A comparative evaluation for adsorption of dye on Neem bark and Mango bark powder

Transcription

1 Indian Journal of Chemical Technology Vol. 18, January 2011, pp A comparative evaluation for adsorption of dye on Neem bark and Mango bark powder Ruchi Srivastava a * & D C Rupainwar b a Institute of Engineering and Technology, Utter Pradesh Technological University, Lucknow, India b Bansal Institute of Engineering and Technology, Lucknow, India Received 21 April 2010; accepted 15 November 2010 The use of low cost adsorbent has been investigated as a replacement for the current expensive methods of removing dyes from wastewater. As such, Neem bark and Mango bark generated as a wood waste is collected and converted into a powder form and then used as a low-cost adsorbent for removal of dyes from wastewater. Adsorption studies are carried out at different temperatures, ph, initial dye concentrations and adsorbent doses. The adsorption of malachite green (dye) is found to increase with increase in temperature. The linear form of Langmuir and Freundlich models fitted the adsorption data. The results indicated that Langmuir adsorption isotherm fitted the data better than Freundlich isotherm. Thermodynamic parameters such as the free energies, enthalpy and entropy of adsorption of the dye-mango bark, Neem bark powder systems are also evaluated. The negative values of free energy indicated the feasibility and spontaneous nature of the process, and the positive heats of enthalpy suggest the endothermic nature of the process. The adsorption of Malachite green follow the second-order kinetics in both the adsorbents. Keywords: Adsorption, Adsorption isotherm, Bark powders, dyes, Batch mode Dyes are widely used in various industries, such as textiles, paper, plastics, cosmetics and leather, for coloring their final product. The release of colored wastewater from these industries may present an ecotoxic hazard and introduce the potential danger of bioaccumulation, which may eventually affect man through the food chain. Many techniques have been used to remove harmful dyes from colored wastewater. Activated carbon is the most popular adsorbent, which is capable of adsorbing many dyes with a high adsorption capacity 1, but it is expensive and the costs of regeneration are high because desorption of the dye molecules is not easily achieved 2,3. Currently sorption process is proved to be one of the effective and attractive processes for the treatment of these dye-bearing wastewaters 4-6. Also this method will become inexpensive, if the sorbent material used is of inexpensive material and does not require any expensive additional pretreatment steps. Previously several researchers had proved several low cost materials such as pear millet husk carbon 7, Aspergillus niger 8, rice husk, hair, cotton waste, bark 9, perlite 10, carbonized press mud, bagasse bottomash 11, raw kaolin, pure kaolin, calcined raw kaoline, *Corresponding author ( abhiruchi124@yahoo.com) calcined pure kaoline 12, coir pith 13, guava seeds activated carbon 14, iron humate 15, neem sawdust 16, clay 17 and mango seed kernel 18. Neem tree (Azadirachta indica) and Mango tree (Mangifera indica) are native to the Indian subcontinent. In the present study mango bark powder and neem bark powder, a waste materials obtained from wood industry have been used as an adsorbents for the removal of malachite green. Malachite green was found to be toxic to human cells and might cause liver tumor formation. The use of this dye has been banned in several countries and not approved by US Food and Drug Administration. However, due to its ease and low cost to manufacture, it is still used in certain countries with less restrictive laws for nonaquaculture purposes. Hence, the dye removal is of great importance 19. For any sorbent to be feasible, it must combine high and fast adsorption capacity with inexpensive regeneration 20. The present study is aimed towards the development of an industrially viable, cost effective and environmentally compatible adsorbent for the removal of malachite green from wastewater. To evaluate the efficiency of developed adsorbents, adsorption batch and kinetic studies were performed.

