Water Air Soil Pollut (2013) 224:1654 DOI 10.1007/s11270-013-1654-6

Hexavalent Chromium Removal From Aqueous Solutions by Fe-Modified Peanut Husk M. T. Olguín & H. López-González & J. Serrano-Gómez

Received: 1 March 2013 / Accepted: 10 July 2013 / Published online: 18 August 2013 # Springer Science+Business Media Dordrecht 2013

Abstract Cr(VI) adsorption from aqueous solutions on peanut husk modified with formaldehyde (PeH-F) and peanut husk modified with formaldehyde and Fe (PeHFFe) was evaluated as a function of shaking time, initial pH, chromium concentration, and temperature. Results showed that the Cr(VI) is preferentially adsorbed by PeHFFe at pH 2 than pH 6. It also was found that the chromate equilibrium sorption capacity for PeH-FFe is at least six times higher than for PeH-F. The optimum pH to remove chromium is 2 for both materials; however, PeH-FFe has a higher efficiency for the chromium removal. Finally, Cr(VI) adsorption also depends on chromium concentration and temperature. The adsorption data as a function of concentration obey Linear, Freundlich, and Langmuir isotherms at pH 2 and 6. The Cr(VI) maximum capacity of PeH-FFe at pH 2 was 33.11 mg Cr(VI)/g, slightly higher than that at pH 6 (31.75 mg Cr(VI)/g). The linear isotherm shows that the pH affect the Cr(VI) distribution into the aqueous/solid phases. The negative value of ΔH° and positive values of ΔG° indicate that the chromium adsorption process is an exothermic and non-spontaneous process. The characterization of the peanut husk modified with formaldehyde and peanut husk modified with formaldehyde and Fe by scanning electron microscopy, Raman, and IR spectroscopies as well as the textural characteristics of the noliving biomasses were also considered in this work.

M. T. Olguín (*) : H. López-González : J. Serrano-Gómez Departamento de Química, Instituto Nacional de Investigaciones Nucleares, A. P. 18-1027. Col. Escandón, Delegación Miguel Hidalgo, C.P. 11801 México, D. F., Mexico e-mail: [email protected]

Keywords Chromium . Iron peanut husk . Adsorption . Kinetic . Isotherms . Thermodynamic parameters

1 Introduction Heavy metals such as Th, Cd, Pb, Cr, As, Hg, Cu, and Ni are affecting the environment because of their toxicological effects. Among these heavy metals, pollution by chromium is of considerable concern since it can cause strong environmental problems. The use of chromium in electroplating, textile dyeing, battery manufacturing, mining, metallurgical engineering, etc. produces effluents containing Cr(VI) with concentrations up to hundreds of milligrams per liter. Cr(VI) is highly toxic to living organisms, and is widely recognized to be a human carcinogen. Cr(III), the other common chemical form of chromium is much less toxic than Cr(VI) (Kowalsky 1994). Usual procedures for removing metal ions from contaminated waters include precipitation, reduction, electrolytic removal, ion exchange, reverse osmosis, and adsorption (Chakravarti et al. 1995; Gode and Pehlivan 2005; Rengaraj et al. 2001; Juang and Shiau 2000; Cimino et al. 2000), with adsorption being a simple, versatile, and low cost-effective method to eliminate heavy metals from aqueous solutions. Thus, biosorption process with non-living biological materials as adsorbents, can be an alternative method for metal removal. In recent years, many biomaterials such as non-living biomass of plants (Ucun et al. 2008), algae (Dziwulska et al. 2004), fungi (Marandi 2011), bacteria (El-Zahrani and ElSaied 2011), and yeast (Machado et al. 2008) have been investigated as adsorbents to separate Cr(VI) from waste waters.

