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Keywords

Lead; Biosorbent; Kinetic parameters; Biosorption capacities; Delonix regia pod

Introduction

Toxic Heavy metals can be released into water through metal smelters, effluents from plastics, textiles, There is evidence that present in the environment, even in low concentration of heavy metals cause dermal damage and cancer [1,2]. Lead is considered as the most toxic metal exists in several industrial wastes, such as chemicals, lead acid storage batteries. Lead poisoning in human causes damaging to the kidneys, liver, and brain [2,3]. The removal of heavy metal from contaminated sites is very important to restore ecosystem functions and stability [4]. The search for low-cost techniques to remove heavy metals from waste water using agricultural materials such as Maize leaves, loquat leaves (Eriobotrya japonica), Psidium guajava leaves, Scolymushis panicus, Azadirachta indica (Neem leaves), Ulmus leaves, Oleaeuropaea (Olive leaves), and Prunusvium leaves [5], rice straw, rice bran, rice husk, hyacinthroots, neem leaves [6]. Delonix regia is a species of flowering plant in the family Fabaceae, subfamily Caesalpinioideae [7]. Delonix regia possesses several medicinal characters [8]. The effect Delonix regia biosorbent for the removing of Methylene Blue dye [9], Hg (II) ion from water [10] and Pb, Cu and Co ions [11]. Chemical treatment of biomass with NaOH and citric acid increases its cation uptake ability as the carboxyl groups of the biomass increases [12] Ion-exchange has been suggested as one the mechanisms for heavy metal removal from aqueous solution [2,13]. This study can introduce an economic value biosorbent for removing of toxic heavy metal by using nanosized Delonix regia pod.

Experimental

From Sigma-Aldrich, Pb(NO₃)₂, HCl, citric acid and NaOH were purchased .

Sample collection

The pods of Delonix regia were obtained from Shandawil Research Station, Agriculture Research Center, Sohag, Egypt.

Instruments

Nano size of the investigated biosorbent was obtained by using Retsch Muhle Brinkann Spectro Mill MS Micro-Grinding Mixing. Biosorbent was characterized by X-ray powder diffraction using a Philips X'Pert PRO MPD. (EDAX) unit was used to analyse the chemical composition of the synthesized nanostructures. Fieldemission scanning electron microscopy was used for studying the morphology of sample. Functional groups on the biosorbent surface were detected by using (FT-IR, 2000, PerkinElmer). mVISE- pH-temperature bench Meters was used to adjust pH of the solutions. Transmission electron microscopy images were obtained with a 2000 EX (II0 microscope (J E O L-Japan). A shaker bath (Heidolph M R-3001) was used for shaking. E-B-A, 20 zentrifugen D78532 tuttlingen was used to centrifuge the sample after the adsorption process. The concentration of Pb²⁺ ions was determined using (AAS) (model PerkinElmer-Analyst, 200).

Sample pretreatment

Delonix regia pods were cleaned with water, and then dried. Delonix regia pods were grinded to obtain a fine powder. The fine powder was used as biosorbent in the experiments.

Treatment of Delonix regia (DR) by Citric Acid

Chemical modification of nano sized powder Delonix regia (DR) using NaOH followed by citric acid treatment. The synthesis of CADR was carried out as followed, 200 grams of the powder was placed in 4 L of 0.1 N NaOH,

then was stirred at 300 rpm for 1 h at 23oC to remove base. The powder was rinsed with water and added to 4 L of distilled water. This biomass was mixed with citric acid (CA) in a ratio of 1.0 g powder to 7.0 mL of CA (0.6 M). The acid/powder Slurry was dried over night at 50°C and then heated to 120oC for 1.5 h. Citric acid (CA) treated DR powder (CADR) was filtered and washed in a Buchner funnel under vacuum with 150–200 mL of distilled water per gram of the product to remove excess CA. This volume of water was sufficient to remove un reacted CA since no turbidity from lead citrate was observed when the washed powder was suspended in 10 mL of water to which 10 mL of 0.1 M lead nitrate was added. The modified powder was dried at 50oC overnight [2,14,15].

