-
Research ArticleFabricationofCeramsiteAdsorbent
fromIndustrialWastes for theRemoval of Phosphorus from Aqueous
Solutions
Yue Yin ,1 Gaoyang Xu ,1 Linlin Li ,1 Yuxing Xu ,1 Yihan Zhang
,1
Changqing Liu ,1 and Zhibin Zhang2
1School of Environmental and Municipal Engineering, Qingdao
University of Technology, Qingdao 266033, China2School of Municipal
and Environmental Engineering, Shandong Jianzhu University, Jinan
250101, China
Correspondence should be addressed to Changqing Liu;
[email protected]
Received 4 July 2020; Revised 21 September 2020; Accepted 6
October 2020; Published 26 October 2020
Academic Editor: Leonardo Palmisano
Copyright © 2020 Yue Yin et al.*is is an open access article
distributed under the Creative Commons Attribution License,
whichpermits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
A more applicable adsorbent was fabricated using industrial
wastes such as red mud, fly ash, and riverbed sediments. *e
heavymetal inside the raw materials created metal hydroxy on the
adsorbent surface that offered elevated adsorption capacity
forphosphorus.*e required equilibrium time for the adsorption is
only 10min.*e theoretical maximum adsorption capacity of
theadsorbent was 9.84mg·g−1 inferred from the Langmuir adsorption
isotherm. Higher solution pH favored phosphorus adsorption.Kinetics
study showed that the adsorption could be better fitted by the
pseudo-second-order kinetic model. *e presence ofcoexisting anions
had no significant adverse impact on phosphorus removal.*e
speciation of the adsorbed phosphorus indicatedthat the adsorption
to iron and aluminum is the dominating adsorption mechanism.
Moreover, a dynamic adsorption columnexperiment showed that, under
a hydraulic time of 10min, more than 80% of the phosphorus in the
influent was removed and thesurplus phosphorus concentration was
close to 0.1mg L−1. *e water quality after adsorption revealed its
applicability in realtreatment. Consequently, the adsorbent
synthesized from industrial wastes is efficient and applicable due
to the high efficiency ofphosphorus removal and eco-friendly
behavior in solutions.
1. Introduction
Wastewater discharging to water bodies such as rivers andlakes
will deteriorate the water quality. Phosphorus is one ofthe most
influential pollutants in wastewater, and excessivephosphorus leads
to eutrophication [1]. Eutrophication hasbecome a serious
environmental problem worldwide as it isaccompanied by rapid
overgrowth of algae which will depletethe oxygen in the water and
suffocate the aquatic animals[2, 3]. In addition, phosphorus
scarcity is another trouble-some issue, mined rock phosphate is the
major source ofphosphorus, and the existing mine rock phosphate
will be-come exhausted in less than 100 years [4]. In
wastewatertreatment, most of the technologies are designed only
fol-lowed by the wastewater discharge threshold without thepurpose
of phosphorus recovery, but in China, approximately1378 t of
phosphorus was discharged directly without anyrecycling in 2018
(http://www.mohurd.gov.cn/csjs/xmzb/
index.htm). In order to recover the phosphorus for
reusesimultaneously, it is urgent to develop new technologies
thatcould remove the phosphorus in the wastewater completelyand
recover the phosphorus resource. *e application ofproper adsorbents
could be one of the solutions to meet therequirements [5–7].
Several reports have investigated theability of phosphorus removal
and recovery of different ad-sorbents [8, 9]. For example, rare
earth element lanthanumand graphene were used as materials of
adsorbents because oftheir high phosphate attention capability [10,
11]. *e cal-culated adsorption capacity was higher than most of the
low-cost adsorbents. However, the cost of the adsorbents such
aslanthanum-based and graphene-based adsorbents is notmentioned,
but considering its high-price raw materials andcomplicated
fabrication synthesis process, the cost will beunacceptable in
wastewater treatment. Furthermore, the spentadsorbents need further
disposal. Consequently, these dis-advantages hinder practical
applications.
HindawiJournal of ChemistryVolume 2020, Article ID 8036961, 13
pageshttps://doi.org/10.1155/2020/8036961
mailto:[email protected]://www.mohurd.gov.cn/csjs/xmzb/index.htmhttp://www.mohurd.gov.cn/csjs/xmzb/index.htmhttps://orcid.org/0000-0001-6309-8605https://orcid.org/0000-0003-2709-1136https://orcid.org/0000-0003-1851-693Xhttps://orcid.org/0000-0003-3719-6396https://orcid.org/0000-0003-4004-094Xhttps://orcid.org/0000-0002-6114-3238https://creativecommons.org/licenses/by/4.0/https://doi.org/10.1155/2020/8036961
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In the past decades, the adsorbents made from haz-ardous
materials have gained great concerns because of itsremoval capacity
of anionic pollutants and low cost. Manyliterature studies have
reported the use of fly ash [12], redmud [13], tailings [14], and
blast furnace slag [15] tomanufacture ceramsite adsorbents to
remove phosphorusfrom aqueous solutions. Wang et al. [12] reported
aphosphorus adsorption comparison among red mud, flyash,
ferric-alum water treatment residual, and theirmodified materials,
and the results demonstrate that theiron-modified materials were
better than HCl-modifiedmaterials, and ferric-alum water treatment
residual wasbetter than red mud and fly ash. Another research
byTangde et al. [16] investigated the phosphate adsorptiononto
activated red mud, and the results indicated that themaximum
adsorption capacity of activated red mud was112.36mg·g−1 at optimum
pH 2. However, to the best of theauthors’ knowledge, no literature
is mixing contaminatedriverbed sediments with red mud and fly ash
to fabricateceramsite adsorbent. For one thing, the riverbed
sedimentsare in a great amount of silicon which is the main
com-ponent for producing ceramsite, the clay used in the past
isexhausting in earth, and replacing clay with riverbedsediments
can be prompted in construction and watertreatment works [17]. In
addition, the incineration processwill stabilize the heavy metal
inside the riverbed sedimentsand reduce the heavy metal leaching
which favored itspractical application.
