Nova Biotechnol Chim (2022) 21(2): e1267 DOI: 10.36547/nbc.1267 1 Nova Biotechnologica et Chimica Adsorption of Zn (II) ions from refinery wastewater by sulfuric acid- modified bentonite: Kinetic and isotherm studies Dihia Bellache1,2,, Karim Moussaceb2, Jean-Claude Bollinger3, Farouk Boudrahem4 1Department of Process Engineering, Faculty of Science and Applied Science, University of Bouira, 10000 Bouira, Algeria 2Laboratory of Materials Technology and Process Engineering), Faculty of Technology, A/MIRA Bejaia University, Targa- Ouzemour Road, 06000 Bejaia, Algeria 3Water Soil Environment Research Group, University of Limoges, 87060 Limoges, France 4Environmental Engineering Laboratory, Faculty of Technology, A/MIRA Bejaia University, Targa-Ouzemour Road, 06000 Bejaia, Algeria  Corresponding author: d.bellache@univ-bouira.dz Article info Article history: Received: 17th November 2021 Accepted: 7th February 2022 Keywords: Adsorption Bentonite Isotherm Kinetic Wastewater Zinc Abstract A local bentonite clay from Maghnia (Algeria) was activated with chemical method characterized and tested for its ability to adsorb Zinc (II) from refinery wastewater. Batch experiments were conducted to study the effects of the main parameters such as contact time, initial metal concentration and agitation speed on the adsorption of Zn (II) by local bentonite clay. Experiences have led to the following results: an adsorption rate of the order of 98 % with operating conditions of pH = 4.5, agitation speed of 400 rpm and temperature of 25 ºC. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to analyze the kinetic data obtained at different concentrations. The pseudo-second-order kinetic model agrees very well with the experimental results. In order to determine the best-fit isotherm, in the studied concentration range of Zn(II) at 25 ºC, the experimental equilibrium data were analyzed using tow adsorption isotherm models: Langmuir and Freundlich models, these two models give a good fit. Introduction A number of industries, such as metal plating facilities, mining operations, tanneries, nuclear power plants, fertilizers and battery productions, often discharges heavy metals, this can lead to the contamination of freshwater and marine environment (Low and Lee 2000). Metal ions in water can occur naturally from anthropogenic sources and from leaching of ore deposits, which mainly include solid waste disposal and industrial effluents. The levels of heavy metals in water system have substantially increased over time with rapid development of industrial activities (Nouri et al. 2006). The main sources of zinc in the environment are the manufacturing of brass and bronze alloys and galvanization (Arias and Sen 2009). It is also utilized in paints, rubber, plastics, cosmetics, and pharmaceuticals. Zinc is an essential element for life and act as micronutrient when present in trace amounts, the maximum daily dose not to be exceeded is 40 mg for an adult. However, high zinc can cause eminent health problems, such as stomach cramps, vomiting, skin irritations, anemia, and nausea (Zwain 2012). mailto:d.bellache@univ-bouira.dz Nova Biotechnol Chim (2022) 21(2): e1267 2 Various methods are available to remove and isolate these heavy metals from water and wastewater such as ion exchange, chemical precipitation, membrane filtration, adsorption, and electrochemical treatment technologies (Fu and Wang 2011). Adsorption is very promising because of the advantages of easy operation, low cost, and possibility of metal recovery (Dang et al. 2021). These methods have proven their ability in removing heavy metals from wastewater; however, several factors need to be considered when choosing the appropriate method. Adsorption has been proven to have better performance compared to other methods as mentioned in many studies (Kamari et al. 2014) The adsorption ability of clay is caused by a net negative charge on the structure of fine grain silicate minerals. This negative charge is neutralized by the adsorption of positively charged species, giving clay the ability to attract and hold cations such as heavy metals. The large surface area of