Hindawi
Journal of Chemistry
Volume 2017, Article ID 5763832, 8 pages
https://doi.org/10.1155/2017/5763832
Research Article
Removal of Cd (II) from Aqueous Media by Adsorption onto
Chemically and Thermally Treated Rice Husk
María Camila Hoyos-Sánchez,1 Angie Carolina Córdoba-Pacheco,1
Luis Fernando Rodríguez-Herrera,2 and Ramiro Uribe-Kaffure3
1
Department of Biology, University of Tolima, Altos de Santa Helena, C. P. 730006 Ibagué, Colombia
Department of Chemistry, University of Tolima, Altos de Santa Helena, C. P. 730006 Ibagué, Colombia
3
Department of Physics, University of Tolima, Altos de Santa Helena, C. P. 730006 Ibagué, Colombia
2
Correspondence should be addressed to Ramiro Uribe-Kaffure; rauribe@ut.edu.co
Received 8 March 2017; Revised 9 May 2017; Accepted 15 May 2017; Published 6 June 2017
Academic Editor: Wenshan Guo
Copyright © 2017 Marı́a Camila Hoyos-Sánchez et al. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Chemically and thermally treated rice husks were evaluated as a potential decontaminant of toxic Cd (II) in aqueous media. Rice
husk (RH), a by-product from rice milling, was chemically treated with HCl and NaOH. Then, thermal treatments to 300, 500, and
700∘ C were applied. The chemical composition and morphological characteristics of RH were evaluated by different techniques.
The specific surface area analysis of RH samples by BET nitrogen adsorption method provided specific surface areas ranging from 6
to 14 m2 /g. SEM, FTIR, and EDX analyses of RH were carried out to determine the surface morphology, functional groups involved
in metal binding mechanism, and C/O and C/Si ratios, respectively. The maximum Cd (II) adsorption capacity was 28.27 mg/g at
an optimum pH, 6.0. The kinetic studies revealed that adsorption process followed the pseudo-second-order kinetic model.
1. Introduction
Although many different definitions have been proposed to
the term “heavy metal,” some based on density, some on
atomic number or atomic weight, and some on chemical
properties [1], the term is often used to denote a group of
metals and semimetals (metalloids) that have been associated
with contamination and potential toxicity or ecotoxicity.
While some are essential for growth, reproduction, and
survival of living organisms, the contamination by heavy
metals has become a significant environmental problem
[2, 3]. In order to minimize the hazardous effects of such
elements on the environment and human health, there is a
particular need for the development of efficient techniques
for removing heavy metals from water sources.
Among the heavy metals, cadmium, which exists commonly in Cd (II) form in aqueous media, poses severe
risks to human health. It has been reported that cadmium
intoxication can lead to kidney [4], bone [5], and pulmonary [6] damage among others. Therefore, the increase
in environmental cadmium concentrations, mainly for its
use in industrial processes, added to the fact that it has not
shown any physiological function within the human body [7],
validates the study of techniques for cadmium removal from
aqueous media.
In recent years, a wide variety of techniques have been
applied for removal of heavy metal from aqueous media: ion
exchange [8], bioremediation by microorganism [9], biometallurgy [10], and bioelectrochemical metal recovery [11],
among others. In this context, adsorption has been referenced
as an efficient and easy-to-use alternative. By this method,
environmental pollutants are removed and concentrated on a
specific area for better handling and disposal. Materials such
as activated carbon and clays, among others, have shown a
potential contaminants adsorbent capacity. However, in the
need to find inexpensive and high availability materials, there
are a growing number of studies on agroindustrial waste as
bagasse from sugar [12], stem of papaya [13], shell bean [14],
banana peel [15], coffee residues [16], orange peel [17], among
others, to be used as adsorbent materials.
2
Previous reports have shown the potential of raw rice
husk and rice husk ash as adsorbent materials for metals
in aqueous media [18–20]; however, chemical and physical
changes on the material are required to optimize their adsorbent capacity [21]. This study was aimed to evaluate the Cd
(II) adsorption capacity onto different adsorbent materials
obtained from rice husk chemically and thermally treated
(not necessarily as ash). In addition, it tries to determine the
experimental pH and equilibrium time conditions required
to achieve the highest percentage of Cd (II) adsorption onto
rice husk.
2. Materials and Methods
2.1. Samples Preparation. Rice (Oryzika-I) husks were provided by a local industry (Molino Caribe), located in Espinal
city, Colombia. To prepare the samples, the rice husks were
manually cleaned and thoroughly washed with distilled water
to remove all dirt. Then rice husks were crushed and passed
through a steel sieve; particle sizes ≤ 100 𝜇m were obtained.
At this point, chemical composition analysis was performed.
