Investigation of cesium sorption on biotite weathered by solutions containing different cations

Abstract:

Pyllosilicate minerals have higher reactivity than other silicate minerals and can control the mobility and distribution of nuclear element in both natural environments and nuclear waste sites. Radioactive ¹³⁷Cs is one of the important components of nuclear waste and, therefore, it is very important to obtain informations on the reation of ¹³⁷Cs with phyllosilicate minerals to estimate its fate in near-surface geochemical environments. We artificially weathered biotite with solutions containing different cations. 0.2 g of ground biotite samples were mixed with 50 ml of 1 M solutions of K, Ca, Na, Mg, Rb, and Cs. Our study shows that the cations in the solution have different effects on the Si release caused by the dissolution of plate of biotite and K release which is more affected by the ion exchange. Among cations, Na and Mg show the most significant effect on the weathering, which was verified by Si release, XRD, and SEM. Those two ions increase the weathering of biotite by the formation of expandable layers. However, the cations have different effects on the ion exchange. Generally, Na, Rb, and Cs have significant effects on the replacement of K from the interlayers. Those ions have the same charge as K and similar radius to that. The results of the sortion experiments of Cs on the weathered biotite imply that both plate weathering and cation exchange have different effects on the sorpion of Cs. The weathered biotite reacted with Na and Mg solutions which contain expandable layers, have the highest amount of Cs sorbed on biotite. However, the samples reacted with Cs, Rb, and K, which probably fit into the frayed edge sites, block additional sorption on the frayed edge site, show the lower amount of Cs sorbed on biotite.