clays (up to 800 m2.g-1) also contributes to the high adsorption capacity, there are three basic classes of clays: kaolinite, micas (such as illite), and smectites (e.g., montmorillonite). Of the three species, montmorillonite clays have the smallest crystals, the largest surface area, and the highest cation exchange capacity. Thus, montmorillonite clays would be expected to have the highest adsorption capacity (Haider et al. 2014). Studies such as those conducted by (Bellir et al. 2013; Sen et al. 2013; Vasconcelos et al. 2013) have investigated the potential of bentonite for the removal of zinc ion. Although the results involving zinc removal by bentonite are significant and promising, the properties of adsorbents for optimizing the conditions of the process need to be better understood. This study explored the feasibility of utilizing an Algerian activated bentonite for the adsorption of zinc from refinery wastewater. Various parameters affecting adsorption process, such as contact time, initial zinc concentration, adsorbent dosages, agitation speed and the medium temperature were investigated. The kinetic adsorption results have been analyzed using both pseudo-first-order and pseudo-second-order kinetics models. The mechanism of adsorption process has been explained based on intra-particle diffusion model. Finally, the Langmuir and Freundlich models were applied for the analysis of the adsorption equilibrium. Experimental Characteristics of refinery wastewater The main physicochemical parameters on the quality of refinery wastewater are shown in Table 1. The determination of these parameters is performed according to standard analytical methods (Rodier et al. 2009). Based on this table, the physicochemical characteristics of the refinery water are within the limits of wastewater standards, except COD and chloride and zinc concentrations that exceed current standards. Table 1. Physical-chemical characteristics of refinery wastewater and the OMS limit values of wastewater parameters. COD – Chemical Oxygen; TSS – Total Suspended Solids. Characteristic of raw bentonite In this study, bentonite obtained from Maghnia (North-Western part of Algeria) and supplied by ENOF “National Company of useful and non- ferrous products, Algeria” was used as an adsorbent. Its chemical and physico-chemical characteristics are summarized in Table 2 and Table 3. Preparation of acid-activated bentonite The Na-bentonite was prepared with a procedure similar to already reported (Khalaf et al. 1997). 30 g of crude bentonite was mixed with 1 L of 1 M NaCl solution and stirred for 24 h. After three successive treatments, the homoionic bentonite was Parametres Values Normes pH 7.07 6,5 – 8,5 Conductivitym S/Cm 40.89 2,8 Turbidity (NTU) 85.6 5 – 30 TSS [mg.L-1] 387.8 30 COD [mg.O2.L -1] 1601.24 120 Chloride [mg.L-1] 2098.03 200 Sulfate [mg.L-1] 33.18 250 Chromium (VI) [mg.L-1] 0.02 0,1 Lead [mg.L-1] 0.04 0,5 Zinc [mg.L-1] 6.7 3 Nova Biotechnol Chim (2022) 21(2): e1267 3 dialyzed in deionized water until it was free of chloride. Then it was separated by centrifugation to eliminate all other solid phases (quartz, and calcite) Boutahala and Tedjar 1993). In a conical flask, 50 g of purified bentonite and 250 mL of sulfuric acid solution (0.5 M and 1 M). The mixture was homogenized and allowed to stand at room temperature for 24 h. The resulting activated clay was centrifuged and washed with distilled water several times until it was free of SO4 2− as indicated by the AgNO3 test and was then dried at 100 – 107 ºC for 24 h. Acid-activated bentonite with different concentration of sulfuric acid at 0.5 M end 1 M are noted respectively B05 and B1, was then stored for further use in the adsorption tests. Table 2. Chemical composition of bentonite sample. Constituent SiO2 MgO Al2O3 K2O CaO F2O3 Na2O TiO2 As Weight [%] 69.4 1.1 14.7 0.8 0.3 1.2 0.5 0.2 0.05 Loss of ignitions = 11 Table 3. Physico-chemical properties of Bentonite. Surface area [m².g-1] CEC [eqg-1] pH Exchangeable cation [meq/100g] Ca2+ Mg2+ Na+ K+ 80 0.97 6.2 30.6 12.8 36.2 9.5 Batch adsorption study The ability of bentonite to adsorb Zn(II) ions from refinery