2 68 INDIAN J. CHEM. TECHNOL., JANUARY 2011 Materials and Methods Dye solution preparation The dye, Malachite green, CI = 42,000, chemical formula =C 50 H 52 N 4 O 8, MW= , λ max = 617 nm. The stock solution was prepared by dissolving the required amount of dye in double distilled water. Working solutions of the desired concentrations were obtained by successive dilution. Dye concentration was analyzed using absorbance values with a UV vis spectrophotometer (Model GBC Cintra 40). Sorbent Neem bark and Mango bark used in the present work were collected from local wood shops. The collected barks were washed with permuted water several times to remove dirt particles and water soluble materials. The washing process was continued till the wash water contained no colour. 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 such as µm. Finally, the product was stored in a vacuum desiccator until required. The developed powders are designated as MBP (Mango bark powder) and NBP (Neem bark powder). The powder having mesh size was used in both the sorption and kinetic studies unless otherwise stated. The surface structure of Neem bark and Mango bark was analyzed by scanning electronic microscopy (SEM) at two different magnifications. SEM micrographs were obtained using model (SC 7640 UK). The textural structure examination of Neem bark and Mango bark particles can be observed from the SEM photographs at 2500 magnifications (Fig. 1a,b). These photographs reveal that Neem bark and Mango bark exhibit a caves-like, uneven and rough surface morphology. Instrument The ph of the solution was measured by using a ph meter (Model 744, Metrohm). Absorbance measurements were made 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., 617 nm for malachite green. The agitation of the system under investigation was carried out on a thermostat-cum shaking assembly (model MSW 275). The zero point of charge (ph zpc ) of Neem bark powder and Mango bark powder was estimated by using the alkalimetric titration method 21. Characterization of Neem bark powder and Mango bark powder is summarized in Table 1. Table 1 Characteristics of Neem bark powder and Mango bark powder Parameters Values NBP MBP Ash content (%) Bulk density(mg/m 3 ) ph ZPC Surface area (m 2.g -1 ) Volatile matter (%) C (%) H (%) N (%) Fig. 1 Scanning electron micrograph of (a) Neem bark powder and (b) Mango bark powder at 2500

3 SRIVASTAVA & RUPAINWAR: EVALUATION OF ADSORPTION OF DYE ON NEEM AND MANGO BARK PAWDER 69 Sorption procedure Sorption studies were performed by the batch technique to obtain rate and equilibrium data. The batch technique was selected because of its simplicity. Batch sorption studies were performed at different temperatures, dye initial concentrations and adsorbent doses to obtain equilibrium isotherms. For isotherm studies, a series of 100 ml conical flasks were employed. Each conical flask was filled with 50 ml of dye solution of varying concentrations ( M) separately and adjusted to the desired ph and temperature. The suspensions were stirred at 400 rpm at 25 C for 7 h until equilibrium was reached. Aqueous samples were taken from the solutions and the concentrations were determined. The contact time and other conditions were selected on the basis of preliminary experiments, which demonstrated that the equilibrium was established in 120 min for Neem bark powder and 150 min for Mango bark powder. The effect of ph was observed by studying the adsorption of malachite green over a broad ph range of 2-9. The sorption studies were also carried out at different temperatures, i.e., 283, 298 and 313 K to delineate the effect of temperature and to evaluate the sorption thermodynamic parameters. Adsorption of malachite green was also studied at different initial concentrations of the dye solution and doses of adsorbents. Effect of initial dye concentration A mass of 0.5 g of each adsorbent (NBP and MBP) was contacted with 50 ml MG solutions of dye concentrations mol.l -1 at (ph 5 and 2) for NBP and MBP respectively, using water-bath maintained at 25 C. The agitation speed was kept constant at 400 rpm. At predetermined intervals of time, samples were analyzed for the final concentration of MG by a UV/Vis spectrophotometer. Effect of ph The effect of ph on the amount of color removal was analyzed over the ph range from 2-9. The ph was adjusted using 0.1 N NaOH and 0.1 N HCl solutions. In this study, 50 ml of dye solution was agitated with 