Sorption of 17β-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms

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JECE 641 1–8 Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx

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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece

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Sorption of 17b-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms

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Sangeeta Patel a, * , Jie Han b , Wei Gao a

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a b

Department of Chemical and Materials Engineering, The University of Auckland, 20 Symonds Street, Auckland 1010, New Zealand Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, IL, USA

A R T I C L E I N F O

A B S T R A C T

Article history: Received 6 November 2014 Accepted 30 April 2015

This study is aimed at investigating the removal of 17b-estradiol (E2) from aqueous solutions using bone char derived from waste cattle bones. The cattle bones were surface treated with acetone and pyrolyzed in an oxygen depleted environment. The obtained bone char was then used for the adsorption of 17bestradiol. This work involves studying the batch adsorption process with respect to the effect of contact time, initial concentration and role of dosage of adsorbent. The adsorption kinetic studies revealed that the adsorption of E2 on bone char obeys the pseudo second order kinetic model. In addition, the adsorption kinetics was also assessed for the intraparticle diffusion model. This study shows that the adsorption of E2 on bone char was a very complex mechanism involving the diffusion process. Increasing the bone char dosage led to an increase in the removal of E2. With a bone char dosage of 50 g L
1, about 95.3% of E2 was removed from aqueous solutions. The experimental adsorption isotherm data were fitted to Langmuir and Freundlich isotherm models. The saturated bone char was regenerated using ethanol/ water solution. The preliminary reusability study showed that the adsorption capacity was restored to 85% of its initial capacity in the third cycle. ã 2015 Published by Elsevier Ltd.

Keywords: Adsorption 17b-estradiol Bone charcoal Kinetic studies Isotherms Regeneration

6

Introduction

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Soils as our natural capital assets need to be well preserved to maintain their quality to be productive for farmland use and livestock rearing. Water being the most vital ingredient influences the soil quality to a significant level. Therefore, its quality needs to be controlled to be free of pollutants by economical means. New Zealand is an agriculture intensive country where most of the country’s economy is based on dairy, horticulture and meat industry. Due to this fact, there is a huge pressure on the pastoral landscape which is becoming more dynamic and sophisticated by the day. Micropollutants in water are a rapidly emerging global problem that seriously threatens environmental and human health. There are several natural and synthetic chemicals that interfere with the endocrine system of humans and animals commonly known as the endocrine disruptive chemicals (EDCs). These chemicals have an antagonistic effect on the aquatic species and human beings. Research shows that a variety of chemicals enter the environment and the amounts are increasing day by day [1]. Only 20% of the

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animals urine is taken up by the grass and the rest goes down directly to the waterways resulting in 40% of New Zealand’s lakes becoming worse [2]. In addition, due to the growing dairy demands, there is an expansion of the dairy industry being planned in Waikato and Canterbury region. Growing plants across the river banks are also unable to stop the animal wastes getting into the water ways [2]. There are some EDCs which are being commissioned nationwide along with gaining the international regulatory attention [1]. A number of survey reports were presented where the ubiquitous presence of EDCs were identified in receiving waterways and treated effluents [3]. There are several reports on the adverse effects of these EDCs, which include reproductive abnormalities in fishes and alligators. An unusual sexual behaviour was observed in female herring gulls. In addition, animals were observed to have thyroid problems, metabolism changes and defects in off springs, whereas humans developed cryptorchidism, hypospadias and testicular cancer [4]. EDCs include a wide range of synthetic and natural chemicals. But among them, the steroid hormones are the most potent ones. The steroid hormones commonly found in the waste waters are estrone (E1), 17b-estradiol (E2), estriol (E3) and 17a-ethinylestradiol (EE2) [5]. These hormones reach the environment through the animal wastes and sewages since all humans

* Corresponding Author: Tel.: +64 21 022 27650; fax: +64 9 3737463. E-mail address: [email protected] (S. Patel). http://dx.doi.org/10.1016/j.jece.2015.04.027 2213-3437/ ã 2015 Published by Elsevier Ltd.

