View of GROUNDNUT HUSK (ARACHIS HYPOGAEA) AS AN ADSORBENT: EVALUATION OF ADSORPTIVE CHARACTERISTICS FOR CR (VI) FROM AQUEOUS SOLUTION

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Vol.03, Issue 09, Conference (IC-RASEM) Special Issue 01, September 2018 Available Online: www.ajeee.co.in/index.php/AJEEE

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GROUNDNUT HUSK (ARACHIS HYPOGAEA) AS AN ADSORBENT: EVALUATION OF ADSORPTIVE CHARACTERISTICS FOR CR (VI) FROM AQUEOUS SOLUTION

Anjali Nihore¹

Department of Applied Chemistry

Shri G. S. Institute of Science & Technology, Indore, 452003 MP., India [email protected]

Nitish Gupta²

Department of Applied Chemistry

Shri G. S. Institute of Science & Technology, Indore, 452003 MP., India [email protected]

Abstract— In the present study, the removal of chromium (VI) from aqueous solutions using groundnut husk (Arachis hypogaea) was investigated. Effect of experimental parameters namely adsorbent dose, pH, reaction time, temperature and initial metal concentration studied in a batch system which reveals that Cr(VI) adsorption increases with increasing dose and reached maximum at 9 g/L at optimum pH 6. The adsorption kinetics studied by fitting the data into pseudo-first and pseudo-second-order kinetic models and pseudo-second-order model fitted well with a high correlation coefficient.

Isotherm data analyzed by Langmuir and Freundlich adsorption isotherm; Langmuir isotherm gave a better fit to the experimental data. Results indicate that groundnut husk can provide an efficient and cost-effective technology for eradicating chromium from aqueous solution.

Index Term — Groundnut husk; Adsorption kinetics; Langmuir and Freundlich isotherm;

chromium

I INTRODUCTION

In today’s world of developing countries, increased industrial activities escalate the environmental pollution such as contamination of heavy metals (Zn, Cu, Cr, Pb, Hg, Ni, Cd, As etc.) in water bodies. The increased level of heavy metals in rivers, lakes, seawater, and other natural water represents a toxic threat to plants, animals and human health [1]. Chromium has vast application in industries electroplating, tanning dyes and paints and metal finishing, but the improper treatment of the waste from these industries results in increased contamination of chromium in the ecosystem. Generally, chromium exists in two oxidation states i.e., Cr (III) and Cr (VI) in the environment. Cr (VI) observed to be very soluble in water and highly toxic even in a trace concentration to the living bodies, with a potential carcinogenic effect.

However, Cr (III) is considered as a source element which influences the metabolic activities in living organisms in the trace amount but an increased amount of chromium may also result in skin allergies and cancer. Therefore chromium should be regained from the industrial wastewater before its discharge in the natural water system. Consequently, in many countries more strict legislation has been introduced

to control water pollution. [2-3]

For the control of water pollution, serious efforts have been made by a number of researchers across the world.

Various methodologies and techniques have been reformed such as chemical precipitation, ion exchange, flotation, reverse osmosis solvent extraction, bioremediation and the adsorption process etc. However, most of these methods bear some disadvantage like, incomplete metal removal, expensive equipment, regular monitoring system, reagent or energy requirements or producing toxic sludge or other disposal waste products. However, Adsorption proved to be a better technology for the removal of heavy metals.[ 4-6]

In recent years, the uses of natural adsorbents as an alternative to replace the conventional adsorbents have become the new field of research. A number of research workers used variety of low cost adsorbents from agricultural and industrial wastes such as seaweeds [7] clays [8] , biochar [9], green algae [10], dolochar [11], chitosan [12-13], modified groundnut hulls [14], etc., for the removal of chromium (VI) from waste aqueous streams. Generally, plant fibers contain mainly lignin, cellulose, hemi-cellulose, and some pectin and extractives. These contents have attracting groups or sites like carboxylic acid,

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2 phenolic and to some extent hydroxyl and carbonyl group which are responsible for metal sorption. [15]. Strong bonding of metal ions by the hydroxyl, carboxylic and phenolic groups often involves complexation and ion exchange [16].

