ing he adso p ion/deso p ion expe imen was p obably he esul o alkalini y o EAIV, which
oxidises he MBCH su ace and c ea es oxygen-con aining unc ional g oups [37]. The p esence o Zn(II) on he MBCH su ace a e he
6
h
adso p ion cycle was p o ed by mapping (Fig. 6e).
The s abili y o MBCH was also e alua ed on he de e mina ion o Fe concen a ion eleased o he ex ac ion agen s du ing
eusabili y expe imen s. Wi h inc easing adso p ion/deso p ion s eps, he pe cen age o eleased Fe dec eased in all EAs. EAI and EAII
did no in luence he eleasing o Fe (<14% in EAI and <2.9% in EAII, he yellow line in (Fig. 3a and b) signi ican ly. Al hough EAIII
(EDTA-2-Na) seems o be an e icien ex ac ion agen o Zn(II), Cd(II) and Pb(II) deso p ion, 66% o Fe was eleased du ing he 1
s
deso p ion s ep (Fig. 3c). These esul s co espond wi h he esul s o Wang e al. [13] ( eleased Fe was highe han 90% om
composi e) and I hika e al. [14]. This e ec was possibly due o he s onge chela ing p ope ies o EDTA [38]. The amoun o Fe
eleased du ing deso p ion in EAIV was lowe han 0.05% mo eo e , obse ed only in he 1
s
deso p ion s ep; hus, he elease o Fe is
no p esen in (Fig. 3d). The alkaline ex ac ion agen did no in luence he elease o Fe and he p ese a ion o magne ic p ope ies o
MBCH a e he 5
h
cycle was e i ied using he ib a ing-sample magne ome e .
3.2.4. MBCH emo al a e by magne
Magne ic sepa a ion o MBCH a e eusabili y expe imen al esul s a e p esen ed in (Fig. 4a). The highes u bidi y was measu ed
in he solu ions be o e magne ic sepa a ion (s ep 1). A e 1s magne ic sepa a ion, u bidi y o MBCH a e eusabili y expe imen s
signi ican ly dec eased and dec eased wi h inc easing exposu e ime o magne . The u bidi y was changed negligibly, and 15 min o
sepa a ion was su icien . Mo eo e , he yield a e magne ic sepa a ion was 96.5% o MBCH, 92.5% o MBCH a e eusabili y in EAI,
96.5% in EAII and 96% in EAIV, espec i ely. The MBCH, a e ea men in EAIII, los he magne ic esponse, which co esponds wi h
a high po ion o Fe leached o EAIII in he 1
s
eusabili y s ep and he weakes magne ic esponse (see inse o Fig. 5b).
3.2.5. FTIR
Fig. 4b p esen s he no malised FTIR spec a o o iginal BCH, MBCH and MBCH a e he 5
h
s ep o he eusabili y s udy in each
ex ac ion agen . I is e iden ha all spec a a e simila ; hus, he same unc ional g oups a e p esen ed. The mos p onounced i-
b a ions in he BCH sample we e connec ed o he ib a ion o he –OH g oup, whe e s e ching ib a ion is p esen ed a ~3300 cm
−1
,
and de o ma ion ib a ion should be p esen ed a ~1650 cm
−1
, bu i is o e layed by e y in ensi e ib a ion o C=O and i s shoulde
a 1584 and 1698 cm
−1
, espec i ely. These wo ib a ions o he C=O g oup may be connec ed o a ious unc ional g oups, such as
ca boxylic, es e , ke one, aldehyde, and quinones. In all samples, he p esence o C–H bonds in he –CH
2
and –CH
3
g oups was p o en
( ou bands in he ange 2965–2845 cm
−1
) [39]. Al hough, due o he e y s ong band o –OH ib a ion, i canno be s a ed how much
he amoun o o ganic pa di e s in he samples. In he spec a, bands connec ed o he p esence o a ious Si–O–Si ib a ions we e
Fig. 4. a) Changing in u bidi y o MBCH samples a e magne ic sepa a ion b) No malised FTIR spec a, c) log-no mal pa icles size dis ibu ion
(PSD) o he EAI, EAII, EAIII, EAIV, in de ail BCH and MBCH samples.
M. Toka ˇ
cíko ´
a e al.
Wa e Resou ces and Indus y 30 (2023) 100219
9
also de ec ed (1091, 795 and 467 cm
−1
) [40]. O he weak ib a ions can be explained as di e en s e ching, bending and de o ma ion
ib a ions o C–H, C–O [41], and possibly ino ganic molecules (see Table 1). All o he desc ibed bands a e isible in all measu ed
spec a; hei posi ions a e no shi ed signi ican ly, and only he in ensi ies o he bands a y. The mos signi ican dec ease in in-
ensi y is obse able om he di e en Si–O bands, which can be caused by he i on bonding in o he silicon pa o he MBCH.
