Acknowledgment
To my supervisor, Assoc. Prof. Dr. Nguyen Van Ri and
Master. Nguyen Tien Duc in Department of Analysis Chemistry.
I express great appreciation for your time, support patience
and guidance throughout this study your continuous enthusiasm and
knowledge of the topic relating to this project were an inspiration to
me.
Also I am thankful to all my classmates for being great
friends and helping me so much

March, 29
th
, 2012
Doan Thi Bich Ngoc
1
Table of Contents
Abstract (English)
Pollution of arsenic is an acute problem not only in Vietnam but also in
worldwide. It is estimated about 57 million people are using surface
2
water with the arsenic concentration is higher than the World
Health Organization standard of 10 mg / l (ppb). Arsenic in groundwater is of
natural origin and it is released from the sediments due to the
anoxic conditions or from the weathered and runoff ores
containing arsenic. Arsenic is a poisonous compound that can cause some
diseases such as lung cancer, skin cancer, bladder cancer and respiratory
diseases. For this reason, there are many studies to find out the useful
method to reduce arsenic concentrations in water.
In this report, I used the method of atomic absorption
spectrometry with graphite furnace to determine the arsenic levels
in water and study the use of laterite material to absorb arsenic from

reported recently from the USA, China, Chile, Bangladesh, Taiwan, Mexico,
Argentina, Poland, Canada, Hungary, Japan and India. Among them the
largest population at risk is in Bangladesh followed by West Bengal in India.
Twenty one countries in different parts of the word, groundwater contains
arsenic. Many countries in the world are carrying on investigation on arsenic.
Historically, colorimetric and gravimetric methods have been used for
determination of arsenic. In recent years, atomic absorption spectrometry
(AAS) has become the method of choices. However a commonly used
technique for the measurement of arsenic is the highly sensitive hydride
generation atomic absorption spectrometric method. After examine arsenic, if
arsenic is over legal limit in water, those countries must remove arsenic.
There are traditionally technologies to remove arsenic from water (oxidation,
precipitation/coagulation/membrane separation) with far less attention paid to
adsorption. The sorption capacities of both available and developed sorbents
used for arsenic remediation together with the traditional remediation
methods. We have incorporated most of the valuable available literature on
arsenic remediation by adsorption. Existing purification methods for drinking
water; wastewater; industrial effluents, and technological solutions for arsenic
have been listed. Arsenic sorption by commercially available carbons and
other low-cost adsorbents are surveyed and critically reviewed and their
option efficiencies are compared. Some commercially available absorbents
are also surveyed. An extensive table summarizes the sorption capacities of
various adsorbents. Some low-cost adsorbents are superior including treated
slag, carbons developed from agricultural waste (char carbons and coconut
husk carbons), biosorbents (immobilized biomass, orange juice residue),
goethite and some commercial adsorbents, which include resins, gels, silica,
treated silica tested for arsenic removal come out to be superior. Desorption
5
of arsenic followed by regeneration of sorbents has been discussed. Strong
acids and bases seem to be the best desorbing agents to produce arsenic

AsO
3
, H
3
AsO
3
,
H
3
AsO
3
2-
), arsenic acids (H
3
AsO
4
, H
3
AsO
4
-
, H
3
AsO
4
2-
), arsenites, arsenates,
methyl arsenic acid, dimethylarsinic acid, arsine, etc. Arsenic (III) is a hard
acid and preferentially complexes with oxides and nitrogen. Conversely,
arsenic (V) behaves like a soft acid, forming complexes with sulfides.

