ION EXCHANGE EQUILIBRIUM STUDIES OF Pb 2+ AND Cu 2+ ON NATURAL CLINOPTILOLITE, BENTONITE AND VERMICULITE

Size: px

Start display at page:

Download "ION EXCHANGE EQUILIBRIUM STUDIES OF Pb 2+ AND Cu 2+ ON NATURAL CLINOPTILOLITE, BENTONITE AND VERMICULITE"

Solomon Abel Sharp
5 years ago
Views:

1 ION ECHANGE EQUILIBRIUM STUDIES OF Pb 2+ AND Cu 2+ ON NATURAL CLINOPTILOLITE, BENTONITE AND VERMICULITE M.A. Stylianou 1, V.J. Inglezakis 2 and M. Loizidou 3 1 University of Cyprus, Department of Civil & Environmental Engineering, NIREAS-International Water Research Center, Subsurface Research Laboratory, Nicosia, Cyprus 2 Nazarbayev University, School of Engineering, Chemical Engineering Department, Astana, Republic of Kazakhstan 3 National Technical University of Athens, School of Chemical Engineering, Unit of Environmental Science and Technology (UEST), Athens, Greece Keywords: Clinoptilolite; Bentonite; Vermiculite; Heavy metals; Ion exchange; Isotherms; Equilibrium Presenting author stylianou.a.marinos@ucy.ac.cy Abstract In the present study ion exchange of Pb 2+ and Cu 2+ on natural minerals is examined. Three different natural minerals were used, zeolite (clinoptilolite, -5mm), vermiculite (-5mm) and bentonite (montmorillonite) (<9μm). Equilibrium studies were conducted in batch mode under the same normality for both metals (.1 N). The equilibrium isotherms for the metals studied showed that in the case of lead, all minerals exhibit a favourable-type isotherm; and in the case of copper, clay minerals exhibit favourable-type isotherms but zeolite exhibit a linear and sigmoid type isotherm (changing from favorable to unfavorable equilibrium for values of normalized concentration close to.25.3) respectively. Furthermore, it is concluded that all studied isotherms follow the selectivity order: Bentonite>Zeolite>Vermiculite. According to the equilibrium isotherms, the selectivity series are: (i) Zeolite: Pb > Cu, (ii) Bentonite: Pb > Cu and (iii) Vermiculite: Cu > Pb. The Langmuir and Freundlich models were applied and fitted the equilibrium data for the metal ion uptake. Keywords: clinoptilolite; bentonite; vermiculite; copper; lead; ion-exchange; equilibrium; 1. Introduction Natural minerals, such as clays and zeolites, are used as ion exchangers due to their high ion exchange capacity. Ion-exchange properties of clay minerals and zeolites, have long been known. Bentonite, vermiculite and zeolites are natural aluminosilicates. Bentonite mostly consists of 8% montmorillonite forms crystals of the smallest size of all clay minerals. Zeolites have an open, three-dimensional framework structure with pores (channels) and interconnecting cavities in the aluminosilicate lattice. Clays such as bentonite and vermiculite have a looser layer structure than zeolites [1, 2]. Ion exchangers are characterized by their equilibrium behavior, which is dependent on the initial solution concentration (normality), ph and temperature [3]. A common way to represent the equilibrium in adsorption and ion-exchange systems is the equilibrium isotherm. The equilibrium isotherm represents the

2 distribution of the adsorbed material between the adsorbed phase and the solution phase at equilibrium. This adsorption isotherm is characteristic for a specific system at a particular temperature. It should be underlined that for ion exchange systems, specific system represents one equilibrium curve only under constant temperature and normality [1]. The sorption on zeolitic particles is a complex process due to their porous structure, inner and outer charged surfaces, mineralogical heterogeneity, existence of crystal edges, broken bonds, and other imperfections on the surface. The most commonly used Langmuir isotherm defines the equilibrium parameters of homogenous surfaces, monolayer adsorption and distribution of adsorption sites. The Langmuir and Freundlich adsorption models are widely used because they are convenient to describe experimental results in a wide range of concentrations [4]. The aim of this study is to present equilibrium experimental data and simplified isotherm models for Pb 2+, Cu 2+ exchange on natural clinoptilolite, bentonite and vermiculite. Also selectivity series deduced from equilibrium isotherms and maximum exchange level (MEL) data are compared for both metals and all three minerals. 2. Materials and methods 2.1. Samples and Characterization Three different natural minerals were used in this study, zeolite (clinoptilolite, -5mm), vermiculite (-5mm) and bentonite (<9μm). Zeolite and bentonite were supplied by S&B Industrial Minerals SA and vermiculite by IGME (Institute of Geology & Mineral Exploration). Clinoptilolite and vermiculite were crushed and milled into powder (<9μm) for further analysis. The chemical composition of the materials was obtained through RF analysis with the use of an ARL Advant P sequential RF (Table 1). Table 1. Chemical composition of mineral samples. Zeolite Bentonite Vermiculite %w/w %w/w %w/w SiO2 7 55,9 47 Al2O3 12, 18, 16,6 Fe2O3,727 3,85 12,3 CaO 3,4 3,63,575 MgO,765 3,53 21,6 Na2O,34 3,52 -- TiO2 13,76,922 K2O 3,31,611,35 LOI 9,45 8,75 -- LOI: mass loss upon firing at 11 o C 2.2. Equilibrium isotherms studies

