町田 基

Heavy metal removal from aqueous solution onto activated carbons (ACs) by adsorption is briefly reviewed from the aspects of the structure, surface chemistry of ACs, and temperature and pH of aqueous solutions based on our previous studies. Oxygen and nitrogen atoms on the AC surface play an important role as well as solution pH for the adsorption of the heavy metal ions on ACs. In spite of the small uptake amounts of heavy metals indicated so far by ACs, there seems to be much room to study for increasing the adsorption capacity. ACs would still have a high potential for the removal of ionic pollutants in aqueous solution due to their availability and easy regeneration.

Activated carbons (ACs) oxidized and out-gassed were prepared by introducing acidic functional groups in the warming nitric acid and eliminating them in He flow at 1000^oC, respectively. Adsorption time course of 4-chlorophenol (4CP) on the carbons was examined in aqueous solutions. Though any significant pH variation could not be observed for the oxidized AC, the pH for the out-gassed AC obviously decreased as a result of concurrently releasing chloride ions from the carbon surface into the aqueous solution. Measuring surface functional groups on the 4CP adsorbed carbon rinsed with methanol to thoroughly remove physically adsorbed 4CP indicated that the hydroxyl groups increased by 2.5 times as many as the released chloride ions, and the basic sites decreased in contrast. 4CP is estimated to degrade on the out-gassed carbon, releasing chloride ions in the aqueous solution and forming chemical bonding between decomposed phenolic compound and some basic sites on the surface.

The turbidity maximum (TM) is a special region where the maximum concentrations of suspended particulate material (SPM) occur relative to SPM concentrations both upstream and downstream of an estuary. Therefore, SPM concentrations show a specific distribution in an estuary. Published observations of SPM concentrations within a short, weakly tidal, and microtidal estuary are not sufficient. We investigated longitudinal and vertical distributions of SPM and salinity at spring and neap tides in the weakly mixed, microtidal MIYAKO river estuary. The maximum concentration of SPM in the water column of the tidal area occurred at a constant distance from the mouth of the MIYAKO river estuary at ebb tide. The phenomena of the maximum concentration of SPM in the water column of a tidal area do not correspond to the definition of TM. The distance of the maximum concentration of SPM from the river mouth is not affected by tidal range. The maximum concentration of SPM in the water column of a tidal area increases with tidal range. The order of the maximum concentration of SPM in the MIYAKO river estuary is comparable to that in other microtidal estuaries. We presumed the export of SPM in the MIYAKO river estuary is comparable to that in other microtidal estuaries We presumed the export of SPM in the MIYAKO river from our own investigated data.

濁水のような密度が高い流体が水域へ流入すると, 水域内では流体の濃度差によって密度流が発生し, 拡散, 混合および余剰となった水の流出が起こる.水域からの流出水の密度が一定の密度範囲に制限されている場合には, 流入水が流出水に及ぼす影響を予測する必要がある.本研究では, 水域のモデル実験設備を用いて水域内の密度流の拡散と混合の特性を調べた.水域内で発生する密度差は, 流入直後に形成される密度流厚さよりも, 水域内の流出側の壁で反射された後の密度流厚さに大きく影響を及ぼすことが判った.高密度流体が流入した後の水域内の密度変化および流出部での越流水の密度は, 水域の長さ, 時間, 浮力のフラックスの関数として表せることを次元解析により明らかにした.さらに, 越流水の密度を混合希釈度合いと時間を用いて次元解析に基づき, 時間を変数とした実験式を導いた.

Joint Research on Environmental Science and Technology for the Earth