Rubber wood sawdust was carbonized into charcoal by chemical treatment which was used for removal of lead ion from aqueous solution. The work involves batch experiments to investigate the pH effect, initial concentration of adsorbate, contact time, and adsorbent dose. Experimental data confirmed that the adsorption capacities increased with increasing inlet concentration and bed height and decreased with increasing flow rate. Adsorption results showed a maximum adsorption capacity of 37 mg/g at 308 K. Langmuir, Freundlich, and Temkin model adsorption isotherm models were applied to analyze the process where Temkin was found as a best fitted model for present study. Simultaneously kinetics of adsorption like pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were investigated. Thermodynamic parameters were used to analyze the adsorption experiment. Fourier transform infrared spectroscopy, scanning electron microscope, and energy dispersive X-ray spectroscopy confirmed the batch adsorption of lead ion onto chemically carbonized rubber wood sawdust.
Water pollution due to contamination of toxic lead ions is a serious problem for human health and environment. Lead discharged from petrochemical, organic, and inorganic fertilizer, oil refineries, and automobile industries contaminates the ground water and surface water [
In this study chemically carbonized rubber wood sawdust (CCRWSD) was utilized for removal of lead ions from synthetic wastewater. The pH effect, initial concentration, contact time, and adsorbent dose in batch mode were investigated. In addition isotherm, kinetic, and thermodynamic study were carried out to compare the experimental data and to understand the adsorption behavior of lead ion onto CCRWSD.
Rubber wood sawdust was collected from rubber wood processing industry, Nagechera, Tripura, India. The carbonization and activation were done in two steps, where in first step rubber wood sawdust (10 gm) was added in concentrated sulphuric acid (11 mL, 98% m/m) for carbonization and kept for 10 minutes. Then in second step carbonized black slurry was mixed with concentrated nitric acid (6.6 mL, 65% m/m) and kept in air oven at 150°C for 24 hours. Carbonized sawdust was centrifuged with deionized water until the pH became neutral and dried in
Atomic absorption spectrophotometer (Perkin Elmer Model AAS 700) was utilized to determine the lead concentration in effluent and influent samples. Fourier transform infrared spectroscopy (FTIR) (Bruker 3000 Hyperion, Germany) was used to study the functional group present in adsorbent. Scanning electron microscope (SEM) (JELO JSM7600F) supported by EDS (energy dispersive X-ray spectroscopy) (Oxford AZtech energy system) was utilized to characterize the surface of adsorbent.
Batch experiment was carried out in a thermostatically controlled magnetic stirrer at 30°C with the speed of 120 rpm. A 0.5 g of CCRWSD was utilized at different concentration (5 mg/L to 30 mg/L) and at different pH (2.1 to 6.8). The experiment was done at different adsorbent dose (0.25 g/L to 5 g/L). For thermodynamic study the adsorption experiment was conducted in three different temperatures (303 K, 313 K, and 323 K). After completing every batch experiment the solution was filtered and sample was tested to know the residual lead concentration.
Before and after adsorption functional groups were identified by using FTIR in the range of 400–4000 cm−1 as shown in Figures
FTIR spectra of CCRWSD.
FTIR spectra of lead ion loaded CCRWSD.
SEM image of CCRWSD.
SEM image of lead ion loaded CCRWSD.
EDS spectra of CCRWSD.
EDS spectra of lead ion loaded CCRWSD.
Adsorption capacity is increased with the increasing of solution pH from 2.1 to 5.6 and then starts to decrease with increasing pH as shown in Figure
Effect of pH on the adsorption of lead ions onto CCRWSD (
Effect of contact time on adsorption of lead ion onto CCRWSD is shown in Figure
Effect of contact time on the adsorption of lead ions onto CCRWSD (
It is found that adsorption capacity increases from 9.82 to 36.4 mg/g with the increase in initial lead ion concentration from 5 to 30 mg/L. At lower concentration maximum adsorption sites are available for adsorption of lead ion. On the other hand at higher concentration many lead ions left unabsorbed in the solution as the entire binding site get saturated by lead ion.
