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IRON AND ALUMINUM OXIDE CHARACTERIZATION FORHIGHLY-WEATHERED ALABAMA ULTISOLSJoey N. Shaw aa Department of Agronomy and Soils , Auburn University , 202 Funchess Hall, Auburn, AL,36849, U.S.A.Published online: 05 Feb 2007.
To cite this article: Joey N. Shaw (2001) IRON AND ALUMINUM OXIDE CHARACTERIZATION FOR HIGHLY-WEATHEREDALABAMA ULTISOLS, Communications in Soil Science and Plant Analysis, 32:1-2, 49-64, DOI: 10.1081/CSS-100102992
To link to this article: http://dx.doi.org/10.1081/CSS-100102992
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COMMUN. SOIL SCI. PLANT ANAL., 32(1&2), 49– 64 (2001)
IRON AND ALUMINUM OXIDECHARACTERIZATION FOR HIGHLY-WEATHERED ALABAMA ULTISOLS
Joey N. Shaw
Department of Agronomy and Soils, Auburn University,202 Funchess Hall, Auburn, AL 36849
ABSTRACT
Characterization of oxide and oxyhydroxide iron (Fe) and alumi-num (Al) forms in highly-weathered Ultisols of the southeasternUnited States is necessary to develop further understanding of col-loidal-facilitated transport of pollutants, sorption of contaminants,erosion, and soil genesis. The objective of this study was to exam-ine Fe and Al oxides from several highly-weathered Ultisols andevaluate their relationships with particle size fractions and othersoil chemical and physical properties. Samples contained in theargillic horizon of 13 highly-weathered pedons were examined.These pedons either contained kandic horizons, were in a kaoliniticmineralogical family, or were in a siliceous mineralogical familywith a subactive cation exchange capacity activity (CEC) class.Standard characterization analyses were performed on all pedons.Samples were fractionated into a coarse (2 to 2000 mm) and fine(�2 mm) fraction, and ammonium oxalate (Feo and Alo) and di-thionite-citrate-bicarbonate (Fed and Ald) extractable Fe and Al
49
Copyright � 2001 by Marcel Dekker, Inc. www.dekker.com
Fax: (�1) 334-844-3945; E-mail: jnshaw�acesag.auburn.edu
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were quantified in each. Selective dissolution treatments were con-ducted on �2 mm fractions prior to mineralogical analyses. Amodified differential XRD (DXRD) was used for further Fe oxidecharacterization. Pretreatments worked well for concentratingcrys-talline oxide forms. All Fe and Al extracted forms were higher in thefine than the coarse fraction. The Fe oxides were highly crystalline,but a significantly higher ratio of Feo/Fed was found in the fine ascompared to the coarse fraction (0.041 to 0.020, respectively). Bothgoethite and gibbsite quantities were negatively correlated with ef-fective cation exchange capacity (ECEC) (r � �0.54 and �0.80,respectively). The Feo/ Fed ratio in the �2 mm fraction was posi-tively correlated (r � 0.49) with hematite content, while it wasnega-tively correlated with goethite quantities (r � �0.61), suggesting aferrihydrite precursor is associated with hematite formation.
INTRODUCTION
Characterization of Fe and Al oxides, hydroxides, and oxyhydroxides (re-ferred to as oxides) in low activity (as per cmol of CEC/g of clay), well-drained,Ultisols is important for evaluating studies on colloidal-facilitated transport ofpollutants, sorption of contaminants, erosion, and soil genesis (1,2,3). Highly-weathered Alabama Ultisols possess a kaolinitic or siliceous mineralogy with akandic horizon, or an argillic horizon with a subactive CEC activity class (CEC/total clay ratio �0.24) (if siliceous mineralogy). In these soils, the Fe and Al inthe oxide minerals originates from primary mineral (e.g., biotite) weathering (4).Iron and Al oxides are concentrated in argillic horizons because these horizonstypically exhibit the maximum pedogenic expression and concentration of pedo-genic minerals (5).
Iron oxides occur as a continuum of crystalline, paracrystalline, and amor-phous forms in soils, and are operationally defined by their extracting medium(6). Iron oxide forms that can be extracted by dithionite-citrate-bicarbonate (Fed)are referred to as ‘‘free’’ (nonsilicate bound) Fe oxides, whereas ammonium oxa-late extractable (in the dark) forms (Feo) consist of amorphous and poorly-crystal-line oxides and organically bound Fe (7). Ferrihydrite, a poorly crystalline Feoxide form, is thought to contribute largely to Fe in oxalate extractions of subsoilhorizons, whereas well-drained, highly-weathered soils tend to have high quanti-ties of crystalline goethite (a-FeOOH) and hematite (Fe2O3) (8,9). Many studieshave investigated the role of Fe oxides on soil color, and it has been shown yel-lower to brownish hues indicate appreciable goethite content while redder huesindicate higher hematite contents (6). Iron oxide minerals in highly-weathered en-
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vironments often possess appreciable Al substitution (9–11), which has beenshown to lead to brighter colors in synthesized soil hematites (12).
