Application of a heterogeneous adsorbent (HA) for the removal of hexavalent chromium from aqueous solutions: Kinetic and equilibrium modeling

Varsha Srivastava; Mrigank Shekhar; Deepak Gusain; Fethiye Gode; Yogesh C. Sharma

doi:10.1016/j.arabjc.2013.11.049

View/Download PDF

Buy Reprints

PDF

Translate this page into:

Original article

10 (

2_suppl

); S3073-S3083

doi:

10.1016/j.arabjc.2013.11.049

Application of a heterogeneous adsorbent (HA) for the removal of hexavalent chromium from aqueous solutions: Kinetic and equilibrium modeling

Varsha Srivastava^{^a}, Mrigank Shekhar^{^b}, Deepak Gusain^{^a}, Fethiye Gode^{^c}, Yogesh C. Sharma^{^a,⁎}

a Department of Chemistry, Indian Institute of Technology (Banaras Hindu University) Varanasi, Varanasi 221 005, India

b Department of Applied Sciences, National Institute of Foundry and Forge Technology, Ranchi 834003, India

c Department of Chemistry, Suleman Demierl University, Isparta, Turkey

⁎Corresponding author. Tel.: +91 542 6701865; fax: +91 542 2368428. ysharma.apc@itbhu.ac.in (Yogesh C. Sharma)

Received: 2013-6-18, Accepted: 2013-11-27, Published: 2013-05-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

In the present study, a heterogeneous adsorbent material (HA) was used as an adsorbent for the removal of Cr(VI) from aqueous solutions at laboratory scale. Cr(VI) containing water was treated with heterogeneous adsorbent(HA).Chromium solutions of various initial concentrations were treated with adsorbent in batch mode experiments to investigate the adsorption characteristics of heterogeneous adsorbent (HA). Kinetics of adsorption of Cr(VI) ions on adsorbent was investigated by using pseudo first order and second order kinetic models. Removal processes were found to be governed by pseudo second order model. Intraparticle diffusion model was also analyzed for this system. Removal was found to be increased by increasing the temperature from 298 to 318 K which indicates the endothermic nature of the process. Various two parameter isotherm models viz. Langmuir, Freundlich, Elovich, Tempkin, Dubnin–Raduskevich (D–R), Harkin–Jura and BET isotherm were applied on resultant data for equilibrium modeling. It was observed that heterogeneous adsorbent (HA) particles were highly efficient for the removal of Cr(VI).

Keywords

Chromium

Equilibrium modeling

Rice husk

Silica

Show Related Articles from PubMed

1 Introduction

Contamination of water and waste water by various heavy metals is a serious environmental problem as metals have widespread applications resulting in the release of higher amount of heavy metals in the environment beyond their acceptable limits. Metals are non-biodegradable and have tendency of bioaccumulation and pose various health problems both in humans and animals. Among various heavy metals, Cr(VI) is one of the most important priority pollutants due to its vast applications in various industries such as electro plating, alloying, leather tanning, textile dyeing, steel fabrication and wood preservative treatment (Chen et al., 2011; Kowalshi,1994; Rao et al., 2010 ). On the other hand, hexavalent chromium poses various health problems such as liver damage and pulmonary congestion (Chen et al., 2010). It is also known to be carcinogenic (Pang et al., 2011). According to USEPA, the maximum contamination level for Cr(VI) in domestic water supplies is 0.05 mg/L and for effluent discharge to inland surface water is 0.1 mg/L (Jain et al., 2010). Reverse osmosis, chemical precipitation, filtration, ion exchange, evaporation, caustic oxidation and reduction, membrane separation and adsorption are the well known techniques used for the treatment of Cr containing effluents. Most of these techniques involve high cost, long operation time, incomplete metal removal and sludge generation. Adsorption is one of the most promising techniques due to its low initial cost and simplicity of design (Karthikeyan et al., 2005; Sharma et al., 2010). Among various available adsorbents, activated carbon has been very popular for the removal of a variety of pollutants for the last many decades but due to its high cost, search for other alternative adsorbent materials is of immense interest. Utilization of agricultural waste for the synthesis of adsorbent materials may solve the problems to some extent (Mussatto et al., 2010; Owlad et al., 2010; Zhang et al., 2010 ). Various low-cost materials and agricultural wastes have been used for the removal of Cr(VI) from aqueous solutions (Garg et al., 2007; Khazaei et al., 2011). Research on the modification of low cost materials for the enhancement of removal efficiency has also been carried out by various researchers.

In the present manuscript, removal efficiency of heterogeneous adsorbent (HA) for Cr(VI) has been investigated. Kinetics and equilibrium modeling of removal process have been carried out by applying various models.

2 Materials and method

2.1

2.1 Synthesis and characterization of heterogeneous adsorbent (HA) material

Rice husk was used as a precursor for the preparation of silica. For this purpose, rice husk was collected from the local rice mill. Silica was prepared by thermal treatment of rice husk. Detailed procedure of preparation of silica particles is given elsewhere (Srivastava et al., 2013). Synthesized silica particles were mixed with ironoxide nanoparticles. For this, solutions of Fe²⁺ and Fe³⁺ ions in 2:1 ratio were prepared and precipitated by ammonia solution. After completion of precipitation, precipitate was dried in hot air oven. After drying, iron oxide nanoparticles and silica particles were mixed together in a 1:1 ratio and were ground to mix properly. A mixture of both materials was then sieved to get uniform sized particles. Sieved particles were named as heterogeneous adsorbent (HA) which was used as adsorbent material for the removal of Cr(VI) from aqueous solutions. EDX of silica and heterogeneous adsorbent (HA) was also investigated. Scanning electron microscopy (SEM) was used to observe changes in surface characteristics during the synthesis of heterogeneous adsorbent (HA) from precursors.

