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WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES

Prasad et al.

World Journal of Pharmacy and Pharmaceutical Sciences

SJIF Impact Factor 5.210

Volume 4, Issue 11, 1600-1610

Research Article

ISSN 2278 – 4357

KINETICS OF HEAVY METAL (Cr & Ni) REMOVAL FROM THE WASTEWATER BY USEING LOW COST ADSORBENT T. Brahmaiah1, L. Spurthi2, K. Chandrika2, S. Ramanaiah1, and K. S. Sai Prasad1* 1 2

Dept. of Geology, S.V.University, Tirupati.

Sri Jayachamarajendra College of Engineering, Mysore. ABSTRACT

Article Received on 07 Sept 2015, Revised on 01 Oct 2015, Accepted on 24 Oct 2015

Heavy metal toxicity due to industrial wastewater has been a threat to the environment for the past many decades, especially in the developing countries such as India, China and Thailand where cost effectiveness of the removal process is a major factor. In this research,

*Correspondence for

the effectiveness of two natural adsorbents, untreated and treated rice

Author

straw (RS), which are cheaply available in these countries for the

K. S. Sai Prasad

removal of Chromium metal from synthetic wastewaters were studied.

Dept. of Geology, S.V.University, Tirupati.

Adsorption experiments were carried out using rice straw as an agricultural residue to adsorb some heavy metals like Cr and Ni from

India.

aqueous solution. Rice straw was treated with two different methods like acid treatment and alkali treatment in order to increase their metalbinding capacity. The adsorption process is affected by various parameters such as such as adsorbent dose, pH and contact time are of vital importance. Adsorption equilibrium data was well fitted with Lagergren second order kinetics for both untreated and treated rice straw as adsorbents. This indicates that the rate limiting step may be chemical sorption rather than diffusion. KEYWORDS: Rice Straw (RS), Adsorption, Sodium Hydroxide, Kinetics. INTRODUCTION Environmental pollution is currently one of the most important issues facing humanity. It was increased exponentially in the past few years and reached alarming levels in terms of its effects on living creatures. Toxic heavy metals are considered one of the pollutants that have direct effect on man and animals. Rapid growth in human population is one of the major causes of environmental pollution. Increased industrialization and urbanization throughout www.wjpps.com

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the world results in consistent release of toxic effluents, several industrial processes generate metal containing wastes. One of the pollutants is heavy metals. Heavy metals are non-degradable metals. Several industrial wastewater streams may contain heavy metals such as Cr, Cu, Pb, Zn, Ni, etc., including the waste liquids generated by metal finishing or the mineral processing industries. Heavy metals are natural components of the Earth's crust. They cannot be degraded or destroyed. To a small extent they enter our bodies via food, drinking water. Heavy metals can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and groundwater. Heavy metals pollution can originate from natural and anthropogenic sources. Heavy metal pollution of surface and underground water sources results in considerable soil pollution. Heavy metals are dangerous because they tend to bioaccumulate. Bioaccumulation means an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment. These heavy metals are persistence, accumulate and not metabolized in other intermediate compounds and do not easily breakdown in the environment. These metals are accumulating in food chain through uptake at primary producer level and then through consumption at consumer level.[10] The treatment of heavy metals is of special concern due to their recalcitrance and persistence in the environment. Various methods for heavy metal removal from wastewater have been extensively studied. These technologies include chemical precipitation, ion exchange, adsorption, membrane filtration, coagulation–flocculation, flotation and electrochemical methods. Adsorption is one of the simple and effective methods of heavy metal removal.[3] The main objective of the present study is to evaluate the efficiency of locally available waste products as adsorbents on the removal of chromium from wastewaters. The specific Objectives of the present study are: To conduct the batch adsorption test to know the effect of adsorbent dosage, pH and contact time on the removal of chromium and nickel from wastewater. Treatment Methods There are numerous methods currently employed to remove and recover the metals from our environment and many physico-chemical methods have been proposed for their removal from www.wjpps.com