In Shandong province, China, the heavy industry ac-counts for a
large proportion which caused too much in-dustrial wastes such as
redmud and fly ash [18]. On the otherhand, river pollution is not
peculiar in Shandong, and manyrivers were polluted at different
levels. With the effort thegovernment made in recent years, the
water in rivers is nowless polluted or unpolluted; nevertheless,
the sediments onthe riverbed have been compromised due to
long-termcontamination. *is large amount of the sediments cannotbe
treated only by in situ solidification because most of thesediments
are active and unable to be repaired easily. In thisstudy, fly ash
and red mud were added into contaminatedriverbed sediments to
fabricate ceramsite. Hence, usingthese waste materials to
manufacture ceramsite will stabilizethe pollutants inside,
effectively lower the ecological risk ofthe waste, and utilize the
elements present in the waste tostrengthen the adsorption
capacity.
*e objective of this study is to investigate the feasibilityof
“use the waste to treat the waste,” and in other words,
theadsorption capacity of ceramsite made from the combina-tion of
red mud, fly ash, and contaminated riverbed sedi-ments. To meet the
real application, the adsorption time inthis study was set at
10minutes while the equilibrium time inother research studies
ranged from 0.5 to 48 hours. Also, thepH in every experiment
(except for pH study) was set at 7 tobe more representative.
Kinetic and adsorption isothermwere investigated to analyze the
adsorption process, alongwith the effect of pH, coexisting anions,
and dosage. *especiation of the adsorbed phosphorus was further
inves-tigated to characterize the adsorption mechanism. For
theapplication of ceramsite, the real wastewater adsorption,
dynamic column adsorption, and desorption experimentswere also
elucidated.
2. Materials and Methods
2.1. Materials. All chemicals used in this study were
ofanalytical grade purchased from Sinopharm Chemical Re-agent Co.,
Ltd. All data were triplicated, the values wereaveraged, and the
relative standard deviations were below8% in all values.*e red mud
and fly ash were obtained fromthe industry in Shandong province. *e
heavy metal con-taminated riverbed sediment was sampled from a
heavy-polluted river located in Shandong province. *e chemicaland
mineral compositions of the raw materials used in thisresearch are
given in Table 1 and Figure 1, respectively.Deionized water was
used in this study.
2.2. Synthesis of Ceramsite. Raw materials were air-dried for10
days to remove moisture and then ground to pass a 48-mesh sieve. *e
riverbed sediment, fly ash, red mud, andsawdust were mixed at 5 : 3
:1 : 1 (w/w) and deionized waterwas added (20 wt%). *e mixture was
ground into pellets(diameter: 8–10mm) and dried at 105°C for 4
hours in anoven. *e origin pellets were incinerated in a muffle
furnaceat 900°C for 1 hour with a ramp at 10°Cmin−1. *e
achievedceramsite was cooled naturally, ground to pass 20-meshsieve
(∼1.27mm), and stored in a desiccator for future use.
2.3. Characterization of Ceramsite. *e chemical composi-tion was
determined by X-ray fluorescence spectroscopy(XRF-1800, SHIMADZU).
Mineralogical detection wascarried out using X-ray diffraction
(XRD, Rigaku) using Curadiation (45 kV, 40mA). *e surface
morphologies wereexamined by scanning electron microscopy
(SU8000,Hitachi). BET surface area was detected by
MicromeriticsASAP2460.*e point of zero charge of ceramsite made
fromindustrial wastes was tested according to the solid
additionmethod [19]. Briefly, each flask contained 0.1 g ceramsite
and100mL 0.01M KNO3 solution with pH between 2 and 10and was shaken
for 10min to reach equilibrium. *e initialpH was adjusted by using
0.1M HCl and 0.1M NaOH, andthe final pH of the solutions
wasmeasured.*e change of thepH value (before and after shaking) was
designated as ΔpHwhich was plotted against initial pH, and the pH
at the pointof zero charge (pHpzc) value was at the initial pH
valuewhereΔpH is equal to zero (where the curve intersects
theX-axis) [20].
2.4. Static Adsorption Methods. To study equilibriumphosphorus
adsorption capacity, 0.5 g ceramsite was addedinto a conical flask
with 50mL of a phosphate concentrationvarying from 1 to 20mgL−1. *e
mixture was shaken at120 rpm for 10min in a thermostatic shaker.
After that, themixed solution was filtered through a 0.45 μm
membraneand the phosphate concentration was detected using
themolybdenum-blue complex method. *e phosphorus ad-sorption
capacity of ceramsite (qe (mg g−1)) and the removal
2 Journal of Chemistry
-
rate of the phosphorus (R(%)) were calculated by the fol-lowing
equations:
qe �C0 − Ce(
a, (1)
R �C0 − Ce(
C0× 100%, (2)
where C0 (mg·L−1) is the initial phosphorus concentration,Ce
(mg·L−1) is the phosphorus concentration at equilibrium,and a
(g·L−1) is the adsorbent dosage.