Extraction of Al oxide forms with ammonium oxalate and dithionite-citrate-bicarbonate has not been shown to be systematic with regard to mineral types, butit is commonly thought both oxalate (Alo) and dithionite-citrate-bicarbonate (Ald)extracts Al from poorly crystalline oxides (13). Because significant Al substitu-tion commonly occurs in Fe oxide minerals, it is difficult to partition the amountof extracted Al that resides in poorly crystalline Al oxide minerals and the amountresiding in substituted Fe oxide minerals.
Many studies have evaluated the influence Fe and Al oxides have on soilproperties. These minerals have been shown to affect soil erodibility (1), soil ag-gregation (14,15), colloid translocation (2) and anion (3,16,17), cation (6), andpesticide (18) adsorption. Several workers have shown that the ability of a soil tosorb charged solutes is often correlated with Feo and Alo quantities (19,20). Sub-surface horizons enriched with oxides can be exposed at the surface under accel-erated erosion and on disturbed or tilled sites, thus the evaluation of these oxideforms as per particle size enrichment is important for evaluating sediment attachedrunoff of pollutants.
Although it has been shown that extractable Al and Fe forms tend to in-crease with decreasing particle size (21), the relationships between physical andchemical soil properties and oxide mineralogy has not been thoroughly evaluatedfor these highly-weathered Alabama Ultisols. Evidence has suggested crystallineFe oxides tend to occur as discrete particles, while amorphous forms are oftenassociated with phyllosilicate surfaces in clay fractions (22). In coarser fractions,Fe oxides have been shown to occur as coatings on quartz grains (15). The objec-tives of this study were 1) to evaluate the size partitioning of extractable Fe andAl forms and 2) to evaluate relationships between soil’s chemical, physical, andmineralogical properties and Fe and Al oxide forms in these soils.
MATERIALS AND METHODS
Samples were collected from portions of the argillic horizon (mainly Bt1)contained in the control section of 13 pedons sampled during Cooperative SoilSurvey activities in Alabama (Tables 1 and 2). These pedons were chosen becausethey typified highly-weathered soils of the region. Pedons were sampled fromeither: 1) the Piedmont physiographic province with metamorphic and igneouscrystalline-rock parent materials, or, 2) the Upper Coastal Plain physiographicprovince with parent materials consisting of highly-weathered transported mate-rial mostly eroded from the Piedmont plateau. All pedons were Ultisols, possessedeither kandic horizons or were in a subactive CEC activity class, and were in
IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 51
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kaolinitic or siliceous mineralogical families (Table 1). Samples from the argillichorizon ranged in color from dark red to yellowish-brown, and ranged from sandyloam to clay textured (Table 2). These pedons were all well-drained and appear tohave not been impacted by contemporary fluctuating water tables that would sig-nificantly alter Fe oxide forms (23).
Samples were crushed to pass a 2-mm sieve, and particle-size analyses wereconducted on all samples by the pipette method (24). Sand grains were separatedinto standard size fractions by sieving. Base cations [calcium (Ca), magnesium(Mg), potassium (K), and sodium (Na)] were extracted with 1 M NH4OAc (pH 7)and measured with atomic absorption spectroscopy (AAS), and cation exchangecapacity (CEC) was obtained by the NH4OAc (pH 7) method (25). Aluminum wasextracted with 1 M KCl, and was measured by titration (25). Effective cation ex-change capacity (ECEC) was calculated by summing the extractable bases andKCl Al.
For each whole soil, acid ammonium oxalate in the dark was used to extractnoncrystalline (poorly crystalline and organically bound) Fe (Feo) and Al (Alo)forms, and dithionite-citrate-bicarbonate (DCB) was used to extract ‘‘free’’ Fe(Fed) forms consisting of both oxide (crystalline and noncrystalline) and organi-cally bound forms (25). Poorly crystalline, organically bound, and Al containedin Fe oxide minerals was extracted with DCB (Ald) (25). Quantities of each ex-tracted form were measured by atomic AAS. The product of Fed–Feo for the wholesoils was interpreted as a measure of Fe in crystalline oxide form.
Samples were fractionated into a coarse fraction consisting of sand � silt(2 to 2000 mm), and a clay fraction (�2 mm) using centrifugation (26). Separatecoarse fraction samples were extracted with acid ammonium oxalate and DCB,
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Table 1. Classification of Pedons from 13 Alabama Locations
Pedon Family
S92AL-123-1 Fine-loamy, kaolinitic, thermic Typic KanhapludultS92AL-123-2 Fine-loamy, kaolinitic, thermic Typic KandiudultS92AL-123-3 Fine, kaolinitic, thermic Typic KanhapludultS92AL-123-5 Fine, kaolinitic, thermic Typic KanhapludultS92AL-123-7 Loamy, siliceous, subactive, thermic Arenic HapludultS93AL-123-1 Fine, kaolinitic, thermic Typic HapludultS95AL-087-1 Fine-loamy, kaolinitic, thermic Rhodic KandiudultS95AL-087-3 Fine-loamy, siliceous, subactive, thermic Typic PaleudultS95AL-087-4 Fine-loamy, siliceous, subactive, thermic Plinthic PaleudultS95AL-123-1 Fine, kaolinitic, thermic Typic HapludultS95AL-123-3 Fine, kaolinitic, thermic Typic HapludultS96AL-123-1 Fine, kaolinitic, thermic Typic KanhapludultS97AL-123-2 Fine, kaolinitic, thermic Rhodic Kandiudult
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IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 53
Tabl
e2.
