Environmental Science and Pollution Research Efficient removal of lead (II) and methylene blue from aqueous solution using ecofriendly Rosmarinus officinalis waste: Kinetic, isotherm and thermodynamic studies. --Manuscript Draft-Manuscript Number: Full Title: Efficient removal of lead (II) and methylene blue from aqueous solution using ecofriendly Rosmarinus officinalis waste: Kinetic, isotherm and thermodynamic studies. Article Type: Research Article Keywords: Eco-friendly biosorbent, methylene blue, lead (II), Rosmarinus officinalis, Waste materials valorization, thermodynamics parameters. Corresponding Author: Amel CHAABOUNI, Doctor Faculté des Sciences de Sfax Cité Elhabib Rue de Soukra Km3, Sfax TUNISIA Corresponding Author Secondary Information: Corresponding Author's Institution: Faculté des Sciences de Sfax Corresponding Author's Secondary Institution: First Author: Zied MARZOUGUI, Ph.D First Author Secondary Information: Order of Authors: Zied MARZOUGUI, Ph.D Amel CHAABOUNI, Doctor Boubaker ELLEUCH, Professer Order of Authors Secondary Information: Funding Information: Abstract: The biosorption of lead (II) ions and methylene blue from aqueous solution using an eco-friendly adsorbent ROBW (e.g., Rosmarinus officinalis biowaste obtained as byproduct from locally extraction industries of essential oils) has been considered in this work. The biosorption experiments were carried out batch wise where the influence of physicochemical key parameters such as initial pH solution, contact time, initial adsorbate concentration, the amount of biosorbent, temperature and biosorbent particle size were evaluated. The results of the study indicated that with the increased adsorbent doses the adsorption capacity values decreased while the removal percentage of adsorbate increased, whereas, no influence of particles size was evidenced. The maximum biosorption occurred at pH 8.0 and 5.0, for methylene blue and lead (II) ions respectively. The biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The equilibrium data fitted very well to the Langmuir model with a maximum monolayer biosorption capacity of 52.63 and 43.47 mg/g, for methylene blue and lead (II) ions respectively. Thermodynamic parameters such as Gibbs free energy, enthalpy and entropy were determined. Our study suggests that ROBW can be used as cost-effective and efficient adsorbents for the removal of heavy metals and cationic dyes from contaminated waters. Suggested Reviewers: Raja Ben Ammar , Professer University of Sfax [email protected] I suggest Pr. Ben Ammar as reviewer because she is an expert in their field; environemental process and wastewater treatment Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Nesrine BOUJELBENE, Dr University of Sfax [email protected] I suggest Dr Boujilben because she is an expert in her Environmental Chemistry, Green Chemistry, and Analytical Chemistry Ragab Ragab, Professer center for ecology and hydrology [email protected] I suggest Pr Ragab as reviewer because he is an expert in her Environmental impact assesment, Environmental science and water ressources Opposed Reviewers: Additional Information: Question Response Are you submitting to a Special Issue? No Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Manuscript Click here to download Manuscript Manuscrit ROBW_ 29_10_2015..docx Click here to view linked References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Efficient removal of lead (II) and methylene blue from aqueous solution using eco-friendly Rosmarinus officinalis waste: Kinetic, isotherm and thermodynamic studies. Zied MARZOUGUI, Amel CHAABOUNI, Boubaker ELLEUCH Laboratory Water-Environments and Energy (3E), National School of Engineers of Sfax B.P. 1173, 3038, Sfax-Tunisia. Correspondence to: Amel Chaabouni: [email protected] 1 Abstract 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 The biosorption of lead (II) ions and methylene blue from aqueous solution using an ecofriendly adsorbent ROBW (e.g., Rosmarinus officinalis biowaste obtained as by-product from locally extraction industries of essential oils) has been considered in this work. The biosorption experiments were carried out batch wise where the influence of physicochemical key parameters such as initial pH solution, contact time, initial adsorbate concentration, the amount of biosorbent, temperature and biosorbent particle size were evaluated. The results of the study indicated that with the increased adsorbent doses the adsorption capacity values decreased while the removal percentage of adsorbate increased, whereas, no influence of particles size was evidenced. The maximum biosorption occurred at pH 8.0 and 5.0, for methylene blue and lead (II) ions respectively. The biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The equilibrium data fitted very well to the Langmuir model with a maximum monolayer biosorption capacity of 52.63 and 43.47 mg/g, for methylene blue and lead (II) ions respectively. Thermodynamic parameters such as Gibbs free energy, enthalpy and entropy were determined. Our study suggests that ROBW can be used as cost-effective and efficient adsorbents for the removal of heavy metals and cationic dyes from contaminated waters. Key words: Eco-friendly biosorbent, methylene blue, lead (II), Rosmarinus officinalis, Waste materials valorization, and thermodynamics parameters. 