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Removal of Lead from water using eggshell powder as an adsorbent


Removal of Lead from water using eggshell powder as an adsorbent
Ajay Vikram Singh1
Research Scholar
1Department of Chemistry,
Shri Venkateshwara University, Gajraula, UP, India

Dr. Pradeep Kumar1
Assistant Professor
1Department of Chemistry,
Shri Venkateshwara University, Gajraula, UP, India

Considerable research has been carried out over the last decade on the protection against plant and animal life degradation. Several big cities contribute to increase this problem, as they are sources of industrial effluents. In order to reduce the environmental pollution, a number of studies have been considered to minimize the problems caused by the commonly employed treatment of metal bearing effluents [1]. The traditional methods for removing heavy metals have several disadvantages. Chemical precipitation leads to the production of toxic sludge. Due to the economics of dealing with large volumes of liquids and of solvent losses, solvent extraction is limited to streams containing more than I g/l of the targeted heavy metal. Application of the ion-exchange process is rather expensive due to the cost of synthetic ion exchange resins. Furthermore, they are not always selective enough to allow an effective recovery of heavy metals present in the waste [2].
Alternative methods of metals removal and recovery based on biological materials have been considered. Since commercial biotechnological processes such as alginate extraction result in the production of large quantities of biomass and since this material is currently viewed as a low value by product, these industries represent an ideal source of non-living material for use as biosorbens [3]. In addition, since metal bio-sorption by non-living biomass is a metabolism independent process, it is not ruled by physiological restriction.
Mining and metallurgical waste are the most considerable sources   of environmental pollution by heavy metals. Due to the health hazard   presented by heavy metals, development of effective and economic removal technologies is necessary. In the case of removal of toxic metals from waste waters, biosorption has been involved. This method is based on the use of the metal binding capacities of various biological materials, including algae, fungi and bacteria [4,5].
Fungus belongs to groups of organisms  with very well known heavy metal sorption capacity. It has been demonstrated that some fungi species are typically associated with heavy metal rich substrata and can be even considered as hyper accumulators of heavy metals [6]. Alternatively fungi can be exposed to heavy metals from the atmosphere and are very well known from biomonitoring studies focused on heavy metal pollution [7].
Heavy metals such as lead, mercury, arsenic, copper, zinc and cadmium are highly toxic when adsorbed into the body [9]. Lead one of the earliest metals recognized and used by humans, has a long history of beneficial use to humankinds, but now been recognized as toxic and as posing a widespread threat to humans and wildlife [8]. Treatment of lead from polluted water and wastewater has received a great deal of attention. Treatment process for metals contaminated waste streams include chemical precipitation, membrane filtration, ion exchange, carbon adsorption, and coprecipitation/adsorption. Cost effective alternative   technologies or sorbents for treatment of metals contaminated waste streams are needed. Natural materials that are available in large quantities, or certain waste products from industrial or agricultural operations [10], may have potential as inexpensive sorbents. Due to their low cost, after these materials have been ex pended, they can be disposed of without expensive regeneration [11]. The effectiveness of sorption for the removal of heavy metals has been shown in a number of studies [9]. Natural materials that are available in large quantities,   are certain waste products from industries, may have potential as inexpensive heavy metal sorbents [11]. One cheap and easily available   material having possibilities as suitable sorbent for heavy metal is eggshell. Due to their high calcium content, eggshells usually have no commercial importance. Disposal of eggshells is also a serious problem   for egg processing industries due to stricter environmental regulations and high landfill costs [12]. In USA annually 120,000 tons of waste eggshells are genera ted and disposed in landfills [13].
In the present paper it is proposed to apply hen eggshells as low-cost sorbent of lead. The eggshell (which is almost entirely disposed of as waste) is currently used as source of calcium   in   animal feeds   and   human health supplements (i.e. for osteoporosis) [14].  Environmental parameters affecting the sorption process such as pH, contact time, metal ion concentration, sorbent concentration and sorbent size were evaluated. The equilibrium sorption data were evaluated by Langmuir, Freundlich, Redlich-Peterson and Temkin isotherm models.
Materials and methods
Sorbent
The sorbent used in the present paper is hen eggshell powder. Eggs are one of the first multifunctional food products, with various important gradients. They are well known for  their whipping, gelling   and emulsification properties in addition to their high quality protein   (15]. The shell accounts for about 9-12 % by its total weight depending   on egg size. It comprises about 94% CaC03 with small amounts of MgCO3, calcium phosphate and other organic matter including   protein [1 6]. Most good quality eggshells from commercial layers contain approximately 2.2 grams of calcium in the form of CaCo3 weighing 5.5 grams. The average eggshell contains about 0.3 %  phosphorous and 0.3 % magnesium and traces of sodium, potassium, zinc, manganese, iron and copper [17].
Preparation of sorbent
Eggshells were collected from Andhra University college of Engineering hostels, Visakhapatnam, Andhra Pradesh, India. Shells were washed with deionized water several times to remove dirt particles. The dried eggshell power of 75-212 ┬Ám particle size was used as sorbent without any pretreatment for lead sorption.
Chemical
Analytical grades of Pb(NO3)2, HCl and NaOH were from merck, India. Lead ions were prepared by dissolving its corresponding Nitrate salt in distilled water. The pH of solutions was adjusted with 0.1 N HCl and NaOH. All the experiments were repeated five times and the average values have been reported. Also, blank experiments were conducted to ensure that no sorption was taking place on the walls of the apparatus used.

