Denitrification coupled to pyrite oxidation is a major process that has been observed in many groundwater aquifers based on numerous geochemical data. However, pure chemical reaction between nitrate and pyrite could not take place neither experimentally in the natural sediment nor be detected in marine system. Our understanding of the mechanisms of this redox process in natural groundwater system is still limited. Based on theories of several authors, the stimulation by activators or microbial catalysis will be expected to explain the electron transfer between nitrate and pyrite. Since Fe(III) is detected as a well-known oxidant for pyrite even at neutral pH, Fe(III) is assumed to be an effective oxidant for pyrite in the presence of nitrate. At the pyrite surface, Fe(III) is reduced to Fe(II) which is reoxidized to Fe(III) by nitrate. Fe(III) will be added in the reactor as the chemical activator. During an Fe(II)/Fe(III) shuttle electrons should be transported between nitrate and pyrite. Microbial catalysis by bacteria, such as Fe(II) oxidizing or sulfide reducing bacteria, is considered to affect the denitrification and pyrite oxidation rates significantly. Therefore, Bacteria are supposed as microbial activator to simulate the electron transfer from pyrite to nitrate.
The goal of the work is, during controlled laboratory batch-experiments to understand the mechanism of the anaerobic oxidation of pyrite coupled to nitrate reduction in the anoxic groundwater sediment. Batch Experiments are separated to abiotic and biotic conditions to individually assess the pure chemical and microbial stimulation. The most effective form of Fe(III) should be elected and the effects of different microorganisms will be investigated.
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