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Applied Surface Science 303 (2014) 1–5

Contents lists available at ScienceDirect

Applied Surface Science

jou rn al h om ep age: www.elsev ier .com/ locate /apsusc

emoval of fluoride from groundwater by adsorption ontoa(III)- Al(III) loaded scoria adsorbent

hengyu Zhanga,b,c, Ying Lub,c, Xueyu Linb,c, Xiaosi Sub,c, Yuling Zhangb,c,∗

Key Laboratory of Songliao Aquatic Environment, Ministry of Education, Jilin Jianzhu University, Changchun 130118, P.R. ChinaKey Lab of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun 130026, P.R. ChinaInstitute of Water Resources and Environmental Jilin University, Changchun 130026, P.R. China

r t i c l e i n f o

rticle history:eceived 4 November 2013eceived in revised form 3 January 2014ccepted 27 January 2014vailable online 5 February 2014

eywords:luoride removal

a b s t r a c t

The La3+-Al3+ loaded scoria (La-Al-Scoria) was prepared as adsorbent for the fluoride removal fromgroundwater. The connecting time experiment indicated that the fluoride adsorption process reachedequilibrium within 5 hours. The kinetics of fluoride ion adsorption onto La-Al-Scoria was followed thepseudo-second order with correlation coefficient value (R2) of 0.997. The isotherm data was well fittedto both of the Freundlich and Langmuir isotherm models, the R2 of Freundlich and Langmuir were 0.98and 0.97, respectively. Subsequently, the adsorbent was characterized by scanning electron microscope(SEM), Energy dispersive analysis of X-ray (EDX), X-ray diffraction analysis (XRD) and X-ray Photoelec-

dsorption isothermsineticsanthanum-Aluminum loaded Scoria

tron Spectroscopy (XPS) measurements. SEM visual expressed that the dense canal surface structureof natural scoria appeared a large amount of rod-like composite after modification. The XRD and XPSinstrumental studies revealed that the La3+ and Al3+ were loaded on the surface of modified scoria andthe fluoride ion was adsorbed on the La-Al-Scoria. The large amount of La-Al-O composite oxide existedonto the surface of La-Al-Scoria was the immanent cause for the excellent adsorption capacity of fluorideion.

© 2014 Published by Elsevier B.V.

ntroduction

Groundwater is an important source of drinking water in widelyanged arid and semi-arid area. Excess fluoride ion (>1.5 mg/L) inrinking water might be the cause of dental and skeletal disease1], which is a great concern to the located human health. Theeason of the high concentration of fluoride ion in groundwaters mainly due to some geochemical reactions in sub-surface [2].he water-mineral interaction lead the fluoride ion concentrationn groundwater is very difficult to decrease in nature condition.herefore, many technologies, such as electro coagulation [3],hemical precipitation [4], adsorption [5], ion exchange [6], andembrane technology [7] have been applied to remove fluoride

rom groundwater. Among various methods, the adsorption haseceived extensive attention for the removal of fluoride ion fromroundwater in poorly developed areas.

The applicability of adsorption methods is highly depend-nt on the adsorptive materials. Recently, many studies haveocused on the search of natural materials such as quick lime [8],

∗ Corresponding author. Institute of Water Resources and Environmental Jilinniversity, Changchun 130026, P.R. China.Tel.: +86 0431 88492306.

E-mail address: zhangyl8@jlu.edu.cn (Y. Zhang).

169-4332/$ – see front matter © 2014 Published by Elsevier B.V.ttp://dx.doi.org/10.1016/j.apsusc.2014.01.169

kaolinites [9], red mud [10] and hydroxyapatite [11] were exam-ined for adsorbents. However, the adsorptive efficient of naturalmaterial has been rated low when compared to chemical material[12]. Though activated alumina as the chemical material [13] seemsto be a popular and effective material to removal fluoride ion fromgroundwater, it is difficult to be widely used due to its high cost.Hence, recent studies focused on the research of modified meth-ods have been recommended. Due to the high electrical affinity forfluoride ion, some rare earth elements and metal ions such as La3+

[14–16], Ce3+ [17], Al3+ [18] and Fe2+ [19] are used to improve thefluoride adsorption capacity of modified adsorbents. These kinds ofions loaded onto natural materials appeared more appropriate andattractive in various chemical modifications [20,21].