For kinetics studies, 0.5 g ceramsite was added intophosphate
solution (concentration� 10, 5, and 2mgL−1),and the mixture was
shaken for different times (10 s–600 s)and tested as previously
mentioned. For the effect of pH onphosphorus adsorption, phosphorus
solutions were pre-pared at different initial pH conditions using
0.1M HCl or0.1M NaOH (phosphorus concentration� 10mg·L−1
andadsorbent dosage� 1 g·L−1) and shaken for 10min at 25°C.In the
dosage effect study, different adsorbent dosages wereapplied from
0.5 to 10 g·L−1, mixing with phosphorus so-lutions of 50mg·L−1 and
shaking for 10min. To determinethe effect of coexisting anions on
phosphorus adsorption, thecompeting coexisting anions such as Cl−,
F−, SiO32−, andSO42− were added.
*ere are three kinds of phosphorus adsorbed on theadsorbents,
namely, physically adsorbed phosphorus (phys-P), Fe/Al adsorbed
phosphorus (Fe/Al-P), and Ca/Mg
adsorbed phosphorus (Ca/Mg-P). To determine the speci-ation of
the phosphorus adsorbed on the ceramsite, amodified sequential
extraction procedure was used based on[21] after equilibrium
(experimental condition: 10min,120 rpm, initial phosphorus
concentration� 20mg·L−1, andadsorbent dosage� 5 g·L−1). To be
specific, the extractionprocedure is shown in Table 2.
For recyclability of the spent adsorbent, different solu-tions
were prepared to conduct desorption experimentsincluding 0.1M NaCl,
0.1M Na2CO3, 0.1M NaOH, 0.1MHCl, and 0.1M H2SO4. *e experiment
conditions were asfollows: 10 g·L−1 adsorbent, 50mg·L−1 phosphorus,
10min,and 120 rpm. For real adsorption applications, water sam-ples
were collected from different places such as watertreatment plants,
wastewater treatment plants, parks, river,and city runoff. Unless
otherwise stated, the pH of allphosphate solutions used in this
study was adjusted to 7.
2.5. Dynamic Column Adsorption. Dynamic adsorption wasconducted
using laboratory-scale adsorption columns. *ecolumns were made from
polymethyl methacrylate with aninner diameter of 30mm and a height
of 100mm. *ecolumn was packed with 20 g ceramsite with a
functionalvolume of 50ml. *e effluent was prepared by
dissolvingKH2PO4 with deionized water to achieve different
initialconcentrations, and the HRT was maintained at 10min.
3000
2000
1000
0
Relat
ive i
nten
sity
(a.u
.)
0 20 40 60 802-theta (degrees)
HematiteChabaziteCalcite
(a)
Relat
ive i
nten
sity
(a.u
.)
60000
50000
40000
30000
20000
10000
00 20 40 60 80
2-theta (degrees)
GypsumCocsite
(b)
Figure 1: XRD spectra of (a) red mud and (b) fly ash.
Table 1: Chemical compositions of raw materials (% by mass).
SiO2 Al2O3 CaO Fe2O3 SO3 Na2O TiO2Riverbed sediment 56.58 14.52
13.29 6.68 1.00 1.02 0.88Red mud 20.86 22.40 3.73 36.00 0.52 10.46
5.00Fly ash 1.55 0.72 44.60 0.23 52.47 0.23 NDND�not detected.
Journal of Chemistry 3
-
3. Results and Discussion
3.1. Characterization of Ceramsite. XRD patterns of the
rawmaterials and the adsorbent before and after adsorption aregiven
in Figures 1 and 2. As from Figure 1(a), the crystallinephases of
the raw red mud are identified as hematite,chabazite, and calcite.
Figure 1(b) shows that the mainmineral compositions of fly ash are
gypsum and coesite. *eiron, aluminum, silicon, and calcium present
in the red mudand fly ash support the structure of the adsorbent
andfunction as the major activated site to adsorb phosphorus.*e XRD
pattern of adsorbent before and after adsorption isdepicted in
Figure 2, and it can be seen that the adsorbenthas a stable
crystalline structure comparing to raw materials.Additionally, no
obvious change is observed in the XRDpattern after adsorption
indicates its great stability forphosphorus adsorption in aqueous
solutions.
Figure 3 shows the morphology of ceramsite adsorbentwith SEM
which confirms the porous surface of the ad-sorbent. *is
heterogeneous surface will increase theadsorption capacity due to
its higher specific surface area;meanwhile, porous surface will
intercept the pollutantsmore easily and facilitate the adsorption
process. *e BETsurface area of this adsorbent was 12.89 m2·g−1
whichfavors its adsorption, and the average pore size is15.96
nm.
*e FTIR spectrum of ceramsite adsorbent is given inFigure 4. *e
broad band at 3398 cm−1 and a weak peak at1633 cm−1 of ceramsite
adsorbent are due to the stretchingvibrations of surface -OH or
water [22]. Further, the peaks at1011 cm−1 and 1077 cm−1 are
related to the Fe-OH and Si-O,respectively, which are the
fundamental groups for theadsorption of phosphorus in this study
[23, 24]. *e band at578.7 cm−1 pertains to symmetric stretching
vibrations ofFe-O in crystalline lattice of Fe3O4 [25].
