Scholarly article on topic 'Potential of a low-cost bentonite for heavy metal abstraction from binary component system'

Potential of a low-cost bentonite for heavy metal abstraction from binary component system Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Keywords
{Adsorption / Bentonite / "Heavy metals" / Equilibrium / Kinetics / Thermodynamics}

Abstract of research paper on Chemical sciences, author of scientific article — Kovo G. Akpomie, Folasegun A. Dawodu

Abstract A low-cost and easily obtainable Nigerian bentonite (UAB) was utilized for the removal of heavy metals (Nickel and Manganese) from a binary system. The bentonite was used without chemical modification in order to keep the process cost low. A Fourier transform infrared spectrum was utilized to determine the surface functional groups responsible for adsorption. Scanning electron microscopy revealed a porous surface of UAB. Batch adsorption methodology was applied to study the effect of pH, initial metal ion concentration, adsorbent dose, adsorbent particle size, ligands (citric acid and EDTA), contact time and temperature on the adsorption process. The isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Scatchard isotherm. Scatchard plot analysis revealed the heterogeneous nature of UAB. Kinetic parameters were tested using the pseudo-first order, pseudo-second order, intraparticle and film diffusion models. The presence of film diffusion mechanism was found to play a major role in the adsorption process. Thermodynamic studies revealed an endothermic, spontaneous and physical adsorption process. Importantly, over 90% of both metal ions were desorbed from the bentonite in desorption studies. The results indicated the potential of UAB as a low-cost and eco-friendly adsorbent for the removal of Ni(II) and Mn(II) ions from aqua media.

Academic research paper on topic "Potential of a low-cost bentonite for heavy metal abstraction from binary component system"

beni-suef university journal of Basic and applied sciences xxx (2015) 1-13

HOSTED BY

10 11 12

20 21 22

60 61 62

ELSEVIER

Available online at www.sciencedirect.com

ScienceDirect

journal homepage: www.elsevier.com/locate/bjbas

Potential of a low-cost bentonite for heavy metal abstraction from binary component system

Q5Q1 Kovo G. Akpomie a'' , Folasegun A. Dawodu

a Department of Chemistry (Industrial), University of Ibadan, Ibadan, Nigeria

b Materials and Energy Technology Department, Projects Development Institute (PRODA), Federal Ministry of Science and Technology, Enugu, Nigeria

ARTICLE INFO

ABSTRACT

Article history: Received 19 June 2014 Accepted 5 December 2014 Available online xxx

Keywords:

Adsorption

Bentonite

Heavy metals

Equilibrium

Kinetics

Thermodynamics

A low-cost and easily obtainable Nigerian bentonite (UAB) was utilized for the removal of heavy metals (Nickel and Manganese) from a binary system. The bentonite was used without chemical modification in order to keep the process cost low. A Fourier transform infrared spectrum was utilized to determine the surface functional groups responsible for adsorption. Scanning electron microscopy revealed a porous surface of UAB. Batch adsorption methodology was applied to study the effect of pH, initial metal ion concentration, adsorbent dose, adsorbent particle size, ligands (citric acid and EDTA), contact time and temperature on the adsorption process. The isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Scatchard isotherm. Scatchard plot analysis revealed the heterogeneous nature of UAB. Kinetic parameters were tested using the pseudo-first order, pseudo-second order, intraparticle and film diffusion models. The presence of film diffusion mechanism was found to play a major role in the adsorption process. Thermo-dynamic studies revealed an endothermic, spontaneous and physical adsorption process. Importantly, over 90% of both metal ions were desorbed from the bentonite in desorption studies. The results indicated the potential of UAB as a low-cost and eco-friendly adsorbent for the removal of Ni(II) and Mn(II) ions from aqua media.

Copyright 2015, Beni-Suef University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

4.0/).

Introduction

The pollution of water with toxic substances is a major problem because it affects the environmental quality as well as plants, animals and human health. Heavy metals are one of the toxic substances and are hazardous even at very low concentrations (Liu et al., 2008). Heavy metals are harmful because they are non-biodegradable, bio-accumulate in the

food chain and are persistent in nature (Ceribasis and Yetis, 2001). Manganese for instance is toxic mainly because of its organoleptic properties (Taffarel and Rubio, 2009). Nickel which is used to produce ferrous steel cutlery and mainly obtained from Ni/Fe storage batteries is responsible for gastrointestinal irritation and lung cancer in humans when present above the threshold limit (Greenwood and Earnshaw, 1993). As a result of the toxic effect of these heavy metals, the need for their removal from industrial wastewaters is very

* Corresponding author. Department of Chemistry (Industrial), University of Ibadan, Ibadan, Nigeria. Tel.: +2348037617494.

E-mail address: kovoakpmusic@yahoo.com (K.G. Akpomie). Peer review under the responsibility of Beni-Suef University http://dx.doi.org/10.1016Zj.bjbas.2015.02.002

2314-8535/Copyright 2015, Beni-Suef University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

80 81 82

99 100 101 102

110 111 112

120 121 122

128 129

bENi-suef university journal of Basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

important. This led to the use of many techniques for their removal from wastewaters by many researchers such as solvent extraction, ion exchange, chemical precipitation, membrane separation, reverse osmosis, electrolysis and adsorption (Tewari et al., 2005). These techniques are expensive, complicated; time consuming and sometimes ineffective in the lowering of concentration ranges (Schiewer and Patil, 2008).

The adsorption technique has been found to be superior to the other techniques for removal of heavy metals, in terms of cost, flexibility, simplicity of design, ease of operation, insensitivity to toxic pollutants and better removal efficiency (Amer et al., 2010; Mohan et al., 2008). Also, it does not result in the formation of harmful substances like most of the other techniques. Activated carbon has been found to be the most effective adsorbent for the removal of metals from solution due to its high adsorption capacity. However, it is expensive and this limits its wide spread use in most industries and developing nations. As a result, many researchers have studied the use of several low-cost adsorbents for the removal of metal ions from solution, so as to minimize the problem of high cost involved in the use of activated carbon. Some of the low-cost adsorbents that have been utilized include agricultural waste and biomass materials, clays, zeolites, siliceous materials, fly ash and bentonite (Bhattacharyya et al., 2008; Dawodu et al., 2012a; Vaghetti et al., 2008). This study is an extension in the same direction in utilizing a commonly available adsorbent, namely, bentonite for the removal of heavy metals from solution. Bentonite was chosen because it is present in an abundant amount in Afuze, Owan east local government area, Edo state, Nigeria and can be utilized as a cheap alternative adsorbent. Bentonite has also been reported to have a high adsorption capacity for heavy metals due to its high specific surface area, small particle size, high porosity and high cation exchange capacity (Doulia et al., 2009).

This paper reports the use of a natural Nigerian bentonite for the simultaneous adsorption of Ni(II) and Mn(II) ions from aqueous solution as a low cost adsorbent. The bentonite was used without chemical modification or treatment in order to keep the process cost low. The effect of pH, initial metal ion concentration, contact time, adsorbent dose, particle size, temperature and ligand were determined. Equilibrium, kinetic and thermodynamic parameters were also evaluated to help provide a comprehensive explanation of the sorption process.

