Chemical mineralogical characterisation of clay sediments around ferrara (italy) a tool for an environme

Chemical–mineralogical characterisation of clay sediments
around Ferrara (Italy): a tool for an environmental analysis
Gianluca Bianchini
a,
*
, Rocco Laviano
b
, Stefano Lovo
a
, Carmela Vaccaro
a
a
Dipartimento di Scienze della Terra, Universita
`
di Ferrara, corso Ercole I D’Este 32, 44100 Ferrara, Italy
b
Dipartimento Geomineralogico, Universita
`
degli Studi di Bari, via E. Orabona 4, 70125 Bari, Italy
Received 27 October 2000; received in revised form 18 June 2001; accepted 19 July 2001
Abstract
The content of heavy metals in water and soil is a key parameter for evaluating the geochemical vulnerability of an
ecosystem. These elements display a limited solubility and are easily trapped and adsorbed by phyllosilicate minerals; they
are thus preferentially partitioned in the fine fraction of sediments. In this light, an analysis of recent river sediments gives
information on possible water pollution, and more in general on the related ecosystem. We therefore investigated the
chemical–mineralogical features of clay sediments outcropping around the town of Ferrara, paying particular attention to
their fine fraction (grain size < 2 Am).
X-ray fluorescence (XRF) analyses indicate that the abundance of transition trace elements, such as Cr and Ni, is
positively correlated with MgO wt.%, and discriminates two well-delineated populations of samples, respectively
characterised by high (Cr > 180 ppm; Ni>100 ppm) and low (Cr < 180 ppm; Ni < 100 ppm) contents of these elements. The
mineralogical composition of the fine fraction ( < 2 Am) was investigated through X-ray powder diffraction (XRPD)

integrated with differential thermal (DTA) and thermogravimetric analyses (DTG), showing that: low-Cr samples are
characterised by a higher proportion of clay minerals in which smectite + mixed layers are more abundant than chlorite
(Sm + ML/Chl>1); on the other hand, the high-Cr samples have a coarser grain size, and a lower abundance of clay
minerals in which chlorite (Mg-rich chlorite in this group of samples) predominates over smectite + mixed layers (Sm + ML/
Chl < 1). These two distinct groups of samples are ascribed to different sources: high-Cr lithologies are related to the
sedimentary contribution of the Po river, whereas low-Cr sediments plausibly derive from small rivers of Apennine origin
(e.g. the Reno river). Within the high-Cr group, concentrations of Ni and Cr tend to be higher than those indicated by the
current environmental Italian legislation. However, in the study –case presented here, the detected high heavy-metal
concentrations are not related to urban–industrial–agricultural activities, but instead appear to be typical of the original
lithologies.
An integration of similar scientific contributions would be useful to set up a geochemical–mineralogical database as a
first step toward the preparation of more complete thematic maps. These would provide information relative to the
behaviour (e.g. distribution and abundance) of chemical elements within the different geochemical spheres, and would be
0169-1317/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.
PII: S 0169-1317(01)00086-2
*
Corresponding author.
E-mail address: (G. Bianchini).
www.elsevier.com/locate/clay
Applied Clay Science 21 (2002) 165 – 176
useful for recognising and interpreting possible geochemical anomalies induced by pollution processes. D 2002 Elsevier
Science B.V. All rights reserved.
Keywords: Clay sediments; Environment; Geochemical monitoring
1. Introduction
The Po river alluvial plain in the province of
Ferrara (Northern Italy) constitutes the terminal part
of the most important drainage basin of the Italian
peninsula, and is a delicate ecosystem. The Po river
flows through highly urbanised and industrialised
areas, and consequently its superf icial waters, associ-

ated ground waters, and deposited sediments have to
be carefully monitored for pollution.
To recognise and interpret possible anthropogenic
geochemical anomalies within the soils and sediments
outcropping in the area, it is necessary to assess the
‘‘intrinsic baseline’’ (for each monitored parameter)
typical of the natural system and related to the
chemical characters of the original lithologies (Marini
Fig. 1. Simplified map of the area (province of Ferrara) reporting the sampling locations, the estimated ages of sedimentation, and the
chemical –mineralogical affinity of the studied fine sediments. The characters of the mentioned sample groups (i.e. low Cr, high Cr) and the
related origin are discussed in the text.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176166
and Ottonello, 1999). The definition of the ‘‘blank’’
for each chemical parameter is critical for discrim-
ination between ‘‘natural’’ anomalies typical of the
deposited sediments and the chemical fingerprint
induced by subsequent human activity. In particular,
this study is focused on the chemical–mineralogical
characterisation of sediments outcropping around the
town of Ferrara, paying particula r attention to the fine
fraction (grain size < 2 Am) within which some key
chemical species (e.g. heavy metals) tend to concen-
trate, frequently exceeding the permitted limits set by
the Italian nati onal environmental regulations. The
study approach outlined here is a suitable method
for evaluating the environmental conditions and
investigating contamination and pollution in an area
containing sensitive natural systems, including impor-
tant parks and water resources (e.g. the Ostellato
natural oasis and the Po delta nature park).

