Decoupling mass transfer steps in fluoride electrosorption kinetics using a Rotating Packed Electrode

Electrosorption has emerged as an efficient and sustainable technology for the removal of pollutants from drinking water. In this work, fluoride removal was achieved through electrosorption using activated carbon impregnated with lanthanum under forced-flow conditions that simulate a continuous process, aiming to approximate the material's performance under realistic operational scenarios. These hydrodynamic conditions were replicated using a 3-D Rotating Packed Electrode (RPE) as the working electrode, whose configuration in a three-electrode cell was designed through computational simulations. The effects of key experimental parameters: rotational rate, initial fluoride concentration, and pH on the electro-assisted adsorption process were investigated. The controlled hydrodynamics provided by the RPE decreased the time required to reach adsorption equilibrium from 60 min under static conditions to 40 min at 2000 rpm, yielding an adsorption capacity of 3.33 ± 0.08 mg/g and an adsorption rate of 50.4 ± 0.8 mg/g·h at pH 6 with the La(III)-modified carbon electrode, outperforming the pristine activated carbon. Furthermore, the implementation of the RPE allowed the identification of three pseudo-equilibria in the kinetic profile and enabled the proposal of a mass transfer mechanism for both materials, which supports the correlation of equilibrium times from batch experiments with residence times in continuous systems. • CFD simulations allowed designing the Rotating Packed Electrode (RPE). • The RPE enables defining fluoride adsorption kinetics and equilibrium times. • Adsorption equilibrium on La-AC drops from 60 to 40 min at 2000 rpm. • Electrosorption equilibrium on La-AC drops to 30 min at 2000 rpm.