2.2

2.2 Preparation of metal solutions

In the present study, stock Cr(VI) solution was prepared by dissolving potassium dichromate in double distilled water. Solutions of different initial concentrations of Cr(VI) were prepared by proper dilution of stock solution. pH of the solutions was maintained by 0.1 M HCl/NaOH. Ionic strength of the solutions was maintained at 0.01 M NaClO₄.

2.3

2.3 Batch adsorption experiments

Removal studies were carried out in batch mode experiments. 50 ml chromium solution of different concentrations was taken in a 125 ml capped reagent bottle. 0.15 g of adsorbent was added in each reagent bottle containing 50 ml of Cr(VI) solution and then agitated at 100 rpm on temperature controlled shaker for various time intervals to observe the saturation time. After saturation time, adsorbent was separated from solutions by centrifugation.

2.4

2.4 Analysis of residual concentration of Cr(VI)

Residual concentration of Cr(VI) in each sample was determined by an Atomic Absorption Spectrophotometer(AA 7000, Shimadzu, Japan). Amount adsorbed per unit mass of adsorbent was calculated by the following equation.

(1)

q_{e} = (\frac{C_{i} - C_{e}}{W}) * V

where C_i and C_e are the initial and equilibrium concentrations of Cr (VI) respectively (mg/L), q_e is the amount adsorbed per unit mass of the adsorbent (mg/g); W is the amount of adsorbent (g/L).

3 Result and discussions

3.1

3.1 Characterization of adsorbent

To study the major component of rice husk and rice husk silica, EDX of both materials has been taken and it was observed that synthesized RH-silica has only Si and O atoms (Fig. 1a). After thermal treatment, no peaks of other elements were observed which are present in rice husk. EDX of heterogeneous adsorbent (HA) confirms the presence of iron oxide (Fig. 1b). Surface morphology of rice husk (RH), RH-silica and heterogeneous adsorbent (HA) are shown in Fig. 2a–c. It is clear from Fig. 2a that RH has a rough surface. On thermal treatment it is converted into silica. Fig. 2b shows that silica particles are of different morphologies. Further, heterogeneous adsorbent (HA) has both the particles i.e. silica and iron oxide particles. In heterogeneous adsorbent (HA) there is heterogeneity in particle size (Fig. 2c).

a, b EDX of RH-silica and heterogeneous adsorbent (HA).

SEM of (a) rice husk (b) RH-silica (c) heterogeneous adsorbent (HA).

3.2

3.2 Comparison of removal efficiencies of rice husk, rice husk silica, and iron oxide particles

To compare the removal efficiencies of rice husk, rice husk silica, iron oxide particles and prepared heterogeneous adsorbent material, 0.15 g of adsorbent material was mixed with 50 ml of chromium solution (conc. 5 mg/L) in separate reagent bottles and were shaken in thermostatic shaker for 60 min at 100 rpm. After 60 min. adsorbent materials were separated from the solution and residual concentration of Cr(VI) in each sample was determined to check the efficiency of adsorbent materials.

Comparison of removal efficiencies of rice husk, rice husk silica, and iron oxide particles is shown in Fig. 3. Among all, iron oxide was found to be the best material. Detailed study on removal efficiency of iron oxide nanoparticles for chromium removal has already been conducted previously (Sharma et al., 2009). To reduce the cost of adsorbent material, a heterogeneous adsorbent material was prepared by rice husk silica and iron oxide nanoparticles. Fig. 3 depicts, that rice husk silica gives 60.95% removal while on addition of iron oxide nanoparticles, the removal efficiency increased to 88.95%.

Removal efficiency of four different adsorbent materials for the removal of Cr(VI) from aqueous solutions (Conc. 5 mg/L, dose 0.15 g/50 ml, contact time 60 min, agitation speed 100 rpm, Temp. 298 K).

3.3

3.3 Kinetics of removal process

Amount adsorbed per unit mass of adsorbent at different time intervals indicates that there is increasing trend of amount adsorbed in each concentration range. But when compared from the concentration point of view, the value of amount adsorbed at the equilibrium is higher for higher concentration. It is clear from Fig. 4 that removal increased with time but after 60 min it acquired equilibrium and thereafter no significant change in removal was observed. It can be explained on the basis that in the beginning, the removal is higher due to availability of greater number of active sites but as the time increases, active surfaces become saturated with adsorbate species resulting in the decrease in removal (%).

Effect of initial Cr(VI) concentration on uptake model (adsorbent doses 0.15 g; pH 2.5, concentration of Cr(VI) solutions (4–6 mg/L); Temperature 250C).

For investigation of kinetics of removal process, pseudo first order and second order kinetic models were applied to the data. Values of different kinetic parameters for different concentrations at 25 °C were calculated. The linearized form of pseudo first order and second order kinetic model can be expressed as follows (Srivastava et al., 2011):

Pseudo first order kinetic model:

(2)

log (q_{e} - q_{t}) = {logq}_{e} - \frac{k_{1}}{2.303} t

Pseudo second order kinetic model:

(3)

\frac{t}{q_{t}} = \frac{1}{k_{2} q_{e}^{2}} + \frac{1}{q_{t}} t

(4)

h = k_{2} q_{e}^{2}

where k₁(per min) and k₂ (g/mg min) are the rate constants of pseudo first order and second order reactions respectively, q_e and q_t are the amounts of adsorbate adsorbed at equilibrium and at any time respectively (mg/g). h is known as initial sorption rate. The value of k₁ was determined from the slope of the linear plots of ‘log (q_e −q_t) vs. t’ for different concentrations (Fig. 5a). The values of q_e and k₂ for pseudo second order kinetic model were determined by the slope and intercept of the straight line of the plot ‘t/q_t vs. t’ respectively (Fig. 5b). The values of k₁, K₂, h, calculated q_e, experimental q_e, and correlation coefficients, R² for different concentration ranges are given in Table 1. The experimental value of q_e agreed well with calculated value of q_e in the case of pseudo second order model. Further, on comparison of R² value it can be revealed that pseudo second order model can explain the system in a better way than pseudo first order kinetic model.

