The present work investigates the potential of
Phenol is one of the crucial pollutants released from the wastewater originating from the chemical industries like pulp and paper, gas and coke manufacturing, tanning, textile, plastics, rubber, pharmaceutical industries, ferrous industries and petroleum refinery and its substantial concentration in wastewater is listed in Table
The concentration of phenol in wastewater released from various industries.
Industrial source | Phenol concentration, mg/L |
---|---|
Petroleum refineries | 40–185 |
Petrochemical | 200–1220 |
Textile | 100–150 |
Leather | 4.4–5.5 |
Coke ovens | 600–3900 |
Coal conversion | 1700–7000 |
Ferrous industry | 5.6–9.1 |
Rubber industry | 3–10 |
Pulp and paper industry | 22 |
Wood preserving industry | 50–953 |
Phenolic resin production | 1600 |
Phenolic resin | 1270–1345 |
Fiberglass manufacturing | 40–2564 |
Paint manufacturing | 1.1 |
Phenol causes adverse effects on public health and environment. As per United States Environmental Protection Agency (USEPA) the allowable concentration of phenol in surface water should be less than 1.0
Various treatment methods such as biodegradation, biosorption, membrane separation, pervaporation, solvent extraction, distillation, and adsorption using activated carbon prepared from various precursors had been reviewed by Girish and Ramachandra Murty [
But the drawback associated with the above materials is high cost and being nonrenewable in nature, which is a major economic consideration. This has excited a growing research interest in the production of activated carbon from locally available agricultural materials, especially for application concerning wastewater treatment [
A vast number of agricultural materials have been used as adsorbents for the removal of phenolic compounds from wastewater. These include date stone [
In the process of quest for new agricultural wastes as precursor for adsorbent, attempts have been made to produce adsorbent from dry stem of lantana trees by the chemical treatment process.
A systematic study of the adsorption of phenol on chemically treated lantana material was reported. It also addresses the batch experiments conducted to study the effect of process variables such as pH, adsorbent dosage, initial phenol concentrations, and temperature on adsorption. The optimum experimental conditions were determined and thermodynamic studies were carried out to determine the nature of the adsorption process. From the literature, it is understood that the adsorption of phenol can be by three possible mechanisms: the
Phenol has a chemical formula C6H5OH with a molecular weight of 94 g/mol. Phenol of analytical grade (Merck India Ltd.) was used for the preparation of stock solution of concentration 1000 mg/L. The experimental solutions of concentration varying from 25 to 250 mg/L were prepared by diluting the stock solution to accurate proportions.
The other chemicals potassium hydroxide (Merck India Ltd., AR grade), potassium nitrate (Merck India Ltd., AR grade), zinc chloride (Merck India Ltd., AR grade), hydrochloric acid (SD Fine Chemicals, India, AR grade), sulphuric acid (SD Fine Chemicals, India, AR grade), and orthophosphoric acid (SD Fine Chemicals, India, AR grade) were used for the chemical treatment of carbon.
The material
The proximate analysis of the untreated carbon.
Parameter | Value (%) |
---|---|
Volatile matter | 46.66 |
Moisture | 6.66 |
Ash | 5.229 |
Fixed carbon | 41.451 |
The various properties were determined by the standard procedures [
The influence of various experimental parameters such as pH, adsorbent dosage, contact time, and temperature on the adsorption of phenol from aqueous solutions was optimised in a batch mode of studies. The pH of solution was maintained at 2.5 to 12 by adding 0.1 M HCl or 0.1 M NaOH; the adsorbent dosages of both HCl and KOH treated carbon were varied from 0.25 to 3 g and the temperature varied from 298 to 328 K. After optimising the experimental parameters, the equilibrium and kinetic and thermodynamic studies were conducted in 250 mL conical flasks containing 200 mL phenol solution of different initial concentrations of 25, 50, 100, 150, 200, and 250 mg/L under the optimum conditions. The flasks were agitated in a temperature controlled shaker at 140 rpm and 298 K for 7 h and 8 h, respectively, for adsorbent treated with HCl and KOH, respectively, until equilibrium was established. After reaching the equilibrium time, the samples were taken from the flasks and filtered and the residual phenol concentrations were analysed using double beam UV spectrophotometer (UV-1700, Shimadzu, Japan). The samples were analysed spectrophotometrically at a wavelength of 270 nm by the aid of technical calibration curve prepared prior to the analysis [
The amount of phenol adsorbed per gram of carbon (
The percentage removal of the phenol is given by
The kinetic studies were carried out similar to those of equilibrium studies. The aqueous samples were collected at regular intervals and the concentrations of phenol solutions were similarly measured.
