Hydrochemistry on a waste disposal area of sand

Transactions on Ecology and the Environment vol 24, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
Hydrochemistry on a waste disposal area of
sand mining activities at Analandia, Sao Paulo
State, Brazil, and
their
implications on
the
mobilization of uranium
D.M. Bonotto & E.G.de Oliveira
Departamento de Petrologia e Metalogenia/Departamento de
Geologia Aplicada, Institute de Geociencias e Ciencias
Exatas-UNESP, C.P. 178, 13506-900 Rio Claro, Sao Paulo,
Brasil
Email: [email protected]
Abstract
Groundwaters and surface waters from an area of treatment of sand for industrial
purposes at Analandia municipality, nearly in the center of Sao Paulo State,
Brazil, were chemically and isotopically analysed with two aims: to evaluate if
the anthropogenic activities that has taken place for the last 6 years is affecting
the quality of the hydrological resources and to relate the hydrogeochemical
behaviour of the uranium isotopes ^U and ^*U with the pattern of circulation of
groundwaters.
Introduction
The Sao Paulo State in Brazil, due to its advanced stage of agricultural
and industrial growth, has a great diversity of problems related to the
interaction between the society and the environment. The sand mining
activities in Depressao Periferica geomorphological province are presently
very important, because potentially they can be a source of anthropogenic
impacts, since several chemicals are used for the treatment of natural sand
like HO, H2SO4, NaOH and NaaSiO^ generating mine tailings that can
Transactions on Ecology and the Environment vol 24, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
72
Risk Analysis
pollute the surface and underground hydrological resources. The
knowledge of the concentrations of dissolved elements and compounds is
needed in order to establish their background values and to predict their
potential increase in future years, thus, thefirstobjective of this work is to
compare the values obtained for various parameters in waters from the
studied area with those defined by the national standards for drinking
water.
The U content and ^U/^*U activity ratio (AR) of dissolved U have
been utilized to determine patterns of groundwater flow. For instance, the
waters of the Canizo Sand Formation of South Texas [1] exhibit a pattern
of changing across reducing barriers where, in general, the samples from
the outcrop area and shallow aquifer are characterized by relatively high
U concentrations and low AR's, whereas the samples from downdip show
much lower U concentrations and higher AR's. A similar tendency was
observed for groundwaters in a drill hole from the Lodeve U deposit, SW
of the French Massif Central [2] where, higher U concentrations and
lower AR's characterized the oxidizing upper part of the aquifer (50-100
m depth), whereas lower U concentrations and higher AR's characterized
the more reduced lower part of the aquifer (100-150m depth). The second
aim of this work is to relate the measured values for dissolved U content
and AR's with the pattern of groundwater flow in the studied area.
Geological features at the mine tailings area
The studied area belongs to CRS-Mineragao Industria e Comercio Ltda.,
being located about 5 km from Analandia city, nearly in the center of S3o
Paulo State at 22°8'S and 47°40'W (Fig. 1), and situated at the
northeastern edge of the Parana sedimentary basin. Several stratigraphic
units of this basin cropp-out in the region, where the main features of the
geology at the studied area are similar to those described for a sand
deposit 5 km distant [3], which belongs to another company and whose
lithology includes the Lower and Upper units from Piramboia Formation,
the Botucatu Formation and the weathered cover developed over
Piramboia Formation (red-yellow latosols). The Lower unit from
Piramboia Formation consists of a consolidated whitish sandstone (after
washing) with well-preserved sedimentary structures, whose thickness is
more than 80 m, the retention after grinding is greater on the 0.125 mmsize sieve, and the Fe oxide mineral content is low. The occurrence of
small clay lenses of variable lateral size is very common in this unit. The
Upper unit from Piramboia Formation is a light pink saprolite
characterized by thin sedimentary structures and a very brittle sandstone
located above the water table, whose concentration of Fe oxide is also low
Risk Analysis
73
Transactions on Ecology and the Environment vol 24, © 1998 WIT Press, www.witpress.com,
ISSN 1743-3541
52°W
46°W
Ux—'
w/
20°S
f 4ns Idnc ,a\
zl ~-—^
• v
=:
\
24°S
t
^
X
\
/
M
LEGEND
Contour Level (meters)
Slope
Footway
^ Surface Water
pggnj
Sampling Poin
Stream
^
Mining Front
Dam
Decantation Tank
N
Figure 1: Location of the Analandia city at Sao Paulo State, Brazil, and
sketch map of the mine tailings area.
