Competitive Sorption and Transport - Transport and Fate of Chemicals in Soils: Principles and Applications - page 240

Environmentally, the occurrence of vanadium in petroleum and coal is of
high significance because fuels constitute major sources of vanadium emis-
sions to the atmosphere (Dechaine and Gray, 2010). A large fraction of the
vanadium-rich atmospheric particles may enter the soil environment as par-
ticulate fallout or dissolved in rain. Vanadate and vanadyl ions are versatile
at forming complexes that inhibit or stimulate activity of many enzymes by
specific mechanisms.
Here we present vanadium transport and adsorption results for two soils
with contrasting properties: a Sharkey clay (very fine, montmorillonitic,
nonacid, Vertic Haplaquept) and Cecil soil ((clayey, Kaolinitic, thermic Typic
Kanhapludult). The Sharkey soil has an organic matter content of l.4l%o and
a pH of 5.9, whereas Cecil soil has an organic matter content of 0.74%o and a
pH of 5.6. Miscible displacement experiments were carried out using soil col-
umns under saturated condition and state-flux was slowly saturated upward
with 0.01 N NH 4 Cl background solution for 4 d prior to V pulse application.
A vanadium pulse of 100 mg L -1 of NH 4 VO 3 in 0.0l N NH 4 Cl was applied
to each column and was followed by 0.0l N NH 4 Cl solution. The effluent
solution from each column was collected using a fraction collector. To assess
the impact of the presence of P on vanadium mobility in the soil columns,
100 mg L -1 of P as -NH 4 H 2 PO 4 was mixed with the vanadium pulse solution.
Moreover, periods of stop-flow (or flow interruption) of 2 d duration were
implemented to test whether equilibrium or kinetic processes are the domi-
nant transport mechanism.
Vanadium adsorption by the two soils represents contrasting behavior
with regard to intensity as well as kinetics. Sharkey soil exhibited stron-
ger affinity for vanadium than Cecil soil. In addition, Cecil soil, which is
predominantly kaolinitic, exhibited extremely limited kinetic reaction (see
Figures 7.35 and 7.36). When compared to 1 d retention, after 4 d of reaction
an increase of only 30% was observed. In contrast for Sharkey soil, which
is predominantly montmorillonitic, there was a threefold increase in vana-
dium adsorption when compared to 1 d sorption. The K d values for Cecil
soil were 1.70 and 2.31 L/kg, after 1 and 4 d sorption, respectively. The cor-
responding K d values for Sharkey soil were 73.03 and 360.91 L/kg, after 1
and 21 d sorption, respectively. The presence of P resulting in decreasing the
amount of V sorbed varied among the two soils. In fact, the impact of P on
reduced vanadium sorption was greatest for Sharkey soil, where a onefold
decrease was observed. In contrast, only 50% decrease in vanadium sorption
was observed for Cecil soil (Figures 7.35 and 7.36).
The mobility of vanadium (V) as well as phosphorus (P) is presented by
the BTCs presented in Figures 7.37 and 7.38. These BTC's represent different
column scenarios. In column 1, a pulse of vanadium was followed by a pulse
of phosphorus, which was subsequently followed by a pulse of a mixed
solution of P plus V. In Figure 7.37, the sequence of pulse applications was P
followed by a pulse of V and subsequently by a mixed pulse. For column 2
shown in Figure 7.38, the soil column received three consecutive pulses of