binary adsorption of copper and sulfates on …multilayer model is complex and multiparameter, thus...

Silviya Lavrova-Popova, Zvezdelina Yaneva

647

BINARY ADSORPTION OF COPPER AND SULFATES ON BARIUM-MODIFIED CLINOPTILOLITE

Silviya Lavrova-Popova1, Zvezdelina Yaneva2

ABSTRACT

The binary adsorption of copper cations and sulfate anions by surface modified natural clinoptilolite was investigated. The efficiency of the adsorbent was studied using batch adsorption technique under different experimental conditions by varying parameters such as initial ions concentration in the aqueous solution, clinoptilolite mass and contact time. An assessment of the equilibrium and the kinetics of copper and sulfates ions sorption was made. The experimental results were fitted to the Freundlich, Baudu, and the Multilayer isotherms. It was established that the Baudu isotherm best describe the binary removal of Cu2+ and SO4

2- by modified clinoptilolite with incorporated barium ions on its surface (CLIBa). Before the clinoptilolite modification (CLI), the removal of both copper and sulfate ions was best described by Baudu and Multilayer isotherms, respectively. The removal of Cu2+ is probably due to physiosorption, while that of SO4

2- - to at least two different in nature mechanisms - complexation and adsorption. The Ba-modification of the natural clinoptilolite led to a 1.1 times decrease and 4.8 times increase of the copper and sulfate removal efficiency. The kinetics of Cu2+ and SO4

2- adsorption onto modified clinoptilolite followed pseudo second-order model which suggests that both ions were adsorbed on the CLIBa surface via chemical interaction and intraparticle diffusion mechanisms.

Keywords: Cu2+ cations, SO42- anions, modified clinoptilolite, binary adsorption.

Received 10 January 2018Accepted 20 April 2018

Journal of Chemical Technology and Metallurgy, 53, 4, 2018, 647-656

1University of Chemical Technology and Metallurgy 8 Kliment Ohridsky, 1756 Sofia, Bulgaria E-mail: [email protected] Unit, Department of Pharmacology Animal Physiology and Physiological Chemistry Faculty of Veterinary Medicine, Trakia University Students Campus, 6000 Stara Zagora, Bulgaria E-mail: [email protected]

INTRODUCTION

Acid mine drainages contain a variety of heavy metals and sulfates in high concentrations. Widely used method for treatment of such type of wastewaters is chemical precipitation. However, this method success-fully removes metal ions, but is not effective enough for anions removal. It is known that high sulfates con-centrations can damage tubing installations and living organism’s health [1 - 3]. However, many countries have not adopted permissible limits for sulphates contents in the discharged wastewaters [4]. For their removal a number of methods are used, such as: biological sul-

phate reduction, in-situ remediation, electrochemical processes, adsorption, etc. [5 - 8]. The usage of natural minerals for adsorption is an attractive method due to their large deposits in the nature and low cost. Among them clinoptilolite is suitable for the removal of sulfur dioxide, ammonium ions, etc., as well as for variety of heavy metals such as Cu, Pb, Zn, Cd and Ni [9 - 13]. After its surface modification with inorganic salts such as NaCl, BaCl2, etc., thereby achieving its surface charge transformation from negative to positive [14, 15], it can be used as an adsorbent for negatively charged ions such as sulfates, nitrates, etc. [16 - 19]. The binary adsorption studies are more complex [20, 21] and best

Journal of Chemical Technology and Metallurgy, 53, 4, 2018

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reflect the reality because the presence of single ions in wastewaters is a rare case.

The aim of this study is to investigate the binary ad-sorption of copper and sulfates ions on barium-modified clinoptilolite.

EXPERIMENTALChemicals

Pure for analysis BaCl2.2H2O, NaCl, H2SO4, CuSO4.5H2O and deionized water were used in the ex-periments. The zeolite used is clinoptilolite ((Na,K,Ca)2-

3Al3(Al,Si)2Si13O36·12H2O) with particle size of 0.1 - 0.8 mm, obtained from the eastern part of the Rhodope mountains in Bulgaria.

