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The present investigation entails the biosorption studies of radiotoxic Strontium (90Sr), from aqueous medium employing dry cow dung powder (DCP) as an indigenous, inexpensive and, eco-friendly material without any pre or post treatments. The Batch experiments were conducted employing 90Sr(II) as a tracer and the effect of various process parameters such as optimum pH, temperature, amount of resin, time of equilibration, agitation speed and concentration of metal ions have been studied. The kinetic studies were carried out employing various models but the best fitting model was Lagergren pseudo-second order model with high correlation coefficient R 2 value of 0.999 and cation exchange capacity of DCP was found to be 9.00 mg/g. The thermodynamic parameters for biosorption were evaluated as ΔG° = −5.560 kJ/mol, ΔH° = −6.396 kJ/mol and ΔS° = 22.889 J/mol K, which indicated spontaneous and exothermic process with high affinity of Sr(II) for DCP.
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Biosorption of radiotoxic
90
Sr by green adsorbent: dry cow
dung powder
Nisha Suresh Barot Hemlata Kapil Bagla
Received: 29 October 2011 / Published online: 20 November 2011
!Akade
´miai Kiado
´, Budapest, Hungary 2011
Abstract The present investigation entails the biosorp-
tion studies of radiotoxic Strontium (
90
Sr), from aqueous
medium employing dry cow dung powder (DCP) as an
indigenous, inexpensive and, eco-friendly material without
any pre or post treatments. The Batch experiments were
conducted employing
90
Sr(II) as a tracer and the effect of
various process parameters such as optimum pH, temper-
ature, amount of resin, time of equilibration, agitation
speed and concentration of metal ions have been studied.
The kinetic studies were carried out employing various
models but the best fitting model was Lagergren pseudo-
second order model with high correlation coefficient R
2
value of 0.999 and cation exchange capacity of DCP was
found to be 9.00 mg/g. The thermodynamic parameters for
biosorption were evaluated as DG"=-5.560 kJ/mol,
DH"=-6.396 kJ/mol and DS"=22.889 J/mol K, which
indicated spontaneous and exothermic process with high
affinity of Sr(II) for DCP.
Keywords Biosorption !Radiotoxic strontium !
Dry cow dung powder !Green adsorbent
Introduction
In the domain of toxic radionuclide persisting in our envi-
ronment,
90
Sr is considered as one of the most hazardous
fission product due to its long physical half-life of 29 years
[1] and its inevitable presence in the water, soil and food
chain. The anthropogenic activities such as nuclear weapon
testing, reprocessing of liquid spent fuel, etc. are major
source of
90
Sr in our environment. Strontium is referred as a
bone seeker as it imitates the calcium in the human body
and increases the risk of bone cancer, leukemia, etc. [2]. On
the contrary, if managed scientifically, it has also been
proved to be aiding to mankind.
90
Sr has been used as a
power source for radioisotope thermoelectric generators
(RTGs), as well as used in cancer therapy and in forensic
sciences [3]. Hence, there is a great necessity to adapt a
methodology which can be employed for the eco-friendly
removal of
90
Sr from the aqueous system with a view of
reprocessing the same and to reap out its aforementioned
benefits.
In the field of radionuclide research, some of the well
established processes such as chemical precipitation, mem-
brane process, liquid extraction, and ion exchange [4,5] have
been applied as a tool for the removal of this metal ion. These
all methods are not considered to be greener due to some of
their shortcomings such as incomplete metal ion removal,
high requirement of energy and reagents, generation of toxic
sludge or other waste materials which in turn require treat-
ments for their cautious disposal. Eventually, it adds on to the
cost, time and feasibility of the entire procedure.
The greener and cleaner approach of biosorption is a
sure solution to this situation. Biosorption phenomenon is
acquiring strong footage due to its mechanism based on
non-directed physico-chemical interactions that occur
between metal species and dead biomass. Biosorption deals
with both living biomass as well as non-living aggregates
of biomaterial. But biosorption by dead biomass is often
faster [6], since only passive cell wall based binding
transport, into the cell takes place.
