AGRO WASTE USED AS NATURAL SORBENTS FOR ACID RED 51 UPTAKES

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1 AGRO WASTE USED AS NATURAL SORBENTS FOR ACID RED 51 UPTAKES LAURA CARMEN APOSTOL 1, LUCIANA PEREIRA 2, MADALENA ALVES 2, MARIA GAVRILESCU 1 1 The "Gheorghe Asachi Technical University of Iaşi, Faculty of Chemical Engineering and Environmental Protection, 73, Dimitrie Mangeron Blvd., , Iaşi, Romania, apo.laura@ch.tuiasi.ro 2 IBB-Instituto Biotecnologia e Bioengenharia, Centro Engenharia Biológica, Universidade do Minho, Campus de Gualtar, , Braga, Portugal Acid Red 51, commonly named as Erythrosine B (Ery B), a water-soluble xanthene class of dye, is widely used in cosmetics, foodstuffs, medicines and textiles. Some procedures for textile wastewater remediation, such as photochemical and chemical degradation are not recommended mainly due to the formation of toxic by-products. Therefore, development of low-cost and efficient methods, such as sorption on agricultural waste is a good alternative. The present paper aims to investigate the removal of Ery B by sorption on agro-waste. Pumpkin seeds hull (PSH) has been chosen as a sorbent. Batch experiments were conducted for the study of the influence of some parameters on dye adsorption efficiency, such as: dye concentration (5 to 50 mg L -1 ), temperature (20, 30, 40, 50ºC) and the dosage of adsorbents (5 to 30 g L -1 ). Kinetic studies of Ery B adsorption on PSH were carried out at 25ºC, using aqueous solutions with 10, 20 and 30 mg L -1 of dye. All the experiments were conducted at the natural ph of the solution, 5.6. The results showed that the hazardous water-soluble dye Ery B can be efficiently removed from the aqueous solutions by adsorption over PSH. Using 20 g L -1 of PSH the amount of dye uptake was around 3.5 mg g -1. Adsorption has been correlated with the different adsorption isotherms and based on the data free energy of adsorption ( Gº), enthalpy ( Hº), and entropy ( Sº) were calculated. Keywords: adsorption, pumpkin seed hull, xanthene dye. INTRODUCTION Acid Red 51 is a water-soluble xanthene class of dye widely used since 1973 in different industries such as a colorant in foodstuffs (baked goods, fruit cocktails), cosmetics (lipsticks, bubble baths) or drugs (tablet, capsule). The large majority of the dyes from this class are toxic, carcinogenic or mutagenic for humans and animals (Dees et al., 1997). The amount of Erythrosine B used in preserved cherries is at maximum 200 mg.kg -1 (Food Standards, 2008); however, the presence of xanthene dyes is visible in water at very low concentrations. Different studies for its elimination from wastewater have been done through degradation methods but those may exhibit the disadvantage of sub-products generation with higher toxicity within the system (Hasnat et al., 2007; Uddin et al., 2007). Even though that adsorption does not result in chemical degradation of the pollutant, it can be a good alternative treatment method when low costly and environmentally friendly sorbents are employed (Gupta et al., 2006; Caliman et al., 2009). Some examples of these unconventional adsorbents are pinus bark powder (Ahmed, 2008), hazelnut shells (Ferrero, 2007), nut shells (de Oliveira Brito et al., 2009) or bottom ash and de-oiled soya (Mittal et al., 2006). The sorption potential and property of pumpkin seed hulls (PSH) were investigated by Hameed and El-Khaiary (2008) for the removal of basic dye methylene blue. In the present work, Ery B removal by sorption on PSH was investigated. The advantage of using that type of natural material is twofold: on one hand, it can act as an effective and economic adsorbent for 351

