Immobilization of S. duplicatum supported silica gel matrix and its application on adsorption – desorption of Cu (II), Cd (II) and Pb (II) ions
Suharso
a,⁎ , Buhani
a, Sumadi
baDepartment of Chemistry, Faculty of Mathematic and Natural Sciences, University of Lampung, Indonesia
bDepartment of Electrical Engineering, Faculty of Engineering, University of Lampung, Indonesia
a b s t r a c t a r t i c l e i n f o
Article history:
Received 18 March 2010
Received in revised form 31 May 2010 Accepted 18 June 2010
Available online 10 July 2010 Keywords:
Adsorption–desorption Continuous method S. duplicatum Immobilization
It has been carried out a research adsorption–desorption of metal ion Cu (II), Cd (II) and Pb (II) onSargassum duplicatum(S. duplicatum) biomass immobilized by silica gel with a continuous method using a set of adsorption equipment controlled automatically. From the optimum result of this equipment, it has been obtained that an average offlow rates Cu (II), Cd (II) and Pb (II) ions byS. duplicatumbiomass immobilized by silica gel is 1.3 mL min−1. Adsorption process of metal ions Cu (II), Cd (II) and Pb (II) onS. duplicatum biomass immobilized by silica gel is optimum at pH of 5.0 with the adsorption capacities of 280.112, 130.513 and 113.660μmol g−1respectively. On the competition adsorption, the Cu (II) ion is more adsorbed on S. duplicatumimmobilized by silica gel with the adsorption selectivity coefficient (α)N1. The uses of 2.0 mmol L−1HCl as eluent of Cu (II), Cd (II) and Pb (II) ions adsorbed onS. duplicatumimmobilized by silica gel resulted recovery percent (%) are 98.63 ± 0.56, 84.79 ± 0.40 and 70.11 ± 0.17, respectively.
Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction
The contamination of heavy metals in the environment as a serious problem has been increasing continuously as a result of industrial activities and technological development, posing a significant threat to the environment and public health because of their toxicity, accumulation in the food chain and persistence nature[1–3]. Several heavy metals from industrial waste water such as Cu, Cd, and Pb cannot be degraded biologically and chemically[4–6]. Some of the methods have been developed to reduce the heavy metal ion concentration from waste water such as chemical precipitation, ion exchange, evaporation, electroplating and membrane processes.
However, these methods are either inefficient or expensive when heavy metals exist in low concentrations[7,8]. One of the alternative techniques is an adsorption method using biological materials as adsorbent, mainly because of its low cost, high metal binding capacity, high efficiency in dilute effluent and environmental friendly[9–11].
The key success of the adsorption process is determined by the adsorbent selectivity used. Several kinds of the adsorbent used are specific and nonspecific solid adsorbent (active carbon, silica, clays, zeolite, and cation exchange resin). The nonspecific solid adsorbent has a problem such as low capacity adsorption, low selectivity, long equilibrium times, and unstable mechanically and thermally[12].
Recently, it has been more developed specific adsorbent containing specific ligand interacting with metal ions derived from modification of
supporting solid as inorganic material (like silica) or a polymer. The silica gel is the ideal supporting solid material because of its stability at acid conditions and nonswelling. It has also high mass selectivity, porosity, and surface area, and endurance at high temperature. In addition, it has active sites as a silanol group (≡SiOH) and siloxane (≡Si―O―Si≡) on its surface[13,14].
The weakness of the utility of silica gel as the adsorbent is low adsorption effectiveness through metal ions, caused by low oxygen ability (silanol and siloxane) as electron pair donor, resulting low metal ionic bounding on silica surface. The low oxygen ability as donor is a consequence of oxygen bounded directly in Si atom in the silica structure. Therefore, it is urgent to immobilize specific active group on the surface of silica gel. The modification of silica gel surface can be done with immobilizing organic functional group which is able to as complex of heavy metal ions derived from natural product such as algae biomass and fungi or synthesis organic compound containing active sites rolling as a ligand upon metal ions.
Algae biomass from several algae species is effective to bind metal ions from water environment[15]. These are caused because algae biomass contains several functional groups which are able to role as a ligand of metal ions. As reported from previous research result, the interaction ofS. fluitansamong Fe (II) and Fe (III) ions occurs via complex formation between metal ions and carboxyl group as well as sulphonate group from biomass[16]. However, biosorption process of metal ion Cd (II) onSargassumbiomass followed with protonation of hydrogen ion from its biomass[17]. In addition, FTIR spectrum on green algae biomass (Spirogyra) showed the existence of amino, carboxyl, hydroxyl, and carbonyl groups which were responsible for biosorption of metal ions [11]. Other research revealed that
⁎ Corresponding author.
