ISSN : 0970 - 020X, ONLINE ISSN : 2231-5039
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Removal of Lead (ΙΙ) by Lumbang, Aleurites moluccana Activated Carbon Carboxymethylcellulose Composite Crosslinked with Epichlorohydrin

Nelson R. Villarante1, Ronnette Anne E. Davila1 and Derick Erl P. Sumalapao2,3

1Department of Physical Sciences and Mathematics, College of Arts and Sciences, University of the Philippines Manila, Manila, Philippines.

2Department of Biology, College of Science, De La Salle University, Manila, Philippines.

3Department of Medical Microbiology, College of Public Health, University of the Philippines Manila, Manila, Philippines.

Corresponding Author E-mail: derick.sumalapao@dlsu.edu.ph

DOI : http://dx.doi.org/10.13005/ojc/340211

Article Publishing History
Article Received on : November 05, 2017
Article Accepted on : January 01, 2018
Article Metrics
ABSTRACT:

Removal of Pb(II) using lumbang activated carbon carboxymethylcellulose composite crosslinked with epichlorohydrin was investigated. Batch adsorption studies were performed to evaluate the effects of pH, contact time, temperature, adsorbent dose, and metal concentration. To characterize the adsorbent, proximate analysis, bulk density, DSC, FT-IR, and SEM analysis were performed. Results of FT-IR revealed that crosslinking did not alter the structure of carboxymethylcellulose due to the presence of the –COO functional groups, while the presence of the C-O signal indicates that the adsorbent was successfully crosslinked by epichlorohydrin. Furthermore, SEM results showed highly porous nature of the prepared adsorbent. The optimized parameters of the adsorbent were pH 3, contact time of 15 min, 30oC temperature, adsorbent dose of 4 g/L at 5 ppm Pb (II) solution. With these optimized parameters, 73% removal of Pb (II) was attained in aqueous solutions, while 37% removal was observed in the wastewater sample. Moreover, the adsorption process was best described by Dubinin-Radushkevich isotherm and obeyed the pseudo-second order kinetic model.

KEYWORDS:

Biosorption; Pb(II); Lumbang; Aleurites Moluccana; Activated Carbon Carboxymethylcellulose; Epichlorohydrin Crosslinking

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Villarante N. R, Davila R. A. E, Sumalapao D. E. P. Removal of Lead (ΙΙ) by Lumbang, Aleurites moluccana Activated Carbon Carboxymethylcellulose Composite Crosslinked with Epichlorohydrin. Orient J Chem 2018;34(2).


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Villarante N. R, Davila R. A. E, Sumalapao D. E. P. Removal of Lead (ΙΙ) by Lumbang, Aleurites moluccana Activated Carbon Carboxymethylcellulose Composite Crosslinked with Epichlorohydrin. Orient J Chem 2018;34(2). Available from: http://www.orientjchem.org/?p=44352


Introduction

The presence of heavy metals in different water sources poses danger in aquatic ecosystems and risks in human health. One of these heavy metals is Pb(II), a naturally occurring, toxic, and commercially useful metal1,2. To address these problems of heavy metal contamination in water, adsorbents were developed. One of the conventional adsorbents used is activated carbon (AC) due to its large adsorption capacity, rapid adsorption kinetics, and relative ease of regeneration3,4. However, commercially available activated carbon is expensive, and production of this adsorbent from agricultural wastes emerged as a reasonable alternative. Activated carbon can be obtained from materials with high carbon content5. The nature of the precursor and the methods performed in the production of activated carbon affects the final adsorption properties of the adsorbent6. Due to the developing trend in the production of activated carbon from cheaper raw materials and from renewable biomass, the conversion of various environmental wastes such as coconut shells7, tamarind wood8, snail shell waste9, pine cones2, and hazelnut husks10 to activated carbon were already successfully investigated. Moreover, activated carbon is usually coated with compounds to further enhance its adsorption capacity11. In addition to activated carbon, carboxymethylcellulose (CMC) which is an ionic polysaccharide containing carboxyl groups is also used for heavy metal adsorption. CMC-derived adsorbents are cheap, abundant, and biodegradable, a good starting material for adsorbent preparation12. To improve the physical and chemical properties of carboxymethylcellulose, it is usually crosslinked with epichlorohydrin (ECH), a colorless liquid and moderately soluble in water, but miscible with most polar substances13.