N. S. Barot !H. K. Bagla (&)
Department of Nuclear & Radiochemistry, Kishinchand
Chellaram College, 124 D. W. Road, Churchgate, Mumbai,
Maharashtra, India
e-mail: hemabagla@gmail.com
N. S. Barot
e-mail: barot_nisha@hotmail.com
123
J Radioanal Nucl Chem (2012) 294:81–86
DOI 10.1007/s10967-011-1539-3
Author's personal copy
Literature survey reveals that in the domain of natural
adsorbent, materials such as Rhytidiadelphus squarrous
[7], magnetically modified yeast cells [8], Azolla filiculo-
ides [9], brucite [10], clay minerals [11], Oscillatoria
homogenea cynobacterium [12], Cystoseira indica brown
alga [13], seeds of Ocimum basilicum [14], Pakistani coal
[15], etc. have been utilized for Sr(II) removal. These
naturally available materials require some degree of
physical and chemical enhancement so as to optimize,
which add on to the economy of entire adsorption process.
The HA has been successfully extracted by authors from
DCP and this piece of work has been published in the
International Journal [16]. Also, biosorption with living
media leads to biological and chemical sludge due to
growing biomass and nutrients. Hence, for the efficient
biosorption method, economy of environmental remedia-
tion dictates that the biomass must come from nature or
even has to be a waste material.
Materials and methods
Adsorbent
DCP (100 mesh) was provided by Keshav Shrushti,
Research Centre on Cow product (Thane, India) and due
precautions were taken to avoid the contaminations. DCP is
naturally available bio-organic, complex, polymorphic
fecal matter. It is enriched with minerals, carbohydrates,
fats, proteins, bile pigments, aliphatic–aromatic species
such as ‘humic acid’ and many functional groups such as
carboxyl, phenols, quinols, amide, etc. which enhances its
adsorption properties.
Characterization of DCP
Cow dung powder was dried properly before its utilization,
so as to prevent its oxidation by acid due to presence of
mixture of alcohols if any. The absence of alcohol is also
supported by FTIR analysis of DCP, which is devoid of any
characteristic band of alcohol. The integrity of DCP before
and after the adsorption was studied by measuring the mesh
size and was found to be same; indicating during adsorp-
tion process there was no physical attrition of resin. All the
characterization techniques have been carried out at Indian
Institute of Technology, IIT, Powai, Mumbai. The DCP has
been characterized using XRF technique for its quantitative
as well as qualitative elemental composition and for the
complete elemental assay, complimentary to XRF tech-
nique, C, H, N, S, O technique, has also been obtained as
detailed in Table 1.
The SEM pattern of DCP clearly reveals the surface
texture and porosity of the DCP. The porous morphology
of DCP is responsible for the easier diffusion during
adsorption process. For the confirmation of biosorption
process EDAX (Energy dispersive X-ray analysis) spec-
trum of DCP, after and before the adsorption of Sr(II) have
been studied. The EDAX spectrum of DCP before and after
biosorption of Sr(II) (Fig. 1a, b), indicated that Si, K, Ca,
Ti, Mn, Fe, Zn are naive metal ion of the matrix and after
biosorption of Sr(II) on DCP, Sr(II) was present along with
all other natural elements indicating that ion exchange is
not the mechanism for Sr(II) adsorption on DCP.
Adsorbate
All the chemicals used were of analytical grade. The stock
solution of Sr(II) 1 mg/mL was prepared using SrCl
2
and
distilled water. All the solutions were standardized by
standard analytical methods [17].
Tracer technique
It is the radio analytical technique in which micro amount
of radioactive isotope is added to a system in order to trace
or monitor [18] the chemical reaction of a certain element
in the system. In comparison to classical approach, tracer
technique offers some unique advantage such as, high
sensitivity, non-destructive pattern, freedom from reagent
blank, etc. The Radiotracer
90
Sr(II) (beta-emitter) was
procured from BRIT (Board of Radiation and Isotope
Technology, Mumbai, India).
