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Removal of chromium by continuous flow using wool packed columns

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Adnan Manassra at Al-Quds University
Adnan Manassra
Mustafa Khamis at Al-Quds University
Mustafa Khamis
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Abstract and Figures

Wool was utilized for the removal of Cr from aqueous solution. The wool fibers exhibited selective removal of Cr(VI) at pH 1.0. Breakthrough curves showed that wool can absorb Cr(VI) up to the maximum range studied (600 mg /26 g) without saturation. The removal efficiency was found to be independent of the flow rate (between 2.3 and 6 mL/min) and the wool fiber length. Temperature was found to enhance the de-sorption process. The percentage of removal increased from 84% to 97% by increasing the Cr(VI) initial concentration from 5 ppm to 200 ppm. The results suggest cooperative binding of Cr(VI) to different binding sites on wool, or structural changes of the wool upon Cr(VI) binding. The affinity of wool sites for binding of Cr(VI) depends on local variations in pH leading to two distinguished modes. The first mode is reversible binding accompanied with small enthalpy change indicating physisorption. The second mode is irreversible with strong electrostatic interactions indicating chemisorption.
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!!
ISSN:!1579*4377!
REMOVAL OF CHROMIUM BY CONTINUOUS FLOW USING
WOOL PACKED COLUMNS
Manassra, A.*, Khamis, M., Ihmied, T and ElDakiky, M
+
.
Faculty of Science and Technology, Al-Quds University, Jerusalem, P.O.Box 20002, East Jerusalem, Palestine
amanasra@admin.alquds.edu
ABSTRACT
Wool was utilized for the removal of Cr from aqueous solution. The wool fibers exhibited
selective removal of Cr(VI) at pH 1.0. Breakthrough curves showed that wool can absorb
Cr(VI) up to the maximum range studied (600 mg /26 g) without saturation. The removal
efficiency was found to be independent of the flow rate (between 2.3 and 6 mL/min) and the
wool fiber length. Temperature was found to enhance the de-sorption process. The
percentage of removal increased from 84% to 97% by increasing the Cr(VI) initial
concentration from 5 ppm to 200 ppm. The results suggest cooperative binding of Cr(VI) to
different binding sites on wool, or structural changes of the wool upon Cr(VI) binding. The
affinity of wool sites for binding of Cr(VI) depends on local variations in pH leading to two
distinguished modes. The first mode is reversible binding accompanied with small enthalpy
change indicating physisorption. The second mode is irreversible with strong electrostatic
interactions indicating chemisorption.
KEYWORDS
Chromium, thermodynamics, continuous removal, wool, wastewater.
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INTRODUCTION
Chromium compounds are widely used by industries, such as metallurgical, electro-plating,
production of paints and pigments, tanning, and wood preservation [1, 2]. Large quantities of
this element are being discharged into the environment [3, 4]. The tanning industry is a large
contributor of pollution of water resources by Chromium ions. Chromium exists in +3 and
+6 oxidation states, as all other oxidation states are not stable in aqueous solution [5].
Hexavalent chromium, Cr(VI), is both toxic and carcinogenic. It is soluble in water and is
very mobile in biological systems. On the other hand, Cr(III) is less toxic, relatively
insoluble, and less mobile than Cr(VI). Hence, remediation of Cr(VI) contaminated soil and
groundwater has focused on reduction of Cr(VI) to Cr(III) [6, 7]. Leaching and seepage of
Cr(VI) from the soil into groundwater poses a considerable health hazard [8]. Recently,
direct metabolic reduction of Cr(VI) has received significant interest, since the technology
appears to be cost effective and does not produce secondary wastes [9-14].
Attempts to remove and/or recover chromium from wastewater by adsorption have
gained great interest in the last ten years. Several sorbents have been employed to remove
chromium from polluted waters, such as activated carbon [1, 15-17], biopolymers [18, 19],
non-living microorganisms, mineral solids [5, 20], soybean [9], bone charcoal [21, 22], fly
ash [23], sphagnum moss peat [24], pinus pinaster bark [25], leaf mould [26], coconut tree
sawdust carbon [27], and wool [28, 29]. Removal of Cr(III) ions by sand filtration [30]
suggested that flow techniques can provide efficient method for environmental remediation
of chromium (III) in polluted areas. In our laboratory, different low cost sorbents, such as
wool, olive cake, sawdust, pine needles, almond shells, cactus leaves and charcoal were
utilized for the removal of chromium ions from synthetic and industrial wastewater using
batch reactor. Natural wool yielded the largest adsorbed amounts of Cr(VI) whereas almond
shell was a poor sorbent [28]. Furthermore, it was demonstrated that at low pH, Cr(VI) is
selectively removed thus leaving Cr(III) in solution [28]. This observation opens the
horizon for utilizing wool in columns with continuous flow for the speciation of Cr(III) and
Cr(VI).
In this study, our aim was to use wool as sorbent for chromium ions by utilizing the
continuous flow technique to improve the efficiency and applicability of the removal and
speciation process. The continuous flow technique was carried out by using columns packed
with wool. The effect of pH, contact time, flow rate, initial metal concentration, sorbent size,
and temperature on the removal and speciation of chromium were assessed.
MATERIALS AND METHODS
Chemicals
All chemicals used were of analytical grades and used without any further purification.
Distilled deionized water was used for all sample preparations. The adsorbent used in this
study was wool. Wool was sheered from sheep, washed with distilled water and detergent,
dried to constant weight; then the fibers were sized to 0.5, 1, and 2 cm length along the fiber
longitude, prior to use. A 5000.0 ppm stock solution of Cr(VI) was prepared by dissolving
7.0719 g of AR grade K
2
Cr
2
O
7
in 0.500 L of distilled water. A 5000.0 ppm Cr(III) stock
solution was prepared by dissolving 12.8111g of AR grade CrCl
3
.6H
2
O in 0.500 L of
distilled water. Standard solutions of 0.0500, 0.100, 0.500, 1.00, 2.50, 3.50, and 5.00 ppm
M.Dakiky!et al. EJEAFChe, 9 (3), 2010. [651-663]
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Cr(VI) were used to prepare a calibration curve by appropriate dilution of stock solution.