Without any other physical or chemical treatment on rice
husk, we select the first sample, RHw (rice husk without
treatment).
Chemical and Thermal Treatment on Rice Husks. According
to previous reports, the treatment of rice husks with HCl
helps in removing impurities such as inorganic salts [22].
Besides, it also helps to remove traces of different oxides
such as potassium oxide (K2 O) from the use of fertilizers
in rice cultivation [23]. On the other hand, washing with
NaOH generates an increase in the adsorption capacity of rice
husk, because it can partially degrade some components of
the husk, exposing reactive functional groups, as OH, which
could retain the contaminating molecules [24, 25]. Also, this
washing removes surface impurities that can interfere with
the adsorption [21].
According to the above, cleaned and sieved rice husk was
soaked in 0.5 M HCl solution (1 : 20) at room temperature for
4 h in permanent agitation on a shaker to 200 RPM. Rice
husk was then washed, filtered, and soaked in 0.5 M NaOH
solution (1 : 20) at the same above-mentioned conditions.
Finally, rice husk was repeatedly washed with distillated
water and dried at 40∘ C for 48 h. This treated rice husk was
designated as RHc (rice husk chemically treated).
In order to choose the adequate temperatures for the rice
husk’s thermal treatment, at this time a thermogravimetric
analysis was carried out in oxygen flow, with temperature rise
of 10∘ C per minute until 700∘ C, in a STA 7200 TGA analyzer.
From thermogravimetric results, the working temperatures
were chosen, coinciding with temperatures for which the
greatest mass losses occur. Samples were then heated by
increasing the temperature for 3 hours to the desired value
and maintained at that value for 3 hours.
2.2. Samples Characterization. Specific surface area determination was conducted to assess the structural changes
of the rice husk induced by chemical and thermal treatment. Specific surface area was measured according to the
Journal of Chemistry
Brunauer-Emmett-Teller (BET) method, based on the nitrogen adsorption by sample surface. The assays were conducted
at 77 K in a surface area analyzer (Autosorb-iQ 07165, Quantachrome Instrument).
The morphological characteristics and elemental analysis
of rice husks were evaluated using a JEOL, 6490-LV scanning
electron microscope equipped with an EDX (Inca Energy 250
EDS System LK-IE250, Oxford). The rice husk samples were
covered with a thin layer of gold and an electron acceleration
voltage of 20 kV was applied.
The functional groups on rice husks were characterized by
a Fourier Transform Infrared Spectrometer (Thermo Nicolet
NEXUS 670 FTIR). The spectral range was varied from 4000
to 400 cm−1 .
2.3. Adsorption Experiments. Working solutions of Cd (20,
40, 60, 80, and 100 mg/L) were prepared by diluting the stock
solution (1000 mg/L) in deionized water. Each adsorbent
material (at a concentration of 3 g of sorbent/L of solution)
was soaked in a Cd (II) solution. Solutions were under
constant stirring at room temperature (22∘ C) for 5 days;
pH was maintained at 6 during the whole process. Finally,
the solutions were filtered and quantification of residual Cd
(II) in solutions was carried out using atomic absorption
spectrometry (Perkin Elmer 3110).
The adsorption of Cd (II) ions onto rice husk materials
was calculated using the following equation:
(𝐶𝑜 − 𝐶𝑒 ) 𝑉
(1)
,
𝑚
where 𝑞𝑒 is the amount of metal ions adsorbed onto rice husk
(mg/g), 𝐶𝑜 and 𝐶𝑒 (mg/L) are the initial and equilibrium
concentrations of metal ions, 𝑉 (L) is the volume of solution,
and 𝑚 (g) is the adsorbent mass. Similarly, the percentage of
adsorption for each adsorbent material was determined by
the following equation:
𝑞𝑒 =
% Ads =
𝐶𝑜 − 𝐶𝑒
× 100.
𝐶𝑜
(2)
2.4. pH and Kinetics of Adsorption Studies for the Best Sample.
Once the material with the best adsorption capacity was
found, the effect of pH on Cd (II) adsorption onto this
material was evaluated. The best adsorbent material was
soaked in different Cd solutions (20 mg/L) at pH 4, 5, and
6. It was under constant stirring at room temperature (22∘ C)
for 6 days. From capacity adsorption results, the best working
pH value was determined.
In order to evaluate the reaction time required in the
adsorption process, the best adsorbent material, at the best
pH value, was placed in contact with eleven independent
Cd (II) solutions (100 mg/L). It was under constant stirring
at room temperature (22∘ C). Pseudo-first-order and pseudosecond-order kinetic models were applied to results of
adsorption capacity in order to predict the nature of the
kinetics.