3 Equilibrium studies were conducted as follows. A measured quantity of zeolite, bentonite and vermiculite (Table 2) were added to a vessel containing 1 ml of metal solution under.1 N normality. Every 1 to 2 days the solution was analyzed for metal concentrations until no further uptake from the minerals was observed. Total sampling volume was 2% of the total solution volume. The exchange temperature was kept constant during the batch reaction time at 27 ± 1 C. Final ph was recorded and in all cases, it was found to be lower than 5, indicating that no precipitates were formed. All chemicals used were analytical grade reagents and high-purity deionized water. ph was initially adjusted to 4 in order to avoid precipitation during all ion exchange experiments by using HNO 3. The concentration of metal ions is measured by AAS, using a Perkin Elmer Model 238 spectrophotometer. The mean standard error of concentration measurements was 1.5±1%. Table 2. Measured quantities of minerals used for equilibrium isotherm studies Clinoptilolite Bentonite Vermiculite (g) Pb (9) * (9).5-3. (12) Cu.1-12 (14).1-4 (13).1-12 (14) *(9) Number of samples in that range 2.3. Maximum exchange level Maximum exchange level (MEL) of ion-exchange materials was measured using the repeated equilibrations method [5]. MEL studies (repeated batch equilibrations) were conducted as follows: a measured quantity of mineral (.2 1. g) was added in a vessel containing measured volume of metal solutions (1 ml) at initial concentration of.1n, with ph initial adjustment, as above. Every 7 days the solution was analyzed for metal concentrations and then replaced with fresh solution of the same metal, until no further uptake from the mineral was observed. The term Maximum Exchange Level is introduced for the upper limit (saturation) equilibrium loading [6]. 3. Results and discussion 3.1. Equilibrium experiments Equilibrium isotherms The equilibrium isotherms for the metals studied are presented in Fig. 1, where (=C eq /C o ) is the reduced concentration of metal in the liquid phase, in respect to initial metal concentration, and (=q eq /q o ) the relative equilibrium concentration of metal in the solid phase, in respect to the MEL for the specific metal. It can be seen that equilibrium: is strongly favorable for Pb 2+, for all three samples, and with the order: bentonite>zeolite>vermiculite is strongly favorable for Cu 2+, in the case of bentonite, favorable in the case of vermiculite, and linear in the case of zeolite. The selectivity order is: bentonite>vermiculite>zeolite

4 1 1,9,9,8,8,7,7,6,6,5 -Z,5 -Z,4,3 -B -V,4,3 -B -V,3,4,5,6,7,8,9 1,3,4,5,6,7,8,9 1 (a) (b) Figure 1. Normalized isotherms for (a) Pb 2+, (b) Cu 2+ According to the equilibrium isotherms, the selectivity order is: For clinoptilolite samples is Pb > Cu which is the same in all reported equilibrium isotherm studies in the literature [4, 7-9]. For bentonite samples the differences between Pb and Cu isotherms are minimal. The selectivity is Pb > Cu which is the opposite to the reported results in the literature [1]. For vermiculite samples selectivity is following the order: Cu > Pb for >.4 and the opposite for <.4 which is in agreement with similar experiments in the literature [11]. Observed differences in the published equilibrium data are considered to be connected with both the specifics of ion exchange material and the differences in the experimental techniques used. For instance, the dependence of equilibrium isotherms and selectivity upon the concentration of the solution is well known [5, 9]. In order to compare different metals, based on equilibrium isotherms, the same normality for all metals should be used, for the same exchanger at the same temperature, which is not the case for a number of relevant studies [9]. 1 1,9,9,8,8,7,7,6,6,5,5,4,3 Pb,4,3 Pb Cu Cu,3,4,5,6,7,8,9 1 (a),3,4,5,6,7,8,9 1 (b)