Analytical solutions were prepared by dilution of the stock solution and adjusting the pH to
desired value by addition of either 1 M HCl or 1 M NaOH.
Instrumentation
pH was measured using MH-30G pH meter equipped with combined glass electrodes
calibrated with buffers 4.00 and 7.00. Total chromium concentrations were determined by a
VARIAN VISTA-charged Coupled Device Axial simultaneous Inductively Coupled Plasma-
Atomic Emission Spectrometer (VISTA CCD ICP-AES) with a concentric nebulizer. The
experiments were conducted using columns made of glass packed homogeneously with
wool. The internal diameter and length of columns were 2.4 cm and 50.0 cm, respectively.
The flow rate was adjusted by a tap at the bottom of the columns to either 2.3 mL/min, or 6.0
mL/min according to the experimental design.
Methods
The adsorption process was conducted in two modes. In the first mode, a constant
concentration of Cr(VI) ions was continuously applied and eluted. In the second mode, a
fixed concentration of either Cr(III), Cr(VI) or a mixture of both ions was loaded in the
columns and then total Cr release was studied by passing through the column solutions
having specific pH. It is worth mentioning that Cr(III) and Cr(VI) are stable under our
experimental conditions [5]. For the first mode, three liters of Cr(VI) solution of 5.00, 50.0,
100.0, and 200.0 ppm having pH 1 passed through the wool columns at constant flow rate
of 2.3 mL/min. For the second mode, 100.0 mL of each 5.00, 50.0, 100.0 and 200.0 ppm ion
solutions were first loaded on the columns at pH 1 and then Cr release was determined by
passing through the column solutions having pH values from 2.0 to 8.0. The concentration
of Cr in each eluted fraction was measured and consequently Cr uptake by wool was
calculated from the difference between the initial Cr concentration and Cr concentration in
the eluent. These experiments were carried out at room temperature in order to assess the
influence of pH, contact time, flow rate, initial concentration of chromium and sorbent size
on the efficiency of removal of chromium ions by wool. The de-sorption process was
investigated at three different temperatures and the thermodynamic parameters were
obtained. Each experiment was repeated three times and the percentage error was less than
2%.
RESULTS AND DISCUSSION
The ability of wool fibers to adsorb heavy metals ions, such as copper, cobalt, nickel, zinc
and chromium from their aqueous solutions were reported [28, 29, 31]. Capacity of wool to
adsorb metal ions from their effluent suggested the presence of a variety of reactive
chelating sites in wool. This led to the use of chromium in dying wool by a complexation
process with the dye substrate. By investigating this mechanism in our lab, wool was found a
good sorbent for hexavalent chromium at low pH by batch technique [28].
In this study, the continuous flow technique was used to speciate chromium (III) and
chromium (VI) by wool using the above specified two modes.
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FIRST MODE-CONTINUOUS APPLICATION OF CR(VI) SOLUTIONS
EFFECT OF CR(VI) CONCENTRATION IN THE ELUENT ON ITS PERCENT REMOVAL.
The effect of initial Cr(VI) concentration in the applied solution on the percentage of its
removal by wool was investigated. At each concentration three liters were applied
continuously to the column and collected in different fractions of 100 mL The percent
removal of Cr(VI) in the total collected fractions was found to increase from 84% for
initial concentration of 5.00 ppm to 97% for the initial concentration of 200.0 ppm at room
temperature and pH 1, Table [1]. Figure 1 presents the variation of the amount of Cr(VI)
removed in mg/g wool in each eluted fraction. Inspections of this figure reveal that no clear
breakthrough occurred. Hence, the adsorption process of Cr(VI) on wool proceeds in non-
classical fashion in which, most likely, structural changes of wool are continuously taking
place so that the numbers of active sites increase, thus accommodating more Cr(VI). This
points out to the possibility of cooperative adsorption of Cr(VI) on different binding sites of
wool. These structural changes might involve hydrogen bonding cleavage and formation due
to the presence of Cr(VI) on the active sites of wool, hence allowing more active sites to be
accessible for binding. Figure 2 displays the percentage removal of Cr(VI) in each fraction
collected. The data support the previous conclusion that no breakthrough is obtained. The
percent removal varies in each applied concentration from 100% to 84% for the lowest
applied concentration. Table 1displays the variation of the total removal of Cr by wool (in
mg of Cr(VI) per grams of wool) as a function of the initial concentration of Cr(VI) loaded
in the column. A linear relation existed between the mass of Cr(VI) adsorbed per 1.0 g wool
and initial concentrations of Cr(VI) loaded on the column. This suggests that higher
concentrations in solution in the vicinity of wool, result in shifting the equilibrium towards
more surface coverage of wool.
Table [1]: Percentage removal and total mass of Cr(VI) removed by wool as function of its continuously applied
concentration, using the first mode. Total volume applied = 3.0 L. Flow rate = 2.3 ml/min. Wool size = 0.50 cm.
Wool weight = 26 g. Wool depth = 19 cm. T= 25.0
о
C. Standard deviation of three replicates is given between
parentheses
Initial concentration of
Cr(VI) (ppm)
% Removal of Cr(VI) by
Wool
Mass of Cr(VI) (mg)
removed/one gram of
wool
5.0
84.
(1.0)
0.48
(0.01)
50.
91.
(1.5)
5.3
(0.09)
100.
95.
(1.7)
11.0
(0.19)
200.
97.
(1.6)
22.4
(0.37)
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Figure [1]: Uptake of Cr(VI) by wool as function of its applied volume using first mode. Total volume applied
= 3.0 L. Flow rate = 2.3 ml/min. Wool size = 0.50 cm. Wool weight = 26 g. Wool depth = 19 cm. T= 25.0
о
C.
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Figure![2]:!!Percentage!removal!of!Cr(VI)!by!wool!as!function!of!its!applied!
volume.!Total!volume!applied!=!3.0!L.!Flow!rate!=!2.3!ml/min.!Wool!size!=!0.50!
cm.!Wool!weight!=!26!g.!Wool!depth!=!19!cm.!T=!25.0!
о
C.!
!
