Reduction of nitrate to ammonia by zero-valent iron

The reduction of nitrate to ammonia occurs with nearly complete conversion 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 conditions of pH 6.0 buffer, (i.e. 0.1 M 4-morpholineethanesulfonic acid adjusted to pH 6.0) and pH 7.0 buffer (0.1 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid adjusted to pH 7.0), the rate constants were 0.0408 min(-1) and 0.0143 min(-1), respectively. In unbuffered solutions there was no loss in nitrate and no production of ammonia. A more concentrated nitrate solution (100 mL of 1.0 M sodium nitrate) was also reduced 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.