Zong-Sheng Liang,Bao-Dong Song,Yong-Ling Liu,Yong Liu,Hai-Tao Ren,Song-Hai Wu,Shao-Yi Jia,Xu Han
Natural pyrite has a strong ability to immobilize Ni(II) impurities. However, the differences in the oxidation reactivity between Ni(II)-adsorbed pyrites [Py*-Ni(II)] and Ni(II)-structurally incorporated pyrites [Py-Ni(II)] are still not clearly understood. In this study, Ni(II)-free pyrite (Py-free), Py*-Ni(II), and Py-Ni(II) were prepared, and their oxidation reactivity were compared. Our results show that Ni(II) can be successfully incorporated into the crystalline structure of Py-Ni(II) by replacing structural Fe(II) with the formation of sulfur defects on the surface of Py-Ni(II). The oxidation reactivity of different pyrites depends on how Ni(II) is immobilized in pyrite and follows the order of Py-0.08 > Py-0.02 > Py-free > Py*-Ni(II) [Py-0.02 and Py-0.08 are named according to the Ni(II):Fe(II) molar ratios in the starting material for the synthesis of Py-Ni(II)], indicating that structurally incorporated Ni(II) enhances the oxidation rate of pyrite, whereas adsorbed Ni(II) does the opposite. Differences in the electrochemical properties also indicate that structurally incorporated Ni(II) enhances the electron-transfer rates at the Py-Ni(II) surface, thus increasing the oxidation rates of pyrite. Variations in H2O2 concentrations confirm that the high electron-transfer rates induced by structurally incorporated Ni(II) enhance the reaction rates between dissolved oxygen and the pyrite surface, producing H2O2 at pHs 2.5 and 7.0. The presence of Fe(III)-S(-II) defects also significantly contributes to the production of H2O2. Variations of cumulative ·OH indicate that structurally incorporated Ni(II) improves the production of ·OH at pHs 2.5 and 7.0. The significantly higher concentrations of ·OH than those of H2O2 at pH 2.5 indicate that ·OH plays an important role in pyrite oxidation under acidic condition. The comparable concentrations of H2O2 and ·OH at pH 7.0 suggest that H2O2, ·OH, and even Fe(IV) formed between pyrite and H2O2 contribute to pyrite oxidation under pH-neutral condition.
Wang Wanfeng,Liang Fang,Guo Yanling,Wu Ruijie,Pan Feng,Jin Caixia,Wang Jun
Since nitrosamine disinfection by products is highly carcinogenic, they have attracted considerable attention due to their increased presence in ambient waterways and potable water supplies. For the present study, the potential formation of nitrosamines from corresponding precursor secondary amines during ozonation was investigated. The results revealed that five nitrosamines were observed during the ozonation of their corresponding secondary amines. The molar yields initially increased and then decreased with longer contact times and higher ozone doses. These phenomena indicated that ozone not only promoted nitrosamine formation but also degraded the formed nitrosamines. High pH had a positive influence on nitrosamine formation at room temperature. Further, coexisting substances including nitrate, nitrite, humic acid, and tert-butanol inhibited the generation of nitrosamines due to hydroxyl radical (·OH) competition and scavengers, whereas in the presence of hydroxylamine, nitrosamine formation increased considerably without ozone due to its capacity for independent formation between secondary amines and hydroxylamine. Further, the generation of nitrosamines from secondary amines was primarily attributed to O 3 and ·OH oxidation, which was produced through the decomposition of ozone. The transformation pathways were mainly comprised of the indirect routes between the O 3 /·OH intermediates. The findings of this study were helpful toward expanding the knowledge of nitrosamine formation during the corresponding precursor secondary amine ozonation process.
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