Hydroxylamine and Nitrilotriacetic Acid Co-Improved Fe(III)/Peroxydisulfate Process for Elimination of Organic Pollutant: Performance, Influence Factors and Mechanism

To resolve two main drawbacks of Fe(II/III)/peroxydisulfate (PDS) system, i.e., sluggish Fe(II) regeneration and strongly acidic operating environment, hydroxylamine (HAm) and nitrilotriacetic acid (NTA) were introduced simultaneously to Fe(III)/PDS system to degrade orange G (OG) under neutral condition in this study. The results shown that Fe(III)-NTA/HAm/PDS system could effectively remove OG at pH 7.0 and the removal ratio of OG reached 86.4% in 15 min. In this system, Fe(III)/Fe(II) could complex with NTA to improve their solubility, leading to the broadening of pH application range from acidic condition to weakly alkaline circumstance (pH 3–9) and the decrease of iron sludge production; HAm could drive Fe(III)/Fe(II) cycle via reducing Fe(III) to Fe(II), ensuring the sustainability of catalytic reaction and lowering the Fe(III) dosage. Sulfate radical (SO 4 ·− ) and hydroxyl radical (HO·) mainly contribute to OG degradation in Fe(III)-NTA/HAm/PDS process. The increase of reagents dosage could accelerate the removal of OG, while excess HAm (> 1 mM) and NTA (> 25 µM) could depress OG degradation because of their competition with OG for active radicals. The existence of Cl − (0.5–5 mM) could slightly promote the removal of OG, but HCO 3 − (0.5-5–mM) and fulvic acid (2–10 mg L − 1 ) obviously suppressed OG degradation. This research offers a strategy to extend the pH application range of Fe(II/III)/PDS process with low Fe dosage and a technique to remove OG from contaminated water. Graphical abstract