Efficacy of Acacia raddiana gum polysaccharide as a corrosion inhibitor for mild steel in concentrated sulfuric acid media: experimental and theoretical study

Acacia raddiana gum (ARG) is a natural resource from the Moroccan Sahara, rich in polysaccharides and proteins, which gives it inhibitory potential. It is easy to extract and yields a sufficient quantity of active material. The objective of this study is to prepare an extract of Acacia raddiana gum, evaluate its inhibitory effectiveness on mild steel, and study the effect of the gum alone as well as its action in combination with potassium iodide (KI). Electrochemical tests were carried out in a 1 M H₂SO₄ medium at 298 K. The results show that KI significantly enhances the gum’s inhibitory efficacy. Maximum efficacy reaches 89.69% in the presence of 300 ppm ARG and 40 ppm KI. This confirms that this improvement reflects a synergistic effect between ARG and KI. The inhibition mechanism indicates that iodide ions and the gum’s functional groups act cooperatively. This interaction promotes the formation of a compact protective film at the steel/solution interface. The film limits the access of corrosive species to the metal surface. The theoretical approach shows that quantum chemistry calculations (DFT) can be used to identify the active adsorption sites. Molecular dynamics simulations show that the gum preferentially adsorbs on steel. Heteroatoms and side chains play a key role in the inhibition process.