Preparation of Solution

Aqueous solution of Pb²⁺ ions was prepared by weighing out 1.60 g of Pb(NO₃)₂ and dissolved in a 1000 ml volumetric flask with de-ionized water to obtain a 1000 mg/L concentration. Different initial concentrations of Pb²⁺ ions were prepared by Dilution.

Batch Biosorption Experiments

Effect of concentration of metal ion

A total of 50 ml of Pb²⁺ ions solution of different concentrations was added to 0.3 g of the Adsorbent in a flat bottle and then the mixture was stirred for 1 hr on a shaker at 300 rpm.

Effect of pH

Experiments were carried out at different pH (2:10) and pH was adjusted by using 0.1 M (NaOH) or 0.1 M (HCl). A total of 50 ml of Pb²⁺ ions solution of concentration (20 mg/L) was added to 0.3 g of the Adsorbent in a flat bottle, then the mixture was stirred for 1 hr on a shaker at 300 rpm.

Effect of dosage

In each biosorption experiment, 50 ml of Pb²⁺ ions solution of concentration (20 mg/L) was added to different dosage of the adsorbent in bottle and then the mixture was stirred for 1 hr on a shaker at 300 rpm.

Effect of contact time

In the biosorption kinetics experiment, 0.2 L of Pb²⁺ ions solution of different concentrations was added to 1.2 g of the adsorbent in flat bottle and then the mixture was stirred for 1 hr on a shaker at 300 rpm and a contact time (20: 120) minutes with time interval 20 minutes.

Effect of temperature and determination of thermodynamic parameters

A total of 50 ml of different concentrations of Pb²⁺ ions solution was added to 0.3 g of the adsorbent in bottle at different temperature and then the mixture was stirred for 1 hr on a shaker at 300 rpm. Then the mixture was centrifuged and the concentration of Pb²⁺ions was determined. Were calculated using the relationships (1) and (2) [2,16,17] can be used to calculate ΔH, ΔS, and ΔG( the thermodynamic parameters for the adsorption process.

lnb = ΔS°/R - ΔH°/RT (1)

ΔG° = ΔH°-T ΔS°(2)

Calculation of metal uptake

The Pb²⁺ions uptake at equilibrium was calculated by:

(3)

where q_e is Pb²⁺ ions absorption capacity, v is the volume of the Pb²⁺ ions solution and w is the amount of the adsorbent, Co and Ce are initial Pb²⁺ ion concentrations and Ce are final (equilibrium) Pb²⁺ ion concentrations. The efficiency of the Pb²⁺ ions removal was also determined using;

(4)

Where, RE% is the percentage of the removed Pb²⁺ions.

Kinetics study

The mechanism of the adsorption of Pb²⁺ions was studied using pseudo first order kinetic models , the intraparticle diffusion and pseudo second order kinetic models [2,18-20] and they are giving in a linear form by Equations 5, 6 and 7, respectively

ln(q_e-q_t) = lnq_e – k₁t (5)

(t/q_t)=1/ (k₂q²_e) + (t/q_e) (6)

q_t = k_int t^0.5 (7)

kinetic models are tested for suitability using correlation coefficient (R₂) [2,20,21].

Effect of chemical treatment

A total of 50 ml of Pb²⁺ ions solution of (20 mg/L) concentration was added to 0.3 g of the chemically treatment adsorbent (CADR) in bottle, then the mixture was stirred on a shaker for 1 hr at 300 rpm and the concentration of Pb²⁺ ions was determined .

Results and Discussion

Characteristics of the biosorbent

FTIR spectral analysis: FTIR spectral analysis of Delonix regia pod (DR) (Figure 1a) and Pb²⁺ ions loaded Delonix regia pod (Pb- DR) (Figure 1a) were carried out. FTIR data of Delonix regia (DR) indicates the functional groups. The main characteristic cellulose peak appears in the region of 1000-1200 cm⁻¹. [22]. The strong and broad peak at 3298 cm⁻¹, indicated the N-H bond of amino groups and hydroxyl group. The shift in the peak to 3330 cm⁻¹ in the spectra of the metal loaded Delonix regia pod powder shows the binding of Lead ions with hydroxyl and amino groups [23-25] peak at 2916 cm⁻¹ in the spectra of the Delonix regia pod powder indicated CH3 and CH2 groups. The peak at 1594 cm⁻¹ indicates CO, OH and C-O groups, the Shift to 1612 cm⁻¹ indicated the metal binding. Band at 1036 cm⁻¹ indicated the C-O of alcohols, the shift to 1028 cm⁻¹ indicated binding of Pb²⁺ ions with C-O group [2,24-26]. Peak at 1738 cm⁻¹, which is indicative of carbonyl group, shifted to wave number of 1732 cm⁻¹ after Pb²⁺ adsorption [2,27,28]. Band at 1243 cm⁻¹ indicates carboxylic acids which shifted to 1233 cm⁻¹ after adsorption of Pb²⁺[29]. The shifts in the absorption peaks indicate the binding of metal ions on the surface of the powder.

