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Journal of Hazardous Materials 231 232 (2012) 114 119
Contents lists available at SciVerse ScienceDirect
Journal of Hazardous Materials
j our na l ho me p age: www.elsev ier .com
Effect o ero
Cilai TanCollege of Reso
h i g h l
The select Ammoniu The result
a r t i c l
Article history:Received 29 March 2012Received in revised form 21 June 2012Accepted 21 June 2012Available online 29 June 2012
Keywords:Zero-valent iroNitrate reductSoil and grounLoess soilCationsAnions
le reafor soil and groundwater nitrate remediation under acidic or near neutral conditions. But few studies havebeen reported about it and the effects of coexistent ions under alkaline conditions. In this study, nitratereduction by Fe0 was evaluated via batch tests in the presence of alkaline soil and common cation (Fe2+,Fe3+ and Cu2+) and anion (citrate, oxalate, acetate, SO42, PO43, Cl and HCO3). The results showed thatcation signicantly enhanced nitrate reduction with an order of Fe3+ > Fe2+ > Cu2+ due to providing Fe2+
3
1. Introdu
The loesinant terra6.24 105 kresource issource for the industrindustrial wtilizer to imincreasinglyinvestigatiobasin (a typthat nitratethe drinking[2]. Excessivdiseases [3
CorresponE-mail add
0304-3894/$ http://dx.doi.oniondwater remediation
directly or indirectly. Most anions enhanced nitrate reduction, but PO4 behaved inhibition. The pro-motion decreased in the order of citrate > acetate > SO42 > Cl HCO3 oxalate PO43. Ammoniumwas the major nal product from nitrate reduction by Fe0, while a little nitrite accumulated in the begin-ning of reaction. The nitrogen recovery in liquid and gas phase was only 5678% after reaction due toammonium adsorption onto soil. The solution pH and electric conductivity (EC) varied depending on thespecic ion added. The results implied that PRB based Fe0 is a potential approach for in situ remediationof soil and groundwater nitrate contamination in the alkaline conditions.
2012 Elsevier B.V. All rights reserved.
ction
s plateau, an arid or semi-arid region, is the predom-in in the northwest of China, comprising an area ofm2. Loess soil is an alkaline soil. In this area, water
scarce and groundwater is the predominant waterpeople living, agricultural and industrial use. But asial and agricultural development, nitrogen-containingaste efuent discharge, excessive use of nitrogen fer-prove food output for increasing population induced
nitrate contamination in the groundwater [1]. Ann on sub-aqueous nitrate contamination in Guanzhongical loess plateau), Shaanxi Province in China, indicated
concentration in most groundwater markedly exceeded water standard (GB 5749-2006) of China (10 mg N L1)e nitrate in drinking water can cause cancer and other
]. Loess soil is an alkaline soil that has an average pH
ding author.ress: [email protected] (Z. Zhang).
value above 8.0, and HCO3, SO42, Cl, Na+, Ca2+, and K+ are themajor ions in the soil and groundwater [4].
Many studies have shown that nitrate reduction by Fe0 was anacid-driven and surface-mediated process, which was spontaneousunder acidic condition, or near neutral condition with the help ofcatalysts [58]. Permeable reactive barrier (PRB) based Fe0 has beensuccessfully used for in situ groundwater contamination remedi-ation, including nitrate, under acidic or near neutral conditions[9]. But no study has been reported whether or not it could workunder alkaline condition, such as in alkaline loess plateau. Granu-lar iron reactivity is predominantly controlled by the groundwatergeochemistry (e.g., coexistent ion and pH) [10,11]. The coexistentions behaved different impacts on Fe0 reactivity depending on thetarget pollutants [12,13]. Fe2+, Fe3+ and corresponding hydroxidesare the oxidative products from Fe0 corrosion. Lots of previousstudies showed that Fe2+ or Fe3+ enhanced Fe0 degradation of pen-tachlorophenol [14], chromate [15] and nitrate [16,17]. Cu(II) wasusually added as a catalyst for enhancing pollutants removal by Fe0
[6,14]. Cations (Fe2+, Fe3+ and Cu2+) without soil have been provedto promote nitrate reduction by Fe0 but there were no distinct effectby Ca2+, Na+ and K+ based on the former studies [17]. Therefore, we
see front matter 2012 Elsevier B.V. All rights reserved.rg/10.1016/j.jhazmat.2012.06.042f common ions on nitrate removal by z
g, Zengqiang Zhang , Xining Sunurces and Environment, Northwest A&F University, Yangling, Shannxi 712100, China
i g h t s
ed cations and anions enhance nitrate reduction by Fe0 in alkaline soil.m is major nal product from nitrate reduction.s prove the feasibility of using Fe0 for groundwater nitrate remediation.