Table 2: Uptake of Cr(VI) ions by wool after loading the columns with fixed initial mass of the ion, using second mode.
The initial loaded amounts of Cr(III), Cr(VI) and the 1:1 mixture of two ions on the columns were 6.0 mg.
6.0 mg, 3.0 mg and 3.0 mg, respectively. The eluent volume for each subsequent solution was 0.50 L. The
length of wool fiber is 0.50 cm. The mass and depth of wool in the column were 26 g and 19 cm,
respectively. T = 25.0
о
C. Standard deviation of three replicates is given between parentheses.
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Columns
Cr species added
Cr species added to the columns
Cr(III)
Cr(VI)
Mass of Cr (mg) leached at pH = 1
6.0
(0.01)
0.83
(0.01)
Mass of Cr (mg) leached at pH = 2
0.00
0.89
(0.01)
Mass of Cr (mg) leached at pH = 3
0.00
0.09
(0.001)
Mass of Cr (mg) leached at pH = 4-8
0.00
0.00
EFFECT OF FLOW RATE ON PERCENT REMOVAL OF CR(VI)
The effect of the flow rate on the percentage removal of the metal ion by wool was
investigated. The results showed that changing the flow rate at a certain range had no
significant effect on the percentage removal of Cr(VI) by wool from aqueous solution. The
removal of Cr(VI) at flow rates 2.3 and 6.0 ml/min stayed at 87% . It is known in the
literature that increasing the flow rates to higher values results in decreasing the removal
efficiency of the adsorbate species [32] which is in direct contraction to our observation.
Hence our results could be explained by the fact that in both flow rates the minimum contact
time was achieved between wool and free ions in solution. Hence the contact time factor
was not important at these two flow rates. We have also investigated the effect of fiber
length on the efficiency of removal. Three different wool lengths of 0.5, 1, and 2 cm along
the fiber longitude were used. The percent removal was found to be the same for all the sizes
tested. This points out that at this scale of wool, no packing effect is observed. Size effect
could be of measurable factor when nano scales are involved.
SECOND MODE-FIXED INITIAL LOAD OF CR
EFFECT OF CR FORM ON PERCENT REMOVAL
The adsorption of Cr(III), Cr(VI) and a 1:1 mixture of both ions was tested at three identical
columns packed with wool as described in the materials and method section. Table [2]
shows that at pH = 1 wool adsorbs 86% of Cr(VI), 0% of Cr(III) and 50% of a mixture of
Cr(III) and Cr(VI). The elution of the adsorbed chromium ions with solutions having pH 4
to 8 did not release any of the Cr(VI) adsorbed on wool initially. However, at pH 2 and 3,
15% and 1.5% of the remaining amount of absorbed Cr(VI) was eluted from the column.
These results can be explained by the presence of Cr(VI) as HCrO
4
-
and its favorable
interaction with the positively charged functional groups on the wool surface at low pH [33].
The 0% removal of Cr(III) is a result of the repulsion of the positive Cr(III) ions by the
positively charged active centers of R-NH
3
+
on the highly protonated wool at low pH. These
results are in full agreement with previous work on batch adsorption [28].
EFFECT OF INITIAL MASS OF CR(VI) LOADED IN THE COLUMN ON ITS PERCENT REMOVAL
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The adsorption process was followed at different initial mass of Cr(VI) ions loaded in the
column and then eluted with 1.0 L eluent having pH =1 divided to 10 equal fractions. Table
3 summarizes the results for the percentage removal in the total eluted fractions of Cr by
wool. The results indicate that the percent removal increased with increasing the initial
loaded mass of Cr(VI). In order to assess the fractionation of this total percentage upon the
different fraction collected, the mass of Cr(VI) in each 100 ml fraction eluted was
determined and plotted as function of fraction number (Figure 3). Inspection of Figure 3
reveals that at low loaded amount of Cr in the column, most of the mass of the eluted Cr was
found in the first few fractions, whereas the rest of the adsorbed Cr in the column was
resistant to elution. It should be noted that Table 3 indicates that overall just a small fraction
of Cr was desorbed from the column. Hence, the decreased amounts of Cr which are shown
to be eluted in Fig.4 at later stages are not due to depletion of Cr from the filter. On the other
hand, as the initial load of Cr increases, the amount of Cr in each fraction increases. This
result points out to the possible existence of two binding sites on wool: the first one involves
weak interactions between Cr(VI) ions and wool leading to reversible binding. The second
mode involves strong electrostatic attraction between the positively charged centers on wool
and the negatively charged HCrO
4
-
ions leading to the observed irreversible binding and
hence resistance to elution as observed above.
Figure [3]: Mass of Cr(VI) eluted in each 100. ml fraction at different initial load of the Cr on the
column. pH of eluent = 1. Flow rate 2.3 ml/min. Wool size = 0.50 cm. Wool weight = 26 g.
Wool depth = 19 cm. T= 25.0
о
C.
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Table [3]: Effect of initial mass of Cr(VI) ion loaded in the wool column on the percent removal of Cr(VI) using
second mode. Eluent pH = 1, total eluted volume =1.0 L divided into 10 equal fractions. Flow rate 2.3 ml/min. Wool
size = 0.50 cm. Wool weight = 26 g. Wool depth = 19 cm. Standard deviation of three replicates is given between
parenthesis.
Initial mass of Cr(VI)
(mg)
% of Cr(VI) which remains
adsorbed by Wool after elution by
1L
0.50
80.
(1.1)
1.0
82.
(1.4)
5.0
81.
(1.1)
10.
82.
(1.3)
20.
86.
(1.6)
DE-SORPTION THERMODYNAMICS
It was observed from analysis of the first grab sample after the column is left overnight that
the concentration of Cr(VI) in the leacheate increased abruptly (Fig. 4). Investigating this
behavior showed that the increase of Cr(VI) concentration in the leacheate due to column
stagnation depended on both the time of stagnancy and the initial concentration of Cr(VI)
passing through the column. In order to explain this behavior, we suggest the existence of
different binding sites on wool with different affinity towards Cr adsorption. Some of these
sites bind Cr in an irreversible, chemi-sorption type, whereas other binding sites bind Cr via
weak forces which lead to reversible adsorption [34].
