Isotherm and Kinetic Studies of Adsorption of Heavy Metals on to Ecchornia Crassipes

 

P. Vijetha*

VFSTR University, Vadlamudi, Guntur (Dist), Andhra Pradesh, India

 

ABSTRACT:

Environmental problems are increasing day by day due to rapid industrialization. Therefore there exists great demand for removing heavy metals from the waste water. Many methods were available from literature for removing heavy metals from wastewater out of which Bioadsorption using Biomass is found to be more economical and ecofriendly compared to physico–chemical methods. In the present work, Ecchornia crassipes is used as an adsorbent for removing heavy metals like Pb and Zn from waste water. Ecchornia crassipes which contains high content of lignin can have high metal binding capacity. The effect of various parameters like PH, Biomass Dosage, Initial Metal Ion Concentration and Temperature on metal biosorption was studied. Biosorption experimental data is well described by both Freundlich and Langmuir Isotherm models. The experimental data obtained is well suited with the pseudo second order kinetics.

 

 

 

INTRODUCTION:

Heavy metals, generally called as environmental heavy metals if present in the excess amount than the required level may affect environment and human body. Especially Lead and Zinc are well known as toxic environmental pollutants. The quality of air, water and soil is badly degraded due to the presence of heavy metals and many health related issues occurred in plants, animals and human beings. Bioaccumulation is a serious problem that can be encountered with heavy metals [1]. These heavy metals enter in to water bodies from industrial waste, consumable waste, acid rains etc.

 

Lead if presents in small amounts in food or water is good for health, but if it is present in excess amounts leads to many health effects like Nausea, Diarrhea, Stomach Cramps, Vomiting etc., and sometimes also leads to kidney and liver damage. Zinc a natural chemical element which is abundant on earth enters in to water bodies from many sources like powerplants, metal factories, waste incinerators etc., when exposed to high doses it can become carcinogenic and toxic [2].

 

EXPERIMENTAL WORK:

In the present work Pb and Zn heavy metal ions were tested. Stock solutions of these metal ions were prepared according to the atomic adsorption standards by diluting the distilled water to the required concentrations. Completely ground Echornia crassipes was obtained from LIC tobacco company, Guntur, Andhra Pradesh. Composition of the Echornia crassipes is as follows: Total Solids–94.2%, Volatile Solids-72.0%, Carbon–43.0%, Lignin–30%, Ash -28.0%, Calcium-4.29%, Nitrogen-2.37%, Potassium-1.70%, Magnesium -0.70% [3]. From the stock solutions, required concentrations of working solutions are taken for carrying out the experiments. From the working solutions, required amounts for experiments are taken in stoppered conical flasks .These stoppered conical flasks were put in the orbital shaker and rotated at a speed of 60-70 rpm at room temperatures.

 

The dependency of Pb and Zn removal capacity of Ecchornia crassipes on parameters like pH and adsorbent dosage was obtained by agitating 4.5 g/L of Ecchornia crassipes in a series of Erlenmeyer flasks, containing 100 ml of Pb and Zn solutions having a initial concentrations of 200mg/L. The experiments were carried out for different pH ranges from 3.0 to 8.0 and with a known amount of Ecchornia crassipes ranging from 2 to 8 g/L. The effect of initial concentration on the equilibrium uptake of Pb and Zn by Ecchornia crassipes was studied by taking 5 g/L of Ecchornia crassipes and the initial concentration of Pb and Zn in the range of 25 to 250 mg/L in the 250 ml flasks.

 

The amount of Pb and Zn metal ions adsorption was determined from the following equation given below:

q_e=(C_o-C_e)V/W

 

Where

C_o=Initial metal ion concentration

C_e=Equilibrium metal ion concentration

q_e=Equilibrium metal ion concentrations on Ecchornia crassipes(mg/g)

V=volume of metal ion solutions taken

W=weight /mass of the Ecchornia crassipes used (g)

 

Effect of PH:

PH of the working solution has a solid influence on the biosorption of metal ions. In order to know about the influence of PH on metal ions adsorption on to Ecchornia crassipes experiments were carried out at different values of pH. As the values of PH increased from 3.0 to 6.0, the percentage removal of metal ions increased from 65 to 90 and from 6.0 to 9.0 it remains constant at 90.Therefore further experiments were carried out at the pH of 6.0.