Please cite this article in press as: S. Patel, et al., Sorption of 17b-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.04.027

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S. Patel et al. / Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx

and animals excrete these steroid hormones. Therefore, an efficient and cost effective treatment process needs to be developed. Presently, the treatment technologies to remove these EDCs from the wastewater include adsorption, advanced oxidation, biological degradation and membrane filtration [6]. Adsorption using activated carbon (AC) is generally used to remove organic pollutants [6] which has proved to be a promising method to remove estrogens. Usually, these activated carbons are manufactured from a wide range of carbon based materials. Due to high surface area and porosity the AC is efficient in adsorbing pollutants [7], but the regeneration of the used AC proves to be a difficult task. Recently, many new adsorbents are being prepared and tested for their efficiency in estrogen removal. These include activated carbon prepared from agro wastes [8], slurry wastes [9], chitin [10], moso bamboo [11] and biochar [12]. Q3 Nowadays, bone char is being explored for its adsorption capacity and efficiency. Bone char is a readily available source which is prepared by pyrolysis process, where they undergo a thermal treatment at a range of 400–500  C in a limited supply of air. It has a long history of removing color from sugar solution, defluoridation and removing heavy metals but to the best of our knowledge, it has not been used for the removal of estrogens. Being a mixed adsorbent having about 80–90% hydroxyapatite and 10% amorphous carbon, it gets distinguished from other available adsorbents [7]. It has already proved its efficiency in removing pyrogen such as endotoxin [13], air pollutant [14], bacterial spores [15], heavy metals [16–18], dyes [19,20] and organic compounds [21,22] from aqueous solutions. This study demonstrates the use of bone char as a new class of solid adsorbent for treating E2 from water. 17-b estradiol is a human sex hormone which is essential for the development of female reproductive tissues including bone health. It has been selected for this study since it is persistent in treated effluents and highly estrogenic. The efficiency of the bone char has been studied in a batch adsorption process.

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Experimental

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Materials and reagents

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Bone char prepared under laboratory conditions was tested for the adsorption of E2 in water. Cattle bones (bovine and bull) were obtained from Biomaterials Laboratory. 17b-estradiol (98%), Sodium Chloride (99.5%) was purchased from Sigma–Aldrich. Details on E2 characteristics are shown in Table 1. Acetonitrile Table 1 Structure and properties of E2 [3].

Molecular formula-C18H24O2 Mol. mass Solubility Vapor pressure Log Kow pKa

272.38 g mol
1 3.90 mg L
1 (27  C) 3  10
8 Pa 3.1–4.01 10.5–10.7

(HPLC grade) was supplied by Tedia and deionized water (18.2 MV) was obtained from the laboratory MilliQ water purification system. Stock solutions were prepared at a concentration of 200 mg L
1 by dissolving the solid compound in ethanol and stored at 5  C. Working aqueous solutions of the standards were prepared by diluting the stock solution with deionized water. Following this procedure predetermined concentration of E2 solutions were prepared for calibration measurements.

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Preparation of bone char

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Bone char was prepared from waste cattle bones. The bones were initially washed and boiled in deionized water for about 3– 4 h to get rid of the protein pieces. These cleaned bones were dried in an oven (Contherm, Thermotec 2000) at 110  C for 80–85 h and were allowed to cool at room temperature. After this, the bones were broken down and ground to a desired mesh size 1–2 mm. The obtained granules were treated with acetone followed by washing with hot distilled water. These washed samples were dried and transferred to a muffle furnace to carry out the pyrolysis process in a limited supply of air (Supplementary data, Fig. S1).