2. Location of the sampling areas—preliminary
description of the investigated sediments
Fine sediment outcrops were selected for the sam-
pling areas (Fig. 1) using a lithological map of Ferrara
(edited by the provincial administration of Ferrara).
Samples were collected using a manual drill at depths
of 70–100 cm, to exclude levels containing high
amount of vegetable matter and/or disturbed by agri-
cultural activity.
From available geomo rphologica l studies, it is
possible to associate these sediments with a fluvial–
lagoon–lacustrine environment (Bondesan, 1990; Ste-
fani et al., 1999). These geomorphological investiga-
tions further define the sedimentary history of the
area, enabling the samples to be assigned to three
different chronological intervals (Bondesan, personal
communication):
1. sediments over 2000 years old (samples 1, 2,
3, 4, 6, 15, and 23);
2. sediments rangingbetween 2000and 1000years
old (samples 5, 13, 14, 16, 17, 18, 19, and 24);
3. sediments less than 1000 years old (samples 7,
8, 9, 10, 11, 12, 20, 21, and 22).
Granulometric analysis was performed on a set of
these samples (covering the three mentioned sedimen-
tation periods and representative of the various sectors
of the area) in a two-stage process. Firstly, the samples
were wet sieved to separate the coarser particles (>63
Am), then decantation experiments were carried out
(gravity settling in deionized water) to characterize the

finer fraction. The analysis indicated that the clay
fraction ( < 2 Am) ranges between 44 and 74 wt.%, the
silt fraction (2–63 Am) between 25 and 49 wt.%, and
that the sand fraction (>63 Am) is subordinate ( < 9
wt.%) (Table 1, Fig. 2).
Fig. 2. Grain size distribution of the studied sediments. Symbols:
n = low-Cr sediments; 5 = high-Cr sediments.
Table 1
Grain size distribution of the studied sediments (wt.%)
Samples Sand
(>63 Am)
Silt
(2 – 63 Am)
Clay
(<2 Am)
Low Cr 3 2 31 67
6 2 48 50
7 2 36 62
10 2 31 67
11 1 25 74
14 3 33 64
x 234 64
High Cr 2 9 47 44
15 7 49 44
16 2 45 53
17 7 42 51
19 3 40 57
20 5 44 51
x 545 50
x = Average value.

G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 167
CO
2
content analyses were carried out (by simple
volumetric technique; Jackson, 1958) to constrain the
amount of carbonates present. The maximum values
were up to 17.8 wt.% in sample 16 (see Table 2),
which indi cates that some samples could be better
classified as marly–clay; in this sample, petrographic
microscope analysis indicates that the recorded high
amount of calcite is present as micrite, whereas
detrital calcite (coarse grains/rock fragments) was
not detected.
3. Chemical – mineralogical data set
Chemical compositions of the major and trace ele-
ments (reported in Table 3) of the sampled sediments
(tout-venant) were determined by X-ray fluorescence
(XRF) using a Philips PW 1400 spect rometer, follow-
ing the methodology of Franzini et al. (1975) and Leoni
and Saitta (1975).
Major element s presen t the following composi-
tional ranges: SiO
2
= 47.0–54.6%, TiO
2
= 0.5–0.8%,
Al
2
O
3

= 15.1 –21.0%, Fe
2
O
3
tot = 5.1–8.2%,
MnO V 0.1%, MgO = 2.5–4.7%, CaO = 1.3–11.1%,
Na
2
O = 0.3–0.8%, K
2
O = 2.2–3.6%, P
2
O
5
V 0.3%,
LOI = 9.0 –17.9. Further examination of these data
(Fig. 3) highlights:
(1) a lack of correlation between the SiO
2
% and
oxides of the other major elements, indicating that the
SiO
2
% content is mainly related to the abundance of
quartz;
(2) that K
2
O% and Rb ppm (usually characterised
by similar geochemical behaviour) are positively
correlated with Al

2
O
3
% (correlation coefficient
r
2
>0.75), as usually observed in illite-rich fine sedi-
ments;
(3) a negat ive correlation between CaO% and
Al
2
O
3
%(r
2
= 0.60), indicating that CaO is mainly
hosted within carbonates, thus precluding a significant
presence of CaO-b earing silicates;
(4) a coherent positive correlation between the CaO
wt.% and CO
2
(r
2
= 0.95) content;
(5) positive correlations between MgO% and tran-
sition trace elements, such as Cr (r
2
= 0.58) and Ni
(r
2

