Interface mechanisms of the catalytic ozonation of humic acids over siliceous ferrihydrite: Morphology, stability, and the catalytic process

Clay minerals inhibit the release of Cd(II) during the phase transformation of Cd(II)-ferrihydrite coprecipitates

Clay minerals and iron (hydr)oxides are important geosorbents in controlling the migration of heavy metal cations in the environment. Despite the widespread occurrence of clay minerals/iron (hydr)oxides composites, their complex mutual effects on the fate of heavy metal cations are not well recognized. In this work, we investigated the effect of clay minerals on the redistribution of Cd(II) during the phase transformation of ferrihydrite containing coprecipitated Cd(II) (Cd-Fh). Three systems were considered: i.e., Cd-Fh, Cd-Fh/kaolinite composite, and Cd-Fh/montmorillonite composite. Our results showed that the transformation of Fh into goethite and hematite caused the release of Cd(II), while the presence of kaolinite and montmorillonite inhibited the phase transformation of Fh and the release of Cd(II), with montmorillonite being more effective in these process. Multiple factors contributed to the reduced release of Cd(II), including the retarded transformation of Fh, the buffering of solution pH, and the re-adsorption of the released Cd(II). Our findings show that clay minerals have multiple effects in reducing the release of heavy metal cations from Fh during its transformation process, which sheds new light on understanding the critical roles of nanominerals in modulating the migration and bioavailability of heavy metal cations in the environment.

Efficient remediation of the field soil contaminated with PAHs by amorphous porous iron material activated peroxymonosulfate

An amorphous porous iron material (FH) was firstly self-synthesized using a simple coprecipitation approach and then utilized to activate peroxymonosulfate (PMS) for the catalytic degradation of pyrene and remediation of PAHs contaminated soil on site. FH exhibited more excellent catalytic activity than traditional hydroxy ferric oxide and possessed stability at a pH range of 3.0-11.0. According to quenching studies and electron paramagnetic resonance (EPR) analyses, non-radicals (Fe(IV) = O and 1O2) were the major reactive oxygen species (ROS) in the FH/PMS system's degradation of pyrene. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) of FH before and after the catalytic reaction, as well as active site substitution experiments and electrochemical analysis all verified that PMS adsorbed on FH could produce more abundant bonded hydroxyl groups (Fe-OH) which dominated the radical and non-radical oxidation reactions. Then, a possible pathway for pyrene degradation was presented according to gas chromatography-mass spectrometry (GC-MS). Furthermore, the FH/PMS system exhibited excellent catalytic degradation in the remediation of PAH-contaminated soil at real sites. This work provides a remarkable potential remediation technology of persistent organic pollutants (POPs) in environmental and will contribute to understanding the mechanism of Fe-based hydroxides in advanced oxidation processes.

Improvement of coal gasification reverse osmosis concentrate treatment by Cu-Co-Mn/AC catalytic ozonation

Approximately 20% of concentrate will be produced from coal gasification wastewater after reverse osmosis treatment. The organic matter contained in the concentrate affects its evaporation crystallisation; therefore, the refractory organics must be removed. In this study, Cu-Co-Mn/AC catalytic ozonation was used to treat reverse osmosis concentrate (ROC). With the addition of the Cu-Co-Mn/AC catalyst, the production of ·OH increased by 82 μmol/L, thereby enhancing the ozonation performance. The pH, ozone dosage, and catalyst dosage all affected the catalytic ozonation performance. By constructing a response surface model, it was found that the catalyst dosage had the most significant effect on the catalytic ozonation performance. The predicted optimal reaction conditions were pH = 9.02, ozone dosage = 1.08 g/L, and catalyst dosage = 1.33 g/L, under which the chemical oxygen demand (COD) removal reached a maximum of 81.49%.