Nitrate reduction by fluoride green rust modified with copper

Nitrate reduction by the fluoride form of green rust modified with copper (GR-F(Cu)) was investigated using a batch reactor system. The extent of nitrate reduction was measured by measuring the increase in concentration of ammonia, which is the final product of nitrate reduction by GR. This approach was required, because nitrate could be removed from solution by ion exchange without reduction. The rate of ammonium production was investigated over the range of pH 7.8–11. The fastest reaction was achieved at pH 9 when GR was present at a concentration of 0.083 M as Fe(II) and 1 mM of Cu(II) was added. The rate at pH 9 was enhanced by a factor of 2.5 compared to that at pH 7.8 by comparing the time elapsed to transform all nitrate to ammonium. Kinetics of nitrate reduction by GR-F at pH 7.8 were affected by the concentration of Cu(II) added. The rate constants for ammonium production increased from 0.012 to 1.52 h−1 as Cu(II) additions increased from 0 to 2.5 mM, but the reaction rate at 5 mM was slightly decreased to 1.25 h−1. The mechanism of enhanced rates of nitrate reduction by addition of Cu(II) could not be fully determined in this study. However, XRD results showed that magnetite was produced in the reaction of Cu(II) and GR-F and SEM shows the production of nano-size particles which were not fully identified in this study. In addition, the concentration of Fe(II) in GR was observed to linearly decrease with concentration of Cu(II) added.