= 0.83); these elements are usually associated in
sediments containing chlorite and serpentine, in turn
derived from weathering of mother rocks rich in
olivine, pyroxenes, and spinel;
(6) the existence of two well-delineated popula-
tions of samples discriminated by Cr and Ni (Stu-
dent’s t-test: t >10.84, P > 99.99% for Cr; t > 9.24,
P > 99.99% for Ni): these are characterised by high
(Cr > 180 ppm; Ni > 100 ppm) and low (Cr < 180 ppm;
Ni < 100 ppm) concentrations of these elements, here-
after named as high-Cr and low-Cr groups.
To visualise the trace element distribution, the data
presented here have been normalised to the composi-
tion of fine sediments from the Po river (sampled and
analysed by ourselves). In the normalised multi-ele-
ment plot of Fig. 4, most elements show only a limited
scattering within the two sample groups. On the other
hand, the concentration of Ba and Sr (possibly hosted
in carbonates and feldspar) varies widely in both
groups.
The mineralogical composition of these lithotypes
was carried ou t through X-ray powder diffraction
(XRPD; Philips PW1010/80 diffractometer with
graphite-filtered CuKa radiation). Particular attention
was devoted to investigating the fine fraction of these
sediments which, due to the high surface area and the
particular nature of the related minerals (mainly clay
minerals), tend to trap and concentrate possible pol-
lution substances. In this light, for a better character-
isation of the constituent clay minerals, X-ray dif-

fractometric analysis was carried out on the < 2-Am
fraction (in which the different clay minerals are more
clearly recognised) of each selected sample; in partic-
ular, X-ray investigation was carried out on randomly
oriented samples, and also on glycolated and heat-
Table 2
CO
2
and CaCO
3
content of the studied sediments
Samples CO
2
CaCO
3
Low Cr 3 5.13 11.67
6 5.97 13.58
7 6.21 14.11
10 5.08 11.55
11 4.73 10.76
14 6.54 14.87
x 5.61 12.76
High Cr 2 4.67 10.62
15 5.83 13.26
16 7.82 17.78
17 3.68 8.37
19 1.36 3.09
20 1.57 3.57
x 4.15 9.45
x = Average value.

G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176168
Table 3
Major (wt.%) and trace element (ppm) analyses of the studied sediments
Elements Low-Cr samples High-Cr samples
SL3 SL6 SL7 SL8 SL9 SL10 SL11 SL12 SL14 x SL 1 SL 2 SL 4 SL 5 SL 13 SL 15 SL 16 SL 17 SL 18 SL 19 SL 20 SL 21 SL 22 SL 23 SL 24 x
SiO
2
50.38 49.09 49.68 49.63 49.00 47.88 47.42 49.86 47.20 48.90 47.02 54.58 53.49 51.54 45.48 49.02 45.57 51.11 51.27 52.59 42.49 50.55 48.88 43.05 53.02 49.31
TiO
2
0.71 0.68 0.68 0.75 0.75 0.72 0.72 0.73 0.68 0.71 0.66 0.62 0.72 0.70 0.70 0.66 0.67 0.70 0.74 0.70 0.53 0.65 0.67 0.56 0.68 0.66
Al
2
O
3
16.66 15.83 15.15 19.05 18.46 17.63 18.56 17.68 15.90 17.21 16.42 15.28 20.96 20.53 18.51 15.28 14.94 17.07 17.94 19.30 16.14 14.97 17.10 15.07 16.24 17.05
Fe
2
O
3
5.81 5.88 5.81 6.95 7.09 6.49 6.78 6.27 6.76 6.43 7.61 5.45 6.06 7.46 8.23 5.93 6.09 6.14 6.51 6.81 5.55 5.68 6.53 5.15 5.88 6.34
MnO 0.09 0.10 0.12 0.10 0.12 0.10 0.09 0.09 0.14 0.10 0.08 0.11 0.04 0.07 0.05 0.12 0.12 0.07 0.07 0.05 0.06 0.11 0.08 0.09 0.09 0.08
MgO 2.81 2.76 2.59 3.15 3.03 3.01 3.17 3.27 2.99 2.98 4.32 4.45 3.20 3.25 3.35 4.55 4.32 4.69 4.23 4.21 3.17 4.32 4.20 3.66 4.43 4.02
CaO 8.64 9.72 8.91 6.47 7.65 7.93 7.60 6.98 9.72 8.18 8.00 6.95 1.32 2.51 8.23 9.31 11.04 6.37 4.82 2.68 2.58 10.57 7.05 11.03 6.17 6.58
Na
2
O 0.59 0.51 0.56 0.35 0.36 0.39 0.32 0.39 0.48 0.44 0.44 0.76 0.71 0.55 0.34 0.63 0.53 0.67 0.48 0.51 0.46 0.61 0.48 0.73 0.67 0.57
K
2
O 2.61 2.51 2.48 3.38 3.37 2.99 3.21 2.97 2.58 2.90 2.68 2.45 3.38 3.58 2.80 2.30 2.22 2.51 2.67 3.05 2.30 2.26

