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Shabudeen et al. Int. J. Res. Chem. Environ. Vol.3 Issue 1 January 2013(60-65)
International Journal of Research in Chemistry and Environment Vol. 3 Issue 1 January 2013(60-65) ISSN 2248-9649 Research Paper
Utilising the Pods of Delonix regia Activated Carbon for the Removal of Mercury (II) by Adsorption Technique * 1,3
Syed Shabudeen P. S.1, Daniel S. 2, Indhumathi P.3
Department of Chemistry, Kumaraguru College of Technology, Coimbatore, INDIA 2 RVS College of Engineering and Technology, Coimbatore, INDIA
(Received 17th July 2012, Accepted 20th November 2012) Available online at: www.ijrce.org Abstract: Adsorption studies of Mercury (II) from aqueous solution on the pods of Delonix regia activated carbon were investigated under the varying conditions of agitation time, metal ion concentration, adsorbent dose, pH and particle size. The activation is carried out by different methodologies, Pyrolysis activation, Sulfuric acid activation, Calcium chloride activation, Ammonium carbonate activation, Sodium sulphate activation, Sulfuric acid with ammonium per sulphate activation. The characteristic of this activated carbon was determined. In which the Sulphuric acid activated carbon is employed for this adsorption studies. In this adsorption studies, the adsorption equilibrium reached in 150 min for 10, 20, 30 mg/L of Hg (II) concentration. Adsorption followed Langmuir isotherm. The percent removal increased with increase in pH from 2 to 10 remains static from pH 5 to 10. The efficiency of particle size was also performed which showed the minimum particle size was found to be effective. Desorption studies were performed with dilute sodium hydroxide solution. Keywords: The Pods of Delonix regia activated carbon, Mercury (II), Adsorption, isotherm, pH, Adsorbent dosage, Desorption.
Introduction
exchange, alum and iron coagulation and adsorption on activated carbon [8]. Effective and economic removal of Hg (II) from wastewaters resulted in a search for nonconventional adsorbents like fly ash, iron oxide-dispersed activated carbon fibres [9] , polymerized onion skin [10], peat moss [11], polymerized saw dust [12] and cellulose [13]. Namasivayam and Senthilkumar [14] have recently reported the removal of Hg(II) from aqueous solution using 'waste' Fe(III)/Cr(III) hydroxide [15] has recently reviewed under unconventional adsorbents used for the removal of heavy metal and dyes. Reports have appeared on preparation of activated carbons derived from rice husk [16] and coconut shell [17] and peanut hull carbon (PHC) [18-21] and it have been successfully employed for the removal of heavy metals from aqueous solutions. The objective of the present study is to investigate the feasibility of using this the pods of Delonix regia activated carbon for the removal of Hg(II) from water by adsorption.
Mercury is one of the most toxic metals found in the environment [1]. If mercury enters in to the food chain, larger accumulation of mercury compounds results in humans and animals and results a disaster. The major sources of mercury pollution in the aquatic environment are industries such as chloralkali, paint, pulp and paper, oil refining, electrical, rubber processing and fertilizer units . In the effort of removing this pollutant was attempted by utilizing fly ash [2] as non conventional adsorbent. According to the Indian Standard Institution (ISI), the tolerance limit for Hg (II) for discharge into inland surface waters is 0.001mg/L [3] and for drinking water, 0.001mg/L [4] . Mercury causes damage of the central nervous system and chromosomes, impairment of pulmonary function and kidney, Chest pain and dypnoe [5,6]. The harmful effects of methyl mercury include the contamination of fish in Minimata Bay [7].
Material and Methods
Hence it is essential to remove Hg (II) from wastewaters before its transport and cycling into the environment. Conventional methods for the removal of Hg (II) from wastewater include sulphide precipitation, ion
Adsorbent: The pods of Delonix regia activated carbon is collected from our campus in which these plataions are planted on scenic view, and was cut into smaller pieces,
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Shabudeen et al. Int. J. Res. Chem. Environ. Vol.3 Issue 1 January 2013(60-65) dried in sunlight for 24 h. The dried matter was used for carbon preparation by chemical activation method. The pods was mixed with concentrated H2SO4 acid and kept in a hot air oven at 80°C ± 5 for 12h. The carbonized material was washed with tap water and finally with distilled water to remove free acid. Then it was soaked in 1% (W/V) sodium bicarbonate solution overnight to remove any residual acid. The material was washed with distilled water and dried at 80°C for 6 h. After cooling, the material was taken out ground using a mortor and pestle. It was then sieved to obtain particles ranging 125-250 µm, 250 500µm, 500 - 750µm mesh fraction. The fraction was used in all adsorption experiments, where the effect of particle size was also investigated. Physico-Chemical characteristics of carbon are summarized in Table 1, it also revels the characteristics of the adsorbent prepared by other means. (Figure 1)
Freundlich adsorption isotherm was obtained from the studies on the effect of carbon dosage on the percent removal. Effect of pH on Hg(II) removal was studied using 50 mg of carbon dose and Hg(II) concentrations of 10 and 20 mg/L. Efficiency of different particle size varying from 125 - 750 µm of 50 mg50 ml mercury concentration of 20 mg/L were-experimented. Effective carbon concentration for mercury removal from wastewater also determined. The wastewater characteristics are furnished in (Table 2).
