V 'N U Journal o f Science. M athem atics - Physics 25 (2009) 15-19
Arsenic removal from water by magnetic Fei.xCOxFe 204 and Fei-yNiyFe 204 nanoparticles
Nguyen Hoang Hai*, Nguyen Dang Phu
C e n te r f o r M a te r ia ls S cien ce, F a c u lty o f P h ysics, C o lle g e o f S cien ce, V N U 3 3 4 N gu yen Trai, H anoi, Vielncun
R eceived 12 March 2009
A b s r t a c t This paper studied the cffccls o f Co, Ni replacement in ứie Fei.^Co^Fe204 and Fci,yNiyFc204{x, y = 0, 0.05, 0.1, 0.2, 0.5) nanoparticles, pH, weight o f nanoparticles/ml o f water and lim e o f stirring on the arscnic removal ability. The results showed that small amount o f 0.25 g/I o f F c304 nanoparticlcs after stirring time o f 3 m inutes can reduce the arsenic concenưation from 0.1 mg/1 to 0.01 mg/1. The removal was also affected by the pH of the water Absorption of arsenic by nanoparticies was effective when pH was sm aller than 7 and reduced with the increase o f pH. At pH o f 13, there was a sư ong release o f arsenic ions from arsenic-absorbed nanoparticles back to water. The tim e o f stiư in g was studied from 1 minute to 2 hours, the optimal time was about few minutes. Co and Ni presence was reported to maintain saturation magnetization stable under working conditions. For C o rcplaccmcnt, absorption does not change significantly when X <
0 .! and slightly reduccs when X > Q . \ . The presence o f Ni improved the absorption in most eases.
K eyw ords: Magnetic nanoparticles, ferrites, arscnic removal, water ưcatment.
Ỉ. Introduction
Arsenic occurs naturally in rocks, soil, water, air, plants and animals. It can be further released into th.e environment through natural activities such as volcanic action, erosion o f rocks and forest fires, or thirough human actions. Higher levels of arsenic tend to be found more in ground water sources than in sarface water sources of drinking water. Arsenic-conlaminaled water has been a serious problem especially in Vietnam, Bangladesh and some areas in the world [1, 2]. Human exposure to arsenic can cause both short and long term health effects. Short or acute effects can occur within hours or days of exposure. Long or chronic effects occur over many years. Long term exposure to arsenic has been linked to cancer o f the bladder, lungs, skin, kidneys, nasal passages, liver and prostate. Short term exposure to high doses o f arsenic can cause other adverse health effects [3, 4]. The World Health On-ganization (WHO) maximum permissible concentration (MPC) value was set as 0.01 mg/1 which hais been applied in many countries. There are many arsenic-removal techniques which have been av'ailable such as coprecipilation, adsorption in fixed-bed fillers, membrane filiation, anion exchange,
Corresponding author. Tcl.: (84-4) 3 5582216 E-mail; nhhai@ vnu.vn
15
16 N.H. Hai, N.D. Phu / VNU Journal o f Science, M athematics - Physics 25 (2009) Ỉ5 -Ỉ 9
electrocoagulation, and reverse osmosis [5, 6]. Iron oxides have been reported to have a high a ffin iity for the adsorption o f arsenic and arsenate [7-9] due to the ability to form inner-sphere bidentaite- binuclear complexes with iron oxides [10-11]. Iron oxide nanoparlicles with large surface area ;arc promising for arsenic removal. Some researches have been paid to study the effects of environment on arsenic adsorption ability o f magnetite FC304 nanoparticles [9, 12]. Magnetite nanoparticles haive highest saturation magnetization o f 90 emu/g among iron oxides. Therefore, magnetite nanopartic:les can be used to adsorb arsenic ions followed by magnetic decantation. Other iron oxides amd hydroxides have been reported to have arsenic ability. However, magnetic properties of th ese compounds are much less than that of magnetite. Oxidation o f magnetite which resulted to the reduice of the saturation magnetization was found. In a research of our group reported that replacement of Fie in Fc304 by a small amount o f or can improve the oxidation resistance of the compoumd [14], Oxidation resistance is an important factor for arsenic removal under atmospheric conditions. In this paper, we studied arsenic adsorption ability of Fei.^Co^Fc204 (Co-ferrites) and Fei.vNiyFe204 (N i- ferrites) (jc, >- = 0, 0.05, 0.1, 0.2, 0.5) nanoparticles.