Table 1 XRF data of DCP
S.No. Elements % Occurrence
1 Na 0.946
2 Mg 2.853
3 Al 1.684
4 Si 22.691
5 P 3.883
6 K 3.343
7 Ca 2.360
8 Ti 0.329
9 Mn 0.115
10 Fe 2.419
11 Cl 1.560
12 Cr 0.014
13 N 1.086
14 H 1.800
15 S 1.202
16 C 13.087
17 O 13.018
82 N. S. Barot, H. K. Bagla
123
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Batch equilibration mode
A known amount of DCP was mixed with 10 mL of solution
containing radiotracer and 1 mg/mL solution of carrier. The
pH was adjusted using dil. HCl and NaHCO
3
as per the
requirement. The resultant aliquot was equilibrated for
10 min with mechanical stirrer and was then centrifuged.
After separating supernatant, adsorbent was washed with
5 mL of distilled water and activity present in supernatant
was measured using end window type Geiger–Muller
Counter (PEA GCS 101P) in conjugation with a decade
scalar, timer and a high voltage unit, for the beta-emitter.
The effect of different experimental parameters such as
pH (from 1 to 10), metal ion concentration (0.5–20 mg/mL),
contact time (0–30 min), agitation speed (0–5,000 rpm),
amount ofadsorbent (50–650 mg), temperature (283–363 K),
have been studied so as to optimize the parameters for
developing efficient adsorption process. The kinetic and
thermodynamic studies have also been carried out so as to
optimize the system under study for the removal of
Sr(II) ions from aqueous medium. All experimental data
were measured in triplicate and percentage sorption was
calculated using formula given below:
%Adsorption ¼AiðÞ%AðfÞ
AiðÞ &100
where A(i) =activity taken, A(f) =total activity in
supernatant.
Results and discussion
All the aforementioned parameters were comprehensively
studied for the optimization of the system. The results
revealed that having 10 min of contact time, at 4,000 rpm
of agitation speed, at the optimum pH of 6, 350 mg of DCP
can effectively remove Sr(II) up to 85–90%.
Effect of pH
DCP being heterogeneous adsorbent possess positively
charged site owing to some proteins, enzymes and negatively
charged sites due to presence of some acidic groups. Hence,
on varying the pH of a solution, the overall surface charge of
DCP could be modified so as to get maximum adsorption.
The adsorptive behavior of Sr(II) ions on DCP might be
explained on the basis of electrostatic force of attraction
between the oppositely charged adsorbate and adsorbent. On
varying the pH from 1 to 10 as shown in Fig. 2, it was
observed that, the optimum pH for maximum adsorption of
Sr(II) on DCP was at pH 6. At low pH, adsorption became
unfavorable due to electrostatic repulsion between the posi-
tive charged surface, in excess of H
?
ions, and Sr(II) ions,
resulting in the decrease in the adsorption. The neutral range
of pH favored the adsorption of Sr(II) ions on the DCP which
was indicative from the figure.
On further increase in pH, the adsorption was found to
decrease, which may be due to preference of Sr(II) ions to
form a stable complex of SrCO
3
then to get adsorbed on
DCP surface. It was observed that the maximum sorption
of Sr(II)on DCP was obtained at pH 6.
Effect of amount of adsorbent
Adsorption being surface phenomenon, the extent of
adsorption is directly proportional to the surface area
Ti Zn
Mn
Fe
Ti
Ti Mn
Fe
Zn
Ca ZnSi
Mn
Fe
0 2 4 6 8 10 12 14 16 18 20 22
keV
Full Scal e 21521 cts Curs o r : 8.081 (5970 cts)
PA - 2
0 2 4 6 8 10 12 14 16 18 20 22
keV
Full Scal e 21693 cts Curs o r : 2.768 (11808 cts)
DCP-6_ PA - 1
A
B
Fig. 1 EDAX spectrum before (a) and after biosorption (b)
Fig. 2 Effect of pH on adsorption (contact time =10 min; amount
of resin =350 mg; metal ion concentration =1 mg/mL; agitation
speed =4,000 rpm at room temperature)
Biosorption of radiotoxic
90
Sr by green adsorbent 83
123
Author's personal copy
available. Increasing the adsorbent amount, increase in
adsorption percentage was observed. After certain dose of
adsorbent, maximum adsorption sets in after which the
percentage adsorption was almost constant. This suggests
that after optimum dose, number of ions bound to adsorbent
and the number of free ions remained constant even with
further addition of the adsorbent. It may be due to partial
aggregation of active adsorbent sites [19]. Our results sug-
gest that optimum amount of DCP for Sr(II) was 350 mg.