In order to quantify the thermodynamics of adsorption, de-sorption studies were
performed on wool samples that were loaded with known initial mass of Cr(VI) and then
equilibrated with 3.0 liter aqueous solution with pH = 1 at 20.0, 27.0, and 35.0
o
C. Aliquots
from these solutions were analyzed for Cr(VI) concentration at different times and are
presented in Fig. 5. Inspection of this figure reveals that the maximal fractions of chromium
(VI) that leached from wool at pH = 1 were 31%, 35% and 40% at 20.0, 27.0 and 35.0
o
C,
respectively.
The process of Cr(VI) de-sorption can be summarized by the following reversible
process.
Wool-Cr(VI)
(s)
Cr(VI)
(aq)
Thermodynamic parameters such as equilibrium constant (K), free energy change
(ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were calculated using the
following equations [35]:
K = (M
L
) / (M
i
- M
L
)
L
.………..1
ΔH° was obtained from the slope of plot of ln K versus 1/T according the integrated
form of vant' Hoff equation (equation 2):
ln K = - ΔH°/RT + C …………...2
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ΔG° and ΔS° were obtained from equations 3 and 4.
ΔG° = -RT(ln K) ..……………....……3
ΔG° = ΔH° - TΔS°……….………….4
Where: K is the equilibrium constant of de-sorption, M
i
is the initial mass of Cr on
wool, M
L
is the mass of Cr leached, ΔH° is the change in Enthalpy of de-sorption, ΔG° is
the change of Free energy of de-sorption, ΔS° is the change entropy of de-sorption, T is
the temperature in Kelvin and R is the universal gas constant in J K
-1
mol
-1
.
Table 4 summarizes all the thermodynamic data for the desorption process. The
positive values of the free energy and enthalpy change indicate that the de-sorption process
is endothermic. The positive values of entropy change indicate, as expected, an increase in
the randomness at the solid / solution interface during the de-sorption process.
Figure [4]: Mass of Cr(VI) eluted in collected fraction. Fraction volume = 100. ml. Total applied volume = 10.0
L. pH of applied solution = 1. Wool size = 0.50 cm. Wool weight = 26 g. Wool depth = 19 cm. T= 25.0
o
C. O.
N stands for overnight.
Table [4]: Thermodynamic parameters for the de-sorption of Cr(VI) from wool. Volume of solution = 3.0 L. pH = 1.
Mass of wool = 26 g. Wool depth = 19 cm. Wool size = 0.50 cm. Initial mass of Cr(VI) on wool = 604 mg. Contact
time = 180 min. Standard deviation of three replicates is given between parenthesis.
Temperature / ºC
K
(0.01)
Δ G°/ ( KJ /mol)
(0.2)
ΔH°/ ( KJ /mol)
(0.2)
ΔS° / (J /mol K)
(2.0)
20.0
0.46
1.9
18.1
55.3
27.0
0.55
1.5
18.1
55.4
35.0
0.66
1.1
18.1
55.3
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Figure [5]: Mass of Cr(VI) desorbed from wool as function of contact time. Volume of solution = 3.0 L. pH =
1. Mass of wool = 26 g. Wool depth = 19 cm Wool size = 0.50 cm. Initial mass of Cr(VI) on wool = 604 mg.
Contact time = 180 min.
CONCLUSIONS
The continuous flow method utilizing wool as stationary phase provides a powerful
technique for the speciation of Cr(III) and Cr(VI) from their aqueous solutions. Cr(III) is
found to pass through the column without any significant removal at pH =1, whereas Cr(VI)
removal reached 97% at initial concentration of 200 ppm. Hence, at pH =1, Cr mixtures can
be separated by this method for the quantitative determination of the individual ions. The
desorption studies revealed that 85% of Cr adsorbed is irreversibly bound and resists elution
with eluents having pH values from 1-6. Thermodynamic parameters of adsorption were
found to be thermodynamically favorable with only small part to be desorbed at pH =1 and
2. Breakthrough curves indicated that wool can be a powerful sorbent for large concentration
of Cr with no significant saturation. The relationship between concentration of Cr and the
amount of Cr adsorbed by adsorbents was found to be linear in the concentration range
studied. We recommend the application of these findings in the construction of simple,
M.Dakiky!et al. EJEAFChe, 9 (3), 2010. [651-663]
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cheap, and reliable speciation columns in analytical chemistry. Furthermore, this method can
find applications in the field of industrial wastewater treatment. The potential recovery of the
Cr(VI) from the wool and consequently the regeneration of the fiber and recycling of
chromium ions are currently investigated.
ACKNOWLEDGEMENTS
The authors would like to thank the staff of the Center for Chemical and Biological Analysis
at Al-Quds University for the ICP analysis of the samples. Special thanks to Professor
Shlomo Nir for reviewing the manuscript. This project was supported by Al-Quds
University.
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... Figure 10 reveals that removal of Cr(VI) by wool loaded with ARS reaches a maximum of 77.8% at pH 2.0, and remains almost constant at higher pH. In previous studies [39][40][41], the optimum pH for Cr(VI) removal by free wool was 2.0, indicating that reduction of Cr(VI) is catalyzed by hydrogen ions. In this study, removal of Cr(VI) by wool loaded with ARS is essentially independent of pH. ...
... Based on the above results, Figure 13 shows a proposed two-step mechanism for removal of Cr(VI) by wool loaded with ARS (ARS-W). The second step is similar to that proposed in previous reports for removal of Cr(VI) by other natural adsorbents, but with ARS yielding oxidation products [39,41]. ...
... Processes 2019, 7, x FOR PEER REVIEW 11 of 14 reports for removal of Cr(VI) by other natural adsorbents, but with ARS yielding oxidation products [39,41]. ...