E-mail addresses:[email protected],[email protected](Suharso).
0011-9164/$–see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.desal.2010.06.037
Contents lists available atScienceDirect
Desalination
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / d e s a l
sulphonate group onS.fluitansbiomass gave contribution on complex formation between biomass and metal ion[18].
Sargassum duplicatumbiomass has high ability to bind metal ions (batch method), but it has low density, degradable biologically and chemically as well as ineffective to be used as columnfilling material to adsorb continuously[19]. The immobilization of algae biomass with silica gel supporting matrix can increase the quality of the adsorbent to be used as columnfilling material in the continuous adsorption process. This technique can also increase the chemical stability and adsorption capacity through metal ions.
In this research, it has been carried out the immobilization ofS.
duplicatumalgae biomass using silica gel matrix and it was applied to the adsorption instrument controlled automatically. The adsorbent of the immobilization result was used as the adsorption columnfilling material to determine the adsorption effectiveness of metal ions Cu (II), Cd (II), and Pb (II) in the laboratory scale for its application of adsorption–desorption process.
2. Materials and methods 2.1. Materials
All reagents in analytical grade i.e. Na2SiO3, Cu(NO3)2, Pb(NO3)2, Cd(NO3)2, H2SO4, CH3COONa, CH3COOH, HCl, and NaOH were obtained from Merck Co. Inc. (Germany). Adsorbent: Algae biomass was collected from Lampung Sea Cultivation Bureau (Balai Budidaya Laut Lampung), Indonesia. It was washed with distilled water to remove dirt and was kept on a filter paper to reduce the water content. More, the biomass was sun dried for 3 days followed by drying in an oven at 60 °C for 12 h and then ground on an agate stone pistol mortar. Furthermore, the biomass was sieved to select the particles between 100 and 200 mesh sizes for use.
2.2. Equipment
Measurements of pH were made using a pH meter (Orion 4 Star).
The metal solution was analyzed using an atomic absorption spectrophotometer (AAS) model PerkinElmer 3110. The TJeol-T330A was used for a scanning electron microscopy (SEM). BET surface area was measured using a gas sorption analyzer NOVA 1000 version 2.00.
Infrared spectra of the adsorbent were recorded on an IR Prestige-21 (Shimadzu).
2.3. Immobilization of algae biomass
Specific algae biomass powder with specific sizes (0.03–1.00 g) was mixed with H2SO43 M. Then, the mixture was added Na-silicate solution 1:1 up to gel formation for 1 h. The formed gel was left for one night. Then, it was washed with water up to pH neutral. The gel was dried in oven (80 °C) for 2 h. The dried gel was ground and sieved with a sieve of 200 meshes.
2.4. Adsorption–desorption procedure
The adsorption process was carried out by continuous method using an adsorption column controlled automatically using a programmable logic control (PLC)[20]. The adsorption column was plugged with a small portion of glass wool at both ends. Before used, the column was treated by HCl 0.5 mol L−1and washed by double distilled water until free from acid. The metal ion solution with the concentration of 100 mg L−1wasflowed in column which wasfilled by 1.0 g adsorbent with variety offlow rates 1.0–3.5 mL min−1 at 27 °C to investigate an optimumflow rate.
Adsorption pH was determined byflowing 100 mg L−1of metal ion (Cu (II) or Cd (II) or Pb (II)) in adsorption column at the optimum flow rate with various pHs of 3–8. The experiments of single-metal
adsorption were performed byflowing metal ion solution at various concentrations of 0.0–400.0 mg L−1into the adsorption columnfilled 1.0 g adsorbent at the optimum offlow rate and pH. The adsorption competition experiments were performed by flowing 100 mL of multi-metal solution of Cu (II), Cd (II) and Pb (II) with the concentration of 0.5 mmol L−1 into the adsorption column filled 1.0 g adsorbent at the optimum conditions from the single-metal adsorption experiments. Desorption experiments were carried out with eluting the metal ions onS. duplicatumadsorbent immobilized by silica gel using 100 mL of water and 0.1 M HCl. The metal ions obtained from adsorption and desorption results were analyzed by AAS.
