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NOM Present in Biosorbent
Peat for Decontamination of
Water Containing Metallic
Specie
Ana Paula dos S. Batista
2
CHROMIUM
Moreover, the metal can be oxidized to the more
carcinogenic and mutagenic Cr(VI), which is toxic
to human body tissue owing to its oxidizing
potential and ability to permeate biological
membranes3
Cr(III) is a metal commonly found in
wastewaters, and although thought to be
an essential nutrient required for sugar
and fat metabolism in organisms
long-term exposure has been linked to skin
allergies and cancer.
BIOSORPTION
4
Humic substances are the main
component of the natural organic matter
(NOM) present in biosorbent peat.
Typical carbon and hydrogen contents of peat
are in the ranges 40–60% and 4–6%, respectively.
High contents of carbon and organic matter are important
characteristics, which influence the extent of metal uptake
by the biosorbent.
5Fernandes et al.,Removal of methylene blue from aqueous solution by peat, J. Hazard. Mater. 144
(2007) 412–419.
Biosorption is a viable technique
for metal removal from
wastewaters.
Sergipe mineral
reserve of 21
bogs:
estimated at
800,000 t on a dry
basis (CPRM - Research Center of
Mineral Resources, Brazil).
6
only in the smallest state
in Brazil
Peat is a natural humic substance with
recognized potential for wastewater
treatment due to its ability to sequester
metals.
The abundance of alkyl-C
functional groups plays an important role
in complexation and ion exchange during
metal ions fixation
7
D. Mohan, C.U. Pittman Jr., Activated carbons and low cost adsorbents for remediation
of tri- and hexavalent chromium from water, J. Hazard. Mater. 137 (2006) 762–811.
OBJECTIVE
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Objective
Investigate the performance
of three different samples of
peat, to check which has
better adsorption capacity /
removal of chromium (III) in
aqueous solution.
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9
PROCEDURE
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Three peat samples were
collected from different
Brazilian states
Sergipe State
Santo Amaro das Brotas city-
(SAO)
Itabaiana city -
(ITA)
Sao Paulo State
Ribeirão Preto city- (SAP)
collected at a depth of
10 cm of peat bogs
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.The raw peat was air-dried at room temperature
and the material was then sieved though a 9 mesh
grid
a) wet sample b) air drying
c) grinding,
d) after screening
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Adsorpiton Experiment
Batch adsorption experiments were
conducted in a constant temperature
shaker bath at 25±0.2 ◦C and 125 rpm.
Fixed volumes of 50mL aliquots of
aqueous 10.0mgL−1 Cr(III) solution were
added to 100mg of peat in stoppered
polyethylene flasks, adjusting the initial
pH of solutions to a value of 5.0 (except
for the pH study) with either 0.1 molL−1
HCl or 0.1mol L−1 NaOH solution
Millex-HV 0.45m syringe
driven filter unit was used for
removal of the supernatant for
subsequent analysis.
13
After filtration, a Shimadzu Model AA-6800 atomic
absorption spectrometer was used for detection of
Cr(III) concentrations in the supernatant solutions.
Each experiment corresponded to one datapoint, the
sample being taken at predetermined time intervals
up to a maximum of 72 h, without alteration of the
final volume.
14
After determining the time required for adsorption
equilibration, the experiments were repeated at other
initial pH values, in the range 3–7.
q = (c0 − c)v
m
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q - is the sorption capacity in mg of metal per g of dry peat
C0 - the initial metal ion concentration in mgL−1
C - the final metal ion concentration in mgL−1
v - the volume of the liquid in L, and m the weight of the peat adsorbent in g
The amounts of Cr(III) adsorbed onto the peat were then calculated from the difference between the initial and final
concentrations of the solution, using the equation:
Results and
discussion
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Peat Samples
Caracterization
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18
Scanning Electron Microscopy
(a) SAO peat
(b) SAP peat
(c) ITA peat
Strands of plant material
Mineral phase
Santo Amaro das Brotas city, Sergipe
Itabaiana city , Sergipe
Ribeirão Preto city, São Paulo
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X-ray diffractometry of peat samplesAmorphous matter
Crystalline Structures
(a) SAO peat
(b) SAP peat (c) ITA peat
Santo Amaro das Brotas city, Sergipe
Itabaiana city , SergipeRibeirão Preto city, São Paulo
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The SEM, XRD and elemental analyses showed
that only the SAO sample possessed true peat
characteristics.
Typical compositions of peat are in the
range 40–60% C and 4–6% H
Fernandes et al., J. Hazard. Mater. 144 (2007) 412–419.
Adsorption Capacity
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4.90±0.01 mgg−1
1.70±0.01 mgg−1
1.40±0.01 mgg−1
Maximum uptakes of chromium, at equilibrium pH 4.0
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Adsorption experiments investigating the
influence of pH
were undertaken using only the SAO peat
due to
Its ready availability in large
quantities in Sergipe State its higher
adsorption capacity.estimated at 800,000 t
on a dry basis (CPRM - Research Center of Mineral Resources,
Brazil).
pH Influence
24
25
Uptake by peat is usually ascribed to
processes including:
ion exchange
surface adsorption
complexation
adsorption–complexation
26
R
O
OH
R COOM H+
+M+
+
Humification of peat produces humic substances possessing
carboxylic and phenolic acid groups within their structures
ion exchange
27pH influence
Ion Exchange
At low pH, competition with H+
At high pH, solubility; tending to precipitate as Cr(OH)3release protons on reaction with metals
Cr Speciation
Reducing the pH during adsorption
CONSIDERATIONS
28
Equilibrium pH values may be attributed to the
buffering capacity of peat.
29
Highest adsorption
(retention >95.0%)
at equilibrium pH 4.0
using the Santo Amaro
das Brotas peat.
was achieved
most significant buffering by humic
substances
occurs in
pH range 4.0–6.0E. Tipping, Cation Binding by Humic Substances, Cambridge University Press, 2002
carboxylic acid functional group
two acidic functional
groups on an aromatic
ring can result in pKa’s
of between 2.9 (or
lower) and 4.4.
30
adsorption efficiency
the amount of organic matter present
was associated with
31
Experimental data for the adsorption of Cr(III)
from aqueous solution onto SAO peat were
fitted to the Langmuir equation
an equilibrium adsorption
capacity, qmax, of
5.60mgg−1
close to the
experimentally
determined value
4.90±0.02 mgg−1
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a viable material for decontamination
of effluents containing Cr(III) ions
SAO peatFrom Sergipe State, Brazil
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Acknowledgements
and brazilian agencies
CAPES, FAPESP and CNPq
Sergipe Federal University
Prof. Dr. William J. Cooper
for this opportunity
financial support of this work:
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