(a) and (b) pseudo first order and second order kinetic plot.

Table 1 Values of pseudo first order and pseudo-second order constants for adsorption of Cr(VI) on heterogeneous adsorbent (HA)at different concentrations.

Values of pseudo first order and pseudo-second order constants
Concentration (mg/L)	q_e (mg/g) Experimental	Pseudo first order rate constant(k₁)	q_e (mg/g) Calculated	R²	Pseudo second order rate constant(k₂)	q_e (mg/g) Calculated	h	R²
4	1.221	0.045	0.349	0.959	0.379	1.223	0.568	0.997
5	1.483	0.043	0.464	0.923	0.277	1.479	0.606	0.996
6	1.693	0.037	0.513	0.997	0.251	1.672	0.703	0.998

3.4

3.4 Intraparticle diffusion study

In any adsorption process sometimes intraparticle diffusion is the rate controlling step. To confirm the possibility of intraparticle diffusion in the present system, the kinetic data were analyzed by using the well known Weber Morris intraparticle diffusion model. It can be expressed by the following equation (Yadav et al., 2012):

(5)

q_{t} = k_{id} t^{\frac{1}{2}} + c

where k_id (mg/g min^1/2) is the intraparticle diffusion rate constant and C is the intercept .

The values of k_id and C can be calculated from the slope and intercept respectively of the plot ‘q vs. t^0.5’ (Fig. 6). In the above expression (Eq. 5) the value of the intercept ‘C’ is related to the thickness of the boundary layer.

Intraparticle diffusion plot at different concentrations (adsorbent doses 0.15 g; pH 2.5, Concentration of Cr(VI) solutions (4–6 mg/L), Temperature 25 °C).

In case of higher values of ‘C’, intraparticle diffusion will be rate limiting step. Intraparticle diffusion will be the rate-limiting step if the regression of q_t versus t^1/2 is linear and passes through the origin (Huang et al., 2009). In the present study intraparticle diffusion is not the only rate-limiting step. The values of k_id for different concentrations are given in Table 2. In case of involvement of intraparticle diffusion the plot of uptake (q) versus the square root of time will be linear and lines will pass through the origin.

Table 2 Values of intraparticle diffusion constants for adsorption of Cr(VI) on heterogeneous adsorbent (HA) at different concentrations.

Concentration (mg/L)	K_dif (mg/g min^1/2)	C	R²
4	0.045	0.864	0.9969
5	0.060	1.008	0.9929
6	0.075	1.102	0.9909

3.5

3.5 Effect of temperature

Removal of adsorbate by adsorption process may be affected by various parameters. Among them temperature is one of the important parameters which can strongly affect any adsorption process.

Temperature study was carried out at three different temperatures 298, 308 and 318 K to observe the effect of temperature variation on the removal process. Effect of temperature on % removal of Cr(VI) is shown in Fig. 7. It depicts that removal was higher at 318 K. Increasing trend of Cr(VI) removal on increasing temperature indicates the endothermic nature of the process of removal of Cr. It is due to the enhancement of adsorbent sites at high temperature. It also shows that adsorbate species is attached by chemisorptions.

Effect of temperature on the removal of Cr(VI) (adsorbent doses 0.15 g; pH 2.5; Concentration of Cr(VI) solution 4 mg/L).

4 Equilibrium modeling

Equilibrium modeling is important to decipher any removal process and gives an idea about the capacity of adsorbent which is necessary to design any treatment plant at industrial scale. Various isotherm models were studied in the present investigation for equilibrium modeling. Each isotherm model describes some of the salient features of the adsorption process. Various two parameter isotherm models such as Langmuir, Freundlich, Tempkin, Dubnin–Raduskevich (D–R), Elovich, Harkin–Jura isotherm and BET isotherm models were applied on resultant data.

4.1

4.1 Langmuir isotherm

Langmuir isotherm model assumes that there are uniform energies of adsorption at the surface of adsorbent and after adsorption; there is no migration of adsorbate molecules on the surface plane. According to this isotherm, there is monolayer coverage of adsorbent active surface. Langmuir isotherm is expressed as follows (Kumar et al., 2006):

(6)

q_{e} = \frac{q_{m} K_{L} C_{e}}{1 + K_{L} C_{e}}

The calculations of various isotherm parameters were carried out by its linearized form. Langmuir isotherm can be linearized in the following different forms:

(7)

\frac{C_{e}}{q_{e}} = \frac{1}{q_{m}} C_{e} + \frac{1}{K_{L} q_{m}}

(8)

\frac{1}{q_{e}} = (\frac{1}{K_{L} q_{m}}) \frac{1}{C_{e}} + \frac{1}{q_{m}}

(9)

q_{e} = q_{m} - (\frac{1}{K_{L}}) \frac{q_{e}}{C_{e}}

(10)

\frac{q_{e}}{C_{e}} = K_{L} q_{m} - K_{L} q_{e}

Values of different isotherm parameters were calculated for all the linearized forms to investigate the variation in parameters. In the above equations, C_e (mg/L) and q_e (mg/g) are the concentrations of adsorbate and amount of adsorbate adsorbed at equilibrium, respectively. q_m (mg/g) and K_L (L/mg) are the terms related to capacity and energy of adsorption, respectively. Values of various parameters are given in Table 3 (Fig. 8).