The adsorption capacity, the distribution ratio, and the selectivity coefficient were calculated using the following equations:
%Adsorption=ðCe=CoÞ× 100; Q=ðCo−CeÞV=W; D
=Q=Ce; αM1=M2=DCd=DM;
where Q represent the adsorption capacity (mg g−1), Co and Ce
represent the initial and equilibrium concentrations of metal ions (mmol L−1),Wis the mass of adsorbent (g),Vis the volume of metal ion solution (L),Dis the distribution ratio (L g−1),αis the selectivity coefficient.
3. Results and discussion 3.1. Characterization of adsorbent
The infrared spectroscopy (Fig. 1) presents a useful initial detection with the success of immobilization process. This proposal can be clarified by comparing the precursor and modified surface. The broad symmetric stretching mode assigned to Si―O―Si appeared at 1087.85 cm−1. The spectrum relating to the matrix silica shows a band at 964.41 cm−1 identified as terminal Si―OH deformation groups on silica surface and another band associated with Si―O is located at 470.63 cm−1. For three adsorbents of immobilized biomass algae with sodium silica, the spectra can be characterized for a partial loss of Si―OH deformation mode originally presented at 964.41 cm−1, and also for the appearance of new band at 2924.09 and 2854.65 cm−1 ascribed to stretching vibration modes of CH groups derived fromS. duplicatumbiomass[21].
The determination of the specific surface area (SBET) is based on the adsorption on gaseous nitrogen at several pressures and at 77.40 K. The precursor silica gives a value of 199.800 m2g−1, while the S. duplicatumbiomass immobilized on silica gel is 121.192 m2g−1. Decreasing the surface area after immobilization is due to the presence of pendant groups, which blocks the access of molecules of gaseous nitrogen into the structure of the silica[12,22]. The scanning electron micrograph clearly revealed the surface texture and morphology of the adsorbent (Fig. 2). The microscopy showed that silica biosorbent is heterogeneous porous materials by a silica matrix with inclusions ofS. duplicatumbiomass.
3.2. Effect offlow rates
Theflow rates of Cu (II), Pb (II) and Cd (II) ion solution in adsorption column are important parameter to control the adsorption times and the adsorption result analysis because the retention elements on the adsorbent depend on theflow rates of the sample solution.
The effect of the adsorptionflow rates of Cu (II), Cd (II) and Pb (II) on metal ion capacity adsorbed onS. duplicatumbiomass immobilized by silica gel was studied with investigatingflow rate changes of 1.0– 3.5 mL min−1. The initial concentration of metal ion and the amount of adsorbent in column are 100 mg L−1and 1.0 g. FromFig. 3, it can be seen that the adsorption of Cu (II), Cd (II) and Pb (II) ion reduces while the flow rates increase. At the flow rate of 3.5 mL min−1, the
adsorption of metal ions is the lowest because the interaction time between metal ion and the adsorbent in column is shorter[23,24], causing the lack of effective of the interaction between metal ions and adsorbent. The optimum flow rate is at 1.3 mL min−1, at this condition theflow rate is not too slow with the amount of maximum adsorbed metal.
3.3. Effect of pH
The effect of pH on Cu (II), Cd (II), and Pb (II) ion retention byS.
duplicatumbiomass immobilized was studied using the adsorption
column. 100 mL of Cu (II), Cd (II), and Pb (II) ion solution with each of the concentration of 100 mg L−1wasflowed into the adsorption column at theflow rate of 1.3 mL min−1, at 27 °C and at various pHs of 3–8.Fig. 4shows that generally, adsorption of metal ions Cu (II), Cd (II), and Pb (II) has a relative of the same model as increasing adsorption from pH of 3 to around 5 (optimum) and decreasing adsorption at above of pH 6. The sorption metal ion depends on solution pH, which influences interaction of ions to corresponding functional groups. On theS. duplicatumadsorbent immobilized silica gel exists functional group of –COOH as a main formation of polysaccharide and peptide group (–CO, NH2, and CONH2) as a Fig. 1.Infrared spectrum of (a) silica adsorbent from Na2SiO3, (b)S. duplicatumbiomass, and (c) the result of immobilization betweenS. duplicatumbiomass and silica gel.
formation of pectin and protein derived from biomass and –OH group from silica gel as an electron pair donor upon metal ions. The interaction of the adsorbent with the metals ion was determined by the extent of protonation of functional groups, which in turn depended on the solution pH. With increasing pH, these groups deprotonated and thus formed negatively charged sites[6]. At pH
values higher than 6.0, Pb (II), Cu (II) and Cd (II) ions precipitated out because of high concentration of OH ions in the adsorption medium[20,25,26].
