Effects of different param-eters, such as pH value, initial arsenic concentration, adsorbent dosage, contact time and ionic strength, on the AsV adsorption were studied.. Adsorption, sur
Trang 1Sugarcane bagasse treated with hydrous ferric oxide as a potential adsorbent for the removal of As(V) from aqueous solutions
E Pehlivana,⇑,1, H.T Tranb, W.K.I Ouédraogoc, C Schmidtd, D Zachmannd, M Bahadird
a
Department of Chemical Engineering, Selcuk University, Campus, 42079 Konya, Turkey
b
Hanoi University of Science, Hanoi, Vietnam
c
Laboratoire de Chimie Organique: Structure et Réactivité, UFR-SEA, Université de Ouagadougou, 03 BP 7021 Ouagadougou 03, Burkina Faso
d
Institute of Environmental and Sustainable Chemistry, Technische Universitaet Braunschweig, Germany
a r t i c l e i n f o
Article history:
Received 16 January 2012
Received in revised form 1 September 2012
Accepted 24 September 2012
Available online 8 November 2012
Keywords:
Sugarcane bagasse
Adsorption
Arsenic
Iron oxide-based adsorbent
a b s t r a c t
The mechanism of As(V) removal from aqueous solutions by means of hydrated ferric oxide (HFO)-trea-ted sugarcane bagasse (SCB-HFO) (Saccharum officinarum L.) was investiga(HFO)-trea-ted Effects of different param-eters, such as pH value, initial arsenic concentration, adsorbent dosage, contact time and ionic strength,
on the As(V) adsorption were studied The adsorption capacity of SCB-HFO for As(V) was found to be 22.1 mg/g under optimum conditions of pH 4, contact time 3 h and temperature 22 °C Initial As(V) con-centration influenced the removal efficiency of SCB-HFO The desorption of As(V) from the adsorbent was 17% when using 30% HCl and 85% with 1 M NaOH solution FTIR analyses evidenced two potential binding sites associated with carboxyl and hydroxyl groups which are responsible for As(V) removal Adsorption, surface precipitation, ion exchange and complexation can be suggested as mechanisms for the As(V) removal from the solution phase onto the surface of SCB-HFO
Ó 2012 Elsevier Ltd All rights reserved
1 Introduction
Among various elemental species, arsenic is near the top of the
toxic list Arsenic enters water bodies through both natural erosion
processes and anthropogenic activities High levels of arsenic in
drinking water are a crucial problem in many countries, e.g
Mex-ico, Bangladesh, Vietnam, and Argentina (Farias et al., 2003; Fazal &
Kawaci, 2001)
Arsenic is released into the environment while using pesticides,
treating wood, producing glass and electronic devices,
manufactur-ing copper and other metals, as well as producmanufactur-ing fertilisers
Ar-senic ions occur in surface and ground waters in both organic
and inorganic species, the inorganic forms being the predominant
ones, e.g arsenite (H2AsO3and arsenate (H2AsO4) (Fazal &
Kaw-aci, 2001)
While arsenic is toxic to plants and animals, inorganic arsenic
species are strong carcinogens to humans (Ng, 2005) Usually,
ar-senic is taken up and accumulated in the human body through
drinking water, the food chain, and inhalation of polluted air The
human toxicity of arsenic ranges from skin lesions to cancer of
the brain, liver, kidney, and stomach Arsenic intake causes
distur-bance of nervous system functions and can lead to death (Boddu,
Abburib, Talbottc, Smitha, & Haasch, 2008) Because of these ef-fects, the World Health Organisation (WHO) and the United State Environmental Protection Agency (USEPA) reduced the arsenic standard concentration in drinking water from 50 to 10 mg/l ( Envi-ronmental Protect Agency, 1999) If this concentration is exceeded
in surface and ground waters in many countries, it is essential to develop effective methods for the removal of arsenic ions from the water supply