and the dominant particle-size after milling is in the range 0.125-0.25
mm. A 1-30 cm thick stone line profile [4] occurring as an irregular
replica of the topography divides this unit and the above located mantle of
weathering, which is constituted by tabular blocks of sandstones cemented
by black coloured limonite, dark red ferruginous concretions, small tablets
of limonite cementing sandstone, SiC>2 pebbles, weathered yellowish
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74
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sandstone and major concentration of heavy minerals (hematite, magnetite
and ilmenite). The Botucatu Formation is represented in the area by
weathered sandstones with high content of Fe oxide and particle-size
predominantly in the range 0.5-1 mm. The weathered cover developed
over Piramboia Formation includes: peat soil, creep soil, and soil above
the stone line. The peat soil is light grey-black coloured, and occurs from
the point of the discharge of the water table up to the contour level
corresponding to that of the local streams. The creep soil is very clayey
(12-20%), occurs on the steep ground, being characterized by a redbrownish colour, values of Fe oxide content of about 5000 ppm, and
presence of limonite concretions between 2 and 6 m depth. The soil above
the stone line is yellow-orangish coloured, its thickness may attain 18m,
occurs where the ground slope is smooth, has a clay content varying
between 7 and 18%, and a higher Fe oxide content near the surface due to
the laterization, which diminishes with increasing depth, rising again at
the stone line position.
Sampling and analytical methods
The study of the hydrologic environment around the waste disposal area
involved the sampling of groundwaters from 3 boreholes (Table 1) drilled
for characterizing the subsurface flow and of surface waters from Ponte
Funda stream that receives most of the area drainage (Fig. 1). The aquifer
system developed in the weathered cover over Piramboia Formation,being
performed three campaigns of water sampling in December 1991. The
samples were stored in polyethylene bottles, and depending on the
requirements of the analysis, they were distributed as unfiltered and
unpreserved (i.e. for temperature, pH, Eh, dissolved C>2, conductivity and
bicarbonate determinations), filtered through 0.45 jam membrane and
unpreserved (i.e. for major ions analyses) and filtered and preserved with
different acids (i.e. for U isotopes and trace element determinations).
Standard analytical techniques were used for obtaining the composition
of the major and minor elements in waters, for example, methyl orange
end-point titration, potentiometry, flame photometry, ion selective
Table 1: Characteristics of the boreholes (BH) at the studied area. Data
for water table depth obtained on 3 and 4 December 1991.
Parameter
Unit BH 1 BH2
BH3
75
75
75
mm
Diameter
711.5 688.0 685.0
m
Altitude of the top
5.5
16.0
5.5
m
Total length
1.60
13.20 2.96
m
Water table depth
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75
electrode, inductively-coupled plasma emission, and alpha-spectrometry
for determinations of the U content and AR [5]. The results of the
measurements are reported in Table 2.
Hydrochemistry and water quality
The studied groundwaters belong to a low-temperature aquifer system,
whose Eh-pH field indicates it is transitional, tending to be reducing in
character. When the chemical data obtained for the surface and
groundwaters are compared with the maximum (minimum in the case of
dissolved oxygen) permissible concentration limits in drinking water
established by the national standards NTA-60 (Sao Paulo State Register
12486 published on 20 October 1978) and CON AM A No. 20 (National
Register for fresh waters belonging to class 2, published on 18 June
1986), it is possible to verify that the analytical techniques utilized for the
measurements of NHL*, P, Cd and Pb have detection limits above the
permissible levels. With the exception of pH, all other values obtained for
the investigated parameters don't suggest the occurrence of any
environmental impact related to the sand mining activities.
The pH values could be attributed to some anthropogenic input,
however, the cation Na* and anions SO/" and Cl, which are potentially
important to affect the area, are present in very low concentrations,
confirmed by the low values of conductivity and dry residue, reflecting, in
the case of the groundwaters, the composition of rainwater with small
amounts of silica added from contact with the aquifer. Such pattern of
chemical data is not much amenable to plot on a standard Piper diagram
[6], because there is a lack of the preponderance of typical anions and
cations, and the mixed character is identified in some situations (Fig. 2).
The rainwater interaction with the weathered mantle developed over
Piramboia Formation when it enters the aquifer by percolating through the
unsaturated zone until it meets the water table constitutes another
explanation for the low pH values, because the pH of several soil
suspensions representative of horizons from three pedological profiles
was determined both in water and in KCI solution and the most of the
obtained values are strongly acid (pH<4.5) or moderately acid (pH
between 4.5 and 5.5) [7]. If the chemical data obtained for the waters are
used to study stability relations of mineral phases in the systems K^OAWs-SiOz-ItO, CaO-A^Oa-SKVHsO and NazO-AlzOg-SiOz-HzO [8],
it is observed that they fall into the kaolinite field of stability (Fig. 3),
information confirmed by the use of X-ray diffraction in the
mineralogical identification of samples from the weathered cover
Transactions on Ecology and the Environment vol 24, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
76
Risk Analysis
developed over Piramboia Formation, since kaolinite was identified as the
second most abundant mineral phase (SiO] was thefirst)[7].
