The factors influencing synthesis of birnessite in alkali media

Birnessite is one of the most common manganese oxides in soils and sediments. The factors influencing synthesis of birnessite in alkali media are systematically investigated. The results show that fluxion velocity of reactive suspension and the rate of O2 flow significantly influence the synthesis of birnessite. Vigorous stirring make the synthesis facile to produce pure crystalline birnessite. However the pretreatment of the reacting solutions by addition of N2 and the reaction temperature have no effect on the synthesis. Not only at a low temperature ( 5 ℃) but also at room temperature (25 ℃) could pure birnessite be synthesized. The optimum synthetic condition of pure birnessite is as follows: NaOH to Mn molar ratio of 13.7, the O2 flow rate of 2 L/min, and oxidation for 5 hours with vigorous stirring at room temperature. The average composition of the synthesized pure birnessite is Na0.25MnO2.07·0.66H2O.