Clinoptilolite modificationThe clinoptilolite modification was conducted by mix-

ing 10 g of natural clinoptilolite (CLI), with particle size of 0.1 - 0.8 mm, with NaCl and the resulting suspension was shaken at room temperature to activate the material surface for further modification. The solid phase was rinsed with deionized water and after that it was dried. The modifi-cation of the pre-treated clinoptilolite was carried out by contacting the activated clinoptilolite with BaCl2.2H2O. The suspension was shaken again on a plate shaker. Then the modified adsorbent was rinsed with deionized water and dried. The sample was denoted as CLIBa.

Standard solutionsStandard solutions containing both Cu2+ (1 - 100

mg dm-3) and SO42- (50 - 350 mg dm-3) ions were used.

Analytical methodologyThe Cu2+ ions concentration was determined using

ICP–OES (“Prodigy” High dispersion ICP-OES, Tell-

edyne Leeman Labs) and the SO42- concentration - by

following a standard procedure [22].

Adsorption equilibrium studyThe adsorption equilibrium for the binary removal

of Cu2+ and SO42- was studied, using 50 mL model solu-

tions containing both Cu2+, in concentrations between 5 and 35 mg dm-3, and SO4

2-, in concentrations between 50 and 350 mg dm-3, contacting with 1 g of CLIBa and CLI for comparison, respectively. Shaking was carried out for 96 hours. Then samples were taken, filtered through blue ribbon filter paper to remove adsorbent particles and analyzed.

The equilibrium capacity of the adsorbents (mg g-1) was computed as follows [23]:

𝑞𝑞𝑒𝑒 = (𝐶𝐶𝑜𝑜 − 𝐶𝐶𝑒𝑒)𝑉𝑉

𝑚𝑚

where Co and Ce are the initial and equilibrium ions concentrations (mg dm-3), respectively, V is the volume of solution (dm3), and m (g) is the mass of the adsorbent.

The obtained results were described by Freundlich, Baudu and Multilayer equilibrium models (Table 1) [24 - 26].

Adsorption kinetics studyIn order to establish the influence of the contact

time and adsorbent dosage on the binary Cu2+ and SO42-

adsorption, 2 dm3 solutions with initial Cu2+ concentra-tion of 10 mg dm-3 and SO4

2- concentration of 100 mg dm-3, respectively, were prepared. Three to five grams of CLIBa were put in contact with the aqueous solution at constant mixing at 200 rpm (Heidolph RZR 2100 elec-tronic) for 1 h. Samples were taken after 60 min, filtered through blue ribbon filter paper for removal of suspended particles and analyzed. The kinetics data obtained were

Isotherm Non-linear expression Plot

Freundlich 𝑞𝑞𝑒𝑒 = 𝐾𝐾𝐹𝐹𝐶𝐶𝑒𝑒𝑛𝑛𝐹𝐹

𝑞𝑞𝑒𝑒 𝑣𝑣𝑣𝑣.𝐶𝐶𝑒𝑒 Multilayer 𝑞𝑞𝑒𝑒 = 𝑄𝑄𝑚𝑚𝐾𝐾1𝐶𝐶𝑒𝑒

(1 − 𝐾𝐾2𝐶𝐶𝑒𝑒)[1 + (𝐾𝐾1 − 𝐾𝐾2)𝐶𝐶𝑒𝑒]

Baudu 𝑞𝑞𝑒𝑒 = 𝑞𝑞𝐵𝐵𝑏𝑏𝐵𝐵𝐶𝐶𝑒𝑒 (1+𝑥𝑥+𝑦𝑦)

1 + 𝑏𝑏𝐵𝐵𝐶𝐶𝑒𝑒 (1+𝑥𝑥)

Table 1. Isotherm models used for experimental results interpretation.


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analyzed by comparative estimation of the applicability of the pseudo second-order model, mixed-order model and the intraparticle diffusion model (Table 2) [27 - 31].

Removal efficiencyThe efficiency of ions removal by CLIBa was cal-

culated according to the formula:

RЕ, % = �𝐶𝐶𝑜𝑜 − 𝐶𝐶𝑡𝑡𝐶𝐶𝑜𝑜

�100 where Co is the initial ion concentration and Ct is the concentration at a certain moment, mg dm-3.