India is one of the largest producers of groundnut with its utility as premier oil seed. Madhya Pradesh comes under the top ten groundnut producing states in India.

The groundnut oil industries produce a large amount of groundnut husks which dumped to nearby areas or burnt. These large quantities of ground husk possess limited way of its disposal. Therefore in the present study two objectives were addressed first is to protect our ecosystem from unwanted waste and second is to remove toxic Cr(VI). Batch studies carried out specifically on adsorption isotherms, adsorption kinetics and effects of various parameters like reaction time, the dose of adsorbents, initial metal ion concentration, temperature and pH.

II MATERIALS AND METHOD A. Preparation of biosorbent

Agricultural biomass i.e. groundnut husk was used as an adsorbent for the removal of chromium from aqueous solution. To remove the impurities like the mud, debris and other soluble impurities groundnut husk washed several times with deionized water and were oven grind.

After crushing and grinding it was sieved to obtain average particles of 100 mesh size and were stored in sealed polythene bags and use for the further experiment.

B. Preparation of synthetic stock solution

All the chemicals used were of analytical reagent grade. Deionized water was used throughout the experimental studies. The stock solution of chromium was prepared by dissolving Cr(NO3)6 (Merck India make) in 1000 ml of deionized water and pH adjusted to value 6 by addition of 0.1M HNO3 and 0.1M NaOH as appropriate. The pH of the test as well as the stock solution was adjusted with pH ± 0.1 accuracies using a digital pH meter (Elico Model LI-612) with a combination glass electrode.

C. Batch equilibrium study

Adsorption experiments employed at 25⁰C ± 1⁰C with pH 6.0 ± 0.1. In 100ml of the solution of chromium nitrate, 1 gm of adsorbent (groundnut husk) was agitated at 200 rpm on a mechanical shaker for an experimental require time in 250 ml Erlenmeyer flask and kept for time ranges from 5-240 mins. Metal ion concentration was used in the range of 10- 500 mg/l Preliminary experiments revealed that adsorption is fast and the removal rate is negligible after 2 h.

Therefore, the contact time of 2 h was used for a batch test. At the end of reaction time, the mixture was filtered and the metal content of the filtrate was analysed using Atomic Absorption Spectrophotometer (Shimadzu Model Analyst- 6300).

.D. Sorption kinetics and isotherm study Sorption kinetics studies are significant in the study of biosorption since they not only provide valuable insights into the reaction pathways but also describe the solute uptake rate which in turn controls the residence time of sorbate at the solid-liquid interface [17]. The metal uptake qt (mg/g) was determined as follow

qt = (Co - Cf) V/m (1) Where, Co and Cf are the initial and final

metal ion concentration (mg/L), respectively; V is the volume of solution (L) and m is the groundnut husk weight in dry form (g). The kinetics of the adsorption data was analysed using two kinetic models, pseudo-first-order and pseudo-second- order kinetic model. These models are expressed as follows.

 The pseudo-first order model (linear form) [18]

log(qe-qt) = logqe -2.303k/t (2)

 The pseudo-second order model(linear form)

t /qt = 1/ kqe2 + 1/qe . t (3) Where, qe and qt are the sorption capacities at equilibrium and at time t, respectively (mgg^-1) and k1 (min^-1) and k2 (g mg^-1min^-1) are first and second order rate constants.

The adsorption isotherm represents the relationship between the amount adsorbed by a unit weight of solid adsorbent and the amount of solute remaining in the solution at equilibrium.

The equilibrium data for the removal of

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3 Cr(VI) by adsorption on groundnut husk at all the temperatures were fitted in the Freundlich [38] and Langmuir isotherm models;

 Freundlich isotherm (linear form) lnqe = 1/n lnCe + lnk (4)

 Langmuir isotherm (linear form) 1/qê = 1/ θ⁰b.1/Cê+ 1/θ⁰(5) Where, qê is the amount of metal ions adsorbed per unit weight of adsorbent (mg/g), Ce is the equilibrium concentration of metal ions (mg/L). k and 1/n are the Freundlich constants related to adsorption capacity and adsorption intensity, respectively similarly Ɵô (mg/g) and b(L/mg) are the Langmuir constants related to the adsorption capacity and binding energy of adsorption, respectively.