0.5 g of Neem bark powder and Mango bark powder separately for 24 h, which is more than sufficient to reach equilibrium. The samples were then centrifuged and the left out concentration in the supernatant solution were analyzed using UV- Spectrophotometer by monitoring the absorbance changes at a wavelength of maximum absorbance. Results and Discussion Effect of contact time and initial concentration The sorption efficiency of MG increased gradually with increasing contact times and reached a plateau afterwards. At this point, the amount of dye being sorbed onto the sorbent was in a state of dynamic equilibrium with the amount of dye desorbed from the sorbent. The contact time needed for MG solutions to reach equilibrium at initial concentration of mol.l -1 was 120 min for NBP and 150 min for MBP. The rapid sorption observed during the first 20 min is probably due to the abundant availability of active sites on the Neem bark powder and Mango bark powder particle surface, and with the gradual occupancy of these sites, the sorption becomes less efficient. It is also noticed that an increase in the initial MG concentration leads to a decrease in the percentage of MG removal (Fig. 2). As the initial MG concentration increases from 10-6 to 10-4 mol.l -1, the equilibrium removal of MG decreases from 88.45% - Effect of sorbent dose Samples of NBP and MBP (0.5, 1.0 and 2.0 g) were added to 50 ml dye solution. The initial dye concentration was 10-5 mol L -1 (ph 5 and ph 2 for NBP and MBP ) at constant temperature (25 C) and stirring at the speed of 400 rpm. Effect of temperature The effect of temperature (at 283, 298, 313 K) on the sorption of MG by Neem bark powder and Mango bark powder was studied at 0.5 g sorbent and initial MG concentration of 10-5 mol L -1 (ph 5 and 2 respectively) for 7 h contact time. Fig. 2 Effect of initial concentrations for removal of malachite green over Neem bark powder and Mango bark powder

4 70 INDIAN J. CHEM. TECHNOL., JANUARY % for Neem bark powder and from 99.45% % for Mango bark powder. This effect can be explained as follows: at low dye/sorbent ratios, there are number of sorption sites in Neem bark powder and Mango bark powder structure. As the dye/sorbent ratio increases, sorption sites are saturated, resulting in decreases in the sorption efficiency 19. 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 bark doses from 0.5 to 2 g/50 ml increases the percentage of dye removal from aqueous solution from 35.5% to 85.4% for neem bark powder and 40.54% to 91.5% for mango bark powder. This may be attributed to increased sorbent surface 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 neem bark powder and mango bark powder to dye concentration ratios, there is a superficial sorption onto the sorbent surface that produces a lower dye concentration in the solution than when the sorbent to dye concentration ratio is lower. This is because a fixed mass of both the adsorbents can only sorb a certain amount of dye. Therefore, the higher the sorbent dosage is, the larger the volume of effluent that a fixed mass of neem bark powder and mango bark powder can purify 22. 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 for both adsorbents (NBP and MBP), indicating that the sorption is an endothermic process. This may be a result of increase in the mobility of the dye 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, creation of some new sorption sites or the increased rate of intraparticle diffusion of MG molecules into the pores of the sorbent at higher temperatures 23,24. It can also be said that increasing temperature may also produce a swelling effect within the internal structure of the carbons enabling more dye molecules diffusion into the sorbents 25. Effect of ph The results of the experiments done at different ph values, which were conducted to determine the optimum ph range for dye adsorption on Neem bark powder and Mango bark powder are shown in (Fig. 3). The percentage removal of MG by Neem bark powder was optimum at ph 5.0 whereas the optimum ph for removal of MG by Mango bark powder was at ph 2.0. Several reasons may be attributed to dye sorption behaviour of the biosorbent relative to solution ph. The surface of both 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. The adsorption of Malachite green increases with decrease in the ph of the solution. This can be explained by considering the zero point charge of both the adsorbents. The ph at the ph ZPC of the adsorbents are reported to be 6.80 and 6.03 for NBP and MBP, respectively. 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 favors association of anionic dye. Thus, 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 dye onto negatively charged surface of the adsorbents 25. 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. Sorption equilibria provide fundamental physiochemical data for evaluating the applicability of sorption process as a unit operation. To Fig. 3 Plot of ph versus % removal of malachite green over Neem bark powder and Mango bark powder

