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EC number: 294-409-3
CAS number: 91722-09-7
Substance formed during processing of liquid steel or during production of iron castings. Consists primarily of fused silicates and trace elements as oxides as well as trace of alloying elements.
High Kd values for trace elements indicate that the distribution of trace elements between slags (solid phase) and their leachates (liquid pahse) is almost exclusively on the side of the solid phase, and very low mobility of trace elements is predicted.
Kd values of trace elements in
A literature review was done on soil−liquid
partitioning coefficients (Kd) of several trace elements of
toxicological relevance. Although the reported values scattered,
mobility and bioavailability of the elements could be predicted. The kd
values especially for the metals cadmium, copper, lead, nickel, and zinc
exhibited a relationships to variations in the pH of the soil solution,
the content of metals and organic matter of the soil (SOM). Multiple
linear regressions showed highest correlations to linear regression with
pH or with pH and log of one of the other parameters. Solubility of
trace metals was interpreted as competitive adsorption of metal cations
and hydrogen ions.
Arithmetic Means of Kd values
(L/kg) of elements in soil/water
Zn 11615 (Sauvé et al. 2000)
Kd values of trace elements of
Soil-to-water partition coefficients Kd
of individual trace elements occurring in slag were calculated from
their concentration in the solid slag, divided by their concentrations
in leachate. In total, slag from 58 steel works with blast furnaces,
basic oxygen furnaces (converters) and/or electric arc furnaces, were
examined for leachability at acidic and neutral pH values.
The calculated Kd values are
higher than 1000 L/kg with few exceptions due to calculation procedure
using half the limit of detection as an estimate for concentration in
leachates. These calculated results comprise arsenic and tin in blast
furnace slag (Kd= 300 and 500 L/kg, for arsenic and tin,
respectively) and mercury in the EAF slag (Kd= 900
L/kg). With very low levels both in the slag and in the leachate, the
following Kd's were calculated: 700 L/kg for molybdenum in
BOS, 535 L/kg for chromium-VI in EAF, and 819 L/kg for arsenic in EAF.
The Kd values of different slags
were similar. Their differences between the slags did not exceed one
order of magnitude.
The high Kd values suggest that
the trace elements are very tightly bound into the matrix. Leaching of
trace elements is extremely low and transport in soil will be very slow
(Proctor et al. 2000).
These results were confirmed by data on
total trace element levels in slags and the corresponding leaching data
taken from a report of the German Oekoinstitut. The Kd values
(L/Kg) calculated for ABS are
The Kd values (L/kg) for GBS are
There are no relevant differences in the
adsorption/desorption properties of the 2 subtypes of blast furnace slag
in regard to the Kd of the trace elements tested (data taken
from Oekoinstitut 2007).
determine the kd values of trace elements of toxicological relevance in
the slags ABS, BOS, and EAF C, existing concentration data of the BfG of
trace elements in solid slag and natural rocks were compared with their
respective concentrations in leachates of slags and natural rocks.
values of Hg and Tl could not be determined, because no data had been
measured in leachates. The Kd values of As and Cd are low
(e.g. >20 L/Kg) because these elements (and Hg and Tl) are not present
in slags and basalt at relevant levels. The same is most likely correct
for Pb. For Ni (< 700, >4000 L/kg), Cu (> 9400, > 6000 L/kg), Zn (>
40000, >6600 L/kg) and Cr (> 800000, > 10000 L/kg) high Kd
values have been obtained, suggesting a very tight binding of these
elements into slag and basalt, respectively (data taken from BfG 2008).
The environmental behaviour of slags was
evaluated from the total content and solubility of analytes in the
slags. A simple re-evaluation of the existing data was done to determine
the retention potential of slags for trace metals and other analytes.
All Kd values obtained were very high suggesting that the
analytes examined are effectively retained by slags. The solid/liquid
adsorption coefficients Kd of both ABS and GBS were high (L/kg): ABS: Ca
1312, Mg 97500, Fe 66110, Mn 329220, SiO2 1684; GBS: Ca
10978, Mg 19500, Mn 109750, SiO2 7424 (data taken from LECES
Kd values of ABS and GBS in comparison
with natural rocks
To elucidate the risk of the use of slags in
the environment in comparison to natural rock, the 2 types of leaching
experiments were performed: Ordinary availability tests consisting of
two leachings at neutral and acidic pH (NT ENVIR 003) and oxidised
availability tests at fully oxidising conditions by addition of hydrogen
peroxide (NT ENVIR 006, 1999). 9 different types of natural rock
material were used for comparison.
The leaching behaviour of natural rocks and
blast furnace slags was very similar. Most of the metals exmined were
less soluble from slags than from natural rock. As both total content of
the trace elements of toxicological relevance, as well as their
solubility under extreme environmental conditions, were supplied, Kd
values can be derived (in the report inverse Kd values are
given as the percentage of the total released into leachate). In
general, these Kd were lower than typical Kd values of these elements in
slags. The environmental relevance of the findings was clarified by
comparison with natural rocks. The slags released less trace metals than
the natural rocks, suggesting that their use in the environment poses no
hazard (Tossavainen 2002).
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