Showing papers by "Deli Wu published in 2017"

Rapid selective circumneutral degradation of phenolic pollutants using peroxymonosulfate-iodide metal-free oxidation : role of iodine atoms

Abstract: The development of environmentally friendly, oxidation-selective advanced oxidation processes (AOPs) for water decontamination is important for resource recovery, carbon dioxide abatement, and cost savings. In this study, we developed an innovative AOP using a combination of peroxymonosulfate (PMS) and iodide ions (I–) for the selective removal of phenolic pollutants from aqueous solutions. The results showed that nearly 100% degradation of phenol, bisphenol A, and hydroquinone was achieved after reaction for 4 min in the presence of 65 μM PMS and 50 μM I–. PMS-I– oxidation had a wide effective pH range, with the best performance achieved under circumneutral conditions. The ratio between [PMS] and [I–] influenced the degradation, and the optimal ratio was approximately 1.00 for the degradation of the phenols. Neither sulfate nor hydroxyl radicals were found to be the active species in PMS-I– oxidation. Instead, we found evidence that iodide atoms were the dominant oxidants. In addition, both Cl– and Br– a...

Opposite effects of dissolved oxygen on the removal of As(III) and As(V) by carbonate structural Fe(II)

Abstract: Freshly prepared carbonate structural Fe(II) (CSF) was used to immobilize As(III) and As(V) in wastewater under oxic and anoxic conditions. Dissolved oxygen was found to exert opposite effects on these two arsenic species. The sorption density of As(III) was higher under oxic conditions, whereas that of As(V) was higher under anoxic conditions. X-ray diffraction and infrared spectroscopic analyses indicated that crystalline parasymplesite (Fe(II)3(AsO4)2·8H2O) was formed when As(V) was removed under anoxic conditions, while an amorphous Fe-As-containing precipitate was formed when As(III) was removed under oxic conditions. The distribution of arsenic and iron between the solution and sediments suggested that the oxidation of structural Fe(II) promoted coprecipitation process and inhibited surface complexation. X-ray photoelectron spectroscopic analyses revealed that more As(III) was oxidized under oxic condition, which contributed to a higher sorption capacity for As(III). The formation of parasymplesite through surface complexation/precipitation was proposed to be more effective for the removal of As(V) by CSF, while As(III) was more efficiently removed through coprecipitation. Together, the results suggest that CSF may be an effective material for sequestering both As(III) and As(V). In addition, attention should be paid to the dissolved oxygen content when remediating different arsenic species.

Immobilization of selenite from aqueous solution by structural ferrous hydroxide complexes

Abstract: Ferrous hydroxyl complexes (FHCs) were synthesized by precipitation from Fe(II) sulfate salts with sodium hydroxide in an anoxic atmosphere. Effects of the [Fe(II)]/[OH−] ratio, dosage and sequential extraction scheme were elaborated on selenium (Se)(IV) removal by FHCs. Se(IV) removal by FHCs was more coincident with the pseudo-second order kinetic model. The BET isotherm was the best fit model for the data of equilibrium experiments and R2 was 0.9902. Se(IV) removal by FHCs changed with various [Fe(II)]/[OH−] ratios, and the maximum removal capacity was 256.41 mg g−1 by FHC ([Fe(II)]/[OH−] = 1 : 2). X-ray photoelectron spectroscopy results indicated the mechanism of Se(IV) removal by FHC([Fe(II)]/[OH−] = 1 : 1) to be a combination of adsorption and reduction, whereas reduction was the primary mechanism for Se(IV) removal by FHC([Fe(II)]/[OH−] = 1 : 4). A sequential extraction scheme was employed to study Se speciation before and after the reaction. Se species were classified into five groups (water-soluble, exchangeable, elemental Se, oxide-containing iron state, selenide). Results indicated that elemental Se was the primary species in the reaction products.