Biosorption of Pb(II) ions from aqueous solution by cow hooves (CHs) was investigated as a function of initial pH, contact time, and biosorbent dosage through batch studies. Equilibrium experiments were performed at three different temperatures (298, 308, and 318 K) using initial Pb2+ concentration ranging from 15 to 100 mgg−1. This study revealed that maximum uptake (96.2% removal) of Pb2+ took place within 30 minutes of agitation, and the process was brought to equilibrium within 60 minutes of equilibration. The equilibrium data were modelled using Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. The Langmuir isotherm model fitted the data best at all temperatures considered. The Lagergren second-order kinetic model fitted the biosorption process better than the first-order model. The negative values obtained for both Gibb’s free energy change and enthalpy change are an indication of the spontaneous and exothermic nature of the sorption of Pb2+ onto CH. A study of the FTIR spectral obtained before and after Pb2+ sorption showed that carbonyl, hydroxyl, amino, and carboxyl groups were involved in the sorption process.
The presence of heavy metals in the environment, particularly the aquatic environment, cannot be over emphasized. Their presence in the environment has become a great threat all over the years because of their nonbiodegradability, toxicity, persistency, and bioaccumulation tendency [
Therefore, to conform to these standards and to keep a safe environment, it becomes absolutely necessary to reduce the amount of this deleterious metal from aqueous wastes generated from industries before they are released into the environment. This necessity has seriously enhanced the demand for new technologies for metal removal from wastewater [
In recent decades, adsorption has proved to be one of the simplest and most effective treatment methods for the removal of heavy metals from wastewater. Adsorption of heavy metals from wastewater using activated carbon has gained a wide acceptability industrially because of its high porosity, large internal surface area, relatively high mechanical strength, high degree of surface activity, and high affinity for metals [
Biosorption can be defined as the passive uptake of toxicants by dead/inactive biological materials or by materials derived from biological sources [
Cow hoof is an inedible byproduct that can be obtained freely from local abattoirs in Nigeria. Cow hoof is known to contain insoluble protein called keratin [
This study was aimed at investigating the feasibility of using cow hoof powder as an alternative biosorbent for the removal of Pb2+ ions from aqueous solution. The Langmuir, Freundlich, and Dubinin-Raduskevich (D-R) isotherm models were used to fit the equilibrium data while Lagergren kinetic models were used for kinetic modelling.
Cow hooves were obtained from an abattoir along Ekiti State University Road, Ado Ekiti, Nigeria. The hooves were thoroughly washed with distilled water and sun-dried for a month. After sun drying, the hooves were washed again with distilled water and oven-dried at 105°C. The dried hooves were ground and sieved using sieve of mesh size 212
The influence of different parameters like solution pH, equilibration time, and sorbent dosage on the removal of Pb(II) was investigated through batch experiments at 298 K. Half gramme (0.5 g) of CH was suspended in 50 mL of 50 mgL−1 Pb(II) solution in 150 mL conical flasks for each experimental run. This mixture was agitated using thermostatic water bath shaker (SearchTech 82) for 60 minutes unless stated otherwise at a constant speed. The effects of solution pH on the biosorption process were assessed by adjusting the solution pH between 2.0 and 6.0 using dilute HCl or dilute NaOH solution. The solution pH was not adjusted above 6 because precipitation was noticed at pH above 6. HI 2210 pH metre, Hanna Instruments, was used for pH measurement. The effect of contact time was investigated by varying the agitation time from 0 to 150 minutes. For each experimental run, the mixture of the biosorbent and the solution was centrifuged after agitation and the concentration of metal ion present in the liquid phase (supernatant) was determined using atomic absorption spectrometer (AAS). The amount of metal ions adsorbed per unit mass of biosorbent was determined according to the following equation:
Equilibrium isotherm studies were conducted by agitating 0.5 g of CH with 50 mL of lead(II) solution (pH of 3.5) for 60 minutes at 298, 308, and 318 K. The initial metal concentration ranged from 15 to 100 mgL−1. The samples were then centrifuged and analysed as described earlier.
The possibility of functional groups involvement in the biosorption of Pb(II) by CH was determined using FTIR spectroscopic analysis. The major functional groups that can be noticed on the biosorbent surface are OH (3314 cm−1 band), C=O (1658.6 cm−1 absorption, band), C-O (1239.11 cm−1 and 1039.63 cm−1), C-C (2931.42 cm−1), and amino group (1530.58 cm−1 and 1393 cm−1) (Figure
FTIR spectral characteristics of cow hoof before and after Pb(II) biosorption.
FTIR peak | Frequency (cm−1) before adsorption | Frequency (cm−1) after adsorption | Difference | Assignment |
---|---|---|---|---|
1 | 3754.28 | 3771.42 | −17.14 | –NH stretching |
2 | 3314.00 | 3457.14 | −143.14 | Bonded –OH group |
3 | 2931.42 | 2942.85 | −11.43 | Aliphatic C–H groups |
4 | 2365.71 | 2365.71 | — | S–H stretching |
5 | 1658.60 | 1649.48 | 9.12 | C=O stretching of an amide |
6 | 1530.58 | 1535.19 | −4.61 | Amino/nitro compound |
7 | 1393.00 | 1390.15 | 2.85 | Nitro compound |
8 | 1239.11 | 1239.11 | — | C–N stretching |
9 | 1039.63 | 1059.58 | −19.95 | C–O stretching |
FTIR spectra of (a) unloaded CH and (b) Pb2+ loaded CH.
