Impact of Mixing-Driven Calcite Precipitation on Solute Transport: Laboratory Visualization and Tracer Test Analysis

Understanding the effects of mixing-driven precipitation on solute transport behavior is critical for reactive transport predictions, yet its complexity, arising from the interplay of flow dynamics, solute transport, and geochemical reactions, remains a significant challenge. In particular, mineral precipitation modifies the hydraulic properties of porous media. The impact of this process on the solute transport behavior remains largely unexplored and is crucial for accurate reactive transport predictions. This study presents a controlled laboratory investigation of mixing-driven calcite precipitation (MDP) in an intermediate-scale Hele-Shaw cell, simulating a coarse-sand porous medium. The experiment allowed for direct visualization of the spatiotemporal evolution of precipitation while continuously monitoring hydraulic properties. Self-organized heterogeneities in the precipitate structure were observed, with calcite layers forming symmetric patterns aligned with the main flow, contrasting with the asymmetry predicted by a semi-analytical model under idealized conditions. Tracer tests conducted before and after precipitation demonstrated significant impacts on solute transport, including the emergence of strong anomalous transport features, such as earlier solute arrival, a distinct double peak, and pronounced tailing. These findings highlight the critical role of precipitation-induced heterogeneities in shaping transport behavior, emphasizing the need to integrate these dynamics into reactive transport models for improved predictive accuracy.