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Analytical and characterization methods

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The textural characterization was done by Brunauer–Emmett– Teller (BET) method using N2 adsorption at 77.35 K and a relative pressure (P/P0) range of 0.0001–1 using TriStar 3000 surface area analyzer. All the samples, prior to analyzing was outgassed at 100  C for 2–3 h. The surface morphology of the prepared bone char was characterized by Philips XL30S field-emission scanning electron microscope (SEM). Transmission electron microscope (TEM) was used to study the crystallinity and diffraction patterns of the samples prepared. The micrographs were obtained using Technai F20 operating at 200 kV. For the TEM analysis, the samples were prepared by dispersing a very small amount of it in ethanol. This solution was kept in an ultrasonic bath for about 2 h until the powder was broken down into fine particles. After this a drop of the diluted sample was placed on the copper grid coated with a thin carbon film. 17-b estradiol solution samples were analyzed on a Shimadzu Prominence1 HPLC system equipped with a UV detector. The analysis was performed using a C18 reverse-phase column (5 mm, 4.6  150 mm, Agilent) at 205 nm wavelength with 0.2 mL sample injection. Acetonitrile and deionized water were mixed at (45:55, vol.) and used as mobile phase at a flow rate of 1.0 mL min
1.

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Point of zero charge measurements

133

To quantify the pH at the point of zero charge (pHpzc) the below given procedure was followed [23]. A series of 20 mL of 0.1 mol L
1 NaCl solutions in glass bottles was prepared. The initial pH of the NaCl solution was adjusted by 0.1 mol L
1 of NaOH or HCl. After this 0.01 g of bone char was added to each glass bottle and sealed thoroughly. These bottles were then allowed to equilibrate at the room temperature (18  C) for 3 days. The final pH was measured and plotted against D pH.

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Adsorption experiments

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Parameters affecting the adsorption process Adsorption of E2 on bone char was studied as a function of contact time, initial concentration and dosage of adsorbent. The samples were prepared with an initial measured concentration of 5 and 9 mg L
1. To analyze the effect of adsorbent mass, the dosage

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Please cite this article in press as: S. Patel, et al., Sorption of 17b-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.04.027

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was varied between 0.5 and 50 g L
1. These affecting parameters have been discussed in detail in the Results and discussion section. Kinetics experiments Batch adsorption experiment was conducted to investigate the efficiency of the prepared bone char as an adsorbent for removing E2 from water. Initial concentrations of 5 and 9 mg L
1 were prepared by diluting the 200 mg L
1 stock solution. A constant dosage of 2.5 g L
1 of bone char was added into E2 solution. The solutions were agitated for 24 h at 150 rpm in an incubator shaker at a controlled temperature (25  C). The adsorption kinetics was studied by adding bone char into 40 mL of E2 solution. The samples were extracted at regular intervals and filtered by 0.2 mm regenerated cellulose syringe filters (13 mm dia, Phenomenex). The filtered samples were collected in glass vials for the Chromatography analysis. A calibration curve was established for the HPLC peak area and the concentration of E2 in water. The retention time of E2 was determined as 5.8 min. Equilibrium isotherms The equilibrium experiments were carried out by adding bone char into a series of 20 mL of E2 solutions. The E2 solution was prepared at a concentration of 2 mg L
1 and the bone char dosage was varied between 0.5 and 50 g L
1. The solutions were agitated for 24 h at 150 rpm in an incubator shaker at a controlled

3

temperature (25  C). The equilibrium of adsorption is usually evaluated by Langmuir and Freundlich isotherm models. The Langmuir isotherm model is expressed as: 1 1 1 1 ¼ þ qe qo q0 bC e

1 1 þ bC 0

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(2)

where C0 is the initial concentration of the solute. The RL value indicates the adsorption situation to be irreversible: RL = 0, favourable: 0 < RL < 1, linear: RL = 1 and unfavourable: RL > 1 [19,24]. The Freundlich isotherm model is an empirical equation, which in its linear form is expressed as: 1 logqe ¼ logkf þ logCe n

172

(1)

where qe (mg g
1) is the amount of solute adsorbed at equilibrium; Ce (mg L
1) is the equilibrium concentration of solute in the solution; q0 (mg g
1) is denoted as the maximum adsorption capacity and b (L mg
1) is the binding energy constant. The dimensionless separation factor RL can be expressed as RL ¼

171

181 180 182 183 184 185 186

(3)

where qe (mg g
1) and Ce (mg L
1) represent the same parameters as denoted in Langmuir isotherm model. kf mg g
1 (mg L
1)
1/n is

Fig. 1. Surface morphology of the bone char.