In this paper, novel synthesis of low-cost lumbang (Aleurites moluccana) activated carbon carboxymethylcellulose composite crosslinked with epichlorohydrin (LAC/CMC/ECH) by irradiation was performed and its adsorption capacity using Pb(II) in aqueous medium and wastewater sample was evaluated. A microcosm adsorption study of LAC/CMC/ECH hydrogel composite on Pb (II) removal as a function of pH, temperature, contact time, initial concentration of adsorbate, and adsorbent dose was investigated. The physicochemical characterization of the composite was limited to proximate analysis and bulk density, differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). Moreover, adsorption kinetics and isotherm studies were also done to assess the possible mechanism of interaction. The LAC/CMC/ECH composite is useful for the general remediation of wastewater generated from industries and laboratories, especially those that contain large amount of Pb (II) as treatment of these contaminated water may reduce toxicity in aquatic ecosystems.

Materials and Methods

Reagents and Plant Material

Lumbang (Aleurites moluccana) seed shells were collected from the College of Forestry, University of the Philippines Los Baños, while the wastewater samples were collected from Pasig River in Sta. Cruz, Manila, Philippines. Sodium carboxymethylcellulose (MW: ~250,000) and (±) epichlorohydrin were purchased from Sigma-Aldrich. Lead nitrate (99.9% purity, Merck Chemicals) was used for the preparation of the Pb (II) aqueous medium.  Electron beam irradiation was performed at the Irradiation Facility at Philippine Nuclear Research Institute (PNRI).

Preparation of the Charcoal

To prepare lumbang activated carbon (LAC), dry lumbang seed shells were crushed, dried, and washed with water to remove impurities before subjecting to a traditional pyrolytic burrow method. A shallow burrow was made wherein the shells were incinerated for 5 h, with the soil as cover to prevent entry of oxygen. Afterwards, the charcoal was washed with deionized water, sorted to a particle size ranging from 0.149-0.250 mm, and washed with deionized water.

Activation of the Charcoal

In the activation process, CaCl2 was used as the activating agent7. The collected charcoal was pulverized and was soaked in 25% CaCl2 solution for 24 h, washed five times with deionized water, and oven-dried at 100oC.

Preparation of the Composite

To prepare 20 wt.% CMC and 5 wt.% LAC, 20 g of CMC and 5 g of LAC with 5 g of NaOH in deionized water were mixed14,15. Afterwards, 10 mL of ECH was added to the 90 mL of CMC solutions, and was mixed thoroughly. The resulting mixture was sent to the irradiation facility at PNRI and was irradiated by electron beam at 25 kGy to facilitate crosslinking. The irradiated adsorbent was oven-dried at 50 oC for 16 h, pulverized, washed with deionized water, and sorted using a 40-60 mesh sieve to obtain a uniform size of 0.420-0.814 microns.

Characterization of the Composite

Bulk Density (BD)

A certain amount of adsorbent was placed inside a 10-mL graduated cylinder up to a specified volume. The weight of the adsorbent was measured and the bulk density was calculated using the equation

Equation 1

Proximate Analysis

Proximate analysis includes the analysis of moisture, ash, crude fat, crude fiber, and crude protein contents. Samples were sent to the Biotech Central Analysis Laboratory, University of the Philippines Los Banos, Philippines.

Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) analysis was conducted for the composites on a Perkin-Elmer DSC 4000 apparatus under N2 flow with the samples hermetically sealed in aluminum pans.

Scanning Electron Microscopy

Samples of the composite before and after adsorption were sent to the Surface Morphology Laboratory, De La Salle University, Philippines for SEM analysis using a JSM-5310 scanning microscope.

FT-IR Spectroscopy

The FT-IR spectra were recorded at room temperature in the range of 4000–500cm-1 on a ThermoScientific Nicolet 6700 FT-IR spectrometer using a KBr pellet sampling method and were accumulated for 16 scans.

Adsorption Experiments

Adsorption experiments were done by batch studies in 15-mL conical tubes by soaking the dried composite in 5 mL of aqueous Pb (II) solutions, and agitating this using SHZ-82A water bath shaker at 156 rpm. Pb (II) determination was done using AAS (Shimadzu AA-6300).  Adsorption study as function of pH, contact time, temperature, adsorbent dosage, and initial Pb (II) concentration was conducted.