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Among the plants, peanut husk has been widely used as biosorbent of heavy metals. Most of the works with peanut husk have been devoted to the removal of cations and just a few to anions. Biosorption of Cu(II) and Cr(III) ions from aqueous solutions by peanut shell biomass was investigated by Witek-Krowiak et al. (2011) and they found that this biomass possesses high affinity and sorption capacity for Cu(II) and Cr(III) ions (25.39 and 27.86 mg/g, respectively). Carbon obtained from peanut husk has been used by Ricordel et al. (2001) for the adsorption of Pb2+, Zn2+, Ni2+, and Cd2+, evaluating the effects of particle size and of carbon doses. The results showed that Pb2+ has best affinity to carbon prepared from peanut husk. Hexavalent chromium removal from aqueous medium by activated carbon obtained from peanut shell was searched by Al-Othman et al. (2012). Results showed that monolayer adsorption capacity was 16.26 mg/g for oxidized carbon and 13.68 for unoxidized carbon. Chemically modified peanut skin was used by Randall et al. (1978) to separate heavy metal cations from aqueous solutions. They found that peanut skin, when treated with formaldehyde to polymerize tannins, is a highly efficient substrate to remove quantitatively Ag1+, Cd2+, Cu2+, Hg2+, Pb2+, and Zn2+. However, other type of chemical modification, for instance with iron (Serrano-Gómez et al. 2010), can also be utilized to separate toxic elements in anionic chemical form, and in this work formaldehyde-modified peanut husk and Femodified peanut husk were used in batch experiments to investigate their potential for removing Cr(VI) from aqueous solutions by varying the pH, contact time, chromium concentration and temperature.

2 Material and Methods 2.1 Raw Material Raw peanut husk was collected from a local market in Toluca city, México. Peanut husk was first washed with distilled water to remove dust, dried at 353 K for 5 h and then crushed and sieved to the desired particle size (20 mesh). 2.2 Formaldehyde-Modified Peanut Husk The no-living biomass was washed with a 0.2 % formaldehyde aqueous solution as far as this solution became

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clear after contacted several times with the peanut husk. The formaldehyde-modified material was referred as to PeH-F.

2.3 Fe-Modified Formaldehyde-Peanut Husk A 20-g sample of PeH-F was contacted with 850 mL of 0.1 N FeCl3 aqueous solution in a 500 mL glass beaker. The suspension was heated to boiling temperature with constant stirring. After 1 h of boiling the suspension was cooled to room temperature, then the supernatant was discarded. These operations were repeated two more times, and then the red-brown peanut husk was washed with distilled water to eliminate the chloride ions. AgNO3 test was used to detect chloride ions in the discarded liquid. The red-brown solid was recovered by filtration and then allowed to dry at room temperature for 3 days. Finally the Fe-modified material, referred to as PeH-FFe, was heated at 353 K for 5 h.

2.4 Cr(VI) Solutions Cr(VI) adsorption experiments were performed with a concentration that simulates contaminated industrial effluents: 25 ppm of Cr (as CrO42− ions) aqueous solution at pH 5.5.

2.5 Effect of Initial pH One hundred milligram samples of PeH-F or PeH-FFe were shaken for 24 h in separate glass vials, with 10 mL of 25 ppm Cr aqueous solution, at pH values from 2 to 12. After shaking the suspension was centrifuged for phase separation. The liquid was recovered with a pipette and the solid was discarded. The Cr content in the liquid was determined as described below. All the experiments were performed in duplicate.

2.6 Kinetic The experimental conditions to obtain the kinetic of the adsorption processes were similar to those described before; however, in this case the initial pH value of the Cr solution was maintained at 5.5 and the mixtures were shaken from 0.25 to 24 h.

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2.7 Isotherms

2.9.4 Specific Area and Porosity

For the isotherms, 100 mg of samples were contacted in glass vials with 10 mL of 50 to 300 ppm Cr solution for 24 h at 293 K for both pH values 2 and 6. Two separate vials were used for each Cr concentration. The measurements of Cr were performed as described in the next paragraph. The experimental data were examined using Freundlich and Langmuir adsorption models.

Specific areas and total pore volume of solid samples were determined by the N2 Brunauer–Emmett–Teller (BET) method in a surface analyzer BELSORP-28SA. The dried and degassed samples were then analyzed using a multipoint N2 adsorption–desorption method at room temperature.

