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1600
Webster (P = 0 mg/L)
1400
1200
1000
800
C o = 80 mg/L
C o = 100 mg/L
C o = 150 mg/L
600
400
0
200
400
600
800
1600
Webster (P = 100 mg/L)
1400
1200
1000
800
C o = 80 mg/L
C o = 100 mg/L
C o = 150 mg/L
600
400
0
200
400
600
800
Reaction Time (h)
FIGURE 7.22
Zn concentration in Webster soil versus time during adsorption and desorption for various
initial Zn concentrations. Dashed curves are multireaction model (MRM) simulations.
results, Zn desorption kinetic results reported by Rupa and Tomar (1999)
showed that for increasing level of applied P to 20 and 40 mg/kg subsequent
decrease in Zn desorption by 20% to 31% and 39% to 53% were observed.
As previously reported the P-induced Zn sorption may be related to
increased surface negative charges and/or creation of specific sorption sites
as a result of P sorption on OM, Fe/Al oxides and clays (Barrow, 1987; Bolland,
Posner, and Quirk, 1977; Xie and Mackenzie, 1989). Xie and Mackenzie (1989)
postulated that sorption of P on OM and oxides can form inner-sphere sur-
face complexes that increase negative charges, resulting in increased surface
Zn retention. Kuo and McNeal (1984) proposed that the added P act as a
“bridge” between soil surfaces and sorbed Zn, or sorbed P alters the soil
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