2 1. Introduction 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Rapid industrialization and urbanization have resulted in the generation of large quantities of aqueous effluents, many of which contain high levels of toxic pollutants such as dyes and heavy metals; Dyes are widely used in many industries like textile, leather, cosmetics, paper printing, plastic, pharmaceuticals, food, etc… to color their products. Dyes can be toxic to the aquatic life in receiving waters, being some of them mutagenic and carcinogenic. Most of the manufacturers always go for the most stable dyes making them highly persistent in the environment (I.A. Aguayo-Villarreal et al. 2013; I.D. Mall et al. 2006). In addition, the degradation by-products of some synthetic organic dyes represent a potential environmental hazard since they contain aromatic amine compounds that are toxic to many organisms (Jenifer et al. 2014). Particularly, textile industries usually discharge huge amount of wastewater mainly containing synthetic dyes. In a typical dyeing and finishing mill, about 100 liters of water is consumed on an average for every ton of clothes processed (Md. Motiar et al. 2011). On the other hand, metal processing and metal working industry, particularly electroplating and surface finishing, is an important sector producing enormous amounts of wastewaters containing mainly heavy metals ions (Bozic et al. 2009). The major concern with heavy metals is their ability to accumulate in living organisms, causing severe disorders and diseases. Detrimental effects on ecosystems and the health hazards associated with dyes and heavy metals have been established beyond any doubt, making it absolutely necessary to be removed (Marina et al 2014). Various treatment procedures have been developed for the removal of these contaminants from industrial effluents such as ion exchange, reduction, chemical precipitation and coagulation, membrane separation, osmosis and reverse osmosis, and electrolytic technologies (Saliha et al. 2007; Yuying et al. 2015). However, the necessity of using expensive chemicals in some methods as well as accompanying disposal problem are among the drawbacks of these conventional methods (Yuying et al. 2015) and therefore limit their wide scale application (Muhammad et al. 2009). As a result of these short comings, adsorption is considered as an efficient and economical method that can be used for the removal of toxic pollutants from effluents and industrial wastewaters with high retention efficacy when applied with the proper adsorbent (Jenifer et al. 2014), especially if the adsorbent is inexpensive and readily available. Indeed the cost of used adsorbents is the most important restricted factor in view of applicability of the adsorption process (A. Ozer. 2007). Currently activated carbon is the most widely used adsorbent for dyes and metal ions removal but due to its expensive production and regeneration, it is still considered uneconomical. 3 Therefore, there is a growing need to find up low-cost, locally available, and effective 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 adsorbent for contaminants treatments (Vesna et al. 2014). This difficulty can be overcome by using raw biomass wastes generated in agriculture and forestry industries. The native exchange capacity and general biosorption characteristics of these biological materials derive from their components: cellulose, hemicelluloses, pectin, lignin, and proteins; which are biopolymeric materials containing a variety of functional groups that can adsorb certain contaminants in water (Litza et al. 2013). The advantage of using agricultural and forestry solid wastes as adsorbents is that it saves disposal costs while alleviating potential environmental problems (Chun-Shui et al. 2009). Therefore, in recent years, extensive research has been undertaken to investigate the application of a number of natural resources including agro-industrial waste as efficient, locally available and low-cost biosorbent to remove several contaminants from water and wastewater. Recent studies have shown that various types of biomasses, Viscum album L (Saliha et al. 2007), coir pith (Md. Motiar et al. 2011), deciduous trees sawdust (D. Bozic et al. 2009), Mango peel waste (Muhammad et al. 2009), agave bagasse (Litza et al. 2013), sugar extracted spent rice biomass (Muhammad et al. 2012), dried cactus cladodes (Noureddine et al. 2013), pine bark (Ali et al. 2009), etc. have the potential to be efficient and cost-effective biosorbent. In continuation of these efforts, the waste biomass of Rosemary (Rosmarinus Officinalis) was evaluated to determine its potential as metals and dyes biosorbent. Rosemary is a woody shrub with a pine needle like leaves. Its trusses of blue flowers last through spring and summer, R. officinalis is growing wild in bioclimatic zones in Tunisia; e.g., 38 thousand tons are generated annually in Tunisia (The Tunisian Ministry of Agriculture, Water and Fisheries Resources). High quantities of Rosemary’s biomass are used in several local distilleries for the extraction of essential oil by hydro-distillation. After extraction of the oil, the remained biomass of Rosemary, is considered to be a waste and is discharged or incinerated, becoming a problem for environmental protection. Therefore, an advantageous waste management process for that remained biomass is by utilizing them as a biosorbent for purifying effluents. At present, there is no information about using Rosemary’s waste biomass as a biosorbent earlier. In this study, Rosemary’s waste biomass obtained at no-cost from a local distillery in Kasserine-Tunisia, was evaluate as a new, inexpensive and environment-friendly adsorbent material (ROBW) for treating aqueous solution containing toxic metals and dyes. Lead ions (Pb2+) and methylene blue (MB) were selected as representatives of heavy metal and dye, respectively. The study includes an evaluation of the effects of various process parameters 4 such as, the pH solution, adsorbent concentration, contact time, contaminants concentration 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 and temperature. The kinetics, isotherms and thermodynamics of MB and Pb(II) adsorption onto ROBW were also evaluated.. 2. Materials and methods 2.1. Biosorbent preparation Rosmarinus officinalis biowaste (ROBW) after the extraction of the essential oil was collected from a local distillery in Kasserine-Tunisia, the biowaste was thoroughly washed with tap water, then washed twice with distilled water to remove dirt particles. Afterward samples were cut into small pieces and were oven dried at 70°C for 24 h, then ground and sieved to a particle size of 63- 500 µm. The adsorbent thus obtained ROBW was stored in a glass bottle for future use without further treatment. 