Environ Sci Pollut Res DOI 10.1007/s11356-012-0892-2
RESEARCH ARTICLE
Studies on the removal of nickel from aqueous solutions using modified riverbed sand Sandeep Yadav & Varsha Srivastava & Sushmita Banerjee & Fethiye Gode & Yogesh C. Sharma
Received: 24 February 2012 / Accepted: 22 March 2012 # Springer-Verlag 2012
Abstract This paper highlights the utility of riverbed sand (RS) for the treatment of Ni(II) from aqueous solutions. For enhancement of removal efficiency, RS was modified by simple methods. Raw and modified sands were characterized by scanning electron microscope (SEM), Energy Dispersive Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR) to investigate the effect of modifying the surface of RS. For optimization of various important process parameters, batch mode experiments were conducted by choosing specific parameters such as pH (4.0–8.0), adsorbent dose (1.0–2.0 g), and metal ion concentrations (5–15 mg/L). Removal efficiency decreased from 68.76 to 54.09 % by increasing the concentration of Ni(II) in solution from 5 to 15 mg/L. Removal was found to be highly dependent on pH of aqueous solutions and maximum removal was achieved at pH 8.0. The process of removal follows first-order kinetics, and the value of rate constant was found to be 0.048 min−1 at 5 mg/L and 25 °C. Value of intraparticle diffusion rate constant (kid) was found to be 0.021 mg/g min1/2 at
Responsible editor: Vinod Kumar Gupta S. Yadav Department of Applied Sciences, National Institute of Foundry and Forge Technology, Ranchi 834003, India V. Srivastava : Y. C. Sharma (*) Department of Applied Chemistry, Institute of Technology, Banaras Hindu University, Varanasi 221005, India e-mail:
[email protected] S. Banerjee Department of Chemistry, University of Allahabad, Allahabad 211002, India F. Gode Department of Chemistry, Suleman Demierl University, 32260 Isparta Turkey
25 °C. Removal of Ni(II) decreased by increasing temperature which confirms exothermic nature of this system. For equilibrium studies, adsorption data was analyzed by Freundlich and Langmuir models. Thermodynamic studies for the present process were performed by determining the values of ΔG°, ΔH°, and ΔS°. Negative value of ΔH° further confirms the exothermic nature of the removal process. The results of the present investigation indicate that modified riverbed sand (MRS) has high potential for the removal of Ni(II) from aqueous solutions, and resultant data can serve as baseline data for designing treatment plants at industrial scale. Keywords Adsorption . Batch study . Isotherm . Nickel . Riverbed sand . Thermodynamics
Introduction The presence of heavy metals in the environment is of major concern because of their toxic nature and tendency for bioaccumulation in the food chain even in relatively low concentrations (Bhatnagara and Minocha 2010; Gupta et al. 2002, 2009a, b; Jain et al. 1995). The discharge of water containing heavy metals causes critical pollution problems. Nickel(II) ion is one such heavy metal frequently encountered in wastewater streams from industries such as electroplating, battery manufacture, mineral processing, steam– electric power plants, paint formulation, porcelain enameling, etc. (Gupta et al. 2007a; Nabarlatz et al. 2012; Kleinubing et al. 2012). Since toxic nickel ions dissolve in water, they can eventually reach the top of the food chain and thus become a risk factor for people’s health. Ni(II) belongs to the so-called “essential” metal because trace amount of nickel is beneficial to humans as an activator of some enzyme systems, but its high concentration may cause headache, dizziness, nausea and vomiting, chest pain, tightness of the chest, dry cough and
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shortness of breath, rapid respiration, cyanosis and extreme weakness, pulmonary fibrosis, lung cancer, dermatitis renal edema, and gastrointestinal disorder (Ewecharoen et al. 2008; Xu et al. 2006; Akhtar et al. 2004; Gupta et al. 2010a, b). The tolerance limit of nickel in drinking water is 0.01 mg/L, and for industrial wastewater, it is 2.0 mg/L (Sharma et al. 2008). However, effluents of different industries contain higher concentrations of nickel than its acceptable limit. Due to toxicity of Ni(II), it is essential to remove Ni(II) from industrial effluents before they are discharged. Several treatment methods such as membrane filtration, chemical precipitation, chemical oxidation/reduction, ion exchange, filtration, electrochemical treatment, solvent extraction, coprecipitation, and adsorption have been reported for the removal of metallic ions from water and wastewater (Gupta et al. 1997, 2007b; Jain et al. 1997; Ali and Gupta 2007; Totlani et al. 