2. Experimental

2.1. Preparation of adsorbent

The bentonite was obtained from Afuze, in Owan east local government area, Edo state, Nigeria. It was then dissolved in excess distilled water in a pretreated plastic container, stirred to ensure uniform dissolution and then sieved through a 500 mm mesh, in order to get rid of plant materials and unwanted particles. The suspension was allowed to settle for 24 h and then excess water was decanted. The bentonite residue was sundried for several days and then dried in an

oven at 105 °C for 4 h, to get rid of water present. The dried bentonite was then pulverized and passed through mesh sieves of sizes 100-500 mm, to obtain the unmodified Afuze bentonite (UAB). The prepared adsorbent was then preserved in an air-tight polythene bag until use.

Adsorbent characterization

The elemental composition of UAB was determined after digestion of the sample with nitric acid and by the use of the Atomic Absorption Spectrophotometer (AAS) (Buck scientific model 210VGP) as described (Papafilippaki et al., 2008). Cation exchange capacity (CEC) of UAB was determined by the ammonium acetate method (Rhoades, 1982). The pH point of zero charge (pHpzc) was carried out as described (Onyango et al., 2004), while the slurry pH of UAB was obtained by soaking 1g of the adsorbent in 50 ml of distilled water, then stirred for 24 h and filtered, after which the final pH was determined by the use of a pH meter. A Fourier Transform Infrared (FTIR) spectrum of UAB was determined by the Fourier Transform Infrared spectrophotometer (Shimadzu FTIR 8400s). The BET surface area and pore property of UAB was determined via nitrogen adsorption-desorption isotherms by the use of a micromeritics ASAP 2010 model analyzer. The Scanning Electron microscope (SEM) (Hitachi S4800 model) was used to access the morphology of the adsorbent. X-ray diffraction (XRD) analysis was determined using a model MD 10 Randicon diffractometer operating at 25kv and 20 mA. The scanning regions of the diffraction were 16-72° on the 29 angle.

2.3. Preparation of binary solution

All the reagents used in this study were of analytical grade obtained from Sigma Aldrich and were used without further purification. A binary stock solution containing 1000 mg/L of Ni(II) and Mn(II) ions was prepared by dissolving appropriate amounts of NiSO4 • 6H2O and MnSO4 • H2O in 1L double distilled water. The stock solution was used to prepare dilute solutions of different working concentrations (100-500 mg/L). The pH of the solution was altered to values ranging from 2.0 to 8.0 by the drop wise addition of 0.1M NaOH or 0.1M HCl when required.

2.4. Batch adsorption

The adsorption of Ni(II) and Mn(II) ions unto UAB was studied by the use of batch adsorption procedure. The effects of various operating parameters on adsorption were determined. Each experiment was performed in duplicate and the mean value was computed to ensure quality assurance. At the end of a given contact time for each experiment, the solution mixture was filtered using whatmann No.1 filter paper and the residual Ni(II) and Mn(II) ion concentration in the filtrate was determined using the AAS. The batch experiments were performed under optimum experimental condition as described: The effect of pH was determined at pH values of 2-8 by adding 0.1 g of UAB to 50 ml of solution, at a solution concentration 100 mg/L, contact time 180min, adsorbent particle size 100 mm and at room temperature of 300 K. Initial metal ion

80 81 82

99 100 101 102

110 111 112

120 121 122

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

concentration effect was determined in the concentration range (100-500 mg/L) at pH 6.0. The effect of adsorbent dose was studied in the range 0.1-0.5 g, while the effect of particle size was studied by varying the particle size of UAB from 100 to 500 mm. Contact time was studied in the range 20-300min, and temperature in the range of 300-323 K in a thermo-stated water bath for temperature regulation.

Furthermore, the effect of two ligands, citric acid (CA) and EDTA on the simultaneous adsorption of both metal ions from solution unto UAB were also determined. The ligands were made to different concentrations of 100 mg/L of CA and EDTA (0.1-CA and 0.1-EDTA), 500 mg/L of both ligands (0.5-CA and 0.5-EDTA) and 1000 mg/l of both ligands (1.0-Ca and 1.0-EDTA), in solution containing 100 mg/L of both metal ions at a pH 6.0, contact time 180min, particle size 100 mm and a temperature of 300 K. This was performed by adding 0.1 g of UAB to 50 ml of the solution containing the metal ion and a ligand.

The residual Ni(II) and Mn(II) ions obtained from the filtrate determined by the AAS were analyzed to evaluate the adsorption capacity (mg/g) of UAB and the percentage removal (E) using Equations (1) and (2) respectively:

qe = V(Co-Ce)/m E(%) = 100[(Co-Ce)/Co]

(1) (2)

where qe is the adsorption capacity of the adsorbent for metal ions (mg/g), Co is the initial metal ion concentration in solution (mg/L), Ce is the equilibrium concentration of metal ions (mg/L), V is the volume of solution used (L) and m is the dry weight (g) of the adsorbent used.

2.5. Desorption studies

In order to remove the bounded Ni(II) and Mn(II) ions adsorbed unto the adsorbents. Desorption experiment was performed using de-ionized water and HCl as stripping agent. The Ni(II) and Mn(II) loaded adsorbents were prepared. To study the effect of different concentrations of HCL on desorption, 0.1 g of dried metal loaded adsorbent was mixed with 50 ml of different concentration of HCl (0.05-1.0 M) and agitated for 1hr, then filtered and the concentration of eluted metal was determined in the filtrate by the AAS. The percentage desorption was calculated by the equation:

% Desorption = 100[CDVD]/qem

where CD (mg/L) is the concentration of metal ions in the desorbed solution, VD (L) is the volume of desorbed solution, m(g) is the mass of adsorbent used for desorption studies and qe (mg/g) is the adsorption capacity of the adsorbent for metal ions. The time needed to complete desorption was also estimated at different time intervals of (5-60min) using 0.1M HCl. Three cycles of adsorption/desorption was performed to determine the reusability of the adsorbents. The adsorption and desorption experiments were performed under the same conditions as above. After each cycle the adsorbents were washed with de-ionized water and dried in the oven.

3. Results and discussion

3.1. Characterization of adsorbent

The physicochemical characterization of UAB is presented in Table 1. From the Table, it is observed that UAB is composed mainly of silica and alumina as the major constituents, while other elements are present in smaller amounts as impurities (Dawodu et al., 2012b). The pH point of zero charge (pHpzc) can be defined as the pH at which there is a net zero charge on the surface of the adsorbent. The functional groups on an adsorbent surface may acquire a negative or positive charge depending on the pH of the solution. There exist a relationship between the pHpzc and adsorption capacity of an adsorbent, which is that cations adsorption will be favorable at pH values higher than the pHpzc when the surface of the adsorbent is negatively charged, while anions adsorption will be favored at pH values lower than the pHpzc when the adsorbent surface is positive (Nomanbhay and Palanisamy, 2005). The pHpzc of UAB as shown in Table 1, is 2.8, this implies that the adsorbent is suitable for adsorption of metal ions even at low pH values (as low as pH 3.0). Also, UAB was found to have a high cation exchange capacity (CEC) of 146.13Meq/100 g, which is desirable for an effective adsorption. The adsorbent also recorded a BET surface area (SBET) of 69.34 m2/g, a total pore volume (TPV) of 0.0824 cm3/g and an average pore diameter of 47.53 Â. When compared to the SBET values obtained for bentonites by other researchers, which include 34.1 m2/g reported by Guerra et al. (2013), 20 m2/g and 56 m2/g obtained by Shu-li et al. (2009) and 31.5 m2/g reported by Xifang et al. (2007), UAB was found to have a higher surface area which is desirable for efficient sorption. Some factors contribute to the variation in SBET values of different bentonite samples, which are the type and purity of the bentonite, the saturating cation, the out-gassing temperature and the method of preparation of the sample.