Effect of contact time
To optimize contact time for the experiment, keeping all
other parameters constant, contact time was varied from 0
to 30 min. The results reveals that as contact time
increased, percentage adsorption also increased, but after
some time, it gradually approached a constant value,
denoting attainment of equilibrium. Further increase in
contact time, did not increase adsorption due to desorption
of ions on the available adsorption sites of adsorbent.
Effect of metal ion concentration
Metal ion concentration was varied from 0.5 to 20 mg. As
shown in Fig. 3, percentage adsorption decreased with
increase in metal ion concentration. In case of low metal ion
concentration, the ratio of number of moles of metal ions to
the available surface area of adsorbent was lower and sub-
sequently the fractional adsorption becomes independent of
metal ion concentration [20]. On increasing the concentra-
tion of Sr(II) ions, the metal ion concentration becomes
higher than that of the sorbent binding sites, resulting in
decreased sorption percentage. This study reveals that
350 mg of DCP can absorb 20 mg/mL of Sr(II) up to 50%.
Also, on increasing the amount of DCP, the removal of Sr(II)
can be increased even at higher metal ion concentration.
Effect of temperature
In the process of biosorption, temperature plays a vital role
and these processes are normally exothermic. Hence, the
extent of adsorption generally increases with decrease in
temperature. For this purpose the temperature was varied
between 283 and 363 K. Our results reveal that the
adsorption of metal ions increases at lower temperature and
were found to be maximum at the room temperature range.
On further increasing the temperature, percentage adsorp-
tion was decreased and it may be due to desorption caused
by an increase in the available thermal energy. Also, higher
temperature induces mobility of adsorbate, eventually
causing desorption, due to weakening of adsorptive forces
between the active sites of adsorbent and adsorbate species
and also between the adjacent molecules of the adsorbed
phase [21]. Hence, the temperature ranges, i.e. 293–303 K
favors the adsorption rate of the system under study.
Effect of agitation speed
This experiment proved that speed of agitation has
important role in the process of biosorption. All agitation
speeds were found to have a positive impact on the system.
Increasing the speed at rate of 500 rpm, percentage
adsorption showed markedly high values. This is because
agitation facilitates proper contact between the metal ions
in solution [22] and the binding sites and thereby promotes
effective transfer of adsorbate ions to the adsorbent sites.
The agitation speed of 4,000 rpm was standardized.
Thermodynamic parameters
Thermodynamic considerations are necessary to conclude
whether the process is spontaneous or not. The Gibb’s free
energy change, DG"is an indication of spontaneity of
chemical reactions. The free energy of biosorption reaction
can also be evaluated by considering the biosorption
equilibrium constant K
a
which is given by the following
equation:
DG'¼%RT ln Kað1Þ
Where, DG"is the standard free energy change (J), Ris
the universal gas constant =8.314 J/mol K, and Tis
absolute temperature (K). The free energy change for the
temperature range of 293–308 K using Eq. 1has been
evaluated and has obtained the negative values of DG"for
the entire range as shown in Table 2. Any reaction if
occurs spontaneously at a given temperature, its DG"is
always a negative quantity. The negative value also
confirms the feasibility and the spontaneous nature of
biosorption process of Sr(II) on DCP with DG
308
"=
-5.560 kJ/mol.
