Phase-field modeling of Microbially Induced Calcite Precipitation

Goal
The main goal of the project is to model and numerically simulate Microbially Induced Calcite Precipitation (MICP), first in droplet-based microfluidic devices and then in the pore space of porous materials, using the phase-field approach. MICP is a technique through which calcium carbonate (or calcite) precipitation is promoted by appropriate bacteria or microbes. These living species can produce urease, an enzyme which catalyzes the hydrolysis of urea into ammonium, bicarbonate and hydroxyl ions. The bicarbonate then reacts with the calcium ions (from the environment), resulting in the precipitation of calcium carbonate. The model and the corresponding numerical simulation tool can provide a useful complement to experimental investigations to gain insight and help realizing and optimizing carbon capture from existing construction materials.

Methodology
Our idea is to start from a basic phase-field model for precipitation and dissolution, neglecting for the moment the presence of bacteria. To this end, the first step is the definition of a sharp-interface model, characterized by the Fick’s diffusion equation in the liquid and two conditions at the moving interface: a balance law (balance between diffusion flux and reaction flux) and a kinetic law (relating the velocity of the interface to the reaction flux). The combination of these two conditions is the so-called Stefan condition (relating the velocity of the interface to the concentration gradient). The phase-field model (or diffuse-interface model) under investigation will then couple the diffusion process in the liquid with the chemical reaction at the interface. After validation, our model will be specialized for MICP with the support of experimental data.