Figure 1a:FT-IR spectral analysis of biosorbent Delonix regia pod (D-R) and Pb²⁺ loaded Delonix regia pod (Pb-DR).

Figure 1b: FT-IR spectral analysis of the modified biosorbent Delonix regia (CADR) and Pb²⁺ loaded the modified Delonix regia (Pb-CADR).

Also FT-IR for detection the groups on the modified biosorbents [Citric Acid (CA) treated DR powder (CADR) before and after the biosorption of Pb²⁺ ions (Pb-CADR) was shown in Figure 1b.

Comparison of the IR spectra of samples of DR and CA modified DR (CADR) revealed that a characteristic stretching vibration absorption band of carboxyl group at 1733 cm⁻¹ is present in the IR spectrum of CADR samples. This indicates the esterification between alcohol groups of cellulose in DR and citric acid

The broad absorptions around 2500-3500 cm⁻¹ centered at 3343 confirm the existence of carboxylic OH groups and free COOH groups after CA modification. It appears from Figure 1b that the different functional groups on CADR are responsible for biosorption of Pb²⁺ A change in peaks position at 3328 cm⁻¹ in the spectrum of Pb²⁺ loaded CADR indicates the binding with hydroxyl groups. The peak at 1733 cm⁻¹ shifted to 1728 cm⁻¹ in the spectrum of Pb²⁺ loaded CAMO indicating the binding of metal ions to carboxylic groups also [2,30,31].

Elemental analysis: To determine the chemical composition of the biosorbent. Elemental analysis of Delonix regia (pod) is shown in Figure 2.

Figure 2: EDS spectrum of the investigated nanosized plant.

Scanning electron micrograph (SEM): SEM of biosorbent Delonix regia pod(D-R) (Figure 3) are used to show the morphology of Delonix regia pod, which exhibits the structure porosity of biomass. The surface morphology of Delonix regia pod powder showed that the powder was a fine particle. The particles have a large number of steps and edges.

Figure 3: Scanning electron micrograph of biosorbent Delonix regia pod (DR).

XRD analysis: XRD of the Delonix regia pod powder is shown in Figure 4 indicates the amount of amorphous material in the sample. XRD of the adsorbent Delonix regia indicate that the structure of Delonix regia pod powder has a small different change due to the appearance of amorphous peak at 2θ=44.7 after adsorption process confirming adsorption of Pb²⁺ ions.

Figure 4: XRD patterns of the adsorbent Delonix regia pod (DR) powder before and after equilibration with Pb²⁺ ions (Pb-DR).

Transmission electron microscopy (TEM): The sample was subjected to TEM analysis (Figure 5a) to indicate the particle size and the major size of the particles was found to be 18 nm (Figure 5b).

Figure 5a: TEM image of nanosized biosorbent Delonix regia pod (D-R).

Figure 5b: Calculated Histogram for particle Size distribution of Delonix regia pod.

Effect of initial concentration: Figure 6 and Table 1 illustrated the effect of metal ions concentration on Pb²⁺ ions biosorption is in (q_e) increases as the concentration rises, as Pb²⁺ ions are more available for interaction with the biosorbent. The Pb²⁺ ions R. E for initial concentration 10 and 20 mg/L are 94.3% and 93.5%, respectively and decreases as the concentration increases. A greater chance was available for metal removal at low concentrations, biosorption sites took up the available Pb²⁺ ions when increasing concentrations. So, initial concentration of Pb²⁺ ions solutions increases the biosorption [2,32-34].

