Effects of common dissolved anions on the reduction of para-chloronitrobenzene by zero-valent iron in groundwater

Batch tests were conducted to evaluate the influences of several common dissolved anions in groundwater on the reduction of para-chloronitrobenzene (p-CNB) by zero-valent iron (ZVI). The results showed that p-CNB reduction was enhanced by both Cl⁻ and SO₄²⁻. HCO₃⁻ could either improve or inhibit p-CNB reduction, depending on whether the mixing speed was intense enough to rapidly eliminate Fe–carbonate complex deposited on ZVI surface. Above a concentration of 100 mg L⁻¹, NO₃⁻ increased the p-CNB reduction rate. The reduction rate by ClO₄⁻ decreased because the ClO₄⁻ competed with p-CNB for electrons. The p-CNB reduction was inhibited by PO₄³⁻, SiO₃²⁻ and humic acid, in the order humic acid < PO₄³⁻ < SiO₃²⁻, since these ions could form inner-sphere complexes on iron surface. The reaction even ceased when the ion concentrations were greater than 4, 0.5, and 30 mg L⁻¹, respectively. The results indicated that common dissolved anions in groundwater should be taken into account when ZVI is applied for contaminated groundwater remediation.