wastewater was studied under various optimized conditions of concentration of metals, and contact time, adsorbent dosage and strength speed. Batch adsorption experiments were carried in 250 cm3 Erlenmeyer flasks with known amount of the adsorbent and 100 mL of solution, with pH = 4.5, the initial pH of the solutions was adjusted with 0.1 M HNO3 or 0.1 M NaOH to the desired value. The Erlenmeyer were kept at the desired temperature under constant agitation. After 70 min, the suspensions were centrifuged and the solutions were analyzed for Zn(II) ions by atomic absorption spectrometry AA-6501F. The amount of adsorbed at any time, qt (mg.g -1), was calculated using Eq. 1: (1) where, Ci and Ct are the initial and liquid-phase concentrations at any time t of Zinc solution (mg.L- 1), respectively, V is the volume of wastewater (L) and m is the mass (g) of the adsorbent used. The removal efficiency, E (%) of the system, is Eq. 2 (Boudrahem et al. 2011): (2) Results and Discussion Adsorbent characterization The FTIR spectra of natural bentonite and acid activated bentonite were taken in the range of 4,000 – 400 cm-1 (Shimadzu FTIR-8400, SHIMADZU Corp., Tokyo, Japan). FTIR spectra are illustrated in Fig. 1 and 2. Positions and assignment of the vibrational bands of this clay are shown in Table 4. The broad and slight bands at 3,627 and 3,435 cm-1 are due to the O–H stretching vibration of the silanol (Si–OH) groups from the solid and H–O–H vibration of the water molecules adsorbed on the silicate surface. The band at 1,634.5 cm-1 reflects the bending H–O–H bond of water molecules, which is retained in the silicate matrix. The most intensive and sharp band at 1,039 cm-1 represents the Si–O–Si groups of the tetrahedral sheets. Where the bands around 515 and 523 cm-1 is are ascribed to Si–O–Al (where Al is the octahedral cation) and to Si–O–Si bending vibration. Furthermore, the sharp bands at 790 with reflexion at 778.4 cm-1 confirm the presence of quartz admixtures in the sample (Tomic et al. 2011). Nova Biotechnol Chim (2022) 21(2): e1267 2 FTIR spectroscopy is very sensitive to modification of the clay structure upon acid treatment, as illustrated in Fig. 1. In FTIR-spectrum of the acid activated bentonite, weakening of absorption band intensity at 3,437 and 1,639 cm−1 is marked (Fig. 2). It corresponds to the process of removal of interlayer water (Schrader and Loeb 1992). Absorption peaks between 3,435 and 3,627 cm-1 are due to stretching bands of the OH groups. 4000 3000 2000 1000 1,4 1,2 1,0 0,8 0,6 0,4 A ( % ) Wave number(cm -1 ) Fig. 1. FTIR spectrum of raw bentonite. 4000 3500 3000 2500 2000 1500 1000 500 2 4 6 8 10 12 14 16 18 20 22 24 1 M 0.5 M A (% ) Wave number(Cm -1 ) Fig. 2. FTIR spectrum of acid activated bentonites. While the band at 1,639 cm-1 corresponds to the OH deformation of water to observe natural bentonite and acid activated bentonite, but the peak intensities of both the acid-activated bentonites are lower than that of natural bentonite. Absorption band reduction at 3,627 cm-1 indicates development of dehydroxylation process. This is believed to occur as a result of acid activation of bentonite (Ozcan and Ozcan 2004). In addition, the transformation of the tetrahedral sheet was found at 781 cm-1 and 783 cm-1 for B1 and B05 activated bentonites respectively. The acid activation leads to the formation of amorphous silica, indicated by the increased intensity of the peak, which may expose more adsorption sites (Komandel et al. 1990). Table 4. FTIR band assignments of raw and activated bentonites. Maxima [cm-1] Assignements 3,627 et 3,435 –OH stretching 3,443 –OH stretching, hydratation 1,637 et 1,639 –OH stretching, hydratation 1,039 et 1,038 Si–O stretching (in plane) 523 et 515 Si–O–Al bending 477 et 458 Si-O-Si 790 et 799 Quatrz Effect of contact time and initial Zn (II) concentration on the adsorption Fig. 3 represents a plot of the amount of zinc metal ion adsorbed (mg.g-1) versus contact time for Zn- B05 and Zn-B1 system at different initial metal ion concentration range. 