Table 1: Pb²⁺ions Removal Efficiency and q_e at different initial concentrations

Figure 6: Effect of initial Pb²⁺ ions concentration on Pb²⁺ ions removal efficiency And q_e (b) by Delonix regia pod.

Effect of pH: Figure 7 and Table 2 illustrated the effect of pH of a solution in the adsorption process. R.E. and q_e increase as the pH increase. The amount of Pb²⁺ ions removed by the Delonix regia at low pH 2 was low (1.91 mg/g) and R.E. 57.3% compared to the amounts removed at pH 4 to 10 were ranged from (2.7 mg/g and R.E. 81% at pH 4) to 3.12 mg/g and R.E. 93.5% at pH 5. Because at low pH the concentration of H+ is high [19], as H⁺ ions were being removed by the biosorbent, instead of the Pb²⁺ ions, [21,35] at higher concentration of H⁺ ions, the biosorbent becomes more positive charge on the surface and the attraction between biosorbent and Pb²⁺ ions is reduced [36]. At higher pH the capacity of the adsorbent reduced, the reduction in adsorption may be due to the increasing of OH^- ions, or Pb²⁺ ions were precipitated as lead hydroxide [2,37].

Table 2: Pb²⁺ ions removal efficiency q_e at initial concentration of 20 mg/L at different pH values

Figure 7: Effect of pH on Pb²⁺ ions removal efficiency and q_e at initial concentration 20 mg/L.

Effect of biosorbent dosage: It is an effective factor to study the capacity of a biosorbent. R.E. increases with least value of 64.65% obtained with 25 mg and highest value of 95.04% with 500 mg of the biosorbent, this because at high dosage, there is an increase in surface area and availability of biosorption sites, but q_e decreases as a decrease in the amount of Pb²⁺ ions adsorbed per unit weight of biosorbent [2,38-40]. These results are illustrated in Figure 8 and Table 3.

Table 3: Pb²⁺ ions removal efficiency and q_e at different biosorbent dosage

Figure 8: Effect of biosorbent dosage on Pb²⁺ ions removal efficiency and q_e.

Effect of contact time: Table 4 and Figure 9 illustrated the effect of contact time for the adsorption of Pb²⁺ ions by Delonix regia. The amount of Pb²⁺ ions absorbed increased with an increase in the contact time and reach equilibrium in 60 minutes. This because long contact time and availability of active sites, it was followed by a reduction in the metal uptake. There was a slightly increasing or remain constant in the Pb²⁺ ions removal, as the sites are less available [2,41,42].

Table 4: Effect of contact time on Pb²⁺ ions removal efficiency and q_e at different initial concentrations (10, 30 and 50) mg/L by Delonix regia pod

Figure 9: Effect of contact time on Pb²⁺ ions removal efficiency and q_e at different initial concentrations (10, 30 and 50) mg/L by Delonix regia pod.

Effect of temperature: Table 5 and Figure 10 illustrated the effect of the temperature on adsorption, the Pb²⁺ R.E. and q_e by Delonix regia increases while the temperature is increasing, as the active sites have increased and encourages the process of biosorption, due to increase in the movement of the Pb²⁺ ions and pore size indicating an endothermic process [2,43-45].

Table 5: Effect of temperature on Pb²⁺ ions removal efficiency and q_e at differentinitial Concentrations (10, 20, 50) mg/L by Delonix regia pod

Figure 10: Effect of temperature on Pb²⁺ ions removal efficiency at different Initial concentrations (10, 20, 50) mg/L by Delonix regia pod.

Adsorption isotherm: Pb²⁺ ions distribution between the solid and liquid phases can be described by the Freundlich and Langmuir isotherms [46] q_e increased with the initial concentration of Pb²⁺ as expected [47,48]. q_m is 15.26 mg/g of Delonix regia. Langmuir model suggests that the adsorption take places on homogeneous sites. Langmuir isotherm equation is represented by equation 8 in a linear form [2,49].

(8)

Plot of C_e /q_e against C_e give a line with intercept 1/q_m b and slope 1/q_m is obtained (Figure 11), which shows Lead biosorption isotherms of Langmuir. From the intercept and slope the Langmuir parameters (b and qm) are calculated. These values may be used for compared and correlate the biosorptive properties of Delonix regia of the Freundlich has the linear form [2,50].