Table 3 Values of different isotherm parameters for adsorption of Cr(VI) on heterogeneous adsorbent (HA).

Langmuir isotherm constants (Type 1)		Tempkin isotherm
q_m (mg/g)	2.195	B_T (mg/g)	0.395
K_L (L/mg)	3.723	A(L/mg)	48.98
R²	0.999	R²	0.991

Langmuir isotherm constants (Type 2)		Elovich isotherm
q_m (mg/g)	2.194	q_m	0.704
K_L (L/mg)	3.726	K_E	3.39
R²	0.999	R²	0.966

Langmuir isotherm constants (Type 3)		DR isotherm
q_m (mg/g)	2.195	q_m	4.873
K_L (L/mg)	3.725	β	4.287
R²	0.997	E	0.341

Langmuir isotherm constants (Type 4)		R²	0.996
q_m (mg/g)	2.195	Harkin–Jura isotherm
K_L (L/mg)	3.725	A	2.039
R²	0.999	B	0.772

Freundlich isotherm constants	R²	R²	0.949
K_F (mg/g)(L/g)n	1.669	BET isotherm
1/n	3.984	Q°	18.51
R²	0.981	B	27.0
		R²	0.991

Langmuir plot for the removal of Cr(VI).

4.2

4.2 Freundlich isotherm

The Freundlich isotherm is based on both monolayer (chemisorption) and multilayer adsorptions (physisorption) with interaction between adsorbed molecules.

Freundlich model is expressed as follows (Srivastava et al., 2011, 2013):

(11)

q_{e} = K_{f} C_{e}^{1 / n}

The linearized form of the equation is expressed as follows:

(12)

{logq}_{e} = \frac{1}{{nlogC}_{e}}

where K_F (mg/g (L/mg)^1/ⁿ) is the adsorption capacity of the adsorbent, 1/n is the empirical constant indicating adsorption intensity (L/mg), q_e is the amount of adsorbate adsorbed by a unit mass of adsorbent at equilibrium (mgg⁻¹) and C_e is the residual concentration of Cr(VI) remaining in the solution (mg/L).

Values of Freundlich parameters were calculated from the intercept and slope of the linear plot ‘log q_e vs. log C_e’ (Fig. 9a). Value of ‘n’ gives an idea about the applicability of adsorption process. If the value of n > 1 then it represents favorable adsorption conditions. The values of Freundlich parameters ‘K_f’ and ‘n’ are given in Table 3. Linear plots confirm the applicability of Freundlich isotherm model to the system.

Various isotherm plots for Cr(VI) removal (a) Freundlich; (b) Tempkin; (c) Elovich; (d) Dubnin–Raduskevich (D–R); (e) Harkin–Jura isotherm; and (f) BET isotherm models.

4.3

4.3 Tempkin isotherm

Tempkin isotherm assumes that the heat of adsorption of all the adsorbate molecules in the layer decreases linearly with coverage due to adsorbate–adsorbate repulsions (Zheng et al., 2009). Tempkin isotherm has generally been applied in the following form:

(13)

q_{e} = \frac{RT}{b} {lnAC}_{e}

The linearized expression of Tempkin isotherm can be expressed as follows:

(14)

q_{e} = B_{T} lnA + B_{T} {lnC}_{e}

where B_T = RT/b, T is the absolute temperature (K), A is the equilibrium binding constant (L/mg), R is the gas constant (8.314 J/mol^.K) and B₁ is related to the heat of adsorption. The values of Tempkin isotherm parameters viz. B_T and A can be calculated from the slope and the intercept of the plot q_e vs. ln C_e (Fig. 9b). The values of Tempkin isotherm parameters with the corresponding R² values are given in Table 3.

4.4

4.4 Dubnin–Raduskevich (D–R) isotherm

Another important isotherm is Dubnin–Raduskevich(D–R) isotherm. This isotherm was employed for the investigation of characteristics of adsorption and the porosity apparent free energy (Khan et al., 1995). The D–R equation assumes the heterogeneous surface of the adsorbate. It is usually expressed in the following form:

(15)

{lnC}_{ads} = {lnq}_{m} - β ε^{2}

where C_ads (mg/g) is the amount of metal ions adsorbed per unit weight of the adsorbent, q_m (mg/g) is the adsorption capacity, β (mol² J⁻²) is the activity coefficient related to the mean sorption energy, ɛ is the Polanyi potential. Following equation can be used for the calculation of Polanyi potential

(16)

ε = RTln (1 + \frac{1}{C_{e}})

where R (8.314 J/mol K) is the gas constant. The values of β and q_m were calculated from the slope and intercept of the plot ln C_ads vs ɛ² respectively (Fig. 9c). The mean sorption energy E (kJ/mol) can also be calculated using the following relationship:

(17)

E = \frac{1}{\sqrt{2 β}}

Value of DR-isotherm parameters is given in Table 3. On the basis of the value of adsorption energy E it can be estimated that whether the process is physical (E < 8 kJ mol⁻¹) or chemical (E value lies 8 and 16 kJ/mol) and over 16 kJ/mol the adsorption type can be explained by a stronger chemical adsorption than ion exchange (Wang et al., 2004).

