Aqueous speciation and pH effect on the sorption behavior of uranium by montmorillonite

Clay minerals occur widely in nature and play a very important role in agri culture, mineral recovery and chemical manufacturing. Among the many proper ties which affect clay behaviour, water binding and ion exchanging appear t o be the most important The study of the cation exchange capacity of soils is of great theoretical and practical importance since the CEC determines i n many ways the behavior of nutrients, chemical amendments, and many toxic compounds entering the soils. Sorption interactions with montmorillonite an d other clay minerals in soils are potantially important mechanisms for att enuating the mobility of heavy metal cations through the subsurface environ ment. In this work the cation exchange capacity (CEC) of montmorillonite fr om west Anatolia, and sorptions interactions with montmorillonite for atten uating the mobility of uranium were studied. The CEC value was found to be 77 meq/100 g montmorillonite. The relative importance of test parameters e. g., contact time, particle size, pH and U(+6) aqueous speciation was determ ined. The results show that sorption on montmorillonite is a funtion of pH depending strongly on the aqueous U(+6) species. It reaches a maximum at ne ar neutral pH(pH=7). At low and at high pH solutions the sorption values of uranium are poor. These sorption values were attributed to the formation o f aqueous U(+6) carbonate complexes in alkaline conditions and the ion-exch ange process between UO2+2 species and interlayer cations on montmorillonit e in acidic solutions.