e i n f o a b s t r a c t
Zero-valent iron (Fe0)-based permeab/ locate / jhazmat
-valent iron from alkaline soil
ctive barrier (PRB) technology has been proved to be effective
C. Tang et al. / Journal of Hazardous Materials 231 232 (2012) 114 119 115
also investition by Fe0
inorganic ioexistent orgselected to
The objeions in soilpresence ofpractical apin the loess
2. Materia
2.1. Materi
Unless ograde and water.
Nitrate sstock solutsodium salting Industrapproximatwith a spec[18] calculder = 0.762/as m. Irolarge amoudegassed ddried in vacfrom no.1 Aversity, ChiSoil sample1.0 mm nyloas: pH (soil:organic car3.68%, totalN 0.018 mgSO42 75 m
copper were not detectable. All processes were performed as themethods for the examination of water and wastewater of China(4th edition).
perim
eredrth-cven r weecic
V/Wtermg N
n conealed
at 20st wintai
suspssedllectiniti5.0 mge, f, nito detactioove 2) weactieasualyseC.
alyt
sca obtae nitred ul con
usinFig. 1. SEM photograph of iron grains.
gated the effects of Fe2+, Fe3+ and Cu2+ on nitrate reduc-in the presence of loess soil. Moreover, the commonns such as Cl, HCO3, SO42, PO43 and potential co-anic ions such as citrate, oxalate and acetate have beenevaluate their effects on nitrate removal by Fe0.ctive of this study was to evaluate the effects of common
and groundwater on nitrate reduction by Fe0 in the alkaline soil, aiming to give some possible guidance toplication of PRB technology for in situ removal of nitrate
plateau area in the future.
ls and methods
als
therwise indicated, all chemicals used were reagent
2.2. Ex
Tapsoil (Easoil (opowdeand spto soilthe deof 60 ma aniowere sshakertrol teonly coa littleand pawas coas the about a syrinnitrateorder tafter reto remgas (Nafter rand mthe an24 1
2.3. An
Theused toder. Thmeasuthermaminedall aqueous solutions were prepared with deionized
olution was prepared using NaNO3. Cation and anionions were prepared with corresponding chloride ands, respectively. The iron particle (Tianjin Zonghengx-ial &Trading Chemical Reagent Co., China) size wasely 50100 m in diameter (Fig. 1), irregular in shape,ic surface area 0.01520.0076 m2 g1, following Liaosating method, i.e. the specic surface of iron pow-D m2 g1, D represents the iron diameter, reportedn powder was pretreated with 0.5 mol L1 HCl untilnts of gas escaped (about 35 min), then washed witheionized water to remove the residual HCl and thenuum container for further use. The soil was obtainedgricultural Experiment Station of Northwest A & F Uni-na, air-dried and sieved via a 2.0 mm nylon screen.s used for chemical analysis additionally sieved via an screen. The properties of the soil can be summarized
water = 1:2.5 w/v) 8.35 0.12, moisture content 5.21%,bon 1.71%, total N (Kjeldahl-N) 523 mg kg1, total iron
copper 29.05 mg kg1, nitrate-N 0.94 mg kg1, nitrite- kg1, ammonium-N 0.595 mg kg1, Cl 96 mg kg1,g kg1, HCO3 82 mg kg1, dissolvable iron and
a DDS-307respectivelspectrophospectrophoreduction mits reactionnitroprussiFe2+ was dtotal dissolhydroxylamaverage val
3. Results
3.1. Effect o
As illustremoval. NiFe0 at 144 h49.6% remobe becausede and oxsmelled duents
ask (250 mL) was used as the reactor. 42.2 g raw loessumuli-Orthic Anthrosoles), corresponding to 40.00 g drydry at 105 C), and 5.00 g (in excess) pretreated ironre added into each reactor, followed by adding nitrate
