Specific Surface Area by Colorimetry and Image Analysis

Specific surface area is more informative than grain size for fine-grained sediments where Ss > 1 m2/g. In fact, specific surface area plays a central role in engineering properties and processes in fine-grained soils, including pore size and bioactivity; fabric, plasticity, and rheology; hydraulic and electrical conductivity; compressibility and residual friction angle; and all forms of coupled processes. This research advanced a dye adsorption method using digital image colorimetry implemented with smartphone technology. In particular, this research adopted a water-based approach to reach internal surfaces in platy phyllosilicates, selected short dye molecules to reduce the range of potential molecular contact area, and developed a physics-based adsorption model to analyze the complete data set to minimize the uncertainty in specific surface area determinations. The study involved fine-grained soils with distinct mineralogy and specific surface area (from 1 to 600 m2/g) and various cationic dyes and a protein to explore the effect of molecular size, shape, and pH. Crystal violet emerged as a reliable dye for soil characterization. Time-dependent measurements confirmed second-order kinetics and highlight the importance of adsorption time.