Investigation of mulberry leaf and olive pomace extracts as green corrosion inhibitors for carbon steel protection: Experimental evaluation and process optimization

Abstract Corrosion of carbon steel in hydrochloric acid is a significant industrial concern, particularly during acidizing and other acidic processes. This study investigates mulberry leaf and olive pomace extracts as sustainable corrosion inhibitors for carbon steel in 1 M HCl and evaluates their combined performance and process optimization. Weight-loss measurements and scanning electron microscopy (SEM) were employed to assess corrosion behavior and surface protection, while Response Surface Methodology (RSM) based on a Central Composite Design (CCD) was used to optimize inhibitor dosage, temperature, and immersion time. Olive pomace extract exhibited superior inhibition performance compared with mulberry leaf extract, reaching approximately 85% inhibition efficiency at 2000 ppm. Notably, combining the two extracts did not produce synergistic enhancement; instead, anti-synergistic behavior was observed, suggesting competitive interactions among their phytochemical constituents. SEM observations further confirmed that olive pomace produced a more uniform and compact protective film on the carbon steel surface. RSM and ANOVA demonstrated reliable prediction of corrosion rate and inhibition efficiency, while optimization showed that inhibition efficiencies above 80% could be achieved under harsh conditions at 60 °C and up to 72 h using approximately 1350–1500 ppm olive pomace extract. The key novelty of this work lies in identifying the anti-synergistic behavior of mulberry–olive pomace combinations and establishing olive pomace, an agro-industrial by-product, as an effective and potentially practical green inhibitor for carbon steel in acidic environments.