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Phenol pollution is widely environmental and health problems that require new insights and urgent attention. A iron-bearing catalyst (FRM/2%A) was prepared with red mud by HCl dissolution, ascorbic acid reducing and precipitation of filter liquor, and activated H2O2 to degrade the phenol in synthetic wastewater. Results show that FRM/2%A had the highest degradation efficiency (99.3 %) in the reaction time of 5 min among investigative samples, due to the production of ferrous polymetallic oxides on the catalyst and the formation of mesoscopic particles and microcellular structures. The optimal conditions were 1 g/L of catalyst dosage, 5 mM of H2O2 concentration, 3–6 of initial pH and 100 mg/L of initial concentration of phenol in the FRM/2%A/H2O2 system. The degradation data fit into the pseudo-first-order kinetics model and the reaction rate constant (k) of FRM/2%A was 0.865 min−1. The removal efficiency (77 %) of COD below the value (99.3 %) of phenol degradation implied the intermediates generating during the phenol degradation. The possible degradation pathway was proposed as phenol → catechol → benzoquinone → muconic acid → small molecular organic acids → CO2 and H2O. The findings suggested a new way for the synthesis of the efficient catalyst with RM and optimal operating strategies for the treatment of phenol wastewater.

M-cresol, one of phenolics, is highly toxic, refractory, and threatens human health and ecological safety. The study on the efficient m-cresol degradation technologies is crucial and helpful to restrain its discharge into water body. A composite of MnO-doped red mud (RM) to activate peroxymonosulfate (PMS) for the m-cresol degradation was fabricated and employed, favorable to the recycling and utilization of RM. Considering the catalytic activity and cost, 0.1 M/RM@G exhibited an excellent degradation capacity attributing to strong Fe3O4 and MnO synergy and was considered as the best catalyst among the investigative catalysts. 100 % of m-cresol and 71.4 % of COD could be degraded within 90 min under 2 g/L catalyst, 10 mM of PMS, 3-8 of initial pH and 50 mg/L m-cresol in the 0.1 M/RM@G/PMS system. The reaction rate constant (0.045 min−1) of 0.1 M/RM@G was much larger than RM@G (0.012 min−1), ARM (0.0048 min−1) and WRM (0.0028 min−1). Main Mn and Fe active components and abundant mesoporous structures on the catalyst surface could efficiently drove electron transfers, and further accelerated the redox cycles of Mn(III)Mn(II) and Fe(III)Fe(II) for activating PMS. 1O2 played a crucial role in degrading m-cresol. Based on the experiment data, the generation mechanism of radicals and the possible pathways of m-cresol degradation were proposed in the 0.1 M/RM@G/PMS system. This finding provides a new way for the synthesis of the efficient catalyst with RM and optimal operating strategies for the treatment of m-cresol wastewater.

To improve the effectiveness of recycling, echelon utilization, and recovery mechanism of waste power batteries (WPBs), 12 recycling modes were proposed based on extended producer-responsibility principle. By employing profit and sensitivity analyses, we found that resource-recovery companies (Rs) are the key for recycling, echelon utilization, and recovery mechanism. For R, the high resale price of waste LiNixMnyCo1−x−yO2 batteries was not conducive to recovering waste batteries. However, the recycling behavior of R was beneficial for resisting the risk of high resale price of waste LiNixMnyCo1−x−yO2 batteries. This condition increased the profits by saving on the buying cost and reselling of WPBs to echelon-utilization companies. Following the decrease in the number of recyclers in the recycling system, the profits of R also increased. However, when the proportion of recycled waste LiNixMnyCo1−x−yO2 batteries was 100%, the profits of R faced risks due to the high resale price of waste LiNixMnyCo1−x−yO2 batteries. For other recyclers, only the power-battery manufacturers (Ms) were willing to reduce the resale price of waste LiNixMnyCo1−x−yO2 batteries to let R earn profit because R supplied regenerated materials to M at a lower price than the material companies. This condition created a cycle for WPB recovery and reduced the use of raw materials. Thus, Mode M–R was considered as the optimal recycling mode.

In this study, electric field and ball milling were used to leach Mn2+ from low-grade pyrolusite (LGP). The effects of current density, reaction time, reaction temperature, ball-to-powder weight ratio, and ball milling time on the leaching efficiency of Mn2+ from LGP as well as the leaching mechanism were systematically studied. The results showed that the combined use of electric field and ball milling enhanced the leaching of Mn2+ from LGP. The leaching efficiency of Mn2+ reached 97.79% under the optimum conditions of LGP-to-pyrite mass ratio of 1:0.18, current density of 30 mA/cm2, LGP-to-H2SO4 mass ratio of 1:0.4, liquid-to-solid ratio of 5:1, ball-to-powder weight ratio of 1:1, ball milling time of 2 h, temperature of 80 °C, and leaching duration of 120 min. This value was 25.95% higher than that attained without ball milling and 41.45% higher than that attained when neither ball milling nor electric field was employed. Pyrite was fully oxidized to generate additional SO42− and Fe3+, and was further hydrolyzed to form jarosite (KFe3(SO4)2(OH)6) and hydronium jarosite (Fe3(SO4)2(OH)5·2H2O) via ball milling and electric field application. Moreover, the electric field changed the surface charge distribution of the mineral particles and promoted collisions between them as well as the collapse of the crystal lattice, further improving the leaching efficiency of Mn2+ from LGP. This study provided a new method for leaching Mn from LGP.

Phosphogypsum (PG) contains a lot of soluble phosphate (PO 4 3- -P) and fluorine ion (F - ), which seriously has hindered the sustainable development of the phosphorous chemical industry. In this study, a new burning raw material (BRM) as an intermediate product in the cement production process was used for PO 4 3- -P and F - stabilize in PG. The stabilizing mechanism of PO 4 3- -P and F - were investigated by Fourier Transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM), X-ray fluorescence (XRF) and X-ray spectroscopy system (XPS). The effect of PG and BRM weight ratio, solid-to-liquid ratio, reaction time, and reaction temperature on the concentrations of PO 4 3- -P and F - were studied. The results showed that the concentration of F - in the PG leaching solution was 8.65 mg/L and the stabilizing efficiency of PO 4 3- -P was 99.78%, as well as the pH of the PG leaching solution was 8.12 when the weight ratio of PG and BRM was 100:2, and the solid to liquid ratio was 4:1, reacting for 24 h at the temperature of 30 ℃. PO 4 3- -P and F - were mostly solidified as Ca 5 (PO 4 ) 3 F, CaPO 3 (OH), Ca 5 (PO 4 ) 3 (OH), Ca 2 P 2 O 7 ·2H 2 O, CaSO 4 PO 3 (OH)·4H 2 O, CaF 2 , and CaFPO 3 ·2H 2 O. Leaching test results indicated that the concentrations of PO 4 3- -P, F - and heavy metals were less than the integrated wastewater discharge standard (GB8978-1996). This study provides a new harmless treatment method for PG., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)