3.2. Static Adsorption Studies
3.2.1. Adsorption Isotherms. *e adsorption isotherm dataare
given in Table 3. *e maximum phosphorus adsorptioncapacity of
ceramsite is achieved using different initialphosphorus
concentrations at different temperatures. *eisotherm data are shown
in Figure 5 together with the datafitting by Langmuir isotherm. As
from Figure 5(a), theincrease of the environment temperature cannot
improvethe adsorption capacity under low phosphorus concentra-tion,
whereas a prominent increase was observed under highphosphorus
concentration, indicating an endothermic na-ture of the adsorption
process. *is nature was not signif-icant under low phosphorus
concentration due to sufficient
adsorption. *e highest phosphorus adsorption capacitiesare 9.18,
10.56, and 11.61mg·g−1 achieved at 25, 35, and 45°C.*e Langmuir
model and Freundlich isotherm are used to fitthe adsorption data,
and the isotherm equations areexpressed as follows [7, 26]:
Ce
qe�
1KLqmax
+1
qmaxCe,
ln qe � lnKF +1nlnCe,
(3)
where Ce (mg·L−1) is the phosphorus concentration atequilibrium,
qe is the adsorption capacity. qmax (mg·g−1)represents the
theoretical maximum adsorption capacity, KL(L·mg−1) is the
equilibrium constant related to adsorptionenergy, KF (mg·g−1) is
the Freundlich adsorption capacity,and the n is the Freundlich
constant.
As shown in Table 3, the experiment data are fitted wellat every
control temperature with the Langmuir isothermmodel with higher
correlation coefficients but poorly withFreundlich isotherm, and
this means that the adsorption ofthe phosphorus onto the ceramsite
is limited to monolayercoverage [27]. *e theoretical maximum
adsorption ca-pacities calculated from the Langmuir model are 9.84,
11.52,and 13.05mg·g−1, respectively, at 25, 35, and 45°C, which
isat the medium level of the previously reported researchstudies
listed in Table 4; however, the adsorption time in thisstudy is
only 10 minutes which is less than most of the otherresearch
studies. We thought the time as a vital operatingparameter in
adsorption because the long adsorption du-ration is impossible in
wastewater treatment due to a largecost.
Table 2: Extraction procedure for different speciation of
phosphorus.
Step Method Speciation1 1 g spent adsorbent added to 25ml 1M
NH4Cl, stirring for 1 h at 120 rpm (25°C) Phys-P2 Residual
adsorbent added to 25ml 0.1M NaOH, stirring for 1 h at 120 rpm
(25°C) Fe/Al-P3 Residual adsorbent added to 25ml 0.5M HCl, stirring
for 1 h at 120 rpm (25°C) Ca/Mg-P4 Subtracting above 3 speciation
phosphorus from equilibrium phosphorus amount Loss-P
12000
8000
4000
0
Relat
ive i
nten
sity
(a.u
.)
0 20 40 60 802-theta (degrees)
Pristine adsorbentSpent adsorbent
Figure 2: XRD spectra of adsorbent before and after
adsorption.
4 Journal of Chemistry
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*e essential feature of the Langmuir isotherm can bepresented in
terms of the constant, RL, which is expressed asfollows [28]:
RL �1
1 + KLC0. (4)
*e value of RL represents whether the phosphorusadsorption is
favorable or unfavorable. If 0
-
the pseudo-first-order and pseudo-second-order model areused to
fit the adsorption data, and the equations are asfollows [37,
38]:
ln qe − qt( � ln qe − K1t,
t
qt�
1K2q
2e
+t
qe,
(5)
where qe and qt are the amount of phosphorus adsorbed perunit
mass adsorbent at equilibrium and at different time t,respectively.
K1 (min−1) and K2 (g·mg−1·min−1) are the ki-netic rate
constants.
All the experimental data fit the pseudo-second-ordermodel well
with higher correlation coefficients as shown inTable 6. It is also
notable that the experimental qe agrees withthe calculated qe
derived from the pseudo-second-ordermodel, and this also
demonstrates that the phosphorusadsorption onto ceramsite followed
the pseudo-second-order model which means that the adsorption might
be therate-limiting step [39].
3.2.3. Effect of Operational Conditions. *e adsorption
ofphosphorus onto ceramsite was highly affected by the initialpH
condition because it changed the surface charge on the
12
8
4
0
q e (m
g·L–
1 )
0 4 8 12Ce (mg·L–1)
25°C35°C45°C
(a)
0 4 8 12Ce (mg·L–1)
1.2
0.8
0.4
0.0
C e/q
e (g·
L–1 )
25°C35°C45°C
(b)
Figure 5: (a) Adsorption of phosphorus onto ceramsite; (b)
Langmuir model fitting (pH� 7, t� 10min, adsorbent dosage� 1 g·L−1,
and120 rpm).
Table 4: Removal capacity comparison of different phosphorus
adsorbents.
AdsorbentExperimental conditions
qe (mg·g-1) ReferenceAdsorbent dosage (g·L−1) Time (hours)
pHMg-loaded biochar 1 4 7 31.15 [30]Modified bauxite residue 40 24
NA 0.35–2.73 [31]Fe-loaded ceramic adsorbent 1 3 7 18.48
[32]Acid-engineered pumice 2 0.5 5–7 9.74 [33]Granular mesoporous
ceramic 10 24 4.0–12.0 5.96 [34]Lithium silica fume 2 6 7 24.10
[35]Wasted low-grade iron ore 10 1 5.6 11.44 [36]Industrial waste
ceramsite 1 0.167 7 9.84 *is study
Table 5: *e RL values at different initial phosphorus
concentrations.