Arsenic removal, using low-cost adsorbents, such as lignocellu-losic materials and agricultural by-products has been under inves-tigation since the last decade Agricultural by-products are of particular interest since these materials are produced in great amounts and are easily available worldwide In Vietnam, sugarcane industries produce large amounts of SCB that could be applied for arsenic removal from water streams It was reported that the main components of SCB are cellulose (46.0%), hemicellulose (24.5%), lig-nin (19.95%), fat and waxes (3.5%), ash (2.4%), silica (2.0%), and oth-ers (1.7%) (Sene, Converti, Felipe, & Zilli, 2002) The polysaccharides found in sugarcane bagasse are biopolymers with many hydroxyl and/or phenolic groups that can be chemically modified to form new compounds with various properties (Navarro, Sump, Fujii, & Matsumura, 1996) The arsenic removal from water streams could
be achieved by using various techniques (Fe-electro-coagulation/ co-precipitation, coagulation–microfiltration, oxidation/precipita-tion, coagulation/precipitaoxidation/precipita-tion, reverse osmosis, filtraoxidation/precipita-tion, nano-filtration, ion-exchange) and different adsorbents (cellulose beads loaded with iron oxyhydroxide, iron-oxide coated sand, granular
0308-8146/$ - see front matter Ó 2012 Elsevier Ltd All rights reserved.
⇑ Corresponding author Tel.: +90 332 2232127; fax: +90 332 2410635.
E-mail address: erolpehlivan@gmail.com (E Pehlivan).
1 Present address: Department of Chemical Engineering, Selcuk University, Konya
42079, Turkey.
Contents lists available atSciVerse ScienceDirect
Food Chemistry
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / f o o d c h e m
Trang 2ferric hydroxide, activated carbon, fly ash, zeolites,
Calix[4]arene-grafted magnetite nanoparticles) have been used for the removal
of arsenic (Guo & Chen, 2005; Gupta, Basu, & De, 2007; Leupin &
Hug, 2005; Singh & Pant, 2004; Badruzzaman, Westerhoff, &
Knap-pe, 2004; Mondal, Balomajumder, & Mohanty, 2007; Sayin et al.,
2010) Some of these new techniques are rather expensive for
lim-ited size water treatment systems situated in rural residential
dis-tricts and they are in the developmental stages; consequently,
innovative cost-effective treatment processes are urgently needed
Adsorption is considered as an economical and effective
tech-nique for arsenic removal because of its lower cost, and availability
of suitable adsorbents and their regeneration Although the
adsorption capacity of agricultural by-products is usually less than
those of synthetic adsorbents, these materials could be an
inexpen-sive alternative for water treatment plants In order to enhance
their adsorption capacity, these materials are modified with
vari-ous organic compounds having different functional groups
The SCB contain biopolymers, mainly of polysaccharides with
hydroxyl, carboxyl and/or phenolic groups that can be chemically
modified to form new compounds with different properties With
this investigation, we aimed at combining the beneficial effects
of both the polysaccharides and iron oxyhydroxides, such as
SCB-HFO, to form a new adsorbent for the removal of As(V) ion from
aqueous solutions and compare their performance with other
adsorbents for the same purpose The influences of
physical–chem-ical key parameters, e.g pH, the initial concentration of arsenic, the
amount of adsorbent, contact time, the point of zero charge
(pHzpc) and ionic strength, were investigated in this study
2 Materials and methods
2.1 The preparation of sugarcane bagasse SCB
SCB, obtained from a suburb of Hanoi, Vietnam, was powdered
in a ball mill (BLB Braunschweig) and sieved in a sieving machine
(Retsch, West of Germany) The sample having the sieve fraction of
125–200lm was washed thoroughly with deionised water, and
dried in an aerated oven at 60 °C for 24 h The air-dried and
pow-dered SCB (50 g) was hydrolysed by using 1.15 M H2SO4(w/w of
dry material, at 80 °C for 30 min) for removing starch, proteins
and sugars Thereafter, the low molecular weight lignin
com-pounds were removed by stirring the solid for 24 h at room
tem-perature in 0.1 M NaOH solution (ratio SCB/sodium hydroxide is
5) After thorough washing, the adsorbent was dried in an oven
at 50 °C and stored in a desiccator prior to further experiments
2.2 The modification of SCB with ferric nitrate Fe(NO3)3to SCB-HFO