Effect of pH

Batch studies at different pH (2-7) were conducted by soaking the adsorbent in 10 ppm of Pb (II) in each microcosm. Each container was agitated (156 rpm) for 1 h at 30oC.

Effect of Contact Time

Optimum contact time was determined by soaking the adsorbent in 10 ppm of Pb (II) ions.  Each microcosm was prepared at 30oC and pH 3.  The rate of adsorption was monitored every 15 min for a period of 2 h.

Effect of Temperature

The same preparation was made, except for the varying temperature conditions. The microcosm which was maintained at pH 3 was incubated at different temperatures (20-40oC) for a period of 15 min.

Effect of Adsorbent Dosage

Microcosms with different adsorbent doses (1-7 g/L) were amended with 10 ppm of Pb (II) in aqueous solutions. The rate of adsorption was monitored at the following optimum conditions: pH of 3, 30oC temperature, 15 min contact time.

Effect of Pb (II) Concentration

The composite was soaked in 5, 10, 20, 30, 40, 50, 60, and 70 ppm aqueous solutions of Pb (II) at the optimum pH, contact time, temperature, and adsorbent dose.

Adsorption Isotherms

Adsorption isotherms represent the relationship of the amount of metal adsorbed with the adsorbent dose. These provide information about the mechanism of adsorption and the adsorptivity of the composite towards the metal of interest16. In this study, Langmuir, Freundlich, Temkin, and the Dubinin-Radushkevich isotherms were investigated.

Langmuir Isotherm

Monolayer adsorption onto the surface of the adsorbent is assumed by the Langmuir isotherm. In this model, it is assumed that binding of metals onto the adsorbent is homogeneous, and that adsorption will no longer take place once equilibrium has been established. Also, this model predicts an equal distribution of metal ions between the liquid and solid phases17. The linear form of the Langmuir isotherm is described by

Equation 2

where qis the amount of metal adsorbed per gram of the adsorbent (mg/g), Ce is the maximum monolayer capacity (mg/g), Q0 is the maximum monolayer coverage capacity (mg/g), and KL is the Langmuir isotherm constant.

Freundlich Isotherm

The Freundlich isotherm is an empirical equation used to model multilayer adsorption on heterogenous adsorbents, with the assumption that sites of adsorption exponentially increase with an increase in the heat of absorption18. This can be expressed mathematically as

Equation 3

where qe is the amount of metal adsorbed per gram of the adsorbent (mg/g), Ce is the equilibrium concentration of the adsorbate (mg/L), n is the adsorption intensity, and Kf is the Freundlich isotherm constant.

Temkin Isotherm

The Temkin isotherm considers the adsorbent-adsorbate interactions, with the assumption that the heat of adsorption of the molecules in the layer would exhibit a linear, instead of a logarithmic, decrease17. This relationship is described by

Equation 4

where qe is the amount of metal adsorbed per gram of the adsorbent (mg/g), Ce is the equilibrium concentration of the adsorbate (mg/L), AT is the equilibrium binding constant, and B is the heat of sorption constant.

Dubinin-Radushkevich Isotherm

The Dubinin-Radushkevich isotherm (D-R isotherm) predicts whether the mechanism of adsorption is physical or chemical. It is also useful for the estimation of the porosity and the free energy of adsorption. The D-R isotherm is a more general form of the Langmuir isotherm19. The linear form of the D-R isotherm is expressed as

Equation 5

where qe is the amount of metal adsorbed per gram of the adsorbent (mg/g), qs is the theoretical isotherm saturation capacity, Kad is the Dubinin-Radushkevich isotherm constant (mol2/J2), and  is the mean adsorption energy.

Adsorption Kinetics

Adsorption kinetic studies were performed using the first order, second order, pseudo-second order, and the Elovich models20,21.

Wastewater Analysis and Efficiency Experiment

Under optimized conditions, the dried adsorbent was soaked in wastewater samples obtained from Pasig River, Sta. Cruz, Manila, Philippines. First, the wastewater sample was filtered before the adsorption study was conducted, and then was subjected to acid digestion using concentrated HNO3 by heating 50 mL of the sample to 80oC, followed by the addition of 15 mL HNO3, before atomic absorption spectrophotometer (AAS) analysis22. Other metals present in wastewater like cadmium and magnesium were also determined but were not subjected to adsorption study.

