Red mud, a Fe-rich waste generated from the aluminum industry, was recovered as an adsorbent for wastewater treatment. The separation process of red mud from water after adsorption, including centrifugation and filtration, was complicated. This study demonstrated an alternative option to recycle red mud for preparing magnetic adsorbent via a facile hydrothermal route using ascorbic acid as reductant. Red mud is weakly magnetized and consists of andradite, muscovite, hematite, and cancrinite. After hydrothermal treatment, andradite in red mud was reductively dissolved by ascorbic acid, and transformed into magnetite and morimotoite. With increasing hydrothermal temperature, the dissolution of andradite accelerated, and the crystallite size of magnetite increased. When the hydrothermal temperature reached 200 °C, the prepared adsorbent P-200 showed a desirable saturation magnetization of 4.1 Am²/kg, and could be easily magnetically separated from water after adsorption. The maximum adsorption capacity of P-200 for Zn²⁺ was 89.6 mg/g, which is eight-fold higher than that of the raw red mud. The adsorption of Zn²⁺ by P-200 fitted the Langmuir model, where cation exchange was the main adsorption mechanism. The average distribution coefficient of Zn²⁺ at low ppm level was 16.81 L/g for P-200, higher than those of the red mud (0.3 L/g) and the prepared P-120 (1.48 L/g) and P-270 (5.48 L/g), demonstrating that P-200 had the best adsorption capacity for Zn²⁺ and can be served as a practical adsorbent for real-world applications. To our knowledge, this is the first study to report the conversion of red mud into a magnetic adsorbent under mild conditions.

Although belowground litter decomposition critically influences lacustrine wetland soil carbon dynamics, the organ-specific microbial mechanisms driving soil organic carbon (SOC) accumulation remain unclear. Existing research has predominantly focused on aboveground litter, leaving a significant gap in the understanding of how roots and rhizomes differentially regulate carbon cycling through microbial community assembly and survival strategies. This study took Phragmites australis (a plant characteristic of lacustrine wetland) as the research object and examined how decomposing belowground litter from different organs affects microbial-mediated SOC accumulation through a one-year in situ field incubation in Jingyuetan National Forest Park, Changchun City, Jilin Province, China. Our findings reveal that root litter exhibited the highest decomposition rate, which was accelerated by intermittent flooding, reaching up to 1.86 times that of rhizome. This process enriched r-strategist microbial taxa, intensified homogeneous selection, and expanded niche width, directly promoting SOC accumulation. Rhizome litter decomposition enhanced dispersal limitation, promoted K-strategist microbial dominance, and indirectly modulated SOC through soil acidification. Mixed-litter treatments significantly enhanced SOC accumulation (up to three times higher than single-litter treatments) through synergistic nutrient release (non-additive effects < 0.04) and reinforced microbial network interactions. SOC accumulation varied significantly with the flooding regime as follows: non-flooded > intermittent flooding > permanent flooding. This study provides new insights into the microbially driven mechanisms of plant-organ-specific decomposition in the carbon cycling of wetland ecosystems.

When reclaimed water was recharged into groundwater containing a low content of ferrous iron, Fe-rich particles were generated and started to transport into the porous medium. X-ray powder diffraction and Mössbauer spectroscopy analysis showed that the generated Fe-rich particles were in a poorly crystallized ferrihydrite phase. After the formation of ferrihydrite particles, the mass loss of contaminants was calculated, which was 88.2% for Al, 93.3% for Zn, and 41.6% for chemical oxygen demand (COD). Protein-like compounds were predominant in the removed COD. Bovine serum albumin (BSA) was used as a model to investigate the effect of proteins on the transport of ferrihydrite particles in porous medium. Results showed that the attachment efficiency of ferrihydrite particles on the porous medium decreased from 100% to 75% with the increase of BSA concentration from 10 mg/L to 100 mg/L. BSA was attached to the surface of ferrihydrite particles via electrostatic adsorption. Thus, the zeta potential of ferrihydrite particles changed from positive to negative, and the particles became less aggregated, thereby enhancing particle mobility. This observation provided evidence that protein residues in reclaimed water enhance the transport of Fe-rich particles in saturated porous medium.

The recovery of metals from electroplating sludge has gained significant attention due to the dual imperatives of resource valorization and environmental protection. To address these challenges, a simple, waste-liquid-free process was developed for efficiently recovering nickel from Ni-rich electroplating sludge, with subsequent in situ utilization for electroplating. The sludge consisted of 24.2 wt% Ni, 1.9 wt% Fe, 8.8 wt% Al, and 25.3 wt% moisture. After sulfuric acid leaching, a brief hydrothermal treatment was introduced to transform Fe and Al from the leachate into easily filterable natroalunite particles, yielding a purified Ni-rich solution with Fe and Al concentrations each below 0.1 g L⁻¹. Two main valorization routes for Ni were established. First, the purified solution serves directly as an electrolyte for nickel electrodeposition onto iron substrates, producing uniform, compact, and thermally stable coatings. This route achieves impressively high nickel recovery (nickel loss <2%) and avoids the need for organic additives or redox reagents, eliminating the generation of liquid waste. Second, downstream purification of the solution involves P204 extraction to further remove Fe and Al and extract Ni, followed by evaporation and crystallization to produce electroplating-grade NiSO₄ crystals (25.4 wt% Ni), compliant with industrial standards. Additionally, the natroalunite-rich by-products are readily filterable and hold promise as precursors for flocculant production. Overall, this process enables high-efficiency nickel recovery, minimizes secondary pollution, and provides versatile end-product options, highlighting its promise for sustainable resource utilization in the metal finishing sector.

Accurate identification of HMs contamination in mine tailings is essential for understanding pollution and supporting remediation. However, conventional laboratory monitoring is labor-intensive, time-consuming, and spatially discontinuous, while UAV hyperspectral inversion is limited by spectral inconsistency, unstable performance under small-sample conditions, and insufficient interpretability. Here, we developed an interpretable UAV–laboratory synergistic framework for Cd and Pb mapping in the Yitong open-pit mine. Forty site-level soil samples, composited from 200 subsamples, were linked with UAV hyperspectral observations. Direct Standardization was used to harmonize UAV and laboratory spectra. A weighted voting ensemble (RF, GBDT, and XGBoost) achieved the best performance (R² = 0.85), outperforming the individual models and showing slightly higher stability than CNN (R² = 0.84). Environmental covariates (pH, SOM, SMC) revealed distinct metal-specific prediction patterns: Cd was mainly associated with pH–SOM interactions, whereas Pb was more strongly associated with SOM–SMC coupling. SHAP and Grad-CAM identified sensitive spectral regions, with Cd linked to the 440–580 nm range and Pb to the 720–740 nm range. Overall, this study provides an integrated framework that combines spectral transfer correction, stable multi-model inversion, and mechanism-oriented interpretability for HMs monitoring in complex mining environments.