| In recent years, the oxidation technologies based on sulfate radicals(SO) have aroused increasing interest of the researchers all over the world because of its excellent feasibility in treating refractory organic pollutants due to the high stability and oxidation ability compared to the hydroxyl radicals(·OH). Iron ions activation is the most appropriate method in activating persulfate to produce SO due to its effective activation ability, better environmentally friendly property and low cost. However, in the process of PS activation by Fe2+, there are still some drawbacks such as the fast Fe2+ deactivation, great radicals quenching by excessive Fe2+ and low p H adaptability. In order to solve the above problems, the organic chelating agents were employed to promote the PS activation. In addition, in view of the gradual recession of PS activation because of the continuous consumption of active Fe2+, the hydroxylamine reduction and photochemical reduction methods were applied to promote the regeneration of Fe2+ which would further improve the PS activation. The main research contents and conclusions are as follows:(1) EDDS was employed to promote the decolorization of OG by PS oxidation actived with Fe2+. The promoting roles and mechanisms of EDDS in the Fe2+ activated PS process were preliminary discussed by investigating the EDDS/Fe2+ complexing ratio, Fe3+ concentration, OG concentration and p H on the OG decolorization efficiency due to the PS oxidation. The results showed that However, OG decolorization efficiency in EDDS-Fe2+-PS system was higher than that in Fe2+-PS system because of the continuous activation of PS when the OG concentration was as high as 1.25 m M. When the molar ratio of EDDS/Fe2+ was 1/1, the accessibility of Fe2+ could be reduced to 11.9% which was able to improve the solubility of Fe2+ and reduce the reaction rate of Fe2+, while when EDDS/Fe2+ was 2/1, Fe2+ was completely protected and has no reactivity. Furthermore, Fe3+ would exchange with the chelated Fe2+ which provided another approach for Fe2+ releasing. However, this process was only observed in case of the EDDS/Fe3+ < 2/1. The higher OG concentration was in favor of increasing the competition ability to radicals which decreased the degradation of EDDS and the release of Fe2+. Therefore, PS activation efficiency was inhibited in processes with high OG concentration. When p H was increased, Fe2+ was more likely to be oxidized. Besides, the conditional stability constant of EDDS-Fe2+ gradually increased when p H was elevated which would decrease the reactivity of Fe2+. For these reasons, more PS was remained in higher p H condition.(2) Several chelating agents with different hydrocarbon chain length and dentates were employed to promote the Fe2+ activated PS oxidation. The influence mechanisms of ligands on Fe2+ reactivity were further studied by evaluating the effects of different complexation ratios and p H on PS activation and aniline degradation. The results showed that the influence of chelating agents on Fe2+ reactivity was achieved by controlling the accessibility of Fe2+. Other than the way of chelating between Fe2+ and chelating agents, the complexation ratio also determined the accessibility of Fe2+. The influence of EDDS on Fe2+ accessibility was the most significant and with the increase of complexation ratios, Fe2+ accessibility was gradually reduced in all stuied systems. In addition, the oxidation of chelating agents played an important role in promoting the regeneration of Fe2+ which was beneficial to accelerate the PS activation and especially occurred in the tartaric acid system. Oxalic acid presented the least significant chelating performance of Fe2+ and PS activation was highly affected by p H. EDDS had the strongest shielding effect on Fe2+ and this effect would be enhanced when p H was increased. Consequently, PS activation efficiency under neutral and alkaline in EDDS processes decreased significantly. Citric acid and tartaric acid had the moderate shielding ability of Fe2+ and PS still could be effectively activated under high p H conditions. Furthermore, the decomposition of tartaric acid could promote the Fe2+ regeneration which led to more than 90% PS decomposition in all p H conditions.(3) Hydroxylamine was applied to promote Fe2+ regeneration and strengthen the PS oxidation of OG activated by EDDS-Fe2+. The influence mechanisms of hydroxylamine on promoting Fe2+ activated PS oxidation of OG were studied by systematical investigating the effects of hydroxylamine concentration, adding times, p H and EDDS concentration on PS activation and OG decolorization. Results showed that the addition of hydroxylamine significantly accelerated the transformation of Fe3+ into Fe2+ and promoted the PS activation. But the excessive hydroxylamine would increase the consumption of PS and reduced the decolorization rate of OG significantly. When the hydroxylamine was added in terms of several times, PS decomposition was improved with the increase of addition times, but the increase of PS and OG decomposition efficiency was gradually restrained at the same time. Moreover, several times addition of hydroxylamine reduced the effective utilization of PS. When the initial p H was 3 and 7, after the addition of hydroxylamine, PS decomposition increased sharply. While when p H was 10, the contribution of hydroxylamine to PS activation was much less significant. When the molar ratio of EDDS/Fe2+ gradually increased, the accessibility of Fe2+ was decreased accordingly which resulted in the continuous decline of corresponding PS decomposition and OG decolorization.(4) UV was applied to promote oxalic acid-Fe2+/Fe3+ activated PS oxidation of aniline. The influence mechanisms of UV on iron cycle and the promotion on PS activation was elaborated by studying the transformation of Fe3+ in case of UV and the investigation of the Fe C O concentration, PS concentration and p H effects on oxidative degradation of aniline in detail. The results showed that the introduction of the UV promoted the Fe2+ generation in ferric oxalate, ferric citrate and Fe3+ solution and the largest generation rate of Fe2+ was observed in the ferric oxalate process. With the increase of concentration of ferric oxalate, PS decomposition was enhanced gradually, but when the concentration of ferric oxalate was higher than 0.75 m M, the degradation efficiency of aniline was even lower. With the increase of PS concentration, aniline degradation efficiency was also improved. Nevertheless, the increase of aniline degradation efficiency was gradually suppressed. Acidic conditions were more favorable for the formation of Fe C O which had much better photochemical properties, as a result, when the initial p H was lower, PS decomposition was promoted more effectively. However, a large amount of generated Fe2+ also led to a significant quenching of free radicals which decreased the degradation efficiency of aniline. |
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