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Journal of Applied Sciences and Environmental Management, Vol. 12, No. 2, 2008, pp. 81-87 Equilibrium Sorption studies of Fe, Cu and Co ions in aqueous medium using activated Carbon prepared from Recinius Communis Linn. KARTHIKEYAN, G; SIVA ILANGO, S Department of chemistry,Gandhigram Rural University, Gandhigram - 624 302,
Tamil Nadu,India.
e-mail: drg_karthikeyan@rediffmail.com Tel.: +91 469 2609705 Fax: +91 451 2454466 Code Number: ja08032 ABSTRACT Recinius Communis Linn a commonly found herbal plant was used to prepare activated carbon by physicochemical activation method. The sorption capacity of this bio-resource material to remove Fe(III), Cu(II) and Co(II) from aqueous solutions was determined by batch tests. The influences of important parameters such as contact time, dosage, pH, pH zpc, co-ions and temperature on metal adsorption process were investigated. The equilibrium data were fitted to Langmuir and Freundlich isotherms. The batch adsorption rate for the sorption process was explained on the basis of intraparticle diffusion. Various thermodynamic parameters like ΔG0 , ΔH0 and ΔS0, and were analyzed to observe the nature of adsorption. The metal adsorption process on the surface of adsorbent was verified as a surface phenomenon by performing SEM and XRD analysis. Metals can be distinguished from other toxic pollutants, since they are not biodegradable and can be accumulated in living tissues, causing various diseases and disorders. Conventional methods for removing metals from industrial effluents include chemical precipitation, coagulation, solvent extraction, electrolytic processes, membrane separation, ion exchange, reverse osmosis, ultra filtration, biological systems and adsorption (Gode and Pehlivan, 2005) Adsorption processes for removal of metals have been found cheaper and more effective than the several technologies. (Gupta et al., 2003) Numerous by products of agro – industrial productions and agricultural by – products have been studied for potential use as inexpensive sorbents. (Ho, 2003) Many examples are available in the literature concerning the direct or activated use of these materials as adsorbents. (Cochrane et al, 2006; Bailey et al, 1999; Abia et al, 2002) This study deals with the investigation of Fe(III), Cu(II) and Co(II) removal from aqueous solutions by adsorption on activated carbon prepared from Recinius Communis Linn (RC). MATERIALS AND METHODS The preparation of activated carbon from RC consisted of carbonization of the plant material. Dried raw leaves were cut into small pieces and the carbonization was conducted in a muffle furnace at 400°C. The heating period was 2 hours. After carbonization, the carbon was ground using domestic mixie. The activated carbon obtained was kept in a desicator and were characterized for the physical parameters which are given in Table 1. Adsorption equilibrium study of these metal ions was carried out in 250ml stoppered Iodine flask. The concentration of the metal ions was determined by UV/ Visible spectrophotometer (UV 240 Shimaduzu). All other water quality parameters were analyzed by using standard methods (APHA, 1998). The pH measurements were done with a pH electrode (Systronics) and pHZPC (pH of zero point charge) was determined by pH drift method. (Jia et al, 2002) The surface morphology of the raw and treated activated carbons was visualized by SEM with a HITACHI-S-3000H model. XRD pattern was recorded using X1 per PRO (model), PAN analytical (make). Computations were made using Microcal Origin, (version 6.0) software. RESULTS AND DISCUSSION The effect of time on the adsorption of metal ions by RC for iron(III), copper(II) and cobalt(II) with 50ml of 20 ppm of each metal ion solutions were studied. Fig.1 shows the effect of contact time on adsorption of the adsorbent. The effect of the activated carbon RC dose on the removal of metal ions is shown in fig.2. The adsorption increased from 45 to 90 percentages with increase in adsorbent dose from 50 mg to 500mg. The pH dependence of iron(III), copper(II) and cobalt(II) take onto RC is shown in fig.3. It is well known that these metal ions undergo hydrolysis reactions in water and form insoluble complexes with increasing pH. (James and Healy, 1972) This phenomenon is conceded as important for understanding the adsorption behaviour of all metal ions onto these activated carbons. Up to pH 5.0 due to the presence of H+ ions of the acid used for adjusting pH. However, this effect causes in the pH range of 5.0-7.0. (Celik et al, 1995) The influence of other co-ions such as and which are commonly present in water, on the adsorption of iron(III), copper(II) and cobalt(II) by the activated carbon was investigated. Fig. 4 gives the effect of co-ions on the adsorption of copper(II) as representative plot. In all the cases, the presence of these co-ions did not significantly alter the metal ions adsorption process by the activated carbon. Equilibrium data are basic requirements for thw design of adsorption systems and adsorption models are used for the mathematical description of the adsorption equilibrium of the metal ions on to the adsorbent. The results obtained on the adsorption of iron(III), copper(II) and cobalt(II) were analyzed by the well – known models given by Langmuir and Freundlich. Langmiur isotherm. The linear form of Langmuir isotherm equation is given as
