The pronounced toxicity and non-biodegradability of cadmium (Cd) necessitate effective adsorption-based remediation technologies. However, adsorption performance evaluated on pristine minerals may deviate substantially in non-sterile environments where mineral surfaces are rapidly colonized by microorganisms and biofilms. Here, a model bio-mineral interface (SiFhB) was constructed by immobilizing a heavy metal-tolerant bacterium (Cupriavidus sp. H200) onto microscale silicon-doped ferrihydrite (SiFh). SEM and FTIR confirmed successful colonization and the coexistence of mineral and biomass functional groups at the interface. Biocoating markedly reduced the BET specific surface area from 135.2 to 42.6 m2 center dot g-1, indicating a substantial loss of accessible mineral surface. Batch experiments under environmentally relevant variables (pH, ionic strength, and coexisting cations) showed that Cd2+ uptake by SiFhB is strongly condition-dependent and is inhibited by increasing ionic strength and by competing Cu2+, Zn2+, and Pb2+. Adsorption kinetics followed the pseudo-second-order model (R2 = 0.9999), suggesting chemisorption, and the isotherm was best described by the Langmuir model with a maximum capacity of 17.12 mg center dot g-1 (as-prepared composite mass basis). The pHdependent removal profile exhibited a mechanistic superposition of mineral Fe-OH sites and bacterial functional groups, demonstrating an adsorption-behavior shift induced by bio-coating. Overall, these results show that microbial coating can impose an apparent capacity penalty through site masking and biomass dilution, while altering the adsorption response of mineral-based adsorbents. This study provides a realistic framework for evaluating and managing biofilm impacts when translating mineral adsorbents from laboratory tests to nonsterile environments.