Study On Compound Additive Of Electrolytic Manganese

At present, SeO2 and SO2 are both widely used as additives of electrolytic manganese at home and abroad. Although selenium additives have high current efficiency than sulfur compounds, the advantages of using selenium compounds are countered by the danger of selenium inclusion in the product at significantly higher levels(0.08%), and the purity of the products is usually less than 99.9%, at the same time, Se is toxic and dangerous to the environment. With the development of new materials, as magnetic materials for example, the demand for the purity of manganese have become increasingly highly, the application and export of electrolytic manganese with Se at high levels have been restricted. When SO2 was used as electrolysis additive, the purity of product is higher (Mn>99.9%), however, sulfur contained in product become the main impurity and is about0.04%, the current efficiency become lower than SeO2.The aim of this work is to develop mixed additives which are beneficial for the current efficiency and reducing sulfur content in manganese deposits. SO2 is used as the main additive with minimal dosage of plants, while compound A, B, C, D and inorganic ion E were chosen as auxiliary additives based on many literatures. Methods of galvanostatic electrolysis in laboratory installation, electrochemical techniques and electrolysis testing in plant were used in this study.The galvanostatic electrodeposition experiments for electrolytic manganese were carried out in a three-electrode diaphragm laboratory installation using synthetic electrolyte, which contains 0.309 g·L-1 SO2 and a series of amount of auxiliary additives A, B, C, D and E respectively. It's found that the effect of auxiliary additive A and B are better. When the amount of additive A is 0.75 mL·L-1, the current efficiency is 66.83%, and the sulfur content in products is only 0.017%, It was also noted that the anode sludge produced in anode chamber was less during the electrolysis progress when additive A was used. When the amount of additive B is 5mg·L-1, the current efficiency can reach 69.57%, and the sulfur content in products is 0.027%. However, without of any auxiliary additives, the current efficiency and the sulfur content are 65.3% and 0.029%, respectively. Influencing factors of current efficiency and the sulfur content in deposits were analyzed theoretically. The morphology of manganese electrodeposited with different additives was examined by SEM and XRD respectively. The SEM micrographs of Mn obtained in presence of additive A and C show large coarse clusters, while the SEM images of Mn with additive B, D, E and single SO2 show compact coatings made up of uniformly sized polygonal grains. XRD patterns corresponding to the manganese deposits obtained in the presence of these additives showed that the crystal structure of manganese deposits were allα-Mn, the crystal structure of deposits remains essentially unchanged with these different additives.Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were used to study the behavior of additives in the progress of manganese electrodeposition. Its mechanism was discussed by using the theory of electrodeposition and the basic principle of electrode kinetics. It's found that auxiliary additives presented in electrolyte made the reduction potential of Mn2+ become more positive, accelerated the electrode reaction rate by means of"ψ1 effect"and played a role in activating the electrode.Compound additives SO2-A and SO2-B were tested in plant. The result showed that these two compound additives had better performance than the additive which was actually used in the plant. Detection Methods of Mg2+ and Co2+ in electrolyte of the plant were developed. The maintenance and management of electrolyte process were introduced.