Table 2. Chemical analyses of groundwaters (BH) and stream waters (S)
at the studied area, which were sampled on 3 and 4 December 1991.
Parameter
Temperature
Dissolved O:
pH
S2
SI
BH1 BH2 BH3
26
31
26
25
26
8.0
10.0
4.5
7.5
7.1
4.8
4.4
3.9
4.2
5.0
4.6'
5.2'
+217
+183
Eh'
mV
40
40
40
50
50
Conductivity (25°C) fiS/cm
3.3
3.3
3.7
Silicon
3.0
4.2
mg/L
12.0
1.0
8.0
2.9
5.1
mg/L
Bicarbonate
<2.0
<2.0
<2.0
<2.0
mg/L <2.0
Sulfate
0.6
0.4
0.3
1.2
0.9
mg/L
Chloride
0.04
0.05
0.04
mg/L 0.06 0.05
Fluoride
0.03
0.03
0.09
0.02
mg/L 0.03
Nitrate + Nitrite
mg/L <0.2
Ammonium
<0.2
<0.2
<0.2
<0.2
mg/L <0.1
Phosphorus
<0.1
<0.1
<0.1
<0.1
mg/L <0.02 <0.02 <0.02 <0.02 <0.02
Boron
mg/L <0.1
Aluminum
<0.1
<0.1
<0.1
<0.1
0.1
0.1
0.3
0.8
mg/L
1.6
Sodium
0.2
0.3
0.2
0.6
0.5
mg/L
Potassium
0.1
0.1
0.4
1.5
mg/L
Calcium
1.6
0.1
0.1
mg/L
Magnesium
<0.1
<0.1
<0.1
0.02
mg/L 0.02 0.03
Barium
<0.02 <0.02
mg/L <0.02 <0.02 <0.02^ <0.02 <0.02
Total iron
mg/L <0.02 0.04
Manganese
<0.02 <0.02 <0.02
0.02
mg/L 0.02 <0.02
Zinc
<0.02 <0.02
0.02
0.02
mg/L 0.02
Copper
<0.02 <0.02
mg/L <0.1
<0.1
<0.1
Lead
<0.1
<0.1
mg/L <0.02 <0.02 <0.02 <0.02 <0.02
Cadmium
mg/L <0.05 <0.05 <0.05 <0.05 <0.05
Total chromium
mg/L <0.02 <0.02 <0.02 <0.02 <0.02
Nickel
20
24
32
36
40
DryResidue(105°C) mg/L
1.35
0.05
Uranium^
Hg/L
0.80
1.32
*WUAR*
* Measured on 12/20/91; Measured after aeration and filtration;
^Uncertainty ±10% corresponding to la standard deviation.
Unit
°C
mg/L
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77
The total Fe concentration reported in Table 2 for BH3 doesn't reflect
the actual value, because after exposure to the atmosphere, an originally
light and colorless high-Fe water turned red as ferric species formed,and a
reasonably high amount of material precipitated, implying that the
measurement only refers to the supernatant phase after filtering in 0.45pm
membrane. The major Fe-bearing mineral in the area is limonite, which
has been commonly identified in the weathered mantle developed over
Piramboia Formation [3].When a solution containing Fe*" is neutralized
(pH increases), or aerated (Eh increases), or both, amorphous hydrous Fe
oxides precipitate, reordering, subsequently, into more crystalline Fe
oxides such as goethite or hematite [9], pattern not confirmed by the
reported data for waters of BH1 and BH3 since, if the direction of the
flow-through water from BH1 up to BH3 is taken into account, then, it is
possible to verify that the pH decreases, Eh increases, and aeration
(dissolved 62) decreases. The lower aeration related to the Eh rise in BH3
probably can be attributed to the dissolved O] consumption for the
oxidation of Fe^ to Fe% corresponding to 34 mV the difference on Eh
Groundwaters
G1 - Borehole 1
G2 - Borehole 2
G3 - Borehole 3
Surface waters
S1 - Upstream
S2 - Downstream
100%
100%
Figure 2: Chemical data for the studied waters plotted on a Piper diagram.
Transactions on Ecology and the Environment vol 24, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
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Risk Analysis
values measured in BH1 and BH3, which agrees very reasonably with 32
mV evaluated from the theoretical relationship between the Eh, pHand
fiigacity of O2 [9], i.e.:
Eh = 1.23 + 0.01479 log[OJ - 0.05916pH
(1)
Mobilization of uranium isotopes
A CO: partial pressure corresponding to about 0.1 atm for groundwaters
from BH1 and BH3 can be evaluated by Henry's law on using 0.033
mol/L.atm as constant [10], as well a total dissolved COz content
estimated from HCCV and pH data shown in Table 2. The Eh-pHfieldfor
U species under this condition of pressure shows that its transport in the
area may be occurring mainly as UC^ (Fig. 4). The AR for dissolved U
logJ!<l
[H+]
, [Ca*]
log-—^ 10
-5
-4
-3
Figure 3: Chemical data for the studied waters plotted on diagrams
representing the stability relations of some mineral phases in the systems
> at 25°C and 1 atmosphere [8].