OH
2
-
and AsO
3
3-
.
1.2 Arsenic and water
Arsenic can be found in seawater (2-4 ppb), and in rivers (0.5-2 ppb).
Half of the arsenic present is bound to particles. Freshwater and seas algae
contain about 1-250 ppm of arsenic, freshwater hydrophytes contain 2-1450
ppm, marine mollusks contain 1-70 ppm, marine crustaceans 0.5-69 ppm, and
fishes 0.2-320 ppm (all values are based on dry mass). In some marine
organisms, such as algae and shrimp, arsenic can be found in organic
compounds.[1]
The legal limit for arsenic in water applied by the World Health
Organization (WHO) is 10 µg/L.
1.2.1 Arsenic react with water
Elementary arsenic normally does not react with water in absence of
air. It does not react with dry air, but when it comes in contact with moist air a
layer is formed. The layer has a bronze color, and later develops a black
surface. An example of an arsenic compounds that reacts strongly with water
is orpiment. This is an amorphous arsenic compound. Reaction mechanism:
As
2
S
3
+ 6 H
2
O → 2 H

1.3.1 The environmental effects of arsenic in water
Arsenic is an essential compound for many animal species, because it
plays a role in protein synthesis. It is unclear whether arsenic is a dietary
mineral for humans. Arsenic toxicity is another important characteristic. The
boundary concentration of arsenic is 2-46 ppm for freshwater algae.
Plants absorb arsenic fairly easily, so that high-ranking concentrations may be
present in food. The concentrations of the dangerous inorganic arsenics that
are currently present in surface waters enhance the chances of alteration of
genetic materials of fish.
1.3.2 The health effects of arsenic in water
Arsenic related illness is usually caused by consumption of
contaminated drinking water. In the old days it was applied as a poison,
because symptoms of arsenic poisoning resemble cholera symptoms, and
therefore the intentional factor was shaded.
Arsenic in drinking water is an issue of global importance; therefore the
legal limit was decreased to 10μg /L. This legal limit is not met in countries
such as Vietnam and Bangladesh, where millions of people consume drinking
water with an arsenic content of over 50μg /L. This problem results in long-
term chronic health effects, such as skin disease, skin cancer, and tumors in
lungs, bladder, kidneys and liver.
1.3.3 Arsenic contamination of water in the world
Arsenic in natural waters is a worldwide problem. Arsenic pollution has
been reported recently in the USA, China, Bangladesh, Taiwan, Mexico,
Argentina, Poland, Canada, Hungary, New Zealand, Japan, and India. The
largest population with known groundwater arsenic contamination is in
Bangladesh, followed by West Bengal in India. Larger regions in the USA are
affected. Vulnerable areas in Nepal, Pakistan, Thai-land, Laos, Cambodia,
and Sumatra have barely or not been examined so far. Many other countries
and districts in South East Asia, such as Vietnam, Cambodia, and China have
geological environments conducive to generation of high-arsenic

on the role of arsenic as a carcinogen
Some locations in the United States, such as Fallon, Nevada, have long
been known to have groundwater with relatively high arsenic concentrations
(in excess of 0.08 mg/L). Even some surface waters, such as the Verde River
in Arizona, sometimes exceed 0.01 mg/L arsenic, especially during low-flow
periods when the river flow is dominated by groundwater discharge. [3]
9
1.3.4 Arsenic contamination of water in Vietnam
Arsenic contamination of water has become a crucial water quality
problem in many part of the world. The contamination of groundwater by
arsenic in Bangladesh is the largest poisoning of a population in history. At
Vietnam the Vietnamese capital of Hanoi is situated at the upper end of the 11
000 km2 Red River Delta of northern Vietnam, which is inhabited by 11
million people and is one of the most populous areas in the world. Together
with the Mekong Delta, the Red River Delta (Bac Bo Plain) has become one
of the most productive agricultural regions of Southeast Asia. The rural
population is growing rapidly and has, in the last 5-7 yr, moved away from
using surface water or water from shallow dug wells as sources for drinking
water in favor of groundwater pumped from individual private (family based)
tube wells. Groundwater exploitation in the city of Hanoi began 90 yr ago.
Today, eight major well fields supply water to city treatment facilities, which
process 500 000m3 of water per day. [4-6]
The results of the measuring campaign of September 1999 in the rural
districts. The results from the investigated family-based tube wells reveal that
50% of the samples exceed the Vietnamese guideline value of 50 µg arsenic
per liter with an average concentration of all the samples amounting to 159 µg
/l. Peak values of 3000 µg arsenic per liter, south of Hanoi. The situation in a
district (peak value of arsenic in water) is particularly alarming: with an
average value of 432 µg /l, 90% of the analyzed samples revealed
concentrations of 51– 3000 µg /l.