ion stock solutions, resulting in a nal ratio of liquid = 5:1 (a national standard of water and soil ratio forination of soluble ions in soil), a nitrate concentrationL1, a cation concentration of 1.0 mM and 2.0 mM, orcentration of 1.0 mM and 3.0 mM. Then the reactors
tightly with rubber stopple, and placed in a complanate0 rpm. The headspace was air. At the same time a con-thout iron powder and ions and another control testning iron powder were prepared. After shaking 1 min,ension was extracted from the reactor using a syringe,
through a 0.45 m ber lter membrane. The ltrateed for pH and EC measurement, which was recordedal values. Subsequently, at the designed time intervall of suspension was extracted from the reactor withollowed by lter. The ltrate was collected for pH, EC,rite, ammonium, and dissolved iron measurement. Inect the gas phase constitute in the headspace of reactorn, the reactors were ashed using argon gas (>99.99%)air in the headspace in the beginning of reaction. Theas collected and analyzed using gas chromatographon. The NH3 was collected in 0.10 M NaOH solutionred as NH4+. All tests were conducted in duplicate ands were nished within 24 h at room temperature of
ical methods
nning electron microscopy (SEM, Hitachi S-450) wasin the microstructure and size information of iron pow-rogen gas in the headspace in reactor after reaction wassing gas chromatograph (GC-7800, Agilent) equippedductivity detector. The solution pH and EC were deter-g a pHS-3 C model exact pH meter (Lei-ci, China) and
model Electric Conductivity Detector (Lei-ci, China),y. Nitrate measurement was achieved by the ultraviolettometric method at 220 nm and 275 nm using a UV1102tometer [19]. Nitrite was analyzed by the hydrazineethod at 540 nm, and ammonium was measured using
with phenol and hypochlorite and catalyzed sodiumde to form indophenol at 636 nm [19]. The dissolvedetermined as phenanthroline method at 510 nm. Theved iron was analyzed as Fe2+ after its reduction usingine hydrochloride [19]. All results presented are theue of duplicate.
and discussion
f cations
rated in Fig. 2a, acid pretreated Fe0 enhanced nitratetrate removal rate of 69.2% was achieved by pretreated. By contrast, it was tend to constant after 120 h and onlyval was observed using raw Fe0 alone at 144 h. It might
acid pretreated removed the passive layer (e.g., sul-ide (Fe2O3)) on the Fe0 surface. A rotten-egg smell wasring acid pretreatment. Previous studies also showed
116 C. Tang et al. / Journal of Hazardous Materials 231 232 (2012) 114 119
50
60
70
/L
blank
Fe0
acidFe0
a
10
12b
Fig. 2. Nitrate en, (bwas a nitrate s
that acid prand perchloicantly pro92% and 98presence ofCu2+, respewithin 30 hrespectivelydue to the rimplied thavious studiunder acidition (pH > 8Fe0/cation, 20 h and themainly occuFe0 reactionconsistent wciency of Feby ultrasouucts (mainlCaCO3, FeCOwhich decrreduction [such as Fe2
tial for nitroxide lm reducing nietry of 0.75under neuttion would could acceleformation iand enhanc
occureact
Fe0
Fe0 0
10
20
30
40
250 50 75 100 125 150 175 200
Nit
rate
-Nm
g
Time (h)
1.0mM Fe2+
2.0mM Fe2+
1.0mM Fe3+
2.0mM Fe3+
1.0mM Cu2
2.0mM Cu2
0
2
4
6
8
0
pH
0
1
2
3
4
5
6
500 100 15 0 200
Nitri
te-N
(mg
/L)
Time (h)
c
Blank Acid Fe 0
1.0 mM Fe2+ 2.0 mM Fe2+
1.0 mM Fe3+ 2.0 mM Fe3+
1.0 mMCu2+ 2.0 mM Cu2+
0
5
10
15
20
25
0
Am
mo
nia
-N
mg
/L
reduction by Fe0 in the presence of loess soil and different cation: (a) nitrate nitrogolution without Fe0 and additional cation. The same means in the Figs. 3 and 4.
