Isotherm Studies Of Cu And Ni Biosorption Using Tobacco Waste

 

P. Vijetha*

 

ABSTRACT:

Due to rapid industrialization and globalization, environmental problems are increasing day-by-day. 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, Tobacco waste is used as an adsorbent for removing heavy metals like Cu and Ni from waste water. Tobacco waste 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 copper and nickel are well known as toxic environmental pollutants [1]. 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 [2]. Bioaccumulation is a serious problem that can be encountered with heavy metals [3]. These heavy metals enter in to water bodies from industrial waste, consumable waste, acid rains [4] etc.,

 

Copper 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.

 

Nickel a natural chemical element which is abundant on earth enters in to water bodies from many sources like power plants, metal factories, waste incinerators etc., when exposed to high doses it can become carcinogenic and toxic.

 

EXPERIMENTAL WORK:

In the present work Cu and Ni 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 tobacco dust was obtained from LIC tobacco company, Guntur, Andhra Pradesh. Composition of the tobacco dust 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%.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 Cu and Ni removal capacity of tobacco waste on parameters like pH and adsorbent dosage was obtained by agitating 5 g/L of tobacco waste in a series of Erlenmeyer flasks, containing 100 ml of Cu and Ni solutions having a initial concentrations of 200mg/L. The experiments were carried out for different pH ranges from 2.0 to 8.0 and with a known amount of tobacco waste ranging from 3 to 9 g/L. The effect of initial concentration on the equilibrium uptake of Cu and Ni by tobacco waste was studied by taking 5 g/L of tobacco waste and the initial concentration of Cu and Ni in the range of 25 to 500 mg/L in the 250 ml flasks.

 

The amount of Cu and Ni 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 tobacco waste(mg/g)

V = volume of metal ion solutions taken

W = weight /mass of the tobacco waste 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 tobacco waste experiments were carried out at different values of pH. As the values of PH increased from 2.0 to 6.0, the percentage removal of metal ions increased from 60 to 85.6 and from 6.0 to 8.0 it remains constant at 85.6.Therefore further experiments were carried out at the pH of 6.5.

 

It was found from the literature that tobacco waste contains Aromatic structures , non aromatic double bonds, H- bonded C=0 of conjugated ketones and quinines and symmetric coo-groups[5]. 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 tobacco dust 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 tobacco dust is lower thereby resulting in the decrease of metal removal efficiency [10].

 

Table - 1:   Effect of PH on Percent Removal

Fig: 1  Graph of PH vs % Removal

 

Effect of biomass concentration:

Experiments were also carried out to test the effect of biosorbent dosage on metal ions adsorption. Different doses of biosorbent starting from 0.5, 1.0, 1.5 …..5 g/L were taken and from the results it was observed that from 0.5 to 1 g/L of biosorbent dosage, metal removal capacity increases and thereafter it remains constant from 1.0 to 5 g/L. This may be due to the reason that till the time dosage is increased to 1 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. Therefore all the experiments in this study were carried out with a biosorbent dosage of 1.0g/L.

 

Table – 2  :  Effect of Wt of biomass on % Removal

 

Fig:2  Graph of Wt of Biomass Vs % Removal

Effect of initial metal ion concentration

The equilibrium metal ions removal capacity of tobacco waste/dust for both the initial metal ion concentrations was studied.the concentration ranges selected for this work is in the range of 1 to 20 mg/L.It was obseved that for Cu ,% metal  removal values increases from 60 to 85.6 when the metal ion concentration increases from 0 to 15mg/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 cu 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 tobacco waste and the metal ions[6].

 

Table 3: Effect of % Removal vs Initial concentration for Cu

 

Fig-3: Graph of Initial concentration vs % Rrmoval for Cu

 

For Ni, biosorption capacity of tobacco dust goes on increasing from 1 to 12 mg/L range of metal ion concentration and from 12 to 20 mg/L of initial metal ion concentration,it remains constant.therefore all the experiments in the present study are carried out for the initial nickel concentration of 12 mg/L.these effects of initial metal ion concentrations were shown in the figure below.

