CHAPTER 15 • Redox Processes of Chromium in Sea Water
Fig. 15.3. Calculated values of
pe for the most important redox couples and Cr in the most
usual pH range of sea water.
The following conditions were
assumed:
[Mn2+] = [Fe 2 +] = 10- 7 M;
O2 = 0.2 atm; [H20 2] = 10- 7 M;
for the redox couples
Cr(VI)/Cr(III), N03 -/NHt,
O~-/HS-, Fe(III)/Fe(II) a concentration ratio of 1/1 was chosen
Fig. 15.4. Values of log kJ for the
oxidation of Cr(III) (1.9 11M)
with H20 2 (447 flM) at 25 DC as a
function of pH (NaCl04 1 M)
(Pettine and Millero 1990)
.::C
en
..2
15~--------------------------------,
C==::::::::=-__ ~IO~i~fr~ __________ ~
10 1
° HO
5
CrOUCr(OH~
o
-5
SO~- IHS-10
7.5
8.0
8.5
9.0
pH
1.0
0.5
0.0
0
0
-0.5
-1.0
-1.5
uncorrected for aging
0
corrected for aging
-2.0
7
8
9
10
11
pH
viation from the linearity above pH 9. This deviation was caused by aging Cr(Ill) solutions over a short time before the addition of H 2 0 2 • The effect was noted at pH > 9
where the kinetics of the aging process increased markedly (Fig. 15.5) and was due to