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the measure of adsorption capacity and the Freundlich intensity parameter 1/n indicates the intensity of adsorptive interactions. If 1/n = 1, partition between the two phases are not concentration dependent. If 1/n < 1, it indicates a normal adsorption and if 1/ n > 1, it indicates cooperative adsorption [25]. The experimental data were then fit to Langmuir and Freundlich isotherm model and analyzed further.

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Sorbent regeneration and reuse

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Saturated bone char from the adsorption studies was used in the regeneration studies. Since, 17-b estradiol is sparingly soluble in water; it was expected that using a solvent which would facilitate desorption of E2 from bone char [26]. The bone char was regenerated by solvent washing method, where ethanol/water (1/ 1; v/v) was used as a solvent. The saturated bone char was agitated in 20 mL solvent for 2 h (150 rpm) on a shaker. After this desired time, the regenerated bone char was filtered and reused. The bone char reusability was assessed by conducting three cycles of E2 adsorption and regeneration.

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Results and discussion

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Characterization of bone char

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Surface area and SEM analysis The nitrogen adsorption isotherm was obtained from the adsorption data acquisition program at a relative pressure (P/P0) range of 0.0001–1. The surface area, SBET of the prepared bone char was found to be 114.15 m2 g
1 with a pore diameter of 9.63 nm and a total pore volume of 0.294 cm3 g
1 (Supplementary data, Fig. S2). This value of the bone char surface area is expected to be advantageous for its usage in removing E2 from aqueous solutions. The prepared bone char was found to be mesoporous in nature. The surface morphology of the prepared bone char is shown in Fig. 1. As

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per the morphology, the prepared bone char has a rough surface with a porous structure.

220

TEM analysis From the TEM images and diffraction patterns obtained for both raw bone powder and as prepared bone char, shown in Fig. 2. The high resolution images of the raw bone powder indicate that it is poorly crystalline whereas the prepared bone char is crystalline, with most of the crystals oriented in a single direction. The obtained diffraction pattern for the raw bone powder does not show sharp rings which is also an indicative of being amorphous in nature. Whereas the diffraction pattern for the bone char shows sharp whereas distinct rings indicating comparatively well crystalline structure.

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Point of zero charge

233

As per Yang et al. often surface functionality plays a dominant role in determining the adsorption efficiency of the carbon [27]. Though the effect of surface functionality is complicated but the overall impact of these functional groups determine the point of zero charge (pHzpc) or neutral charge on its surface. Based on the experimental results, the point of zero charge for the bone char was measured about 5.9 from the Fig. 3. It has been well reported that below pHpzc, the surface charge is positive whereas above pHzpc the surface charge is negative [27,28]. The positive charge on the adsorbent surface may enhance the removal of E2 [8]. Therefore, in this study, it was decided to work at pH below the pHpzc value and hence the adsorption studies were conducted at pH 5.

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Adsorption studies

247

Adsorption of E2 on bone char was studied using batch adsorption process with respect to contact time, initial concentration and dosage of adsorbent.

248

Fig. 2. TEM image and diffraction pattern of the (a–c) raw bone powder (d–f) prepared bone char.

Please cite this article in press as: S. Patel, et al., Sorption of 17b-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.04.027

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mesopores. The adsorbed amount of E2 adsorbed on to bone char increased by increasing the contact time. After 24 h the removal of E2 was 50% and 41% for 5 and 9 mg L
1, respectively.

267

Effect of initial concentration The effect of initial concentration of E2 on bone char sorption characteristics was investigated as shown in Fig. 4. As per these plots the amount of E2 adsorbed on bone char with a dosage of 2.5 g L
1 was evaluated with initial concentrations of 5.0–9.0 mg L
1. It was observed that the amount of E2 adsorption increased when the initial concentration increased from 5 to 9 mg L
1. The amount adsorbed was 0.10 and 0.14 mg g
1 respectively after 24 h. As seen in Fig. 4, the removal efficiency decreased with the increase in the initial concentration of E2. At the contact time of about 360 min, the removal of E2 was 41.59% and 17.63% for 5 and 9 mg L
1 respectively.

