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KINETICS OF CHEMICAL WEATHERING IN B-HORIZON SPODOSOL FRACTION
Citation:
Asolekar, S., R. Valentine, AND J. Schnoor. KINETICS OF CHEMICAL WEATHERING IN B-HORIZON SPODOSOL FRACTION. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-92/454.
Description:
Studies on a B horizon soil from Maine have been conducted to etermine the weathering rate dependence on hydrogen ion concentration in soil solution. Effects of soil concentration and solution chemistry on chemical weathering rate were also investigated. he studies used a laboratory pH-stat semicontinuous reactor at pH 2.7 and 3.5 for two concentrations of B horizon soil. Homogenized B horizon soil in the size range 63-125 Km was washed in deionized water and acetone and used without further treatment. Results obtained from titrations of 10, 30, and 100 g/L of soil at a constant pH of 2.7 suggest the weathering rate, expressed in ueq H+/hr/g soil, does not depend on the soil concentration in the pH-stat reactor. To test the effect of solute concentration on weathering rate, experiments were performed at two different concentrations of accumulated solutes. Weathering rates were the same at both solute concentrations, indicating that significant back reactions were not likely occurring. Weathering rate at pH 2.7 was estimated in the range 0.53-0.93 beg H+/hr/g soil, at pH 3.0 as 0.52 beg H+/hr/g soil, at pH 3.5 as 0.36 Keg H+/hr/g/soil, and at pH 4.0 as 0.04 beg H+/hr/g soil. Assuming a weathering rate proportional to (H+)m, the fractional order m was determined to be approximately 0.8. Results echanism.