Special Conference Edition, November, No 2018 http://dx.doi.org/10.4314 314/bajopas.v11i1.2S Bayero Journal of Pure and Applied Sciences, 11(1): 8 - 16 ISSN 2006 – 6996 ADSORPTION OF O LEAD AND COPPER IONS FROM AQUE UEOUS SOLUTIONS USING MULTI-WALL LC CARBON NANOTUBE/KAOLINITE COMPOS OSITE BEADS a Ahmed Salisu isua*, Magaji Ilu Bardea and bUmar Abdulganiy niyu Department of Pure and Indust strial Chemistry, Faculty of Natural and Applied Science, Sc Umaru Musa Yar’ad ’adua University Katsina, PMB 2218, Nigeria, b Department of Chemistry, Faculty Fa of Science, Yusuf MaitamaSule University, y, P.M.B 3220 Kano, Nigeria, * Corresp sponding author: ahmed.salisu@umyu.edu.ng ABSTRACT In this study, adsorption of lea lead (Pb) and copper (Cu) ions from aqueous so solution by kaolinite clay composite beads was investigated inv in batch systems. Alginate (cross sslinker), kaolin and Multiwall carbon nanotube (MCNT) (MC were used in the preparation of the com omposite beads. The composite beads were charact acterized using the following techniques, SEM,, TGA and XRD. The adsorption parameters such h as a pH, metal concentration, adsorbent dose se and shaking time were also studied. The Lang ngmuir and Freundlich isotherm models were e a applied to describe the adsorption equilibrium pr process. The Langmuir model fitted well with th experimental data based on correlation coefficien ients with maximum adsorption capacity (qmax) of 83.33 mg/g and 76.92 mg/g for lead and coppe per ions, respectively. It was observed that th the equilibrium time for both metal ions were attained at in 60 minutes. Reusability studiess revealed that the composite beads maintained d good adsorption capacity after being use sed repeatedly. The composite beads could be used ed in the treatment of metal-bearing effluents. ts. Keywords: Kaolin, alginate, ca carbon nanotube, beads, effluents starch, chitin and algina inate are the most abundant, cheap, renewabl ble and possess many functional groups (Crini, 2006). 20 Alginic acid or its salts called alginate te are among the polysaccharides that occur ur in the cell walls of large number of algae e species. Alginate (polysaccharide) isa copolym lymer which consist of two residues i.e β-1, 4-llinked-D-mannuronic acid (M-block) and α-1,, 4-linked-L-guluronic acid (G-block) (Hauget al., 1966). Alginate form egg-box structure in dilute ea aqueous solutions of BaCl2 and CaCl2 due to pr presence of carboxyl (COOH) and hydroxyl (OH H) functional groups acting as ligands (Holan et al., 1993). Carbon nanotubes have been exte xtensively researched for the removal of metal al ions from aqueous solutions due to their highly hly porous and hollow structure, relatively large sspecific surface area and easily modified surfaces ces (Iijimi, 1991; Xiong et al., 2006; Xuet al., 2006) 6).Clayis another lowcost mineral that has a high hig cation ex-change capacity in solution. Man any clays have been studied for detoxification ion of metals from wastewaters e.g. montmori orillonite (Sdiri et al., 2011, Zhu et al., 2015), be entonite(Chen et al., 2012, Ye et al., 2015) and kaolinite(Jiang et al., 2010). In the presen ent study, composite beads was developed using ing alginate (as cross linker), multiwall carbon n nanotubes (MWCNT) and kaolinite for the remov oval of Pb2+ and Cu2+ ions from aqueous solutions. s. INTRODUCTION The preservation of the en environment has become increasingly important nt in view of the ecological problems brough ght about by industrialization and urbanizat ation (Kumar et al., 2017). Lakes and riverss are a particularly vulnerable to contamination as a result of the discharge of large quantities of effluents from industries and municipalities.. The T presence of heavy metals such as cadmiu ium, chromium, cobalt, copper, lead, me ercury, nickel, chromium, tin and zinc in rivers rs and waterways may result to serious public h health problems and threaten many aquatic orga rganisms (Alloway and Ayers, 1996, Wase e and Foster, 1997).Conventional toxic h heavy metals wastewater treatment techn hniques include chemical precipitation, ion-exchange, electrochemical processes, mem embrane filtration and adsorption. In this content, a cost-effective treatment of wastewater cont ontaminated with heavy metals is required as env nvironmental