RESULTS AND DISCUSSION

Adsorption equilibriumThe experimental equilibrium data of binary Cu2+ and

SO42- adsorption on CLI and CLIBa were described by

Freundlich, Multilayer and Baudu models (Figs. 1, 2). The calculated isotherm model parameters for the investi-gated systems, as well as the values of the error functions are presented in Table 3. The R2 values obtained from the applied three isotherm models for all cases indicate that the adsorption is favorable (R2 varies between 0.863 and 0.998).

Table 2. Kinetic models used for experimental results interpretation.

Fig. 1. Experimental and model isotherms for the Cu2+ and SO42- ions sorption on CLI.

Kinetic model Non-linear expression Linear expression Plot

Pseudo second-order model

Mixed order model

Intraparticle diffusion model -


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The experimental isotherm of Cu2+ adsorption on the non-modified natural clinoptilolite is L-type (Fig. 1a), which suggests progressive saturation of the sorbent. The curve does not reach a plateau, which means that the CLI does not exhibit limited sorption capacity. As can be seen from the plots in Fig. 1 and Fig. 2, as well as from the data in Table 3, Baudu model predicts in a more detailed way the systems behavior due to the fact that it has higher number of isotherm parameters. An excep-tion is the system CLI-SO4

2-, which is better described by the Multilayer isotherm. The predicted by Baudu model maximum Cu2+ sorption capacity of the CLI (2.25 mg g-1) was higher than the experimentally obtained (1.46 mg g-1). The experimental equilibrium data for CLI-Cu2+ is satisfactorily described by Freundlich iso-therm (R2 0.997), too. Both models have approximately equal values of R2, SSE, MSE and RMSE. According to the Freundlich model the copper ions concentration on the adsorbent surface will increase until there is an increase of Cu2+ concentration in the aqueous media. This empirical model describes adsorption processes on heterogeneous surface [32]. The constant nF is indicative of the intensity of the adsorption process. At nF = 1, the adsorption is linear, which means that the adsorption sites are homogeneous in energy and no interaction between the adsorbed species occur. At nF < 1, the ad-sorption process is favorable and physical in nature. The values below unity represent convex isotherm (L-type), where the sorption energy decreases with an increase in the sorbate surface concentration [33]. The Freundlich coefficient nF for the system CLI-Cu2+ is 0.52, which is a confirmation for favorable adsorption.

The experimental isotherm of SO42- sorption on CLI

(Fig. 1-b) is S-type, which means the removal of these ions is a result of at least two separate mechanisms [34]. The point of inflection shows the concentration, at which the adsorption surmounts to complexation. This experimental data was best described by the multilayer adsorption isotherm, which is similar to BET isotherm. These isotherms represent a multilayer adsorption mechanism, i.e. the adsorption occurs layer by layer with no transmigration between layers, and well describes adsorption behavior of molecules from aqueous media over a wide concentration range. The multilayer model is complex and multiparameter, thus providing better interpretation of the physical nature of the adsorption process. The high R2 and low errors SSE, MSE and RMSE values (Table 3) confirm the statement that the multilayer adsorption model well describes the experimental S-type adsorption isotherm.

It is known that natural clinoptilolite successfully adsorbs metal ions, and this is proven by the results obtained. The average removal efficiency obtained using 1 g CLI was 86.5 % (Table 4) and a maximum adsorption capacity of 1.46 mg g-1 was achieved. The successful cations removal is due to the negatively charged clinoptilolite surface. Thus it is not capable of removing simultaneously negatively charged ions from the aquatic media. An average removal efficiency of 10.1 % in regard to SO4

2- with the same CLI amount was obtained and the achieved maximum adsorption capacity was 1.21 mg g-1. It is scientifically significant to study the change in the removal efficiency of both cations and anions after CLI surface modification by the incorporation of barium ions. 77.7 % and 48.8 % average binary removal of Cu2+ and SO4

2-, respectively,

Fig. 2. Experimental and model isotherms for the binary Cu2+ and SO42- ions sorption on CLIBa.


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by CLIBa was achieved. The modification of the CLI led to 1.1 times decrease and 4.8 times increase of the copper and sulfate removal efficiency. After the applied modification a change in the adsorption capacity of the new material (CLIBa) towards Cu2+ and SO4

2-, respec-tively, was also observed.