etreatment enhanced Fe0 reactivity toward nitrate [20]rate [21] reduction. The introduction of cation signif-moted nitrate reduction by pretreated Fe0. 96%, 99%,% of nitrate removal were observed after 144 h in the
1.0 mM Fe2+, 2.0 mM Fe2+, 1.0 mM Cu2+ and 2.0 mMctively. But complete removal of nitrate was achieved
might redox
2Fe3+ +
Cu2+ +
and 20 h in the presence of 1.0 mM and 2.0 mM Fe3+,. The pH in most systems was above 8.0 after 3.0 helease of OH from iron corrosion (Fig. 2b). The resultst nitrate reduction by Fe0 could occur at pH > 8.0. Pre-es showed that nitrate reduction by Fe0 was effectivec condition (pH < 7.0) but neglectable in alkaline condi-.0) [7,8,22]. In the systems including pretreated Fe0 orthe added nitrate was removed rapidly in the beginningn gradually decreased. It implied that nitrate reductionrred in the presence of fresh Fe0. It was well known that
with pollutants was surface mediated [23]. This wasith former researches that the decontamination ef-
0 was fast in the beginning of reaction or polished Fe0
nd [24,25]. As the reaction process, iron corrosion prod-y as hydroxide and iron oxides) and precipitates (e.g.,3) deposited on the surface of Fe0 due to increasing pH,
eased Fe0 reactivity and restrained the further nitrate26]. On the other hand, some iron corrosion products+, Fe(OH)+, Fe(OH)2, and green rust have great poten-ate reduction [27]. Huang et al. [28] reported that theon the surface of Fe0 could not prevent the iron fromtrate if plenty of Fe2+ was available with a stoichiom-
mol Fe2+ for 1.0 mol nitrate reduction to ammoniumral conditions. Once the Fe2+ was depleted, the reac-stop immediately. Another study also showed that Fe2+
rate iron corrosion and facilitate passive oxides trans-nto conductor (Fe3O4), which favored electron transfered nitrate reduction by Fe0 [16]. The key role of Fe2+
The addFe3+ > Fe2+ >addition of (2)). Althouadsorbed Fereported Cunitrate reducatalytic efited due to(e.g., iron ox6 mg N L1
Cu2+ additiafter 16 h areported threduction cduced. Lessand subseqIt might beto nitrite bu[30], whichthe reactionto precipitathe accumuFe0 or corro
In the sytivity (EC) dstabilized asumption o25 50 75 100 12 5 150
Time (h)
Blank Acid Fe 0
1.0 mM Fe2+ 2.0 mM Fe2+
1.0 mM Fe3+ 2.0 mM Fe3+
1.0 mM Cu2+ 2.0 mM Cu2+
05 100 150 200
Time (h)
Fe0
Acid Fe0
1 mMFe2+
2 mMFe2+
1 mMFe3+
2 mMFe3+
1 mMCu2+
2 mMCu2+
d
) pH, (c) nitrite nitrogen, and (d) ammonia nitrogen. Blank treatment
r in this study, because Fe2+ could be produced fromion after external cation was added as below:
3Fe2+ (1)
Cu0 + Fe2+ (2)ed cation enhanced nitrate reduction with an order of Cu2+ in the same concentration. Apparently, the directFe2+ is better than indirect from Cu2+ replacement (Eq.gh dissolved Fe2+ was not detectable, Fe(OH)2 or surface2+ might contribute the enhancement. Previous studies0 could accelerate electron transfer and then increasection by Fe0 as a catalyst [6,14]. But in this study itsciency in enhancing electron transfer might be inhib-
passivation by non-conducting soils and precipitatesides, hydroxide). Nitrite accumulated sharply to nearlyin the rst 10 h with the effect of Cu2+ (Fig. 2c). Moreon favored nitrite accumulation. But nitrite decreasednd less than 1.0 mg N L1 in 30 h. An et al. [29] alsoat FeCu nanoparticles signicantly enhanced nitrateomparing with nano-Fe alone, but more nitrite was pro-
than 2.0 mg N L1 nitrite accumulated in the beginninguently decreased rapidly in the presence of Fe2+ or Fe3+.
because Cu2+ or Cu0 could catalyze nitrate reductiont it was weak or not in catalyzing nitrite to ammonia
led to the accumulation of nitrite at the beginning of. Subsequently, Cu2+ or Cu0 lost its catalytic activity duetion and passivation by nonconducting substances. Butlated nitrite disappeared later due to the reduction ofsion products [27].stems with external addition of cation, electric conduc-ecreased rapidly in the beginning of reaction and thenfter 16 h (data not shown). This was due to the con-f nitrate and adsorption/co-precipitation of ions on the
C. Tang et al. / Journal of Hazardous Materials 231 232 (2012) 114 119 117
50
60
70
Blank
AcidFe0
chloride
A (1.0 mM )
50
60
L
Blank
Acid Fe 0
chloride
sulfate
B (3.0 mM)
Fig. 3. NitrateCH3COO .
