Modeling solute transport by centrifugation

Graduation date: 1988Measurement of physical and chemical solute transport\ud properties of a soil/waste system is necessary to predict\ud pollutant migration in soils. The adsorption component of\ud solute transport is most often determined in the laboratory\ud by performing column studies and batch equilibrium tests.\ud Both of these methods suffer from disadvantages. Batch\ud equilibrium tests performed with dilute solids concentrations overestimate the sorption distribution coefficient due\ud to the solids effect and column studies with fine grained\ud soils require a long period of time to conduct. An alternate to these methods involves the use of a constant head\ud permeameter that fits in a laboratory centrifuge. Centrifugation\ud testing alleviates the disadvantages of batch\ud equilibrium and column methods by imposing a confining\ud stress in the soil sample at a solids concentration similar\ud to that in the field and producing a greater pore water\ud velocity.\ud The centrifugal technique was evaluated by conducting experiments with a kaolinite soil/chloride solute system\ud under different conditions of inertial acceleration and\ud column size. Sorption distribution coefficients, Kd's, were estimated by modeling the generated solute breakthrough\ud curves with a solute transport curve fitting program. The\ud results produced almost identical Kd values for the range of\ud inertial accelerations and column sizes considered in the\ud program.\ud Another set of centrifuge experiments was conducted\ud with phenol solute. Kd's determined in the centrifuge were\ud compared with values measured in batch equilibrium tests\ud performed with the same materials. Although the Kd values\ud determined in the centrifuge were lower than the values\ud predicted by extrapolating the batch sorption data, the\ud results were consistent with the solids effect. The introduction of a parameter which takes into account the surface\ud area of the solids demonstrated a better correlation between\ud the centrifuge and batch data. However, these tests tech\ud niques are fundamentally different and a strong correlation\ud between the two was not expected.\ud With the centrifuge technique developed, physical and\ud chemical sorption data can be generated in fine grained\ud soils with respect to: sorption mechanisms of various\ud compounds, sorption kinetics, the solids effect and the\ud effects of pH, ionic strength, and confining stress