Articles

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.

Secondary Aluminum Dross and Salt Slag Treatment: A Critical Review of Integrated Value Recovery, Risk Control, And Industrial Readiness

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Secondary aluminum dross and salt slag are heterogeneous secondary resources whose entrained metal, alumina-bearing phases, aluminum nitride (AlN), chlorides, fluorides, and fine particles create coupled recovery and safety constraints. This structured critical narrative review maps 106 publications from 2020 to 2026 and evaluates physical, thermal, aqueous, and product-oriented routes without claiming systematic review or PRISMA compliance. Conservative evidence coding identified one industrial campaign (Class A), one pilot study (Class B), no continuous integrated Class C study, 86 laboratory studies on real dross (Class D), five modeling or proof-of-concept studies (Class E), and 13 supporting reviews or contextual sources. Selected studies reported metallic aluminum recovery above 92% and up to approximately 98%, chloride removal above 92%, and AlN conversion of 92.45–99.03%; these results are not directly comparable because of differences in feed assays, particle size, residence time, and system boundaries. A metal-first sequence is therefore conditionally preferred when the net value of recovered metal justifies the operation and when removal reduces the hydrogen inventory of the wet circuit. Stoichiometrically, 1 kg AlN can generate 0.415 kg NH₃ (0.597 m³ at 25 °C and 1 atm), while 1 kg metallic Al can generate 0.112 kg H₂ (1.360 m³) under complete reaction. Washing, controlled hydrolysis, salt crystallization, gas capture, and mineral conversion must consequently be designed as one integrated system. Laboratory production of alumina, spinel, refractories, adsorbents, or cementitious materials demonstrates conversion, not circularity, unless product specifications, durability, leaching stability, multi-cycle recycle, controlled purges, and harmonized life-cycle and techno-economic boundaries are verified. The review provides route-specific readiness ratings, quantitative design bases, and objective go/no-go gates for industrial development.