Birnessite is a common weathering and oxidation product of manganese-bearing rocks.An O2 oxidation procedure of Mn(OH)2 in the alkali medium has been used to synthesize birnessite.Fast and powder X-ray diffraction(XRD...Birnessite is a common weathering and oxidation product of manganese-bearing rocks.An O2 oxidation procedure of Mn(OH)2 in the alkali medium has been used to synthesize birnessite.Fast and powder X-ray diffraction(XRD),transmission electron microscopy(TEM),electron diffraction(ED),energy dispersed X-ray analysis(EDAX),infrared spectroscopy(IR)techniques and chemical composition analysis,Eh-pH equilibrium diagram approaches were employed to investigate the reaction process and pathways of birnessite formation.Results showed that the process of the birnessite formation could be divided into four stages:(1)forma-tion stage for hausmannite and feitknechtite,(2)stage of transformation of hausmannite and feitknechtite to buserite,(3)buserite crystal growing stage,and(4)stage of conversion of buser-ite into birnessite.Mn(OH)2 was mainly present as amorphous state only for a short initial time of oxidation reaction.In the oxidation process,buserite formed following two pathways by recrys-tallization after dissolution of the intermediates,and the transformations of the minerals de-pended on the Eh determined by the dissolved O2 concentration on their surfaces.The results are fundamental in further exploration on the mechanism of birnessite formation in the alkali medium.A great practical significance would also be expected with respect to the areas of mate-rial sciences.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.40403009 and 40101017)by Research Fund for the Doctoral Program of Higher Education(Grant No.2002050411).
文摘Birnessite is a common weathering and oxidation product of manganese-bearing rocks.An O2 oxidation procedure of Mn(OH)2 in the alkali medium has been used to synthesize birnessite.Fast and powder X-ray diffraction(XRD),transmission electron microscopy(TEM),electron diffraction(ED),energy dispersed X-ray analysis(EDAX),infrared spectroscopy(IR)techniques and chemical composition analysis,Eh-pH equilibrium diagram approaches were employed to investigate the reaction process and pathways of birnessite formation.Results showed that the process of the birnessite formation could be divided into four stages:(1)forma-tion stage for hausmannite and feitknechtite,(2)stage of transformation of hausmannite and feitknechtite to buserite,(3)buserite crystal growing stage,and(4)stage of conversion of buser-ite into birnessite.Mn(OH)2 was mainly present as amorphous state only for a short initial time of oxidation reaction.In the oxidation process,buserite formed following two pathways by recrys-tallization after dissolution of the intermediates,and the transformations of the minerals de-pended on the Eh determined by the dissolved O2 concentration on their surfaces.The results are fundamental in further exploration on the mechanism of birnessite formation in the alkali medium.A great practical significance would also be expected with respect to the areas of mate-rial sciences.
