Removal of hazardous triphenylmethane dye through adsorption over waste material mango bark powder

Transcription

1 Indian Journal of Chemical Technology Vol. 18, November 2011, pp Removal of hazardous triphenylmethane dye through adsorption over waste material mango bark powder Ruchi Srivastava 1* & D C Rupainwar 2 1 Institute of Engineering and Technology, MS 124, Sector D, Aligang, Lucknow , India 2 Bansal Institute of Engineering and Technology, P-49 Nehru Enclave, Gomtinagar, Lucknow , India Received 13 September 2010; accepted 4 October 2011 This study deals with the use of low cost, easily available, high efficiency and ecofriendly adsorbent as an ideal alternative to the currently used expensive methods of removing dye from waste water. The potential of mango bark powder for the removal of malachite green (triphenylmethane dye) from simulated water has been investigated. Studies are conducted to delineate the effect of ph, temperature, initial dye concentration and adsorbent concentration. Equilibrium isotherms are determined to assess the maximum adsorption capacity of the adsorbent. The adsorption data have been correlated with Freundlich and Langmuir isotherms which are used to suggest a plausible mechanism of the ongoing adsorption processes. The maximum adsorption capacity obtained from Langmuir equation is found to be mol.g -1 on mango bark powder. The adsorption of dye is found to be a second order rate equation. Thus, low cost mango bark powder can be an attractive option for dye removal from diluted industrial effluents. Keywords: Adsorption, Kinetics, Mango bark powder, Thermodynamics, Triphenylmethane dye Adsorption of hazardous soluble chemicals from waste water onto the surface of a solid adsorbent has provided a new dimension to the waste water treatment technology 1. The adsorption process has proved itself more versatile and efficient than other methods such as coagulation, chemical oxidation, and froth flotation 2. Other advantages of adsorption are its ability to separate a wide range of chemical compounds, easy operational procedures, and facilitation of recovery of costly organic and inorganic materials 3,4. Because of these facts, the adsorption technique is being widely used for waste water treatment. Coloured compounds are the most easily recognizable pollutants in the environment. Most industries use dyes and pigments to colour their products. Discharge of dye-bearing waste water into natural streams and rivers from textile, paper, carpet, and printing industries poses a severe problem, as dyes impart toxicity to aquatic life and are damaging the aesthetic nature of the environment. Many of the dyes used in industry are stable to light and oxidation, as well as resistant to aerobic digestion 5. One of the major challenges associated with adsorption by activated carbon is its cost effectiveness. Hence, *Corresponding author. abhiruchi124@yahoo.com research of the recent past mainly focused on utilizing waste materials as alternatives to activated carbon. Seed kernal 6, agricultural waste 7-9, fly ash 10,11, peat 12, de-oiled soya 13 tree fern 14,15 pine saw dust 16,17 and hen feathers 18 are some of the waste materials which have been fruitfully tried for this purpose 19, 20. Malachite green (MG) is an extensively used biocide in the aquaculture industry world-wide. It is highly effective against important protozoal and fungal infections Basically, it works as an ectoparasiticide. It has also been used to control skin flukes and gill flukes. Aquaculture industries have been using malachite green extensively as a topical treatment by bath or flush methods without paying any attention to the fact that topically applied therapeutants might also be absorbed systemically and produce significant internal effects. On the other hand, it is also used as a food colouring agent, food additive, a medical disinfectant and anthelminthic as well as a dye in silk, wool, jute, leather, cotton, paper and acrylic industries 23. However, malachite green has now become a highly controversial compound due to the risks it poses to the consumers of treated fish. Both clinical and experimental observations reported so far reveal that Malachite green is a multi-organ toxin 24, e.g. found renal changes in rabbit following repeated oral dosing of this dye. It decreases food