2.2. Adsorbates preparation Methylene blue (MB), used as a cationic dye model for this experiment, was purchased from Sigma Aldrich and used without further purification. A stock solution (1000 ppm) of MB dye was prepared by dissolving 1.0 g of MB in 1 L of distilled water. The experimental solutions of desired concentration were prepared by diluting the stock solution with distilled water. The concentration of MB dye was measured at λmax= 665 nm using UV–visible spectrophotometer (Spectro UV-VIS Double PC UVD-2950 LABOMED, INC). Lead ions Pb(II) which is one of the most toxic heavy metal for human was used as a cationic heavy metal model for this study. Pb(NO3)2 was purchased from Sigma Aldrich. A stock solutions (1000 ppm) of Pb(II) ions was prepared by dissolving appropriate amount of Pb(NO3)2 in distilled water. The experimental solutions of desired concentration were prepared by diluting the stock solution with distilled water. The initial and final metal concentrations were determined by atomic absorption technique using flame atomic absorption Thermo Scientific, model ICE 3000 AA Spectrophotometer. The desired pH value of solution was adjusted by adding either 0.1 M HCl (0.1 M) or NaOH (0.1 M) solution and was measured using a WTW in Lab pH-720 Meter. 2.3. Biosorbent characterization 2.3.1. Point of zero charge The point of zero charge (pHPZC) of the ROBW, which corresponds to the point of balance between positive and negative charges on the material surface, was determined by the solid 5 addition methods (V. Ponnusami et al. 2008; Muhammad et al. 2009; Dahu et al. 2013; Vesna 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 et al. 2014). To a series of 100 mL stoppered flask, 50 ml of NaCl (0.1 M) solution was transferred. The initial pH (pHi) values of the solutions were roughly adjusted from 2 to12 by adding either 0.1 HCl or NaOH. The pHi values of the solutions were then accurately noted, and 0.2 g of ROBW was added to each flask, which were securely capped immediately. The suspensions were then shaken at 250 rpm using an orbital shaker, allowed to equilibrate for 7 hours and the pH values of the supernatant (pHf) were measured. The difference between the initial and final pH value, (ΔpH= pHi - pHf ) was plotted against the pHi and the point of intersection of the resulting curve at which ΔpH=zero gave the pHPZC. 2.3.2. FTIR and SEM analysis FTIR spectroscopy (PerkinElmer Spectrum Version 10.00.00) was done to identify the chemical functional groups present on ROBW. IR absorbance data were obtained in wave numbers in the ranging from 4000 to 400 cm−1. The surface morphology of the ROBW was performed with scanning electron microscopy QUANTA 200 (FEI), operating at an acceleration voltage of 20 kV. The granules were mounted on circular aluminum stubs with double sided adhesive tape and coated with gold for test. 2.4. Batch adsorption experiments The ability of ROBW to adsorb MB and Pb(II) was tested at different conditions (see Table 1) using a series of batch tests in a shaker-incubator instrument (OI®SI50). For each test, 25 mL of the adsorbate solution with the desired composition was poured into a 50 mL stoppered flask, a given amount of ROBW was added, the temperature of the incubator was adjusted to the desired level, and the instrument was used to stir the mixture at 200 rpm for a preset time. As soon as the mixing time was completed, the mixtures were centrifuged and the clear supernatant liquids were analyzed for the residual Pb2+ concentrations by using atomic absorption spectrophotometer, and for the residual MB concentrations by using UV–visible spectrophotometer. The adsorption capacity (qe) and removal efficiency (R %), were calculated according to the following equations (1) and (2), respectively: Ci − Cf V W Ci − Cf R% = ( ) x 100 Ci qe = 6 (1) (2) Where Ci and Cf (mg/L) are the initial and final adsorbate concentrations in solution, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 respectively, V (L) is the volume solution and W (g) is the used adsorbent mass. For timedependent data, Ct replaces Ceq and qt replaces qe in Eq (1). The effect of the experimental operational parameters such as the initial pH, the adsorbate concentration, the ROBW dose, the ROBW particles size, the contact time, and the temperature on MB and Pb (II) removal was analyzed by plotting either qe or R% versus the investigated variable. After finding the optimum conditions for the tested variables, the kinetics, equilibrium, and thermodynamics parameters of MB and Pb (II) adsorption onto ROBW were determined and evaluated. 3. Results and discussion 3. 1. Biosorbent characterization 3. 1.1. FT-IR of ROBW The FTIR spectrum of ROWB is shown in Fig. 1. The spectra are complex due to numerous different types of functional groups on the surface of adsorbent. Peaks were assigned to various groups in accordance with their respective wave numbers (cm−1) as reported in literature, the wide band observed at 3351 cm-1 indicates that free and intermolecular bonded O-H groups were present, which is consistent with the peak at 1028 cm-1 and assigned to alcoholic C-O stretching vibration. The band at near 2925 cm-1 was assigned as the stretching vibration of the C-H in -CH, -CH2 and -CH3 groups that were present in the lignin structure. The peak observed at 1601 cm−1 is assigned to C= C ring stretch of aromatic rings. In addition, the bands at 1508 and 1423 cm−1 confirm the presence of C=C relating to aromatic rings. The band at 1238 cm−1 is assigned to phenolic hydroxyl groups present in lignin. The spectrum also displays a strong band at1734 cm−1, which is assigned to the carbonyl group stretching from ester or carboxylic acid group. The band at 1641 cm−1 is assigned to carboxylate ion groups. These FTIR bands indicate that the ROBW presents different surface structures, e.g., aliphatic, aromatic, cyclic and different functional groups such as, hydroxylic, phenolic and carboxylic groups (A.A. Jalil et al. 2012; María Ángeles et al. 2010; Betina et al. 2009) that can be deprotonated thus being potential adsorption sites for interaction with cationic dyes such as the MB and with cationic metal such as Pb (II). Fig. 1. FTIR Spectrum of ROBW. 7 3. 1.2. SEM analysis of ROBW 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 The surface morphology of ROWB, as visualized by SEM is depicted in Fig. 2. It was found that ROBW belongs to a nonporous solid material with respect to its surface smoothness. Such arrangement is similar to what was reported for rice straw; Felycia Edi et al. 2013. Fig. 2. SEM micrograph of Rosmarinus officinalis biowaste. 