J Polym Environ (2010) 18:523–531 DOI 10.1007/s10924-010-0216-x
ORIGINAL PAPER
Chemically Modified Banana Fiber: Structure, Dielectrical Properties and Biodegradability A. C. H. Barreto • M. M. Costa • A. S. B. Sombra D. S. Rosa • R. F. Nascimento • S. E. Mazzetto • P. B. A. Fechine
•
Published online: 9 June 2010 Ó Springer Science+Business Media, LLC 2010
Abstract Banana fibers, as well as other lignocellulosic fibers, are constituted of cellulose, hemicellulose, lignin, pectin, wax and water soluble components. The abundance of this fiber combined with the ease of its processing is an attractive feature, which makes it a valuable substitute for synthetic fibers that are potentially toxic. In this work, the structure characterization of the banana fiber modified by alkaline treatment was studied. Some important properties of this fiber changed due to some chemical treatments, such as the crystalline fraction, dielectric behavior, metal removal (governed by solution pH) and biodegradation. Our results showed that treated banana fiber is a low cost alternative for metal removal in aqueous industry effluents. Thus, for regions with low resources, the biosorbents are an A. C. H. Barreto S. E. Mazzetto P. B. A. Fechine Laborato´rio de Produtos e Tecnologia em Processos-LPT, Departamento de Quı´mica Orgaˆnica e Inorgaˆnica, Universidade Federal do Ceara´, Fortaleza, Brazil M. M. Costa Departamento de Fı´sica, Universidade Federal de Mato Grosso, Cuiaba´, MT, Brazil A. S. B. Sombra Laborato´rio de Telecomunicac¸o˜es e Cieˆncia e Engenharia dos Materiais-(LOCEM)-Departamento de Fı´sica, Universidade Federal do Ceara´, Fortaleza, Brazil D. S. Rosa Laborato´rio de Polı´meros Biodegrada´veis e Soluc¸o˜es Ambientais, Universidade de Sa˜o Francisco, Itatiba, SP CEP 13251-900, Brazil R. F. Nascimento P. B. A. Fechine (&) Departamento de Quı´mica Analı´tica e Fı´sico-Quı´mica, Universidade Federal do Ceara´-UFC, Campus do Pici, CP 12100, Fortaleza, CE CEP 60451-970, Brazil e-mail:
[email protected]
alternative to diminish the impact of pollution caused by local industries, besides being a biodegradable product. Keywords Banana fiber Impedance spectroscopy Structure Metal removal Biodegradability
Introduction The interest in using natural fibers has increased significantly in the last few years [1], especially because of its use as an agent of reinforcement and more recently as a heavy metals bioadsorbent. The abundance in nature combined with the ease of its processing is an attractive feature, which makes it an important substitute for synthetic fibers which are potentially toxic [2]. These lignocellulosic fibers possess many characteristics which make their use advantageous: low cost, low density, specific resistance, biological degradability, neutral CO2, renewability, good mechanical properties and non-toxic. Besides that, they can be easily modified by chemical agents [3]. The banana fiber is one of them. Banana is the common name for the fruit and also for the herbaceous plants of the genus Musa (Musa sepientum), which produce the commonly eaten fruit [4]. Symbol of tropical countries and known throughout the world, banana is one of the most popular fruits in Brazil. Due to favorable climate and nature, it is largely cultivated and can be found and acquired all along the year. There are more than 100 countries which produce bananas and Brazil is the largest one [5] after India and Ecuador. The macrocomponents which form the lignocellulosic fibers are cellulose, hemicellulose, lignin, pectin, wax and soluble substances, being the first three components responsible for the physical and mechanical proprieties of
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these fibers [6, 7]. The production of bananas generates a large amount of fibrous tissue by-product, since after removing the fruit, producers discard the pseudo-stem of the plant, leaving it in the soil so that they decompose naturally. This process creates several problems, amongst them the proliferation of fungi which causes diseases to bananas and the launching of methane (CH4) in the atmosphere, one of the gases responsible for the greenhouse effect. An important point is the extraction of fibers so that there is no damage to the nature: the trunk is removed from where it would be discarded and only the organic residues of the banana culture are used, which results in no ecological imbalances. The reuse of the by-product and low environmental impact procedures represent a sustainable alternative for new materials. A good example is the use of agro-industry residues as bioadsorbent for the restoration of industry effluents [8]. The literature shows excellent results concerning residues of carrots, peanut peels, rice, nuts, sugar cane bagasse, among others [9, 10]. The technology of effluents treatment starting from agro-industry residues has been used to help companies adapt to environmental laws in a way that their effluents are framed in the demanded patterns without aggression to the environment. The objective of this work was to carry out structure characterization of the banana fibers from the Northeast region of Brazil, modified by alkaline treatment. X-Ray Diffraction (XRD), Infrared Spectroscopy (IR), Thermogravimetric (TG) and Impedance Spectroscopy (IS) were employed. Additionally, it also studied the absorption capacity of heavy metals on the banana fiber surface and the biodegradability results. This simple adsorption process was performed to solve wastewater treatment problems by removal and recovery of metals from plating wastewater for possible recycling in the industry.
