Ryo Nishimoto

Enhanced humification by carbonated basic oxygen furnace steel slag – II. Process characterization and the role of inorganic components in the formation of humic-like substances

Enhanced humification by abiotic catalysts is a potentially promising supplementary composting method for stabilizing organic carbon from biowastes. In this study, the role of steel slag in the transformation of humic precursors was directly characterized by measuring the variance in dissolved organic carbon (DOC), spectroscopic parameters (E(600)), and the concentration and molecular weight change of humic-like substances (HLS) during the process. In addition, a mechanistic study of the process was explored. The results directly showed that steel slag greatly accelerated the formation of HLS. The findings indicate that Fe(III)-and Mn(IV)-oxides in steel slag act as oxidants and substantially enhance the polycondensation of humic precursors. Moreover, the reaction appears to suppress the release of metals from steel slag to a certain extent under acidic conditions. This can be attributed to the cover of HLS on the external surface of steel slag, which is significant for its environmentally sound reuse.

Potassium monopersulfate oxidation of 2,4,6-tribromophenol catalyzed by a SiO2-supported iron(III)-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin

Iron(III)-porphyrin complexes are generally regarded as green catalysts, since they mimic the catalytic center of cytochrome-P450 and widely used as green catalysts for degrading halogenated phenols in wastewater, such as landfill leachates. However, iron(III)-porphyrins are deactivated by self-oxidation in the presence of an oxygen donor, such as KHSO5. In the present study, to enhance the reusability of an iron(III)-porphyrin catalyst, iron(III)-5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (FeTCPP) was immobilized on a functionalized silica gel. The oxidative degradation of 2,4,6-tribromophenol (TrBP), a widely used brominated flame retardant that is found in landfill leachates, was examined using the prepared catalyst. In addition, the influence of humic substances (HSs), major components of leachates, on the TrBP oxidation was investigated. Concerning the effect of pH, more than 90% of the TrBP was degraded in the pH range of 3–8 in the absence of HS, while the optimal pH for the reaction was in the range of pH 5-7 in the presence of HS. Although the oxidation of TrBP was inhibited in the presence of HSs, more than 90% of the TrBP was degraded in the presence of 50 mg L−1 of HS. Thus, the prepared catalyst, SiO2-FeTCPP, showed a high catalytic activity and could be reused up to 10 times even in the presence of HS.

Fe-loaded zeolites as catalysts in the formation of humic substance-like dark-coloured polymers in polycondensation reactions of humic precursors

Abstract To enhance the catalytic activities of zeolites for the polycondensation reactions of humic precursors, Fe was loaded into a zeolite via an ion-exchange reaction and the resulting product was subjected to calcination at 773 K. Two types iron-loaded zeolites were prepared using one equivalent (Fe-Z-1) and 10-equivalents (Fe-Z-10) of Fe2+ to the cation-exchange capacity of a natural zeolite from Niki town (Hokkaido, Japan). X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) spectra showed that the Fe(II) that was originally loaded into the cation-exchange sites in the zeolite became oxidized to a Fe(III) ionic species during the preparation. The catalytic activities of each zeolite were evaluated, based on the degree of darkening for reaction mixtures containing catechol, glycine and glucose as model humic precursors. The catalytic activities of Fe-Z-1 and Fe-Z-10 were higher than that for an untreated zeolite, and increased with the amount of Fe in the zeolite.

Sorption of Pentachlorophenol to Organo-Clay Complexes Prepared by Polycondensation Reactions of Humic Precursors

The surfactant-modified bentonite has been focused on the adsorption of hydrophobic organic contaminants in aqueous solutions, because the surfactant (e.g. quaternary alkylammonium salt) intercalation leads to the formation of highly hydrophobic domains. Humic substances (HSs) can serve as naturally occurring surfactants of higher affinity to hydrophobic organic contaminants, such as pentachlorophenol (PCP). However, HSs cannot be loaded into interlayer of montmorillonite in bentonite (Bent) because of their larger size. In the present study, the humin-like substance (HuLS) was loaded to the montmorillonite interlayer via polycondensation reactions of glycine and catechol as humic precursors. The montmorillonite basal spacing was expanded by forming the HuLS-bentonite complex (HuLS-Bent), showing the intercalation. The Freundlich adsorption coefficients of PCP for HuLS-Bent and Bent (K f) were evaluated at pH 4.0, 5.5 and 6.5. While K f values decreased with an increase in pH, K f values for the HuLS-Bent (83–1,220) were larger than the reported values for other organically modified clays (19–100 at pH 3–6). These results suggest that the prepared HuLS-Bent is effective in the removal of PCP from water.