270

Role of dosage in adsorption Dosage of adsorbent plays a very important in the entire adsorption process. Experiments were carried out with the E2 concentration keeping constant at 2 mg L
1 with the rotation speed 150 rpm and temperature 25  C. Increasing the amount of adsorbent gives more number of available adsorption sites to the pollutants to get attached to the adsorbent. Therefore, increasing the amount of the adsorbent eventually increases the absorbable area giving rise to an increased removal percentage of E2 from aqueous solutions. The effect of increasing the mass of adsorbent on the removal of E2 is shown in Fig. 5. The results show that the adsorbent dosage at 50 g L
1 could remove 95.3% of E2 from aqueous solutions.

282

Adsorption kinetics

295

To access the feasibility of the adsorption process, the adsorption kinetics was studied. Kinetic studies describe the interactions between the adsorbent and adsorbate through the mathematical models. The pseudo first order kinetic model, pseudo second order kinetic model and the intraparticle diffusion model were evaluated. The results did not fit the pseudo first order kinetic model; hence the other two models have been studied in detail in the following section.

296

Pseudo second order kinetic model Fig. 6 shows the time profile of E2 adsorption by bone char under batch process, for two different initial E2 concentrations (5 and 9 mg L
1).

304

268 269

2

1

∆pH

0

0

2

4

6

8

10

-1

-2

-3

Initial pH

Fig. 3. Point of zero charge measurement. 251 252

The amount of E2 adsorbed at equilibrium (qe) and the estrogen removal efficiency were calculated from the equations as below: qe ¼

C0
Ce V M

(4)

C0
C Effeciency ¼  100 C0

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Effect of contact time The contact time also plays a major role in the E2 adsorption on to bone char. The effect of contact time on the adsorption of E2 is shown in Fig. 4. It can further be observed that initially the uptake of E2 was greater up to 6.5 h and after that it slowly reached apparent equilibrium. This initial rapid uptake of E2 could be due to the availability of the adsorption sites, macropores and

1.6 5 mg/L

1.4

100

9 mg/L

1.2

90 80

1

70

Removal (%)

256

where Ce and C0 are the equilibrium and initial concentrations of E2 (mg L
1), qe is the equilibrium E2 concentration on the adsorbent (mg g
1), V is the volume of E2 solution (L), M is the mass of adsorbent (g). The results obtained have been discussed in more detail in the following sections.

Amount adsorbed (mg g-1)

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(5)

0.8 0.6

50 40 30

0.4

20

0.2 0

60

10

0

200

400

600

800 Time (min)

1000

1200

1400

1600

Fig. 4. Effect of contact time on the adsorption of E2 on bone char at pH 5 with bone char dosage of 2.5 g L
1.

0

0

5

10

15

20

25

30

35

40

45

50

Adsorbent dosage (g L-1 )

Fig. 5. Effect of adsorbent dosage on E2 adsorption onto bone char with an initial concentration of 2 mg L
1, rotation speed 150 rpm, and temperature 250  C.

Please cite this article in press as: S. Patel, et al., Sorption of 17b-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.04.027

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5 mg/l

9

9 mg/l

Concentration (C, mg L-1)

8 7 6 5 4 3 2

0

200

400

600

800

1000

1200

1400

Time (min)

The pseudo-second order kinetic model is given as t 1 t ¼ þ q kq2e qe

313 314

1400

5 mg/l

1200

y = 0.7977x + 258.92 R² = 0.9987

9 mg/l

1000

t q-1 (min g mg_1)

312

(6)

where k is the rate constant of pseudo-second order sorption, q and qe represent the adsorption capacity at time t and equilibrium respectively. It can be observed that the E2 concentration in solution decreases rapidly in the first 6 h of the beginning of the batch

