Distribution of naturally occurring radionuclides (U, Th) in Timahdit black shale (Morocco)

Abstract

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.

Uptake of uranium and thorium by native and cultivated plants

“…There are numerous reports in literature on biogeochemistry of U and Th (Sheppard and Evenden, 1988;Mazor, 1992;Mortvedt, 1994;Voigt et al, 2000;Vera Tomé et al, 2002Thiry et al, 2005;Tsuruta, 2006;Galindo et al, 2007). Unfortunately, large part of available publications refers to the studies performed either in highly contaminated areas or in nutrient solutions that have been artificially 'spiked' with radionuclides.…”

Study of the partitioning of uranium and thorium in moroccan black shale

“…The substantially higher content in uranium (42.5 µg.g -1 ) is not surprising, since it is well established that black shale and sediments rich in organic matter deposited under reductive conditions are capable of scavenging redox sensitive elements such as Re, V and U [10]. According to SEM and X-ray diffraction [11], calcite, dolomite, quartz and clays constitute the main bulk composition of the inorganic matrix. This is an indication that chemical weathering is minimal.…”

Radium geochemistry in Na–Cl type groundwater in Niigata Prefecture, Japan

“…Black shale with high U concentration was found around the world although no available data for U and Th in black shale from Niigata Prefecture. For example, high U content and its 232 Th/ 238 U activity ratio of as low as 0.04 were reported in black oil shale obtained from Morocco (Galindo et al, 2007). If 226 Ra in Na-Cl type groundwater were derived from uraniferous rock with low 232 Th/ 238 U activity ratios, the 228 Ra/ 226 Ra activity ratios would be expected to become very lower (as discussed later).…”