Production and Characterization of the Properties of Soap using Alkali from Agricultural Waste
Abstract
This study evaluated the potential of agricultural wastes, namely yam (Dioscorea rotundata), cassava (Manihot esculenta), and plantain (Musa paradisiaca) peels, as sustainable sources of alkali for soap production. The peels were dried, calcined, and subjected to aqueous extraction to obtain alkali-rich solutions for soap production using the semi-boiled method. Eight soap formulations, comprising single and blended alkali sources, were produced with palm kernel oil, while a commercial laundry soap (Canoe Soap) served as the control. The elemental composition of the ashes was determined using Energy Dispersive X-ray Fluorescence (EDXRF), and the soaps were evaluated for pH, moisture content, Total Fatty Matter (TFM), Free Caustic Alkali (FCA), Total Alkali, foam height, and heavy metal content. Data were analyzed using one-way Analysis of Variance (ANOVA) and Tukey's HSD test at p < 0.05. Plantain peel ash contained the highest potassium oxide (K₂O) content (20.30%), followed by yam (17.17%) and cassava (5.16%). Significant differences (p < 0.05) were observed among the formulations for all physicochemical properties. The ternary blend (yam–cassava–plantain) produced the best-quality soap, recording the highest TFM (87.63%), greatest foam height (510 mL), acceptable pH (10.00), and safe FCA (0.19%), outperforming the commercial control. Heavy metal analysis showed that although the raw ashes contained detectable concentrations of some metals, the finished soaps contained non-detectable levels of Pb, Zn, and Cr, indicating that the aqueous extraction and saponification processes effectively minimized heavy metal transfer. The formulated soaps complied with WHO and Standards Organisation of Nigeria (SON) safety requirements. These findings demonstrate that agricultural waste-derived alkalis, particularly blended formulations, provide a safe, sustainable, and cost-effective alternative to synthetic alkalis for producing high-quality soap while promoting agricultural waste utilization and environmental sustainability.