Figure 11: Linearized biosorption isotherms of Langmuir.

(9)

From a plot, a line with slope and intercept 1/n and log K_f respectively is obtained (Figure 12). The slope, 1/n , indicate the intensity of adsorption and log K_f indicate the adsorption capacity [51] parameters of Pb²⁺ ions adsorption was given in Table 6a dimensionless constant separator factor (R_L) can classify the Isotherms [52] stated as:

Table 6: Isotherm constants of Pb²⁺ ions biosorption on Delonix regia pod at various temperatures.

Figure 12: Linearized biosorption isotherms of Freundlich.

(10)

R_L Mathematical calculation indicates the shape of isotherm , irreversible if (R_L=0), linear if (R_L=1), unfavorable if (R_L>1) favorable if (0<R_L<1). R_L values have arrange from 0.059 to 0.333 (Table 7) n values were greater than 1 [53], these values indicating a formation of a bond between Pb²⁺ ions and adsorbent and indicating favorable biosorption. This indicate that Pb(II) ions adsorption on Delonix regia is favorable. Linearity coefficient (R²) can be used to examine the fitting of the models. According to linearity coefficients (R²=1) Freundlich models has a good fit models and adsorption of Lead ion on Delonix regia follow Freundlich isotherm models.

Table 7: A dimensionless constant separator factor (R_L) for Langmuir type biosorption process.

Thermodynamic studies

From a plot lnb against 1/T, thermodynamics equilibrium constant was used to obtain the other thermodynamic parameters. The biosorption capacity of the Delonix regia for Lead increased as temperature increased, indicating the adsorption process was endothermic. Thermodynamic parameters (ΔG,° ΔS° and ΔH°) were determined using the equations (1), (2) [54], the slope ΔH°/R, and intercept ΔS°/R are obtained and the values of ΔH° and ΔS° were calculated (Table 8). The adsorption process of Lead ions on the Delonix regia was endothermic as ΔH° values were Positive. a positive ΔG° value suggested an ion-exchange mechanism occur in the biosorption of Pb²⁺ and a complex formed by Pb²⁺ with the Delonix regia [2,55] An increase in randomness during the biosorption as the Positive ΔS◦ value [2,56-58].

Table 8: Thermodynamic parameters for the biosorption process

Kinetic studies on the biosorption of Pb²⁺ ions

Pseudo first order, pseudo second order kinetic and the intra particle diffusion models can be used to test the mechanism of the adsorption of metal ions [2,19-21]. The adsorption kinetic of the adsorbed Pb²⁺ ions was studied (Figures 13 and 14). Correlation coefficient, R² can be used to test the suitability of these models [2,21] The variable and constant of each kinetic model were calculated and were presented in Table 9, the calculated q_e determined from the plot of the pseudo first order model differs from the experimental q_e. This indicates that pseudo first order model is not good in studying the kinetics of the biosorption of Pb²⁺ ions compared to pseudo second order models (R²=0.999) for Pb²⁺ ions, Table 9. So the second order kinetics is good in studying the kinetics of the biosorption of Pb²⁺ ions, as the calculated qe (7.54 mg/g are very close to the experimental qe (7.6 mg/g), suggesting that the biosorption of the Pb²⁺ ions solutions involves the Pb²⁺ ion and the Delonix regia biosorbent particles [2,58,59].

Table 9: Kinetic parameters of Pb²⁺ ions biosorption at different initial concentration.

Figure 13: Pseudo-first order for sorption of Pb²⁺ ions by Delonix regia pod.

Figure 14: Pseudo-second order for sorption of Pb2+ ions by Delonix regia pod.

Effect of chemical treatment of the biosorbents on biosorption efficiency

The effect of chemical treatment of the biosorbents by esterifying with NaOH followed by citric acid treatment (CADR) on the R. E compared with (DR) was studied and shown in Table 10. It was observed that the R.E.% of metal ions by (CADR) was higher than the R.E.% of metal ions by (DR) and this was due to the Chemical treatment of biomass with NaOH and citric acid increases its cation uptake ability as the carboxyl groups of the biomass increases [2,31,32].

Table 10: Effect of chemical treatment of Biosorbent on biosorption efficiency.