3.2. Effect of initial pH The initial pH of metal and dye solutions has been recognized by many authors as the major parameter controlling metal and dye adsorption processes (Biswajit et al. 2013). This is mainly due to the fact that protons are strong competing adsorbate ions and partly due to the chemical speciation of the metal ions and dye in solution and the fact that the pH of a solution influences the ionization of the functional groups of the adsorbents, hence consequently sets the surface charge of adsorbent (Lei et al. 2014; D. Bozic et al. 2009). The pHZPC plot for ROBW is shown in Fig.3 and was determined as 5.3. This indicates that at pH lower than pHpzc the surface of adsorbent will be positively charged, and it will be negatively charged if the pH is made greater than the pHpzc (I.D. Mall et al. 2006; Milan et al. 2013; Dahu et al. 2013). Fig. 3 Point of zero charge (pHpzc) curve of ROBW. Investigation of the effects of initial pH on the adsorption of the dye is important because industrial dye wastewater is discharged at a pH that differs from the environmental pH (A.A Jalil et al. 2012). In this study, the effects of initial pH on MB adsorption capacity and removal efficiency using ROBW adsorbent were evaluated, and the results were illustrated in Fig. 4. The uptake of MB is low under conditions that are highly acidic and become higher as the pH increases reaching a maximum at pH 8 (see Fig. 4. a), the maximum adsorption capacity reaches (45.49 mg/g) while the maximum removal efficiency reaches (72.78 %). Further increase in the pH shows no significant change. The H+ ions effectively competed with the MB cations, which caused dye uptake to reduce at low pHs, when the pH increases, competing effect of hydronium ions for binding sites on ROBW surface decreased, so the retention is favored. Furthermore at pH higher than the pHzpc, the negative charge density at the adsorbent surface increases hence positively charged MB uptake increases. Similar observation was also reported in literature (Biswajit et al. 2013; V. Ponnusami et al. 2008). In order to continue this work, the pH value for the rest of the experiments was fixed at 8, as 8 being an intermediate value of acidity of the optimized pH range. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Fig. 4 Effect of initial pH on the adsorption capacity and removal efficiency for MB (a) and Pb(II) (b) of ROBW. The effect of the pH on the Pb(II) biosorption onto the ROBW was evaluated, and the results were illustrated in Fig. 4. b. It can be observed, that the biosorption of Pb(II) is highly pH-dependent, The uptake of Pb(II) ions is low under highly acidic conditions (qe=1.82 mg/g and R%= 8.72 %) and increases as the pH increases, the maximum adsorption capacity of ROBW for Pb(II) reaches (19.90 mg/g) and the removal efficiency of Pb(II) reaches the optimum value of (95.5%) at pH 5. Low adsorption capacities observed for Pb(II) ions in high acidic medium may be due to the fact that hydrogen ion strongly compete with Pb(II) for binding sites on the adsorbent. As solution pH increases, the hydrogen ion concentration of the solution decreases, there by competing effect of hydronium ions for binding sites on ROBW surface decreased, so Pb(II) uptake was increased (Augustine. 2009). Another aspect that must be considered is the dissociation degree of functional groups from biosorbent surface which increases as the pH increases and so does the number of negatively charged sites, and in consequence, the number of electrostatic interactions will increase, so this increases Pb(II) uptake (Dumitru et al. 2012). This is in accordance with the earlier observations of Ali Gundogdu et al. 2009, and D. Božić et al. 2009. In order to continue this work, the pH value for the rest of the experiments was fixed at 5 since experiments could not be conducted beyond pH 6.0 to avoid precipitation of Pb(II) ions as Pb(OH)2. From an engineering point of view, it is important to note that the stripping of adsorbed metal from the loaded ROBW can be performed by high acidic solutions, transferring the adsorbed heavy metals from the adsorbent back into the aqueous phase. 3.3. Effect of particle size In order to see how adsorbent particle size affects the MB and Pb(II) uptake, a series of experiments was performed using different particles size (63-500 µm) keeping the other parameters constant as indicated in table 1. MB or Pb(II) uptake versus particle size adsorbent are represented in Fig. 5. Fig. 5. Influence of the ROBW particle size on the uptake of MB (a) and Pb(II) (b). Fig. 5 show that there is no remarkable change on the capacity uptake when the particle size change, so the uptake can be considered as being independent of particles size as indicated by some authors (Noureddine et al. 2013; Yanfang et al. 2013). This phenomenon 9 can be explained by the specific shape of the particles which was flaky, as shown in the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 optical photograph (see Fig. 6). Therefore, this geometrical surface for these particular particles is higher than spherical particles of the same volume. Changing the particle size in the chosen sieve fractions, particles size range from 63 to 500 µm, does not change significantly the real surface area and the adsorption degree remains almost constant with changing particles size. Such arrangement is similar to what was reported by D. Božić et al. 2009. Fig. 6. Optical photograph of the Rosmarinus officinalis waste: particle size < 100 µm. 3.4. The effect of contact time and biosorption kinetics The results of sorption studies, carried out as a function of contact time, for MB and Pb(II) were presented in Fig. 7. The initial high rate of adsorption of metal ions is due to free active binding sites on the surface of the adsorbent. As the number of available sites decrease the rate of adsorption of metal ions also decreases. It suggested that the removal of MB or Pb(II) by the ROBW adsorbent took place in two distinct steps: a relatively quick phase, followed by a slow increase until the equilibrium was reached. The necessary time to reach the equilibrium was about 60 min. Though there was a slight increase of adsorption quantity after 60 min, it did not bring any remarkable effect, so a contact time of 60 min was selected for all further studies. Fig. 7. Effect of contact time on the adsorption capacity for MB (a) and Pb(II) (b) by ROBW. The kinetics of the ROBW-adsorbate interactions was tested with different kinetic models including pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The pseudo-first-order equation is among the most widely used to predict metal and dye adsorption experiments (Gholamreza and Rasoul. 