2012; Shaidan et al. 2012). The shortcomings of most of these methods are high operational and maintenance costs, high-energy consumption, and complicated procedure involved in these processes. Further, generation of toxic sludge is another serious problem (Pahlavanzadeha et al. 2010; Aksu 2002; Gupta and Rastogi 2009). Comparatively, adsorption process seems to be a more attractive method in water pollution control in terms of cost, simplicity of design, operation, and reduction of trace quantities of heavy metals (Sharma et al. 2010; Gupta et al. 2006a, b; Srivastava et al. 1997; Gupta and Ali 2004). Activated carbon has been found to be the most promising and widely used adsorbent in wastewater pollution control globally and has been successfully utilized for the removal of diverse types of pollutants including metal ions (Gupta et al. 2007c, 2009a, b). However, high capital and regeneration cost of activated carbon limits its large-scale applications for the removal of metallic pollutants, and this has encouraged researchers to look for low cost alternative adsorbents (Bhatnagara and Minocha 2010; Gupta and Rastogi 2008a, b). The objective of the present study is to investigate the adsorption of Ni(II) ions on modified riverbed sand (MRS). Modification of riverbed sand (RS) was carried out for the enhancement of adsorption efficiency of adsorbent for Ni(II) ions. Removal efficiency of modified adsorbent was investigated by using batch adsorption experiments. Various important parameters were studied for the optimization of the nickel removal process. Kinetic, thermodynamic, and equilibrium studies were also carried out for better understanding of the removal process.
Ganges southern tributaries. The riverbed sand (RS) was collected from shallow waters near the bank from upstream. The sand was then stored in polyethylene bags, which was treated with 5 % H2SO4 and 1 M KMNO4. RS was modified by soaking it in 40 % H2SO4 for 4 h. After modification, RS was washed repeatedly with distilled water. Finally, the MRS was dried in a hot air oven for 24 h. Dried modified riverbed sand was named as MRS. After drying, both the MRS and RS were characterized by different sophisticated techniques. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDS) observations were carried out with a Jeol, Japan, JSM 6390LV microscope equipped with an Oxford Links-Isis energy dispersive X-ray analyzer for investigation of composition and surface characteristics of RS and MRS. An electron acceleration voltage of 20 kV was applied for SEM observation. The FTIR of RS and MRS were measured on a Fourier Transform Infrared Spectrophotometer (Varian 1600 FT-IR Scimitar Series) to elucidate the presence of functional groups on the surface of RS and MRS. For FTIR, 5 mg of RS and MRS was encapsulated in 400 mg of KBr. A translucent disk was made by pressing the ground mixed material with the hydraulic pellet press (PCI Services, Bhandup, Mumbai) for 1 min. The spectra were recorded in a FTIR within the range of 500–6,000 cm−1. Batch adsorption experiments Removal efficiency of MRS was investigated by usual batch adsorption experiments. Stock solution of nickel was prepared by dissolving the required amount of NiSO4·6H2O in deionized water. Standard solutions of required concentrations were prepared by diluting the stock solution. pH of solutions was adjusted with 0.1 M HCl/0.1 M NaOH solutions as required. Batch adsorption experiments were conducted by taking 50mL solution of Ni(II) in 250 mL of reagent bottles at desired pH value, contact time, temperature, dose, and adsorbate concentration. The ionic strength of the aqueous solutions was maintained at 1.0×10−2 M NaClO4. Adsorption experiments were conducted at 25 °C (±0.5) and at an agitation rate of 100 rpm on a shaking thermostat water bath. After the equilibrium time, the adsorbent was separated from the aqueous solutions by centrifugation (Remi 24, New Delhi, India) at 10,000 rpm for 15 min. The residual concentration of Ni(II) in each aliquot was determined by using an atomic absorption spectrophotometer (Shimadzu AA7000, Japan) (APHA 1985). The percent of nickel removal and the amount of metal adsorbed were determined as follows:
Materials and methods Removalð%Þ ¼ Preparation of adsorbent The sand sample was collected from the riverbed of Son River (Bihar) of central India, which is the largest of the
C0 Ce 100 C0
Amount adsorbedðqe Þ
C0 Ce V M
ð1Þ
ð2Þ
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where C0 and Ce are the initial and equilibrium concentrations of Ni(II) (milligram per liter), M is the mass of adsorbent (gram), V is the volume of solution (liter), and qe is the amount adsorbed (milligram per gram).