A plot of ln K
a
, versus temperature 1/T 910
3
, was
found to be linear, Fig. 4. The values of DH"and DS"were
determined from the slope and intercept of the plot. The
enthalpy change DH", and the entropy change DS", for the
Fig. 3 Effect of metal ion concentration on adsorption (pH =6;
contact time =10 min; amount of resin =350 mg; agitation speed =
4,000 rpm at room temperature)
84 N. S. Barot, H. K. Bagla
123
Author's personal copy
biosorption process were deduced from the graph to be
-6.396 kJ/mol and 22.889 J/mol K, respectively. The
negative value of enthalpy suggests the exothermic reac-
tion. The positive value of entropy change suggest the
increase in the randomness at the solid/liquid interface
reflecting affinity of DCP for the Sr(II) ions.
Kinetic parameter
The kinetic adsorption data could be processed to under-
stand the dynamics of the biosorption reaction in terms of
the order of the rate constant. The different kinetic models
such as first order, second order, pseudo-first order, pseudo-
second order and the intraparticle diffusion have been
studied. But among these models, best fitting model was
Lagergren pseudo-second order model. The correlation
coefficients have R
2
values close to one as shown in
Table 3, indicating the applicability of pseudo-second
order model to the present system. The kinetic data was
treated with the Lagergren pseudo-second order kinetic
model [23]. It is generally expressed as follows:
dqt
dt ¼k2qe%qt
!"
2ð1Þ
where q
e
and q
t
is adsorption capacity at equilibrium and at
time t, respectively (mg/g) and k
2
is the second order rate
constant of adsorption (g/mg min). Integrating Eq. (1) for
the boundary conditions q=0 to q=q
t
at t=0 to t=tis
to obtain the following equation:
t
qt
#$
¼1
k2q2
e
#$
þ1
qe
#$
tð2Þ
The plot of t/q
t
versus tshould show a linear relationship
if the second order kinetics is applicable and same is
evident from the graph. The equilibrium rate constant, k
2
and equilibrium capacity or adsorption capacity or cation
exchanged capacity, q
e
were determined from the slope and
intercept of the line in Fig. 5. The applicability of this
model suggested that biosorption of elements under study,
on DCP was based on chemical reaction, between metals
and active sites of the biosorbent.
Conclusions
A simple and eco-friendly method for the utilization of DCP
as an effective green adsorbent material for the removal of
radiotoxic
90
Sr from aqueous medium has been developed.
Being naturally and easily available, DCP can be employed
without any pre or post treatment. Hence, it has an edge over
other processed natural and synthetic adsorbent considering
their production cost, time, and energy efficiency.
Acknowledgments We thank Gemmological Institute of India,
Mumbai, for providing EDAX facility. We are also thankful to Dr.
Raju Apte, Head of Gaushala, Keshav Shrushti, Thane, for providing
DCP.
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An ideal adsorbent must be relatively cheap, abundant, easily undergo modification, and exhibit better removal efficiency. Animal wastes are much better adsorbents in comparison with activated carbon adsorbents with respect to being cost-effective and their zero regeneration process factor. The review aims to report the efficiency of utilized cow-dung based adsorbents for the sequestration of a wide spectrum of pollutants from aqueous media. It discusses the potential of utilizing cow dung as a cheap and effective adsorbent. It was observed that cow dung-based adsorbents were efficient for the removal of dyes, heavy metals, and other pollutants from aqueous solutions. The maximum reported uptake capacity of dyes and heavy metals was 501 mg/g and 625.26 mg/g for Methylene blue and lead, respectively, which were both for cow dung activated carbon. The Langmuir and Freundlich isotherm models emerged as the best-fit models for almost all studies. Based on the review outcome, a pseudo-second-order model was reported as the kinetic model of best fit in all cases. Other adsorption studies such as adsorption mechanism, thermodynamic modelling, desorption, column adsorption, and competitive adsorption were also included in this study. Finally, the study identified some knowledge gaps that could aid future investigation in this research field. Summarily, it can be deduced that cow dung-based adsorbent has exhibited good potential as an adsorbent for the mitigation of pollutants from water.