2 470 INDIAN J. CHEM. TECHNOL., NOVEMBER 2011 intake, growth and fertility rates; causes damage to liver, spleen, kidney and heart; inflicts lesions on skin, eyes, lungs and bones; and produces teratogenic effects in rats and mice 25. Malachite green is highly cytotoxic to mammalian cells 26 and carcinogenic to liver, thyroid and other organs of experimental animals. Keeping these in view, it is considered worthwhile to formulate an easy and reliable method for dye removal and the use of mango bark powder as an adsorbent through adsorption technique is exploited. The present studies include adsorption kinetics and equilibrium uptake of indigo carmine and methylene blue using the adsorbent. The results of these studies are presented hereunder. Experimental Procedure Dye solution preparation An accurately weighed quantity of dyes (indigo carmine and methylene blue) was dissolved separately in double-distilled water to prepare stock solution. Dye concentration was determined using absorbance values measured before and after treatment using spectrophotometer. Experiments were carried out at initial ph values ranging from 2 to 10. Preparation of sorbent Mango bark used in the present work was collected from local wood shops. The collected barks were washed with permuted water several times to remove dirt particles and water soluble materials. The washed materials were then completely dried in an air oven at C for 24 h till the barks could be grinded into fine powder by the local mixer grinder. The products so obtained were sieved to the desired particle sizes ( µm). Finally, the product was stored in a vacuum desiccator until required. Equipment The ph of the solution was measured by using a ph meter (Model 744, Metrohm). Absorbance measurements were done on a GBC UV visible spectrophotometer (Model Cintra-40). The spectrophotometer response time was 0.1 s and the instrument had a resolution of 0.1 nm. Absorbance values were recorded at the wavelength for maximum absorbance (λ max ), i.e. 610 nm for indigo carmine and 660 nm for methylene blue. The agitation of the system under investigation was carried out on a thermostatcum shaking assembly (Model MSW 275). The zero point of charge (phzpc) of mango bark powder (MBP) was estimated by using the alkalimetric titration method 27. General characterization (Table 1) of mango bark powder was obtained in the laboratory through various experimental set-up. Results and Discussion Effect of contact time and initial concentration The sorption efficiency of malachite green (MG) increases gradually with increasing contact time. At this point, the amount of dye being sorbed onto the sorbent is in a state of dynamic equilibrium with the amount of dye desorbed from the sorbent. The contact time needed for MG solution to reach equilibrium at initial concentration of mol.l -1 is 150 min. It is also noticed that an increase in the initial dye concentration leads to a decrease in the percentage of MG removal. As the initial dye concentration increases from 10-6 mol.l -1 to 10-4 mol.l -1, the equilibrium removal of the dye solution (malachite green) decreases from 69.76% to 40.89%. This effect can be explained as follows: at low dye/sorbent ratios, there are number of sorption sites in mango bark powder structure. As the dye/sorbent ratio increases, sorption sites are saturated, resulting in decrease in the sorption efficiency. Thus, it can be said that the sorption is increased instantly at initial stages due to rapid attachment of dye to the surface of the sorbent, and then keeps increasing gradually until the equilibrium is reached and remains constant. Effect of sorbent dosage An increase in the mango bark dose from 0.5 g/50 ml to 2 g/50 ml increases the percentage of dye removal from aqueous solution from 68.45% to 39.65%. This may be attributed to increased sorbent contact area and availability of more sorption sites resulting from the increased dose of the sorbent. The increase in sorbent dose at constant dye concentration and volume will lead to unsaturation of sorption sites through the sorption process. At higher mango bark powder to dye concentration ratio, there is a superficial sorption onto the sorbent surface that produces a lower dye concentration in the solution than at lower sorbent Parameter Table 1 Characteristics of mango bark powder Value Ash content, % Bulk density, mg/m ph ZPC 6.80 Volatile matter, % C, % H, % 4.69 N, % 0.83

3 SRIVASTAVA & RUPAINWAR: REMOVAL OF TRIPHENYLMETHANE DYE BY MANGO BARK POWDER 471 to dye concentration ratio. This is because a fixed mass of the adsorbents can only sorb a certain amount of dye. Therefore, the higher the sorbent dosage, the larger is the volume of effluent that a fixed mass of mango bark powder can purify 28. Effect of temperature The sorption studies were carried out at three different temperatures 10, 25 and 40 C The removal percentage of MG, increase with the increasing temperature i.e. From 38.25% to 63.98% for adsorbent (MBP), indicating that the sorption is an endothermic process. This may be a result of increase in the mobility of the dyes with increasing temperature. Furthermore, the enhancement in the sorption capacity might be due to the enhancement of sorptive interaction between the active sites of sorbent and sorbate ions. It can also be said that increasing temperature may produce a swelling effect within the internal structure of the adsorbents enabling more dye molecules diffusion into the sorbents 29. Effect of ph The results of the experiments done at different ph values, conducted to determine the optimum ph range for dyes adsorption on mango bark powder are shown in (Fig. 1). The percentage removal of MG over mango bark powder is found to be optimum at ph 5. Several reasons may be attributed to dye sorption behavior of the biosorbent relative to solution ph. The surface of bark powder may contain a large number of active sites and the solute (dye ions) uptake can be related to the active sites and also to the chemistry of the solute in the solution. This can be explained by considering the zero point charge of the adsorbent. The ph at the ph ZPC of the adsorbent (MBP) is Thus, it seems that for ph values below the zeta potential of adsorbents, positive charge density on the surface increases, the charge developed in the acid medium favours association of anionic dye. The positive charge density would be found more on the dye molecule at ph less than the zeta potential on adsorbent surface and this accounts for the higher uptake of malachite green 30. Isotherm Analysis The analysis and design of sorption process requires the relevant adsorption equilibria, which is the most important piece of information in understanding an adsorption process. To facilitate estimation of the adsorption capacities the two wellknown equilibrium adsorption models, namely Freundlich 31 and Langmuir 32, were employed. Langmuir isotherm The Langmuir equation assumes that maximum adsorption occurs when the surface is covered by the adsorbate. The distribution of dyes between the solidsolution interface equilibrium has been described by the linear form of Langmuir equation, as given below: (C e /q e ) =(1/bQ 0 ) +(C e /Q 0 ) (1) where C e is the concentration of dye solution (mol. L -1 ) at equilibrium; q e is the amount of dye adsorbed per unit weight of adsorbent (mol. g -1 ); b is related to the energy of adsorption (L. Mol -1 ); and Q 0 (mol. g -1 ) is the maximum amount of dye adsorbed at equilibrium. Values of Q 0 and b were calculated from the slope and intercept of the linear plot (C e /q e versus C e ). The isotherm was found to be linear over the entire concentration range studied with a good linear regression coefficient (R 2 = 0.991) for MG. The fact that the Langmuir isotherm fits the experimental data may be due to homogeneous distribution of active sites Fig. 2 on the bark powder. The values of monolayer saturation capacity Q 0 calculated from Fig. 1 Plot of ph vs. % removal of malachite green over mango bark powder Fig. 2 Langmuir isotherm constants for the adsorption of malachite green over mango bark powder