In this study, we attempt to utilize the natural scoria, bomb-sized vesicular pyroclastic rock with basaltic composition[22,23],modified by rare earth (La3+) and metal (Al3+) elements to developa new adsorbent (La-Al-Scoria). The adsorption capacity of sco-ria to remove heavy metal ions has been considerable studiedand reported mainly due to its valuable properties: large spe-cific surface area, negatively charged surface, light in weight, low

cost and local availability [24–27]. However, little or no literatureis available about the adsorption of defluoridation onto scoria ingroundwater. Thus, the main objectives of this work are to inves-tigate the isotherm and kinetic modeling of fluoride adsorption on

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hermally treated La-Al-Scoria and reveal the adsorption charac-eristics of fluoride ion on the prepared composite.

aterial and methods

aterials

Scoria was purchased from Huinan, Hebei province, China. Dis-illed water was used throughout the experiments. Stock fluorideon solution of 1,000 mg/L was prepared from dried sodium fluo-ide. The solutions of required concentrations were prepared byiluting the stock solution. All other chemicals were analyticalrade and obtained from Chemical Engineering Company of Beijing,hina.

reparation of La-Al- Scoria

The natural scoira was washed with distilled water and thenixed with Al2SO4, NaOH and La(NO)3 solution in the mass ratios

f 100:5:1.5:0.34. After 12 hours, the modified scoria was dried inn oven at 90 ◦C for 2 hours and thermally in the furnace treatedt 300 ◦C for 2 hours. Finally, modified scoria was washed with dis-illed water to neutral pH, and the La-Al-Scoria was stored in aolyethylene bottle for the following experiment.

dsorption experiments

50 ml fluoride ion solution was added to 100 ml polyethyleneottle with the concentration of 4.89 mg/L and desired pH value of.2. The La-Al-Scoria (1.00 g) was added into a polyethylene bottlend shaken in incubator shaker at 200 rpm and kept at 10 ± 1 ◦C.t each interval, the solution was collected and then filtered with.45 �m membrane for analysis. In the adsorption isotherm exper-

ment, the initial fluoride concentration was in the range of 0.21 -0.82 mg/L. Residual fluoride ion was analyzed by a fluoride selec-ive electrode (Model No. PF-1 C, Weiye Instruments, Shanghai,hina) and the amount of fluoride adsorbed was calculated by fol-

owing equation [28]:

e = (C0 − Ce) × V

W(1)

here qe is the adsorption capacity (mg/g) at equilibrium, C0 ande are the initial and equilibrium fluoride concentrations (mg/L),espectively, V is the volume (mL) of solution and W is the mass (g)f adsorbent used. Experiments were conducted in duplicates, andhe mean values were reported.

haracterization of La-Al-Scoria

A high qualitatively Scanning Electron Microscope (SEM) (JSM-700F, JEOL Ltd., Japan) was used to exam the surface morphologyf natural scoria and La-Al-Scoria. The crystallization of naturalcoria and La-Al-Scoria were studied by X-Ray Diffraction AnalysisXRD) (XD-3, Shimadzu Corporation, Japan) over a range of 10-40◦

n 2 theta angle. The binding energies and atom ratios of the ele-ents of La-Al-Scoria before and after adsorption were obtained

y using X-Ray Photoelectron Spectroscopy (XPS) (ESCALAB 250,hermo Corporation, USA). A conventional Al K� anode radiation

ource was used as the excitation source. The binding energiesere calibrated by the C1s binding energy at 284.8 eV. XPS datarocessing and peak fitting were performed using a nonlinear least-quares fitting program.

Fig. 1. Time vs. adsorption capacity of fluoride with initial concentration of4.89 mg/L.

Results and discussion

Effect of connecting time

In order to investigate the connecting time for the removal offluoride ion from groundwater, the connecting time was variedfrom 1 to 900 min. The effect of connecting time on the removalof fluoride ion was shown in Fig. 1. It was observed that adsorptioncapacity of La-Al-Scoria improves slightly by increasing connect-ing time from 1 to 5 h. After that, the adsorption capacity no furtherchanged significantly. Thus, 5 h connecting time was found suitablefor adsorption equilibrium.

Kinetics studies

The time dependent adsorption data were analyzed by using thekinetic equations. Two models were used to describe the kinetics:Pseudo-first order kinetic model and Pseudo-second order kineticmodel [29].