0 20 40 60 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 3.5 mg/l 4.2 mg/l 5,7 mg/l 6.3 mg/l 6.7 mg/l q t( m g g -1 ) t(min) 0 20 40 60 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 3.5 mg/l 4.2 mg/l 5,7 mg/l 6.3 mg/l 6.7 mg/l q e (m g g -1 ) t(min) Fig. 3. Effect of contact time on Zn (II) metal ion adsorption by B05 (A) and B1 (B) for different initial Zn (II) ions concentration. Conditions: pH = 4.5; adsorbent dose = 1 g.L-1; agitation speed = 400 rpm and T = 25 ºC. A A B B05 B1 4 Nova Biotechnol Chim (2022) 21(2): e1267 3 From these plots, it is found that the amount of adsorption i.e. mg of adsorbate per gram of adsorbent increases with increasing of contact time at all initial metal ion concentrations and equilibrium is attained within 50 min for both the systems further it was observed that the amount of metal ion uptake, qt (mg.g -1) is increased with increase in initial metal ion concentration. The increase in adsorption is more pronounced for Zn- B1 system compared to Zn-B05 system the difference in the zinc sorption onto the bentonites may be due to the difference in the mineralogical compositions and associated cations in the exchangeable sites (Sheta et al. 2003). These kinetic experiments clearly indicate that the adsorption of Zn (II) on acid activated clay surface is a two-step process: a rapid adsorption of metal ions to the external surface is followed by possible slow intraparticle diffusion in the interior of the particles (Sen and Sarzali 2008). This two-stage process is also due to the presence of two different types of binding sites on the adsorbents. The two- stage sorption mechanism with the first rapid and quantitatively predominant and the second slower and quantitatively insignificant, has been extensively reported in literature (Yang et al. 2010). Effect of agitation speed The experiments were undertaken with different agitation speeds of (200, 400, 600,800 and 1,000) rpm keeping constant the other process variables. Fig. 4 show that the high amount of Zn(II) ions adsorbed at equilibrium (5.5 and 3.1 mg.g-1 for B1 and B05, respectively) is obtained with an agitation speed of 400 rpm for both adsorbents. The adsorbed amount of Zn(II) increases with an increase of the agitation speed from (200 to 400) rpm, and at higher stirring speed (> 400 rpm), the sorbed amount of Zn(II) decreases. When increasing the agitation speed (< 400 rpm), the diffusion rate of metal ions from the bulk liquid to the liquid boundary layer surrounding sorbent particles becomes higher because of an enhancement of turbulence and a decrease of the thickness of the liquid boundary layer. At higher stirring speeds (> 400 rpm), the decrease of the sorbed amount of Zn(II) is attributed to the rejection of the adsorbent part, which is found plated against the internal walls of the reactor (Boudrahem et al. 2011). 0 200 400 600 800 1000 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 q t (m gg -1 ) Agitation speed(rpm) B05 B1 Fig. 4. Effect of agitation speed on the sorption of Zinc by both activated clay B1 and B05. Conditions: pH = 4.5; initial concentration of Zn(II) = 6.7 mg.L-1 and T = 25 ºC. Effect of adsorbent dosage The effect of adsorbent dosage on the adsorption of zinc (II) was studied at different dosages in the solution at pH 4.5. As shown in Fig. 5, the adsorption percentage of zinc (II) removed ions increased as the dosage of bentonite increased from 1.0 to 3.0 g.L-1. This may be explained by the metal ions competing for limiting adsorption sites at a lower bentonite dosage. 0 10 20 30 40 50 60 0 20 40 60 80 100 E (% ) t(min) 1g/l 2g/l 3g/l Fig. 5. Effect of dosage of B1 activated bentonite on the sorption of Zinc. Conditions: pH = 4.5; initial concentration of Zn(II) = 6.7 mg.L-1 and temperature = 25 ºC. The increase in the adsorption percentage with an increase in adsorbent dosage was due to an increase in active sites on the adsorbent, thus facilitating the 5 Nova Biotechnol Chim (2022) 21(2): e1267 2 penetration of metal ions to the sorption sites (Sarı et al. 2007a; 2007b). These observations agree with others reported in the literature for the adsorption of metals ions by different materials (Mishra and Patel 2009). Effect of the medium temperature Fig. 6 shows