Removal of lead from aqueous solution on glutamate intercalated layered double hydroxide

Shen Yanming; Liu Dongbin; Li Shifeng; Fan Lihui; Chen Shuai; Md Atiqul Haque

doi:10.1016/j.arabjc.2013.08.005

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Original Article

10 (

2_suppl

); S2295-S2301

doi:

10.1016/j.arabjc.2013.08.005

Removal of lead from aqueous solution on glutamate intercalated layered double hydroxide

Shen Yanming^⁎, Liu Dongbin, Li Shifeng, Fan Lihui, Chen Shuai, Md Atiqul Haque

School of Chemical Engineering, Shenyang University of Chemical Technology, Shenyang 110142, PR China

⁎Corresponding author. Tel.: +86 024 89383529; fax: +86 024 89383760. sym6821@sina.com.cn (Shen Yanming)

Received: 2013-2-19, Accepted: 2013-8-9, 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

Glutamate intercalated Mg–Al layered double hydroxide (LDH) was prepared by co-precipitation and the removal of Pb²⁺ in the aqueous solution was investigated. The prepared samples were characterized by XRD, FT-IR and SEM. It was shown that glutamate can intercalate into the interlayer space of Mg–Al LDH. The glutamate intercalated Mg–Al LDH can effectively adsorb Pb²⁺ in the aqueous solution with an adsorption capacity of 68.49 mg g⁻¹. The adsorption of Pb²⁺ on glutamate intercalated Mg–Al LDH fitted the pseudo-second-order kinetics model and the isotherm can be well defined by Langmuir model.

Keywords

Layered double hydroxides

Hydrotalcite-like compounds

Glutamate

Heavy metal ions

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1 Introduction

Presence of highly toxic heavy metal ions and synthetic chemicals in ground water, drinking water, and aqueous effluents has impact on human aquatic life. Wastewater with heavy metal ions originate from a large number of industries (Ngah and Hanafiah, 2008; Barakat, 2011). The concentration of these metals in wastewater may therefore rise to a level that can be hazardous to human health, livestock and the aquatic environment. Various treatment methods such as chemical precipitation, reverse osmosis, ion exchange, solvent extraction, coagulation and adsorption are utilized to remove metal ions from aqueous solutions (Erdem et al., 2004). However, due to the economic constraints, the development of cost effective and clean processes is desired, such as coagulation, chemical precipitation, solvent extraction, electrolysis, reverse osmosis, and ion exchange. However, these techniques have certain disadvantages such as incomplete removal, high energy requirement and operational cost, use of chemicals, and generation of toxic sludge or other waste products that again require disposal (Kushwaha et al., 2012). Of all these methods, adsorption has proved to be the most effective, especially for effluents with moderate and low concentrations (Malakootian et al., 2008). Different solids such as activated carbon, zeolites, clay minerals, agricultural or forest waste fibers, etc., have been tested as adsorbents (Meena et al., 2010; Erdem et al. 2004; Carriazo et al., 2007; Singha and Das, 2012 ).

Recently the layered double hydroxides (LDHs), also known as hydrotalcite-like compounds (HTLcs) or anionic clays, have also derived interest, due to their large ionic exchange capacities (Kameda et al., 2005; Perez et al., 2006; Kameda et al., 2008; Zhao et al., 2011; Chen et al., 2012; Li et al., 2013 ). In general, LDHs have a general formula of [M²⁺₁₋_xM³⁺_x(OH)₂]Aⁿ⁻_x_/_n·yH₂O, where M²⁺ and M³⁺ are the di- and tri-valent metals, respectively, for example Mg²⁺ and Al³⁺, that occupy octahedral sites in the hydroxide layers, Aⁿ⁻ is an anion, and x is the ratio M³⁺/(M²⁺ + M³⁺) (Bontchev et al., 2003). Interestingly, the anion in the interlayer can be exchanged by other anions, so LDHs can be used as effective adsorbents for the removal of a variety of organic and inorganic anions from aqueous solution (DelHoyo, 2007).