corrosion padsorption systems cofrom nitratthe system in liquid ph(NH3) was 5ammoniumheadspace and stirringdetected inhigh pH (8solved iron adsorbed an
3.2. Effect o
As shownitrate redution. The into cation, nslowed dowlibrium compretreated 0
10
20
30
40
250 50 75 100 125 150 175
Nitra
te-N
mg/L
Time(h)
sulfate
bicarbonat e
oxalate
citrate
phosphate
acetate
0
10
20
30
40
0
Nitra
te-N
mg/
400
500
600
700
800
900
8.5
8.9
9.3
9.7
10.1
10.5
200 40 60 80 100 120C
on
du
ctivity (
us/c
m)
pH
Time (h)
a
pH
Conductivity
8
8.5
9
9.5
10
10.5
11
0
pH
700
10.5
c10.2400
500
600
8
8.5
9
9.5
10
200 40 60 80 100 120
Co
nd
uctivity (
us/c
m)
pH
Time(h)
pH
Conductivity
8.2
8.6
9
9.4
9.8
20
pH
reduction by Fe0 as affected by different external anions: (A) 1.0 mM; (B) 3.0 mM, and
roducts of iron. Finally, both the reduction reaction andreached equilibrium and then EC kept constant. In allntaining Fe0, ammonium was the major nal producte reduction (Fig. 2d). More ammonia was detected inwith more nitrate removal. The total nitrogen recoveryase (i.e., NO3-N, NO2-N and NH4+-N) and gas phase673% (data not shown). It was due to the adsorption of
onto soil and precipitates. NH3 gas was observed in theof reactor after reaction due to relative high pH (>8.0). But no N2 and other nitrogen oxide compounds were
headspace. Ammonia volatilization in the system with9) was also observed in previous studies [31,32]. Dis-and copper were undetectable in the system because ofd deposited in high pH.
f anions
ed in Fig. 3A and B, all anions except PO43 enhancedction by Fe0. Contrarily, PO43 inhibited nitrate reduc-uence was favored at higher concentration. Similaritrate decreased sharply during the rst 16 h and thenn. But it took longer time before they reached equi-paring with cation. In the control treatment (i.e., onlyiron without external anion addition) 72.5% of nitrate
removal w84.7% in thof Cl, resammoniuminsignicanThe enhancthe promotstrength bythe premisintermediaeasily conv[27,34]. The124 h in thThe externaerated ironstrength thenhancemethe promotof surface rtion of greewas also efthat both Gichiometricsystem ext25 50 75 100 12 5 150 175
Time(h)
bicarbonate
oxalate
citrate
phosphat e
acetate
300
500
700
900
1100
20 40 60 80 100 120
Conductivity (
us/c
m)
Time (h)
b
pH
Conductivity
750d350
450
550
650
0 40 60 80 100 120
Conductivity (
us/c
m)
Time (h)
pH
Conductivity
the pH and EC of 3.0 mM anions: (a) Cl , (b) SO42 , (c) HCO3 , (d)
as observed after 124 h. But it increased to 76.6% ande presence of 1.0 mM and 3.0 mM external additionpectively (Fig. 3A, B). The corresponding increase of
was also observed (data not shown). Nevertheless,t nitrite accumulated and nearly disappeared after 60 h.ement of nitrate reduction by Fe0 might result fromion of iron pitting corrosion and the increase of ionic
Cl [33]. Iron corrosion and electron release wase of pollutants degradation by Fe0 [23]. Nitrite, as thete product from nitrate reduction, was not stable anderted to ammonium by Fe0 and iron corrosion products
nitrate removal efciency was 84.4% and 92.9% aftere presence of 1.0 mM and 3.0 mM SO42, respectively.l addition of ion increased ionic strength and then accel-
corrosion. Distinctly, sulfate contributed stronger ionan chloride with the same concentration. Hence, itsnt was better. Moreover, previous studies indicated thation of SO42 and Cl might contribute to the increaseeactivity or sorption capacity of Fe0 and the produc-n rust (e.g., [Fe4IIFe2III(OH)12SO4yH2O], GRSO42 ), whichfective for nitrate reduction [10,27,35]. It was provedRSO42 and Fe4.5Fe1.5(OH)12Cl1.5xH2O (GRCl ) could sto-ally reduce nitrate to ammonium [27]. Thus, in theernally adding Cl and SO42, nitrate reduction was
118 C. Tang et al. / Journal of Hazardous Materials 231 232 (2012) 114 119
650
10
10.2
/cm
)
a
12
650
700
10
10.5
2
s/c
m)
b
anion
probably paThe promottration, respresence ofand GRCl , [36]. A greein the systeintroductioand 93.4% itive effectCH3COO >and the othin pH and Eincreased aand then kiron corrosby Fe0 contquent ammof other ionIt implied thwould be re