800 y = 0.4851x + 289.47 R² = 0.9427

600 400 200 0

0

200

400

600

800

1000

1200

1400

Time (min)

(a)

1.6

Sorbed Concentration of E2 (mg g-1)

310 309 311

5 mg/L

1.4

y = 0.039x - 0.0159 R² = 0.9905

9 mg/L

1.2 1 0.8

y = 0.027x + 0.0493 R² = 0.9812

0.6 0.4

-0.2

Intraparticle diffusion model The kinetic data of E2 adsorption was also analyzed using Weber–Morris intraparticle diffusion model. Theoretically, this model gives a complex mathematical relationship. The intra-particle diffusion model is given as

325

0

5

10

15

20

25

Square root of time (min0.5)

30

35

Fig. 7. Data fit to (a) pseudo-second order kinetic model where t represents time, q is the adsorption capacity at any particular time and (b) intaparticle diffusion model with various initial concentrations and bone char dosage: 2.5 g L
1. The dashed lines are the linearized kinetic models.

317 318 319 320 321 322 323 324

326 327 328 329

(7) 331 330 332

Adsorption equilibrium and isotherms

353

Studies were conducted to observe the adsorption capacity of bone char for E2 in water. The adsorption isotherm of E2 was established on bone char by batch adsorption. The adsorption data were fit to the Langmuir and Freundlich isotherm models as shown in Fig. 8. These models have been used extensively to describe the adsorption phenomena. The correlation coefficient (R2) suggests that both models fitted the experimental data and the results summarized in Table 3. This could be due to the distribution of both homogeneous and heterogeneous adsorption sites on the surface of the bone char. The bone char has a maximum adsorption capacity of q0 = 10.12 mg g
1, kf = 0.346 mg g
1 (mg L
1)
1/n. The Langmuir

354

Model

Parameters

Initial concentrations 5 mg L
1 9 mg L
1

Pseudo-second order model

k (g mg
1 min
1) R2

0.0024 0.999

0.0008 0.943

Intraparticle diffusion model

kp (mg g
1 min
1/2) R2

0.027 0.981

0.04 0.991

40

(b)

316

where qt is the adsorption capacity at time t, kp is the intraparticle diffusion rate constant and C is the intercept. This adsorption mechanism involves three steps. In the first step, the mass transfer of adsorbate from the bulk phase to particle surface takes place. The second step involves the boundary layer diffusion, sorption on the sites and the final step is given by intra particle diffusion [20]. The sorption on the sites is considered to be a very rapid step, hence requirement of longer contact time for equilibrium is said to be governed by intraparticle diffusion [32]. The general approach to analyze the adsorption process controlled by intraparticle diffusion is to plot the amount adsorbed q (mg g
1) versus the square root of time, t0.5 as shown in Fig. 7(b). The plots show several stages indicating the occurrence of the diffusion in the pores [33]. The intraparticle diffusion constant, kp value is obtained from the slope of the linear portion of the curve. The results obtained are summarized in Table 2. From the results obtained, it was clear that the intraparticle diffusion was slow and the rate limiting step. But the linear portions did not pass through the origin, indicating that the E2 adsorption process on bone char was very complex process, where along with the surface adsorption, intraparticle diffusion also contributes to the rate limiting step.

Table 2 Kinetic parameters of E2 adsorption on bone char.

0.2 0

315

qt ¼ kp t0:5 þ C

Fig. 6. Adsorption kinetics, time profile of E2 with various initial concentrations and bone char dosage: 2.5 g L
1. 308

adsorption process. The best adsorption data were obtained for the pseudo second order kinetic model as shown in Fig. 7(a). This model assumes that a chemisorption mechanism is involved in the adsorption process and the rate of site is proportional to the square of number of unoccupied sites [29]. The results are summarized in Table 2. The adsorption kinetics shows a linearized form for the plot of pseudo-second order model. This suggests that the rate limiting step could be chemical sorption or ion exchange [29]. Such behaviour of bone char has been reported by various researchers [19,30,31].