Mo eo e , in he case o he sample EAIV, he e is an obse able sligh ly di e en shape o he spec a, p obably caused by di e en
a ios o unc ional g oups in he sample. The same bands a e isible, bu bands co esponding o he p esence o Si–O bonds a e only
shoulde s and he band a 1376 cm
−1,
connec ed o he de o ma ion o he C–O bond and o –OH in phenolic g oups [42,43], is mo e
in ensi e. The compa ison o in ensi ies a ios be ween bands a 1584 and 1376 cm
−1
i was demons a ed ha he band a 1376 cm
−1
is he mos in ensi e o he sample EAIV and hus, he sample had p obably he highes amoun o he phenol –OH g oup, which is
connec ed o he be e adso p ion ac i i y [2]. These indings co espond o he esul s om adso p ion expe imen s (see Fig. 3).
3.2.6. Pa icle size dis ibu ion
The pa icle size dis ibu ions (PSD) o he expe imen al samples a e shown in Fig. 4c. The pa icle size pa ame e s such as mode
diame e (d
m
), and diame e s d
10
and d
90
( ep esen ed he 90% o he dis ibu ion lying below he d
90
, and 10% o he popula ion lies
below he d
10
) a e summa ised in Table 5.
The na u e BCH and MBCH samples showed bimodal pa icle size dis ibu ions wi h i s ela i ely iden ical d
m
alues co e-
sponding wi h pa icle size 5.9
μ
m (BCH sample) and 6.7
μ
m (MBCH sample), see in he de ail o Fig. 4c. The bigge ac ions
co espond o d
m
alues wi h he size 101.5
μ
m (BCH sample) and 88.6
μ
m (MBCH sample). Al hough he PSD o he BCH sample had
an asymme ical and b oade cu e shape, he PSD o he MBCH showed a symme ical cha ac e . I can be assumed ha he p ocess o
magne ic modi ica ion o he BCH sample con ibu ed o he size a angemen o la ge ac ions in he olume o he MBCH sample.
The lowe ange o d
10
and d
90
alues can also e idence his ac .
The bimodal cha ac e o he PSD cu es was p ese ed o he EAIV sample (Fig. 4c), wi h he di e ence ha he PSD cu es
di iding he smalle ac ions om he la ge ones a e con inuous and signi ican ly wide . PSD cu es show olume changes in he
EAIV sample when he olume o he ine ac ion (d
m
=11.6
μ
m) inc eased om 0.45% (MBCH) o 2.2% (EAIV) and con e sely, he
olume ac ion o he la ge ac ion (d
m
=88.6
μ
m) dec eased om 15.2% (MBCH) o 8.5%.
PSD cu es o he EAI, EAII, EAIII and EAIV samples show a monomodal cha ac e wi h a na ow dis ibu ion in he a ea o d
m
alues, which ha e signi ican ly lowe d
m
alues in he ange o 82–82.8
μ
m compa ed o he o iginal MBCH sample. A ac ion o e y
ine pa icles emain in he olume o he samples, bu hey a e ep esen ed only by 0.4%. The PDS alues ag ee well wi h he pa icle
size shown in he SEM images (see Fig. 6).
PSD da a (wi h espec o he symme ic na u e o PSDs) we e used o nume ical e alua ion o he speci ic su ace a ea (SPA). The
SPA alues shown in Table 5 we e calcula ed om he pa icle size dis ibu ion alues and physical pa ame e s such as ma e ial densi y
using Equa ion (15) men ioned below.
SPA =6∑Vi
di
ρ
∑Vi
=6
ρ
DS
(15)
whe e V
i
is a ela i e olume o he pa icle size class d
i
,
ρ
is he densi y o samples, D
S
is he mean diame e co ela ed by su ace a ea-
he Sau e diame e .
Iden ical alues o SPA ~1500 cm
2
/cm
3
we e calcula ed o BCH and MBCH inpu samples. SPA alues in he 839–2066 cm
2
/cm
3
ange co espond o changes in he size ac ion alues and hei olume ic ep esen a ion in indi idual samples. The lowes SPA
alues co espond wi h he ex ac ion agen used and he elease o Fe
x
O
y
pa icles. On he con a y, he highes SPA alue we e
Fig. 5. a) Measu ed oom empe a u e magne isa ion cu es o na i e (BCH) and magne ically modi ied biocha (MBCH). Poo magne ic esponse
o he na i e biocha (BCH) is shown in he inse . b) Magne isa ion cu es o magne ically modi ied biocha a e he i h adso p ion/deso p ion
s ep using ex ac ion agen s EAI, EAII, EAIII, and EAIV.
M. Toka ˇ
cíko ´
a e al.