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Effects of bentonite and zeolite minerals on mobility of lead in paddy soil in Chi Dao commune, Van Lam district, Hung Yen province, Vietnam

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EnvironmEntal SciEncES
|
EnvironmEntal sciEncE
90
SEPTEMBER 2022
Volume 64 Number 3
Introduction
Lead content in natural soil ranges from 10 to 50 ppm [1].
Due to biogeochemical cycling changes and imbalances from
manmade activities such as use of fertilizer [2, 3], manure [4],
sludge disposals [5], or polluted irrigation water [6, 7] result
in the accumulation of lead in soil and create risks to human
health and ecology [8]. Lead in soil may be in a soluble form,
or found as lead inorganic compounds PbS, PbSO
4
, PbSO
4
.
PbO, α-PbO [9], or be associated with organic compounds
such as amino acids, fulvic acids, and humic acids [10]. The
mobility of lead in soil is largely controlled by pH [11, 12],
the presence of organic matter [13], and clay mineral content
[14]. Lead phytoavailability and toxicity are dependent on
their speciation.
Zeolite is the general name for aluminosilicate minerals
called tectosilicates, which have three-dimensional
frameworks [15]. Zeolite has high cation exchange capacity
and selective absorption, so it is widely used in environmental
treatment especially for heavy metal absorption in
contaminated soils [16-19]. Chemical stabilization of heavy
metals by adding artificial additives has been evaluated as one
of the most cost effective in situ remediation techniques for
metal contaminated sites [16, 20]. Chemical stabilization may
lead to a decrease in extractable metal content in soil [21] and
metal phytoavailability in plants [16, 22].
Used lead-acid battery recycling activities in Minh Khai
handicraft village, Chi Dao commune, Van Lam district, Hung
Yen province, Vietnam discharges copious amounts of acidic
wastewater and causes soil and water pollution. Some studies
reported that Pb concentration in soils in the handicraft village
exceeded the allowable value [23, 24] and causes major
health issues in the local community [25, 26]. Therefore the
agricultural soil surrounding the handicraft village is not safe
enough for cultivation.
This study was implemented to evaluate and determine
a suitable in situ remediation for Pb-contaminated sites by
adding artificial minerals into soils to immobilize lead and
decrease its phytoavailability in rice plants. Some effects of
additives on the rice growth (such as plant height, number of
panicles, length, and weight of plain rice) in this study were
also determined.
Materials and methods
Materials
Zeolite minerals:
In this study, minerals of zeolite 4A and
zeolite
Faujasite
were synthesized from silica particles of rice
straw. The hydrothermal crystallization method was used to
synthetize
zeolite
minerals and the products, shown in Table
1, were characterized using x-ray powder diffraction (XRD)
Effects of bentonite and zeolite minerals on mobility of lead in paddy soil
in Chi Dao commune, Van Lam district, Hung Yen province, Vietnam
Tu Ngoc Nguyen
*
,
Huy Quang Trinh, Cong Huy Vo
Vietnam National University of Agriculture
Received 25 October 2021; accepted 28 November 2021
*
Corresponding author: Email:
Abstract:
Used lead-acid battery recycling activities in Minh Khai handicraft village, Chi Dao commune, Van Lam district, Hung
Yen province, Vietnam has markedly increased the lead (Pb) content in paddy soil. Reducing the mobility of lead and lead
accumulation in rice plants/plain rice are major priorities to reduce the impacts of lead in paddy soil. Application of the
minerals zeolite (4A and Faujasite) and bentonite (natural and modified) to lead-contaminated soil has been carried out in
lab scale for three years. The results showed the efficiencies in reducing accumulated lead in rice were 58 and 56% after
adding the artificial additives
zeolite 4A and
zeolite Faujasite, respectively. These results were better than those of modified
bentonite and natural
bentonite, which were only 44 and 24%, respectively. The control efficiency of Pb accumulated in rice
plants between the supplemented samples of
zeolite Faujasite,
zeolite 4A, modified
bentonite, and natural
bentonite were
69, 56, 42, and 40%, respectively, compared with the control samples. The addition of minerals to the soils has also resulted
in decreases of the growth and yield of the experimental rice plants compared with the control samples. In this research,
0.1 to 0.2% of
zeolite Faujasite showed the best results in terms of reducing Pb content in soil as well as low effect on plant
growth. This research opens up on-site pollution control solutions for lead-contaminated agricultural soils.
Keywords:
heavy metals, lead immobilizing, minerals, rice uptake.
Classification number:
5.3
DOI : 10.31276/VJSTE.64(3).90-96
Environm
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Environm
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september 2022
Volume 64 Number 3
and observed by scanning electron microscope (SEM).
