Copper Slag Softening, Fayalite Destruction And Magnetite Reduction Through Coal-Based And Hydrogen-Based Processes

Copper smelting generates approximately 2.2–3.0 tons of slag per ton of metallic copper produced, creating a significant environmental and resource management challenge. This comprehensive review analyzes 20+ Scopus-indexed research articles focusing on slag softening techniques, fayalite (Fe₂SiO₄) decomposition, and magnetite (Fe₃O₄) reduction in copper metallurgical residues. The research encompasses thermodynamic modeling, kinetic analysis, and process optimization using bothcoal-based direct reduction and hydrogen-based reduction pathways. Coal-based direct reduction achieves iron recovery rates of 98.13% under optimal conditions (1300°C, 30 min, 35 wt% coal dosage, 20 wt% CaO), with activation energies ranging from 175.3 to 221.9 kJ/mol across different temperature regimes. Hydrogen reduction demonstrates comparable effectiveness with 85.12% metal reduction ratio at 1373.15 K with 40% H₂ partial pressure. Thermodynamic analysis confirms the feasibility of key reduction reactions with negative Gibbs free energy values (−95.3 to −188.4 kJ/mol at 1300°C). The fayalite reduction process follows a twostage mechanism: phase boundary-controlled reaction at initial stages (E_a = 175.32–202.37 kJ/mol) transitioning to diffusioncontrolled processes (E_a = 173.45–297.71 kJ/mol). Novel slag modification techniques including lime decomposition of fayalite melt show promise, though mass transfer limitations from Ca₂SiO₄ coating formation present critical challenges. This review provides comprehensive kinetic models, thermodynamic databases, and practical insights for optimizing iron extraction from copper slag, contributing to circular economy principles and sustainable metallurgical processing.

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