The extraction of rare earth elements (REEs) from phosphogypsum (PG) is of great significance for the effective utilization of rare earth resources and enhancing the resource value of PG waste residues. This study used Aspergillus niger (A. niger) fungal culture filtrate as a leaching agent to investigate the behavior of extracting REEs from PG through direct and indirect contact methods. According to the ICP-MS results, direct leaching at a temperature of 30 °C, shaking speed of 150 rpm, and a solid–liquid ratio of 2:1, achieved an extraction rate of 74% for REEs, with the main elements being yttrium (Y), lanthanum (La), cerium (Ce), and neodymium (Nd). Under the same conditions, the extraction rate of REEs from phosphogypsum using an A. niger culture filtrate was 63.3% higher than that using the simulated organic acid-mixed solution prepared with the main organic acid components in the A. niger leachate. Moreover, the morphological changes observed in A. niger before and after leaching further suggest the direct involvement of A. niger’s metabolic process in the extraction of REEs. When compared to using organic acids, A. niger culture filtrate exhibits higher leaching efficiency for extracting REEs from PG. Additionally, using A. niger culture filtrate is a more environmentally friendly method with the potential for industrial-scale applications than using inorganic acids for the leaching of REEs from PG.

With the rapid development of modern industry, particularly in the fields of electric vehicles and renewable energy technologies, the demand for rare earth elements (REEs) has surged dramatically. Phosphogypsum (PG), which is an industrial waste product generated during the production of phosphoric acid through the sulfuric acid process, is rich in REEs. However, traditional chemical leaching methods pose environmental pollution and resource wastage issues. This study aims to explore the feasibility and optimal conditions for bioleaching REEs from phosphogypsum using Gluconobacter oxydans (G. oxydans). The phase composition and components of phosphogypsum, as well as the growth characteristics and leaching efficiency of G. oxydans, were analyzed in detail using SEM, EDS, XRD, and XRF techniques. Experimental results indicate that G. oxydans can effectively leach REEs from phosphogypsum under conditions of 28 °C, an agitation speed of 150 rpm, and a liquid-to-solid ratio of 4:1, with a maximum leaching efficiency of 24.67%. Moreover, it is revealed in the study that G. oxydans exhibits selectivity in leaching REEs. Specifically, the leaching efficiency for Nd is significantly enhanced at low pH values. This research provides a theoretical basis and practical application example for the efficient and environmentally friendly recovery of REEs from phosphogypsum.

Red mud (RM), a solid waste byproduct of the alumina industry, has accumulated in significant global stockpiles. Currently, the primary application of RM involves magnetic separation to recover iron oxides, while the residual RM is predominantly landfilled. Due to its strong alkalinity, RM can serve as a substitute for strong alkalis or sodium salts in the alkali activation of concrete, thereby accelerating setting time and improving early-age strength. Building on this property, this study designs and develops an RM based rapid setting filling support material, primarily composed of RM, which features rapid setting and high early strength. This material is intended as a substitute for high-water-content materials in gob-side entry retaining for coal mining. Experimental results demonstrate that when RM content reaches 70% and cement content is 10%, the Rapid-Setting Filling Support Material (RSM) achieves satisfactory compressive strength and initial setting time, coupled with excellent economic performance. The compressive strengths at 1 day, 3 days, 7 days, and 28 days are 6.12 MPa, 8.97 MPa, 11.25 MPa, and 12.33 MPa, respectively, meeting all requirements specified in the 'Technical Requirements for Roadside Bag Filling for Gob-side Entry Retaining with High-Water Material' (GB/T 39336-2020). The RSM also exhibits good durability, with primary hydration products including C–S–H gel, ettringite, and calcium carbonate, all of which contribute to strength development. Leaching tests reveal that heavy metal ion concentrations in the RSM leachate comply with integrated emission standards for Class III groundwater and wastewater, confirming its safe application. Considering the annual increase of approximately 13,000 km in roadway length for coal mining in China, the demand for filling and support materials is substantial. Consequently, the findings of this study hold significant economic and environmental value, with the potential to promote green mining practices and the circular economy.

Biological matter evolution provides an idea for the human design and synthesis of new materials. However, biomimetic materials only stay in laboratory-scale models, and their large-scale industrial applications are yet to be realized. Here, inspired by nacre’s architecture, we report a continuous, large-scale method to fabricate phosphogypsum composites by reactive extrusion strategy. After curing for seven days, with more than 50 wt% of beta-hemihydrate phosphogypsum (β-HPG), the compressive strength and softening coefficient were 24.98 MPa and 0.78, increasing by 110.0% and 20.0%, respectively, compared to the pouring method. The results show that the screw extrusion process can improve the mechanical strength and waterproof properties of β-HPG hydration specimens without any special chemical admixtures and cements.

Accurate quantification of phosphogypsum (PG) filler in epoxy composites is essential for quality control and performance optimization. Conventional separation by muffle furnace calcination suffers from slow epoxy decomposition and risks thermal degradation of CaSO₄, leading to inaccurate PG quantification. This study introduces a microwave-assisted separation method that leverages molecular vibration heating to achieve faster heating rates and more uniform temperature distribution, enabling complete epoxy removal while minimizing CaSO₄ decomposition. Comprehensive characterization (X-ray diffraction, XRD; Fourier transform infrared spectroscopy, FT-IR; scanning electron microscopy-energy dispersive spectroscopy, SEM-EDS) confirms the structural integrity of the isolated PG filler. Among five quantification methods evaluated, inductively coupled plasma optical emission spectrometry (ICP-OES) based on sulfur content provides the highest accuracy (spike recovery: 91–99.8%, relative standard deviation, RSD ≤ 4.2%), while gravimetry suffices for single-filler systems. This work establishes a reliable analytical framework for PG characterization in epoxy composites, supporting quality control and resource valorization.