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

Abstract

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.