Ten grams of pretreated SCB were mixed for 48 h with 300 ml of
0.05 M ferric nitrate Fe(NO3)3in a 1 l beaker Aliquots of 1 M NaOH
were added dropwise into the beaker under continuous stirring,
keeping the pH between 2.8 and 3.5 After 48 h of the covering
pro-cess, the suspension was filtered and washed with de-ionised
water several times until neutral pH was obtained Coated
adsor-bent SCB-HFO was dried in an oven at 50 °C Furthermore, it was
stored at room temperature until used
2.3 Preparation of standards and reagents
Reagents used were purchased from Merck (Darmstadt,
Ger-many) and were of analytical grade MgSO47H2O (Fluka, Seelze,
Germany), Na3PO412H2O (Sigma–Aldrich, Seelze, Germany) and
NaNO3(Merck) were used for studying the effects of ionic strength
As(V) stock solution was purchased from Merck Iron Nitrate
(Fe(NO) ) was used for modification of the adsorbent All
glassware was cleaned with diluted nitric acid and rinsed with deionised water Standard acid (0.1 M HCl) and base (0.1 M NaOH) solutions were used for the pH adjustment of the solution The AAS standard solution of 1000 mg/l As(V) was prepared by transferring the contents of a Titrisol ampule with As2O5in H2O (Merck, Germany) into a 1 l volumetric flask, which was filled up
to the mark at 20 °C according the instructions by Merck The working solutions of different concentrations were prepared by diluting the stock solution immediately before starting the batch studies The As analyses were performed with a Hitachi Atomic Absorption Spectrophotometer (HG-AAS, Series Z-2000; Hitachi Corporation, Japan) which was connected to a hydride formation system (model HFS-3; Hitachi) For hydride generation, the follow-ing solutions were used: (i) 1.2 M HCl (p.a., Merck); (ii) NaBH4– NaOH-solution: solute 10 g NaBH4(p.a., Fluka) in 1 l of H2O (Seral-pure) by adding 4 g of NaOH (p.a., Merck); the solution was pre-pared immediately before use; (iii) KI-solution as a reduction agent; 20% (w/v; reduction to As(III)) All standards, reference solu-tions, and sample solutions were adjusted to 0.24 M HCl and 2% KI The reduction agent was added at least 30 min before analysis In general, a 5-point calibration was run before starting the analyses (0–20lg/l) For monitoring of a possible signal drift, reference solutions of 5 and 10lg/l were used As levels were measured every 5–7 samples For generation of hydride, HCl (1.2 M) and NaBH4-solution were pumped into the reaction chamber in the hy-dride formation system; sample and standard solutions were added The flow rates of HCl and NaBH4 were 8–10 ml/min for sample and standard 12 ml/min A 12 cm quartz cuvette was mounted above the standard burner flame zone that ran with air (0.5 MPa) and C2H2(1.2 l/min) Argon was used as carrier gas with
a flow rate of 0.3 l/min for constant transfer of As-hydride from the reaction cell to the cuvette The 193.7 nm emission line of the As-hollow-cathode lamp was used Due to the long transport dis-tances for reaction solutions and hydride gas, the absorption sig-nals should be followed thoroughly; with pre-integration times
of at least 120 s for rinsing memory effects and to yield a constant common analytical signal An integration time of 5 s is standard Under these conditions, the instrumental detection limit was 0.2lg/l As a reducing agent, 2 ml of 30% HCl and 2 ml of 20% (w/v) KI were added to 20 ml of the standard or sample As(V) solu-tion and left for about 15 min for conversion of As(V) to As(III) ions 2.4 Batch adsorption experiments
The defined amounts of SCB-HFO were added in 50 ml of aque-ous As(V) solutions of different concentrations and shaken, using a rotary shaker (Retsch, Germany), at 120 rpm for certain time inter-vals (15 min–24 h) Supernatant was filtered through a cellulose acetate filter (pore size 0.2lm) and analysed for As(V), using a HG-AAS The mass balance of As(V) adsorbed per mass unit of the SCB-HFO (mg/g) was calculated by the following (Eq (1)) ( Al-tun & Pehlivan, 2012):
where Ciand Ceare the initial and equilibrium As(V) concentrations
