Mining waste into environmental remediation: sustainable Mg/Fe-LDH derived from Amazonian copper residues for efficient Congo red removal

Abstract The improper disposal of mining residues poses significant environmental challenges, particularly in ecologically sensitive regions such as the Amazon. In this study, Amazonian copper mining residues (ACMR) were employed as a sustainable source of ferric iron (Fe 3 ⁺) for the synthesis of Mg/Fe layered double hydroxides (Mg/Fe-LDH). Chemical and mineralogical analyses revealed elevated concentrations of SiO 2 , Al 2 O 3 , and Fe 2 O 3 , with partial acid dissolution of iron-bearing minerals facilitating Fe 3 ⁺ recovery. X-ray diffraction confirmed the formation of a highly crystalline Mg/Fe-LDH phase with rhombohedral symmetry (R-3 m space group). Scanning electron microscopy and BET analyses revealed a plate-like morphology and a mesoporous structure with a specific surface area of 49.8 m 2 g⁻ 1 . The environmental performance of the synthesized material was assessed through Congo red (CR) dye removal from aqueous solutions. The pseudo-second-order model best described adsorption kinetics, and equilibrium data were well fitted by the Langmuir isotherm, yielding a theoretical maximum adsorption capacity of 435.19 mg g⁻ 1 at 313.15 K, a value that surpasses most inorganic and hybrid adsorbents reported in the literature. Thermodynamic analysis confirmed that the adsorption process was spontaneous and endothermic. This study demonstrates an environmentally sustainable pathway for converting mining waste into a high-performance adsorbent, highlighting the potential of Mg/Fe-LDH derived from ACMR as a cost-effective material for dye-contaminated wastewater treatment.