Irradiation effect on physico-chemical properties of clay minerals

Abstract The purpose of the present work was to study the exposure of various doses of γ-irradiation (10 5 , 10 6 , 10 7 , 3×10 7 Gy) on types and concentration of radiation-induced defects, deuteration, changes in specific surface and solubility of minerals irradiated in D 2 O solution in closed capsules. Some clay minerals (perfect and imperfect kaolinites, palygorskite, montmorillonite), muscovite, synthetic gibbsite and brucite were investigated. A sharp increase of the A- (Si–O − ) and B-centres (Al VI –O − –Al VI bridge) concentration in the dose interval 10 5 –10 7 Gy in both investigated kaolinites has been established. These concentrations are higher both in the initial and irradiated samples of well-ordered kaolinite. In irradiated palygorskite, montmorillonite and muscovite, such concentration is considerably lower than in kaolinites. The concentration of the A-centres and their stabilization are determined by the composition of the tetrahedral structural fragment of a mineral: kaolinite ([Si 4 O 10 ])>montmorillonite, palygorskite ([Al 0.5 Si 3.5 O 10 ])>muscovite ([AlSi 3 O 10 ]), and also by the presence of mobile water molecules on the surface and in the interlayer space of a mineral: perfect kaolinite (water molecules are practically absent)>imperfect kaolinite>montmorillonite (the maximum amount of water molecules). Concentration of the B- and B′-centres is even more sensitive in the presence of mobile water molecules in mineral like the A-centres concentration. In irradiated montmorillonite, the B′-centre was not found. The B-centre model has been refined: an unpaired electron in the B-centre in kaolinite (1:1 structure) is located on an oxygen ion of an outer OH-group, and in the B′-centre in minerals with 2:1 structure—on an inner OH-group. The deuteration begins at lower irradiation doses in those minerals, in which the maximum amount of the radiation-induced centres appears. The lower limit of the beginning of deuteration at small irradiation doses rises in the following sequence: brucite 3+ ions from kaolinite increases, but that of Si 4+ ions—decreases, for montmorillonite and palygorskite the inverse dependence takes place. It can be explained by the increase in the amount of the different types of radiation-induced defects in these minerals.