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wastewater. Removal of heavy metals from wastewater is usually achieved by physical and chemical processes which include precipitation, coagulation reduction membrane procession change and adsorption.[7,1&6] These methods have been found to be limited, since they often involve high capital and operational costs and may be associated with the generation of secondary waste which presents treatment problems. All the chemical methods have proved to be much expensive and less efficient than the adsorption process. In contrast, the adsorption technique is one of the preferred methods for removal of heavy metals because of its efficiency and low cost.[8&6] The investigations of Qaiser et al., and Kailas Doke et al.,[9&2] showed that adsorption kinetic studies reveal that the adsorption of Cr(VI) onto activated carbon was pseudo-second order chemisorptions and that the agricultural waste biomass wood apple shell can be effectively utilized for the preparation of activated carbon and become a promising adsorbent for the removal of Cr(VI) from aqueous solutions. MATERIALS AND METHODS Analytical method The concentration of chromium was determined from a wastewater using Inductively Coupled Plasma Spectrophotometer (ICP). Preparation of synthetic wastewater Standard chromium solution was prepared by adding 2.8287g of potassium dichromate (K2Cr2O7) to 1 liter of distilled water. The resulting concentration of the solution was 100µg of chromium (VI) per milliliter of solution. The initial chromium (VI) concentration (20mg/l) was prepared by dilution.[9] Standard Nickel solution was prepared by adding 1g of nickel metal in 20ml of nitric acid and was allowed to dissolve completely and was diluted to 1 liter.

The initial nickel

concentration (85 mg/l) was prepared by dilution. MATERIALS Rice straw which is an agricultural byproducthas been used as low cost adsorbent. Untreated rice straw was prepared by cutting the straw into small pieces, washed with distilled water, dried in an oven over a period of 24 hrs and then grind into fine powder. Treated rice straw was prepared by using sodium hydroxide solution. 16 g of powdered rice straw was treated

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with 240 mL of sodium hydroxide solution and dried in oven at 100°C over a period of 24 hrs.[8] Experimental procedure Adsorption experiments were conducted in batch process, that is, the solution was kept in separate beakers and was stirred continuously for a particular time and finally samples were analyzed in batches for residual chromium concentration. Batch adsorption The influence of rice straw on metal ions removal was investigated under the following experimental conditions. Batch experiments were conducted for varied pH, adsorbent dose, initial chromium concentration and contact time. At desired intervals, effluent samples were collected, filtered using whattman filter paper and analyzed for concentration of chromium. The amount of metal ion adsorbed was calculated as. % Adsorption = (Ci – Cf)/ CiX 100

(1)

Where Ci and Cf are the initial and final concentrations of the metal ions in the solution (ppm). RESULTS AND DISCUSSIONS Adsorption studies have been conducted for the removal of chromium and nickel from synthetic wastewater. In order to design any adsoption system, optimization of various operating parameters such as adsorbent dose, pH and contact time are of vital importance. To ascertain the above parameters batch adsorption studies were conducted. Based on the objectives of the present study, laboratory adsorption tests were conducted and the results have been discussed in the following sections. Batch adsorption technique is widely used for water and wastewater treatments. In batch adsorption process the various operating parameters such as adsorbent dose, pH and contact time have been investigated. These batch adsorption data have been used to study the Lagergren first and second order kinetics. The batch adsorption data has been used in the adsorption isotherm models such as Freundlich, Langmuir and Tempkin equations. Effect Of pH The pH of the aqueous solution plays a vital role in controlling the adsorption process. The pH of aqueous solution governs the adsorption of metal ions. The effect of pH on the www.wjpps.com

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adsorption capacity of raw and modified rice straw may be attributed to the combined effect of the nature of the surface and the amount of adsorbed species. The minimal adsorption at very low pH may be due to the higher concentration and high mobility of H +, which are preferentially adsorbed rather than metal ions. The effect of pH on chromium and nickel removal using both treated and untreated rice straw has been studied. At very low pH, the percentage adsorption decreased due to the involvement of less number of anions on the positive surface. At higher pH due to more OH- ions adsorbent surface carrying net negative charges, which tend to repulse the metal anions.[4] Therefore, maximum removal from aqueous solution was achieved at higher pH. From the Fig.1, it is seen that adsorption rate for chromium increases with increase in pH for both treated and untreated rice straw from pH 2 to pH 6 and pH 2 to pH 4 respectively and there onwards chromium removal was found to be gradual.