The FTIR spectra of UAB before and after adsorption of Ni(II) and Mn(II) ions are illustrated in Fig. 1. The spectra of UAB before adsorption of metal ions showed absorption bands at 3697.66 cm-1 and 3622.44 cm-1 which corresponds to the inner surface -OH stretching vibrations. The presence of the

Table 1 - Physicochemical characterization of UAB.

Parameter Value

SiO2 (%) 53.12

Al2Ö3 (%) 22.81

CaO (%) 4.01

MgO (%) 1.87

Na2O (%) 1.02

Fe2O3 (%) 2.65

K2O (%) 1.27

TiO2 (%) 0.51

MnO (%) 0.42

LOI (%) 12.32

Sbet (m2/g) 69.34

TPV (cm3/g) 0.0824

APD (Â) 47.53

pHpzc 2.8

Slurry pH 2.2

ECEC (meq/100 g) 146.13

80 81 82

99 100 101 102

110 111 112

120 121 122

bENi-suef university journal of Basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

Fig. 1 - FTIR spectra of (a) unloaded UAB, (b) metal loaded UAB after adsorption.

outer surface -OH stretching was indicated by the bands at 3443.05 cm-1 and 3416.05 cm"1. The band at 2360.95 cm"1 also corresponds to the -OH stretching vibration. Absorption at

charged metal ions to the surface of UAB. The Si-O group was also involved in the adsorption as can be observed by their shifts in absorption frequency from 1035.81 cm"1 to

1631.83 cm"1 indicates the -OH bending vibration of water 1033.88 cm"1, 696.33 cm"1 to 694.4 cm"1, 779.27 cm"1 to

and may also be due to the presence of the -COO" symmetric stretching vibration (Li et al., 2011). The occurrence of the outer -OH stretching and the symmetric -COO" stretching vibration suggest the presence of smectite structure (Ekosse, 2005). The Si-O bending vibration was indicated by absorption bands at 1163.11-1008.8 cm"1, while the Si-O stretching vibrations were observed at 798.56-644.25 cm"1. The presence of the Al-O bending vibration was revealed by the band at 914.29 cm"1, while absorptions at 538.16-432.07 cm"1 correspond to the Al-O-Si skeletal vibrations (Njoya et al., 2006; Vempati et al., 1996).

After the adsorption of Ni(II) and Mn(II) ions from the binary solution by UAB, there were shifts in the frequency of absorption from 3443.05 cm"1 to 3446.91 cm"1, 2360.95 cm"1 to 2347.45 cm"1, 1631.83 cm"1 to 1629.9 cm-1 and the disappearance of the band at 3416.05 cm"1 which indicated the use of the negatively charged -OH group for binding of positively

754.19 cm"1 and the disappearance of the bands at 1105.25 cm"1 and 644.25 cm"1. Also, the shift in the frequency of absorption from 538.16 cm"1 to 540.09 cm"1 also indicates the involvement of the Al-O-Si linkage in the adsorption process. In general, the shifts in these adsorption bands after sorption confirm the occurrence of the adsorption process.

The SEM image of UAB is shown in Fig. 2, the morphology of the adsorbent revealed a porous structure with particle aggregation of various sizes, the presence of pores in the adsorbent is very important as this would influence greatly the uptake of the metal ions from the solution unto adsorbent.

Furthermore, the XRD spectrum of UAB (Fig. 3) showed smectite-illite as principal clay minerals and quartz, feldspar and kaolinte as impurities or accessory materials. Similar composition has been reported by Guerra et al. (2013) on the characterization of Brazilian bentonite but with the exception of kaolinite impurity.

80 81 82

99 100 101 102

110 111 112

120 121 122

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

Fig. 2 - Sem image of unloaded UAB.

3.2. Influence of pH

The initial pH of a solution may change the surface charge of an adsorbent, the degree of ionization of adsorbate in solution and the extent of dissociation of the functional groups on the adsorbent (Nandi et al., 2009). Therefore it plays an important role in adsorption. The effect of pH on the simultaneous adsorption of Ni(II) and Mn(II) ions unto UAB is shown in Fig. 4. An increase in the percentage removal of both metal ions with increase in pH was obtained. A significant adsorption of both metal ions was mainly achieved at pH values of 4 and above (pH values greater than the pHpzc of 2.8), this is due to the fact that the surface of the adsorbent became negative at these pH values, thereby favoring the adsorption of metal ions (Nomanbhay and Palanisamy, 2005). The increased competition between the hydrogen ions H+ and the metal cations in solution at lower pH values for available active sites on UAB was responsible for the lower adsorption recorded at these values. This is because a large number of active sites on UAB will be positively charged at low pH. At higher pH values, the active sites becomes negative because fewer H+ ions are available in solution thereby reducing the competition between the protons and metal ions for the active sites of UAB, resulting in a higher percentage removal (Igberase et al., 2014). As the solution pH increases further (pH > 6.0), the onset of metal hydrolysis and precipitation begins, due to the likelihood of precipitaton of the hydroxide forms of the adsorbate

Fig. 4 - The effect of initial pH of solution on the adsorption of Ni(II) and Mn(II) ions unto UAB.

species (Akpomie and Dawodu, 2014). Therefore an optimum pH of 6.0 was chosen in this study, to investigate the effect of other operating parameters on adsorption, since optimum removal was achieved and metals precipitation was avoided at this pH.

3.3. Influence of metal ion concentration

The ability of UAB to remove Ni(II) and Mn(II) ions simultaneously from solution at different initial metal ion concentration was determined and presented in Fig. 5. As observed a decrease in percentage removal of both metal ions with increase in initial metal ion concentration was achieved, until an equilibrium removal was obtained at higher concentrations of 400-500 mg/L. This could be explained that each adsorbent has a fixed number of active adsorption sites, which are available to adsorb more metal ions at lower concentrations, but as the concentration increases, the active sites becomes saturated leading to a reduction in the percentage removal. On the other hand, an increase in the uptake capacity for both metal ions with increase in initial metal ion concentration was obtained. This sorption characteristic indicated that surface saturation is a function of the initial metal ion concentration in solution. The reason for this trend

Fig. 3 - X-ray diffraction (XRD) Spectra of the unmodified bentonite.

80 81 82

99 100 101 102

110 111 112

120 121 122

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

Fig. 5 - Effect of initial metal ion concentration on (a) the percentage removal of Ni(II) and Mn(II) ions unto UAB, (b) the adsorption capacity of UAB for Ni(II) and Mn(II) ions.

is that, at lower concentrations, fewer metal ions are available in solution, therefore maximum binding of the metals on the active sites of UAB was not achieved, but as the concentration increases, the presence of a high concentration gradient generates a stronger driving force which overcomes resistances to mass transfer, in the process, making maximum use of the active sites resulting in higher adsorption per unit mass of UAB (Dawodu and Akpomie, 2014).