4.5

4.5 Elovich isotherm

Elovich isotherm is expressed as the following form (Ncibi, 2008; Ekpete et al., 2011):

(18)

\frac{q_{e}}{q_{m}} = K_{E} C_{e} exp (- \frac{q_{e}}{q_{m}})

Linearized form of Elovich isotherm is expressed as follows:

(19)

ln (\frac{q_{e}}{C_{e}}) = ln (K_{E} q_{m}) - \frac{q_{e}}{q_{m}}

where, q_m is the Elovich maximum adsorption capacity and K_E (L/g) is the Elovich equilibrium constant. Elovich constant was calculated from the slopes and the intercepts of the plot ln (q_e/c_e) versus q_e as shown in Fig. 9d. Equilibrium constant obtained from the Elovich isotherm plot are tabulated in Table 3.

4.6

4.6 Harkin–Jura isotherm

H–J isotherm assumes the possibility of multilayer adsorption with the existence of heterogeneous pore distribution (Gupta et al., 2013; Theivarasu et al., 2010):

H–J isotherm equation can be expressed as follows:

(20)

q_{e} = {(\frac{A}{B_{2} + {logC}_{e}})}^{\frac{1}{2}}

(21)

\frac{1}{q_{e}^{2}} = \frac{B}{A} - \frac{1}{A} ({logC}_{e})

where A and B are the isotherm parameters which were calculated from the slope and intercept of plot 1/q_e² verses Log C_e (Fig. 9e) values are given in Table 3.

4.7

4.7 BET (Braunauer, Emette and Teller) isotherm

BET (Braunauer, Emette and Teller) model assumes multilayer adsorption of any adsorbate. According to BET isotherm, there is no migration between the adsorbed molecules on the surface and assumes to be uniform surface energies. For the coverage of first layer, energy of adsorption is responsible while for the adsorption of subsequent layer condensation energy will take part .BET equation can be expressed as follows (Kamari et al., 2009):

(22)

q_{e} = \frac{{BC}_{e} Q^{o}}{{(C}_{s} - C_{e}) [1 + (B - 1) (C_{e} / C_{s})]}

where C_s is the saturation concentration of the solute, C_e is the measured concentration in solution at equilibrium (mg/L), Q° is the number of moles of solute adsorbed per unit weight of adsorbent in forming a complete monolayer on the surface (mg/g), q_e is the number of moles of solute adsorbed per unit weight at concentration.

B is a constant expressive of the energy of interaction with the surface. The linear form of BET isotherm can be expressed as follows:

(23)

\frac{C_{e}}{{(C}_{s} - C_{e}) q_{e}} = \frac{1}{{BQ}^{o}} + (\frac{B - 1}{{BQ}^{o}}) (\frac{C_{e}}{C_{s}})

Value of different isotherm parameters were calculated from the slope and intercept of plot ‘C_e/(C_s−C_e) q_e against (C_e/C_s)’(Fig. 9f). BET isotherm parameters with their respective correlation coefficient are given in Table 3. On studying Table 3, it is clear that Langmuir isotherm model is the best one for the present system.

Values of Langmuir isotherm parameters calculated from the all four types showed approximate same value with very small differences.

Freundlich adsorption capacity was calculated and found to be 1.669 (mg/g). In the case, value of regression coefficient is greater than 0.99 for all studied isotherm models except Elovich isotherm and Harkin–Jura isotherm model. The value of E < 8 kJ/mol suggests that the process of removal of Cr(VI) is physical in nature.

5 Effect of competing ions on chromium removal

Some anions such as ${SO}_{4}^{2 -}$ , ${PO}_{4}^{3 -}$ , ${NO}_{3}^{2 -}$ and Cl⁻ usually coexist with Cr(VI) in water. Presense of these competing ions may decrease the adsorption capacity of adsorbent material and therefore effect of various competing ions on the removal of Cr(VI) by adsorption on heterogeneous adsorbent (HA) were studied. Chromium soluion (5 mg/L) having a molar concentration of competing ions (0.05, 0.10,0.15 and 0.20 M) were prepared to investigate the effcet of the presense of competing ions on removal of Cr(VI) from the aqueous solutions. Effect of competing ions on removal of Cr(VI) is shown in Fig. 10. It is clear from this figure that removal decreased by increasing concentration of competing ions. The selected competing anions ( ${SO}_{4}^{2 -}$ , ${PO}_{4}^{3 -}$ , ${NO}_{3}^{2 -}$ and Cl⁻) decreased the removal of Cr(VI).

Effect of competitive ions on removal of Cr(VI) by adsorption on heterogeneous adsorbent (HA).

Among all anions, ${PO}_{4}^{3 -}$ exhibits the largest competing effect followed by ${SO}_{4}^{2 -}$ . Formation of inner-sphere surface complexes may be the reason of reduction in the removal of Cr(VI). Another competing ion ${SO}_{4}^{2 -}$ having similar configuration as of chromate, also showed significant reduction in Cr(VI) removal. ${SO}_{4}^{2 -}$ is usually adsorbed at both inner-/outer-sphere surface complexes.(Hsia et al., 1994; Lefevre, 2004). Thus, for heterogeneous adsorbent (HA) the effect of competitive anions on Cr(VI) removal was found to be as follows: $Phosphate > sulphate > nitrate > chloride$

6 Conclusions

Present study revealed that heterogeneous adsorbent (HA) has potential for the removal of Cr(VI) from aqueous solutions. EDX of silica and heterogeneous adsorbent (HA) confirm elemental composition of both materials. Further, SEM revealed that the adsorbent possesses a rough surface suitable for adsorption. Removal efficiency of adsorbent was found to be significant. It was observed that metal uptake decreased with decreasing initial metal concentrations. Maximum removal for each concentration range has been achieved in 60 min. Removal process was endothermic in nature. Cr(VI) removal followed second order kinetics. It was also observed that intraparticle diffusion was not a rate governing step. Various isotherm models were applied to investigate the removal process and it was found that Langmuir isotherm is the most suitable isotherm for this process. On the basis of this study, it can be concluded that application of low cost precursor for the synthesis of modified adsorbent can be a better alternative of high cost adsorbents. It seems that this study can be a source for the synthesis of low cost, highly efficient adsorbent for the removal of Cr(VI) rich effluents. However removal studies for other toxic heavy metals are in progress.