Fig.1: Effect of pH on the removal of chromium and Nickel Effect of adsorbent dosage The adsorbent dosage is an important parameter in adsorption studies because it determines the capacity of adsorbent for a given initial concentration of metal ion solution. To study the effect of adsorbent dose on adsorption of chromium, a plot is drawn for percent removal versus adsorbent dosage for fixed initial concentrations of 20mg/l for chromium for both untreated and treated adsorbent shown in Fig-2. From these figure, it is evident that the percent removal of chromium for both treated and untreated adsorbent increases with increase in adsorbent dosage. This may be due to some of the adsorption sites remaining unsaturated during the adsorption process. In the present study adsorbent dosage was varied and equilibrated at an initial chromium ion concentration of 20 mg/l. The removal efficiency decreased with increase in adsorbent dosage for a given initial metal concentration. The

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percent removal of chromium concentration for both treated and untreated adsorbent increased with increase in adsorbent dosage. The increase in the adsorbent dosage leads to a greater availability of the exchangeable sites or surface area of the adsorbent. For chromium, the optimum dosage for untreated and treated rice straw was found to be 8g/100ml.

Fig.2: Effect of adsorbent dosage on the removal of Chromium and Nickel Effect Of Contact Time Equilibrium time is a crucial parameter for an optimal removal of metal ions in the wastewater. From the Fig 4.5, it is observed that at 40 min the chromium removal was found to be maximum of 65% at 50 min, it was found to be 91% for untreated and treated rice straw (Fig.3).

Fig.3: Effect of contact time on the removal of chromium and Nickel

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ADSORPTION KINETICS In the adsorption process, to understand and predict how time affects mobility and retention of heavy metals, it is important to study the kinetics of the adsorption. In order to define the adsorption kinetics of heavy metal ions, the kinetic parameters for the adsorption process were studied. Lagergren pseudo first order kinetics The pseudo-first order model of Lagergren[5], was widely used for the adsorption of liquid adsorbate on solid adsorbent on the basis of adsorption capacity at different time intervals. The general form of pseudo-first order equation is given by, =

(

)

(4.1)

The linear form is given by, (4.2) Where, qe and qt represents the amount of adsorbate adsorbed (mg/g) at any time t and at equilibrium time, respectively and k1 represents the adsorption rate constant. Plots were made between log (qe-qt) versus time, for chromium shown in Fig. 4. and Fig .5 for chromium and nickel respectively. It is evident from these plots that, with increase in time there was exponential decrease on the removal of chromium and nickel. However, with treated adsorbent the nature of chromium removal showed exponential increase with time. The equilibrium rate constants k1 were determined.

Fig .4: Pseudo first order kinetics for chromium removal

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Fig .5: Pseudo first order kinetics for nickel removal Lagergren Pseudo Second Order Kinetics: The general form of pseudo-second order equation is given by, = k2 (qe - qt)2

(4.3)

The linear form of the above equation is given by, =

+

t

(4.4)

Where, k2 is the pseudo second order rate constant (g/mg-min). In the present study, adsorption rate constants were determined using Lagergren second order equation by plotting t/qt versus qe, are depicted in Fig.6 and Fig.7, for untreated and treated adsorbent for chromium and nickel removal, respectively. From the figures, it is observed that all the plots showed a linear fit indicating second order kinetics. The values of k2 was found to be 0.00230 and 0.00962 for chromium for untreated and treated rice straw, respectively. High regression co-efficient (R2) showed adsorption follows pseudo second order kinetics for untreated and treated rice straw (Table-1). The assumption behind the pseudo second order kinetics model was that the rate limiting step which might be chemisorptions involving valence forces through sharing or exchange of electrons between adsorbent and adsorbate. It may also be assumed that adsorption model ions occur through chemisorptions.

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Table -2: Pseudo first order and second order kinetics constants for chromium and nickel Parameter Chromium Untreated RS Treated RS Nickel Untreated RS Treated RS

Pseudo first oder kinetics K1 R2

Pseudo second order kinetics K2 qe R2

0.0368 0.0184

0.999 0.989

0.0023 0.0096

15.873 19.230

0.960 0.988

0.0506 -0.0207

0.985 0.990

0.0160 0.0326

50 71.428

0.988 0.979

Fig .6: Pseudo second order kinetics for chromium removal

Fig.7: Pseudo second order kinetics for nickel removal Similar study was made by Kailas Doke and Ejazuddin M. Khan[2], it was found that the pseudo-second order model fitted very well to the adsorption of Cr(VI) onto activated carbon from wood apple shell, indicating that the adsorption process follows chemisorptions.