Results and discussion Characterization of adsorbent The chemical composition of RS and MRS were analyzed by EDS (Table 1). It is clear from chemical composition of both the samples that silica is a major constituent in form of silicon oxide (SiO2) (Table 1). These oxides undergo surface hydroxylation (i.e., introduction of a –OH group) in aqueous solution, which results in the formation of surface hydroxyl compounds. Their subsequent dissociation gives negatively or positively charged surface. The surface morphology RS and MRS were evaluated using a scanning electron microscope. Figures 1a, b and 2a, b show the SEM micrographs of the RS and MRS at different magnifications, respectively. It is clear from Fig. 1b that the silica sand has a large number of porous structures because of fine crystals that are staggered in three-dimensional spaces. Figure 2a and b are SEM of MRS at 100 and 5,000 magnifications, respectively. SEM images of MRS demonstrate the roughness of the surface which is clearly visible in Fig. 2b as slopes and grooves. These slopes and grooves increase the surface area, thus the adsorption capacity of the adsorbents, and also these slopes and grooves act as reactive adsorption centers for adsorption of nickel in this case. FTIR of RS and MRS is shown in Fig. 3. The peaks found at 759.49 cm−1 show the presence of silica (Si–O bond) and 1,783 cm−1 indicates the presence of four-membered cyclic compounds, which are probably organic in nature.
Table 1 Chemical composition of RS and MRS sample (wt.%)
Element
O Al Si Au S K N Total
River bed sand (RS)
Modified riverbed sand (MRS)
40.35 0.77 39.84 19.04 0 0 0 100
23.57 7.56 25.00 11.98 0.06 13.38 18.45 100
Fig. 1 a and b SEM images of riverbed sand (RS) at ×100 and ×5,000 magnification
Effect of modification of riverbed sand (RS) After modification of the adsorbent, preliminary batch experiments were carried out to compare the removal efficiency of raw RS and MRS. It was found that percentage of removal of Ni(II) on raw RS was 37.8 %, and after modification, removal of Ni(II) increased to 68.7 %. It is clear from Fig. 4 that after modification, the adsorbent displayed increased removal efficiency for nickel. Further, the time of equilibrium also came down from 180 min to 120 min for modified adsorbent. Effect of contact time and concentration Two parameters, namely, contact time and initial concentration, have a pronounced effect on the removal of adsorbate species from aqueous solutions. A known amount of adsorbent (20.0 g/L) was added to a batch containing 50 mL solution of Ni(II) in 250 mL polythene bottles, and after attainment of equilibrium, adsorbent was separated by centrifugation. To determine equilibrium time, the adsorption of Ni(II) onto MRS at three initial concentrations viz. 5, 10, and 15 mg/L was measured as a function of contact time. The removal of Ni(II) was rapid in the first 90 min, reached equilibrium at 120 min, and remained constant up to 150 min
Fig. 2 a and b SEM images of modified riverbed sand (MRS) at ×100 and ×5,000 magnification
Environ Sci Pollut Res Fig. 3 FTIR spectra of RS and MRS
180
MRS RS
160
Transmittance (%)
140 120
1783.39
100
1793.80 80
759.49
60
759.49 186.29
40 20
32.59
349.661 0 3000
2500
2000
1500
1000
500
0
-1
Wavenumber ( cm )
(Fig. 5). Removal increases from 54.09 to 68.76 % by decreasing adsorbate concentration from 15 to 5 mg L−1. At low initial concentrations of Ni(II), the uptake is higher because the ratio of Ni(II) ions to the number of available adsorption sites is small, and consequently, there is less competition among the Ni(II) ions and binding sites (Nasernejad et al. 2005). The higher removal in the low concentration range is of industrial application (Panday et al. 1985).
Ni(II) removal increased from 68.76 to 78.04 % by increasing dose from 1.0 to 2.0 g (Fig. 6). It may be due to availability of greater active surface for adsorption (Gupta et al. 2010a, b). As the adsorbent dosage increases, the adsorbent sites available for Ni(II) metal ions also increase and consequently, better adsorption takes place.
