Environmental Engineering Reference
In-Depth Information
300
200
100
0
-100
-200
-300
-400
-500
Upper Bound
Lower Bound
0 10 20 30 40 50 60 70 80 90 100
Slag content in slag-cement mixes (wt %)
FIGURE 8.3
Matrix oxidation potential with slag content in slag-cement mixes regenerated
from the data in References 29 to 31.
Eh (Volts)
2.0
Tc - N - H2O - System at 25.00 C
1.5
TcO4(-a)
1.0
0.5
0.0
-0.5
-1.0
TcO2
-1.5
H2O Limits
0 2 4 6 8 10 12 14
pH
-2.0
C:\HSC5\EpH\TcN25.iep
ELEMENTS
Tc
N
Molality
1.000E+00
1.000E+00
Pressure
1.000E+00
1.000E+00
FIGURE 8.4
E
h
-pH diagram for Tc(VII)-Tc(IV) (generated using the HSC 5® software).
Sodium hydrosulfite is effective at the alkaline pH of many waste residuals and
so does not usually require pH adjustment before addition. And it remains effective
even after the highly alkaline solidification reagents are added, allowing both the
hydrosulfite and S/S reagents to be added together. The relatively high cost of sodium
hydrosulfite limits its use in S/S treatment.
Often treatment may be two-part. For example, re-speciation to free inorganic
arsenate (AsO
4
3-
) is necessary for inorganic arsenic species containing the arsenite
(AsO
3
2-
) ion, for arsenic sulfides containing As(III) (e.g., As
2
S
3
), and for organoarseni-
cals. This re-speciation is most commonly accomplished by the use of strong oxidizing
agents such as KMnO
4
, K
2
S
2
O
8
, NaOCl or Ca(OCl)
2
, or H
2
O
2
, under alkaline conditions.
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