Mor
phol
ogic
al,P
hysi
cal,
and
Che
mic
alD
ata
for
Port
ions
ofth
eA
rgill
icH
oriz
onof
the
13Pe
dons
Sam
ple
Hor
.M
unse
llSa
ndSi
ltC
lay
Ca
Mg
KN
aA
lE
CE
CC
EC
pHFe
daFe
obA
l dc
Al o
d
Col
or(%
)(c
mol
ckg
�1 )
H2O
(%)
S92A
L-1
23-1
-2B
t110
YR
5/6
52.0
16.9
31.1
0.85
0.55
0.15
0.11
1.00
2.67
4.40
4.90
2.76
0.06
0.38
0.13
S92A
L-1
23-2
-3B
t110
YR
5/6
58.9
13.7
27.4
0.47
1.10
0.21
0.13
0.97
2.89
4.57
5.00
2.00
0.05
0.33
0.10
S92A
L-1
23-3
-3B
t12.
5YR
4/6
41.1
14.5
44.4
0.15
1.10
0.15
0.18
0.23
1.80
5.78
5.60
6.71
0.34
0.40
0.18
S92A
L-1
23-5
-4B
t17.
5YR
5/6
35.4
13.6
50.9
2.16
0.93
0.05
0.04
0.62
3.81
6.33
5.13
3.52
0.07
0.43
0.11
S92A
L-1
23-7
-4B
t17.
5YR
5/6
66.1
14.4
19.5
0.14
0.32
0.28
0.04
1.46
2.25
3.59
4.92
1.37
0.05
0.18
0.11
S93A
L-1
23-1
-2B
t12.
5YR
3/6
37.3
22.5
40.2
0.70
0.61
0.03
0.13
0.04
1.51
7.23
5.39
5.93
0.22
0.45
0.17
S95A
L-0
87-1
-4B
t22.
5YR
3/6
52.1
17.5
30.4
0.94
0.32
0.22
0.00
1.26
2.75
4.68
4.71
2.00
0.18
0.14
0.12
S95A
L-0
87-3
-5B
t25Y
R4
/648
.623
.028
.51.
490.
950.
090.
000.
012.
544.
915.
861.
650.
040.
220.
12S9
5AL
-087
-4-4
Bt
10Y
R5/
850
.521
.827
.71.
700.
530.
140.
000.
743.
115.
965.
291.
470.
030.
250.
15S9
5AL
-123
-1-3
Bt
10Y
R5/
635
.610
.653
.80.
461.
870.
050.
263.
195.
8211
.03
5.41
3.65
0.10
0.43
0.19
S95A
L-1
23-3
-2B
t12.
5YR
4/6
27.8
23.1
49.1
0.42
0.11
0.06
0.04
2.44
3.06
6.70
4.94
6.85
0.20
0.51
0.16
S96A
L-1
23-1
-2B
t12.
5YR
5/6
43.2
20.3
36.5
0.59
0.70
0.06
0.01
0.92
2.27
5.71
5.13
3.41
0.22
0.26
0.20
S97A
L-1
23-2
-2B
t12.
5YR
3/4
37.4
23.0
39.5
2.62
0.91
0.05
0.03
0.01
3.61
5.58
5.95
5.98
0.28
0.43
0.21
aFe
dis
dith
ioni
te-c
itra
te-b
icar
bona
teex
trac
tabl
eFe
.bFe
ois
oxal
ate
extr
acta
ble
Fe.
cA
l dis
dith
ioni
te-c
itra
te-b
icar
bona
teex
trac
tabl
eA
l.dA
l ois
oxal
ate
extr
acta
ble
Al.
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and the quantity of Feo, Alo, Fed, and Ald in the coarse fraction were determinedusing the following techniques. For the oxalate extractions, 60 mL of 0.2 M am-monium oxalate (pH 3) were added to coarse fractions. Because particle size dis-tribution varied, the initial wt. of sand � silt varied between 4.98 and 8.71 g.Samples were shaken for 4 h in the dark at room temperature, and centrifuged at1,800 rpm for 6 min. The supernatant was decanted, filtered, and brought to vol-ume. The Feo and Alo in the extractant was measured with AAS and reported as apercentage of the whole soil and the coarse fraction. For the DCB extractions,50 mL of 0.3 M sodium citrate/1 M sodium bicarbonate solution were added tothe coarse fraction. Initial wt. ranged from 4.99 to 8.60 g. Successive incrementsof sodium dithionite were added (with stirring) to samples placed in a hot waterbath (80�C), and samples were washed four times (decanted at each washing) with0.3 M sodium citrate/1 M sodium bicarbonate solution. The Fed and Ald in thecoarse fraction was measured with AAS and reported as a percentage of the wholesoil and the coarse fraction.