analysis. For example, arsenite and arsenate in soil can be speciated after a
hydrochloric acid and chloroform extraction procedure. Water has been used
11
for the extraction of soluble arsenic compounds from soil with the aid of
ultrasonic treatment
2.1.4 Supercritical fluid extraction
There are very few publications on the use of supercritical fluid
extraction (SFE) for the determination of arsenic. Wenclawiak & Krah (1995)
reported a procedure for the measurement of arsenic species using SFE
followed by GC or SFC detection.
2.2 Macro-measurement
Most procedures for the separation and determination of arsenic are
based on distillation and hydrogen sulfide precipitation methods. Beard &
Lyerly (1961) reported a gravimetric method for the measurement of arsenic
following extraction of arsenic as AsCl
3
by benzene in strong hydrochloric
acid. The recovery was close to 100% when 20 mg was spiked into an
aqueous solution.
2.3 Colorimetric methods
George et al. (1973) carried out a collaborative study for a colorimetric
measurement of arsenic in poultry and swine tissues using silver
diethyldithiocarbamate (AgDDTC) as the complexion agent. The sensitivity
was 0.1 mg/kg in tissues. Dhar et al. (1997) reported a detection limit of 0.04
mg/liter with 95% confidence limit using AgDDTC in chloroform with
hexamethylenetetramine.
2.4 Methods for total inorganic arsenic
Methods for the analysis of inorganic arsenic based on its conversion to
arsenic trichloride or arsenic tribromide by treatment with 6 mol/liter
hydrochloric acid or hydrobromic acid have been described. The arsenic

example, arsenic species in seawater have been measured using hydride
generation and cold trapping, coupled with AFS detection at 193.7 nm. They
found detection limits of 2.3, 0.9, 2.4 and 3.7 ng/liter for arsenite, arsenate,
MMA and DMA respectively (in a 5 ml sample), with a precision of 3.5%.
2.6 ICP methodologies
ICP-MS is more susceptible to isobaric interferences arising from the
plasma. For example, hydrochloric acid and perchloric acid are not desirable
for sample preparation, because the chloride ions generated in the plasma
combine with the argon gas to form argon chloride (ArCl). This has the same
mass as arsenic (75) which could lead to error if not corrected. Therefore,
whenever possible, only nitric acid should be used in sample preparation.
13
2.7 Voltammetry
Voltammetric stripping methods are mostly based on the chemical
reduction of As (V) to As (III) before the deposition step, because it has been
generally assumed that As (V) is electrochemically inactive. Mercury and
gold (or gold-plated) electrodes are most commonly used for the
determination of arsenic.
2.8 X-ray spectroscopy
Particle-induced X-ray emission spectrometry (PIXES) is an analytical
technique that entails the bombardment of a sample (target) with charged
particles, resulting in the emission of characteristic X-rays of the elements
present. PIXES is a multi-elemental technique with a detection limit of
approximately 0.1 μg As/g. It has the advantage of using small samples (1 mg
or less) and being a non-destructive technique.
14
Chapter 3: Arsenic remediation
There are several methods available for removal of arsenic from water
in large conventional treatment plants. The most commonly used technologies
include oxidation, co-precipitation and adsorption onto coagulated flocs, lime

4
)
3
.7H
2
O are
effective in removing arsenic from water. Ferric salts have been found to be
more effective in removing arsenic than alum on a weight basis and effective
over a wider range of pH. In both cases pentavalent arsenic can be more
effectively removed than trivalent arsenic. In the coagulation-flocculation
process aluminum sulfate, or ferric chloride, or ferric sulfate is added and
dissolved in water under efficient stirring for one to few minutes. Aluminium
or ferric hydroxide micro-flocs are formed rapidly. The water is then gently
stirred for few minutes for agglomeration of micro-flocs into larger easily
settable flocs. During this flocculation process all kinds of microparticles and
negatively charged ions are attached to the flocs by electrostatic attachment.
Arsenic is also adsorbed onto coagualted flocs. As trivalent arsenic occurs in
non-ionized form, it is not subject to significant removal. Oxidation of As(III)
to As(V) is thus required as a pretreatment for efficient removal. This can be
achieved by addition of bleaching powder (chlorine) or potassium
permanganate as shown in Equations 2 and 3. The possible chemical
equations of alum coagulation are as follows: Alum dissolution:
Al
2
(SO4)
3
.18H2O = 2Al
3+
+ 3SO4
2-

