Use of laterite as a sustainable catalyst for removal of fluoroquinolone antibiotics from contaminated water.

Although there is a growing interest in Fenton oxidation processes based on natural catalysts, the use of laterite soil to promote sequential adsorption/oxidation treatments of fluoroquinolone antibiotics has been scarcely investigated. In this work, the ability of an african laterite containing goethite and hematite to remove flumequine (FLU), used as a representative compound of fluoroquinolone antibiotics, was evaluated under dark and UVA irradiation. Batch experiments and liquid chromatography analyses showed that the presence of laterite can enhance FLU removal from heavily contaminated water through both sorption and oxidation reactions (up to 94% removal of 77 µmol L-1 of FLU and 72% of mineralization). The heterogeneous reaction rate is dominated by the rate of intrinsic surface chemical reactions including sorption and oxidation of FLU, and light-induced reduction of FeIII sites to produce FeII. Based on the probe and scavenging experiments, OH radicals were mainly involved in the heterogeneous oxidation reaction. The photo-assisted Fenton process showed a high efficiency of FLU removal even in the presence of a second fluoroquinolone antibiotic, norfloxacin (NOR), which can be co-found with FLU in affected environments. Determinations of kinetic rate constants and total organic carbon (TOC) for five sequential adsorption/oxidation cycles showed that laterite exhibited no deactivation of surface sites and an excellent catalytic stability. This cost-effective and environmentally friendly remediation technology may appear as a promising way for the removal of fluoroquinolone antibiotics from multi-contaminated waters.

Activation of persulfate by irradiated laterite for removal of fluoroquinolones in multi-component systems.

Although several emerging contaminants (e.g. fluoro(quinolones) (FQs)) have been simultaneously detected in environmental systems, there is very limited information on their elimination from contaminated waters in multi-component systems. In this study, removal of three FQs including flumequine (FLU), ciprofloxacin (CIP) and norfloxacin (NOR) were investigated in single and mixture systems, using natural laterite soil and persulfate (PS) under UVA irradiation. Both sorption and oxidation reactions contribute to the removal of FQs from aqueous phase, whereas quenching experiments showed that SO4- is mainly responsible for the FQs oxidation. The kinetic rate constants can be ranked as follows: CIP > NOR > FLU, regardless of whether the compound was alone or in mixture. The higher degradation rate constant of CIP relative to those of NOR and FLU could be explained by the high reactivity of SO4- radical with cyclopropane-ring containing compounds. Fall in oxidation performance was observed in synthetic wastewater, probably due to sulfate radical scavenging by wastewater components. However, degradation rate constants of CIP in wastewater remains unchanged in mixture systems as compared to single ones. This environmentally friendly remediation technology may appear as a promising way for the removal of fluoroquinolone antibiotics from multi-contaminated waters.

Fenton-like oxidation and mineralization of phenol using synthetic Fe(II)-Fe(III) green rusts.