The nitrthe systemtively. The not shown)and inner-scorrosion aphosphate cthe competnitrate rem84.2%) (Fig.motion to nnitrate (>95and 3.0 mMat the last pbeginning o
nions adsn thie theoug
redulutiother d asd th450
550
9
9.2
9.4
9.6
9.8
200 40 60 80 100 120
Conductivity (
us
pH
Time(h)
pH
Conductivity
8
8.5
9
9.5
10
200 40 60 80 100
pH
Time(h)
c
pH
Conductivity
8.5
9
9.5
0
pH
Fig. 4. The time course of pH and EC in the presence of 3.0 mM
rtially resulted from green rusts (GRCl ) and GRSO42 .ion of HCO3 was similar to Cl at the same concen-ulting in a nitrate removal of 76.4% and 85.7% in the
1.0 mM and 3.0 mM, respectively. Similar to GRSO42the GRHCO3 also had potential for nitrate reductionn color was observed after settling during experimentsm with externally adding Cl, SO42 and HCO3. Then of 1.0 mM and 3.0 mM CH3COO achieved 88.25%nitrate removal, respectively. As a whole, the pos-s of the four anions above decreased in the order:
other aused aeffect idissolv
AlthnitrateThe soeach obehavetion, an SO42 > Cl HCO3. Although the rst ion was organicers were inorganic, they exhibited similar variationC during the whole reaction period. The solution pHnd EC decreased signicantly within the rst 40 h,ept stable (Fig. 3a, b, c, d). Both alkaline release fromion and acidity consumption from nitrate reductionributed to pH increase. Nitrate reduction and subse-onium adsorption, the adsorption and co-precipitations onto iron hydroxides all contributed to EC decrease.at other co-existent contaminants (e.g., heavy metals)moved simultaneously by adsorption and precipitation.ate removal rate was 62.4% and 60.9% (Fig. 3A, B) in
externally adding 1.0 mM and 3.0 mM PO43, respec-nitrogen recovery was the highest in all anions (data. Phosphate has been reported to form co-precipitationphere complexes on the surface of iron inhibited ironnd electron transfer [37,38]. Although the addition ofould increase ion strength and promote iron corrosion,itive adsorption was stronger. Oxalate achieved similaroval rate as Cl in the same concentration (76.3% and
3A, B). Among all anions, citrate achieved the best pro-itrate reduction by Fe0. Almost complete removal of%) was observed after 124 h in the presence of 1.0 mM
citrate. The reactors containing citrate were very cleareriod of the experiment, though they were turbid in thef reaction as other systems. But the reactors containing
low pH led ions, whichprecipitatiodecreased tsimultaneohigher conc
In conctive effectsloess soil. rate > acetacation, nitrotion was obdetected af
4. Fe0-bas
Accordinby Fe0 fromanions (Cl
to the promof green runicantly ereduced to cess whichMore iron concentrati700
800
900
1000
1100
0
Conductivity (
us/c
m)
500
550
600
0 40 60 80 100 120
Conductivity (
u
Time(h)
pH
Conductivity
: (a) PO43 , (b) C2O42 , (c) citrate.
s were always turbid. Considering citrate was usuallyorbent or chelator in industry, it might have the sames study. Citrate as a chelator could destabilize and nally
passive oxide layer on the surface of iron [37].h PO43, oxalate and citrate behaved differently onction, they exhibited similar variation in pH and EC.n pH and EC varied repetitive and showed opposite to(Fig. 4). A possible explanation was that the added ion
a buffer alone or together with some ions in soil solu-us they prevented the solution pH from uctuating. The
to dissolve the precipitates and/or desorb the adsorbed
caused a rise of EC. Contrarily, the high pH inducedn/co-precipitation and then more adsorption, whichhe EC. Consequently, the solution pH and EC changedusly and exhibited a uctuant situation, especially withentration.lusion, all anions excluding PO43 revealed posi-
on nitrate reduction by Fe0 in the presence ofThe promotion effect decreased in the order: cit-te > SO42 > Cl HCO3 oxalate PO43. Similar togen recovery was only 6178%. Some nitrite accumula-served in the beginning, but less than 1.0 mg N L1 waster reaction in all systems with different anion present.
