Characterization of water bamboo husk biosorbents and their application in heavy metal ion trapping

Microchemical Journal 113 (2014) 59–63

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Characterization of water bamboo husk biosorbents and their application in heavy metal ion trapping Hillary B. Asberry a, Chung-Yih Kuo b, Chin-Hau Gung c, Eric D. Conte a,⁎, Shing-Yi Suen c,d,⁎⁎ a

Department of Chemistry, Western Kentucky University, Bowling Green, KY 42101, USA Department of Public Health, Chung Shan Medical University, Taichung 402, Taiwan Department of Chemical Engineering, National Chung Hsing University, Taichung 402, Taiwan d Center of Nanoscience and Nanotechnology, National Chung Hsing University, Taichung 402, Taiwan b c

a r t i c l e

i n f o

Article history: Received 12 October 2013 Received in revised form 18 November 2013 Accepted 18 November 2013 Available online 27 November 2013 Keywords: Water bamboo husk Biosorbent Heavy metal ions Adsorption isotherm Breakthrough curve

a b s t r a c t The use of plant-based biosorbents for removing environmental pollutants from water is gaining widespread attention. In this paper, the 45–250 μm biosorbents were prepared from the husks of water bamboo (Zizania caduciflora Turcz.), with a pore size distribution of 5.7–13.8 nm and surface area of 1.87 m2/g. These water bamboo husk particles contained OH and COOH groups and had a zero point of charge between pH 2 and 3. An optimal negative charge on particle surface was achieved at pH 5. Moreover, their cation exchange capacity was about 1.3 meq/g. When trapping metal ions at pH 5, the prepared biosorbents exhibited strong affinity to Cu2+, Cr3+, Pb2+, and Fe3+. Adsorption isotherms and breakthrough studies were generated for Fe3+ (stronger affinity) and Ni2+ (weaker affinity), and the interpretation of results indicated that the water bamboo husk particles are well suited to trap these ions at low concentrations. Also, column trapping of metal ions (breakthrough volume: 75 bed volume for Ni2+ and 90 bed volume for Fe3+) proved much more efficient than static adsorption. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Heavy metal ions are usually released into streams as waste products from industries such as mining operations, metal plating facilities, tanneries, etc. [1,2]. Heavy metals from these polluted streams can then enter into the surrounding soil, surface water, and groundwater. When the polluted water is consumed by living organisms, the toxic heavy metals can accumulate and cause harm [3]. Some commonly expelled heavy metals are nickel (Ni) and copper (Cu). Nickel can be discharged into the environment from silver refinery, storage battery, electroplating, and zinc base casting industries. The toxicity of nickel has been documented to cause cancers of nose, lung and throat [4] as well as other conditions such as gastrointestinal distress, pulmonary fibrosis, and skin dermatitis [5]. Many of the copper ions released into the environment are a consequence of metal cleaning and plating baths, paper board mills, wood-pulp production, and fertilizer industries. When the body intakes an excessive amount of copper, it accumulates in the liver and can result in cirrhosis [2,6]. Copper poisoning has also been correlated with various conditions such as hemochromatosis and gastrointestinal catarrh. Moreover, copper is harmful to aquatic species even in trace amounts [7].

⁎ Corresponding author. Tel.: +1 270 7456019; fax: +1 270 7456293. ⁎⁎ Correspondence to: S.-Y. Suen, Department of Chemical Engineering, National Chung Hsing University, Taichung 402, Taiwan. Tel.: +886 4 22852590; fax: +886 4 22854734. E-mail addresses: [email protected] (E.D. Conte), [email protected] (S.-Y. Suen). 0026-265X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.microc.2013.11.011

