Negative magnetoresistance effect in pre-magnetized decimeter-sized zero-valent iron plate during heavy metal removal

Current heavy-metal wastewater treatment methods face significant limitations, creating a need for new technologies. Zero-valent iron (ZVI) shows potential, but the core-shell structure of ZVI is an obstacle due to the low electrical conductivity ( σ ) of its shell, limiting electron transfer from the core to the surface for metal removal reactions. In this study, we enhance the shell’s σ in a pre-magnetized decimeter-sized ZVI plate (MMDZVIP) through reinforced negative magnetoresistance (NMR) effect. Magnetoresistance measurements reveal that MMDZVIP exhibits an NMR effect. MMDZVIP shows a magnetoresistance ratio ( MR ) of -123%, an σ 1.95 times and removal efficiencies 1.91 to 5.18 times that of unmagnetized plates when magnetized to 449 mT. Heavy-metal removal experiments showed nearly 100% removal efficiency at 354 mT, with performance retention above 99.7% after 9 cycles, demonstrating high durability. The mechanism behind the results is as follows: During the removal process, the migration of releasing electrons is aligned to form a current along the normal direction of the MMDZVIP plate. This current is primarily driven by electron consumption on the plate’s surface, where the removal reaction occurs. With pre-magnetization, NMR and Hall effects acted on the releasing electron current and synergistically and significantly enhance the shell's σ . Our work introduces a novel method for enhancing NMR in materials, advancing heavy-metal treatment technologies beyond current limitations.