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Abstract
The long-lived radionuclides in radioactive wastes have been
considered to be dangerous pollutants. They can migrate to groundwater
causing serious environmental problems [1]. Uranium and thorium are widely
spread elements throughout the environment. The main sources of uranium
and thorium are soils, rocks, tailings of some minerals processing activities,
black sand and seawater. In water most of the dissolved uranium (about 0.003
ppm) derives from rocks and soil that the water runs over. The most important
ores of uranium are tyuyamunite (Ca(UO2)2V2O8.8H2O), autunite
(Ca(UO2)2(PO4)2.8-12H2O), torbernite (Cu(UO2)2(PO4)2.8-12H2O), coffinite
(USiO4), uraninite (UO2) and pitchblende (U3O8). 232Th and other isotopes
such as 234Th, 230Th and 228Th are present in seawater. These thorium isotopes
are primarily produced by natural uranium isotopes (238U, 235U and 234U) that
are soluble in seawater [2]. The most important ores of thorium are thorite
(ThSiO4), thorianite (ThO2) and monazite [(Ce,La,Y,Th)PO4] [3,4]. Thorium
and uranium are elements in the actinides series. They are silvery metals that
are solids at room temperature and radioactive (each element has different
isotopes, which can produce different type of radiation).