All the experiments were performed in triplicate;
ANOVA and Fisher’s exact tests were employed for statistical
analyses of data.
Journal of Chemistry
3
317.9∘ C
100
80
0.8
−51.29%
0.6
60
0.4
466.6∘ C
40
80.3∘ C
−22.81%
20
0.2
Weight loss rate (mg/min)
−7.72%
1.0
Weight (%)
Table 2: Features of all prepared samples.
1.2
0.0
0
100
200 300 400 500
Temperature (∘ C)
600
700
Figure 1: Raw rice husk’s thermogravimetric analyses.
Table 1: Raw rice husk chemical composition.
Compound
Cellulose
Hemicellulose
Lignin
Ash
Moisture
Percentage (%)
30.6
18.3
29.9
19.5
4.9
3. Results and Discussion
3.1. Sample Preparation. Table 1 shows the RHw composition
determined by chemical analysis. These results are in the
same range of previously reported values [26] and are
significant since superficial OH groups present in compounds
such as cellulose, hemicellulose, and lignin could interact
with the contaminants in the adsorption process [27]. In
addition, chemical analysis shows that rice husk contains 19%
ash, which, according to previous reports, is composed of
95% silica (SiO2 ), an important aspect for its use as adsorbent
material [28].
Thermogravimetric analyses (Figure 1) showed that the
overall mass loss of rice husk can be divided into steps
related to loss of moisture, hemicellulose, cellulose, and
lignin. Thus, a mass loss of 7.72% at 100∘ C was confirmed
due to the elimination of moisture retained in this material.
Afterwards, a second step was obtained between 250 and
350∘ C, corresponding to the highest mass loss (51.29%). This
step is related to hemicellulose and cellulose decomposition,
as well as loss of the remaining adsorbed water [29]. Lignin
decomposition occurs in the 360 to 520∘ C range. Finally, no
significant mass loss was observed at higher temperatures
indicating the presence of oxides.
From TGA results, the calcination temperatures for
thermal treatment on rice husk were chosen: 300∘ C near
to the maximum mass loss peak and 500∘ C after the loss
of compounds that could influence the material adsorption
capacity. Additionally, the 700∘ C value was selected, because
no more mass losses are presented and only rice husk mineral
Material
RHw
RHc
RHc300
RHc500
RHc700
Rice husk features
Without any treatment
With chemical treatment
With chemical and thermal treatment to 300∘ C
With chemical and thermal treatment to 500∘ C
With chemical and thermal treatment to 700∘ C
residue remains. After this thermal treatment, calcined samples at 300, 500, and 700∘ C were obtained (namely, RHc300,
RHc500, and RHc700, resp.).
In summary, after chemical and thermal treatments on
rice husks, five materials were prepared and physiochemically characterized. Onto these materials, Cd (II) adsorption
capacity was evaluated. Table 2 shows the five materials
prepared for Cd (II) adsorption.
3.2. Samples Characterization. The specific surface area of
rice husk samples was determined by nitrogen adsorption
isotherm at 77 K using an Autosorb-iQ 07165, Quantachrome
Instrument. Values of specific surface area of rice husk
samples were calculated by Brunauer-Emmett-Teller (BET)
method and are consigned in the last column of Table 4.
There, an important decrease in the specific surface area value
of rice husk chemically treated (4 m2 /g) in relation to the
sample without treatment (13 m2 /g) can be seen. This change
can be attributed to the effects of NaOH on the material either
by partial degradation of some components of the rice husk,
generating merging of smaller pores (micropores) into large
pores (mesopores) [30], or because of the fixing of NaOH on
the surface of the material which may cause blockage in the
pores.
With the thermal treatment, RHc300 sample showed the
greatest specific surface area of all studied materials, 14 m2 /g,
probably due to changes in pore volume. However, the higher
calcination temperature, the smaller specific surface area,
as can be seen for samples RHc500 (7 m2 /g) and RHc700
(6 m2 /g). In this regard, Della et al. [31] reported that
higher increases in rice husk calcining temperature cause an
agglomeration effect, diminishing porosity. But also our own
previous research results (without publishing) indicate that,
in rice husk treated with NaOH and calcined at 700∘ C, silicon
dioxides were organized into a crystalline structure known as
cristobalite. Due to the fact that the rice husk specific surface
area increases when silica in the ash is amorphous [31, 32], the
presence of cristobalite could explain the decrease in specific
surface area in RHc700 sample.