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CONCLUSIONS In the present study, batch adsorption tests were conducted on the removal of chromium and nickel present in wastewater. The optimum pH for chromium of untreated and treated rice straw was pH 4 and pH 6 respectively. Similarly for nickel, for untreated and treated rice straw was pH 4. From the results, the optimum adsorbent dosage was found to be 8g/100ml and 12g/100ml of untreated rice straw for chromium and nickel respectively and 8g/100ml of treated rice straw for both chromium and nickel respectively. The results of the effect of contact time on the removal of chromium show that the rate of chromium removal is very rapid during the first 40min for untreated rice straw and 50min for treated rice straw and thereafter remains constant. Similarly for nickel, the rate of nickel removal is very rapid during first 40min for untreated rice straw and 50min for treated rice straw respectively and thereafter it remains constant. The equilibrium rate constant (k2) of second order kinetics was found to be 0.00230 and 0.00962 for untreated and treated rice straw for chromium. Adsorption equilibrium data was well fitted with Lagergren second order kinetics for both untreated and treated rice straw as adsorbents. This indicates that the rate limiting step may be chemical sorption rather than diffusion. The diffusion kinetics study shows that adsorption rate is mainly governed by intraparticle diffusion on the removal of chromium and nickel using treated and untreated rice straw as adsorbents. REFERENCES 1. Bushra Fatima and Rubina Farooq, (2009), “ Biosorption of Aqueous Lead (II) on Rice Straws (oryza sativa) by flash column process”, World Applied Sciences Journal, 7(10): 1263-1268. 2. Kailas Doke M and Ejazuddin Khan M, (2012), “Equilibrium, kinetic and diffusion mechanism of Cr(VI) adsorption onto activated carbon derived from wood apple shell”, Arabian Journal of Chemistry, 6(1): 94-98. 3. Khaled Mohamed Mostafa, Abdul Rahim Samarkandy and Azza Awad El-Sanabary, (2012), “Harnessing of Chemically Modified Rice Straw Plant Waste as unique Adsorbent for Reducing organic and inorganic Pollutants”, International Journal of Organic Chemistry, 2: 143-1516.

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4. Khaldoun Al-Sou'od, (2012), “Adsorption Isotherm Studies of Chromium (VI) from Aqueous Solutions using Jordanian Pottery Materials”, APCBEE Procedia, 1(3): 116 – 125. 5. Lagergren, S. (1989), Zur theorie der sogenannten adsorption gelöster stoffe. Kungliga Svenska Vetenskapsakademiens. Handlingar, Band., 24(4): 1-39. 6. Mousa W M, Soliman S I, El-Bialy A B and Hanaa A Shier, (2013), “Removal of some Heavy Metals from Aqueous Solution using Rice Straw”, Journal of

Applied Sciences

Research, 9(3): 1696-170. 7. Mukhtar-ul-Hassan, Hafiza Naila Khalid, Nayab Batool, Dania Ahmad,Sara Khatoon, Hafza Nameni M, Alavi Moghadam M R and Arami M, (2008), “Adsorption of hexavalent chromium from aqueous solutions by wheat bran”, International Journal of Environmental Science and Technology, 5(2): 161-168. 8. Nameni M, Alavi Moghadam M R and Arami M, (2008), “Adsorption of hexavalent chromium from aqueous solutions by wheat bran”, International Journal of Environmental Science and Technology, 5(2): 161-168. 9. Qaiser, Suleman; Saleemi, Anwar Rasheed And Ahmad, Muhammad Mahmood. (2007), Heavy metal uptake by agro based waste materials. Electronic Journal of Biotechnology, 10(3): 409-416 10. Upendra Kumar, (2013), “Agricultural products and by-products as a low cost adsorbent for heavy metal removal from water and wastewater: A review”, Scientific Research and Creativity, 1(1): 1-5.

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