Table 4: Effect of % Removal vs Initial concentration for Ni

 

Fig-4: Graph of Initial concentration vs % Rrmoval for Ni

 

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 Cu, It is observed that the % Removal of the metal ions increases with the increase in the contact time till 2.5 hrs and thereafter it remains constant.The experiments were carried out by taking the biosorbent dosage of 1.0 g/L,initial metal ion concentration of 15 mg/L and the pH of the solution as 6.5[9].Thereafter by the observations ,the remaining experiments were performed with the contact time duration of 2.5 hrs or 150 min.

 

Table-5: Effect of Contact time Vs % Removal for cu

 

Fig – 5: Effect of contact time vs % removal for Cu

 

For Ni ,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 Vs % Removal for Ni

Fig – 5: Effect of contact time vs % removal for Ni

 

Analysis of adsorption isotherms:

The relation ship 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[10].

 

Fig-6 : Effect of 1/qe vs 1/ce for Cu

 

In the present study the two most widely used isotherms such as Langmuir and Freundlich isotherms were used[7].Both Langmuir and Freundlich isotherm constants and the correlation coefficients (R²) are obtained and are given in the below table.From the experimental data values ,Freundlich adsorption isotherm model was best fitted in to the experimental data.

 

Langmuir Equation: 1/q_e = 1/q_max + (1/bq_max)(1/c_e)

Freundlich Equation: lnq_e =ln K_F + 1/n ln C_e

 

 

Table 6 : Variables of Langmuir and Freundlich adsorption isotherms for Cu

qe	Ce	1/qe	1/Ce	lnqe	lnCe
0.15	1	6.666666667	1	-1.897119985	0
0.324	1.76	3.086419753	0.568181818	-1.127011763	0.565313809
0.5265	2.235	1.899335233	0.447427293	-0.641503947	0.804241228
0.753	2.47	1.328021248	0.4048583	-0.283690051	0.904218151
0.99	2.6	1.01010101	0.384615385	-0.010050336	0.955511445
1.284	2.16	0.778816199	0.462962963	0.249980205	0.770108222
1.498	2.52	0.667556742	0.396825397	0.404130885	0.924258902
1.712	2.88	0.58411215	0.347222222	0.537662278	1.057790294

 

Table 7 : Variables of Langmuir and Freundlich adsorption isotherms for Ni

ci	ce	qe	1/ce	1/qe	lnqe
2.5	1.35	0.115	0.740741	8.695652	-2.16282
5	2.01	0.299	0.497512	3.344482	-1.20731
7.5	2.55	0.495	0.392157	2.020202	-0.7032
10	3.11	0.689	0.321543	1.451379	-0.37251
12.5	4.22	0.828	0.236967	1.207729	-0.18874
15	4.56	1.044	0.219298	0.957854	0.043059
17.5	5.32	1.218	0.18797	0.821018	0.19721
20	6.08	1.392	0.164474	0.718391	0.330742

 

 

Fig-7 : Graph of lnqe vs lnCe for Cu

 

Fig-8 : Effect of 1/qe vs 1/ce for Ni

 

Fig-9 : Graph of lnqe vs lnCe for Ni

 

CONCLUSIONS:

1.Based on the % metal removal values obtained from the experimental studies it was proven that tobacco waste is one of the best adsorbent for the removal of heavy metal ions .

2.In case of Cu,the % metal removal values are as high as 85.6 whereas in case of Ni ,it is 69.6.

3.Incase of Cu,the Regression coefficient (R²) value using Freundlich isotherm  is 0.925 whereas using Langmuir isotherm is 0.683.

4.Incase of Ni,the regression coefficient (R²) value using Freundlich isotherm is 0.880 whereas using Langmuir isotherm is 0.610.

5.Therefore from isotherm studies ,obtained experimental data is best suited with the Freundlich adsorption isotherm model for both Cu and Ni metal ions .

 

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Accepted on 21.02.2017           © RJPT All right reserved