Environmental Engineering Reference
In-Depth Information
Blast-Furnace Sludge - Removal Capacities
Results from the sorption beaker tests showed good removal capacity, 93-100%, for
Cd, Cr, Cu, Ni, Pb and Sn at all concentrations and pH ~9 (Fig
1a
). The pH decreased
slightly in the beakers from 9.2 to 8.1 during the experiment. The removal capacity
for V and Zn was 46-98%, and for Cs and Mo in the range 19-71%. The removal
capacity for Cd, Cr, Cu,
Sn and Zn was also good, 92-100% in the solutions at pH 7.0 (Fig.
1b
); pH
remained stable during the experiment. The capacity for Ni was 83-89%, for Mo
2-12%, and a leaching of V and Cs was indicated. At pH 5.6 (maintained stable)
the removal capacity was lower, 32-99%, for Cr, Cu, Mo, Sn and V (Fig.
1c
). The
removal of Cd and Ni was only 6-14%, indicating a leaching of Zn, Cs and Pb. Due
to the low capacity for several of the metals, blast-furnace sludge should not be used
as a sorbent material in solutions at pH 5.6 or lower. On the other hand, the carbonates
in the sludge effectively protect water solutions from acidification. A leaching of
Zn and Pb from the sludge in pure water was indicated at pH 5.6, at pH 7.0 a leaching
of V, and at pH ~9 a leaching of Zn, V and Pb.
Old Furnace Sludge - Removal Capacities
The results for the old furnace sludge stirred with real leachate and spiked with the
multi-metal solutions and pH ~9 are presented in Fig.
2
. The pH in the beakers
decreased from 9.2 to 8.7 during the experiment. The removal capacity of this mate-
rial was slightly lower than that of the 'new' sludge. The capacity for Cd, Cr, Cu, Ni,
Pb, Sn and Zn was in the range 98-100%. As with the 'new' sludge, the capacity was
lower for Mo and V, 8-96%, and even a leaching of Cs was indicated. A leaching of
V and Zn was indicated from the old sludge in pure water at pH ~9. Ageing of the
material and the use of real leachate reduce the sorption capacity and should be taken
into consideration when laboratory results are applied to real-life situations.
Blast-Furnace Slag - Sorption Capacities
The sorption capacities in the solution with the highest metal concentration are pre-
sented in Table
2
. The results show a trend of capacities increasing with pH for most
of the metals. The material had a slightly higher capacity for Cu than for Zn, which
could be explained by the differences in terms of electron configuration and the
Jahn-Teller effect
[15]
that strengthens the complex binding of copper to sorption
surfaces. For the metals in concentrations from 0.50-5.0 mg/L, the sorption capacity
order was: Cr = Sn > Ni > V > Mo. Lead was the only metal in the concentration
range 0.10-1.0 mg/L and it should be noted that furnace slag has been found to have