2.8 Chromium Determination

3 Results and Discussion

Chromium was quantified in the remaining solutions using an atomic absorption spectrometer, model GBC 932 plus. The wavelength used to measure Cr was 360.5 nm. For each experiment, and before determining the Cr in the liquid samples, a Cr calibration curve was obtained using Cr standard aqueous solutions.

3.1 Effect of Initial pH

2.9 Characterization of PeH-FFe 2.9.1 Scanning Electron Microscopy The unmodified and modified no-living biomasses were mounted directly onto samples holders for scanning electron microscopy. The images were observed at 20 keV with a Phillips XL30 electron microscopy. Elemental chemical analyses of the materials were carried out by energy X-ray dispersive spectroscopy with a DX-4 probe. 2.9.2 Raman Spectroscopy A microRaman LabRam HR Jovyn Ivon Horiba was used for Raman spectroscopy, using a Nd:YAG laser and λ=432 nm. Power was 80 mW which was attenuated 10 times during the measurement. Laser focalization was done on the powder sample under ×50 objective. Spectra were obtained between 200 and 1,400 cm−1.

The effect of initial pH on adsorption of chromium is shown in Fig. 1 for PeH-F and PeH-FFe. For both adsorbents, the removal of chromium decreases as the pH increases from 2 to 12. Also for both materials, at pH 2, the percent removal values of chromate ions are the highest being the value for PeH-FFe higher (96. 88 % or 5.4 mg/g) than for PeH-F (70.16 % or 3.91 mg/g). These results show the highest efficiency of PeH-FFe to separate Cr(VI) anions from aqueous solutions. pH controls the process of adsorption as it affects the surface charge of the adsorbent as well as the degree of ionization and the species of adsorbate. With a 25 ppm Cr concentration and at a pH 2, the chemical species present in aqueous solution using MEDUSA Program, are HCrO4− (about 90 %) and H2CrO4/Cr2O72− (<10 %). At pH 4, the HCrO4− anion is the unique chemical species in solution, while HCrO4− (about 85 %) as well as CrO42− (about 15 %) are present when the pH is 6. These two Cr chemical species are also present in aqueous solutions when the pH is 8, although their percentages are different: CrO42− ions (about 97 %) and HCrO4− (about 3 %). At

2.9.3 IR Spectroscopy Infrared (IR) spectra in the 4,000–400 cm−1 range were recorded for the PeH-F and PeH-FFe samples before and after the Cr(VI) adsorption, using a Nicolet Magna-IR 550 FTIR. Samples were prepared using the standard KBr pellets method.

Fig. 1 Effect of initial pH of aqueous solution on Cr(VI) removal by PeH-F (filled diamond) and PeH-FFe (filled square)

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pH values of 10 and 12, only CrO42− ions exist in aqueous solutions. At acidic pH values, the surface of the material PeH-FFe becomes positively charged because of the formation of positive groups –Fe–OH2+ where the negatively charged chromium species bind through electrostatic attraction. This adsorption reaction is based on the finding that at low pH values Cr(VI) adsorption is increased and at high pH values Cr(VI) adsorption decreases (Saha and Orvig 2010); being this decreasing due to a deprotonation of the –Fe–OH groups present on the surface of PeH-FFe grains.

In both cases (pH 2 and 6), it was observed that the adsorption decreased as the initial concentration of Cr(VI) ions increase, i.e., the adsorption is higher in the more dilute chromate solutions because of more surface active sites per gram of adsorbent are available for adsorption of a lesser number of anions at higher dilutions (Fig. 3). Adsorption data as a function of chromate concentration in solution were analyzed for Linear, Freundlich, and Langmuir adsorption isotherms. The Linear model is expressed as:

3.2 Kinetic

where qe is the amount of Cr(VI) adsorbed at equilibrium by the PeH-FFe (in milligram per gram), Ce is the Cr(VI) concentration in the solution at equilibrium (in milligram per liter) and Kd is the distribution coefficient (in liter per gram). It was found that the Cr(VI) is preferentially adsorbed by the PeH-FFe at pH 2 than pH 6 according with the Kd values showing in Table 1; however, the R2 is less than 0.9000. When applying the Freundlich model to experimental data, the logarithm of the amount of Cr(VI) adsorbed at equilibrium (log qe) was plotted versus the logarithm of Cr(VI) concentration (log Ce) in residual solutions at equilibrium. The adsorption data fitted well to the linearized Freundlich equation.