Following the optimized parameters, the adsorption ability of the adsorbent was tested in an organic compound, methylene blue23. The adsorption abilities of commercial AC, LAC, CMC, LAC/CMC, and LAC/CMC/ECH were also tested in aqueous solutions of Pb (II) using the optimized parameters.

Results and Discussion

Adsorbent Characterization

Bulk Density, Moisture Content, and Proximate Analysis

The bulk density, moisture content, and proximate analysis of the adsorbent were determined (Table 1). Bulk density is the ratio of the mass of the pulverized adsorbent with the volume, and it is indicative of porosity. It is dependent on the density of the adsorbent, as well as on its arrangement in space. Based from the result, 0.56 g of adsorbent occupies 1 cm3. A bulk density greater than 0.4 indicates that the adsorbent is highly porous24, this means that the prepared adsorbent is highly porous. Moisture content is the amount of water in the sample that causes variations in the weight, density, and viscosity of the adsorbent, while ash content is defined as the mineral matter, such as clay or silica, present in the raw material that may alter the pore development of the composite. Ash content may be acquired from the environment as a contaminant during the collection of raw materials. Therefore, lower ash content equates to a better pore structure. Crude fat refers to the fat-soluble material present in the sample, while crude fiber refers to the amount of indigestible cellulose, and lastly, crude protein content refers to the total nitrogen content of the sample. Based on the proximate analysis results (Table 1), the protocol employed in the production of charcoal is effective due to the low ash content and moisture content.

Table 1: Bulk density, moisture content, and proximate analysis of the adsorbent.

Bulk Density (g/mL) 0.56
Moisture Content (%) 5.07
Ash Content (%) 1.67
Crude Fat (%) 3.51
Crude Fiber (%) 72.43
Crude Protein Content (%) 1.81

 

Differential Scanning Calorimetry

The DSC profile of the LAC/CMC/ECH composite was investigated (Figure 1). The peak at 70.95oC with a ΔH = 540.05 J/g is the endothermic peak for the loss of water. At this point, the material undergoes a phase change from solid to liquid25. On the other hand, the peak at 304.68oC denotes the disintegration of the composite.

FT-IR Spectroscopy

The adsorption peaks of the carboxylate group of CMC at 1600 cm-1 (asymmetric stretching vibration) and 1453 cm-1 (symmetric stretching vibration) in both spectra were observed in the FT-IR spectra overlay of LAC/CMC and LAC/CMC/ECH composites (Figure 2). The bands at 3400 cm-1 and 2900 cm-1 were due to stretching vibration of –OH and C-H, respectively. The peak at around 1062 cm-1 is a typical stretching frequency of the ether group of the polysaccharide while the medium peak at around 1328 cm-1 can be attributed to the C-O stretch of the carboxylate.

The medium ring deformation band observed at 871 cm-1 in the LAC/CMC/ECH composite is due to the presence of the ECH, and is not observed in LAC/CMC composite. Furthermore, the peak at around 1421 cm-1 in LAC/CMC was shifted to 1452 cm-1 in LAC/CMC/ECH with the appearance of peak at around 871 cm-1 which is possibly attributed to the formation of intramolecular hydrogen bonding that would occur between the –OH of ECH and neighboring oxygen of the CMC and AC. Moreover, there is a change in the spectral profile of the composite before and after adsorption of Pb (II) ion (Figure 3). There is a decrease in the intensity around 1452 cm-1 and the disappearance of C-O-C bending vibration of the ECH at around 871 cm-1 possibly reflecting the interaction with Pb (II) through complexation reaction. A new broad peak was also observed at around 2180 cm-1 after adsorption of Pb (II) ion.

Figure 1: Differential scanning calorimetry profile of the LAC/CMC/ECH composite. Figure 1: Differential scanning calorimetry profile of the LAC/CMC/ECH composite.

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Figure 2: Overlaid spectra of LAC/CMC (red) and LAC/CMC/ECH (blue) composites. Figure 2: Overlaid spectra of LAC/CMC (red) and LAC/CMC/ECH (blue) composites.

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Figure 3: Spectra of the LAC/CMC/ECH composite before (blue) and after (red) Pb(II) adsorption. Figure 3: Spectra of the LAC/CMC/ECH composite before (blue) and after (red) Pb(II) adsorption.