It is essential to remove these heavy metal ions from industrial sources before they enter the environment. Common removal processes include chemical precipitation, ion exchange, adsorption, membrane filtration, electrochemical filtration, etc. [1,2,8], among which adsorption is considered a simple and efficient method. Many natural biosorbents that are inexpensive and region-specific agricultural wastes are now being used popularly and gaining widespread attention [2,9]. Plant waste biosorbents that demonstrated the ability to adsorb heavy metal ions are pomegranate peel [1], gooseberry fruit [2], banana peel [10], peanut hull [11], Ponkan mandarin peel [12], papaya wood [13], almond husk [14], sunflower leaves [15], wheat shell [16], and so on. In Taiwan, the husks of water bamboo (Zizania caduciflora Turcz.) are one of the major agricultural wastes. Water bamboos grow best during the summer when the climate in Taiwan is warm, humid, and sunny. Their husk wastes are readily available, free of expense, and ecofriendly. To reuse water bamboo husk wastes in special applications has become an important issue in Taiwan. In a previous literature [17], the fibers obtained from water bamboo husks were characterized by nuclear magnetic resonance, elemental analysis, pyrolysis, and thermal techniques, which had verified their applicability in pulping and composite materials. In the present study, water bamboo husks would be utilized to prepare the biosorbent particles for trapping heavy metal ions from water. To the best of our knowledge, the use of water bamboo husks as biosorbent material has not been reported before. In this paper, the characterization of water bamboo husk particles and their potential on the removal of heavy metal ions would be systematically investigated.

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2. Experimental 2.1. Materials The outer husks of water bamboo were the wastes of local markets in Taichung, Taiwan. Solutions of Ni2+ and Fe3+ were made with deionized water using reagent grade salts (NiSO4·6H2O and FeCl3·6H2O, both purity 99%) from SHOWA. The pH was adjusted to 5 with 0.1 M sodium hydroxide and nitric acid (SHOWA) using a Istek Model 720P pH meter. Moreover, a mixture of multiple ions adopted in this study was the ICP Multi Element Standard Solution IV from Merck (USA). Each ion concentration was 1000 ± 10 mg/L. This solution was diluted and its pH was adjusted to 5 prior to use. 2.2. Preparation and characterization of water bamboo husk particles Water bamboo husk was cut into small pieces (about 1 cm), washed with deionized water, and then dried in an oven at 60 °C for 24 h. An industrial grinder (RT-02A, Rong Tsong Precision Technology, Taiwan) was adopted to grind the chopped husks into powders for 1 min, which was repeated 3 times. The resulting particles were rinsed with deionized water and dried in the oven at 60 °C for 24 h. Particles ranging from 45 to 250 μm were obtained using a Retsch sieving machine (Mesh no. 60 (250 μm) and no. 325 (45 μm), Germany). For decoloration, the water bamboo husk particles were placed in 1 L of fresh deionized water and washed with an ultrasonic cleaner for 30 min, which was repeated 3 times in sequential. The particles were then immersed in 1 L of fresh deionized water and heated at 50 °C for 24 h. Finally, the particles were filtered from the solution, and dried in the oven at 60 °C for 24 h. The photos for pristine water bamboo husk, chopped pieces, and the prepared particles are shown in Fig. 1. The functional groups on water bamboo husk particles were characterized using a FTIR spectroscopy (FT-720, Horiba, Japan). The spectrum was obtained with 650 cumulative scans from 4 to 4000 cm − 1. The pore size distribution and surface area of water bamboo husk particles were measured by a Micromeritics BET (ASAP 2010, USA). Prior to measurement, the particles were degassed at 120 °C, under vacuum for 24 h. In addition, the pH at zero point of charge (pHzpc) for water bamboo husk particles (2 mg in 10 mL of water for 10 min) was determined with a zeta potential meter (Zetasizer Nano-ZS, Malvern, USA). The procedures for ion exchange capacity (IEC) measurement were as follows. 50 mg of water bamboo husk particles were soaked in 20 mL of 0.1 M HCl solution and shaken at 100 rpm and room temperature for 24 h. The acid was poured out and the particles were washed with 50 mL of deionized water for 3 h to remove the traces of acid. After the removal of deionized water, 20 mL of 0.01 M NaOH was added and the particles were immersed in NaOH solution for 24 h. The IEC was determined from the alkalinity reduction in NaOH solution by back titration using 0.01 M HCl as IEC (meq/g) = MO,NaOH − ME,NaOH, where MO,NaOH and ME,NaOH are the moles of NaOH before and after the equilibration, respectively.