The Pseudo-first order kinetic model of linear form equation isgiven by the following:

ln(qe − qt) = ln qe − k1t

2.303(2)

where k1 is the pseudo-first-order rate constant of adsorption(1/min), qe and qt are the amounts of fluoride adsorbed at equi-librium (mg/g) and at time t (min), respectively. A linear form plot(Fig. 2a) of connecting time t versus ln(qe - qt) gives the slop of k1.The Pseudo-second order kinetic model of linear form equation isgiven by the following:

t

qt= 1

k2qe2

+ t

qe(3)

where k2 is the pseudo-second-order rate constant of adsorption(g/(mg min)). k2 and qe were calculated from the slop and interceptof connecting time t versus t/qt linear plot (Fig. 2b).

The values of the rate constants of pseudo-first-order (k1) andpseudo-second-order (k2) were 0.747 and 0.022, respectively. Thelarger k2 value usually means the lower adsorption rate of fluorideion adsorption process onto La-Al-Scoria. The calculated adsorp-tion capacity (qe = 0.112) of Pseudo-second order kinetic model wasalso closed to the value (qexam = 0.113) of experiments. Fig. 2a and

b also showed the correlation coefficient values of pseudo-first-order (R2 = 0.864) and pseudo-second-order (R2 = 0.997) kinetics,and the adsorption of fluoride ion on the La-Al-Scoria was regardedas pseudo-second-order rather than pseudo-first-order.

S. Zhang et al. / Applied Surface Science 303 (2014) 1–5 3

Fig. 2. (a) Pseudo-first order kinetic, (b) Pseudo-second order kinetic for the removalof fluoride ion by La-Al-Scoria.

Table 1The value of parameters for Freundlich and Langmuir isotherm models.

Freundlich LangmuirParameter Value Parameter Value

K (mg/g) 23.91 Q0 (mg/g) 1.25

A

Fitf

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n 0.94 b (l/g) 0.36R2 0.98 R2 0.97

dsorption isotherms

The isotherms in this study were analyzed by using thereundlich and Langmuir isotherm equations [30]. The Freundlichsotherm model assuming that the fluoride ion adsorption processakes place on the non-uniformity La-Al-Scoria surfaces. The linearorm of Freundlich isotherm equations is given as:

n qe = 1n

ln Ce + ln K (4)

here qe is the amount of fluoride ion adsorbed per unit weightf La-Al-Scoria at equilibrium (mg/g), K and n are the Freundlichonstants, Ce is the equilibrium concentration of fluoride ion inolution (mg/L). The Freundlich constants were calculated by theinear plot of lnCe versus lnqe (Fig. 3a) and listed in Table 1.

The Langmuir isotherm model indicated that the monolayerdsorption process for fluoride ion onto the non-uniformity La-l-Scoria surface. The linear form of Langmuir equation is given

s:

Ce

qe= 1

Q0b+ Ce

Q0(5)

Fig. 3. (a) Freundlich adsorption isotherm, (b) Langmuir adsorption isotherm forthe removal of fluoride ion by La-Al-Scoria.

where qe is the amount of fluoride ion adsorbed per unit weightof La-Al-Scoria at equilibrium (mg/g), Q0 is the maximum adsorp-tion capacity (mg/g), b is the Langmuir constant, and Ce is theequilibrium concentration of fluoride ion in solution (mg/L). TheLangmuir constants were obtained by the linear plot of 1/Ce versus1/qe (Fig. 3b) and listed in Table 1.

The calculated correlation coefficients (R2) showed the experi-mental data fitted the Freundlich and Langmuir isotherm modelswell, which were 0.98 and 0.97, respectively. The comparisonof fluoride isotherms adsorption process fitting on the La-Al-Scoria indicated the possibility simultaneous validity of multipleisotherms under the studied fluoride ion concentration.