2.61
2.43 2.45 2.65
P
2
O
5
0.28 0.32 0.32 0.18 0.24 0.24 0.21 0.21 0.28 0.25 0.32 0.27 0.00 0.03 0.21 0.30 0.33 0.17 0.15 0.06 0.15 0.31 0.20 0.34 0.22 0.20
LOI 11.42 12.6 13.69 9.98 9.95 12.62 11.93 11.54 13.27 11.89 12.46 9.08 10.14 9.78 12.1 11.89 14.16 10.5 11.12 10.04 26.58 9.97 12.2 17.89 10.15 12.54
Pb
a
24 14 18 23 23 20 18 20 19 20 28 29 37 36 30 26 20 28 25 28 23 25 24 40 22 28
Zn
a
104 106 111 122 124 120 123 119 106 115 117 101 107 136 125 96 102 106 124 125 103 91 121 94 104 110
Ni 86 80 69 82 82 80 84 94 89 83 152 134 112 106 138 146 145 155 162 156 123 132 151 119 138 138
Co 19 21 16 20 20 18 19 19 18 19 21 19 17 22 19 20 21 29 32 28 20 19 21 15 22 22
Cr 120 108 101 136 143 134 119 125 122 123 237 214 268 222 244 224 210 288 281 284 221 221 258 195 228 240
V 133 121 117 163 155 148 161 151 144 144 124 111 174 177 162 112 124 146 158 174 131 108 138 116 124 139
Th 16 11 11 12 14 14 19 16 18 14 15 10 15 13 15 13 15 12 14 13 11 10 11 10 9 12
Nb 18 14 14 14 16 16 20 16 15 16 11 13 19 16 16 11 15 17 18 17 12 13 16 10 15 15
Zr 145 147 137 125 129 126 123 132 126 132 115 153 118 132 115 147 131 142 132 125 103 135 125 97 133 127
Rb 147 141 124 174 176 163 172 152 134 154 152 118 198 195 182 122 128 150 164 184 139 122 154 128 128 151
Sr 265 279 258 254 268 282 284 252 272 268 424
221
160 191 223 257 301 243 219 171 151 279 229 579 215 257
Ba 860 440 283 310 336 316 890 818 583 537 1035 888 835 496 422 495 1017 617 279 250 430 411 435 368 418 560
Y 22222320191920232021 172416172325 22242316182419162421
Ce 105 50 83 82 65 67 97 118 111 87 63 41 81 62 78 29 75 77 81 83 64 48 78 63 52 65
x =Average value.
a

Semiquantitative analyses.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 169
treated oriented samples (Moore and Reynolds, 1997).
These data were further supplemented with differential
thermal (DTA) and thermogravimetric (DTG) analyses
(Fig. 5), kindly performed by M.F. Brigatti (University0
of Modena; see Brigatti et al., 1995, 1996 for metho-
dological details). Results indicate that the fine frac-
tion is made up of various proportions of illite (Ill),
chlorite (Chl), kaolinite (K), smectite (Sm), interstra-
tified mineral phases (ML: chlorite–smectite and
subordinate kaolinite–smectite), and low percentages
of serpentine, quartz, and carbonate. DTA–DTG
measurements also indicate the presence of organic
matter.
A semiquantitative evaluation of the mineralogical
composition (within the < 2-Am fraction; see Table 4)
was obtained by applying the analytical methods of
Schultz (1964) and Shaw et al. (1971), modified by
Laviano (1987).
Fig. 3. Variation diagrams reporting XRF data carried out on the studied sediments: Ni (ppm) and Cr (ppm) vs. MgO (wt.%); CaO (wt.%),
Fe
2
O
3
(wt.%), K
2
O (wt.%), and Rb (ppm) vs. Al
2
O

3
. Symbols: n = low-Cr sediments; 5 = high-Cr sediments.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176170
Illite, is 2M polytype with Al
3+
as the mai n
octahedral cation, K
+
as the chief interlayer cation,
and the degree of paragonitization varying from 5% to
25% (Yoder and Eugster, 1955; Bradley and Grim,
1961; Dunoyer De Segonzac, 1970; Srodon and Eberl,
1984). The degree of crystallinity (E) of illite varies
from 150 to 200 A
˚
(Weber et al., 1976; Wang and
Zhou, 2000).
Smectite (montmorillonite type) is more dominant
in low-Cr samples, with more Ca
2+
than Na
+
exist-
ing as interlayer cations and a medium degree of
crystallinity ( v /p = 0.6; Biscaye, 1965). In contrast,
Fig. 4. Trace element distribution of the studied sediments. Data are normalised to the composition of present Po river fine sediments (sampled
and analysed by ourselves) around Ferrara (concentration expressed as ppm): Pb = 24, Zn = 91, Ni = 130, Co = 19, Cr = 221, V = 103, Th = 10,
Nb =11, Zr = 88, Sr = 186, Ba = 306, Y = 15, and Ce = 52.
Fig. 5. Representative TG, DTG, and DTA curves. Similar analyses are available also for samples 10, 11, 14, and 19.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 171