Figure 2 shows SEM microphotographs of RHw, RHc,
and RHc300 samples. Image of RHw sample (Figure 2(a))
shows a section of the rice husk where well-defined and
organized cavities are observed. Although in image of
RHc sample (Figure 2(b)) the structure is preserved, some
cracking of cavities can be observed. This cracking, which
generates deformation of the pores and loss of regularity,
could be explained by the intracellular breakdown that NaOH
causes [33]. Furthermore, some agglomerations observed on
4
Journal of Chemistry
(a)
(b)
(c)
Figure 2: Microphotographs of RHw (a), RHc (b), and RHc300 (c) materials.
the material may possibly be due to NaOH fixed on the
surface.
RHc300 sample microphotograph (Figure 2(c)) shows
that the collapse of rice husk structure continues not only
by intracellular breakdown caused by NaOH but also by
the combustion that generates degradation in the material
structure and loss of part of carbon phase.
Figure 3 shows SEM microphotographs of RHc500 and
RHc700 samples. Both samples show a surface with less
roughness than RHc300 (Figure 2(c)) sample, but RHc700
(Figure 3(b)) has the cleanest surface with well-defined pores
on it.
Figures 4 and 5 show the IR spectrum for thermally
untreated and treated samples, respectively. In all spectra,
above 1,200 cm−1 the organic part of rice husk can be distinguished, and below 1,200 cm−1 the presence of vibrations
corresponding to different forms of silicon appears [34].
Figure 4 shows the IR spectrum for RHw and RHc
samples. RHw sample spectrum (dashed line) has some
highlighted bands, as the characteristic of hydroxyl groups
(-OH) at 3,418 cm−1 , the vibration of C-H at 2,918 cm−1 ,
and the one at 1,650 cm−1 corresponding to C=C bond
vibration. These bands, also reported by other authors [35,
36], correspond to the main organic compounds of the rice
husk: cellulose, hemicellulose, and lignin. Also, a significant
band at 1,100 cm−1 , evidence of Si-O bonds present in cyclic
siloxanes, is observed. The presence of cyclic siloxanes could
be confirmed by peaks occurring between 470 and 800 cm−1 .
Additionally, the peaks at 1,101 and 3,418 cm−1 , distinctive of
-Si-O and -O-H, could be evidence of silanol groups [34, 36].
There are few differences in spectra shown in Figure 4;
however, for RHc sample (solid line), widening of the band
corresponding to the vibrations of the OH and a decrease
in the intensity of the band associated with cyclic siloxanes
at 1,100 cm−1 can be seen. These changes are only due to the
chemical treatment.
On the other hand, there are significant differences
between thermally treated and untreated rice husks. Figure 5
shows the spectrum of all thermally treated samples, RHc300,
RHc500, and RHc700.
It can be seen that as the heat treatment temperature
increases, the characteristic bands of main rice husk organic
Journal of Chemistry
5
(a)
(b)
Figure 3: Microphotographs of RHc500 (a) and RHc700 (b) materials.
100
Table 3: C/O and C/Si ratios obtained by EDX analysis for all
adsorbent materials.
80
70
Transmittance (%)
90
60
Material
RHw
RHc
RHc300
RHc500
RHc700
Ratio
C/O
1.8
1.5
1.1
0.5
0.3
C/Si
4.5
18.9
1.2
0.6
0.4
50
4,000 3,500 3,000 2,500 2,000 1,500 1,000
Wavelength (cm−1 )
500
0
RHw
RHc
Figure 4: IR spectrum of RHw (dashed line) and RHc (solid line)
samples.
100
80
70
60
50
40
30
Transmittance (%)
90
20
3,900
3,400
2,900
2,400 1,900 1,400
Wavelength (cm−1 )
900
10
400
RHc300
RHc500
RHc700
Figure 5: IR spectrum of RHc300 (dashed line), RHc500 (solid line),
and RHc700 (dotted line) samples.
compounds are decreasing. On the contrary, the band corresponding to the -Si-O vibration (1,100 cm−1 ) is gaining
intensity, probably due to the formation of silica-rich ashes.
The C/O and C/Si relationships for each sample were
obtained by energy-dispersive X-ray spectroscopy (EDX)
analysis and are contained in Table 3. According to the
results, the RHw material has the highest C/O ratio, because
the rice husk is composed mostly of carbonaceous rings of
lignin, cellulose, and hemicellulose. The C/O relationship
for chemically treated husk rice (RHc) is lower than that
in the raw material (RHw); this agrees with IR results that
showed an increase in OH groups for RHc sample. Besides,
the C/Si ratio for the RHc material increases relative to the
one for raw material (see Table 3), indicating a decrease in
silicon (as reported in the IR analysis). The Si decrease may
be due to effect of NaOH washing on the material, since it
has been reported that NaOH is capable of reacting with the
silicon present in the husk forming sodium silicates, which
are soluble and could be removed with water washes carried
out after chemical treatment of the husk [25, 37].
