Promoting nitrate reduction kinetics by nanoscale zero valent iron in water via copper salt addition

Abstract

Several methods were proposed to enhance nitrate reduction kinetics and removal from water by nanoscale zero valent iron (Fe0). One of them was the addition of other contaminants/components to nitrate-contaminated water, which is less common, but it can gain effective results and promote nitrate reduction kinetics. In this study, nano-Fe0 was synthesized under optimum conditions and characterized using transmission electron microscopy, surface area analyzer, X-ray diffraction and particle size analyzer. Nitrate removal performance was carefully investigated via batch experiments under different conditions of pH, presence/absence of oxygen and distinctive nitrate concentrations (50, 100, 200, 300, and 500mg/L), comparing between nitrate removal by nano-Fe0 with and without copper salt (copper chloride) addition. Optimum addition ratio of CuCl2/Fe (0.05wt/wt) was collected from experimental results, which was used to conduct the rest of batch experiments. Kinetics of nitrate removal among several batch experiments were examined by applying different models, and it was found that most profiles obeyed first-order rate equation. The presence of copper ions during nitrate reduction imposes two electrochemical reactions; one stimulates iron corrosion and another reaction causes hydrogen-electrocatalytic reduction of nitrate. Both reactions boosted removal efficiency and kinetics around 3.5 times more than that by ordinary pristine nano-Fe0 alone, i.e. nitrate removal time was reduced from one hour to 20min. Moreover, the stability of removal efficiency and kinetics under the influence of pH and dissolved oxygen was higher as well.