Cyclic Sequential Removal of Alizarin Red S Dye and Cr(VI) Ions Using Wool as a Low-Cost Adsorbent
Article
Full-text available
  • May 2020
Alizarin red S (ARS) removal from wastewater using sheep wool as adsorbent was investigated. The influence of contact time, pH, adsorbent dosage, initial ARS concentration and temperature was studied. Optimum values were: pH = 2.0, contact time = 90 min, adsorbent dosage = 8.0 g/L. Removal of ARS under these conditions was 93.2%. Adsorption data at 25.0 °C and 90 min contact time were fitted to the Freundlich and Langmuir isotherms. R2 values were 0.9943 and 0.9662, respectively. Raising the temperature to 50.0 °C had no effect on ARS removal. Free wool and wool loaded with ARS were characterized by Fourier Transform Infrared Spectroscopy (FTIR). ARS loaded wool was used as adsorbent for removal of Cr(VI) from industrial wastewater. ARS adsorbed on wool underwent oxidation, accompanied by a simultaneous reduction of Cr(VI) to Cr(III). The results hold promise for wool as adsorbent of organic pollutants from wastewater, in addition to substantial self-regeneration through reduction of toxic Cr(VI) to Cr(III). Sequential batch reactor studies involving three cycles showed no significant decline in removal efficiencies of both chromium and ARS.
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... However, there is a lack of experimental data on the use of biofibers in fixed bed column systems for metal biosorption. The studies evaluating the efficiency of continuous biosorption of Cr(VI) from synthetic aqueous solutions by short-chain polyaniline synthesized on jute fibers [139], Hibiscus Canabicus kenaf fibers [140], and wool fibers [141] can be mentioned as proof of concept. Additionally, for practical purposes, the information provided by fixed bed col studies is much more relevant and useful. ...
... However, there is a lack of experimental data on the use of biofibe fixed bed column systems for metal biosorption. The studies evaluating the efficien continuous biosorption of Cr(VI) from synthetic aqueous solutions by short-chain p aniline synthesized on jute fibers [139], Hibiscus Canabicus kenaf fibers [140], and fibers [141] can be mentioned as proof of concept. ...
Insights into the Applications of Natural Fibers to Metal Separation from Aqueous Solutions
Article
Full-text available
  • May 2023
There is a wide range of renewable materials with attractive prospects for the development of green technologies for the removal and recovery of metals from aqueous streams. A special category among them are natural fibers of biological origin, which combine remarkable biosorption properties with the adaptability of useful forms for cleanup and recycling purposes. To support the efficient exploitation of these advantages, this article reviews the current state of research on the potential and real applications of natural cellulosic and protein fibers as biosorbents for the sequestration of metals from aqueous solutions. The discussion on the scientific literature reports is made in sections that consider the classification and characterization of natural fibers and the analysis of performances of lignocellulosic biofibers and wool, silk, and human hair waste fibers to the metal uptake from diluted aqueous solutions. Finally, future research directions are recommended. Compared to other reviews, this work debates, systematizes, and correlates the available data on the metal biosorption on plant and protein biofibers, under non-competitive and competitive conditions, from synthetic, simulated, and real solutions, providing a deep insight into the biosorbents based on both types of eco-friendly fibers.
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... Many biopolymers find use in separative technology as adsorbents of either plant [1][2][3][4][5] or animal origin [6][7][8][9][10][11][12]. Both groups of biopolymeric adsorbents have been obtained from waste material after being treated using some suitable modifying techniques of chemical or physical character. ...
... However, this order changed to Cu(II) > Zn(II) > Pb(II) > Co(II) when the uptake was recalculated as mmol/g. Manassra et al. [8] utilized wool-packed columns to remove either Cr(VI) or Cr(III) from aqueous solutions using different eluent pH values. A low pH of 1 was effective for Cr(VI) uptake and higher pH was better for Cr(III). ...
Why Natural or Electron Irradiated Sheep Wool Show Anomalous Sorption of Higher Concentrations of Copper(II)
Article
Full-text available
Sorption of higher concentrations of Cu(II) solution onto natural sheep wool or wool irradiated by an electron beam was studied. Sorption isotherms were of unexpected character, showing extremes. The samples with lower absorbed doses adsorbed less than non-irradiated wool, while higher doses led to increased sorption varying with both concentration and dose. FTIR spectra taken from the fibre surface and bulk were different. It was concluded that there was formation of Cu(II)-complexes of carboxylic and cysteic acids with ligands coming from various keratin macromolecules. Clusters of chains crosslinked through the ligands on the surface limit diffusion of Cu(II) into the bulk of fibre, thus decreasing the sorption. After exhausting the available ligands on the surface the remaining Cu(II) cations diffuse into the keratin bulk. Here, depending on accessibility of suitable ligands, Cu(II) creates simple or complex salts giving rise to the sorption extremes. Suggestion of a mechanism for this phenomenon is presented.
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... They include ion exchange, membrane filtration, reverse osmosis, and adsorption [6,9,10]. Different adsorbents have been employed to remove chromium from polluted waters such as bentonite [4], activated aluminum and activated charcoal [11], wool [12], soya cake [13], peach kernel and nutshell [14], and functionalized activated carbon [15]. ...
Micelle-Clay Adsorption Efficiency towards the Removal of Cr(VI) from Aqueous Solutions
Chapter
Full-text available
  • Jan 2021
The removal efficiency of either clay (montmorillonite) or micelle-clay complex towards Cr(VI) in aqueous solutions was investigated. The micelle-clay complex was prepared from the adsorption of critical micelle concentration of octadecyltrimethylammonium ions onto clay. Batch experiments were conducted to investigate the effects of pH, contact time and adsorbent dosage on the removal efficiency of Cr(VI) from aqueous solutions. The experimental results were found to fit Langmuir adsorption isotherm in a significant manner. Columns charged with a mixture of micelle-clay complex and sand were used to assess the Cr(VI) removal efficiency under continuous flow at different pH values. The findings demonstrated that the micelle-clay complex used in this study was capable of removing Cr(VI) from aqueous solutions without any prior acidification of the sample. In additions, they revealed that the removal effectiveness of the complex was about 100% when optimal conditions for both batch and continuous flow techniques were used.
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... That is why adsorption of metal cations is reported in several papers [6][7][8]. However, anion removal is also examined [9][10][11][12]. All the authors applied the adsorbate concentrations under 10 mmol/L probably because the increasing concentration decreases the removal percentage. ...
