The corrosion of hazelnut shell ash (HSA) prepared in 1% NaCl solution at different concentrations (75 mL, 25 mL, 10 mL) was investigated on iron (Fe) at 25 °C using electrochemical techniques. The investigations carried out using open-circuit potential (EOCP), electrochemical impedance spectroscopy (EIS), and current–potential (Tafel) polarization techniques. The results showed that the addition of HSA significantly shifted the potential of the Fe in the cathodic direction and raised the pH of the solution (pH 5.8 to ~10) at all concentrations. Furthermore, containing 10 mL of HSA, the corrosion current density (icorr) decreased from 0.50 µA cm⁻² to 0.15 µA cm⁻² according to Tafel results, achieving an improvement of approximately 70%. Inductively coupled plasma mass spectrometry (ICP-MS) analyses revealed that Fe, Ni, Cr, and Co heavy metal ions migrated into the working solution; it was determined that the addition of HSA significantly reduced the concentration of these ions in the solution. The decrease was particularly pronounced for Fe ions; Fe²⁺/Fe³⁺ concentrations decreased from 0.203 ppm to
Yanardağ et al. (Tue,) studied this question.