Enhanced paramagnetic Cu²⁺ ions removal by coupling a weak magnetic field with zero valent iron

A weak magnetic field (WMF) was proposed to enhance paramagnetic Cu²⁺ ions removal by zero valent iron (ZVI). The rate constants of Cu²⁺ removal by ZVI with WMF at pH 3.0-6.0 were -10.8 to -383.7 fold greater than those without WMF. XRD and XPS analyses revealed that applying a WMF enhanced both the Cu²⁺ adsorption to the ZVI surface and the transformation of Cu²⁺ to Cu⁰ by ZVI. The enhanced Cu²⁺ sequestration by ZVI with WMF was accompanied with expedited ZVI corrosion and solution ORP drop. The uneven distribution of paramagnetic Cu²⁺ along an iron wire in an inhomogeneous MF verified that the magnetic field gradient force would accelerate the paramagnetic Cu²⁺ transportation toward the ZVI surface due to the WMF-induced sharp decay of magnetic flux intensity from ZVI surface to bulk Cu²⁺ solution. The paramagnetic Fe²⁺ ions generated by ZVI corrosion would also accumulate at the position with the highest magnetic flux intensity on the ZVI surface, causing uneven distribution of Fe²⁺, and facilitate the local galvanic corrosion of ZVI, and thus, Cu²⁺ reduction by ZVI. The electrochemical analysis verified that the accelerated ZVI corrosion in the presence of WMF partly arose from the Lorentz force-enhanced mass transfer.