III RESULTS AND DISCUSSION

A. Effect of reaction time on removal efficiency

Fig. 1 shows the removal of Cr (VI) with reaction time. It is clear that removal efficiency increased with an increase in contact time before equilibrium is reached because all the active sites of the adsorbent surface are occupied by Cr(VI), therefore another metal attachment was not possible on the adsorbent surface.

Other parameters such as dose of adsorbent and pH of the solution were kept constant. It can be seen from the fig.1 that removal efficiency of Cr(VI) reached to maximum value 93% , 90% and 82% for 10, 50 and 100 mg/l metal ion concentration respectively, after 2 h and then no further significant increase was observed for contact time up to 3.5 h.

According to these results, a contact time of 2 h was selected for the rest of the batch experiments.

0 50 100 150 200 250

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

10 mg/l 50 mg/l 100 mg/l

Percentage Adsorption

Reaction time (min)

Fig. 1: Effect of reaction time on percentage adsorption of Cr (VI) ions

from aqueous solution.

B. Effect of dose of adsorbent

Fig. 2 shows the removal of Cr (VI) with dose of the adsorbent for all different concentrations. It is clear from the figures that the removal of Cr(VI) ions increased with increase in adsorbent doses. This is expected because the number of adsorption sites (surface area) increases with the weight of adsorbent and hence, results in a higher percentage of metal removal at a high dose [19]. As seen in fig.2, optimum groundnut husk dosages can be used in chromium removal are 0.9 g and further experiments were carried out using this optimum dose.

0.0 0.5 1.0 1.5 2.0

10 20 30 40 50 60 70 80 90 100

10 mg/l 50 mg/l 100 mg/l

Percentage adsorption

Dose of Adsorbent (g)

Fig. 2: Effect of Adsorbent dose on percentage adsorption of Cr (VI) ions

C. Effect of initial metal ion concentration

The experimental studies were carried out with varying initial metal ion concentrations of chromium, ranging from 10 to 500 mg/L using 0.9 gm of groundnut husk dose at pH 6.0; the results are shown in fig. 3. The equilibrium sorption capacity of the biomass for chromium ions increased while the percentage adsorption decreased with a rise in initial metal ion concentration. This increase in loading capacity is probably due to a high driving force for mass transfer [20]. However, the percentage adsorptions of Cr (VI) ions on groundnut husk were decreased from 91%

to 43% . This may be attributed to lack of sufficient surface area to accommodate much more metal ion available in the solution.

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4

0 100 200 300 400 500

0 10 20 30 40 50 60 70 80

90 Percentage Adsorption

Loading capacity

Initial metal ion conc. mg/l

0 2 4 6 8 10

Loading Capacity (mg/g)

Fig. 3: Effect of Initial metal ion concentration and loading capacity

on percentage adsorption of Cr (VI) ions from aqueous solution.

D. Effect of temperature

Temperature has a pronounced effect on the adsorption capacity of the adsorbent.

The adsorptive separation of chromium ions from a 100 ml test solution containing 10, 50, 80 and 100 mg/L metal ions was studied with 0.9g groundnut husk at temperature ranges from 30- 60 ^oC(with increment of 5⁰C); the results are shown in fig. 4. The quantity of metal ions adsorbed per unit weight of adsorbent (mg/g) is observed to decrease with increase in temperature for all concentration of metal ions in test solution studied, indicating exothermic nature of the adsorption of chromium ions on groundnut husk.

30 35 40 45 50 55 60

60 65 70 75 80 85 90

10 mg/l 50 mg/l 80 mg/l 100 mg/l

Temperature (⁰C)

Fig. 4: Effect of Temperature on percentage adsorption of Cr (VI) ions

E. Effect of pH

The pH is one of the most important environmental factors influencing not only site dissociation, but also the solution chemistry and the speciation of the heavy

metals. The binding of metal ions by surface functional groups is strongly pH dependent [21]. The effect of pH of the solution on chromium removal efficiency is shown in fig. 5. It is clear from the figures that as pH of the solution increases the metal uptake increased. This may be attributed due to the fact that as pH of the solution increased, the overall surface on the adsorbent became negative and sorption increased. In the range of pH 6 to 7.1, the insoluble hydroxide of chromium starts precipitating from the solution, making true sorption studies impossible.