Some anions, such as ethylenediaminetetraacetate (EDTA), citrate, glutamate, malate, etc., were found to be effective for the leaching of heavy metals due to the formation of chelate complexes (Mosekiemang and Dikinya, 2012). It was found that EDTA anion-intercalated LDH rapidly and selectively took up heavy metal ions such as Cu²⁺, Cd²⁺, Pb²⁺ and Cd²⁺ from aqueous solution, which was attributable to the formation of an EDTA–metal complex in the interlayer of LDH (Kameda et al., 2005; Perez et al., 2006). Other chelating agents such as citrate, malate, and tartrate were also attempted to intercalate into Mg–Al LDHs and then used to uptake Cu²⁺ and Cd²⁺ from aqueous solution (Kameda et al., 2008). Glutamic acid is a readily biodegradable chelating agent (Kołodyńska, 2010), in this paper, we prepared glutamate intercalated Mg–Al LDH and used it as an absorbent to remove Pb²⁺ from aqueous solutions. The performance for the removal of Pb²⁺ by glutamate intercalated Mg–Al LDH was investigated.

2 Materials and methods

2.1

2.1 Materials

All the reagents were of chemical reagent grade (Sinopharm Chemical reagent Company, Ltd., China) and were used without further purification.

2.2

2.2 Absorbent preparation

Glutamate intercalated Mg–Al LDH was labeled as Mg–Al–G LDH in this experiment. The theoretical formulae for Mg–Al–G LDH with Mg/Al molar ratios of 3 and 2 can be described as Mg_0.75Al_0.25(OH)₂(C₅H₈NO₄)_0.25 and Mg_0.67Al_0.33(OH)₂(C₅H₈NO₄)_0.33, respectively. The co-precipitation reaction can be expressed by Eqs. (1) and (2) (Kameda, 2008), where the stoichiometric coefficients were calculated based on the neutralization of the positive charge on the Al-bearing brucite-like octahedral layers due to the replacement of Mg with Al at the Mg/Al molar ratio of 3.0 and 2.0.

(1)

0.75 {Mg}^{2 +} + 0.25 {Al}^{3 +} + 0.25 C_{5} H_{8} {NO}_{4}^{-} + 2 {OH}^{-} \to {Mg}_{0.75} {Al}_{0.25} {(OH)}_{2} {(C_{5} H_{8} {NO}_{4})}_{0.25}

(2)

0.67 {Mg}^{2 +} + 0.33 {Al}^{3 +} + 0.33 C_{5} H_{8} {NO}_{4}^{-} + 2 {OH}^{-} \to {Mg}_{0.67} {Al}_{0.33} {(OH)}_{2} {(C_{5} H_{8} {NO}_{4})}_{0.33}

Considering the reaction equilibrium, the amount of glutamate was 2.0 times the stoichiometric quantities required by Eqs. (1) and (2).

The Mg-Al solution with a Mg/Al molar ratio of 3.0 or 2.0 was prepared by dissolving Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O in 250 mL of deionized water, while the total metal ion concentration was 1 mol L⁻¹. The glutamate solution with designed molar ratio was prepared by dissolving sodium glutamate in 250 mL of deionized water. The Mg–Al solution was added dropwise to the glutamate solution at room temperature with stirring. The solution pH was adjusted to 10.5 by addition of 0.5 mol L⁻¹ NaOH solution using a pH-stat throughout the preparation. After the addition of the Mg–Al solution, the resultant suspension was kept for stirring for 1 h at a constant pH of 10.5. The Mg–Al–G LDH particles were recovered by filtering the resultant suspension, which was followed by repeated washing with deionized water and drying at 80 °C for 12 h. Nitrogen (N₂) was bubbled into the solution throughout the operation to minimize effects due to dissolved CO₂.

2.3

2.3 Characterization techniques

The phases of the resultant samples were analyzed by X-ray diffraction (XRD) using a Brucker D8 ADVANCE diffractometer under CuKα radiation (λ = 0.15406 nm), operating at 40KV and 40 mA over 2θ range from 3 to 75°. FT-IR spectra were recorded on Nicolet Nexus 470 spectrometer (Thermo Nicolet Corporation, USA) under scan range 400–4000 cm⁻¹ using KBr pellets(1/10 wt.%). The morphology of the sample was studied using a scanning electron microscope (SEM) (JEOL 6360LV).

2.4

2.4 Adsorption experiments

Stock aqueous solution containing 500 mg L⁻¹ Pb²⁺ was prepared by dissolving Pb(NO₃)₂ in deionized water. Stock solution was further diluted with deionized water to the desired concentration for obtaining test solutions.

