Effect of precursor type on the reduction of concentrated nitrate using zero-valent copper and sodium borohydride.

In this study, we demonstrated that the choice of precursor has a strong effect on the reduction of nitrate (NO) using zero-valent copper (Cu) synthesized by sodium borohydride (NaBH). Different precursors: CuSO, CuO, CuO, Cu powder, and Cu mesh were used to reduce NO at 677 mg-N/L under the reducing conditions of NaBH. Compared with the prehydrolyzed samples, those prepared without prehydrolysis exhibited lower reduction rates, longer times and higher concentrations of nitrite (NO) intermediate. It was found that one-time addition of NaBH resulted in higher reduction rate and less NO intermediate than two-step addition. Results showed that Cu from CuSO possessed the smallest particle size (890.9 nm), highest surface area (26.0 m/g), and highest reaction rate (0.166 min). Values of pseudo-first-order constant (k) were in the order: CuSO > CuO > CuO > Cu powder >Cu mesh. However, values of surface area-normalized reaction rate (k) were approximately equal. It was proposed that NO was reduced to NO on Cu, and then converted to NH and N, respectively; H generated from both NaBH hydration and Cu (II) reduction contributed to NO reduction as well.