ed PRB implication in the loess plateau area
g to the above results, reductive removal of nitrate an alkaline (pH > 8) soil was possible. The major
, SO42, HCO3) can accelerate nitrate reduction dueotion of iron corrosion and the possible occurrence
sts. The Fe0 corrosion products, Fe(II) and Fe(III), sig-nhanced nitrate reduction. Moreover, nitrate can benitrogen gas by hydrogenotrophic denitrication pro-
consumed H2 deriving from iron corrosion [39,40].powder may be consumed in the regions where theon of PO43 is higher. Some organic ligands (e.g.,
C. Tang et al. / Journal of Hazardous Materials 231 232 (2012) 114 119 119
citrate, acetate and oxalate) would promote not only nitratechemical reduction by Fe0 but also microorganism denitrication.For example, the denitrication rates decreased in the of orderacetate > H2 > S > thiosulphate > ferrous iron in microcosm [41]. Cer-tainly, therenvironmenThe iron in rpassivationfor the reacFe0 [42]. Thtion and relBut it is stilwater nitradeveloped i
5. Conclus
The resuline loess plreduction recould be acanions (citrsame concein the ordeorder of citOnly PO43
Ammoniumreduction. Nwas less threcovery inDissolved iring on the potential tenitrate cont
Acknowled
We acknResearch LaResearch DrD. Strahm, Seattle, U.Sthe professence, Northanonymous
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quaniron. .B. Hateffe91.. Huannitratn, T. ted Fe10) 98. Hao
meta. Hwaitratection . Hwao valeukudape of n(1996. Hu, tallic i.H. Ha
role o. Su, Renic re. TechnHarmsion ofros. S. Su, late, c(2004n, T. Litricteria, iswas. Eng
Devlinnitratifer, John, undw. Techne are lots of concomitant contaminants in the specict, of which the effects still need to investigate in detail.eactors after reaction was black and agglomeration. The
of iron surface resulting from high pH should accounttion expiration, which would decrease the longevity ofus, in an alkaline loess plateau area, more Fe0 consump-ative short longevity of PRB may be the main concern.l an alternative approach to remediate soil and ground-te contamination if no other better technologies to ben future.
ions
lts indicated that nitrate reduction by Fe0 in the alka-ateau area was possible. High pH did not inhibit nitrateaction immediately. By contrast, the remove efciencycelerated by some cations (Fe3+, Cu2+ and Fe2+) andate, acetate, oxalate, Cl, SO42 and HCO3). At thentration, the promotion effect of the cation decreasedr of Fe3+ > Fe2+ > Cu2+, but the anions decreased in thisrate > acetate > SO42 > Cl HCO3 oxalate PO43.exhibited an inhibition for nitrate reduction by Fe0.
was the major detectable nal product from nitrateitrite, the intermediate product of nitrate reduction,
an 1.0 mg N L1 after 100 h reaction. But the nitrogen liquid and gas phase was only 5678% in all systems.on was not detectable. The pH and EC varied depend-character of added ion. This study implied that it is achnique to use Fe0-based PRB for in situ remediation ofamination in the loess plateau area.
gements
owledge Mr. Su Chunming, National Risk Managementb., U. S. Environmental Protection Agency, 919 Kerrive, Ada, Oklahoma, for editing the paper, and Dr. BrianUniversity of Washington, College of Forest Resources,., for correcting expression in the paper. We also thankor Yao Yaqin for SEM micrograph, College of Life Sci-west A & F University. We also acknowledge editor and
reviewers for their suggestion and comments.
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Effect of common ions on nitrate removal by zero-valent iron from alkaline soil1 Introduction2 Materials and methods2.1 Materials2.2 Experiments2.3 Analytical methods
3 Results and discussion3.1 Effect of cations3.2 Effect of anions
4 Fe0-based PRB implication in the loess plateau area5 ConclusionsAcknowledgementsReferences