The quantities of Feo, Alo, Fed, and Ald in the clay fraction were measuredwith the same techniques as used for the coarse fraction. Initial weights for theclay samples were calculated by determining the suspension density, then dispens-ing a known volume.
For mineralogical analyses, both treated and untreated samples were ana-lyzed to minimize the confounding effects of goethite on gibbsite quantificationand vice versa during thermal analyses (27). Clay fractions were split into un-treated, DCB treated to remove Fe oxide minerals, and NaOH treated to removegibbsite. The NaOH treatment involved placing clay separates in 100 mL of 0.5 MNaOH and boiling for 2.5 min, then centrifuging (28). Treated and untreatedsamples were K-saturated, 150 mg of clay were suction oriented onto glass slides,and samples were analyzed by X-ray diffraction (XRD) at room temperature and300� (29). The XRD analyses were used as a qualitative assessment of the effec-tiveness of the pretreatments on preferential removal of oxide minerals. Figure 1illustrates that the pretreatments for differential oxide removal were successful.The goethite (110) and hematite (104) peaks are absent in the DCB treated sample,the gibbsite (002) appears to have been selectively removed with the NaOHtreatment.
Treated and untreated samples were analyzed by thermogravimetric analy-ses (TGA). These analyses were conducted from 25�C to 625�C in a N atmo-sphere, and kaolinite was quantified on the untreated sample (using the theoreticalwater loss of 14.0%), goethite was quantified in the NaOH treated sample (theo-retical water loss of 10.1%), and gibbsite was quantified in the DCB treatedsample (theoretical water loss of 31.2%). The goethite and gibbsite quantities ob-tained in treated amounts (slightly higher weight loss due to concentration of re-sistant minerals) were normalized to total sample amounts by calculating a ratio
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of water loss in the untreated to the treated sample, and multiplying the treatedsample quantities by this ratio. Kaolinite was also quantified using differentialscanning calorimetry (DSC). Samples were analyzed in covered Al pans in a Natmosphere, and were heated from 300�C to 625�C. Kaolinite was quantified us-ing integrated endotherms and standards created from a bauxite source consistingof 56.0% kaolinite. For the quantitative mineralogy results, kaolinite quantitiesare averages obtained by the TGA and DSC methods (30).
The amount of hydroxy interlayered vermiculite (HIV) and quartz (Qtz) wasestimated using the techniques of Karathanasis and Hajek (30). This method usesthe proportional intensity of HIV and Qtz XRD peaks to an internal kaolinitestandard (corresponding peaks to d-spacings of 1.40 nm for HIV, 0.72 nm forkaolinite, and 0.425 nm for Qtz were used). In order to estimate hematite content,the quantity of goethite determined with TGA analyses was converted to % Feusing its theoretical formula. The % Fe in FeOOH form was then subtracted from
IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 55
Figure 1. X-ray diffractograms of the clay fraction (� 2 mm) for sample #S93Al-123-1-2. Samples shown are for DCB treated (K saturated) at 25�C and 300�C, NaOH treated (Ksaturated) at 25�C and 300�C, and untreated (K saturated) at 25�C and 300�C.
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the Fed -Feo content of the clay, and the difference was hypothesized to be Fe inFe2O3 form.
A modified differential X-ray diffraction (DXRD) technique was utilized forfurther evaluation of Fe oxide minerals (31) (Fig. 2). The modification to the stan-dard method was that pretreated, suction oriented samples were analyzed. Thedifferential diffractograms were calculated as (31):
A � kB � C (1)i i i
where Ai � number of counts at angle I in the NaOH treated sample; Bi � numberof counts at angle I in the DCB treated sample; Ci � number of counts at angle Iin the differential diffractogram; k � scale factor. The k factor was created byvisually assessing the optimum multiplier such that the created diffractogram in-tensities did not fall substantially below or above the XRD baseline (31).
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Figure 2. Modified differential X-ray diffractograms (DXRD) of the clay fraction (� 2mm) for six samples. Samples are: a) S95-123-1-3, b) S92AL-123-5-4, c) S97AL-123-2-2,d) S96AL-123-1-2, e) S95AL-087-1-4, f) S92AL-123-3-3. Notice samples a, b, and c haverelatively more goethite while samples d, e, and f possess relatively more hematite.
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RESULTS AND DISCUSSION
Whole Soil Analyses
Soils with redder hues tended to have higher amounts of Fed (Table 2), simi-lar to findings from other researchers (9). Overall, these highly-weathered soilstended to have low amounts of Feo, suggesting a highly-crystalline nature to theFe oxides in these soils (Table 2). Analyses of representative XRD patterns fromthe clay fraction generated using DXRD confirmed the crystallinity of the soilgoethite and hematite (Fig. 2). It was hypothesized that most of the Feo existed aspoorly-crystalline oxide minerals because these subsurface environments werethought to contain relatively low quantities of organic matter. Extremely low Feo
and subsequently low quantities of poorly crystalline Fe forms in these soils aresimilar to findings by other researchers on similar soils (7,9). For whole soils,extractable Al forms did not display any noticeable trend (Table 2).