Experimental Procedure Mercerization A chemical treatment (mercerization) was carried out to partially remove the lignin, hemicelluloses and other residues from the surface of the fibers, roughening their surface. Banana fibers were treated with NaOH solutions (0.25, 0.5 and 1%) at temperature intervals of 60–70 °C, for 6 h. After this stage, the fibers were washed several times with distilled water to remove NaOH excess from the surface, until the water no longer indicated any alkalinity reaction. Subsequently, the fibers were dried at 60 °C for 24 h. The ones obtained after alkaline treatment were dipped in NaClO/H2O solution in the proportion of 1:1,
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under heating of 60 °C for 4 h. At this point, the fibers presented strong bleaching effect, being subsequently washed with distilled water until they were free from NaClO. Adsorption Analysis Standard solution of the metal ions Cu(NO3)26H2O, Zn(NO3)26H2O, Cd(NO3)26H2O, Pb(NO3)2 and Ni(NO3)2 6H2O (1000 mg L-1) from MERCK (Sa˜o Paulo, Brazil) were used for adsorption analysis. The ion concentrations were determined by atomic absorption spectrophotometry (AAS, GBC 933 plus model) in an air-acetylene flame. Structural Characterization of the Banana Fibers X-ray diffraction (XRD) patterns were obtained from banana fiber disks at room temperature (300 K) by continuous scanning mode on powder diffractometer Rigaku, model DMAXB. The samples were pulverized and their particles were compacted in a cylindrical mold into disc form (Ø 1.7 cm) and submitted to the pressure of 111 MPa. Cu-Ka tube was operated at 40 kV and 25 mA, using the Bragg–Bretano geometry with scan speed of 0.5°/min and step size of 0.02° (2h) in the angular range of 10°–30° (2h). The banana crystalline fraction (F) was obtained through separation and integration of crystalline and amorphous peak areas, under the X-ray diffraction peaks. The X-ray fluorescence (XRF) measurements were performed on disc form samples with wavelength-dispersive X-ray fluorescence spectroscopy (Rigaku ZSX Mini II), equipped with Pd anode X-ray tube and operated at 40 kV and 1.2 mA. The infrared measurements were performed using a Perkin Elmer 2000 spectrophotometer in the 400 to 4000 cm-1 range. The samples were previously dried and grounded to powder and pressed (10 lg of sample to 100 mg of KBr) in disk format for measurements. The thermal stability of the fibers was evaluated by thermogravimetric analysis (TGA). The decomposition analysis was performed under either nitrogen and air atmospheres in a constant flow of 60 cm3.min-1, with the heating rate of 10 °C/min and mass weight of 10 mg. Dynamic experiments using equipment Shimadzu Thermogravimetric Analyser TGA 50H, AC115V were carried out with temperature programs from 30 to 600 °C. The morphological characterization of the banana fibers was done by Scanning Electron Microscopy (SEM). This technique was applied to observe the surface morphology and to make a microstructure analysis of both natural and chemically treated forms. The micrographs were obtained by the electronic microscope model DSM 960/Zeiss, with 20 kV electron beam. The samples were coated with Au by
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‘‘sputter counter’’, with argon plasma model BALZERS 5CD50. Impedance Spectroscopy The fiber disks were used to obtain the dielectrical measurements in an impedance analyzer Solatron model SI 1260 equipped with an accessory (Sample Holder-1296A), to detect the ac dielectric behavior at room temperature (25 °C). The real (e0 ) and imaginary (e00 ) parts of relative permittivity and dielectric loss factor (tgd = e00 /e0 ) were measured. All the samples were kept under vacuum before the measurements. It covered the region of 10 Hz to 700 kHz at room temperature. The experimental error of the impedance spectroscopy was approximately 10-3 at the analyzed frequency. For experiments to study the dielectric properties as a function of the measurement temperature, it was necessary to have a