The experimental isotherms of both systems: CLI-Ba-Cu2+ and CLIBa-SO4

2-, are L-type, which means that the sorption behavior of the cations and anions from the aqueous phase was similar. It was established that Baudu model best describes the equilibrium of Cu2+ sorption on CLIBa (Fig. 2a, Table 3). The latter is confirmed by R2 value (0.998), which is closer to 1, as well as by the low values of the error functions. The maximum predicted by Baudu model sorption capacity in regard to Cu2+ is 5.534 mg g-1 and the experimentally achieved was 1.195 mg g-1. According to the plots in Fig. 2a the three model isotherms almost overlap, which means that they describe the experimental data satisfactorily. The sorption capacity of CLIBa is 1.2 times lower than that of CLI in regard to

copper ions. The system CLIBa-SO42- is best described

by Baudu model, too (Fig. 2b, Table 3). The predicted by Baudu model maximum sorption capacity (qm 13.838 mg g-1) of CLIBa was higher than the experimentally obtained (qe 5.29 mg g-1). Despite of the relatively high R2 values of the Freundlich and Multilayer models in terms of the systems CLIBa-Cu2+ and CLIBa-SO4

2-, the high values of the corresponding error functions (Fig. 2b) determine deviations between the model and experimen-tal isotherms. Consequently, the adsorption behavior of the sulfate anions on CLIBa at equilibrium conditions is best predicted by the four-parameters model of Baudu.

Adsorption kineticsThe experimental kinetic curves of copper and sul-

fates ions on CLIBa, plotted as Ct vs t (Fig. 3) displayed that the sorption rate in the initial stages of the process was the highest. The system reached equilibrium within the first 10 min after the beginning of the process. The highest adsorption capacities attained in respect to Cu2+

and SO42- were 0.8 mg g-1 and 35.37 mg g-1, respectively.

The experimental data were modelled by the pseudo second-order, mixed pseudo first/pseudo second-order kinetic models, as well as by the intraparticle diffusion model. The values of the calculated parameters and error functions are presented in Table 5.

According to the experimental results and model data, the kinetic behavior of the system CLIBa-Cu2+ with 3 g CLIBa was best described by the mixed order model (Table 5, Fig. 4).

The experimental series with 4 g and 5 g CLIBa were best represented by the pseudo second-order model. The

Table 3. Values of the equilibrium model parameters and error functions.

Table 4. Removal efficiency (%) of Cu2+. and SO42- from

the equilibrium study.

System CLI CLIBa Cu2+ SO4

2- Cu2+ SO42-

Equilibrium model

Model parameters Error function Model

parameters Error function Model parameters Error function Model

parameters Error function

Two parameter model

Freundlich isotherm

KF 0.517 R2 0.997 KF 0.038 R2 0.949 KF 0.431 R2 0.981 KF 1.042 R2 0.943 nF 0.522 SSE 0.005 nF 0.598 SSE 0.059 nF 0.398 SSE 0.022 nF 0.309 SSE 1.439 MSE 0.001 MSE 0.012 MSE 0.004 MSE 0.288 RMSE 0.032 RMSE 0.108 RMSE 0.066 RMSE 0.536

Three parameter model

Multilayer isotherm

qm -1.115 R2 0.995 qm -0.472 R2 0.983 qm -0.942 R2 0.991 qm -3.199 R2 0.863 K1 -0.792 SSE 0.008 K1 -0.456 SSE 0.019 K1 -0.750 SSE 0.010 K1 -0.907 SSE 3.471 K2 -0.749 MSE 0.002 K2 -0.454 MSE 0.005 K2 -0.730 MSE 0.002 K2 -0.905 MSE 0.868 RMSE 0.045 RMSE 0.069 RMSE 0.049 RMSE 0.931

Four parameter model

Baudu isotherm

qm 2.449 R2 0.998 qm 3.819 R2 0.949 qm 5.534 R2 0.998 qm 13.838 R2 0.990 bo 0.264 SSE 0.004 bo 0.010 SSE 0.059 bo 0.090 SSE 0.003 bo 0.006 SSE 0.254 x -0.524 MSE 0.001 x -0.885 MSE 0.020 x -6.546 MSE 0.001 x 0.349 MSE 0.085 y 0.190 RMSE 0.037 y 0.485 RMSE 0.140 y 5.880 RMSE 0.030 y -0.160 RMSE 0.291