2011; Ali et al. 2009; A. Ozer. 2007; Muhammad et al. 2009). The model has the following form: 𝑑𝑞 = 𝐾1 (𝑞𝑒 − 𝑞𝑡 ) 𝑑𝑡 Where qt (mg/g) is the adsorption capacity of adsorbate adsorbed at time t, qe is adsorption capacity of adsorbate adsorbed at equilibrium (mg/g), and k1 is the rate constant of the adsorption (min−1). After definite integration by applying the conditions qt=0 at t=0 and qt=qt at t=t, it turns into the following equation: ln(q e − q t ) = lnq e − K1 t 10 Straight line in the graph (see Fig. 8) of ln (qe−qt) versus (t) can suggest the applicability of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 this kinetic model, qe.cal and k1 are determined from the intercept and slope of the plot, respectively and presented in table 2. The pseudo-first-order data do not fall on straight lines. The correlation coefficient is less than 0.88, which is indicative of a poor correlation and the theoretical qe,cal values found from this model is not in a good agreement with the experimental qe,exp. Values. Therefore, the pseudo-first-order model is not suitable for modeling the biosorption of MB and Pb(II) onto ROBW. The pseudo-second-order kinetic model is in the following form 𝑑𝑞 = 𝐾2 (𝑞𝑒 − 𝑞𝑡 )2 𝑑𝑡 Where k2 (g/mg.min) is the rate constant of the second order equation; qt (mg/g) the adsorption capacity at time t (min), and qe (mg/g) is the adsorption capacity at equilibrium. After definite integration by applying the conditions qt=0 at t=0 and qt=qt at t=t the equation above turns into the following: t 1 1 = t+ qt qe K 2 q2e The plot of t/qt versus (t) should give a straight line if second order kinetics is applicable, and qe and k2 can be determined from slope and intercept of the plot, respectively (Ali et al. 2009; E.I. El-Shafey et al. 2010; I.D. Mall et al. 2006). The linear plot of t/qt versus t for the pseudo-second-order kinetic model is shown in figure 8. The pseudo-second-order rate constant k2 and the value of qe were determined from the model and are presented in table 2. The value of correlation coefficient is close to 1, and the theoretical qe,cal values found from this model is closer to the experimental one qe,exp value. In view of these results, It can be said that the adsorption process of MB or that of Pb(II) onto ROBW follow pseudo-second order kinetic model which implies that the chemical binding reaction is the rate-limiting step. Several other adsorption studies using biosorbent such as B.H. Hameed et al. 2008 and Azlan et al. 2014, showed that the adsorption process followed the pseudo-second order kinetic model. The kinetic rate models mentioned above could not identify the diffusion mechanism, hence the obtained results were further analyzed by using the intraparticle diffusion model expressed as: 𝑞𝑡 = 𝐾𝑖𝑑 𝑡1/2 + 𝐶 11 Where qt (mg/g) is the adsorption capacity at time t(min), and Kid (mg/g.min) is the rate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 constant of intraparticle diffusion. A straight line in the graph of qt versus t½ suggests the applicability of the intraparticle diffusion model. Kid and C can be determined from the slope and intercept of the plot, respectively (Ali et al. 2009; Md. Motiar et al. 2011). The intraparticle rate constant Kid and C parameters were obtained from the plot of qt versus t½ and the results are given in table 2. The correlation coefficient obtained from the model is not satisfactory, indicating that the intraparticle diffusion model may not be the controlling factor in determining the kinetics of the process. This is consistent with the nonporous structure previously identified by the SEM analysis. Fig. 8. Pseudo-first-order (1) and pseudo-second-order (2) models for the adsorption onto ROBW. Tab. 2. Adsorption kinetic parameters of Rosmarinus officinalis waste. 3.5. Biosorption isotherms Adsorption isotherm describes the relationship between the amount of the adsorbate adsorbed at equilibrium by adsorbent and the equilibrium concentration of adsorbate in the solution, which is the most important piece of information in understanding an adsorption process (Fei et al. 2011). They are characterized by certain constants and describe the mathematical relationship between the quantity of adsorbate and concentration of adsorbate remaining in the solution at equilibrium. There are several isotherm equations describing the equilibrium and the most common of them are Langmuir, Freundlich, Temkin and DubininRadushkevish models. In the present investigation, this four adsorption models were employed for adsorption isotherm modeling of the experimental data (A. Ozer. 2007; Jonathan et al. 2009). Linear regression is used to determine the best-fitting isotherm and the applicability of isotherm equations is compared by judging the correlation coefficients, R2. Langmuir isotherm is based on two assumptions that the forces of interaction between adsorbed molecules are negligible and once a molecule occupies a site no further sorption takes place. The linear form of Langmuir model can be described as follows: Ce 1 1 = Ce + q e q max q max K L Where qe (mg/g) is the absorption capacity of MB or Pb(II) adsorbed per unit weight of ROBW, Ce (mg/L) is equilibrium concentration of solute, qmax (mg/g) indicates the monolayer adsorption capacity of ROBW and the Langmuir constant KL (L/mg) is a direct measure of the intensity of adsorption and it can be calculated from the plot of Ce/qe versus 12 Ce. The feasibility of adsorption onto ROBW was further analyzed using a dimensionless 