Image analysis technique for quantifying fluorescein concentration profiles in clays

Abstract

The image analysis technique approach links the dye concentration and color intensity, enabling quantification of spatial and temporal dye dynamics in clay media. In this study, batch adsorption tests and two-dimensional diffusion experiments with three types of clays (kaolinite, montmorillonite, and bentonite) were conducted for quantifying the vertical distribution of fluorescein dye tracer to evaluate the feasibility of the image analysis technique. In clay domains, color intensities were measured using images obtained during diffusion experiments, and these intensities were converted to aqueous fluorescein concentrations. Concentration profiles simulated from a one-dimensional analytical solution agreed well with those measured by the LRV technique with a single-channel application for kaolinite (blue channel, EB = 0.94 and 0.96) and montmorillonite (green channel, EG = 0.99 and 0.91) in the early (31.1, 54.6 PVs) and later (75.7, 93.9 PVs) diffusion times, respectively. The single-channel application for the bentonite was appropriate for concentration ranges of 0 − 400 mg/L for the blue channel and 400 − 1800 mg/L for the green channel. For quantifying the bentonite concentration profile with a wide range of dye concentrations (0 − 1800 mg/L), multi-channel application (blue + green channels) was required. Measured LRV concentration profiles with the multi-channel application showed better agreement (EB+G = 0.94) with simulated concentration profiles from the analytical solution than those with the single-channel application (EB = 0.56). The results of this study offer guidance on the application of the LRV approach as a non-destructive optical dye measurement method to diffusion problems between high and low permeability zones.