Co, mg dm-3 CLI CLIBa Co,

mg dm-3 CLI CLIBa

Cu2+ SO42-

5 93.91 88.32 50 19.21 69.72 10 90.98 88.64 100 11.42 61.90 15 87.56 84.19 150 7.68 59.82 25 84.56 71.85 250 7.24 35.40 30 82.27 68.28 300 7.91 34.07 35 79.51 65.12 350 7.26 31.68


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constants k2 and qe were calculated by linear regression analyses from the slope and intercept of the plots t/qt vs t (Table 5, Fig. 5).

The analyses of the experimental data, model param-eters and error functions proved that the pseudo second-

order model fully correlated the kinetics experimental data of SO4

2- sorption on CLIBa in respect to the three series investigated (Table 5, Fig. 6).

The good agreement between the pseudo second-order model fit and the experimental data suggests that

Fig. 3. Experimental kinetics curves of the Cu2+ and SO42- sorption on CLIBa.

Fig. 4. Experimental data and mixed order model for the CLIBa-Cu2+ system. Operating conditions: Co = 10 mg dm-3, mads. = 3 g, pH = 5, T = 20oC.

Fig. 5. Application of the pseudo second-order model to the CLIBa-Cu2+ system (R2 = 0.994). Operating condi-tions: Co = 10 mg dm-3, mads. = 4 g, pH = 5, T = 20oC.

Table 5. Values of the kinetics model parameters and error functions for the studied systems.

Pseudo second-order model Mixed order model Intraparticle diffusion model

System Mass, g Model parameter Error function Model parameter Error function Model parameter Error function

k2 qe R2 MSE RMSE k1 k2 f2 R2 MSE RMSE ki1 ki2 Ri12 Ri2

2

Cu2+-CLIBa 3 0.032 1.346 0.703 105.993 10.295 0.037 -0.0121 -0.409 0.943 0.009 0.097 0.054 0.183 0.716 0.933 4 0.314 0.974 0.994 2.734 1.653 0.047 0.2197 0.814 0.980 0.002 0.045 0.176 0.058 0.759 0.887 5 0.285 0.796 0.963 27.754 5.268 -0.047 0.4557 1.148 0.875 0.007 0.082 0.173 0.054 0.933 0.831

SO42--CLIBa

3 0.031 51.149 0.999 0.000 0.012 -0.347 0.1132 1.063 0.985 3.321 1.822 1.419 0.727 0.941 0.858 4 0.049 39.877 1.000 0.000 0.011 -0.289 0.193 1.039 0.992 1.014 1.007 0.734 0.612 0.916 0.937 5 0.176 35.344 1.000 0.000 0.003 -0.112 0.319 1.01 1.000 0.052 0.227 0.914 0.130 0.831 0.918


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Cu2+ and SO42- were adsorbed on the CLIBa surface via

chemisorption. To determine whether film diffusion or intraparticle

diffusion is the rate limiting step, the intraparticle dif-fusion model was tested. According to the Weber and Morris theory [35], when the plot of qt versus t1/2 is linear and passes through the origin, then intraparticle diffu-sion occurs and it is the rate limiting step. Otherwise, another mechanism along with intraparticle diffusion is also involved. When the sorption process is controlled by more than one mechanism, then a plot of qt versus t1/2

is multi-linear and the initial section represents external surface adsorption, the second - intra-particle diffusion within the pores, and the third region is the final equi-librium stage, where intraparticle diffusion starts to slow down due to the extremely low adsorbate concentrations left in the solutions [36]. The values of the intra-particle

diffusion model constants are presented in Table 6. The plots of the intraparticle diffusion model for

Cu2+ and SO42- sorption have two and three sections,

respectively, which means that the intraparticle diffu-sion was not the only mechanism involved. The plots did not pass through the origin and C ≠ 0, which is evidence that the above-mentioned statement is consist-ent. The C values indicate the thickness of the boundary layer which was observed to be very thin. The low C values suggested that the role of surface diffusion as the rate-limiting step in the overall sorption process is less significant. In contrast, the intercept values for the CLIBa-SO4