Table 3 also shows that for heat treated materials a
progressive decrease in C/O and C/Si ratios is observed. This
is due to the combustion process that generates progressive
loss in carbon phase, while the silicon remains constant
(relative to the RHc sample).
6
Journal of Chemistry
Table 4: Specific surface area, adsorption capacity, and percentage of Cd (II) adsorption onto adsorbent materials.
RHw
RHc
RHc300
RHc500
RHc700
Adsorption
Capacity (mg/g)
7.44
17.45
28.27
2.03
2.03
3.3. Adsorption Experiments. Experimental data of Cd (II)
adsorption on all studied materials were fitted to the Langmuir and Freundlich isotherms models. According to the
parameters obtained in the setting of these models, the RHw
and RHc materials adapt to Freundlich isotherm model, while
the remaining materials, RHc300, RHc500, and RHc700, fit to
Langmuir isotherm model.
Results of Cd (II) adsorption analysis for all samples are
shown in Table 4. Although the major factors influencing
adsorption are the textural characteristics of adsorbents,
the results obtained and given in Table 4 do not show
a direct relationship between the adsorption capacity and
specific surface area of the samples. This could indicate that
adsorbate-adsorbent interaction occurs mainly thanks to the
active sites and functional groups present in each material.
These results agree with previously reported studies [38, 39].
From data in Table 4, it can be seen that adsorption
capacity for RHc sample was increased by more than 2 times
the value of RHw sample. This indicates that chemical treatment with NaOH effectively generates changes in the original
structure of rice husk, probably causing surface groups that
act as active sites and promote the affinity between Cd (II) and
the sample. In this regard, it has been reported that modification of lignocellulosic residues by NaOH treatment produces
changes in the fibers structure of biomass, which improve its
accessibility properties, in addition to possibly adding active
groups on the surface of material or leaving exposed surface
groups because degradation caused on structure [24].
The RHc300 sample showed the highest Cd (II) adsorption capacity. This is probably due to chemical characteristics:
its structure still has a carbon-oxygen phase from the organic
composition of raw rice husk; it has phase silicon groups such
as SiOH available on the surface, resulting from the thermal
treatment; and it possibly has active OH- groups incorporated
by treating with NaOH. The presence of all these active groups
on the surface of CAq300 favors interaction between sample
and Cd (II), generating greater efficiency in this material
compared to others [40–43].
The similarities in the physicochemical characteristics of
RHc500 and RHc700 samples could explain the coincidence
in their Cd (II) adsorption capacities.
Finally, from adsorption analysis, RHc300 was determined as the best sample in adsorbing Cd (II); therefore
this material was selected to determine the effect of pH and
kinetics of equilibrium on Cd (II) adsorption.
3.4. pH and Kinetics of Adsorption Studies for RHc300 Sample.
The effect of solution pH on Cd (II) adsorption for RHc300
sample (selected as the best adsorbent) was studied. The
Adsorption
Percentage (%)
31
75
95
5
8
Specific surface area
BET (m2 /g)
13
4
14
7
6
35
30
25
qe (mg g−1 )
Material
20
15
10
5
0
0
20
40
60
80
t (h)
100
120
140
160
Figure 6: Equilibrium time for Cd (II) adsorption onto RHc300
sample at pH = 6. Dashed line only shows data trend.
results showed that at pH 5 and 6 the adsorption percentages
are similar (98.83 and 98.89%, resp.), whereas the adsorption
at pH 4 was smaller, 98.36%. Statistically, it was determined
that the means of adsorption are different.
Figure 6 shows the Cd (II) adsorption capacity (𝑞𝑒 ) on
RHc300 sample as a function of time. From the graph, it was
determined that equilibrium time for adsorption is 72 hours.
After this time, changes in the adsorption capacity are less
than 1 mg/g.
From experimental data of equilibrium time for Cd (II)
adsorption onto RHc300 sample, the highest correlation
coefficient (𝑅2 = 0.999) was obtained for the pseudo-secondorder kinetic model. This implies that chemisorption is
the rate-limiting step in the adsorption process [44]. As
chemisorption is characterized by formation of monolayer,
this result is consistent with our assumption of Langmuir
isotherm model, which states that the monolayer adsorption
occurs on specific sites of the homogeneous surface. Additionally, these results are also consistent with those obtained
by Kumar et al. [45] who found that adsorption of Cd (II) on
rice husk ash fits the pseudo-second-order kinetic model.
4. Conclusions
The chemical (HCl and NaOH) and thermal treatments
(300∘ C for 3 h) on rice husk increase its Cd (II) removal
efficiency almost four times. Although chemical and thermal
treatments produced changes in the specific surface area of
Journal of Chemistry
studied samples, the adsorption capacity of samples shows
no direct relationship with their specific surface area. Thus,
it could be considered that, in this system, the binding
adsorbate-adsorbent is mainly due to the presence of active
groups on the surface of adsorbent materials.