3.4. Effect of adsorbent dose

Adsorbent dose is known to have a great effect in adsorption studies. The amount of adsorbent available in solution determines the number of active binding sites available for metal ions (Zafar et al., 2007). The effect of adsorbent dose on the adsorption of Ni (II) and Mn(II) ions from aqueous solution unto UAB is presented in Fig. 6. An increase in percentage removal of both metal ions with increase in adsorbent dose was observed. This increase is attributed to an increase in the number of active sites available for metal ions to bind with increase in the dosage of UAB (Li et al., 2003). Furthermore, a reverse trend was observed in which a decrease in the adsorption uptake capacity of both metal ions with increase in adsorbent concentration was obtained. This decrease may be

Fig. 6 - Effect of adsorbent dose on (a) the percentage removal of Ni(II) and Mn(II) ions unto UAB, (b) the adsorption capacity of UAB for Ni(II) and Mn(II) ion.

due to the higher UAB dose, providing more active sites, which resulted in the adsorption sites remaining unsaturated during the adsorption process (Raji and Anirudhan, 1997). This may also be due to decrease in the total surface area of the adsorbent and an increase in the diffusion path length caused by the aggregation of UAB particles (Unuabonah et al., 2008). Therefore an adsorbent dose of 0.1 g was chosen in this study due to its higher adsorption capacity.

3.5. Equilibrium isotherm modeling

Equilibrium adsorption isotherms provide useful information for designing and optimizing operating procedure for adsorption systems. Adsorption isotherms can be used to relate the adsorbate concentration in the bulk and the adsorbed amount at the interface at equilibrium. In this regard, the Langmuir, Freundlich and Temkin isotherms were applied to the experimental data and their parameters are given in Table 2.

Firstly, the Langmuir isotherm has been used empirically because it provides information on uptake capabilities and is capable of reflecting the usual equilibrium sorption behavior. This isotherm assumes that the forces that are exerted by chemically unsaturated surface atoms (total number of active

80 81 82

99 100 101 102

110 111 112

120 121 122

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

Table 2 - Equilibrium isotherm constants for the

adsorption process.

Isotherm models Ni(II) Mn(II)

Langmuir isotherm

qL (mg/g) 200 166.7

Kl (L/mg) 0.007 0.004

r2 0.885 0.689

Freundlich isotherm

Kf (mg/g) (mg/L)Vn 5.35 3.61

n 1.74 1.79

r2 0.987 0.924

Temkin isotherm

B (mg/g) 41.02 31.09

A (L/g) 0.075 0.053

r2 0.916 0.817

Scatchard Plot

qm (mg/g) 206.3 149.2

b (L/mg) 0.007 0.005

r2 0.775 0.470

sites) do not extend further than the diameter of one sorbed molecule and therefore adsorption is restricted to a mono-layer (Langmuir, 1918). The Langmuir isotherm model can be expressed as:

Ce/qe = 1/qLK + Ce/q.

The parameters qL (mg/g) and KL (L/mg) represents the monolayer adsorption capacity of UAB and the Langmuir affinity parameter respectively. The constants qL and KL were calculated from the slope and intercept of the linear plot of Ce/ qe versus Ce. From Table 2, the low regression coefficient (r2) for Ni(II) (0.885) and Mn(II) (0.689) showed that the Langmuir isotherm did not fit the equilibrium data properly for both metal ions. This might suggest that the surface of UAB is heterogeneous and not homogenous in nature. Furthermore, in order to investigate if the adsorption of both metal ions unto UAB is a favorable one, an important separation factor (RL) of the Langmuir isotherm was applied as given:

Rl = 1/[1 + KLCO]

If the value of RL is considerably less than 1.0 but greater than 0, then the adsorption is said to be favorable. On the other hand, it is unfavorable when RL is greater than 1.0. For different initial concentrations, Co values ranging from 100 to 500 mg/L used, the values of RL range from 0.22 to 0.58 for Ni(II) and 0.33 to 0.71 for Mn(II) ions, which indicated a favorable adsorption of both metal ions unto UAB.

The Freundlich isotherm is an empirical expression based on adsorption onto a heterogeneous adsorbent surface (more than one type of binding sites). The linear form of this isotherm can be represented as (Freundlich, 1906):

logqe = logKF + [1/n]LogCe

where KF is the Freundlich constant related to the sorption capacity (mg/g) (mg/L)1/n and n is a dimensionless constant related to the adsorption intensity of the adsorbent. Therefore, the plot of logqe versus logCe gives a straight line of slope 1/n and intercepts logKF. It is seen from Table 2 that the Freundlich isotherm provided a very good fit to the experimental data as the r2 values of 0.987 for Ni(II) and 0.924 for

Mn(II) are high. This may suggest that the adsorption of both metal ions unto the surface of UAB is heterogeneous in nature. The Freundlich constant KF indicates the sorption capacity of the sorbent and the value of KF was found to be 5.35 and 3.61 for Ni(II) and Mn(II) ions respectively. The slope 1/n of 0.57 and 0.56 for Ni(II) and Mn(II) ions respectively, ranging between 0 and 1, is a measure of the surface heterogeneity, becoming more heterogeneous as its value gets closer to zero (Hameed et al., 2007). If the value of n lies between 1 and 10, then the adsorption is said to be favorable (Slejko, 1985). The value of n obtained for both metal ions lie in this range indicating again a favorable adsorption unto the surface of UAB.

The Temkin isotherm is based on the assumption that the free energy of adsorption is dependent on the surface coverage and takes into account the interactions between adsorbents and metal ions. The linear form of the Temkin isotherm model equation is expressed as (Tempkin and Pyzhev, 1940):

qe = BlnA + BlnCe

A linear plot of qe versus lnCe enables the determination of the Temkin constants, A and B. Where A is the equilibrium binding constant corresponding to the maximum binding energy (L/mg), B = RT/b, is related to the heat of adsorption, b is the Temkin isotherm constant, T is the absolute temperature (K) and R is the ideal gas constant (8.314 J/molK). From the linear regression shown in Table 2, the r2 values of 0.916 and 0.817 for Ni(II) and Mn(II) ions respectively, are lower than the Freundlich values. Therefore, the adsorption of both metal ions unto UAB does not follow the Temkin isotherm closely.

Furthermore, in order to obtain more comprehensive information about the nature of the binding sites on the adsorbent and to analyze the results of the equilibrium isotherm, the scatchard plot analysis also called independent site oriented model was applied to the experimental data. The scatchard equation is given as (Anirudhan and Suchithra, 2010):

qe/Ce = qmb-qeb

The constants qm (mg/g) and b (L/mg) are the scatchard isotherm parameters. The shape of the scatchard plot provides useful information about the interactions between metal ions and the adsorbent. If a straight line is obtained from the plot of qe/Ce versus qe, then the adsorbent presents only one type of binding site, but if a deviation from linearity was obtained, it implies that the surface of the adsorbent presents more than one type of binding sites (heterogeneous in nature) (Anirudhan and Suchithra, 2010). The r2 values of 0.775 for Ni(II) and 0.470 for Mn(II) ions (Table 2) showed a great deviation from linearity. This implies that the surface of UAB is heterogeneous and this clarifies the reason why the Freundlich model (heterogeneous adsorption) gave the best fit to the equilibrium data than the Langmuir and Temkins isotherms.