oxide surface site
Fe(OH)
3
(s) + H
3
AsO
4
→ FeAsO
4
.2H
2
O + H
2
O (4)
≡FeOH
o
+ AsO
4
3-
+ 3 H
+
→ ≡FeH
2
AsO
4
+ H
2
O (5)
17
≡FeOH

concentration of arsenic. The iron precipitates [Fe(OH)
3
] formed by oxidation
of dissolved iron [Fe(OH)
2
] present in groundwater, as discussed above, have
the affinity for the adsorption of arsenic. The Fe-As removal relationship with
good correlation in some operating IRPs has been plotted in Figure 4. Results
show that most IRPs can lower arsenic content of tubewell water to half to
one-fifth of the original concentrations. The efficiency of these community
type Fe-As removal plant can be increased by increasing the contact time
between arsenic species and iron flocs. Community participation in operation
and maintenance in the local level is absolutely essential for effective use of
these plants.[12]
18
B: Experimental Results
Chapter 1: Determination of arsenic content in natural water by
graphite furnace atomic absorption spectrometry.
Atomic absorption spectrometry (AAS) is an easy, rapid method and
has been widely used for the determination of trace elements in natural water.
However, it has not been used for direct determination of As because of poor
sensitivity. The sensitivity is greatly enhanced by coupling a hydride
generation method with flame [14] and flameless [15] atomic absorption
spectrometry. Walcerz et al. [16] and Sturgeon and Gregoire [17] reported
unique preconcentration methods. That is, generated hydrides were
transferred to the inner wall of the graphite furnace, then the furnace was
heated at a high temperature, vaporized As was determined by AAS [18] and
ICP-MS [19]. However, the hydride generation method has a tendency to
interference by coexisting ions [20]
1 Reagents and apparatus

1. Device Name: Atomic Absorption Spectrophotometer (AAS)
2. Marking: AA - 6800
19
3. Manufacturer: Shimazdu - Japan
4. Panorama photo equipment
5. The main technical parameters
5.1. AA-6800F Main Unit
+The body can pair the more other systems
+ Includes: monochromatic radiation sources, Division of samples, optical
systems and electronic systems, unit measure signaling interfacing with
computer controlled Wizard software
+ Being able to switch automatically measuring techniques to measure
furnace flame and graphite
5.2. The system is GFA-EX7 graphite
+ Furnace system, the power supply line, accompanied by accessories:
cuvette graphite, graphite electrodes,
5.3. Automatic samplers ASC-6100
+ Can be used to increase automation for all measurement techniques:
flame, furnace measurements, measuring hydride, measurement of cold
air
+ Can not use that measure by hand.
5.4. Ministry of HVG hydride -1
+ Includes main unit, quartz cuvette, mixer, loop response, the
separation of liquid and air nozzle connected to form the ASC-6100
+ To measure the ability to create the element hydrides: As, Se, Hg,
5.5. Ministry of cold MVU-1A
+ Includes main unit, reactor, the stirring words, the circulating gas and
sealed cuvette.
+ Hg measured with high sensitivity of 0.1 ppb
5.6. Gas supply system

