Study On The Adsorption Behavior Of U(VI) And Th(IV) On Kaolin

Kaolinite is the most widely clay minerals in geologic enviornment which occurring 1:1 aluminosilicate. Both uranium and thorium are important radioactive heavy metal contaminants because of their long half time, obvious radioactivity and biological toxicity during nuclear fuel cycle and application of nuclear technology. So, it is essencial to understand the sorption and migration behavior of them on geologic body mainly contains clay minerals including kaolinite. In this work, the effect of contact time, pH, ionic strength, coexisting cations (Li+, Na+, K+)/anions (CO32-, SO42-, PO43-) and the humic substances (HA/FA) on the sorption of U(?) and Th(?) on kaolinite were investigated in batch experiments. The results showed that:(1) The sorption of U(?) on kaolinite kinetically accorded with the pseudo-second-order model. The behavior of sorption of U(?) on kaolinite was pH depended and coexisting cations/anions influenced the sorption greatly. Ion strength had little influnce indicated that surface complexation was the dominant sorption mechanism. HA could enhanced the sorption of U(?) at pH<6.0, while inhibited the sorption at pH>6.0. It was proved that there was relativity between the sorption of U(?) and the sorption of HA on kaolinite.(2) According to the kinetic experiments, the sorption of Th(?) on kaolinite could be interpreted by a pseudo-second-order model. The results indicated that pH and ionic strength influenced the sorption of Th(?) greatly. The co-existing anoions (CO32-, SCV2-, PO43-) had different influences on the sorption of Th(?). HA enhanced the sorption at low pH, while decreased the sorption as the increasing pH. The ion exchange and surface complexation are both the dominant mechanisms in the sorption of Th(?) on Kaolinite. Langmuir function fitted the experiment well with R2= 0.9939.Wide and overall factors were considered in the experiment designs and the factors had close integrations with the geology environment of nuclear facilities and nuclear waste disposal sites. The conclusion had certain reference value and guiding sence for making sorption-migration experiments of transuranien, designing of nuclear waste disposal sites and the safety disposal of nuclear waste.