Effect of adsorbent dose
Temperature is an important parameter affecting adsorption processes. Most of the adsorption processes are exothermic in nature, but in some cases, endothermic adsorption is also reported (Sharma et al. 1991). In the present investigation, the adsorption of Ni(II) by MRS was investigated at three different temperatures: 25, 30, and 35 °C. It was found that the percentage of removal decreases from 68.76 to 39.48 % by increasing temperature from 25 to 35 °C (Fig. 7). It indicates that adsorption of Ni(II) on MRS is exothermic
The effect of adsorbent dose on the adsorption of Ni(II) ions was studied by varying the adsorbent dose between 1.0 and 2.0 g/50 mL of aqueous solutions of Ni(II) ions at 25 °C. This parameter strongly affects the adsorption process in an aqueous solution and also determines the capacity of the adsorbent for a given initial concentration of the adsorbate. 90 80
Effect of temperature
Modified riverbed sand(MRS) Raw riverbed sand(RRS)
70
5mg/L 10mg/L 15mg/L
60
60
Removal (%)
% Removal
70
50 40 30
50 40 30
20
20
10
10
0 50
100
150
200
250
Contact time(min)
Fig. 4 Effect of modification of adsorbent on the removal of Ni(II) (pH 6.0, temperature 25 °C, concentration 5 mg/L, dose 1.0 g, rpm 100)
0 0
20
40
60
80
100
120
140
160
Contact Time (min)
Fig. 5 Effect of contact time and concentration on the removal of Ni(II) by adsorption on MRS (pH 6.0, temperature 25 °C, dose 1.0 g, rpm 100)
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-0.8
80
1.0g 1.5g 2.0g
-1.0 -1.2
60
log(qe-q)
Removal (%)
70
50 40
-1.6 -1.8 0
30
25 C 0 30 C 0 35 C
-2.0
20
-2.2
10 0
-1.4
-2.4
0
20
40
60
80
100
120
140
10
20
30
40
50
60
70
80
90
100
Contact time (min)
160
Contact Time (min)
Fig. 6 Effect of adsorbent dose on the removal of Ni(II) by adsorption on modified silica sand (concentration 5 mg/L, pH 6.0, temperature 25 °C, rpm 100)
Fig. 8 Lagergren’s plot for the adsorption of Ni(II) on modified sand at different temperatures
that the process of removal is governed by pseudo-firstorder kinetics. in nature and a higher removal of Ni(II) can be achieved at lower temperatures. Kinetic modeling Kinetic modeling of the removal of Ni(II) by modified sand was carried out by Lagergren’s model which is expressed as follows (Bhattacharya et al. 2008; Gupta and Ali 2008): logðqe qt Þ ¼ log qe
kad t 2:303
ð3Þ
where kad is the rate constant (per minute), qe and qt are the amount of nickel adsorbed (milligram per gram) at equilibrium and at any time t. The values of kad were obtained from the slope of linear plot of ‘log (qe −qt) vs. t’ (Fig. 8). The values of kad and correlation coefficients, R2, are given in Table 2. The straight line plots of log (qe−qt) vs. t confirm
70
0
25 C 0 30 C 0 35 C
Removal (%)
60 50 40 30
Intraparticle diffusion model The most commonly used technique for testing whether the removal involves intraparticle diffusion is by fitting the experimental data to an intraparticle diffusion model. Kinetic data was further analyzed using the intraparticle diffusion model (Weber and Morris 1963). Values of the rate constant of intraparticle diffusion, kid, were calculated from the slopes of the linear portions of the plots of “amount adsorbed vs. square root of time” (Fig. 9) at different temperatures by using the following equation: qt ¼ kid t 1=2
ð4Þ
where kid is the intraparticular diffusion rate constant (milligram per gram square root minute). It is an empirically found functional relationship common to most adsorption processes where uptake varies almost proportionally with ‘t1/2’ rather than with contact time. The values of kid at different temperatures are given in Table 3. If intraparticle diffusion is rate-limiting, then plots of ‘adsorbate uptake, qt, vs. the square root of time (t1/2)’ would be linear. It is clear from Fig. 9 that the intercept of the line does not pass through the origin and the correlation coefficients (R2) are less than 0.96 suggesting that two or more steps are involved in the nickel adsorption onto the MRS. The deviation of the straight line in Weber and Morris’ model may be due to difference in the rate of mass
20 10 0
0
20
40
60
80
100
120
140
160
Contact Time
Fig. 7 Effects of temperature on the removal (%) of Ni(II) by adsorption on modified silica sand (concentration 5 mg/L, pH 6.0, dose 1 g, rpm 100)
Table 2 Lagergren’s constants for adsorption of Ni(II) on MRS at different temperatures
Temperature (°C) 25 30 35
Kad (min−1) 0.03765 0.03256 0.02870
R2 0.99 0.99 0.98
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75
0
25 C 0 30 C 0 35 C
0.16
70 60
0.14