5 SRIVASTAVA & RUPAINWAR: EVALUATION OF ADSORPTION OF DYE ON NEEM AND MANGO BARK PAWDER 71 facilitate estimation of the adsorption capacities the two well-known equilibrium adsorption models, Freundlich 26 and Langmuir 27 models 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 given as: (C e /q e ) =(1/bQ 0 ) +(C e /Q 0 ) (1) where C e is the concentration of the dye solution (mol L -1 ) at equilibrium, q e is the amount of dye adsorbed per unit weight of adsorbent (mol g -1 ) and b is related to the energy of adsorption (l mol -1 ). Values of Q 0 and b were calculated from the slope and intercept of the linear plot, C e /q e versus C e (Fig. 4a,b) The isotherm was found to be linear over the entire concentration range studied with a good linear regression coefficient (R 2 = and 0.993) for Neem bark powder and Mango bark powder, showing that data correctly fit the Langmuir model in both the cases. The Langmuir parameters are given in Table 2. The monolayer saturation capacity (at 25 C) of NBP and MBP for adsorption of malachite green was 0.36 and 0.53 mmol g -1. The fact that Langmuir isotherm fits the experimental data very well confirms the monolayer coverage of dye onto sorbent particles and also the homogenous distribution of active sites on the material, since the Langmuir equation assumes that the surface is homogenous. lnq e = lnk F + l/n lnc e (2) The equilibrium data were further analyzed using the linearized form of Freundlich equation using the same set of experimental data. The calculated Freundlich isotherm constants and the corresponding coefficient of determination values were shown in Table 2. From Table 2, it was observed that both the Freundlich and Langmuir isotherms could well represent the experimental sorption data of MG by Neem bark powder and Mango bark powder, but the Langmuir expression was better in both the cases. The (a) (b) 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: Table 2 Langmuir and Freundlich isotherms constants for the adsorption of malachite green on Neem bark powder and Mango bark powder Langmuir constants Fig. 4 Langmuir isotherm constants for the adsorption of malachite green over (a) Neem bark powder and (b) Mango bark powder 10 C 25 C 40 C Adsorbent Q 0 (x10 4 mol.g -1 ) b(x10-3 l.mol -1 ) R 2 Q 0 (x 10 4 mol.g -1 ) b(x 10-3 l mol -1 ) R 2 Q 0 (x 10 4 mol g -1.) b(x 10-3 l.mol -1 ) R 2 NBP MBP Freundlich constants K f (x10 3 mol.g -1 ) 1/n R 2 Adsorbent 10 C 25 C 40 C 10 C 25 C 40 C 10 C 25 C 40 C NBP MBP

6 72 INDIAN J. CHEM. TECHNOL., JANUARY 2011 magnitude of the exponent n gives an indication on the favorability of sorption. It is generally stated that values of n in the range 2-10 represent good, 1-2 moderately difficult, and less than 1 poor adsorption characteristics 28. The thermodynamic parameters, ( H 0 ) and ( S 0 ) for the adsorption process are also determined using the Erying,s plot, ln K c versus 1/T (figure not shown) as per Eq.(3): ln K c = S 0 /R - H 0 /RT (3) where (K c = C ad /C e ) is the ratio of the amount of dye adsorbed on the adsorbent, C ad to that in the adsorbate, C e from the values evaluated H 0 and S 0 at different temperatures (10,25,40 C). G 0 are also calculated using Eq. (4): G 0 = H 0 - T S 0 (4) The values obtained from thermodynamic analysis are given in Table 3. The negative values of G 0 indicate the feasibility and spontaneous nature of adsorption. The similar results were reported earlier 20,29. Positive values of H 0 for the process further confirms the endothermic nature of the process whereas the positive value of entropy change ( S 0 ) reflect good affinity of the dye towards both the adsorbents 30. When the adsorbate gets adsorbed on the surface of the adsorbents, water molecules previously bonded to the dye cation gets released and dispersed in the solution, this results in an increase in the entropy 