The maximum Cd (II) adsorption capacity was
28.27 mg/g at an optimum pH 6.0 for RHc300 sample. On
the other hand, the kinetic studies revealed that adsorption
process followed the pseudo-second-order kinetic model.
This implies that chemisorption is the rate-limiting step in
the adsorption process.
Although other adsorbents have shown the same or even
greater adsorption efficiencies, as Duolite GT-73 [46], rice
husk has high availability and low cost. This indicates that the
RHc300 material, which requires less energy investment than
rice husk ash, could be an excellent alternative for removing
Cd (II) from aqueous media for pH values ranging from 4 to
6.
7
[11]
[12]
[13]
[14]
[15]
Conflicts of Interest
[16]
The authors declare that there are no conflicts of interest
regarding the publication of this paper.
Acknowledgments
The authors acknowledge University of Tolima for the financial support (Project code 860113). The authors also thank
Group on Porous Solids and Calorimetry, Department of
Chemistry, Faculty of Science, University of the Andes, for
experimental support.
References
[1] J. H. Duffus, ““Heavy metals”—a meaningless term?” Pure and
Applied Chemistry, vol. 75, no. 9, article 1357, 2003.
[2] Z. Rengel, Heavy Metals as Essential Nutrients, Springer, Berlin,
Heidelberg, Germany, 2004.
[3] U. Forstner and G. T. W. Wittmann, Metal Pollution in the
Aquactic Environment, Springer, 2nd edition, 1979.
[4] O. Barbier, G. Jacquillet, M. Tauc, M. Cougnon, and P. Poujeol,
“Effect of heavy metals on, and handling by, the kidney,”
Nephron - Physiology, vol. 99, no. 4, pp. 105–110, 2005.
[5] G. Kazantzis, “Cadmium, osteoporosis and calcium metabolism,” BioMetals, vol. 17, no. 5, pp. 493–498, 2004.
[6] J. Y. Barbee Jr. and T. S. Prince, “Acute respiratory distress
syndrome in a welder exposed to metal fumes,” Southern
Medical Journal, vol. 92, no. 5, pp. 510–512, 1999.
[7] J. Godt, F. Scheidig, C. Grosse-Siestrup et al., “The toxicity of
cadmium and resulting hazards for human health,” Journal of
Occupational Medicine and Toxicology, vol. 1, article 22, 2006.
[8] A. Bożęcka, M. Orlof-Naturalna, and S. Sanak-Rydlewska,
“Removal of lead, cadmium and copper ions from aqueous
solutions by using ion exchange resin C 160,” Gospodarka
Surowcami Mineralnymi, vol. 32, no. 4, pp. 129–140, 2016.
[9] S. He, B. Ruan, Y. Zheng, X. Zhou, and X. Xu, “Immobilization
of chlorine dioxide modified cells for uranium absorption,”
Journal of Environmental Radioactivity, vol. 137, pp. 46–51, 2014.
[10] W.-Q. Zhuang, J. P. Fitts, C. M. Ajo-Franklin, S. Maes, L.
Alvarez-Cohen, and T. Hennebel, “Recovery of critical metals
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
using biometallurgy,” Current Opinion in Biotechnology, vol. 33,
pp. 327–335, 2015.
H. Wang and Z. J. Ren, “Bioelectrochemical metal recovery
from wastewater: A review,” Water Research, vol. 66, pp. 219–
232, 2014.
V. K. Gupta and I. Ali, “Utilisation of bagasse fly ash (a sugar
industry waste) for the removal of copper and zinc from
wastewater,” Separation and Purification Technology, vol. 18, no.
2, pp. 131–140, 2000.
S. Basha, Z. V. P. Murthy, and B. Jha, “Sorption of Hg(II) onto
carica papaya: experimental studies and design of batch sorber,”
Chemical Engineering Journal, vol. 147, no. 2-3, pp. 226–234,
2009.
A. Saeed, M. Iqbal, and W. H. Höll, “Kinetics, equilibrium
and mechanism of Cd2+ removal from aqueous solution by
mungbean husk,” Journal of Hazardous Materials, vol. 168, no.
2-3, pp. 1467–1475, 2009.
J. Anwar, U. Shafique, Waheed-uz-Zaman, M. Salman, A. Dar,
and S. Anwar, “Removal of Pb(II) and Cd(II) from water by
adsorption on peels of banana,” Bioresource Technology, vol. 101,
no. 6, pp. 1752–1755, 2010.