BACKGROUND, AIM, AND SCOPE: In literature, the environmental applications of green rust (GR) have mainly been pointed out through the reduction of inorganic contaminants and the reductive dechlorination of chlorinated organics. However, reactions involving GR for the oxidation and mineralization of organic pollutants remain very scantly described. In this study, the ability of three synthetic Fe(II)-Fe(III) green rusts, GR(CO (3)(2-)), GR(SO(4)(2-)), and GR(Cl(-)), to promote Fenton-like reaction was examined by employing phenol as a model pollutant. Unlike the traditional Fenton's reagent (dissolved Fe(II) + H(2)O(2)), where the pH values have to be lowered to less than 4, the proposed reaction can effectively oxidize the organic molecules at neutral pH and could avoid the initial acidification which may be costly and destructive for the in situ remediation of contaminated groundwater and soils. The green rust reactivity towards the oxidative transformation of phenol was thoroughly evaluated by performing a large kinetic study, chemical analyses, and spectroscopic investigations. MATERIALS AND METHODS: The kinetics of phenol removal was studied at three initial phenol concentrations for three green rusts under similar conditions (pH = 7.1; 1 g L(-1) of GR; 30 mM H(2)O(2)) and reaction rates were calculated based on mass and surface area. The oxidation rate constants are compared with that of magnetite, a well-known mixed iron (II, III) oxide. The mineralization of phenol was investigated at various H(2)O(2) doses and GR concentrations. In order to describe the phenol transformation in GR/H(2)O(2) system, several investigations were performed including HPLC and ion exclusion chromatography analysis, TOC, dissolved iron, and H(2)O(2) concentration measurements. Finally, X-ray powder diffraction and Raman spectroscopy were used to identify the oxidation products of GRs. RESULTS AND DISCUSSION: In GR/H(2)O(2) system, the kinetics of phenol removal at neutral pH was very fast and independent of the initial phenol concentration. No aromatic intermediates were detected and final by-products are mainly of short chain organic acids (oxalic acid and formic acid). Green rusts exhibit different reactivity toward Fenton-like oxidation of phenol. Both on mass and surface area basis, the reactivity of Fe(II)-Fe(III) species toward the oxidation of phenol was highest for GR(Cl(-)), little less for GR(SO(4)(2-)) or GR(CO(3)(2-)), and even less for magnetite (Fe(3)O(4)). Phenol degradation pseudo-first order rate constants (k(surf)) values were found to be: 13 x 10(-4), 3.3 x 10(-4), 3.5 x 10(-4), and 0.4 x 10(-4) L m(-2) s(-1) for GR(Cl(-)), GR(SO(4)(2-)), GR(CO(3)(2-)), and Fe(3)O(4), respectively. The mineralization yield of phenol as well as the decomposition rate of H(2)O(2) was higher for GR(Cl(-)) than for GR(SO(4)(2-)) or GR(CO(3)(2-)), mainly due to the higher Fe(II) content of GR(Cl(-)). Both X-ray diffraction analysis and Raman spectroscopy showed that the oxidation of GR with H(2)O(2) may lead to feroxyhyte (delta-FeOOH), with possible formation of poorly crystallized goethite (alpha-FeOOH), depending on GR type. CONCLUSIONS: This original work shows that the heterogeneous Fenton-like reaction using GR/H(2)O(2) is very effective toward degradation and mineralization of pollutants. In summary, this study has demonstrated that the green rust-promoted oxidation reaction could contribute to the transformation of water contaminants in the presence of H(2)O(2.) RECOMMENDATIONS AND PERSPECTIVES: These results could serve as the basis for the understanding of the transformation of organic pollutants in iron-rich soils in the presence of chemical oxidant (H(2)O(2)) or for the development of wastewater treatment process. However, some experimental parameters should be optimized for a high-scale application. Further work needs to be done for the reactive transport and transformation of organic compounds in a green rust-packed column. The reusability of GR in mineral-catalyzed reaction should be also investigated.

Reductive transformation and mineralization of an azo dye by hydroxysulphate green rust preceding oxidation using H(2)O(2) at neutral pH.

In this study, the reactivity of hydroxysulphate green rust (GR(SO(4)(2-))) toward reductive transformation, oxidative degradation and mineralization of organic compounds was evaluated using Methyl Red (MR) as model pollutant. The GR(SO(4)(2-)) was synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), Mössbauer spectroscopy and Fourier Transform Infrared (FTIR) analyses. Reductive decolourization of MR solution occurred in the presence of GR(SO(4)(2-)), while no total organic carbon (TOC) decay was observed during the equilibration time. Significant TOC removal (87%) was noted when H(2)O(2) was added to the GR(SO(4)(2-))/MR mixture after the preliminary reduction step. UV-Vis analysis, dissolved iron and H(2)O(2) concentration measurement, and batch sorption test showed that the heterogeneous Fenton-like reaction is the main mechanism by which the pollutant was mineralized. Increasing of H(2)O(2)/Fe(II) ratio did not affect significantly the mineralization rate of MR. However, slight decolourization of MR and absence of TOC abatement were noted when both MR and H(2)O(2) were simultaneously mixed with the GR(SO(4)(2-)). XRD analysis, Mössbauer spectroscopy and FTIR spectroscopy revealed that the oxidation end-products of GR(SO(4)(2-)) were mainly a poorly crystallized goethite when GR was oxidized after equilibrating with MR in solution. However, a badly crystallized iron oxide was formed when GR was immediately oxidized. In all cases, the interlayer anion (SO(4)(2-)) was ejected from GR structure to aqueous solution. These results suggest that the GR(SO(4)(2-))/H(2)O(2) system could be used to promote the reduction/oxidation reaction of organic pollutants.