| Summary: | Ferrihydrite, FHY, was synthesized and characterized for morphology, mineralogy, surface area, hydrodynamic diameter and surface charge properties before molybdenum (Mo) and vanadium (V) adsorption. The potentiometric titration results showed first direct evidence that CO<sub>2</sub> affects FHY surface sites at pH 6–9. Beside CO<sub>2</sub>, particles concentration may affect surface properties with an impact on adsorption performance. Additional new adsorption simulation results on theoretical surface coverage vs. experimental results obtained at varying particles concentration help theoreticians and experimentalists to better estimate and apply anion adsorption processes to real environments and suggest that simulation may not always be entirely reliable. Uptake capacities obtained experimentally, varying pH, particles and metals concentrations, were plotted to assess their synergetic effect and derive trends for future process optimization. Adsorption kinetics and isotherms were also considered. Experimentally derived values for maximum uptake capacities (0.43 and 1.20 mmol g<sup>−1</sup>, for Mo and V, respectively) and partitioning coefficients have applications, such as in making decisions for anions removal from wastewaters to achieve depollution efficiency or concentration required for effluents discharge and also implications in elements cycling from a geochemical perspective. In this work, the 3D plotting of the main adsorption process parameters obtained experimentally showed inter-correlations between significant process parameters that influence the adsorption process, and provides guidelines for its optimization and indicates that laboratory data can be transposed to real systems.
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