where Ce is the equilibrium concentration of the adsorbate (mg/L), qe is the amount of adsorbate adsorbed per unit mass of adsorbent (mg/g), Q0 and b are Langmuir constants related to adsorption capacity and rate of adsorption. The Langmuir curves pertaining to the Cu(II) adsorption by RC is provided in fig.5 as representative plot. The Langmuir constants b and Qo were calculated from equation (2) and the values are given in Table 2. The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless equilibrium parameter (RL ) which is defined by,
where b is the Langmuir constant and C0 is the initial concentration (mg/L). The value of RL indicates the type of the isotherm to be either favourable (0 < RL < 1), unfavourable (RL > 1), linear (RL = 1) or irreversible (RL = 0) (Mor et al, 2007). The value of RL was found to be less than one and this again confirmed that the Langmuir isotherm model was favourable for adsorption of metal ions onto the activated carbon under the conditions used in this study. Freundlich isotherm The well-known logarithmic form of Freundlich isotherm is given by the following equation,
where Ce is the equilibrium concentration of the adsorbate (mg/L) and qe is the amount of adsorbate adsorbed per unit mass of adsorbent (mg/g). Kf and n are Freundlich constants representing the adsorption capacity and intensity of adsorption respectively. The values of Kf and 1/n were obtained from the slope and intercept of the plot of log qe verses log Ce . The slope of l/n ranging between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, becoming more heterogeneous as its value gets closer to zero. (Raji and Anirudhan, 1997) Freundlich constants Kf and n values were calculated and listed in Table 2 and the plot is given in fig.6. Thermodynamic parameters with the adsorption viz., standard free energy change (ΔG° ), standard enthalpy change (ΔH° ) and standard entropy change ΔS° were calculated using the equation below and the values are given in Table 3. ΔG° = - RTln Ko, (4) where ΔG° the is the free energy of adsorption, T is the temperature and R the Universal gas constant. The adsorption distribution coefficient Ko for the adsorption reaction was determined from the slope of the plot ln(qe / ce) against Ce at different temperature and extrapolating to zero Ce according to method suggested by Khan and Singh. (Khan and Singh, 1987) The adsorption distribution coefficient may be expressed in terms of enthalpy change (ΔH° ) and entropy change (ΔS° ) as a function of temperature,
Where the values of ΔH° and ΔS° can be obtained from the slope and intercept of the plot of ln K0 against 1/T. (Meenakshi and Viswanathan, 2007) From a mechanistic point of view, to interpret the experimental data, production of the rate-limiting step is an important factor to be considered in the sorption process. Though kinetic and equilibrium isotherm studies help to identify the adsorption process, predicting the mechanisms is required for design purpose. For a solid - liquid sorption process, the solute transfer is usually characterized by either external mass transfer (boundary layer diffusion) or intraparticle diffusion or both. This is determined by plots of the amount of metal adsorbed against the square root of time, t 1/2 for three different temperatures. According to Weber, an intraparticle diffusion coefficient is defined by the equation. qt=Kpt1/2 , (6) qt = the amount of metal ions adsorbed per unit mass of adsorbents at any
time t The plots of intraparticle diffusion curves shows initial curved portion followed by linear portion and a plateau. The first sharper portion is the external surface adsorption or instantaneous adsorption stage. The second portion is the gradual adsorption where the intraparticle diffusion is rate controlled. The third portion is final equilibrium stage where the intraparticle diffusion starts to slow down due to extremely low solute concentration in solutions. (Chenung et al, 2007) Fig.7 shows Cu(II) adsorption by RC as representative plot. SEM images of the activated carbon before and after of iron(III) sorption are shown in fig.8 above as representative images. Comparison of these micro graphs before and after iron(III) sorption shows that there adsorption of metal ions on the surface of the activated carbon. XRD patterns of the treated adsorbents showed significant changes. The XRD data of the treated activated carbon provided evidence of decrease in the peak intensity at 2? values which shows that adsorption of iron(III) on the surface of the adsorbent and at the same it dose not alter the crystalline structure of the material. (Gopal and Elango, 2007) Fig. 9 above indicate the decrease in the peak intensity values after adsorption of RC, on iron(III) as representative. Acknowledgement: This work was supported by Rajiv Gandhi National Drinking Water Mission, Department of Drinking Water Supply, Ministry of Rural Development, Government of India, New Delhi. REFERENCE
Copyright 2008 - Journal of Applied Science and Environmental Management The following images related to this document are available:Photo images[ja08032f3.jpg] [ja08032f2.jpg] [ja08032t1.jpg] [ja08032t2.jpg] [ja08032f6.jpg] [ja08032f5.jpg] [ja08032t3.jpg] [ja08032f7.jpg] [ja08032f4.jpg] [ja08032f1.jpg] [ja08032f8.jpg] [ja08032f9.jpg] |
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