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Scanning Electron Microscopy

Scanning electron micrographs of LAC and LAC/CMC/ECH (before and after adsorption) composites were obtained using JSM-5310 scanning microscope (Figure 4). There is an increase in porosity of the surface when a pure LAC (Figure 4a-b) was crosslinked with CMC and ECH (Figures 4c-d). Moreover, the surface morphology of the LAC/ CMC/ ECH after adsorption of Pb(II) ion is quite different (Figure 4e-f) as the pores become circular and smaller after adsorption.

Figure 4: SEM images of a) lumbang AC (x1000) b) lumbang Figure 4: SEM images of a) lumbang AC (x1000) b) lumbang


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AC (x2000) c) LAC/CMC/ECH composite – before adsorption (x1000) d) LAC/CMC/ECH composite – before adsorption (x5000) e) LAC/CMC/ECH composite – after adsorption (x3500) f) LAC/CMC/ECH composite– after adsorption (x10000).

Adsorption Experiment

Effect of pH

The effect of pH on Pb (II) adsorption on LAC/CMC/ECH composite (10 ppm Pb initial concentration, 5 g/L adsorbent dose, 60 min contact time, 30oC temperature, constant agitation) showed that the highest percent removal is at pH 3 (Figure 5a). At lower pH, the carboxyl group is in the form -COOH due to the protonation of the carboxyl functional groups present in the adsorbent. However, starting at pH 3, these carboxyl groups become carboxylate anions, binding Pb (II) ions through electrostatic interactions12. Some studies have reported that adsorption between pH 3 to 5 produces the maximum percent removal. At lower pH, hydrogen ions will compete with the binding of Pb (II), whereas, at basic pH, precipitation of Pb (II) will take place. There is a negligible difference in the percent removal between pH 4 and 5, and there is an approximately 6% difference between the percent removal at pH 3. On the other hand, adsorption at pH 6 decreased and this may be attributed to the onset of Pb (II) precipitation. However, the gradual increase of uptake at pH 7 may be due to the complete deprotonation of the adsorbent26.

Effect of Contact Time

The effect of contact time on Pb (II) adsorption on LAC/CMC/ECH composite (initial Pb concentration: 10 ppm, adsorbent dose: 5 g/L, pH: 3, temperature: 30oC constant agitation) was examined (Figure 5b). The percent removal values were compared across time intervals, there was no significant difference identified (p>0.05). In particular, a 65.15% removal was identified during the 15 min. and when compared to 63.60% removal during the 30 min., no significant difference was identified (p>0.05). Moreover, there is a negligible difference in the percent removal between time intervals which indicates that at an agitation rate of 156 rpm, the amount of Pb (II) removed is nearly constant for each time interval.

Effect of Temperature

The optimum temperature is at 30oC when the effect of temperature on Pb (II) adsorption on LAC/CMC/ECH composite (initial Pb concentration: 10 ppm, adsorbent dose: 5 g/L, pH: 3, contact time: 15 mins constant agitation) was assessed (Figure 5c). An increase in temperature results to a decrease in percent removal since at higher temperature, the kinetic energy increases, facilitating desorption.

Effect of Adsorbent Dose

The effect of adsorbent dose on Pb (II) adsorption on LAC/CMC/ECH composite (initial Pb concentration: 10 ppm, temperature: 30oC, pH: 3, contact time: 15 min constant agitation) yielded an optimum adsorbent dose of 4 g/L (Figure 5d). Lower doses adsorbed less Pb (II) since lower amount of the adsorbent has lower adsorption sites20,21. However, beyond 4 g/L there is a continuous decrease in the percent removal which means that the adsorptive capacity of the adsorbent was not highly utilized due to its aggregation. It is also possible that the increased amount of adsorbent resulted to overcrowding which can possibly lead to the overlapping of the adsorption sites27.

Effect of Metal Concentration

The highest percent removal was seen at 5 ppm Pb (II) concentration when the effect of metal concentration on Pb (II) adsorption on LAC/CMC/ECH composite (adsorbent dose: 4 g/L, temperature: 30oC, pH: 3, contact time: 15 min, constant agitation) was examined (Figure 5e). It can also be observed that as the concentration of the metal increases, the percent removal decreases which reflects the limited number of adsorption sites in the composite and that at high concentrations, the adsorption sites become saturated20,21,28.