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 1 parameter: R L = 1+K L Ci where Ci (mg/L) is the initial concentration of MB or Pb(II) ions and KL (L/mg) is the Langmuir isotherm constant. The adsorption process can be defined as irreversible irreversible (RL = 0), favourable (0< RL <1), linear (RL =1) or unfavourable (RL >1) (Chun-Shui et l. 2009). Freundlich isotherm is an empirical equation based on sorption on a heterogeneous surface or surface supporting sites of varied affinities (Jonathan et al. 2009). The linear form of Freundlich is given by the following equation: 1 log q e = logK F + log Ce n Where KF (mg/g) and 1/n (L/g) are Freundlich constants, related to adsorption capacity and adsorption intensity, respectively. KF and 1/n can be calculated from the plot of log qe versus log Ce. Dubinin-Radushkevich (D–R) isotherm model were applied to determine the sorption type (physical or chemical sorption), which is more general than the Langmuir model because it does not require homogenous sorption sites or constant sorption potential. The linear from of the model is described as; 𝐿𝑛 𝑞𝑒 = 𝐿𝑛 𝑞𝑚𝑎𝑥 − Bε2 ε is the Polanyi potential which is equal to: ε = 𝑅𝑇 𝐿𝑛 (1 + 1 ) 𝐶𝑒 The plot of lnqe vs. ε2 (figure not shown) should give a straight line from which the values of B and qmax for ROBW were calculated. Using the value of B, the mean sorption energy, E (kJ/mol), was evaluated as: 𝐸= 1 √−2𝐵 This parameter gives information about chemical or physical sorption. The magnitude of E is between 8 and 16 kJ/mol, the process follows chemical sorption, while for the values of E < 8 kJ/mol, the process is of a physical nature (Chun-Shui et l. 2009; Augustine. 2010). Temkin isotherms describe certain adsorbent/adsorbate interaction on adsorption isotherms. Temkin isotherm suggested that the heat of adsorption of all the molecules in the layer would decrease linearly with coverage because of those interactions. The Temkin model is given by: 13 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 𝑞𝑒 = 𝑅𝑇 𝑅𝑇 . 𝐿𝑛 𝐴 + . 𝐿𝑛 𝐶𝑒 𝑏 𝑏 Where b refers to the Temkin constant related to heat of sorption (kJ mol−1), A to the Temkin isotherm constant (L g−1), R to the gas constant (8.3145 J mol−1 K−1), and T to the absolute temperature (K). The A and b constants were determined from the slope and intercepts of the plots obtained by plotting qe versus Ln Ce (figure not shown) and are listed in Table 3. Isotherms parameters with correlation coefficients R2 for the adsorption of MB and Pb(II) onto ROBW were summarized in table 3. From the comparison of the R2 values, it was evident that for the studied systems, the Langmuir model is very suitable to describe the adsorption behavior for both MB and Pb (II) ion. Furthermore, the theoretical saturated adsorption capacities simulated using the Langmuir model; 52.63 and 43.47 mg/g for MB and Pb2+ ions, respectively, are very close to the experimental results. Moreover, the calculated values of RL fall between 0 and 1, which indicate the favourable adsorption of MB and Pb2+ ions by ROBW. The adsorbent surface is therefore said to be homogeneous in terms of surface functional groups and bonding energy with no side interactions with the adsorbed ions and/or molecule. It also assumes that the interactions take place by adsorption of one ions or molecule per binding sites. Fig. 9. Langmuir (a) and Freundlich (b) isotherm models for the adsorption of ROBW. Tab. 3. Adsorption isotherm parameters of R. officinalis waste. Tab. 4. Comparison of adsorption capacities of various adsorbents for MB and Pb(II) ions. As comparison, the maximum adsorption capacities of several biomass-based sorbents for sequestering MB and Pb(II) from water are listed in Table 4. Nonetheless, this comparison is not precise, since the experimental conditions are different. It is apparent that the adsorption capacity of ROBW was comparable with other adsorbents. Moreover, it is worth to emphasize that sorbent used in this work has not been modified chemically and can still successfully compete with other biomass-based sorbents which some of them have been processed which would increase the adsorbent cost. 3.6. Thermodynamic parameters The thermodynamic parameters were evaluated to investigate the nature of the adsorption of MB and Pb2+ onto ROBW. The adsorption enthalpy (ΔH°), entropy (ΔS°) and Gibbs free energy (ΔG°) were calculated using the following thermodynamic functions: 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 𝛥𝐻 ° 𝛥𝑆 ° + 𝑅𝑇 𝑅 𝐶𝑒 (𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑛𝑡) 𝐿𝑛 𝐾𝐶 = 𝐶𝑠 (𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛) 𝐿𝑛 𝐾𝐶 = − ΔG° = −𝑅𝑇 𝐿𝑛 𝐾𝐶 Where Kc; is the equilibrium constant of the adsorption. Cs is the concentration of the adsorbate on adsorbent (mg/L) and Ce is the equilibrium concentration of adsorbate (mg/L) (A.A. Jalil et al. 2012). R is the universal gas constant (8.314 J/mol.K), T is the absolute temperature (K). Enthalpy and entropy values of adsorbate were obtained from the plot of ln Kc versus 1/T (see figure 10) which resulted in a straight line with a slope of (-ΔH°/R) and an intercept of (ΔS°/R). From table 5, the overall ΔG° during the adsorption was negative for the range of temperatures investigated, which indicate that the process is feasible and the adsorption is spontaneous with high preference of MB and of Pb(II) for the ROBW. Increasing temperature from 20 to 40 °C (293–313 °K) for 250 mg/L of MB and for 400 mg/L of Pb(II), led to a more negative value of ΔG°, indicating that higher temperatures energetically favor the feasibility and spontaneity of the biosorption process. This may be attributed to the faster mobility of solute molecules in the solution at elevated temperatures that enhanced their adsorptivity toward the biomass surface (Yan-Ru et al. 2013). The positive value of ΔH° suggests that the adsorption process was endothermic (Mohd Shaiful et al. 2013) which was also supported by the increase in adsorption capacity for ROBW with the increase in temperature (see table 5), and that the magnitude (25.71 kJ mol-1 for the BM and 21,74 kJ mol-1 for the Pb(II), respectively) was in the heat range of physisorption (<40 kJ mol1 ) (A.A. Jalil et al. 2012). This is consistent with previous work reported on the adsorption of noxious chromium on acrylic acid grafted lignocellulosic adsorbent (Vinod Kumar et al. 2013), lead(II) on Viscum album L (Saliha and Emine. 