Mitsuo Manaka

Experimental examination of the relationships among chemico‐osmotic, hydraulic, and diffusion parameters of Wakkanai mudstones

Sequential permeability and chemical osmosis experiments on Wakkanai mudstones were performed to explore the relationships between the semipermeability of clayey rocks and the hydraulic and diffusion parameters as well as the pore structure characteristics. The wide ranges in osmotic efficiency (0.0004–0.046) and intrinsic permeability (8.92 × 10−20 to 1.24 × 10−17 m2) reflect the variation in the pore size distributions of the Wakkanai mudstones. A regression analysis between osmotic efficiency and permeability shows that the osmotic efficiency is proportional to the inverse of permeability, suggesting that the permeability is indeed indicative of the degree of semipermeability. Osmotic efficiency was determined invariant with the effective diffusion coefficient for the Wakkanai mudstones (3.59–8.36 × 10−11 m2/s) due to their small osmotic efficiencies (≤0.046). The wide variation in osmotic efficiencies and pore structure characteristics of Wakkanai mudstones indicates that the nanoscale pores enable semipermeability in Wakkanai mudstones. However, the pressure evolution caused by chemical osmosis is limited by the connected wide pores that are the main conduits for water, thus dissipating the osmotic pressure buildup induced by the semipermeability of nanoscale pores.

Natural attenuation of dissolved uranium within a small stream of central Japan

In this study, we investigated the natural attenuation of the uranium (U) load in the surface water within a humid forest in Japan. Surface water and sediments that had accumulated behind dams in the area were investigated in terms of their mineralogy and chemistry. The chemistry of the surface water was analyzed by field measurements of pH, dissolved oxygen (DO) concentration, and electrical conductivity (EC), as well as laboratory analyses via inductively coupled plasma mass spectrometry and ion chromatography. We determined U levels in the surface water; the distribution of U in phases within the sediment was estimated using a sequential extraction procedure. The results of this investigation indicate that U, which within the study area is derived from pegmatites at a mine, is attenuated by uptake onto the surface of organic material and uptake by amorphous material that forms over time within the dammed sediments. The U concentration within the sediment was as great as 8 mg kg−1, whereas the downstream U concentrations and loads in surface water decreased from 1.69 μg l−1 and 11.0 mg min−1 to 0.115 μg l−1 and 2.31 mg min−1, respectively.