Bentonites as Natural Sources of Thorium and Uranium

Abstract

Bentonites are natural reservoirs of various elements and are of interest because they are sources of thorium and uranium, which are transition elements that provide nuclear energy. The objective of this work was to study the plausible association(s) of these elements with other transition elements of interest. The contents of 18 transition elements (cerium, cobalt, chromium, copper, iron, hafnium, lanthanum, manganese, molybdenum, neodymium niobium, nickel, tantalum, thorium, uranium, vanadium, yttrium, zinc, and zirconium) in 38 bentonites determined experimentally by X-ray fluorescence spectroscopy (XRF) were analyzed. The contents of the elements were plotted in (x,y) graphs and then fitted to polynomial functions (orders 1 through 6). According to the coefficient of determination (r2: 0.5 ≤ r2 strong, 0.3 ≤ r2 ≤ 0.5 medium, and r2 ≤ 0.3 weak), the contents of thorium, uranium, niobium, and nickel related strongly, thus the presence of niobium and nickel served to predict the presence of detectable concentrations of thorium and uranium. The equations showing higher r2 values were 1. {Th} = 1e-6{Nb}5 − 3e-4{Nb}4 + 1.9e-2{Nb}3 − 5.4e-1{Nb}2 + 7.3{Nb} − 6.3, r2 = 0.53. 2. {Th} = −3e-8{Nb}6 + 9e-6{Nb}5 − 1e-3{Nb}4 + 4.7e-2{Nb}3 − 1.1{Nb}2 + 11.5{Nb} − 16, r2 = 0.54. 3. {Th} = 5e-6{Ni}4 − 1.5e-3{Ni}3 − 1.5e-1{Ni}2 − 5.8{Ni} + 9e+1, r2 = 0.49. 4. {Th} = −7e-8{Ni}5 + 3e-5{Ni}4 − 5.1e-3{Ni}3 + 3.4e-1{Ni}2 − 9.5{Nb} + 1e+2, r2 = 0.56. 5. {Th} = 2e-9{Ni}6 − 8e-7{Ni}5 + 2e-4{Ni}4 − 1.5e-2{Ni}3 − 7e-1{Ni}2 − 1e+1{Ni} + 1e+1, r2 = 0.60. 6. {Th} = −1e-4{U}5 + 1.3e-2{U}4 − 4.3e-1{U}3 + 5.7e-1{U}2 − 2e+1{U} + 5e+1, r2 = 0.54. 7. {Th} = 6e-6{U}6 − 9e-4{U}5 + 4.5e-2{U}4 − 1.1{U}3 + 1e+1{U}2 − 5e+1{U} + 1e+2, r2 = 0.64. 8. {U} = 8e-6{Nb}4 − 1.2e-3{Nb}3 + 4.8e-2{Nb}2 − 4.3e-1{Nb} + 6.8, r2 = 0.48. 9. {U} = 2e-7{Nb}5 − 4e-5{Nb}4 + 2.8e-3{Nb}3 − 7.6e-2{Nb}2 + 1.1{Nb} + 1.9, r2 = 0.5. 10. {U} = 1e-8{Nb}6 − 3e-6{Nb}5 + 2e-4{Nb}4 − 8e-3{Nb}3 + 1.3e-1{Nb}2 − 5.4e-1{Nb} + 5.4, r2 = 0.51. 11. {U} = 1.8e-1{Th} + 2.6, r2 = 0.49; {U} = 1.7e-3{Th}2 − 2.9e-2{Th} + 6.3, r2 = 0.60. 12. {U} = 2e-5{Th}3 − 1.7e-3{Th}2 + 1.4e-1{Th} + 4.5, r2 = 0.58; {U} = −5e-7{Th}4 + 2e-4{Th}3 − 1.5e-2{Th}2 + 5.5e-1{Th} + 1.5, r2 = 0.6. 13. {U} = −7e-9{Th}5 + 2e-6{Th}4 − 1e-4{Th}3 − 3e-4{Th}2 + 2.7e-1{Th} + 2.9, r2 = 0.6. 14. {U} = 2e-9{Th}6 − 8e-7{Th}5 + 1e-4{Th}4 − 8.1e-3{Th}3 − 2.4e-1{Th}2 + 15, r2 = 0.65. This study provided a joint experimental and theoretical approach to optimize the recovery of thorium and uranium and to save invaluable onsite and off-site natural resources and work time. The findings might expand on other studies reporting the quantification of transition metals on bentonite matrices. For instance, the concentrations of nickel reported in studies using bench techniques could serve as the basis to calculate the contents of thorium.