Adsorption capacity increases from 3.96 mg/g to 37 mg/g with the decreasing of adsorbent dose from 5 g/L to 0.25 g/L. As binding sites of adsorbent increase with the increasing adsorbent amount the removal percentage increases.
In batch adsorption process, Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherm models were utilized to describe the equilibrium data.
Langmuir adsorption isotherm [
Parameters of Langmuir, Freundlich, and Temkin adsorption isotherm constants for adsorption of lead onto CCRWSD.
Langmuir | Freundlich | Temkin | Dubinin-Radushkevich | ||||
---|---|---|---|---|---|---|---|
|
41.15 |
|
27.63 |
|
8.16 |
|
32.06 |
|
2.73 |
|
2.44 |
|
308.76 |
|
0.0031 |
|
0.859–0.960 |
|
0.988 |
|
34.1 |
|
12.70 |
|
0.992 |
|
0.993 |
|
0.954 |
Langmuir isotherm (pH = 5.6,
Langmuir isotherm can be checked by the value of
Linear form of the Freundlich isotherm is expressed as [
Freundlich isotherm (pH = 5.6,
Temkin isotherm model is generally expressed as [
Temkin isotherm (pH = 5.6,
Linearized form of Dubinin-Radushkevich isotherm equation [
D-R isotherm (pH = 5.6,
These parameters give the information about sorption mechanism, either chemical ion-exchange or physical sorption. D-R parameters are calculated from the plot of
After calculation of all isotherms it is observed that the value of correlation coefficients (
Adsorption kinetic studies were conducted to have a better and broader understanding of the dynamic behaviour of lead adsorption onto CCRWS. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models are applied to study the adsorption process.
Pseudo-first-order model [
The values of
A pseudo-first-order, pseudo-second-order, and intraparticle diffusion model parameter for adsorption of lead ion onto CCRWSD.
Constants | Initial concentration (mg/L) | |||
---|---|---|---|---|
5 | 10 | 15 | 20 | |
|
9.82 | 19.31 | 28.05 | 35.8 |
Pseudo-first order | ||||
|
7.58 | 16.52 | 27.29 | 31.87 |
|
0.0283 | 0.0377 | 0.0301 | 0.0458 |
|
0.991 | 0.995 | 0.984 | 0.990 |
Pseudo-second order | ||||
|
10.12 | 2.02 | 3.26 | 37.45 |
|
0.016 | 0.600 | 0.199 | 0.004 |
|
0.998 | 0.995 | 0.988 | 0.998 |
Intraparticle diffusion | ||||
|
0.709 | 1.488 | 2.294 | 2.763 |
|
0.873 | 0.895 | 0.926 | 0.872 |
Pseudo-second-order model [
Pseudo-second-order model (pH= 5.6, dose = 0.5 g/L, contact time = 180 min, and temperature = 30°C).
Adsorption process is also checked by applying intraparticle diffusion model which is expressed as [
Intraparticle diffusion model (pH= 5.6, dose = 0.5 g/L, contact time = 180 min, and temperature = 30°C).
Results of the model are summarized in Table
Thermodynamic study of lead ion adsorption by CCRWSD was conducted in three different temperatures (303, 313, and 323 K). Gibbs free energy (
Thermodynamic plot for adsorption of lead ions onto CCRWSD (pH = 5.6, dose = 0.5 g/L, contact time = 180 min, and concentration = 20 mg/L).
A summary of calculated thermodynamic parameter is given in Table
Thermodynamic parameters for lead adsorption (pH = 5.6, dose = 0.5 g/L, contact time = 180 min, and concentration = 20 mg/L).
|
|
|
|
---|---|---|---|
303 | +10.474 | +51.332 | −5.064 |
313 | −5.627 | ||
323 | −6.089 |
CCRWSD was found as a feasible adsorbent medium with maximum adsorption capacity of 37 mg/g in batch mode. The adsorption capacity is greatly affected by the pH of sample solution and its concentration. Batch experimental data shows a good agreement with Temkin isotherm model and the pseudo-first-order kinetic model. For low cost and high adsorption capacity CCRWS would be a good promising adsorbent for lead contaminated wastewater treatment.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors are thankful to Director of National Institute of Technology Agartala for providing necessary research facilities.