high-Cr samples exhibit a very low degree of crystal-
linity (v /p = 0.3).
Mg–Fe-bearing chlorite, with a high degree of
crystallinity, is always present; however, high-Cr
samples are comparatively richer in chlorite that
appear to be distinctively richer in Mg
2+
.
It is not possible to distinguish the X-ray double
reflections in kaolinite; the crystallinity index reflects
this (Brindley, 1961; Hincley, 1963), and as a result, a
low–medium degree of crystallinity is found in both
sample groups.
Interstratified minerals are characterised by 60 –
70% of smectite layers within low-Cr samples, and by
30–40% of smectite layers within high-Cr samples.
As mentioned, subordinate K/Sm mixed layers are
also present.
Summarising, the low-Cr samples are characterised
by a comparatively fine grain size, together with a
high proportion of clay minerals in which smecti-
te + interstratified minerals are more represented than
chlorite (Sm + ML/Chl>1). On the other hand, the
high-Cr samples have a coarser grain size, and a lower
abundance of clay minerals in which chlorite (Mg-rich
chlorite in this group of samples) predominates over
smectite + mixed layers (Sm + ML/Chl < 1).
Examination of the >63-Am fraction, using a trans-
mitted light microscope and XRPD analysis, revealed
that these coarse grains are mainly characterised by

quartz, minor amounts of carbonates and feldspars,
and lithic fragm ents containing amphiboles – pyrox-
enes, muscovite, biotite, chlorite, and serpentine (the
last-named mineral is ubiquitous only in high-Cr
sediments), with magnetite as a main Fe oxide in both
groups of samples.
4. Discussion
4.1. Possible origin and provenance of the studied
sediments
To address the implications of the analyses under-
taken, and to interpret the significance of the two men-
tioned sample groups (high Cr, low Cr), the presented
data were compared with the composition of sediments
related to rivers of Apennine provenance such as the
Reno and Panaro (Dondi et al., 1993; Dinelli and
Lucchini, 1998), and also with recent sediment s of
the Po river (Dinelli et al., 1999 and authors’ data re-
ported in Fig. 4).
It can be seen that the low-Cr samples show
chemical analogies with sediments of rivers sourced
from the Bolognese Apennine (in which femic and
ultrafemic rocks do not outcrop), whereas the high-Cr
samples show a chemical affinity with the Po sedi-
ments. Within the latter samples, the high Ni, Cr (and
V) concentration is related to the high abundance of
chlorite ( F serpentine), presumably formed by weath-
ering processes of ultrafemic–femic mineral paragen-
eses that are widespread in the western sector of the
Po drainage basin where igneous and metamorphic
rocks (and also ophiolite complexes) are present.

Coherently, Tomadin and Varani (1998) indicate
the predominance of smectite (typical of the low-Cr
samples) as the mineral fingerprint of fine sediments
of Apennine origin.
In this light, the tendency toward finer grain size
(and higher homogeneity of grain size) envisaged in
low-Cr samples can be interpreted considering that
they mainly represent reworked sediments, mainly
derived from erosion–weathering of sedimentary
rocks outcropping in the Bolognese Apennine.
It can be observed (in the map of Fig. 1) that the
samples included in the low-Cr group preferentially
outcrop in the southern/southwestern sector of the
investigated area, and are more widespread within
Table 4
Mineralogical composition (wt.%) of clay fraction ( < 2 Am)
Samples Cm Sm +
ML
Ill K Chl Qtz Fld Cal
Low Cr 3 92 31 28 16 17 5 3 tr
69230291716422
79128341118423
10 90 32 29 18 15 3 2 1
11 95 33 30 16 16 3 2 tr
14 90 30 26 18 16 4 2 4
x 92 31 29 16 16 4 2 2
High Cr 2 81 16 26 11 28 9 4 6
15 83 15 26 13 29 5 4 8
16 82 17 27 12 26 5 3 10
17 87 16 31 13 27 4 3 6

19 87 18 28 11 30 7 4 2
20 91 24 27 14 26 5 4 tr
x 85 18 28 12 28 6 4 5
Cm = clay minerals; Sm = smectite; ML= mixed layers; Ill =illite;
K = kaolinite; Chl = chlorite; Qtz = quartz; Fld = feldspars; Cal = cal-
cite; tr = trace; x = average value.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176172
the younger sediments. This fact could be explained
by considering the significant man-made hydrogeo-
logical modifications that occurred in the XIV–XVI
centuries throughout the Ferrarese territory (Bonde-
san, 1990). During this period, important hydrogeo-
logical developments were carried out to divert certain
apenninic torrent – river s (e.g. Ren o) into the southern
branches of the Po river (flowing south of Ferrara at
that time). These modifications induced the progres-
sive decadence of these southern Po branches, due to
the deposition of considerable amount of sediments
carried by these torrents. The alteration of the hydro-
geological system can explain the widespread pres-
ence of Reno-like compositions (low-Cr) within the
most recent terrains.
4.2. Environmental analysis and implications
Trace amounts of heavy metals are ubiquitous
within rocks, soils, surface, and ground water. Natural
background concentrations vary from place to place,
owing to different bedrock composition and hetero-
geneous distribution among the various geochemical
environments.
Organisms tend to concentrate these elements, and

