Moringa Seed Cake Biochar: A Novel Binder for Sustainable Remediation of Lead-Contaminated Soil

Abstract

The present investigation applies the stabilization/solidification technique for lead (Pb)-contaminated soil remediation utilizing an organic binder to negate the environmental consequences caused by inorganic binders such as cement. This research synthesized novel biochar by slow pyrolysis of moringa seed cake or de-oiled cake (waste generated after oil recovery) and tested its physicochemical characteristics, which revealed that it possesses a high pH and abundant surface functional groups that can act as potential adsorption sites for lead. Furthermore, the effects of biochar content (0% to 10% w/w) and curing time on the stabilization of soil contaminated with Pb at a concentration of 5,000 mg/kg were evaluated. The toxicity characteristic leaching test showed that treatment with 10% w/w biochar and 28 days of curing reduced Pb leachability to regulatory limits with over 89% immobilization efficiency. Moreover, the soil strength and the pH increased steadily with the biochar content and curing time while maintaining stability after 56 to 90 days of curing. Microstructural characterization revealed the underlying mechanisms in effectively stabilizing lead in soil, including precipitation, surface complexation with functional groups (C═O, O═C─ O), and lead encapsulation in calcium silicate hydrates (C─ S─ H).