Observation of proton diffusion in porous media using pH-imaging technology

We propose the application of pH-imaging technology to the observation of p roton transport in porous media. A flat pH-imaging sensor based on the elec trochemical-semiconductor principle was employed for imaging. Porous media were formed by packing particles with a few hundred-micrometer diameter suc h as silica sands, glass-beads and ion-exchange resins. These particles wer e packed on the pH-imaging sensor, respectively, followed by the addition o f an acid solution from the top surface of the layer. The pH distribution f ormed on the interface between the sensor and the layer was repeatedly imag ed with a 3 min time resolution. The dependence of proton transport on the particle type and size was clearly imaged and quantitatively evaluated. The proposed method was confirmed to be useful for understanding mass transpor t in porous media, thus enabling contribution to fundamental research invol ving the transport of chemicals in soil/aquifer/reservoir, such as bioremed iation and microbial-enhanced oil recovery (Microbial EOR).