3.6. Effect of particle size

The particle size of an adsorbent can also have a significant effect on the adsorption potential of the adsorbent, so

80 81 82

99 100 101 102

110 111 112

120 121 122

iENi-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

characterization of its effect is important for a comprehensive adsorption study. Fig. 7 shows the effect of varying UAB particle size from 100 to 500 mm on the percentage removal of Ni(II) and Mn(II) ions from solution. As observed, a decrease in the percentage removal of both metal ions with increase in particle size was recorded. This indicated that the adsorption of metal ions is dependent on the particle size of UAB. This decrease may be attributed to a decrease in the total surface area of UAB with increase in particle size. At smaller particle sizes, the higher surface area of UAB allows for easy diffusion of metal ions unto the active sites of the adsorbent (Karthikeyan et al., 2004). Similar trend have also been reported by some workers (Karthikeyan et al., 2004; Quek et al., 1998).

Influence of contact time

Time dependent study was performed because adsorption rate is one of the influential factors that must be taken into consideration before the design of an adsorption system. The profile of time dependent study on the simultaneous adsorption of Ni(II) and Mn(II) ions unto UAB is shown in Fig. 8. The result showed that for Ni(II) ions, the removal rate was rapid within the first 100min after which it increased slightly attaining equilibrium around 120min with 71.2% of the Ni(II) ion removed. The adsorption rate was constant with further increase in contact time from 140 to 180min (72.7% removal) but further increase in contact time up to 300min led to a slight decrease in percentage removal (69.5%). Similarly, for Mn(II) ions, a rapid adsorption rate was achieved within 140 mins after which equilibrium was achieved at 160-180min (61.4% removal) and further increase in contact time up to 300min, recorded a slight decrease in percentage removal (from 61.4 to 57.3%). An equilibrium time of 180min was utilized in this study to ensure optimum removal of both metal ions was achieved. Also, the slight decrease in the percentage removal of both metal ions at 300 min, may be due to adsorption and desorption taking place simultaneously on the adsorbent surface. The rapid percentage removal obtained initially for both metal ions is due to the presence of abundant

Fig. 7 - Effect of adsorbent particle size on the adsorption of Ni(II) and Mn(II) ions unto UAB.

Fig. 8 - The effect of contact time on the adsorption of Ni(II) and Mn(II) ions unto UAB.

active sites on the surface of UAB which were later occupied as time progresses, thereby resulting in the inability of UAB to remove the metal ions at the later stages of the adsorption process (Vimala and Das, 2009).

Furthermore, Ni(II) ions were adsorbed at a faster rate with higher percentage removal than Mn(II) ions. This may be explained by considering the ionic radii of the two ions, Ni(II) (0.69 A) and Mn(II) (0.80 A), during sorption of metal ions, the ions of smaller ionic radii tend to move faster to potential adsorption sites (Abia and Asuquo, 2006). As a result, it is possible that Ni(II) ions diffuse faster through the pores of UAB and are easily adsorbed than the larger Mn(II) ions, which accounted for the faster rate and higher percentage removal of Ni(II) when compared to Mn(II) ions.

3.8. Adsorption kinetics

Adsorption kinetics governs the rate of reaction, which determines the residence time and is one of the important characteristics defining the efficiency of an adsorbent. The kinetics of metal sorption can be controlled by several independent processes which could act in series or in parallel, such as bulk diffusion, film diffusion, chemisorptions and intraparticle diffusion. In the quest to investigate the mechanism of adsorption of Ni(II) and Mn(II) ions unto UAB and the potential rate controlling steps. The pseudo first order, pseudo second order, intraparticle and liquid film diffusion kinetic models were applied to the experimental data and their kinetic parameters are presented in Table 3.

The lagergren pseudo first order model considers that the rate of occupation of adsorption sites is proportional to the number of the unoccupied sites and the linear form of this model equation is given as (Lagergren, 1898):

log(qe-qt) = logqe-(K,t/2.303)

where K is the lagergren rate constant of adsorption (min-1), qe and qt are the amounts of metal ions adsorbed (mg/g) at equilibrium and time t respectively. The slope and intercept of the plots of log(qe - qt) versus t were used to determine the

80 81 82

99 100 101 102

110 111 112

120 121 122

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

Table 3 - Kinetic rate equation parameters for the

adsorption process.

Kinetic Models Ni(II) Mn(II)

qeexp (mg/g) 36.35 30.7

Pseudo-First order

qecal (mg/g) 72.28 38.19

KI (min-1) 0.035 0.018

r2 0.974 0.956

Pseudo-second order

h (mg/gmin) 0.79 0.39

K2 (g/mgmin) 0.285 x 10-3 0.99 x 10-4

qecal (mg/g) 52.63 62.5

r2 0.959 0.913

Intraparticle Diffusion

Kd (mg/gmin1/2) 2.94 2.82

I 1.345 4.606

r2 0.889 0.965

Liquid film Diffusion

Kfd (mg/gmin) 0.036 0.021

r2 0.954 0.974

first order rate constant K and the equilibrium adsorption capacity qe for both metal ions.

The pseudo second order model is based on the assumption that adsorption follows a second order mechanism. So the rate of occupation of adsorption sites is proportional to the square of the number of unoccupied sites (Zafar et al., 2007). The linear form of the pseudo second order equation is expressed as:

t/qt = 1/K2qe2 + t/qe

where K2 (g/mgm in) is the equilibrium constant of pseudo second order adsorption. The initial sorption rate (h) can be calculated from the equation:

h = K2qe2

The applicability of the pseudo second order model was tested by a linear plot of t/qt versus t with a slope of 1/qe, the value of K2 was calculated from the intercept of the plot.

The diffusion mechanism was determined by the intra-particle diffusion model (Weber and Morris, 1963). This is due to the fact that metal ions are transported from the aqueous phase to the surface of the adsorbent and subsequently they can diffuse into the interior of the particles if they are porous. The intraparticle diffusion equation is given as (Weber and Morris, 1963):

qt = Kit1'2 + C (12)

where C is the intercept and Kd (mg/gmin172) is the intra-particle diffusion rate constant. Intraparticle diffusion is the sole rate determining step if the plot of qt versus t1/2 is linear and passes through the origin (C = 0). Values of qt and C were obtained from the slope and intercept of the plot and are shown in Table 3.

When the transport of the adsorbate from the liquid phase up to the solid phase boundary plays the most significant role in adsorption, the liquid film diffusion model can be applied (Taffarel and Rubio, 2009):

ln(1-F) = -Kfdt

where F is the fractional attainment of equilibrium (F = qt/qe) and Kfd is the adsorption rate constant (mg/gmin). A linear plot of -ln(1 - F) versus t with zero intercept would suggest that the kinetics of adsorption is controlled by diffusion through the liquid film surrounding the solid adsorbent. The constant Kfd was obtained from the slope of the plot.

A comparison of the correlation coefficient results (Table 3), showed that both the pseudo-first order and pseudo second order models gave good fits to the experimental data for both metal ions. However, the r2 values presented by the Pseudo first order model were better than that of the Pseudosecond order model, which indicates greater conformity of the adsorption process to the former. However, the calculated qe values (qecal) obtained from both models showed a great discrepancy with the experimental qe value (qeexp) for the sorption of Ni (II) ions. It has been reported that despite the good fit of the pseudo-first order model, the deviations of the experimental and calculated qe is as a result of the time lag, due to boundary layer or external resistance control at the beginning of the sorption process (Gautam et al., 2014). However, the qecal of the pseudo-first order model for adsorption of Mn (II) ion was closer to the qeexp than that presented by the pseudo-second order model.