Table 1 Characteristics of activated carbon prepared from the pods of Delonix regia S. No 1 2 3 4 5 6 7 8 9 10 11 12 13
Name of the Experiment pH Conductivity ms/cm Na(ppm) K(ppm) Fe(ppm) Ash content (%) Moisture content (%) Volatile matter (%) Fixed carbon Porosity (%) Matter soluble in water (%) Matter soluble in acid (%) Surface area (g/cm2)
H2SO4 7.12 0.09 0.26 0.04 0.12 0.98 0.3 17 90 90 0.35 1.5 230
Figure 1: From the SEM analysis it is found that there are holes and honey comb structure on the surface of the adsorbent, which would have more surface area available for adsorption than the flat surface
Adsorbate: The adsorbate stock solution of 1000 mg-1 Hg (II) was prepared by dissolving 1.354g of HgCl2 in distilled water. This stock solution was diluted as required to obtain standard solution containing 10-30 mg/L of Hg (II).
Table 2 Composition of Hg – Containing Synthetic Wastewater Compound Hg (II) CaCO3 HCl Fe NaCl MgCl2 6H2O NaCO3
Batch mode Adsorption Studies: Batch mode adsorption studies were carried out with 50 mg of adsorbent and 50ml of Hg(II) solution' of a desired concentration pH 5.0 in 100 ml conical flasks and were agitated for predetermined time intervals at room temperature in a mechanical shaker. At the end of the agitation the suspension were centrifuged at 3000rpm and the filtrate were used for estimation of Hg (II) by spectrophotometrically using Rhodamine . Langmuir isotherm study was carried out with different initial concentrations of Hg(II) from 5 to 60 mg/L while maintaining the adsorbent dose at 50 mg/50 ml Effect of carbon dosage on percent removal was studied using Hg(II) concentrations of from 30 to 50 mg/L.
Concentration 50 190 5 2 3250 50 350
Desorption Studies: Desorption studies were carried out as follows .After adsorption experiment with 20 mg/L Hg(II) and 50 mg of carbon, the mercury loaded carbon was separated and gently washed with distilled water to remove any unabsorbed Hg(II). Several such spent
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Shabudeen et al. Int. J. Res. Chem. Environ. Vol.3 Issue 1 January 2013(60-65) adsorbent samples were prepared. The Hg(II) loaded adsorbent samples were desorbed by agitating for 150 min NaOH (0.25 - 2.00 M). The amount of Desorption was also estimated.
Results and Discussion Effects of agitation time and initial concentration of Hg(II): The effect of agitation time on the removal of Hg (II) by pods of Delonix regia activated carbon was shown in the (Figure 2). The removal increases with time and attains equilibrium in 150 min in 10, 20, 30 mg/L respectively. This activated carbon is 150 mm. This indicates the carbon is efficient for adsorption technique. The equilibrium time for commercial activated carbon (CAC) was 120, 150 & 180 min, for 10, 15 & 20mg/ L of Hg (II) [22].
Figure 3: Lagergren Kinetics
Figure 2: The effect of agitation time on the removal of Hg (II) by pods of Delonix regia activated carbon Figure 4: Effect of particle size on Hg (II) adsorption on the pods of Delonix regia activated carbon
Adsorption kinetics: The kinetics of Hg (II) adsorption on pods of Delonix regia activated carbon follows first order rate of expression given by Lagergren [23] Log10 (qe-q)=log10 – Kad t / 2.303
Effect of carbon dosage: The removal of Hg (II) as a function of carbon dosage was indicated in the (Figure 5). The Increasing carbon dosage increased the percent removal of Hg (II). For quantitative removal of Hg (II) from 50 ml of 30, 40, 50 mg/L, maximum dosage of 190, 175 & 200 mg is required.
(1)
Where q is the amount of Hg(II) adsorbed (mg/g) at time t, qe is the amount adsorbed (mg/g)at equilibrium time and Kad is the rate constant of adsorption. Linear plots of log ]0 (qe-q) versus t show the applicability of equation (1) for pods of Delonix regia activated carbon. The K aa values*" at different initial metal ion concentrations were calculated from the slopes of the plots (Figure 3). The Kad values found to be 0.0124, 0.0139 and 0.0177 for 10, 20&30 mg /l, of Hg (II) concentrations. Effect of particle size on Hg(II) adsorption: The adsorption of Hg(II) from a solution of initial concentration 20 mg/L has been found to increase from 59 to 74% with a decrease in the particle size from 125 – 750 m at room temperature pH 5.0. The study shows enhancement of Hg (II) removal with decrease of particle size of the adsorbent attributed to the increase in the surface area is represented in the (Figure 4).
