Colloidal interactions of thorium
Abstract
Some organic and inorganic colloids have a strong affinity to bind radionuclides, and therefore, enhance their mobility. This study attempted to determine the interactions of thorium with colloidal humic acid and colloidal silica under various aqueous conditions and organic carbon from Blue point, Muddy, and Rogers Springs. A colloidal distribution study was done in spiked Lake Tahoe and Mono Lake samples. Plutonium was studied as an example for other radionuclides. Based on these studies, both thorium and plutonium were associated mostly with particles smaller than 0.45{dollar}\mu{dollar}m. Humic acid and organic carbon were found to have little influence on thorium speciation at pH 6 to 8. Thorium complexation was dominated by the hydrolysis and polynuclear species of thorium. The dissociation of thorium from colloidal silica surfaces, as studied by ligand promoted dissolution, could potentially follow the following reaction scheme:{dollar}{dollar}\eqalign{\rm Th{-}S + Xyl&{{\rm k\sb1\atop\longrightarrow}\atop{\longleftarrow\atop\rm k\sb{{-}1}}}\rm Th{-}S{-}Xyl\ (fast)\qquad\rm Where\ S{=}Colloidal\ silica\cr \rm Th{-}S{-}Xyl &{{\rm k\sb2\atop\longrightarrow}\atop{\longleftarrow\atop k\sb{-2}}} \rm Th{-}Xyl + S\ (slow)\cr}{dollar}{dollar}.