Physics
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.2361l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 10, pp.2361-2386
Physics
47
Scientific paper
In this paper, we discuss the recent kinetic work on water-rock interactions. Standard activity-activity diagrams are reinterpreted, using a mass transfer kinetic model and recent data on the relative rates of mineral reactions. The development of a fully integrated rate law is discussed, with special attention to the important effects of deviation from equilibrium on the rates of mineral-water reactions. The combined effects of temperature, pH, ionic strength, and saturation conditions on the overall dissolution and precipitation rates of minerals must be properly described before any seriously quantitative model of coupled fluid flow and chemical reaction can be undertaken. A rate law that integrates these effects is proposed. The functional dependence of the rate on G r , the free energy change for the mineral reaction, is discussed, based on recent experimental work. An important result is the presence of a surface transition in the reaction mechanism leading to a very strong nonlinear dependence of the dissolution rates on G r . The possible role of dislocation defects in this surface transition is discussed. The relation of global weathering rates and geochemical cycles to the recent experimental and theoretical water-rock kinetic work is explored. The temperature effect on the silica content of streams is reevaluated. The variation of silica concentration with runoff in the rivers of the world is quantified, using a coupled fluid flow and reaction model and the full rate law developed for a proto-granite system by the kinetic experiments. Implications of the water-rock kinetic data for the current geochemical cycles models are discussed with especial emphasis on the link between physical weathering and chemical weathering.
Burch Timothy E.
Ganor Jiwchar
Lasaga Antonio C.
Nagy Kathryn L.
Soler Josep M.
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