2- system and the error values are greater for the second and third linear sections of the plots, which probably means that the surface diffusion has a greater role as the rate-limiting step. As the values of the R2, R1

2, R22 and R3

2 (Tables 5 and 6) are commensurable, a categorical conclusion whether chemisorption or intraparticle diffusion was the general rate control-ling mechanism during the binary copper and sulfates sorption on the CLIBa could not be done. Either of the proposed processes probably dominates during the dif-ferent sorption stages.

The main removal of Cu2+ and SO42- becomes within 10

min and 1 min, respectively, after the contact between the Ba-modified clinoptilolite with the model solution (Table 7). Then a slight change of the concentrations was observed. It is noticeable that the adsorption of copper ions is slower than that of the sulphate ions. Probably the sulfate anions removal is contributed also to a complexation process.

CONCLUSIONSThe binary adsorption equilibrium and kinetics of

copper cations and sulfate anions were experimentally studied using natural and modified clinoptilolite. The

Fig. 6. Application of the pseudo second-order model to the CLIBa-SO4

2- system (R2 = 1.000). Operating conditions: Co = 100 mg dm-3, mads. = 5 g, pH = 5, T = 20oC.

Table 6. Intraparticle diffusion model constants and coefficients of binary Cu2+ and SO42- adsorption on CLIBa.

System ki1 ki2 ki3 C1 C2 C3 R12 R2

2 R32

CLIBa-Cu2+

3 g 0.06 0.16 - 0.09 0.21 - 0.561 0.992 -

4 g 0.23 0.04 - 0.10 0.61 - 0.911 0.901 -

5 g 0.03 0.05 - 0.44 0.35 - 0.781 0.831 -

CLIBa-SO42-

3 g 44.13 1.42 0.73 0 42.53 45.39 1 0.941 0.858

4 g 35.27 0.73 0.61 0 34.92 35.23 1 0.916 0.937

5 g 32.50 0.91 0.13 0 31.97 34.32 1 0.831 0.918


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clinoptilolite modification led to 1.2 times decrease and 4.4 times increase of the maximum adsorption capacity in terms of the copper and sulfate ions, respectively. A categorical conclusion whether physical adsorption or chemisorption, as well intraparticle diffusion was the gen-eral rate controlling mechanism during the binary copper and sulfate ions on modified with barium ions clinoptilo-lite could not be withdrawn. Probably, the mechanism of sorption included physiosorption, complexation, and in-traparticle diffusion during the later stages of the process.

REFERENCES

1. Finlex, Ministry of Social Affairs and Health, 1352/2015 Sosiaali-ja terveysministeriön asetus talousveden laatuvaatimuksista ja valvontatut-kimuksista (In Finnish), http://www.finlex.fi, 2015 (Accessed 1 December 2015).

2. A. M. Silva, R. M. F. Lima, V. A. Leão, Mine water treatment with limestone for sulphate removal, J. Hazard. Mater., 221-222, 2012, 45-55.

3. C. Namasivayam, M. V. Sureshkumar, Removal of sulphate from water and wastewater by surfactant-modified coir pith, an agricultural solid waste by adsorption methodology, J. Environ. Eng. Manage., 17, 2007, 129-135.

4. H. Runtti, P. Tynjälä, S. Tuomikoski, T. Kangas, T. Hu, J. Rämö, U. Lassi, Utilisation of barium-modified analcime in sulphate removal: Isotherms, kinetics and thermodynamics studies, J. Water Process Eng., 16, 2017, 319-328.

5. S. Bratkova, B. Koumanova, V. Beschkov, Biologi-cal treatment of mining wastewaters by fixed-bed bioreactors at high organic loading, Biores. Technol., 137, 2013, 409-413,

6. O. Gibert, T. Rötting, J. L. Cortina, J. de Pablo, C. Ayora, J. Carrera, J. Bolzicco, In-situ remediation of acid mine drainage using a permeable reactive barrier in Aznalcóllar (Sw Spain), J. Hazard. Mater., 191, 2011, 287-295.

