Arsenic Removal Properties of Laterite Soil by Adsorption Filtration Method
S.A.M. Waliul Hoque,
M. Saiful Islam
Laterite soil samples were studied to monitor their
efficiency in removing arsenic from contaminated water by adsorption filtration
method in laboratory condition. Prepared 10 mg L-1 solution
of As3+/As5+ was passed through the six soil samples.
At room temperature, a batch of three different samples adsorbs 1010,
925 and 932.5 mg kg-1 of arsenic and their removal efficiency
were found to be 58.74, 65.32 and 65.39%, respectively. At 100 °C
temperature, the three specimens studied show the adsorptivity of 54.40,
63.47 and 58.69%, while the respective amount adsorbed was calculated
848, 694 and 760 mg kg-1, respectively. Studied IR spectra
of the sample of different temperature gradients revealed that the efficiency
of a particular composite is high temperature sensitive and the most important
and noticeable performance of soil samples is observed when the samples
are treated at room temperature, this is the optimum temperature for these
soil samples. Above this temperature the efficiency decline gradually.
Arsenic contamination of groundwater resources poses the greatest threat
on the health of millions of people worldwide, particularly in the densely
populated river deltas of Southeast Asia (Lenny et al., 2008).
Another study also mentioned that an estimated 100 million people in Bangladesh
and in the eastern part of India are currently affected by widespread
arsenic poisoning caused by drinking water drawn from the underground
(Ng et al., 2003). For Bangladesh, the limit set for arsenic contaminated
drinking water is 0.005 mg L-1 though the recommendation by
World Health Organization is 0.001 mg L-1. Also, the US Environmental
Protection Agency (USEPA) has adopted an arsenic maximum contaminant level
of 0.001 mg L-1, which was enforced in January 23, 2006.
It is now revealed that most of the international drinking water standards
are in the range of 0.004-0.005 mg L-1 arsenic (Elizade-González
et al., 2001a). For this reason, there is growing interest in using
low-cost materials to remove arsenic from water. One of the promising
methods appears to be adsorption of inorganic arsenic compounds from solution
using both natural and synthetic sorbents. Some low-cost natural matters,
e.g., activated red mud (Altundogan et al., 2002) and natural zeolites
(Elizade-González et al., 2001b), were tested as potential
sorbents of As species. Furthermore, removal of arsenic using granular
adsorptive media is currently the most widely used option for small community
systems and individual homes (USEPA, 2003).
Since, arsenic is typically present in natural water at low concentration
(micromolar to nanomolar), its adsorption and desorption behavior on mineral
surfaces plays an important role in regulating its aqueous concentration
in groundwater and surface water. It is established that under oxidized
condition, arsenate has strong affinity to bind with Fe+3 oxide
minerals as an inner-sphere complex, probably predominately as a bidentate,
binuclear surface complex (Foster, 2003). In recent past, the application
of iron oxide studied to remove metals from water and wastewater (Benjamin
et al., 1996) and arsenic removal with iron oxides has been investigated
(Raven et al., 1998; Driehaus et al., 1998; Joshi and Chaudhuri,
1996; Wilkie and Hering, 1996).
The groundwater`s in aquifers of Lower Pleistocene and older age, beneath
the Madhupur Tract and the Barind Tract, are free from arsenic pollution
and iron because these aquifers are oxic and particularly where iron has
been recrystallized as more stable phases such as hematite and reductive
dissolution of iron oxyhydroxides does not occur in them (Ravenscroft
et al., 2001). In addition, the fine iron-manganese concretions
recorded in Madhupur`s soil (Brammer, 1996). The present research investigated
the performance of laterite soil a potential source of iron oxide collected
from Madhupur Tract on removing arsenic.
MATERIALS AND METHODS
Soil sample collection: In 20th August 2006, soil samples were
collected from shibpur Sub-District (Upazila) in different levels at 10,
20 and 30 m from the surface and they labeled SS1, SS2 and SS3, respectively.
Shibpur is one among the Sub-District (Upazila) of Norshindi and it is
located at the middle west of Norshindi District. This Sub-District is
located at 23 °56` (north) and 24 °07` (north) longitude at the
north and the south, respectively and 29 °39` (east) and 90 °50
(east) latitude at the east and the west, respectively. The distance of
Shibpur from Dhaka city and Norshindi District is 56 and 7 km, respectively.
About 2/3 land area located at the south and west of Shibpur is formed
by the sediment of the river Brahmaputra, but the remaining one third
land area is formed by ancient Madhupur Tract.
Column preparation: Six columns were made with 5 g uniformly grained
soil. Among them three columns were made with untreated soil samples of
SS1, SS2, SS3 and another three columns were made with soil samples SS1
(100°), SS2 (100°), SS3 (100°) (particle size 0.1 cm) that
treated with 100 °C temperature. The prepared 10 mg L-1
As3+/As5+ solution was passed through the columns
until the saturation volume of the six soil samples were reached. Water
sample that passed through the columns was collected on the sample bottles
after several time intervals. The absorbance of the samples was measured
in the spectrophotometer. The flow rates of the columns were measured
and it was range of 2-2.5 mL min-1.
Arsenic detection method: The silver diethyldithiocarbamate (SDDC)
colorimetric method is based on the evolution of arsine gas in which inorganic
arsenic is reduced to arsine, AsH3, by zinc in acid milieu,
the arsine is bubbled through a solution of silver diethyldithiocarbamate,
AgS.CS.N(C2H5)2, in pyridine or chloroform;
a red soluble complex is formed that can be measured photometrically at
a specific wavelength of 535 rim (Eaton et al., 2005).