Temperature (°C)RL values at different initial phosphorus
concentrations
1mg·L−1 2mg·L−1 5mg·L−1 10mg·L−1 15mg·L−1 20mg·L−1
25 0.43 0.27 0.13 6.90×10−2 4.71× 10−2 3.57×10−2
35 0.42 0.27 0.13 6.79×10−2 4.63×10−2 3.51× 10−2
45 0.46 0.30 0.15 7.83×10−2 5.36×10−2 4.08×10−2
6 Journal of Chemistry
-
adsorbents, and the pH condition can be considered as oneof the
most influential factors in adsorption behavior [40].To investigate
the pH dependence of phosphorus adsorptioncapacity, adsorption was
conducted under different pH
conditions varying from 1 to 13 with an initial concentrationof
10mg L−1 and adsorbent dosage of 1 g·L−1. As shown inFigure 7, the
adsorption capacity was on the rise followingthe initial pH from 1
to 5, achieving the highest adsorption
10
8
6
4
2
0
0 200 400 600
Phos
phor
us co
ncen
trar
tion
(mg·
L–1 )
t (s)
10mg·L–1
5mg·L–1
2mg·L–1
(a)
2
1
0
–1
–2
–30 100 200 300 400 500
In (q
e–q t
)
t (s)
10mg·L–1
5mg·L–1
2mg·L–1
(b)
250
200
150
100
50
0
0 200 400 600t (s)
t/qt (
s·g/m
g)
10 mg L–1
5 mg L–1
2 mg L–1
(c)
Figure 6: (a) Adsorption kinetics of phosphorus onto ceramsite;
(b) pseudo-first-order model fitting; (c) pseudo-second-order model
fitting(pH� 7, t� 10min, adsorbent dosage� 0.5 g·L−1, 120 rpm, and
25°C).
Table 6: Pseudo-first-order and pseudo-second-order kinetics
constants.
Phosphorus concentration(mg·L−1)
Experimental value qe(mg·g−1)
Pseudo-first-order model Pseudo-second-order model
K1 (min−1)qe
(mg·g−1) R2 K2
(g·mg−1·min−1)qe
(mg·g−1) R2
2 2.72 7.20×10−3 2.03 0.9901 5.96×10−3 2.94 0.99315 5.63 4.51×
10−3 3.10 0.9526 4.10×10−3 5.70 0.991810 14.89 6.85×10−3 5.73
0.9687 3.37×10−3 15.17 0.9991
Journal of Chemistry 7
-
capacity at pH� 5, and after that, a negative influence of pHwas
observed. *e same tendency was also observed in otherresearch
studies but with higher adsorption capacity in lowpH conditions
[12]. *is result may be because the pH has agreat influence on the
phosphorus species and ceramsitesurface charge. As it is well known
the phosphorus specieswere greatly influenced by pH, under 25°C
condition, thepredominated phosphorus species were H2PO4−,
HPO42−,and PO43− with the pH starting from 2.1, 7.2, and
12.3,respectively, resulting in more negatively charged phos-phorus
species with the increase of pH [12].*e point of zerocharge of pH
is plotted in Figure 8 which was in the pH rangefrom 7 to 8, with
lower pH than pHpzc, the surface of theadsorbent was positively
charged, and on the contrary, thesurface was negatively charged
with higher pH than pHpzc.Hence, when the surrounding pH was lower
than pHpzc,with the decrease of pH, the amount of the
positivelycharged sites on the ceramsite increased. However,
theadsorption behavior under low pH was compromised whichmay be
owing to the less negative form of phosphorus(H3PO4 and H2PO4−),
while with the increase of pH, theincreased percentage of HPO42−
built a strong bond with theFe/Al surface resulting in better
adsorption performance.Besides, the extremely low pH surrounding
may disassemblethe fraction of ceramsite which will release more
anions intothe solution competing with phosphorus. While
underhighly alkaline condition, the surface charge was
highlynegative which should have an adverse impact on phos-phorus
removal; however, the alkaline condition promotedthe transformation
of HPO42− to PO43− which is more activeto form strong precipitation
with iron and aluminumcausing stable adsorption behavior under high
alkalinecondition. *e pH-dependent adsorption curve indicatedthat
the adsorption was inhibited under low pH (1–3) andstayed active
afterward even at pH� 13.*e solution pH wasalso measured after
reaching equilibrium, presented as blue
quadrates in Figure 7, and it was seen that the equilibriumpH
increased slightly with initial pH ranging from 1 to 9 anddecreased
at highly alkaline conditions, which also can beused to demonstrate
that negatively charged particles werereleased under the acid
condition and compete withphosphorus anions.