Adsorption Isotherms

The parameters and constants of the different isotherm models were calculated. Among these isotherm models, the D-R isotherm, with almost unity coefficient of determination (R2), best describes the adsorption process (Table 2). The value of the mean free energy (E) of adsorption for the D-R isotherm indicates whether the adsorption process is physisorption, an ion exchange, or a strong chemical adsorption. An E value less than 8 kJ/mol signifies physisorption, whereas between 8 and 16 kJ/mol suggests an ion exchange, and over 16 kJ/mol a stronger chemical adsorption than ion exchange29,30,31. Hence, the adsorption process described in this study has a physisorption adsorption mechanism.

Figure 5: Effect of (a) pH, (b) contact time, (c) temperature, (d) dose, and (e) metal concentration on Pb (II) adsorption on LAC/CMC/ECH composite. Figure 5: Effect of (a) pH, (b) contact time, (c) temperature, (d) dose, and (e) metal concentration on Pb (II) adsorption on LAC/CMC/ECH composite.


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Table 2: Parameter estimates of the different isotherm models.

Isotherm Model Parameter Estimated Value
Langmuir(R2=0.585) Qo 2.245
kL (L/mg) 0.806
RL 0.166
Freundlich(R2=0.952) 1/n 0.242
kf (mg/g) 1.088
Temkin(R2=0.952) AT (L/mg) 11.840
bT (kJ/mol) 5.795
B 0.428
Dubinin-Radushkevich(R2=0.971) qs (mg/g) 0.007
Kad (mol2/J2) 2.0 x 10-6
E (kJ/mol) 0.500

 

Adsorption Kinetics

Among the four identified kinetic equations, the pseudo-second order model best described the adsorption process (R2=0.998). According to the pseudo-second order model, although physisorption is the mechanism of adsorption on the adsorbent surface, the adsorption process is rate-limited by chemisorption32,33. Furthermore, this supports the assumption that the adsorption process follows the D-R isotherm which describes the adsorption process to be physisorption. The pseudo-second order model is applicable in the kinetic studies of heavy metals and dyes sorption20,21,33,34.

Efficiency Experiment

The adsorption efficiency of commercial AC, LAC, CMC, LAC/CMC, and LAC/CMC/ECH towards Pb (II), under the optimized parameters, were compared. The prepared adsorbent exhibited the highest percent removal (72.61%) which suggests that LAC/CMC/ECH is a better adsorbent (Figure 6).

Wastewater Analysis

The wastewater sample as detected by AAS contained various metallic substances aside from Pb(II) (Table 3). In addition, Cu(II) was also determined, however it was below the detection limit of the instrument. LAC/CMC/ECH adsorbent was used for the Pb (II) uptake in the three solution systems (Figure 7). The adsorbent exhibited commendable percent removal of dye and Pb(II) form methylene blue and Pb(II) aqueous solutions, respectively. However, the percent removal of Pb(II) in the wastewater sample is relatively low. This can be attributed to the presence of other substances in the wastewater sample that may interfere with the adsorption process.

Figure 6: Comparison of the percent removal of commercial AC, lumbang AC, CMC, LAC/CMC, and LAC/CMC/ECH. Figure 6: Comparison of the percent removal of commercial AC, lumbang AC, CMC, LAC/CMC, and LAC/CMC/ECH.

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Table 3: Heavy metals identified in the wastewater sample.

Metal Average Concentration (ppm)
Lead

1.138

Cadmium

0.085

Magnesium

2.124

 

Figure 7: Comparison of the percent removal of Pb (II) in aqueous solutions, methylene blue, and wastewater sample under optimum conditions. Figure 7: Comparison of the percent removal of Pb (II) in aqueous solutions, methylene blue, and wastewater sample under optimum conditions.

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Conclusion

A low-cost activated carbon was successfully prepared and used to synthesize the LAC/CMC/ECH hydrogel adsorbent. The adsorbent was characterized using bulk density, proximate analysis, DSC, FT-IR spectroscopy, and SEM. With the optimized parameters for adsorption: pH 3 for 15 min at 30oC with 4 g/L adsorbent and 5 ppm Pb (II) concentration, Pb (II) was removed at high percentages in both aqueous and methylene blue solutions, and in wastewater samples. The adsorption process was best described by the Dubinin-Radushkevich isotherm and obeyed the pseudo-second order kinetic model.

Acknowledgment

This work was supported by the National Institutes of Health, University of the Philippines Manila [NIH 2015-017].

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