Arsine generation: Ten milliliter collected water sample was taken
into the generator flask followed by the addition of 5 mL concentrated
hydrochloric acid, 2 mL 15% potassium iodide and 10 drops of stannous
chloride solution. It was allowed to stand, with random agitation for
about 15 min to ensure complete reduction of As (V) to As (III). The absorption
tube was charged with 4.00 mL of SDDC solution. Cotton wool impregnated
with lead acetate solution was placed in the scrubber to absorb any hydrogen
sulphide, which may be subsequently evolved. After adding 3.0 pure granulated
zinc to the solution in the generating flask, the scrubber-absorber was
connected immediately. The evolution of arsine is 99% complete in 30 min
and virtually complete in about 45 min. The volume of the solution was
readjusted, if necessary, to the original volume and then poured into
a 1 cm cell and the absorbance was recorded at 535 nm using the reagent
(SDDC solution) as the reference.
Preparation of standard curve for arsenic measurement: To measure
the arsenic content in the collected water sample, it was essential to
prepare standard curves. For this purpose, a mother solution of 10 mg
L-1 (As3+/As5+ at 1:1 ratio) was prepared
and this solution was diluted to many other intermediate solutions of
different concentrations. After preparing all these solutions, their absorbance
was measured in spectrophotometer (M-390). Then, standard curve was generated
for total arsenic (As) in various concentrations.
RESULTS AND DISCUSSION
To establish suitable arsenic removal technique by column adsorption
filtration, some arsenic removing materials were prepared from easily
available chemicals and in this study, the value of the raw material and
production cost is considered. Different types of adsorbing materials
such as Activated Alumina (AA), Modified Activated Alumina (MAA), Granular
Ferric Hydroxide (GFH), Granular Ferric Oxide (GFO) and granular titanium
dioxide (TiO2) have been developed and implemented in recent
years (Bang et al., 2005; Jing et al., 2005; Westerhoff
et al., 2006). Compared to the number of reports on removal of
arsenic by iron oxide, only limited studies have been conducted by laterite
soil. One recent study revealed that laterite soil is very effective for
arsenic adsorption as the pH of the raw water did not change after arsenic
removal and iron was not leached (Maji et al., 2007). In the present
study, 10 mg L-1 arsenic solution is passed through the soil
samples until the saturation volume to calculate the adsorption capacity
and establish the suitable state of the sample on temperature sensitivity.
At room temperature, comparative study on the three different soil samples
showed that the amount of arsenic adsorption in SS1 is higher than that
of SS2 and SS3. The amount of arsenic passed through the column SS1 is
2470 mg kg-1 and the amount of arsenic absorbed 1010 mg kg-1
in Table 1. So, the average arsenic adsorbing capacity
of SS1 which is collected from 10 m deep is 58.74% (5 g of the absorbent).
It is also found that the amount of arsenic passed through the columns
SS2 and SS3 are 2667 and 2695 mg kg-1 and the amount of arsenic
absorbed 925 and 932.5 mg kg-1, respectively (Table
1). So, the average arsenic adsorbing capacity of SS2 and SS3 are
65.32 and 65.39%, respectively (5 g of the absorbent).
At 100 °C temperature, the amount of arsenic passed through the three
columns is 1860, 1900, 1840 mg kg-1 and the amount of arsenic
absorbed 848, 694, 760 mg kg-1, respectively in Table
2. Among these three soil samples SS1 (100 °) which collected
from 10 m deep showed better performance on arsenic adsorption than that
of the other two collected from 20 and 30 m.
The average arsenic adsorbing capacity of SS1 (100 °), which treated
at 100 °C temperature, is decreased by 4.34% than that of SS1 at room
temperature whereas the arsenic adsorbing capacity of SS2 (100 °)
and SS3 (100 °) are declined by 1.85 and 6.70% than that of SS2 and
SS3. The result of the column studies showed that the removal efficiencies
of the soil sample SS1, SS2 and SS3 are at their best as obtained and
the removal efficiency of the soil sample SS1 (100 °), SS2 (100 °),
SS3 (100 °) is lowest, when they heated to 100 °C in Fig.
At elevated temperature hydrated ferric oxide losses its chemical hydration
bond tended to move towards the stoichiometric composition Fe2O3.
The IR spectrums of the soil samples SS1, SS2 and SS3 exhibits sharp peak
above 3500 cm-1, which indicates the presence of trace amount
of free hydroxyl group in the soil sample whereas there are no such peak
is found for other three samples that treated at 100 °C temperature.
Therefore, the present study suggests that laterite soils that contain
hydrated ferric oxide have better performance in removing arsenic from
contaminated water. Although, this type of finding is completely absent
on the other study, the present study also supports the previous study
by Maji et al. (2007), that natural laterite soil is very effective
for removing arsenic in small scale. In addition, as the present study
investigated the soil samples performance for 10 mg L-1 arsenic
contaminated water, it can be undoubtedly used to achieve better performance
for low level arsenic contamination.
||The comparison of the amount of As adsorbed by all the
|| Arsenic (As3+/As5+ at 1:1 ratio)
removing performance at room temperature
|| Arsenic (As3+/As5+ at 1: 1 ratio)
removing performance at 100 °C
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