Removal Of Typical Organic Pollutants From Water By Trivalent Iron Enhanced Potassium Ferrate

With the rapid development of industry,the pollution of antibiotics,pesticides and other organic substances has become gradually acute.Organic pollutants have a serious impact on human life and ecological environment.Potassium ferrate?K₂FeO₄?is a green,highly effective oxidant,which can obviously oxidaze and remove the organic matters.However,K₂FeO₄ is difficult to be widely used owing to the high cost and defects in preparation.It is particularly important to find a method to reduce the dosage amount of K₂FeO₄.Previous studies have found that the ferric iron salt?Fe????can enhance the oxidation of K₂FeO₄ to remove arsenic,diclofenac?DCF?and phenylmethyl sulfoxide?PMSO?in water,while the strengthening mechanism and influencing factors are still unclear.In this study,Fe???was used to promote K₂FeO₄ remove typical organic pollutants in water.By comparing K₂FeO₄ single oxidation system,Fe???single adsorption system,and Fe???enhanced K₂FeO₄ oxidation system,it was found that after adding 1600 ?M of Fe???,the removal rate of sulfamethoxazole?SMX?increased from 37% to 75%,and the removal rates of bisphenol A?BPA?and carbamazepine?CBZ?also certainly increased.However,regardless of the presence of Fe???,K₂FeO₄ never reacted with pchlorobenzoic acid?p CBA?.This showed that Fe???could partially improve the removal rate of organics which were easily oxidized by K₂FeO₄,but couldn't promote the reaction of K₂FeO₄ with organics that cannot be oxidized by K₂FeO₄ itself.In order to explore the mechanism on how Fe???enhanced organic matter removal,kinetic experiment and model fitting were carried out.It was found that adding 400 ?M of Fe???to the K₂FeO₄ oxidation system would increase the second-order reaction rate constant k0 of K₂FeO₄ self-decomposition from 78 M^-1s^-1 to 160 M^-1s^-1,and the contribution rate of the intermediate valence iron increased from 65% to 88%;addition of 3200 ?M Fe???would increase the reaction rate constant k2 of Fe?IV?and SMX from?1.5±0.1?×10⁶ M^-1s^-1 to?1.0±0.1?×108 M^-1s^-1,the reaction rate constant k3 of Fe?V?and SMX increased from?9.0±0.1?×104 M^-1s^-1 to?1.5±0.1?×10⁶ M^-1s^-1.Therefore,the mechanism of Fe???enhancing K₂FeO₄ in removal of SMX was shown below.First,Fe???catalyzed the self-decomposition procedure of K₂FeO₄ to produce more active intermediate valence iron,which increased the contribution of intermediate valence iron in the removal of SMX,thereby the reaction rate of SMX and K₂FeO₄ was accelerated.Second,Fe???catalyzed Fe?V?and SMX reactions directly,along with Fe?IV?and SMX,so as to increase the reaction rate constants of these processes.Due to the complex composition of natural water,this article has studied the complexing agent,humic acid,ions and pH on the enhancement of Fe???enhanced K₂FeO₄ oxidation removal The impact of SMX capabilities to clarify the effect of different components on the enhancement of Fe???.The results showed that the addition of 2000 ?M sodium oxalate,sodium pyrophosphate,sodium citrate and sodium ethylenediamine tetraacetate?EDTA?to the Fe???reduced the removal rate of SMX from 78% to 35% and 20%,11% and 1%,respectively.In addition,the addition of 20 mg C/L humic acid reduced the removal rate of SMX from 78% to 9%.The result indicated that both the complexing agent and humic acid could inhibit the strengthening effect of Fe???on the oxidation and removal of SMX by K₂FeO₄,Besides,as the inctease of complexing agent molecular complexity,the inhibitory effect would also be promoted significantly.However,Fe???species,Ca2+?Mg2+ and HCO3-nearly didn't affect the strengthening effect of Fe???.Although the pH of natural water does not change drastically,it has a great influence on the organic removal of K₂FeO₄ by oxidation.The effect of pH on the strengthening effect of Fe???was studied,and it was found that the SMX removal rate in the Fe???strengthening system increased the most at pH = 7.The results of this study indicated that Fe???was an ideal catalyst for improving the practical effect of K₂FeO₄ and reducing the amount of K₂FeO₄.