Enhanced removal of lead complexes using phosphide-modified nanoscale zero-valent iron: The boosting impact of the iron cycle

Abstract

Heavy metal complexes, known for their high stability, present significant challenges for removal using conventional methods. In this study, we propose a novel one-step approach for eliminating Pb-EDTA from wastewater, using phosphide-modified nano-zero-valent iron (P-NZVI). Through comprehensive isotherms and kinetic analyses, we demonstrate the critical role of NaH₂PO₄ as the phosphorus source in P-NZVI synthesis. Our results show that P-NZVI achieves an exceptional adsorption capacity for Pb-EDTA, reaching up to 256.9 mg Pb/g, with a kinetic constant of 0.011 g/(mg·min). The removal mechanism involves the displacement of complexed Pb by Fe(Ⅲ) and the subsequent sequestration of released Pb by P-NZVI. Additionally, we observe that ultraviolet light initiates the photolysis of Fe(Ⅲ)-EDTA, converting Fe(Ⅲ) to Fe(Ⅱ) in the solution. This transformation triggers an iron cycling process, further promoting the decomplexation of Pb-EDTA. Moreover, P-NZVI maintains robust performance even in the presence of high concentrations of coexisting ions (25 g/L), while generating minimal toxic leaching from the reaction residue. Importantly, our studies confirm the effective performance of P-NZVI in real-world wastewater scenarios. In conclusion, P-NZVI proves to be a highly effective material for the removal of Pb complexes under challenging water conditions, offering a simple yet effective process with significant environmental benefits.