laws become more stringent (Kad adirvelu et al., 2002).Great deals of low cost ost materials are available in large quantities such s as natural materials, agricultural waste o or industrial byproducts that can be utilized as adsorbents (Lu and Gibb, 2008; Javed et al., ., 2007). Some of these materials can be used ass adsorbents with little processing or by sim simple chemical modification. Biopolymer such ch as cellulose, 8 Special Conference Edition, November, 2018 MATERIALS AND METHODS Sodium alginate, multi wall carbon nanotubes were purchased from Sigma-Aldrich. Kaolin clay was collected from Dutsin-Ma L.G.A. Katsina State. Pb(NO3)2 and Cu(NO3)2·3H2O salts were purchased from Loba Chemie (England). Stock solutions of Pb+2 and Cu+2ions s(1000 mg/L) were prepared by dissolving 3.880 g of Cu(NO3)2·3H2O and 1.599g of Pb(NO3)2 salts in separate beakers (250 cm3) with deionized water respectively and the solutions were transferred to a 1.0litre volumetric flasks each was followed by the addition of 100 mL of 0.1M HNO3 and they were made to mark. Desired concentrations of the metal solutions were prepared by serial dilution of the stock solutions using deionized water. Other chemical reagents were of analytical grade and used as received. Preparation of the Adsorbent The kaolin clay was sieved and washed with distilled water to remove dirt and other particulate matters. The resulting slurry was allowed to sediment and later decanted, thereafter dried in an oven to constant weight. The composite beads were then prepared by dispersing sodium alginate (2.00 g), kaolin clay (6.00 g) and MCNT (3.00 g) in 200cm3 of deionized water and mechanically stirred. The resultant colloidal solution obtained was added drop-wise into a stirred 200cm3 of CaCl2(0.1 M) solution using a syringe. Solid gel beads were immediately formed. The beads were allowed to stay in the CaCl2 solution for 24 hours to stabilize. Subsequently, the beads were thoroughly washed with excess deionized water to removed CaCl2 from the surfaces. Thereafter, the gel beads were dried in the oven until constant weight (Wayne and Fong, 2012). Batch Adsorption Experiments The adsorption experiments were performed by batch equilibrium according to the method described by Pathania et al., 2013 with some modifications. The experiments were carried out in 250cm3conical flasks by mixing 0.4g of the adsorbent with 50cm3of each metal ion solutions of concentrations, 50, 100, 150, 200, 250, and 300mg/L and pH= 4.0 at room temperature using a shaker operating at 300rpm. The samples were taken out from the conical flask on the shaker at specified time intervals and the remaining metal ions in the solutions were separated from the adsorbent by filtration and the filtrates were analyzed by using flame atomic absorption spectrophotometer (Shimdzu, 6800, Japan, 210) to determine the equilibrium metal ion concentrations. All the experiments were conducted in duplicate and averages of duplicate readings were presented. The percentage removal of metal ions and the amount of metal ions adsorbed on the composite beads at equilibrium (qe) were calculated using equations (1) and (2) respectively: × 100 (1) Percentage Removal (%) = qe (mg/g) = ( ) × V (L) (2) where Cois the initial metal ions concentration (mg/L),Ce is the equilibrium concentration of metal ions in solution (mg/L), V is the volume of metal ions solution used (L) and w is the weight of the adsorbent used (g). The equilibrium data obtained were tested using the linear forms of Langmuir and Freundlich isotherm models, as shown in equation (3) and (4), respectively; Characterization Thermogravimetric analyses (TGA) were carried out usingQ500 TGA Thermal analyzer(USA). The analysis was conducted in an inert atmosphere from 30°C to 800°C at a heating rate of 20°C min-1 (Ahmedy et al., 2013). The scanning electron microscope (SEM) micrograph of the beads and its surface morphology were examined using JEOL JSM 6390LV (Japan). Before SEM observation, all samples were fixed on aluminum stubs and coated with gold using auto fine coater (model JFC-1600). (Salisu et al., 2015) Powder X-ray diffraction patterns were recorded on ARL X’TRAX-ray Diffractometer S/N: 197492086 (Thermoscientic, Switzerland)using graphite monochromatic CuKα1 (1.5406 Å) and Kα2operated