Therefore, at these pH values both sorption and precipitation would be the effective mechanism to remove the metal ions from the aqueous solution [22].

1 2 3 4 5 6 7 8 9 10

30 40 50 60 70 80 90 100

pH 10 mg/l 50 mg/l 100 mg/l

Fig. 5: Effect of pH on percentage adsorption of Cr (VI) ions from aqueous

solution

F. Sorption Isotherms and kinetic study The linear plots of log qe Vs. Log Ce (fig.6) and 1/qe Vs. 1/Ce (regression analysis) at different temperatures for Cr(VI) ions (fig.7) suggest the applicability of Freundlich and Langmuir adsorption isotherm respectively.

The value of isotherm constants reported in table-1 can be calculated from intercept and slope of plot log qe Vs. Log Ce and 1/qe

Vs. 1/Ce.

The pseudo-first order rate constant k¹ (min^-1) was calculated by plotting log (qe – q) vs. t, pseudo-second order rate constant k² (g mg^-1min^-1) values were calculated by plotting t/q^t vs. t. The value of rate constants and adsorption capacity is reported in table 2.

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5

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 -0.2

0.0 0.2 0.4 0.6 0.8 1.0

30 ⁰C 35 0C 40 0C 45 0C 50 0C 55 0C 60 0C

log qe

log Ce

Fig. 6: Freundlich adsorption isotherm of Cr (VI) ions from aqueous solution.

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

30 ⁰C 35 ⁰C 40 ⁰C 45 ⁰C 50 ⁰C 55 ⁰C 60 ⁰C

1/Qe

1/Ce

Fig. 7: Langmuir adsorption isotherm of Cr (VI) ions from aqueous solution.

Table 1 - Langmuir and Freundlich isotherm constant and correlation

coefficient

Tem p.

(⁰C)

Freundlich Isotherm

Langmuir Isotherm

1/n Kf θ

(mg/g) b (l/mg)

R² 30 1.0294 1.203 12.49 0.0777 0.999 35 1.2227 1.030 78.43 0.0104 0.953 40 1.5876 1.074 32.36 0.0194 0.952 45 1.7147 1.036 65.57 8.8932 0.949 50 1.8570 1.039 60.61 8.8850 0.999 55 2.2711 1.030 78.74 5.5918 0.945 60 2.8038 1.027 86.36 4.1300 0.943

0 20 40 60 80 100

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

10 mg/l 50 mg/l 100 mg/l

log(qe-qt)

Time (min)

Fig. 8: Pseudo first order graph for Cr(VI) ions adsorption.

0 50 100 150 200 250

10 mg/l 50 mg/l 100 mg/l

t/qt

Time, min

Fig. 9: Pseudo second order graph for Cr(VI) ions adsorption.

Table 2 - Pseudo first order (K1) and pseudo second order (K2) rate constants

Initial Cr(VI) ion conc.(mg/l)

Pseudo first

order Pseudo second

order

qe K1 qe K2

10 1.02 0.0700 0.97 0.1504

50 3.47 0.0319 5.01 0.0626

100 11.87 0.0408 10.39 0.0233

IV. CONCLUSION

In this paper, groundnut husk were used for the removal of Cr (VI) from aqueous solutions. The experiments conducted in the batch system. Results revealed that the adsorption of Cr(VI) increases with increase in adsorbent dose as the number of active sites also increases, with maximum uptake at adsorbent uptake 9g/L. The pH studies indicate that adsorption is strongly pH dependent with maximum adsorption

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6 obtained at pH 6 and at higher pH precipitation of chromium hydroxyl species onto the adsorbents (pH 5.3 –7.1). The Pseudo-second order model fitted well with high correlation coefficient and the Langmuir adsorption agreed well with experimental data and maximum adsorption capacity obtained to be 78.43 mg/g. Thus removal of chromium from aqueous solution using groundnut husk having an efficient and cost-effective results may consider as a promising technology for water purification.

V. ACKNOWLEDGMENT

Authors are thankful to MP Council of Science and Technology for financial support (Grant no. 1084/CST/R&D/2012) REFERENCES

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