N. Azouaou, Z. Sadaoui, A. Djaafri, and H. Mokaddem,
“Adsorption of cadmium from aqueous solution onto untreated
coffee grounds: equilibrium, kinetics and thermodynamics,”
Journal of Hazardous Materials, vol. 184, no. 1-3, pp. 126–134,
2010.
V. Lugo-Lugo, C. Barrera-Dı́az, F. Ureña-Núñez, B. Bilyeu, and
I. Linares-Hernández, “Biosorption of Cr(III) and Fe(III) in
single and binary systems onto pretreated orange peel,” Journal
of Environmental Management, vol. 112, pp. 120–127, 2012.
C. R. T. Tarley and M. A. Z. Arruda, “Biosorption of heavy
metals using rice milling by-products. Characterisation and
application for removal of metals from aqueous effluents,”
Chemosphere, vol. 54, no. 7, pp. 987–995, 2004.
X. Liu, X. Chen, L. Yang, H. Chen, Y. Tian, and Z. Wang, “A
review on recent advances in the comprehensive application of
rice husk ash,” Research on Chemical Intermediates, vol. 42, no.
2, pp. 893–913, 2016.
Renu, M. Agarwal, and K. Singh, “Heavy metal removal from
wastewater using various adsorbents: a review,” Journal of Water
Reuse and Desalination, 2016, article jwrd2016104.
U. Kumar and M. Bandyopadhyay, “Sorption of cadmium
from aqueous solution using pretreated rice husk,” Bioresource
Technology, vol. 97, no. 1, pp. 104–109, 2006.
A. Chakraverty, P. Mishra, and H. D. Banerjee, “Investigation of
combustion of raw and acid-leached rice husk for production of
pure amorphous white silica,” Journal of Materials Science, vol.
23, no. 1, pp. 21–24, 1988.
S. Chandrasekhar, K. G. Satyanarayana, P. N. Pramada, P.
Raghavan, and T. N. Gupta, “Review processing, properties and
applications of reactive silica from rice husk—an overview,”
Journal of Materials Science, vol. 38, no. 15, pp. 3159–3168, 2003.
B. S. Ndazi, S. Karlsson, J. V. Tesha, and C. W. Nyahumwa,
“Chemical and physical modifications of rice husks for use
as composite panels,” Composites Part A: Applied Science and
Manufacturing, vol. 38, no. 3, pp. 925–935, 2007.
B. S. Ndazi, C. Nyahumwa, and J. Tesha, “Chemical and thermal
stability of rice husks against alkali treatment,” BioResources, vol.
3, no. 4, pp. 1267–1277, 2008.
P. T. Williams and N. Nugranad, “Comparison of products from
the pyrolysis and catalytic pyrolysis of rice husks,” Energy, vol.
25, no. 6, pp. 493–513, 2000.
8
[27] D. Sud, G. Mahajan, and M. P. Kaur, “Agricultural waste material
as potential adsorbent for sequestering heavy metal ions from
aqueous solutions—a review,” Bioresource Technology, vol. 99,
no. 14, pp. 6017–6027, 2008.
[28] N. Soltani, A. Bahrami, M. I. Pech-Canul, and L. A. González,
“Review on the physicochemical treatments of rice husk for production of advanced materials,” Chemical Engineering Journal,
vol. 264, pp. 899–935, 2015.
[29] H. Yang, R. Yan, H. Chen, D. H. Lee, and C. Zheng, “Characteristics of hemicellulose, cellulose and lignin pyrolysis,” Fuel, vol.
86, no. 12-13, pp. 1781–1788, 2007.
[30] T. N. Ang, G. C. Ngoh, and A. S. M. Chua, “Comparative study
of various pretreatment reagents on rice husk and structural
changes assessment of the optimized pretreated rice husk,”
Bioresource Technology, vol. 135, pp. 116–119, 2013.
[31] V. P. Della, I. Kühn, and D. Hotza, “Rice husk ash as an alternate
source for active silica production,” Materials Letters, vol. 57, no.
4, pp. 818–821, 2002.
[32] R.-S. Bie, X.-F. Song, Q.-Q. Liu, X.-Y. Ji, and P. Chen, “Studies on
effects of burning conditions and rice husk ash (RHA) blending
amount on the mechanical behavior of cement,” Cement and
Concrete Composites, vol. 55, pp. 162–168, 2015.
[33] S. Chakraborty, S. Chowdhury, and P. Das Saha, “Adsorption of
Crystal Violet from aqueous solution onto NaOH-modified rice
husk,” Carbohydrate Polymers, vol. 86, no. 4, pp. 1533–1541, 2011.