in mg/l, respectively V is volume of the As(V) solution in ml, and W
is the weight of adsorbent in mg
The effect of initial pH (2–10) on the As(V) uptake by SCB-HFO was studied by using 50 ml of 5 mg/l As(V) solution and 4 g/l of adsorbent dosage at 23 °C To study the effect of initial As(V) con-centration, 10, 20, 30, 50, 75, 100, 200 and 300 mg As/l, 4 g adsor-bent/l, pH 4, and a temperature 23 °C were applied The effects of contact time (15 min–24 h) and adsorbent amount (0.1–0.25 g) were studied with an initial As(V) concentration of 2 mg/l, pH 4 and temperature 23 °C
Trang 33 Results and discussion
3.1 FT-IR analysis
SCB is a cellulose matrix, which has different binding sites,
including carboxyl (–COOH) and hydroxyl (–OH) groups All
infra-red spectra of raw and treated materials were recorded using
an ATR technique at 4000–520 cm1and 32 scans with a BRUKER
FT-IR Tensor 27 The broad and strong band at 3343 cm1is due
to the hydroxyl group (–OH) and the absorption band at
2897 cm1due to the alkyl groups of the biomass Absorption at
1729 cm1was attributed to stretching vibration of the carboxyl
group The bands observed at 1034 cm1were assigned to C–O
stretching of alcohols and carboxylic acids (Fig 1a)
Fig 1bshows the SEM analysis of samples SCB and SCB-HFO
The surface charge of sorbent was characterised by measuring
the zeta potential for the treated adsorbent that indicates the
sur-face charge of a particle at a certain distance from the sursur-face of
shear plane For materials that undergo acid base reactions, the
surface charge depends on pH The sorption of the As(V) is
ex-pected to be favoured at a pH less than pHzpc (zpc: zero point
charge) of the adsorbents (Kamala et al., 2005) SCB-HFO has
iron-oxyhydroxide groups, which are positively charged at pH smaller
than 6 (Fig 2a) For that reason, the adsorption experiments were
performed at pH 4 The reactivity of HFO coated on SCB is similar to
iron oxide surface sites and the active form of this adsorbent is the
hydrolysed surface species „FeOH, which behaves like an
amphoteric site with a point of zero charge 5.8 (Fig 2a)
3.2 The influence of pH on As(V) sorption Solution pH normally has a large impact on adsorption perfor-mance (Arief, Trilestari, Sunarso, Indraswati, & Ismadji, 2008) The effect of pH on As(V) adsorption was investigated using different kinds of adsorbents and it produced similar results (Rahaman, Basu, & Islam, 2008) Fig 2b shows the relationships between
pH value and sorption yield of As(V) It was indicated that most
of the As(V) ions were bound to the adsorbent at an initial pH range of 2–4 Therefore, there is more adsorption under acidic conditions as well as in the near neutral region, i.e at pH 2–6; even more than 30% sorption is still observed up to pH 10 The sorption yield reached a maximum value of 98% at pH 4 for As(V) ions
Many investigations were conducted on the adsorption of solu-ble arsenic species from adsorbent surfaces The electrostatic force
is one important factor in the adsorption mechanisms In the aque-ous solution, the As(V) species predominate as a single negatively charged anion (H2AsO4) at pH 3–6 and a double negatively charged form (HAsO42) at pH up to 11, which can be adsorbed
on the SCB-HFO by substituting hydroxyl In natural waters, the electrostatic force between the negatively charged As(V) species and the usually positively charged iron oxyhydroxide surface is much stronger, resulting in a better adsorption of As(V) If the arsenic concentration decreases, the electrostatic force for the sorption is not strong enough to remove arsenic for meeting the acceptable limit values in drinking water (Vaclavikova, Matik, Jakabsky, & Hredzak, 2005)
Fig 1a FT-IR spectrum of raw SCB (black) and SCB-HFO (red) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Trang 4Another possible reaction mechanism assumes that hydroxyl
groups coordinate with As(V) ions (Boddu et al., 2008) At elevated
pH, As(V) sorption was decreased due to the competition of the
OH-groups bound to the matrix surface with the free hydroxyl