at 40 kV and 30 mA (Gupta, et al., 2013) Langmuir isotherm The general formula of the Langmuir isotherm for adsorption can be expressed as = + (3) Where qm is the maximum adsorption capacity and QLLangmuir constant To validate this model, a plot of Ce/qevsCe must be linear. The value of parameters, qm and QL can be obtained from calculation of the slope and the intercept (Langmuir, 1916; Langmuir, 1918). The essential feature ofthe model can be stated in a dimensionless constant, referred to as separation factor or equilibrium parameter (RL) which can be calculated using equation (4),(Hoand Wang, 2008). (4) R = 9 Special Conference Edition, November, 2018 reflections in a range of 8 – 65o (2&), depicted in Fig. 1. Besides the XRD of the material showed a prominent reflection at 2& values of roughly 13& and 25&, corresponding to the d values of 6.5139 and 3.6115, respectively. Those are the typical characteristic peaks of kaolinite (Moore and Reynolds, 1997). Again the other peaks corresponding to the 2& value in the range of 15-24& and 26–65& are also characteristic of kaolinite, quartz, illite + quartz, goethite, gibbsite, and dickite (Moore and Reynolds, 1997; Jiang et al., 2010;Emam, et al., 2016). Freundlich Isotherm. The Freundlich adsorption isotherm can be expressed using equation below (5) Iog q! = Iog K # + Iog C! $ Where qe is the amount of metal ion adsorbed at equilibrium time, Ce is the equilibrium concentration of metal ion in solution. KF and n are isotherm constants which indicate the capacity and the intensity of the adsorption, respectively(Freundlich, 1906). Intensity [a. u.] d = 6.5193; 2θ = 13.5710 d = 3.6115; 2θ = 24.6250 RESULTS AND DISCUSSION Characterization XRD Studies of the kaolinite clay The single crystal X-ray crystallographic technique is the most accurate source of information regarding the structure of a material (Sanghavi et al., 2013). Thus, XRD of the Kaolin was scanned in the range of 3 – 60o at a wavelength of 1.54Å to ascertain the level of crystallinity. The material exhibited sharp crystalline peaks, and its pattern accounts for six 10 20 30 40 2θdegree 50 60 Figure 1: XRPD pattern of the kaolinite clay. Peaks 2θ [°] θ[°] sinθ[°] sin2(θ) 1000sin2(θ) 1000sin2θ/CF h2+k2+l2 hkl 1 2 3 4 5 6 8.759 13.571 18.959 24.629 26.588 27.494 4.379 6.786 9.479 12.314 13.294 13.747 0.07636 0.11816 0.16469 0.21327 0.22995 0.23763 0.00583 0.0140 0.0271 0.0455 0.0529 0.0565 5.8300 13.9600 27.1200 45.4900 52.8700 56.4700 1.00 (1) 2.39 (2) 4.65 (5) 7.80 (8) 9.07 (9) 9.69 (10) 100 110 210 220 300 310 d-spacing [Å] obscal 10.08778 6.51933 4.67713 3.61179 3.34992 3.24153 10.0877 6.51919 4.67706 3.61169 3.34987 3.24145 a in Å 10.0877 6.5193 4.6771 3.6117 3.3499 1.6207 weight loss at 30-125°C was due to evaporation of moisture. The second weight loss at 200300°C was due to breakage of C−O−C glycosidic bond and release of gases such methane carbon (IV) oxide as reported (Nuran and Fatma, 2013). Thermogravimetric Analysis The thermal stability of the beads was investigated by TGA. Thermogram of calcium alginate and the composite beads were presented in Fig. 2. Three major steps of weight loss were observed in Fig.2a. The initial 10 Special Conference Edition, November, No 2018 However, in the case of the ccomposite beads (Fig. 2b), four major steps of weight w loss were observed. It can be seen that at degradation of the alginate backbone and relea lease of the gases occurred at 400°C which h indicates that the thermal stability of the composite co beads was higher due the inclusion of o carbon nanotube and kaolinite greater than alginate a alone. Figure 2: TGA therm ermogram of (a) calcium alginate and (b) composit site bead the surface texture and porosity po of beads with holes and small openings ngs on the surface, thereby increasing the contact co area, which facilitates the pore diffusio on during adsorption. The porous nature is clearly rly evident from these micrographs. The diameter ter of the bead was found to be 1 mm ±2 as m measured by the SEM machine. Scanning Electron Microscope e (SEM) ( Scanning electron microscopy (S (SEM) is a useful tool to evaluate the surface e morphology of materials. The micrograph images i of the composite bead and its surface ce morphology is shown in Figure 3. It is obviouss that t the surface morphology of the bead is sph pherical in shape with rough surfaces and por orous. The SEM micrographs of the composite e beads illustrate Figure 3: SEM image age of the (a) composite bead and (b) surface mor orphology negatively charged carbox oxyl groups and the metal ions (Salisu et al., 2015b). 