31. Adsorption kinetics study Successful application of the adsorption demands innovation of cheap, non-toxic, easily available adsorbents of known kinetic parameters and adsorption characteristics. Adsorption kinetics can be modeled by applying pseudo first-order Lagergren equation 32 and pseudo second-order model 33. The pseudo-first-order rate equation is presented as: log(q e q t ) = log q e (k 1 /2.303) t (5) where q e and q t are the amounts of dye adsorbed at equilibrium and at time t respectively, and k 1 is the rate constant of pseudo first-order sorption (l min 1 ). The parameters of the pseudo-first-order model are summarized in Table 4a. The values of determination coefficient for the plots were in the range (figure not shown). This finding suggested that the sorption process does not follow the pseudo-firstorder rate equation. An expression of the pseudo second order rate is given as: t/q t = (1/k 2 q t 2 +1/q e ) t (6) where K 2 is the pseudo-second-order rate constant (g mol -1 min -1 ), q e is the amount of dye sorbed at equilibrium (mol.g -1 ), and q is the amount of dye cation on the surface of the sorbent at any time t (mol g -1 ). The plots of t/q versus t give a straight line for all the initial dye concentrations for both the adsorbents studied as showed in (Fig. 5), confirming the applicability of the pseudo-second-order equation. The parameters of the pseudo-second-order sorption kinetic model are summarized in Table 4b. The Table 4a First-order rate constants and second-order rate constants for the adsorption of malachite green onto Neem bark powder and Mango bark powder at different temperatures Adsorbent 10 C 25 C 40 C K 1 R 2 K 2 R 2 K 1 R 2 K 2 R 2 K 1 R 2 K 2 R 2 NBP MBP K 1 = (x10 3 min -1 ), K 2 = (g mol -1 min -1 ) Table 3 Thermodynamic parameters of the adsorption - G H S Adsorbent 10 C 25 C 40 C MBP NBP G =(kj/mol), H =(kj/mol), S =(kj/mol/k-1) Table 4b Comparison of kinetic parameters for the adsorption of malachite green onto Neem bark powder and Mango bark powder Adsorb q e,exp (x10 4 mol.g -1 ) q e,cal -1 (x10 4 mol.g -1 ) q e,cal -2 (x10 4 mol.g -1 ) 10 C 25 C 40 C 10 C 25 C 40 C 10 C 25 C 40 C NBP MBP

7 SRIVASTAVA & RUPAINWAR: EVALUATION OF ADSORPTION OF DYE ON NEEM AND MANGO BARK PAWDER 73 determination coefficient values of the pseudo-secondorder model exceeded 0.99 in both the cases (i.e. removal of MG by NBP and MBP) and the calculated sorption capacity values determined from pseudosecond-order model were more consistent with the experimental values of sorption capacity. Therefore, the pseudo-second order model better represented the sorption kinetics for the removal of malachite green on neem bark powder and mango bark powder respectively. Intraparticle diffusion It is important to estimate which is the rate-limiting step (pore or film diffusion) involved in the sorption process. The three consecutive steps in the sorption of a sorbate by a sorbent are: (i) transport of sorbate molecules from the bulk solution to the external surface of the sorbent by diffusion across the liquid boundary layer (film diffusion), (ii) diffusion of the sorbate within the pores of the sorbent (intraparticle diffusion) and (iii) sorption of the sorbate on the active sites. It is generally accepted that the last step is usually very rapid in comparison to the first two steps. Therefore, the overall rate of sorption is controlled by either film or intra-particle diffusion. Since neither the pseudo-first-order nor the pseudo-second-order model can identify the diffusion mechanism, the kinetic results were analyzed by the intra-particle diffusion model. The rate parameter of intra-particle diffusion can be defined as 34 : Fig. 5 Pseudo-second order reaction(t/q t ) for removal of malachite green on Neem bark powder and Mango bark powder at different initial dye concentrations, sorbent dose= 0.5 g/50 ml, T= 25 C, ph 2 for MBP and 5 for NB q = k id.t 1/2 +C (7) where q (mol.g -1 ) is the amount of MG sorbed at time t, C (mol. g -1 ) the intercept, and k id (mol g -1 min -1/2 ) is the intra-particle diffusion rate constant. The kinetic results can be used to determine if particle diffusion is the rate-limiting step for dye sorption onto material. (Fig. 6 a,b) shows the amount of dye sorbed versus t 1/2 for intra-particle transport of MG by neem bark powder and mango bark powder at different initial dye concentrations. It was found that the rate constant increased with