[34] M. Rozainee, S. P. Ngo, A. A. Salema, and K. G. Tan, “Fluidized
bed combustion of rice husk to produce amorphous siliceous
ash,” Energy for Sustainable Development, vol. 12, no. 1, pp. 33–
42, 2008.
[35] M. Akhtar, S. Iqbal, A. Kausar, M. I. Bhanger, and M. A.
Shaheen, “An economically viable method for the removal
of selected divalent metal ions from aqueous solutions using
activated rice husk,” Colloids and Surfaces B: Biointerfaces, vol.
75, no. 1, pp. 149–155, 2010.
[36] X. Luo, Z. Deng, X. Lin, and C. Zhang, “Fixed-bed column study
for Cu2+ removal from solution using expanding rice husk,”
Journal of Hazardous Materials, vol. 187, no. 1-3, pp. 182–189,
2011.
[37] T.-H. Liou and S.-J. Wu, “Characteristics of microporous/
mesoporous carbons prepared from rice husk under base- and
acid-treated conditions,” Journal of Hazardous Materials, vol.
171, no. 1–3, pp. 693–703, 2009.
[38] A. Erto, L. Giraldo, A. Lancia, and J. C. Moreno-Piraján, “A
comparison between a low-cost sorbent and an activated carbon
for the adsorption of heavy metals from water,” Water, Air, and
Soil Pollution, vol. 224, no. 4, article no. 1531, pp. 1–10, 2013.
[39] N. A. Medellin-Castillo, R. Leyva-Ramos, R. Ocampo-Perez et
al., “Adsorption of fluoride from water solution on bone char,”
Industrial and Engineering Chemistry Research, vol. 46, no. 26,
pp. 9205–9212, 2007.
[40] T. H. Baig, A. E. Garcia, K. J. Tiemann, and J. L. GardeaTorresdey, “Adsorption of heavy metal ions by the biomass of
Solanum elaeagnifolium (Silverleaf night-shade),” in Proceedings of the Hazardous Waste Research, pp. 131–142, 1999.
[41] K. K. Krishnani, X. Meng, C. Christodoulatos, and V. M. Boddu,
“Biosorption mechanism of nine different heavy metals onto
biomatrix from rice husk,” Journal of Hazardous Materials, vol.
153, no. 3, pp. 1222–1234, 2008.
[42] V. C. Srivastava, I. D. Mall, and I. M. Mishra, “Characterization
of mesoporous rice husk ash (RHA) and adsorption kinetics
of metal ions from aqueous solution onto RHA,” Journal of
Hazardous Materials, vol. 134, no. 1–3, pp. 257–267, 2006.
Journal of Chemistry
[43] V. C. Srivastava, I. D. Mall, and I. M. Mishra, “Adsorption
thermodynamics and isosteric heat of adsorption of toxic metal
ions onto bagasse fly ash (BFA) and rice husk ash (RHA),”
Chemical Engineering Journal, vol. 132, no. 1-3, pp. 267–278,
2007.
[44] Y. S. Ho, “Review of second-order models for adsorption
systems,” Journal of Hazardous Materials, vol. 136, no. 3, pp. 681–
689, 2006.
[45] P. S. Kumar, K. Ramakrishnan, S. D. Kirupha, and S. Sivanesan,
“Thermodynamic and kinetic studies of cadmium adsorption
from aqueous solution onto rice husk,” Brazilian Journal of
Chemical Engineering, vol. 27, no. 2, pp. 347–355, 2010.
[46] T. Vaughan, C. W. Seo, and W. E. Marshall, “Removal of selected
metal ions from aqueous solution using modified corncobs,”
Bioresource Technology, vol. 78, no. 2, pp. 133–139, 2001.
International Journal of
Medicinal Chemistry
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
International Journal of
Photoenergy
Organic Chemistry
International
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com
Advances in
International Journal of
Analytical Chemistry
Physical Chemistry
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 201
Volume 2014
International Journal of
Carbohydrate
Chemistry
Journal of
Quantum Chemistry
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Submit your manuscripts at
https://www.hindawi.com
The Scientific
World Journal
Hindawi Publishing Corporation
http://www.hindawi.com
Journal of
International Journal of
International Journal of
Inorganic Chemistry
Volume 2014
Journal of
Theoretical Chemistry
Hindawi Publishing Corporation
http://www.hindawi.com
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Spectroscopy
Hindawi Publishing Corporation
http://www.hindawi.com
Journal of
Analytical Methods
in Chemistry
Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Chromatography
Research International
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Electrochemistry
Hindawi Publishing Corporation
http://www.hindawi.com
Applied Chemistry
Bioinorganic Chemistry
and Applications
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Journal of
Journal of
International Journal of
Catalysts
Chemistry
Spectroscopy
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Volume 2014