20 The optimum pH obtainedare in agreem ement with the data reported by other authorss ((Chen and Lim 2007; Lim et al., 2009). Howeve ver, the variation of metal uptake by the adsor sorbent between lead and copper ions can be exp xplained based on the metal ion charge den ensity ionic radii, consequently the incre rease metal-binding affinity of Pb2+ over tha hat of Cu2+ can be attributed to the preferenc nce of Pb2+ for binding with the carboxylate ions io both in the mannuronic and guluronic re residues of alginate. Adsorption Studies Effects of Initial pH hly dependent on Heavy metal adsorption is highl pH solution. The pH value affec ects the solubility of the metal ions in solution. T The effect of pH change on adsorption of lead d a and copper was investigated in the range of 2-8 8 as shown in Fig. 4. It was observed that the maximum ma removal percentage (94.88 and 91.54 %) % for Pb+2 and Cu+2respectively took place at an optimum of pH 4.It has been established that th alginate has pK avalue in the range of 3.4 to 4.5, therefore electrostatic attraction ex exists between 11 Special Conference Edition, November, 2018 protons and metal ions in the solutions as a result of repulsion between adsorbent surface (positively charged) and incoming metal ions, thus lowering the rate of adsorption (Ahmed et al., 1998). However, at higher pH beyond 8, precipitation may takes place instead of adsorption. This behaviour has also been reported by other authors (Haug, 1961; Haug and Smidstrod, 1965). The authors reported that the affinity of alginate to metal ions follows the order Pb2+> Cu2+> Cd2+> Ba2+> Ca2+> Co2+> Ni2+.The decreased of percentage removal at lower pH may be due to the competition between 100 Pb Cu % Removal 80 60 40 20 2 3 4 5 6 7 8 pH Figure 4: Effect of pH on the adsorption of metal ions by composite beads at which the metal ions were adsorbed. It was observed that 86% and 69% removal took place within 70 minutes for both Pb2+ and Cu2+, respectively. This could be attributed to the high affinity and interaction between adsorbent and metal ions in the solution due to the sufficient equilibrium time. Effects of Contact Time In order to determine the effect of the contact time, 0.4g of the adsorbent was stirred with a 50cm3 solution of initial metal concentration (100mg/L) for a time interval between 10 to 90 minutes at pH= 4. The data obtained was presented in Figure 5. The increases in contact time at 300 rpm stirring rate increased the rate 100 Pb Cu % Removal 80 60 40 20 0 20 40 60 80 100 Time (minutes) Figure 5: Effect of contact time on adsorption of metal ions by composite beads 12 Special Conference Edition, November, 2018 metal ions, but eventually decrease with the increased in the initial concentration. This can be attributed to the exhaustion of available active sites on the adsorbent required for the high initial concentration of the metal ions adsorption (Salisu et al., 2016). Effects of Initial Metal ions Concentration The effect of initial concentration of Pb2+ and Cu2+ metal ions on the percentage removal by the composite beads was investigated in the range of 50-300 mg/L and the results were shown in Fig. 6.The removal percentage was found to be high at lower concentration of the 100 % Removal 80 Pb Cu 60 40 20 50 100 150 200 250 300 Concentration (mg/L) Figure 6: Effect of concentration of metal ions on adsorption by composite beads allowed more adsorption. Furthermore, the observed reduction of metal ions uptake at higher dosage may be attributed to crowding effects, so that the active sites on the adsorbent become obscured for metal binding. Other researchers have also reported the crowding effects in the adsorption of heavy metals (Kandah and Meunier, 2007). Effects of Adsorbent Dose The effect of adsorbent dosage(0.1-0.5g) on percentage removal of Pb2+ and Cu2+ was shown in Figure 4. It was observed that the percentage removal increased with an increase in adsorbent dose up to 0.4 g, thereafter percentage