Also, when investigating the diffusion mechanism, the r2 values obtained from the intraparticle diffusion model showed a good correlation for Mn(II) ions (0.965) but not for Ni(II) ions (0.889). This indicated the presence of intra-particle diffusion mechanism on the sorption of Mn(II) ions unto UAB, although it was not the sole rate determining step due to the occurrence of the intercept. The intercept of the plot reflects the boundary layer effect; the larger the intercept the greater is the contribution of the surface sorption in the rate determining step. The value of the intercept (4.606) indicated the existence of some surface phenomenon which indicates further that intraparticle diffusion is not the sole rate determining step in the adsorption of Mn(II) ions unto UAB.

However, the good and better r2 values obtained in the liquid film diffusion model for both metal ions showed the existence of film diffusion mechanism in the adsorption of Ni(II) and Mn(II) ions unto UAB. This implies that the adsorption process is largely controlled by the film diffusion mechanism although not solely since the plots did not pass through the origin (r2 values are not equal to 1). The conformity of the adsorption to the film diffusion mechanism suggests that process is most likely a physical adsorption one. This may be one of the reasons the kinetic data did not provide the best fit with the pseudo second order model, as the pseudo second order model depicts a chemisorptions mechanism. A physical adsorption mechanism is usually desired in adsorption as it implies a lower energy barrier for the metal ions to overcome for their adsorption and also promotes easy desorption of the metal ions from the adsorbent when required (Dawodu and Akpomie, 2014).

3.9. Effect of ligands

The essence of most adsorption studies is for treatment of industrial wastewaters, in order to get rid of toxic substances such as heavy metals that can be detrimental to human

80 81 82

99 100 101 102

110 111 112

120 121 122

iENi-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

health, plants and aquatic life. Most of the effluents from industries usually contain organic substance beyond heavy metals. It is therefore important to understand the behavior of the heavy metals in the presence of organic ligands towards their adsorption onto UAB. The batch adsorption technique was also applied to the simultaneous adsorption of Ni(II) and Mn(II) ions in the presence of ligands, such as citric acid (CA) and EDTA, having low and high complexation constants respectively. The concentrations of the ligands were varied in order to understand the effect of ligand concentration on the adsorption of the metal ions. The result illustrating the percentage removal of both metal ions is shown in Fig. 9. It was observed that the presence of CA and EDTA resulted in a decrease in the percentage removal of both metal ions compared to the condition when they were absent (WTL). Also, as the concentration of CA and EDTA increased from 100 to 1000 mg/L, a decrease in the percentage removal of both metal ions was obtained. This may be as a result of the formation of metal-ligand complexes at higher concentrations, which resulted in a more difficult diffusion of the complexes unto the surface and interlayer's of UAB due to larger sizes.

Furthermore, it was observed that the presence of EDTA hindered the adsorption of both metal ions compared to CA, this is probably due to the larger sizes of the complexes formed by EDTA due to a high complexation constant of the ligand than that formed by CA (Abollino et al., 2003). Another very important observation is the fact that Mn(II) ions had a higher percentage removal in the presence of both ligands and at all concentrations than Ni(II) ions. A good explanation to the fact is that although Ni(II) ions have smaller ionic radii than Mn(II) ions, Ni(II) ions have larger complexation constants in the presence of both ligands than Mn(II) ions (Sillen and Martell, 1979; Smith and Martell, 1989). Thus Ni(II) forms larger complexes with EDTA and CA which hinders their introduction in the interlayer of UAB. We obtained a similar result in another of our study using kaolinite clay as adsorbent (Dawodu and Akpomie, 2014).

3.10. Thermodynamics of sorption

The influence of temperature of solution on the percentage removal of Ni(II) and Mn(II) ions from solution unto UAB is presented in Fig. 10. A slight increase in the percentage removal of both metal ions with temperature increase was obtained. This indicates that the adsorption process is an endothermic one. As temperature increases, the metal ions acquire more energy to overcome the energy barrier between the metals and UAB, simultaneously creating more additional adsorption sites on the adsorbent surface due to dissociation of some of the surface components on UAB (Bhattacharyya and Gupta, 2006). Thermodynamic parameters such as changes in Gibbs free energy (DG0), changes in enthalpy (DH0) and change in entropy (DS0) for the adsorption process were calculated using the following equations (Bhattacharyya and Gupta, 2006):

DG0 = —RTlnKc

Kc = Ca/Ce

lnKc = -(DH0/RT) + (DS0/R)

where T is the temperature (K), R is the ideal gas constant (8.314 J/molK), Kc is the thermodynamic equilibrium constant, Ca (mg/L) is the concentration of metal ion adsorbed and Ce (mg/L) is the equilibrium concentration of metal ion in solution. The values of DH0 and DS0 were calculated from the slope and intercept of the linear plot of lnKc versus 1/T (Fig. 11). The calculated thermodynamic parameters are presented in Table 4. The positive values of DH0 suggested that the adsorption of both metal ions is endothermic, which is supported by the increase adsorption of both metal ions with rise in temperature. The positive values of DS0 also indicated an increase in randomness at the solid-solution interface during the fixation of the adsorbate on the active site of the adsorbent. The values of DS0 also reveal whether the adsorption process involves an associative or dissociative mechanism. If the value change is larger than "10 J/molK, it implies a dissociative

Fig. 9 - Effect of ligands on the adsorption of Ni(II) and Mn(II) ions from solution unto UAB.

Fig. 10 - Effect of solution temperature on the percentage removal of Ni(II) and Mn(II) ions from solution unto UAB.

80 81 82

99 100 101 102

110 111 112

120 121 122

beni-suef university journal of basic and applied sciences xxx (2015) 1-13

16 1l 1S

ig 20 21 22

26 2l 2S

36 3l 3S

46 4l 4S

56 Sl SS Sg б0 б1 б2

Fig. 11 - Thermodynamic plot on the adsorption of Ni(II) and Mn(II) ions unto UAB.

mechanism (Unuabonah et al., 2008). The values of AS0 obtained for both metal ions are 68.87 and 57.57 J/molK for Ni(II) and Mn(II) respectively, this reveals a dissociative mechanism. A spontaneous adsorption process was indicated by the negative values of AG0 obtained at all temperatures for both metal ions. Furthermore, the heat evolved (AH0) during physical adsorption is in the range 2.1-20.9 kJ/mol, while that of chemisorptions generally falls in the range 80-200 kJ/mol (Liu and Liu, 2008). From Table 4, the values of AH0 for Ni(II) and Mn(II) are 18.29 kJ/mol and 16.13 kJ/mol respectively, which reveals that the simultaneous adsorption of both metal ions unto UAB is a physical adsorption one. This corroborates our result obtained in the kinetic analysis where a physical adsorption mechanism was suggested.

3.11. Desorption and adsorbent recycling

For efficient adsorbent recycling and safe post treatment of metal loaded adsorbents, it is very important to remove and recover metals from the metal loaded adsorbents. The reuse of adsorbents helps minimize the cost of the entire process.

Table 4 - - Thermodynamic parameters for the adsorption

process.

