Nitrate Reduction of the Siilinjärvi/Finland Mine Water with Zero-valent Iron and Iron Waste as Alternative Iron Sources

Nitrate reduction was optimized in water from the Siilinjärvi/Finland mine site with iron powder and iron nanoparticles. Iron waste from a mold machining industry was then tested as a potential alternative. Complete reduction of nitrate from the mine water was achieved with the iron powder and nanoparticles at pH 2. The iron waste, though less efficient, still achieved 53% nitrate reduction. Examination of the surface of the iron powder and waste by SEM–EDS showed iron corrosion: crystals of iron oxides grew on the iron surface as the pH increased during NO₃ ⁻ reduction, until about pH 5. The major by-product of the NO₃ ⁻ reduction of mine water was NH₄ ⁺, with low NO₂ ⁻ concentrations (< 7%). Although iron powder and nanoparticles were more reactive, the iron waste results are promising. Despite its low BET surface area, the use of iron waste to treat high volumes of mine water would appear to have economical and sustainable advantages. More efficient NO₃ ⁻ reduction could possibly be attained with iron waste of higher BET surface area and/or by combining it with other chemical treatments.