For the investigation of the effect of dosage on phos-phorus
adsorption, the adsorption experiments were con-ducted with
different dosage amounts ranging from 0.5 to10 g·L−1 in the
presence of 50mg·L−1 initial phosphorus at120 rpm for 10min (Figure
9). *e phosphorus adsorptionrate significantly increased from
15.905% to 99.24% withincreasing ceramsite dosage amount from 0.5
to 5 g·L−1. *eadsorption rate stayed constant after 5 g·L−1
adsorbent withthe effluent phosphorus concentration below
1.5mg·L−1.With the increase of the dosage amount, the active
sitesincreased which can adsorb more phosphorus, leading to
aninevitable increasing adsorption rate, and on the other hand,the
phosphorus adsorption capacity in unit mass decreasedfrom 15.905 to
0.995mg g−1 because, with the increase ofadsorbents, the adsorption
force of specific surface area gotweakened [41]. It was seen from
that, considering largeinitial phosphorus concentration, 5 g·L−1
adsorbent wasfound to be an effective dosage.
Figure 10 presents the influence of the coexisting anionson the
phosphorus adsorption including Cl−, F−, SiO32−, andSO42− anions at
different concentrations (20 and100mg·L−1). *e blue line in this
figure represents the ad-sorption capacity without coexisting
anions under the sameexperimental conditions, and as from the
comparison, theinfluence of the anions in descending order was as
follows:SO42−, SiO32−, F−, and Cl−. All four anions present in
thesolutions affected the phosphorus adsorption of ceramsite,but
still, no remarkable impact was detected. From Fig-ure 10, with
20mg·L−1 of coexisting anions, the phosphateremoval rate achieved
99.31%, 99.12%, 98.89%, and 98.69%for Cl−, F−, SiO32−, and SO42−,
respectively. Under higherconcentration of coexisting anions
(100mg·L−1), no signif-icant decrease was detected. Sulfate,
because iionic radii(2.3 Å) is similar to that of phosphate (2.38
Å) which willcause competitive adsorption, was the most
influential anion
12
8
4
0
q e (m
g g–
1 )
0 4 8 12Initial pH
12
8
4
0
Equi
libriu
m p
H
Adsorption capacityEquilibrium pH
Figure 7: Effect of pHon the phosphorus adsorption behavior
andfinalpH after reaching equilibrium (t� 10min, adsorbent dosage�
1g·L−1,120 rpm, initial phosphorus concentration� 10mg·L−1, and
25°C).
1
0
–1
–2
∆pH
2 4 6 8 10Initial pH
Figure 8: Point of zero charge of ceramsite.
8 Journal of Chemistry
-
[42]. However, the detrimental effect caused by this
com-petitive anion is negligible.*is suggested that the
adsorbentshowed an exceptional anti-interference ability to
othercoexisting anions, proving the applicability of the
adsorbentin complicated real water treatment.
3.2.4. Speciation Analysis of Adsorbed Phosphorus. To figureout
the phosphorus adsorption mechanism of ceramsite, thespeciation of
the adsorbed phosphorus was distinguishedusing the sequential
extraction procedure. From Figure 11,the Fe/Al-P was the dominating
adsorption speciation, ac-counting for 85.91% of all the phosphorus
adsorbed. *isdemonstrated that the adsorption of phosphorus
wasdominated by iron and aluminum which were the major
components of the red mud (36.00% and 22.40%, respec-tively,
Table 1), and the phosphorus was precipitated on thesurface of the
ceramsite with iron and aluminum. In ad-dition, 2.74% and 9.42% of
phosphorus were adsorbed byphysical adsorption and Ca/Mg
adsorption, and the lowpercentage of Ca/Mg adsorption was due to
the less activecalcium in the ceramsite. Furthermore, only 1.93% of
thetotal adsorbed phosphorus was not detected (loss-P); itindicated
that all phosphorus was adsorbed at the surface ofthe ceramsite,
and little phosphorus was removed with thedissolved iron or
aluminum. Because of that, the phosphoruswill remain on the surface
of the ceramsite and can bedesorbed using desorbing agents for the
recovery ofphosphorus.
3.2.5. Desorption of Phosphorus. Phosphorus desorptionfrom the
ceramsite is to help regenerate the adsorbents, andthen the
regenerated adsorbents can be used to adsorbphosphorus again.
Preliminary research studies have indi-cated that sodium hydroxide,
sodium bicarbonate, andsodium chloride can be used to regenerate
the adsorbents[40, 43]. In this study, the desorption studies were
conductedwith different desorbing agents such as 0.1M NaCl,
0.1MNa2CO3, 0.1M NaOH, 0.1M HCl, and 0.1M H2SO4, andphosphorus
released from the adsorbents was measured toensure the most
functional desorbing agent. Unlike thepreliminary research studies,
the sodium hydroxide andsodium chloride barely desorbed the
phosphorus from thesurface, especially for sodium hydroxide, with
less than 10%desorbing percentage. *is might be caused by the
reasonthat the majority of the phosphorus was adsorbed by ironand
aluminum, and adding OH− will make the precipitationless soluble
and difficult to break down. As from Figure 12,the best performance
was achieved for 0.1M HCl and 0.1MNa2CO3 with 82.48% and 75.46%
desorbing phosphorus oftotal phosphorus adsorbed, respectively.
0.1M H2SO4 was
96
98
100
SO42–SiO32–F–
Ads
orpt
ion
perc
enta
ge (%
)
20 mg L–1
100 mg L–1
Cl–
Adsorption without coexisting anions
Figure 10: *e effect of coexisting anions on phosphorus
ad-sorption (pH� 7, t� 10min, adsorbent dosage� 2 g·L−1, 120
rpm,initial phosphorus concentration� 10mg·L−1, and 25°C).