3.4. Single-metal adsorption
Adsorption of Cu (II), Cd (II) and Pb (II) ion from solution on S. duplicatumbiomass immobilized on silica gel was investigated with using adsorption column. FromFig. 5, it can be seen that the adsorption of metal ions increases while the concentration of metal ions increases. The adsorption of metal ions runs slowly andfinally the adsorption of metal ions stops while equilibrium has been reached (the adsorbent is so full of metal ions bonded). Based on the recommendation of batch procedure that was performed in determining the adsorption capacity using Langmuir Equation[19], the average of adsorption capacities for Cu (II), Cd (II) and Pb (II) ion on theS. duplicatumbiomass immobilized on silica gel using the column method are 280.11, 130.51 and 113.66μmol g−1adsor- bent for 3 times of measurement, respectively. From these data, it can be known that the adsorption capacity of the Cu (II) ion is highest among Cd (II) and Pb (II) ion. The Cu (II) ion has smallest ionic size among Cd (II) and Pb (II) ion (rCu (II) = 87, Cd (II) = 109, and Pb (II) = 133 pm)[27]. These cases cause that Cu (II) ion exist in aquo complex formation [M(H2O)6]2+ which has the highest mobility among Cd (II) and Pb (II) ion in the solution[28], so it is more adsorbed onS. duplicatumbiomass immobilized on silica gel.
Fig. 2.SEM images of (a) silica adsorbent from Na2Si2O3; and (b) the result of immobilization ofS. duplicatumbiomass.
Fig. 3.The effect of the solutionflow rates on the adsorption of Cu (II), Cd (II) and Pb (II) ions with the conditions: 1.0 g of the adsorbent; 100 mg L−1of metal ions; the total flow time of 60 min; and temperature of 27 °C.
Fig. 4.Effect of pH on the sorption of Cu (II), Cd (II) and Pb (II) ions on theS. duplicatum biomass immobilized on silica gel with the conditions: 1.0 g of the adsorbent; 100 mg L−1 of the metal ions; 1.3 mL min−1of theflow rate solution; and 27 °C.
Fig. 5.The effect of Cu (II), Cd (II) and Pb (II) initial concentration on the adsorption quantity ofS. duplicatumbiomass immobilized on silica gel. Other conditions: 1.0 g of the adsorbent; 100 mg L−1of metal ions; 1.3 mL min−1of theflow rate solution; pH 5.0; and 27 °C.
3.5. Adsorption competition
In order to know the adsorption selectivity of S. duplicatum biomass immobilized on silica gel, it was performed the adsorption competition of Cu (II), Cd (II) and Pb (II) ion in multi-metal solution at the optimum conditions of the single-metal solution obtained previously using the adsorption column as listed inTable 1.
From the data in Table 1, they show that Cu (II) ion is more adsorbed onS. duplicatumbiomass immobilized on silica gel while it is competitive among Cd (II) and Pb (II) ion in multi-metal solution with the adsorption selectivity coefficient (α)N1. These are correlations with the results obtained in the single-metal adsorption experiments.
3.6. Desorption
Desorption of Cu (II), Cd (II) and Pb (II) ion on S. duplicatum biomass immobilized on silica gel was performed in the column using water and HCl 0.1 mol L−1 as eluent (Fig. 6). Water was used to release metal ion adsorbed through a physical interaction as a cavity.
The HCl was used to elute metal ions adsorbed through chemical interaction as electrostatic or covalent interaction[24,29]. FromFig. 6, it can be seen that Cu (II) ion is the most released in desorption process compared with Cd (II) and Pb (II) ion because the interaction between Cu (II) and Cl−ion is strongest. These match with the value of coordinate bond energy total of Cu2+–Cl−, Cd2+–Cl−and Pb2+–Cl−, 621, 564 and 494 kcal mol−1 at 298.16 °C, respectively [28]. The HCl solution was recommended as metal ion eluent adsorbed on S. duplicatumbiomass immobilized on silica gel.
