Abstract
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 CO2 affects FHY surface sites at pH 6–9. Beside CO2, 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−1, 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.
Highlights
Ferrihydrite (FHY) is a well-known poorly ordered iron oxyhydroxide that forms in different terrestrial environments mostly under neutral conditions and acidic ones such as acid mine drainage [1,2]
At a particle concentration of 0.1 g L−1, only 40% of molybdenum was adsorbed and the adsorption equilibrium was achieved after 300 min
These results underline the higher affinity of vanadium compared to molybdenum for ferrihydrite surfaces at pH 7
Summary
Ferrihydrite (FHY) is a well-known poorly ordered iron oxyhydroxide that forms in different terrestrial environments mostly under neutral conditions (i.e., deep-sea hydrothermal systems, soils, rivers) and acidic ones such as acid mine drainage [1,2]. The most important characteristics of ferrihydrite are its small size and extremely high surface area, which leads to its high affinity to adsorb different cations and anions that could be considered contaminants. Adsorption is a process frequently used in wastewater treatment and depollution technologies, soil treatment procedures as well as occurring in natural systems with the impact of the geochemical cycling of elements. A good adsorbent, from a process engineer point of view, for environmental depollution purposes, has to feature the following characteristics: available/synthesis and non-expensive, environmentally friendly, distinct surface properties (i.e., surface area and charge properties), good selectivity for target pollutants and a high uptake capacity to provide superior pollutant removal efficiency from polluted waters and to be potentially reusable in multiple adsorption cycles.
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