that the effect of temperature on the retention of Zn(II) ions is explained by the fact that an increase in temperature leads to a moderately considerable increase in the adsorption capacity, and which becomes increasingly less effective after 15 min of contact, the elimination rate curves for different temperatures become superimposed. The increase in temperature provides energy for the ionic particles which in turn allows them to surpass the repulsion forces with the supports up to a certain limit, beyond which the temperature becomes ineffective “state of saturation”. It can be seen from the analysis of Fig. 6 that the bentonite removal rate reaches approximately 82 % for all temperatures studied. 0 10 20 30 40 50 60 0 20 40 60 80 25°C 35°C 45°C E (% ) t(min) Fig. 6. Effect of dosage of B1 activated bentonite on the sorption of Zinc. Conditions: pH = 4.5; initial concentration of Zn(II) = 6.7 mg.L-1, adsorbent dose = 1 g.L-1, agitation speed = 400 rpm. Adsorption kinetics The kinetics of adsorption describes the rate of metal ions uptake on activated Bentonites and this rate controls the equilibrium time. The kinetics of adsorbate uptake is required for selecting optimum operating conditions for the full-scale batch process (Gupta et al. 1997). The kinetic parameter, which is helpful for the prediction of adsorption rate, gives important information for designing and modelling the processes. The kinetics of the adsorption data was analyzed using different kinetic models, such as pseudo-first-order and pseudo-second-order models. Pseudo-first-order model The kinetic data were treated with the Lagergren first-order model Eq. 3 (Lagergren 1898): (3) where k1 is the adsorption rate constant for the first order adsorption, qtis the amount of heavy metal adsorbed at time t (mg.g-1) and qe is the amount of heavy metal adsorbed at saturation (mg.g-1). The integration of the Eq. 3 gives the following expression Eq. 4: (4) where C1 is the integration constant for first order reaction kinetic. If it is supposed that q = 0 at t = 0, then (Eq. 5): (5) Values of adsorption rate constant k1 for the zinc(II) adsorption onto acid activated bentonites (B1, B05) were determined from the straight-line plot of against t. The data were fitted with a poor correlation coefficient (Table 5), indicating that the rate of removal of zinc onto both acid-activated bentonites does not follow the pseudo first-order equation. Pseudo-second-order reaction kinetic Adsorption data was also evaluated according to the Pseudo second-order reaction kinetic proposed by Ho and McKay (Ho and McKay 1998; Eq. 6): (6) 6 Nova Biotechnol Chim (2022) 21(2): e1267 3 where k2 is the second order reaction constant. If Eq. 6 is integrated, the following expression is obtained (Eq. 7): (7) In Eq. 7, C2 is the integration constant of the second order reaction kinetic. With an algorithmic arrangement, the following statement is formed (Eq. 8): (8) The pseudo second order model can be determined experimentally by plotting t/qt against t, and the constants qe and K2 obtained from the slope and intercept. The pseudo second order kinetic parameters and the R2 value obtained are given in Table 5. This model can thus be applied to the adsorption data, as indicated by the good R2 value obtained. This implies that the rate-limiting step is a chemisorption involving valency forces caused by sharing or exchange of electrons between sorbent and sorbate species in solution (Unlu and Ersoz 2006). The pseudo second order model have been reported to give very good fits to experimental data by many researchers (Sarı et al. 2007a; 2007b). Table 5. Calculated kinetic parameters for pseudo first-order and second order for the adsorption of zinc onto acid activated bentonites. Adsorbent Concentration [mg.L-1] qeexp [mg.g-1] k [g.mg-1.min-1] qe cal [mg.g-1] R2 P se u d o - fi r st - o r d e r k in e ti c B05 3.500 1.920 0.085 3.414 0.911 4.200 2.250 0.088 3.857 0.916 6.700 3.100 0.079 4.275 0.909 B1 3.500 3.120 0.066 3.421 0.955 4.200 3.680 0.07 3.849 0.968 6.700 5.500 0.084 6.61 0.915 P se u d o - se c o n d - o r d e r k in e ti c B05 3.500 1.920 0.001 5.649 