3.7. Recovery
Recovery of Cu (II), Cd (II) and Pb (II) metal ion byS. duplicatum biomass immobilized on silica gel was studied with flowing 0.5 mmol L−1of the single-metal solution into the adsorption column and then 10 mL of 0.1, 0.5, 1.0, and 2.0 mol L−1HCl with the recovery result as inTable 2.
3.8. Comparison with other adsorbent
If the obtained data of this work is compared with other researches (Table 3), the value of adsorption capacity for Cu (II) ion on theS.
duplicatum biomass adsorbent immobilized silica gel from this research is relatively high (17.93 mg g−1 adsorbent). From the other researches, the adsorption processes run using batch method, so the interaction between metal ion and adsorbent is more effective because of higher collision frequency. At this work, the adsorption process was undertaken with continuous method causing relatively lower collision frequency between metal ion and active sites.
However, the comparison of the adsorption capacities shows that the adsorbent produced by the immobilization process at this work is effective to bind metal ions.
4. Conclusions
The adsorbent produced by the immobilization process fromS.
duplicatum biomass with silica gel and adsorption equipment controlled automatically can be applied on the adsorption–desorption process of Cu (II), Cd (II) and Pb (II) metal ions at the average optimumflow rates of 1.3 mL min−1. Adsorbent ofS. duplicatumhas big adsorption capacity upon Cu (II), Cd (II) and Pb (II) metal ions in the single-metal solution and it is more selective upon Cu (II) ion in the multi-metal solution as well as it can be applied in recovery of Cu (II), Cd (II) and Pb (II) ion in solution.
Acknowledgements
Sincere thanks are due to Directorate of Research and Community Services, Directorate General of Higher Education (DIKTI), National Table 1
The adsorption competition of Cu (II), Cd (II) and Pb (II) ion in multi-metal solution onS.
duplicatumadsorbent immobilized on silica gel.
Metal ions Initial concentration (mmol L−1)
Equilibrium concentration (mmol L−1)
Adsorption (%) D (L g−1) α
Cu (II) 0.50 0.03 94 1.567
Cd (II) 0.50 0.13 74 0.285 Cu (II)/
Cd (II) = 5.50
Pb (II) 0.50 0.19 62 0.163 Cu (II)/
Pb (II) = 9.60
Table 2
Elution recovery (%) for Cu (II), Cd (II) and Pb (II) ion adsorbed onS. duplicatumbiomass immobilized on silica gel.
Metal ions
HCl concentration (mol L−1)
0.1 0.5 1.0 2.0
Recoverya(%)
Cu (II) 72.24 ± 0.45 77.34 ± 0.60 93.83 ± 0.19 98.63 ± 0.56 Cd (II) 66.06 ± 0.27 72.69 ± 0.75 78.03 ± 0.26 84.79 ± 0.40 Pb (II) 54.23 ± 0.27 58.20 ± 0.49 64.78 ± 0.21 70.11 ± 0.17
ax s(n = 3), xis average value for three determination andsis standard deviation.
Table 3
Adsorption characteristics of different biomasses for Cu (II) removal.
Adsorbents Uptake in mg g−1
Category pH Temp (°C)
Adsorption methods
References
Aspergillus niger
23.62 Biomass 6.0 33 Batch [6]
F. vesiculosus 23.40 Biomass 5.5 RT Batch [30]
Sphagnum peat moss
16.10 Biomass 4.0 RT Batch [31]
Biomatrix 10.80 Biomass 5.5 RT Batch [32]
Coffee husk 7.50 Biomass 4.0 RT Batch [33]
Silica—S.
duplicatum
17.93 Biomass 5.0 27 Column This work
Fig. 6.Desorption of Cu (II), Cd (II) and Pb (II) ion on adsorbent with water and 0.1 mol L−1HCl. Other conditions; the eluent volume of 100 mL and theflow rate of 1 mL min−1.
Education Department of Indonesia (DEPDIKNAS), forfinancial help of this research (Research Grant XIV, Contract number: 028/SP2H/PP/
DP2M/III/2007, 29 March 2007).
References
[1] M. Riaz, R. Nadeem, M.A. Hanif, T.M. Ansari, K. Rehman, J. Hazard. Mater. 161 (2009) 88–94.
[2] H.N. Bhatti, B. Mumtaz, M.A. Hanif, R. Nadeem, Process Biochem. 42 (2007) 547–553.