SEM and EDX studies

The scanning electron microscope images (SEM) of the rawscoria and La-Al-Scoria were shown in Fig. 4a and Fig. 5a. It wasobserved from Fig. 4a that the scoria possess groove with a largeamount of dense canal like structure. After the modifications(Fig. 5a), a large amount of rod-like on the adsorbent indicated thatmodifications changed the surface structure of raw scoria. Energydispersive analysis of X-Ray (EDX) was employed to analyzethe elements of raw scoria and La-Al-Scoria. The EDX pattern ofraw scoria and La-Al-Scoria were shown in Fig. 4b and Fig. 5b,respectively. From the Fig. 4b, it was observed a component whichriches of silicium, aluminum and oxygen, etc. The EDX spectrumof La-Al-scoria (Fig. 5b) evident performed that the presence of

lanthanum ions along with other principal elements. The previousresults provided an evidence for the lanthanum ion successfullyloaded onto the surface of La-Al-scoria. Moreover, the increase in

4 S. Zhang et al. / Applied Surface Science 303 (2014) 1–5

Fig. 4. (a) SEM micrograph and (b) EDX spectrogram of Raw Scoria.

Fig. 5. (a) SEM micrograph and (b) EDX spectrogram of La-Al-Scoria.

Fig. 6. XRD patterns of (a) raw Scoria and (b) La-Al-Scoria.

oxygen content may due to the presence of La-Al-O composite andwhich would exhibit the positive effect on fluoride ion adsorption.

XRD studies

Fig. 6a and b showed the XRD spectra of raw Scoria and La-Al-Scoria. It can be seen from Fig. 6a that the crystalline peaks of rawscoria at 2� = 27.6◦ and 35.5◦ were the characteristic peaks of SiO2.However, the new crystalline peaks at 2� =22.4◦, 24.2◦ and 30.5◦

(Fig. 6b) appeared by cooperated thermally treatment and the La-Al-loaded of raw Scoria, which belong to the crystalline peaks ofLa-Al-O composite. It indicated that the lanthanum and aluminumwere loaded at the surface of La-Al-Scoria as the composite oxide,which is the effect functional group of La-Al-Scoria for adsorbingfluoride ion. The spectrum of La-Al-Scoria appeared an amorphousnature, which also made the La-Al-Scoria better activity for fluorideion [31–33].

XPS studies

The XPS spectra of the raw Scoria and La-Al- Scoria were usedto quantitative estimated the chemical elements. Survey spectraof the raw scoria showed that the major element peaks of O1s

and Al2p were 532 [34] and 73 eV, respectively (Fig. 7). How-ever, after the modification by La3+ and Al3+ loading, two elementpeak of O1s and Al2p respectively einstein shifted 0.2 ev and

Fig. 7. XPS scan of raw scoria and La-Al-Scoria.

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Fig. 8. XPS scan of raw scoria and La-Al-Scoria after fluoride ion adsorption.

ypsochromic shifted 0.9 eV compared with raw Scoria, and thatxhibited element peaks at 851 eV corresponding to La3d [35,36]or La-Al-Scoria. Thus results proved that the La–Al-O formedreferable crystalline, which consisted with the previous resultsf the SEM and XRD.

Fig. 8 depicted that the XPS spectra of raw scoria and La-Al-coria after fluoride ion adsorption. The board peak of La-Al-Scoriat 677 eV was assigned to F1s photoemission. However, there waso peak of F1s onto the raw scoria after adsorption, indicating thathe less adsorption capacity of fluoride ion onto raw scoria, whichonsisted with the adsorption experimental data. Furthermore,he element peaks of Al2p hypsochromic shifted 0.25 eV comparedith raw scoria. This can be explained that the interaction betweenuoride ion and La-Al-O composite by the form of electrostaticttraction. The above results explained that the large amount ofa-Al-O composite oxide existed onto the surface of La-Al-Scoriaas the immanent cause for the excellent adsorption capacity ofuoride ion.

onclusion

In this study, a new La-Al-Scoria adsorbent was synthesizedor the removal of fluoride ion from groundwater. The adsorptioninetics of La-Al-Scoria could be described by pseudo-second orderinetic model. The equlibrium data were fitted to Freundlich andangmuir adsorption isotherms. The amorphous structure of La-Al-coria gave good conditions for fluoride ion adsorption. The largemount of La-Al-O composite oxide existed onto the surface ofa-Al-Scoria was the immanent cause for the excellent adsorptionapacity of fluoride ion.

cknowledgement

We acknowledge the financial support of the National Naturalcience Foundation of China (Grant No.41203050) and the Geologi-al Survey Project of China (Grant No. 121201122094). The authorslso would like to highly thank Prof. Wei Feng and Dr. Cong Lu ofilin University, P.R. China for their kindly help.

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