Clay minerals, radioactivity

In addition to cosmic ray spallation also produces many other radioactive nuclides. °Be is another example. Once cosmogenically produced, atoms of °Be are rapidly removed from the atmosphere by meteoric precipitation, and are absorbed onto surfaces of solid particles such as clay minerals. Hence, newly formed marine sediment contains some initial concentration of °Be. After removal from the atmosphere, the concentration of °Be in sediment decays away by p-decay to °B with a half-life of 1.51 million years (and a decay constant of 4.59 X 10 yr ). 

The origin of Aeolian dust from Chinese desert to Japanese islands was studied with ESR of dust, mostly fine grains of quartz.132 Suspended particulate matter (SPM) collected by environmental protection agency was measured with ESR.133 Dust soot of automobiles was also measured to check the motor combustion rate. Adsorption of NO, Mn2+ and Gd3 on clay minerals, bentonite and se-piolite134 has been studied using paramagnetic ions as tracers for radioactive elements. And studies have been carried out on how divalent and trivalent cations diffuse and blocked by surrounding clay minerals, in the context of their leak from nuclear waste repository to the environment.135... 

G. D., "Sorption Behavior of Trivalent Actinides and Rare Earths on Clay Minerals," ACS Symposium Series on Radioactive Waste in Geologic Storage, R. F. Gould, Ed., Miami Beach, Florida, Sept. 11-15, 1978. 

The first term on the right-hand side of equation (2.14), termed the rate factor, represents the direct contamination of herbage by fallout during the growing season. The second term, lag rate factor, is the contribution from the previous year s fallout. This includes the contribution of uptake from the surface soil and matt and also the effects of carry-over of silage and other feeding stuffs from one year to the next. The third term, soil factor, represents the contribution of root uptake, allowing for radioactive decay and reduced availability as nuclides move down the soil profile and become fixed to clay minerals. 

Nagy, N. M., J. Kdnya, and Gy. Wazelischen-Kun. 1999. The sorption and desorption of carrier-free radioactive isotopes on clay minerals and Hungarian soils. Coll. Surf. 152 245-250. 

Dumat, C., and Staunton, S. (1999). Reduced adsorption of caesium on clay minerals caused by various humic substances. J. Environ. Radioact. 46, 187-200. 

The radioactive chromium (51Cr) found in Columbia River sediments contaminated with effluent from a nuclear reactor facility was not released by the major cations of sea water or by 0.05 M CuS0424 . The results of previous work in this laboratory (New England Aquarium) showed that of the silver(I) and cadmium(II) adsorbed on the clay minerals kaolin and montmorillonite, in essentially deionized water, less than half was desorbed on mixing with sea water25 . One may postulate from results such as these that most of the heavy metals occluded within a complex organic... 

Montmorillonite has a high CEC value, but kaolinite and chlorite without interlayer cations have low CEC. Clays with high CEC play a leading role in the electrical conduction of shales and shaly sands (see Section 8.5). In case of radioactive ions , the abiUty of clay minerals to adsorb ions results in a contribution to natural radioactivity (see Section 5.2) (Table 1.2). 

Controlled by transport and sedimentation processes and the chemical environment, uranium occurs in both detrital and chemical sediments (shale, sandstone, conglomerate, carbonate) and is also common in tuff and phosphates. Carbonates rich in organic matter that form under reducing conditions are often very high in uranium. These radioactive carbonates are often productive reservoirs. Uranium is also adsorbed by clay minerals excessively high uranium content in shales indicates source rock (Baker Adas, 1985). 

Thorium and potassium are the mineral significant radioactive components. Clay minerals (and mica and feldspar) are characterized by different ratios of the two elements or a different position in a thorium versus potassium plot (Fig. 5.8 upper figure). This can be used for an estimate of dominant clay mineral in a formation and also for detection of mica or feldspar. 

Some aluminosilicate minerals appear to meet the above criteria rather well, especially with regard to low leachability and chemical and physical stability 1, 2). A low-temperature process for converting the wastes to aluminosilicates with low leachability has now been found (3). Aqueous waste solutions containing NaOH, NaNOa, NaN02, NaAl02, mixed fission products, and minor amounts of other salts are mixed with powdered clays (kaolin, bentonite, halloysite, or dickite) and allowed to react at 30°-100°C to form small crystals of the mineral cancrinite. The sodium aluminosilicate crystal lattice of cancrinite contains large amounts of trapped salts and radioactive fission products. The process is applicable to caustic radioactive liquids such as neutralized Purex wastes or to salts or oxides produced by evaporation or calcination of these liquid wastes. 

Hydrological models that treat fluid behavior in sedimentary environments that lie under some kilometers of overburden are likely to require much greater time spans than is customary in studying near-surface processes. The longer-lived isotopes of transuranic elements and their daughters present in buried radioactive waste will persist for several million years (Bredehoeft et al., 1978). An example of a substance that needs, in principle, to be retained indefinitely because of the strict limits set upon its allowable concentration in drinking water is nitrate, an anion that is unfortunately not adsorbed effectively by clays and other common subsurface minerals. 

The issue in coal mines is less complicated coal mines are so far underground that groundwater is full of minerals that contain radium. The mining process often channels these underwater flows to the surface, where excess radium can accumulate. Research into sulfate used in treatments has found, however, that certain natural clays preferentially absorb radium. Strategic placement of the clay can allow for collection and removal of radioactive isotopes. 

Thermoluminescent dating (TL). This technique is useful for dating pottery and ceramics (Wagner et al, 1983). It is based on the cumulative effect of radiation from disintegrating radioactive isotopes present in minerals of most rocks, clays and soils. The ionizing radiation may cause electrons to detach from their parent atom and become trapped in lattice defects of the material. As the material ages, defects accumulate. When a ceramic object is fired, trapped electrons are freed and, since radioactive minerals are incorporated in the object, defects start to accumulate again. 

Restoration of the protective properties of artificial sorption screens created on the ways of radioactive nuclide naigration from accumulating ponds is no less an important problem. Usually, clay soils with high sorption ability and containing such minerals as smectite and illite are applied for constructing such screens. In addition, artificial protective screens made of other disperse soils (from sand to loam) are applied the sorption ability of such soils is artificially enhanced beforehand with strengthening compoundssuch as oxalic silica-alumina gel. These compounds decrease the filtration ability of the screen and raise its sorption characteristics. 

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