Process Safety and Environmental Protection最新文献

The increased demand for rare earth elements in advanced technological applications and supply shortages call for metal recovery from secondary sources. Permanent magnet (Nd₂Fe₁₄B or NdFeB) may serve as a potential secondary source due to its high rare earth (Nd+Pr+Dy: ∼30 %) content and its vast application. The present study utilizes a chloridizing roasting (CaCl₂.2 H₂O) pre-treatment process followed by water leaching, acid leaching (0.5 M HCl, S/L =1/10 g/ml, 90 °C, 3 h), oxalic acid precipitation and calcination (850 °C, 2 h) to obtain mixed rare earth oxides. The process was optimized based on temperature (400–700 °C), dosage (CaCl₂.2H₂O: NdFeB=0.5:1–2.5:1), and time (30–120 min) on the rare earth dissolution. The theoretical activation energy for the chloridizing roasting process is estimated as 22.3 (OFW) and 16.7 kJ/mol (KAS), while the experimental activation energy for Nd and Dy dissolution was determined to ∼29.3 and ∼17.7 kJ/mol, respectively depicting product layer diffusion-controlled kinetics. Higher dosages of CaCl₂.2H₂O (1.5:1 and 2:1) favored NdOCl formation, thereby, higher dissolution; however, further higher dosage (2.5:1) leads to reduced Nd dissolution due to higher CaO formation and acid consumption by Ca during leaching. Incomplete oxidation at lower temperatures (400 °C) and iron dissolution impair the Nd dissolution and selectivity. Excessive oxidation at >700 °C favors the formation of NdFeO₃, decreasing Nd dissolution. The maximum dissolution of Nd was ∼89 %, while for Dy, it was ∼88 % at optimum conditions of 600 °C, 90 min, 2:1. Water leaching post-roasting leads to ∼87 % Ca removal and the precipitation efficiency of rare earth oxalates was 99 %. The overall extraction for rare earth elements was ∼89 %, and 1 kg of NdFeB powder can yield ∼285 g of rare earth oxides (∼239 g Nd₂O₃, ∼14 g Dy₂O₃) with 96 % purity. Further, this study demonstrates that using CaCl₂.2 H₂O as a solid chlorinating agent in chlorination roasting enhances recovery rates of mixed rare earth oxides while providing a safer and more environment-friendly alternative for industrial applications.

Improving the selectivity of the reactive intermediates such as ${\mathrm{ClO}}^{-}$ and $•\mathrm{OH}$ by modifying nickel foam electrodes with ion exchangeable layered materials would greatly enhance the efficiency of high-salinity wastewater treatment. A universal pattern was verified herein that through functioning as a permeable overlayer regulating the transport of cations/anions, ${\mathrm{ClO}}^{-}$ and $•\mathrm{OH}$ could be the predominant intermediates in the anionic/cationic layered material modified electrode. The significance of selectivity enhancement includes improving electrochemical efficiency and reducing the usage of chemical reagents. For instance, it is demonstrated that electrochemically degrading high salinity azo wastewater using decorated electrodes would be as effective as chemical treatment. Furthermore, electrochemical oxidation using cation layered material modified electrode could reduce the pKa of the oxidized cellulose filter paper as effectively as using ${H_{2}O}_2$.

This study explored the dynamic processes of algae-bacteria biofilms in the remediation of aquaculture pond effluents as a novel treatment strategy. The purification capacity of the biofilms, changes in community composition, and their impact on the dissemination of antibiotic resistance genes (ARGs) were investigated under the application of sulfamethoxazole (SMX) at concentrations ranging from 100 to 1000 μg/L. The study also considered the factors influencing the abundance and diversity of ARGs and mobile genetic elements (MGEs) across different seasons, including the roles of environmental parameters and microbial community structure.The results showed that, although exposure to SMX reduced nutrient removal efficiency, photosynthetic activity, and increased oxidative stress levels, the biofilms maintained relatively high purification efficiency (with nutrient removal rates ranging from 67.62 % to 93.23 % and SMX removal rate reaching 50.13 % ± 12.34 %), demonstrating adaptability to SMX stress. Network analysis identified key microbial carriers responsible for ARG dissemination, highlighting the complex interactions between environmental factors, microbial communities, and resistance gene propagation. These findings enhance our understanding of biofilm-based water treatment systems and the seasonal factors affecting the dynamics of ARGs and MGEs.