Mg–Al–G LDH was added to solution with a certain Pb²⁺ concentration, and the resultant suspension was kept at designed temperature. The solution pH was adjusted to 5.0 by addition of 0.1 mol L⁻¹ HNO₃ throughout the experiment to prevent the precipitation of Pb²⁺ hydroxides. N₂ was bubbled into the solution throughout the operation. Samples of the suspension were withdrawn at different time intervals and immediately filtered through a 0.45 μm membrane filter. The filtrates were submitted for analysis of the metal ions. The concentration of Pb²⁺ was determined by atomic adsorption spectrophotometry. The amounts of adsorbed (q_e) Pb²⁺ were calculated from the difference between the initial (C₀) and equilibrium (C_e) concentrations. The adsorption percentage was calculated according to the following formula:

(3)

Adsorption (%) = (C_{0} - C_{e}) / C_{0} \times 100

All experimental data were the average of triplicate determinations and the relative errors were about 5%.

3 Results and discussion

3.1

3.1 Characterization of the absorbent

The XRD pattern of Mg–Al–G LDH is shown in Fig. 1. Nitrate intercalated Mg–Al LDH was prepared for comparison with Mg–Al–G LDH, owing to the ${NO}_{3}^{-}$ existing in the solution during the preparation. Here, both the Mg–Al–NO₃ LDH and Mg–Al–G LDH have the same Mg/Al molar ratio of 3.0. It can be seen that Mg–Al–NO₃ LDH exhibits sharp, distinct peaks, which are attributed to hydrotalcite (JCPDS No. 20–0700), showing the structure of a layered double hydroxide. The peaks presented in the XRD pattern of Mg–Al–G LDH are similar with those of Mg–Al–NO₃ LDH, though they are slightly broad and weak, suggesting that glutamate intercalated Mg–Al LDH possesses the basic structure of Mg–Al LDH. Compared to that of Mg–Al–NO₃ LDH, (003) peak of Mg–Al–G LDH shifts to a lower angle, showing the enlargement of the interlayer spacing (Bontchev et al., 2003). For Mg–Al–NO₃ LDH, the observed basal spacing, d₀₀₃, is 0.76 nm, while the interlayer spacing is 0.28 nm, considering the layer thickness of 0.48 nm. For glutamate intercalated Mg–Al LDH, the basal spacing is 0.81 nm, while the interlayer spacing is 0.33 nm. These results suggest that glutamate ion, which is larger than ${NO}_{3}^{-}$ , is intercalated into the interlayer of the Mg-Al LDH.

XRD patterns of Mg–Al–NO3 LDH and Mg–Al–G LDH.

The FT-IR spectra of samples are shown in Fig. 2. The spectrum for Mg-Al LDH intercalated with ${NO}_{3}^{-}$ shows bands characteristic of LDH containing ${NO}_{3}^{-}$ as the counteranions in the interlayer (Bontchev et al., 2003). The broad and intense band around 3500 cm⁻¹ is attributed to the stretching vibration of the hydroxyl groups in the layer and of water molecules. The medium intensity absorption band around 1640 cm⁻¹ is due to the deformation mode of water molecules. A sharp and intense band appears at 1380 cm⁻¹ which is ascribed to the vibration of the ${NO}_{3}^{-}$ ion. For glutamate intercalated Mg–Al LDH, the spectrum also exhibits similar bands when compared with those of Mg–Al–NO₃ LDH. However, compared to that of Mg–Al–NO₃ LDH, the intensity of broad band between 1250 and 1520 cm⁻¹ increases. The band is an overlapped band which contains bands at 1350, 1420, 1520 and 1650 cm⁻¹, which are the characteristic bands for glutamic acid. The band at 1380 cm⁻¹ is also observed and shifts to a higher wave number compared to that of Mg–Al–NO₃ LDH, showing the ${NO}_{3}^{-}$ is still in the interlayer space, but it bonds weakly to the LDH layer sheets.

FT-IR spectra of Mg–Al–NO3 LDH, Mg–Al–G LDH and glutamic acid.

SEM image (Fig. 3) shows that glutamate intercalated Mg–Al LDH exhibits loose lamellar structure. This structure will be favorable for metal ions to diffuse and penetrate into the interior part of each adsorbent particle and be trapped on the LDH.

SEM image of glutamate intercalated Mg–Al LDH.