increasing dye concentration. The determination coefficient values for this diffusion model are between and Any increase in the value of C indicates the abundance of solute in the boundary layer. Bangham, s equation Kinetic data can further be used to check by using Banghams equation 35 : Fig. 6 Intra-particle diffusion for removal of malachite green over (a) Neem bark powder at ph 5 and (b) Mango bark powder at ph 2, temperature= 25 C, dose= 0.5 g/50 ml ln. ln (C 0 /C 0 - q t m) = log (K o m/ V) + a ln (t) (8) where C 0 is the initial concentration of adsorbate in solution (mg.l -1 ), V is the volume of the solution (ml), m is the mass of adsorbent per liter of solution (g.l -1 ) q t is the amount of adsorbate retained at time t, a and K 0 are constants, values are summarizes in Table 5. The logarithmic plot (Fig. 7) according to

8 74 INDIAN J. CHEM. TECHNOL., JANUARY 2011 required amount of MBP and NBP to reduce the colour content by 90% at various volumes of effluents can be calculated. For example, 10 L of the solution is to be treated. The required masses of NBP and MBP are and mmol for MG, respectively, for 90% dye removal. Fig. 7 Bangham, s plot for removal of malachite green onto Neem bark powder and Mango bark powder at different concentrations, ph 2 for MBP and 5 for NBP, temperature= 25 C, dose= 0.5 g/50 ml above equation yielded perfect linear curves for adsorption of malachite green by neem bark powder and mango bark powder, showing that the diffusion of adsorbate into pores of the adsorbent basically controls the adsorption process, although it is not the only rate controlling step. Designing batch adsorption from isotherm data Adsorption isotherm can be used to predict the design of single-stage batch adsorption systems 36. Consider an effluent containing V liter of solvent (water) and the dye concentration reduced from C o to C 1 g dye per liter solvent. The amount of adsorbent is M g and the solute loading changes from q o to q 1 mmol dye per gram adsorbent. When fresh adsorbent is used, q 0 = 0 and the mass balance equates the dye removed from the liquid to that picked up by the solid: V (C o -C 1 ) = M (q o - q 1 ) = M q 1 (9) If the system is allowed to come to equilibrium, then: C 1 C e and q 1 q e In case of adsorption of Malachite green onto Neem bark powder and Mango bark powder, Langmuir isotherm gives the best fit to experimental data. Consequently, the Langmuir equation can be best substituted for q 1 in the rearrangement form of Eq. (11), giving adsorbent/solution for a giving change in dye concentration, C o C e at this particular system: M/V = C o C e / q 1 = C o C e / q e C o C e / K L C e / 1+a L C e (10) where K L and a L are Langmuir constants and an initial dye concentration of 100 m mol/l is assumed and the Conclusions The results of this study suggests the possibility of recycling an agricultural waste byproducts as adsorbent for the treatment of dyeing industry wastewater. (i) Neem bark powder and Mango bark powder are a promising adsorbent for removal of dye Malachite green. (ii) The experimental data produced perfect fit with the Langmuir isotherm for both the adsorbents, this suggest the monolayer coverage of Malachite green with adsorption capacity (at 25 C) was 0.36 and 0.53 mmol g -1 for NBP and MBP respectively. (iii) The kinetics of the adsorption of dye (Malachite green) onto NBP and MBP reports to be pseudo second order chemical reaction kinetics. (iv) This pseudo second-order kinetics is further supported by Bangham, s equation. (v) The rate of adsorption of Malachite green, onto NBP and MBP increased with increasing temperature. Thus suggesting the reaction to be spontaneous and endothermic in nature. Both Neem bark powder and Mango bark powder act as a good adsorbent for removal of Malachite green from industrial and other effluents. However, the Q 0 values at different temperatures and the surface area values showed that Mango bark powder act as a better adsorbent for the removal of dye. Acknowledgement The authors thank the Director, Institute of Engineering and Technology, Lucknow, for providing the necessary facilities and his keen interest in this work. References 1 Lin S H, J Chem Technol Biotechnol, 57 (1993) Mckay G & Ramprasad G P, Water Res, 21 (1987) Lina J X, Zhana S L & Fanga M H, J Environ Manage, 83 (2007) Gupta V K, Ali I & Suhas D, J Colloid Interface Sci, 265 (2003) 257.

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