The equilibrium of the adsorption was determined by plotting the % removal of chromium against time for the no-living biomass PeH-F and PeH-FFe, as shown in Fig. 2. From the plot, the equilibrium time was set to 15 min for both materials, and the equilibrium sorption capacity was found to be 4.17 mg/g for PeH-FFe, and 0.65 mg/g for PeH-F by Cr(VI). These values indicate that the equilibrium sorption capacity for PeH-FFe by Cr(VI) is at least six times higher than for PeH-F. 3.3 Isotherms The effect of chromium concentration on adsorption of Cr(VI) by PeH-FFe was investigated by using chromium solutions whose pH values were 6. Additionally, as discussed before, the optimum pH of Cr(VI) adsorption by PeH-FFe was 2, therefore the effect of chromium concentration was also investigated adjusting the pH to this value in order to compare the Cr(VI) adsorption behavior by PeH-FFe.

Fig. 2 Removal of chromium versus time by (filled diamond) PeH-F and (filled square) PeH-FFe

qe ¼ C e K d

Log qe ¼ ð1=nÞlog C e þ log K F

ð1Þ

ð2Þ

Fig. 3 Cr(VI) adsorption isotherms by PeH-FFe at pH 2 and 6

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Table 1 Parameters from the Linear, Langmuir and Freundlich isotherm models applied to the sorption of Cr (VI) by PeH-FFe at different pH values pH

Linear

Isotherm models Freundlich

Kd (L g−1)

R2

KF mgg−1(Lmg−1)1/n

Langmuir 1/n

n

qmax (mg g−1)

R2

KL (L mg−1)

R2

2

0.114

0.840

1.144

0.557

1.79

0.998

33.110

0.010

0.938

6

0.101

0.967

0.310

0.764

1.31

0.996

31.746

0.005

0.850

where 1/n and KF are the Freundlich constants indicating the adsorption intensity and the adsorption capacity, respectively. From the slope and intercept of the plot, the numerical values of the Freundlich constants, i.e., 1/n and KF, computed using the least square techniques were found to be 0.7 times less and 3.7 times higher at pH 2 than pH 6. The value of 1/n<1 in both cases (pH values 2 and 6) found in this work confirms that the Freundlich model is valid for the Cr(VI) adsorption on PeH-FFe with R2>0.9900. Furthermore, this suggests that the adsorbent surface is heterogeneous with an exponential distribution of the active centers and that the adsorbed species have no appreciable interaction among them. The values of KF and n changed with pH. The value of n showed an indication of the favorability of adsorption (Daneshvar et al. 2002; Malik 2004). The values of n suggested that Cr(VI) is more favorably adsorbed by PeH-FFe at pH 2 (n=1.79) than at pH 6 (n=1.31) as was mentioned above (Table 1). The Cr(VI) adsorption data were also fitted to the Langmuir isotherm to obtain the maximum adsorption capacity, using the following linearized form:

C e =qe ¼ ð1=K L qmax Þ þ ðC e =qmax Þ

ð3Þ

where Ce is the concentration of Cr(VI) in solution (in milligram per liter), qe is the amount of Cr(VI) in the adsorbent (in milligram per gram), KL and qmax are Langmuir constants which are related to the adsorption energy and maximum adsorption capacity, respectively. Langmuir constants KL and qmax were calculated from the intercepts and slops of plots of Ce/qe versus Ce, respectively, and are given in Table 1 along with correlation coeffcients (R2). From Table 1 it is clear that the adsorption capacity of PeH-FFe for Cr(VI) is slightly higher at pH 2 than at pH 6, although in the last case the determination coefficient was less than 0.9000. Table 2 summarizes some reported adsorption capacities for Cr(VI) of various chemically modified no-living biomasses. Very few reports about these materials modified with Fe can be found in the literature; however, many other types of chemical modification have been investigated. Upon comparing the Cr(VI) adsorption capacity of PeH-FFe either at pH 2 (33.11 mg/g) or at