[3] M.N. Zafar, R. Nadeem, M.A. Hanif, J. Hazard. Mater. 143 (2007) 478–485.
[4] N. Chiron, R. Guilet, E. Deydier, Water Res. 37 (2003) 3079–3086.
[5] D.P. Quintanilla, A. Sanchez, I. del Hierro, M. Fajardo, I. Sierra, J. Hazard. Mater.
B134 (2006) 245–256.
[6] M. Mukhopadhyay, S.B. Noronha, G.K. Suraishkumar, Bioresour. Technol. 98 (2007) 1781–1787.
[7] E.W. Wilde, J.R. Beermann, Biotecnol. Adv. 11 (1993) 781–812.
[8] N. Kuyucak, B. Volesky, Biotechnol. Lett. 10 (1998) 137–142.
[9] B. Volesky, Z.R. Holan, Biotechnol. Prog. 11 (1995) 235–250.
[10] R. Patel, S. Suresh, Bioresour. Technol. 99 (2008) 51–58.
[11] V.K. Gupta, A. Rastogi, J. Hazard. Mater. 152 (2008) 407–414.
[12] D.P. Quintanilla, A. Sanchez, I. del Hierro, M. Fajardo, I. Sierra, J. Colloid Interface Sci. 313 (2007) 551–562.
[13] V. Camel, Spectrochim. Acta B 58 (2003) 1177–1233.
[14] N. Jiang, X. Chang, H. Zheng, Q. He, Z. Hu, Anal. Chim. Acta 577 (2006) 225–231.
[15] P.O. Harris, G.J. Ramelow, Environ. Sci. Technol. 24 (1990) 220–228.
[16] M.M. Figueira, B. Volesky, H.J. Mathieu, Environ. Sci. Technol. 33 (1999) 1840–1846.
[17] J. Yang, B. Volesky, Environ. Sci. Technol. 33 (1999) 751–757.
[18] E. Fourest, B. Volesky, Environ. Sci. Technol. 3 (1996) 277–282.
[19] Buhani, Suharso, Z. Sembiring, Indo. J. Chem. 6 (2006) 245–250.
[20] Buhani, Suharso, Z. Sembiring, Report of Research Grant XIV, Directorate General of Higher Education (DIKTI), National Education Department of Indonesia, 2007.
[21] Buhani, Narsito, Nuryono, E.S. Kunarti, Desalination 251 (2010) 83–89.
[22] A.G.S. Prado, J.A.A. Sales, R.M. Carvalho, J.C. Rubin, C. Airoldi, J. Non-Cryst. Solids 333 (2004) 61–67.
[23] A. ErzÖz, R. Say, A. Denizli, Anal. Chim. Acta 502 (2004) 91–97.
[24] X. Chang, N. Jiang, H. Zheng, Q. He, Z. Hu, Y. Zhai, Y. Cui, Talanta 71 (2007) 38–43.
[25] M. Shamsipur, J. Fasihi, A. Khanchi, R. Hassani, K. Alizadeh, H. Shamsipur, Anal.
Chim. Acta 599 (2007) 294–301.
[26] E. Birlik, A. Ersoz, A. Denizili, R. Say, Anal. Chim. Acta 565 (2006) 145–151.
[27] G.L. Miessler, D.A. Tarr, Inorganic Chemistry, Prentice Hall, Englewood Cliffs, New Jersey, 1990, pp. 197–202.
[28] A.E. Martell, R.D. Hancock, Metal Complexes in Aqueous Solution, Plenum Prsess, New York, 1996, pp. 7–8.
[29] Y. Cui, X. Chang, X. Zhu, H. Luo, Z. Hu, X. Zou, Q. He, Microchem. J. 87 (2007) 20–26.
[30] A. Grimm, R. Zanzi, E. Bjornbom, A.L. Biores, Technology 99 (2008) 2559–2565.
[31] J.L. Gardea-Torresdey, L. Tang, J.M. Salvador, J. Hazard. Mater. 48 (1996) 191–206.
[32] K.K. Krishnani, X. Meng, C. Christodoulatos, V.M. Boddu, J. Hazard. Mater. 153 (2008) 1222–1234.
[33] W.E. Oliveira, A.S. Franca, L.S. Oliveira, S.D. Rocha, J. Hazard. Mater. 152 (2008) 1073–1081.
