地圏・水圏の有害重金属挙動に対する粘土の役割(<特集>地球サブシステムとしての粘土圏の役割 : 環境親和物質としての粘土)

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Clays occur in the lithosphere as soils, sediments and weathered rocks. In addition, clays also occur in the hydrosphere in oceans, lakes and rivers. These clays play an important role in controlling geochemical cycling of toxic heavy metals, such as arsenic and lead, because clays have very large and chemically active surface areas on which toxic heavy metals can be adsorbed. Clay particles containing Fe oxyhydroxide are formed by the mixing of hot, oxygen poor hydrothermal vent fluids with cold, oxygen rich seawater in hydrothermal plumes associated with seafloor hydrothermal systems at mid ocean ridges. These clay particles can scavenge heavy metals as As from seawater during transportation away from the vents. Heavy metals then become fixed in deep sea marine sediments during the precipitation of Fe oxyhydroxides metal complexes. Deep deep sea marine sediments on oceanic plates are fated to be transported to island arcs and to be subducted into the deep crust where temperatures are much higher than the dehydration temperatures of clay minerals. During dehydration, heavy metals are relieved from clay particle surfaces. These heavy metals may then be carried upward with hydrothermal fluids generated by clay dehydrations resulting in the contamination of island arc crusts. These geological processes concerning clay metal interactions are keys for explaining why the crust of Japanese island, a typical island arc system, has elevated heavy metal concentrations. The interaction of heavy metals and marine sediment clay particles are also important to understand soil contamination processes on land by heavy metals. The clay particles will relieve As when the marine sediments subject weathering and pore water become alkaline due to carbonate dissolution.
日本粘土学会の論文
2003-03-28

地圏・水圏の有害重金属挙動に対する粘土の役割(<特集>地球サブシステムとしての粘土圏の役割 : 環境親和物質としての粘土)

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