Radiation-modified wool for adsorption of redox metals and potentially for nanoparticles
Article
Full-text available
  • Oct 2020
Electron beam irradiated sheep wool with absorbed radiation doses ranging from 0 to 165 kGy showed good adsorption properties toward copper cations. The Cu(II) being Lewis acid generated several types of complex salts based on carboxylates or cysteinates with ligands available in keratin. Under these conditions, cross-links were formed between the keratin chains. Experimental data obtained from Cu(II) adsorption using the concentration of 800-5,000 mg/L were tested for fitting to 10 isotherm models. Various compositions and architectures of the Cu(II)-complexes were specified to be responsible for different isotherm model fittings. The copper cation showed adherence to Langmuir, Flory-Huggins, and partially Redlich-Peterson models. The latter clearly distinguished the native wool from the modified ones. Another aim is to investigate the conditions for the adsorption of anti-microbial nanoparticles in addition to the redox-active metals on radiation-modified wool taking into account that the diffusion of nanoparticles into the modified wool is governed by electrostatic interactions.
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... Based on previous literature on the mechanism of adsorption of T. Dokmaji, et al. Environmental Nanotechnology, Monitoring & Management 14 (2020) 100319 chromium ions by different adsorbents (Fiol et al., 2008;Manassra et al., 2010;United States Environmental Protection Agency (USEPA, 1992), the following mechanism is proposed for the removal of Cr(III) and Cr(VI) by MWCNTs-M-SLS and MWCNTs-CTAB, respectively (Fig. 7). This figure allows for the observation of fast kinetics for the removal of both ions, since the removal of these ions by the ion exchange mechanism does not require any activation leading to the observed kinetics. ...
Chemically Modified Nanoparticles Usage for Removal of Chromium from Sewer Water
Article
  • Jun 2020
In this work, multiwall carbon nanotubes (MWCNTs) were chemically modified to yield products that speciate and selectively remove trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) from wastewater. The surface of MWCNTs were modified with cationic surfactant cetyl trimethyl ammonium bromide (CTAB), and yielded a product (MWCNTs-CTAB) that can remove Cr(VI) with 98% efficiency at optimum conditions. Surface modification with anionic surfactant sodium lauryl sulfate (SLS) after magnetization with magnetite (M) yielded a product (MWCNTs-M-SLS) that can remove Cr(III) with 99% efficiency at optimum conditions. Removal of Cr(III) by MWCNTs-M-SLS and Cr(VI) by MWCNTs-CTAB best fitted to Langmuir isotherm model with an adsorption capacity of 66.2 and 27.8 mg/g, respectively. Adsorption kinetics for removal of Cr(III) by MWCNTs-M-SLS and Cr(VI) by MWCNTs-CTAB, demonstrated that adsorption is very fast (< 5 min). Thermodynamic studies indicated that adsorption of Cr(VI) by MWCNTs-CTAB is an endothermic process with enthalpy, entropy and free energy of adsorption of 14.1 KJ/mol, 51.6 J/mol.K and -1.30 KJ/mol, respectively. Adsorption-desorption study of chromium from impregnated MWCNTs-CTAB was performed at different temperatures. At 25 °C, removal efficiency dropped from 98% to 73% to 60%, and at 35 °C, removal efficiency dropped from 98% to 75% to 61%, indicating that temperature did not have a significant effect on the regeneration process. Results indicate that a sequential plant can be designed and engineered for simultaneous speciation and removal of both ions from wastewater.
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... Some economical and abundant adsorbents were also reported for removal of Cr species from water and food samples like activated carbon (Khamis et al. 2009), agricultural by-products, waste materials, and minerals (Kuo et al. 2007;Lin et al. 2016;Ščančar and Milačič 2014). Reported data in the literature indicated that natural adsorbents for speciation analysis of Cr III and Cr VI are micelle-clay complexes and polymeric materials (Manassra et al. 2010). Several analytical techniques such as precipitation, ion exchange, adsorption, electrochemical precipitation, membrane separation, reverse osmosis, solvent extraction, and biosorption have been used for the removal of chromium (Qurie et al. 2013;Vinodhini and Das 2009;Zghida et al. 2003). ...
Chromium Speciation in Water Samples by Loading a New Sulfide-Containing Biodegradable Polymer Adsorbent in Tip of the Syringe System
Article
Full-text available
A new adsorbent poly-3-hydroxybutyrate-2-(dodecylthiocarbonothioylthio)-2-methylpropionate triester (PH-DTT-MPT) was first time loaded in a micropipette tip for speciation of chromium in different water samples. Total chromium (Cr), trivalent chromium (CrIII), and hexavalent chromium (CrVI) in different natural water samples were determined by electrothermal atomic absorption spectrometry. Known concentration of CrIII and CrVI was passed through a biodegradable polymer for investigation of the behavior of the newly used adsorbent. The newly used copolymer absorbed the CrIII on surface of the PH-DTT-MPT at pH 7.0, while CrVI was not adsorbed in desired pH value. After passing the real and standard solutions through the micropipette, then 2.0 mol L⁻¹ HCl was used for elution of CrIII from the biodegradable polymer. Total Cr was calculated after reducing CrVI into CrIII by specific concentration of hydroxy ammonium chloride (HONH2·HCl). The concentration of CrVI in different natural water samples was estimated after back calculation of CrIII from total chromium. Effect of analytical parameters like adsorbent, pH, eluent, sample volume, flow rates, and interfering ions was also studied. The LOD, LOQ, RSD, and EF of the developed method were calculated as 6.1 ng L⁻¹, 20 ng L⁻¹, 1.17%, and 90, respectively. Validation of developed method was checked by certified reference materials and spiking addition method. The developed method was successfully applied for determination of total Cr, CrIII, and CrVI in various natural water ecosystems.
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... Wool was found to be effective for complete removal of Cr(VI) from aqueous solutions. The optimum parameters for Cr(VI) adsorption and reduction into Cr(III) using wool in batch mode have been reported [2,[20][21]. ...