capacitor of the fibers (disks), which was obtained by the silver electrode (Joint Metal-PC200) being deposited by painting technique as a bottom and upper electrode. Subsequently, copper leads were fixed on the surfaces using silver paste and the disks were dried for 48 h at room temperature. The experiment was performed using the same device, equipped with a mini oven to detect ac dielectric behavior as a function of the temperature. The temperature was tuned from 30 to 90 °C with a stability of 0.1 °C in air. In order to study the frequency and temperature dependence of the interfacial polarization effect, which generates electric charge accumulation around the fiber, displacing relaxation peaks, electrical modulus (M) were used: M ¼ 1=½e0 j e00 ¼ M0 þ jM00
ð1Þ
Metal Adsorption The experiment for estimating the adsorption capacity of the treated and not treated adsorbent material was realized in duplicate utilizing erlenmeyers of 100 mL containing 0.3 g of the material in 15 mL of synthetic multielementary solution (Pb?2, Ni?2, Cd?2, Zn?2 and Cu?2), with concentration of 100 mg/L at pH 5.0 and kept in agitation at room temperature (28 ± 2 °C) during 24 h. The adsorption capacity of the adsorbent, Q (mg of the metal/g of adsorbent), was determined based on the difference of concentration of the metal ions used in the equation: QW ¼ VðCo Ce Þ
ð2Þ
Where Q is the capacity of adsorption (mg/g), Co and Ce are the concentration (mg/L) of the solute in the initial solution and in equilibrium respectively, V is the volume of the solution (L) and W is the mass of the adsorbent (g).
The determination of the metal ions concentration before and after adsorption was carried out with a spectrophotometer of atomic absorption (AAS, GBC 933 plus model). Biodegradability The specimens were weighed and buried in simulated soil at room temperature (24 °C). The simulated soil consisted of 23% of loamy silt, 23% of organic matter (cow manure), 23% of sand and 31% of distilled water (all w/w). Biodegradation was monitored for 150 days by measuring the mass retention. The buried specimens were recovered, washed with distilled water and dried at room temperature until there was no further variation in weight, after which they were then weighed. The experiments were done in triplicate.
Results and Discussion Structure Characterization NaOH 0.25, 0.5 and 1% chemically treated banana fiber, as well as raw state banana fiber, were analyzed by XRD to obtain information about their crystalline fraction. As an instance, Fig. 1 shows the XRD patterns for NaOH 1% treated banana fiber. The points in the diffractogram indicate the values obtained by the experiment, which we can compare with the calculated values (continuous curve). One can also observe the deconvoluted peaks used to obtain the calculated profile. Three peaks (continuous curve) are presented in the directions of 15.2°, 16.5° and 22.4°. They assign the cellulose standard profile from ICDD [11], see Fig. 1. Ouajai and Shanks [12] observed these same directions in hemp fiber and labeled them as 101, 101 and 002 diffraction planes from cellulose crystalline phase. Besides this phase, there was an amorphous phase (a broad dot straight) characterized mainly as lignin. This polymer is associated to the cellular wall, conferring mechanical strength to the fiber, and when its concentration increases, the crystalline fraction decreases. For Banana 1% it was found 73.9% of the crystalline fraction, while for raw banana it was found 63.5%. This difference was due to the lignin be partially removed in alkaline solution, i. e., the banana fiber lost part of its amorphous component. Additionally, there were intermittent highly ordered areas among the cellulose molecules in the elementary fibril, the so-called crystalline regions, separated by less ordered or amorphous regions [13]. The diffractograms for the raw fiber, Banana 0.25% and Banana 0.5% were omitted due to the similarity in the profiles. The two last presented 79.2% and 64.4% of the crystalline fraction, respectively.
