Phosphorylated ZVI composites with self-activating interfaces: Synergistic multi-metal removal via in-situ Fe-Cu galvanic coupling and Zn-mediated passivation inhibition

Zero-valent iron (ZVI) is recognized as an eco-friendly material for heavy metal remediation, yet its application was constrained by surface passivation. A mechanical ball milling method was utilized to synthesize phosphorylated ZVI (ZVI/PR) through incorporation of natural phosphate rock (PR), where PO₄^3--induced corrosion was harnessed to enhance sustained Fe(II) release. The ZVI/PR removed 70 % Cr(VI) within 24 h in the single-metal system, which was significantly increased to 97 % and 77 % in Cu(II)-Cr(VI) and Zn(II)-Cr(VI) binary-metal system, respectively. The apparent reaction rate constants increased by 1.4 and 4.34 times with the presence of Zn(II) and Cu(II). Mechanistic investigations revealed two synergistic pathways: 1) Cu(II) was adsorbed and reduced to Cu(0) onto the ZVI/PR surface forming Fe-Cu bimetallic interfaces, which established galvanic cells that enhanced electron transfer; 2) Zn(II) inhibited the formation of Fe³⁺ oxide layer, preserving reactive sites and reducing passivation. This dual mechanism facilitated simultaneous removal of Cu(II)/Zn(II)/Cr(VI) through synergistic redox and adsorption processes. The use of industrial byproduct phosphate rock, combined with mechanochemical activation, presented a cost-effective surface engineering strategy. This approach enabled multi-contaminant remediation via controlled interfacial corrosion and modulated electron transfer of ZVI.