Design and optimization of a batch sequential contactor for the removal of chromium(VI) from industrial wastewater using sheep wool as a low-cost adsorbent
Article
  • Apr 2018
Cr(VI) removal from wastewater streams using sheep wool in sequential batch contactors (SBC) mode was investigated. The influence of the number of contactors on removal efficiency was also studied. SBC was carried out in tanks containing 100 and 1000 mL solutions. Four SBC runs ensured complete removal of Cr(VI) whereas three runs reduced its concentration from 100 to 0.06 mg/L. Experiments in both tanks gave similar results, thus permitting scalability to a pilot plant and eventual industrial scale utilization. Regeneration studies were carried out using KCl. The optimum parameters in terms of time, concentration and temperature were 25 min, 0.10 m and 50.0°C. Simultaneous adsorption-desorption cycles showed
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Effective removal of chromium from aqueous solution by adsorption on powdered wool: In-Silico studies of adsorption mechanism
Article
  • Sep 2022
Industrial wastewater contains a significant quantity of Chromium (VI) which is greatly mobile in water and soil. It is genotoxic, carcinogenic and accumulates in plant and animal bodies. Current work reports the chromium removal by adsorption on powdered wool. Wool was powdered mechanically to 90-120 mesh size. Powdered wool before and after chromium adsorption was characterized using FTIR, BET, EDX, XRD, TGA, and FE-SEM. Powdered wool (175 mg) removed 99.43% of Cr(VI) from the solution at pH 2.1 on shaking for 3.5 minutes at 20°C. Observed Langmuir adsorption capacity on powdered wool for Cr(VI) was 23 mg at 20°C. Used powdered wool was regenerated by washing with pH 12.6 buffer solutions and reused without much decrease in its adsorption capacity up to three cycles (91.0% removal). Cr(VI) binding mechanism with powdered wool protein was studied using molecular docking and observed predominant interacting forces were hydrogen bonding and Van-der-Waals forces revealed.
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Removal of chromium (VI) from aqueous solution by natural clay
Article
Full-text available
  • Aug 2018
The adsorption of chromium (VI) from aqueous solution was carried out using natural clay from western area in Saudi Arabia. The adsorbents used are characterized by X-ray diffraction (XRD) and other physico-chemical techniques. The various parameters affecting the adsorption process were investigated involving effect of initial concentration of Cr (VI) ion, temperature factor, dosage of adsorbent, pH of the solution, contact time and rotational per minute (RPM). Optimum conditions for adsorption process were; 50 mg/L-1 initial concentration of Cr(VI), adsorbent dose =1g, temperature ~ 25 o C, 3 hours contact time and pH=2, the obtained results were used to calculate the adsorption efficiency. Removal of chromium ion was found as highly depends on pH and initial Cr (VI) concentration of the solution. Langmuir isotherm was applied to get a maximum adsorption capacity of 18.68 mg/g. Although experimental data confirm with Langmuir isotherm model. The results of this study confirm that the material can be considered as effective adsorbents for the removal of chromium (VI).
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Adsorption of chromium ion by acid activated low cost carbon
Article
Full-text available
  • Oct 2007
A carbonaceous adsorbent prepared from an indigenous waste by acid treatment was tested for its efficiency in removing chromium ion. The parameters studied include agitation time, initial chromium ion concentration, carbon dose, pH and temperature. The adsorption followed first order reaction equation and the rate is mainly controlled by intra-particle diffusion. Freundlich and Langmuir isotherm models were applied to the equilibrium data. The adsorption capacity (Qm) obtained from the Langmuir isotherm plots were 11.51, 11.69, 12.00 and 12.57 mg/g respectively at an initial pH of 7.0 at 30, 40, 50 and 600C. The temperature variation study showed that the chromium ion adsorption is endothermic and spontaneous with increased randomness at the solid solution interface. Significant effect on adsorption was observed on varying the pH of the chromium ion solutions. Almost 65% removal of chromium ion was observed at 600C. The Langmuir and Freundlich isotherms obtained, positive H0 value, pH dependent results and desorption of dye in mineral acid suggest that the adsorption of chromium ion on BC involves physisorption mechanism.
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Interactions of chromium with microorganisms and plants
Article
Full-text available
  • Jun 2001
Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.
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Adsorption of Chromium(VI) on Chitosan‐Coated Perlite
Article
  • Jan 2003
Chitosan‐coated perlite beads were prepared by drop‐wise addition of a liquid slurry containing chitosan and perlite to an alkaline bath. The beads were characterized by SEM and EDS x‐ray microanalysis. The chitosan content of the beads was 23%, as determined by a pyrolysis method. Adsorption of hexavalent chromium from aqueous solutions on chitosan‐coated perlite beads was studied under both equilibrium and dynamic conditions. The effect of pH on adsorption was also investigated. The data were fitted to the Langmuir adsorption isotherm. The adsorption capacity of chitosan‐coated perlite was found to be 104 mg/g of adsorbent from a solution containing 5000 ppm of Cr(VI). On the basis of chitosan, the capacity was 452 mg/g of chitosan. The capacity was considerably higher than that of chitosan in its natural and modified forms, which was in the range of 11.3 to 78 mg/g of chitosan. The beads loaded with chromium were regenerated with sodium hydroxide solution of different concentrations. A limited number of adsorption‐desorption cycles indicated that the chitosan‐coated beads could be regenerated and reused to remove Cr(VI) from waste streams.
