Parkia biglobosa (African Locust Bean) Pulp as a Green Inhibitor for Mild Steel Corrosion

This work investigated corrosion inhibition potential of Parkia biglobosa (P. biglobosa) pulp on mild steel in 1.0 M HCl and 0.1M NaOH aqueous solutions at 301 and 321 K, aimed at converting a cellulosic renewable waste into an environmentally friendly answer to the challenge of mild steel corrosion, especially in chemical industries. Weight loss of mild steel coupons over a period of 120 hrs. were measured at varying concentrations (0.0-7.5 g/L) of P. biglobosa pulp. The data did not strictly fit the Langmuir isotherm, having a slope greater than unity and suggesting that adsorbing species from P. biglobosa pulp occupied more than one active site. This was collaborated by the quantum chemical parameters evaluated. Results of the investigations showed that P. biglobosa pulp is a good green inhibitor for mild steel corrosion in both acidic and alkaline media. An optimum dosage of 4.5 g/L resulted to 85.73 % inhibition efficiency () at 301 K while at 321 K, the optimum dosage was 1.0 g/L of the pulp with an inhibition efficiency ≈ 50 % and 55 % in the acidic and alkaline medium respectively. The values decreased with increase in temperature and were strongly collaborated by values (- 0.86 Lcm-2h-1 at 301 K and - 0.498/0.55 Lcm-2h-1 at 321 K) of order (b) of the reaction. The corrosion reaction showed a large rate constant ( and in acidic and alkaline medium respectively) at ambient temperature; reflecting the fast nature of the process. Values of the standard free energy of adsorption () were negative for the process both at ambient and elevated temperature indicative of a spontaneous process and stable layer of adsorption. These values were less than – 40 kJmol-1, suggestive of a physisorption mechanism. This was collaborated by higher adsorption activation energy () in presence of the inhibitor than in its absence.