Conclusion

1. Nano size of Flamboyant Pod (Delonix regia) was used for biosorption of toxic Pb²⁺ ions from solution and is consider a very effective biosorbent in the removal of heavy metals. This study indicated that: The Adsorption process depends on temperature, pH, Contact time, dosage and metal ion concentration.

2. Adsorption of Pb²⁺ ions from solutions obeyed Freundlich isotherm models. q_m of Pb²⁺ ions on Delonix regia is 43.62 mg g⁻¹.

3. The biosorption process was endothermic an ion-exchange mechanism applies in the biosorption of (Pb²⁺ ions). This confirmed by thermodynamic studies.

4. Second order kinetics models is a better than the pseudo first order in studying the kinetics of the biosorption of Pb²⁺ ions.

References

1. Abdel-RahmanLH, Abu-Dief AM,  Abd- El Sayed MA, Zikry MM (2016) Chemistry and Materials Research 8: 8-22.
2. Agarwal S,  Tyagi I,  Gupta VK, Dehghani MH, Jaafari  J,et al. (2016) Rapid removal of noxious nickel (II) using novel γ-alumina nanoparticles and multiwalled carbon nanotubes: Kinetic and isotherm studies. J Mol Liquids 224: 618-623. 
3. Aharoni A, Ungarish M (1977) Kinetics of activated chemisorption part 2. Theoretical models. J Chem Soc Faraday Trans73:456-464.
4. Aksu Z (2001)Biosorption of Reactive Dyes by Dried Activated Sludge: Equilibrium and Kinetic Modeling. Biochem Eng J 7:79-84.
5. Ali EN, Alfarra SR, Yusoff MM, Rahman MLR (2015) Environmentally Friendly Biosorbent from Moringa oleifera Leaves for Water Treatment.  IJESD 6: 165-169.
6. Azarpira H, Mahdavi Y,  Balarak D (2016) Removal of Cd(II) by adsorption on agricultural waste biomass. Der Pharma Chemica 8: 61-67.
7. Balarak D, Azarpira, H,  Mostafapour FK (2016) Thermodynamics of removal of cadmium by adsorption on Barley husk biomass Der Pharma Chemica 8: 243-247.
   
