Articles

Application of Magnesium Sulfate in In-Situ Leaching of Rare Earth Elements: Mechanisms, Performance and Environmental Implications

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Ion-adsorption clay deposits are among the most important sources of heavy rare-earth elements (REEs), particularly in southern China, where extraction is commonly performed by in situ leaching (ISL) using ammonium salts. Although ammonium sulfate and related lixiviants achieve high extraction efficiencies via ion-exchange mechanisms, their large-scale use has raised significant environmental concerns, including ammonium contamination, soil degradation, and groundwater pollution. In recent years, magnesium sulfate (MgSO₄) has emerged as a potential alternative lixiviant with lower environmental impact. This review critically analyzes the application of MgSO₄ in the in-situ leaching of REE-bearing ion-adsorption clays, focusing on ion-exchange mechanisms, leaching performance, hydrodynamic behavior, and environmental implications. The thermodynamic and geochemical aspects governing Mg²⁺–REE exchange reactions are examined together with laboratory, column, and pilot-scale studies. Comparative analyses with conventional ammonium-based lixiviants are discussed in terms of extraction efficiency, selectivity, reagent consumption, and environmental footprint. The review also identifies key research gaps related to process optimization, hydrogeological modeling, and large-scale implementation. Overall, MgSO₄-based leaching systems represent a promising pathway toward more sustainable rare-earth extraction, although further technological and environmental validation is required before full-scale industrial deployment.

Phytomining as an Emerging Metal Recovery Route: A Critical Review of Plant Uptake Mechanisms, Processing Strategies, And Industrial Constraints (2020–2025)

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Phytomining has re-emerged as a promising strategy for the sustainable recovery of valuable and critical metals from soils, mine tailings, and industrial residues, while simultaneously contributing to environmental remediation. This critical review synthesizes advances published between 2020 and 2025, focusing on the biological, agronomic, and metallurgical foundations that govern phytomining performance and scalability. Recent progress in hyperaccumulator selection, soil amendments, plant–microbe interactions, and biomass processing has expanded the range of target metals beyond nickel to include gold, platinum-group metals, rare-earth elements, and scandium. However, field-scale deployment remains constrained by trade-offs between biomass productivity and metal concentration, as well as by the efficiency and cost of downstream ash processing and metal recovery. By integrating reported case studies, techno-economic assessments, and environmental indicators, this review positions phytomining within circular economy and nature-based remediation frameworks. Key knowledge gaps have been identified in process integration, quantitative performance metrics, and long-term sustainability, providing a roadmap for transitioning phytomining from experimental trials to industrially relevant applications.