3.2

3.2 Selection of the absorbent

The adsorption of metal ions on chelating agent-intercalated LDH was mainly by chelation, but a certain precipitation of amorphous metal and isomorphous substitution might also be involved in the adsorption processes (Kameda et al., 2008; Pavlovic et al., 2009). The process is influenced by pH value, owing to the different present state of Pb²⁺ at different pH values (Zhao et al., 2011). In this work, the pH values were kept at 5.0, the adsorption of Pb²⁺ was mainly achieved by chelation (Kameda et al., 2008). Therefore, more chelating agents are in the interlayer, higher adsorption percentage can be observed. Here, we chose two types of Mg–Al–G LDH with Mg/Al ratios of 2 and 3 for the selection of the absorbent for later investigations. Fig. 4 shows the Pb²⁺ adsorption percentage as a function of contact time on these two types of Mg-Al–G LDHs.

The adsorption percentage of Pb2+ as a function of contact time on different Mg–Al–G LDHs. Other experimental conditions: initial Pb2+ concentration = 100 mg L−1, LDH dosage = 1.0 g L−1.

For both Mg–Al–G LDHs, the Pb²⁺ removal percentages approach the adsorption equilibrium values after 120 min. The equilibrium adsorption percentages for Mg–Al–G with Mg/Al ratio of 2.0 and 3.0 are about 65.32% and 56.13%, respectively, suggesting that the adsorption percentage on Mg–Al–G LDH with lower Mg/Al ratio is more than that on Mg–Al–G LDH with higher Mg/Al ratio. This is attributed to the fact that, compared to those of Mg/Al ratio of 3.0, there are more positive charges in the layer for Mg/Al ratio of 2.0, as a result more glutamate ions are intercalated into the interlayer space to compensate excessive positive charges, keeping the compound neutral. Therefore, the Mg–Al–G LDH with Mg/Al ratio of 2.0 was selected in later investigations.

3.3

3.3 Effect of contact time and kinetics study

3.3.1

3.3.1 Effect of contact time

Fig. 5 indicated the adsorption of Pb²⁺ on Mg–Al–G LDH as a function of contact time. It can be seen that the Pb²⁺ amount absorbed increases rapidly within the first 30 min, and then increase slowly until 120 min, approaching the adsorption equilibrium values.

Effect of contact time on Pb2+ adsorption by Mg-Al-G LDH and kinetics fitting curves. Other conditions: initial Pb2+ concentration = 20 mg L−1, LDH dosage = 1.0 g L−1.

3.3.2

3.3.2 Kinetics of Pb²⁺ adsorption

Based on the obtained data shown in Fig. 5, the adsorption kinetics of Pb²⁺ on Mg–Al–G LDH was analyzed by applying the pseudo-first-order and pseudo-second-order kinetic models to fit the experimental data. The pseudo-first-order kinetic model describes the adsorption of the liquid/solid system based on solid capacity. The model can be written as (Zhao et al., 2011):

(4)

\frac{{dq}_{t}}{dt} = k_{1} (q_{e} - q_{t})

where q_e and q_t are the capacities of metal ions adsorbed (mg·g⁻¹) at equilibrium and time t (min), respectively and k₁ is the pseudo-first-order rate constant (min⁻¹). After integration between boundary conditions (t = 0 to t and q_t = 0 to q_e), Eq. (4) can be rewritten as:

(5)

\ln (q_{e} - q_{t}) = \ln q_{e} - k_{1} t

Thus the values of q_e and k₁ can be determined experimentally by plotting log(q_e−q_t) versus t and extracting information from the least squares analysis of slope and intercept and substituting into Eq. (5). The values of q_e and k₁ calculated from the linear form analysis are listed in Table 1.

Table 1 The kinetics models for the adsorption of Pb²⁺ on Mg–Al–G LDH.

q_e_,exp (mg g⁻¹)	Pseudo-first-order			Pseudo-second-order
	k₁ (min⁻¹)	q_e (mg g⁻¹)	R²	k₂ (g mg⁻¹ min⁻¹)	q_e (mg g⁻¹)	R²
19.28	0.07725	15.62	0.978	0.0054172	20.95	0.994

The pseudo-second-order adsorption kinetic model is expressed as following formulation (Zamani et al., 2013):

(6)

\frac{{dq}_{t}}{dt} = k_{2} {(q_{e} - q_{t})}^{2}

where k₂ (g·mg⁻¹ h⁻¹) is the pseudo-second-order rate constant for the adsorption, and is a complex function of the initial concentration of solute. Eq. (6) can be rearranged to give the linear expression:

(7)

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

Thus the values of k₂ and q_e can be calculated from the intercept and the slope of the linear relationship between t/q_t and t. The kinetic model parameters are obtained from fitting results and presented in Table 1. From the relative coefficient, it can be seen that the pseudo-second-order kinetic model fits the adsorption of Pb²⁺ on Mg–Al–G LDH better than the pseudo-first-order model.

