REDUCTION OF NITRATE TO AMMONIA BY ZERO-VALENT IRON

The reduction of nitrate to ammonia occurs with nearly complete conver sion at room temperature and pressure under aerobic conditions in the presence of iron and either HCl or a pH buffer. A 50.0 mL solution of 12.5 millimolar nitrate is rapidly reduced to ammonia when exposed to 4.00 g of 325 mesh iron at pH 5.0, 0.05 M sodium acetate/acetic acid. The pseudo-first order rate constant was 0.053 min(-1). Under conditio ns of pH 6.0 buffer, (i.e. 0.1 M 4-morpholineethanesulfonic acid adjus ted to pH 6.0) and pH 7.0 buffer (0.1 M 4-(2-hydroxyethyl)-1-piperazin eethanesulfonic acid adjusted to pH 7.0), the rate constants were 0.04 08 min(-1) and 0.0143 min(-1), respectively. In unbuffered solutions t here was no loss in nitrate and no production of ammonia. A more conce ntrated nitrate solution (100 mL of 1.0 M sodium nitrate) was also red uced to ammonia in the presence of 2.5 M HCl with the slow addition of 50.0 g of 325 mesh iron. (C) 1997 Elsevier Science Ltd.