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Adsorption of hexavalent chromium by chitosan‐based polymeric surfactants
Article
Chitosan-based polymeric surfactants (CBPSs) were prepared by the partial N-acylation of amine groups on chitosan with acid anhydrides. To apply the CBPSs for the removal of Cr(VI) commonly found in wastewater, a batch test was conducted to evaluate the adsorption capacity. The removal efficiency of Cr(VI) by the CBPS depended on several factors, including the solution pH, CBPS dose, and ionic strength. Our results show that the CBPSs exhibited a greater adsorption capacity for Cr(VI) than have other modified chitosans reported in the literature. The maximum adsorption capacity of Cr(VI) was 180 mg/g of CBPS at a final pH of 5.3. From the results of dynamic light scattering, we propose that the removal mechanism of Cr(VI) by the CBPSs was mainly through the adsorption of negatively charged chromium ions by positively charged amine groups on the CBPSs followed by colloidal precipitation because of its lower solubility. Conclusively, we found that the CBPS was significantly effective for the removal of Cr(VI). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 44–50, 2005
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Removal of Hexavalent Chromium from Wastewaters by Bone Charcoal
Article
  • Feb 1999
The adsorption of hexavalent chromium onto bone charcoal was studied as a function of time, amount of charcoal, pH, concentration of chromium and sample volume. The cross interference with other elements was also investigated. Tests were carried out with solutions of chromium(VI) at concentrations between 5 and 25 mg · L–1. Chromium removal efficiencies higher than 90% were achieved at pH = 1 using 2 g of bone charcoal and a stirring time in the order of 30 min. Acid and alkaline pretreatments of bone charcoal did not improve the sorption capacity of bone charcoal against Cr(VI). The presence of other ions had practically no influence on the chromium removal. The presence of a matrix of tannery effluents did not reduce the removal capacity of bone charcoal for Cr(VI), but it was confirmed that only 47% of Cr(III) can be removed using these conditions.
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Removal of Some Heavy Metals From Polluted Water by Aquatic Plants: Studies on Duckweed and Water Velvet
Article
The uptake of iron and copper by duckweed (Lemna minor L.) and water velvet (Azolla pinnata R.Br) was investigated in solutions enriched with 1·0, 2·0, 4·0 and 8·0 ppm of these two metal ions which were renewed every 2 days over a 14-day test period. The uptake rate of both the metal ions was highest when the initial concentration in the test solutions was 1·0 ppm. The concentrations of iron of copper remaining, after 2 days, in the solutions treated with duckweed or water velvet at 2·0, 4·0 and 8·0 ppm ion level increased over the 14 days, except in solutions treated with water velvet at iron concentrations of 2·0 and 4·0 ppm. The presence of one metal ion in solution decreased the uptake rate of the other metal ion; e.g. when duckweed was kept in a solution containing copper alone at 8·0 ppm level, the value of the metal concentration factor after 14 days was 51·20. However, in the presence of an equal concentration of iron the value of this factor was 26·53, indicating the influence of iron on the uptake rate of copper.
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The Treatment of Chromium Wastewaters Using the Sorptive Potential of Leaf Mould
Article
Previous work has shown that a range of relatively low-cost organic materials can be used to absorb chromium ions from aqueous solution. The results of batch adsorption trials indicate that leaf mould also has the potential for use in this way. The optimum pH for the process was found to be 2·0, with the kinetics following a second-order reaction rate. Intraparticulate diffusion was not a rate-determining step at this pH.
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Heavy metal contaminants removal by soil washing
Article
The feasibility of soil washing for decontaminating a silty sand spiked with cadmium, chromium, lead, and zinc was evaluated in laboratory-scale batch and column experiments. Soil samples were subjected to chelant extraction using a solution of disodium salt of ethylenediaminetetraacetic acid (Na(2)EDTA), sodium metabisulfite (Na(2)S(2)O(5)) solution (an inexpensive reducing reagent), and a solution containing a mixture of the two reagents. Batch and column washing of the contaminated soil with deionized water (DI water) revealed that approximately 70% of the cadmium in the sample is weakly bound and readily mobilized in aqueous solution at neutral pH, followed by approximately 25%-30% of zinc, approximately 20%-25% chromium, and only approximately 10% of lead. Of the washing reagents tested, Na(2)EDTA solutions were generally more effective than Na(2)S(2)O(5) for removing heavy metals from the soil samples. Na(2)EDTA preferentially extracted lead over zinc and cadmium but exhibited little impact on chromium removal. Cadmium and, especially zinc, removal by a 0.01-M Na(2)EDTA solution were enhanced considerably by inclusion of 0.1 M Na(2)S(2)O(5), suggesting that a mixture of the two reagents may provide an economically optimum solution for certain contaminated soils.
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Environmental Monitoring of Chromium in Air, Soil, and Water
Article
  • Sep 1997
Historical uses of chromium have resulted in its widespread release into the environment. In recent years, a significant amount of research has evaluated the impact of chromium on human health and the environment. Additionally, numerous analytical methods have been developed to identify and quantitate chromium in environmental media in response to various state and federal mandates such as CERCLA, RCRA, CWA, CAA, and SWDA. Due to the significant toxicity differences between trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium, it is essential that chromium be quantified in these two distinct valence states to assess the potential risks to exposure to each in environmental media. Speciation is equally important because of their marked differences in environmental behavior. As the knowledge of risks associated with each valence state has grown and regulatory requirements have evolved, methods to accurately quantitate these species at ever-decreasing concentrations within environmental media have also evolved. This paper addresses the challenges of chromium species quantitation and some of the most relevant current methods used for environmental monitoring, including ASTM Method D5281 for air, SW-846 Methods 3060A, 7196A and 7199 for soils, sediments, and waste, and U.S. EPA Method 218.6 for water.
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Chromium Adsorption and Cr(VI) Reduction to Trivalent Chromium in Aqueous Solutions by Soya Cake
Article
Chromium as Cr(VI) is a industrially produced pollutant. Hexavalent chromium can be reduced to the trivalent state using various reductive agents or it can be removed from solution by surface-active adsorbents. In this study, both of these methods were evaluated using soya cake. A high efficiency for reduction of Cr(VI) to trivalent chromium was observed at pH < 1. Increasing the temperature, also increased the yield. Experimentally, the optimum time and soya cake mass were 5h and 0.7 g, respectively. In the second treatment method, a high efficiency for adsorption of chromium was also observed at pH < 1. The favorable temperature for adsorption was found to be 20 degrees C. Experimentally, the best time was 1h and with increasing soya cake mass up to 30 g, the adsorption efficiency was increased. Dissolution of LiCl in the experimental solutions, increased the efficiency of adsorption, however, this effect was not observed in the case of KCl. Langmuir isotherm constants, Q and b, for ground soybeans, were found to be 2.8 x 10(-4)mg/mg and 0.623, respectively. Freundlich isotherm constants, K(f) and n, were found to be 1.4 x 10(-4) and 4.99, respectively.
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