removal was found to be decreasing, which may be attributed to saturation of the adsorbent which will not 100 Pb Cu % Removal 80 60 40 20 0.1 0.2 0.3 0.4 0.5 0.6 Adsorbent dose (g) Figure 7: Effect of adsorbent dose on adsorption of metal ions by composite beads 13 Special Conference Edition, November, 2018 equation based on higher correlation coefficients and adsorption capacity for both metal ions. The separation factor, RL has been found to be less than unity in both cases which indicated that the adsorption was favourable. Although, the adsorption process revealed that it is a monolayer adsorption which implies that there is formation of covalent bond between the adsorbate and the adsorbent surface, notwithstanding there may be also other weak forces attraction (Van der Waals interactions) that could occurred during the adsorption process. Thus, it can be generally concluded that the adsorption process assumed a monolayer adsorption process. The maximum adsorption capacity of the composite beads, qmax, constants and correlation coefficients were represented in Table 1. Equilibrium Studies Adsorption isotherms are very useful tools for theoretical evaluation and modelling of adsorption process and performance. The Langmuir and Freundlich isotherms are the most common model for describing adsorption equilibrium in solid-liquid interface. The Langmuir model assumes a homogeneous surface coverage with respect to the energy of adsorption, which is constant and independent on the degree of occupation of an adsorbent’s active centres (Langmuir, 1916). The value describes the isotherm type: unfavourable (RL> 1), linear (RL = 1), favourable( 0< RL< 1) or irreversible (RL= 0). (Langmuir, 1916). In general, the data obtained from the adsorption equilibrium studies revealed that Langmuir isotherm showed a better fitting (Table 1)as compared with Freundlich isotherm Table 1: Langmuir and Freundlich isotherms constants and correlation coefficients Freundlich isotherm Langmuir isotherm Metal ion (KF) (n) (R2) (QL) ,(qe) RL (mg/g) (g/L) (L/mg) (mg/g) Pb 72.25 2.32 0.930 0.015 83.33 0.6 Cu 66.75 1.43 0.918 0.044 76.92 0.3 (R2) 0.999 0.996 washed with deionized water before the next cycle. It was observed that in the first cycle, the percentage removal was 79% for lead and 82% for copper, but in the subsequent cycles, percentage removal was found to be greater than 95% for both lead and copper. This could be attributed to increase the surface porosity of the adsorbent as a result of interaction with the acid. A similar trend was reported on the adsorption and desorption of alginate beads using HCl (Salisu et al., 2016). The result showed that the alginate composite beads maintained good adsorption capacity for several cycles. Reusability Studies Adsorbent substances can be restored to original conditions by desorption process that usually involve the application of heat or by using a suitable solvents (usually mineral acids) (Wilson, 1994). Desorption experiments were performed to evaluate the possibility of reusability and regeneration of the alginate composite beads as an adsorbent. Adsorptiondesorption cycles were repeated for five consecutive times using metal ion concentration of 100 mg/L, HCl (0.1 M, 10 mL) as adsorption solvent and 0.2 g of the adsorbent. The adsorbent was thoroughly Pb Cu 100 % Removal 80 60 40 20 0 1 2 3 4 5 6 Number of cycles Figure 8: Adsorption-desorption cycles of the adsorbent[ Extraction conditions: metal ion concentrations, 100 mg/L, adsorbent dose 0.4g, batch volume 50cm3, desorption solution, 0.1 M HNO3 (10cm3), contact time 1 h] 14 Special Conference Edition, November, 2018 CONCLUSION A composite alginate adsorbent was prepared and used for the removal of lead and copper ions from aqueous solutions. There are several factors affecting the adsorption of metal ions onto alginate composites, however, pH was the significant factor to be considered. The optimum conditions found were 4, 150mg/L and 0.4g for pH, metal ions concentrations and adsorbent dose, respectively. The equilibrium data fitted better with Langmuir isotherm equation, with maximum adsorption of 83.33mg/g and 76.92mg/g for lead and copper ions respectively. The adsorption equilibrium was achieved within 1 hr. 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