Precision Periodate Spectrophotometric Method for Determination of Manganese in Manganese Ores

Abstract

The main objective of this work was to develop a rapid and precise Spectrophotometric method to determine manganese content in manganese ores to replace the slow and tedious conventional methods. Ten Sudanese manganese ores were collected from different localities. A complete chemical analysis was carried out using different methods. Manganese content results ranged from 16.9% to 54.5 %. For comparison, total manganese content was determined by the volumetric Vo1hard method and the developed periodate spectrophotometric method. Sample decomposition was carried out by two methods, conc. hydrochloric, and nitric, perchloric, hydrofluoric and hydrochloric acid mixture. This 4-acid digestion is a rapid, powerful procedure suitable for preparing solution for manganese determination by both volumetric and spectrophotometric methods, especially in ores of high barite content. The developed colorimetric method utilizes potassium periodate to oxidize manganese (II) ion in sulphuric – phosphoric- nitric acid mixture to intensively colored manganese (VII) ion. The absorbance was measured at 525nm. The method gave accurate, precise results with a coefficient of variation of 0.184%, which is comparable to that obtained from the Volhard volumetric method, 0.187%. No statistically significant differences were found between the results of the two analytical methods. The accuracy and precision of the method were confirmed by two standard reference materials of manganese ore. The spectrophotometric method is recommended as a standard method for the determination of total manganese content in manganese ores to replace the conventional volumetric method specially in samples of high barium sulphate content. In comparison with AAS and ICP, the spectrophotometric is also more favorable instrumental method for determination of manganese as major component in ores.

The result of manganese dioxide content, determined by arsenious oxide method , revealed that manganese ore from Berber area is of a high grade pyrolusite with low impurities and can be used as a depolarizer in dry cells and in production of ferromanganese.