Clay Mineralogy
Quantitative mineralogical results are reported in Table 3. Significant ( p �0.05) correlation (r � 0.86) between the ratio of oriented XRD peak intensities ofthe hematite (110) :goethite (110) as compared to the measured ratio of % hema-tite: % goethite was found (when the two samples that did not contain goethitewere removed from the analyses to avoid division by 0). Similarly, good correla-tion (r � 0.65, p � 0.05) was found between the measured ratio of % hematite:%goethite and the ratio of XRD peak intensities for hematite (104) � goethite (130):goethite (110). At a minimum, this suggested relatively decent Fe oxide quantita-tive estimates were obtained using the techniques described in this study. Similarto other studies (31), it is also believed these XRD peak intensity ratios createdusing a modified DXRD can provide reasonable estimates of Fe oxide quantitiesin similar soils.
As shown in other studies, samples with redder hues possessed relativelyhigher hematite quantities than samples with browner hues (Table 3). Even forthis highly-weathered mineral suite, these soils possessed a fairly wide range inoxide (hematite, goethite, and gibbsite) and phyllosilicate (kaolinite, HIV, andmica) content in the clay fraction.
Comparison of Coarse and Fine Fractions
Significantly ( p � 0.05) higher extractable Fe and Al forms were found inthe clay as compared to the coarse fractions (Table 4). Differences existed when
IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 57
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58 SHAW
Tabl
e3.
Qua
ntita
tive
Min
eral
ogic
alC
ompo
siti
onof
�2m
mFr
acti
on
Sam
ple
Hor
.M
unse
llC
olor
Kln
.(%
)G
i.(%
)H
IV(%
)Q
tz(%
)H
em.
(%)
Goe
.(%
)M
icaa
Sum
Tota
l
Fe2O
3
and
FeO
OH
/Fe
OO
Hb
Fe2O
3/Fe
OO
Hc
S92A
L-1
23-1
-2B
t110
YR
5/6
36.9
38.
4440
.48
3.49
1.14
13.7
1n
104.
20.
520.
39S9
2AL
-123
-2-3
Bt1
10Y
R5/
644
.45
0.65
13.3
10.
260.
0011
.22
x84
.90.
330.
24S9
2AL
-123
-3-3
Bt1
2.5Y
R4
/631
.99
15.1
68.
431.
2611
.41
2.36
x85
.61.
621.
80S9
2AL
-123
-5-4
Bt1
7.5Y
R5/
656
.75
2.07
17.0
81.
060.
0013
.68
n90
.60.
320.
27S9
2AL
-123
-7-4
Bt1
7.5Y
R5/
643
.68
1.59
13.8
80.
960.
963.
42x
79.5
0.54
0.41
S93A
L-1
23-1
-2B
t12.
5YR
3/6
56.9
69.
826.
851.
232.
1611
.28
n88
.30.
680.
54S9
5AL
-087
-1-4
Bt2
2.5Y
R3/
648
.37
0.79
15.3
42.
264.
540.
00x
86.3
––
S95A
L-0
87-3
-5B
t25Y
R4
/646
.84
2.60
22.8
80.
863.
640.
00n
76.8
––
S95A
L-0
87-4
-4B
t10
YR
5/8
43.7
24.
9334
.29
1.14
0.00
8.97
n93
.10.
000.
00S9
5AL
-123
-1-3
Bt
10Y
R5/
659
.28
0.91
12.3
61.
260.
0010
.51
n84
.30.
200.
14S9
5AL
-123
-3-2
Bt1
2.5Y
R4
/629
.60
10.2
417
.64
0.43
3.78
13.0
5x
89.8
0.45
0.37
S96A
L-1
23-1
-2B
t12.
5YR
5/6
42.5
711
.97
19.4
53.
720.
737.
71n
86.5
1.41
1.06
S97A
L-1
23-2
-2B
t12.
5YR
3/4
56.0
91.
1015
.27
1.67
3.00
12.7
4n
89.9
1.12
0.55
aE
stim
ated
from
XR
D,n
�0
%,x
�15
%.
bR
atio
ofX
RD
inte
nsit
ies
for
0.26
9nm
:0.4
15–
0.41
8nm
,cor
resp
ondi
ngto
hem
atite
(104
)(I
�10
)an
dgo
ethi
te(1
30)
(I�
3):g
oeth
ite(1
10)
(I�
10).
cR
atio
ofX
RD
inte
nsit
ies
for
0.25
2nm
:0.4
15–
0.41
8nm
,cor
resp
ondi
ngto
hem
atite
(110
)(I
�5)
:goe
thite
(110
)(I
�10
).
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IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 59
Tabl
e4.
