2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P85 LAbORATORy STuDy OF ARSENIC
MObILITy IN STREAM SEDIMENTS AND
IMPOuNDMENT MATERIAL uSING COLuMN
ExPERIMENTS
VEROnIKA VESELSKá and EDGAR HILLER
Comenius University in Bratislava, Faculty of Natural
Sciences, Department of Geochemistry, Mlynská dolina,
842 15 Bratislava, Slovak Republic,
veselska@fns.uniba.sk
Introduction
High arsenic contents in the impoundment situated near
the village of Poša in the upper part of the catchment of the
Kyjov brook in eastern Slovakia, represent an environmental
problem because of As mobilization and transport from
the impoundment material and significant contamination
of surface water of the Kyjov brook (the mean As values
of 11,385 μg As dm –3 , 1,778 μg As dm –3 and 295 μg As dm –3
measured in the Kyjov brook during 2000, 2005 and 2007
respectively) 1 . Decreasing concentrations of As in surface
water are involved in delimited using of impoundment in last
few years.
Arsenic distribution in different stream sediment constituents
and its mobilization determine As concentration in
aquatic environment and affect its bioavailability and toxicity
to the biosphere 2,3 .
The major processes controlling As leaching from sediments
to natural waters include mineral (co)precipitation/
dissolution, adsorption/desorption, chemical and biological
transformations. The conditions present such as pH, redox
potential, solution composition, the sediment properties and
mineralogical composition of the sediment determine the
dominant processes affecting the environmental fate of As in
the stream sediments and ist leaching behaviour 4,5 .
The main objective of this study was to investigate leaching
behaviour of As from the heterogeneous impoundment
material and the three stream sediments and the evaluation of
the total As mobility.
Experimental
The samples used in this work are either the stream
sediments of the Kyjov brook taken at the distance of 100,
1,000 and 2,000 m from the impoundment (denoted as KY-
100, KY-1000 and KY-2000) or the impoundment material
(denoted as KY-0).
Continuous column leaching experiments were conducted
under standard conditions (25 ± 3°C, 101,325 Pa) to
provide information about As release, its binding and desorption
kinetic. The experiments were run in duplicates. Each of
the two glass columns per one sample was filled with 50 g of
a dry sample (a < 1 mm fraction) and columns were during
five days flushed with 1.3 dm 3 of 0.0125M solution, that was
prepared to resemble the composition of surface waters of the
Kyjov brook and contained by 2 × 10 –5 M PO 4 3– , 2.8 × 10 –3 M
Cl – and 3.2 × 10 –3 M SO 4 2– . The upward flow was regulated at
s509
a rate of 0.2 ml min –1 . During the experiment, 14 samples of
leachates were collected from each of the columns, pH values
were measured and the concentrations of As were determined
by graphite furnace atomic absorption spectrometry (Perkin-
Elmer 4110 ZL).
Results
The results of the column experiments showed that
theAs release from the solid samples was likely controlled
by Fe and Mn oxohydroxides, pH values of the geosorbents
and leachates and also organic carbon content. It was also
observed that the time was an important factor influencing
the As release.
Significant correlations of the amounts of As released
from the solid samples with its total contents (r = 0.975,
P < 0.05) (Fig. 1.) as well as with total organic carbon contents
(r = 0.942; P < 0.05) were found. The total organic carbon
content was measured using a Leco RC-412 multiphase
determinator at 550 °C.
The impoundment material (KY-0) has the highest total
organic carbon content (37 %), which is likely attributed to
the fact that stored sludge consists of fly ashes derived from
coal and chemical waste combustion. Alkaline character of
the KY-0 (pH = 8.55) as well as high leachate pH (pH ~ 9.0)
enhance release of As and its transport to the liquid phase.
The results of various studies showed that the amounts of As
oxyanions released from different solid geosorbents increase
in alkaline conditions, mainly when pH > 8(ref. 6 ) The maximum
As concentration in column leachates from KY-0 was
determinated after 25 hours, when the easily soluble fraction
of As weakly bound on the solid surface was released. The
late hindered As release from KY-0 could be caused by the
presence of mullites and vitreous phases. It is suggested here
that some fraction of As may be only hardly available to be
released because of its strong binding within the heterogenous
components.
Fig. 1. Relationships between the amounts of As released and
total contents of As, Fe as a ammonium-oxalateextractable Alox,
Feox in the log-log form