Studies on the Removal of Pb(II) from Aqueous Solutions by Adsorption with E. Globulus Leaf Powder through Response Surface Methodology

Research Article

Austin Chem Eng. 2017; 4(1): 1049.

Studies on the Removal of Pb(II) from Aqueous Solutions by Adsorption with E. Globulus Leaf Powder through Response Surface Methodology

Hymavathi D and Prabhakar G*

Department of Chemical Engineering, S.V. University College of Engineering, Tirupati, Andhra Pradesh, India

*Corresponding author: Garimella Prabhakar, Department of Chemical Engineering, S.V. University College of Engineering, Tirupati, Andhra Pradesh, India

Received: April 12, 2017; Accepted: May 17, 2017; Published: May 24, 2017


An exhaustive batch experimental investigation to treat lead-laden waters by adsorption using leaf powder of Eucalyptus globulus is reported. Based on full factorial approach, optimum conditions to yield a removal of 96.58% are identified as initial ion concentration of 20mg/L, sorbent dosage 25g/L at a pH of 5.0 and a temperature of 303K. Freundlich model adequately represents the equilibrium and the maximum adsorption capacity is found to be 6.803mg/g. The process is endothermic and spontaneous. Adsorption follows second order kinetics. The adsorption process compares well with other similar studies.

Keywords: Pb(II) removal; Adsorption; E. globules; Equilibrium; Kinetics; RSM


Co: Initial Concentration of Pb(II) solution (mg/L); Ce: Equilibrium Concentratin of Pb(II) solution (mg/L); qe: Amount Sorbed Per Unit Weight Of Biosorbent At Equilibrium (mg/g); qet: Equilibrium Metal Uptake Capacity At Time (mg/g); qmax: Maximum Metal Uptake Capacity (mg/g); qt: Metal Uptake Capacity At Time t (mg/g); Kdiff: Intra-Particle Diffusion Rate Constant; c: Thickness Of Boundary Layer; m: Mass Of Adsorbent (g); w: Adsorbent Dosage (g/L); V: Volume of the Pb(II) solution (L); b=kL: Affinity Constant Or Energy To Biosorption (L/g); n: number(dimensionless); Kf : Freundlich coefficient (mg/g); K1 : First Order Equilibrium Rate Constant (1/min); K2: Second Order Equilibrium Rate Constant (g/mg.min); AT: Temkin Adsorption Intensity, (L/g); AE: Elovich constant; BE: Initial Adsorption Rate; E: Mean Free Energy Of Sorption Per Of The Molecule Of Sorbate; bT: Heat Of Adsorption Constant


R: Universal Gas Constant (8.314mol-1K-1); X1: Initial Concentrations of Pb(II) (mg/L); X2: pH(dimensionless); X3: Adsorbent Dosage (g/L); X4: Absolute Temperature (K); RSM: Response Surface Methodology; ANOVA: Analysis Of Variance; Max: Maximum Metal Uptake Capacity; Diff: Intra-Particle Diffusion Rate Constant


Water contamination is mainly due to the accumulation of heavy metals, from different industries like metallurgical, battery, electroplating and metal finishing industries, chemical manufacturing and tanneries [1,2]. Among heavy metals viz., Co, Cr, Zn, Cd, Cu, Pb, Hg, As, Al and Ni, Pb(II) is one of the most toxic ion causing serious health issues related to liver damage, nervous system, kidneys, reproductive system, neurological activity and also causes high hypertension [3,4]. Maximum allowable concentration for Pb(II) ion limit value of 0.01mg/L in drinking water recommended by World Health Organization [5] and the permissible level of Pb(II) in wastewater is 0.05mg/L given by the Environmental Protection Agency (EPA) [6]. Conventional methods - chemical precipitation [7], reverse osmosis [8], ion exchange [9], coagulation [10], electro dialysis [11] and ultra filtration [12] were studied earlier. These methods were found to be not so promising due to incomplete metal removal, high reagent and high energy requirements.

