Characterization and regeneration of low-cost adsorbents for heavy metal removal: Insights from contaminant transport in Sri Lankan agricultural soils

Chronic Kidney Disease of unknown etiology (CKDu) is a major public health concern in the North Central Province (NCP) of Sri Lanka, where groundwater heavy metal contamination is suspected as a key contributing factor. This study investigates the mobilization and transport of in-situ heavy metals in agricultural soils from Medawachchiya and Horowpathana and examines the movement of artificially introduced Cadmium and Lead through soil column experiments. Four locally available, low-cost bio-adsorbents namely, Mahogany sawdust (MG-A), Jackfruit peels (JF-A), Rice husk (RH-A), and Coconut husk (CH-A) were evaluated for Cd²⁺ removal from synthetic groundwater. Among them, MG-A demonstrated the highest adsorption efficiency (73.12% for 80 mg/L and 92.2% for 10 mg/L), outperforming JF-A (60.07%), RH-A (36.73%), and CH-A (16.54%). Adsorbent characterization using FTIR, FE-SEM, and BET analyses revealed that surface functionality and porosity played key roles in adsorption performance. Regeneration studies showed that acid (HCl) treatment restored the adsorption capacity of MG-A by 91.49%, indicating strong reusability potential. The novelty of this research lies in integrating soil transport experiments with bio-waste-derived adsorbent development, providing a comprehensive understanding of heavy metal mobility and remediation. These findings demonstrate a sustainable, community-adaptable approach for mitigating Cd²⁺ contamination in groundwater, offering practical and scalable solutions to reduce CKDu risks in vulnerable regions.