Fig. 1. Photos of pristine water bamboo husk, chopped pieces, and the prepared particles.

diluted to fit within calibration range. The adsorbed metal ion capacity was calculated using the difference between the final and initial concentrations. In the batch desorption experiment, the water bamboo husk particles loaded with metal ions (c0 = 10 mg/L) were immersed in 50 mL of desorption solution for 1 and 3 h at room temperature and with shaking at 100 rpm. Two desorption solutions were tested: 0.1 M HNO3 (pH 1.8) and 0.01 M EDTA. The desorbed metal ion amount was evaluated by multiplying the metal ion concentration in desorption solution by the solution volume.

2.3. Batch adsorption/desorption experiment

2.4. Column adsorption experiment

The adsorption capacity was studied for metal ion solution at pH 5 and room temperature in batch process. In this experiment, 250 mg of water bamboo husk particles were placed in a 100 mL wide-mouth vial and immersed in 50 mL of the metal ion solution, shaking on the TKS OS 701 orbital shaker (Japan) at 100 rpm. Adsorption equilibrium was reached after 3 h of contact time. Then, the solution was filtered to remove the sorbent particles. The metal ion concentration was analyzed using either a PerkinElmer AA3300 Flame Atomic Adsorption Spectrometer (USA) for a single metal ion or a Horiba ULTIMA2 ICP (Japan) for a mixture of metal ions. Some of the samples were

250 mg of water bamboo husk particles were carefully packed in a glass column with length of 30 cm and inner diameter of 1 cm (Adjusta chrom®). The bed height was 1.4 cm. Thus, the bed volume was about 1.1 mL. A metal ion solution of 10 mg/L was fed into the column using a HPLC pump (Waters 600 controller/600 system pump, USA) in up-flow direction. The flow rate was 1 mL/min, and the pressure drop was about 23–32 psi. The fractions of column effluent were collected at 10 mL in each vial. The metal ion concentration in each fraction was determined by the Flame Atomic Absorption Spectrometer.

H.B. Asberry et al. / Microchemical Journal 113 (2014) 59–63

3. Results and discussion

5

3.1. Properties of water bamboo husk particles

0

70

-5

zeta potential

The particle diameter of the water bamboo husk sorbents prepared in this study ranged from 45 to 250 μm. The BET measurement gave a pore size distribution of 5.7–13.8 nm for these particles, which is close to that of Ponkan mandarin peel particles (3–13 nm) [12] but slightly larger than banana peel particles (1.05 nm) [10]. The specific surface area of water bamboo husk particles, also determined by BET, was found to be 1.87 m2/g. This result is near those for banana peel (2 m2/g) [10] and Pu-erh tea powder (40 mesh, 1.71 m2/g) [18]. Nevertheless, it is much smaller than that reported for Ponkan mandarin peel (119.3 m2/g) [12] and much larger than pine cone powders (0.0993 m2/g (raw pine cone) and 0.122 m2/g (acid-treated pine cone)) [19]. The pore size and surface area of biosorbents vary with the agricultural material adopted. Water bamboo husk provides the properties similar to most of the plant wastes studied in the literature. To identify the functional groups on water bamboo husk particles, their FTIR spectrum was recorded and the result is presented in Fig. 2. The spectrum is very similar to the results of other biosorbents. The broad band at 3420 cm−1 was mainly ascribed to the OH group, whereas the band at 2920 cm−1 was assigned to the aliphatic CH groups [2,10–12,18–21]. Moreover, the peaks at 1710 and 1640 cm−1 were attributed to the CO bond of carboxylic acids [2,10–12,18–21]. The above FTIR results indicate that water bamboo husk particles contain OH and COOH groups. Accordingly, positively-charged heavy metal ions would be able to bind with these active groups under appropriate pH conditions, via charge interaction, and adsorbed onto the water bamboo husk particles. The pHzpc of water bamboo husk particles was determined by zeta potential at the range of pH 2–6. As illustrated in Fig. 3, the zeta potential was positive (0.56 mV) at pH 2 but switched to negative at pH 3 (−5.78 mV). Accordingly, the pHzpc value of water bamboo husk particles should be between 2 and 3, which is slightly lower than those reported for Pu-erh tea powder (pHzpc = 3.6) [18] and tea waste (pHzpc = 4.3) [21]. The zeta potential of water bamboo husk continued to decrease with increasing pH and then remained stable at pH 6. An optimal negative charge on particle surface was achieved at pH 5 (− 26.40 mV). It is also worthy to note that the weakly acidic COOH groups are usually the main sites on plant waste sorbents for the uptake of cationic substances [10,22]. The pKa of COOH group is about 3.5–5.5 so that a majority of carboxyl groups are deprotonated at pH values in this range, resulting in more negatively-charged sites [22]. Our zeta potential results are in good agreement with the above explanation.