ions Under alkaline conditions, the surface of SCB-HFO will
be-come negatively charged, causing a repulsive force versus the
anio-nic species of As(V), resulting in a decreasing sorption efficiency
(Rahaman et al., 2008) The formation of surface complexes
be-tween positively charged surface groups „FeOH2 and negatively
charged As(V) ions can be described according to the following
equilibrium (2 and 3) (Sherman & Randall, 2003):
2 FeOHþ
2þ H2AsO
4 ¡½ð FeOÞ2 AsOðOHÞþ H3Oþ
þ H2O ð2Þ
FeOHþ2þ H2AsO4 ¡½ Fe ðOÞ2 AsOðOHÞþ H3Oþ ð3Þ
In this situation, arsenate adsorption on the adsorbent can
oc-cur through non-specific coulombic interactions (outer-sphere
adsorption) and formation of monodentate (2) and bidentate (3)
surface complexes In another case, ligand exchange on the surface
(inner-sphere adsorption) might happen during the following
equilibrium (4 and 5) (Jeon, Baek, Park, Oh, & Lee, 2009):
FeOHþ2þ H2AsO
4¡ Fe O AsO3H2þ H2O ð4Þ
2 FeOH þ H2AsO2¡ Fe2 O2AsO2H þ 2OH ð5Þ
Different situations in the adsorption of As(III) and As(V) can be expressed by their respective speciations in aqueous medium As(III) is present as an anion above pH 9 (and the experimental data between pH 3 and 8); it is thus reasonable to accept that the neutral form, H3AsO3, interacts with the adsorbent (Dupont, Jolly, & Aplincourt, 2007) When pH increases from 4 to 10, the As(V) biosorption decreased because of the decrease of electro-static interactions between the positively charged surface groups („FeOH2) and the anionic As(V) species which prevents the for-mation of surface complexes (Dupont et al., 2007) Physical forces, e.g van der Waals and London forces, might slightly overlap the adsorption processes
3.3 The determination of Fe(III) amount loaded onto SCB The amount of Fe(III) (in hydrated ferric oxide) loaded onto SCB was determined after acid digestion In order to avoid uncontrolled reactions, 0.1 g of SCB-HFO was kept for 24 h at room temperature
in aquatic conditions The digestion was completed by raising the temperature to 90 °C until the sample became dry; 10 ml of 1 M HCl were added to the solution, and stirred several times After
12 h, 2 ml of digested solution were drawn off and diluted to
10 ml The concentration of Fe(III) in the solution was analysed
by GF-AAS
3.4 Adsorption isotherm models Two well established equilibrium models, after Langmuir and Freundlich, were applied for the adsorption study The Freundlich model assumes a heterogeneous sorbent surface and different binding energies for the active sites (Altun & Pehlivan, 2007) The Langmuir isotherm is frequently used for the adsorption of metal ions from aqueous solutions (Langmuir, 1918)
The general form of the Langmuir model is given below (4):Langmuir equation
Ce
qe¼
Ce
As
þ 1
AsKb
ð4Þ where As(mol g1) and Kb (l mol1) are the coefficients, qeis the weight of adsorbate which was adsorbed per unit mass of adsor-bent, and Ceis the analyte concentration in aqueous phase at equi-librium.Freundlich equation:
ðx
mÞ ¼ kC
1=n
where 1/n is the adsorption intensity, k is the adsorption yield, x/m
is the mass of adsorbate adsorbed per unit mass of adsorbent and Ce
is the element concentration at equilibrium in the aqueous phase The modified formula of this equation was obtained as follows (Eq (6)):
log x m
¼ log k þ1
Table 1shows that the values of Kfand n were 1.55 106and 0.18 for As(V) adsorption However, R2was calculated for Freund-lich as 0.79, that is much lower than 0.99 for the Langmuir iso-therm It was shown that the Langmuir model described the adsorption of the As(V) onto SCB-HFO better than did the Freund-lich model It could be concluded that the Langmuir isotherm
mod-el better fits the equilibrium data
Fig 3a shows that the non-linear relationship between the amount of As(V) ion adsorbed on SCB-HFO depends on the arsenic concentration The maximum sorption capacity (As) of adsorbent was found to be 22.1 mg/g for As(V) The Kbvalue was found to
be 0.45 for As(V) sorption
Fig 2a The pH point zero of charge (pHpzc) of SCB-HFO.