consequently their presence in waters, even at low
concentrations, is considered dangerous due to their
toxic effects (Hg in aquatic ecosystems is a notorious
example; Jackson, 1998 and references there in). It
follows that, as part of an environmental assessment,
the content of heavy metals in waters and soils is a
key parameter necessary for evaluating the geochem-
ical vulnerability of an ecosystem.
Heavy elements usually exhibit a limited solubility,
and are easily trapped and adsorbed by phyllosilicate
minerals; as a consequ ence, they may be preferentially
partitioned within the fine fraction of sediments (Baldi
et al., 1997). This fact is related to the typical layer–
lattice alluminosilicatic structure of clay minerals, cha-
racterised by well-developed basal cleavage (001 pla-
nar faces) with permanent negatively charged sites.
Such structures induce electrostatic binding of cations
within the 001 faces (Jackson, 1998 and references
therein).
The fact that heavy elements a re preferentially
retained by the fine fraction of river sediments can
be used as a tool to detect pollution of an ecosystem.
However, to understand the possible presence of a
pollution process induced by human activity, it is
necessary to define the baseline (or ‘‘blank’’) of each
monitored key parameter (i.e. the typical concentra-
tions in an unpolluted environment). Within the con-
sidered area, this information can be obtained through
a geochemical characterisation of the sediments that
have not been affected by pollution and anthropogenic

activities.
In this study, the baseline approach enabled us to
highlight the concentration of the monitored parame-
ters in the natural system, as the studied terrains
sedimentated at times when the envir onment was still
unaffected by anthropic activity. Our data also indi-
cate the geochemical evolution of the Po basin in the
last 3000 years.
The concentrations of transition elements recorded
in the sediments sampled in the Ferrara surroundings
were compared with the maximum concentrations
admissible in terr ains used for agricultural (Italian
Legislative decree 27/01/1992, no. 99) and residential
(Italian Legislative decree 25/10/1999, no. 471) pur-
poses.
Within the high-Cr group of samples, the concen-
trations of Ni, Cr, V, and Co tend to b e higher than
those indicated by the current environmental legisla-
tion. However, in the study–case presented here, the
high concentration s detected are n ot associated to
urban – industrial–agricultural activities, but instead
appear to be typical of the original lithologies (Fig.
6). This has been further verified by taking into
account an extensive data set (authors’ data: ca. 100
samples) of bricks from precisely dated historic build-
ings of Ferrara . In fact the composition of these bricks
show remarkable analogies with the clay composi-
tions presented in this study.
Moreover, the chemical and mineralogical data
presented here provide an initial i nsight into the

elemental partition between competing clay minerals.
Different mecha nisms for trapping solution-electro-
lytes by the various clay minerals have been docu-
mented, and many authors also underlined existing
relationships between clay mineralogy and concentra-
tions of metallic elements (Brigatti et al., 1995, 1996;
Pitsch et al., 1992; Helios-Rybicka et al., 1995).
The implications become apparent when one con-
siders that clay (sl) is often used as a barrier to isolate
waste disposal sites from the surrounding environ-
ment. These studies could be applied to defining and
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 173
characterising the most suitable clay materials to be
used as liners and capping layers in landfills, as well
as to treat leachates.
Baldi et al. (1997) investigated the interaction
between solutions containing metallic ions and natural
clay sediments, thus individuating the key role of
smectite in buffering the abundance of heavy metals.
Pusch (1998) confi rmed the important role of smectite
for landfill-sealing purposes because of its high
exchange capacity.
Taking into account ion-exchange values reported
in the literature for the various clay minerals (CEC
values expressed as meq/100 g at pH 7; Faure, 1998)
and the modal proportions reported in Table 4 (refer-
Fig. 6. Boxplots reporting the compositional distribution of Cr and Ni in the studied samples, in present-day sediments from the Po river and
rivers sourced within the Bolognese Apennine, and in the bricks of the historic buildings of Ferrara (plausibly made with similar fine sediments;
authors’ data). The limit concentrations admissible in terrains (Italian Legislative Decree 25/10/1999, no. 471) have been also reported for
comparison.