8. Balarak D, Joghataei A, Azarpira H, Mostafapour FK (2016)Isotherms and thermodynamics of  Cd (II) Ion  Removal by adsorption onto Azolla Filiculoides. IJPT15780-15788.
9. Balarak D, Yari AR, Mostafapour FK, Mahdavi Y, Joghataei A (2016) Agricultural Waste as Adsorbent for Removal of Chromium (VI) from Aqueous Solution. Arch Hyg Sci 5: 310-318.
10. Bhatti HN, Khalid R, Hanif MA (2009) Dynamic biosorption of Zn (II) and Cu (II) using pretreated Rosa gruss an teplitz (red rose) distillation sludge. Chem Eng J 148: 434-443.
11. Bhatti HN, Nasir AW, Hanif MA (2010) Efficacy of Daucuscarota L waste biomass for the removal of chromium from aqueous solutions.Desalination 253:78-87.
12. Boparai HK, Joseph M, O'Carroll DM (2011) Kinetics and thermodynamics of cadmium ion removal by adsorption onto nanozerovalent iron particles. J Hazard Mater 186: 458-465.
13. Burke D(2005)The complete Burke's backyard: the ultimate book of fact sheets. Murdoch Books p: 269.
14. Corupcioglu MO, Huang CP (1987)The Adsorption of Heavy Metals onto Hydrous Activated Carbon. Water Research 21:1031-1044.
15. Donmez GC Aksu Z, Ozturk A,  Kutsal TA (1999)Comparative Study on Heavy Metals Biosorption of Some Algae. Process Biochem34: 885-892.
16. Dursun AY (2006) A comparative study on determination of the equilibrium, kinetic and thermodynamic parameters of biosorption of copper and lead ions ontopretreated Aspergillusniger. Biochem Eng J 28: 187-195.
17. Egila JN, Dauda BEN, Jimoh T (2010) Biosorptive removal of cobalt (II) ions from aqueous solution by Amaranthushydridus L stalk wastes. African J Biotechnol 9: 8192-8198.
18. Farhan AM, Al-Dujaili AH, Awwad AM (2013) Equilibrium and kinetic studies ofcadmium(II) and lead(II) ions biosorption onto Ficus carcia leaves. Inter J Indust Chem 24.
19. Farrokhzadeh H, Taheri E,  Ebrahimi A, Fatehizadeh A,  Dastjerdi MV, et al. (2013) Effectiveness of Moringa oleifera powder in removal of heavy metal from aqueous solution. Fresenius Environmental Bulletin J 22:1516-1523.
20. Halpern SD, Ubel PA, Caplan AL (2002) Solid-organ transplantation in HIV-infected patients. N Engl J Med 347:284-287.            
21. Hasar H (2003) Adsorption of nickel (II) from aqueous solution onto activated carbon prepared from almond husk. J Hazard Mater B97: 49-57.
22. Hashem MM, Elhmmali A, Ghith EE, Saad MM, Khouda (2007) Utilization of chemically modified Alhagiresidues for the removal of Pb (II) from aqueous solution. Energy Edu Sci Technol 20: 1-19.
23. Ho YS, McKay G (1898) The Kinetics of Sorption of Divalent Metal Ions onto Spagnum Moss Peat. Water Res 34: 735.
24. Ho YS (2006) Review of second order models for adsorption systems. JHazard Mater 136: 681-689.
25. Hossain A, Bhattacharyya SR, Aditya G (2015) Biosorption of cadmium from aqueous solution by shell dust of the Freshwater snail Lymnaealuteola. Environ Technol Innovation 4: 82-91.
26. Jain CK, Singhal DC, Sharma MK (2004) Adsorption of zink on bed sediment of River London: adsorption models and kinetics. J Hazard Mater B 114: 231-239.
27. Jimoh TO, Iyaka YA, Nubaye MM (2012) Sorption Study of Co (II), Cu(II) and Pb(II) ions Removal from Aqueous Solution by Adsorption on Flamboyant Flower (Delonix regia). American J Chem 2: 165-170.
28. Jimoh T, Egila JN, Dauda BEN, Iyaka YA (2011) Preconcentration and removal of heavy metal ions from aqueous solution using modified charcoal. J Environ Chem Ecotoxicol 3: 238-243.
29. Juang LC, Wang CC, Lee CK (2006) Biosorption of Basic Dye onto MCM-41. Chemosphere 64: 1920-1928.
30. Kumar KV, Ramamurthi V, Sivanesan S (2006) Biosorption of Malachite Green, a Cationic onto Pithophorasp, a Fresh Water Algae. Dye pigments 69: 102-107.
31. Langergren S(1898) About the Theory of So-Called Biosorption of Soluble Substances. K Sven Vetenskapsakad handlingnaar Band 24: 1-39.
32. Langmuir I (1918)The Adsorption of Gases on Plane Surfaces of Glass, Micaand Platinum. J Am Chem Soc 40: 1361-1403.
33. Larous S, Meniai AH, Lehocine MB (2005)Experimental study of the removal of copper from aqueous solutions by adsorption using sawdust. Desalination 185: 483-490.