The proximate analysis of the raw powder which was carried out is shown in Table
The removal capacity, average particle size, pore volume, and the specific surface area for various carbons.
Chemically treated carbons | |||||||
---|---|---|---|---|---|---|---|
Untreated | H3PO4 | KNO3 | H2SO4 | ZnCl2 | HCl | KOH | |
Particle size, |
23.86 | 17.98 | 16.19 | 19.71 | 14.22 | 11.59 | 11.68 |
Specific surface area, m2/g | 115.15 | 109.90 | 210.59 | 170.71 | 206.65 | 349.56 | 328.72 |
Pore volume, m3/g | 0.1113 | 0.1305 | 0.1789 | 0.1716 | 0.1392 | 0.2780 | 0.2761 |
% Phenol removal | 68.9 | 72.6 | 82.3 | 84.1 | 76.2 | 94.4 | 95.2 |
The FTIR spectra of adsorbent treated with HCl before and after phenol adsorption are shown in Figure
The FTIR spectral analysis of adsorbent treated with HCl.
Peak | Frequency (cm−1) | Difference | Assignment | |
---|---|---|---|---|
Before adsorption | After adsorption | |||
1 | 3620 | 3610 | −10 | O–H stretching in phenol |
2 | 1203 | 1218 | −15 | C–O group in alcohol |
3 | 1689 | 1697 | +8 | C=O stretch of carboxylic acid |
4 | 1558 | 1566 | +8 | C=C bond of aromatic ring |
The FTIR spectra of adsorbent treated with HCl before and after phenol adsorption.
The adsorbent treated with KOH showed the FTIR spectrum as given in Figure
The FTIR spectral analysis of adsorbent treated with KOH.
Peak | Frequency (cm−1) | Difference | Assignment | |
---|---|---|---|---|
Before adsorption | After adsorption | |||
1 | 3610 | 3633 | +23 | O–H stretching in phenol |
2 | 1365 | 1362 | −3 | C–O ring of alcohol |
3 | 2923 | 2920 | −3 | C–H stretching of alkane group |
4 | 1743 | 1712 | −31 | C=O in carboxylic group |
The FTIR spectra of adsorbent treated with KOH before and after phenol adsorption.
Because of the amphoteric nature of a carbon surface, the adsorption properties are influenced by the pH value of the solution. Phenol is a weak acid with acid dissociation value (pKa) of 9.8 and it dissociates into phenoxide ion when pH > pKa. At higher pH values the concentration of the negatively charged phenoxide ion increases and the electrostatic repulsions occur between the negative surface charge of the carbon and the phenoxide anions in solution. At lower pH values, phenolic compounds are present as the unionized acidic compounds [
The effect of pH on % removal for adsorbent treated with HCl (initial concentration: 150 mg/L; volume: 200 mL; dosage: 0.75 g/L).
Similarly, from Figure
The effect of pH on % removal for adsorbent treated with KOH (initial concentration: 150 mg/L; volume: 200 mL; dosage: 1 g/L).
To study the effect of adsorbent dose on phenol adsorption, the experiments were conducted at initial phenol concentration of 200 mg/L. Figures
The effect of adsorbent dosage on % removal for adsorbent treated with HCl (initial concentration: 150 mg/L; volume: 200 mL; pH: 7.5).
The effect of adsorbent dosage on % removal for adsorbent treated with KOH (initial concentration: 150 mg/L; volume: 200 mL; pH: 8.5).
The initial concentration gives an important driving force required to overcome all mass transfer resistances of all molecules between the aqueous and solid phases [
The plot showing the effect of initial concentration on % removal for the adsorbents (the initial concentration: 25 to 250 mg/L; dosage: 0.75 g/L for adsorbent (HCl) and 1 g/L for adsorbent (KOH); volume: 200 mL).
The plot showing the time v/s % removal for adsorbent treated with HCl (the initial concentration: 25 to 250 mg/L; dosage: 0.75 g/L; volume: 200 mL).
The plot showing the time v/s % removal for adsorbent treated with KOH (the initial concentration: 25 to 250 mg/L; dosage: 1 g/L; volume: 200 mL).
The effect of temperature on the adsorption of phenol at various concentrations onto adsorbent treated with HCl and KOH is shown in Figures
The plot showing the effect of temperature on % removal for adsorbent treated with HCl (the initial concentration: 25 to 250 mg/L; dosage: 0.75 g/L; volume: 200 mL).
The plot showing the effect of temperature on % removal for adsorbent treated with KOH (the initial concentration: 25 to 250 mg/L; dosage: 1 g/L; volume: 200 mL).
