A simplified technique for measuring diffusion coefficients in rock blocks

This study demonstrates a simple laboratory method to measure diffusion coe fficients of reactive and nonreactive solutes in rock blocks. A demonstrati ve diffusion measurement device consists of a small plastic cell with magne tic stirrers, the porous rock block to be measured, and nonreactive tracer solution. Concentrations of the tracer (as specific conductance) are measur ed in the cell continuously with data recorded using a PC. The specific con ductance versus time data are fitted to an analytical solution that is nume rically inverted to estimate the diffusion coefficient. Mathematical develo pment is demonstrated, and a sensitivity analysis shows that diffusion coef ficient as low as 10(-9) cm(2)/s can be measured over a test period of 12 d ays.