Figure 5: Effect of carbon concentration on Hg (II) adsorption
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Shabudeen et al. Int. J. Res. Chem. Environ. Vol.3 Issue 1 January 2013(60-65) Adsorption isotherms: The Langmuir applied for adsorption equilibrium [24]
isotherm was
Ce 1 Ce = = qe Q0 b Q0
Freundlich Adsorption Isotherm: The linear plot of log X/m Vs log Ce showed that the adsorption followed Freundlich adsorption isotherm model. The values of X/m and Ce observed from the adsorption experiments carried over by using pods of Delonix regia activated carbon of different particle sizes of constant mass was agitated with Hg(II) solution of known concentration . Based upon these experiments Freundlich adsorption isotherm plot was formed by plotting log X/m Vs log Ce and the slope and intercept of this linear portion of isotherm plots were determined by adopting graphical methodology. These slope values had indicated adsorption intensity ‘n’ and the intercept values indicated an idea about adsorption capacity KF.
(2)
Where Ce is the equilibrium concentration (mgV, adsorbate/ litre of solution), qe is the amount of Hg(II) adsorbed at equilibrium (mg/g ) and Qo and b are Langmuir constants related to adsorption capacity and energy of adsorption, respectively. The linear plot of CJq, versus Ce shows that the adsorption obeys Langmuir isotherm model. Qo and b were determined from the slope. The essential characteristics of a Langmuir isotherm can be expressed in terms of a dimension less constant separation factor or equilibrium parameter, RL [25], Which is defined by: RL =
The adsorption process, the surface energy qe is a function of heat for adsorption. The term KF and n are adsorption constants are used to explain adsorption process. The Freundlich adsorption isotherm is as follows, qe = X/m = KF Ce1/n , ln X/m = ln qe = ln KF + 1/n ln Ce , where qe, Ce, X and M are adsorbed amount on the adsorbent at equilibrium, equilibrium concentration of solution (mg/l), amount of solute adsorbed (mg) and weight of the adsorbent used (g). The constant K F represents the quantity of solute adsorbed in mg/g adsorbent for a unit equilibrium concentration which is an approximate indicator of adsorption capacity. These constants can be evolved by linearising the above equation by adopting mathematical techniques.
1 1 bC o
Where Co is the initial metal ion concentration (mg/L) and b is the Langmuir constant (1 mg/L ). According to Hall et al [25] it has been shown using mathematical calculations that the parameter, RL indicates the shape of the isotherm as follows (Figure 6). Table 3 RL values between 0 and 1 at different concentrations indicate favourable adsorption of Hg(II) onto pods of Delonix regia activated carbon. RL values were found to be 3.16, 5.32, 7.48, 9.64 for 5-20 mg /l, of Hg (II) concentrations RL value RL > 1 RL = 1 0< RL=1 RL = 0
The 1/n is a measure of adsorption intensity. It was learnt that, If n = 1 then that the partition between the two phases was independent of the concentration. If the 1/n value is below one it indicates a normal adsorption. On the other hand 1/n being above one indicates cooperative adsorption. It is generally stated that the value of ‘n’ that is in the range of 2 to 10, represents good adsorption isotherm. It was also observed that the ‘n’ values of the adsorbent for the dye at various temperature and particle sizes were found out and this value is from 2 to 10, which confirmed that the activated carbon underwent a favourable for Freundlich isotherm. The experimental data were attempted to fit into Freundlich adsorption isotherms, and it was efficiently and most effectively fitted. It clearly indicated that the system followed Freundlich adsorption isotherm model and the adsorbent’s surface under study were heterogeneous. The correlation coefficient was evolved with graphical techniques (Figure 7), and it was tabulated (Table 4). Table 4 Freundlich constants for the adsorption of reactive orange at various particle sizes at 300K Particle Size n x 10 KF x 10 R2 µm 0.5960 1.170 0.8034 250 0.7372 1.781 0.8304 150 0.7091 1.889 0.7393 100
Type of isotherm unfavourable Linear Favourable Irreversible
Figure 6: Lagmuir isotherm
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Shabudeen et al. Int. J. Res. Chem. Environ. Vol.3 Issue 1 January 2013(60-65)
Figure 7: Freundlich Isotherm
Figure 9: Effect of pH on removal of Hg (II) using the pods of Delonix regia activated carbon
Effect of pH: The effect of initial pH on the removal of Hg(II) by the pods of Delonix regia activated carbon is revealed in (Figure 8 Figure 9). It can be shown by stability constant calculations the predeminam species at pH >4.0 is Hg(OH)2 and at pH.