Adsorption isotherm describes the relationship between the amount of a solute adsorbed and its concentration in the equilibrium solution at a constant temperature. Adsorption isotherm is important to understand the solute-adsorbent interactions and optimization of the use of adsorbents. Several models have been investigated in the literature to describe experimental data of adsorption isotherm. The equilibrium isotherms like Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms were analysed in this study. A trial and error procedure was employed to estimate the above isotherms parameters by minimizing the error distribution between experimental data and predicted data using the solver add-in with Microsoft’s Excel [
The Langmuir isotherm is based on the assumption that the adsorption process will take place uniformly within the adsorbent surface and with uniform distribution of energy level [
The Langmuir isotherm is
The Langmuir isotherm can also be expressed by a separation factor (
Table showing the nature of the process depending on the value of separation factor (
|
Unfavourable |
|
Linear |
|
Favourable |
|
Irreversible |
The
Freundlich isotherm [
Temkin isotherm [
The Temkin isotherm has been used in the following form:
The Dubinin-Radushkevich model [
The calculated isotherm constants by nonlinear method are represented in Tables
The various parameters and the model equation for adsorbent treated with HCl.
Isotherm model | Model parameter |
|
Model equation |
---|---|---|---|
Langmuir |
|
0.9955 |
|
|
|||
Freundlich |
|
0.9869 |
|
|
|||
Temkin |
|
0.91827 |
|
|
|||
D-R |
|
0.9323 |
|
The various parameters and the model equation for adsorbent treated with HCl.
Isotherm model | Model parameter |
|
Model equation |
---|---|---|---|
Langmuir |
|
0.9964 |
|
|
|||
Freundlich |
|
0.9811 |
|
|
|||
Temkin |
|
0.90717 |
|
|
|||
D-R |
|
0.9283 |
|
The comparison of various isotherm models for adsorbent treated with HCl.
The comparison of various isotherm models for adsorbent treated with KOH.
The comparison of maximum monolayer adsorption capacity of phenol onto various agricultural adsorbents from the literature is presented in Table
Comparison of monolayer adsorption capacity for phenol onto other various adsorbents.
Adsorbent |
|
Reference |
---|---|---|
Date stones | 90.3 | [ |
|
80 | [ |
Vegetal cords | 6.21 | [ |
Banana peel | 688.9 | [ |
Palm seed coat | 18.3 | [ |
Oil palm empty fruit bunch | 4.868 | [ |
Date pit | 262.3 | [ |
Black stone cherries | 133.33 | [ |
Vetiver roots | 145 | [ |
Sugarcane bagasse | 35.71 | [ |
|
9.25 | [ |
|
112.5 | Present work |
|
91.07 | Present work |
The feasibility of the adsorption process was estimated by the determination of thermodynamic parameters like free energy change (
The determined thermodynamic parameters for adsorbent treated with HCl.
Conc. |
|
|
|
|
|
|
---|---|---|---|---|---|---|
mg/L | 298 K | 308 K | 318 K | 328 K | ||
25 | −7077.08 | −6781.68 | −6486.28 | −6190.88 | −15880.00 | −29.54 |
50 | −6623.08 | −6357.68 | −6092.28 | −5826.88 | −14532.00 | −26.54 |
100 | −6248.73 | −6046.07 | −5843.41 | −5640.75 | −12288.00 | −20.266 |
150 | −5748.2 | −5557.2 | −5366.2 | −5175.2 | −11440.00 | −19.1 |
200 | −5339.3 | −5167.8 | −4996.3 | −4824.8 | −10450.00 | −17.15 |
250 | −5264.41 | −5101.37 | −4938.33 | −4775.29 | −10123.00 | −16.304 |
The determined thermodynamic parameters for adsorbent treated with KOH.
Conc. |
|
|
|
|
|
|
---|---|---|---|---|---|---|
mg/L | 298 K | 308 K | 318 K | 328 K | ||
25 | −7352.88 | −7038.48 | −6724.08 | −6409.68 | −16722 | −31.44 |
50 | −6901.54 | −6703.84 | −6506.14 | −6308.44 | −12793 | −19.77 |
100 | −6548.55 | −6432.63 | −6316.71 | −6200.79 | −10003 | −11.5921 |
150 | −5976.61 | −5871.5 | −5766.4 | −5661.29 | −9108.8 | −10.5107 |
200 | −5738.52 | −5640.32 | −5542.13 | −5443.94 | −8664.7 | −9.8194 |
250 | −5498.06 | −5415.18 | −5332.29 | −5249.41 | −7968 | −8.28839 |
The van’t Hoff plot for adsorbent treated with HCl.
