Industrial jarosite as a functional pigment in epoxy and alkyd anticorrosive coatings

The mitigation of metallic corrosion remains a critical socio-economic and technical challenge, necessitating the transition toward sustainable and high-performance protective materials. This study explores the valorization of jarosite-a hazardous industrial waste from zinc hydrometallurgy-as a functional pigment in organic coatings. Formulations were developed using epoxy and alkyd matrices, with jarosite concentrations maintained below the Critical Pigment Volume Concentration (CPVC ~ 30%) to ensure full polymeric encapsulation. The pigment was characterized by a polymodal particle size distribution (1.1-22 μm) and high surface area (12.2 m²/g), contributing to a dense packing effect. The anticorrosive performance was evaluated through Electrochemical Impedance Spectroscopy (EIS), salt spray exposure, and pull-off adhesion tests. SEM/EDS analysis revealed that the irregular prismatic morphology of jarosite crystals is consistent with the formation of a tortuous diffusion pathway, suggesting delayed electrolyte diffusion. EIS results showed that the epoxy-jarosite system maintained superior barrier properties, with low-frequency impedance modules (|Z|_0.01 Hz) remaining above 10¹⁰ Ω.cm² for 5-8 wt% loadings throughout 100 days of immersion. Leaching assessments via ICP-OES revealed divergent immobilization behavior between the binder systems: while the epoxy matrix achieved effective retention of Pb and Cd below the quantification limit, the alkyd matrix exhibited a measurable release of Cd (40 µg/L), indicating partial immobilization efficiency under highly saline conditions.