100
80
6020
0
Perc
enta
ge (%
)
Phys-P Fe/Al-P Ca/Mg-P Loss-PSpeciation of adsorbed
phosphorus
Figure 11: Speciation analysis of adsorbed phosphorus
onceramsite (pH� 7, t� 10min, adsorbent dosage� 2 g·L−1, 120
rpm,initial phosphorus concentration� 10mg·L−1, and 25°C).
100
80
60
40
20
0
Adso
rptio
n pe
rcen
tage
(%)
0 5 10Adsorbent dosage (g L–1)
16
12
8
4
q e (m
g g–
1 )
Adsorption percentageAdsorption capacity
Figure 9: *e effect of dosage on phosphorus adsorption (pH� 7,t�
10min, 120 rpm, initial phosphorus concentration� 50mg·L−1,and
25°C)
Journal of Chemistry 9
-
also found to be very effective in the desorbing
procedure.However, when testing the concentration of iron and
alu-minum in the solutions after desorption, higher concen-tration
was observed with 0.1M HCl and 0.1M H2SO4,indicating the adsorbent
was dissolved under the acidicsolutions which caused desorption of
phosphorus. *e ironand aluminum concentrations after desorption
were 0.53and 1.23mg L−1 for 0.1M HCl and 0.50 and 0.96mg·L−1
for0.1M H2SO4, respectively. Furthermore, nearly no iron/aluminum
was detected after desorption using sodiumcarbonate. Consequently,
sodium carbonate was chosen asthe desorption agent for future
use.
3.2.6. Phosphorus Adsorption of Real Water Samples. Totruly
investigate the feasibility of application for phosphorusremoval
using the ceramsite, the real water samples fromdifferent sources
were collected and the detail of the samplesis listed in Table 7.*e
water samples were collected from (a)water treatment plant, (b)
wastewater treatment plant, (c)park, (d) river, and (e) runoff. *e
collected water samplesinitially contained phosphorus
concentrations ranged from0.04 to 3.23mg·L−1, and the COD ranged
from 14 to 142.*eresults of phosphorus concentration before and
after ad-sorption are shown in Figure 13. *e phosphorus
concen-trations after adsorption decreased under 0.5mg·L−1
exceptfor sample 6 which possessed more complicated waterquality;
however, it still adsorbed almost half of the phos-phorus present
in the water. *is suggested that the ap-plication of ceramsite for
real water treatment was feasiblefor low-contaminated aqueous
solutions and also promisingfor complicated water samples if the
appropriate adsorbentdosage was applied.
3.3. Dynamic Column Adsorption. Due to practical pur-poses, the
column adsorption experiment was conducted inthis research. Figure
14 shows the effect of inlet phosphorusconcentrations on the
effluent phosphorus concentration (C
is the effluent phosphorus concentration and C0 is the
initialphosphorus concentration). *e results show that
afterapproximately 30 and 40 minutes, with initial
adsorbateconcentration at 2 and 5mg·L−1, the phosphorus
concen-tration in the effluent rises dramatically, indicating
theadsorbent column has been broken through. Also, higheradsorbate
concentration promotes the saturation time. After50 minutes, the
effluent phosphorus concentration is close tothe influent
phosphorus concentration (2mg·L−1) whichindicates the adsorbent
column is completely exhausted bythe phosphorus. With initial
phosphorus concentration at2mg·L−1, the water samples collected
prior to 34 minutesmeet the threshold of the Chinese discharge
standard ofpollutants for municipal wastewater treatment
plant(GB18918-2002), with the phosphorus concentration lowerthan
0.3mg·L−1.*at is, the ceramsite adsorbent can remove85% phosphorus
using a fixed-bed column in a realapplication.
3.4. Water Quality after Adsorption. *e water quality
afteradsorption was tested by ICP-MS, to ensure the safety of
theceramsite use in water treatment. Unlike other research
100
80
60
40
20
0
Perc
enta
ge (%
)
Different desorbing agents
0.1
M N
aCl
0.1
M N
a 2CO
3
0.1
M N
aOH
0.1
M H
Cl
0.1
M H
2SO
4Figure 12: Percentage of phosphorus released from
ceramsiteusing different desorbing agents (equilibrium: pH� 7, t�
10min,adsorbent dosage� 1 g·L−1, 120 rpm, initial
phosphorusconcentration� 10mg·L−1, and 25°C).
Table 7: Details of collected water samples.
SampleID pH
Temperature(°C)
COD(mg·L−1)
NH4+-N(mg·L−1) PO4
3−(mg·L−1)
1 7.64 17.2 24 11.73 2.902 7.44 16.9 21 0 2.903 7.57 14.3 19
6.74 2.524 8.07 22.2 38 0.16 0.245 6.61 12.8 13 0.04 0.046 7.59
12.4 142 13.11 3.237 7.51 21.5 31 16.43 1.398 6.98 20.2 26 8.02
1.12
3
2
1
0
100
80
60
40
20
0
Phos
phor
us co
ncen
trat
ion
(mg
L–1 )
Phos
phor
us ad
sorp
tion
rate
(%)
1 2 3 4 5 6 7 8Collected water samples
Before adsorption
A�er adsorption
Adsorption rate
Figure 13: Phosphorus adsorption behavior of collected
watersamples (equilibrium: t� 10min, adsorbent dosage� 2 g·L−1,120
rpm, and 25°C).