Table 2 Cr(VI) adsorption capacities for different non-living biomasses No-living biomass

qmax (mg g−1)

Reference

Seaweed Cystoseira indica oxidized by potassium permanganate Seaweed Cystoseira indica modified by cross-linking with epichlorydrin

20.1 24.2

Shaik et al. 2008

Seaweed Cystoseira indica washed by distilled water

17.8

Groundnut husk, modified with sulfuric acid and Ag impregnation Terminalia arjuna nuts, modified with ZnCl2

11.40 28.43

Owland et al. 2009

Fe(III)-treated Staphylococcus xylosus

43.48

Aryal et al. 2011

Peanut shell-charcoal

116.3 at pH 2

Varga et al. 2013

Activated carbon from peanut shell by chemical activation with KOH

16.26 oxidized 13.68 unoxidized

Al-Othman et al. 2012

Peanut husk modified with formaldehyde and iron (PeH-FFe)

33.1 at pH 2 31.7 at pH 6

Present work

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pH 6 (31.75 mg/g) to the corresponding values of other chemically modified biomaterials showed in Table 2, it can be seen that PeH-FFe has a maximum adsorption capacity higher than those of chemically modified seaweed Cystoseira indica (modified with potassium permanganate or epichlorydrin and washed only with distilled water)(Shaik et al. 2008), Groundnut husk, activated with sulfuric acid and Ag impregnation, and Terminalia arjuna nuts, activated with ZnCl2 (Owland et al. 2009). Fe(III)-treated Staphylococcus xylosus (Aryal et al. 2011) has a maximum adsorption capacity a little higher than PeH-FFe, and both Fe-modified materials displays a superior performance to sorb Cr(VI) over the no-living biomasses chemically modified in a different way. It is important to comment that when the peanut husk is converted to charcoal (Varga et al. 2013) the Cr(VI) adsorption capacity of this material is higher than that of PeH-FFe at the same pH value of 2; however, when the peanut husk is carbonized to obtain activate carbon (Al-Othman et al. 2012) the Cr(VI) maximum adsorption capacity is lower than that obtained by the material used in this work.

Water Air Soil Pollut (2013) 224:1654 Table 3 Thermodynamic parameters for the adsorption of Cr(VI) on PeH-FFe ΔH° (kJ mol−1)

T Equilibrium (K) constant (Kc)

ΔS° ΔG° (KJ (kJ K−1 mol−1) mol−1)

303 0.7413

753.94

313 0.6607

1,078.29 −9,086.8777 −32.4877

323 0.5888

1,422.07

333 0.5370

1,720.998



logK c ¼



−ΔH ΔS þ ð2:303RT Þ 2:303R

and ΔG ¼ −RT lnK c

ð5Þ

where Kc is the equilibrium constant given by the expression Kc=Fe/(1−Fe) and Fe is the fraction sorbed at

3.4 Effect of Temperature The effect of temperature on the adsorption of chromate ions on PeH-FFe was also investigated. The temperature was varied from 303 to 333 K. With the temperature dependence data, the changes in the thermodynamic parameters ΔH°, ΔS°, and ΔG° (standard enthalpy, standard entropy and Gibbs free energy, respectively) were evaluated using the van't Hoff equation (Qadeer et al. 1993; Saeed 2003):

