Potential of Waste Basil Seeds for Gadolinium Ion Removal from Aqueous Solutions

This study examined the potential of waste basil seeds (BSs) calcined at 500°C or 1000°C (BS500 or BS1000, respectively) for gadolinium removal from aqueous solutions. Gadolinium ion adsorption onto the produced adsorbents was also assessed in relation to a number of parameters, including initial concentration, adsorption temperature, exposure time, and pH. Higher initial concentrations, adsorption temperatures, and exposure times (BS, BS500 ≒ BS1000) resulted in an increase in the quantity of adsorbed gadolinium ions; To further understand the adsorption mechanism, detailed analyses of elemental distribution and binding energy were conducted. According to the proposed mechanism, gadolinium adsorption onto BS1000 may involve an ion exchange process, wherein hydrogen ions from functional groups such carboxyl and hydroxyl groups on the surface of BS1000 are replaced by gadolinium ions. Additionally, the effects of coexisting ions on gadolinium adsorption were investigated, revealing that while monovalent cations did not impact gadolinium ion adsorption capacity, divalent and trivalent cations significantly reduced it. Finally, the desorption of gadolinium ions was tested using desorption agents such as distilled water, hydrochloric acid, and sodium hydroxide. The results revealed that a 100 mmol/L hydrochloric acid solution was particularly effective for desorbing gadolinium ions. Overall, BS1000 demonstrates promising properties as an adsorbent for gadolinium ion removal from aqueous solutions.