Diffusiophoresis-induced colloidal aggregation to inhibit mineral dissolution

In this work, we present a new mechanism of interaction between mineral dissolution and colloidal transport using microfluidic experiments. We show that diffusiophoresis, the movement of colloidal particles driven by solute concentration gradients, can direct colloids toward a dissolving mineral surface. A calcium carbonate piece exposed to an acidic flow in a microchannel is the source of a concentration gradient for diffusiophoresis.

The injected acid solution is seeded with microparticles. We observe an accumulation of negatively charged colloids near the mineral surface, leading to particle aggregation, which ultimately inhibits dissolution by forming a passivating layer. When diffusion dominates, we observe the diffusiophoretic migration of particles toward the dissolving mineral in good agreement with theoretical predictions. Under advection-dominated conditions, flow velocities exceed diffusiophoretic velocities by two orders of magnitude. In this regime, particles close to the source of concentration are driven by diffusiophoresis, while those farther away are transported by advection only. In this case, continuous acid injection maintains the concentration gradient over time, enabling the formation of a dense and stable passivation layer.

This new mechanism could be harnessed to turn undesirable processes, such as the dissolution of underground confinement barriers or the release of toxic compounds from contaminants trapped in the subsurface, into positive feedback, where the resulting concentration gradients drive colloids toward reactive zones for remediation.