Abstract
The dependence of oxygenation kinetics of Fe(II)to Fe(III) on pH and DO was examined in relation to the mechanism of phosphate release from sediments.
In determination of the oxygenation kinetics of Fe(II), the observed redox potential was used for estimation of the Fe(II) concentrations in solutions. The oxygenation rate of Fe(II) increased with pH and DO. In the region DO≥1mg·
l-1, the oxygenation rate(
r) was independent to oxygen concentration and varied remarkably with pH as
r =
k2·[Fe(II)]·P0
2·[OH
-]
2 for 5.6≤pH≤7.0,
r=
k1/2·[Fe(II)]·P0
2·[OH
-]
1/2for 7.0<pH≤8.0, and
r=
k0·[Fe(II)]·P0
2 for 8.0<pH≤9.0. Whereas in the region of DO<1mg·
l-1, the rate was found to depend on DO. That is
r=
k2·[Fe(II)]·[OH
-]
2·[DO]/2.5(1+[DO]) for 5.6≤pH≤7.0,
r=
k1/2·[Fe(II)]·[OH
-]
1/2·[DO]/(1+3.2[DO]) for 7.0<pH≤8.0.
The dependence of the oxygenation rate of Fe(II) on DO and pH found in the present study showed a quantitative agreement with the dependence of the phosphate release rate from sediments on DO, which has been reported in numerous literature. It suggests that the mechasism of phosphate release is essentially explained by the oxygenaion kinetics of Fe (II).
