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This study presents a critical review on the application of magnetite-based catalysts to industrial wastewater decontamination by heterogeneous Fenton oxidation. The use of magnetic materials in this field started only around 2008 and continues growing increasingly year by year. The potential of these materials derives from their higher ability for degradation of recalcitrant pollutants compared to the conventional iron-supported catalysts due to the presence of both Fe(II) and Fe(III) species. In addition, their magnetic properties allow their easy, fast and inexpensive separation from the reaction medium. The magnetic materials applied up to now can be classified in three general groups: magnetic natural minerals, in-situ -produced magnetic materials and ferromagnetic nanoparticles. A survey of the catalysts investigated so far is presented paying attention to their nature and competitive features in terms of activity and durability. [ABSTRACT FROM AUTHOR]

Highlights: [•] CWPO of chlorophenols with Fe x O y /γ-Al2O3 catalysts is more efficient than Fenton oxidation. [•] Increasing the temperature improves both the oxidation rate and mineralization degree. [•] The Fe x O y /γ-Al2O3 catalysts are highly active and stable upon CWPO of chlorophenols. [•] CWPO (Fe3O4/γ-Al2O3) at high temperature is the preferable strategy for chlorophenols oxidation. [•] Fe3O4/γ-Al2O3 catalyst can be easily recovered from the liquid phase by a magnet. [Copyright &y& Elsevier]

This work explores the potential application of naturally-occurring minerals as inexpensive catalysts in heterogeneous Fenton, namely catalytic wet peroxide oxidation (CWPO). The availability, low cost and environmentally friendly character of those materials make them interesting candidates for such application. The performance of magnetite, hematite and ilmenite as CWPO catalysts has been tested under different working conditions, which include temperature (25–90 °C), H 2 O 2 dose (250–1000 mg L −1 ) and catalyst concentration (1–4 g L −1 ). The operating temperature plays a key role on the rate of H 2 O 2 decomposition so that with magnetite H 2 O 2 conversion after 4 h increased from 8 to 99% by increasing the temperature from 25 to 90 °C. Based on the reaction mechanism proposed, a kinetic model was developed which successfully described the experimental results on H 2 O 2 decomposition. The catalytic performance of the minerals tested at temperatures above the ambient was demonstrated using phenol (100 mg L −1 ) as target pollutant. Unprecedented efficiencies of H 2 O 2 consumption, higher than 80% were achieved, allowing high oxidation and mineralization, i.e. complete phenol conversion and almost 80% TOC reduction at 75 °C with a catalyst loading of 2 g L −1 and the theoretical stoichiometric amount of H 2 O 2 for complete mineralization of phenol (500 mg L −1 ). Magnetite is particularly attractive, since it showed the highest activity and can be easily separated from the liquid phase given its magnetic properties. All the minerals tested suffered low iron leaching and magnetite and hematite showed a good reusability upon three consecutive runs. However, in this case long-term durability is not a crucial issue, given the availability and low cost of these minerals. [ABSTRACT FROM AUTHOR]

• The removal of all the pharmaceuticals included in the EU Watch List was investigated. • The inexpensive magnetite catalyst showed a high activity and a reasonable stability in CWPO. • Total conversion of all drugs was reached under ambient temperature and circumneutral pH. • The pollutants were highly mineralized (>50%), being the final products short-chain acids. • The process was successfully tested in three real WWTP effluents. The European Union (EU) approved in 2015 a Watch List of pollutants of emerging concern especially harmful for the aquatic environment (Decision 2015/495/EU). In this work, we explore the application of an inexpensive and environmentally-friendly catalytic system based on modified natural magnetite (Fe 3 O 4 -R400) and H 2 O 2 for the removal of all the pharmaceuticals included in the EU Watch List (hormones: estrone, 17-beta-estradiol and 17-alpha-ethinylestradiol; macrolide antibiotics: azithromycin, clarithromycin and erythromycin; and the non-steroid anti-inflammatory diclofenac). The experiments were carried out with a representative initial concentration of the drugs (1000 μg L−1) at a circumneutral pH value (pH 0 = 5) within the temperature range of 17–50 °C. A low catalyst concentration (0.2 g L−1) was used while the applied amount of H 2 O 2 corresponded to the stoichiometric one for the complete mineralization of the drugs (4–6 mg L−1). Operating under ambient-like conditions, total conversion of the target pollutants as well as the aromatic intermediates was achieved. Notably, total organic carbon was strongly reduced (>50%), being the residual carbonaceous products short-chain organic acids. The applicability of the catalytic system was demonstrated using different real wastewater treatment plant (WWTP) effluents spiked with the mixture of pharmaceuticals. Apart from the complete removal of pharmaceuticals in relatively short reaction times (60–90 min), the disappearance of total coliforms was warranted. Remarkably, the catalyst showed a reasonable stability, with low iron leaching (<0.7 mg L−1) and maintaining its magnetic properties almost unchanged. [ABSTRACT FROM AUTHOR]