Iron clogging mechanism around injection wells during groundwater recharge in shallow iron-rich aquifer: insight from spatiotemporal evolution.

Iron deposits in the filters and porous media around injection wells could induce severe clogging, thereby limiting the sustainability of groundwater heat pump (GWHP) systems. During the water injection in shallow iron-rich aquifers, iron clogging exhibits both spatial and temporal evolution in terms of its composition and formation processes. This study employed a two-dimensional sand tank experiment with continuous multicomponent groundwater to explore the spatiotemporal evolution of clogging around the injection well. The results suggested that upper-layer clogging was dominated by high-crystallinity iron oxides, goethite, and lepidocrocite, primarily caused by oxidation corrosion of filter. The evolution of lower-layer clogging occurred in stages with distinct material-mechanism-impact relationships. The initial phase (0-15 days): clogging comprised of calcium carbonate and low-crystallinity iron oxides induced by oxygen enrichment and CO₂ depletion during the early injection period, causing a 10% hydraulic head difference to increase. Mid-stage (15-35 days): microbial aggregates, SiO₂, and lower-crystallinity iron oxides dominated as hydrodynamic shifts elevated pH and redox potential, accelerating microbial growth and iron oxide deposition, amplifying hydraulic head difference to 60%. Stabilization phase (after 35 days): biofilms and extracellular polymeric substances (EPS) secretion by microbial communities consolidated pore occlusion, sustaining stable hydraulic resistance. Each stage transitioned from abiotic mineral precipitation to biologically reinforced clogging, progressively restricting permeability through synergistic physicochemical and microbial processes. This study highlighted a novel understanding of the evolution of iron clogging within an injection well located in a shallow iron-rich aquifer, and proposed region- and stage-specific strategies for clogging mitigation and control.