... Testing of Nuclear weapon testing and liquid spent reprocessing fuel like human activities are major source of its pollution. Its toxicity increases the risk of fatal diseases like blood cancer (Barot and Bagla 2012). Cowdung powder have diverse characteristics that act as site with positive charge to enzymes that result in biosorption of 90Sr from any aqueous medium (Barot and Bagla 2012). ...
... Its toxicity increases the risk of fatal diseases like blood cancer (Barot and Bagla 2012). Cowdung powder have diverse characteristics that act as site with positive charge to enzymes that result in biosorption of 90Sr from any aqueous medium (Barot and Bagla 2012). ...
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In the present review, farmyard manure is explained as a perfect source of nutrients for plant growth as well as for soil microbiota. It is one of the efficient and effective organic manures. It can provide organic matter to soil microbes as a source of carbon. An increase in microbial population leads to the degradation of pesticides and heavy metals to less harmful compounds. In addition to it, ions of harmful elements get adsorb on organic colloids and become immobile in soil. Application of farmyard manure not only increases the availability of nutrients in the soil but also improves the soil properties like soil structure, water holding capacity, bulk density, cation exchange capacity, etc. Studies revealed that farmyard manure is an excellent organic manure for sustaining good soil health along with achieving desired food production.
... Literature survey reveals that Sr(II) and its radioactive counterparts like 90 Sr and 85 Sr have been separated from aqueous solutions by employing water imbibed seeds of Ocimum basilicum [8], chemically modified biosorbents derived from Azolla filiculoides [9], immobilized moss [10], lichen like Hypogymnia physodes [11], modified eggshell waste [12], saponified orange juice residue [6], roots of Taraxacum officinale [13] and dry cowdung powder [14]. A diverse range of microbial cultures including Scenedesmus spinosus [15], Aspergillus terreus [16], Saccharomyces cerevisiae [17], Oscillatoria homogenea cyanobacterium [18], among several others [19][20][21] have also been employed for the biosorption of Sr(II). ...
... Most of these sorbents require extensive pre-treatment processes and longer durations of reaction time, some require living microbial flora for uptake of metal ions, which adds on to the sludge produced, questioning the green nature of the process. From the aforementioned biosorbents, dry cowdung powder (DCP) [14] is a notch over the others as it is a humified biological waste matter, not requiring any pre-treatment. Its notable high affinity for Sr(II) is intriguing, thus the present investigation attempts to explore the potentiality of humic acid, a prime component of DCP, for the uptake of Sr(II). ...
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Uptake of Sr(II) from simulated low level radioactive waste, employing radiotracer ⁸⁵⁺⁸⁹Sr, has been carried out with humic acid by a batch equilibration biosorption study. The process exhibited rapid kinetics and at optimized parameters, Sr(II) was biosorbed from simulated reactor and reprocessing waste by 84 ± 2% and 75 ± 2% respectively. Kinetic modelling revealed that the process follows Ho and McKay’s linear pseudo second order kinetics, indicating chemisorption mechanism of binding. Thermodynamic studies ascertain the exothermic, spontaneous and feasible nature of the process. This work proved the viability of humic acid for Sr(II) removal as an eco-friendly, cost effective alternative to conventional techniques.
... mm). (Marešová et al., 2011), fungus Aspergillus terreus (Khani et al., 2012), dry cow dung powder (Barot and Bagla, 2012), fruit kernels (Pap et al., 2017;Turk Sekulić et al., 2018), carb carapace (Lu et al., 2007;Rae et al., 2009), fishbone (Park et al., 2013) and alginate beads (Gok et al., 2013). However, despite the extensive literature on metal biosorption, little information is available for Sr 2+ removal from aqueous media. ...
