Fe(II)/SulfiteProcess with Rapid Fe(II) OxidationEnhances <i>p</i>‑Arsanilic Acid Oxidation and SimultaneousArsenic Adsorption

Most studies focus on the oxidation capability of the Fe(II)/sulfite (Fe(II)/S(IV)) process for organic pollutants but overlook the phenomenon of rapid iron particle formation. The coupling of oxidation and <i>in situ</i> adsorption by iron particulates holds great potential for the deep removal of organometallic compounds. Herein, the removal of an organoarsenic compound of <i>p</i>-arsanilic acid (<i>p</i>-ASA) by Fe(II)/S(IV) was investigated. This process demonstrated efficient and rapid <i>p</i>-ASA degradation, achieving 95% <i>p</i>-ASA removal (10 μM) within 3 min, which is comparable to those of the Fe(II)/PDS and Fe(II)/PMS processes. Various evidence indicated that SO₅^•– was the primary radical driving <i>p</i>-ASA degradation, selectively attacking the amino group with As(V) as the ultimate byproduct. Ultrafast Fe(II) oxidation and iron particle formation were observed, with over 90% of Fe(II) ions converted into insoluble iron particles within 30 s. However, the Fe(II)/PDS and Fe(II)/PMS processes generated very few iron particles. It was found that S(IV)’s proton-taking feature increased the pH, significantly promoting Fe(II) oxidation, hydrolysis, and precipitation. The formed iron particles were amorphous ferric(oxyhydr)oxides, and showed great efficiency for As(V) adsorption during their formation. As a result, the Fe(II)/S(IV) process showed superior efficiency for total arsenic removal. In addition, the process remained effective under real water matrices. Overall, this study offers theoretical and data-driven guidance for applying this promising one-step procedure for effectively treating organic arsenic in water.