Sustainable corrosion inhibition of carbon steel in hydrochloric acid using repurposed expired clarithromycin as a reverse of mining

Abstract Corrosion of carbon steel in acidic environments represents a major challenge in many industrial operations, particularly during pickling, acidizing, mining, and cleaning processes. In this study, expired clarithromycin (CTM) was evaluated as a green corrosion inhibitor for carbon steel in 1.0 M hydrochloric acid using complementary chemical (weight loss and hydrogen evolution) and electrochemical (potentiodynamic polarization and electrochemical impedance spectroscopy) techniques. Surface morphology and composition were analyzed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The corrosion rate decreased progressively with increasing CTM concentration, with inhibition efficiency exceeding 90% at 5 mM and 298 K. The protective effect is attributed to the adsorption of CTM molecules onto the steel surface, forming a stable and durable barrier. Thermodynamic analysis revealed negative ΔG° ads values ranging from − 33.88 to − 37.58 kJ mol⁻ ¹ , indicating spontaneous adsorption via a mixed physicochemical mechanism. A decrease in the adsorption equilibrium constant ( K ads ) at elevated temperatures suggested partial desorption of pre-adsorbed molecules. In contrast, high adsorption energy values confirmed strong interactions between CTM and the metal surface. These findings demonstrate the feasibility of repurposing expired pharmaceuticals as effective and environmentally friendly corrosion inhibitors. The study highlights a sustainable and cost-effective strategy for protecting carbon steel in acidic media, aligning with green chemistry principles and offering a practical approach to pharmaceutical waste valorization in corrosion inhibition technology.