The Extraction of Some Water Bound Metal Ions using Palmitic Acid as a Green Extractant

Abstract

Background: Nickel (Ni²⁺) and iron (Fe²⁺) ions from industrial wastewater pose environmental risks because of their toxicity and persistence in water systems. Conventional extraction methods often use toxic organic reagents, which has increased interest in greener alternatives. Naturally occurring fatty acids, such as palmitic acid, have potential as biodegradable extractants for metal ion removal through solvent extraction techniques. Aims: This study aimed to investigate the removal of Ni2+ and Fe2+ ions from aqueous solutions using palmitic acid and to determine the effects of selected extraction parameters on process efficiency. Study Design / Methodology: A liquid-liquid extraction process was used. Specific parameters of the aqueous phase, including ion concentration and pH, as well as the concentration of palmitic acid in the organic phase, were regulated. Results: The results showed that the removal of these ions from the aqueous solutions depended on the initial ion concentration, palmitic acid concentration and equilibrium pH. Based on the percentage removal efficiency and distribution coefficient, ion removal increased with increasing initial ion concentration, palmitic acid concentration and equilibrium pH. The highest percentage removal efficiency and distribution coefficient values were obtained at an initial ion concentration of 50 ppm, a palmitic acid concentration of 10 ppm and an equilibrium pH of 5.5. Using the slope analysis method, the oxidation state of the ions was validated and the nature of the extracted metal ion-organic complex was determined. The range of the standard Gibbs free energy for the extraction of Ni2+ and Fe2+ ions was between 62.88 and 70.24 KJ mol-1. Conclusion: The results showed that palmitic acid had the capacity to remove Ni2+ and Fe2+ metal ions found in water. Its extraction capability depended on the initial concentrations of Ni2+ and Fe2+ ions in the aqueous phase and the concentration of palmitic acid. From the optimisation of the pH levels, most metal ions were removed from the aqueous phase at pH 5.5. From slope analysis, it was affirmed that a complexation reaction involving two acidic hydrogen atoms from two molecules of palmitic acid complexed with one ion of Ni2+ and Fe2+ during the extraction.