Metal Temp Kc DG0 (kJ/ DH0 (kJ/ DS0 (J/ r2

ion (K) mol) mol) molK)

Ni(II) 300 2.66 -2.44 18.29 68.87 0.976

308 2.98 -2.79

313 3.42 -3.20

318 3.98 -3.6S

323 4.41 -3.98

Mn(II) 300 139 -1.16 16.13 S737 0.994

308 1.84 -1.S6

313 2.06 -1.88

318 2.32 -2.23

323 2.48 -2.44

An effective adsorbent must not only have a high adsorption capacity but also a good desorption potential and recycling ability. The desorption of Ni(II) and Mn(II) ions using distilled water (DW) and different concentration of HCL is shown in Fig. 12. As observed, optimum desorption of both metal ions was obtained at a HCl concentration of 0.1 M. This concentration of HCl was then used as the stripping agent for the desorption experiment. This result is important because it will help to establish the appropriate concentration of desorbing agent to be utilized during desorption of metal ions from

Fig. 12 - (a) Effect of de-ionized water (DW) and HCl concentration on desorption, (b) Effect of time on desorption (c) Adsorption performance as a function of three operational cycles.

бб 6l 6S 69

16 ll lS

56 Sl SS Sg go gi

94 9S 96 9l

95 99 100 101 102

106 10l 10S

110 111 112

116 11l 11S

120 121 122

126 12l 12S

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

60 61 62

metal loaded UAB. Also, the fact that up to 30.1% of Ni(II) and 32.6% of Mn(II) ions were desorbed by the use of DW only showed that physical adsorption must have played a major role in the adsorption process (Meitei and Prasad, 2013). Furthermore, the time needed to complete desorption was also estimated at time intervals of 1-60min using 0.1M HCl as desorbing agent. This was done in order to ascertain the rate of desorption of the metal ions from UAB. As shown in Fig 12, it is observed that desorption of both metal ions was very rapid, up to 90% of the maximum elution of the metal ions occurred within 5min after which it increased slightly until an optimum desorption was achieved around 20min. the rapid desorption kinetics elucidates the applicability of the desorption process (Nessim et al., 2011).

In determining the reusability of UAB for metals adsorption, three cycles of adsorption desorption studies was performed as shown in Fig. 12. The results showed that the adsorption of both metals after the first cycle were the same as the initial adsorption. The ability of UAB to retain its initial adsorption despite possibility of weight loss might be due to the acid treatment of the desorbing agent (0.1M HCl) during desorption of the metal ions causing the opening of the pore spaces of the adsorbent (Igberase et al., 2014). However, the percentage removal decreased from 72.3 to 60.4% and 60.3 to 50.6% for Ni(II) and Mn(II) ions respectively from the 1st to the 3rd cycle of adsorption. The diminishing adsorption of metals over the cycles may be due to the destructive effect of the desorbing agent (with continuous use) and the weight loss of UAB during desorption (Nessim et al., 2011). But in general, these observations still prove that UAB could be recovered and reused for metal adsorption using 0.1M HCl as desorbing agent. The eluted metal ions in the desorbing solution are present in appreciable concentrations and can easily be recovered using chemical reduction techniques (Chen and Lim, 2005).

Conclusions

This study evaluated the use of a readily available Nigerian bentonite, (UAB) as a low-cost adsorbent for the removal of Ni(II) and Mn(II) ions from solution. UAB presented a high surface area when compared to other bentonites reported by researchers. The chemical characterization and FTIR studies revealed the presence of silanol and aluminol groups on the surface of UAB responsible for the sorption of metal ions. UAB recorded a high adsorption potential for Ni(II) than Mn(II) possibly due to the smaller ionic radii of Ni(II) compared to that of Mn(II) ions. The adsorption of both metal ions were found to be dependent on the operating parameters such as pH, initial metal ion concentration, contact time, particle size, adsorbent dose, ligands (CA and EDTA) and temperature. The scatchard plot analysis revealed the heterogeneous nature of UAB confirmed by the Freundlich isotherm which provided the best fit to the experimental data. Thermodynamic studies revealed a spontaneous, endothermic and physical adsorption process. Desorption of both metal ions from UAB also revealed a high desorption potential (over 90% of both metals were desorbed) using 0.1M HCL as desorbing agent. The high adsorption capacity of both metal ions obtained from the

Langmuir equation, 200 mg/g for Ni(II) and 166.7 mg/g for Mn(II) and also the favorable adsorption indicated by the Langmuir parameter RL and Freundlich constant n, revealed the potential of UAB as a low cost adsorbent for Ni(II) and Mn(II) ions from aqueous stream.

Uncited references

Raji and Anirudhan, 1997. Q4

REFERENCES

Abia AA, Asuquo ED. Lead(II) and nickel(II) adsorption kinetics from aqueous solution using chemically modified and unmodified agricultural adsorbents. Afr J Biotechnol 2006;5(16):1475—82. Q2

Abollino O, Aceto M, Malandrino M, Sarzanini C, Mentasti E. Adsorption of heavy metals on Na-montmorillonite: effect of pH and organic substances. Wat Res 2003;37:1619-27.

Akpomie KG, Dawodu FA. Efficient abstraction of nickel (II) and manganese (II) ions from solution onto an alkaline-modified montmorillonite. J Taibah Uni Sci 2014;8:343-56.

Amer MW, Khalili FL, Awwad AM. Adsorption of lead, zinc and cadmium ions on polyphosphate modified kaolinite clay. J Environ Chem Ecotoxicol 2010;2(1):01-8.

Anirudhan TS, Suchithra PS. Equilibrium, kinetic and

thermodynamic modeling for the adsorption of heavy metals onto chemically modified hydrotalcite. Ind J Chem Technol 2010;17:247-59.

Bhattacharyya AK, Naiya TK, Mandal SN, Das SK. Adsorption, kinetic and equilibrium studies on removal of Cr(VI) from aqueous solution using different low-cost adsorbents. Chem Eng J 2008;137:529-41.

Bhattacharyya KG, Gupta SS. Kaolinite, montmorillonite and their modified derivatives as adsorbents for removal of Cu(II) from aqueous solution. Sep Purif Technol 2006;50:388-97.

Ceribasis HI, Yetis U. Biosorption of Ni(II) and Pb(II) by

phanaerochate chrysosporium from a binary metal system kinetics. Water SA 2001;27(1):15-20.

Chen JP, Lim LL. Recovery of precious metals by electrochemical deposition method. Chemosphere 2005;60:1384-92.

Dawodu FA, Akpomie GK. Simultaneous adsorption of Ni(II) and Mn(II) ions from aqueous solution unto a Nigerian kaolinte clay. J Mater Res Technol 2014;3(2):129-41.

Dawodu FA, Akpomie GK, Abuh MA. Batch sorption of Pb(II) from aqueous solution by ekulu clay-equilibrium, kinetic and thermodynamic studies. Int J Multidisc Sci Eng 2012a;3(10):32-7.

Dawodu FA, Akpomie GK, Ogbu IC. The removal of cadmium(II) ions from aqueous solution by the use of afuze bentonite: equilibrium, kinetic and thermodynamics studies. Int J Sci Eng Res 2012b;3(12):1-8.

Doulia D, Leodopoloud C, Gimouhopoulos K, Rigas F. Adsorption of humic acid on acid-activated Greek bentonite. J Coll Interf Sci 2009;340:131-41.

Ekosse GE. Fourier transform infrared spectrophotometer and X-ray powder diffractometry as complementary techniques in characterizing clay size fraction of kaolin. J Appl Sci Environ Manag 2005;9(2):43-8.

