| This thesis refers to iron that is ubiquitous in marine environment. Iron is one of the important elements for the phytoplankton growth, but in seawater the dissolved iron is very little because it exists mainly in the form of solid phase and colloid phase. It was proved that solid and colloid phase iron could be converted to dissolved iron under the irradiation of light, and the existence of organic compounds could enhance this conversion. The complex of organic acid-iron also can undergo photochemical reaction with a product of Fe( II) which may be assimilated directly by phytoplankton in seawater. Therefore, the study on the photochemical behaviors of iron in seawater is of significance in the aspects of marine chemistry, biogeochemistry, and environmental chemistry.Analysis method of iron in the process of photochemistry was adopted according to the present laboratory conditions. The influence of various factors such as pH, light intensity, and temperature on the iron photochemistry was detailedly studied. Eight organic acids including Malonic acid, Succinic acid, Adipic acid, Malic acid, Citric acid, Tartaric acid, Alanine, Cysteine were used to compare their effects on the iron photochemistry. In addition, the photochemistry of 3 -FeOOH in seawater under the existence of organic acid was also studied.In this paper, the concentration of Fe( II ) was measured by Ferrospectral spectrophotometer method. In order to reduce the influence of Fe(III), KH2PO4-Na2HP04 buffer was used instead of HAc-NaAc. The concentration of labile Fe was analyzed by CIS SPE -AAS method.Our results showed that photochemistry of complex of organic acid-iron and 3 -FeOOH occurred remarkably under the irradiation of high-pressure Hg lamp at pH 4.0, 6.0 and 8.1. The production of Fe( II) mayenhance the biological availability of iron in seawater, due to its easy assimilation by phytoplankton. The photochemical reaction rate of Fe was controlled by both the reduction rate of Fe(III) and re-oxidation rate of Fe(II).The concentration of Fe( II ) in the photoreaction of complex of organic acid-iron increased according to exponential reaction kinetic pattern. At pH 6.0 and 8.1, the reduction rate of Fe(III) and oxidation rate of Fe( II) exhibited a first-order reaction kinetic pattern, which can be described by the following equation:[Fe(Il)]t = kreil[Fe(III)}ini x[l-exp{-(kred + kjt}]/(kred + kM)Where kreci is the first-order rate constant of Fe(III) reduction , kox is the oxidation rate constant of Fe( II) and [Fe(III)]ini is the initial concentration of Fe(III).When / approaches to infinity, a steady state concentration of Fe( II) a can be obtained and the kred can be calculated by a and kox. At near neutral pH, the activity of organic acids examined declined by the sequence below: Tartaric> Adipic>Citric>Succinic>Malic>Malonic.The concentration of Fe( II) in the photochemical reaction of P -FeOOH linearly increased at the initial stage and then remained basically stable during the later process of reaction. The comparison showed that the difference of concentrations between the labile Fe and Fe( II) increased with increasing pH, because the Fe( II) was easily oxidized under high pH value.When the proportion of organic acid and iron was between 2 and 10, kred values increased with the concentration of organic acid in pH near neutral pH. The increase appeared to be linear for the complex of organic acid-iron, but nonlinear for P -FeOOH.Our study showed that the photoreaction rate of Fe was greatly influenced by pH. Low pH would benefit the photochemistry. Although the photo-reactivity of organic acid-Fe complex largely decreased under highpH, photoreaction of P -FeOOH can still occur under as high pH as 8.1 in the present of oxalate. This is of importance for the dissolution of -FeOOH in seawater.It was found that high light irradiation could enhance the photoreaction rate of Fe. This point was especially obvious for P-FeOOH.Although a and kox values changed with reaction temperature, kred value remained stable...
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