4 472 INDIAN J. CHEM. TECHNOL., NOVEMBER 2011 Langmuir equation is found to be mol.g -1. The Langmuir parameters are shown in Table 2. The essential characteristics of Langmuir equation can be expressed in terms of a dimensionless separation factor R L 33, as shown below: R L = 1/ (1 + bc 0 ) (2) where b is the Langmuir constant ; and C 0, the initial concentration of the sorbate in solution. The values of R L indicates the type of isotherm to be irreversible (R L = 0), favorable (0 < R L < 1), linear (R L = 1) or unfavorable (R L > 1). Freundlich isotherm The Freundlich expression is an exponential equation and therefore, assumes that as the sorbate concentration increases, the concentration of sorbate on the sorbent surface also increases. The linear form of the Freundlich isotherm is: ln q e = ln K f + l/n. ln C e (3) where q e is the amount of solute adsorbed per unit weight of adsorbent (mol.g -1 ); C e, the equilibrium concentration of the solute in the bulk solution (mol.l -1 ); K f, the constant indicative of the relative adsorption capacity of the adsorbent (mol.g -1 ); and 1/n, constant indicative of the intensity of adsorption. The equilibrium data were further analyzed using the linearized form of Freundlich equation and the same set of experimental data. The calculated Freundlich isotherm constants and the corresponding coefficient of determination values are shown in Table 2. It is observed that both the Freundlich and Langmuir isotherms could well represent the experimental sorption data of malachite green over mango bark powder, but the Langmuir expression is better in the case. It is generally stated that the values of n in the range 2 10 represent good, 1 2 moderately difficult, and <1 poor adsorption characteristics 34. Adsorption kinetics study Successful application of the adsorption demands innovation of cheap, non-toxic and easily available adsorbents of known kinetic parameters and adsorption characteristics. Adsorption kinetics can be modeled by applying pseudo first-order Lagergren equation 35 and pseudo second-order model 36. Pseudo first-order rate equation is presented as follows: log(q e q t ) = log q e (k 1 /2.303) t (4) where q e and q t are the amounts of dye adsorbed at equilibrium and at time t respectively; and k 1, the rate constant of pseudo first-order sorption (L min 1 ). The parameters of the pseudo first-order model are summarized in Table 3. The values of determination coefficient for the plots are found to be in the range This finding suggests that the sorption process does not follow the pseudo first-order rate equation. An expression of the pseudo second order rate is given below: t/q t = (1/K 2 q e 2 t+1/q e ) t (5) where K 2 is the pseudo second-order rate constant (g. mol -1 min -1 ); q e, the amount of dye sorbed at equilibrium (mol.g -1 ); and q t, the amount of dye cation on the surface of the sorbent at any time t (mol. g -1 ). The plots of t/q t versus t give a straight line for all the initial dye concentrations for both the dyes (Fig. 3), confirming the applicability of the pseudo secondorder equation. The parameters of the pseudo secondorder sorption kinetic model are summarized in Table 3. The determination coefficient values of the pseudo second-order model exceed 0.99, and the calculated sorption capacity value determined from Table 2 Langmuir and Freundlich constants for the adsorption of malachite green on mango bark powder Constants 10 C 25 C 40 C Langmuir Isotherm Q , mol.g b 10-2, l mol R Freundlich Isotherm K f 10 2, mol g /n R Table 3 Comparison of kinetic parameters for the adsorption of malachite green on mango bark powder and Bangham, s constants for adsorption of malachite green at three different adsorbate concentrations Kinetic parameters Constant 10 C 25 C 40 C qe,exp 10 4,, mol.g qe,cal , mol.g qe,cal , mol.g qe,cal -1 = First -order kinetics. qe,cal -2 = Second-order kinetics Bangham, s constants Constant 2 g.l -1 1 g.l g.L -1 Kb, mg.l a R