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Fig. 2 Infrared spectroscopy of banana fibers: a raw, b treated with NaOH 0.25%, c treated with NaOH 0.5% and d treated with NaOH 1% Fig. 1 XRD of the banana 1% showing the crystalline and amorphous phases obtained by deconvoluted in comparison to data from ICDD
The IR spectra of the raw and the modified banana fibers are shown in Fig. 2. It can be observed that the components of biomass are most likely consisted of alkenes, esters, aromatics, ketenes and alcohol, with different oxygen-containing functional groups [14]. The main spectrum of the raw fiber exhibited O–H stretching absorption of around 3430 cm-1, C–H stretching absorption of around 2920 cm-1, C=C benzene stretching ring of around 1635 cm-1 and C–O–C stretching absorption of around 1058 cm-1. These absorptions are characteristic of lignocellulosic fiber. The vibrational modes after chemical treatment did not suffer significant changes and the main bands appeared approximately in the same range of wave numbers. The TG/DTG curves presented a slight modification in thermal stability by lowering the fiber degradation temperature. This occurred due to the surface macrocomponents be removed after the chemical treatment, as shown in Fig. 3. The first peak below 100 °C corresponds to moisture evaporation [15]. Some studies [16–18] showed that
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there are three forms of water absorbed on cellulosic materials due to the fact that cellulose is a hydrophilic fiber. They are non-freezing bound water, freezing bound water (producing an own glass transition) and free water. The major event on the fiber degradation during the TG experiments, under nitrogen atmosphere, occurred in the range of 230–400 °C for raw and treated fiber. These events were attributed to the degradation of a-cellulose and hemicellulose. There were no sudden changes as a function of the chemical treatment, agreeing with the results of IR spectra. The last event occurred in the range of 450–500 °C and it was attributed to lignin decomposition and ultimate degradation of the sample. Yang et al. [14] reported that lignin is a macrocomponent difficult to decompose. Figure 4a is relative to the raw fiber and shows the SEM morphology at an amplification of 5009. One can notice a regular structure with discrete net fibrils, where the presence of hemicelluloses, lignin, and wax contributes to a homogeneous morphology of the natural composite. For comparison, Fig. 4b shows the micrograph of the banana treated with NaOH 1% at the same amplification factor of the raw banana. After alkaline treatment, the soluble
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Fig. 4 SEM (Scanning Electron Microscopy) of raw banana fiber a before and b after alkali treatment (NaOH 1%) at an amplification of 5009 Fig. 3 Thermal analysis of the raw banana fiber and the fiber treated with different alkaline solution
components (hemicelluloses, lignin, and wax) were partially removed, resulting in the exhibition of the banana fibrils. Some cavities also appeared due to modifications on the surface. This effect increases the superficial area of the banana fiber and can contribute to improve its metal adsorption capacity. Consequently, the banana fiber can be used as an efficient natural material to remove toxic metal ions from electroplating industry wastewater. The 3.3 section illustrates these aspects. Impedance Spectroscopy Characterization Figure 5 shows the real part (e0 ) of the dielectric permittivity and tgd of the samples. It was not detected dielectric relaxation process in this frequency range for dielectric permittivity measurements. The rise of the alkaline solution concentration, used for chemical treatment of the banana fiber, caused an increase of the e0 values. It was obtained 5.49 for e0 at 10 Hz to raw state fiber, whereas this value reached 12.59 to fiber treated with NaOH 1%, for instance. It happened due to partial removal of the amorphous components, which possess e0 values lower than cellulose crystalline phase. The tgd values also increased
