clay and granite

Arsenic (As) migration and transformation in the supergene environment and eucalyptus planting have essential effects on ecology or even human health, respectively. However, the combined environmental impact of As migration and transformation and eucalyptus planting has not been studied. Here we report a case of soil As contamination caused by eucalyptus planting and address the fate of As in Longmen county, Guangdong Province, China. We found high As content in weathered arsenopyrite bearing granite or granite-derived soil, where a large area of eucalyptus is planted. The release of organic acids from eucalyptus roots promoted the electrochemical reaction of arsenopyrite to produce AsO

Topics: Arsenates; Arsenic; Arsenites; Clay; Eucalyptus; Humans; Minerals; Oxygen; Soil

The method of indoor artificial rainfall simulations was applied to compare the characteristics of runoff and sediment yield under different slope gradients (5°, 8°, 15°, and 25°) and rainfall intensities (30, 60, 90, 120, and 150 mm/h) for two kinds of different hillslopes with weathered granite and with exposed soils respectively from the laterite layer (L-soil) and sand layer (S-soil). The results show that the distribution of runoff yield significantly varied with soil types as the surface flow was predominant for L-soil while interflow was the main runoff form for S-soil. Both surface flow and sediment yield of L-soil was more than that of S-soil, and the changing trends for L-soil were more regular. The relationships between surface flow, sediment yield, and rainfall intensity can be expressed by power functions (R

Topics: China; Clay; Geologic Sediments; Rain; Sand; Silicon Dioxide; Soil; Water; Water Movements; Weather

The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (approximately 1 x 10(-3) M) and alkaline (pH > or = 8) waters.

Topics: Aluminum Silicates; Bentonite; Clay; Colloids; Hydrogen-Ion Concentration; Kinetics; Radioactive Waste; Refuse Disposal; Silicon Dioxide; Soil Pollutants, Radioactive; Water Pollutants, Radioactive

Hydrated bentonite is a very plastic material and it is expected to enter in the rock microfractures at the granite/bentonite boundary of a deep geological high-level waste repository. This process is enhanced by the high swelling pressure of the clay. Since bentonite has a very good sorption capability for many radionuclides, the displacement of the clay might lead to a "clay-mediated" contaminant transport into the rock. The aim of this work is to study the contaminant transport into granite microfractures using nuclear ion beam techniques, and to determine to what extent the clay can favour it. To do so, bentonite previously doped with uranium, cesium and europium was put in contact with the surface of granite sheets. Granite sheets contacted with non-doped bentonite and with radionuclide solutions were also prepared as references. This allowed analysing the differences in the diffusion behaviour of the three systems: clay, radionuclides and clay plus radionuclides. A combination of Rutherford backscattering spectrometry (RBS) and other nuclear ion-beam techniques such as particle-induced X-ray emission (PIXE) and microPIXE was used to study the depth and lateral distribution of clay and contaminants inside granite. It was also tried to evaluate not only the diffusion depth and diffusion coefficients but also the different areas of the granite where the diffusants have a preferential access.

Topics: Aluminum Silicates; Bentonite; Clay; Diffusion; Forecasting; Geological Phenomena; Geology; Radioactive Waste; Silicon Dioxide; Spectrum Analysis; Waste Management