Highly Selective Reduction of Nitrate by Zero-Valent Aluminum (ZVAI) Ball-Milled Materials at Circumneutral pH: Important Role of Microgalvanic Cells for Depassivation of ZVAl and N<sub>2</sub>-Selectivity
Yan Li, Xuhui Mao, Chaoqi Chen, Lieyu Zhang, Wenjie Liu, Xu Wang, Lang He, Tao Xu
Abstract
The passivation of zero-valent aluminum (ZVAl) limits its application in environmental remediation. Herein, a ternary composite material Al–Fe–AC is synthesized via a ball-milling treatment on a mixture of Al 0, Fe 0, and activated carbon (AC) powders. The results show that the as-prepared micronsized Al–Fe–AC powder could achieve highly efficient nitrate removal and a nitrogen (N 2 )-selectivity of >75%. The mechanism study reveals that, in the initial stage, numerous Al//AC and Fe//AC microgalvanic cells in the Al–Fe–AC material could lead to a local alkaline environment in the vicinity of the AC cathodes. The local alkalinity depassivated the Al 0 component and enabled its continuous dissolution in the subsequent second stage of reaction. The functioning of the AC cathode of the Al//AC microgalvanic cell is revealed as the primary reason accounting for the highly selective reduction of nitrate. The investigation on the mass ratio of raw materials manifested that an Al/Fe/AC mass ratio of 1:1:5 or 1:3:5 was preferable. The test in simulated groundwater suggested that the as-prepared Al–Fe–AC powder could be injected into aquifers to achieve a highly selective reduction of nitrate to nitrogen. This study provides a feasible method to develop high-performance ZVAl-based remedial materials that could work in a wider pH range.