with chemical treatment used in the fibers. However, e0 and tgd reached minor values with increase of the frequency and they were kept rather constant after 1 kHz. The imaginary (M00 ) and real (M0 ) parts of module as a function of the frequency were measured at room temperature. Figure 6 shows these features, where the peaks in M00 values happened approximately in the same frequency range, indicating the appearance of a dielectric relaxation process. For the M00 behavior, this process was more intense for banana fiber treated with NaOH 0.5% and NaOH 1% than that with NaOH 0.25% and in its raw state. Note that an opposite behavior happened for M0 , where fiber in raw state had higher values than other samples. The relaxation process behavior was studied as a function of the measurement temperature. In Fig. 7, one can observe this process from 30 °C until 90 °C for banana fiber treated with NaOH 0.25%. It was noticed that measurements from 30 to 60 °C did not present significant changes in the frequency of relaxation, i.e., this process was not thermally activated. However, up to 60° it was seen that the relaxation peaks were displaced at shorter frequencies due to moisture evaporation. This weight loss process below 100 °C was commented in thermal analyses results, see also Fig. 3. Einfeldt et al. [19, 20] studied polysaccharides in dielectric relaxation process. They analyzed the imaginary (e00 ) and real (e0 ) parts of dielectric
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0
Fig. 5 Dielectric permittivity (er ) and loss tangent (tgd) of the raw banana fiber and the fiber treated with different alkaline solution
permittivity as a function of the frequency, and it was observed an increase of stabilization effect for wet cellulose when compared to dried fibers. In our case, we also observed relaxation peaks due to cellulose presence in the banana fiber, where water molecules are bond to the hydrophilic groups of the anhydroglucose, resulting in an increase of the dipolar moment of the side groups and affecting the polymer main chain dynamics. Furthermore, water can also produce an additional relaxation process [21] in addition to the pure polymer relaxation. This effect could have contributed to the broadening of the peaks, mainly at 30 °C. Metal Adsorption Unfortunately, there are many places contaminated by toxic heavy metals discharged of industrial wastewater. This is a serious environmental problem. The presence of metals in water streams and marine water is a significant health threat to aquatic communities. Due to this, a large number of researches have been developed to test low cost
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Fig. 6 Real (M0 ) and imaginary (M00 ) parts of module as a function of the frequency for raw banana fiber and fiber treated with NaOH 0.25 and 1%
adsorbents for metal ion removal [22–27]. Thus, we carried out a preliminary study on metal removal from a multielementar solution using banana fiber. The results of metal removal for all the treated adsorbents are given in Table 1. It was noted that banana fiber treated with NaOH is more efficient than raw banana fiber in the metal removal from aqueous solution (100 mg/L metal ion at pH 5). However, the treatment with NaOH 0.25% was chosen due to better results. Based on these results, the experiments of pH effect on metal adsorption were carried out using banana fiber. The metal ions were investigated due to their discharge in electroplating industry wastewater. In this study, the metal removal by banana fibers followed the order Pb2? [ Cu2? [ Zn2? [ Cd2?[ Ni2?. Ni2? ions have the lower adsorption, probably due to its minor ionic radius [22], in contrast with Pb2?, which has the biggest ionic radius. The X-ray fluorescence (XRF) measurements were performed to obtain information about metal ions present on fiber surface treated with NaOH 0.25% before and after metals adsorption, and the results are shown in Table 1. It
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529 Table 2 Weight percent obtained by XRF of the ions in the raw banana and banana treated with NaOH 0.25% in different pH of the multielementar solution wt% Adsorption on fiber treated Metal ions
Raw fiber
pH 1
pH 3
pH 5
pH 7
pH 9
Ca
65.18
14.88
12.55
13.97
18.13
21.05
Si4?
17.53
7.40
3.47
2.26
2.91
3.48
3?
Fe
6.80
Cl-
4.25
Al3?
3.25
–
1.47
K?
2.96
5.28
2.17
Pb2?
–
3.65
20.82
22.74
Cu2?
–
2.06
22.47
21.91
14.93
11.89
Ni2?
–
2.98
6.95
7.64
15.45
16.55
Cd2? Zn2?
– –
– 2.04
3.78 7.11
3.73 7.67
3.69 15.18
3.59 11.10
2?
Fig. 7 Real (M0 ) and imaginary (M00 ) parts of module as a function of the frequency, from 30 °C until 90 °C, for banana fiber treated with NaOH 0.25%
Table 1 Metal removal for the raw banana fibers and for fibers treated with alkaline solution Fibers
Metal removal (%) Pb2?
Cu2?
Ni2?
Cd2?
Zn2?
