Evaluation of Un-Preprocessed Expired Piroxicam Drugs as Corrosion Inhibitor for Mild Steel in Hydrochloric Acid

Illegal disposal and recirculation of expired drugs is a global menace which can be solved by their re-utilization as corrosion inhibitors. Thus, helping to combat the current widespread corrosion-induced wastage of expensive mild steel infrastructure. The experimental investigation evaluated the capability and effectiveness of an expired drug (piroxicam) for inhibiting mild steel corrosion in blank 0.5M HCl and acidic environments containing 2 to 8 g/L of the expired drug. Spectrometry, weight loss analysis, atomic absorption spectroscopy, microscopy, polarisation and electrochemical impedance study (EIS) were employed. Analyses revealed drastic inhibition of corrosion in mild steel by expired piroxicam drug in the acid. Corrosion currents (i_corr) obtained at all concentrations of the expired drug were reduced in comparison to that of the uninhibited environment. The solution resistance recorded was not significantly altered; charge transfer resistances were increased while the capacitance of the electrochemical double layers (Double layer capacitance) as well as the concentration of dissolved iron (Feⁿ⁺) ions in the environment, were all reduced with increasing concentration of the expired drug. Although moderate amounts of the expired drug delivered appreciable levels of corrosion inhibition when dissolved directly into the corrosive environment and without any pre-treatment, increased concentration of expired drug resulted in increased corrosion inhibition efficiency. The highest corrosion inhibition efficiency obtained was 97.6% and was from the acidic environment that contained 8 g/L of expired piroxicam drug. The expired piroxicam drug inhibited corrosion of mild steel in 0.5M HCl acid via spontaneous physical adsorption (physisorption) process(s), obeying Langmuir’s adsorption isotherm.