 

It was found from the literature that Ecchornia crassipes contains Aromatic structures , non aromatic double bonds, H- bonded C=0 of conjugated ketones and quinines and symmetric coo-groups[4]. At a PH of 6–7, the reaction with metal ions will be promoted due to the chemical structures of the surface cell walls of the Echornia crassipes such as the ligands of functional groups like amino groups, phosphate and carboxyl groups. Therefore the metal removal efficiency is high in the range of 6.0 to 8.0.At lower PH values positive charge in the Echornia crassipes is lower thereby resulting in the decrease of metal removal efficiency.

 

Table 1:Effect of PH on % Removal

PH	% Removal
0	43.2
3	55.6
4	65
5	78.6
6	85.2
7	90
8	90
9	90

 

Fig 1 : Effect of PH on % Removal

 

Effect of biomass dosage:

Experiments were also carried out to test the effect of biosorbent dosage on metal ions adsorption. Different doses of biosorbent starting from 0.05, 1.0, 1.5 3g/L were taken and from the results it was observed that from 0.5 to 1.5 g/L of biosorbent dosage, metal removal capacity increases and thereafter it remains constant from 1.5 to 3 g/L. This may be due to the reason that till the time dosage is increased to 1.5 g/L, all the metal ions were adhered to the sites of biosorbent and now there are no sites empty in the biosorbent and also due to the concentration difference occurring between the adsorbate and adsorbent at higher dosages of biosorbent[5]. Therefore all the experiments in this study were carried out with a biosorbent dosage of 1.5g/L.

 

Table 2: Effect of biomass dosage on % Removal

Wt of Biomass	% Removal
0	0
0.05	35.6
1	85.6
1.5	90
2	90
2.5	90
3	90

 

 

Fig 2: Effect of biomass dosage on % Removal

Effect of initial metal ion concentration:

The equilibrium metal ions removal capacity of Ecchornia crassipes/dust for both the initial metal ion concentrations was studied.the concentration ranges selected for this work is in the range of 25 to 250 mg/L.It was obseved that for Pb, % metal removal values increases from 60 to 90. when the metal ion concentration increases from 25 to 125mg/L and from 15 to 20 mg/L of initial metal ion concentrations,% metal removal values remains constant.Therefore all the expeiments in the present work are carried out for the initial Pb concentrations of 15mg/L.The increase in the biosorption capacity for the initial metal ions concentration may be due to the higher rate of interaction between the Ecchornia crassipes and the metal ions[6].

 

Table 3 :Effect of Initial metal ion concentration on % Removal

Ci (initial concentration) (mg/L)	Ce (final concentration)(mg/L)	% Removal
25	10	60
50	17.6	64.8
75	22.35	70.2
100	24.7	75.3
125	26	79.2
150	15	90
175	17.5	90
200	20	90

 

For Zn, biosorption capacity of Echornia crassipes goes on increasing from 25 to 150 mg/L range of metal ion concentration and from 150 to 200 mg/L of initial metal ion concentration,it remains constant.therefore all the experiments in the present study are carried out for the initial Zinc concentration of 150 mg/L.these effects of initial metal ion concentrations were shown in the figure below.

 

Table 4: Effect of Initial metal ion concentration on % Removal

Ci(initial concentration)	Ce(final concentration)	% Removal
25	10.5	58
50	16.8	66.4
75	16.275	78.3
100	18.8	81.2
125	21.25	83
150	15.6	89.6
175	18.2	89.6
200	20.8	89.6

 

 

Fig 3: Effect of Initial metal ion concentration on % Removal of Pb and Zn

Effect of Contact time:

The changes in the pecentage removal with contact time of metal ions and biosorbent are studied and are shown in below Fig. For Pb, It is observed that the % Removal of the metal ions increases with the increase in the contact time till 3 hrs and thereafter it remains constant.The experiments were carried out by taking the biosorbent dosage of 1.5 g/L,initial metal ion concentration of 150 mg/L and the pH of the solution as 6.0.Thereafter by the observations ,the remaining experiments were performed with the contact time duration of 3 hrs.