As(V)
0
20
40
60
80
100
120
pH
Fig 2b Sorption of As(V) on SCB-HFO as a function of pH (50 ppm As(V) in 50 ml of
solution at different pH values; temperature 22 ± 2 °C).
Trang 5Iron compounds are reported to be effective for the removal of
As(V) ions Several Fe(III) oxides/oxyhydroxides, e.g amorphous
hydrous ferric oxide HFO (FeOOH), poorly crystalline hydrous
fer-ric oxide–ferrihydride (Wilkie & Hering, 1996), goethite (a-FeOOH)
and akaganeite (b-FeOOH), were investigated for removing As(V)
from aqueous solutions Other sorbents, based on iron
oxides/oxy-hydroxides, e.g iron oxide-coated polymeric minerals (
Katsoyian-nis & Zouboulis, 2002), iron-hydroxide-coated alumina (Hlavay &
Polyak, 2005), and natural iron ores (Zhang, Singh, Paling, &
De-lides, 2004) were also investigated A comparison of the removal
capacities, for As(V), of different sorbents materials is given in
Ta-ble 2showing that the SCB-HFO presented in this study had a
med-ium sorption capacity compared with others
3.5 The effect of adsorbent dose on sorption of As(V) by SCB-HFO
The effect of adsorbent amount on As(V) sorption was studied
with the initial As(V) ion concentration of 50 ppm at 22 ± 2 °C
and pH 4 The amount of SCB-HFO changed from 0.1–0.25 g It
was indicated that the equilibrium concentration in the dissolved
phase decreased when increasing the amount of adsorbent (Fig 3b) The optimum amount of SCB-HFO was found to be 0.25 g/50 ml of As(V) solution When the dosage was increased, the number of surface sites in the structure of the adsorbent lattice increased This shows that the main factors governing the adsorp-tion of arsenic species are the electrostatic interacadsorp-tion between ironoxyhydroxide sites of the adsorbent and the anionic arsenic species Hence, facilitating the binding of arsenate resulted from both electrostatic interactions and hydrogen bonding
3.6 Desorption efficiency The desorption of the adsorbed As(V) from SCB-HFO was stud-ied by eluting with 30% HCl and 1 M NaOH (each 20 ml) The re-sults were given in Table 3 The desorption of As(V), using 30% HCl, was 17%, whereas the highest recovery of 85% was reached with 1 M NaOH pH of the solution phase was adjusted by adding HCl and NaOH solutions The results showed that the adsorbent can be successfully reused upon treatment with 0.1 M NaOH solu-tion, which may be referred to the displacement of As(V) bound to the adsorbent with OHions
Table 1
Langmuir and Freundlich isotherm constants.
Langmuir isotherm parameters Freundlich isotherm parameters
A s (mg/g) K b R 2
K f (mg/g) n R 2
22.1 0.45 0.99 1.55 10 6
0.18 0.79
0
5
10
15
20
25
As(V) concentration (ppm)
Fig 3a Sorption isotherm of As(V) on SC-HFO as a function of initial As (V)
concentration (10–300 ppm As(V); 50 ml; 0.2 g adsorbent; pH 4; 22 ± 2 °C; contact
time 3 h).
