Articles

Conventional Ion-Exchange and Chelating Resins for Metal Recovery: A Critical Comparison of Selectivity, Dynamic Performance, Regeneration, and Process Integration

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Conventional ion-exchange and chelating resins are widely used for metal recovery, purification, and polishing, yet they are still frequently compared using equilibrium capacity rather than process function. This structured critical review examines how charge-driven exchange and ligand-controlled coordination translate into selectivity, kinetics, breakthrough behavior, regeneration, fouling, resin lifetime, and flowsheet integration. Topic-structured searches covering 2018–31 August 2026 yielded 313 candidate records, of which 110 peer-reviewed publications were retained for critical synthesis. Evidence was weighted from batch equilibrium and kinetic studies through fixed-bed or reactor operation, regeneration, real-matrix validation, pilot or multicolumn demonstrations, and selected industrial-scale applications. Across rare-earth elements, Cu–Ni–Co systems, battery-recycling liquors, Sc/V/Ga separations, Zr/Hf and radionuclide systems, precious metals, and industrial wastewaters, the evidence shows that equilibrium qmax and single-solute distribution coefficients are poor stand-alone indicators of process readiness. Representative dynamic studies report outcomes ranging from a Cu breakthrough capacity of 16.51 mg g−1 to an REE eluate concentration factor of 236×, while selected continuous and industrial-scale studies demonstrate high product purity, sustained metal recovery, and concentrated regenerates when feed chemistry and cycle design are controlled. Conventional and chelating resins are therefore best viewed as complementary rather than substitutive technologies. The review proposes a minimum reporting framework for scale-up-relevant studies based on representative feed chemistry, working capacity, breakthrough criteria, regenerant demand, product purity, multicycle durability, and flowsheet integration. Hybrid flowsheets emerge as a particularly defensible strategy for converting resin selectivity into process value.

From Upgraded Titanium Slag to Modern Metallurgical Slag Engineering: Technologies, Industrial Applications, and Readiness- A Critical Review

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Metallurgical slags are increasingly treated as dynamic secondary resources rather than inert residues, yet the literature remains fragmented across metal recovery, mineral-phase engineering, material valorization, carbon management, and industrial implementation. This structured critical narrative review evaluates a recent core corpus of 111 publications from 2020–2026 and supplements it with selected pre-2020 foundational sources required to establish the historical Upgraded Slag (UGS) lineage in titanium metallurgy. The recent corpus was descriptively coded by primary slag family, evidence function, and implementation maturity; steelmaking/ferrous systems account for 60 studies, copper/fayalitic slags for 16, cross-cutting or mixed systems for 15, ferroalloy/Cr–Mn slags for 7, Ti-bearing slags for 4, and Ni/ferronickel slags for 3. Eighty publications primarily provide mechanistic or product-performance evidence, 13 provide system-assessment evidence, and 12 are reviews or contextual sources. The synthesis distinguishes historical titanium-slag upgrading from the broader family of modern thermal, chemical, redox, physical, hydrometallurgical, carbonation, and electrochemical interventions. It shows that credible upgrading requires more than high recovery: a controllable phase transformation must be coupled with effective separation, qualified metal or material products, a safe and useful residual matrix, and realistic integration with plant infrastructure. Representative industrial evidence is strongest in copper-slag flotation and settling, selected hot-stage steel-slag operations, and heat-recovery applications, whereas many high-value functional-material routes remain laboratory-led. A five-gate framework—value inventory, engineerability, separation and safety, integration, and system performance—is applied to representative routes to connect mechanisms with product specifications, TEA/LCA, and industrial readiness. The resulting perspective positions slag upgrading as site-specific product and process design within circular metallurgy rather than as generic residue reuse.