7. M. Mamelkina, S. Cotillas, E. Lacasa, C. Sáez, R. Tuunila, M. Sillanpää, A. Häkkinen, M.Rodrigo, Removal of sulfate from mining waters by electro-coagulation, Sep. Purif. Technol., 182, 2017, 87-93.

8. J. Liu, R. Zhu, X. Liang, L. Ma, X. Lin, J. Zhu, H. He, S. C. Parker, M. Molinari, Synergistic adsorption of Cd(II) with sulfate/phosphate on ferrihydrite: An in situ ATR-FTIR/2D-COS study, Chem. Geol., 477, 2018, 12-21.

9. S. J. Allen, E. Ivanova, B. Koumanova, Adsorption of sulfur dioxide on chemically modified natural clinoptilolite. Acid modification, Chem. Eng. J., 152, 2009, 389-395.

Table 7. Dependence of Cu2+. and SO42- removal efficiency on time.

Removal efficiency, % CLIBa-Cu2+ CLIBa-SO42-

Time, min 3 g 4 g 5 g 3 g 4 g 5 g

1 2.50 4.90 7.50 66.17 70.54 81.24 3 3.40 6.40 9.50 67.13 72.50 84.91 5 2.70 12.00 13.00 69.13 73.92 85.89 8 3.90 13.10 13.00 69.41 74.34 85.89

10 4.50 15.00 13.00 69.84 74.76 86.73 15 6.50 16.00 14.00 72.65 75.04 87.15 20 6.60 17.00 13.00 73.07 76.17 87.44 30 11.40 17.00 15.00 73.92 76.73 87.44 40 12.30 17.30 16.00 74.34 78.00 87.58 50 12.90 18.70 20.00 75.05 79.69 88.15 60 18.40 18.70 20.00 77.58 79.69 88.43


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10. E. Ivanova, B. Koumanova, Adsorption of sulfur diox-ide on natural clinoptilolite chemically modified with salt solutions, J. Hazard. Mater., 167, 2009, 306-312.

11. E. Ivanova, M. Karsheva, B. Koumanova, Adsorp-tion of ammonium ions onto natural zeolite, J. Univ. Chem. Technol. Met., 45, 3, 2010, 295-302.

12. J. Taparcevska, L. Markovska, B. Koumanova, V. Meshko, Diffusion models for adsorption kinetics of Zn2+, Cd2+ and Pb2+ onto natural zeolite, Water Sci. Technol., 62, 5, 2010, 1136-1142.

13. M. Kostova, E. Ivanova, G. Stefanov, B. Koumano-va, Sorption of lead ions on natural clinoptilolite part II. Fixed bed simulations, J. Univ. Chem. Technol. Met., 45, 3, 2010, 283-294.

14. V. Inglezakis, Modified Zeolites: Pretreatment of Natural Zeolites by Use of Inorganic Salts, Natural Zeolites, Chapter 9a, 2012, 156-165.

15. K. Margeta, N. Z. Logar, M. Šiljeg, A. Farkaš, Natu-ral Zeolites in Water Treatment – How Effective is Their Use, In: W. Elshorbagy, R. K. Chowdhury (Eds.), Water Treatment, Chapter 5, p. 81, 2013, ISBN 978-953-51-0928-0, DOI: 10.5772/2883.

16. L. Lu, J. Yeow, An adsorption study of indoxyl sulfate by zeolites and polyethersulfone–zeolite composite membranes, Mater. Design., 120, 2017, 328-335.

17. J. De Los Santos, J. Cornejo-Bravo, E. Castillo, N. Bogdanchikova, S. Farías, J. Mota-Morales, E. Reynoso, A. Pestryakov, J. Ventura, Elimination of sulfates from wastewaters by natural aluminosilicate modified with uric acid, Resource-Efficient Tech-nologies, 1, 2, 2015, 98-105.

18. D. Mitrogiannis, M. Psychoyou, I. Baziotis, V. J. Inglezakis, N. Koukouzas, N. Tsoukalas, D. Palles, E. Kamitsos, G. Oikonomou, G. Markou, Removal of phosphate from aqueous solutions by adsorption onto Ca(OH)2 treated natural clinoptilolite, Chem. Eng. J., 320, 2017, 510-522.