2 solving the problem of colour pollution; on the other hand, an effective and useful exploitation of agriculture waste is achieved. MATERIALS AND METHODS Adsorbate The acid dye used in this study, Erythrosine B, was purchased from Sigma Aldrich (C.I. Acid Red 51, 45430). A stock solution of 500 mg.l -1 was prepared by dissolving an accurately weighed amount of Ery B in 1000 ml distilled water. For the experimental assays, dilution of this stock was done to achieve the desired concentration, always when necessary. Adsorbent Pumpkin, Cucurbita pepo L., is an herbaceous, monoecious, annual plant of the Cucurbitaceous family. The collected hulls were washed several times with distilled water to remove any adhering dirt and dried at 40ºC for 24h to constant weight. The dried sample was crushed using a Retsch GM 200 laboratory mill and stored in plastic boxes for further use. No other chemical or physical treatments were used prior to adsorption experiments. Batch Adsorption Studies Batch experiments in 250 ml flasks, containing 50 ml of the Ery B solution at the desired concentration and the PSH, were conducted. The effect of phase contact time, initial dye concentration (range of 10 to 30 mg L -1 ) and adsorbent dosage (10, 20 or 30g L -1 ) on the removal of Ery B from aqueous solution was investigated. The flasks were incubated at 25ºC and 120 rpm in an isothermal shaker (IKA KS 4000 IC) for 24 h, period when dye removal reached the equilibrium. All the experiments were carried out in triplicate and at the natural ph of the solution (ph = 5.6); ph measurements were done with a Hanna 213 ph-meter. Dye removal was monitored by measuring the absorbance at the λ max of the dye, 524 nm, in a T60 UV-Visible spectrophotometer and the concentrations at different times converted by using the ε of dye (ε 540 nm = 6,7282 M -1.cm -1 ). Equilibrium experiments were carried out in triplicate as described previously for the decolourisation kinetic studies, using initial dye concentrations in the range of 10 to 50 mg.l -1. The flasks were incubated at different temperature (20, 30, 40, 50ºC). The sorption efficiency and the sorption capacity were calculated applying the Equations 1 and 2: Ci Ce R (%) = *100 (1) Ce q e Ci Ce = * V m where: qe is the amount of dye adsorbed onto PSH a equilibrium time, mg.g -1, Ci, the initial dye concentration (mg L -1 ); Ce, the equilibrium concentration of dye (mg L -1 ); m, the amount of dried sorbent used (g); V, the volume of the solution (L). (2) 352

3 RESULTS AND DISCUSSION Effect of Adsorbents Dosage In order to investigate the influence of adsorbent dosage on dye adsorption, experiments were carried out at initial dye concentration of 20 mg L -1, while the amount of adsorbent added varied from 5 to 30 g L -1. Figure 1 shows the results of Ery B adsorption, at the equilibrium, at various PSH dosages. The values of q t (amount of dye adsorbed onto PSH at time t, mg g -1 ) decreased with the increase of PSH dose from 0.25 to 1.5 g: 1.8 to 0.5 mg g -1, respectively This result is explained by the change in the concentration gradient between the dye content in solution and the surface of the PSH q e (mg.g -1 ) 2 60 R (%) q t (mg.g -1 ) mg.l mg.l mg.l m (g/25ml) Figure 1. Influence of PSH amount on Erythrosine B sorption (Ci = 20 mg.l -1 ) Time (h) Figure 2. Effect of contact time for different concentrations of Erythrosine B Effect of Contact Time and Initial Dye Concentration The effect of contact time on the adsorption of Ery B on PSH was studied at 25ºC varying the initial dye concentration from 10 to 30 mg L -1. The results obtained indicate that the amount of dye adsorbed per mass unit of PSH increased with contact time for the three dye concentrations tested. The initial Ery B concentration also influences the dye uptake, being higher for the assay with 30 mg L -1 (Figure 2). Kinetics Studies The kinetic of adsorption was analyzed using the Lagergren s pseudo-first-order and Ho s pseudo-second-order models (Ho and McKay, 1999). The Lagergren equation models for the boundary conditions, t = 0...t and q = 0...q, gives the kinetics of adsorption process as follows (Equation 3): qt = qe(1 e k 1 t ) (3) where: q e is the equilibrium adsorption capacity (mg g 1 ); k 1 is the pseudo-first order rate constant (min 1 ). The data were further processed according to a pseudo-second order kinetic model on the basis of the Equation (4): t 1 1 = + t 2 qt k 2q qe e where: k 2 is the rate constant of pseudo-second order adsorption (g mg 1 min 1 ). The experimental results of the dye uptake (q t ) versus time were analyzed with both models (non-linear regression form of pseudo-first order; linear regression form of (4) 353