Table 2
Arsenic removal capacities of different sorbents.
Adsorbent Q max (mmol g 1
) pH References Akaganeite 1.79 7.5 Deliyanni, Bakoyannakis, Zouboulis, and Matis (2003)
Akaganeite 0.93 3.5 Vaclavikova et al (2005)
Goethite 0.330 5.0 (Matis, Lehmann, & Zouboulis, 1999)
Hydrous ferric oxide HFO 1.340 4.0 Wilkie and Hering (1996)
Fe(III) loaded resin 0.800 1.7 (Rau, Gonzalo, & Valiente, 2003)
Fe-hydroxide coated alumina 0.210 6.6–7.2 Hlavay and Polyak (2005)
Coconut-shell carbon 0.430 5.0 Lorenzen, van Deventer, & Landi (1995)
Peat-based carbon 0.070 5.0 Lorenzen, van Deventer, & Landi (1995)
Magnetite 0.350 6.5 Javier, Maria, de Joan, Miquel, and Lara (2007)
0 2 4 6 8 10 12 14
Adsorbent amount (g)
Fig 3b Sorption of As(V) on SCB-HFO as a function of adsorbent amount (50 ppm As(V) in 50 ml of solution at pH 4; adsorbent amount 0.1–0.25 g; temperature
22 ± 2 °C.
Table 3 The relationship of desorption and pH values.
Leaching agent pH Desorption (%)
Trang 63.7 The effects of the ionic strength (competing anions) on As(V)
removal
The ionic strength of the solution might compete with the As(V)
removal, in particular in the case of other co-occurring multiple
charged anions Therefore, the removal of 50 ppm As(V) in 50 ml,
through 0.2 g of SCB-HFO, was investigated in parallel in the
pres-ence and abspres-ence of PO43(50 ppm), NO3(50 ppm), and SO42
(250 ppm) The pH of the solutions was adjusted to 4.0 and the
samples were agitated for 3 h at 200 rpm The results confirmed
that As(V) removal was suppressed by PO43ions The adsorption
capacity for As(V) was decreased by 6.5%, but the other anions
did not affect the adsorption process
4 Conclusion
The occurrence of arsenic in water is of major concern in many
countries The threshold values of arsenic in drinking water have
been set by public authorities, worldwide, at 10lg l1 In this
study, a novel adsorbent from sugarcane bagasse, as a low-cost
agro-waste, was developed, through treatment with
iron(III)oxy-hydroxide (SCB-HFO), that seems to have promising properties
for the removal of As(V) from aqueous solutions
The main factors determining the adsorption of As(V) on this
sorbent are electrostatic interactions, ligand exchange, and
chela-tion between positively charged surface groups „FeOH2 and
neg-atively charged As(V) ions The adsorption capacity of SCB-HFO
was found to be 22.1 mg/g for As(V) under optimum conditions
of 3 h agitation at pH 4, and 22 °C As(V) ions could be desorbed
successfully from SCB-HFO by using 1 M NaOH and the absorbent
was thus regenerated Among typical anions in surface waters, only
phosphate (50 ppm) suppressed As(V) removal by the adsorbent
whereas nitrate and sulfate did not affect the sorption process
The presented findings suggest that SCB-HFO is an inexpensive
adsorbent for As(V) removal from aqueous solutions
Acknowledgements
This investigation was performed at the Guest Chair within the
project ‘‘Exceed-Excellence Center for Development
Cooperation-Sustainable Water Management in Developing Countries’’ at the
Technische Universitaet Braunschweig, Prof Pehlivan being the
visiting professor, and Ms Tran and Mr Ouédraogo are the
interna-tional exchange staff members The Exceed Project is granted by
the German Federal Ministry for Economic Cooperation and
Devel-opment (BMZ) and German Academic Exchange Service (DAAD);
their financial support is gratefully acknowledged
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