+ choose a type conditions and appropriate equipment to transfer
samples for analysis from the initial state (solid or liquid) into a vapor state of
free atoms. It is the process of sample atoms. The equipment to perform this
process called chemical model of atomic systems.
+ Screening of a light beam emitted by the element to be analyzed
through atomic vapor cloud has been prepared above. The atoms of the
element to determine the vapor cloud would absorb the radiation and produce
certain of its absorption spectrum. Here, a beam intensity of a light had been
absorbed by atoms and depends on the concentration of elements in the
environment to absorb. Source emitting a light beam to determine the
elements called monochromatic radiation source.
AAS 6800 + atoms can form chemical flame or no flame (using
graphite furnace) has very high sensitivity when to fold hundreds of
thousands of times in the flame measurements should be able to identify the
elements traces with very small concentrations.
7. The parameters of the model that the device can be measured:
Concentrations of heavy metals such as (Cu, Pb, Zn, Cd, Hg, As, B, Cr, Al,
Fe, Ni, ) the alkali and alkaline earth metals (Ca, Mg, K, Na ) have
environmental components in soil, water, air, fertilizer and agricultural
products.
9. Basic requirements for sample: Most of all in solid form (to be
destroyed by the microwave), liquid, gas (to be absorbed in the solution and
then measuring machine)
* Electric flask heater 250ml
* Volumetric flask 10ml, 25ml, 50ml, 100ml, 250ml
* Pipette 1ml, 2ml, 5ml, 10ml…… micropipette 20-5000µl
21
Test condition
HCL light (mA) 10 (70% I
Max

Ram
(s)
Ar(ml/ph)
1: Dry 120/250 30 30 500-400
2: Cineration 600/700 30 15 800-1000
3:Atomization
spectrometry
2550/2600 3 0 30
4: Clean cuvet 2700 2 0 1000
Analysis of spectral lines
22
No Spectral line
(nm)
LOD (ppb) LOQ (ppb) C
Max
(ppb)
1 As-193,70 0.2 2 20
2 Survey the conditions of spectrometry.
To study a good result, the study selected parameters measured in accordance
with a quantitative analysis of chemical elements is a work essential and
important in AAS techniques.
Preliminary survey we chose the following conditions to conduct optimal
machine parameters:
- Solution As: 50ppb in HNO
3
0.5%, modified Pd(NO
3
)
2
0.03%

examined the lamp intensity value: 6; 7; 8; 9;10; and 11 mA with 20ppb
arsenic solution in HNO
3
solution 0.5%, 0.03% Pd(NO
3
)
2
. Survey results the
lamp intensity given in Table 1.
Table 1: Survey intensity hollow cathode lamps
I (mA) 6 7 8 9 10 11
Abs 0.0602 0.0596 0.0650 0.0656 0.0657 0.0573
RSD (%) 9.2275 2.9541 4.4135 5.8585 5.5356 1.4523
Graph 1: Survey intensity hollow cathode lamp
From the result, we see that at intensity 10mA, the measurement arsenic has a
high sensitive and stable. Therefore, the intensity hollow cathode lamps
10mA was chosen in my experiment.
2.3 Survey measured slit width of atomic absorption spectrometer
Beam emitted of the element analysis is emitted from the hollow cathode
lamp after passing through the environment will be oriented to the slot of
monochrome system. This system, the collimated light beam and splits, then
only one spectral line to measured direction of the measurement of
monochromatic slit. This spectrum affects to photoelectric to generate the
signal intensity of absorption lines. Therefore, slit measurements shall be fit
for the spectral lines so that the signal is sensitive enough to reach stability
and eliminates the crowded spectral lines of other elements on both sides of
the research spectrum.
For AA-6800 machine, we can choose the slit size is measured: 0.2; 0.5 and 1
nm
The survey results come with slit width As 20ppb solution in solution 0.5%,

NO
3
, ascorbic acid, oxalic acid…
- Group 2: Group of substances when added to the sample analysis can
form thermal stability compounds, difficult evaporation. So allowing
raises the temperature of ash, chemical atom, retaining the analyte and
the background of the high temperature. This group can be said to
nitrates of Pd, Mg, Ni, Cu or sodium phosphate and ammonium
NH
4
H
2
PO
4
and (NH
4
)
2
HPO
4
Besides the two types can be combined in order to increase the
likelihood of the background, rising temperatures of atoms, so will get
better results. However, the laboratory conditions, we choose
substances modified Pd (NO
3
)
2
, Mg(NO
3
)

2
PO
4
Abs RSD Abs RSD Abs RSD Abs RSD
25