Ext
ract
able
Fean
dA
lFor
ms
inE
ach
Size
Frac
tion
Ave
rage
dfo
rA
llSo
ilsa
Perc
enta
geof
Who
leSo
il
Fed
(%)
Feo
(%)
Al d
(%)
Al o
(%)
Fed–
Feo
b
(%)
Feo/F
e d(%
)
Perc
enta
geof
Part
icle
Size
Frac
tion
Fed
(%)
Feo
(%)
Al d
(%)
Al o
(%)
Fed–
Feo
b
(%)
Cla
y(�
2m
m)
2.68
a0.
12a
0.24
a0.
14a
2.56
a0.
041a
6.15
a0.
35a
0.83
a0.
45a
5.79
aC
oars
e(2
to20
00m
m)
0.96
b0.
02b
0.10
b0.
02b
0.93
b0.
020b
1.65
b0.
04b
0.17
b0.
03b
1.62
bls
d0.
750.
060.
080.
030.
700.
015
1.35
0.13
0.29
0.10
1.27
aM
eans
follo
wed
byth
esa
me
lette
rar
eno
tsig
nific
antly
diff
eren
t(p
�0.
05).
bE
stim
ate
ofth
eam
ount
ofFe
incr
ysta
lline
oxid
efo
rm.
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ORDER REPRINTS
extractable forms were based on both a percentage of the whole soil as well as apercentage of the size fraction. For example, the averaged amount of Fed in theclay fraction was 2.68% of the whole soil and 6.15% of the clay fraction. Thesedifferences are thought to be due to several reasons including: 1) most pedogenicminerals (including Fe and Al oxides) are clay sized, and 2) oxides (particularlypoorly crystalline) have been shown to be associated with phyllosilicate mineralsconcentrated in the clay fraction, and 3) clay fractions have higher surface areas.Undoubtedly, a combination of these and other factors result in these differences.The Feo/Fed ratio, although extremely low, was twice as high in the clay as in thecoarse fraction (0.041 to 0.020, respectively), suggesting a higher concentrationof poorly crystalline Fe forms in the clay fraction. This could be attributed to: 1)the contemporary formation of a pedogenic poorly-crystalline Fe oxide form (e.g.,ferrihydrite), or 2) phyllosilicate–oxide associations inhibiting oxide crystalliza-tion (32), or 3) retardation of Fe oxide crystallization due to the presence of Aland Si in solution (33). Researchers have noted the inhibition of Fe oxide crystal-lization in the presence of clay minerals, which may be the case for these soils(32,34). The Feo/Fed ratio in the clay fraction was significantly positively corre-lated (r � 0.49) with hematite content, while it was negatively correlated withgoethite quantities (r � �0.61). Hematite quantities were also correlated with thelow amounts of %Feo in the clay fraction (r � 0.75). This suggests a ferrihydriteprecursor may favor hematite formation at the expense of goethite, which is simi-lar to what other workers have found (6).
Significant correlations for certain properties are given in Table 5 (reportedif p � 0.10). For these soils, hematite quantities in the clay fraction were nega-tively correlated with goethite amounts (r � �0.51), but were positively corre-lated with gibbsite quantities (r � 0.49). Goethite quantities were correlated withthe %Ald in the clay fraction (r � 0.67), which suggests appreciable Al substitu-tion in this mineral.
Both gibbsite and hematite quantities were negatively correlated with ECEC(r � �0.54 and �0.80, respectively). Because of the pH of these soils (Table 2),these Fe and Al oxides are thought to have significant (�) charge, thus it is notsurprising to see ECEC negatively correlated with hematite and gibbsitequantities.
Interestingly, gibbsite amounts were negatively correlated with kaolinitequantities (r � �0.61), suggesting a possible desilication of kaolinite and trans-formation to gibbsite may be occurring in some of these soils. Alternatively, thismay indicate that preferential leaching of gibbsite as compared to kaolinite maybe occurring (2). It was also interesting to note in the clay fraction, a fairly highcorrelation between %Alo and gibbsite (r � 0.83) was found. Although it isthought ammonium oxalate in the dark is not a good extractant of crystalline Aloxide forms, future work needs to be done to more fully evaluate the forms of Alextracted with this method. The %Fed in the clay was correlated with the same
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IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 61
Tabl
e5.
Cor
rela
tion
Mat
rix
a
% Hem
%G
oeth
%G
ibb
% HIV
% Kao
%Fe
o
clay
%A
l ocl
ay%
Fed
clay
%A
l dcl
ay%
Feo
co.
%A
l oco
.%
Fed
co.
%A
l dco
.pH
EC
EC
b
KC
lA
l% BS
c
%H
em–
�0.
510.
49n
n0.
75n
nn
nn
nn
n�
0.54
nn
%G
oeth
–n
nn
nn
0.53
0.67
nn
0.59
0.68
nn
nn
%G
ibb
–n
�0.
610.
620.
830.
57n
nn
nn
n�
0.80
n�
0.52
%H
IV–
nn
nn
0.51
nn
nn
nn
nn
%K
ao–
nn
nn
nn
nn
nn
nn
%Fe
ocl
ay–
0.64
0.71
nn
n0.