61

-10 -15 -20 -25 -30

1

2

3

4

5

6

pH Fig. 3. Zeta potential results of water bamboo husk particles.

Moreover, pH 5 is also the optimal value for trapping metal ions by Ponkan mandarin peel particles [12]. Subsequently, in the following adsorption processes, the solution pH was fixed at 5 in order to adsorb plenty of positively-charged metal ions.

3.2. Batch adsorption results In batch process, 250 mg of water bamboo husk particles were employed to adsorb heavy metal ions from a 50-mL mixture (23 kinds of metal ions) with a concentration of 5 mg/L for each single ion (prepared by diluting the standard solution) at pH 5 and room temperature. In this case apparent equilibrium was established within 3 h of contact time. The adsorption of water bamboo husk particles was more favorable to seven metal ions in a competitive circumstance and their adsorption results are shown in Fig. 4. The other 16 metal ions exhibited negligible adsorption. In Fig. 4, ions having a strong affinity to water bamboo husk biosorbent included Cu2+, Cr3+, Pb2+, and Fe3+. The adsorption percentage ranged from 15.5% (Ni2+) to 99.8% (Fe3+). Ni2 + and Fe3 + were thus selected for the subsequent investigations on static and dynamic adsorption. The adsorption isotherms of Ni2+ and Fe3+ are presented in Fig. 5 (solid symbols, red color), along with the extent of adsorption (open

100

60

adsorption %

transmitance %

80 50 40 30

60 40

20 20 10 0 4000

0 3000

2000

1000

wavenumber (cm-1) Fig. 2. FTIR spectrum of water bamboo husk particles.

Ni2+

Zn2+

Cd2+

Cu2+

Cr3+

Pb2+

Fe3+

Fig. 4. Batch adsorption performance for seven metal ions at pH 5 and room temperature, solution volume = 50 mL, particle amount = 250 mg, contact time = 3 h, c0 of each ion in the mixture = 5 mg/L.

H.B. Asberry et al. / Microchemical Journal 113 (2014) 59–63

10

100

8

80

Ni2+

6

Fe3+

4 2 0

60

Ni2+ 0

50

100

150

200

40

Fe3+ 250

3.3. Batch desorption results

adsorption %

q (mg/g)

62

20

0 300

ceq (mg/L) Fig. 5. Adsorption isotherms of Ni2+ and Fe3+ at pH 5 and room temperature, solution volume = 50 mL, particle amount = 250 mg, contact time = 3 h.