4 pseudo-second order). From the regression results (Table 1), the values of q e obtained from pseudo-second-order model are much closer to the experimental results than q e obtained from the Lagergeren s model. Table 1. Pseudo-first-order and pseudo-second-order rate constants C 0 (mg.l -1 ) q exp (mg.g -1 ) Pseudo-first-order mode Pseudo-second-order model q e (mg.g -1 ) k 1 (h 1 ) R 2 q e (mg.g -1 ) k 2 (g.mg -1 h -1 ) R The higher R 2 values obtained by pseudo-second-order indicate that the adsorption kinetics data are well represented by this model. The linear relationships between initial Erythrosine B concentration and the rate constants suggest that several mechanisms play a role in the adsorption process, such as ion exchange and physical adsorption (Hameed and El-Khaiary, 2008). Equilibrium Studies The data obtained from sorption experiments are generally represented with equilibrium isotherms. In the present study, the Ery B sorption was analyzed by Langmuir and Freundlich isotherm models. The fundamental assumption of the Langmuir isotherm model is that sorption takes place at specific sites with in the sorbent (Haris and Sathasivam, 2009). The linearized form of the Langmuir equation is given below (Equation 5): 1 1 = q q e max qmax k L ce where: q e is the amount of dye sorbed at equilibrium (mg g 1 ); C e is the unsorbed dye concentration in aqueous solution (mg L 1 ); q max is the monolayer sorption capacity of the sorbent (mg g 1 ); K L is the Langmuir sorption constant (L mg 1 ), which is related to the free energy of sorption (Akar et al., 2008). The essential feature of the Langmuir isotherm can be expressed by means of R L, a dimensionless constant referred to as separation factor or equilibrium parameter. The values of R L indicate the shape of isotherms to be either favourable (0<R L <1), unfavourable (R L >1), linear (R L =1) or irreversible (R L =0). The R L values obtained in our study indicated that Ery B sorption process was favourable at all the studied temperatures (Table 2). The Freundlich isotherm is an empirical equation based on sorption on heterogeneous surface and also possibly in multilayer sorption. Linear form of the Freundlich equation is commonly presented as (Khattri and Singh, 2009): 1 ln qe = ln kf + lnc (6) e n where: K F (L g 1 ) and n (dimensionless) are Freundlich constants. The Freundlich constant K F and n are the indicative of the extent of the sorption and the degree of nonlinearity between solution concentration and sorption; n is a measure (5) 354

5 of sorption intensity (Han et al., 2008).The Langmuir and Freundlich constants and regression coefficients for the Ery B sorption are presented in Table 2. Ery B sorption process was well described by both isotherm models with R 2 values of higher than The sorption capacity of PSH for ERY B was 1.82 mg g -1. This value was ~ 6 fold lower than the obtained by Hameed and El-Khaiary (2008) for methylene blue also with PSH and at the same temperature, mg g -1. This may be explained by the structural differences of the dyes. Table 2. Sorption isotherm constants for the sorption of Erythrosine B onto PSH at different temperatures T Langmuir Freundlich (ºC) q max (mg g 1 ) K L (mg L 1 ) R 2 R L n K F (L g 1 ) R Thermodynamic Parameters Thermodynamic parameters such as free energy change ( Gº), enthalpy change ( Hº) and entropy change ( Sº) were determined using the Equations (7, 8) (Patel and Suresh, 2008): G ο = RT ln (7) K c ο ο ο G = H T S (8) where: Gº = change in free energy, kjmol -1 ; Hº = change in enthalpy, kjmol -1 ; Sº = change in entropy, Jmol -1 K -1 ; T = absolute temperature, K; R = gas constant = 8.314x10-3; Kc = equilibrium constant, L mol -1. Thermodynamic parameters obtained from the slope and intercept of Van t Hoff plots are shown in Table 3. The negative values of G demonstrate that adsorption is highly favourable and spontaneous and the positive values of S reveal that the increased disorder at the solid solution interface of PSH with Ery B adsorbent, while some structural changes in the dye occur during adsorption. Table 3. Thermodynamic parameters for the sorption of Erythrosine B on PSH Thermodynamic parameter Temperature (K) K c (L mmol -1 ) Gº (kj mol -1 ) Hº (kj mol -1 ) Sº (J mol -1 K -1 ) CONCLUSIONS PSH, a low-cost and wide available biomaterial was shown as an attractive candidate for the effective removal of the hazardous water-soluble dye Erythrosine from aqueous solutions. 355