Acknowledgement

One of the authors (Varsha Srivastava) is thankful to the Department of Science and Technology for providing financial assistance in form of WOS-A project. Authors are also thankful to the Department of Metallurgical Engineering, IIT-BHU for providing the facility of SEM analysis.

References

Chen S., Yue Q., Gao B., Xu X., . Equilibrium and kinetic adsorption study of the adsorptive removal of Cr(VI)using modified wheat residue. J Colloid Interf. Sci.. 2010;349:256.
[Google Scholar]
Chen G.Q., Zhang W.J., Zeng G.M., Huang J.H., Wang L., Shen G.L., . Surface-modified phanerochaete chrysosporium as a biosorbent for Cr(VI) contaminated wastewater. J Hazard. Mater.. 2011;186:2138.
[Google Scholar]
Ekpete O., Horsfall Jnr A.M., Tarawou T., Nepal J., . Adsorption of chlorophenol from aqueous solution on fluted and commercial activated carbon. Chem. Soc.. 2011;27:1.
[Google Scholar]
Garg U.K., Kaur M.P., Garg V.K., Sud D., . Removal of hexavalent chromium from aqueous solution by agricultural waste biomass. J. Hazard. Mater.. 2007;140:60.
[Google Scholar]
Gupta V.K., Pathania D., Sharma S., Agarwal S., Singh P., . Remediation of noxious chromium (VI) utilizing acrylic acid grafted lingo cellulosic adsorbent. J. Mol. Liquids. 2013;177:343.
[Google Scholar]
Hsia T.H., Lo S.L., Lin C.F., Lee D.Y., . Characterization of arsenate adsorption on hydrous iron-oxide using chemical and physical methods. Colloid Surf. A. 1994;85:1-7.
[Google Scholar]
Huang J.H., Wang X.M., Deng X., . Synthesis, characterization, and adsorption properties of phenolic hydroxyl group modified hyper-cross-linked polymeric adsorbent. J. Colloid Interface Sci.. 2009;337:19.
[Google Scholar]
Jain M., Garg V.K., Kadirvelu K., . Adsorption of hexavalent chromium from aqueous medium onto carbonaceous adsorbents prepared from waste biomass. J. Environ. Manag.. 2010;91:949.
[Google Scholar]
Kamari A., Ngah W.W., Liew L., . Chitosan and chemically modified chitosan beads for acid dyes sorption. J. Environ. Sci.. 2009;21:296.
[Google Scholar]
Karthikeyan T., Rajgopal S.L., Miranda R., . Chromium (VI) adsorption from aqueous solution by Hevea Brasilinesis sawdust activated carbon. J. Hazard. Mater. B. 2005;124:192.
[Google Scholar]
Khan S.A., Rehman U.R., Khan M.A., . Adsorption of chromium (III), chromium (VI) and silver (I) on bentonite. Waste Manage.. 1995;15:271.
[Google Scholar]
Khazaei I., Aliabadi M.H., Mosavian T.H., . Use of Agricultural Waste for Removal of Cr(VI)from Aqueous Solution. Iran. J. Chem. Eng.. 2011;8(4):11. (Autumn), IAChE
[Google Scholar]
Kowalshi Z., . Treatment of chromic tannery wastes. J. Hazard. Mater.. 1994;39:137.
[Google Scholar]
Kumar V., Sivanesan S., . Isotherm parameters for basic dyes onto activated carbon:Comparison of linear and non-linear method. J Hazard. Mater. B. 2006;129:147.
[Google Scholar]
Lefevre G., . In situ Fourier-transform infrared spectroscopy studies of inorganic ions adsorption on metal oxides and hydroxides. Adv. Colloid Interfac.. 2004;107:109.
[Google Scholar]
Mussatto S.I., Fernandes M., Rocha G.J.M., Órfão J.J.M., Teixeira J.A., Roberto I.C., . Production, characterization and application of activated carbon from brewer’s spent grain lignin. Bioresour. Technol.. 2010;101:2450.
[Google Scholar]
Ncibi M.C., . Applicability of some statistical tools to predict optimum adsorption isotherm after linear and non-linear regression analysis. J Hazard. Mater.. 2008;153:207.
[Google Scholar]
Owlad M., Aroua M.K., Daud W.A.W., . Hexavalent chromium adsorption on impregnated palm shell activated carbon with polyethyleneimine. Bioresour. Technol.. 2010;101(14):5098.
[Google Scholar]
Pang Y., Zeng G., Tanga L., Zhang Y., Liu Y., Lei X., Li Z., Zhang J., Liu Z., Xiong Y., . Preparation and application of stability enhanced magnetic nanoparticles for rapid removal of Cr(VI) Chem. Eng. J.. 2011;175:222.
[Google Scholar]
Rao R., Rehman A.K., . Adsorption studies on fruits of Gular (Ficus glomerata): removal of Cr(VI) from synthetic wastewater. J Hazard. Mater.. 2010;181:405.
[Google Scholar]
Sharma Y.C., Srivastava V., Weng C.H., Upadhyay S.N., . Removal of Cr(VI) from wastewater by adsorption on iron nanoparticles. The Cand.J. Chem. Eng.. 2009;87(2009):921.
[Google Scholar]
Sharma Y.C., Srivastava V., Mukherjee A.K., . Synthesis and application of nano-al₂o₃ powder for the reclamation of hexavalent chromium from aqueous solutions. J. Chem. Eng. Data. 2010;55:2390.
[Google Scholar]
Srivastava V., Weng C.H., Singh V.K., Sharma Y.C., . Adsorption of nickel ions from aqueous solutions by nano alumina: kinetic, mass transfer, and equilibrium studies. J. Chem. Eng. Data. 2011;56(4):1414.
[Google Scholar]
Srivastava V., Weng C.H., Sharma Y.C., . Application of a thermally modified agrowaste material for an economically viable removal of Cr (VI) from aqueous solutions. J. Hazard. Toxic Radioactive Waste. 2013;17(2):125.
[Google Scholar]
Theivarasu C., Mylsamy S., . Equilibrium and Kinetic adsorption studies of Rhodamine-B from aqueous solutions using cocoa (Theobroma cacao) shell as a new adsorbent. Int. J Eng. Sci. Technol.. 2010;2:6284.
[Google Scholar]
Wang C.C., Juang L.C., Lee C.K., Hsu T.C., Lee J.F., Chao H.P., . Effects of exchanged surfactant cations on the porestructure and adsorption characteristics of montmorillonite. J. Colloid Interf. Sci.. 2004;280:27.
[Google Scholar]
Yadav S., Srivastava V., Banerjee S., Weng C.H., Sharma Y.C., . Adsorption characteristics of modified sand for the removal of hexavalent chromium ions from aqueous solutions: Kinetic, thermodynamic and equilibrium studies. Catena. 2012;100:120.
[Google Scholar]
Zhang H., Tang Y., Cai D., Liu X., Wang X., Huang Q., Yu Z., . Hexavalent chromium removal from aqueous solution by algal bloom residue derived activated carbon: equilibrium and kinetic studies. J. Hazard. Mater.. 2010;181:801.
[Google Scholar]
Zheng H., Liu D., Zheng Y., Liang S., Liu Z., . Sorption isotherm and kinetic modeling of aniline on Cr-bentonite. J. Hazard. Mater.. 2009;167:141.
[Google Scholar]

