Nitrate reduction in real mine water using zero-valent iron (ZVI) and iron waste

Nitrate is present in blasting agents used by the mining industry and thus can contaminate mine water. Despite several methodologies that have been applied for the removal of nitrate, many approaches produce harmful by-products such as nitrite, and other technologies have disadvantages, such as the high energetic costs and high biomass production. In this study, the three iron sources (ZVI) iron nanoparticles, iron powder and iron waste from a mold industry were used for the reduction of nitrates from mine water. By performing a pH and iron dosages optimization with iron powder, pH 2 showed to be the only pH capable of reducing nitrate from a range of 2 to 4. The use of 4 g/L and 20 g/L of iron nanoparticles and iron powder, respectively, reduced nitrate completely in 180 and 270 min. The iron waste tested reduced 53% and 44% for washed and unwashed iron surface of the waste, respectively, showing that the waste does not have many impurities that could affect the experiment. In spite of the surface area being determinant for choosing the load of iron and for showing the kinetics of the reaction, it proved that the type of byproduct formed at the end of the chemical reduction of nitrate is not relevant. The main by-product generated was NH4 (+) and < 7% of NO2 -was produced. The iron waste showed to be an interesting source of iron for this environmental application. This is true not only from an economical point of view but as a greener approach since a waste is used as a raw material instead of promoting the production of other materials for mine water remediation.