5 1,9,8,7,6,5,4 Pb,3 Cu,3,4,5,6,7,8,9 1 (c) Figure 2. (a) Zeolite; (b) bentonite and (c) vermiculite isotherms Maximum exchange levels In Table 3 the MELs of natural clinoptilolite, bentonite and vermiculite for the two metals studied are presented. The selectivity series deduced from MEL values follows the order bentonite>vermiculite>zeolite and is the only difference from the equilibrium isotherms derived series is for the case of Pb (zeolite> vermiculite); equilibrium isotherms are considered, however, a better tool for obtaining selectivity series. MEL is measured under intense conditions of repeated equilibrations, for close to and higher than.9, where according to the specific form of the isotherms, the curves may be closed and the local selectivity differences may be masked, due to the experimental error. Differences in series resulted from isotherms and MELs are also reported in the related literature [12]. Although it can be seen that MEL values; in the case of bentonite; for lead and copper are very close and this may explain the difference. Table 3. Minerals Maximum exchange level (MEL) Capacity (meq/g) Clinoptilolite Bentonite Vermiculite Maximum exchange level (MEL) Pb 1,668 ± 219 2,667 ±,31 1,974 ±,341 Cu,856 ± 44 2,6 ±,491 1,699 ±, Sorption Isotherms A common way to represent the equilibrium in adsorption and ion-exchange systems is the equilibrium isotherm. The equilibrium isotherm represents the distribution of the adsorbed material between the adsorbed phase and the solution phase at equilibrium. This isotherm is characteristic for a specific system at a particular temperature [1]. Freundlich and Langmuir isotherms are two of the most widely used equations, to describe solid-solution adsorption systems. Adsorbents that exhibit the Langmuir isotherm behavior are supposed to contain fixed individual sites, each of which equally adsorbs only one molecule, forming thus a monolayer, namely, a layer with the thickness of a molecule. Adsorbents that follow the Freundlich isotherm equation are assumed to have a heterogeneous surface consisting of sites with different adsorption potentials, and each type of site is assumed to adsorb molecules, as in the Langmuir equation. The isotherm relationships are [1]:

6 La La ( 1 La), C e, C o qe (1) q max Fr (2) where q e is the solid-phase concentration in equilibrium, q max is the capacity of the packing material (MEL in the case of ion exchange systems), C e is the equilibrium concentration of metal cations, Fr and La are the Freundlich and Langmuir constants. The parameter La is also called the separation factor and provides a quantitative description of the equilibrium regions: La= for irreversible, La<1 for favorable, La=1 for linear, ans La>1 for unfavorable adsorption. The same holds for Fr in Freundlich s isotherm [1]. In Figures 3 and 4, the fit of Freundlich and Langmuir isotherms on equilibrium experimental results are presented, and the following remarks can be concluded: Pb: It was found that Freundlich isotherm fitted the data better than Langmuir isotherm for zeolite and bentonite samples, but for vermiculite sample both models give good fit for the data. Cu: In the case of zeolite both models give good fit for the data for <.6, and are characterized as linear forms. In the case of bentonite Freundlich isotherm fitted the data better, but in the case of vermiculite (except Χ<) no model fits the data. Studies in the literature focused on clinoptilolite and heavy metals sowed that the Langmuir isotherm is mostly followed for Pb [13-16] and also for Cu [3, 17-18]. For bentonite samples similar studies also showed that the Langmuir isotherm is followed [19-2] for Cu and Pb ions. Furthermore, in the case of vermiculite Langmuir isotherm is followed in the case of Cu [18] and Freundlich isotherm in the case of Pb [21]. (a) (b)

7 (c) Figure 3. Isotherms Freundlich (Fr)-Langmuir (L) for Pb2+ (were Z=Zeolite, B=Bentonite, V=Vermiculite (a) (b) (c) Figure 4. Isotherms Freundlich (Fr)-Langmuir (L) for Cu2+ (were Z=Zeolite, B=Bentonite, V=Vermiculite Conclusions In the present study ion exchange equilibrium of Pb 2+ and Cu 2+ on natural clinoptilolite, bentonite and vermiculite is examined. The results showed that in the case of lead, all minerals exhibit a favourable-type isotherm. In the case of copper, clay minerals exhibit favourable-type isotherms but zeolite exhibit a linear and