2007), malachite green (MG) on bivalve shell-treated Zea mays L (A.A. Jalil et al. 2012), and methylene blue on chemically modified Ficuscarica adsorbent (Mohd Shaiful et al. 2013). The positive value of ΔS° suggested increase randomness at the solid/solution interface during the fixation of the adsorbate on the active sites of the adsorbent which indicates that the affinity of ROBW toward the considered adsorbent was high. This was due to the fact that before the adsorption process starts, the adsorbate ions in solution are heavily solvated and the system becomes more ordered. The adsorbed water molecules, which are displaced by the adsorbate species, gain more translational energy than when is lost by the adsorbate ions, thus allowing the prevalence of randomness in the system (Bulut and Tez. 2007). 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Fig. 10. Plot of ln KC versus 1/T for the adsorption of MB and Pb(II) ions onto R. officinalis waste. Tab.5. Thermodynamic parameters for the MB and Pb(II) removal by using R. officinalis waste. 3.7. Effect of adsorbent dosage The amount of pollutant per unit mass of adsorbent removed from a fixed concentration and fixed volume of polluted water is known to depend on the mass of adsorbent used (Augustine et al. 2010). Fig.11 shows the effect of ROBW dose on MB and Pb (II) adsorption. The results of the study indicated that with the increased adsorbent doses the removal percentage of adsorbate increased to reach a plateau. Increasing the ROBW dose would increase the number of available adsorption sites, thereby resulting in the increase in removal percentage of MB or Pb(II) ions, as already reported in several papers (Augustine et al. 2010; S. Larous et al. 2005). On the other hand, increasing the mass of ROBW in contact with a fixed concentration and fixed volume of adsorbate solution caused a reduction in the qe values mg/g. The negative effect on sorption capacity might be due to the binding of almost all adsorbate to the sorbent at higher adsorbent dose and the establishment of equilibrium at lower values of qe indicating the adsorption sites remains unsaturated (Shaik et al. 2009). Another reason might be due to the particle interaction, such as aggregation, resulting from high adsorbent dose. Such aggregation would lead to decrease total surface area of the adsorbent and increase in diffusional path length (Hui et al. 2011; Sana et al. 2014) Fig. 11. Effect of Rosmarinus officinalis biowaste amount on the removal of MB (a) and Pb(II) (b). 3.8. Biosorption ability of ROBW for other heavy metals Wastewaters such as industrial effluents may contain large amounts of various heavy metal ions. Therefore, biosorption capacity of R. Officinalis was also tested for removal of the Cd(II), Cr(III) and Cu(II) ions from aqueous solution. The metal solutions with 500 mg.L−1 initial concentrations containing 4.0 g L−1 of ROBW were treated separately at pH 4.5, 4 and 5.5, respectively. The results showed that ROBW can efficiently remove Cd(II), Cr(III) and Cu(II) ion and it was more sensitive to Cd(II) ions than the others. The following order of metal uptake per unit weight of ROBW was observed: Cd2+ (58.82 mg.g−1) > Pb2+ (43.47 mg.g−1) > Cr3+ (35.71 mg.g−1) > Cu2+ (26.31 mg.g−1). 4. Conclusions The results of this study indicate that Rosmarinus officinalis biowaste obtained as by16 product from locally extraction industries of essential oils is an efficient, low-cost, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 environmental friendly bio-adsorbent and can be successfully used to remove heavy metals and dyes from aqueous solution. The obtained results showed that the adsorption of MB and Pb2+ by ROBW was fast, and equilibrium was achieved in less than 60 min. The adsorption was highly dependent on the pH of the solution and initial adsorbents concentration. The uptake can be considered as being independent of particles size. Modeling of the biosorption results indicated that the pseudo-second order model offers a better correlation of experimental kinetic data and Langmuir models is a suitable option for modeling the sorption isotherms of metal ions and dyes, giving maximum adsorption capacity of 52.63 mg/g and 43.47 mg/g at 20 °C, for MB and Pb (II) ions removal, respectively. The negative ΔG° values indicated that the adsorption process was feasible and spontaneous, and the positive values of ΔH° and ΔS, shows that the sorption process is endothermic in nature and there is high affinity of the adsorbent for the sorbate. 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Figure Correspondence to: Amel Chaabouni: [email protected] Figure 3: Point of zero charge (pHpzc) curve of ROBW. 3.5 3 2.5 pHi - pHf 2 1.5 1 0.5 0 -0.5 0 2 4 6 -1 -1.5 pHi 8 10 12 Figure Correspondence to: Amel Chaabouni: [email protected] Figure 4: Effect of initial pH on the adsorption capacity for MB (a) and Pb(II) (b) by ROBW. qe (mg/g) R% 80 100 (a) MB 80 60 R% qe(mg/g) 60 40 40 20 20 0 0 0 2 4 6 pH qe (mg/g) 8 10 12 R% 30 100 (b) Pb(II) 80 20 R% qe(mg/g) 60 40 10 20 0 0 0 1 2 3 pH 4 5 6 Figure Correspondence to: Amel Chaabouni: [email protected] Figure 5: Influence of the ROBW particle size on the adsorption of MB (a) and Pb(II) (b). (a) MB 50 qe(mg/g) 40 30 20 10 0 63-80 80-100 100-125 125-315 315-500 Q(µm) (b) Pb(II) 20 qe(mg/g) 15 10 5 0 X<63 63<X<100 100<X<125 Q(µm) 125<X<150 150<X315 315<X<400 Figure Correspondence to: Amel Chaabouni: [email protected] Figure 6: Optical photograph of the Rosmarinus officinalis waste: particle size < 100 µm. Figure Correspondence to: Amel Chaabouni: [email protected] Figure 7: Effect of contact time on the adsorption capacity for MB (a) and Pb(II) (b) by ROBW. 50 (a) MB 40 qt(mg/g) 30 20 10 0 0 60 120 180 240 300 360 420 480 t(min) 25 (b) Pb(II) 20 qt(mg/g) 15 10 5 0 0 60 120 180 t(min) 240 300 Figure Correspondence to: Amel Chaabouni: [email protected] Figure 8: pseudo-first-order (1) and pseudo-second-order (2) models for the adsorption of ROBW. 12 14 (1) MB 10 10 8 8 t/qt t/qt (1) Pb(II) 12 6 6 4 4 2 2 0 0 0 100 200 300 400 500 0 600 50 100 t (min) 150 200 250 300 t(min) 2 5 (2) MB 4 Ln (qe-qt) Ln (qe-qt) (2) Pb(II) 3 2 1 1 0 0 0 100 200 300 t (min) 400 500 600 0 200 400 600 t (min) 800 1000 1200 1400 Figure Correspondence to: Amel Chaabouni: [email protected] Figure 9: Langmuir (a) and Freundlich (b) isotherm models for the adsorption of ROBW. 7 14 (a) MB (a) Pb(II) 12 5 10 4 8 Ce/qe Ce/qe 6 3 6 2 4 1 2 0 0 0 100 200 300 0 400 100 Ce (mg/L) 200 300 400 500 600 0.15 0.2 0.25 Ce (mg/L) 3 3 (b) MB 2.5 2.5 (b) Pb(II) 2 2 log qe log qe 1.5 1 1.5 1 0.5 0 0 0.5 1 1.5 0.5 2 -0.5 0 -1 -0.05 log Ce 0 0.05 0.1 log Ce Figure Correspondence to: Amel Chaabouni: [email protected] Figure 10: Plot of ln KC versus 1/T for the adsorption of (a) MB and (b) Pb(II) ions onto R. officinalis waste. 