Gluconic acid as the supplementary additive realizing high-efficiency production of metal manganese with decreased dosage of toxic selenium dioxide

Abstract

Minimizing the dosage of toxic SeO2 additive in electrolyte for electrochemical deposition of metal manganese without compromising the current efficiency has long been the desire for electrolytic manganese industry. Herein, by combinative usage of SeO2 and gluconic acid (GlcA) as the composite additives, 50 % of SeO2 dosage can be cut down while the current efficiency can be increased from 67 % to 90 % at the same time, realizing the energy consumption being reduced by 23 % at the optimized concentration of 1.84 g/L GlcA. The electrochemical tests and electrode surface characterizations as well as density functional theory calculations jointly imply that the addition of GlcA can greatly increase the diffusion coefficient of Mn2+ from 1.5 × 10−6 cm2/s to 5.6 × 10−5 cm2/s, accelerating the approaching of Mn2+ towards the electrode surface by decreasing the diffusion barrier energy from 17.93 kJ/mol to 11.51 kJ/mol. On the electrode surface, the SeO32− is responsible for facilitating the electrochemical deposition of metal Mn by forming the MnSe intermediate while GlcA is in charge of restraining the activation of H2O molecule for inhibiting H2 generation, synergistically contributing to the efficient production of electrolytic metal manganese. The results can provide new insights for the environmentally friendly and high-efficiency upgrading of manganese industry.