Fig. 4 Plot of log Kc vs. 1/T for the Cr(VI) adsorption on PeH-FFe

ð4Þ

Fig. 5 SEM images of a PeH-FFeb and b PeH-FFea

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equilibrium (Hasany et al. 2000), T is the temperature in kelvin, and R is the gas constant (8.3143 kJ K−1 mol−1). Making the expression −ΔH°/(2.303R) equal to −0.47 from the equation displayed in Fig. 4, the value of change in enthalpy (ΔH°) was found to be −9,086. 99 kJ mol−1. The negative value of ΔH° corresponds to an exothermic adsorption process (Granados-Correa and Serrano-Gómez 2009). In a similar way, ΔS° was calculated using the expression ΔS°/(2.303R) and the numerical value 1.683 from the equation in Fig. 4. The negative value of ΔS°=−32.49 kJ K mol−1 indicated the decreasing randomness at the solid/liquid interface during the sorption of Cr(VI) on PeH-FFe (Tewari et al. 2005). Calculated values of ΔG° are summarized in Table 3. The positive sign of ΔG° indicate the non-spontaneous behavior of the sorption process. The numerical values of ΔG° increase as the temperature increases, which mean that the adsorption reaction occurs more favorably at lower temperatures. This is supported by the values of Kc obtained at different temperatures since they decrease with the rise in temperature, as depicted also in Table 3.

Fig. 6 Energy patterns of a PeH-FFeb and b PeH-FFea

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3.5 Characterization of PeH-FFe 3.5.1 Scanning Electron Microscopy Figure 5 (a and b) shows the images of the biomaterial PeH-FFe before (PeH-FFeb) and after (PeH-FFea) carrying out the chromate ion adsorption. Outstanding changes were observed in the morphology after the PeH-FFe was in contact with the Cr(VI) aqueous solution. As can be seen in Fig. 5a, the surface of PeH-FFeb looks very rough with small particles on it. On the contrary, after the adsorption of Cr(VI), PeH-FFea shows the presence of a laminated structure with well defined plates (Fig. 5b). Figure 6 (a and b) shows the energy pattern of PeH-FFeb and PeH-FFea, respectively. The elemental composition of PeH-FFeb was: C= 36.15±5.0, O=39.04±6.16, Al=0.47±0.19, Cl=1.93± 0.67, and Fe=22.45±9.7 wt.%; while for PeH-FFea, in addition to the elements detected in the PeH-FFe, Cr was also observed, and the elemental composition was found to be C=33.13±4.72, O=42.21±4.85, Al=0.66± 0.38, Cl=1.45±0.27, Fe=21.74±8.46 and Cr=0.81±0.22

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Fig. 7 Raman spectra of solid potassium chromate (solid line) and Cr(VI) adsorbed by PeH-FFe (broken line)

wt.%. These results show clearly the Cr uptake by the biomaterial PeH-FFe. 3.5.2 Raman Spectroscopy Figure 7 shows the Raman spectra of K2CrO4 in solid form and adsorbed Cr(VI) by PeH-FFe. The Raman spectra of the no-living biomass with Cr(VI) indicated that chromium was adsorbed on PeH-FFe considering that the peak of CrO42− at 239 cm−1, taken as a reference, was shifted to 252 cm−1 after the adsorption of the Cr(VI) onto PeH-FFe. Therefore, this shift could indicate the interaction, in a different environment, between Cr (VI) and the no-living biomass (Liu and Huang, 2011). 3.5.3 IR Spectroscopy The main bands in the IR spectrum of the biomaterial PeH-F were recognized as follows: the wavenumber at 3431 cm−1 indicates the presence of OH groups on the peanut husk. The 1633 cm−1 band results from CO stretching mode, conjugated to a NH deformation mode and is indicative of amide band, while the 1052 cm−1 band is assigned to CO or CN groups. No modification was observed in the IR spectrum of PeH-FFe, obtained after the treatment of PeH-F with FeCl3 aqueous solution. Thus, both spectra of PeH-F and PeH-FFe reveal the presence of several functional groups for binding Cr(VI) chemical species on the peanut husk.

