As a large-volume industrial solid waste generated during the production of wet-process phosphoric acid, the primary disposal method for phosphogypsum (PG) currently involves centralized stockpiling, which requires substantial land use. Additionally, PG contains impurities, such as phosphorus, fluorine, and alkali metals, that may pose potential pollution risks to the surrounding environment. However, the mechanisms governing the co-release of phosphorus and fluorine impurities alongside valuable metal cations during leaching remain unclear, posing challenges to efficient disposal and utilization. This study compares the leaching characteristics of cations and anions in PG of different particle sizes through static pH leaching experiments. Using Visual MINTEQ simulation combined with XRD, XPS, and FT-IR characterization methods, we analyzed the leaching mechanisms and key controlling factors for various metal elements and inorganic elements, like phosphorus and fluorine, under different pH conditions. The experimental results show that Ca, Al, Fe, Ti, Ba, Sr, Y, and PO₄³⁻ in PG are more easily released under acidic conditions, while Si, Zn, Co, and F are primarily influenced by the content of soluble components. The dynamic “dissolution–crystallization” reaction of CaSO₄·H₂O significantly impacts the leaching of fluorine, and the XRD, XPS, and FT-IR characterization results confirm the presence of this reaction during the leaching process. This research provides theoretical guidance for the environmental risk assessment of stockpiled PG and the recovery of phosphorus, fluorine, and valuable metal resources from PG.

Ocean manganese nodules, which contain abundant Cu, Co, Ni and Mn resources, were reduced using biomass (sawdust) pyrolysis technology. Valuable metals were further extracted by acid leaching after the reduction process with high efficiency. The effects of sawdust dosage, reduction temperature, and time were investigated to obtain optimal operating parameters. The extraction rates of Mn, Cu, Co, and Ni reached as high as 96.1%, 91.7%, 92.5%, and 94.4%, respectively. Results from TGA show that the main pyrolysis process of sawdust occurs at temperature range of 250–375 °C with a mass loss of 59%, releasing a large amount of volatile substances to reduce the ocean manganese nodules. The pyrolysis activation energy of sawdust was calculated to be 52.68 kJ∙mol⁻¹ by the non-isothermal kinetic model. Additionally, the main reduction reaction behind the main sawdust pyrolysis process was identified by the comparison of the assumed and actual TG curve. The thermodynamic analysis showed that the high valence manganese minerals were gradually reduced to Mn₂O₃, Mn₃O₄, and MnO by CO generated from sawdust pyrolysis. The shrinking core model showed that the reduction process is controlled by the surface chemical reaction with activation energy of 45.5 kJ∙mol⁻¹. The surface of reduced ore and acid leached residue exhibited a structure composed of relatively finer pores and rougher morphology than the raw ore.

Because of its low whiteness, complex composition, radioactivity and high impurity percentage, the usage of phosphogypsum (PG) resources is limited. A theoretical foundation for upgrading and bleaching PG can be obtained by researching the presence and status of impurities in the material and its symbiotic connection with gypsum. This paper makes use of an automatic mineral phase analyzer, optical microscope, XRF, XRD and SEM-EDS. After analyzing the chemical makeup of PG, phase composition and particle size composition, the distribution law and symbiotic interaction between impurities and gypsum in various particle sizes were discovered. Using a flotation test, the process mineralogy analysis results were confirmed. According to the XRF and XRD study results, the primary impurity elements in PG are Si, P and F. Si is more abundant in PG that is between +850 μm and −37.5 μm in size. The concentrations of gypsum and quartz in PG are 82.59% and 8.73%, respectively, according to the results of XRD and process mineralogy. The monomer dissociation degree of the gypsum mineral phase is as high as 90.47%. Gibbsite and pyrite are the primary causes of the low whiteness of PG and are clearly related to the quartz mineral phase. The coupling process of “flotation + pickling” produced purified PG with a purity of 95.35%, whiteness of 70.76% and SiO₂ content of 2.73%. The quality met the first-class index standards of PG in GB/T23456-2018.

The leachate from ion-adsorbed rare earth tailings poses challenges to the application of the anaerobic ammonium oxidation (anammox) process in this field due to its large fluctuations in ammonia nitrogen concentration (50–300 mg/L) and high flow rate (4000–10,000 m³/d). This study investigated the effects of nitrogen-loading rate (NLR) regulation on denitrification performance through reactor operation and elucidated the mechanisms of NLR impacts on anammox processes via microbial community analysis and metabolic profiling. The results revealed a nonlinear relationship between nitrogen loading and system performance. As NLR increased, both denitrification efficiency and anammox bacterial abundance (rising from 5.85% in phase P1 to 11.43% in P3) showed synchronous enhancement. However, excessive nitrogen loading (>3.68 kg/m³·d) or nitrogen starvation led to performance deterioration and reduced anammox bacterial abundance. Microbial communities adopted modular collaboration to counteract loading stress, with modularity indices of 0.563 and 0.545 observed in the inhibition phase (P2) and starvation phase (P4), respectively. Zi-Pi plot analysis demonstrated a significant increase in inter-module connectivity, indicating reinforced interspecies interactions among microorganisms to resist nitrogen-loading fluctuations.

Weathered crust elution-deposited rare earth ores represent a significant source of medium and heavy rare earth elements. Their mineralization mechanism fundamentally involves the adsorption and enrichment of rare earth ions on the surfaces of secondary minerals within the weathering crust. To elucidate the role of nano-sized iron oxide–clay mineral composites in the migration and enrichment of rare earth elements (REEs) in weathered crusts, α-Fe₂O₃, oolitic hematite, Fe₂O₃-kaolinite, and FeOOH-kaolinite composites were selected as adsorbents. Using La³⁺, Ce³⁺, and Y³⁺ as target ions, their adsorption performance and fractionation mechanisms were systematically investigated through batch adsorption experiments combined with characterization techniques including Langmuir/Freundlich model fitting, Zeta potential, XPS, and FT-IR. The results demonstrate that the adsorption of REEs on iron oxides and their composites follows the Langmuir model (R² > 0.96), indicating monolayer homogeneous adsorption. The FeOOH-kaolinite composite exhibited the highest adsorption capacity (0.6531 mmol/g for Ce). Amorphous iron oxide–clay mineral composites showed superior complexation adsorption and enrichment capabilities due to their higher oxygen vacancy concentration (Oβ/Oα = 3.86 for FeOOH-kaolinite), whereas crystalline iron oxide–clay mineral composites contributed significantly to REE fractionation and enrichment. Among the influencing factors, elevated temperature (20–60 °C) favored the adsorption process, with an activation energy > 4.2 kJ/mol indicating chemical adsorption dominance. Within the pH range of 3.0–7.0, adsorption capacity increased with rising pH, with Ce being more sensitive to ionic strength and pH variations. The adsorption mechanism was further elucidated through post-adsorption XPS, FT-IR in the low-wavenumber region, and desorption studies. This study confirms that iron oxide–clay mineral composites regulate the enrichment and fractionation of REEs in weathered crusts through the interplay of their surface properties and environmental factors, providing a scientific basis for refining the metallogenic theory and guiding the exploration and development of weathered crust elution-deposited rare earth ore resources.

To improve the magnesia removal effect of collophane and increase the P2O5 grade of phosphorus concentrate, the fatty acid collector mixed with sodium dodecyl sulfate (SDS) was used as the compound collector in reverse flotation for magnesia removal in acid system. Solution surface tension...