Three-Dimensional Reactive Transport Modelling of Multi-Well Injection Strategy for MICP-Based Heavy Metal Immobilization in Contaminated Porous Media

Microbila induced calcite precipitation (MICP) evolved as a biogeo-technology for simultaneous immobilization of heavy metals and bio-cementation. In this study, a three-dimensional reactive transport model was developed in COMSOL Multiphysics, to study the immobilization of Pb2+ and Cd2+ coupled with MICP in contaminated porous media. The model is based on a unified hydro-biogeochemical approach, which includes: Darcy flow, advection–diffusion transport, microbial ureolysis, carbonate generation, Langmuir adsorption, and mineral precipitation. The numerical stability was checked by convergence study, CFL study, gravity field application, and Darcy velocity characterization. The gravity driven velocity for chemical species transport ranged in 1 × 10−6 m/s and allowed the reactive plume to penetrate to depths of up to 3 m as revealed by the simulation results. High concentrations of CaCO3 reached (about 2000 ppm) with sustained ureolysis resulting in extensive heavy metal immobilization. Heavy metal immobilization was achieved by coupled adsorption and carbonate precipitation, where the concentration of PbCO3 was around 1000 ppm, and CdCO3 was around 190 ppm.Observed precipitation order was CaCO3 > PbCO3 > CdCO3, which corresponds to the differences in geochemical affinity and mineralization potential. The proposed framework is effective and scalable for domain-wide heavy‑metal immobilization via multi-well telescopic injection simulation.