The effect of pH on the biosorption of Pb(II) by CH is presented in Figure
Effect of pH on the percentage removal of Pb using cow hoof.
Figure
Effect of contact time on the removal of Pb(II) by CH,
The effect of biosorbent dosage on the removal of lead (II) ions by CH was investigated by agitating CH powder of different masses ranging from 0.3 g to 2.5 g with 50 mL of 50 mgg−1 Pb(II) solution at 298 K. The result of this investigation is presented in Figure
Effect of sorbent mass on the removal of Pb,
Analysis of the equilibrium data is important to develop an equation which could be used for design purposes [
The Langmuir model assumes that the uptake of metal ions occurs on a homogeneous surface by monolayer biosorption without any interaction between the biosorbed ions. The linear form of this model can be expressed as
Separation factor (
Co (mgL−1) | 298 K | 308 K | 318 K |
---|---|---|---|
15 | 0.093 | 0.072 | 0.114 |
25 | 0.058 | 0.045 | 0.071 |
50 | 0.029 | 0.023 | 0.037 |
75 | 0.020 | 0.015 | 0.025 |
100 | 0.013 | 0.012 | 0.018 |
Langmuir plots for the removal of Pb(II) by CH at pH 3.5, agitation time of 60 minutes, and different temperatures.
The Freundlich isotherm model gives an expression encompassing the surface heterogeneity and the exponential distribution of active sites and their energies [
The Dubinin-Radushkevich isotherm which also assumes a heterogeneous surface can be expressed in the following linear form:
The Langmuir, Freundlich, and D-R isotherm parameters at different temperatures are presented in Table
Isotherm parameters for the removal of Pb (II) by cow hoof at different temperatures.
Isotherm | Parameter | Temperature (K) | ||
---|---|---|---|---|
298 | 308 | 318 | ||
|
8.640 | 8.912 | 9.52 | |
Langmuir |
|
0.65 | 0.85 | 0.52 |
|
0.9854 | 0.9969 | 0.9888 | |
|
3.097 | 3.394 | 2.909 | |
Freundlich |
|
2.503 | 2.50 | 2.164 |
|
0.7478 | 0.8388 | 0.824 | |
|
5.719 | 6.948 | 7.38 | |
D-R |
|
−0.0878 | −0.0935 | −0.1742 |
|
2.386 | 2.312 | 1.694 | |
|
0.6802 | 0.8472 | 0.8803 |
A comparison of the adsorption capacities for the biosorption of Pb(II) ions on different biosorbents used in the literature with cow hoof is summarized in Table
Comparison of biosorption capacity (
Biosorbent | Temperature (K) |
|
Reference |
---|---|---|---|
Wheat bran | 293 | 68.97 | [ |
|
NA | 56.2 | [ |
|
NA | 2.79 | [ |
|
298 | 92.3 | [ |
|
323 | 0.7 | [ |
|
NA | 1.59 | [ |
Modified peat | NA | 230 | [ |
|
298 | 50.9 | [ |
Corncob | NA | 8.29 | [ |
Corn starch | NA | 28.8 | [ |
Cow hoof | 298 | 8.42 | Current study |
The adsorption kinetics of the biosorption of Pb(II) were analysed using Lagergren first-order and Lagergren second-order kinetic models [
The rate constants
Kinetics’ parameters for the biosorption of Pb (II) onto CH at 298 K.
|
|
|
|
| |
---|---|---|---|---|---|
First order | 4.81 | 1.9525 | 0.0145 | — | 0.6780 |
Second order | 4.81 | 4.76 | — | 0.248 | 0.9983 |
Second-order kinetic plots for the biosorption of Pb(II) onto CH at 298 K.
Thermodynamic parameters are important factors that determine the feasibility and spontaneity of an adsorption process. These parameters were determined by carrying out equilibrium studies at different temperatures to obtain corresponding values of
Thermodynamic constants for the biosorption of Pb onto CH at different temperatures.
|
Δ |
|
|
|
---|---|---|---|---|
298 | −10280.4 | −33265.14 | −77.13 | 8.314 |
308 | −9509.1 | 8.314 | ||
318 | −8737.8 | 8.314 |
It can be concluded from this study that powder obtained from cow hooves can be utilized as a low-cost biosorbent for the removal of Pb2+ from aqueous solutions with 96.2% efficiency within 30 minutes of agitation. The biosorption process is a function of the biosorbent dosage, the initial solution pH, and temperature. The efficiency of Pb2+ removal increased with increase in the amount of CH dosed while the pH of 3.5 was recorded for maximum Pb2+ removal. The isotherm studies revealed that Langmuir model fitted the equilibrium data better than Freundlich and D-R models. The Langmuir maximum adsorption capacities increased from 8.64 to 9.52 mgg−1 when the temperature was raised from 298 K to 318 K. The FTIR spectral of the unloaded and Pb2+ loaded CH revealed that carbonyl, carboxyl, hydroxyl, and amino groups played a vital role in the biosorption process. The thermodynamic parameters revealed that the biosorption process was exothermic and spontaneous.