Model accounting for the Cr(III) electroprecipitation kinetics in an electrochemical reactor based on CFD and mass transport contributions

The present research proposes a comprehensive kinetic model for chromium removal in synthetic tannery wastewater using an electroprecipitation process. The experimental process is conducted in a rotating cylinder electrode reactor (batch) using TiO₂/RuO₂ as cathodes, and AISI 1018 carbon steel as anode releasing iron species which induce the electroprecipitation. The theoretical analysis considers the simultaneous solution of the Reynolds averaged Navier-Stokes (RANS), and kinetic-based mass conservation equation to describe the distribution of ionic species inside the reactor. The electrode kinetics describing the flux production of Fe²⁺ species on the anode is also considered under full electrokinetic control conditions (secondary current distribution). The model proposed here can explain the experimental Cr³⁺ and Fe²⁺ concentration profiles, as a function of RCE rotation rate and applied current density; and it reveals that the chemical homogeneous precipitation of iron chromite is the most predominant reaction, compared to other precipitation contributions. Kinetic and transport parameters are determined by the fitting of the model to experimental data. Rationalization of the electroprecipitation reactor design can improve the contact between electrogenerated Fe²⁺ and Cr³⁺ in the effluent, to optimize its removal through the manipulation of operating conditions (e.g. mixing, current density, electrode configuration).