Reduction of concentrated nitrate by using in situ synthesized zero-valent copper

Although zero-valent iron represents a promising approach for reduction of nitrate (NO3-) in water, its application in concentrated nitrate is limited by surface passivation. In this study, an alternative approach using in situ synthesized zero-valent copper (Cu-0) produced by borohydride (NaBH4) was investigated. Complete reduction was observed within 55 min by reacting 677 mg-N/L of NO3- with CuO (0.312 g/L) and NaBH4 (4.16 g/L) at 60 degrees C. The pseudo-first-order rate constant was 0.059 min(-1), and it increased threefold when the CuO dose was increased to 1.24 g/L. Increasing the NaBH4 dose produced less nitrite (NO2-) throughout the experiments, indicating that it is the primary agent for reducing NO2-. The initial pH exerted a significant effect on the reaction rate, and NO3- was rapidly reduced when the initial pH was less than 4. Based on the research findings, possible reaction pathways for NO3- reduction by Cu-0 are proposed in this work.