3.4

3.4 Effect of initial Pb²⁺ concentration and adsorption isotherm

3.4.1

3.4.1 Effect of initial Pb²⁺ concentration

Fig. 6 indicates the effect of initial Pb²⁺ on the adsorption capacity of Pb²⁺ on Mg–Al–G LDH. It can be found that the adsorption capacity increases, but the adsorption percentage decreases, with the increase in initial Pb²⁺ concentration.

Effect of initial Pb2+ concentration on Pb2+ adsorption by Mg–Al–G LDH. Other conditions: LDH dosage = 1.0 g L−1.

3.4.2

3.4.2 Adsorption isotherms

The adsorption isotherms for Pb²⁺ on Mg–Al–G LDH are shown in Fig. 6. The Langmuir and Freundlich isotherm models are used to simulate the adsorption isotherms. The Langmuir model assumes that adsorption occurs in a monolayer with all adsorption sites identical and energetically equivalent (Tan et al., 2009). Its form can be described by the following equation:

(8)

q_{e} = \frac{{bq}_{\max} C_{e}}{1 + {bC}_{e}}

Eq. (8) can be expressed in linear form:

(9)

\frac{C_{e}}{q_{e}} = \frac{C_{e}}{q_{\max}} + \frac{1}{{bq}_{\max}}

where C_e is the equilibrium concentration of metal ions remained in the solution (mg L⁻¹); q_e is the amount of metal ions adsorbed on per weight unit of solid after equilibrium (mg g⁻¹); q_max, the maximumadsorption capacity, is the amount of adsorbate at complete monolayer coverage (mg g⁻¹), and b (L mg⁻¹) is a constant that relates to the heat of adsorption. Furthermore, a dimensionless constant called separation factor (R_L, also called equilibrium parameter) is commonly used to predict whether an adsorption system is favorable or unfavorable:

(10)

R_{L} = \frac{1}{1 + {bC}_{0}}

where b is Langmuir constant (L mg⁻¹). The value of R_L indicates the adsorption process to be irreversible (R_L = 0), favorable (0 < R_L < 1) linear (R_L = 1) or unfavorable (R_L > 1) (Bulut et al., 2008). The Freundlich isotherm model allows for several kinds of adsorption sites on the solid surface and represents properly the adsorption data at low and intermediate concentrations on heterogeneous surfaces. The equation is represented by the following equation:

(11)

q_{e} = k_{F} C_{e}^{n}

Eq. (11) can be expressed in linear form:

(12)

\ln q_{e} = \ln k_{F} + n \ln C_{e}

where k_F (mg¹⁻ⁿ g⁻¹ Lⁿ) represents the adsorption capacity when metal ion equilibrium concentration equals to 1, and n represents the degree of dependence of adsorption with equilibrium concentration. The relative values calculated from the two models are listed in Table 2.

Table 2 The parameters for the Langmuir and Freundlich fitting to Pb²⁺ adsorption on Mg–Al–G LDH.

Langmuir				Freundlich
q_max (mg g⁻¹)	b (L mg⁻¹)	R²	R_L	k_F(mg^1-n Lⁿ mg⁻¹)	n	R²
68.49	0.367	0.9967	0.0227∼0.214	20.24	0.3392	0.9608

From R² values listed in Table 2, the Langmuir model fits the experimental data better than the Freundlich model, indicating that the whole surface has identical adsorption activity and therefore the adsorbed Pb²⁺ ions do not interact or compete with each other, and they are adsorbed by forming an almost complete monolayer coverage of the Mg–Al–G LDH particles (Zhao et al., 2011). The R_L values for the adsorption of Pb²⁺ on Mg–Al–G LDH are in the range of 0.0227–0.214 implying that the adsorption process is favorable. Moreover, q_max calculated from Langmuir model is 68.49 mg·g⁻¹.