 

Table 5: Effect of Contact time on % Removal (Pb)

TIME	% REMOVAL
0	0
30	65
60	70.32
90	72.56
120	75.4
150	81.3
180	90
210	90
240	90

 

For Zn, it is observed that % Removal of the metal ions increases with the increase in the contact time up to 3 hrs and after that it remains constant. So, further experiments in this study are carried out with the contact time duration of 3 hrs or 180 min.

 

Table 5: Effect of Contact time on % Removal (Zn).

TIME	% REMOVAL
0	0
30	35.2
60	46.8
90	52.32
120	60.121
150	64.5
180	89.6
210	89.6
240	89.6

 

 

Fig 4: Effect of Contact time on % Removal

 

Analysis of adsorption isotherms:

The relationship between metal ions concentration in the solution and the amount of metal ions adsorbed on the surface of the adsorbent is provided by the adsorption isotherm.In the present study the two most widely used isotherms such as Langmuir and Freundlich isotherms were used.Both Langmuir and Freundlich isotherm constants and the correlation coefficients (R²) are obtained and are given in the figures 5 and 6. From the experimental data values, Freundlich adsorption isotherm model was best fitted in to the experimental data.

 

Langmuir Isotherm Equation:

_{,1-/qe .}=_{,1-/qmax .}+(_,1/-bqmax.)_,1-/ce.

 

Freundlich Isotherm Equation:

 _lnqe=lnkF+,1-/n . _l,n-ce.

 

 

Fig 5: Langmuir Isotherm Graph for Pb and Zn

 

 

 

Fig 6: Freundlich Isotherm Graph for Pb and Zn

 

 

 

CONCLUSIONS:

Based on the % metal removal values obtained from the experimental studies it was proven that Ecchornia crassipes is one of the best adsorbent for the removal of heavy metal ions .In case of Pb,the % metal removal values are as high as 90 whereas in case of Zn ,it is 89.6.Incase of Pb,the Regression coefficient (R²) value using Langmuir isotherm is 1 whereas using Freundlich isotherm is 0.269.Incase of Zn, the regression coefficient (R²) value using Langmuir isotherm is 0.827 whereas using Freundlich isotherm is 0.635.Therefore from isotherm studies ,obtained experimental data is best suited with the Langmuir adsorption isotherm model for both Pb and Zn metal ions.

 

REFERENCES:

1.     S. Mondal, “Methods of dye removal from dye house effluent-an overview,” Environmental Engineering Science, 25 (3), 2008, 383–396.

2.     R. Ahmad and R. Kumar, Adsorption studies of hazardous malachite green onto treated ginger waste, Journal of Environmental Management, 91 (4); 2010, 1032–1038.

3.     Kadirvelu, K.; Thamaraiselvi, K.; Namasivayam, C. Removal of heavy metals from industrial wastewaters by adsorption onto activated carbon prepared from an agricultural solid waste. Bioresour. Technol. 76 (1); 2001, 63–65.

4.     Alyüz, B; Veli, S.: Kinetics and equilibrium studies for the removal of nickel and zinc from aqueous solutions by ion exchange resins. J. Hazard. Mater. 167 (1-3); 2009, 482–488.

5.     Gaber Edris, Yahia Alhamed, Abdulrahim Alzahrani . Biosorption of Cadmium and Lead from Aqueous Solutions by Chlorella vulgaris Biomass: Equilibrium and Kinetic Study 39 (1); 2014, 87-93.

6.     Flávio André Pavan, Ana Cristina Mazzocato, Yoshitaka Gushikem. Removal of methylene blue dye from aqueous solutions by adsorption using yellow passion fruit peel as adsorbent 99 (8); 2008, 3162-3165.

 

 

 

Accepted on 19.06.2018        © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(10): 4463-4466.