symbols, green color). The well-known Langmuir isotherm model for homogeneous monolayer adsorption was adopted to analyze the isotherm data: q¼

qm ceq K d þ ceq

ð1Þ

where q is the adsorbed metal ion capacity (mg/g adsorbent), ceq is the aqueous metal ion concentration at equilibrium (mg/L), q m is the maximum metal ion adsorption capacity (mg/g), Kd is the equilibrium dissociation constant (mg/L). The best-fit values of the model parameters estimated from Eq. (1) by nonlinear regression analyses are: q m = 8.4 mg/g and K d = 72.4 mg/L (R 2 = 0.90) for Ni2 + ; q m = 4.7 mg/g and K d = 14.6 mg/L (R2 = 0.92) for Fe3 +. The isotherm simulation results are also shown in Fig. 5 as red lines (solid line for Ni2 + and dashed line for Fe3 +). After further calculation, the qm values for the prepared water bamboo husk particles were 0.143 mmol/g for Ni2+ and 0.084 mmol/g for Fe3+. Considering the charge number on each metal ion (2 for Ni2+ and 3 for Fe3+), the saturated adsorption capacity of Ni2+, 0.286 meq/g, is close to that of Fe3+, 0.252 meq/g. On the other hand, the measured cation exchange capacity of water bamboo husk particles was about 1.3 meq/g. When comparing qm to this value, it reveals that only 20% of the negatively-charged sites on the particles were occupied by metal ions. Accordingly, the maximum possible metal ion adsorptivity for the prepared water bamboo husk biosorbents should be 5 times than the measured values, i.e. about 40 mg Ni2+/g and 25 mg Fe3+/g, which are comparable to the maximum adsorption capacities listed in Refs. [22,23]. In addition, an extraordinary and interesting isotherm behavior happened in Fig. 5: Ni2 + exhibited lower adsorption capacities at lower concentrations but higher capacities at higher concentrations, in comparison with Fe3+. An intersection for both isotherms occurred at ceq ≈ 60 mg/L. This explains why Ni2+ revealed a lower adsorption percentage than Fe3+ at an initial concentration of 5 mg/L as shown in Fig. 4, although Ni2+ had a larger qm. On the other hand, the dissociation constant (Kd) for Ni2+ was larger than that for Fe3+. However, Kd is the reciprocal of the affinity constant. It indicates that Fe3+ revealed stronger interaction with water bamboo husk particles than Ni2+, which could be attributed to their difference in charge number. Also shown in Fig. 5 is the extent of adsorption versus the equilibrium concentration. It is found that the adsorption percentage decreased drastically with the increasing concentration. Conclusively, water bamboo husk particles should be more suitable for the adsorption of lowconcentration heavy metal ions in water in order to attain higher removal efficiency.