3.5

3.5 Effect of LDH dosage

The effect of LDH dosage on the adsorption of Pb²⁺ on Mg–Al–G LDH is shown in Fig. 8. The adsorptions of Pb²⁺ were obtained at a contact time of 120 min by varying the adsorbent dosage from 0.5 to 4.0 g L⁻¹ in a lead ion solution with an initial concentration of 50 mg L⁻¹. Fig. 8 shows that the Pb²⁺ adsorption capacity on Mg–Al–G LDH decreases drastically with increasing LDH dosage, while the Pb²⁺ adsorption percentage increases almost to around 100% when the LDH dosage is more than 2 g L⁻¹. Larger LDH amount means more surface binding sites were provided for the adsorption of lead ions at the same unit weight, and so the adsorption percentage should increase naturally. However, at low adsorbent content, all kinds of surface sites are entirely exposed for adsorption and the surface gets to saturation faster, resulting in a higher adsorption capacity. But at higher particle concentrations the availability of higher energy sites decreases with a larger fraction of lower energy sites becoming occupied, leading to a lower adsorption capacity (Huang et al., 2008). Besides, higher adsorbent amount enhances the probability of collision between solid particles and therefore creates particle aggregation, causing a decrease in the total surface area and an increase in diffusion path length, which contribute to the decrease in the adsorption capacity of Pb²⁺ on Mg–Al–G LDH. From the results shown in Fig. 8, it is found that the LDH dosage of 2 g L⁻¹ can supply sufficient sites for the adsorption (See Fig. 7).

Effect of LDH dosage on Pb2+ adsorption by Mg-Al-G LDH. Other conditions: initial Pb2+ concentration = 50 mg·L−1.

Adsorption isotherm, and Langmuir and Freundlich model fitting to Pb2+ adsorption on Mg–Al–G LDH. Experimental conditions: initial Pb2+ concentration = 10–120 mg L−1, LDH dosage = 1.0 mg L−1, Mg/Al = 2.0.

4 Conclusions

Glutamate intercalated Mg–Al LDH can be prepared by co-precipitation. XRD and IR confirmed the successful intercalation of glutamate into the interlayers of Mg–Al LDH. Glutamate intercalated Mg–Al LDH can effectively adsorb Pb²⁺ in the aqueous solution. The adsorption of Pb²⁺ on glutamate intercalated Mg–Al LDH fitted the pseudo-second-order kinetics model and the isotherm can be well defined by the Langmuir model. The adsorption capacity calculated from the Langmuir model is 68.49 mg g⁻¹, higher than that of Mg–Al LDH. Glutamate intercalated Mg–Al LDH has good potentialities for cost-effective removal of Pb²⁺ from Pb²⁺-contaminated wastewaters.

Acknowledgement

The present work was supported by the project on Scientific Research for Public Interest of Liaoning Province, China (project No. 2011001001).

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Introduction

Materials and methods

Materials
Absorbent preparation
Characterization techniques
Adsorption experiments

Results and discussion

Characterization of the absorbent
Selection of the absorbent
Effect of contact time and kinetics study
Effect of initial Pb2+ concentration and adsorption isotherm
Effect of LDH dosage

Conclusions

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Removal of lead from aqueous solution on glutamate intercalated layered double hydroxide

Abstract

Keywords

Layered double hydroxides

Hydrotalcite-like compounds

Glutamate

Heavy metal ions

1 Introduction

2 Materials and methods

2.1 Materials

2.2 Absorbent preparation

2.3 Characterization techniques

2.4 Adsorption experiments

3 Results and discussion

3.1 Characterization of the absorbent

3.2 Selection of the absorbent

3.3 Effect of contact time and kinetics study

3.3.1 Effect of contact time

3.3.2 Kinetics of Pb2+ adsorption

3.4 Effect of initial Pb2+ concentration and adsorption isotherm

3.4.1 Effect of initial Pb2+ concentration

3.4.2 Adsorption isotherms

3.5 Effect of LDH dosage

4 Conclusions

Acknowledgement

References

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3.3.2 Kinetics of Pb²⁺ adsorption

3.4 Effect of initial Pb²⁺ concentration and adsorption isotherm

3.4.1 Effect of initial Pb²⁺ concentration