Fulltext Views
492

PDF downloads
228

View/Download PDF
Download Citations

BibTeX
RIS

Show Sections

[1] Chen S., Yue Q., Gao B., Xu X., . Equilibrium and kinetic adsorption study of the adsorptive removal of Cr(VI)using modified wheat residue. J Colloid Interf. Sci.. 2010;349:256.
[Google Scholar]

[2] Chen G.Q., Zhang W.J., Zeng G.M., Huang J.H., Wang L., Shen G.L., . Surface-modified phanerochaete chrysosporium as a biosorbent for Cr(VI) contaminated wastewater. J Hazard. Mater.. 2011;186:2138.
[Google Scholar]

[3] Ekpete O., Horsfall Jnr A.M., Tarawou T., Nepal J., . Adsorption of chlorophenol from aqueous solution on fluted and commercial activated carbon. Chem. Soc.. 2011;27:1.
[Google Scholar]

[4] Garg U.K., Kaur M.P., Garg V.K., Sud D., . Removal of hexavalent chromium from aqueous solution by agricultural waste biomass. J. Hazard. Mater.. 2007;140:60.
[Google Scholar]

[5] Gupta V.K., Pathania D., Sharma S., Agarwal S., Singh P., . Remediation of noxious chromium (VI) utilizing acrylic acid grafted lingo cellulosic adsorbent. J. Mol. Liquids. 2013;177:343.
[Google Scholar]

[6] Hsia T.H., Lo S.L., Lin C.F., Lee D.Y., . Characterization of arsenate adsorption on hydrous iron-oxide using chemical and physical methods. Colloid Surf. A. 1994;85:1-7.
[Google Scholar]

[7] Huang J.H., Wang X.M., Deng X., . Synthesis, characterization, and adsorption properties of phenolic hydroxyl group modified hyper-cross-linked polymeric adsorbent. J. Colloid Interface Sci.. 2009;337:19.
[Google Scholar]

[8] Jain M., Garg V.K., Kadirvelu K., . Adsorption of hexavalent chromium from aqueous medium onto carbonaceous adsorbents prepared from waste biomass. J. Environ. Manag.. 2010;91:949.
[Google Scholar]

[9] Kamari A., Ngah W.W., Liew L., . Chitosan and chemically modified chitosan beads for acid dyes sorption. J. Environ. Sci.. 2009;21:296.
[Google Scholar]

[10] Karthikeyan T., Rajgopal S.L., Miranda R., . Chromium (VI) adsorption from aqueous solution by Hevea Brasilinesis sawdust activated carbon. J. Hazard. Mater. B. 2005;124:192.
[Google Scholar]

[11] Khan S.A., Rehman U.R., Khan M.A., . Adsorption of chromium (III), chromium (VI) and silver (I) on bentonite. Waste Manage.. 1995;15:271.
[Google Scholar]

[12] Khazaei I., Aliabadi M.H., Mosavian T.H., . Use of Agricultural Waste for Removal of Cr(VI)from Aqueous Solution. Iran. J. Chem. Eng.. 2011;8(4):11. (Autumn), IAChE
[Google Scholar]