10 Journal of Chemistry
-
studies, the objective of this work is to (1) treat the
hazardousmaterials, (2) reuse them, and (3) ensure the feasibility
foractual use but not for lab researches. Many research studieshave
investigated adsorbents with large adsorption capacityposing
promising future; however, few of them studied thewater quality
after adsorption which is of great significancebecause the
fundamental purpose of the adsorption treat-ment is to treat the
water but not introduce more hazardousions into the water. In
addition, some of themmay study theleaching toxicity, but the
threshold standard they use is forthe identification of hazardous
materials but not forwastewater treatment standards. In this
research, the watersamples after 10min, 20min, and 40min dynamic
ad-sorption were tested to determine the metal
concentrations,compared with the Chinese discharge standard of
pollutantsfor municipal wastewater treatment plant (GB
18918–2002).
*e concentrations of different metals after adsorptionand the
metal leaching concentrations of raw materials areshown in Table 8.
In general, the concentrations aftersintering decreased
significantly compared with the
leaching concentrations of raw materials, suggesting thatthe
fabrication helped stabilize the metals inside the rawmaterials.
Additionally, among the metals tested in thisstudy, there are five
metal pollutants listed as class I pol-lutants: As, Hg, Pb, Cd, and
Cr. *e measurement resultsshowed that the As, Hg, Pb, and Cr
concentrations of allwater samples after adsorption column met
completely thedischarge standard of China. *e Cd concentration
after 40minutes, however, exceeded 0.01mg·L−1 which will
needfurther treatment. *is may be caused by the large presenceof
cadmium inside the red mud (3.68mg·L−1 using TCLPtest), and future
fabrication should focus on the furtherstabilization of the
cadmium. In the wastewater dischargestandard, there are no specific
limits for Fe, Mg, Al, and Caelements; however, in this study, the
concentrations werelowered to an unharmful level. Meanwhile, the
remainingelements were within the discharge standard of
pollutantsfor the wastewater treatment plant. *erefore, the
adsor-bent made in this research is relatively safe to use
inwastewater treatment.
1.0
0.8
0.6
0.4
0.2
0.0
C/C 0
0 20 40 60Time (min)
2 ppm5 ppm
Figure 14: Removal of phosphorus by fixed-bed column (HRT�10min
and dosage� 20 g).
Table 8: Trace metal element concentrations in the effluent
(compared with leaching concentrations from raw materials).
Metals (mg L−1)Water samples after column Toxicity leaching
tests
Maximum contaminant level10min 20min 40min Red mud Fly ash
Riverbed sediment
As 0.03 0.03 0.05 0.36 0.07 0.15 0.10Hg ND ND ND 0.01 0 ND
0.01Pb ND ND ND 0.01 0 ND 0.10Cd 0.01 0.01 0.02 3.68 0.01 0.11
0.01Cr 0.06 0.02 0.04 1.33 0.26 ND 0.10Fe ND ND 0.09 0.96 0.29 0
NMMg 0.46 1.15 1.60 9.31 8.53 30.07 NMAl 0.51 1.05 1.04 2.11 28.86
0.01 NMCa 3.87 18.31 8.12 382.97 427.73 605.03 NMCu 0.01 0.01 0.01
0.05 0.04 0.02 0.50Mn ND ND 0.007 0.01 0.09 5.85 2.00Zn 0.01 0.01
0.03 0.07 0.11 0.46 1.00ND: not detected; NM: not mentioned.
Journal of Chemistry 11
-
4. Conclusion
For the first time, the riverbed sediments, red mud, and flyash
were used as the main materials for ceramsite ad-sorbent
fabrication. *e adsorption capacity for phos-phorus was
investigated along with the mechanism studyand preliminary
application explore. Due to the iron andaluminum present in the raw
materials, the adsorptioncapacity of ceramsite is up to 9.84mg g−1.
*e phosphorusadsorption onto ceramsite follows the Langmuir
mono-layer adsorption model and pseudo-second-order kineticmodel.
*e adsorbent exhibited a great anti-interferenceability to other
anions simultaneously existing in thesolutions; besides, the
results of phosphorus adsorptionfrom collected real water samples
further suggest that theceramsite adsorbent in this research can be
effectiveacross a wide range of conditions and suitable for
dif-ferent water environments. Moreover, it only takes 10minutes
for the adsorbent to reach equilibrium in thesolutions which are
far more rapid than most of theresearch studies; this greatly
lowers the cost of the ad-sorption treatment if applying in
treatment plant.Leaching toxicity of the ceramsite is below the
wastewaterdischarge standard. In a word, this ceramsite
preparedwith industrial wastes is a low-cost, rapid, safe, and
ef-fective adsorbent to remove phosphorus from real water.To a
certain content, the research has realized the purpose“use the
waste to treat the waste”. Further research shouldfocus on
improving the phosphorus adsorption capacityto remove more
phosphorus by optimizing the preparingconditions. In addition, to
avoid second pollution, theleachability of the ceramsite adsorbents
needs to becontrolled which will greatly promote the applicability
ofthe adsorbents.
Data Availability
*e data used to support the findings of this study areavailable
from the corresponding author upon request.
Additional Points
A novel ceramsite adsorbent was prepared with contami-nated
sediment. Adsorbent showed rapid adsorption be-havior and great
adsorption capacity. *e adsorbent can beused for real applications
with no environmental influence.
Conflicts of Interest
*e authors declare that there are no conflicts of
interestregarding the publication of this paper.
Acknowledgments
*is study was funded by the Major Science and
TechnologyInnovation Project of Shandong Province (Grant
no.2018YFJH0902).
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