Birnessite occurs in a wide variety of natural environments, and plays animportant role in soil chemistry. A modified Staehli procedure was used to synthesize sodiumbirnessite in an alkali medium by O_2 oxidation. The...Birnessite occurs in a wide variety of natural environments, and plays animportant role in soil chemistry. A modified Staehli procedure was used to synthesize sodiumbirnessite in an alkali medium by O_2 oxidation. The effects of preparative parameters on thesynthesis of birnessite, such as pretreatment on solutions with N2, reaction temperature, O_2 flowrate, fluxion velocity of the reaction suspension, and dehydration conditions were investigated. Thefluxion velocity of the reactive suspension and O_2 flow rate significantly influenced thesynthesis of birnessite. Vigorous stirring raised the fluxion velocity of the reaction suspensionand easily allowed synthesis of pure crystalline birnessite. However pretreatment of the reactingsolutions with N_2 and the reaction temperature had little effect on the synthesis. Diffusion of O_2was the controlling step during the course of oxidation. The optimum synthetic conditions for purebirnessite were: a NaOH to Mn molar ratio of 13.7, an O_2 flow rate of 2 L min^(-1), and oxidationfor 5 hours with vigorous stirring at normal temperatures. The chemical composition of thesynthesized pure birnessite was Na_(0.25)MnO_(2.07)·0.66H_2O.展开更多
基金Project supported by the National Natural Science Foundation of China (Nos. 40101017 and 40071048) the Senior Visitor Foundation of Chinese Educational Ministry.
文摘Birnessite occurs in a wide variety of natural environments, and plays animportant role in soil chemistry. A modified Staehli procedure was used to synthesize sodiumbirnessite in an alkali medium by O_2 oxidation. The effects of preparative parameters on thesynthesis of birnessite, such as pretreatment on solutions with N2, reaction temperature, O_2 flowrate, fluxion velocity of the reaction suspension, and dehydration conditions were investigated. Thefluxion velocity of the reactive suspension and O_2 flow rate significantly influenced thesynthesis of birnessite. Vigorous stirring raised the fluxion velocity of the reaction suspensionand easily allowed synthesis of pure crystalline birnessite. However pretreatment of the reactingsolutions with N_2 and the reaction temperature had little effect on the synthesis. Diffusion of O_2was the controlling step during the course of oxidation. The optimum synthetic conditions for purebirnessite were: a NaOH to Mn molar ratio of 13.7, an O_2 flow rate of 2 L min^(-1), and oxidationfor 5 hours with vigorous stirring at normal temperatures. The chemical composition of thesynthesized pure birnessite was Na_(0.25)MnO_(2.07)·0.66H_2O.
