Selectivity and affinity of heavy metals and radiometals for organic biomass: Implications for water remediation

Due to both natural and anthropogenic causes, waterways have a history of contamination with different heavy metals and radiometals. Among these, thorium (Th,) uranium (U,) arsenic (As,) and strontium (Sr) are noteworthy threats to humans due to chemical and radiological toxicity. Previous research has focused on inorganic materials to remove these metals. However, the use of recyclable and biodegradable waste materials to remove toxic metals has risen. This study seeks to use pistachio shells as a model for heavy metal selectivity and affinity for organic biomasses. The influence of kinetics and pH on selectivity/affinity of the shell for the metals was investigated. The individual metal affinity seen was Th > U > As > Sr. Selectivity for Th and U over As and Sr was seen at pH < 6, beginning to equalize at pH > 6. The maximum uptake for all metals tested occurs at pH 5 and t >= 2 h. Uptake of these metals follows pseudo-second order, intraparticle kinetics, and Freundlich isotherm. Finally, the selectivity of the shells for heavy metals was investigated using drinking water and seawater samples, with concurrent pronounced uptake of actinides and Sr being observed.