Mathematical modelling of simultaneous nitrate and dissolved oxygen reduction by Cu-nZVI using a bi-component shrinking core model

This article proposes the aqueous system Cu-Fe(0)/NO3 − mathematical modelling through a classical shrinking core model, taking into account the presence of dissolved oxygen in the reaction medium and considering it in the model equation. In this work the nitrate reduction to ammonia was assumed to occur onto the lab-made bimetallic nano zero-valent iron (nZVI) surface, simultaneously with the nZVI consumption due to the oxidation carried out by dissolved oxygen. Kinetic tests were performed on synthetic nitrate solutions (0.5, 1, 1.5 mM) at stoichiometric Cu-Fe(0) nanoparticles concentration and the obtained data were interpreted through a bi-component shrinking core model. The nanoparticles were characterized through X-Ray powder Diffraction method at the end of the process to analyse the oxidation of the particles whereas nitrate, oxygen and Fe(0) concentration were monitored at different time steps of the experiments. The nitrate removal efficiency was close to 80% after 90 min of treatment and the oxygen concentration decreased very rapidly from about 8 mg L−1 to the asymptotic value of (<1 mg L−1). A non-linear regression of the obtained kinetic data allowed to estimate the kinetic and diffusional model parameters that were in line with theoretical considerations and experimental evidences.