2. Materials and m ethods
Magnetite particles with size of 15 nm were prepared by conventional coprecipitation o f Fe'^'" aind ions by OH” at room temperature. In a typical synthesis, 4.17 g o f FeCl3.6H20 and 1.52 g of FeCl2-4H20 (such that Fe^'^fFe“*=2) were dissolved in 80 ml water (concentration o f is 0.1 ĨM) with vigorous stirring. A solution of 6 ml NH4OH 35% was added with the rate o f 1 drop per secondi at room temperature during constant stirring. Black precipitates o f Fc304 (Fe0.Fe203> were formed aind isolated from the solvent by magnetic decantation. Water washing and decantation process wcere repeated four times to remove excess solution. By a similar way, Fei-^Nũ0.Fe203 and Fei-^Co^.Fcz^Oj with JC = 0.05, 0.1, 0.2. 0.5 and ỵ = 0.2, 0.4 nanoparticles were made by replacing by aind using NÌCI2.6H2O and C0CI2.6H2O, respectively. All procedures were conducted under INi atmosphere. Electron Transmission Microscope (TEM) JEMIOIO-JEOL was used to determiine p a ilic lc b'iJLC. T h e bU uclurc w u i cA ainincd b y X -ra y U iffraclom ctcr ( X R D ) D 5 0 0 5 , B rukcr, u s in g Cu Wi^j, radiation. Magnetic properties were measured by Vibrating Sample Magnetometer DMS 880-CT'S.
Arsenic solution (0.1 mg/1 o f As^"*") was obtained by dissolving A S2O 3 in doubly distilled improve t:he oxidation resistance of the compound [16]. Oxidation resistance is an important factor for arscniic removal under atmospheric conditions. In this paper, we studied arsenic adsorption ability of F'C].
^Co^Fc204 (Co-ferrites) and Fei.vNivFc204 (Ni-ferrites) (x, y = 0, 0.05, 0.1, 0.2, 0.5) nanoparticies.
3. Results and discussion
Figure 1 presents the TEM image of the FC304 nanoparticles with particle size o f 10 - 16 nm. T'he particles were almost spherical and low size dispersity. The mean particle size was estimated to ỉbe 13.3 ± 3.1 nm. The surface area of 77.9 mVg was calculated for magnetite sample from the me:an particle and magnetite density (5.18 g/cm^). XRD patterns of magnetite, Co-ferrites (Fig. 2) and Mi- ferrites (not shown) revealed that the particles have the invert spinel crystalline structure as in the builk phase. The presence o f and ions did not change the particle size and reflection peatks significantly. The field dependence of magnetization showed that all samples were superparamagneitic at room temperature. In inverse spinel magnetite, a half of F e^ ions locale at A sites and the half of
N.H, ỉỉa i. N.D. Phu / VNU Journal o f Science, M athematics - Physics 25 (2009) 15-Ì9 17
thhem together with the divalent ions locale at B sites. The and ions prefer to replace at Bi sites. Therefore, the orientation o f spins is as followings:
Fei+ /-* 2+ rp2+ 3'^
COỵ Fe
Fe3+
O Ì '
o f -
/According to Neel theory [15] saturation magnetization for a formula unit o f the Co- and Ni-ferrites ccan be determined by:
= Ì A - 2x)Mb
Magnetic moment of and Co*'" ions is 2 / i g and 3 / i g , respectively. As a result, the saturation cof magnetization of the Co- and Ni-ferrites linearly reduces with JC and y. Figure 3 presents the ssaturalion magnetization as a function of Co and Ni content. A linear dependence was found in the ssamples with the Co and Ni content lower than 0.5. At the higher content (jc, y = 0.5), the Co and Ni iatoms can also place at A sites which resulted in the deviation from the linear dependence.
4 0 0 -
3 0 0
-— ,
3
Cữ
2 0 0
ưic
<D
c 1 0 0
0 -
Fig. 1. TEM image o f the FC3O4nanoparticlcs.
20 (degree)
Fig. 2. X R D patterns o f ứic magnetite nanoparticlcs.
Arsenic adsorption ability of magnetite^ Co- and Ni-ferrites was studied with different conditions of stirring time, concentration of nanoparticles, and pH. Table 1 shows the stirring time dependence of arsenic removal of I g/1 o f Co-ferrites at neutral pH. The starting concentration of o .i mg/1 was reduced about 10 times down to the MPC value of 10 p.g/1 after stiưing lime o f few minutes. The removal process did not seem to depend significantly on the concentration o f X in the Co-feưites.
Similar results were found for the Ni-ferrites, in which arsenic concentration was reduced to the MPC value after few minutes o f stirring and the removal did not change significantly with y. We also studied the effects c f the weight o f nanoparticles on the removal process The stŨTÌng time was fixed to be 3 minutes and the weight of samples was changed from 0.25 g/1 to 1.5 g/1 with step of 0.25 g/1. The results showed that, after 3 minutes, the optimal weight to reduce arsenic concentration down to the value lower than the MFC was 0.25 g/1 for magnetite and 0.5 g/1 for Co- and Ni-feưites.
18 N.H. Hai, N.D. Phu / VNU Journal o f Science, M athematics - Physics 25 (2009) 1 5 -Ỉ9
Fig. 3. Saturation magnetization of the C o and Ni-feưite as a function of (x) and Ni""" O') content.
