Electrolytic manganese production is a cornerstone of many modern industries, from steelmaking to electronics. Traditionally, additives like selenium dioxide (SeO2) have been crucial for improving the efficiency and quality of the deposited manganese. However, concerns regarding selenium's environmental impact and product purity have driven research into more sustainable additive strategies. At NINGBO INNO PHARMCHEM CO.,LTD., we are committed to advancing these processes, and recent studies highlight the significant benefits of employing composite additives, particularly the synergy between sodium sulfite (Na2SO3) and selenious acid (H2SeO3).

The co-electrolysis process, which aims to produce both metallic manganese at the cathode and electrolytic manganese dioxide (EMD) at the anode simultaneously, presents unique challenges. Achieving high current efficiencies for both products while maintaining purity and minimizing energy consumption is a key objective. Conventional methods often rely on a specific concentration of selenious acid to enhance cathodic polarization, thereby inhibiting the hydrogen evolution reaction (HER) and promoting manganese deposition. However, using higher concentrations of SeO2 can lead to increased selenium content in the final product and pose environmental risks.

Research conducted by leading institutions demonstrates that incorporating sodium sulfite as an auxiliary additive can significantly mitigate these issues. When used in conjunction with a minimal amount of selenious acid, Na2SO3 acts as a powerful enhancer. Studies have shown that a composite additive ratio of H2SeO3 at 0.0175 g/L and Na2SO3 at 1.5 g/L yields optimal results. This combination leads to substantially higher cathodic and anodic current efficiencies compared to using selenious acid alone or with other auxiliary agents like sodium dodecyl sulfate (SDS). Specifically, current efficiencies can reach up to 84.59% for the cathode and 80.13% for the anode.

The mechanism behind this improved performance is multifaceted. Sodium sulfite's antioxidative properties help suppress the formation of dendritic crystal branches and enhance the glossiness and adhesion of the manganese coating. Crucially, it further suppresses the hydrogen evolution reaction (HER), a major competitor to manganese deposition, allowing for a lower overall concentration of selenious acid to be effective. This reduction in SeO2 usage is a significant step towards more environmentally friendly and cost-effective production. Furthermore, the composite additives promote the transition of manganese crystals from a less desirable γ-Mn to the preferred α-Mn phase, resulting in a smoother, denser, and more lustrous manganese deposit. The electrolytic manganese dioxide (EMD) produced also exhibits favorable characteristics, appearing as a uniform powder with consistent size and ε-type crystal morphology.

The effectiveness of these composite additives is further supported by electrochemical analysis. Cyclic voltammetry and linear scan voltammetry experiments indicate that the combination of H2SeO3 and Na2SO3 not only improves the manganese deposition potential but also increases the overall amount of manganese reduced. This translates to reduced voltage and energy consumption during the electrolysis process, with reported cathodic energy consumption as low as 4498.02 kW h t⁻¹ and anodic energy consumption at 3001.41 kW h t⁻¹. Such optimizations are vital for large-scale industrial applications.

At NINGBO INNO PHARMCHEM CO.,LTD., we continuously explore innovative solutions to enhance chemical processes. The findings regarding the synergistic effects of sodium sulfite and selenious acid offer a promising direction for the industry to achieve higher efficiency, superior product quality, and greater environmental sustainability in electrolytic manganese and EMD production. This approach represents a significant advancement in our understanding and application of specialized chemical additives for metal refining.