19. J. Schick, P. Caullet, J. Paillaud, J. Patarin, C. Mangold-Callarec, Nitrate sorption from water on a Surfactant-Modified Zeolite. Fixed-bed column experiments, Microporous Mesoporous Mater., 142, 2011, 549-556.

20. E.D. Freitas, A.C.R. Carmo, A.F. Almeida Neto, M.G.A. Vieira, Binary adsorption of silver and copper on Verde-lodo bentonite: Kinetic and equi-librium study, Appl. Clay Sci., 137, 2017, 69-76.

21. M. Chiban, A. Soudani, F. Sinan, M. Persin, Single, binary and multi-component adsorption of some ani-ons and heavy metals on environmentally friendly Carpobrotus edulis plant, Colloids Surf. B., 82, 2011, 267-276.

22. APHA 1992. Standard methods for the examina-tion of water and wastewater. Greenberg A.E. (ed.) 18th edition. American Public Health Association (APHA), American Water Works Association (AWWA), and the Water Environment Federation (WEF): Washington, D.C.

23. B. Vanderborght, R. Van Grieken, Enrichment of Trace Metals in Water by Adsorption on Activated Carbon, Anal. Chem., 1977, 49, 2, 311-316.

24. M. Hamzaoui, B. Bestani, N. Benderdouche, The use of linear and nonlinear methods for adsorption isotherm optimization of basic green 4-dye onto sawdust-based activated carbon, J. Mater. Environ. Sci., 2018, 9, 4, 1110-1118.

25. R. Saadi, Z. Saadi, R. Fazaeli, N. E. Fard, Monolayer and multilayer adsorption isotherm models for sorp-tion from aqueous media, Korean J. Chem. Eng., 32, 5, 2015, 787-799.

26. J. Wang, C. Huang, H. Allen, D. Cha, D. Kim, Ad-sorption Characteristics of Dye onto Sludge Particu-lates, J. Colloid. Interf. Sci., 208, 1998, 518-528.

27. Y. Ho, Second-order kinetic model for the sorption of cadmium onto tree fern: A comparison of linear and non-linear methods, Water res., 40, 2006, 119-125.

28. A. Itodo, F. Abdulrahman, L. Hassan, S. Maigandi, H. Itodo, Intraparticle Diffusion and Intraparticu-late Diffusivities of herbicide on derived activated carbon, Researcher, 2, 2, 2010, 74-86.

29. B. Olu-Owolabi, P. Diagboya, K. Adebowale, Evalu-ation of pyrene sorptionedesorption on tropical soils, J. Environ. Manage., 137, 2014, 1-9.

30. I. Tsibranska, E. Hristova, Comparison of different kinetic models for adsorption of heavy metals onto activated carbon from apricot stones, Bulg. Chem. Commun., 43, 3, 2011, 370-377.

31. Z. Yaneva, M. Staleva, N. Georgieva, Study on the host-guest interactions during caffeine encapsulation into zeolite, Eur. J. Chem., 6, 2, 2015, 169-173.

32. S. Brunauer, P. Emmet, E. Teller, Adsorption of gases in multimolecular layers, J. Am. Chem. Soc., 1938, 60, 2, 309-319.


656

33. A. D. Site, Factors Affecting Sorption of Organic Compounds in Natural Sorbent/Water Systems and Sorption Coefficients for Selected Pollutants. A Review, J. Phys. Chem. Ref. Data, 30, 1, 2001, 187-439.

34. G. Limousin, J. Gaudet, L. Charlet, S. Szenknect, V. Barthès, M. Krimissa, Sorption isotherms: A review on physical bases, modeling and measurement,

Appl. Geochem., 22, 2007, 249-275.35. W. Weber, J. Morris, 1963. Kinetics of adsorption

on carbon from solutions. J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, 31-60.

36. F. Wu, R. Tseng, R. Juang, Comparisons of porous and adsorption properties of carbons activated by steam and KOH, J. Colloid Interf. Sci., 283, 2005, 49-56.

binary adsorption of copper and sulfates on …multilayer model is complex and multiparameter, thus...

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