Novel Application of MnO2–H2O2 System for Highly Efficient Arsenic Adsorption and Oxidation

A novel manganese dioxide–hydrogen peroxide (MnO2–H2O2) system was developed for effective Arsenic (As) removal. Under the specified conditions of no external mechanical stirring, a trace H2O2 concentration of 0.015 wt%, and a MnO2 concentration of 25 mg/L, high removal efficiency (88%) of As (100 µg/L) was achieved by the MnO2–H2O2 system within 30 min, which differs from conventional adsorption processes that require external mechanical stirring and conventional arsenite (As (III)) oxidation–adsorption processes that require high quantities of oxidants (such as ozone) and specially synthesized adsorbents/catalysts. The high removal efficiency of As (III) by the MnO2–H2O2 system was attributed to the turbulent conditions precipitated by the extensively generated oxygen (O2) from the catalytic decomposition of H2O2, the efficient adsorption of As on the surface of MnO2, and the effective generation of reactive radicals including hydroxyl and superoxide radicals (•OH and •O2−). Moreover, the MnO2 adsorbents before and after As removal were characterized systematically, and the generated radicals were verified using electron spin resonance (ESR). The results showed that the formation of inner-sphere surface complexes by the surface hydroxyl groups of MnO2 particles and As was responsible for the effective As adsorption process, and the oxidation of As (III) to arsenate (As (V)) was achieved via the generated radicals. The influences of representative environmental factors on As removal performance and the application of the MnO2–H2O2 system in river water and ground water were further studied and tested. In conclusion, the MnO2–H2O2 system offers several advantages, including low cost, ease of operation, and strong environmental adaptability, making it highly promising for practical water treatment applications.