Abiotic Oxidation Of Mn(Ⅱ) On The Oxidation And Mobilization Of As In The Presence Of Iron Oxides

To control arsenic contamination effectively in water environment, the presentstudy selected-Fe₂O₃and Fe₃O₄to investigate the effects of abiotic oxidation ofMn（Ⅱ） on As（Ⅲ） oxidation and mobilization of As（Ⅲ） and As（Ⅴ）.Firstly, abiotic oxidation of Mn（Ⅱ） on-Fe₂O₃and Fe₃O₄was studied in kineticsand characterization. Secondly, the effects of Mn（Ⅱ） on the oxidation andmobilization of the dissolved and the adsorbed As（Ⅲ） were explored through As（Ⅲ）pre-loaded oxidation experiments and Mn（Ⅱ）-As（Ⅲ） simultaneous oxidationexperiments. Lastly, the effects of Mn（Ⅱ） on the sorption and mobilization of As（Ⅴ）by-Fe₂O₃were investigated via kinetics experiments.Abiotic oxidation of Mn（Ⅱ） to amorphous Mn（Ⅲ,IⅤ）（hydr）oxides （MnOx） on-Fe₂O₃and Fe₃O₄was confirmed. With addition of Mn（Ⅱ） into As（Ⅲ） pre-loadedsystems, the dissolved and the adsorbed As（Ⅲ） was oxidized to As（Ⅴ） at high pH, andthe presence of Mn（Ⅱ） mobilized the adsorbed As（Ⅲ） and As（Ⅴ） in-Fe₂O₃system.High production of the dissolved As（Ⅴ） and significant mobilization of As（Ⅲ） wereeven more evident in-Fe₂O₃suspension with simultaneous addition of Mn（Ⅱ） andAs（Ⅲ）, while Fe₃O₄showed a greater capacity for immobilizing As（Ⅲ） and As（Ⅴ）.The simultaneous addition of Mn（Ⅱ） and As（Ⅴ） into-Fe₂O₃suspension resulted inmore removal of As（Ⅴ） via electrostatic attraction. However, in Mn（Ⅱ） pre-loadedsystem, the removal percentage of As（Ⅴ） at pH8.3decreased by17.0%,20.7%and26.7%after24hours at the aging time of2,12and36hours, respectively. Theconcentrations of the released As（Ⅴ） after addition of1mM Mn（Ⅱ） were23.6,12.9and7.0μM at pH8.5in2,3and4g L-1-Fe₂O₃suspension, respectively.Therefore, the newly formed MnOxon iron oxides could not only oxidize bothdissolved and adsorbed As（Ⅲ） to As（Ⅴ）, but also mobilize a fraction of the adsorbedAs（Ⅲ） or As（Ⅴ） into aquatic environments. It enriches our understanding on the fateof As（Ⅲ） and As（Ⅴ） in the coexistence of iron oxides and Mn（Ⅱ）.