49n
n�
0.73
nn
%A
l ocl
ay–
0.67
nn
n0.
48n
n�
0.71
nn
%Fe
dcl
ay–
0.64
0.53
0.59
0.76
0.75
n�
0.64
nn
%A
l dcl
ay–
nn
n0.
65n
nn
n%
Feo
co.
–0.
990.
700.
650.
54n
n0.
50%
Al o
co.
–0.
750.
780.
60n
nn
%Fe
dco
.–
0.88
nn
nn
%A
l dco
.–
nn
nn
pH–
n�
0.47
0.50
EC
EC
–n
nK
ClA
l–
�0.
57%
BS
–
ar
�0.
80at
p�
0.00
1,r
�0.
68at
p�
0.01
,r�
0.55
atp
�0.
05.
bE
CE
C(e
ffec
tive
cati
onex
chan
geca
paci
ty)i
sba
sed
ona
per
hund
red
gram
ofcl
aysa
mpl
e.cB
Sis
%ba
sesa
tura
tion
.
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ORDER REPRINTS
measure in the coarse fraction (r � 0.76). Although differences existed in theamounts of DCB extractable forms in the fine and coarse fractions, no trend withregard to particle size and DCB extractable forms was evident.
CONCLUSIONS
The selective pretreatments used in this study allowed for a detailed exami-nation of oxide forms for these highly-weathered Alabama Ultisols. Similar toother studies, Fe oxide minerals in the argillic horizon of these soils were shownto be highly crystalline, with a higher concentration of oxide forms found in theclay versus the coarse (sand � silt) fraction. Furthermore, empirical relationshipsexisted that gave evidence to theories derived from other studies concerning Feoxide genesis and occurrence. The low amounts of oxalate extractable Fe formsin these subsoils coupled with the low activity silicate mineralogies dictate theseargillic horizons have a finite capacity to sorb contaminants. The higher ratio ofoxalate extractable and therefore the more reactive Fe forms concentrated in theclay fraction indicate these colloidal materials are more reactive than the bulksoils, thus possibly enhancing colloidal facilitated transport of pollutants.
REFERENCES
1. Rhoton, F.E.; Lindbo, D.L.; Romkens, M.J. Iron Oxides Erodibility Interac-tions for Soils of the Memphis Catena. Soil Sci. Soc. Am. J. 1998, 62, 1693–1703.
2. Kaplan, D.I.; Bertsch, P.M.; Adriano, D.C. Mineralogical and Physico-chemical Differences Between Mobile and Nonmobile Colloidal Phases inReconstructed Pedons. Soil Sci. Soc. Am. J. 1997, 61, 641–649.
3. Manning, B.A.; Goldberg, S. Modeling Competitive Adsorption of Arsenatewith Phosphate and Molybdate on Oxide Minerals. Soil Sci. Soc. Am. J.1996, 60, 121–131.
4. Graham, R.C.; Weed, S.B.; Bowen, L.H.; Amarasiriwardena, D.D.; Buol,S.W. Weathering of Iron-Bearing Minerals in Soils and Saprolite on theNorth Carolina Blue Ridge Front: II. Clay Mineralogy. Clays Clay Miner.1989, 37, 29– 40.
5. Aniku, J.R.; Singer, M.J. Pedogenic Iron Oxide Trends in a Marine TerraceChronosequence. Soil Sci. Soc. Am. J. 1990, 54, 147–152.
6. Schwertmann, U.; Taylor, R.M. Iron Oxides. In Minerals in Soil Environ-ments, 2nd Ed.; Dixon, J.B., Weed, S.B., Eds.; ASA and SSSA: Madison,WI, 1989; SSSA No. 1.
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7. McKeague, J.A.; Brydon, J.E.; Miles, N.M. Differentiation of Forms of Ex-tractable Iron and Aluminum in Soils. Soil Sci. Soc. Am. Proc. 1971, 35,33–38.
8. Schwertmann, U.; Kampf, N. Properties of Goethite and Hematite in Ka-olinitic Soils of Southern and Central Brazil. Soil Sci. 1985, 139, 344 –351.
9. Bigham, J.M.; Golden, D.C.; Bowden, L.H.; Buol, S.W.; Weed, S.B. IronOxide Mineralogy of Well-Drained Ultisols and Oxisols. I. Characterizationof Iron Oxides in Soil Clays by Mossbauer Spectroscopy, X-ray Diffracto-metry and Selected Chemical Techniques. Soil Sci. Soc. Am. J. 1978, 42,816 –825.
10. Fitzpatrick, R.W.; Schwertmann, U. Al-substituted Goethite: An Indicatorof Pedogenic and Other Weathering Environments in South Africa. Geo-derma 1982, 27, 335–347.
11. Norrish, K.; Taylor, R.M. The Isomorphous Replacement of Iron by Alu-minum in Soil Goethites. J. Soil Sci. 1961, 12, 294 –306.
12. Barron, V.; Torrent, J. Influence of Aluminum Substitution on the Color ofSynthetic Hematites. Clays Clay Miner. 1984, 32, 157–158.