... Fig. 9. Sr 2+ outlet concentrations of (a) crab carapace, (b) Kurion-TS-G™ and (c) and SrTREAT® in biosorption columns (initial concentration: 1.4 mg/L; no pH adjustment; dose of sorbent: 10 g; flow rate: 2.8 mL/min; temperature: 20 ± 2°C). Aqueous solutions with a radioactive tracer Dry cow dung powder 9.0 mg/g pH: 6; biosorbent dose: 350 mg; time: 10 min; C 0 : 20 mg/L; rpm: 4000; T: 22°C (Barot and Bagla, 2012) Aqueous solutions from high level natural radiation area γ-Ray irradiated baker's yeast 33.0 mg/g pH: 4.5; biosorbent dose: 4 g/L; time: 1440 min; C 0 : 400 mg/L; rpm: 120; T: 30°C (Dai et al., 2014) Aqueous solutions Orange juice residues 833.4 mmol/kg. pH: 5.6; biosorbent dose: 10 mg; time: 24 h; C 0 : 5 mmol/L; rpm: n.a.; T: 30°C (Paudyal et al., 2014) Single solutions and synthetic wastes Spent coffee grinds 69.0 mg/g pH: 7; biosorbent dose: 0.1 g; time: 1 h; C 0 : 100 mg/L; rpm: 250.; T: 20°C (Imessaoudene et al., 2013) ...
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Removal of Sr2+ from aqueous media presents particular challenges, especially in complex wastes such as nuclear industry liquors. Commercial sorbents while effective, can be highly expensive and subject to negative effects from competing ions. Here we evaluate two potential biosorbents (crab carapace and spent distillery grain) as potential alternatives and compare their performance to two commercial sorbents for Sr2+ removal at industrially relevant concentrations (low mg/L). Physical and structural characterization of the materials was undertaken, and batch and dynamic studies were performed on Sr2+ solutions and simulated nuclear wastewater. Sorption performance was quantified with respect to contact time, initial concentration and ion-competition. Removal efficiencies were 20–70% for the biosorbents compared to 55–95% for the commercial materials. Results indicated sorption was predominantly through monolayer coverage on homogenous sites and could be described using a pseudo-second-order kinetic model. Studies with the simulant liquor showed Sr2+ sorption was reduced by 10–40% due to ion-competition for sites. Characterization of biosorbents before and after Sr2+ sorption suggested that outer-sphere complexation and ion-exchange were the primary Sr2+ removal mechanisms. The efficiency of crab carapace for Sr2+ removal from aqueous media (with adsorption capacity 3.92 mg/g.) at industrially relevant concentrations, together with its mechanical stability, implementation and disposal cost, makes it a competitive option compared to other biosorbents and commercial materials reported in the literature.
... Literature review reveals the characterization studies of DCP carried out by previous researchers 12,13 . It sheds light on the acidic and basic moieties present on the surface of the biosorbent which act as active sites for bonding. ...
... Over the past few years, DCP has been extensively studied as a green biosorbent for the remediation of several heavy metals and radionuclides from waste-waters [29,30]. Characterization of DCP was carried out by N. Barot and H. Bagla [31,32] using SEM and FTIR techniques, which confirmed the existence of phenol, quinol, amide, and carboxyl groups in the binding of metal ions. ...
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Heavy metal pollution is caused due to anthropogenic activities and is considered as a serious environmental problem which endangers human health and environment. The present study deals with biosorption, an eco-friendly technique for the removal of heavy metal Zn(II) from aqueous medium. Various natural materials have been explored for the uptake of metal ions, where most of them are physically or chemically enhanced. Dry cowdung powder (DCP) has been utilized as a low-cost, environmentally friendly humiresin without any pre-treatment, thus demonstrating the concept of Green Chemistry. Batch biosorption studies using ⁶⁵Zn(II) tracer were performed and the impact of different experimental parameters was studied. Results revealed that at pH 6, 94 ± 2% of Zn(II) was effectively biosorbed in 5 min, at 303 K. The process was spontaneous and exothermic, following pseudo-second-order reaction. The mechanism of heavy metal biosorption employing green adsorbent was therefore elucidated in order to determine the optimal method for removing Zn(II) ions. DCP has a lot of potential in the wastewater treatment industry, as seen by its ability to meet 3A's affordability, adaptability, and acceptability criteria. As a result, DCP emerges as one of the most promising challengers for green chemistry and the zero-waste idea.
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