1.6 times higher (0.88 m2/g) than that of iron unmodified material. These results show that the presence of iron increases the specific area of PeH-F, which results in a positive effect on the removal capacity for pollutants in aqueous media. Other parameters as the total pore volume and the mean pore diameter were changed (Table 4) as a consequence of the iron modification of the formaldehyde-peanut husk and both textural characteristics of the material also play a role into the adsorption processes to remove pollutants from wastewater.

4 Conclusions The chromium adsorption on both PeH-F and PeH-FFe depends strongly on pH. At low pH values the Cr(VI) adsorption is the highest and decreases drastically at alkaline pH values being the Cr(VI) removal higher for PeH-FFe. The Cr(VI) adsorption equilibrium was reached in 15 min with both materials. Chromium (VI) initial concentration in solution and temperature affected the chromate adsorption. Adsorption data of Cr(VI) on PeH-FFe fit Linear, Freundlich, and Langmuir isotherms, at pH 2 and 6. The qmax value was found to be 33.11 mg/g at pH 2. The temperature effect

Table 4 Textural parameters of modified peanut husk Sample

Specific surface Total pore volume Mean pore (cm3 g−1) diameter (nm) (m2 g−1)

PeH-F

0.594

0.00370

24.77

PeH-FFe 0.885

0.00654

29.56

3.5.4 Specific Area and Porosity The specific area of PeH-F was 0.59 m2/g. For PeH-F modified with iron (PeH-FFe), the specific area was

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on the Cr(VI) adsorption by PeH-FFe indicated an exothermic and non-spontaneous sorption process. Acknowledgments M. T. Olguín thanks CONACyT project 131174-Q for partial financial support.

References Al-Othman, Z. A., Ali, R., & Nauhad, M. (2012). Hexavalent chromium removal from aqueous medium by activated carbon prepared from peanut shell: adsorption kinetics, equilibrium and thermodynamic studies. Chemical Engineering Journal, 184, 238–247. Aryal, M., Ziagova, M., & Liakopoulou-Kyriakides, M. (2011). Comparison of Cr(VI) and As(V) removal in single and binary mixtures with Fe(III)-treated Staphylococcus xylosus biomass: thermodynamic studies. Chemical Engineering Journal, 169, 100–106. Chakravarti, A. K., Chowdhury, S., Chakrabarty, S., & Mukherjee, D. C. (1995). Liquid membranes multiple emulsion process of chromium (VI) separation from wastewater. Colloid Surface A, 103, 59–71. Cimino, G., Passerini, A., & Toscano, G. (2000). Removal of toxic cations and Cr(VI) from aqueous solution by hazelnut shell. Water Research, 34, 2955–2962. Daneshvar, N., Salari, D., & Aber, S. (2002). Chromium adsorption and Cr(VI) reduction to trivalent chromium in aqueous solution by soya cake. Journal of Hazardous Materials, 94, 49–61. Dziwulska, U., Bajguz, A., & Zylkiewicz, B. (2004). The use of algae Chlorella vulgaris immobilized on cellex T support for separation/preconcentration of trace amounts of platinum and palladium before GFAAS determination. Analytical Letters, 37, 2189–2203. El-Zahrani, H. A., & El-Saied, A. I. (2011). Bioremediation of heavy metal toxicity from factory effluents by transconjugants bacteria. Journal of the Egyptian Society of Parasitology, 41, 641–650. Gode, F., & Pehlivan, E. (2005). Removal of Cr(VI) from aqueous solution by two Lewatit-anion exchange resins. Journal of Hazardous Materials, 119, 175–182. Granados-Correa, F., & Serrano-Gómez, J. (2009). CrO42− ions adsorption by Fe-modified pozzolane. Separation Science and Technology, 44, 924–936. Hasany, M. S., Saeed, M. M., & Ahmed, M. (2000). Adsorption isotherms and thermodynamic profile of Co(II)–SCN complex uptake on polyurethane foam. Separation Science and Technology, 35, 379–394. Juang, R. S., & Shiau, R. C. (2000). Metal removal from aqueous solutions using chitosan enhanced membrane filtration. Journal of Membrane Science, 21, 1091–1097. Kowalsky, Z. (1994). Treatment of chromic tannery wastes. Journal of Hazardous Materials, 37, 137–144. Liu, B., & Huang, Y. (2011). Polyethyleneimine modified eggshell membrane as a novel biosorbent for adsorption and