13. Wada, K. 1989. Allophane and Imogolite. In Minerals in Soil Environments,2nd Ed.; Dixon, J.B., Weed, S.B., Eds.; ASA and SSSA: Madison, WI, 1989;SSSA No. 1.
14. Brito-Galvao, T.C.; Schulze, D.G. Mineralogical Properties of a CollapsibleLateritic Soil from Minas Gerais, Brazil. Soil Sci. Soc. Am. J. 1996, 60,1969–1978.
15. Jones, R.C.; Uehara, G. Amorphous Coatings on Mineral Surfaces. Soil Sci.Soc. Am. Proc. 1973, 37, 792–798.
16. Darland, J.E.; Inskeep, W.P. Effects of pH and Phosphate Competition onthe Transport of Arsenate. J. Environ. Qual. 1997, 26, 1133–1139.
17. Hingston, H.J.; Posner, A.M.; Quirk, J.P. Anion Adsorption by Goethite andGibbsite. J. Soil Sci. 1974, 25, 16 –26.
18. Goetz, A.J.; Walker, R.H.; Wehtje, G.; Hajek, B.F. Sorption and Mobility ofChlorimuron in Alabama Soils. Weed Sci. 1989, 37, 428– 433.
19. Owusu-Bennoah, E.; Szilas, C.; Hansen, H.B.; Borggaard, O.K. PhosphateSorption in Relation to Aluminum and Iron Oxides of Oxisols from Ghana.Commun. Soil. Sci. Plant Anal. 1997, 28, 685–697.
20. Yuan, G.; Lavkulich, L.M. Phosphate Sorption in Relation to ExtractableIron and Aluminum in Spodosols. Soil Sci. Soc. Am. J. 1994, 58, 343–346.
21. Barberis, E.; Marsan, F.A.; Boero, V.; Arduino, E. Aggregation of Soil Par-ticles by Iron Oxides in Various Size Fractions of Soil Horizons. J. Soil Sci.1991, 42, 535–542.
22. Golden, D.C.; Dixon, J.B. Silicate and Phosphate Influence on Kaolin–IronOxide Interactions. Soil Sci. Soc. Am. J. 1985, 49, 1568–1576.
IRON AND ALUMINUM OXIDES FROM ALABAMA ULTISOLS 63
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23. Daniels, R.B.; Gamble, E.E.; Buol, S.W.; Bailey, H.H. Free Iron Sources inan Aquult-udult Sequence from North Carolina. Soil Sci. Soc. Am. Proc.1975, 39, 335–340.
24. Kilmer, V.J.; Alexander, L.T. Methods of Making Mechanical Analysis ofSoils. Soil Sci. 1949, 68, 15–24.
25. Soil Survey Investigation Staff. Soil Survey Laboratory Methods Manual;USDA-SCS, Natl. Soil Survey Center: Lincoln, NE, 1996; Soil Serv. Inv.Rep. 42.
26. Jackson, M.L. Soil Chemical Analyses—Advanced Course. Published by theauthor: Madison, Wisconsin, 1975.
27. Jackson, M.L.; Lim, C.H.; Zelazny, L.W. Oxides, Hydroxides, and Alumi-nosilicates. In Methods of Soil Analysis. Part 1. Physical and MineralogicalMethods, 2nd Ed.; Klute, A., Ed.; ASA and SSSA: Madison, WI, 1986;Agron. No. 9.
28. Wada, K.; Greenland, D. Selective Dissolution and Differential InfraredSpectroscopy for Characterization of Amorphous Constituents in Soil Clays.Clays Clay Miner. 1970, 8, 241–254.
29. Whittig, L.D.; Allardice, W.R. X-Ray Diffraction Techniques. In Methods ofSoil Analysis. Part I. Physical and Mineralogical Methods, 2nd Ed.; Klute,A., Ed.; ASA and SSSA: Madison, WI, 1986; Agron. No. 9, 336 –341.
30. Karathanasis, A.D.; Hajek, B.F. Revised Methods for Quantitative Deter-mination of Minerals in Soil Clays. Soil Sci. Soc. Am. J. 1982, 46, 419–425.
31. Schulze, D.G. Identification of Soil Iron Oxide Minerals by Differential X-Ray Diffraction. Soil Sci. Soc. Am. J. 1981, 45, 437– 440.
32. Arias, M.; Barral, M.T.; Diaz-Fierros, F. Effects of Iron and Aluminum Ox-ides on the Colloidal and Surface Properties of Kaolin. Clays Clay Miner.1995, 43, 404 – 416.
33. Schwertmann, U. Goethite and Hematite Formation in the Presence of ClayMinerals and Gibbsite at 25�C. Soil Sci. Soc. Am. J. 1988, 52, 288–291.
34. El-Swaify, S.A.; Emerson, W.W. Changes in the Physical Properties of SoilClays Due to Precipitated Aluminum and Iron Oxyhydroxides. I. Swellingand Aggregate Stability after Drying. Soil Sci. Soc. Am. Proc. 1975, 39,1056 –1063.
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