34. Levine NI (1998) Physical Chemistry, (4th edn), New York.
35. Malakootian M, Fatehizadeh A, Yousefi N, Ahmadian M, Moosazadeh M (2011)Fluoride removal using Regenerated Spent Bleaching Earth (RSBE) from groundwater: Case study on Kuhbonan water.  Desalination277: 244-249.
36. Mariajancyrani J, Chandramohan G, Ravkumar R (2013) Iosolation and identification of phytoconstituents from Delonix regia leaves. Int J Pharm Sci 5:671-674.
37. Marshall WE, Wartelle LH, Boler DE, Johns MM, Toles CA (1999) Bioresource Technol 69: 263-268.
38. Mathew SB, Pillai AK, Gupta VK (2007) A Rapid Spectrophotometric Assay of Some Organo Phosphorus Pesticide Residues in Vegetable Samples. Spectrochimica Acta Part A 67: 1430-1432.
39. Meena AK, Mishra GK, Rai PK, Rajagopal C, Nagar PN (2005)Removal of heavy meal ions from aqueous solutions using carbon aeogel as an adsorbent. J Hazard Mater 122: 161-170.
40. Minamisawa M, Minamisawa H, Yoshida S, Takai N (2004) Adsorption behavior of heavy metals on biomaterials. J Agric Food Chem 52: 5606.
41. Namasivayam C, Yamuna RT (1995) Adsorption of chromium in tanned leather gloves and relapse of chromium allergy from tanned leather samples. Analyst 123: 935-937.
42. Neto CP, Rocha J, Gil A, Cordeiro N, Esculcas AP (1995) 13C solid-state nuclear magnetic resonance and Fourier transform infrared studies of the thermal decomposition of cork. Solid State Nucl Mag 4: 143-151.
43. Owoyokun TO (2009) Biosorption of Methylene Blue Dye Aqueous Solutions on Delonix regia (Flamboyant Tree) Pod Biosorbent. Pacific J Sci Technol 10: 872-883.
44. Oyebamiji J, Babarinde NAA, Popoola AO, Oninla VO (2009)Kinetic, Equilibrium, and Thermodynamic Studies of the Biosorption of Pb(II) and Pb(II) from Aqueous Solutions by Talinumtriangulare (water leaf). Pacific J Sci Technol10: 428-436.
45. Ozcan AS,Ozcan A (2004) Adsorption of acid dyes from aqueous solutions onto acid-activated bentonite.J Colloid Interface Sci 276: 39-46.
46. Pons MN, Bonte SL, Potier O (2007) Spectral analysis and fingerprinting for biomediacharacterisation. J Biotechnol 113: 211.
47. Ramakrishnan M, Sulochana N (2009) Utilisation of Flame Tree Waste Biomass for the Removal of Hg(II) from Water. Acta Chim Slov 56:282-287.
48. Reddy DHK, Seshaiah K, Reddy AVR, Rao MM, Wang MC (2010)Biosorption of Pb2+ from aqueous solutions by Moringaoleifera bark: Equilibrium and kinetic studies. J Hazard Mater174: 831-838.
49. Reddy DHK, Seshaiah K, Reddy AVR, Lee SM (2012) Carbohydrate Polymers 88: 1077-1086.
50. Reddy DHK, HarinathY, Seshaiah K, Reddy AVR (2010)  Biosorption of Pb(II) from aqueous solutions using chemically modified Moringa oleifera tree leaves. Chem Eng J 162: 626-634.
51. Riaza M, Nadeema R, Hanifa MA, Ansaric TM,Rehmana KJ (2009) Pb(II) biosorption from hazardous aqueous streams using Gossypiumhirsutum (cotton) waste biomass.  J Hazard Mater 161: 88.
52. Singha S, Das SK (2012) Removal of Pb(II) ions from aqueous solution and industrial effluent using natural biosorbents. Environ Sci Pollut Res Int 19: 2212-2226.
53. Srivastava SK, Singh AK, Sharma A (1994) Studies on the uptake of lead and zinc by lignin obtained from black liquoar: a paper industry waste material. Environ Technol 15: 353-361.
54. Stephen IB, Chien JT, Ho GH, Yang J, Chen BH (2006)Equilibrium and Kinetics Studies on Sorption of Basic Dyes by a Natural Polymer ( γ – Glutamic Acid). Biochem Eng J 31: 204-215.
55. Wallace MA (2003) An Evaluation of Copper Biosorption by Brown Seaweed Under Optimized Conditions.  Environ Biotechnol 6:174-184.
56. Weber WJ (1972) Physico-Chemical Processes for Water Quality Control, John Wiley and Sons Inc., New York, NY.
57.  Sun XF, Wang SG, Liu XW, Gong WX, Bao N, et al. (2008) Biosorption of Malachite Green from Aqueous Solutions onto Anaerobic Granules: Kinetic and Equilibrium Studies. Bioresour Technol 99: 3475-3483.
58. Yavuz O, Altunkaynak Y, Guzel F (2003)Removal of copper, nickel, cobalt and manganese from aqueous solution by kaolinite. Water Res 37: 948-952.
59. Zhu B, FanT, Zhang D (2008) Adsorption of copper ions from aqueous solution by citric acid  modified soybean  straw. J Hazard Mater 153: 300-308.