Pore-scale investigation of a novel method for the remediation of trichloroethylene-polluted soils based on compositional ripening with pickering emulsions

This study introduces a novel in situ remediation strategy for soils contaminated with dense non-aqueous phase liquids (DNAPLs), focusing on trichloroethylene (TCE), using solid-stabilized (Pickering) emulsions. Beyond mechanical displacement, these emulsions are engineered to capture TCE via compositional ripening-a spontaneous, entropically driven mass transfer process that occurs when oil phases with differing chemical compositions come into contact or are separated by a continuous aqueous phase enabling molecular diffusion. Silica-stabilized emulsions with adjustable rheological properties (oil volume fraction from 0.01 to 0.21) were formulated and injected in water-wet micromodels containing TCE at its residual saturation, revealing a unique dual mechanism for TCE removal: shear-driven penetration into the pore network followed by gradual uptake of TCE into the emulsion droplets. Droplets swelling and phase redistribution confirmed the occurrence of compositional ripening, resulting in continued reduction of residual TCE saturation, even under static conditions. The proof of concept was done in batch experiments by monitoring the droplet size distribution of mixtures of TCE and emulsion. Micromodel tests confirmed high efficiency, with near-complete capture of capillary-trapped TCE. This dual-action process, combining physical displacement of the TCE with delayed physico-chemical capture under no-flow conditions, makes compositional ripening with Pickering emulsions a promising soil remediation approach.