G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176174
ring to the fine fraction), we calculated theoretical
CEC values of 39–43 and 28 –36 for low-Cr and
high-Cr groups, respectively. A CEC analysis on tout-
venant samples would have envisaged lower absolute
values, possibly characteris ed by a more marked
difference between the two groups of terrains (high-
Cr sediments are significantl y coarser and contain
minor amounts of clay minerals).
Summarising, low-Cr lithologies characterised by
finer grain size, higher abundance of smectite, and
low content of transition elements would be the most
suitable for forming impermeable bottom layers
within landfills of this area.
5. Conclusions
In the study area, the lithological outcrops consist
of silico–clastic sediments (containing a minor
amount of carbonate components), in which clay
and silt fractions prevail, with a subordinate sand
fraction.
Chemical analyses of these samples have been
compared with recent sediments from the Apennine
torrents and Po river, to understand their possible
provenance.
The same analyses have also been compared with
the chemical composition of bricks of historic build-
ings of Ferrara (XII–XVI centuries), made from
similar raw materials in periods in which the human
impact on the environment was negligible.
These comparisons suggest that the concentration

of heavy metals (such as Cr, Ni, V, and Co) is naturally
high, and cannot be a direct consequence of anthro-
pogenic activity.
This data set provides therefore a contribution to
interpreting the vulnerability of the Ferrara area, which
appears to be naturally characterised by high concen-
trations of metallic elements approac hing the legisla-
tive threshold.
An integration of similar scientific contributions
would be useful to set up a geochemical–mineralog-
ical database (Protano et al., 1999; Vetuschi Zuccolini
and Ottonello, 1999) as a first step toward the prepa-
ration of more complete thematic maps.
Such geochemical maps could provide information
relative to the behaviour of chemical elements within
the different geochemical spheres, thereby promoting
better knowledge of the environmental systems (sur-
face waters, ground waters, soils, and underlying
mother rocks). These maps would be useful for ex-
ploiting, i n an environmentally sensitive way, the
available natural resources a nd for understanding the
potential pollution p rocesses.
Acknowledgements
The authors th ank Dr. R. Tassinari, Pr of. G.
Cruciani, and Prof. M.F. Brigatti for their analytical
support, and are also indebted to the referee Prof. F.
Veniale (Pavia University) whose criticism, com-
ments, and suggestions have greatly improved the
paper.
References

Baldi, M., Conti, F., Guado, P., Setti, M., Urbini, G., Vercesi, P.,
1997. Uso di minerali argillosi per la mitigazione della concen-
trazione di metalli pesanti in percolati di discarica per RSU. Atti
Tic. Sc. Terra 39, 95 – 106.
Biscaye, P.E., 1965. Mineralogy and sedimentation of recent deep-
sea clay in the Atlantic Ocean and adjacent seas and oceans.
Geol. Soc. Am. Bull. 76, 803 – 832.
Bond esan, M., 1990. Evoluzione ge omorfologica ed idrografica
della pianura ferrarese. In: Corbo, G. (Ed.), Terre ed acqua-Le
bonifiche ferraresi nel delta del Po. Ferrara, pp. 13 – 20.
Bradley, W.F., Grim, R.E., 1961. Mica clay minerals. In: Brown, G.
(Ed.), The X-ray Identification and Crystal Structures of Clay
Minerals. Mineralogical Society, London, pp. 208 – 241.
Brigatti, M.F., Corradini, F., Poppi, L., 1995. Interaction between
montmorillonite and pollutants from industrial waste water: ex-
change of Zn
2+
and Pb
2+
from aqueous solutions. Appl. Clay
Sci. 9, 383 – 395.
Brigatti, M.F., Campana, G., Medici, L., Poppi, L., 1996. The in-
fluence of layer charge on Zn
2+
and Pb
2+
sorption by smec-
tites. Clay Miner. 31, 477 –484.
Brindley, G.W., 1961. Kaolin, serpentine, and kindred minerals. In:
Brown, G. (Ed.), The X-ray Identification and Crystal Structures

of Clay Minerals. Mineralogical Society, London, pp. 51–131.
Dinelli, E., Lucchini, F., 1998. Element dispersion patterns in the
Reno river valley (Northern Italy) by means of stream sediment
geochemistry. Mineral. Petrogr. Acta XLI, 145 – 162.
Dinelli, E., Amorosi, A., Centineo, M.C., Lucchini, F., 1999. Geo-
chimica dei sedimenti sepolti della Pianura Padana—uno stru-
mento per valutare la qualita’ dell’ambiente. Conf erenza Le
pianure: Conoscenza e salvaguardia; il ruolo delle scienze della
terra, Ferrara. pp. 131–133 (abstract book).
Dondi, M., Ercolani, G., Guarini, G., 1993. Caratteri geochimici,
mineralogici e granulometrici di peliti alluvionali quaternarie
dell’Emilia-Romagna (Italia Settentrionale). Mineral. Petrogr.
Acta XXXVI, 129 – 142.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176 175
Dunoyer De Segonzac, G., 1970. The transformation of clay min-
erals during diagenesis and low-grade metamorphism: a review.
Sedimentology 15, 281 – 346.
Faure, G, 1998. Principles and Application of Geochemistry. Pren-
tice Hall, London, p. 600.
Franzini, M., Leoni, L., Saitta, M., 1975. Revisione di una metodo-
logia analitica per fluorescenza-X basata sulla correzione com-
pleta degli effetti di matrice. Rend. Soc. Ital. Mineral. Petrol. 31,
365–378.
Helios-Rybicka, E., Calmano, W., Breeger, A., 1995. Heavy metal
sorption on competing clay minerals: an experimental study.
Appl. Clay Sci. 9, 369 –389.
Hincley, D.N., 1963. Variability in ‘‘crystallinity’’ values among the
Kaolin deposits of the Coastal Plain of Georgia and South Car-
olina. Clay Miner. 11, 229 –235.
Jackson, M.L., 1958. Soil Chemical Analysis. Prentice-Hall, p.

