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

8

Objective

Investigate the performance

of three different samples of

peat, to check which has

better adsorption capacity /

removal of chromium (III) in

aqueous solution.

9

9

PROCEDURE

10

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

11

.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

12

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

15

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

16

Peat Samples

Caracterization

17

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

19

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

20

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

22

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

23

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

32

a viable material for decontamination

of effluents containing Cr(III) ions

SAO peatFrom Sergipe State, Brazil

33

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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37