1.80 1.60 1.40 (a) MB 1.20 Ln Kc 1.00 0.80 0.60 0.40 0.20 0.00 0.00315 0.00320 0.00325 0.00330 0.00335 0.00340 0.00345 0.00335 0.00340 0.00345 1/T 0.80 0.70 (b) Pb(II) 0.60 Ln Kc 0.50 0.40 0.30 0.20 0.10 0.00 0.00315 0.00320 0.00325 0.00330 1/T Figure Correspondence to: Amel Chaabouni: [email protected] Figure 11: Effect of Rosmarinus officinalis biowaste amount on the removal of MB (a) and Pb(II) (b). R% 100 80 80 60 60 40 40 20 20 0 0 qe (mg/g) 100 0 300 5 10 CW (g/L) qe (mg/g) (b) Pb (II) 15 R% qe (mg/g) (a) MB 20 R% 100 90 250 80 70 60 150 50 40 100 30 20 50 10 0 0 0 1 2 3 4 CW (g/L) 5 6 7 8 9 R% qe(mg/g) 200 Table Nomenclature: Nomenclature A Temkin isotherm constant (L/g) b Temkin sorption energy (Kj/mol) Ci initial MB / Pb(II) concentrations (mg/L) Ct MB / Pb(II) concentrations at time t of reaction (mg/L) Ce MB / Pb(II) concentrations at equilibrium time (mg/L) E D-R sorption energy (kJ/mol) kid constant of intraparticle diffusion (mg/(gmin0.5)) k1 pseudo-first order rate constant (1/min) k2 pseudo-second order rate constant (mg/g.min) kid intraparticle diffusion the rate constant (mg/g.min) kL Langmuir constant (L/mg) KDR D–R constant (mol2/kJ2) KF Freundlich constant (L/mg) Kc=Cs/Ce the thermodynamic equilibrium constant n Freundlich reciprocal of reaction order qt adsorption capacity at time t (mg/g) qe adsorption capacity at equilibrium conditions (mg/g) qmax maximum adsorption capacity (mg/g) R2 correlation coefficient R% removal efficiency R gas constant (8.314 J/(mol.K)) T absolute temperature (°C) or (K) V volume of the MB solution (L) W mass of ROBW added to the solution (g) ε Polanyi potential (J/mol) ΔG° changes of Gibbs free energy Table Correspondence to: Amel Chaabouni: [email protected] Table 1: Experimental runs and conditions. Experiment Conditions pHi WROBW (g/L) Ø µm t (min) [MB] (mg/L) [Pb2+] (mg/L) 2-10 4 100-125 120 250 *** 20 Effect of ROBW dose 8 1-16 100-125 120 250 *** 20 Effect of particle size 8 4 63-500 120 250 *** 20 Effect of contact time 8 4 100-125 10-480 250 *** 20 Effect of MB concentration 8 4 100-125 60 10-500 *** 20 Effect of temperature 8 4 100-125 60 10-500 *** 20-40 2-5 4 100-125 240 *** 100 20 Effect of ROBW dose 5 0.04-40 100-125 240 *** 100 20 Effect of particle size 5 4 63-400 240 *** 100 20 Effect of contact time 5 4 100-125 10-240 *** 100 20 Effect of Pb(II) concentration 5 4 100-125 30 *** 50-800 20 Effect of temperature 5 4 100-125 30 *** 50-800 20-40 Effect of initial pH Effect of initial pH T (°C) Table Correspondence to: Amel Chaabouni: [email protected] Table 2: Adsorption kinetic parameters of Rosmarinus officinalis waste. Adsorbate qeq,exp (mg/g) Pseudo-first-order Intraparticle Pseudo-second-order Diffusion k1 (min−1) qeq,cal (mg/g) R2 k2 (g/mg.min) qeq,cal (mg/g) R2 Kid R2 MB 43.95 0.005 17.09 0.715 0.0016 45.45 0.997 0.202 0.691 Pb(II) 20.19 0.0008 05.72 0.884 0.0159 20.40 1.000 0.027 0.827 Table Correspondence to: Amel Chaabouni: [email protected] Table 3. Adsorption isotherm parameters of R. officinalis waste. Langmuir Freundlich R-D Temkin Adsorbate qmax(mg/g) KL (L/mg) RL range R2 n KF (L/mg) R2 qmax DR E (KJ/mol) R2 b (KJ/mol) A (L/g) R2 MB 52.63 0.14 0.014-0.41 0.998 0.58 0.80 0.738 27.22 1.11 0.759 0.312 3.19 0.891 Pb(II) 43.47 0.053 0.030-0.27 0.979 0.43 0.43 0.721 33.75 0.50 0.883 0.435 3.39 0.933 Table Correspondence to: Amel Chaabouni: [email protected] Table 4. Comparison of adsorption capacities of various adsorbents for MB and Pb(II) ions. Methylene blue dye (MB) Biosorbent Sugar spent rice biomass** Brazilian pine-fruit shell Brazilian pine-fruit shell** Pistachio hull Jerusalem artichoke stalk** Kenaf fibre char peanut hull** Wheat straw ** Maize stem ** Raw pine cone teawastages SalviniaMinima biowaste coconutbunchwaste R. officinalis biowaste Lead Pb (II) Solute coconut dregsresidue Sawdust of walnut Pine bark wheat bran** Sugarcane bagasse Sugarcane bagasse ** Mango peel waste Dried cactus Green algae waste biomass R. officinalis biowaste Operational condition T pH* (°C) -- 25 8.5 25 8 3.7 8.5 3.5 10 6 9.2 8 8 7 8 20 20 30 25 20 25 30 25 25 30 20 7 -4 6 -25 -25 5 25 5 3.5 5 5 25 25 20 20 Adsorption capacity (mg/g) 8.3 185 413 389 363.6 18.18 108.6 132.2 160.84 129.87 173.36 174.75 74.82 52.63 9.74 15.90 76.8 55.56 6.366 7.297 96.32 98.62 66.24 43.47 Note: ∗ pH value corresponds to maximum adsorption capacity. ** The biowaste has undergone a phisico-chemical modification before being used as an adsorbent Ref. Muhammad et al. 2012 Betina et al. 2009 Gholamreza et al. 2011 Lei and Yong-ming. 2014 Dalia et al 2012 Dursun et al. 2007 Wenxuan et al. 2012 Vesna et al. 2014 Mustafa et al. 2013 Masoud et al. 2011 Gloria et al. 2014 B.H. Hameed et al. 2008 This study Azlan et al. 2014 Bulut and Tez. 2007 Ali et al. 2009 A. Ozer. 2007 María Ángeles et al. 2010 Muhammad et al. 2009 Noureddine et al. 2013 Dumitru et al. 2012 This study Table Correspondence to: Amel Chaabouni: [email protected] T°K qeq (mg.g-1) KC ΔG° (Kj.mol-1) ΔH° (Kj.mol-1) ΔS° (j.mol-1K-1) MB 293 303 313 45.26 49.32 52.34 2.63 3.74 5.15 -2.39 -3.26 -4.06 25.71 95.77 Pb(II) Table 5. Thermodynamic parameters for the MB and Pb(II) removal by using R. officinalis waste. 293 303 313 34.96 43.27 48.43 1.17 1.65 2.06 -0.38 -1.25 -1.88 21.74 75.59 Cover Letter Click here to access/download Supplementary Material Cover letter.docx