Chemical reduction of an unbuffered nitrate solution using catalyzed and uncatalyzed nanoscale iron particles

Uncatalyzed and catalyzed nanoscale Fe0 systems were employed for the denitrification of unbuffered 40 mg N L−1 nitrate solutions at initial neutral pH. Compared to microscale Fe0 (<100 mesh), the efficiency and rate of nitrate removal using uncatalyzed and catalyzed nano-Fe0 were highly promoted, in which the maximum promoted rate was obtained using copper-catalyzed nano-Fe0 (nano-Cu/Fe). Nitrate first-order degradation rate constants (kobs) decreased significantly (>70%) with aged nano-Fe0 and aged nano-Cu/Fe, and were recovered with NaBH4 as reductants at levels of about 85 and 75%, respectively. Activation energies (Ea) of nitrate reduction over the temperature range of 10-60 °C were 42.5 kJ mol−1 for microscale Fe0, 25.8 kJ mol−1 for nano-Fe0 and 16.8 kJ mol−1 for nano-Cu/Fe. Unlike microscale Fe0, the kinetics of denitrification by nano-Fe0 and nano-Cu/Fe began to show characteristics of mass transport in addition to chemical reaction control. Ammonium was the predominant end product in all the systems. However, as for nitrite, 40% of the degraded nitrate persisted in the nano-Cu/Fe system. Thus, relative to nano-Cu/Fe, nano-Fe0 is a potential reductant for denitrification of groundwater as far as toxic nitrite generation is concern.