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Risk Analysis
79
greater than unity in BH1 indicates that preferential removal of ^U is
occurring due to the interaction between the groundwater and the mantle
of weathering very probably depleted in ^U, situation often reported for
other systems and interpreted by alternative mechanisms like preferential
chemical dissolution of ^U [11] and ct-recoil release of ^Th at the
rock/soil-water interface [12]. Enhanced chemical dissolution of ^U
relative to ^*U may occur because of radiation damage to the crystal
lattice in the vicinity of^*U decay or because of oxidation of ^U during
the decay processes by which it is formed. However, the AR value lower
than 1 in BH3 is unusual, being associated with a value of dissolved U
concentration about 30 times higher than that measured in BH1. The
simplest explanation for similar cases reported elsewhere [13] is that
sudden, rather than gradual shifts in geochemical conditions may have
occurred, and the "normal" lower than 1 AR value at or near the boundary
of the host matrix is put in solution, causing a simultaneous increase in U
content and decrease in AR. In the present study, the best mechanism for
interpreting the increase on U content in groundwater of BH3 after
exposing the sample to the atmosphere is the U co-precipitation with
Fe(OH)3.The results of the isotopic compositions of dissolved U obtained
in this work showed that a lower U content and a higher AR
characterized the more reduced part of the aquifer, like reported by other
1.0
0.8
CM CN
0.60.4-
CM
o
r
* GROUNDWATER FROM
BOREHOLE 1
f
* GROUNDWATER FROM
BOREHOLE 3
Eh
(volts)
crystalline UCU
amorphous
' UC>2
-0.6
4
6
8 10 12 pH
Figure 4: Data for groundwaters from the studied area plotted on an EhpH diagram showing the stability field of uranyl carbonate complexes at
CO2 partial pressure of 0.1 atm [14].
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investigators [1, 2].However, the direction of the flow-through water in
the studied hydrologic context is opposite to that generally considered,
since it is from the deeper part of the aquifer up to the shallower zone,
involving the generation of a higher U content and a lower AR.
References
[1] Cowart, J.B. & Osmond, J.K. Uranium isotopes in groundwater: their
use in prospecting for sandstone-type uranium deposits, J. Geochem.
Explor, 8, pp. 365-379, 1977.
[2] Toulhoat,?. & Beaucaire,C. Comparison between lead isotopes, ™U/
^*U activity ratio and saturation index in hydrogeochemical exploration
for concealed uranium deposits, J. Geochem. Explor., 41, pp. 181-196,
1991.
[3] Tandel, R.Y., Caracterizagao do arenito Piramboia da Fazenda Sao
Joao em Analdndia, SP, e sua uiilizaqao industrial, USP, Sao Paulo, 75
pp., 1993.
[4] Lecomte,P. Stone line profiles:importance in geochemical exploration,
J. Geochem. Explor., 30, pp. 35-61, 1988.
5] Uso, J. L., Brebbia, C. A. & Power, H. (eds.), Ecosystems and
Sustainable Development, Computational Mechanics Publications,
Southampton and Boston, pp. 193-202, 1998.
[6] Piper, A.M. A graphic procedure in the geochemical interpretation of
water analyses, Trans.Amer.Geophysical Union, 25, pp.914-928, 1944.
[7] Jimenez-Rueda, J.R., Comments about some mineralogical data and
pH values of soil suspensions from Piramboia Formation, 1994.
[8] Carrels, R. M. & Christ, C. L., Solutions, minerals, and equilibria,
Harper & Row, New York, 450 pp., 1965.
[9] Faure, G., Principles and applications of inorganic geochemistry,
Mac Millan Publishing Co., New York, 626 pp., 1991.
[10] Brownlow, H.A., Geochemistry, Prentice-Hall, Englewood Cliffs,
498 pp., 1979.
[11] Rosholt, J.N., Shields, W.R. & Garner, E.L. Isotopefractionationof
uranium in sandstone, Science, 139, pp. 224-226, 1963.
[12] Kigoshi, K. Alpha-recoil ^*Th: dissolution into water and the ^U/
***U disequilibrium in nature, Science, 173, pp. 47-48, 1971.
[13] Ivanovich,M. & Harmon, R.S.(eds.), Uranium series disequilibrium:
applications to environmental problems, Clarendon Press, Oxford, pp.
202-245, 1982.
[14] Andrews, J.N. & Kay, R.L.F. The U contents and *"U/^*U activity
ratios of dissolved uranium in groundwaters from some Triassic sandstones in England, Isotope Geoscience, 1, pp. 101-117, 1983.