6 The sorption process is initially very fast, it attains equilibrium within one day, and follows the second-order kinetic rate model. The results indicate that the amount of dye adsorbed per mass unit of PSH increased with increasing contact time and initial Erythrosine B concentration. The negative values of G show that adsorption is highly favourable and spontaneous. The fact that the sorption of the acidic dye is in favour of temperature indicates that the mobility of the dye molecules increases with the temperature rising. Acknowledgements This work was supported by the Program IDEI, Grant ID_595, Contract No. 132/2007, in the frame of the National Program for Research, Development and Innovation II Ministry of Education and Research, Romania and by BRAIN project ID 6681, financed by the European Social Found and Romanian Government. REFERENCES Akar, T., Ozcan, S.A., Tunali, S., and Ozca, A. (2008), Biosorption of a Textile Dye (Acid Blue 40) by Cone Biomass of Thuja orientalis: Estimation of Equilibrium, Thermodynamic and Kinetic Parameters, Bioresource Technology, 99, Caliman, F.A., Apostol, L.C., Bulgariu, D., Bulgariu, L., and Gavrilescu, M. (2009), Study Regarding the Sorption of Erythrosine from Aqueous Solution onto Soil, Environmental Engineering and Management Journal, 8(6), de Oliveira Brito, S.M., Carvalho Andrade, H.M., Soares, L.M., and de Azevedo, R.P., Brazil Nut Shells as a New Biosorbent to Remove Methylene Blue and Indigo Carmine from Aqueous Solutions, doi: /j.jhazmat Dees, C., Askari, M., Garrett, S., Gehrs, K., Henley, D., and Ardies, C.M. (1997), Estrogenic and DNA- Damaging Activity of Red No. 3 in Human Breast Cancer Cells, Environmental Health Perspectives, 105, Ferrero, F. (2007), Dye Removal by Low Cost Adsorbents: Hazelnut Shells in Comparison with Wood Sawdust, Journal of Hazardous Materials, 142, Food Standards (2008), Initial Assessment Report, Application A603, Red 3 Erythrosine in Food Colouring Preparations, On line at: Gupta, V.K., Mittal, A., Kurup, L., and Mittal, J. (2006), Adsorption of a Hazardous Dye, Erythrosine, over Hen Feathers, Journal of Colloid and Interface Science, 309, Hameed, B.H. and El-Khaiary, M.I. (2008), Removal of Basic Dye from Aqueous Medium Using a Novel Agricultural Waste Material: Pumpkin Seed Hull, Journal of Hazardous Materials, 155, Haris, M.R.H. and Sathasivam, K. (2009), The Removal of Methyl Red from Aqueous Solutions Using Banana Pseudostem Fibers, American Journal of Applied Sciences, 6, Hasnat, M.A., Uddin, M.M., Samed, A.J., Alam, S.S., and Hossain, S. (2007), Adsorption and Photocatalytic Decolorization of a Synthetic Dye Erythrosine on Anatase TiO 2 and ZnO Surfaces, Journal of Hazardous Materials, 147, Ho, Y.S. and McKay, G. (1999), Pseudo-Second Order Model for Sorption Processes, Process Biochemistry, 34, Khattri, S.D. and Singh, M.K. (2009), Removal of Malachite Green from Dye Wastewater Using New Sawdust by Adsorption, Journal of Hazardous Materials, 167, Mittal, A., Mittal, J., Kurup, L., and Singh, A.K. (2006), Process Development for the Removal and Recovery of Hazardous Dye Erythrosine from Wastewater by Waste Materials Bottom Ash and De- Oiled Soya as Adsorbents, Journal of Hazardous Materials, 138, Han, R., Han, P., Cai, Z., Zhao, Z., Tang, M. (2008), Kinetics and Isotherms of Neutral Red Adsorption on Peanut Husk, Journal of Environmental Sciences, 20, Patel, R. and Suresh, S. (2008), Kinetic and Equilibrium Studies on the Biosorption of Reactive Black 5 Dye by Aspergillus foetidus, Bioresource Technology, 99, Uddin, M.M., Hasnat, M.A., Samed, A.J.F., Majumdar, R.K. (2007), Influence of TiO 2 and ZnO Photocatalysts on Adsorption and Degradation Behaviour of Erythrosine, Dyes and Pigments, 75,