Please cite this article in press as: S. Patel, et al., Sorption of 17b-estradiol from aqueous solutions on to bone char derived from waste cattle bones: Kinetics and isotherms, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.04.027

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Adsorption 20

0.04

Amount adsorbed (mg g-1)

Inverse of Sorbed Concentration of E2 (g mg-1)

7

15

y = 3.0172x + 0.1705 R² = 0.9964

10

5

0

0

1

2

3

4

5

6

7

8

9

-0.6

-0.4

0

-0.2

0

0.2

Logarithm of Sorbed Concentration of E2 (mg g-1)

-0.8

0.01

0

1

2

3

Cycles Fig. 9. Adsorption capacity of E2 adsorbed per cycle (150 rpm, dosage = 5 g L
1).

Logarithm of E2 Concentration in solution (mg L-1) -1

0.02

(a)

mg-1)

Inverse of E2 Concentartion in solution (L

0.03

Conclusions

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In summary, this study demonstrated that bone char derived from waste cattle (bovine and bull) bones was a suitable adsorbent to remove 17b-estradiol from water. Bone char was prepared under laboratory conditions where the BET surface area of the bone char was found to be 114.15 m2 g
1. The adsorption of E2 on bone char followed pseudo-second order kinetics. From the intraparticle diffusion studies, the mechanism on E2 adsorption onto bone char was found to be very complex where not only the surface adsorption but also the intaparticle diffusion contributes to the rate limiting step. The adsorption of E2 was affected by the concentration of adsorbent. Increasing the dosage, eventually, increased the E2 removal from water. About 95.3% of E2 was removed from water with a maximum adsorption capacity of 10.12 mg g
1. Solvent washing method ethanol/water (1/1; v/v) was effective in desorbing E2 from saturated bone char and the regenerated bone char was efficiently reused.

385

Acknowledgments

401

The authors gratefully acknowledge support from the department and would like to thank the group members for their assistance. Sangeeta Patel would also like to thank Dr. Shanghai Wei for his invaluable support and assistance during the TEM analysis.

402

Appendix A. Supplementary data

407

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jece.2015.04.027.

408

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dimensionless constant separation factor, RL indicates the adsorption process to be favourable [19]. Whereas, the Freundlich isotherm intensity parameter 1/n indicates linear adsorption leading to identical adsorption energies for all sites [34].

370

Sorbent regeneration and reuse

References

410

371

To test the leachability of the sorbed compounds, experiments were conducted by washing the saturated bone char with ethanol/ water (1/1; v/v) solvent. The solution was agitated for 2 h (150 rpm) on a shaker. Due to the high octanol–water partitioning coefficient (log Kow = 3.1–4.01), 17-b estradiol is highly soluble in the organic solvents. Hence, the solvent washing method was chosen for the regeneration [26] and this method was effective in desorbing E2 from bone char. The reusability of the regenerated bone char was assessed by conducting three cycles of E2 adsorption and bone char regeneration. The results in Fig. 9 show that the regenerated bone char can be used effectively and the adsorption capacity was restored to 85% of its initial capacity in the third cycle.

-0.2 -0.4 y = 1.0427x - 0.4606 R² = 0.9949

-0.6 -0.8 -1 -1.2

(b) Fig. 8. Adsorption isotherms of bone char for E2 in aqueous solution. Experimental data fit to (a) Langmuir and (b) Freundlich isotherm models.

Table 3 Langmuir and Freundlich constants for E2 sorption by bone char. Model Freundlich isotherm model

Langmuir isotherm model

366 367 368

372 373 374 375 376 377 378 379 380 381 382 383

R2

Parameters kf = 0.346 mg g 1/n = 1.043


1


1
1/n

(mg L

q0 = 10.12 (mg g
1) b = 0.033 (L mg
1) RL = 0.92

)

386 387 388 389 390 391 392 393 394 395 396 397 398 399 400

0.995

0.996

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