The arsenic adsorption was reported to be independent of pH in the range o f 4 to 10. However, at high pH value, the adsorption reduced significantly. Arsenic was desorbed from the adsorbent at alkaline pH [9]. Our reported results were conducted at pH o f 7. After arsenic adsorption, t;he nanoparticles were stừred under pH of 13 to study the desorption process. Nanoparticles we;re collected by a magnet and arsenic concentration in the solution was determined by AAS. Resuilts showed that 90% of arsenic was desorbed from nanoparticles. The nanoparticles after desorption diid not show any difference in arsenic re-adsorption ability. The adsorption-desorption process W'as
repeated 4 times, which proved that the nanoparticles can be reused for arsenic removal.
Table 1. Arscnic concentration (|ig/l) remained in water after removal by 1 g/I of the Co-fcrritcs as a function tof the stừring time
Tim e (min) X = 0.05 ^ = 0.1 x = 0.2 ^ = 0.5
1 10 11 6 6.5
3 6 5 8.5 7
7 10 9 4.2 7.8
15 9 12 5 6.9
30 12 4.5 5 11.2
60 4.5 5 8 9.8
4. Conclusion
The presence of and in Fei.^CojcFe204 and Fei.^NiyFe204 with oxidation resistance diid not change significantly arsenic adsorption ability. With small amount o f the materials, simptle preparation, we could reduce arsenic concenưation 10 the value lower than MPC.
Acknowledgm ents. The authors would like to thank the Asia Research Center, Vietnam Nationial University, Hanoi (DT 34/2007/HD-DT) for finance support.
N.H. HaL N.D. Phu / VNV Journal o f Science, Mathematics - Physics 25 (2009) 15^19 19
Rieferences
IIII http://w w w .cpa.gov/safew ater/arscnic
[121 M. Bisscn, F.H, Frimm el, A rsen ic-A review. Part I; Occurrence, toxicity, spcciation, m obility, A cta H y d ro c k Hydrob. 31 (2003) 9.
1'3| L.C.D. Anderson, K .w . Bruland, B iogeochem islry o f arsenic in natural waters: The im pwtance of methylated species. Environ. Sci. TechnoL 25 (1 9 9 1 )4 2 0 .
[^4| w .p . Tseng, H.M. Chu, s . w . H ow, J M. Fong, c . s . Lin, s . Yeh, Prevalence o f skin canccr in an endemic area o f chronic arscnicism in Taiwan, y. Nat. C an cer ỉnst. 40 (1968) 453.
[Í5| L.G. T w idw cll, J. M cC loskey, p. Miranda, M. Gale, Technologies and potential technologies for removing arscnic from proccss and m ine wastewater, in P roceedin gs g lo b a l sym posium on recycling, w aste treatm ent an d clean technology, Ed. I. Gaballah, J. Hager, R. Solozabal, Warrendale, PA. (1999) 1715.
[(6| M. Bisscn, F.H. FrimmcK A rscn ic-A review. Part II: Oxidation o f arsenic and its removal in water ưeatment, A a a H y d ro c k H ydrob. 31 (2003) 97
1'7| M L . Pierce and C .B . M oore, Adsorption o f arscnile and arsenate on amorphous iron hydroxide, W ater Res.
15 (1982) 1247.
[Í8| K.p. Raven, A. Jain, R.H. Locppcrt, Arsenite and arsenate adsorption on íeưihydrite: Kinetics, equilibrium, and adsorption envelopes. Environ. Sci. T ech n ol 32 (1998) 344.
1^9| S. Yean, L. C ong, C.T. Y avuz, J.T. M ayo, w . w . Yu, A T . Kan, V.L. C olvin, M .B. Tom son, Effect o f magnetite particle size on adsorption and desorption o f arsenite and arsenate, J. M ater. Res., 20 (2005) 3255.
[[I()| S. Fcndorf, M.J. Eick, p. Grossl, Arsenate and chromatc retention m cchanisnis on goethite Surface structure, Environ. Sci. Techno!. 31 (1997) 315.
[[II] A. Manccau, T lic m cchanism o f anion adsorption on ironoxides-Evidcnce for the bonding o f arsenate tctrahcdra on free F c ( 0 ,0 H ) ( 6 ) edges, Gcochim . Cosm ochim , A cta 59 (1995) 3647.
|[12J X.ỈI. Sun, H.E. Doner, An investigation o f arsenate and arscnile bonding structure on gocthite by FTIR, Soil 5 c/ 161 (1 9 9 6 )8 6 5 .
1(13] G.A . Waychunas, B .A . Rea, c . c . Fuller, J.A. D avis, Surface ch cm isư y o f fcrrihydrite, Part 1. EXAFS studies o f the geom etry o f coprccipitatcd and adsorbed arsenate. Geochim . C osm ochim , A cta 57 (1993) 2251.
|[14| N.H. Jlai, N .D . Phu, N. Chau, H.D. Chinh, L.H. Hoang, D.L. L eslic-Pelccky, M cchanism for Sustainable M agnetic Nanoparticlcs under Ambient Conditions, J. Korean Phys. Soc. 52 (2007) 1327.
If I Si I N ccl.A m i. de Phvs. 3 ( 1 9 4 8 ) 137.
