Unprecedented roles of submillimetric interelectrode distances and electrogenerated gas bubbles on mineral cathodic electro-precipitation: Modeling and interface studies

For the first time, the roles of submillimetric interelectrode distances (d(elec)) and electrogenerated gas on cathodic mineral electro-precipitation have been investigated, particularly under advanced electro-oxidation condition with boron-doped diamond (BDD) anode. The main objective was to understand how to limit or favor the magnesium hydroxide (Mg(OH)(2)) and calcium carbonate (CaCO3) deposits that progressively passivate the cathode surface during the electrolysis of effluent initially containing calcium (Ca2+), magnesium (Mg2+) and bicarbonate/carbonate (HCO3-/CO32-). As predicted by a new model taking into account the concomitant H-2 evolution reaction (HER), more mineral scaling (Mg(OH)(2) and CaCO3) was observed in decreasing order of d(elec) from 3 mm to 100 mu m at 4 mA cm(-2) . Contrastingly, no deposit was present at the lowest d(elec) (50 mu m), which was due to non-faradaic condition. The applied cathode potential (E-C) decreased with increase of d(elec), which intensified the H-2 gas bubbles production and minimized the electro-precipitation. Supplementary experiments with identical E-C highlighted the additional involvement of O-2 evolution at the anode towards the cathodic mineral scaling, whose role was intensified at submillimetric distances. Finally, novel predictive correlations have been proposed from impedance spectroscopy studies at cathode/electrolyte interface in order to link the charge transfer resistance (R-CT) and the double-layer capacitance (C-DL) with d(elec).

Automated summary

For the first time, the effects of submillimetric interelectrode distances and electrogenerated gas on cathodic mineral electro-precipitation have been investigated. The study found that decreasing interelectrode distance leads to more mineral scaling, while the applied cathode potential and gas production also play important roles.