Table 1 lists the batch desorption results. Prior to desorption, metal ions were loaded onto the water bamboo husk particles at the following conditions: c0 = 10 mg/L, pH 5, room temperature, contact time of 3 h. Two desorption solutions were tested: 0.1 M HNO3 (pH 1.8) and 0.01 M EDTA. The former condition is to make the water bamboo husk particles positively-charged by using a pH lower than pHzpc, following with the release of adsorbed metal ions. The latter is to employ chelators for catching and removing (through a shift in equilibrium) the metal ions from the particle surface. The volume of desorption solution was 50 mL, the same as the loading volume. As shown in Table 1, the optimal desorption condition was 0.1 M HNO3 with a contact time of 3 h. A diminished 1–10% desorption with a shorter contact time (1 h) was observed. Moreover, the desorption efficiency of Ni2 + was higher than Fe3+. This phenomenon is in good agreement with the batch adsorption results, namely Ni2+ had weaker interaction with water bamboo husk particles than Fe3+. In addition, the effect of desorption solution volume under the optimal condition was also investigated. With the volume decreasing from 50 mL to 30 mL and 10 mL, the metal ion desorption percentage was reduced from 99% to 74% and 34% for Ni2+, and from 92% to 65% and 25% for Fe3+, respectively. In most studies of heavy metal ion adsorption using biosorbents, a dilute strong acid (e.g. 0.05–0.1 M HCl and 1–2 M HNO3) was chosen as the desorption solution and the related desorption efficiency was high [2,10,13,22]. In the investigation employing gooseberry fruit for Cu2+ sorption [2], other desorption solutions such as NaCl, Na2SO4, CH3COOH, and EDTA were also tested. However, 0.1 M HCl still achieved the best desorption performance (N 80%). Salts, the weak acid, and the chelating agent were not effective. Furthermore, the desorption solution volume and contact time in most studies are usually identical to the values for adsorption stage [2,13,22]. In the work of adopting papaya wood biosorbent for Cu2+, Cd2+, and Zn2+ sorption [13], shortening the contact time to one half caused a 20% decrease in desorption. The desorption results obtained in this study are very similar to the findings of the above references. 3.4. Breakthrough curves Fig. 6 illustrates the breakthrough curves of Ni2+ and Fe3+ at a short column bed of 1.1 mL volume. The flow rate was 1 mL/min and the feed metal ion concentration was 10 mg/L. When the breakthrough point was determined as c/c0 = 0.1 (the effluent metal ion concentration attained one-tenth of the feed concentration), the related breakthrough volumes were 75 bed volume for Ni2+ and 90 bed volume for Fe3+, respectively. The dynamic adsorption performance of Fe3+ at a low feed concentration was better than Ni2+, which agrees well with the batch results in Figs. 4 and 5. In the study using Ponkan peel as adsorbent [12], the maximum adsorption capacity for Ni2 + was 1.92 mmol/g and the associated breakthrough volume was 110 bed volume (1 bed volume = 5 mL and flow rate = 3.5 mL/min). The Ni2+ breakthrough performance of the water bamboo particles prepared in this study was comparable to that of Ponkan peel biosorbent. Comparing to the static adsorption capacities in Fig. 5, the dynamic capacities of metal ions obtained at breakthrough points in Fig. 6 are 2 fold (for Fe3 +) or 3 fold (for Ni2 +) higher. This phenomenon may be attributed to the mass transfer effect in packed-bed process which forced the metal ions to flow through the intraparticle mesopores and Table 1 Batch desorption results of Ni2+ and Fe3+ using different desorption conditions. Ni2+

0.1 M HNO3 0.01 M EDTA

Fe3+

1h

3h

1h

3h

92.9 ± 0.6% 92.3 ± 0.7%

99.2 ± 0.5% 93.1 ± 0.2%

86.2 ± 1.2% 61.2 ± 1.1%

91.8 ± 1.8% 72.1 ± 1.1%

H.B. Asberry et al. / Microchemical Journal 113 (2014) 59–63

2+

3+

Ni

1.0

Fe

c/c0

0.8 0.6 0.4 0.2 0.0

0

50

100

150

200

250

300

bed volume Fig. 6. Breakthrough curves for Ni2+ and Fe3+ adsorption onto the packed bed of water bamboo husk particles, 1 bed volume = 1.1 mL, particle amount = 250 mg, c0 = 10 mg/L, pH 5, flow rate = 1 mL/min.

reach the binding sites more readily. Consequently, the utilization percentage of the binding sites of water bamboo husk particles was effectively raised by column processes. 4. Conclusions This study has demonstrated the potential of water bamboo husk as biosorbent for removing heavy metal ions from water. Water bamboo husk is easy to obtain in warm areas, especially in Asia, and free of expense. The related sorbent preparation from this agricultural waste is simple. In the current study, seven studied metal ions showed affinity to the prepared water bamboo husk biosorbent, with Cu2 +, Cr3 +, Pb2+, and Fe3+ having the strongest binding. Metal ions having a higher affinity to the sorbent (such as Fe3+) were trapped more efficiently at low feed concentrations. The adsorbed metal ions could be efficiently desorbed by a dilute strong acid solution. Moreover, water bamboo husk particles exhibited a greater metal ion capacity (2 to 3 fold) in a flow-through column process than a static setup. Based on these findings, it is reasonable to suggest that water bamboo husk is a biosorbent suitable for metal ion trapping and may be further applied in solid phase extraction or other adsorption applications. Acknowledgments This work was sponsored by the Ministry of Education of Taiwan (ATU plan) and the US National Science Foundation (NSF OISE0936693).

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