The application of food/agro-waste and spent household products for the environmentally benign separation of thorium

The cost-effective and environmentally benign separation of thorium from an aqueous acidic medium using spent food/agro-byproducts has been demonstrated utilizing used tea leaves, coffee powder, and coconut leaves. The presence of carbonyl functionalities, hydroxyl moieties, and amine moieties was found to be responsible for coordinating with Th4+ ions, while rough sorbent surfaces provide more surface area for Th4+ ions to interact with. The Langmuir isotherm model was found to be applicable, involving monolayer sorption, without any neighboring-group participation, and chemisorption. Pseudo-second-order rate kinetics were revealed, with rate constants for thorium sorption of 3.4 × 10−6 mg g−1 min−1, 2.7 × 10−5 mg g−1 min−1, and 1.9 × 10−5 mg g−1 min−1 for coconut leaves, tea leaves, and coffee powder, respectively. The sorption process was thermodynamically favourable, having ΔG0 values of −5.91 kJ mol−1, −8.60 kJ mol−1, and −7.22 kJ mol−1 for coconut leaves, tea leaves, and coffee powder, respectively. The sorption processes were endothermic in nature (ΔHcoconu0t leaf = 3.30 kJ mol−1, ΔH0tea leaf = 6.33 kJ mol−1, and ΔH0coffee powder = 3.70 kJ mol−1). The overall enhancement in entropy (ΔS0coconut leaf = 0.03 kJ mol−1 K−1, ΔS0tea leaf = 0.04 kJ mol−1 K−1, and ΔS0coffee powder = 0.04 kJ mol−1 K−1) showed the spontaneity of the process. Upon exposure to 100 kGy gamma radiation, the Kd values for thorium were reduced to ∼49.9% of the original values for coconut leaves and tea leaves, while Kd was reduced to 40.4% of the original value for coffee powder.