0.781 4.200 2.250 0.004 4.587 0.939 6.700 3.100 0.010 4.424 0.994 B1 3.500 3.120 0.0107 4.366 0.975 4.200 3.680 0.0123 4.807 0.990 6.700 5.500 0.012 6.666 0.998 Adsorption mechanism Generally, any sorption process can be described by the following three steps: (i) film or surface diffusion, (ii) intraparticle or pore diffusion and (iii) sorption on the interior sites of the sorbent. Since the last step is very rapid, it is assumed that it does not influence the overall kinetics. The rate of adsorption process, therefore, will be controlled by either film diffusion or intraparticle diffusion depending on which step is slower. The Weber– Morris intraparticle diffusion model has often been used to determine if intraparticle diffusion is the rate-limiting step. The intraparticle diffusion equation can be written by following Eq. 9: (9) where kd is the intraparticle diffusion constant (mg.g-1.min-1/2). According to this model, the plot of qt versus the square root of time t 1/2 should be linear if intraparticle diffusion is involved in the adsorption process and if the plot passes through the origin, then intraparticle diffusion is the sole rate-limiting step. It has also been suggested that in instances when the plot is multilinear two or more steps govern the adsorption process (Boparai and Joseph 2011). Linear plots of the intraparticle diffusion model are shown in Fig. 7 and Table 6. For both B05 and B1 acid activated bentonite, the adsorption process can be divided into three stages; the initial first-shape portion of the curve corresponds to the external surface adsorption stage or instantaneous adsorption stage. The second, gradual linear portion corresponds to intraparticle diffusion, and the final represents the equilibrium stage. 7 Nova Biotechnol Chim (2022) 21(2): e1267 2 Therefore, Zn(II) adsorption on both acid activated bentonites can be considered as the combination of surface adsorption and pore-filling by diffusing. Fig. 7. Intraparticle diffusion plot for Zn (II) adsorption onto acid activated bentonites; Condition: pH = 4.5; agitation speed = 400 rpm and T = 25 ºC. Table 6. Calculated parameters of intraparticle diffusion for the adsorption of zinc onto acid activated bentonites. Adsorbents Concentration [mg.L-1] Kd1 [g.mg-1z.min-1/2] R12 Kd2 [g.mg-1.min-1/2] R22 B05 3.500 0.311 0.954 0.159 0.963 4.200 0.362 0.987 0.200 0.975 6.700 0.586 0.993 0.252 0.993 B1 3.500 0.480 0.943 0.306 0.998 4.200 0.604 0.963 0.299 0.997 6.700 0.967 0.999 0.523 0.981 Adsorption Langmuir isotherm The theoretical Langmuir sorption isotherm is based on the assumption that the maximum adsorption occurs when a saturated monolayer of solute molecules is present on the adsorbent surface, the energy of adsorption is constant and there is no migration of adsorbate molecules in the surface plane. The Langmuir isotherm model is expressed as follows Eq. 10 (Langmuir 1918): (10) where kL is the Langmuir constant (L.mg -1) and qmax is the maximum adsorption capacity (mg.g -1). The linearized Langmuir equation is (Eq. 11): (11) The Langmuir constants, qm (maximum adsorption capacity) and kL, can be obtained from plots between Ce/qe versus Ce, with fixed initial conditions. Overall, Langmuir isotherm model has a high regression coefficient (R2) for both the systems. The amount of metal adsorbed at equilibrium, adjusted by Langmuir model, was 8.4 mg.g-1 for the B1 activated clay and 5.64 mg.g-1 for the B05 activated clay. Table 7. Langmuir parameters obtained from Langmuir plots. Adsorbent T [ºC] qmax [mg.g-1] kL [mg-1] R2 RL [mg.L-1] 3.5 4.2 6.7 B05 25°C 5.64 0.33 0.994 0.46 0.41 0.31 B1 25°C 8.40 1.52 0.996 0.15 0.13 0.08 B A B05 B1 8 Nova Biotechnol Chim (2022) 21(2): e1267 3 The essential characteristics of the Langmuir isotherm can be expressed in terms of dimensionless constant separation factor or equilibrium parameter, RL which is defined by Eq. 12 (Hall et al. 1966): (12) The dimensionless separation factor (RL) was calculated, based on Langmuir constant kL and the initial zinc concentration presented in Table 7 for both the systems. These RL values indicates favorable adsorption as it lie in the range < 0