A new low cost adsorbent, activated
Heightened awareness of arsenic toxicity and regulatory changes has prompted considerable research efforts toward developing methods for arsenic removal from drinking water [
Naturally occurring arsenic contaminates groundwater in many countries including Argentina, Australia, Chile, China, Hungary, India, Mexico, Peru, Taiwan, Thailand, and the United States [
Fresh and healthy leaves of
Physical parameters of activated
Number | Physical parameter | Value |
---|---|---|
1 | pH | 8.5 |
2 | Conductivity | 0.18 |
3 | Moisture (%) | 7.05 |
4 | Ash (%) | 10.6 |
5 | Bulk density (Kg/L) | 0.92 |
6 | Specific gravity | 0.86 |
7 | Porosity (%) | 36 |
8 | Surface area (m2/g) | 1.5146 |
9 | Particle size (microns) | >53 |
10 | Color | Black |
All chemicals were of analytical grade (
To evaluate optimum working conditions, batch mode experiments were performed in conical flasks placed on an orbital shaker with 100 mL of As(V) solution having initial concentration 20 mg/L. To study the effect of adsorbent dose in the range (0.2–1.2 g/100 mL) at room temperature (303 K), pH was adjusted to 7.0, and contents were agitated for 140 min at a speed of 120 rpm. Afterwards, suspensions were filtered to remove adsorbent and filtrates were subjected to analysis on ICP-OES to find out the remaining amount of sorbate in aqueous phase with arsenic standards, drawing regression line to interpolate samples concentration. In the next experiment, most favorable adsorbent dose was added according to the findings of previous trial, while pH was changed from 3.0 to 12.0 with speed of agitation 120 rpm, time of contact 140 min, and temperature 303 K. Likewise, in studying the effect of contact time, adsorbent dose and pH were selected optimally in accordance with the findings of previous trials, while time of contact was changed in the range 20–180 min at 303 K, shaking the contents at 120 rpm.
Isotherm studies were performed in four 250 mL Erlenmeyer flasks. Each flask was filled with 100 mL of As(V) solutions of different initial concentrations (5–20 mg/L) and pH was adjusted to 7.0. To each flask, 1.2 g of adsorbent was added, and solutions were agitated at a speed of 120 rpm for 140 min.
The biosorption data have been subjected to Langmuir, Freundlich, Temkin, Dubinin Radushkevich (D-R), and Flory-Huggins (F-H) isotherm models.
A basic assumption of the Langmuir theory is that sorption takes place at specific homogeneous sites within the sorbent. This model can be written in linear form:
On the other hand, the Freundlich equation is represented by the following:
The Temkin isotherm, the simple form of an adsorption isotherm model, has been developed considering the chemisorption of an adsorbate onto the adsorbent and is represented as
The equilibrium data were also analyzed using the D-R isotherm model to determine the nature of biosorption processes as being physical or chemical. The linear presentation of the D-R isotherm equation is expressed by
On the other hand, the Flory-Huggins (F-H) isotherm equation is represented by the following:
Equilibrium constants of various isotherm models for the adsorption of arsenic on activated
Isotherm | Isotherm constants | Temperature | ||
---|---|---|---|---|
303 K | 313 K | 323 K | ||
Langmuir |
|
0.3542 | 0.4134 | 0.4901 |
|
6.2313 | 6.7672 | 7.3752 | |
|
0.9958 | 0.9955 | 0.9945 | |
SD | 0.0257 | 0.0261 | 0.0278 | |
|
||||
Freundlich |
|
34.4215 | 29.8751 | 26.0321 |
|
1.6572 | 1.8756 | 2.1718 | |
|
0.9935 | 0.9916 | 0.9862 | |
SD | 0.0070 | 0.0082 | 0.0104 | |
|
||||
Temkin |
|
22.7653 | 21.7821 | 20.7317 |
|
14.2619 | 13.1447 | 11.8766 | |
|
0.9976 | 0.9965 | 0.9935 | |
SD | 0.1002 | 0.1287 | 0.1839 | |
|
||||
D-R |
|
0.0294 | 0.0204 | 0.0116 |
|
7.4578 | 8.0825 | 9.0467 | |
|
0.9736 | 0.9638 | 0.9478 | |
SD | 0.0326 | 0.0387 | 0.0471 | |
|
||||
F-H |
|
0.6034 | 0.5332 | 0.4364 |
|
59.0391 | 55.1087 | 49.6569 | |
|
0.9935 | 0.9916 | 0.9881 | |
SD | 0.0070 | 0.0082 | 0.0099 |
The adsorbent doses were varied from 0.2 g to 1.2 g. It was observed that the removal of arsenic increased with the increase in dosage, attaining a maximum at 1.2 g of adsorbent dosage (Figure
Effect of adsorbent dose on biosorption of arsenic.
Percentage of arsenic removal was recorded at contact time of 20 min to 180 min. The results are shown in Figure
Effect of time variation on biosorption of arsenic.
The effect of pH on removal of arsenic is shown in Figure
Effect of pH on biosorption of arsenic.
Adsorption of As(V) by
(a) Plot of the Langmuir isotherm for arsenic biosorption onto
The other isotherm models, namely, D-R (Figure
Hence the order of isotherm equations obeyed by the present data is Temkin > Langmuir > F-H > Freundlich > D-R isotherm.
An increase in temperature resulted in an increased rate of Arsenic adsorption onto
The thermodynamic parameters were calculated using the following equations:
Thermodynamic parameters of arsenic sorption on activated
Temperature (K) | Value | |
---|---|---|
|
||
303 | −5.5611 | |
313 | −5.7544 | |
323 | −5.9686 | |
|
608.4237 | |
|
20.3507 |
The change in the free energy (
The values of
This study focused on the biosorption of As(V) onto biosorbent material (
Based on all results, it can be concluded that
The authors declare that there is no conflict of interests regarding the publication of this paper.