Adsorptive treatment of lead waters was probed with different types of waste materials and a few of them are as follows. Nile rose plant [13], chaff [14], rice husk [15], coir fiber waste [16], banana stems [17], wheat bran[18], coffee grounds [19], tree ferns [20], palm kernel fibres [21], crop milling waste-black gram husk [22], pomegranate peels [23] , peanut skins [24], cone biomass of Pinus sylvestris [25], carbon derived from agricultural waste[26], almond shell [27], native and chemically treated olive stone [28], residue of all spice [29], ceder leaf ash [30], cashew nut shell [31], Peanut shell [32], native and chemically treated olive tree pruning [33], pine cone shell [34] and rapeseed biomass [35] were used in the studies and Eucalyptus globulus , leaf powder of cheap and widely available which is preferred as a natural antimicrobial agent, industrial solvent, and deodorant, is tried for the removal of lead from aqueous systems [36,37].

In present work, E. globules L., used as an adsorbent for removal of Pb(II) from aqueous solution and E. glubulus belongs to the family of myrtaceae. Eucalyptus bark was used for the removal of chromium [38] and mercury [39]. Till –to- date, non literature is available on E. globulus leaf powder for removal of Pb(II).

Materials and Methods

Preparation of stock solution

All chemical compounds used are of analytical grade (Merck).

A Stock solution of 500ppm Pb(II) is prepared by dissolving 0.4055mg of 98.5% pure Pb(NO3)2 in 500ml of distilled water. It is diluted to different levels, appropriate to the study. pH of the solution is adjusted using 0.1N NaOH and 0.1N H2SO4. Final Pb(II) ion concentration is obtained by Inductively Coupled Plasma Optical Emission Spectroscope (Perkin Elmer model Optima 8000). FTIR (ALPHA interferometer (ECO-ATR)), Bruker, Germany) in the range of 4000 – 500 cm-1 is employed to identify the functional groups that are involved in adsorption. Elemental composition is recorded by Scanning Electron Microscope, (SEM–EVO MA 15) with Electron Dispersive X- Ray Spectroscope of OXFORD INSTRUMENTS (Inca Penta FET x3).

Preparation and activation of biosorbent

E. globulus leaves are collected in the University Campus, water washed thoroughly to clear the surface impurities, and is then sun dried. They are grounded into a fine powder and 63μm – size particles are collected. The particles are further washed with water to remove coloring agents, dried at room temperature and are stored in air tight bottles for further studies.

Biosorption studies

Sufficient numbers of flasks, each containing 50ml solution of 20mg/L Pb(II) are taken and the solution pH adjusted. A known quantity of adsorbent is added and the flasks are agitated at constant speed on a shaker at room temperature, Flasks are withdrawn at suitable time intervals, the content filtered and Pb(II) estimation in the liquid sample is made. Similarly, the procedure is repeated with different quantities of adsorbent and other parameters to make the study complete. Percentage removal Pb(II) is calculated using the formula

c o c e c o 100      (1) MathType@MTEF@5@5@+=feaaguart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaacaWGJbWaaSbaaSqaaiaad+gaaeqaaOGaeyOeI0Iaam4yamaaBaaaleaacaWGLbaabeaaaOqaaiaadogadaWgaaWcbaGaam4BaaqabaaaaOGaey4fIOIaaGymaiaaicdacaaIWaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeikaiaabgdacaqGPaaaaa@4617@

The equilibrium metal uptake capacity is estimated by using

q e = c o c e c o V    (2) MathType@MTEF@5@5@+=feaaguart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyCamaaBaaaleaacaWGLbaabeaakiabg2da9maalaaabaGaam4yamaaBaaaleaacaWGVbaabeaakiabgkHiTiaadogadaWgaaWcbaGaamyzaaqabaaakeaacaWGJbWaaSbaaSqaaiaad+gaaeqaaaaakiabgEHiQiaadAfacaqGGaGaaeiiaiaabccacaqGGaGaaeikaiaabkdacaqGPaaaaa@469A@

Response surface methodology (C.C.D) and optimization of Pb(II) removal

RSM is a group of mathematical and statistical techniques for modeling and analysis of problems in which the response of a model is influenced by several variables [40]. A 24 full-factorial design, 6 center points and 8 axial points leading to 30 experimental runs is performed to study the effect of the four contributing parameters using statistical software, Design expert 10.0.03 (Ease state, USA). Central Composite Design (CCD) consists of 2n factorial runs with 2*n axial runs and the minimum number of experiments that need be conducted is provided by equation 3.