8 sigmoid type isotherm. Furthermore, it is concluded that all isotherms studied follow the selectivity order of Bentonite>Zeolite>Vermiculite. According to the equilibrium isotherms, the selectivity series are: (i) Zeolite: Pb > Cu, (ii) Bentonite: Pb > Cu and (iii) Vermiculite: Cu > Pb. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms for the metal ion uptake. It was concluded that: (i) Pb: Freundlich model fitted the data better than Langmuir isotherm for zeolite and bentonite samples, but for vermiculite both models fitted the data well. (ii) Cu: In the case of zeolite both models fitted the data well for <.6, and are characterized as linear forms. In the case of bentonite Freundlich isotherm fitted the data better, but in the case of vermiculite (except Χ<) no model fits the data. References [1] V.J. Inglezakis, S.G. Poulopoulos, Adsorption, Ion Exchange and Catalysis, Design of Operations and Environmental Applications, Elsevier, (26) 1st ed., [2] P. K. de Bokx and H. M. J. Boots, The Ion-Exchange Equilibrium, J. Phys. Chem. 1989, 93, [3] A.Z. Woinarski, I. Snape, G.W. Stevens, S.C. Stark. The effects of cold temperature on copper ion exchange by natural zeolite for use in a permeable reactive barrier in Antarctica. Cold Regions Science and Technology (23) 37, [4] J. Peric, M. Trgo, N. Vukojevic Medvidovic, Removal of zinc, copper and lead bynatural zeolite - a comparison of adsorption isotherms, Water Research 38 (24) [5] F. Helfferich, Ion Exchange, Dover, New ork, 1995 [6] Vassilis J. Inglezakis, The concept of capacity in zeolite ion-exchange systems, Journal of Colloid and Interface Science 281 (25) [7] VJ Inglezakis, HP Grigoropoulou. Applicability of simplified models for the estimation of ion exchange diffusion coefficients in zeolites. J Colloid Interface Sci (21) 243: [8] S Kesraoui-Ouki, CR Cheeseman, R Perry. Natural zeolite utilization in pollution control: a review of applications to metal s effluents. J Chem Technol Biotechnol (1994) 9: [9] V.J. Inglezakis, M.D. Loizidou, H.P. Grigoropoulou, Equilibrium and kinetic ion exchange studies of Pb 2+, Cr 3+, Fe 3+ and Cu 2+ on natural clinoptilolite, Water Research 36 (22) [1] Gozen Bereket, Ayse Zehra Aroguz, Mustafa Zafer Ozel, Removal of Pb(II), Cd(II), Cu(II), and Zn(II) from aqueous solutions by adsorption on Bentonite, Journal of Colloid and Interface Science (1997) 187, [11] M. Malandrino, O. Abollino, A.Giacomino, M. Aceto, E. Mentasti Adsorption of heavy metals on vermiculite: Influence of ph and organic ligands. Journal of Colloid and Interface Science (26) 299, ) [12] A Langella, M Pansini, P Cappelletti, B Gerraro, M Gennaro, C Collela. NH 4+, Cu 2+, Zn 2+, Cd 2+ and Pb 2+ exchange for Na + in a sedimentary clinoptilolite, North Sardinia, Italy. Microporous Mesoporous Mater (2) 37: [13] Vassilis J. Inglezakis, Helen P. Grigoropoulou, Modeling of ion exchange of Pb 2+ in fixed beds of clinoptilolite, Microporous and Mesoporous Materials 61 (23) [14] N. Bektas, S. Kara Separ. Removal of lead from aqueous solutions by natural clinoptilolite: equilibrium and kinetic studies. Purif. Tech. (24) 39,

9 [15] Ahmad Al-Haj Ali, Ribhi El-Bishtawi Removal of Lead and Nickel Ions Using Zeolite Tuff, Journal of Chemical Technology & Biotechnology, (1997) 69(1), [16] A. Cincotti, N. Lai, R. Orru, G. Cao. Sardinian natural clinoptilolites for heavy metals and ammonium removal: experimental and modeling, Chem. Eng. J. (21) 84, [17] M.I. Panayotova, Kinetics and thermodynamics of copper ions removal from wastewater by use of zeolite, Waste Management 21 (21) [18] E. Alvarez-Ayuso, Garcia-Sanchez,. Querol, Purification of metal electroplating waste using zeolites, Water Research 37 (23) [19]] R. Donat, A. Akdogan, E. Erdem, H. Cetisli, Thermodynamics of Pb2+ and Ni2+ adsorption onto natural bentonite from aqueous solutions. J. Colloid Interface Sci. (25) 286(1), [2] Gozen Bereket, Ayse Zehra Aroguz, Mustafa Zafer Ozel, Removal of Pb(II), Cd(II), Cu(II), and Zn(II) from aqueous solutions by adsorption on Bentonite, Journal of Colloid and Interface Science 187, (1997)] [21] A. Bourliva, K. Michailidis, C. Sikalidis, and G. Trontsios. Removal of lead (Pb2+) and zinc (Zn2+) from aqueous solutions by adsorption on vermiculite from Askos area in Macedonia (Northern Greece), Bulletin of the Geological Society of Greece. VI, Proceedings of the 1th International Congress, (24)Thessaloniki.

Equilibrium ion exchange studies of Zn 2+, Cr 3+ and Mn 2+ on natural bentonite

Equilibrium ion exchange studies of Zn 2+, Cr 3+ and Mn 2+ on natural bentonite International Conference on Industrial Waste & Wastewater Treatment & Valorization, 21-23 May 2015, Athens, Greece M.A. Stylianou,