Freundlich HMF. Uber die adsorption in losangen. Z Phys Chem 1906;57:385-470.

Gautam RK, Mudhoo A, Lofrano G, Chattopadhyaya MG. Biomass derived biosorbents for metal ions sequestration: adsorbent

80 81 82

99 100 101 102

110 111 112

120 121 122

-suef university journal of basic and applied sciences xxx (2015) 1-13

10 11 12

20 21 22

modification and activation methods and adsorbent regeneration. J Environ Chem Eng 2014;2:239-59.

Greenwood NN, Earnshaw A. Chemistry of the elements. New York: Pergamon Press; 1993. p. 404-5.

Guerra DJL, Mello I, Resende R, Silva R. Application as a

biosorbent of natural and functionalized Brazilian bentonite in Pb(II) adsorption: equilibrium, kinetics, pH and thermodynamic effects. Water Res Ind 2013;4:32-50.

Hameed BH, Din ATM, Ahmed AL. Adsorption of methylene blue onto bamboo-based activated carbon: kinetics and equilibrium studies. J Hazard Mater 2007;141:819-25.

Igberase E, Osifo P, Ofomaja A. The adsorption of Cu(II) ions by polyaniline grafted chitosan beads from aqueous solution: equilibrium, kinetic and desorption studies. J Environ Chem Eng 2014;2:362-9.

Karthikeyan G, Anbalagan K, Muthulakshimi AN. Adsorption dynamics and equilibrium studies of Zn(II) onto chitosan. J Chem Sci 2004;116:119-27.

Lagergren S. About the theory of so called adsorption of soluble substances. K Sven Vetendkapsakad Handl 1898;24(4):1-39.

Langmuir I. The adsorption of gases on plane surfaces of glass, mica and platinum. J Am Chem Soc 1918;40:1361-404.

Li Y, Xia B, Zhao Q, Liu F, Zhang P, Du Q, et al. Removal of copper ions from aqueous solution by calcium alginate immobilized kaolin. J Environ Sci 2011;23(3):404-11.

Li YH, Ding J, Luan ZK, Di ZC, Zha YF, Xu CL. Competitive adsorption of Pb(II), Cu(II) and Cd(II) ions from aqueous solution by multiwalled carbon nanotubes. Carbon 2003;41(14):2787-92.

Liu C, Bai R, Ly QS. Selective removal of copper and lead by diethylenetriamine-functionalized adsorbent: behaviors and mechanisms. Wat Res 2008;42:1511-22.

Liu Y, Liu YJ. Biosorption isotherms, kinetics and

thermodynamics. Sep Purif Technol 2008;61:229-42.

Meitei MD, Prasad MNV. Pb(II) and Cd(II) biosorption on spirodela polyhiza Scheleiden biomass. J Environ Chem Eng 2013;1:200-7.

Mohan D, Singh KP, Singh G, Kumar K. Removal of dyes from wastewater using fly ash as a low cost adsorbent. Ind Eng Chem Res 2008;41:3688-95.

Nandi BK, Goswami A, Purkait MK. Adsorption characteristics of brilliant dye on kaolin. J Hazard Mater 2009;161:387-95.

Nessim RB, Bassioung AR, Zaki HR, Moawad MN, Kandeel KM. Biosorption of Pb and Cd using marine algae. Chem Ecol 2011;27(6):579-94.

Njoya A, Nkoumbou C, Grosbois C, Njopwouo D, Njoya D, Courtin-Nkoumbou A. Genesis of mayouom kaolin deposit (western Cameroun). Appl Clay Sci 2006;32:125-40.

Nomanbhay MS, Palanisamy K. Removal of heavy metal from industrial waste using chitosan coated oil palm shell charcoal. Elect J Biotechnol 2005;8(1):43-53.

Onyango MS, Kojima Y, Aoyi O, Bernardo EC, Matsuda H. Adsorption equilibrium modeling and solution chemistry dependence of fluoride removal from water by trivalent cation-exchange zeolite F. J Coll Interf Sci 2004;279:341-50.

Papafilippaki AK, Kotti ME, Stavroulakis GG. Seasonal variations in dissolved heavy metals in the keritis river, Chania, Greece. Glob Nest J 2008;10:320-5.

Quek SY, Wase DAJ, Forster CF. The use of sago waste for the sorption of lead and copper. Water SA 1998;24:251-6.

Raji C, Anirudhan TS. Kinetics of Pb(II) adsorption by polyacrylamide grafted sawdust. Ind J Chem Technol 1997;4:157-62.

Rhoades JD. Cation exchange capacity in: methods of soil analyst part 2. chemical and microbiological properties. 2nd ed. Hadison, WI, USA: American Society Of Agronomy/Soil Science of America; 1982.

Schiewer S, Patil SB. Modeling the effect of pH on biosorption of heavy metals by citrus peels. J Hazard Mater 2008;157:8-17.

Shu-li D, Yu-zhuang S, Cui-na Y, Bo-hui X. Removal of copper from aqueous solution by bentonite and the factors affecting it. J Min Sci Technol 2009;19:489-92.

Sillen LG, Martell AE. Stability constants of metal ion complexes: organic ligands. IUPAC chemical data series, no.22. Oxford: Pergamon Press; 1979.

Slejko F. Adsorption technology: a step by step approach to process. Eva. Appl.. New York: Marcel Dekker; 1985.

Smith RM, Martell A. Critical stability constants, Vol 6, Second supplement. New York: Plenum Press; 1989.

Taffarel SR, Rubio J. On the removal of Mn(II) ions by adsorption on natural and activated Chilean zeolite. Min Eng 2009;22:336-43.

Tempkin MI, Pyzhev V. Kinetics of ammonia synthesis on protonated iron catalyst. Acta Physicochem USSR 1940;12:217-22.

Tewari N, Vasudevan P, Guha BK. Study on biosorption of Cr(VI) by mucar hiemalis. Biochem Eng J 2005;23:185-92.

Unuabonah EI, Adebowale KO, Olu-Owolabi BI, Yang L, Kong LX. Adsorption of Pb(II) and Cd(II) from aqueous solution onto sodium tetraborate-modified kaolinite clay: equilibrium and thermodynamic studies. Hydrometallurgy 2008;93:1-9.

Vaghetti JCP, Lima EC, Royer B, Brasil JL, Da Cunha BM, Simon NM, et al. Application of Brazilian pine fruit coat as a biosorbent to removal of Cr(IV) from aqueous solution-kinetic and equilibrium study. Biochem Eng J 2008;42:67-76.

Vempati RK, Mollah MYA, Reddy GR, Cocke DL. Intercalation of kaolinte under hydrothermal conditions. J Mat Sci 1996;31:1255-9.

Vimala R, Das N. Biosorption of cadmium(II) and lead(II) from aqueous solution using mushrooms: a comparative study. J Hazard Mater 2009;168:376-82.

Weber WJ, Morris JC. Kinetics of adsorption on carbon from solution. J St Eng Div Am Soc Civ Eng 1963;89:31-60.

Xifang S, Chum L, Zhansheng W, Xiaolin X, Ling R, Hongsheng Z. Adsorption of protein from model wine solution by different bentonites. Chin J Chem Eng 2007;15:632-8.

Zafar MN, Nadeem R, Hanif MA. Biosorption of nickel from protonated rice bran. J Hazard Mater 2007;143:478-85.

60 61 62

80 81 82

99 100 101 102