Page 9 of 9, 1654 detoxification of Cr(VI) from water. Journal of Materials Chemistry, 21, 17413–17418. Machado, M. D., Santos, M. S. F., Gouveia, C., Soares, H. M. V. M., & Soares, E. V. (2008). Removal of heavy metals using a Brewer's yeast strain of Saccharomyces cerevisiae: the flocculation as a separation process. Bioresource Technology, 99, 2107–2115. Malik, P. K. (2004). Dye removal from waste water using activated carbon developed from sawdust: adsorption equilibrium and kinetics. Journal of Hazardous Materials, 113, 81–88. Marandi, R. (2011). Biosorption of hexavalent chromium from aqueous solution by dead fungal biomass of Phanerochaete crysosporium: batch and fixed bed studies. Canadian Journal of Chemical Engineering, 2, 8–22. Owland, M., Arou, M. K., Daud, W. A. W., & Baroutian, S. (2009). Removal of hexavalent chromium-contaminated water and wastewater: a review. Water, Air, and Soil Pollution, 200, 59–77. Qadeer, R., Hanif, J., Saleem, M., & Afzal, M. (1993). Surface characterization and thermodynamics of adsorption of Sr2+, Ce3+, Sm3+, Gd3+, Th4+, UO22+ on activated charcoal from aqueous solution. Colloid & Polymer Science, 271, 83–90. Randall, J. M., Hautala, E., & McDonald, G. (1978). Binding of heavy metal Ions by formaldehyde-polymerized peanut skins. Journal of Applied Polymer Science, 22, 379–387. Rengaraj, S., Yeon, K. H., & Moon, S. H. (2001). Removal of chromium from water and wastewater by ion exchange resins. Journal of Hazardous Materials, 87, 273–287. Ricordel, S., Taha, S., Cisse, I., & Dorange, G. (2001). Heavy metals removal by adsorption onto peanut husks carbon: characterization, kinetic study and modeling. Separation and Purification Technology, 24, 389–401. Saeed, M. M. (2003). Adsorption profile and thermodynamic parameter of the preconcentration of Eu(III) on 2thenoyltrifluroroacetone loaded polyurethane (PUR) foam. Journal of Radioanalytical and Nuclear Chemistry, 256, 73–80. Saha, B., & Orvig, C. (2010). Biosorbents for hexavalent chromium elimination from industrial and municipal effluents. Coordination Chemistry Reviews, 254, 2959–2972. Serrano-Gómez, J., López-González, H., Olguín, M. T., & Bulbulian, S. (2010). As (V) adsorption by uunmodified and Iron modified pozzolane. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 67, 153–158. Shaik, B., Murthy, Z. V. P., & Jha, B. (2008). Biosorption of hexavalent chromium by chemically modified seaweed, Cystoseira indica. Chemical Engineering Journal, 137, 480–488. Tewari, N., Vasudevan, P., & Guha, B. K. (2005). Study on biosorption of Cr(VI) by Mucor hiemalis. Biochemical Engineering Journal, 23, 185–192. Ucun, H., Bayhan, K. Y., & Kaya, Y. (2008). Kinetic and thermodynamic studies of the biosorption of Cr(VI) by Pinus silvestri Linn. Journal of Hazardous Materials, 153, 52–59. Varga, M., Takács, M., Záray, G., & Varga, I. (2013). Comparative study of sorption kinetic and equilibrium of chromium (VI) on charcoals prepared from different low-cost materials. Michrochemical Journal, 107, 25–30. Witek-Krowiak, A., Szafran, R. G., & Modelski, S. (2011). Biosorption of heavy metals from aqueous solutions onto peanut shell a low-cost biosorbent. Desalination, 265, 126–134.