Environmental Engineering Reference
In-Depth Information
complexation of different trace elements (Wu et al.
2004a
;
c
; Plaza et al.
2006
;
Cook and Langford
1995
; Kumke et al.
1998
; Mcgown et al.
1995
)
.
The conditional
stability constants (log
10
K
1
and log
10
K
2
) for the complexation of two major bind-
ing sites of fulvic acid with metal ions are 3.26-6.66 (log
10
K
1
) and 7.0-9.64 (log
10
K
2
) for Cu
2
+
-FA; 5.66 for Fe
3
+
-FA; 4.34-5.70 for Hg
2
+
-FA; 5.46 for UO
2
2
+
-FA;
and 5.9 (log
10
K
1
) for Cm
3
+
-FA, determined in aqueous solution except for lan-
thanides (Table
1
) (Wu et al.
2002a
,
2004
; Fu et al.
2007
; Hays et al.
2004
; Cao
et al.
2004
; Sidenius et al.
1999
; Antunes et al.
2007
; Winzerling et al.
1992
;
Tipping
1994
; Breault et al.
1996
; Mcknight et al.
1983
; Buckau et al.
1992
; Kim
et al.
1991
). Lanthanides (Ln) are strong complexing agents for Suwannee River
Fulvic Acid and show relatively high conditional stability constants that range from
8.90 to 14.58 for Ln-SRFA (Suwannee River Fulvic Acid) complexes at pH 6
−
9 in
aqueous solution. The values obtained for SRFA are relatively lower than for humic
acids extracted from various sources (Table
1
; Sonke and Salters (
2006
)).
The conditional stability constants for Hg
2
+
-DOM complexation are 4.34-5.20
for the peak C at Ex/Em
=
340-355/430-455 nm of humic substances (possibly
fulvic acid) at pH 4.37-7.01 (Wu et al.
2004a
). The conditional stability constants
for Hg
2
+
-FA complexation are 5.01-5.55 (log
10
K
1
) for peak C detected at Ex/
Em
=
330-335/426-434 nm and 5.62-5.72 (log
10
K
2
) for peak A detected at Ex/
Em
=
245/432-438 nm (Fu et al.
2007
). Complexation of river DOM with Hg
2
+
is 3.54-4.93 and 3.64-4.85, determined using linear and non-linear model fitting of
the fluorescence maxima at Ex/Em
=
304, 306/426, 430 nm (Bai et al.
2008
). The
fluorophores or functional groups bound for peak C at longer wavelength are pre-
sumably considered to be the fast binding sites and the fluorophores bound for peak
A, correspondingly, the slow binding sites in fulvic acid. Generally, log
10
K
1
should
be higher than in log
10
K
2
but the result is, in fact, the opposite. The reason behind
this phenomenon is that during the complexation of the fast binding site at peak
C, the decrease in fluorescence intensity occurs simultaneously at peak A of fulvic
acid. Note that the fluorophores bound at a particular peak (e.g., peak C, peak A,
peak T or T
UV
) of a fluorescent molecule are the result of all fluorophores existing
in the molecule. Therefore, any changes in the molecule by photoinduced or micro-
bial degradation can alter its fluorescence properties, inducing new peak position
and fluorescence intensity (Mostofa et al.
2009a
,
2011
; Senesi
1990
). For the fast-
reacting binding site of fulvic acid, the kinetic rate constant (
k
1
) ranges from 0.18
to 0.55 s
−
1
, whilst the
k
2
values for the slow reacting binding site are similar for all
metals (Cu
2
+
, Ni
2
+
, Co
2
+
, Cd
2
+
, and Ca
2
+
) at 0.01-0.02 s
−
1
(Wu et al.
2004c
).
The conditional stability constants for the complexation of humic acid (HA,
two binding sites) with metal ions are 3.99-5.60 (log
10
K
1
) and 8.55 (log
10
K
2
)
for Cu
2
+
-HA; 0.40 (log
10
K
1
) for Mn
2
+
-HA; 0.50 (log
10
K
1
) for Co
2
+
-HA; 0.50-
4.43 (log
10
K
1
) for Zn
2
+
-HA; 6.79-10.0 (log
10
K
1
) for Fe
3
+
-HA; 6.00 (log
10
K
1
)
for Cr
3
+
-HA; 15.0 (log
10
K
1
) for Sc
3
+
-HA; 2.1 (log
10
K
1
) for VO
2
+
-HA; 5.50
(log
10
K
1
) for Hg
2
+
-HA; 4.5-5.3 (log
10
K
1
) and 5.8-7.2 (log
10
K
2
) for As
3
+
-HA;
2.80-4.94 (log
10
K
1
) and 7.15-9.80 (log
10
K
2
) for H
+
-HA; 4.0 (log
10
K
1
) for
Be
2
+
-HA; 1.0 (log
10
K
1
) for Ca
2
+
-HA; 0.5 (log
10
K
1
) for Sr
2
+
-HA; 0.5 (log
10
K
1
)
for Ba
2
+
-HA; 10.0 (log
10
K
1
) for Ga
3
+
-HA; 4.95-5.81 (log
10
K
1
) for Pb
2
+
-HA;