55
Removal (%)
qt (mg/g)
pH 4.0 pH 6.0 pH 8.0
65
0.12 0.10 0.08 0.06
50 45 40 35 30 25 20 15
0.04
10 0.02 5
6
7
8
t
1/2
(min)
9
10
11
1/2
5 0 0
20
40
60
80
100
120
140
160
Contact Time (min)
Fig. 9 Intraparticle diffusion plots for the adsorption of Ni(II) on MRS at different temperatures
transfer in the initial and final stages of adsorption (Panday et al. 1986). The first step in the diffusion model is the mass transfer of adsorbate molecules from bulk solution to the adsorbent surface, and the second stage is the intraparticle diffusion on MRS. Moreover, intra particle diffusion would be the rate-controlling step if the lines pass through the origin, but here it is not the rate-controlling step as concluded by the Fig. 9. Effect of pH The pH of solution greatly influences removal of adsorbate species. Further, pH influences surface properties of the adsorbent by way of functional group dissociation and also surface charges. The removal of Ni(II) ion by MRS was strongly affected by pH in the range of 4.0 to 8.0 as shown in Fig. 10. The experiments were not conducted beyond pH 8.0 to avoid possible nickel hydroxide precipitation. The maximum removal was found to be 68.76 % at pH of 6.0. The pH influences the binding of Ni(II) ions by protonated adsorbent surface. It indicates that there is an interaction of adsorbent binding sites with protons. It is expected that the protonated surface favors the removal of Ni(II) from aqueous solutions (Stumm 1989). At low pH, nickel ions and protons compete for vacant adsorbent sites resulting in low adsorption of nickel. At low pH, H3O+ ions are close to the binding sites of the adsorbent, and this restricts the approach of nickel ions due to repulsion. With increase in Table 3 Values of intraparticle diffusion rate constant for the removal of Ni(II) by adsorption on MRS at different temperatures
Temperature (°C) 25 30 35
Kid (mg/g min1/2) 0.021 0.023 0.013
Fig. 10 Effects of pH on the removal of Ni(II) by adsorption on MRS (concentration 5 mg/L, temperature 25 °C, dose 1 g, rpm 100)
pH, more negatively charged surface attracts more positively charged nickel ions for binding resulting in the higher removal of Ni(II) ions. Equilibrium modeling Equilibrium modeling of the process of adsorption of Ni(II) ions was carried out by using the Langmuir and Freundlich adsorption isotherms. Several mathematical models have been applied for describing equilibrium studies for the removal of pollutants by adsorption on solid surfaces. Selection of an isotherm equation depends on the nature and type of the system. Out of several isotherm equations, the Freundlich and Langmuir isotherm equations have been reported most frequently. In the present study, resultant data was analyzed by Langmuir and Freundlich isotherms. Langmuir adsorption isotherm The Langmuir model assumes that uptake of metal ions occurs on a homogeneous surface by monolayer coverage of the adsorbent and that there is no interaction between adsorbed species. Maximum adsorption corresponds to a saturated monolayer of solute molecules on the adsorbent surface, and the energy of adsorption is constant. The linearized expression of the Langmuir model can be expressed as follows (Sharma et al. 2008):
R2
Ce 1 Ce ¼ 0 þ 0 qe Q b Q
0.95 0.93 0.95
where Ce (milligram per liter) and qe (milligram per gram) are the concentrations of adsorbate and amount of adsorbate adsorbed at equilibrium, respectively. Q0 (milligram per gram) and b (liter per milligram) are the terms related to capacity and
ð5Þ
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energy of adsorption and are known as Langmuir’s constants. The equilibrium data was plotted for ‘Ce / qe vs. Ce’(Fig. 11). For Langmuir isotherm, a dimensionless separation factor can be expressed as follows (Basha et al. 2008): 1 RL ¼ ð1 þ bC0 Þ
Freundlich isotherm model The equilibrium data was also examined by the Freundlich adsorption isotherm model. The Freundlich model assumes
50 0
25 C 0 30 C 0 35 C
40
e
35 30
e
C /q
Temperature (°C)
25
30
35
Langmuir constants
Q0 (mg/g)
0.86
0.67
0.24
Freundlich constants
b (L/mg) R2 RL Kf (mg/g)
0.22 0.99 0.23 0.13
0.11 0.96 0.37 0.10
0.23 0.95 0.22 0.03
n R2
1.71 0.98
1.45 0.99
1.02 0.88
ð6Þ
where C0 is the initial solute concentration (milligram per liter) and b is the Langmuir adsorption equilibrium constant (liter per milligram). The dimensionless constant separation factor, RL, is used to test whether the adsorption is favorable or not. The value of RL indicates the type of the isotherm to be either unfavorable (RL >1), linear (RL 01), favorable (0