No of experiments (N) = 2n+2n+6 (center points) = 2*4+2*4+6=30 (3)

Each variable is investigated at two levels and as the number of factors/operating variables increases, then the number of experimental runs for complete picture also increases.

Y=f (X1, X2, X3 …Xn) (4)

In the present case, four factors - initial metal ion concentration (X1), initial solution pH (X2), adsorbent dosage (X3) and temperature of solution (X4) are selected as independent variables in equation 4 and by fixing the contact time and size of the adsorbent, the percentage removal of Pb(II) is obtained. Percentage adsorption (%Y) is considered as the dependent variable and the experimental design made with range and levels (-2, -1, 0, 1, 2) of independent variables. In the optimization process, the response can be related to the independent variables by quadratic (second degree) equation and the model equation is given in equation 5.

%( y )= β 0 + β 1 X 1 + β 2 X 2 + β 3 X 3 + β 4 X 4 + β 12 X 1 X 2 + β 13 X 1 X 3 + MathType@MTEF@5@5@+=feaaguart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@624C@ (5)

β 14 X 1 X 4 + β 23 X 2 X 3 + β 24 X 2 X 4 + β 34 X 3 X 4 + β 11 X 1 2 + β 22 X 2 2 + β 33 X 3 2 + β 44 X 4 2 MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@6F4A@ where Y is estimate response of the system, β0 is constant coefficient, β1, β2, β3 and β4 are linear coefficients, β12, β13, β14, β23, β24 and β34 are interaction coefficients among the four factors, β11, β22, β33 and β44 are quadratic coefficients, X1, X2, X3 and X4 are independent variables. A multiple regression analysis is then performed to obtain the values of the coefficients. A total of 30 experiments are needed to estimate the biosorption of Pb(II) on to E. globulus L. The responses and corresponding parameters are modeled and optimized using analysis of variance (ANOVA) and by the correlation coefficient (R2). The R2 value shows a measure of how variability in the observed response values can be simplified by experimental factors and their interactions [41].

Results and Discussion

Optimization using response surface methodology (RSM)

It is pointed out that six factors are critical in adsorption. The smaller the particle, the higher is the surface available for transfer and the higher the transfer. However, post adsorption separation puts a limit on the particle size. In the present study a particle of 63μm is used. The time progress of adsorption is studied first and the process has taken 60 minutes to reach equilibrium, Thus, keeping 63μm particle size and 60 minutes of contact time fixed, the effect of other vital parameters, namely, Pb(II) ion concentration, initial solution pH, sorbent dosage and temperature is studied. A total of 30 experimental runs are conducted and the results of the experimentation are in (Table 1). Levels of different process variables in coded and uncoded form for adsorption of Pb(II) using E. globulus L. leaf powder in (Table 2). Thus, 96.58% removal of Pb(II) could be achieved, when 20mg/L Pb(II) is treated with 25g/L E. globulus L. at a pH of 5.0 and temperature of 303K. The interactive contributions of the variables are further studied with model expression given as equation 3.

%Y=96 0.028 X 1 0.78 X 2 + 0.22 X 3 + 0.12 * X 1 X 2 0.17 * X 1 X 3 + 0.14 * X 1 X 4 + 0.66 * X 2 X 3 MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@7046@

0.13 * X 2 X 4 + 0.22 * X 3 X 4 0.40 * X 1 2 0.51* X 2 2 + 0.042 * X 3 2 0.34* X 4 2      (6) MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@6925@