The van’t Hoff plot for the adsorbent treated with KOH.
Adsorption kinetics has been examined to determine the adsorption mechanism. The various kinetic models reported that adsorption depends on the chemical nature of adsorbent, experimental conditions, and the mass transfer process. Therefore, in order to investigate the mechanism of present adsorption process and the rate-determining step, the different kinetic models like pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were verified and the adsorption capacities were found.
The pseudo-first-order kinetic model in linear form is given by Lagergren [
The kinetic constants of first-order and second-order for adsorbent (HCl treated).
Conc. (mg/L) | First-order kinetic | Second-order kinetic | ||||||
---|---|---|---|---|---|---|---|---|
|
|
|
|
|
|
|
| |
25 | 6.2933 | 9.78 | 7.3329 | 0.96574 | 6.82 | 24.90 | 0.1158 | 0.99732 |
50 | 12.48 | 8.5211 | 13.0785 | 0.9729 | 14.16 | 7.98 | 0.1594 | 0.99327 |
100 | 24.64 | 10.20 | 33.148 | 0.95395 | 33.79 | 2.26 | 0.2580 | 0.99569 |
150 | 36.56 | 9.9489 | 51.394 | 0.97226 | 46.30 | 1.65 | 0.3537 | 0.987 |
200 | 47.89 | 9.327 | 60.52 | 0.96477 | 56.445 | 1.50 | 0.4779 | 0.99053 |
250 | 59.7 | 11.51 | 73.9 | 0.9541 | 64.3 | 1.48 | 0.6119 | 0.9898 |
The kinetic constants of first-order and second-order for adsorbent (KOH treated).
Conc. (mg/L) | First-order kinetic | Second-order kinetic | ||||||
---|---|---|---|---|---|---|---|---|
|
|
|
|
|
|
|
| |
25 | 4.76 | 6.49 | 3.8939 | 0.98778 | 5.27 | 2.23 | 0.06193 | 0.9958 |
50 | 9.418 | 6.07 | 7.5262 | 0.98794 | 10.593 | 1.024 | 0.1149 | 0.9939 |
100 | 18.65 | 6.033 | 15.85 | 0.96661 | 20.24 | 0.540 | 0.2212 | 0.9916 |
150 | 27.51 | 5.987 | 23.36 | 0.98688 | 29.152 | 0.3617 | 0.3073 | 0.9913 |
200 | 36.44 | 6.033 | 32.32 | 0.9836 | 37.9836 | 0.246 | 0.3549 | 0.9925 |
250 | 45.28 | 5.941 | 40.49 | 0.98846 | 47.347 | 0.1733 | 0.38838 | 0.9944 |
First-order kinetic plot for adsorbent treated with HCl.
First-order kinetic plot for adsorbent treated with KOH.
The pseudo-second-order kinetic model is given by Ho [
Second-order kinetic plot for adsorbent treated with HCl.
Second-order kinetic model for adsorbent treated with KOH.
The kinetic data can be analysed using the Weber and Morris model [
The kinetics constants of intraparticle diffusion of adsorbent (HCl treated).
Conc. (mg/L) | Intraparticle diffusion | ||
---|---|---|---|
|
|
| |
25 | 0.31785 | 0.63245 | 0.94971 |
50 | 0.62941 | 1.0110 | 0.94412 |
100 | 1.34986 | 1.0986 | 0.95896 |
150 | 2.0777 | 1.210 | 0.94795 |
200 | 2.688 | 1.293 | 0.95319 |
250 | 3.31 | 1.3514 | 0.96728 |
The kinetics constants of intraparticle diffusion of adsorbent (KOH treated).
Conc. (mg/L) | Intraparticle diffusion | ||
---|---|---|---|
|
|
|
|
25 | 0.22104 | 0.473 | 0.97884 |
50 | 0.4467 | 0.752 | 0.98516 |
100 | 0.873 | 1.226 | 0.98991 |
150 | 1.361 | 1.284 | 0.99031 |
200 | 1.78213 | 1.37983 | 0.99469 |
250 | 2.21113 | 1.39943 | 0.99499 |
Intraparticle diffusion plot for adsorbent treated with HCl.
Intraparticle diffusion plot for adsorbent treated with KOH.
If the
To investigate the slow step in the adsorption process, the kinetic data were further studied using the Boyd model given by [
Solving the above two equations (
The
Boyd plot for adsorption of phenol onto adsorbent treated with HCl.
Boyd plot for adsorption of phenol onto adsorbent treated with KOH.
The current study shows that
The authors declare that there is no conflict of interests regarding the publication of this paper.