[13] Kowalshi Z., . Treatment of chromic tannery wastes. J. Hazard. Mater.. 1994;39:137.
[Google Scholar]

[14] Kumar V., Sivanesan S., . Isotherm parameters for basic dyes onto activated carbon:Comparison of linear and non-linear method. J Hazard. Mater. B. 2006;129:147.
[Google Scholar]

[15] Lefevre G., . In situ Fourier-transform infrared spectroscopy studies of inorganic ions adsorption on metal oxides and hydroxides. Adv. Colloid Interfac.. 2004;107:109.
[Google Scholar]

[16] Mussatto S.I., Fernandes M., Rocha G.J.M., Órfão J.J.M., Teixeira J.A., Roberto I.C., . Production, characterization and application of activated carbon from brewer’s spent grain lignin. Bioresour. Technol.. 2010;101:2450.
[Google Scholar]

[17] Ncibi M.C., . Applicability of some statistical tools to predict optimum adsorption isotherm after linear and non-linear regression analysis. J Hazard. Mater.. 2008;153:207.
[Google Scholar]

[18] Owlad M., Aroua M.K., Daud W.A.W., . Hexavalent chromium adsorption on impregnated palm shell activated carbon with polyethyleneimine. Bioresour. Technol.. 2010;101(14):5098.
[Google Scholar]

[19] Pang Y., Zeng G., Tanga L., Zhang Y., Liu Y., Lei X., Li Z., Zhang J., Liu Z., Xiong Y., . Preparation and application of stability enhanced magnetic nanoparticles for rapid removal of Cr(VI) Chem. Eng. J.. 2011;175:222.
[Google Scholar]

[20] Rao R., Rehman A.K., . Adsorption studies on fruits of Gular (Ficus glomerata): removal of Cr(VI) from synthetic wastewater. J Hazard. Mater.. 2010;181:405.
[Google Scholar]

[21] Sharma Y.C., Srivastava V., Weng C.H., Upadhyay S.N., . Removal of Cr(VI) from wastewater by adsorption on iron nanoparticles. The Cand.J. Chem. Eng.. 2009;87(2009):921.
[Google Scholar]

[22] Sharma Y.C., Srivastava V., Mukherjee A.K., . Synthesis and application of nano-al₂o₃ powder for the reclamation of hexavalent chromium from aqueous solutions. J. Chem. Eng. Data. 2010;55:2390.
[Google Scholar]

[23] Srivastava V., Weng C.H., Singh V.K., Sharma Y.C., . Adsorption of nickel ions from aqueous solutions by nano alumina: kinetic, mass transfer, and equilibrium studies. J. Chem. Eng. Data. 2011;56(4):1414.
[Google Scholar]

[24] Srivastava V., Weng C.H., Sharma Y.C., . Application of a thermally modified agrowaste material for an economically viable removal of Cr (VI) from aqueous solutions. J. Hazard. Toxic Radioactive Waste. 2013;17(2):125.
[Google Scholar]

[25] Theivarasu C., Mylsamy S., . Equilibrium and Kinetic adsorption studies of Rhodamine-B from aqueous solutions using cocoa (Theobroma cacao) shell as a new adsorbent. Int. J Eng. Sci. Technol.. 2010;2:6284.
[Google Scholar]

[26] Wang C.C., Juang L.C., Lee C.K., Hsu T.C., Lee J.F., Chao H.P., . Effects of exchanged surfactant cations on the porestructure and adsorption characteristics of montmorillonite. J. Colloid Interf. Sci.. 2004;280:27.
[Google Scholar]

[27] Yadav S., Srivastava V., Banerjee S., Weng C.H., Sharma Y.C., . Adsorption characteristics of modified sand for the removal of hexavalent chromium ions from aqueous solutions: Kinetic, thermodynamic and equilibrium studies. Catena. 2012;100:120.
[Google Scholar]

[28] Zhang H., Tang Y., Cai D., Liu X., Wang X., Huang Q., Yu Z., . Hexavalent chromium removal from aqueous solution by algal bloom residue derived activated carbon: equilibrium and kinetic studies. J. Hazard. Mater.. 2010;181:801.
[Google Scholar]

[29] Zheng H., Liu D., Zheng Y., Liang S., Liu Z., . Sorption isotherm and kinetic modeling of aniline on Cr-bentonite. J. Hazard. Mater.. 2009;167:141.
[Google Scholar]

Application of a heterogeneous adsorbent (HA) for the removal of hexavalent chromium from aqueous solutions: Kinetic and equilibrium modeling

Abstract

Keywords

Chromium

Equilibrium modeling

Rice husk

Silica

1 Introduction

2 Materials and method

2.1 Synthesis and characterization of heterogeneous adsorbent (HA) material

2.2 Preparation of metal solutions

2.3 Batch adsorption experiments

2.4 Analysis of residual concentration of Cr(VI)

3 Result and discussions

3.1 Characterization of adsorbent

3.2 Comparison of removal efficiencies of rice husk, rice husk silica, and iron oxide particles

3.3 Kinetics of removal process

3.4 Intraparticle diffusion study

3.5 Effect of temperature

4 Equilibrium modeling

4.1 Langmuir isotherm

4.2 Freundlich isotherm

4.3 Tempkin isotherm

4.4 Dubnin–Raduskevich (D–R) isotherm

4.5 Elovich isotherm

4.6 Harkin–Jura isotherm

4.7 BET (Braunauer, Emette and Teller) isotherm

5 Effect of competing ions on chromium removal

6 Conclusions

Acknowledgement

References

Suggested read for related articles: