Abstract: Sulfide and carboxymethyl cellulose (CMC) stabilization dual-modified nano zero-valent iron (S-CMC-nZVI) exhibits high reactivity and strong mobility, demonstrating significant potential for remediating organically contaminated groundwater. However, the effects of common groundwater anions on its surface-modified layer and contaminant degradation performance remains unclear. This study investigated the mechanisms and effects of common groundwater anions (SO₂^-4, HCO^-3, NO^-3, Cl^-) on the degradation of nitrobenzene by S-CMC-nZVI, using nitrobenzene as the target pollutant. The results showed that the presence of NO^-3 and Cl^- did not affect the sulfidation degree of the S-CMC-nZVI surface modified layer or the degradation efficiency of nitrobenzene. The addition of SO₂^-4 or HCO^-3 led to a reduction in the sulfidation degree of the surface modification layer, causing peeling and increase in the content of Fe2+ and S2- in the solution. Consequently, the actual n(S)/n(Fe) molar ratios of the material decreased to 0.013 2 and 0.019 1, respectively. The FeS and Fe²⁺ produced by the peeling of the sulfide layer can promote the degradation of nitrobenzene. However, SO₂^-4 will cause the formation of iron oxides on the surface of S-CMC-nZVI, thereby inhibiting the sustained degradation of nitrobenzene. In contrast, HCO^-3 accelerated the decomposition of the oxide layer, facilitating the sustained degradation of nitrobenzene, with a maximum efficiency of 99.6%. This study provides a theoretical reference for the efficient application of S-CMC-nZVI in groundwater remediation.

Key words: groundwater, anion, S-CMC-nZVI, nitrobenzene