Attention has been focused recently on the use of Moroccan black oil shale as the raw material for production of a new type of adsorbent and its application to U and Th removal from contaminated wastewaters. The purpose of the present work is to provide a better understanding of the composition and structure of this shale and to determine its natural content in uranium and thorium. A black shale collected from Timahdit (Morocco) was analyzed by powder X-ray diffraction and SEM techniques. It was found that calcite, dolomite, quartz and clays constitute the main composition of the inorganic matrix. Pyrite crystals are also present. A selective leaching procedure, followed by radiochemical purification and alpha-counting, was performed to assess the distribution of naturally occurring radionuclides. Leaching results indicate that 238U, 235U, 234U, 232Th, 230Th and 228Th have multiple modes of occurrence in the shale. U is interpreted to have been concentrated under anaerobic conditions. An integrated isotopic approach showed the preferential mobilization of uranium carried by humic acids to carbonate and apatite phases. Th is partitioned between silicate minerals and pyrite.

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Moroccan black shale was analysed for uranium and thorium isotopes using alpha-spectrometry. A sequential leaching procedure was used to define the speciation of isotopes of the actinides in the material. As in most other organic rich rocks, uranium is highly enriched in the black shale. This actinide is associated predominantly with humic acids. Thorium ( 232 Th) is a less mobile radionuclide in this environment as was expected from its chemical properties, and in agreement with the most widely adopted views in the published literature. It is partitioned between silicate minerals, pyrite and kerogen. ExperimentalSampling location -The black shale specimen used in this investigation was collected in the region of Timahdit located in the mid-Atlas mountains. The discovery of fossils in the formation has dated the black shale sequence to the Maastrichtian period [7]. The geology of the studied area has been extensively described by Benlioulhaj [8].

Moroccan black shale was analysed for uranium and thorium isotopes using alpha-spectrometry. A sequential leaching procedure was used to define the speciation of isotopes of the actinides in the material. As in most other organic rich rocks, uranium is highly enriched in the black shale. This actinide is associated predominantly with humic acids. Thorium ( 232 Th) is a less mobile radionuclide in this environment as was expected from its chemical properties, and in agreement with the most widely adopted views in the published literature. It is partitioned between silicate minerals, pyrite and kerogen.