Adsorption of uranium and thorium from aqueous solutions by the clay minerals montmorillonite and vermiculite

Abstract

The adsorption of uranium and thorium from aqueous solutions by montomorillonite and vermiculite has been studied. The uranium and thorium concentration of the solutions varied between 100 and 2000 ppm. The behaviour of vermiculite as adsorbent of uranyl ions was found to be identical to montmorillonite, whereas the quantity of the adsorbed hydroxy‐Th ions was much lower than its theoretical cation exchange capacity. The later is attributable to a blocking of vermiculite's cation exchange capacity by hydroxy‐Th islands adsorbed in interlayer. The adsorption phenomena studied by these two minerals appear to be of the Langmuir type. Similar studies were also performed using a synthetic ettringite (calcium aluminum sulphate mineral) and a synthetic aluminosilicate zeolite of the faujasite type. The short‐time behaviour of the ettringite and faujasite seems to be very similar to montmorillonite and vermiculite and also obeys to the Langmuir equation. On the other hand ettringite and faujasite were found to be very sensitive and unstable in the acid environment, where uranium and thorium exist as distinguished cationic species, and therefore cannot be used for adsorption studies of this type.