Selective biosorption of thorium (IV) from aqueous solutions by ginkgo leaf

Low–cost biosorbents (ginkgo leaf, osmanthus leaf, banyan leaf, magnolia leaf, holly leaf, walnut shell, and grapefruit peel) were evaluated in the simultaneous removal of La(3+), Ce(3+), Pr(3+), Nd(3+), Sm(3+), Eu(3+), Gd(3+), Yb(3+), Lu(3+), UO(2)(2+), Th(4+), Y(3+), Co(2+), Zn(2+), Ni(2+), and Sr(2+) from aqueous solutions. In single metal systems, all adsorbents exhibited good to excellent adsorption capacities toward lanthanides and actinides. In a simulated multicomponent mixed solution study, higher selectivity and efficiency were observed for Th(4+) over other metal cations, with ginkgo leaves providing the highest adsorptivity (81.2%) among the seven biosorbents. Through optimization studies, the selectivity of Th(4+) biosorption on ginkgo leaf was found to be highly pH–dependent, with optimum Th(4+) removal observed at pH 4. Th(4+) adsorption was found to proceed rapidly with an equilibrium time of 120 min and conform to pseudo–second–order kinetics. The Langmuir isotherm model best described Th(4+) biosorption, with a maximum monolayer adsorption capacity of 103.8 mg g(–1). Thermodynamic calculations indicated that Th(4+) biosorption was spontaneous and endothermic. Furthermore, the physical and chemical properties of the adsorbent were determined by scanning electron microscopy, Brunauer–Emmett–Teller, X-ray powder diffraction, and Fourier transform infrared analysis. The biosorption of Th from a real sample (monazite mineral) was studied and an efficiency of 90.4% was achieved from nitric acid at pH 4 using ginkgo leaves.