The advantage of the in-situ Br⁻ diffusion experiments, which sets it apart from traditional diffusion studies , lies in its ability to dynamically provide micrometer resolution information of species concentrations in a non-destructive way and at selected time intervals during the ongoing evolution of the experiment. This allows fitting the experimental data while the experiment is still running (in-operando conditions) and adapt the model or parameters of the experiment in real-time, if necessary. It is this capability, made possible by the integration of 3D physics-based modelling, ML as a surrogate model, and optimization algorithms, that distinguishes the DT approach presented here from a conventional modelling approach. The modelling of the present Br⁻ diffusion experiment with non-sorbing Br⁻ ions is a necessary preliminary step in view of the calibration and further development of the DT approach to a more complex counter-diffusion experiment (using the same silicagel-filled capillary system) that includes chemical reactions (typically, CaCO3 nucleation and growth experiments).