Table 1. Properties of zeolite minerals.
No.
Element
Zeolite 4A
Zeolite Faujasite
1
Chemical formula
Na
12
Al
12
Si
12
O
48
.27H
2
O
Na
2
Al
2
Si
2.5
O
9
.
6H
2
O
2
Mineral compositions
Na
2
O; Al
2
O
; SiO
2
Na
2
O; Al
2
O
3
; SiO
2
3
Crystalline size, μm
2.5
4
4
CEC, meq 100 g
-1
341
432
5
Pb absorption efficiency, %
82.67
96.56
6
SEM captured off
(A)
zeolite 4A and
(B)
zeolite
Faujasite
Natural bentonite and modified bentonite minerals:
The natural bentonite in this research was collected from
the Tam Bo bentonite mines, Di Linh district, Lam Dong
province, Vietnam. The mineral was compounded by high
Montmorillonite content (about 64%) while the remains
were Kaolinite (9.5%), Illite (6.0%), Quartz (5.0%), Feldspar
(3.5%), Goethite (3.0%), Canxit (little), and other minerals.
Chemical compositions of the natural bentonite
were mainly
composed of SiO
2
(50.5%), Al
2
O
3
(17.67%), and Fe
2
O
3
(7.0%). The mineral had a CEC of 19.5 meq 100 g
-1
and the
basal spacing of 15.49 Å.
Al-pillared bentonite was created by activating the natural
bentonite with polyoxymetal cations of Al solution. The
activated mineral had CEC of 58.6 meq 100 g
-1
and the basal
spacing of 16.81 Å.
Contaminated-Pb soil samples:
Soil samples used in the
research were collected from the 0-20 cm surface layers of
10 small scale paddy fields surrounding the used lead-acid
battery recycling facilities in Minh Khai handicraft village,
Chi Dao commune, Van Lam district, Hung Yen province,
Vietnam (Fig. 1).
Fig. 1. Soil sampling locations.
Rice plants:
Greenhouse pot experiments were conducted
at the Vietnam National University of Agriculture (VNUA)
and used to evaluate the effects of zeolite
and
bentonite
minerals on the immobility of lead in soil and the growth and
grain yield of rice plants. The Bac Thom No.7 resistance leaf
blight variety was used in the pot experiments. Rice plants of
age 10-13 days after sowing were planted in the experimental
pots. Three rice plants with the same height were planted in
each experimental pot.
Rice grain samples:
The rice grains were used in this
research to determine the effectivity of lead cumulative
control after adding mineral additives to the soil. These rice
grains were collected from the experimental pots.
Methods
Soil analysis:
Soil samples were examined by the PIXE
method (particle-induced x-ray emission) to determine its
chemical composition. Other physio-chemical properties of
the soil samples such as pH, electro-conductivity (EC), texture,
and organic matter (OM) content were also determined.
Plant-available Pb analysis:
Pb phytoavailability was
extracted from soil by the diethylenetriamine pentaacetic acid
(DTPA) method at a pH of 7.3. Each 10 g portion of air-dried
soil was passed through a 2.0-mm sieve to which 20 ml DTPA
extractant was added. The suspensions were shaken at 175
rpm for 2 h. The experiments were terminated by filtration of
the suspension by a cellulose acetate filter, then determining
the soluble ion of Pb using ICP-OES (PE 7300 V-ICP, Perkin
Elmer).
Determination of Pb content in rice plant and grain:
Pb
content in rice plants and grains was determined by using aqua
regia (3:1 HCl/HNO
3
). Briefly, 50 mg of dried sample was
drilled and digested in 50 ml of the aqua regia solution. The
solution was then gently shaken and filtered by a cellulose
acetate filter. The soluble ion of Pb was determined using ICP-
OES (PE 7300 V-ICP, Perkin Elmer).
Greenhouse pot experimental design method:
After
assessing the composition and properties of the soil, the soil
samples were mixed together and then NPK fertilizer was
added with an amount of 25 kg per 360 m
2
(corresponding
1.1 g per experimental pot). This soil was then filled into
the experimental pots (30 cm diameter x 20 cm height). The
experiment was conducted over three seasons. Four types
of minerals (natural and modified bentonite, zeolite 4A, and
zeolite Faujasite) with six treatments (5 levels of additives
from 0.1 to 0.5% and the control) were replicated three times
in one season resulting in 72 pots (4x6x3) in total (Table 2).
The weight of both soil and added mineral was 5 kg in total.
The Bac Thom No.7 resistance leaf blight variety was used in
the pot experiment, which was submerged in 5 cm of water
over the entire growth period. Three seedlings 13 days in a
ge

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