Sorption experiments
Sorption experiments were performed at room temperature (30±1 °C) in a rotary shaker at 180 rpm using 250 mL Erlenmeyer flasks containing 30 mL of different lead concentrations. After one hour of contact (according to the preliminary sorption dynamics tests), with 0.1 g eggshell powder, equilibrium was reached and the reaction mixture was centrifuged for 5 min. The metal content in the supernatant was determined using Atomic Absorption Spectrophotometer (GBC A vanta   Ver 1.32, Australia) after filtering the adsorbent with whatman filter paper. The amount of metal sorbed by eggshell powder was calculated from the differences between metal quantity added to the sorbent and metal content of the supernatant using the following equation:
                                                     (1)
Where is the metal uptake (mg/g); C0 and Cf are the intial and equilibrium metal concentrations in the solution (mg/L), respectively; V is the solution volume (mL); and M is the mass of sorbent (g). The pH of the solution was adjusted by using 0.1 NHCl and 0.1 N NaOH.
The Langmuir [18] sorption model was chosen for the estimation of maximum lead sorption by the sorbent. The Langmuir isotherm can be expressed as,
                                        (2)
          Where indicates the monolayer sorption capacity of sorbent (mg/g) and the Langmuir constant b (1/mg) is related to the energy of sorption. For fitting the experimental data, the Langmuir model was linearized as
                                                 (3)
The Freundlich [19] model is represented by the equation,
                                                               (4)
Where K (mg/g) is the Freundlich constant related to sorption capacity of adsorbent and n is the Freundlich exponent related to adsorption intensity (g/L). For fitting the experimental data, the Freundlich model was linearized as follows,
In                                           (5)
The Redlich-Peterson [20] model is represented by the equation,
                                                           (6)
where A(1/g) and B (1/mg) are the Redlich-Peterson isotherm constants and g is the Redlich Peterson isotherm exponent, which lies between 0 and 1. The linearized from of equation is given by:
                          (7)
Redlich-Peterson isotherm equation contains three unknown parameters A, B and g. Therefore a minimization procedure is adopted to maximize the coefficient of determination, between the theoretical data for qe predicted from the linearized from of Redlich-Peterson isotherm equation and the experimental data.
The Temkin [21] isotherm has generally been applied in the following form,
                                           (8)
where (1/mg) and are Temkin isotherm constants.
Results and Discussion
The effect of contact time
The data obtained from the sorption of lead ions on the eggshell powder showed that a contact time of 60 min was sufficient to achieve equilibrium and the sorption did not change significantly with further increase in contact time. Therefore the uptake and unadsorbed lead concentrations at the end of 60 min are given as the equilibrium values     (, mg/g; , mg/L); respectively (Fig. 1) and the other sorption experiments were conducted at this contact time of 60 min.
Description: D:\Thesis 2015\Warking in Progerss Thesis\Chemistry\Ajay Vikram Singh-8937941200\01.jpg
Figure 1: Effect of contact time of lead uptake by eggshell powder for 20mg/L of metal and 0.1g/mL of sobent concentration.
Effect of pH
It was found that lead uptake by eggshells was a function of solution pH. As shown in Fig. 2, the uptake of lead increased with increase in pH from 2.0 to 6.0. The effect of pH can be explained by ion-exchange mechanism of sorption in which the important role is played by carbonate groups that have cation-exchange properties. At lower pH values lead removal was inhibited, possibly as a result of the competition between hydrogen and lead ions on the sorption sites, with an apparent preponderance of hydrogen ions, which restricts the approach of metal cations as in consequence of the repulsive force.  As,  the pH increased, the ligands such as carbonate groups in eggshells would be exposed, increasing the negative charge density on the sorbent surface, increasing the attraction of metallic ions with positive charge and allowing the sorption onto the cell surface.
Description: D:\Thesis 2015\Warking in Progerss Thesis\Chemistry\Ajay Vikram Singh-8937941200\02.jpg
Effect of metal ion concentration