5 SRIVASTAVA & RUPAINWAR: REMOVAL OF TRIPHENYLMETHANE DYE BY MANGO BARK POWDER 473 Fig. 3 Pseudo second-order reaction (t/qt) for removal of malachite green over mango bark powder at different initial dye concentrations [sorbent dose 0.5 g/50 ml, T 25 C and optimum ph] Fig. 4 Bangham s plot for removal of malachite green over mango bark powder at different concentrations [optimum ph, temperature 25 C and dose 0.5g/50 ml] pseudo second-order model is more consistent with the experimental values of sorption capacity. Therefore, the pseudo second - order model better represents the sorption kinetics for the removal of malachite green over mango bark powder. Bangham, s equation Kinetic data can further be checked by using following Banghams equation 37 : ln. ln (C 0 /C 0 - q t m ) = log (K b m/ V) + a ln (t) (6) where C 0 is the initial concentration of adsorbate in solution (mg.l -1 ); V, the volume of the solution (L); m, the weight of adsorbent per liter of solution (g.l -1 ); q t, the amount of adsorbate retained at time t; and a and K b are the constants (Table 3). The logarithmic plot Fig. 4 according to above equation yields perfect linear curves for adsorption of malachite green on mango bark powder, showing that the diffusion of adsorbate into pores of the adsorbent is not the only rate controlling step 38. Conclusion The findings suggest the recycling of an agricultural waste byproduct as adsorbent for the treatment of dyeing industry waste water. Mango bark powder is a promising adsorbent for removal of malachite green dye. The experimental data show perfect fit with the Langmuir isotherm. This suggests the monolayer coverage of malachite green with adsorption capacity as mol.g -1 The kinetics of the adsorption of malachite green onto MBP reports to be pseudo second-order chemical reaction kinetics. Pseudo second-order kinetics is further supported by Bangham, s equation. The rate of adsorption of malachite green on MBP increases with the increase in temperature, thus suggesting the reaction to be spontaneous and endothermic in nature. Mango bark powder acts as a good adsorbent for the removal of malachite green from industrial and other effluents. References 1 Kumar K V & Porkodi K, Dyes Pigm, 74 (2007) Lakshmi U R & Srivastava V C, J Environ Manage, 90 (2009) Majewska K & Kowalska I, Desalination, 198 (2006) Mallik R & Ramteke, Waste Mang, 9 (2007) Namasivyam C & Kavitha, Biores Technol, 98 (2007) Kumar K V & Kumaran A, Biochem Eng, 27 (2005) Bhattacharya K G & Sharma A, Dyes Pigm, 65 (2005) Zhang J, Li Y & Jing Y, J Hazard Materials, 48 (2007) Chuah T G, Desalination, 175 (2005) Janos P, Buchtova H & Ryznarova M, Water Res, 37 (2003) Acemioglu B, J Colloid Int Sci, 274 (2004) Sun Q & Yang L, Water Res, 37 (2003) Mittal A, Krishnana L & Gupta V K, Sep Purif Technol, 43 (2005) Ho Y S, Chiang T H & Hsueh Y M, Process Biochem, 40 (2005) Ho Y S, Water Res, 37 (2003) Özacar M & Sengil A I, Adsorption, 8 (2002) Özacar M & Sengil A I, Bioresour Technol, 96 (2005) Mittal A, J Hazard Mater, B133 (2006) Mohan D, Singh K P & Kumar Kundan, Ind Eng Chem, 41 (2002) Hoffman G L & Meyer F P, Parasites of Freshwater Fishes: A Review of their Treatment and Control (TFH Publications, Neptune, New Jersey), Schnick R A, Prog Fish Cult, 50 (1988) S J Culp & Beland F A, J Am Coll Toxicol, 15 (1996) Goldacre R J & Philips J N, J Chem Soc, 3 (1949) 24 Culp S J & Blankenship L R, Chem Biol Interact, 122 (1999) Fessard V, Godard T, Huet S & Mourot A, J Appl Toxicol, 19 (1999) Rao V K & Fernandes C L, Tumori, 82 (1996) Noh J S & Schwarz J A, Colloid Interface Sci, 130 (1) (1989) Garg V K, Amita M, Kumar R & Gupta R, Dyes Pigm, 63 (2004) 243.

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