Raw state
88.62
85.27
41.63
85.13
82.61
NaOH 0.25%
97.54
96.31
76.23
86.64
91.27
NaOH 0.5%
98.71
96.89
–
76.26
84.73
NaOH 1.0%
98.41
97.66
–
83.33
87.66
was utilized the semi-quantitative XRF analysis, where the weight percent of the metal ions were measured as a function of the pH (see Table 2). Thus, raw fiber only presented Ca2?, Si4?, Fe3?, Cl-, Al3? and K? before chemical treatment, and it can be noted that Ca2? (65.18%) and Si4? (17.53%) ions are a majority. One can observe that none of the ions investigated was found for banana fiber in raw state. It was also measured the weight percent of these metal ions on treated fiber after adsorption process at different pH. At pH ranged from 1 to 9, it was observed
– 61.67
– 19.16
0.68
0.58
0.53
16.62
11.17
14.70
–
1.19
1.32
–
2.32
3.00
14.38
12.16
that the weight percent of Ca2? varied from 14.88 to 21.05 and for Si4? it varied from 7.40 to 3.48. For all metal ions investigated (Pb2?, Cu2?, Zn2?, Cd2? and Ni2?) it can also be observed a change of the total ions composition at different pH values, indicating a competition effect between metal ions from multielementar solution and ions present in the raw fiber surface, in special at Pb and Cu ions at pH 3 and 5, as shown in Table 2. At low pH, the surface of the fiber remains associated with H3O? ions and in this condition the metal removal decreased. This mechanism happens due to competition between H3O? and other metallic ions by active sites present in the fibers [23–26]. Therefore, at high pH values (\9), the surface of the adsorbent has a higher negative charge, which results in an increased removal of metal ions. These data are in agreement with the results obtained for other materials of low cost, such as coffee residues [28], orange waste [29], coca shells [30], sago waste [31] and saw dust [32, 33]). On the other hand, at very high pH values ([9), metal hydroxide precipitation can occur and, therefore, the removal may not be due to adsorption [32, 34]. Hence, adsorption of Pb2?, Cu2?, Ni2?, Cd2? and Zn2? onto banana fiber is at optimum in the pH range of 3 to 7. In this way, the semi-quantitative XRF analysis was important to show the results without the interference of the metal ions hydrolyzed. Study of the Biodegradation Since the banana fiber is a lignocellulosic fiber, its biodegradation is dependent on environmental conditions and the degradative capacity of the microbial population [35]. Hemicellulose is the fiber’s most accessible component to
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biodegradation, followed by non-crystalline cellulose. Cellulose chains present in crystalline regions interact by intense hydrogen bonds, which considerably modify their biodegradation behavior, when compared to that of chains in non-crystalline regions. The heterogeneity of the chemical bonds in the cross-linked structure of lignin, as well as their aromatic character, is the main obstacle to its biodegradation [35, 36]. Figure 8 shows the result of the fibers (non-treated and treated with alkaline solution) biodegradability exposure to microorganisms in simulated soil during 90 days. All fibers reduced the mass amount until reaching the last day. However, raw banana fiber was more resistant to the action of microorganisms in simulated soil. This happened due to a major presence of the lignin and other compounds, which caused a higher protection of the fibrils. In the plant tissue, lignin functions as a preservative and as a cement between fibers: when associated with hemicellulose, lignin matrix embraces the cellulosic microfibrils to form a protection sheath against foreign microorganisms. As it was commented before, the partial removal of these macrocompounds, as a function of the alkaline treatment, could change the banana fiber features. One can see this behavior in Fig. 8, where there is a decrease of retained mass of the fibers due to an increase of the alkali concentration utilized in the treatment. This loss of weight (microbial biodegradation) was caused by enzymes produced by microbial population in the simulated soil, where the banana fiber treated with NaOH 1% solution was more affected than others. This happened due to an increase of the superficial area (exposition of the cellulosic chains to the enzymes produced by microorganisms) of the banana fiber. Linkages involving heteroatom, such as cellulose and hemicelluloses, are considered susceptible to enzymatic
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degradations. Hemicellulose can be considered as the fiber’s most vulnerable component to biodegradation, because it is located in the non-crystalline domains [37].
Conclusions It was observed by XRD that chemical treatment with NaOH increased the crystalline fraction of the banana fiber, due to partial removal of the lignin (amorphous phase). The vibrational modes obtained by IR spectroscopy did not suffer significant changes after this alkaline process and the main bands appeared approximately in the same range wave number. The dielectric permittivity and the loss factor are dependent on the alkaline solution concentration. It was obtained 12.59 for dielectric permittivity at 10 Hz with the major concentration. The values for the dielectric loss were approximately between 10-1 and 10-2 depending on the sample. These values are reasonable and could also be utilized as an electronic device in conjunction with other materials to do a composite phase. The dielectric relaxation processes observed by the electrical modulus were dependent on the temperature measurements and related to water molecules present in hydrophilic groups of the anhydroglucose. The chemical treatment employed in this work contributed to increase the metal removal, and the values were governed by solution pH. The results showed that treated banana fiber is a low cost alternative for metal removal in aqueous industry effluents. Thus, for regions with low resources, the biosorbents are an alternative to diminish the impact of the pollution caused by local industries, besides being a biodegradable product. Acknowledgements This work was partly sponsored by CAPES and CNPq (Brazilian agencies). Our special thanks to L. A. R. Fechine for the language revision of this paper.
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Fig. 8 Retained mass (%) after exposure time to simulated soil at room temperature for raw fiber and fiber treated with NaOH 0.25, 0.5 and 1%, respectively
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