Induced transformation of antimony trioxide by Mn(II) oxidation and their co-transformed mechanism

摘要

Antimony(Sb)is a toxic and carcinogenic element that often enters soil in the form of antimony trioxide(Sb_(2)O_(3))and coexists with manganese(Mn)in weakly alkaline conditions.Mn oxides such as birnessite have been found to promote the oxidative dissolution of Sb_(2)O_(3),but few researches concerned the co-transformations of Sb_(2)O_(3) and Mn(II)in environment.This study investigated themutual effect of abiotic oxidation of Mn(II)and the coupled oxidative dissolution of Sb_(2)O_(3).The influencing factors,such as Mn(II)concentrations,pH and oxygen were also discussed.Furthermore,their co-transformed mechanism was also explored based on the analysis of Mn(II)oxidation products with or without Sb_(2)O_(3) using XRD,SEM and XPS.The results showed that the oxidative dissolution of Sb_(2)O_(3) was enhanced under higher pH and higher Mn(II)loadings.With a lower Mn(II)concentration such as 0.01 mmol/L Mn(II)at pH 9.0,the improved dissolution of Sb_(2)O_(3) was attributed to the generation of dissolved intermediate Mn(III)species with strong oxidation capacity.However,under higher Mn(II)concentrations,both amorphous Mn(III)oxides and intermediate Mn(III)species were responsible for promoting the oxidative dissolution of Sb_(2)O_(3).Most released Sb(∼72%)was immobilized by Mn oxides and Sb(V)was dominant in the adsorbed and dissolved total Sb.Meanwhile,the presence of Sb_(2)O_(3) not only inhibited the removal of Mn(II)by reducing Mn(III)to Mn(II)but also affected the final products of Mn oxides.For example,amorphous Mn oxides were formed instead of crystalline Mn(III)oxides,such as MnOOH.Furthermore,rhodochrosite(MnCO_(3))was formed with the high Mn(II)/Sb_(2)O_(3) ratio,but without being observed in the low Mn(II)/Sb_(2)O_(3) ratio.The results of study could help provide more understanding about the fate of Sb in the environment and the redox transformation of Mn.