Fig. 3. Shows the effect of metal ion concentration on the sorption of lead by eggshell powder. The data shows that the metal uptake increases and the percentage sorption of lead decreases with increase in metal ion concentration. This increase (5.76 to 24.94 mg/g) is a result of increase in the driving forces i.e. concentration gradient. However, the percentage sorption of lead ions on eggshell powder was decreased from 96.12 to 83.12%. Though an increase in metal uptake was observed, the decrease in percentage sorption may be attributed to lack of sufficient surface area to accommodate much more metal available in the solution. The percentage sorption at higher concentration levels shows a decreasing trend whereas the equilibrium uptake of lead displays an opposite trend. At lower concentrations, all lead ions present in solution could interact with the binding sites and thus the percentage sorption was higher than those at higher lead ion concentrations. At higher concentrations, lower adsorption yield is due to the saturation of adsorption sites. As a result the purification yield can be increased by diluting the wastewaters containing high metal ion concentrations.
Description: D:\Thesis 2015\Warking in Progerss Thesis\Chemistry\Ajay Vikram Singh-8937941200\03.jpg
Figure 3: Effect of intimal ion concentration on the sorption of lead by eggshell powder at 0.1g/30mL of sorbent concentration.
Effect of sorbent size
The effect of different sorbent particle size on percentage removal of lead is investigated and showed in fig. 4. It reveals that the sorption of lead on eggshell powder decrease from 96.12 to 87.25% with the increased particle size from 75 to 212 at an initial concentration of 20mg/L. The smallest size obtained was 75 due to the limitation of available grinder configuration. It is well known that decreasing the average particle size of the sorbent increase the surface area, which in turn increases the sorption capacity.
Description: D:\Thesis 2015\Warking in Progerss Thesis\Chemistry\Ajay Vikram Singh-8937941200\04.jpg
Figure 4: Effect of sorbent size on sorption of lead for 20 mg/L of metal and 0.1g/30mL of sorbent concentration.
Effect of sorbent dosage
Fig. 5 shows the effect of sorbent dosage on the % removal at equilibrium conditions. It was observed that the amount of lead sorbed varied with varying sorbent dosage. The amount of lead sorbed increase with an increase in sorbent dosage from 0.1 to 0.5g. The percentage lead removal was increased from 96.12 to 98.39% for an increase in sorbent dosage from 0.1 to 0.5g at an initial concentration of 20 mg/L.
Description: D:\Thesis 2015\Warking in Progerss Thesis\Chemistry\Ajay Vikram Singh-8937941200\05.jpg
Figure 5: Effect of sorbent dosage on sorption of lead for 20mg/L of metal concentration.
Sorption equilibrium
The equilibrium sorption of lead on the eggshell powder as a function of the initial concentration of lead is shown in Fig. 6. There was a gradual increase of sorption for lead ions until equilibrium was attained. The Langmuir, Freundlich models are often used to describe equilibrium sorption isotherms and Redlich-Peterson and Temkin models are also applied to describe equilibrium sorption isotherms. The calculated results of the Langmuir, Freundlich, Redlich-Peterson and Temkin isotherm constants are given in Table.1.
Description: D:\Thesis 2015\Warking in Progerss Thesis\Chemistry\Ajay Vikram Singh-8937941200\06.jpg
Figure 6: Equilibrium curves for lead onto eggshell powder.
Table 1: Langmuir, Freundlich, Redlich-Peterson and Temkin isotherm constants and correlation coefficients.
Langmuir
Q (mg/g)
29.878

b(l/mg)
0.218

R2
0.959
Freundlich
K(mg/g)
6.613

n (g/l)
0.464

R2
0.995
Redlich-Peterson
A (l/g)
1.988

B(l/mg)
2.381

g
-0.499

R2
0.129
Temkin
Ar (l/mg)
0.281

br
424.922

R2
0.953
It is found that the sorption of lead on the eggshell powder was correlated well with the Freundlich equation and Langmuir equation as compared to Redlich-Peterson and Temkin equations under the concentration range studied. Examination of the Redlich-Peterson and Timkin data shows that these two isotherms are not modeled as well across the concentration range studied.
Conclusion
The present study shows that the eggshell powder was an effective sorbent for the sorption of lead ions from aqueous solution. The effects of process parameters like pH, metal ion concentration, sorbent concentration and sorbent size on process equilibrium were studied. The uptake was also increased by increasing pH up to 6. The sorption isotherms could be well fitted by the Freundlich equation followed by Langmuir equation.

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