MEASURING ADSORPTION-ISOTHERMS USING CONTINUOUS, UNSATURATED FLOW THROUGH INTACT SOIL CORES

Conventional batch adsorption-isotherm experiments are conducted under conditions that are generally not representative of field conditions. Our objective was to develop and illustrate a technique that uses continuous, unsaturated flow through intact soil cores and gives information analogous to standard batch absorption experiments. Soil cores were placed on filter funnels and continuous flow was induced by controlled vacuum. Solution, 10 times the weight of the soil, was applied and recycled until apparent equilibrium concentrations were observed. While the total solution-to-soil ratio was 10:1, the amount in contact with soil at any instant was small. The procedure was replicated on separate cores with different initial solute concentrations to give different final equilibrium concentrations as a function of solute adsorbed per gram of soil. The technique was illustrated by observing adsorption of forest floor dissolved organic C to cores of AB horizon soil, and was compared with conventional batch adsorption data. Isotherms using both methods were linear but the slope of the batch isotherm was somewhat less. This flowthrough technique provides a way to obtain adsorption-isotherm data under more realistic conditions.