498.
Jackson, T.A., 1998. The biogeochemical and ecological signifi-
cance of interactions between colloidal minerals and trace ele-
ments. In: Parker, A., Rae, J.E. (Eds.), Environmental
Interactions of Clays. Springer-Verlag, Berlin, pp. 93–206.
Laviano, R., 1987. Analisi mineralogica quantitativa di argille me-
diante diffrattometria di raggi X. In: ENEA (Ed.), Procedure di
analisi di materiali argillosi. Collana di studi ambientali, Santa
Teresa, Lerici (Sp), pp. 215 – 234.
Leoni, L., Saitta, M., 1975. X-ray fluorescence analysis of 29 trace
elements in rocks and mineral standards. Rend. Soc. Ital. Min-
eral. Petrol. 32, 497–510.
Marini, L., Ottonello, G., 19 99. Use of stream sediment data to
evaluate water–rock interaction processes. Plinius 22, 235–
237 (Italian supplement of Eur. J. Mineral.).
Moore, D.M., Reynolds Jr., R.C. 1997. X-ray Diffraction and the
Identification and Analysis of Clay Minerals, 2nd edn. Oxford
Univ. Press, Oxford, p. 332.
Pitsch, H., Ly, J., Stammose, D., Kabare, I., Lefevre, I., 1992.
Sorbtion of major cations on pure and composite clayey materi-
als. Appl. Clay Sci. 7, 239 – 243.
Pusch, R., 1998. Transport of radionuclides in smectite clay. In:
Parker, A., Rae, J.E. (Eds.), Environmental Interactions of
Clays. Springer-Verlag, Berlin, pp. 7 – 23.
Protano, G., Riccobono, F., Sabatini, G., 1999. La cartografia geo-
chimica d’Italia: Foglio NK32-6 Grosseto. Gli esempi di As, B,
Cd, Co, Cu, Pb, Sb, Zn. Plinius 22, 318 – 319 (Italian
supplement of Eur. J. Mineral.).
Schultz, L.G., 1964. Quantitative interpreta tion of mineralogical
composition from X-ray and chemical data for the Pierre Shale.

U.S. Geol. Surv. Prof. Pap. 391-C, 1 – 31.
Shaw, D.B., Stevenson, R.G., Weaver, C.E., Bradley, W.F., 1971.
Interpretation of X-ray diffraction data. In: Carver, R.E. (Ed.),
Procedures in Sedimentary Petrology. Wiley, New York, pp.
554 –557.
Srodon, J., Eberl, D.D., 1984. Illite. In: Bailey, S.V. (Ed.), Micas.
Review in Mineralogy 13, Mineralogical Society of America,
Washington, DC, pp. 495 – 544.
Stefani, M., Asioli, A., Bondesan, M., Cattani, L., Correggiari, A.,
Roveri, M., Trincardi, F., 1999. Stratigrafia ed evoluzione am-
bientale olocenica della pianura costiera ferrarese e dell’antis-
tante mare adriatico. Conferenza Le pianure: Conoscenza e
salvaguardia; il ruolo delle scienze della terra, Ferrara. 2–4
(abstract book).
Tomadin, L., Varani, L., 1998. Provenance and downstream min-
eralogical evolution of the muds transported by Po River
(Northern Italy). Mineral. Petrogr. Acta 41, 205 – 224.
Vetuschi Zuccolini, M., Ottonello, G., 1999. Towards the national
geological database: logical framework and network interface.
Plinius 22, 374 – 375 (Italian supplement of Eur. J. Mineral.).
Wa ng, H., Zhou, J., 2000. The relationshi p between the Kubler
index, Weaver index and Weber index of illite crystallini ty
and their application. Schweiz. Mineral. Petrogr. Mitt. 80,
187 –198.
Weber, F., Dunoyer De Segonzac, G., Economou, C., 1976. Une
nouvelle expression de la cristallinite
´
de l’illite et des micas.
Notion d’epaisseur apparente des cristallites. C. R. Somm.
Soc. Geol. Fr. 5, 225 – 227.

Yoder, H.S., Eugster, H.P., 1955. Synthetic and natural muscovites.
Geochim. Cosmochim. Acta 8, 225 –280.
G. Bianchini et al. / Applied Clay Science 21 (2002) 165–176176